faDepartment of Inorganic Chemistry, Faculty of Chemistry, Maria Curie-Skodowska University, Maria Curie-Skodowska Sq. 2., 20-031 Lublin, Polandical and Environmental Science, University of Limerick, Limerick, Ireland

" The intraparticle diffusion was not

waste waters from, among others, metal nishing, electroplating,plastics, pigments and mining industries, there is the distinct ten-dency to replace the costly activated carbons (ACs) and ionexchangers (IXs) with various low cost adsorbents, which have me-tal binding capacities [13]. BC is a porous substance, similar inappearance to charcoal that is produced by pyrolysis of feedstockunder oxygen limited conditions [4]. Through pyrolysis abundant

and non-condensable gas (syngas) are obtained [6,7]. Productionof biochar generally releases more energy than it consumes,depending on the moisture content of the feedstock [8]. Pyrolysisconditions and feedstock characteristics largely control the physi-cochemical properties of BC (e.g. composition, particle and poresize distribution) which determine the suitability for a given appli-cation as well as deninge its behavior, transport and fate in theenvironment.

The BC can be mainly used as large scale soil amendment for awide range of environmental and agricultural applications

Corresponding author. Tel.: +48 81 537 57 36; fax: +48 81 533 33 48.

Chemical Engineering Journal 197 (2012) 295305

Contents lists available at

ne

w.E-mail address: kolodyn@poczta.onet.pl (D. Koodynska).BiocharWaste water treatmentKineticsIsotherms

2012 Elsevier B.V. All rights reserved.

1. Introduction

In the removal of hazardous contaminants from industrial

lignocellulose feedstocks, agricultural residues and biorenerywastes, etc. can be utilized [5]. When heated to between 350 and800 C in a N2 atmosphere not only BC but also bio-oil (crude oil)the only rate controlling step of theadsorption process.

a r t i c l e i n f o

Article history:Received 2 February 2012Received in revised form 7 May 2012Accepted 8 May 2012Available online 18 May 2012

Keywords:Metal1385-8947/$ - see front matter 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.cej.2012.05.025a b s t r a c t

Kinetic and adsorption studies on the removal of metal ions such as Cu(II), Zn(II), Cd(II) and Pb(II) ions inthe biochar (BC) samples have been carried out. The effects of several experimental parameters have beeninvestigated using the batch adsorption technique at different temperature. The effectiveness of Cu(II),Zn(II), Cd(II) and Pb(II) ions removal increases with the increasing initial concentration of biochar andmetal ion, pH as well as phase contact time. The maximum adsorption was found in the pH range 5.06.0. The kinetics of adsorption was found to be pseudo second order with intraparticle diffusion as oneof the rate determining steps. Adsorption studies were also performed at different temperatures andmodelled with the Langmuir and Freundlich adsorption isotherms.well by the pseudo second ordermodel.bCarbolea Research Group, Department of Chem

h i g h l i g h t s

" Biochars effectively removed metalions from aqueous solutions.

" Pyrolysis at 400 C seems optimalproducing biochar as the effectivemetal ions sorbent.

" The maximum removal wasobtained in the pH range 56.

" The adsorption kinetic was describedg r a p h i c a l a b s t r a c tD. Koodynska a,, R. Wnetrzak b, J.J. Leahy b, M.H.B. Hayes b, W. Kwapinski b, Z. Hubicki a

Kinetic and adsorptive characterization o

Chemical Engi

journal homepage: wwll rights reserved.biochar in metal ions removal

SciVerse ScienceDirect

ering Journal

elsevier .com/locate /cej

crease in net primary production accrues from the use of biochar

characteristics were measured by N2 adsorption using the BET sur-

ineeincluding contaminant immobilization, soil fertilization as well ascarbon sequestration. It improves soil quality by increasing soilpH (due to its neutral to basic pH), moisture holding capacity (bio-char can have direct and indirect effects on soil water retention,which can be short or long lived), attracting more benecial fungiand microbes as well as improving cation exchange capacity [915]. The benecial effect of biochar application to soils on plantproductivity should be also mentioned. Biochar contains stablecarbon and this carbon remains sequestered for much longer peri-ods than the original biomass [16,17]. Additionally, biochar with ahigh ash content can be considered a source of nutrients. In thecase of low ash content it can be blended with other materials suchas synthetic fertilizers, compost and manures to enhance its nutri-ent value. Furthermore, biochar has been shown to retain nutrientsagainst leaching [18,19].

Generally, BC is characterized by very low homogeneity. Itshould also be mentioned that BC obtained at lower temperatureexhibits low adsorption capacity whereas the high-temperaturematerial is characterized by greater surface area and high micropo-rosity [20]. The physicochemical properties determine the effectsof biochar on soil functions, for example the direct effect on soilwater retention is related to the large inner surface area of biocharwhereas the indirect effect of biochar on water retention of soil isrelated to improved aggregation or structure. Biochar can affectsoil aggregation due to the interactions with soil organic matter(SOM), minerals and microorganisms. The surface charge charac-teristics and their development over time, determine the long termeffect on soil aggregation.

Biochar application is likely to improve the overall sorptioncapacity of soils towards common anthropogenic organic com-pounds (polycyclic aromatic hydrocarbons (PAHs), pesticides suchas among others dichlorodiphenyltrichloroethane (DDT), herbi-cides as well as dyes, naphthalene nitrobenzene and 1,3-dinitro-benzene) and therefore inuence toxicity, transport and fate ofsuch contaminants and reduce their short term risk [2125]. Froman agricultural perspective it can be benecial in terms of reducingpesticide residues in crops but detrimental in terms of reducingherbicide efciency. Therefore compromise between the increasedsorption capacities at high pyrolysis temperature activated biocharand the benets provided by low temperature biochar in terms ofreduced toxicity and absorption should be taken into account inremediation processes. The same situation occurs in the case ofmetal contaminated soil remediation. Biochar with high cation ex-change capacities is the most suitable for use in soil remediation,but it is also likely to retain more plant nutrients by the samemechanism that it immobilizes contaminants. In the literaturethere is some data connected with the adsorption of Cu(II), Zn(II),Ni(II), Cd(II), Pb(II) as well as As(III,V) and Cr(III,VI) using BC de-rived from agricultural residues such as hardwood, corn, peanut,soybean, canola straws, oak bar, rice husk, dairy manure, and broi-ler litter [26,27]. For example, a dairy manure biochar made at350 C sorbed several times more Pb(II) than activated carbons(AC) [28].

Another aspect of the application of biochar is the reduction ofthe greenhouse gas emissions and its positive inuence on the cli-mate changes. It is well known that carbon dioxide is not the onlygas emitted from soil. It has been demonstrated that the amount ofmethane produced as a part of the carbon cycle and nitrous oxideproduced as a part of the nitrogen (N) cycle through the nitrica-tion and denitrication processes can be reduced by the biocharaddition to soils [2931]. This is very important because methaneis over 20 times more effective in trapping heat in the atmospherethan CO2, while N2O has a global warming potential that is 310

296 D. Koodynska et al. / Chemical Engtimes greater than CO2.Biochar in a global context is very important. According to the

International Biochar Initiative Organization, it is estimated thatface area analyser. Moisture content of both the BC samples wasdetermined according to the standard: Solid biofuels. Methodsfor the determination of moisture content. Oven dry method (Part3: Moisture in general analysis sample) ICS 75.160.10, DD CEN/TS14774-3:2004. Ash content was analyzed according to ICS75.160.10, DD CEN/TS 14775:2004 and the volatile matter contentaccording to ICS 75.160.10, DD CEN/TS 15148:2005. The obtaineddata are presented in Table 1. CuCl22H2O, ZnCl2, Cd(NO3)24H2Oand Pb(NO3)2 were used as sources of Cu(II), Zn(II), Cd(II) and Pb(II)ions. The stock solutions were further diluted to the requiredexperimental concentrations. The other chemicals used were ofanalytical grade. Distilled water was used for preparing all thesolutions and reagents.

2.2. Kinetic tests

A stock solution of metal ions (1 mol/dm3) was prepared andsuitably diluted accordingly to the various required initial concen-in soils will be observed.As the presence of metal ions in soil and industrial waste waters

can be an important source of pollution and may be a severe healthhazard in the paper kinetics studies of metal ions Cu(II), Zn(II),Cd(II) and Pb(II) sorption on the BC samples were presented. Theyare important in evaluating adsorption operation for practicalapplications especially for metal ions removal from waste waters.Experiments were undertaken to understand the transport pro-cesses that take place during adsorption and to identify the ratecontrolling steps as well as determining external mass transferand intraparticle diffusion rate coefcients. So far only a limitednumber of studies have involved the kinetic analysis of metal ionsadsorption on the biochars samples.

2. Materials and methods

2.1. Materials

Biochar (BC) samples (denoted as SA4, SA6, SB4, SB6, SC4 andSC6) were obtained from pig and cow manure in a process ofpyrolysis described in previous work [32]. Raw materials for thepreparation of BC samples were collected, using different kind ofpre-treatments (samples: SA4, SA6 pig manure chemically pre-treated slurries using Kemira separation technology; SB4, SB6,SC4 and SC6 dairy cow manure mechanically separated slurriesusing Samson and Bimatech separation technology). The carbon-ization temperatures were 400 and 600 C (the samples obtainedat lower temperature are denoted as 4 and at higher as 6), at ambi-ent pressure over nitrogen gas atmosphere. After the pyrolysis theBCs were ground and then sieved. In the preliminary studies it wasfound that the amount of Cu(II) ions adsorbed increases with thedecreasing particle size of the adsorbent (these data were not pre-sented). This is due to the increase in the available surface areawith the decrease in the particle size. Therefore, the particle sizefraction from 0.420 to 0.600 mm was used as optimal without fur-ther modication for all studies.

Total amount of carbon C, H and N in the BC samples was ana-lyzed using an elemental analyzer. The average pore and surfaceby the year 2050 (i) about 80% of all crop and forestry residues willbe converted to biochar and energy, (ii) energy produced in thepyrolysis process will replace the energy that would have comefrom coal, (iii) signicant decreases in N2O emissions and (iv) in-

ring Journal 197 (2012) 295305trations. Adsorption experiments in the single component systemsas well as in the quaternary ion systems were carried out at roomtemperature (20 1 C) using the batch technique. 50 cm3 of metal

B4

ow0.20.43.40.46.735.337.35

ineeion solutions with the initial concentration ranging from1 103 M to 25 103 M were placed in 100 cm3 conical askswith a required dose of BC samples (0.5 g) and shaken at a constantspeed (180 rpm) for a specic period of contact time. The initial pHof the solutionswere adjusted to 5.0 0.05 or to the required pH va-lue by adding either 1 MHNO3 or 1 MNaOH solutions to avoidmetalions precipitation. The sampleswere shakenmechanically using thelaboratory shaker at different time intervals at 180 rpm. After shak-ing the BC samples were separated by centrifugation at 4000 rpmfor 5 min and the solution was ltered through a 0.22-lmMilliporelter. The concentrations of Cu(II), Zn(II), Cd(II) and Pb(II) in theresidual solutions were analyzed by the atomic absorption spec-trometry method (AAS) at 324.7 nm for Cu(II), 213.9 nm for Zn(II),228.8 nm for Cd(II) and 217.0 nm for Pb(II).

After shaking the BC samples were separated by centrifugationand the concentrations of Cu(II), Zn(II), Cd(II) and Pb(II) in theresidual solutions were analyzed by the atomic absorption spec-trometry method (AAS) at 324.7 nm for Cu(II), 213.9 nm for Zn(II),228.8 nm for Cd(II) and 217.0 nm for Pb(II). The experiments werecarried out in duplicate and the average values were obtained (12% for the percentage removal and 0.0050.01 mg/g for theamount adsorbed).

The adsorption amount (qt) and the adsorption percentage (S%)are calculated according to:

qt c0 ctV

m1

S% c0 ctct

100 2

where qt is the adsorption amount of metal ion at time t (mg/g), S%is the adsorption percentage (%),m is the weight of BC sample (g), Vis the volume of solution (dm3), and c0 and ce are the initial andequilibrium concentrations of M(II) ions in solution, respectively(mol/dm3). When t is equal to the equilibrium contact time, ct = ce,qt = qe, and the amount of M(II) adsorbed at equilibrium, qe, is calcu-lated using Eq. (1).

The effects of experimental parameters such as pH, tempera-

Table 1Physicochemical properties of used BCs.

Parameters SA4 SA6 S

Animal type Pig manure Pig manure C%C 44.13 42.25 6%H 2.49 1.44 2%N 2.09 1.34 1BET surface area (m2/g) 15.56 15.89 2Moisture (wt.%) 5.18 3.79 5Ash content (wt.%) 46.52 50.29 1Volatile matter (wt.%) 19.11 15.08 2

D. Koodynska et al. / Chemical Engture, particle sizes of BC and initial concentration were studied.The kinetics and dynamics of adsorption of Cu(II), Zn(II), Cd(II)and Pb(II) on the BCs samples have been investigated by applyingthe pseudo rst order (PF-order) kinetic equation according to Eq.(3) [33]:

logqe qt logqe k1t

2:3033

and pseudo second order (PS-order) kinetic model is expressed asfollowing equation [34,35]:

tqt 1

k2q2e tqe

4

as well as the intraparticle diffusion model (IPD) (Eq. (5)) [36]:

qt kit1=2 C 5where k1 is the pseudo rst order rate constant (L/min), k2 is therate constant of the pseudo second order adsorption (g/mg min),ki is the intraparticle diffusion rate constant (mg/g min0.5), C is theintercept. Based on the plots of log(qe qt) vs. t, t/qt vs. t and qtvs. t1/2 the kinetic parameters (q1, k1, q2, k2, h, ki, C) were calculated.

2.3. Adsorption tests

The adsorption data of the metal ions ion BCs samples wereanalyzed using the Langmuir (Eq. (6)) and Freundlich isotherm(Eq. (7)) models:

The Langmuir model expressed as [37,38]:

qe q0KLce1 KLce 6

where ce is the equilibrium concentration of the metal ion (mg/dm3), qe is the adsorption capacity at equilibrium (mg/g). The con-stant q0 (mg/g) and KL are the characteristics of the Langmuir equa-tion (dm3/mg) and can be determined from its linearized form(plots of ce/qe vs. ce).

The Freundlich model is [39,40]:

qe KFc1=ne 7where KF is the Freundlich adsorption capacity (mg/g), 1/n is theFreundlich constant related to the surface heterogeneity. The aboveequation can be linearized to calculate the parameters KF and n(plots of logqe vs. logce).

Thermodynamic parameters of the adsorption were calculatedfrom the variations of the thermodynamic equilibrium constantKe which was determined by plotting ln(qe/ce) vs. qe and extrapolat-ing to zero qe. The standard free energy change DGo can be calcu-lated using the equation [41]:

DGo RT lnKe 8The Gibbs free energy, enthalpy and entropy changes are con-

nected with the general thermodynamic expression:

DGo DHo TDSo 9

SB6 SC4 SC6

manure Cow manure Cow manure Cow manure58.76 49.39 45.621.45 2.63 1.461.30 2.81 2.098.01 8.65 11.775.02 6.17 4.7718.75 38.42 45.5413.00 20.86 11.67

ring Journal 197 (2012) 295305 297lnKe DSo

R DH

o

RT10

where DGo is the standard free energy change of the ion exchange(J/mol), R is the universal gas constant (8.314 J/mol K), T is the abso-lute temperature (K), DHo is the enthalpy (kJ/mol), DSo is the entro-py (J/mol K). From the linear plot of DGo vs. T the values of DHo andDSo can be determined from the slope and intercept.

2.4. Apparatus

A laboratory shaker Elpin type 357, (Elpin-Plus, Poland) wasused for agitation. The pH values were measured with a PHM 84pH meter (Radiometer, Denmark) with glass REF 451 and calomelpHG 2018 electrodes. The concentrations of metal ions were mea-

sured with the AAS spectrometer SpectrAA 240FZ (Varian, Austra-lia). The elemental composition of the biochar was carried outusing an Elemental Vireo el Cube analyzer (Abacus Analytical Sys-tems GmbH, Germany). BET surface area was determined using aGemini 2375 V5.01 surface area analyser (Micromeritics Instru-ment Co., USA).

also the degree of ionization and speciation of the metal ions insolution. The effect of initial pH of the Cu(II), Zn(II), Cd(II) and Pb(II)solutions on the amount adsorbed in the BC sampleswas studied byvarying the initial pH, under constant conditions of other processparameters. As follows from the speciation distribution of themetalions at the initial concentration 1 103 M obtained using the Me-dusa software (Hydrochemical Equilibrium Constant Database, RoyalInstitute of Technology, Sweden) in the pH range 1.05.0 almost100% of copper is present in the Cu(II) form. For Zn(II) this rangeis equal to 1.07.0, for Cd(II) 1.08.0 and for Pb(II) 1.05.5. At higherpHs the metal ions start to hydrolize and precipitation occurs. Theresults obtained for Cu(II), Zn(II), Cd(II) and Pb(II) adsorption ef-ciency in the SA6 sample are presented in Fig. 1. It was found thatas pH increases the competition of M(II) ions and protons for bind-ing sites decreases and more binding sites are released, which re-sults in the increase of adsorption effectiveness. Therefore themaximum adsorption efciency was achieved at a pH of about 5.0for Cu(II) (6.34 mg/g) and Zn(II) (4.25 mg/g) and at pH equal to6.0 for Cd(II) (16.60 mg/g) and Pb(II) (19.85 mg/g) and the otheradsorption experiments were performed at these pH values. Athigher pHs the sorption capacity values decrease due to precipita-tion or formation of hydroxide complexes, carbonates or phos-

that the ion exchange or precipitation mechanisms are involvedin the adsorption. The results are presented in Fig. 2ad. The change

0 2 4 6 8 10 120

5

10

15

20

25

pH

q e [m

q/g]

SA6 Cu(II) Zn(II) Cd(II) Pb(II)

0

2

4

6

8

10

12

pHe

Fig. 1. Effect of pH on Cu(II), Zn(II), Cd(II) and Pb(II) adsorption on SA6.

(b

H-pH

298 D. Koodynska et al. / Chemical Engineering Journal 197 (2012) 2953053. Results and discussion

3.1. Effect of dose of BC samples

The inuence of a dose of the adsorbent (in the range 0.051.0 g) on the effectiveness of Cu(II) ions removal was studied forthe SA4, SA6 as well as SC4 and SC6 samples. The adsorption per-centage (S%) increases rapidly with the increasing adsorbent dosefrom 0.05 to 0.50 g and then a slight increase was observed above0.50 g. This may be due to the increase in availability of surface ac-tive sites resulting from the higher dose and conglomeration of theadsorbent. Based on the obtained results the 0.5 g amount of theBC sample was established as optimal (data are not presented).

3.2. Effect of initial pH

The pH is the important parameters in the sorption process opti-mization. It affects not only the surface charge of the adsorbent, but

-1

0

1

2

3

4(a)

H e-pH i

nt1 2 3 4 5 6 7 8 9 10 11 12-4

-3

-2

p

pH

Cu(II)

p

1 2 3 4 5 6 7 8 9 10 11 12-4

-3

-2

-1

0

1

2

3

4(c)

pHe-p

H int

pH

Cd(II)

(

Fig. 2. (ad) Effect of DpH changes on Cu(II), Zin the initial pH values of M(II) solution signicantly affects theadsorption characteristics of BCs indicating that removal of Cu(II),Zn(II), Cd(II) and Pb(II) is enhanced by close to neutral solution.For example, in the case of Cu(II) sorption on SA4 sample it wasfound that the pH values in the solution gradually increased fromthe initial 1.05.0 to 1.68.1 at equilibrium and then decreases fromthe initial 8.012.0 to 6.98.6, respectively after 2 h shaking.

3.3. Effect of initial concentration of metal ions

The effect of initial concentration of Cu(II), Zn(II), Cd(II) andPb(II) on the extent of their removal by BCs (in terms of adsorption

1 2 3 4 5 6 7 8 9 10 11 12-4

-3

-2

-1

0

1

2

3

4)

eint

pH

Zn(II)

1 2 3 4 5 6 7 8 9 10 11 12-4

-3

-2

-1

0

1

2

3

4d)

pHe-p

H int

Pb(II)phates especially in the case of Zn(II), Pb(II) and Cd(II) (increase inthe qe value was observed). Analogous results were obtained in[4,42]. It was also found that initially the pH value difference(DpH = pHe pHini) increases and then decreases, which indicatespH

n(II), Cd(II) and Pb(II) adsorption on SA6.

(b

(d

inee0 60 120 180 240 300 3600

10

20

30

40

50

60(a)

SA4 1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

q e [m

q/g]

30

40

50

60(c)

SB4 1x10-3M 2x10-3M[m

q/g]

D. Koodynska et al. / Chemical Engpercentage S% and amount adsorbed (qt) at different time intervals)was also studied. It was found that S% increases with the increasinginitial concentration of M(II) ions from 1 103 M to 3 103 Mand for Cu(II) adsorption in the SA4 sample these values are equalto 61.2%, 80.0% and 87.2% and for Pb(II) 69.6%, 81.7% and 94.3%. Theresults for Cu(II) and Pb(II) adsorption on BCs are presented inFig. 3af. It is evident that the adsorption rate is rather fast atthe initial stage and then it slows down gradually. As follows fromthe results obtained the time to approach the equilibrium is be-tween 30 to 60 min for Cu(II) and Zn(II) and 120 to 180 min forCd(II) and Pb(II), depending on the initial concentration. Similar re-sults were obtained in the systems described in the literature, e.g.for the Cu(II) and Zn(II) adsorption on BC obtained by pyrolysis ofhardwood and corn straw [11] and Pb(II) removal on BCs obtainedby hydrothermal liquefaction of pinewood and rice husk [42].

3.4. Effect of phase contact time and adsorption kinetics

The adsorption process rate and dynamic behavior of the sys-tem are very important factors for the process design and opera-tion control. Adsorption on an adsorbent from the aqueous phaseinvolves three steps: (i) the transport of the adsorbate from the

0 60 120 180 240 300 3600

10

20 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

q e

0 60 120 180 240 300 3600

10

20

30

40

50

60(e)

SC4 1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

q e [m

q/g]

(f

Fig. 3. (af) Effect on the phase contact time on Cu(II) (red points) and Pb(II) (black pointsreferences to colour in this gure legend, the reader is referred to the web version of th0 60 120 180 240 300 3600

10

20

30

40

50

60)

SA6 1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

q e [m

q/g]

30

40

50

60)

SB6 1x10-3M 2x10-3M[m

q/g]

ring Journal 197 (2012) 295305 299bulk phase to the exterior surface of the adsorbent (lm diffusion),(ii) the transport into the adsorbent by either pore diffusion and/orsurface diffusion (intraparticular diffusion) and (iii) the adsorptionon the surface of the adsorbent. The slowest of these steps deter-mines the overall rate of the adsorption process. Sorption kineticsshows a strong dependence on the physical and/or chemical char-acteristics of the biochar which also inuences the sorption mech-anism. For the kinetic studies the Cu(II) and Pb(II) ions wereselected. The effect of contact time on the amount of their removalon the BC samples was observed at the initial concentration in therange from 1 103 M to 3 103 M.

The biochar samples obtained under different pyrolysis condi-tions have different pore structures and different surfaces there-fore adsorption rates may be controlled by the external lmdiffusion, pore or surface diffusion (intraparticle diffusion) as wellas any combination of these transport resistances. Taking theabove into account the pseudo rst order (PF-order) model sug-gested originally by Lagergren, the pseudo second order (PS-order)model adopted by Ho and McKay and the intraparticle diffusion(IPD) model proposed by Weber and Moriss were used in orderto establish the adsorption kinetic parameters [3336]. They arethe most commonly used to describe the kinetics of the adsorption

0 60 120 180 240 300 3600

10

20 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

q e

0 60 120 180 240 300 3600

10

20

30

40

50

60)

SC6 1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

q e [m

q/g]

0

4

) adsorption on BCs depending on the initial concentration. (For interpretation of theis article.)

er m

ineeTable 2Kinetic parameters for Cu(II) on BCs.

Cu(II) qe,exp PF-order model PS-ord

q1 k1 R2 q2

SA43

300 D. Koodynska et al. / Chemical Engof hazardous contaminants such as metal ions, dyes, herbicides, oil,and organic substances from aqueous solutions on differentsorbents. The previously mentioned parameters (q1, k1, q2, k2, h,ki and C) were obtained with the linear tting procedure and listedin Tables 2 and 3. The appropriate plots of the PS-order kineticmodel are shown in Fig. 4af. The PF-order model did not ade-quately describe the adsorption results of Cu(II) and Pb(II) ionsonto the BCs due to quite low correlation coefcients (R2) between

1 10 M 4.88 2. 068 0.061 0.970 4.592 103 M 11.08 2.205 0.025 0.856 11.413 103 M 15.42 2. 207 0.065 0.851 15.48SA61 103 M 6.33 4.462 0.186 0.866 6.202 103 M 12.62 1.053 0.052 0.789 12.653 103 M 18.52 1.063 0.061 0.862 18.58SB41 103 M 5.94 2.109 0.156 0.906 6.042 103 M 11.76 1.016 0.015 0.606 12.503 103 M 17.08 1.062 0.060 0.930 17.82SB61 103 M 6.32 2.256 0.107 0.719 6.192 103 M 12.67 1.089 0.085 0.962 12.723 103 M 18.44 1.142 0.132 0.775 18.57SC41 103 M 6.25 1.895 0.082 0.964 5.872 103 M 12.63 1.126 0.118 0.828 12.613 103 M 18.63 1.053 0.052 0.914 18.76SC61 103 M 6.30 1.927 0.242 0.900 6.172 103 M 12.57 1.098 0.094 0.965 12.753 103 M 18.91 1.036 0.035 0.886 18.93

Table 3Kinetic parameters for Pb(II) on BCs.

Pb(II) qe,exp PF-order model PS-order m

q1 k1 R2 q2

SA41 103 M 17.50 7.208 0.064 0.816 9.882 103 M 26.27 15.304 0.045 0.704 15.113 103 M 42.05 13.640 0.039 0.977 42.21SA61 103 M 19.44 2.671 0.092 0.979 9.932 103 M 37.38 7.206 0.041 0.917 19.373 103 M 46.22 11.112 0.057 0.943 42.55SB41 103 M 18.15 9.13 0.068 0.909 9.772 103 M 29.43 6.730 0.035 0.978 15.403 103 M 41.57 8.056 0.033 0.977 21.36SB61 103 M 19.30 3.122 0.058 0.925 9.922 103 M 33.75 8.672 0.063 0.772 18.453 103 M 48.47 24.541 0.040 0.718 26.25SC41 103 M 19.25 5.74 0.060 0.920 9.842 103 M 33.04 14.345 0.050 0.966 17.213 103 M 45.38 19.072 0.087 0.883 25.38SC61 103 M 19.81 1.657 0.054 0.925 10.0502 103 M 38.93 30.374 0.142 0.919 20.1213 103 M 52.81 21.742 0.030 0.907 30.030odel IPD model

k2 h R2 ki2 C2 R

2

ring Journal 197 (2012) 295305the predicted and the experimental values (q1 and qe,exp). Takinginto account the R2 values, a better t was achieved when thePS-order model was used. It was also found that for the PS-ordermodel the q2 values increase with the increasing initial concentra-tion, so the process is controlled by the diffusion. This is obviousfor higher initial concentrations, as a more efcient utilization ofthe adsorptive capacities of the adsorbent is expected due to astronger driving force (by a higher concentration gradient).

0.452 6.341 0.981 0.277 1.661 0.9690.197 11.574 1.000 0.131 9.988 0.9190.089 47.170 1.000 0.152 14.303 0.941

0.408 1.162 0.963 0.029 6.169 0.5230.310 37.175 1.000 0.124 11.167 0.7190.133 49.751 1.000 0.351 16.086 0.797

0.139 0.872 0.961 0.666 3.392 0.9980.081 1.280 0.998 0.185 10.136 0.8520.056 23.697 0.999 0.360 14.429 0.964

0.209 1.187 0.963 1.603 2.981 0.6250.116 3.784 1.000 0.213 11.225 0.8780.087 30.120 0.999 0.377 15.784 0.914

0.121 1.222 0.963 0.190 5.520 0.8860.097 15.748 1.000 0.357 10.156 0.9270.049 17.182 1.000 0.685 13.795 0.922

0.806 0.477 0.971 0.050 5.996 0.4540.098 35.088 1.000 0.042 12.295 0.8870.059 128.206 1.000 0.237 16.992 0.880

odel IPD model

k2 h R2 ki2 C2 R

2

0.069 6.770 0.993 1.328 6.899 0.7350.022 14.907 0.995 2.763 8.737 0.7830.011 20.450 0.996 2.051 26.424 0.989

0.293 28.563 0.999 0.692 15.224 0.5840.193 32.525 0.993 1.005 29.477 0.9550.124 72.464 1.000 1.623 34.504 0.957

0.156 6.627 0.991 1.259 9.208 0.9780.123 29.155 0.995 1.105 21.053 0.9830.067 71.426 0.993 1.099 32.503 0.903

0.494 13.755 0.993 0.558 15.489 0.8680.051 17.483 0.995 1.828 17.326 0.8380. 020 47.170 1.000 1.996 20.843 0.803

0.425 16.313 0.993 0.880 12.757 0.9340.055 20.325 0.993 2.983 13.048 0.8020.032 41.152 0.993 2.644 27.416 0.856

0.090 12.165 0.992 0.275 13.138 0.9170.027 27.322 0.989 4.136 17.879 0.7320.013 36.630 0.995 3.303 26.754 0.971

04

8

12(b

8

12(d

inee0 20 40 600

5

10

15

20

25

30(a)SA4

1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

t/qt

15

20

25

30(c)SB4

1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M

-3

t/qt

D. Koodynska et al. / Chemical EngMoreover, the k2 values decrease as the concentration increase. Forexample, for Cu(II) the rate of adsorption was high for the initialconcentration 1 103 M (k2 values in the range 0.1210.806 g/mg min) and low for 3 103 M (k2 values in the range 0.0560.089 g/mg min). The average values of k2 were obtained for theconcentration 2 103 M (0.0810.197 g/mg min). It was also no-ticed that the adsorption capacities of BC samples obtained at atemperature 600 C were slightly higher than those at 400 C,and for example, for Cu(II) they are as follows: 4.59 and 6.20 mg/g for the initial concentration of 1 103 M, 6.04 and 6.19 mg/gfor 2 103 M as well as 5.87 and 6.17 mg/g for 3 103 M,respectively. The analogous values were obtained in the case ofPb(II) ions adsorption. However, such correlations were not foundbetween the k2 values and the temperature of sample preparation.

The possibility of application of the IPD process was also evalu-ated using the Weber and Morris model (Eq. (5)). In order toestablish whether the transport of M(II) ions from the solution intothe pores of the BCs is the rate controlling step, the relationship be-tween qe and t1/2 was plotted. It should be noticed that for obtain-ing the relations on the plots (not presented) there are twoseparate parts attributed to the lm diffusion (the rst part) andto the intraparticle diffusion (the second part). The resulting

0 20 40 600

5

10 3x10 M

t [min]

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4

0 20 40 600

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1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

t/qt

0

4

8

12(f

Fig. 4. (af) PS-order plots of adsorption of Cu(II) (red points) and Pb(II) (black points) onreferred to the web version of this article.)0 20 40 600

5

10

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20

25

30)SA6

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t [min]

t/qt

0

4

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25

30)SB6

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12

ring Journal 197 (2012) 295305 301straight lines do not pass through the origin and therefore theintraparticle diffusion is not the rate limiting step in this process.It was also found that the values of the intraparticle diffusion rateki2 are smaller than the lm diffusion rate ki1 as presented in Tables2 and 3. Additionally, compare the intercept (C2) values, which givean idea about the boundary layer thickness i.e., the larger the inter-cept, the greater is the boundary layer effect. The maximum C2 val-ues were found for the SA6, SB6 and SC6 samples and they wereobserved to increase with the increasing initial concentration indi-cating that the boundary layer effect is more evident for the sam-ples obtained at higher temperatures.

The kinetic data indicated that the mechanism of metal ionssorption by the BC samples is complex and probably a combinationof external mass transfer, intraparticle diffusion through the mac-ropores and micropores of BC and sorption processes. It should bealso noted that the kinetic process tted by the PS-order modelassumes chemisorption. In the case of the rate limited chemisorp-tion the inner-sphere complexation and precipitation involved themetal ions sorption whereas the role of electrostatic ion exchangecan be negligible. For the identication of the preciptiation processthe XRD analysis is a useful tool. In the paper by Cao [43] the exis-tence of the PbCO3, b-Pb9(PO4)6, Pb5(PO4)3Cl and Pb3(CO3)2(OH)2 as

0 20 40 600

5

10 3x10 M

t [min]

0

4

0 20 40 600

5

10

15

20

25

30)SC6

1x10-3M 2x10-3M 3x10-3M 1x10-3M 2x10-3M 3x10-3M

t [min]

t/qt

0

4

8

12

BCs. (For interpretation of the references to colour in this gure legend, the reader is

ineeTable 4Langmuir and Freundlich isotherm parameters and correlation coefcients for theadsorption of Cu(II), Zn(II), Cd(II) and Pb(II) on BCs.

System Cu(II) Zn(II) Cd(II) Pb(II)

SA4 qe,exp 75.49 64.96 106.01 175.29Langmuir q0 78.36 62.13 107.08 175.44

KL 0.002 0.005 0.002 0.011RL 0.241 0.126 0.125 0.017R2 0.981 0.985 0.969 0.996

Freundlich KF 1.89 2.89 2.07 5.99n 1.84 2.10 3.82 4.95R2 0.982 0.985 0.970 0.920

SA6 qe,exp 94.71 80.88 116.71 229.98Langmuir q0 88.23 79.62 117.01 230.70

KL 0.009 0.013 0.003 0.012RL 0.065 0.055 0.164 0.016R2 0.989 0.999 0.998 0.979

Freundlich K 9.62 5.98 1.22 6.13

302 D. Koodynska et al. / Chemical Engwell as PbOP2O5SiO2 was proven. Due to the high phosphorouscontent in the studied BC samples the existence of such kind ofspecies is possible and will be presented in a subsequent paper.

3.5. Adsorption isotherm studies

Sorption on the sorbents prepared from agricultural or indus-trial by-products is reported to be a promising method for remov-ing metal ions from aqueous solution. The sorption capacity of BCsdepends mainly on the polarity, aromaticity, surface area, pore sizedistribution, etc. In the case of biochar samples obtained at differ-ent temperatures, it was found that the sorption both of inorganicand organic species occurs by the partitioning mechanism (on non-carbonized organic fraction) or by the surface adsorption (on car-bonized fraction) depending on the degree of carbonization. Theeffect of the micropore distribution on sorption to BCs is alsoimportant because the increase in micropore volume and pore sur-face area affect on better accessibility of solute molecules and an

F

n 3.09 2.38 4.56 5.76R2 0.887 0.997 0.976 0.821

SB4 qe,exp 74.95 62.43 113.50 212.95Langmuir q0 76.12 58.11 114.75 212.77

KL 0.004 0.006 0.001 0.002RL 0.132 0.114 0.223 0.081R2 0.981 0.970 0.990 0.990

Freundlich KF 4.82 5.59 8.51 12.67n 2.68 2.70 3.06 4.04R2 0.944 0.928 0.830 0.858

SB6 qe,exp 81.92 64.01 122.11 227.95Langmuir q0 88.50 61.91 118.40 219.34

KL 0.005 0.010 0.02 0.001RL 0.106 0.069 0.137 0.130R2 0.998 0.969 0.991 0.984

Freundlich KF 7.58 7.12 9.85 9.65n 3.23 3.11 3.71 3.65R2 0.925 0.964 0.963 0.836

SC4 qe,exp 80.24 50.42 79.55 153.76Langmuir q0 81.50 49.06 78.19 151.52

KL 0.022 0.025 0.008 0.022RL 0.025 0.030 0.044 0.009R2 0.974 0.988 0.984 0.998

Freundlich KF 10.21 12.92 11.24 8.37n 2.92 3.47 3.89 5.36R2 0.854 0.925 0.994 0.822

SC6 qe,exp 85.75 52.28 80.55 160.55Langmuir q0 83.97 51.28 82.30 154.60

KL 0.035 0.061 0.005 0.003RL 0.017 0.010 0.065 0.062R2 0.982 0.999 0.972 0.976

Freundlich KF 11.84 7.01 8.53 11.19n 3.18 2.66 3.48 4.25R2 0.918 0.765 0.993 0.9780 200 400 600 8000

20

40

60

80

100

120

SA420 oCLF

ce [mg/L]

q e [m

q/g]

0

4

8

12

(a)

120(b)

ring Journal 197 (2012) 295305increase of sorption sites. As was mentioned earlier metal ionsadsorption may involve inner-sphere surface complex formationwith free and complexed carboxyl or hydroxyl functional groupsas well as co-precipitation or surface precipitation. The active func-tional sites containing oxygen atoms are responsible for the en-hanced hydrophobicity and afnity for metal ions as well asreduce the competitive adsorption of water molecules [44].

The adsorption data of the metal ions ion BCs samples were ana-lyzed using the Langmuir (Eq. (6)) and Freundlich isotherm (Eq. (7))models. The data for sorption of the above-mentioned metals in theBC samples t closely to the Langmuir adsorption model (Table 4).It is valid for the monolayer sorption onto a surface with a nitenumber of identical sites. In this case the R2 values range from0.9618 to 0.9995, whereas for the Freundlich model they rangefrom 0.8303 to 0.9972. The values of the separation factor, RL, indi-cating the nature of the adsorption process are also presented in Ta-ble 4. They can be classied by RL > 1 unfavorable, RL = 1 linear;0 < RL < 1 favorable; RL = 0 irreversible. In the present study, thesevalues are observed to be in the range 0.0020.022 for Cu(II),

0 200 400 600 8000

20

40

60

80

100

SA440 oCLF

ce [mg/L]

q e [m

q/g]0

4

8

12

0 200 400 600 8000

20

40

60

80

100

120

SA460 oCLF

ce [mg/L]

q e [m

q/g]

0

4

8

12

(c)

Fig. 5. (ac) Effect of temperature on the adsorption capacity of SA4 towards Cu(II)ions (L the Langmiur isotherm, F the Freundlich isotherm).

Zn (0.75 mM Cu + 0.50 mM Cd + 0.25 mMPb)

4.88 6.53 5.60 5.17

ineeTable 5Adsorption capacities (qe, mg/g) of SA4 for Cu(II), Zn(II), Cd(II) and Pb(II) ions in thequaternary component system.

System Cu(II) Zn(II) Cd(II) Pb(II)

qe

Cu (1 mM) 6.47Cu (1 mM Zn + 0.50 mM Cd + 0.25 mM Pb) 5.70 6.50 5.58 5.18Cu (0.75 mM Zn + 0.50 mM Cd + 0.25 mM

Pb)5.78 4.90 5.58 5.18

Cu (0.50 mM Zn + 0.50 mM Cd + 0.25 mMPb)

6.15 3.26 5.59 5.18

Cu (0.25 mM Zn + 0.50 mM Cd + 0.25 mMPb)

6.76 1.62 5.59 5.18

Zn (1 mM) 6.54Zn (1 mM Cu + 0.50 mM Cd + 0.25 mM Pb) 5.37 6.45 5.56 5.17Zn (0.75 mM Cu + 0.50 mM Cd + 0.25 mM

Pb)4.80 6.46 5.57 5.17

Zn (0.50 mM Cu + 0.50 mM Cd + 0.25 mMPb)

3.25 6.47 5.57 5.17

Zn (0.25 mM Cu + 0.50 mM Cd + 0.25 mMPb)

1.62 6.51 5.57 5.17

Cd (1 mM) 11.24Cd (0.25 mM Cu + 0.50 mM Zn + 1 mM Pb) 1.60 3.24 11.08 20.71Cd (0.25 mM Cu + 0.50 mM Zn + 0.75 mM

Pb)1.57 3.27 11.24 15.54

Cd (0.25 mM Cu + 0.50 mM Zn + 0.50 mMPb)

1.62 3.26 11.21 10.36

Cd (0.25 mM Cu + 0.50 mM Zn + 0.25 mMPb)

1.62 3.26 11.21 5.18

Pb (1 mM) 20.72

D. Koodynska et al. / Chemical Eng0.0050.025 for Zn(II), 0.0010.065 for Cd(II) and 0.0010.0625 forPb(II), which indicates that the adsorption process is favorable forall BC samples. Moreover, based on the maximum recorded sorp-tion capacities these samples can be arranged in the following afn-ity series: for Cu(II) SA6 > SC6 > SB6 > SC4 > SA4 > SB4, for Zn(II)SA6 > SA4 > SB6 > SB4 > SC6 > SC4; for Cd(II) SB6 > SA6 > SB4 >SA4 > SC6 > SC4, for Pb(II) SB6 > SA6 > SB4 > SA4 > SC6 > SC4.

Corn straw and hardwood derived BCs were shown to effec-tively adsorb Cu(II) and Zn(II) ions [4]. However, the maximumadsorption capacities for Cu(II) and Zn(II) were 12.5 and 11.0 mg/g as well as 6.8 and 4.5 mg/g, respectively and these values werelower than those presented in this paper. Tong et al. [45] observedthat the adsorption effectiveness of Cu(II) ions on BCs originatingfrom peanut, soybean and canola straws was greater than thaton a commercial activated carbon (AC) in the pH range 3.5 to 5.0.At pH 5.0 the maximum adsorption capacities were equal to88.96, 52.74 and 37.49 mg/g for peanut, soybean and canola bioch-ars, respectively, whereas on AC it was only 11.43 mg/g. Quiteeffective BC for Pb(II) removal was obtained by Liu and Zhang[42] in the hydrothermal liquefaction of pinewood and rice husk.Due to a large amount of oxygen-containing groups on the surface,the adsorption capacities for Pb(II) were: 4.25 and 2.40 mg/g. It isevident that in the case of the removal of metal ions from differentwaste waters the effectiveness of biochar strongly depends on themetal contaminant type. As was shown by Uchimiya et al. [46] alsobiochar type played important role in sorption efciency. Forexample, the removal ability of the digested whole sugar beetbiochar for the metal ions followed the order of Cd(II) > Ni(II) >Pb(II) > Cu(II) while the digested dairy waste biochar followedthe order of Pb(II) > Cu(II) > Cd(II) > Ni(II), which is consistent with

Pb (0.25 mM Cu + 0.50 mM Zn + 1 mM Cd) 1.57 3.24 11.17 20.72Pb (0.25 mM Cu + 0.50 mM Zn + 0.75 mM

Cd)1.53 3.24 8.38 20.95

Pb (0.25 mM Cu + 0.50 mM Zn + 0.50 mMCd)

1.60 3.25 5.60 21.13

Pb (0.25 mM Cu + 0.50 mM Zn + 0.25 mMCd)

1.48 3.24 2.80 21.43Zn (0.50 mM Cu + 0.50 mM Cd + 0.25 mMPb)

3.25 6.53 5.60 5.17

Zn (0.25 mM Cu + 0.50 mM Cd + 0.25 mMPb)

1.62 6.53 5.60 5.17

Cd (1 mM) 11.24Cd (0.25 mM Cu + 0.50 mM Zn + 1 mM Pb) 1.63 3.26 11.18 20.71Cd (0.25 mM Cu + 0.50 mM Zn + 0.75 mM

Pb)1.62 3.26 11.24 15.54

Cd (0.25 mM Cu + 0.50 mM Zn + 0.50 mMPb)

1.62 3.27 11.23 10.36

Cd (0.25 mM Cu + 0.50 mM Zn + 0.25 mMPb)

1.62 3.27 11.23 5.18

Pb (1 mM) 20.72Pb (0.25 mM Cu + 0.50 mM Zn + 1 mM Cd) 1.62 3.26 11.21 20.75Pb (0.25 mM Cu + 0.50 mM Zn + 0.75 mM 1.61 3.26 8.41 20.81Table 6Adsorption capacities (qe, mg/g) of SA6 for Cu(II), Zn(II), Cd(II) and Pb(II) ions in thequaternary component system.

System Cu(II) Zn(II) Cd(II) Pb(II)

qe

Cu (1 mM) 6.51Cu (1 mM Zn + 0.50 mM Cd + 0.25 mM Pb) 6.28 6.52 5.60 5.18Cu (0.75 mM Zn + 0.50 mM Cd + 0.25 mM

Pb)6.36 4.90 5.61 5.18

Cu (0.50 mM Zn + 0.50 mM Cd + 0.25 mMPb)

6.47 3.26 5.60 5.18

Cu (0.25 mM Zn + 0.50 mM Cd + 0.25 mMPb)

6.64 1.63 5.60 5.18

Zn (1 mM) 6.54Zn (1 mM Cu + 0.50 mM Cd + 0.25 mM Pb) 6.47 6.51 5.58 5.17

ring Journal 197 (2012) 295305 303the removal efciency trend of biochars converted from poultry lit-ter [47]. The enhance sorption of both Pb(II) and Cd(II) compare tothe Cu(II) ions is probably attributed to their precipitation withPO34 or CO

23 ions, with less to the surface complexation through

OH groups or delocalized p electrons.It should be also mentioned that there is potential risk associ-

ated with each stage of biochar production, loading processesand storage so suitable health and safety precautions should beemployed. After hazardous metal loading the biochar samplesshould be safely stored. The pelletization is relatively cheap andsimple method to deal with the problem of biochar dust afterloading.

3.6. Effect of temperature

The adsorption of Cu(II), Zn(II), Cd(II) and Pb(II) in the BCs wasalso investigated as a function of temperature. Experiments wereconducted at 20, 40 and 60 C for the initial M(II) ion concentra-tions as in the case of adsorption studies. The maximum adsorptionwas obtained at 60 C. As can be seen from the Langmuir (L) andFreundlich (F) isotherms presented in Fig. 5ac, the temperatureincrease resulted in an increased sorption capacity of the SA4 sam-ples towards Cu(II) ions. Additionally, for the SA6 sample theseisotherms exhibited a sharp initial rise followed by a plateau indi-cating that the BC samples obtained in the pyrolysis at higher tem-peratures are more efcient as sorbent materials. Based on theobtained results the thermodynamic parameters were calculatedusing Eqs. (8)(10). The Gibbs free energy change, DGo, is an indi-cation of the spontaneity of a chemical reaction. Reactions occurspontaneously at a given temperature for negative DGo value.

Cd)Pb (0.25 mM Cu + 0.50 mM Zn + 0.50 mM

Cd)1.62 3.26 5.61 20.99

Pb (0.25 mM Cu + 0.50 mM Zn + 0.25 mMCd)

1.60 3.27 2.80 21.14

the adsorption sites and the sorbed species (so called physicalsorption) should be taken into consideration. Finally, for the DGo

3.7. Competitive adsorption

4. Conclusions

during bio-oil production, J. Colloid Interface Sci. 310 (2007) 5773.

ineeIn the paper presented it was found that Cu(II), Zn(II), Cd(II) andPb(II) strongly adsorb on all investigated manure BCs. Their sorp-tion percentage increases with the increasing initial concentrationof M(II) ions. The particle size and their amount, pH and concentra-tion of solutions, phase contact time and temperature affect theadsorption process. Adsorption data were strongly correlated withthe PS-order kinetic equation and the Langmuir adsorption iso-therm. The kinetic data indicated that the mechanism of metal ionssorption by the BC samples is complex and probably a combinationof external mass transfer, intraparticle diffusion through the mac-ropores and micropores of BC and sorption processes. The BS sam-ples can be used for metal ions removal as alternative to ACs or IXs.

Acknowledgements

This research was partially supported by The Danish Council forStrategic Research, Danish Ministry of Science, Technology andThe adsorption of Cu(II), Zn(II), Cd(II) and Pb(II) in the BC sam-ples in the presence of competing cations was studied with varyinginitial concentrations. The variation in adsorption efciency ofeach ion in the presence of others for SA4 and SA6 is given in Ta-bles 5 and 6. The selectivity of the applied adsorbents towardsCu(II) and Pb(II) ions was seriously affected by the presence ofZn(II) and Cd(II) competing ions as the adsorption capacity in-creases with the decrease of their concentration in the solutions.For instance, the adsorption capacity of the SA4 towards Cu(II) in-creases from 5.70 to 6.76 mg/g (at constant concentrations of Cd(II)and Pb(II) ions) with the decrease of Zn(II) concentrations. For theSA6 these values were from 6.28 to 6.64 mg/g. The same situationwas found in the case of Pb(II) ions adsorption process in the pres-ence of decreasing concentration of Cd(II) ions on the SA4 (thesorption capacity increases from 20.72 to 21.43 mg/g at constantconcentrations of Cu(II) and Zn(II) ions and at decreasing Pb(II)concentration). The analogous trend was observed for the SA6,SB4, SB6, SC4 and SC6.value above 20.0 kJ/mol the adsorption process can be explainedby complexation. For the results presented in this paper it wasfound that the negative DGo values are in the range from 5.16 to5.62 kJ/mol for SA4 and 8.05 to 8.92 kJ/mol for SA6 at temperaturesfrom 293 to 333 K which indicates that the adsorption process wasfavorable. This is consistent with a report presented in [48]. Addi-tionally, for the positive value of DHo (12.32 kJ/mol for SA4 and18.88 kJ/mol for SA6) the adsorption reaction is endothermic andthe positive value of DSo (22.86 J/mol K for SA4 and 39.02 J/mol Kfor SA6) reects the good afnity of an adsorbent for the sorbedspecies. It should be also mentioned that the obtained KL values de-crease as temperature increases for the Langmuir equation.Additionally, the value of DGo is useful for determination of thetype of the adsorption process. Firstly, for the ion exchange mech-anism the DGo value is in the range 1020 kJ/mol. Secondly, for thevalue of DGo up to 20 kJ/mol the electrostatic interaction between

304 D. Koodynska et al. / Chemical EngInnovation, the program for sustainable energy and environmentthe project CLEANWASTE (Project no. J. nr. 2104-09-0056).References

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D. Koodynska et al. / Chemical Engineering Journal 197 (2012) 295305 305

Kinetic and adsorptive characterization of biochar in metal ions removal1 Introduction2 Materials and methods2.1 Materials2.2 Kinetic tests2.3 Adsorption tests2.4 Apparatus

3 Results and discussion3.1 Effect of dose of BC samples3.2 Effect of initial pH3.3 Effect of initial concentration of metal ions3.4 Effect of phase contact time and adsorption kinetics3.5 Adsorption isotherm studies3.6 Effect of temperature3.7 Competitive adsorption

4 ConclusionsAcknowledgementsReferences