Research Article Dechlorination of Hexachloroethane in...

Research ArticleDechlorination of Hexachloroethane in Water Using IronShavings and Amended Iron Shavings Kinetics and Pathways

D L Wu Y X Liu Z G Liu and L M Ma

State Key Laboratory of Pollution Control and Resource Reuse College of Environmental Science and EngineeringTongji University Shanghai 200092 China

Correspondence should be addressed to Z G Liu lzg0532tongjieducn

Received 5 March 2014 Accepted 18 May 2014 Published 30 June 2014

Academic Editor Chaomeng Dai

Copyright copy 2014 D L Wu et alThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

In contrast to previous studies which employed zero-valent iron powder this paper investigated reductive dechlorination ofhexachloroethane (HCA) using iron shavings and bimetallic iron shavings modified with Cu Ag or Pd Results clearly show thatiron shavings offer superior reductive dechlorination of HCA In addition surface-normalized pseudo first-order dechlorinationrates of 00073 Lsdotmminus2sdothminus1 00136 Lsdotmminus2sdothminus1 00189 Lsdotmminus2sdothminus1 and 00084 Lsdotmminus2sdothminus1 were observed in the presence of iron shavings(Fe0) and the bimetallic iron shavings CuFe AgFe and PdFe respectively Bimetallic iron shavings consisting of CuFe andAgFe could greatly enhance the reductive reaction rate PdFe was used to achieve complete dechlorination of HCA within 5hoursThe additives of Ag and Pd shifted product distributions and the reductive dechlorination of HCA occurred via 120573 reductiveelimination and sequential hydrogenolysis in the presence of all iron shavingsThis study consequently designed a reaction pathwaydiagramwhich reflected the reaction pathway andmost prevalent dechlorination products Iron shavings are a common byproductof mechanical processing plants While the purity of such Fe metals may be low these shavings are readily available at low costsand could potentially be used in engineering applications such as contamination control technologies

1 Introduction

Since zero-valent iron (ZVI) was applied to perform thereductive dechlorination of chlorinated alkanes in the early1990s [1] the use of ZVI to treat contaminants has been anattractive research topic [2 3] As a result numerous relevantstudies have been performed on such reductive transfor-mation of contaminants including aromatic compounds [4]heavy metals [5 6] radioactive pollutant [7] and azo dyes[8] Iron media have also been investigated for remediationof nitrate in contaminated groundwater [9] Possible mecha-nisms considered for contaminant reduction on iron mediainclude (i) direct reduction at the metal surface possibly viapitting in the oxide surface (ii) reduction by Fe(II) formed insitu and (iii) reduction by atomic hydrogen [10 11]

In order to enhance the reactivity and functionality ofZVI depositing the other metals such as Ni Cu Pt or Pdas a catalyst onto the iron surface leads to the synthesisof bimetallic iron particles Fennelly and Roberts employedindividual metals and several bimetals (NiFe CuFe) to

investigate the reductive degradation of 111-trichloroethane(111-TCA) [12] this work proved that bimetals can not onlyboost the dechlorination reaction rate but they can alsoexert a large influence on the types of final products Inaddition there have been many reports concerning the useof nanoscale ZVI and nanoscale bimetallic iron to study thereductive treatment of pollutants [13ndash15] Nanoscale iron hashigh dechlorination reactivity but it is very costly to produceand also highly vulnerable to inactivation and aggregation

The most relevant prior research has focused on theuse of ZVI powder or nanoscale iron to investigate thereductive transformation of contaminants in groundwaterBut iron powder and nanoscale-iron consist of extremelyfine particles they readily form inactive films Iron shav-ings which are a common solid waste generated in manymechanical processing plants with an abundant local supplyand relatively low cost are a superior reducing agent In actualengineering applications iron shavings offer stable long-term performance Ma and Zhang have already employedfiller produced from iron shavings in large-scale engineering

Hindawi Publishing CorporationJournal of ChemistryVolume 2014 Article ID 325879 9 pageshttpdxdoiorg1011552014325879

2 Journal of Chemistry

applications containing 910000 kilograms of iron shavings(60000m3d) which have chiefly consisted of industrialwastewater pretreatment and thematerial has been shown toimprovewastewater biodegradability [16]However there hasbeen no systematic research on the specific reaction processesand detailed mechanisms when iron shavings are used toperform the reductive transformation of pollutants Workson the amended iron shavings by Cu Ag and Pd are verylimited as well particularly the AgFe bimetallic iron Oneof the primary goals of this study is to fill this gap Wust etal observed a combined zero- and first-order kinetic modelin describing the dechlorination of TCE and cis-DCE byZVI [17] Arnold and Roberts adapted a modified Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model todescribe iron mediated dechlorination of chlorinated ethy-lene and acetylene [18] However reported reaction rates forvarious chlorinated compounds are highly variable amongdifferent investigators

The characteristics of iron shavings differed from ironpowder greatly and there has been no research reports con-cerning the potential reduction processes and mechanismsof chlorinated hydrocarbons by iron shavings Furthermorebecause most past research on reaction kinetics focused onthe overall kinetics of removal of parent compounds therehas been limited research on the entire kinetics of finalreaction products and intermediate productsThis study usesiron shavings which possess tremendous engineering appli-cation potential as the main reducing agent and comparesthe reaction performance of iron shavings and conventionaliron powder Taking hexachloroethane as the target pollutantthe reductive reactivity of iron shavings and bimetallic ironshavings was investigated in batch experiments as well asthe detailed entire reaction kinetics reaction products andpathwaysThis study might facilitate the development of ironshaving wastewater treatment techniques by providing a full-scale understanding of the mechanism that iron shavingsbring about on the reductive transformation of pollutants

2 Experimental Section

21 Materials and Reagents The chief experimental materialconsisted ofmetallic iron shavings whichwere obtained fromthe machine shop at Tongji University the shavings madeof 38CrMoAl steel with a carbon content of approximately03-04 also contained trace elements including Si MnCr Mo and Al (detailed elemental composition is shownin Table 1) A lathe was used to cut the iron into curlyshavings with a width of 05ndash10 cm length of 3ndash10 cm andthickness of 02mm The specific surface area of the ironshavings was 03m2g (tested by application of the Brunauer-Emmett-Teller (BET)) the appearance of the shavings isshown in Figure 1 The experiment used 100mL reactionbottles (marked volume of 100mL actual volume of roughly120mL) to ensure that the reaction occurred in a tightlysealed vessel and 1mL gas-tight sample collectors were usedto collect samples for analysis Deionized water from Milli-Q (Millipore Corp) deoxygenated by purging with high-purity N

2

was used in all experiments The reagents of

Table 1 Elemental composition of iron shavings used ()

Elemental Content (wt)Fe gt95C 035sim042Si 02sim045Mn 03sim06Cr 135sim165Mo 015sim025Al 070sim110

Figure 1 Image of the unwashed shavings (38CrMoAl steel)

hexachloroethane pentachloroethane tetrachloroethylenetrichloroethylene and dichloroethylene were all HPLC gradeand were purchased from the Sigma Company The NaOHNaHCO

3

HCl CuSO4

AgNO3

and PdCl2

used in thisstudy were analytically pure and were purchased from theSinopharm Chemical Reagent Co Ltd All chemicals wereused as received The purity of the iron powder was 99 itwas purchased from the Shanghai Runjie Chemical ReagentCo Ltd

22 Methods Stock solutions of hexachloroethane wereprepared in methanol 20120583L of stock solution was spikedinto 1000mL of aqueous solution to achieve the desiredinitial concentration Iron shavings were washed in NaHCO

3

solution to remove any surface oil or grease and were soakedin water for several days to allow the surface to rust Therusty iron shavings were then washed in deaerated 01molLhydrochloric acid (HCl) and rinsed 5 times with deaeratedwater 50 g of the shavings was packed into reaction bottleswith marked volume of 100mL and an aqueous solution ofhexachloroethane with a predetermined concentration wasadded The bottles were immediately sealed using Teflon-coated stoppers and crimp-sealed with aluminum foil capsto provide a better seal The reaction bottles were placed ina water bath on a constant temperature shaking incubatorwhich shook at a constant rate of 180 rmin Each experimentwas performed in triplicate including a set of control vials

Journal of Chemistry 3

containing the introduced hexachloroethane solution withthe same concentration as that used in the experiment butwithout iron and a set of blank vials containing only the ironand deaerated Milli-Q water At intervals gas-tight samplecollectors were used to take samples for analysis of reactantsand their transformation products Each sample was 1mLthe samples were then rapidly added to automatic samplingbottles containing 29mL of deionized water for analysisby purge and trap-gas chromatograph Analysis of organiccarbon mass in the controls indicated that the mass variedby less than 5 over the course of a typical experiment

Preparation of CuFe AgFe and PdFe bimetallic ironshavings The bimetallic iron shavings were prepared usinga chemical deposition method by soaking the iron shavingsin CuSO

4

AgNO3

and PdCl2

solutions respectively whichinvolved the deposition of 01 wt of the other metals on thesurface of the iron shavings In this method CuSO

4

AgNO3

and PdCl

2

solutions with desired concentrations were addedto reaction bottles filled with 50 g of iron shavings Afterreaction it is assumed that all the other metals were coatedon the iron shavings to give 01 Cu Ag and Pd by weightrespectively These shavings after being washed were addedto hexachloroethane-water solutions employing the samemethod as described above and samples were taken at fixedintervals for analysis

23 Analysis Qualitative and quantitative analyses of chlori-nated alkanes were performed using XPT-GCMS (purge andtrap-gas chromatographymass spectrometry) A TEKMARAQUAteK70 automatic sampler was used to inject sampleswith a sample volume of 5mL Pretreatment conditions inthe purge and trap concentrator Purge time 11 minutespurge temperature room temperature (25∘C) purge gasflow 40mLmin (high-purity N

2

) Dry purge time 1minpreheating temperature 245∘C sample inject temperature180∘C furnace temperature 150∘C transmission line tem-perature 150∘C GCMS analytical conditions US ThermalGCMS multipurpose instrument equipped with HP-5 cap-illary tube column (inner diameter 025mm liquid filmthickness 025 120583m) length 30m carrier gas high-purityHe flow rate 10mLmin The temperature program wasinitiated at a temperature of 35∘C for 5 minutes heating rate25∘Cmin and final temperature 200∘C held for 1 minuteSampler temperature 200∘C ions source temperature 250∘CMS transmission line temperature 250∘C The sample wasautomatically injected with a split ratio of 10 1

3 Results and Discussion

31 Reductive Dechlorination of HCA by Various Iron Shav-ings When investigating the reductive dechlorination reac-tion rate of HCA in presence of various iron shavings thestudy focused on the effect of iron powder (Fe0) iron shavings(Fe0) and bimetallic iron shavings (CuFe AgFe PdFe) onthe rate of reductive dechlorination of HCA Because thespecific surface area of iron powder is 54m2g while thatof iron shavings is 03m2g in order to ensure that the ironpowder and iron shavings in reactor had the same surface

00

1 32 4 5 6

10

20

30

40

50

60

70

80

90

100

Rem

oval

rate

()

Time (h)

Figure 2 Removal rate ofHCAobtainedwith various iron shavingsInitial concentration of HCA was 60120583molsdotLminus1 (X) Fe0 (powder)(◼) Fe0 (shavings) (I) PdFe (01 wt) (998771) CuFe (01 wt) (times)AgFe (01 wt)

area 278 g of iron powder was added to the bottle As shownin Figure 2 becauseHCA is highly chlorinated it readily gaverise to reductive dechlorination by iron and relatively highreaction rateswere observed in all of the iron shavings systemHowever it is clearly demonstrated that HCA removal ratesobserved in the presence of iron shavings aremuchmore thanthose obtained in the presence of iron powder This impliesthat insofar as the specific surface area of the iron is the sameiron shavings possess better reductive activity than iron pow-dersThe primary mechanism of organic chloride compounddechlorination is thought to be an electron transfer from ZVIto the chloride organic compound [1 19] Thus the electrontransfer at the ironrsquos surface is certainly a probable processfor HCA dechlorination in this system and is assumed tobe the reaction mechanism in this paper Presumably manyelementals that also consist of iron shavings can serve as thecathode to accelerate electron transfer from iron to organicsand lead to the improvement of dechlorination reactions

Identification of reaction products indicated that thevariety of bimetallic iron shavings could shift the product dis-tributions Figures 3ndash6 showed the concentration of differentsubstances as a function of time during reductive dechlorina-tion ofHCAThe initialHCAconcentrationwas 50120583molsdotLminus1HCA that underwent reductive dechlorination at a very fastrate was observed in the Fe0 (shavings) reduction systemThe HCA removal rate reached 90 after 2 h of reactiontime and the chief reaction product was perchloroethylene(PCE) PCE underwent an extremely slow reductive dechlo-rination reaction in the presence of Fe0 alone and almost nodechlorination products of PCE were observed within 5 h Itcan be seen from Figure 4 that the HCA reacted at an evenfaster rate in the CuFe reduction system when comparedwith the Fe0 alone and the HCA removal rate reached 80within 05 h As before the chief reaction product was alsoPCE Because PCE underwent reductive dechlorination atan extremely slow rate in the CuFe system the PCE didnot continue to undergo reductive dechlorination forming


0

0

1 32 4 5 6

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)

Figure 3 Dechlorination of HCA obtained with iron shavingsalone Initial concentration of HCA was 50120583molsdotLminus1 and dosage ofiron shavings was 500 gsdotLminus1 (X) HCA () PCE (lowast) mass balance(control)

00

05 151 2 25 353

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)

Figure 4 Dechlorination of HCA obtained with CuFe (01 wt)Initial concentration of HCA was 50120583molsdotLminus1 and dosage ofamended iron shavings was 500 gsdotLminus1 (X) HCA () PCE (lowast) massbalance (control)

other products within the time allotted for the experimentHowever the removal rate of HCA was found to be faster byCuFe than by Fe0 alone

Figure 5 clearly reveals that HCA is reduced even fasterin the AgFe system than in the Fe0 and CuFe reductionsystems The products are more complex because the chiefreductive dechlorination product PCE can continue toundergo reductive dechlorination to form products such asTCE and DCE The chief reduction products of a diluteHCA solution with AgFe consist of PCE TCE and DCEIn addition since DCE is ordinarily composed of the twoisomersmdashcis-DCE and trans-DCEmdashHCA it has a relativelycomplex reaction pathway The addition of Ag can acceleratethe dechlorination rate ofHCAandPCE significantly achiev-ing nearly 100 removal rate within 2 h and 6 h respectivelyat a near neutral pH Previous researches have shown that in

0

0

2 64 8 10 12 14

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)

Figure 5 Dechlorination of HCA obtained with AgFe (01 wt)Initial concentration of HCA was 50 120583molsdotLminus1 and dosage ofamended iron shavings was 500 gsdotLminus1 (X) HCA () PCE (◻) TCE(loz) trans-DCE (I) cis-DCE (lowast) mass balance (control)

0

0

1 32 4 5

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)

Figure 6 Dechlorination of HCA obtained with PdFe (01 wt)Initial concentration of HCA was 50 120583molsdotLminus1 and dosage ofamended iron shavings was 500 gsdotLminus1 (X) HCA () PCE (998771) TCE(◻) DCE (I) C

2

H4

(lowast) mass balance (control)

bimetallic iron system other metals can serve as a cathode toaccelerate electron transfer from iron [20]

The dechlorination of HCA by PdFe was shown inFigure 6 Unlike the Fe alone CuFe and AgFe materialsthe chief reduction product of HCA with PdFe is ethyleneand the chief intermediate products are PCE and TCE Thisindicates that the dechlorination ofHCAfirst occurs120573 reduc-tive elimination forming PCE and then quickly undergoessequential hydrogenolysis to TCE and TCE is in turn rapidlydechlorinated to ethylene Compared with the Fe0 CuFeand AgFe HCA is even more thoroughly dechlorinated inthe PdFe catalytic reduction system and the final productis the chlorine-free substance ethylene Research literatureindicates that Pd is an excellent hydrogenation catalystand can achieve the complete reductive dechlorination ofchlorinated organic compounds without producing chlorine-containing compounds The H generated by iron corrosion


can be catalyzed on the Pd surface to produce atomichydrogen (Hlowast) for the chlorinated compounds dechlori-nation via Pd-catalyzed hydrodechlorination reactions [21]The use of palladium-plated iron shavings in this researchsimilarly caused HCA to undergo a fully dechlorinatedreaction yielding the final product ethylene Bimetallic ironsare frequently more reactive towards organohalides thanunamended iron and can also alter product distributionsCwiertny et al demonstrated that not all additives enhancedrates of 111-trichloroethane (111-TCA) reduction nor wasthere any clear periodic trend in the observed reactivity [22]And results suggested that absorbed atomic hydrogen ratherthan galvanic corrosion is responsible for the enhancedreactivity of bimetallic reductants

32 Reaction Kinetics The reduction of chlorinated organiccompounds by the iron shavings is a typical solid-liquid inter-face reaction and has the following main reaction formula

RClx + Fe0 +H2

O 997888rarr RHCl119909minus1

+ Fe2+ +OHminus + Clminus (1)

In the reaction process solid Fe0 is always in excess Thevast majority of surface reactions can be described using theLangmuir-Hinshelwood kinetics model When the reactiontakes place in a dilute solution of the reactants the reactionrate equation can be expressed as

minus

119889119862

119889119905

= 119896119887119862 = 119870obs119862 (2)

In this equation 119870obs is the observed reaction rate constantwhich is the experimental reaction rate constant and 119862

represents the concentration of reactants It is well establishedthat the pseudo first-order kinetics could be applied in thereductive dechlorination of chlorinated organics by ZVI andbimetallic iron [1 23] While a dilute solution of HCAwill quickly undergo a reductive dechlorination reaction byany of the iron shavings The first step in the reductivedechlorination of HCA is 120573 reductive elimination whichyields PCE Unlike Fe0 CuFe or PdFe the reductivedechlorination of HCA by AgFe is consequently a reactionnetwork comprising of both one-way continuous reactionsand parallel reactions as in Figure 7

We can write the following reaction rate equations foreach species based on the above pathway

119889 [HCA]119889119905

= minus 119896

1

[HCA] (3)

119889 [PCE]119889119905

= 119896

1

[HCA] minus 1198962

[PCE] (4)

119889 [TCE]119889119905

= 119896

2

[PCE] minus (1198963

+ 119896

4

) [TCE] (5)

119889 [119888119894119904-DCE]119889119905

= 119896

3

[TCE] (6)

119889 [119905119903119886119899119904-DCE]119889119905

= 119896

4

[TCE] (7)

TCE

cis-DCE

trans-DCE

PCE HCA K1 K2

K4

K3

Figure 7 Reaction pathways for HCA reduction by AgFe

Solving (3) (4) and (5) yields

[HCA] = [HCA]0

119890

minus119896

1119905

[PCE] =119896

1

119896

2

minus 119896

1

(119890

minus119896

1119905

minus 119890

minus119896

2119905

) [HCA]0

[TCE] = 1198961

119896

2

[HCA]0

times

119890

minus119896

1119905

(119896

1

minus 119896

2

) (119896

1

minus 119896

3

minus 119896

4

)

+

119890

minus119896

2119905

(119896

2

minus 119896

1

) (119896

2

minus 119896

3

minus 119896

4

)

+

119890

minus(119896

3+119896

4)119905

(119896

3

+ 119896

4

minus 119896

1

) (119896

3

+ 119896

4

minus 119896

2

)

(8)

Zhou et al have established the entire kinetics of 246-trichlorophenol by PdFe including parent compounds anddaughter compounds [21] In accordance with data fromdechlorination experiments using individual species of HCAPCE and TCE we can derive that 119870

1

= 2842 hminus1 1198702

=

1251 hminus1 and 119870

3

+ 119870

4

= 0463 hminus1 Following productanalysis it was found that in this experiment themole ratio ofthe products cis-DCE and trans-DCE was 21 and therefore119870

3

119870

4

= 21 It can then be calculated that 1198703

= 0149 hminus1

and 1198704

= 0314 hminus1 When [HCA]0

= 50 120583mol sdot Lminus1 and all119870 values are substituted into the foregoing reaction kineticsequations one obtains

[HCA] = 50119890minus2842119905

[PCE] = 89 (119890minus1251119905 minus 119890minus2842119905)

[TCE] = 47119890minus2842119905 minus 142119890minus1251119905 + 95119890minus0463119905

(9)

According to the mass balance

[HCA]0

= [HCA] + [PCE] + [TCE]

+ [119888119894119904-DCE] + [119905119903119886119899119904-DCE] (10)

One obtains

[119905119903119886119899119904-DCE] = 0323 (50 minus 8119890minus2842119905 + 53119890minus1251119905

minus95119890

minus0463119905

)


minus95119890

minus0463119905

)

(11)


C C

C

H

C

C

H

C

H

C

H

C

H

H

C

H

C

H

HH

C C

C CH

C C

C C H

C CH H

C CH

HC C

H

H

C CH

H

H

C C HH

C CH

H

H

H

C

H

C

H

H

HH C

H

C

H

H

H

HH

HClHCl

HCl

+

2eminus + H+

2eminus 2eminus

2eminus + H+ 2eminus + H+

2eminus + H+

2eminus2eminus

2eminus + H+2eminus + H+


2eminus

2eminus + H+


2eminus + H+

2eminus + H+

2eminus

2eminus2eminus + H+


Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl

ClCl Cl

ClCl

Clminus2Clminus

2Clminus2Clminus

2Clminus

ClCl

ClCl

Cl

Cl

Cl

Clminus

Clminus Clminus

ClminusClminus

Clminus Clminus

Cl Cl

Cl

Cl Cl Cl

Cl Cl

ClCl

2Clminus

2Clminus

Clminus

Clminus

Clminus Clminus Clminus

ClminusCl

Cl

ClCl

Cl

2Clminus

ClminusClminusCl Cl

2eminus + 2H+

2eminus + 2H+

Figure 8 Proposed pathway for the dechlorination of HCA by iron shavings and amended iron shavings

As a result the entire reaction kinetics of the reductivedechlorination of an HCA solution with an initial concentra-tion of 50 120583molsdotLminus1 in the presence of AgFe can be expressedusing the foregoing equations in this way the curve expressedby the kinetics equation fits the experimental data Similarlythe kinetics of HCA reduction by various iron shavings couldbe calculated according to reaction pathways All the kineticequations were summarized in Table 2

After normalization of the surface of the ironshavings the rate constants 119870

119878119860

are 00073 Lsdotmminus2sdothminus100136 Lsdotmminus2sdothminus1 00189 Lsdotmminus2sdothminus1 and 00084 Lsdotmminus2sdothminus1respectively It was found that the AgFe and CuFe couldenhance reductive dechlorination of HCA obviously TheCuFe can speed up the reaction rate nearly twofold andthe AgFe can increase it about 3 times compared to ironshavings alone While the PdFe catalytic material hasrelatively little effect on the HCA removal rate however it

can make HCA dechlorination to nonchlorinated productsdue to Pd as an excellent hydrogenation catalyst

33 Intermediate Products and Reaction Pathways Fennellyand Roberts observed different 111-trichloroethane (111-TCA) product distributions in NiFe and CuFe systems [12]In order to perform a thorough evaluation of the productsresulting from the reductive dechlorination of HCA a high-concentration aqueous solution of HCA was prepared andthe GCMS system was used The results of this experi-ment clearly indicated that apart from transformation toPCE via 120573 reductive elimination HCA can also undergohydrogenolysis to produce pentachloroethane (PCA) andtetrachloroethane (TeCA) and then trichloroethane (TCA)and dichloroethane (DCA) Furthermore PCE also under-goes further dechlorination in the AgFe and PdFe reductionsystems via hydrogenolysis yielding other products such


Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905


as trichloroethylene (TCE) dichloroethylene (DCE) vinylchloride (VC) and ethylene The reduction of PCE by120573-elimination produces dichloroacetylene (DCAc) whichcan be further reduced to chloroacetylene (CAc) and thenacetylene [24] Reduction products are consequently highlydependent on the bimetallic materials

In AgFe reduction systems as many as 10 species maybe presented including some products of side reactionsDetermination of how these dechlorination products aregenerated is an extremely significant issue in research onthe reaction pathway and reaction mechanism for the reduc-tive dechlorination of HCA by various iron shavings Theproposed degradation pathways of HCA with various ironshavings based on the detected dechlorination products andthe theoretical derivation were shown in Figure 8

Results suggest that the pathway of the reductive dechlo-rination of HCA by iron shavings was found to be predomi-nantly reductive 120573 elimination Apart from this hydrogenol-ysis and dehydrochlorination reactions also occur Previousresearch showed that the chemical degradation of chlorinatedhydrocarbons also progressedwith a stepwise dehalogenationmechanism [1] Reductive 120573 elimination has been shownto be a preferential pathway for compounds possessing 120572120573-pairs of chlorine atoms [25 26] while hydrogenolysisor reductive 120572 elimination is the primary transformationpathway for compounds possessing only 120572-chlorines [12 27]In addition dehydrohalogenation becomes important underbasic conditions [28]

4 Conclusions

The presented study gave insight into the entire dechlorina-tion kinetics and dechlorination pathways of HCA by ironshavings and amended iron shavings Iron shaving is a moreeffective reducing agent than traditional iron powder that isused in early research for dechlorination of HCA in waterThe deposition of Cu Ag and Pd on the surface of ironshavings was found to significantly increase the rate of HCAreduction AgFe shavings increased the HCA reduction ratenearly threefold compared to iron shavings alone and PdFeshavings can promote the complete reductive dechlorina-tion of HCA within 4 h yielding products containing nochlorine The dechlorination of HCA by all types of ironshavings followed pseudo first-order reaction kinetics Thepathway of reductive dechlorination of HCA predominantlyconsists of 120573 reductive elimination and hydrogenolysis anddehydrochlorination reactions also occur Iron shavings arewidely available inexpensivewaste products and possess goodreactivity and longevity usage in treatment of wastewater andthey can be readily used in engineering applications

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was financially supported by the Natural ScienceFoundation of China (Grant nos 41172210 50808136) theFundamental Research Funds for the Central Universities(no 0400219188) and the National Key Technology RampDProgram (no 2013BAC01B01)

References

[1] L J Matheson and P G Tratnyek ldquoReductive dehalogenationof chlorinated methanes by iron metalrdquo Environmental Scienceand Technology vol 28 no 12 pp 2045ndash2053 1994

[2] D L Wu H W Wang J H Fan and L M Ma ldquoCatalyticreduction of CCl4 in water by Fe0 and amended Fe0rdquoHuanjingKexueEnvironmental Science vol 29 no 12 pp 3433ndash34382008

[3] X Zhang BDeng J Guo YWang andY Lan ldquoLigand-assisteddegradation of carbon tetrachloride by microscale zero-valentironrdquo Journal of Environmental Management vol 92 no 4 pp1328ndash1333 2011

[4] B Jafarpour P T Imhoff and P C Chiu ldquoQuantification andmodelling of 24-dinitrotoluene reduction with high-purity andcast ironrdquo Journal of Contaminant Hydrology vol 76 no 1-2 pp87ndash107 2005

[5] M Gheju ldquoHexavalent chromium reduction with zero-valentiron (ZVI) in aquatic systemsrdquo Water Air and Soil Pollutionvol 222 no 1ndash4 pp 103ndash148 2011

[6] N Melitas J Wang M Conklin P ODay and J FarrellldquoUnderstanding soluble arsenate removal kinetics by zerovalentiron mediardquo Environmental Science and Technology vol 36 no9 pp 2074ndash2081 2002

[7] C Noubactep K B D Btatkeu and J B Tchatchueng ldquoImpactof MnO

2

on the efficiency of metallic iron for the removalof dissolved Cr119881119868 Cu119868119868 Mo119881119868 S119887119881 U119881119868 and Zn119868119868rdquo ChemicalEngineering Journal vol 178 pp 78ndash84 2011

[8] J A Mielczarski G M Atenas and E Mielczarski ldquoRoleof iron surface oxidation layers in decomposition of azo-dyewater pollutants in weak acidic solutionsrdquo Applied Catalysis BEnvironmental vol 56 no 4 pp 289ndash303 2005

[9] S Mossa Hosseini B Ataie-Ashtiani and M Kholghi ldquoNitratereduction by nano-FeCu particles in packed columnrdquo Desali-nation vol 276 no 1ndash3 pp 214ndash221 2011

[10] J Klausen S P Trober S B Haderlein and R P Schwarzen-bach ldquoReduction of substituted nitrobenzenes by Fe(II) inaqueousmineral suspensionsrdquo Environmental Science and Tech-nology vol 29 no 9 pp 2396ndash2404 1995

[11] A MMoore C H De Leon and TM Young ldquoRate and extentof aqueous perchlorate removal by iron surfacesrdquo Environmen-tal Science and Technology vol 37 no 14 pp 3189ndash3198 2003

[12] J P Fennelly and A L Roberts ldquoReaction of 111-trichloro-ethane with zero-valent metals and bimetallic reductantsEn-vironmental Science and Technologyrdquo vol 32 pp 1980ndash19881998

[13] C B Wang and W X Zhang ldquoSynthesizing nanoscale ironparticles for rapid and complete dechlorination of TCE andPCBsrdquo Environmental Science and Technology vol 31 no 7 pp2154ndash2156 1997

[14] J Zhang Z Hao Z Zhang Y Yang and X Xu ldquoKinetics ofnitrate reductive denitrification by nanoscale zero-valent ironrdquo


Process Safety and Environmental Protection vol 88 no 6 pp439ndash445 2010

[15] YH Shih C YHsu andY F Su ldquoReduction of hexachloroben-zene by nanoscale zero-valent iron kinetics pH effect anddegradation mechanismrdquo Separation and Purification Technol-ogy vol 76 no 3 pp 268ndash274 2011

[16] L Ma and W X Zhang ldquoEnhanced biological treatment ofindustrial wastewater with bimetallic zero-valent ironrdquo Envi-ronmental Science andTechnology vol 42 no 15 pp 5384ndash53892008

[17] W FWust R Kober O Schlicker and A Dahmke ldquoCombinedzero- and first-order kinetic model of the degradation of tceand cis-DCEwith commercial ironrdquo Environmental Science andTechnology vol 33 no 23 pp 4304ndash4309 1999

[18] W A Arnold and A L Roberts ldquoPathways and kinetics ofchlorinated ethylene and chlorinated acetylene reaction withFe(0) particlesrdquo Environmental Science and Technology vol 34no 9 pp 1794ndash1805 2000

[19] Y H Shih Y C Chen M Y Chen Y T Tai and C P TsoldquoDechlorination of hexachlorobenzene by using nanoscale Feand nanoscale PdFe bimetallic particlesrdquo Colloids and SurfacesA vol 332 no 2-3 pp 84ndash89 2009

[20] D W Elliott and W X Zhang ldquoField assessment of nanoscalebimetallic particles for groundwater treatmentrdquo EnvironmentalScience and Technology vol 35 no 24 pp 4922ndash4926 2001

[21] T Zhou Y Li and T T Lim ldquoCatalytic hydrodechlorination ofchlorophenols by PdFe nanoparticles comparisons with otherbimetallic systems kinetics and mechanismrdquo Separation andPurification Technology vol 76 no 2 pp 206ndash214 2010

[22] D M Cwiertny S J Bransfield K J T Livi D H Fairbrotherand A L Roberts ldquoExploring the influence of granular ironadditives on 111-trichloroethane reductionrdquo EnvironmentalScience and Technology vol 40 no 21 pp 6837ndash6843 2006

[23] H Song and E R Carraway ldquoReduction of chlorinated ethanesby nanosized zero-valent iron kinetics pathways and effectsof reaction conditionsrdquo Environmental Science and Technologyvol 39 no 16 pp 6237ndash6245 2005

[24] W A Arnold and A L Roberts ldquoErratum Pathways ofchlorinated ethylene and chlorinated acetylene reaction withZn(0)rdquo Environmental Science and Technology vol 32 no 19pp 3017ndash3025 1998

[25] W A Arnold W P Ball and A L Roberts ldquoPolychlorinatedethane reaction with zero-valent zinc pathways and rate con-trolrdquo Journal of Contaminant Hydrology vol 40 no 2 pp 183ndash200 1999

[26] E C Butler and K F Hayes ldquoKinetics of the transformationof halogenated aliphatic compounds by iiron sulfiderdquo Environ-mental Science and Technology vol 34 no 3 pp 422ndash429 2000

[27] W A Arnold PWinget and C J Cramer ldquoReductive dechlori-nation of 1122-tetrachloroethanerdquo Environmental Science andTechnology vol 36 no 16 pp 3536ndash3541 2002

[28] P M Jeffers L M Ward L M Woytowitch and N LWolfe ldquoHomogeneous hydrolysis rate constants for selectedchlorinated methanes ethanes ethenes and propanesrdquo Envi-ronmental Science and Technology vol 23 no 8 pp 965ndash9691989

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


applications containing 910000 kilograms of iron shavings(60000m3d) which have chiefly consisted of industrialwastewater pretreatment and thematerial has been shown toimprovewastewater biodegradability [16]However there hasbeen no systematic research on the specific reaction processesand detailed mechanisms when iron shavings are used toperform the reductive transformation of pollutants Workson the amended iron shavings by Cu Ag and Pd are verylimited as well particularly the AgFe bimetallic iron Oneof the primary goals of this study is to fill this gap Wust etal observed a combined zero- and first-order kinetic modelin describing the dechlorination of TCE and cis-DCE byZVI [17] Arnold and Roberts adapted a modified Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model todescribe iron mediated dechlorination of chlorinated ethy-lene and acetylene [18] However reported reaction rates forvarious chlorinated compounds are highly variable amongdifferent investigators

The characteristics of iron shavings differed from ironpowder greatly and there has been no research reports con-cerning the potential reduction processes and mechanismsof chlorinated hydrocarbons by iron shavings Furthermorebecause most past research on reaction kinetics focused onthe overall kinetics of removal of parent compounds therehas been limited research on the entire kinetics of finalreaction products and intermediate productsThis study usesiron shavings which possess tremendous engineering appli-cation potential as the main reducing agent and comparesthe reaction performance of iron shavings and conventionaliron powder Taking hexachloroethane as the target pollutantthe reductive reactivity of iron shavings and bimetallic ironshavings was investigated in batch experiments as well asthe detailed entire reaction kinetics reaction products andpathwaysThis study might facilitate the development of ironshaving wastewater treatment techniques by providing a full-scale understanding of the mechanism that iron shavingsbring about on the reductive transformation of pollutants

2 Experimental Section

21 Materials and Reagents The chief experimental materialconsisted ofmetallic iron shavings whichwere obtained fromthe machine shop at Tongji University the shavings madeof 38CrMoAl steel with a carbon content of approximately03-04 also contained trace elements including Si MnCr Mo and Al (detailed elemental composition is shownin Table 1) A lathe was used to cut the iron into curlyshavings with a width of 05ndash10 cm length of 3ndash10 cm andthickness of 02mm The specific surface area of the ironshavings was 03m2g (tested by application of the Brunauer-Emmett-Teller (BET)) the appearance of the shavings isshown in Figure 1 The experiment used 100mL reactionbottles (marked volume of 100mL actual volume of roughly120mL) to ensure that the reaction occurred in a tightlysealed vessel and 1mL gas-tight sample collectors were usedto collect samples for analysis Deionized water from Milli-Q (Millipore Corp) deoxygenated by purging with high-purity N

2

was used in all experiments The reagents of

Table 1 Elemental composition of iron shavings used ()

Elemental Content (wt)Fe gt95C 035sim042Si 02sim045Mn 03sim06Cr 135sim165Mo 015sim025Al 070sim110

Figure 1 Image of the unwashed shavings (38CrMoAl steel)

hexachloroethane pentachloroethane tetrachloroethylenetrichloroethylene and dichloroethylene were all HPLC gradeand were purchased from the Sigma Company The NaOHNaHCO

3

HCl CuSO4

AgNO3

and PdCl2

used in thisstudy were analytically pure and were purchased from theSinopharm Chemical Reagent Co Ltd All chemicals wereused as received The purity of the iron powder was 99 itwas purchased from the Shanghai Runjie Chemical ReagentCo Ltd

22 Methods Stock solutions of hexachloroethane wereprepared in methanol 20120583L of stock solution was spikedinto 1000mL of aqueous solution to achieve the desiredinitial concentration Iron shavings were washed in NaHCO

3

solution to remove any surface oil or grease and were soakedin water for several days to allow the surface to rust Therusty iron shavings were then washed in deaerated 01molLhydrochloric acid (HCl) and rinsed 5 times with deaeratedwater 50 g of the shavings was packed into reaction bottleswith marked volume of 100mL and an aqueous solution ofhexachloroethane with a predetermined concentration wasadded The bottles were immediately sealed using Teflon-coated stoppers and crimp-sealed with aluminum foil capsto provide a better seal The reaction bottles were placed ina water bath on a constant temperature shaking incubatorwhich shook at a constant rate of 180 rmin Each experimentwas performed in triplicate including a set of control vials




4

AgNO3

and PdCl2


4

AgNO3

and PdCl

2



2




00

1 32 4 5 6

10

20

30

40

50

60

70

80

90

100

Rem

oval

rate

()

Time (h)





0

0

1 32 4 5 6

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


00

05 151 2 25 353

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)




0

0

2 64 8 10 12 14

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


0

0

1 32 4 5

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


2

H4







RClx + Fe0 +H2




minus

119889119862

119889119905

= 119896119887119862 = 119870obs119862 (2)




119889 [HCA]119889119905

= minus 119896

1

[HCA] (3)

119889 [PCE]119889119905

= 119896

1

[HCA] minus 1198962

[PCE] (4)

119889 [TCE]119889119905

= 119896

2


+ 119896

4

) [TCE] (5)

119889 [119888119894119904-DCE]119889119905

= 119896

3

[TCE] (6)

119889 [119905119903119886119899119904-DCE]119889119905

= 119896

4

[TCE] (7)

TCE

cis-DCE

trans-DCE

PCE HCA K1 K2

K4

K3



[HCA] = [HCA]0

119890

minus119896

1119905

[PCE] =119896

1

119896

2

minus 119896

1

(119890

minus119896

1119905

minus 119890

minus119896

2119905

) [HCA]0

[TCE] = 1198961

119896

2

[HCA]0

times

119890

minus119896

1119905

(119896

1

minus 119896

2

) (119896

1

minus 119896

3

minus 119896

4

)

+

119890

minus119896

2119905

(119896

2

minus 119896

1

) (119896

2

minus 119896

3

minus 119896

4

)

+

119890

minus(119896

3+119896

4)119905

(119896

3

+ 119896

4

minus 119896

1

) (119896

3

+ 119896

4

minus 119896

2

)

(8)


1

= 2842 hminus1 1198702

=

1251 hminus1 and 119870

3

+ 119870

4


3

119870

4


= 0149 hminus1

and 1198704



[HCA] = 50119890minus2842119905



(9)


[HCA]0

= [HCA] + [PCE] + [TCE]

+ [119888119894119904-DCE] + [119905119903119886119899119904-DCE] (10)

One obtains


minus95119890

minus0463119905

)


minus95119890

minus0463119905

)

(11)


C C

C

H

C

C

H

C

H

C

H

C

H

H

C

H

C

H

HH

C C

C CH

C C

C C H

C CH H

C CH

HC C

H

H

C CH

H

H

C C HH

C CH

H

H

H

C

H

C

H

H

HH C

H

C

H

H

H

HH

HClHCl

HCl

+

2eminus + H+

2eminus 2eminus


2eminus + H+

2eminus2eminus



2eminus

2eminus + H+


2eminus + H+

2eminus + H+

2eminus

2eminus2eminus + H+


Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl

ClCl Cl

ClCl

Clminus2Clminus

2Clminus2Clminus

2Clminus

ClCl

ClCl

Cl

Cl

Cl

Clminus

Clminus Clminus

ClminusClminus

Clminus Clminus

Cl Cl

Cl

Cl Cl Cl

Cl Cl

ClCl

2Clminus

2Clminus

Clminus

Clminus


ClminusCl

Cl

ClCl

Cl

2Clminus

ClminusClminusCl Cl

2eminus + 2H+

2eminus + 2H+




119878119860





Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




4

AgNO3

and PdCl2


4

AgNO3

and PdCl

2



2




00

1 32 4 5 6

10

20

30

40

50

60

70

80

90

100

Rem

oval

rate

()

Time (h)





0

0

1 32 4 5 6

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


00

05 151 2 25 353

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)




0

0

2 64 8 10 12 14

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


0

0

1 32 4 5

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


2

H4







RClx + Fe0 +H2




minus

119889119862

119889119905

= 119896119887119862 = 119870obs119862 (2)




119889 [HCA]119889119905

= minus 119896

1

[HCA] (3)

119889 [PCE]119889119905

= 119896

1

[HCA] minus 1198962

[PCE] (4)

119889 [TCE]119889119905

= 119896

2


+ 119896

4

) [TCE] (5)

119889 [119888119894119904-DCE]119889119905

= 119896

3

[TCE] (6)

119889 [119905119903119886119899119904-DCE]119889119905

= 119896

4

[TCE] (7)

TCE

cis-DCE

trans-DCE

PCE HCA K1 K2

K4

K3



[HCA] = [HCA]0

119890

minus119896

1119905

[PCE] =119896

1

119896

2

minus 119896

1

(119890

minus119896

1119905

minus 119890

minus119896

2119905

) [HCA]0

[TCE] = 1198961

119896

2

[HCA]0

times

119890

minus119896

1119905

(119896

1

minus 119896

2

) (119896

1

minus 119896

3

minus 119896

4

)

+

119890

minus119896

2119905

(119896

2

minus 119896

1

) (119896

2

minus 119896

3

minus 119896

4

)

+

119890

minus(119896

3+119896

4)119905

(119896

3

+ 119896

4

minus 119896

1

) (119896

3

+ 119896

4

minus 119896

2

)

(8)


1

= 2842 hminus1 1198702

=

1251 hminus1 and 119870

3

+ 119870

4


3

119870

4


= 0149 hminus1

and 1198704



[HCA] = 50119890minus2842119905



(9)


[HCA]0

= [HCA] + [PCE] + [TCE]

+ [119888119894119904-DCE] + [119905119903119886119899119904-DCE] (10)

One obtains


minus95119890

minus0463119905

)


minus95119890

minus0463119905

)

(11)


C C

C

H

C

C

H

C

H

C

H

C

H

H

C

H

C

H

HH

C C

C CH

C C

C C H

C CH H

C CH

HC C

H

H

C CH

H

H

C C HH

C CH

H

H

H

C

H

C

H

H

HH C

H

C

H

H

H

HH

HClHCl

HCl

+

2eminus + H+

2eminus 2eminus


2eminus + H+

2eminus2eminus



2eminus

2eminus + H+


2eminus + H+

2eminus + H+

2eminus

2eminus2eminus + H+


Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl

ClCl Cl

ClCl

Clminus2Clminus

2Clminus2Clminus

2Clminus

ClCl

ClCl

Cl

Cl

Cl

Clminus

Clminus Clminus

ClminusClminus

Clminus Clminus

Cl Cl

Cl

Cl Cl Cl

Cl Cl

ClCl

2Clminus

2Clminus

Clminus

Clminus


ClminusCl

Cl

ClCl

Cl

2Clminus

ClminusClminusCl Cl

2eminus + 2H+

2eminus + 2H+




119878119860





Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

0

1 32 4 5 6

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


00

05 151 2 25 353

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)




0

0

2 64 8 10 12 14

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


0

0

1 32 4 5

10

20

30

40

50

60

Con

cent

ratio

n (120583

M)

Time (h)


2

H4







RClx + Fe0 +H2




minus

119889119862

119889119905

= 119896119887119862 = 119870obs119862 (2)




119889 [HCA]119889119905

= minus 119896

1

[HCA] (3)

119889 [PCE]119889119905

= 119896

1

[HCA] minus 1198962

[PCE] (4)

119889 [TCE]119889119905

= 119896

2


+ 119896

4

) [TCE] (5)

119889 [119888119894119904-DCE]119889119905

= 119896

3

[TCE] (6)

119889 [119905119903119886119899119904-DCE]119889119905

= 119896

4

[TCE] (7)

TCE

cis-DCE

trans-DCE

PCE HCA K1 K2

K4

K3



[HCA] = [HCA]0

119890

minus119896

1119905

[PCE] =119896

1

119896

2

minus 119896

1

(119890

minus119896

1119905

minus 119890

minus119896

2119905

) [HCA]0

[TCE] = 1198961

119896

2

[HCA]0

times

119890

minus119896

1119905

(119896

1

minus 119896

2

) (119896

1

minus 119896

3

minus 119896

4

)

+

119890

minus119896

2119905

(119896

2

minus 119896

1

) (119896

2

minus 119896

3

minus 119896

4

)

+

119890

minus(119896

3+119896

4)119905

(119896

3

+ 119896

4

minus 119896

1

) (119896

3

+ 119896

4

minus 119896

2

)

(8)


1

= 2842 hminus1 1198702

=

1251 hminus1 and 119870

3

+ 119870

4


3

119870

4


= 0149 hminus1

and 1198704



[HCA] = 50119890minus2842119905



(9)


[HCA]0

= [HCA] + [PCE] + [TCE]

+ [119888119894119904-DCE] + [119905119903119886119899119904-DCE] (10)

One obtains


minus95119890

minus0463119905

)


minus95119890

minus0463119905

)

(11)


C C

C

H

C

C

H

C

H

C

H

C

H

H

C

H

C

H

HH

C C

C CH

C C

C C H

C CH H

C CH

HC C

H

H

C CH

H

H

C C HH

C CH

H

H

H

C

H

C

H

H

HH C

H

C

H

H

H

HH

HClHCl

HCl

+

2eminus + H+

2eminus 2eminus


2eminus + H+

2eminus2eminus



2eminus

2eminus + H+


2eminus + H+

2eminus + H+

2eminus

2eminus2eminus + H+


Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl

ClCl Cl

ClCl

Clminus2Clminus

2Clminus2Clminus

2Clminus

ClCl

ClCl

Cl

Cl

Cl

Clminus

Clminus Clminus

ClminusClminus

Clminus Clminus

Cl Cl

Cl

Cl Cl Cl

Cl Cl

ClCl

2Clminus

2Clminus

Clminus

Clminus


ClminusCl

Cl

ClCl

Cl

2Clminus

ClminusClminusCl Cl

2eminus + 2H+

2eminus + 2H+




119878119860





Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




RClx + Fe0 +H2




minus

119889119862

119889119905

= 119896119887119862 = 119870obs119862 (2)




119889 [HCA]119889119905

= minus 119896

1

[HCA] (3)

119889 [PCE]119889119905

= 119896

1

[HCA] minus 1198962

[PCE] (4)

119889 [TCE]119889119905

= 119896

2


+ 119896

4

) [TCE] (5)

119889 [119888119894119904-DCE]119889119905

= 119896

3

[TCE] (6)

119889 [119905119903119886119899119904-DCE]119889119905

= 119896

4

[TCE] (7)

TCE

cis-DCE

trans-DCE

PCE HCA K1 K2

K4

K3



[HCA] = [HCA]0

119890

minus119896

1119905

[PCE] =119896

1

119896

2

minus 119896

1

(119890

minus119896

1119905

minus 119890

minus119896

2119905

) [HCA]0

[TCE] = 1198961

119896

2

[HCA]0

times

119890

minus119896

1119905

(119896

1

minus 119896

2

) (119896

1

minus 119896

3

minus 119896

4

)

+

119890

minus119896

2119905

(119896

2

minus 119896

1

) (119896

2

minus 119896

3

minus 119896

4

)

+

119890

minus(119896

3+119896

4)119905

(119896

3

+ 119896

4

minus 119896

1

) (119896

3

+ 119896

4

minus 119896

2

)

(8)


1

= 2842 hminus1 1198702

=

1251 hminus1 and 119870

3

+ 119870

4


3

119870

4


= 0149 hminus1

and 1198704



[HCA] = 50119890minus2842119905



(9)


[HCA]0

= [HCA] + [PCE] + [TCE]

+ [119888119894119904-DCE] + [119905119903119886119899119904-DCE] (10)

One obtains


minus95119890

minus0463119905

)


minus95119890

minus0463119905

)

(11)


C C

C

H

C

C

H

C

H

C

H

C

H

H

C

H

C

H

HH

C C

C CH

C C

C C H

C CH H

C CH

HC C

H

H

C CH

H

H

C C HH

C CH

H

H

H

C

H

C

H

H

HH C

H

C

H

H

H

HH

HClHCl

HCl

+

2eminus + H+

2eminus 2eminus


2eminus + H+

2eminus2eminus



2eminus

2eminus + H+


2eminus + H+

2eminus + H+

2eminus

2eminus2eminus + H+


Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl

ClCl Cl

ClCl

Clminus2Clminus

2Clminus2Clminus

2Clminus

ClCl

ClCl

Cl

Cl

Cl

Clminus

Clminus Clminus

ClminusClminus

Clminus Clminus

Cl Cl

Cl

Cl Cl Cl

Cl Cl

ClCl

2Clminus

2Clminus

Clminus

Clminus


ClminusCl

Cl

ClCl

Cl

2Clminus

ClminusClminusCl Cl

2eminus + 2H+

2eminus + 2H+




119878119860





Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


C C

C

H

C

C

H

C

H

C

H

C

H

H

C

H

C

H

HH

C C

C CH

C C

C C H

C CH H

C CH

HC C

H

H

C CH

H

H

C C HH

C CH

H

H

H

C

H

C

H

H

HH C

H

C

H

H

H

HH

HClHCl

HCl

+

2eminus + H+

2eminus 2eminus


2eminus + H+

2eminus2eminus



2eminus

2eminus + H+


2eminus + H+

2eminus + H+

2eminus

2eminus2eminus + H+


Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl

ClCl Cl

ClCl

Clminus2Clminus

2Clminus2Clminus

2Clminus

ClCl

ClCl

Cl

Cl

Cl

Clminus

Clminus Clminus

ClminusClminus

Clminus Clminus

Cl Cl

Cl

Cl Cl Cl

Cl Cl

ClCl

2Clminus

2Clminus

Clminus

Clminus


ClminusCl

Cl

ClCl

Cl

2Clminus

ClminusClminusCl Cl

2eminus + 2H+

2eminus + 2H+




119878119860





Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Table2Re

actio

npathwayskinetic

sfor

HCA

redu

ctionby

Fe0(shaving

s)C

uFeA

gFeand

PdFe

Iron

shavings

Pathway

119870

119899

values

Equatio

nsfore

achsubstance

Fe0(shaving

s)PC

E H

CAK1

119870

1

=1098hminus1

[HCA

]=50119890

minus1098119905

[PC

E]=50(1minus119890

minus1098119905

)

CuFe

PCE

HCA

K1

119870

1

=2044hminus1

[HCA

]=50119890

minus2044119905

[PC

E]=50(1minus119890

minus2044119905

)

AgFe

TCE

cis-D

CE

trans

-DCE

PCE

HCA

K1

K2

K3

K4

119870

1

=2842hminus1

[HCA

]=50119890

minus2842119905

119870

2

=1251hminus1

[PC

E]=89(119890

minus1251119905

minus119890

minus2842119905

)

119870

3

=0149hminus1

[TC

E]=47119890

minus2842119905

minus142119890

minus1251119905

+95119890

minus0463119905

119870

4

=0314hminus1

[119905119903119886119899119904-D

CE]=0323(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

[119888119894119904-D

CE]=0677(50minus8119890

minus2842119905

+53119890

minus1251119905

minus95119890

minus0463119905

)

PdFe

TCE

PCE

HCA

C 2H

4K1

K2

K3

119870

1

=1267hminus1

[HCA

]=50119890

minus1267119905

119870

2

=0978hminus1

[PC

E]=219(119890

minus0978119905

minus119890

minus1267119905

)

119870

3

=141hminus1

[TC

E]=minus1500119890

minus1267119905

+496119890

minus0978119905

+1004119890

minus141119905

[C 2

H4]=50+1669119890

minus1267119905

minus715119890

minus0978119905

minus1004119890

minus141119905





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





4 Conclusions




Acknowledgments


References








2


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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