EVALUATION OF LEACHATE CHEMISTRY FROM COAL

REFUSE BLENDED AND LAYERED WITH FLY ASH

Joseph Edward Hunt

Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science

In

Crop and Soil Environmental Sciences

Dr. Matt Eick, Co-Chair

Dr. W. Lee Daniels, Co-Chair

Dr. Lucian Zelazny

10/27/2008

Blacksburg, VA

Keywords: Waste, reclamation, acid mine drainage, oxyanions, water quality

EVALUATION OF LEACHATE CHEMISTRY FROM COAL

REFUSE BLENDED AND LAYERED WITH FLY ASH

Joseph Edward Hunt

(ABSTRACT)

Alkaline fly ash has been studied as a liming agent within coal refuse fills to reclaim

acid-forming refuse. Previous studies focused on bulk blending ash with acid-forming

(pyritic) refuse. A better representation of field conditions is a “pancake layer” of ash

above the refuse. A column study was initiated to evaluate the leachate chemistry from

acid-forming refuse-ash bulk blends vs. ash over refuse layers. An acidic and an alkaline

ash were blended with, or layered over, acid-forming refuse and sandstone and packed

into columns which were leached with deionized water twice a week for 24 weeks under

unsaturated conditions. Leachates were analyzed for pH, electrical conductivity, and a

suite of elements with a focus on the oxyanions of As, Cr, Mo, and Se. A sequential

extraction procedure revealed a significant portion of the elements in the residual fraction

for the refuse/spoil substrates and in metal-oxide bound fractions for the ashes prior to

leaching, and a general trend for a greater proportion of oxyanion elements to be

associated with metal oxide fractions after leaching. Bulk-blended treatments maintained

higher leachate pH than corresponding layered treatments. The acidic ash and refuse

pancaked treatments exhibited relatively high initial concentrations of most elements

analyzed. Pancake layers of ash over refuse are an inadequate co-disposal method to

prevent and mitigate acid mine drainage. Blending alkaline ash with refuse to acid-base

accounting specifications should improve leachate quality overall, but there may be water

quality concerns for loss of Se and other soluble ions during initial leaching events.

iii

TABLE OF CONTENTS

Abstract ii

Table of Contents iii

List of Tables v

List of Figures vi

Acknowledgements ix

Section Page

Introduction 1

Literature Review 2

Coal Refuse 2

Oxyanion Leaching 3

Fly Ash Characterization 5

Leaching Column Studies 8

Fly Ash in the Field 9

Methods and Materials 10

Substrate Characterization 10

Leaching Column Treatments 12

Results 16

Substrate Characterization 16

Leachate Electrical Conductivity 17

Leachate pH 25

Leachate Arsenic 33

Leachate Boron 39

Leachate Chromium 39

Leachate Molybdenum 39

Leachate Selenium 55

Leachate Sulfur 55

Cation Leaching 66

Sequential Extraction Procedures 88

Pre-Leaching 88

iv

Section Page

Post-Leaching 90

Discussion 96

Leachate Electrical Conductivity 96

Leachate pH 97

Arsenic 97

Boron 98

Chromium 99

Molybdenum 100

Selenium 101

Sulfur 101

Cations 103

Sequential Extraction Procedures 104

Conclusion 107

References 110

Appendix 118

v

LIST OF TABLES

Page

Table 1. Selected chemical properties and TCLP extractable 10

As, Cr, Mo, and Se for fly ashes

Table 2. Description of the sequential extraction procedure 11

used in this study

Table 3. Experimental design 14

Table 4. Limits of detection on the ICPES 16

Table 5. Sum of fractions from the SEP 17

Table 6. Percent concentration differences 95

Table A-1. EC data. 118

Table A-2. pH data. 119

Table A-3. As data. 120

Table A-4. B data. 121

Table A-5. Ba data. 122

Table A-6. Co data. 123

Table A-7. Cr data. 124

Table A-8. Cu data. 125

Table A-9. Fe data. 126

Table A-10. Mo data. 127

Table A-11. Ni data. 128

Table A-12. Se data. 129

Table A-13. S data. 130

vi

LIST OF FIGURES

Page

Figure 1. Picture of the leaching column array 12

Figure 2A. Graph of leachate EC (all treatments) 18

Figure 2B. Graph of leachate EC (refuse treatments) 19

Figure 2C. Graph of leachate EC (sandstone treatments) 20

Figure 2D. Graph of leachate EC (Ash #18 treatments) 21

Figure 2E. Graph of leachate EC (Ash #28 treatments) 22

Figure 3A. Bar graph of average EC for Week 2. 23

Figure 3B. Bar graph of average EC for Week 22. 24

Figure 4A. Graph of leachate pH (all treatments) 26

Figure 4B. Graph of leachate pH (refuse treatments) 27

Figure 4C. Graph of leachate pH (sandstone treatments) 28

Figure 4D. Graph of leachate pH (Ash #18 treatments) 29

Figure 4E. Graph of leachate pH (Ash #28 treatments) 30

Figure 5A. Bar graph of average pH for Week 2. 31

Figure 5B. Bar graph of average pH for Week 22. 32

Figure 6A. Graph of leachate As (all treatments) 34

Figure 6B. Graph of leachate As (refuse treatments) 35

Figure 6C. Graph of leachate As (sandstone treatments) 36

Figure 6D. Graph of leachate As (Ash #18 treatments) 37

Figure 6E. Graph of leachate As (Ash #28 treatments) 38

Figure 7A. Graph of leachate B (all treatments) 40

Figure 7B. Graph of leachate B (refuse treatments) 41

Figure 7C. Graph of leachate B (sandstone treatments) 42

Figure 7D. Graph of leachate B (Ash #18 treatments) 43

Figure 7E. Graph of leachate B (Ash #28 treatments) 44

Figure 8A. Graph of leachate Cr (all treatments) 45

Figure 8B. Graph of leachate Cr (refuse treatments) 46

Figure 8C. Graph of leachate Cr (sandstone treatments) 47

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Page

Figure 8D. Graph of leachate Cr (Ash #18 treatments) 48

Figure 8E. Graph of leachate Cr (Ash #28 treatments) 49

Figure 9A. Graph of leachate Mo (all treatments) 50

Figure 9B. Graph of leachate Mo (refuse treatments) 51

Figure 9C. Graph of leachate Mo (sandstone treatments) 52

Figure 9D. Graph of leachate Mo (Ash #18 treatments) 53

Figure 9E. Graph of leachate Mo (Ash #28 treatments) 54

Figure 10A. Graph of leachate Se (all treatments) 56

Figure 10B. Graph of leachate Se (refuse treatments) 57

Figure 10C. Graph of leachate Se (sandstone treatments) 58

Figure 10D. Graph of leachate Se (Ash #18 treatments) 59

Figure 10E. Graph of leachate Se (Ash #28 treatments) 60

Figure 11A. Graph of leachate S (all treatments) 61

Figure 11B. Graph of leachate S (refuse treatments) 62

Figure 11C. Graph of leachate S (sandstone treatments) 63

Figure 11D. Graph of leachate S (Ash #18 treatments) 64

Figure 11E. Graph of leachate S (Ash #28 treatments) 65

Figure 12. Chart of results from SEP for cations prior to leaching 67

Figure 13A. Graph of leachate Ba (all treatments) 68

Figure 13B. Graph of leachate Ba (refuse treatments) 69

Figure 13C. Graph of leachate Ba (sandstone treatments) 70

Figure 13D. Graph of leachate Ba (Ash #18 treatments) 71

Figure 13E. Graph of leachate Ba (Ash #28 treatments) 72

Figure 14A. Graph of leachate Co (all treatments) 73

Figure 14B. Graph of leachate Co (refuse treatments) 74

Figure 14C. Graph of leachate Co (sandstone treatments) 75

Figure 14D. Graph of leachate Co (Ash #18 treatments) 76

Figure 14E. Graph of leachate Co (Ash #28 treatments) 77

Figure 15A. Graph of leachate Cu (all treatments) 78

Figure 15B. Graph of leachate Cu (refuse treatments) 79

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Page

Figure 15C. Graph of leachate Cu (sandstone treatments) 80

Figure 15D. Graph of leachate Cu (Ash #18 treatments) 81

Figure 15E. Graph of leachate Cu (Ash #28 treatments) 82

Figure 16A. Graph of leachate Ni (all treatments) 83

Figure 16B. Graph of leachate Ni (refuse treatments) 84

Figure 16C. Graph of leachate Ni (sandstone treatments) 85

Figure 16D. Graph of leachate Ni (Ash #18 treatments) 86

Figure 16E. Graph of leachate Ni (Ash #28 treatments) 87

Figure 17. Chart of results from SEP for oxyanions before leaching 89

Figure 18A. Chart of results from SEP for oxyanions after leaching 91

for the controls

Figure 18B. Chart of results from SEP for oxyanions after leaching 92

for treatments 18-R-B, 18-R-P (substrate and pancake),

and 18-S-B

Figure 18C. Chart of results from SEP for oxyanions after leaching 93

for treatments 18-S-P (substrate and pancake), 28-R-B,

and 28-R-P (substrate)

Figure 18D. Chart of results from SEP for oxyanions after leaching 94

for treatments 28-R-P (pancake), 28-S-B, and

28-S-P (substrate and pancake)

ix

ACKNOWLEDGEMENTS

I would like to begin by thanking my committee members: Dr. Matt Eick, Dr. W.

Lee Daniels, and Dr. Lucian Zelazny. Much thanks goes to Dr. Eick, who was gracious

enough to accept me as his student and give me free run of his lab. You have been doing

everything at your disposal to ensure my success and your mentorship has been priceless.

I praise Dr. Daniels, who has helped me tremendously throughout my graduate work.

You helped me develop my experiment and have always been available to answer

questions. I am honored and privileged to have had the opportunity to learn under Dr.

Zelazny. Your classes, however challenging, will be one of the more cherished

experiences I will take away from my time here. I must also thank Dr. Dave Parrish, who

is a primary reason I stayed at Virginia Tech to pursue my Master’s degree. You were

always there for me during my undergraduate years and you helped instill in me the

confidence necessary to believe I could accomplish graduate work.

I would like to thank the many people throughout the department that have helped

me through my trials and tribulations. Mike Beck, you have been an invaluable resource

in setting up my columns and displaying my data. Julie Burger, your kindness and

friendship have been a blessing. I appreciate your understanding of the life of a young

graduate student and am grateful for your willingness to listen to my issues. Pat

Donovan, you are one of the most genuinely kind people I have ever met. Your constant

smile, whether while printing out my posters or helping me clean my messes, always

brightened my day. W.T. Price, I thank you for your friendship and your entertaining

stories. The lab was never quite the same when you weren’t there. Athena Tilley, I owe

the majority of my data to your hard work. You always treated me so kindly, even when

I was delivering hundreds of samples for you to analyze. Sue Brown, you have been so

kind, caring, and helpful to me that it is hard to fully express my gratitude. Todd Luxton,

you took me under your wing when I first arrived and showed me many valuable lab

techniques. I truly appreciate the time and effort you took to ensure I was well

acclimated to graduate work. Abbey Wick, your advice and friendship have been very

precious over the short time I have been able to know you.

x

I must also thank the rest of the CSES faculty, staff, and students. You have

accepted me for who I am and have never treated me unkindly. I have the utmost respect

for all of you and am honored to have spent my last two years learning and working

among you. I thank all my friends and family. Your love and support get me through

each and every day.

Finally, I would like to thank the Powell River Project and the Office of Surface

Mining, whose financial support made my graduate study possible.

1

INTRODUCTION

The majority of electricity in the United States is generated from burning coal,

due mainly to its abundance and low cost (NRC, 2006). One disadvantage of using coal

as a source of electricity is the significant amount of unmarketable coal, or coal refuse,

that is generated and must be disposed of properly. The potentially high pyrite (FeS2)

content of coal refuse can be responsible for acidic leachates termed Acid Mine Drainage

(AMD). Under the Surface Mining Control and Reclamation Act (SMCRA), the mine

operator is required to reclaim the refuse pile through stabilization and revegetation of its

surface and to treat any acid mine drainage that may be produced before it enters local

waterways (Daniels et al., 1996; NRC, 2006). One method to assist reclamation that is

not widespread in the U.S. but is gaining in popularity, is the co-disposal of fly ash with

coal refuse (Stewart et al., 1997; Stewart et al., 2001).

Fly ash is the noncombustible mineral component of coal that rises with the flue

gases after coal combustion and is captured by various particle collecting systems

(Daniels et al., 2001; NRC, 2006). Fly ash generally has a silty texture, low bulk density,

low hydraulic conductivity, and low specific gravity, and many fly ashes are alkaline

(Stewart et al., 1997; Daniels et al., 2001). Previous studies have shown the utilization of

alkaline fly ash with coal refuse to be beneficial for plant growth by lowering bulk

density, increasing water holding capacity, and neutralizing the acidity and heavy metal

leaching from the coal refuse (Stewart et al., 1997; Bhumbla et al., 2000; Stewart et al.,

2001; Daniels et al., 2001). However, few studies have thoroughly studied the leaching

of certain trace elements which occur as oxyanions (As, Cr, Mo, Se) from ash/refuse

piles. These elements, particularly As and Se, are becoming a growing concern among

regulators because of increasing instances of environmental release to surface water and

their acute toxicity in aquatic environments (NRC, 2006; Lemly, 2007).

Accordingly, this study was designed to assess the benefits of co-disposing fly ash

with coal refuse with the primary focus on the leaching of trace element oxyanions. This

was accomplished using leaching columns similar to those used in previous studies at

Virginia Tech to simulate the weathering and leaching events that would occur in the

environment (Stewart et al., 1997; Stewart et al., 2001; Daniels et al., 2006). This study

2

also compared two different methods by which fly ash may be co-disposed with coal

refuse. Previous studies have focused on the bulk blending of fly ash with the refuse

(Stewart et al., 1997; Stewart et al., 2001; Daniels et al., 2006). While this may be the

preferable way to co-dispose the two materials, it is difficult to practically execute in the

field. To better represent field conditions it would be more appropriate to simulate a

layer of ash placed on top of a layer of coal refuse. To accomplish this, half of the

columns in this study utilized a “pancake” layer of fly ash above the refuse or mine spoil,

while the other half were bulk blended for comparison.

LITERATURE REVIEW

Coal Refuse

As coal is mined a significant amount of unmarketable waste rock material is

generated. This waste rock has high levels of pyretic S (FeS2) and other impurities or has

too little energy per unit weight to be profitable and is therefore referred to as coal refuse

(Stewart et al., 1997; NRC, 2006). Over 15 million Mg per year of coal refuse is

produced in just the state of Virginia (Daniels et al., 1996). Coal refuse is removed at a

coal prep plant and is separated into two fractions: a coarse fraction and a fine slurry

fraction (Daniels et al., 1996; Stewart et al., 1997; Daniels and Stewart, 2000). The

coarse refuse is disposed of in large compacted fills on the mine site and acts as a dike

behind which the fine slurry is impounded. Coal refuse generally lacks essential plant

nutrients like N and P, has a low water holding capacity, and can be responsible for acid

mine drainage (AMD) due to pyrite oxidation (Daniels et al., 1996; Stewart et al., 1997;

Daniels and Stewart, 2000).

Pyrite oxidizes and produces acidity according to the following set of reactions

(Evangelou, 1998; Geidel and Caruccio, 2000):

FeS2(s) + 7/2O2 + H2O = Fe2+ + 2SO42- + 2H+ (1)

Fe2+ + 1/4O2 + H+ = Fe3+ + 1/2H2O (2)

Fe3+ + 3H2O = Fe(OH)3(s) + 3H+ (3)

3

FeS2(s) + 14Fe3+ + 8H2O = 15Fe2+ + 2SO42- + 16H+ (4)

Prevention of AMD focuses on minimizing O2 and water infiltration into the

refuse pile to prevent the initial reaction steps and then neutralizing any acidity produced

over longer periods of time (Hoving and Hood, 1984; Daniels et al., 1989; Gitt and

Dollhopf, 1991; Skousen et al., 2000). Minimizing oxygen and water infiltration is

accomplished by covering the refuse with a topsoil layer and/or establishing vegetation

directly on the refuse pile, which presumptively limits water and oxygen content to some

extent (Daniels and Stewart, 2000). If the refuse is net acid forming, the acidity is

neutralized with the addition of alkaline amendments to the bulk of the acid forming

materials or to acid drainage discharges (Skousen et al., 2000). Neutralizing acidity

requires accurate acid-base accounting, which is analysis of all the materials used to

determine their potential to produce net acidity or alkalinity in drainage waters over time

(Sobek et al., 2000). Fly ash has been suggested as a possible source of alkalinity to add

to coal refuse piles (Stewart et al., 1997; Daniels et al., 2001; Bhumbla et al., 2000).

Along with adding alkalinity, fly ash may improve water holding capacity and may add

some essential nutrients to the refuse (Bhumbla et al., 2000). However, not all fly ash

materials are net alkaline in reaction and even those that are alkaline are typically low

(<10 %) in calcium carbonate equivalence (CCE) (Stewart, 1995).

Sulfidic minerals such as pyrite often contain heavy metals such as Cu, Ni, and

Zn. These metals are released into solution as sulfides oxidize and produce AMD

(Daniels and Stewart, 2000). The pH of AMD can reach values as low as 1.7, enhancing

the dissolution of other minerals through which the water leaches. The dissolution of

these minerals also produces leachate water enriched with heavy metals. Common

constituents of AMD include high levels of As, Cu, Fe, Mn, Ni, Zn, and sulfates

(Evangelou, 1998; Daniels and Stewart, 2000).

Oxyanion Leaching

The contamination of land and water by potentially toxic oxyanions of elements

such as As, Cr, Mo, and Se has become a growing concern in recent years. These trace

4

elements, and others, can be found in relatively high concentrations in some fly ashes

(Van der Hoek and Comans, 1996; Huggins et al., 1999; Goodarzi and Huggins, 2001).

Selenium is an essential micronutrient for animals in low concentrations, however there

is a narrow range between sufficiency and toxicity (Hamilton, 2004; Lemly, 2004;

Lemly, 2007). Selenium bioaccumulates in the food chain rapidly and has been shown to

cause teratogenic deformities and reproductive failure among wildlife (Lemly, 2004;

Lemly, 2007). Selenium in fly ash is generally found in both the selenite (SeO32-) and

selenate (SeO42-) forms, with both species being toxic (Jackson and Miller, 1999; Lemly,

2004). Variable charge minerals such as Fe and Al oxides, allophane, and edge charges

of kaolinite have the greatest affinity for Se (Hyun et al., 2006). Selenium sorption

decreases with increasing pH as mineral surfaces become increasingly more negative,

thus Se can be mobile under oxidized, alkaline environments (Zhang and Sparks, 1990;

Lemly, 2004; Hyun et al., 2006). Selenate and sulfate sorption onto variable charge

minerals is comparable as both tend to form outer-sphere surface complexes and can be

highly mobile in soil environments. Selenite tends to form stronger inner-sphere

complexes similar to phosphate sorption (Hyun et al., 2006). The presence of competing

anions such as sulfate, phosphate, citrate, and oxalate may decrease the total amount of

Se that can be sorbed to mineral surfaces, thus increasing its potential bioavailability

(Zhang and Sparks, 1990; Hyun et al., 2006).

Arsenic exposure has been linked to bladder, kidney, lung, and skin cancer

(Abernathy et al., 1996; Shi et al., 2004). In most natural environments, As can be found

as arsenate (AsO43-) or the more toxic arsenite form (AsO3

3-) (Jennette, 1981; Jackson

and Miller, 1999; Shi et al., 2004). The pK1 and pK2 of arsenite are 9.2 and 12.7,

respectively; thus under natural pH conditions arsenite generally exists as H3AsO3 and

H2AsO3-. The pK1, pK2, and pK3 of arsenate are 2.3, 6.8, and 11.6, respectively; thus

under natural pH conditions arsenate exists as H3AsO4, H2AsO4-, and HAsO4

2- (Goldberg

and Johnston, 2001). Both As species show a high affinity to sorb to variable charge

minerals such as Fe and Al oxides. Arsenate and arsenite have different sorption

characteristics, however, with arsenate displaying a sorption maximum on Fe and Al

oxides around pH 4 and arsenite displaying one in the pH range of 7.8-8.5 (Goldberg and

Johnston, 2001; Arai et al., 2001). Maximum sorption of oxyanions occurs near their pKi

5

value (McBride, 1994). Arsenate generally forms stronger surface complexes with

minerals compared to arsenite (Goldberg and Johnston, 2001; Arai et al., 2001).

Arsenate is the dominant form found in fly ash (Goodarzi and Huggins, 2001; Shoji et al.,

2002).

Unlike As and Se, most Cr is found as the trivalent cation (Cr3+) in natural

environments. However, due to the highly oxidized nature of fly ash, some Cr may be

found as the hexavalent chromate anion (H2CrO4) (Paustenbach et al., 2003; Kingston et

al., 2005). Hexavalent Cr exposure has been linked to respiratory cancer, kidney damage,

and skin irritation (Paustenbach et al., 2003; Kingston et al., 2005; Johnson et al., 2006).

Hexavalent Cr exists as H2CrO4 , HCrO4-, and CrO4

2- at total CrVI concentrations less

than 10 mM and circumneutral pH. At concentrations higher than 10 mM and more acid

pH, HCrO4- can polymerize into dichromate (Cr2O7

2-). The pK2 of chromate is 6.51,

indicating increased mobility in higher pH environments. Hexavalent Cr can be reduced

to the less toxic and less mobile trivalent Cr by ferrous iron in solution, ferrous iron

minerals, reduced sulfur compounds, or soil organic matter (Palmer and Wittbrodt, 1991).

Molybdenum is another element often associated with fly ash that is

predominantly found as an oxyanion in the environment (Bhumbla et al., 2000).

Molybdenum is an essential micronutrient at low concentrations, but can be toxic to

animals, particularly ruminants, at high concentrations (Bhumbla et al., 2000; O’Connor

et al., 2001). There is a relatively narrow concentration range between which Mo is

sufficient for plant growth (0.5 ug g-1) and potentially toxic to ruminants (10 ug g-1)

causing molybdenosis (Mo induced Cu deficiency) (Neunhauserer et al., 2001; McBride

and Hale, 2004). Existing primarily as an oxyanion above pH 4.2, Mo is more

bioavailable and subject to leaching at circumneutral pH values (McBride and Hale,

2004; Essington, 2004). Molybdenum sorption characteristics are similar to the other

oxyanions, sorbing to variable charge minerals such as Fe and Al oxides and the edges of

phyllosilicate clays at lower pH values (Essington, 2004).

Fly Ash Characterization

Composition of fly ash varies depending on coal source, method of burning, and

the pollution control and residual handling technologies (Daniels et al., 2001; NRC,

6

2006). For example, elemental speciation of Integrated Gasification Coal Combustion

(IGCC) fly ash is different from traditional pulverized coal combustion fly ash, mainly

due to the reducing conditions involved with IGCC (Font et al., 2005). Therefore, it is

impossible to create a complete or general characterization that applies to all fly ashes.

However, there are some minerals that are common to almost all fly ashes and these

include quartz, amorphous aluminosilicates, calcite, and Fe and Al oxides (NRC, 2006).

Despite the inherent variability of fly ash, it is important to try to gain a general

understanding of its composition and how it reacts when exposed to the environment.

Kim et al. (2003) studied many different fly ashes from across the United States

and found them to consist of 40-65% SiO2, ~ 25% Al2O3, 2-30% FeO, and ~ 3% CaO on

average. Kim and Kazonich (2004) later separated these ashes into silicate and non-

silicate phases and determined which elements are associated with each phase. In doing

so, they found Si and Al to be mainly in the silicate phase, Fe to be in both silicate (Fe-

oxides in silicate particles and intergrowths of Fe-oxides and silicates) and non-silicate

(mainly hematite and magnetite) phases, and As and Se to predominantly be associated

with the non-silicate phase (Kim and Kazonich, 2004). Goodarzi and Huggins (2001)

used a sequential leaching procedure of water, NH4OAc, and HCl along with X-ray

absorption fine-structure spectroscopy (XAFS) to determine the speciation of As, Cr, and

Ni in milled coal, fly ash, and bottom ash. They found the majority of As in the fly ash to

be in the oxidized form (arsenate) and associated with acid-soluble minerals such as

carbonates, metasulfides, and oxides. A significant amount of Cr was extracted under

high pH conditions indicating that it was in the oxidized hexavalent form, and the Ni in

fly ash was mainly associated with a glassy matrix (Goodarzi and Huggins, 2001).

Bodog et al. (1996) subjected three different fly ashes to a sequential extraction

procedure (SEP) that determined the associations of select elements with five different

fractions: exchangeable, carbonates, Fe and Mn oxides, sulfides, and residual material.

The three ashes studied were from substantially different sources and showed varying

distribution patterns. In general, they determined Cd to be associated with the more

mobile fractions (exchangeable and carbonates), Cr resided mainly in the sulfide and

residual fractions, and Pb, Zn, and V were predominantly in the residual fraction (Bodog

et al., 1996).

7

In a similar study, Hansen and Fisher (1980) combined two techniques to

determine if select elements were associated with the fly ash matrix or with a

nonmatrix/surface fraction. They analyzed the total concentrations of elements as a

function of ash particle size. If the concentration of an element increased as particle size

decreased they concluded that the element was surface-associated. They also subjected

the ashes to solutions of hydrochloric (HCl) and hydrofluoric (HF) acids. They assumed

HCl dissolves the nonmatrix portions of the ash and HF dissolves both the matrix and

nonmatrix portions of the ash. By combining these two methods they determined that As,

Mo, and Se are predominantly associated with the nonmatrix/surface fraction while Ba,

Co, Cr, and Cu can be found equally in both the nonmatrix and matrix phase (Hansen and

Fisher, 1980). Smeda and Zyrnicki (2002) performed an SEP on two fly ashes that

determined the associations of select elements with four fractions: water soluble, acid

soluble/carbonate bound, reducible/Fe and Mn oxide bound, and oxidizable/sulfide

bound. They discovered significant amounts of B, Cr, and Sr in the water soluble

fraction indicating the potential of these elements to be readily bioavailable. Chromium

also had high levels associated with an oxidizable fraction. The largest fraction for each

of the elements analyzed was the residual fraction (Smeda and Zyrnicki, 2002).

Veranth et al. (2000) reported that Fe in fly ash is typically found in magnetite-

based spinels, hematite, and aluminosilicate glass with the latter being the most readily

leached. Shoji et al. (2002) used XAFS to look at fine particulate matter from coal

combustion of Eastern and Western U.S. coals. As a result, they determined sulfate to be

the dominant form of S, hexavalent Cr was more concentrated in Western U.S. coal ashes

than in Eastern U.S. coal ashes, and As was predominantly in the arsenate form (Shoji et

al., 2002). Hulett et al. (1980) separated fly ashes into three phases (glass, mullite-quartz,

and magnetic spinel) and performed elemental analyses to determine which elements are

associated with which phases. They found Se and As to be associated with the

amorphous glass phase and Cr to be concentrated in the magnetic spinel phase (Hulett et

al., 1980). Mukhopadhay et al. (1996) studied the speciation of elements in coal and its

combustion residues. They determined that fly ash is composed of three types of glass

phases: Fe/oxygen-rich, Fe/Al/Si/oxygen-rich, and Al/Si/oxygen-rich. They found that

8

As in fly ash may occur as both As (III) and As (V) in a glass/ noncrystalline phase

(Mukhopadhay et al., 1996).

Leaching Column Studies

Leaching columns are a method employed to simulate field conditions at a

laboratory scale. They can provide information on potential contaminants or elements of

concern that may be leached from a material when subjected to rainfall (Stewart et al.,

1997) and are superior to batch extractions for simulating both leachate quality and

reaction kinetics. However, column studies are time and labor intensive and are therefore

not used for routine regulatory compliance type analyses (Kim and Kazonich, 2004).

Several column studies have been performed at Virginia Tech to assess the

suitability of co-disposing fly ash with coal refuse (Daniels et al., 1997; Stewart et al.,

1997; Stewart et al., 2001; Daniels et al., 2006). Stewart et al. (1997, 2001) observed that

when an alkaline fly ash is bulk blended with coal refuse in accordance with acid-base

accounting, it is able to neutralize acidity generated by the refuse and minimize

contaminants leaching from the column. However, when the neutralizing potential of the

ash is insufficient to prevent acid mine drainage, elements associated with the ash are

leached along with typical acid drainage metals from the refuse, and the acid elution may

be time-lagged for several years (3+) after co-disposal. Daniels et al. (1997) found that

layers of ash compacted within acidic coal refuse were ineffective in preventing acid

mine drainage. These earlier studies primarily focused on the leaching of major elements

such as Al, Cu, Fe, Mn, Ni, S, and Zn and did not examine a number of other trace

elements. In a later study, Daniels et al. (2006) did examine trace element leaching and

discovered that fly ash bulk blended with coal refuse may contribute additional leaching

of B, Mo, and potentially Se and Cr. However, if the net calcium carbonate equivalence

(CCE) of the ash additions was sufficient to neutralize the refuse acidity and control

solution pH, the concentrations of these and other elements of concern were low in

leachates.

Kim et al. (2003) examined the effect of four different leachants (H2SO4, HOAc,

deionized water, and NaCO3) on the solubility of various cations in fly ashes from across

the country. They discovered most cations in fly ash to be either insoluble or only

9

slightly soluble over the range of leachants utilized. Of note, they determined As and Se

to be more soluble in the basic solutions while Cr was more soluble in acid solutions

(Kim et al., 2003).

Fly Ash in the Field

Bhumbla et al. (2000) reviewed many studies on the use of fly ash as an

amendment to reclaim mine soils. They report higher plant yields when using fly ash as a

liming agent compared to limestone to ameliorate an acidic mine soil. They also report

successful revegetation of a pyritic mine soil when an alkaline fly ash was used as a

topsoil substitute. Furthermore, they observed an increase of As and Mo in the tissues of

select crops grown on fly ash amended mine soils for the first years of the study, and very

little plant uptake of Se (Bhumbla et al., 2000). Punshon et al. (2002) applied a

combination of fly ash and poultry waste to eroded land. They found both As and Se

increased dramatically in grass tissue with high rates of fly ash, but the concentrations

decreased over time (Punshon et al., 2002). Additionally, they observed an increase in

electrical conductivity (EC) in the groundwater with increasing fly ash rates, but no other

significant groundwater effects (Punshon et al., 2002). Adriano et al. (2002) applied fly

ash at different rates to plots of centipedegrass (Eremochloa ophiroides). The fly ash

significantly increased the concentration of As, Ba, Be, B, Mo, and Se in the grass tissue,

but the only groundwater effect was a slight increase in EC.

Zevenbergen et al. (1999) studied the weathering of two alkaline fly ashes and

compared it to the weathering of volcanic ash. Due to the high pH of the fresh fly ash

(>11) it weathered more rapidly than volcanic ash. However, over the course of 8-14

years the fly ash had similar mineralogical compositions to volcanic ash that had

weathered for approximately 250 years. They used x-ray powder diffraction and

transmission electron microscopy (TEM) to characterize the secondary products formed

from the weathering of the fly ash. They discovered the glassy matrix that predominates

in fly ash dissolves into non-crystalline clays (allophane and imogolite) and ferrihydrite.

They concluded that the formation of these clays provides a physical barrier to trace

metal leaching by coating and encapsulating grains and also provides a chemical barrier

by incorporating metals within the clay structures (Zevenbergen et al., 1999).

10

METHODS AND MATERIALS

Substrate Characterization

This study utilized four different materials. Coarse coal refuse and sandstone mine

spoil taken from a SW Virginia surface coal mine (Red River Coal Co.; Wise VA) acted

as substrates in the experiment. Both were derived from the Pennsyvanian aged Wise

formation. The refuse was primarily derived from the Standiford, Taggart, and Phillips

coal seams. The mine spoil was partially weathered Taggart overburden. Both materials

were sieved to 1.25 cm prior to use. The lime requirement of the refuse and sandstone

was determined via a hydrogen peroxide oxidation and titration acidity procedure based

on Barnhisel and Harrison (1976) and O’Shay et al. (1990). Two fly ashes collected from

regional utilities burning Virginia coal were utilized, labeled Ash #18 and Ash #28. All

materials were used in a previous leaching column experiment (Daniels et al., 2006).

Prior to the onset of that experiment, Daniels et al. (2006) performed a series of

characterization analyses on the ashes including pH and EC on saturated paste extracts

(Rhoades, 1996), hot CaCl2 extractable B (Keren, 1996), calcium carbonate equivalence

(CCE; AOAC, 1990), and the Toxicity Characteristic Leaching Procedures (TCLP; U.S.

EPA, 1992). Table 1 shows the results of these analyses. These two particular ashes

were chosen because of their relatively high concentrations of the trace element

oxyanions of interest and to observe the difference between an ash with no liming

capacity (#18; worst case scenario) and an ash with moderate liming capacity (#28).

Table 1: Selected chemical properties and TCLP extractable As, Cr, Mo, and Se.

(Daniels et al., 2006).

Ash pH EC

(dS m-1)

CCE

%

Extr. B

(mg kg-1)

TCLP

As

(mg L-1)

TCLP

Cr

(mg L-1)

TCLP

Mo

(mg L-1)

TCLP

Se

(mg L-1)

18 3.6 11.8 0 91.6 0.38 0.68 0.12 0.32

28 11.5 3.2 7.7 3.6 0.51 0.16 0.23 0.13

EPA CFR 261 Reg. TCLP Limits 5.0 5.0 none 1.0

Fractionation via a sequential extraction procedure (SEP) was performed on both

11

ashes and substrates to determine the composition of each material. The SEP followed

the procedure of Tessier et al. (1979). The method was modified for use on high S

material (fly ash and coal refuse) by substituting MgSO4 with MgCl2 in the first

extraction step. The extraction step for elements associated with organic matter was also

omitted. The sample size used for extraction was 6.00 g at a solution: solid ratio of 5:1.

The procedure involved sequential extraction with 1M MgCl2 for soluble/exchangeable

metals, followed by extraction with 1M Acetic Acid/NaOAc for carbonates, followed by

extraction with 0.2M ammonium oxalate (pH 3) shaken in the dark for 2 hours for

amorphous Fe/Mn compounds, followed by 1 M hydroxylamine hydrochloride/acetic

acid for Fe/Mn crystalline bound forms, and finally, concentrated HCl and HNO3 for

residual bound metals (Tessier et al., 1979; Daniels et al., 2006). Extracts were separated

from solids via centrifugation at high speed (approximately 4000 rpm) for 15-20 minutes.

The supernatant was decanted and filtered through a 0.45 µm membrane filters

(Millipore, MA). The filtrates were preserved to pH < 2 with concentrated nitric acid and

stored at 4° C until analysis. Approximately 5-8 ml DI water was added to the samples

between each extraction step to wash off any excess extracting solution. This water was

separated via centrifugation and discarded before the next extraction step. Table 2

describes the SEP in more detail.

Table 2: Description of the sequential extraction procedure used in this study.

Step Method Fraction

1 30 ml 1 M MgCl2; shake for 1 hour Exchangeable

2 30 ml 1 M NaOAc adjusted to pH 5 with acetic

acid; shake for 3 hours

Carbonates

3 30 ml 0.2 M ammonium oxalate adjusted to pH 3

using conc. HCl; shake in the dark for 4 hours

Amorphous Fe and Mn

Oxides

4 30 ml 1 M NH2OH•HCl in 25% (v/v) acetic acid;

heat at 95°C ± 5°C for 6 hours shaking

occasionally

Crystalline Fe and Mn

Oxides

5 5 ml conc. HCl and 20 ml conc. HNO3 digested in

microwave; brought up to 50 ml volume with DI

Residual

12

At the conclusion of the 6-month leaching study (described later), the materials in

the columns were sampled for use in a post-leaching SEP to give insight into the

chemical changes occurring within the columns and which solid phases may be

controlling the solubility of the elements of concern. The top and bottom 3 cm were

discarded from each column before sampling. For the blended treatments and controls,

the remaining material was homogenized, dried and subjected to the SEP described

above. Two samples were taken from the pancaked treatments: one homogenized sample

from the ash pancake layer and one homogenized sample from the substrate layer.

All chemicals used in this study were reagent grade and solutions were prepared

using Milli-Q Gradient A10 ultrapure water (Millipore, MA). It should be noted that for

the SEP run prior to leaching the residual step was performed using a Milestone Ethos

900 Plus Microwave Digester (Milestone, Italy). However, this instrument was

inoperable when the time came to perform the post-leaching SEP thus the residual step

was then performed using a Lachat Instruments Model BD-46 Block Digester (Lachat

Instruments, WI).

Leaching Column Treatments

The leaching column experiment utilized columns from a previous study on fly

ash/refuse leachates (Daniels et al., 2006). Figure 1 displays the leaching column array

as it was set up in the laboratory.

Figure 1: Picture of the leaching column array. Photo taken by Joseph Hunt, 2007.

These columns were made from 7.5 cm diameter PVC pipe, 38 cm long, and held

a total volume of approximately 1300 cubic centimeters. This experiment tested two

13

different methods of co-disposing fly ash with a substrate using two different substrates

and two different ashes. There were four controls consisting of columns with 80% by

volume coarse refuse and sandstone and 20% by volume Ash #18 and Ash #28. This

maintained a mass balance of material versus what was in the treatments. Each treatment

combination was replicated three times to bring the total number of columns to 36. The

fly ash was bulk blended with the spoil/refuse substrate on a 20% ash v:v basis (but

mixed on a by weight basis to reduce variability). The weight of material needed per

column was determined using estimates of bulk densities of the substrates and ashes

(Daniels et al., 2006).

The alternate method was to place the 20% ash by volume in a “pancake” layer on

top of the substrate to better resemble field conditions where bulk blending is improbable.

The ash in the controls and “pancake” layers were cut with glass beads on a 2:1 beads:

ash ratio to limit the ash from becoming pozzolanic (self-cementing) during the leaching

procedure. All percent volume calculations were based on a column volume of

approximately 1300 cm3. However, approximately 520 cm3 volume extenders were

attached to the “pancake” layer columns because of the necessity to cut the layers with

glass beads, thus the “pancake” layers truly occupied about 43% of the volume in the

columns as opposed to 20% while maintaining the same mass of ash as the blended

columns. Table 3 details the experimental design.

Fine nylon mesh was placed in the rounded endcap on the bottom of the columns

to prevent material from clogging the drainage nipple through which the leachate leaves

the column. Whatman Grade 43 filter paper and a layer of acid washed glass beads were

placed on top of the mesh to further prevent clogging. The columns were packed in

increments, and between increments a small amount of glass beads were added to reduce

preferential flow. A layer of beads was also placed on top to ensure proper infiltration of

the leaching water (Daniels et al., 2006).

14

Table 3: Experimental design.

Column

Numbers

Material Layering Abbreviation Graphic

Symbol for

Figures

1-3 Refuse/Ash 18 Blended 18-R-B

4-6 Refuse/Ash 18 Pancaked 18-R-P

7-9 Sandstone/Ash 18 Blended 18-S-B

10-12 Sandstone/Ash 18 Pancaked 18-S-P

13-15 Refuse/Ash 28 Blended 28-R-B

16-18 Refuse/Ash 28 Pancaked 28-R-P

19-21 Sandstone/Ash 28 Blended 28-S-B

22-24 Sandstone/Ash 28 Pancaked 28-S-P

25-27 Refuse Control R Cntrl

28-30 Sandstone Control S Cntrl

31-33 Ash 18 Control 18 Cntrl

34-36 Ash 28 Control 28 Cntrl

The columns were initially equilibrated by adding deionized water to each column

in 50 ml increments every 2 to 3 hours until breakthrough of leachate was observed.

Once leachate breakthrough was observed an additional 100 mls of deionized water was

added to the columns. This leachate was collected and analyzed as the first leaching

event (Week 0.5). The amount of water added to the columns ranged from 200 to 600

mls, and the amount of leachate collected ranged from 80 to 130 mls, depending on the

treatment.

After equilibration, the columns were leached with 100 ml of deionized water

twice a week for six months under unsaturated conditions. The 100 ml volume is

equivalent to a 1-inch rainfall event for each column to represent accelerated weathering

in the columns. The leachate was allowed to drain for 24 hours into acid-washed high

density polyethylene (HDPE) containers and then collected for analysis. Leachates were

collected after each leaching event for the first 4 weeks. After the first 4 weeks, leachates

were collected once a week for 4 weeks and then once every other week for the duration

15

of the experiment (6 months). Electrical conductivity (EC) and pH were determined for

the leachates on the day of collection using a Cole-Parmer Instrument Co. Conductivity

Meter Model 1481-60 (Chicago, IL) and an Orion perpHecT LogR pH meter Model 370

(Beverly, MA), respectively. After EC and pH were recorded, nine ml unfiltered aliquots

were taken from each replication bottle and placed in a dilution vial for a composite

elemental analysis for each treatment. The leachates from the first two leaching events

were analyzed for a full suite of elements including Al, As, B, Ba, Ca, Co, Cr, Cu, Fe, K,

Mg, Mn, Mo, Na, Ni, P, Pb, S, Se, Si, Sr, and Zn using a Spectro CirOS VISION Model

FVS12 Inductively Coupled Plasma Emission Spectroscope (ICPES) (Marlboro, MA).

Table 4 displays the limits of detection and quantification for the elements analyzed for

this study. The subsequent leachates were analyzed for a narrower list of elements of

interest including As, B, Ba, Co, Cr, Cu, Mo, Ni, S, and Se.

The statistical design of this study was a randomized complete block (RCB). The

computer program SAS 9.1.3 SP4 for Windows was used to perform ANOVA and the

Fisher’s LSD method of means comparison for EC and pH data on select dates (SAS

Institute, NC). Means for the EC and pH data were calculated and graphed with standard

error bars to indicate variance within treatments.

16

Table 4: Limits of detection on the ICPES for selected elements.

Element Limits of Detection under optimum

measuring conditions (mg L-1)

Limit of Quantification

(mg L-1)

Al 0.001 0.044

As 0.015 0.017

B 0.002 0.010

Ba 0.001 0.001

Ca 0.010 0.094

Co 0.002 0.008

Cr 0.002 0.002

Cu 0.002 0.003

Fe 0.002 0.006

K 0.050 0.058

Mg 0.010 0.093

Mn 0.001 0.001

Mo 0.005 0.016

Na 0.015 0.019

Ni 0.006 0.008

P 0.008 0.048

Pb 0.050 0.062

S 0.007 0.086

Se 0.020 0.024

Si 0.006 0.037

Sr 0.001 0.002

Zn 0.002 0.005

RESULTS

Substrate Characterization

Table 1 shows the results of the various analyses performed by Daniels et al. on the

two fly ashes utilized in this study (2006). Ash #18 is a low pH, high EC ash with no

17

calcium carbonate equivalence (CCE) liming capacity. Ash #28 is a high pH, low EC ash

with a CCE equal to 7.7%. Table 5 displays the sum of fractions results of the SEP

performed on all four materials prior to leaching. Fractionation data for these elements

for each material is reported later in the Results section.

Table 5: Sum of fractions from the SEP for select elements.

Material ------------mg kg-1------------

As Ba B Co Cr Cu Mo Ni Se S

Ash #18 119 885 144 40.8 107 115 17.6 60.2 74.5 12,030

Ash #28 58.5 536 80.2 17.0 71.6 56.4 12.3 24.1 17.9 2330

Sandstone 3.4 93.1 2.2 30.1 15.1 5.6 0.5 8.9 10.5 101

Refuse 69.3 157 10.3 12.8 30.2 26.9 0.8 25.5 11.8 18,800

Both ashes contained significant amounts of As, Cr, Mo, and Se, among other

elements, with Ash #18 having higher concentrations than Ash #28. The refuse

contained relatively high concentrations of As and Cr, moderate levels of Se, and low

levels of Mo. The sandstone contained lower concentrations of every element compared

to the refuse, with moderate levels of Cr and Se and low levels of As and Mo. The refuse

had an estimated lime requirement of about 35 Mg CaCO3 per 1000 Mg of material while

the sandstone had an estimated lime requirement of about 3 Mg CaCO3 per 1000 Mg of

material.

Leachate Electrical Conductivity

Leachate electrical conductivity (EC) for the six-month experimental period can be

viewed graphically in Figures 2A-2E. The error bars represent standard errors from the

three replications for each treatment. Week 1 displayed the most variation in EC for all

the treatments. The Ash #18 and refuse treatments displayed more variation in EC than

the Ash #28 and sandstone treatments. The relatively small size of the error bars overall

for the EC data show that the treatments columns generated very uniform results. Figures

3A and 3B display average EC values per treatment for Weeks 2 and 22, respectively.

Initially, there were significant differences between most of the treatments, but by the end

18

05

10

15

20

05

10

15

20

25

Week

EC (dS m-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR C

ontrol

S C

ontrol

18 C

ontrol

28 C

ontrol

Fig

ure

2A: L

each

ate

EC

(dS

m-1

) fro

m le

achi

ng c

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ns fo

r all

trea

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ts.

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; B =

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; P =

Pan

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19

05

10

15

20

05

10

15

20

25

Week

EC (dS m-1)

18-R

-B18-R

-P28-R

-B28-R

-PR Control

Fig

ure

2B: L

each

ate

EC

(dS

m-1

) fro

m le

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20

012345678

05

10

15

20

25

Week

EC (dS m-1)

18-S

-B18-S

-P28-S

-B28-S

-PS C

ontrol

Fig

ure

2C: L

each

ate

EC

(dS

m-1

) fro

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achi

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21

05

10

15

20

05

10

15

20

25

Week

EC (dS m-1)

18-R

-B18-R

-P18-S

-B18-S

-P18 C

ontrol

Fig

ure

2D: L

each

ate

EC

(dS

m-1

) fro

m le

achi

ng c

olum

ns fo

r Ash

#18

trea

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ts.

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; P =

Pan

cake

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22

02468

10

12

14

16

18

05

10

15

20

25

Week

EC (dS m-1)

28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

2E: L

each

ate

EC

(dS

m-1

) fro

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achi

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ns fo

r Ash

#28

trea

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or b

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; B =

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; P =

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23

01234567

18-R-B

18-R-P

18-S-B

18-S-P

28-R-B

28-R-P

28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Treatment

EC (dS m-1)

cbc

g

ded

b

fg

h

a

h

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Fig

ure

3A:

Ave

rage

EC

val

ues

(dS

m-1

) per

trea

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t at W

eek

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Key

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Ref

use;

S =

San

dsto

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ed; P

= P

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24

012345678

18-R-B

18-R-P

18-S-B

18-S-P

28-R-B

28-R-P

28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Treatment

EC (dS m-1)

bcb

ee

c

d

ee

a

ee

e

Fig

ure

3B:

Ave

rage

EC

val

ues

(dS

m-1

) per

trea

tmen

t at W

eek

22.

Val

ues

with

the

sam

e le

tter a

re n

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(alp

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Key

: R =

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

25

of the experiment these differences generally disappeared. Treatment 18-R-B and 18-R-P

only produced significantly different EC values for the first leaching event.

After initially high EC levels, most of the treatments dropped to below 4 dS m-1

after five weeks of leaching. However, leachate from refuse treated with Ash #18, both

blended and pancaked, did not reach values below 4 dS m-1 until the 14th week of

leaching. Both Ash # 18 and the refuse had much higher initial EC determinations via

saturated paste compared to Ash #28 and the sandstone. Leachates from both ash

controls dropped to below 2 dS m-1 after five weeks of leaching, and leachates from the

sandstone control were below 0.1 dS m-1 throughout the majority of the experiment. The

refuse control leachates dropped from 11.8 to 6.1 dS m-1 over the first 2.5 weeks, but rose

again to a value as high as 14.5 dS m-1 in the fifth week due to delayed low magnitude

sulfide oxidation processes. This spike in EC corresponds to a drop in refuse leachate pH

to about 2. There was also a corresponding rise and fall in leachate S due to the oxidation

of sulfide minerals in the refuse.

Leachate pH

Leachate pH data for the six-month experimental period are presented in Figures

4A – 4E. The error bars report standard errors from the three replications for each

treatment. Week 12 displayed the most variation in pH for all the treatments. The Ash

#28 and sandstone treatments displayed more variation in pH than the Ash #18 and refuse

treatments. The relatively small size of the error bars overall for the pH data again

indicates that the treatment replicate columns showed little within treatment variance.

Figures 5A and 5B display average pH values per treatment for Weeks 2 and 22,

respectively. Treatment 18-R-B and 18-R-P only generated significantly different pH

values for the first leaching event. There were no significant differences between

treatments 18-R-P and 28-R-P through the first seven weeks of the study.

The Ash #28 control leachates maintained a pH between 9.8-12 throughout the

experiment. The Ash #18 control leachates began with a pH value slightly under 4 that

gradually rose to approximately pH 6 at the end of the experiment. The sandstone control

leachates maintained a pH between 5.5 and 7 throughout most of the experiment. The

refuse control leachate pH started just below 3 and quickly dropped to a value around 2

26

02468

10

12

14

05

10

15

20

25

Week

pH18-R

-B18-R

-P18-S-B

18-S-P

28-R

-B28-R

-P28-S-B

28-S-P

R C

ontrol

S C

ontrol

18 Control

28 Control

Fig

ure

4A: L

each

ate

pH fr

om le

achi

ng c

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ns fo

r all

trea

tmen

ts.

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ars

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. K

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; B =

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; P =

Pan

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27

012345678

05

10

15

20

25

Week

pH18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

4B: L

each

ate

pH fr

om le

achi

ng c

olum

ns fo

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use

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28

0123456789

05

10

15

20

25

Week

pH18-S-B

18-S-P

28-S-B

28-S-P

S C

ontrol

Fig

ure

4C: L

each

ate

pH fr

om le

achi

ng c

olum

ns fo

r san

dsto

ne tr

eatm

ents

. E

rror

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ent s

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h

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= S

ands

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; B =

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nded

; P =

Pan

cake

d.

29

01234567

05

10

15

20

25

Week

pH18-R

-B18-R

-P18-S-B

18-S-P

18 Control

Fig

ure

4D: L

each

ate

pH fr

om le

achi

ng c

olum

ns fo

r Ash

#18

trea

tmen

ts.

Err

or b

ars

repr

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t sta

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rors

for e

ach

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ey: R

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= S

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tone

; B =

Ble

nded

; P =

Pan

cake

d.

30

02468

10

12

14

05

10

15

20

25

Week

pH28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

4E: L

each

ate

pH fr

om le

achi

ng c

olum

ns fo

r Ash

#28

trea

tmen

ts.

Err

or b

ars

repr

esen

t sta

ndar

d er

rors

for e

ach

trea

tmen

t dat

e. K

ey: R

= R

efus

e; S

= S

ands

tone

; B =

Ble

nded

; P =

Pan

cake

d.

31

02468

10

12

14

18-R-B

18-R-P

18-S-B

18-S-P

28-R-B

28-R-P

28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Treatment

pH

ffg

ee

c

f

b

d

g

c

e

a

Fig

ure

5A: A

vera

ge p

H v

alue

s pe

r tre

atm

ent a

t Wee

k 2.

Val

ues

with

the

sam

e le

tter a

re n

ot s

igni

fica

ntly

dif

fere

nt (a

lpha

=

0.05

). K

ey: R

= R

efus

e; S

= S

ands

tone

; B =

Ble

nded

; P =

Pan

cake

d.

32

02468

10

12

18-R-B

18-R-P

18-S-B

18-S-P

28-R-B

28-R-P

28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Treatment

pH

ii

fg

c

h

b

ed

j

de

a

Fig

ure

5B: A

vera

ge p

H v

alue

s pe

r tre

atm

ent a

t Wee

k 22

. V

alue

s w

ith th

e sa

me

lette

r are

not

sig

nifi

cant

ly d

iffe

rent

(alp

ha =

0.05

). K

ey: R

= R

efus

e; S

= S

ands

tone

; B =

Ble

nded

; P =

Pan

cake

d.

33

for the rest of the experiment. The blended treatments generally maintained a higher

leachate pH than corresponding pancake treatments. This effect was particularly

prevalent with the Ash #28 treatments. Ash #28 blended with refuse maintained a pH

over 6.5 after the first 5 weeks of leaching while Ash #28 pancaked on top of refuse gave

pH values between 3 and 4 throughout the study. Similarly, Ash #28 blended with

sandstone maintained a pH between 7.5 and 8.5 while its pancaked counterpart had pH

values between 4.5 and 6.3, which were below that of the sandstone control for most of

the measurements. Ash #18 treatments did not display such a dramatic difference

between blended versus pancaked methods. Ash #18 blended and pancaked with refuse

both produced similar pH values between 2.6 and 3.5 for most of the experiment. Ash

#18 blended with sandstone produced slightly higher pH values than the pancaked

treatment for most of the measurements, with the blended treatment between pH 3.8 and

5.3 and the pancaked treatment between pH 3 and 5.

Between Weeks 12 and 14 the sandstone and Ash #18 treatments experienced a

significant decline in pH (Figures 4C and 4D). The sandstone control dropped from a pH

of 6.5 in week 10 to a pH of 3 in Week 12, and the pancake treatments over sandstone

both dropped in pH in a similar fashion. Ash #18 blended with sandstone also displayed

a dip in pH, while the Ash #28/sandstone blended treatment did not, indicating that Ash

#28 was able to buffer the acidity produced during this period. The Ash #18 control also

dropped from a pH of 5 to 3.4 during this period. By the 16th week of leaching, all

treatments increased in pH back to values measured for week 10 or higher.

Leachate Arsenic

Figures 6A - 6E show the leachate As concentrations for all treatments. The

refuse control eluted large amounts of As, rising to 29.9 mg L-1 in Week 8. The 18-R-P

and 28-R-P treatments produced leachate As concentrations of 1.9 and 1.7 mg L-1,

respectively, in the first leachates, and then concentrations declined to below 0.05 mg L-1

for the remainder of the study. Treatment 18-R-B generated an initial As level of 0.22

mg L-1 and another spike at Week 12 of 0.11 mg L-1. Treatment 28-R-B produced As

concentrations below 0.06 mg L-1 throughout the study. Treatments 18-S-B and 18-S-P

34

0.01

0.11

10

100

05

10

15

20

25

Week

As (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR C

ontrol

S C

ontrol

18 C

ontrol

28 C

ontrol

Fig

ure

6A: L

each

ate

As

in m

g L

-1 fo

r all

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

35

0.01

0.11

10

100

05

10

15

20

25

Week

As (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR Control

Fig

ure

6B: L

each

ate

As

in m

g L

-1 fo

r ref

use

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

36

0.01

0.11

05

10

15

20

25

Week

As (mg L-1)

18-S-B

18-S-P

28-S-B

28-S-P

S Control

Fig

ure

6C: L

each

ate

As

in m

g L

-1 fo

r san

dsto

ne tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

37

0.01

0.11

10

05

10

15

20

25

Week

As (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

18 Control

Fig

ure

6D: L

each

ate

As

in m

g L

-1 fo

r Ash

#18

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

38

0.01

0.11

10

05

10

15

20

25

Week

As (mg L-1)

28-R

-B28-R

-P28-S-B

28-S-P

28 Control

Fig

ure

6E: L

each

ate

As

in m

g L

-1 fo

r Ash

#28

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

39

both leached comparable amounts of As, with 18-S-P releasing As over a longer

timeframe than 18-S-B.

Leachate Boron

Figures 7A – 7E presents leachate B concentrations for all treatments. Boron

concentrations in the leachate were initially high in ash treatments, and declined to below

10 mg L-1 for all treatments by the 5th week of leaching. Table 5 shows that the ashes

contained much higher B concentrations than the refuse or sandstone, and that Ash #18

had almost twice as much B than Ash #28. Accordingly, the treatments with Ash #18

produced leachates with the highest concentrations of B, with the Ash #18 control

generating nearly 90 mg B L-1 in the first leaching event. Boron in the refuse and

sandstone are predominantly found in the residual fraction, while in Ash #18 and #28 it is

found predominantly in the exchangeable and carbonate fraction, respectively, making it

more prone to leaching from both ashes.

Leachate Chromium

Leachate Cr concentrations for all treatments are illustrated in Figures 8A – 8E.

The Ash #18 control, Treatment 18-R-B, and Treatment 18-R-P produced initial Cr

concentrations of 5, 3.7, and 1.1 mg L-1 in the first leachate, but dropped to below 1 mg

L-1 in all subsequent leachates. The Ash #28 control initially eluted 0.55 mg L-1 of Cr,

and then concentrations dropped to under 0.1 mg L-1 until Week 4. At Week 4,

concentrations began to rise again to as high as 0.8 mg L-1 in Week 6. By Week 12,

concentrations once again dropped below 0.2 mg L-1 and stayed there for the remainder

of the study. The refuse control Cr was at or below 1 mg L-1 in all leachates. The highest

concentration of Cr for the refuse control was 1 mg L-1 on Week 8, which coincided with

the lowest pH value (1.94) for the refuse control. All other treatments were under 1 mg

L-1, with many below detection (0.002 mg L-1).

Leachate Molybdenum

Molybdenum leachate concentrations are displayed in Figures 9A – 9E. The Ash

#28 control is the only treatment with significant Mo leaching as it produced an initial

40

0.01

0.11

10

100

05

10

15

20

25

Week

B (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

28-R

-B28-R

-P28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Fig

ure

7A: L

each

ate

B in

mg

L-1

for a

ll tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

=

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

41

0.01

0.11

10

100

05

10

15

20

25

Week

B (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

7B: L

each

ate

B in

mg

L-1

for r

efus

e tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

=

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

42

0.01

0.11

10

100

05

10

15

20

25

Week

B (mg L-1)

18-S

-B18-S

-P28-S

-B28-S

-PS C

ontrol

Fig

ure

7C: L

each

ate

B in

mg

L-1

for s

ands

tone

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

43

0.11

10

100

05

10

15

20

25

Week

B (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

18 Control

Fig

ure

7D: L

each

ate

B in

mg

L-1

for A

sh #

18 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

44

0.01

0.11

10

100

05

10

15

20

25

Week

B (mg L-1)

28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

7E: L

each

ate

B in

mg

L-1

for A

sh #

28 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

45

0.001

0.01

0.11

10

05

10

15

20

25

Week

Cr (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PS Control

18 C

ontrol

28 C

ontrol

R Control

Fig

ure

8A: L

each

ate

Cr i

n m

g L

-1 fo

r all

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

46

0.001

0.01

0.11

10

05

10

15

20

25

Week

Cr (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR Control

Fig

ure

8B: L

each

ate

Cr i

n m

g L

-1 fo

r ref

use

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

47

0.001

0.01

0.11

05

10

15

20

25

Week

Cr (mg L-1)

18-S

-B18-S

-P28-S

-B28-S

-PS C

ontrol

Fig

ure

8C: L

each

ate

Cr i

n m

g L

-1 fo

r san

dsto

ne tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

48

0.001

0.01

0.11

10

05

10

15

20

25

Week

Cr (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P18 C

ontrol

Fig

ure

8D: L

each

ate

Cr i

n m

g L

-1 fo

r Ash

#18

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

49

0.001

0.01

0.11

05

10

15

20

25

Week

Cr (mg L-1)

28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

8E: L

each

ate

Cr i

n m

g L

-1 fo

r Ash

#28

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

50

0.01

0.11

10

100

05

10

15

20

25

Week

Mo (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR Control

S Control

18 C

ontrol

28 C

ontrol

Fig

ure

9A: L

each

ate

Mo

in m

g L

-1 fo

r all

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

51

0.01

0.11

05

10

15

20

25

Week

Mo (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

9B: L

each

ate

Mo

in m

g L

-1 fo

r ref

use

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

52

0.01

0.11

05

10

15

20

25

Week

Mo (mg L-1)

18-S-B

18-S-P

28-S-B

28-S-P

S Control

Fig

ure

9C: L

each

ate

Mo

in m

g L

-1 fo

r san

dsto

ne tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

=

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

53

0.01

0.11

05

10

15

20

25

Week

Mo (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

18 Control

Fig

ure

9D: L

each

ate

Mo

in m

g L

-1 fo

r Ash

#18

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

54

0.01

0.11

10

100

05

10

15

20

25

Week

Mo (mg L-1)

28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

9E: L

each

ate

Mo

in m

g L

-1 fo

r Ash

#28

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

55

level of 13.4 mg L-1, then concentrations dropped to below 0.4 mg L-1 by the second

week. At Week 3.5, concentrations began to rise again to as high as 1.55 mg L-1 in Week

5. By Week 7, concentrations once again dropped below 0.3 mg L-1 and remained low

for the remainder of the study. Leachate Mo concentrations for all other treatments were

less than 0.25 mg L-1, with many below detection limit.

Leachate Selenium

Figures 10A – 10E present leachate Se concentrations for all treatments. All

refuse treatments produced initial Se elution levels between 1.1 and 2.1 mg L-1, then

concentrations dropped below 0.3 mg L-1 by Week 4. The refuse control Se

concentrations rose again in Weeks 5-8 to values above 0.5 mg L-1 as S oxidation

reactions dominated leachate chemistry. After Week 8, values steadily declined in each

subsequent leachate. Ash #18 control and Ash #28 control produced Week 1 Se

concentrations of 0.33 and 0.23 mg L-1, respectively. In Week 10, the Ash #28 control

experienced a small rise in Se concentration to 0.13 mg L-1. Most of the leachates from

the other treatments were below detection.

Leachate Sulfur

Figures 11A – 11E present total leachate S concentrations for all treatments. For

all treatments except the refuse control, S concentrations declined to below 2000 mg L-1

by the third week of leaching. As has been mentioned above, leachate S concentrations

for the refuse control rose and fell in accordance with the leachate EC and pH due to the

overriding effects of pyrite oxidation and associated sulfate reaction products leaching.

The sandstone control experienced a slight increase in leachate concentration of S in

Week 12. This increase corresponds to a drop in pH for the sandstone control from 6.5 to

3 and a rise in EC from 0.07 to 0.87 dS m-1. In Week 16, treatments 18-R-B, 18-R-P, and

18-S-P all experienced a slight decline in concentration of S leached. The concentrations

rose again for the next measured sampling date (Week 18) and then stayed relatively

constant thereafter.

56

0.01

0.11

10

05

10

15

20

25

Week

Se (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR C

ontrol

S C

ontrol

18 C

ontrol

28 C

ontrol

Fig

ure

10A

: Lea

chat

e Se

in m

g L

-1 fo

r all

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

57

0.01

0.11

10

05

10

15

20

25

Week

Se (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR Control

Fig

ure

10B

: Lea

chat

e Se

in m

g L

-1 fo

r ref

use

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

58

0.01

0.11

05

10

15

20

25

Week

Se (mg L-1)

18-S

-B18-S

-P28-S

-B28-S

-PS C

ontrol

Fig

ure

10C

: Lea

chat

e Se

in m

g L

-1 fo

r san

dsto

ne tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

=

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

59

0.01

0.11

10

05

10

15

20

25

Week

Se (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P18 C

ontrol

Fig

ure

10D

: Lea

chat

e Se

in m

g L

-1 fo

r Ash

#18

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

60

0.01

0.11

10

05

10

15

20

25

Week

Se (mg L-1)

28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

10E

: Lea

chat

e Se

in m

g L

-1 fo

r Ash

#28

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

61

1

10

100

1000

10000

05

10

15

20

25

Week

S (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR C

ontrol

S C

ontrol

18 C

ontrol

28 C

ontrol

Fig

ure

11A

: Lea

chat

e S

in m

g L

-1 fo

r all

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

62

1

10

100

1000

10000

05

10

15

20

25

Week

S (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

11B

: Lea

chat

e S

in m

g L

-1 fo

r ref

use

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

63

1

10

100

1000

10000

05

10

15

20

25

Week

S (mg L-1)

18-S-B

18-S-P

28-S-B

28-S-P

S Control

Fig

ure

11C

: Lea

chat

e S

in m

g L

-1 fo

r san

dsto

ne tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

64

1

10

100

1000

10000

05

10

15

20

25

Week

S (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P18 C

ontrol

Fig

ure

11D

: Lea

chat

e S

in m

g L

-1 fo

r Ash

#18

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

65

1

10

100

1000

10000

05

10

15

20

25

Week

S (mg L-1)

28-R

-B28-R

-P28-S-B

28-S-P

28 Control

Fig

ure

11E

: Lea

chat

e S

in m

g L

-1 fo

r Ash

#28

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

66

Cation Leaching

While oxyanion leaching was the focus of this study, we did examine the leaching

behavior of select metal cations including Ba, Co, Cu, and Ni. Figure 12 displays results

of the pre-leaching SEP for these cations and Figures 13A-16E display the leachate

chemistry for the four cations over the course of the study. The ashes contained higher

concentrations of Ba and Cu than either the refuse or sandstone. The Ba concentrations

for the ashes were particularly high, containing 3 to 9 times more Ba than the refuse or

sandstone. Cobalt concentrations for Ash #18 and the sandstone were relatively high,

while the refuse and Ash #28 contain moderate levels. Nickel concentrations were low in

the sandstone, moderate in the refuse and Ash #28, and high in Ash #18. The dominant

fractions for these metals for all four materials are the crystalline Fe and Mn oxide and

residual fractions, constituting at least 64% for each metal in each material. The

sandstone has the largest percentage of metals in the crystalline Fe and Mn oxide fraction

compared to the other materials.

The Ash #28 control generated large concentrations (up to 12.5 mg L-1) of

leachate Ba from 1.5 to 4 weeks. No other treatment produced concentrations higher than

0.27 mg Ba L-1 for the entire study. Treatments 18-R-B, 18-R-P, 28-R-P, and the refuse

control each produced high initial concentrations of Co equaling 25.1, 34.6, 29.9, and

15.7 mg L-1, respectively. The refuse control continued to leach greater than 5 mg Co L-1

until Week 8, while the other treatments dropped below 5 mg Co L-1 by Week 3. The

Ash #28 control was below detection throughout the experiment and the Ash #18 control

showed an early concentration of 3.2 mg Co L-1 that dropped below 1 mg L-1 for each

subsequent sample. Treatment 18-S-B leached between 1.3 and 4.0 mg Co L-1 for the

first 4 weeks, then dropped below 1 mg L-1 for the remainder of the study.

The Cu leaching dynamics were very similar to Co. Treatments 18-R-B, 18-R-P,

28-R-P, and the refuse control each produced high initial concentrations of Cu equaling

19.3, 33.6, 30.1, and 17.7 mg L-1, respectively. The refuse control continued to leach

concentrations greater than 5 mg Cu L-1 until Week 10, reaching concentrations as high

as 14.5 mg L-1 in Week 5. Treatments 18-R-B, 18-R-P, and 28-R-P dropped below 5 mg

67

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Ba

Co

Cu

Ni

Pb

Zn

Refuse

157

12.8

26.9

25.5

17.6

157

Sandstone

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Ba

Co

Cu

Ni

Pb

Zn

93.1

30.1

5.65

8.90

15.0

48.3

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Ba

Co

Cu

Ni

Pb

Zn

Ash #18

885

40.8

115

60.2

65.7

150

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Ba

Co

Cu

Ni

Pb

Zn

Ash #28

536

17.0

56.4

24.1

21.8

47.7

Exchangeable

Carbonates

Amorphous Fe & M

n

Crystalline Fe & M

n

Residual

Fig

ure

12: P

re-l

each

ing

SEP

resu

lts fo

r Ba,

Co,

Cu,

and

Ni.

Dat

a ar

e th

e m

ean

of th

ree

repl

icat

ions

. V

alue

s at

the

top

of e

ach

bar r

epre

sent

ele

men

tal t

otal

mas

s (m

g kg

-1) v

ia s

um o

f fra

ctio

ns.

68

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Ba (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR C

ontrol

S C

ontrol

18 C

ontrol

28 C

ontrol

Fig

ure

13A

: Lea

chat

e B

a in

mg

L-1

for a

ll tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

=

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

69

0.001

0.01

0.11

05

10

15

20

25

Week

Ba (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

13B

: Lea

chat

e B

a in

mg

L-1

for r

efus

e tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

70

0.01

0.11

05

10

15

20

25

Week

Ba (mg L-1)

18-S-B

18-S-P

28-S-B

28-S-P

S Control

Fig

ure

13C

: Lea

chat

e B

a in

mg

L-1

for s

ands

tone

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

71

0.001

0.01

0.11

05

10

15

20

25

Week

Ba (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

18 Control

Fig

ure

13D

: Lea

chat

e B

a in

mg

L-1

for A

sh #

18 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

72

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Ba (mg L-1)

28-R

-B28-R

-P28-S

-B28-S

-P28 C

ontrol

Fig

ure

13E

: Lea

chat

e B

a in

mg

L-1

for A

sh #

28 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

73

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Co (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P28-R

-B28-R

-P28-S

-B28-S

-PR C

ontrol

S C

ontrol

18 C

ontrol

28 C

ontrol

Fig

ure

14A

: Lea

chat

e C

o in

mg

L-1

for a

ll tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

=

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

74

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Co (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR Control

Fig

ure

14B

: Lea

chat

e C

o in

mg

L-1

for r

efus

e tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

75

0.001

0.01

0.11

10

05

10

15

20

25

Week

Co (mg L-1)

18-S

-B18-S

-P28-S

-B28-S

-PS Control

Fig

ure

14C

: Lea

chat

e C

o in

mg

L-1

for s

ands

tone

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

76

0.01

0.11

10

100

05

10

15

20

25

Week

Co (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

18 Control

Fig

ure

14D

: Lea

chat

e C

o in

mg

L-1

for A

sh #

18 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

77

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Co (mg L-1)

28-R

-B28-R

-P28-S-B

28-S-P

28 Control

Fig

ure

14E

: Lea

chat

e C

o in

mg

L-1

for A

sh #

28 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

78

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Cu (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

28-R

-B28-R

-P28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Fig

ure

15A

: Lea

chat

e C

u in

mg

L-1

for a

ll tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

=

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

79

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Cu (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

15B

: Lea

chat

e C

u in

mg

L-1

for r

efus

e tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

80

0.001

0.01

0.11

05

10

15

20

25

Week

Cu (mg L-1)

18-S-B

18-S-P

28-S-B

28-S-P

S Control

Fig

ure

15C

: Lea

chat

e C

u in

mg

L-1

for s

ands

tone

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

81

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Cu (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P18 C

ontrol

Fig

ure

15D

: Lea

chat

e C

u in

mg

L-1

for A

sh #

18 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

82

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Cu (mg L-1)

28-R

-B28-R

-P28-S-B

28-S-P

28 Control

Fig

ure

15E

: Lea

chat

e C

u in

mg

L-1

for A

sh #

28 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

83

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Ni (mg L-1)

18-R

-B18-R

-P18-S-B

18-S-P

28-R

-B28-R

-P28-S-B

28-S-P

R Control

S Control

18 Control

28 Control

Fig

ure

16A

: Lea

chat

e N

i in

mg

L-1

for a

ll tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

=

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

84

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Ni (mg L-1)

18-R

-B18-R

-P28-R

-B28-R

-PR C

ontrol

Fig

ure

16B

: Lea

chat

e N

i in

mg

L-1

for r

efus

e tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e; S

= Sa

ndst

one;

B =

Ble

nded

; P =

Pan

cake

d.

85

0.001

0.01

0.11

10

05

10

15

20

25

Week

Ni (mg L-1)

18-S-B

18-S-P

28-S-B

28-S-P

S Control

Fig

ure

16C

: Lea

chat

e N

i in

mg

L-1

for s

ands

tone

trea

tmen

ts.

Dat

a ar

e fr

om c

ompo

site

s of

thre

e re

plic

atio

ns.

Key

: R =

Ref

use;

S =

San

dsto

ne; B

= B

lend

ed; P

= P

anca

ked.

86

0.01

0.11

10

100

05

10

15

20

25

Week

Ni (mg L-1)

18-R

-B18-R

-P18-S

-B18-S

-P18 C

ontrol

Fig

ure

16D

: Lea

chat

e N

i in

mg

L-1

for A

sh #

18 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

87

0.001

0.01

0.11

10

100

05

10

15

20

25

Week

Ni (mg L-1)

28-R

-B28-R

-P28-S-B

28-S-P

28 Control

Fig

ure

16E

: Lea

chat

e N

i in

mg

L-1

for A

sh #

28 tr

eatm

ents

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

. K

ey: R

= R

efus

e;

S =

Sand

ston

e; B

= B

lend

ed; P

= P

anca

ked.

88

Cu L-1 by Week 2. The Ash #18 control produced a high initial level of 12.4 mg Cu L-1

then leached concentrations below 1 mg L-1 after Week 3. Both the sandstone and Ash

#28 controls were below 0.02 mg Cu L-1 for the entire study. The Ni leaching pattern

also showed many similarities to Co and Cu leaching. Treatments 18-R-B, 18-R-P, 28-R-

P, and the refuse control each generated high initial levels of Ni equaling 27.5, 35.5, 29.5,

and 14.1 mg L-1, respectively. The refuse control continued to leach concentrations

greater than 5 mg Ni L-1 until Week 10, reaching concentrations as high as 9.8 mg L-1 in

Week 4. Treatments 18-R-B, 18-R-P, and 28-R-P dropped below 5 mg Ni L-1 by Week

3. The Ash #18 control produced a high initial concentration of 7.6 mg Ni L-1 then

leached concentrations under 2 mg L-1 after the first leaching event. Both the sandstone

and Ash #28 controls were below 0.04 mg Ni L-1 for the entire study.

Sequential Extraction Procedures

Pre-Leaching

Figure 17 displays the results of the sequential extraction procedure for As, B, Cr,

Mo, Se, and S in the four materials used prior to leaching. The refuse contained a

significant amount of As, Cr, and S, 69.3, 30.2, and 18,800 mg kg-1, respectively, and

contained little B (10.3 mg kg-1) and Mo (0.8 mg kg-1) and a moderate amount of Se (11.8

mg kg-1). All six of these elements were predominantly found in the crystalline oxide and

residual fractions of the refuse. The sandstone, compared to the refuse, contained

relatively low concentrations of As, B, Cr, Mo, Se, and S totaling 3.4, 2.15, 15.1, 0.5,

10.5, and 101 mg kg-1, respectively. Like the refuse, the crystalline oxide and residual

fractions contained most of these elements, although over 50% of the S in the sandstone

was extracted during the carbonate and exchangeable extractions. Ash #18 contained

relatively high concentrations of As, B, Cr, Mo, Se, and S totaling 119, 144, 107, 17.6,

74.5, and 12,030 mg kg-1, respectively. Significant portions of As, Mo, and Se resided in

the amorphous oxide fraction. Also, approximately 53% of the B and 86% of the S was

extracted during the readily bioavailable carbonate and exchangeable portions of the SEP

in Ash #18. The majority of the Cr (~75%) was found in the crystalline oxide and

residual fractions.

89

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

Ash # 28

58.5

71.6

12.3

17.9

Exchangeable

Carbonates

Amorphous Fe & M

n

Crystalline Fe & M

n

Residual

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

Refuse

69.3

30.2

0.8

11.8 10.3

18,811

Sandstone

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

3.4

15.1

0.5

10.5 2.15

101

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

Ash # 18

119

107

17.6

74.5 144 12,025

80.2

2327

Fig

ure

17: R

esul

ts fr

om S

EP

prio

r to

leac

hing

for A

s, C

r, M

o, S

e, B

, and

S.

Dat

a ar

e th

e m

ean

of th

ree

repl

icat

ions

. V

alue

s at

the

top

of e

ach

bar r

epre

sent

ele

men

tal t

otal

mas

s (m

g kg

-1) v

ia s

um o

f fra

ctio

ns.

90

Ash #28 contained relatively high concentrations of As, B, Cr, Mo, totaling 58.5,

80.2, 71.6, and 12.3 mg kg-1, respectively, and moderate concentrations of Se and S at

17.9 and 2330 mg kg-1, respectively. Like Ash #18, Ash #28 had significant portions of

As and Mo residing in the amorphous oxide fraction; however, it had higher amounts of

these elements in the carbonate fraction compared to Ash #18. The Se in Ash #28 was

distributed relatively evenly between the carbonate, amorphous oxide, crystalline oxide,

and residual fractions. Over 50% of the B in Ash #28 was in the carbonate fraction.

About 42% of the S was extracted with the exchangeable fraction while about 47% was

extracted with the carbonate fraction. Over 60% of the Cr in Ash #28 was in the

crystalline oxide and residual fractions.

Post-Leaching

Figures 18A – 18D display the concentrations of As, B, Cr, Mo, Se, and S from

the SEP performed on the materials after leaching. As expected, total concentrations for

the six elements were significantly lower in the post-leaching materials when compared

to pre-leached materials. Table 6 displays the difference between the initial amount of

element added to the columns and the amount left after leaching as a percent for all

treatments and controls. The columns with pancake treatments were sampled twice: one

homogenized sample from the ash layer and one homogenized sample from the substrate

(refuse or sandstone) layer.

Most of the pancake treatments contained greater elemental concentrations in the

ash layer than in the substrate layer. However, treatment 28-R-P had slightly higher

concentrations of As, Mo, and S in the refuse layer than in the ash layer and treatment 18-

R-P had more S in the refuse layer than in the ash layer. The substrate layers for

treatments 28-R-P and 28-S-P contained greater concentrations of Mo post-leaching than

pre-leaching. Also, the sandstone layers under ash had much higher concentrations of S

post-leaching compared to pre-leaching values.

It is assumed that one can gain insight in the mobility of elements by comparing

the mass of elements in the treatments to corresponding controls post-leaching. An

increase in a treatment compared to the corresponding control would indicate some

amount of sorption/precipitation occurring in the treatment. Treatments 18-R-B, 28-S-B,

91

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

Ash # 28

13.3

8.16

1.12

0.65

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

Refuse

16.2

3.800.63

0.580.47

2898

Sandstone

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

0.993.38

0.27

00.11

60.2

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

Ash # 18

16.9

6.66

2.942.94

6.77

103

18.1

434

Exchangeable

Carbonates

Amorphous Fe & M

n

Crystalline Fe & M

n

Residual

Fig

ure

18A

: Res

ults

of t

he p

ost-

leac

hing

SE

P fo

r As,

Cr,

Mo,

Se,

B, a

nd S

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

.

Val

ues

at th

e to

p of

eac

h ba

r rep

rese

nt e

lem

enta

l tot

al m

ass

(mg

kg-1

) via

sum

of f

ract

ions

.

92

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

18-R-B

27.5

5.98

1.96

0.65

1.57

3305

18-R-P (substrate)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

15.6

3.33

0.40

00.76

2805

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

18-R-P (pancake)

18.95

7.38

3.04

3.36

7.51

407

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

18-S-B

5.86

6.08

1.60

1.14

2.41

131

Exchangeable

Carbonates

Amorphous Fe & M

n

Crystalline Fe & M

n

Residual

Fig

ure

18B

: Res

ults

of t

he p

ost-

leac

hing

SE

P fo

r As,

Cr,

Mo,

Se,

B, a

nd S

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

.

Val

ues

at th

e to

p of

eac

h ba

r rep

rese

nt e

lem

enta

l tot

al m

ass

(mg

kg-1

) via

sum

of f

ract

ions

.

93

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

18-S-P (substrate)

1.16

3.81

0.34

00.57

133

18-S-P (pancake)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

15.4

6.66

2.76

2.67

6.37

119

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

28-R-B

19.6

9.16

1.61

1.04

3.97

2599

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

28-R-P (substrate)

15.2

4.08

1.81

0.32

0.64

2714

Exchangeable

Carbonates

Amorphous Fe & M

n

Crystalline Fe & M

n

Residual

Fig

ure

18C

: Res

ults

of t

he p

ost-

leac

hing

SE

P fo

r As,

Cr,

Mo,

Se,

B, a

nd S

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

.

Val

ues

at th

e to

p of

eac

h ba

r rep

rese

nt e

lem

enta

l tot

al m

ass

(mg

kg-1

) via

sum

of f

ract

ions

.

94

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

28-R-P (pancake)

13.0

7.73

1.26

1.29

17.5

412

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

28-S-P (substrate)

1.08

3.70

0.71

00.30

130

28-S-B

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

4.52

7.54

0.67

0.42

2.63

18.2

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

As

Cr

Mo

Se

BS

28-S-P (pancake)

13.9

8.47

1.30

0.92

18.4

410

Exchangeable

Carbonates

Amorphous Fe & M

n

Crystalline Fe & M

n

Residual

Fig

ure

18D

: Res

ults

of t

he p

ost-

leac

hing

SE

P fo

r As,

Cr,

Mo,

Se,

B, a

nd S

. D

ata

are

from

com

posi

tes

of th

ree

repl

icat

ions

.

Val

ues

at th

e to

p of

eac

h ba

r rep

rese

nt e

lem

enta

l tot

al m

ass

(mg

kg-1

) via

sum

of f

ract

ions

.

95

Table 6: Percent differences in mass (mg) added from pre- to post-leaching for As, B, Cr,

Mo, Se, and S in the four materials. Negative values represent increases in amount of that

element in the material after leaching.

% Difference

Treatment As B Cr Mo Se S

18-R-B 63 93 84 11 96 84

18-R-P (substrate) 78 93 89 50 100 100

18-R-P (pancake) 84 95 93 83 95 99

18-S-B 54 83 73 16 93 60

18-S-P (substrate) 66 74 75 33 100 -3182

18-S-P (pancake) 87 96 94 84 96 77

28-R-B 71 79 74 30 92 98

28-R-P (substrate) 78 94 87 -124 97 99

28-R-P (pancake) 78 78 89 90 93 94

28-S-B 57 78 66 67 96 69

28-S-P (substrate) 68 86 75 -40 100 -2481

28-S-P (pancake) 76 77 88 90 95 -17

R Control 77 95 87 22 95 85

S Control 71 95 78 48 100 40

18 Control 86 95 94 83 96 99

28 Control 77 78 89 91 96 81

18-S-P substrate layer, and 28-S-P substrate layer each displayed a greater amount of

elements in the post-leaching material compared to corresponding controls for all the

elements except Se. Treatment 18-S-B had greater amount of elements in the post-

leaching material compared to the controls for all the elements. Treatment 28-R-B had

greater amount of elements in the post-leaching material compared to the controls for all

elements except for S. The refuse layer under Ash #18 had a greater amount of elements

in the post-leaching material relative to the refuse control solely for B, while the refuse

layer under Ash #28 had greater amount of elements in the post-leaching material relative

to the refuse control for Cr, Mo, and B. The ash layers generally displayed similar

96

amounts of elements in post-leaching materials to the corresponding controls for each

element. Selenium was below detection for three of the four substrates under ash layers

and for the sandstone control.

For most treatments there was a general trend for As, Cr, Mo, Se, B, and S to be

more associated with the crystalline oxide phase and less associated with the residual

phase in the post-leached materials compared to the pre-leached materials. The

percentage of As, Cr, and Mo in the crystalline Fe and Mn oxide fraction increased after

leaching for all of the treatments. After leaching, the percentage of Se associated with

the crystalline Fe and Mn oxide and residual fractions increased in the refuse control,

blended treatments, and substrate layers. The Se in the ash controls and ash pancake

layers became more associated with the amorphous Fe and Mn oxide and carbonate

fractions. Selenium in the Ash #28 pancake layers also became more associated with the

exchangeable fraction. Sulfur became more associated with the exchangeable and

crystalline Fe and Mn oxide fractions for the controls, the Ash #18 treatments, and the

Ash #28 pancake layers after leaching. The Ash #28 blended treatments and substrate

layers under Ash #28 pancakes still displayed significant amounts of S associated with

the residual fraction after leaching.

DISCUSSION

Leachate Electrical Conductivity

Soil saturated paste EC values greater than 4 dS m-1 are considered to be growth

inhibiting to salt sensitive plants (Brady and Weil, 2004). However, these treatments are

directed towards neutralizing potential acidity, not for direct vegetation establishment.

The leachate S concentrations (Figure 11B) closely follow the leachate EC (Figure 2B)

for the refuse control due to the dominant overall effects of pyrite oxidation in the

absence of alkaline amendments. The delayed oxidation of recalcitrant pyritic minerals

in the sandstone may also offer a potential explanation for the sudden drop in pH and

slight rise in EC for the pancaked sandstone treatments and sandstone control in Week

12. However, the sandstone control was the only treatment to display a spike in leachate

S concentration during Week 12. The initial high EC values associated with the Ash # 18

treatments may be attributed to a combination of soluble sulfate and B salts leaching.

97

The Ash #18 control generated significant leachate B concentrations in the first leaching

events (Figure 7D) and also produced high S elution compared to Ash #28 (Figures 11D

and 11E).

Leachate pH

The root growth of many plant species is inhibited when the pH of a soil is less

than 4.5 (Daniels et al., 1996) and a pH of 5.5 or greater is generally required for the

successful establishment of mixed grass and legume vegetation on disturbed land

(Skousen and Zipper, 1997). With this in mind, blending ash with coal refuse is a more

appropriate co-disposal method than layering ash on top of refuse since even the alkaline

ash used in this study produced leachates at pH 4.0 or less when it was pancaked on top

of the refuse. The Ash #28 blended treatments both produced leachate pH between 6 and

8 for the majority of the study. As mentioned above, the pancaked sandstone treatments

and sandstone control experienced a dramatic decline in pH from Week 12 to Week 14

and then a return to a higher pH in Week 16. One hypothesis to explain this behavior is

the delayed oxidation of recalcitrant pyrite minerals in the sandstone. If this were the

case one would expect an increase in leachate S concentrations and consequently an

increase in leachate EC. The sandstone control and pancaked sandstone treatments do

exhibit an increase in leachate EC, however only the sandstone control exhibits an

increase in leachate S. Sulfate precipitation and sorption reactions in the pancake

treatment may be responsible for the absence of increased S concentrations in the

leachate. There was also a drop in pH at the same time in the Ash #18 control which

cannot be as easily explained by recalcitrant pyrite oxidation. Similarly, the fact that only

these three treatments produced the pronounced pH drop in weeks 12 to 14 is curious.

Arsenic

The refuse material itself was most responsible for the leaching of As. The refuse

control contained 69.3 mg kg-1 of As, approximately 86% of which was in the residual

fraction (Figure 17). Despite this, a large amount of As eluted from the refuse control.

From Week 4 to Week 16 greater than 10 mg As L-1 eluted from the refuse control

(Figure 6B). This can be attributed to the refuse control quickly acidifying to pH values

98

near 2, which dissolves the residual minerals in the refuse and releases As and other

elements associated with those minerals. The largest leachate As concentration from the

refuse control (29.9 mg L-1) occurred when the refuse control was at its lowest pH value

(1.94). Daniels et al. (2006) also recorded significant As release from an acidic coal

refuse as pH values fell below 3. The Ash #18 control had the highest total concentration

of As prior to leaching (119 mg kg-1), about 71% of which was in the amorphous Fe and

Mn oxide fraction. The Ash #18 control eluted 0.33 mg As L-1 in the first leachate, and

the Ash #18/sandstone treatments both eluted between 0.1 and 0.3 mg As L-1 for the first

3.5 weeks. Both ash treatments blended with refuse delayed the leaching of As compared

to the corresponding pancake treatments. On the other hand, the blended Ash #18

treatment with the sandstone was the first to leach As while the corresponding pancake

treatment leached As later, but over a longer period of time. The Ash #28 sandstone

treatments and control were below 0.05 mg As L-1 for the entire study. Although both

ashes had high concentrations of As, most of this was associated with oxides of Fe and

Al. Arsenic forms strong surface complexes with these minerals making it resistant to

leaching.

The maximum contaminant level (MCL) for As in drinking water is 0.010 mg L-1,

thus leachate As could be a large concern from the untreated refuse as well as from

concentrated leachates derived from the first few weeks of many of the treatments

(USEPA, 2008). It should be noted that this study represents worst-case within fill water

quality effects of ash/refuse co-disposal. Therefore, direct application of MCLs to the

leachates would be inappropriate. It is possible and likely for As and the other oxyanions

of concern to become attenuated through sorption, dilution, precipitation, or other

mechanisms further down flowpaths within the pile or surrounding geologic media before

they reach surface or ground water. However, MCLs and other regulatory water quality

standards will continue to be mentioned as a point of reference for the elemental

concentrations eluting from the columns.

Boron

Soluble B is a common element associated with fly ash that leaches easily from

fresh ash that has not been exposed to water sluicing or transport (Stewart et al., 2001;

99

Daniels et al., 2001). As such, the treatments with Ash #18, which contained the largest

concentrations of B in the material, generated the largest leachate B concentrations within

the first weeks. The pre-leaching SEP showed that Ash #18 had the largest B

concentration (144 mg kg-1) and that approximately 35% of this was found in the readily

leachable exchangeable fraction (Figure 17). The sandstone and refuse controls

contained minimal amounts of B (10.3 and 2.15 mg kg-1, respectively) compared to the

ashes, and over 90% of the B for both materials was in the residual fraction. The refuse

control never eluted more than 0.14 mg L-1 B, and the sandstone control never eluted

more than 0.04 mg L-1. The Ash #28 control contained 80.2 mg B kg-1, of which

approximately 11% was exchangeable while approximately 76% was found in the

carbonate, and amorphous and crystalline Fe and Mn oxide fractions. The Ash #28

control eluted a maximum of 0.64 mg B L-1 in Week 1. However, when blended with the

acidic refuse and sandstone materials, the Ash #28 treatments eluted as much as 28.3 mg

L-1 B from 28-R-B in Week 1 and 7.7 mg L-1 from 28-S-B in Week 4. This suggests that

the B in the carbonate fraction of Ash #28 is being released as the ash is neutralizing the

acidity in the refuse and sandstone. Field and greenhouse studies have indicated that fly

ash with high levels of B inhibit plant growth, particularly for sensitive species such as

legumes, until the B is adequately leached from the system (Daniels et al., 2001).

Chromium

Chromium was found at much higher concentrations in the two ashes than in the

refuse or sandstone. Ash #18 contained 107 mg Cr kg-1 of which 66% was in the residual

fraction. The Ash #18 control produced high leachate concentrations of Cr in the first 2

weeks and then subsequent leachates contained less than 0.06 mg L-1. Ash #28 contained

71.6 mg Cr kg-1, 62% of which was in the residual fraction. Ash #28 eluted 0.55 mg Cr

L-1 initially and also eluted between 0.11 to 0.80 mg L-1 from Week 4 to Week 16. The

initial leachate Cr from the ashes is likely associated with the easily mobilized

exchangeable fraction. The constant release of Cr from Ash #28 suggests the presence of

some anionic hexavalent Cr in the ash. The pH for the ash during this timeframe was

between 10 and 12, which is an environment in which Cr as the chromate anion may be

prone to leaching.

100

The refuse control consistently eluted between 0.35 and 1 mg L-1 from Week 4 to

the end of the study. This corresponds to refuse control pH values of approximately 2.3

or below. Approximately 99% of the Cr in the refuse control was in the crystalline Fe

and Mn oxide and residual fractions. These two fractions would begin to dissolve at

these low pH values and release associated elements into solution. This is supported by

the largest concentration of Cr in the leachate occurring when the pH was lowest (Week

8).

The MCL for total Cr in drinking water is 0.1 mg L-1 (EPA, 2008). Hence there

may be some water quality concerns for the first few rain events, particularly for the Ash

#18/refuse treatments. The Ash #28 treatment leachates were all below detection for Cr

by Week 2 despite the Ash #28 control eluting over 0.1 mg Cr L-1 for the majority of the

study. This suggests the Cr that leaches from Ash #28 may be sorbed to mineral phases

(i.e. Fe oxides) in either the refuse or sandstone when the ash and substrate are combined.

Molybdenum

Molybdenum concentrations were very low (less than 1 mg kg-1) in both the

refuse and sandstone. Conversely, Ash #18 and Ash #28 contained concentrations of

17.6 and 12.3 mg Mo kg-1, respectively. There was very little leaching of Mo (less than

0.09 mg L-1) from the Ash #18 control and any of the Ash #18 amended treatments. The

Ash #28 control had the largest loss of Mo through leaching. Treatment 28-S-B

produced steady concentrations between 0.18 and 0.25 mg Mo L-1 throughout most of the

experiment. Molybdenum leaching from Treatment 28-R-B slowly increased from Week

1 to Week 8 as the pH of the treatment increased from 4.7 to 6.9. After Week 8, Mo

leaching and pH from this treatment were relatively steady. The Mo leaching from the

Ash #28 blended treatments and Ash #28 control can be attributed to the pH of these

treatments. Molybdenum concentrations increase as pH increases, which is shown in

treatment 28-R-B. The Ash #28 pancake treatments were both below the detection limit

for the entire experiment, suggesting sorption of Mo to minerals in the refuse and

sandstone substrate layer. The concentration of Mo in plant tissue at which Mo toxicity

in ruminants feeding on those plants would be a concern ranges from 10-20 mg kg -1

101

(Sims, 1996). Thus, the concentrations of Mo leaching from any of the treatments are not

likely to be a threat to the environment.

Selenium

The refuse control eluted the most total Se, with a significant portion of leaching

occurring as the pH of the refuse reached 2.0. After the first 2 weeks, the Ash #18

control eluted a minimal amount of Se. The Ash #28 control had three periods where

leachate Se concentrations were over 0.05 mg L-1: the first leachate, Week 10, and Weeks

18-22. This Se release may be due to the dissolution of carbonates in Ash #28.

Approximately 29% of the Se in Ash #28 was found in the carbonate fraction. The

refuse/ash treatments produced the highest leachate concentrations of Se in the first few

weeks, suggesting that when the ash is combined with the refuse, more Se leaches from

the ashes than when they are separate. This could be due to the locally acidic

environment created by the oxidation of pyrite in the refuse, which strips Se from the ash.

The ash treatments blended with refuse eluted more total Se than the pancake treatments,

suggesting that as more ash is exposed to the refuse, more Se could potentially leach.

Ash #18, which had the largest concentration of Se (74.5 mg kg-1) compared to the other

materials (11.8, 10.5, 17.9 mg kg-1 for refuse, sandstone, and Ash #28, respectively),

leached more Se than Ash #28 when combined with the refuse. The ash/sandstone

treatments were below detection for every sample after the first leaching event,

reinforcing the idea that the low pH environment created by the refuse is capable of

stripping Se from the ash. The MCL for Se in drinking water is 0.05 mg L-1 (EPA, 2008).

The Ash #18/refuse treatments exceeded this value for approximately the first 4 weeks of

the study, while the Ash #28/refuse treatments exceeded this value for approximately the

first 3 weeks of the study.

Sulfur

Leachate S closely followed leachate EC for the refuse control due to the large

amount of sulfates produced by pyrite oxidation. The refuse control contained the

highest initial concentrations of S (18,800 mg kg-1) of the 4 materials used in this study.

Ash #18 also contained high concentrations of S (12,030 mg kg-1), approximately 52%

102

of which was in the exchangeable fraction. As expected, the Ash #18/refuse treatments

generated high concentrations of S in the first weeks of the study. The ash treatments

blended with refuse initially eluted less S than their pancaked counterparts, but over time,

the blended treatments eluted more total S. Treatment 18-S-B initially eluted higher

concentrations of S than treatment 18-S-P, but both treatments eventually leached similar

total amounts of S over the course of the study. Treatment 28-S-B initially leached much

higher concentrations (between 400-700 mg L-1 for the first 6 weeks) of S than treatment

28-S-P, but by Week 10, treatment 28-S-B eluted less S than treatment 28-S-P.

Treatment 28-S-P consistently eluted between 20 and 32 mg S L-1 from Week 4 to the

conclusion of the study. Treatment 28-S-B leached much more total S than treatment 28-

S-P.

Collectively, these patterns suggest that over time, the blended ash is subjected to

acidic environments in either the refuse or sandstone that contribute to the leaching of S.

About 34% and 47% of the S in Ash #18 and Ash #28, respectively, was extracted during

the extraction step for carbonates. This suggests the presence of some highly crystalline

sulfate minerals (e.g. gypsum) in both ashes. These minerals may not dissolve readily in

water, but can break down in lower pH environments and release the S.

The sandstone control experienced a small increase in S concentrations in Week

12, going from 3.5 mg L-1 in Week 10 to 15.5 mg L-1 in Week 12. This increase in S was

accompanied by a decrease in pH for the sandstone control from 6.53 in Week 10 to 3.04

in Week 12. The increase in S concentrations for this week was also accompanied by an

increase in leachate Fe concentrations from 0.16 to 11.5 mg Fe L-1 (iron data can be

found in Appendix A-9). This increase in S, Fe, and decrease in pH is most likely

attributed to the oxidation of a limited amount of recalcitrant pyrite occurring in the

sandstone. The sandstone was the most weakly buffered system of all the treatments,

thus it would be possible to see detect changes in the sandstone control that were not seen

in other treatments. The decrease in S concentrations that occurred for treatments 18-R-

B, 18-R-P, and 18-S-P on Week 16 was accompanied by an increase in pH for these

treatments from Week 14 to Week 16. One proposed mechanism for the decrease in S

concentrations as the pH increases slightly is the precipitation of sulfate compounds. The

Secondary Standard for sulfate in drinking water is 250 mg L-1 (EPA, 2008). Every

103

treatment exceeded this value at some point during the experiment except for treatment

28-S-P.

Cations

Despite the very high levels of Ba in the ashes, Ba leaching does not appear to be

an environmental concern from the treatments studied. The MCL for Ba in drinking

water is 2.0 mg L-1 and none of the treatments approached this value (USEPA, 2008).

The Ash #28 control eluted as much as 12.5 mg Ba L-1, but the Ash #28 amended spoil

and refuse treatments all leached concentrations less than 0.25 mg L-1 throughout the

experiment. The low leachate concentrations may be due to precipitation of various Ba

compounds. Barium forms relatively insoluble compounds with carbonates, sulfates, and

chromates – all of which may be present in the treatment materials studied here. The ksp

values for BaCO3, BaSO4, and BaCrO4 are 2.58 * 10-9, 1.07 * 10-10, and 1.17 * 10-10,

respectively.

The Co, Cu, and Ni all exhibited very similar leachate chemistry patterns.

Treatments 18-R-P, 28-R-P, 18-R-B, and the refuse control each displayed extremely

high concentrations of each element in the first leachates, and then concentrations

decreased over time, except for the refuse control, which began to increase again as the

refuse control acidified in Weeks 4-8. These four treatments produced pH values less

than 4.0 throughout the experiment, which was the lowest of all the treatments. Heavy

metal cation solubility generally increases with a decrease in pH. It is noteworthy that

the addition of Ash #18 (blended or pancaked), and Ash #28 (pancaked) to the refuse

increases the concentration of these three metals in the initial leachates substantially

compared to the refuse and ash controls. The metals that leach initially may be

associated with the exchangeable and carbonate fractions, as these are the most readily

leached fractions. These two fractions combined accounted for about 14 to 30% of these

cations in the refuse and about 10 to 14% in Ash #18. The exchangeable fraction for

these metals in Ash #28 was negligible, but the carbonate fraction did account for

approximately 3% Co, 14% Cu, and 4% Ni. There are currently no regulations for Co or

Ni in drinking water. Copper in drinking water is regulated by a Treatment Technique

that requires systems to control the corrosiveness of their water. If more than 10% of tap

104

water samples exceed the action level, water systems must take additional steps. For Cu,

the action level is 1.3 mg L-1 (EPA, 2008). Treatments 18-R-P and 28-R-P exceeded this

value for the first 2 to 3 weeks of leaching. Treatment 18-R-B exceeded this value for the

first 12 weeks.

The blended Ash #28 treatments displayed less leaching than their pancaked

counterparts for Co, Cu, and Ni because the blended treatments maintained higher pH

values than the pancaked treatments. Cations are less readily sorbed to soil minerals at

low pH. Despite Ash #18 having no CCE, treatment 18-S-B maintained a leachate pH

0.5 to 1.3 units higher than treatment 18-S-P from Week 5 to the conclusion of the study.

This slight difference in pH may account for treatment 18-S-B leaching slightly less total

Co and Ni than treatment 18-S-P. Treatment 18-S-P leached slightly less total Cu than

treatment 18-S-B which may be attributed to Ash #18 containing about 20 times more

total Cu than the sandstone. Having the high Cu material in a layer at the top in this case

would force any leaching Cu to travel a farther distance increasing the chance that it

could be sorbed or precipitated before it comes through in the leachate. In contrast,

treatment 18-R-B leached much more total amounts of these cations than treatment 18-R-

P because the blended treatments exposed more of the ash to the acidic environments

produced by the refuse.

Sequential Extraction Procedures

The pre-leaching SEP results indicated the distribution of elements in the

materials used in this study agreed with that of the literature. The elements As, B, Cr,

Mo, and Se were concentrated in the fly ashes relative to the other materials. Arsenic and

Se in the ashes were predominantly associated with non-matrix fractions which has been

suggested by several researchers (Goodarzi and Huggins, 2001; Kim and Kazonich,

2004). The predominant fractions for As and Se in Ash #18 were the Fe and Mn oxides

fractions while these two elements were relatively evenly spread between the Fe and Mn

oxides and carbonate fractions in Ash #28. Ash #28, having the greater CCE, had a

larger percentage of elements associated with the carbonate fraction than Ash #18. The

Cr in the ashes was predominantly found in the residual fraction. Bodog, et al (1996)

also found the majority of Cr in fly ashes studied in the residual fraction. The coal refuse

105

contained high S concentrations, as expected, of which approximately 92% was in the

residual fraction, presumably as pyritic minerals. The S in the ashes was predominantly

extracted during the exchangeable and carbonate phases of the SEP, suggesting the S in

the ashes was in a soluble sulfate form or highly crystalline forms of sulfate minerals

(e.g. gypsum), as indicated by Shoji, et al. (2002). The sandstone was relatively low in

all the oxyanions analyzed. Arsenic, B, Cr, Mo, and Se in the sandstone were

predominantly in the crystalline Fe and Mn oxide and residual fractions.

The post-leaching SEP results showed significant decreases in elemental totals for

all the materials. Percent differences between pre-leaching and post-leaching for

elemental amounts ranged as low as 11% for Mo in treatment 18-R-B and as high as

100% for Se in several treatments. These differences are much greater than can be

accounted for in the mass observed as lost in leachate. A possible explanation for this

discrepancy is the extreme heterogeneity of the materials in the columns due to

geochemical reactions (dissolution, precipitation, sorption) taking place over the course

of the study that may create microenvironments. Subsamples taken from each column for

the second SEP may not be representative of the whole column. A second plausible

explanation is that the top and bottom 3 cm of each column was separated and discarded

before the column material was homogenized and subsampled. The bottom 3 cm of the

column contained a layer of glass beads and filter paper and some trapped eluted solids.

It is quite possible that within this lower 3 cm there was extensive precipitation or

sorption of the oxyanions that prevented them to exit in the leachate. This interface also

represented a significant redox and moisture change. Stewart (1995) reported evidence

of extensive Fe precipitation occurring on glass beads, glass wool, plastic mesh, and filter

paper at the bottom of similar columns. These surfaces may have served as significant

precipitation and sorption sites for the trace elements of interest.

According to the SEP data, Se appeared to be the element that leached most

readily from the combined treatments. Over 91% of the Se was unaccounted for between

pre- and post-leaching for each of the treatments. The substrate layers for treatments 18-

R-P, 18-S-P, and 28-S-P and the sandstone control contained no Se at the conclusion of

the experiment. In contrast, Mo appeared to be the element least readily leached from the

combined treatments. The ash controls and the ash pancake layers were the only

106

treatments that had greater than 70% of Mo unaccounted for between pre- and post-

leaching. The greater concentrations of Mo in the post-leaching substrate layers for

treatments 28-R-P and 28-S-P compared to the pre-leaching materials indicate that Mo is

leaching from the ash layer and precipitating or sorbing to minerals in the underlying

substrate layers.

The higher post-leaching concentrations of S compared to pre-leaching values in

the sandstone layers under ash suggests that sulfates leaching from the ash are

precipitating or sorbing to minerals in the sandstone layer. Treatment 18-S-P displays a

drop in Week 16 in both S and cation (Ba, Co, and Ni) concentrations. It is possible for

sulfates to migrate from the ash layer and precipitate as relatively insoluble sulfates in the

sandstone layer. One relatively insoluble sulfate that could precipitate in the sandstone

layer is BaSO4 (ksp= 1.07 * 10-10).

The post-leaching materials for certain treatments contained greater amounts of

elements than corresponding controls for certain elements, implying there is some minor

sorption or precipitation of these elements occurring in these treatments relative to the

controls. This suggests that there may be some sorption or precipitation of all elements

except Se in treatments 18-R-B. 28-S-B, the 18-S-P substrate layer, and the 28-S-P

substrate layer. Results from treatment 18-S-B indicated minor sorption/precipitation of

all elements, and results from treatment 28-R-B indicated sorption of all elements except

S. The refuse layer under Ash #18 may have sorbed/precipitated some B, and the refuse

layer under Ash #28 may have sorbed/precipitated B, Cr, and Mo.

The increased percentage of As, B, Cr, and Mo in the crystalline Fe and Mn oxide

fraction after leaching for most of the treatments suggests that these elements are sorbing

to Fe or Mn oxides. It is also possible that the association of these elements with Fe and

Mn oxides is accentuated because this fraction is more resistant to weathering than the

exchangeable, carbonate, and amorphous Fe and Mn oxides fractions, and thus is not as

subject to dissolution and leaching of elements as the other fractions. Selenium appears

to be the most readily leached of the oxyanions, which is consistent with its initial

association with readily bioavailable amorphous Fe and Mn oxide and carbonate fractions

as opposed to the crystalline and residual fractions.

107

The association of S with the exchangeable and crystalline Fe and Mn oxide

fractions for the controls and Ash #18 treatments after leaching is due to sulfide minerals

oxidizing in the refuse and sandstone and producing sulfate anions. This sulfate can form

soluble metal sulfates, which would be associated with the exchangeable fraction, or it

can sorb to minerals. Under these conditions, the majority of the sulfate would sorb to

crystalline Fe and Mn oxides. The significant amounts of S still associated with the

residual fraction after leaching in the Ash #28 blended treatments and substrate layers

suggests that Ash #28 was better able to prevent sulfide minerals in those substrates from

oxidizing. This is likely due to Ash #28 maintaining a higher pH (> 4.5), above which

the rate of sulfide oxidation is much slower due to inhibition of T. Ferrooxidans and

limiting solubility of Fe3+(Evangelou, 1998; Geidel and Caruccio, 2000).

CONCLUSIONS

A leaching column study was conducted to evaluate the leachate chemistry from

acid forming coal refuse-fly bulk ash blends vs. ash over refuse layers under unsaturated

conditions. Sandstone is the dominant overburden material in the Appalachians thus

sandstone treatments were also investigated. Leachates were analyzed for pH, electrical

conductivity, and a suite of elements of concern with a focus on the oxyanions of As, Cr,

Mo, and Se. A sequential extraction was performed on the four materials prior to and

after leaching to give insight into the chemical changes occurring within the columns and

into which solid phases may have controlled the solubility of the elements of concern.

Treatments where ash was bulk-blended maintained higher leachate pH than

corresponding layered treatments. Even Ash #28, which was relatively high CCE, was

ineffective at significantly increasing the leachate pH when co-disposed with acid-

forming refuse and sandstone using the “pancake” method. Addition of both ashes

initially increased leachate EC. These initially high values generally declined to

moderate levels (< 4 dS m-1) after approximately five weeks of leaching. The Ash #18

treatments with refuse and Ash #28 pancaked over the refuse exhibited relatively high

initial leachate concentrations of As, Co, Cr, Cu, Ni, S, and Se. Concentrations of these

elements for the Ash #18 treatments declined to low levels after approximately five

weeks of leaching. Ash #28, when blended with refuse or when blended and pancaked

108

with sandstone, produced relatively low concentrations of the elements analyzed. The

blended Ash #28 treatments did exhibit the greatest amount of Mo leaching, but

concentrations never reached levels of environmental concern. However, treatment 28-

R-B produced high Se concentrations for the first 2.5 weeks of the study.

Collectively, these results suggest that pancake layers of fly ash would not be an

effective co-disposal method to prevent or mitigate AMD from a coal refuse pile. Both

ashes were chosen to represent worst-case scenarios of potential oxyanion leaching. Ash

#18 had no CCE and very high oxyanion concentrations while Ash #28, which also had

high oxyanion contents, had insufficient CCE to completely neutralize the potential

acidity of the refuse at the rate it was blended. Hence, these results do not imply the

enhanced leaching of oxyanions at circumneutral pH. Other than Mo, the largest

leaching of these elements occurred when the leachate pH values were acidic (< 4.5).

The Ash #28 blended treatments, which maintained pH between 4.7 and 7.3 for the refuse

and 7.4 and 8.3 for the sandstone, displayed very little leaching of the elements analyzed

here.

The SEP data suggest extensive leaching of the elements of concern from the

columns. However, since the leachate data does not support this on a mass basis for all

the elements analyzed, it is assumed that there was a considerable amount of sorption or

precipitation occurring in the bottom 3 cm of the columns, or perhaps somewhere in the

material that was not sampled post-leaching. The SEP data suggest that Se was relatively

readily leached from these treatments. The other oxyanions showed signs of being

sorbed to the substrate materials, particularly sandstone, in minor amounts. Over the

course of this leaching study, the data suggest that sorption of the oxyanions onto Fe and

Mn oxides became an important mechanism. Furthermore, Ash #28 was able to reduce

the amount of sulfide oxidation occurring in the refuse and sandstone when bulk blended.

In summary, “pancake” treatments of fly ash over coal refuse are therefore not

recommended as a co-disposal method because of their inability to maintain adequate pH

to minimize sulfide oxidation and subsequent acid-stripping of elements from the ash

layers. As has been reported in previous research, bulk blending alkaline fly ash with

coal refuse at rates that meet acid base accounting requirements is capable of preventing

and mitigating AMD from coal refuse piles. There may be water quality, particularly Se,

109

and soluble salt concerns from recently placed lifts of materials following the first few

rain events when ash and refuse are co-disposed.

However, it is important to point out that this study represents worst-case within

fill water quality effects of ash/refuse co-disposal. It is possible for the oxyanions of

concern to become sorbed to minerals, namely Fe or Mn oxides, further down flowpaths

within the pile or surrounding geologic media before they reach surface or ground water.

It should also be noted that the leachate concentrations will become more dilute as they

mix with larger volumes of ground or surface water, potentially lowering concentrations

to below levels of concern. Finally, the geochemistry of the environment down gradient

from the refuse piles will ultimately determine the potential bioavailability of trace

elements leached from coal refuse and fly ash.

110

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11

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ents

. V

alue

s ar

e m

eans

of

thre

e re

plic

atio

ns.

W

eeks

Lea

chin

g

Tre

atm

ent

.5

1 1.

5 2

2.5

3 3.

5 4

5 6

7 8

10

12

14

16

18

20

22

24

18-R

-B

15.1

10

.1

7.31

4.

52

4.62

4.

14

3.91

3.

89

4.25

4.

11

4.26

4.

04

4.01

4.

11

3.51

3.

27

2.86

2.

57

2.46

2.

54

18-R

-P

19.3

10

.9

6.98

4.

96

4.48

4.

26

4.10

3.

97

4.04

3.

61

3.75

3.

64

3.59

3.

95

3.87

3.

07

2.74

2.

51

2.50

2.

48

18-S

-B

6.79

5.

23

4.08

3.

36

3.03

2.

51

1.80

1.

46

0.97

0.

69

0.60

0.

52

0.43

0.

36

0.38

0.

27

0.25

0.

24

0.22

0.

20

18-S

-P

0.44

1.

30

1.88

2.

20

2.27

2.

14

1.87

1.

63

1.42

1.

10

1.01

0.

89

0.78

1.

50

0.81

0.

56

0.53

0.

51

0.44

0.

40

28-R

-B

6.90

4.

69

4.12

3.

63

3.51

3.

36

3.17

3.

13

3.22

2.

75

2.83

2.

59

2.51

2.

50

2.36

2.

24

2.07

2.

15

1.90

1.

66

28-R

-P

17.7

11

.0

6.93

5.

16

4.48

4.

11

3.74

3.

39

2.66

1.

65

1.46

1.

23

1.23

1.

44

1.56

1.

17

1.12

1.

14

1.13

1.

16

28-S

-B

2.57

2.

76

2.65

2.

51

2.56

2.

55

2.51

2.

48

2.62

2.

02

1.51

0.

82

0.54

0.

49

0.49

0.

42

0.36

0.

37

0.34

0.

33

28-S

-P

0.35

0.

25

0.30

0.

28

0.28

0.

27

0.27

0.

26

0.27

0.

22

0.21

0.

20

0.20

1.

23

0.85

0.

16

0.17

0.

18

0.19

0.

19

R C

ntrl

11

.8

10.7

8.

09

6.26

6.

13

7.65

8.

88

10.9

14

.5

13.1

14

.1

13.5

12

.2

11.4

10

.2

9.61

8.

54

7.87

7.

14

6.82

S C

ntrl

0.

14

0.10

0.

10

0.11

0.

10

0.09

0.

08

0.07

0.

08

0.07

0.

07

0.06

0.

07

0.87

0.

70

0.06

0.

08

0.07

0.

05

0.05

18 C

ntrl

10

.7

4.96

3.

24

2.54

1.

95

1.85

1.

50

1.43

1.

25

1.02

0.

99

0.82

0.

79

0.94

1.

00

0.59

0.

45

0.41

0.

33

0.27

28 C

ntrl

12

.2

4.25

3.

03

2.90

2.

68

2.35

0.

76

1.53

0.

35

0.80

0.

76

0.66

0.

53

0.44

0.

38

0.25

0.

27

0.26

0.

23

0.25

11

9

A-2

: Lea

chat

e pH

from

long

-ter

m le

achi

ng c

olum

ns u

nder

the

diff

eren

t exp

erim

enta

l tre

atm

ents

. V

alue

s ar

e m

eans

of t

hree

repl

icat

ions

.

W

eeks

Lea

chin

g

Tre

atm

ent

.5

1 1.

5 2

2.5

3 3.

5 4

5 6

7 8

10

12

14

16

18

20

22

24

18-R

-B

3.46

3.

50

3.50

3.

26

3.20

3.

23

3.21

3.

32

3.32

3.

14

3.27

3.

27

3.25

2.

98

3.01

3.

26

3.36

3.

36

3.32

3.

30

18-R

-P

2.71

3.

10

3.21

3.

15

3.14

3.

05

2.97

3.

12

3.12

3.

12

3.16

3.

14

3.20

2.

95

2.92

3.

19

3.27

3.

16

3.21

3.

27

18-S

-B

3.83

3.

87

3.91

3.

97

3.99

4.

09

4.13

4.

23

4.49

4.

51

4.66

4.

72

4.88

4.

73

4.31

5.

46

5.33

5.

38

5.36

5.

26

18-S

-P

4.93

4.

63

4.29

4.

13

4.06

4.

09

4.02

4.

04

4.12

4.

04

4.09

4.

06

4.22

2.

91

3.52

4.

18

4.31

4.

23

4.33

4.

27

28-R

-B

4.77

5.

58

5.87

6.

03

6.00

6.

23

4.97

6.

70

6.69

6.

89

6.85

6.

93

7.15

6.

83

7.34

7.

12

7.09

7.

20

7.17

7.

36

28-R

-P

2.75

3.

10

3.35

3.

37

3.42

3.

36

3.13

3.

33

3.41

3.

41

3.52

3.

57

3.73

3.

32

3.13

3.

77

3.85

3.

86

3.88

3.

89

28-S

-B

7.72

7.

64

7.68

7.

53

7.48

7.

50

7.85

7.

64

7.82

7.

69

7.60

7.

79

7.88

7.

70

7.77

7.

98

7.93

7.

79

8.29

7.

78

28-S

-P

4.50

5.

03

5.27

4.

97

5.39

5.

78

6.18

5.

86

6.08

5.

56

5.65

5.

82

5.94

2.

96

3.07

6.

20

5.94

6.

10

6.31

6.

14

R C

ntrl

2.

66

2.97

3.

02

2.93

2.

78

2.54

2.

39

2.27

2.

22

2.09

2.

05

1.94

2.

16

2.18

2.

23

2.24

2.

31

2.28

2.

33

2.39

S C

ntrl

6.

50

5.50

5.

54

5.91

6.

14

5.94

6.

53

6.30

6.

58

6.53

6.

59

6.34

6.

53

3.04

3.

21

6.50

6.

49

6.46

6.

43

6.48

18 C

ntrl

3.

78

3.91

4.

04

4.15

4.

22

4.33

4.

32

4.45

4.

58

4.61

4.

74

4.73

4.

97

4.11

3.

44

5.36

5.

64

5.74

5.

90

5.99

28 C

ntrl

12

.7

12.3

12

.3

12.2

12

.2

12.1

11

.7

12.0

10

.9

11.7

11

.6

11.5

11

.3

10.5

10

.5

9.96

10

.6

10.1

9.

95

10.1

12

0

A-3

: Lea

chat

e ar

seni

c in

mg

L-1

. V

alue

s ar

e co

mpo

site

s of

thre

e re

plic

atio

ns. b

d =

belo

w d

etec

tion.

W

eeks

Lea

chin

g

Tre

atm

ent

.5

1 1.

5 2

2.5

3 3.

5 4

5 6

7 8

10

12

14

16

18

20

22

24

18-R

-B

0.22

0.

07

bd

bd

bd

bd

bd

bd

0.03

0.

04

bd

bd

bd

0.11

0.

07

0.04

bd

bd

bd

bd

18-R

-P

1.90

0.

26

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

0.04

bd

bd

bd

bd

bd

bd

bd

18-S

-B

0.25

0.

23

0.33

0.

25

0.16

0.

09

0.05

0.

03

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

18-S

-P

bd

0.10

0.

18

0.16

0.

17

0.17

0.

15

0.11

0.

09

0.07

0.

04

0.06

bd

0.

05

bd

bd

bd

bd

bd

bd

28-R

-B

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

0.04

bd

0.

03

bd

0.04

0.

06

28-R

-P

1.74

0.

26

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

28-S

-B

bd

0.04

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

28-S

-P

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

R C

ntrl

2.

17

0.30

bd

bd

0.

17

2.05

4.

85

10.3

19

.8

20.8

29

.4

29.9

21

.8

16.8

13

.8

12.3

8.

86

6.70

5.

19

4.62

S C

ntrl

bd

0.

02

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

0.05

bd

bd

bd

bd

bd

bd

18 C

ntrl

0.

33

0.05

bd

bd

bd

bd

bd

bd

bd

0.

03

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

28 C

ntrl

bd

bd

bd

bd

bd

bd

bd

bd

bd

bd

0.

03

bd

0.05

bd

bd

bd

bd

bd

bd

bd

12

1

A-4

: Lea

chat

e bo

ron

in m

g L

-1.

Val

ues

are

com

posi

tes

of th

ree

repl

icat

ions

. bd

= be

low

det

ectio

n.

W

eeks

Lea

chin

g

Tre

atm

ent

.5

1 1.

5 2

2.5

3 3.

5 4

5 6

7 8

10

12

14

16

18

20

22

24

18-R

-B

53.5

26

.9

20.3

12

.8

12.7

9.

42

8.63

7.

29

5.57

4.

33

3.76

2.

95

1.92

1.

58

1.37

0.

66

0.81

0.

66

0.61

0.

62

18-R

-P

22.2

19

.8

15.3

12

.3

9.94

7.

77

6.88

6.

15

4.64

3.

24

2.44

1.

97

1.15

0.

91

0.87

0.

44

0.43

0.

36

0.29

0.

25

18-S

-B

10.7

8.

45

15.3

11

.3

8.43

6.

43

5.57

5.

23

3.91

2.

95

2.49

2.

07

1.48

1.

32

1.18

1.

04

0.78

0.

67

0.56

0.

50

18-S

-P

3.48

8.

03

15.7

16

.5

15.1

11

.6

10.0

8.

24

5.76

3.

95

3.23

2.

52

1.58

1.

31

1.00

0.

49

0.61

0.

49

0.40

0.

33

28-R

-B

28.3

17

.8

12.8

9.

66

6.99

5.

10

4.61

4.

34

3.28

2.

58

2.30

1.

85

1.48

1.

37

1.27

1.

08

0.75

0.

69

0.59

0.

50

28-R

-P

0.53

0.

19

0.19

0.

18

0.14

0.

10

0.10

0.

12

0.11

0.

13

0.17

0.

22

0.32

0.

40

0.52

0.

46

0.44

0.

53

0.51

0.

56

28-S

-B

5.00

5.

87

6.07

6.

53

6.31

6.

02

7.36

7.

70

6.78

5.

84

5.04

4.

20

2.95

2.

18

2.04

1.

81

0.96

0.

91

0.73

0.

63

28-S

-P

0.10

0.

04

0.06

0.

06

0.04

0.

04

0.04

0.

05

bd

bd

0.07

0.

07

0.11

0.

18

0.28

0.

38

0.36

0.

43

0.42

0.

45

R C

ntrl

0.

15

0.04

0.

07

0.04

0.

04

0.04

0.

02

bd

0.14

0.

14

0.09

0.

09

0.04

0.

04

0.03

0.

11

0.06

0.

05

0.03

0.

03

S C

ntrl

0.

04

0.03

0.

03

0.02

0.

02

0.02

0.

02

bd

bd

bd

bd

bd

bd

0.01

bd

0.

01

bd

bd

bd

bd

18 C

ntrl

88

.1

24.9

18

.1

13.4

8.

62

6.40

5.

60

4.78

2.

92

2.18

1.

70

1.30

0.

86

0.64

0.

65

0.50

0.

32

0.29

0.

25

0.22

28 C

ntrl

0.

64

0.22

0.

10

0.08

0.

07

0.06

0.

07

0.09

0.

12

0.16

0.

19

0.21

0.

31

0.35

0.

46

0.67

0.

45

0.47

0.

50

0.48

12

2

A-5

: Lea

chat

e ba

rium

in m

g L

-1.

Val

ues

are

com

posi

tes

of th

ree

repl

icat

ions

. bd

= be

low

det

ectio

n.

W

eeks

Lea

chin

g

Tre

atm

ent

.5

1 1.

5 2

2.5

3 3.

5 4

5 6

7 8

10

12

14

16

18

20

22

24

18-R

-B

bd

bd

bd

0.03

0.

03

0.03

0.

02

0.03

0.

03

0.02

0.

02

0.02

0.

02

0.02

0.

02

0.01

0.

02

0.02

0.

02

0.02

18-R

-P

bd

bd

bd

0.00

7 0.

005

0.00

7 0.

009

0.01

0.

01

0.01

0.

01

0.01

0.

10

0.01

0.

01

0.01

0.

01

0.01

0.

02

0.02

18-S

-B

0.02

0.

02

0.07

0.

07

0.06

0.

06

0.08

0.

09

0.08

0.

08

0.10

0.

10

0.10

0.

13

0.13

0.

13

0.12

0.

12

0.11

0.

11

18-S

-P

0.17

0.

04

0.05

0.

06

0.09

0.

09

0.08

0.

09

0.08

0.

08

0.08

0.

09

0.09

0.

08

0.08

0.

04

0.06

0.

06

0.06

0.

06

28-R

-B

0.08

0.

07

0.06

0.

06

0.06

0.

05

0.06

0.

06

0.06

0.

06

0.06

0.

06

0.05

0.

06

0.06

0.

06

0.05

0.

04

0.05

0.

04

28-R

-P

bd

bd

bd

0.00

9 0.

008

0.00

6 0.

009

0.01

0.

02

0.03

0.

04

0.02

0.

04

0.04

0.

04

0.03

0.

03

0.04

0.

03

0.03

28-S

-B

0.10

0.

10

0.08

0.

09

0.10

0.

10

0.11

0.

11

0.07

0.

02

0.04

0.

07

0.27

0.

12

0.17

0.

20

0.05

0.

12

0.12

0.

08

28-S

-P

0.20

0.

20

0.23

0.

20

0.13

0.

09

0.09

0.

09

0.08

0.

10

0.14

0.

18

0.22

0.

19

0.21

0.

16

0.20

0.

15

0.15

0.

16

R C

ntrl

0.

004

0.00

2 bd

bd

bd

bd

bd

bd

bd

bd

0.

004

bd

0.00

5 0.

009

0.00

4 0.

004

0.00

4 bd

0.

002

bd

S C

ntrl

0.

02

0.03

0.

04

0.04

0.

03

0.03

0.

03

0.03

0.

03

0.03

0.

02

0.02

0.

02

0.02

0.

03

0.01

0.

02

0.02

0.

02

0.02

18 C

ntrl

0.

12

0.09

0.

07

0.07

0.

06

0.05

0.

06

0.05

0.

05

0.06

0.

07

0.09

0.

09

0.10

0.

11

0.11

0.

10

0.10

0.

12

0.13

28 C

ntrl

0.

25

0.11

7.

24

12.5

10

.9

6.61

4.

08

3.52

1.

13

0.48

0.

42

0.48

0.

44

0.17

0.

18

0.14

0.

17

0.02

0.

03

0.02

12

3

A-6

: Lea

chat

e co

balt

in m

g L

-1.

Val

ues

are

com

posi

tes

of th

ree

repl

icat

ions

. bd

= be

low

det

ectio

n.

W

eeks

Lea

chin

g

Tre

atm

ent

.5

1 1.

5 2

2.5

3 3.

5 4

5 6

7 8

10

12

14

16

18

20

22

24

18-R

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