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Journal of Environmental Management 90 (2009) 954–960
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Journal of Environmental Management
journal homepage: www.elsevier .com/locate/ jenvman
Adsorption characteristics of Cu and Ni on Irish peat moss
B. Sen Gupta a,*, M. Curran a, Shameem Hasan b, T.K. Ghosh b
a School of Chemical Engineering, Queen’s University Belfast, BT9 5AG, UKb Nuclear Science and Engineering Institute, University of Missouri-Columbia, Columbia, MO 65212, USA
a r t i c l e i n f o
Article history:Received 22 June 2006Received in revised form 21 December 2007Accepted 29 February 2008Available online 21 April 2008
Keywords:AdsorptionCuNiPeat mossBreakthrough curveIsotherms
* Corresponding author. Tel.: þ44 289 097 4554; faE-mail address: [email protected] (B. Sen Gup
0301-4797/$ – see front matter � 2008 Elsevier Ltd.doi:10.1016/j.jenvman.2008.02.012
a b s t r a c t
Peat has been widely used as a low cost adsorbent to remove a variety of materials including organiccompounds and heavy metals from water. Various functional groups in lignin allow such compounds tobind on active sites of peat. The adsorption of Cu2þ and Ni2þ from aqueous solutions on Irish peat mosswas studied both as a pure ion and from their binary mixtures under both equilibrium and dynamicconditions in the concentration range of 5–100 mg/L. The pH of the solutions containing either Cu2þ orNi2þ was varied over a range of 2–8. The adsorption of Cu2þ and Niþ2 on peat was found to be pH de-pendent. The adsorption data could be fitted to a two-site Langmuir adsorption isotherm and themaximum adsorption capacity of peat was determined to be 17.6 mg/g for Cu2þ and 14.5 mg/g for Ni2þ at298 K when the initial concentration for both Cu2þ and Ni2þ was 100 mg/L, and the pH of the solutionwas 4.0 and 4.5, respectively. Column studies were conducted to generate breakthrough data for bothpure component and binary mixtures of copper and nickel. Desorption experiments showed that 2 mMEDTA solution could be used to remove all of the adsorbed copper and nickel from the bed.
� 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Peat is a polar, highly porous, material that could have signifi-cant applications as an adsorbent for removal of heavy metals fromaqueous solutions. Peat mainly contains lignin and cellulose.Functional groups in lignin that include alcohols, aldehydes, ke-tones, acids, phenolic hydroxides, and ethers allow it to bind withvarious metal ions. Several studies have established the potential ofpeat to capture dissolved metals, nutrients, suspended solids, or-ganic matter, oils and odors from domestic and industrial effluents,as well as to adsorb spilled oil or oil from contaminated water (Hoand McKay, 1999a,b; McKay and Porter, 1997; Ringqvist et al., 2002;Ringqvist and Oborn, 2002; Malterer et al., 1996; Gardera-Torres-day et al., 1996; Brown et al., 1997). The exact mechanism of metalion binding to peat is not well understood. Various mechanismsincluding ion exchange, complexation, and surface adsorption havebeen proposed by researchers (Ringqvist et al., 2002). Severalmodels have been tried to describe the physicochemical interactionof peat with ions. These models include: (1) isotherm equations,such as the Freundlich and Langmuir equations; (2) mass actiontype equations, including Donnan exchange, and more general ion-exchange expressions; and (3) composite models (Homatidis et al.,2000). Homatidis et al. (2000) noted that unesterified polyuronicacids present in the cell wall of sphagnum peat are involved in the
x: þ44 289 097 4627.ta).
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cation exchange. Ringqvist and Oborn (2002) reported that car-boxylic and phenolic groups in peat are responsible for the ad-sorption of metal ions on peat. Brown (1992) concluded that theadsorption of metal ions on peats and lignite occurs due tothe attraction between negatively charged surface of peat and thepositively charged metal ions.
A number of studies have been carried out on desorption ofmetal ions from an adsorbent using various solution such as HCland EDTA with a varying degree of success. After several adsorp-tion–desorption cycles, the recovery rate of metal ions from thebiomass has been found to decrease substantially due to the de-pletion of binding sites, and this can also slow down the desorptionprocess (Chu et al., 1997).
EDTA has been known for its ability to form stable complexeswith metal ions and reduces the solubility of metal ions in aqueoussolution. For example, the stability constant (ln K0) for copper–EDTA pair is 18.92. EDTA, therefore, can be used as an effectivedesorbent for regeneration of biosorbents. It is reported that (Chuet al., 1997; Tan, 1999) about 89–95% of adsorbed metal ion can bedesorbed from algal biomass using EDTA. However, the metal re-covery rate dropped after several adsorption–desorption cycles.Traditional methods of removing heavy metals from wastewaterssuch as ion exchange, electrodialysis, chemical precipitation,membrane processes and solvent extraction are not cost effective atlow metal concentrations (Allen et al., 1997; Yetis et al., 2004). Inthis context, peat may be used as a low cost adsorbent to reduceheavy metals and other contaminants as a polishing step to meetthe discharge standards. Peat is abundant in Ireland and is available
Table 1Size distribution of ground peat moss
Size-range (microns) Average weight (g) Weight (%)
>355 3.984 18.9<355, >150 6.917 32.9<150, >106 2.620 12.4<106 7.652 36.3Total 21.173 100
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5 2 4 6 8 12 16 20 24 32Time (hours)
Co
ncen
tratio
n o
f C
u an
d N
i io
ns (p
pm
)
Cu2+
Ni2+
Fig. 1. Concentrations of copper and nickel ions in water-washed solution that wasused to wash the peat prior to an experiment.
02468101214161820
0 1 2 3 4 5 6 7pH
Am
ou
nt u
ptake (m
g/g
)
Fig. 2. Effect of pH on copper (,) and nickel (-) uptake by peat (initial concentrationof both copper and nickel was 100 mg/L at 298 K).
Qe [ðCiLCeÞV
M(1)
B. Sen Gupta et al. / Journal of Environmental Management 90 (2009) 954–960 955
at a very low cost. The objectives of this work were to characterizethe Irish peat in terms of its surface area, porosity, and pore volume,and evaluate its adsorption characteristics for Cu2+ and Ni2+ underboth batch and dynamic conditions and study the regeneration ofpeat using both HCl and EDTA.
2. Materials and methods
Westland Irish moss peat from Northern Ireland was used asadsorbent in this study. It is a common brand of peat used forgardening and horticulture in Ireland. The peat moss samples werewashed for 30 min in HCl solution by shaking in an orbital shaker.After washing, the peat was filtered and washed again with distilledwater until the pH of the filtrate reached neutral. After washing, thepeat samples were dried in an oven at 60 �C for 24 h. The sampleswere then passed through a grinder twice for size reduction. Thesize distribution of ground peat moss particles is shown in Table 1.Analytical grade NiSO4 and CuSO4 (BDH Laboratories, UK) wereused in all experimental work. The concentration of heavy metalswas determined by ICP-AES technique. Surface area of the particleswas analyzed by volumetric BET method using The Sorptomatic1990 (Thermo Scientific, San Jose, USA) and was found to be203.41 m2/g. The average pore diameter was 6.1 m, which was de-termined by porosimetric method (Carlo Erba Milestone 200, USA).
2.1. Experimental procedure
Equilibrium batch adsorption studies were carried out by ex-posing the peat to aqueous solutions of copper and nickel of dif-ferent concentrations in 125 mL Erlenmeyer flasks at 25 �C. About0.4 g peat were added to 100 mL of solution. This amount of peatand solution assured that an equilibrium condition was reached,i.e., the entire metal ion was not adsorbed by the peat, which wouldhave made it difficult to determine the equilibrium point. The pH ofthe solutions was adjusted by adding either 0.1 M hydrochloric acidor 0.1 M sodium hydroxide. The flasks were placed in a constanttemperature shaker bath for 24 h to ensure that equilibrium was
OH
CH2
CH2
CH3
CH3O CH3O
Fig. 3. Binding mechanism o
reached. Following the exposure of peats to copper or nickel ion,the samples were collected for analysis. The solutions were filteredand the filtrates were analyzed for copper or nickel content. Theadsorption isotherm was obtained by varying the initial concen-tration of copper and nickel ions. The amount of metal ion adsorbedper unit mass of adsorbent (Qe) was calculated using the followingequation.
O
CH
CH
CHO
CH3
O
CHOH
C
CH2OH
OH
O
CH3
f peat with metal ions.
024681012141618
0 5 10 15 20 25Time (h)
Am
ou
nt u
ptake (m
g/g
)
a
024681012141618
0 5 10 15 20 25Time (h)
Am
ou
nt u
ptake (m
g/g
)
b
Fig. 4. Uptake of copper and nickel ions as a function of time from different concen-trations of ions in the solution. The initial concentrations of (a) copper and (b) nickel inthe solution were (B) 100 mg/L, (:) 50 mg/L, (6) 20 mg/L, (,) 10 mg/L, and (C)5 mg/L.
Fig. 6. Equilibrium adsorption isotherm of nickel uptake by peat. The symbols (-) areexperimental data and the solid lines are from two-site Langmuir model (Eq. (6))obtained by non-linear regression analysis of the experimental data (amount of peat:4.0 g/L, exposure time: 24 h, temperature: 298 K and pH: 4.5).
B. Sen Gupta et al. / Journal of Environmental Management 90 (2009) 954–960956
where Ci and Ce represent initial and equilibrium concentrations inmg/L, respectively, V is the volume of the solution in liters (L), andM is the mass of the adsorbent in grams (g).
3. Results and discussion
Prior to a run, peat was washed repeatedly with deionizedwater. The objective here was to evaluate the amount of naturalcopper and nickel ions present in the peat prior to adsorption fromthe test solutions. A sample of the washed solution was analyzed forboth copper and nickel. An average of the copper and nickel valueswas calculated and subtracted from the values obtained from thecopper and nickel adsorption experiments with test solutions. Fig. 1shows the values of copper and nickel concentrations in the washedsolution from the peat prior to an adsorption run. Despite some
Fig. 5. Equilibrium adsorption isotherm of copper uptake by peat. The symbols (-) areexperimental data and the solid lines are from two-site Langmuir model (Eq. (6))obtained by non-linear regression analysis of the experimental data (amount of peat:4.0 g/L, exposure time: 24 h, temperature: 298 K, and pH: 4.5).
fluctuations, the values remain relatively constant, indicating thatthe remaining copper and nickel were tightly bound to peat and itsinterference will be negligible.
3.1. Effect of pH
The effect of pH on adsorption of metal ions by peat is shown inFig. 1. In these experiments, the initial pH of copper and nickelcontaining solution was adjusted to the desired value using either0.1 M HCl or 0.1 M NaOH solution. To the pH adjusted copper andnickel solution, peat was added. No attempt was made to maintaina constant pH of the solution using a buffer solution. It was notedthat at the end of 24 h exposures, the pH of all the solutionsincreased. The adsorption of copper by peat increased with theincrease of pH of the solution up to a value of 6.0. A similar resultwas observed with nickel.
Hasan et al. (2007) noted that the exchange of released Hþ ionsoccurs between the surface of the adsorbent and solution resultingin the increase of pH of the solution. It may be noted that thestarting pH of the solution was in the range of 2–6.0, and the finalpH of the solutions was between 4 and 7 depending on the initialpH. The maximum uptake of copper by peat from aqueous solutionwas observed at pH 4.5. The peat showed two distinct regions in thepH curve (see Fig. 2) for both copper and nickel. A sharp increase inadsorption for both copper and nickel in pH range of 2–3.5 wasobserved. In the pH range of 3–5, only a modest increase in theadsorption capacity of peat for both copper and nickel observed. Asharp increase in copper adsorption above pH 4.5 was noted.However, no significant change was noted for nickel (see Fig. 2). Themaximum uptake of nickel ions occurred at a pH of 4.5. Severalresearchers (Deans and Tobin, 1999; Karabulut et al., 2000;Senthilkumaar et al., 2000; Twardowska et al., 1999; Figueira et al.,1997; Hasan et al., 2000) also noted a similar phenomenon withother biosorbents; maximum uptake at pH close to 4. Peat is gen-erally acidic in nature due to the presence of various functionalgroups in lignin that include alcohols, aldehydes, ketones, acids,phenolic hydroxides, and ethers. Copper or nickel ion may formcomplex with surface functional groups of peat such as aromaticcarboxylates –COOH, and phenolic –OH through ion-exchange
Table 2Estimated parameters for the two-site Langmuir model
Ion qm1 qm2 km1 km2 a1 a2
Copper 16.21 2.12 0.164 �2.1� 109 1.29 1.19Nickel 16.4 0.153 2.45 �4.07� 108 1.09 0.09
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80 90 100%
Am
ou
nt u
ptake (m
g/g
)
Fig. 7. Amount of (,) copper, (-) nickel, and (6) total copper and nickel uptake by peat from their binary mixtures of different percentages of copper and nickel (amount of peat:4.0 g/L, exposure time: 24 h, temperature: 298 K, and pH: 4.5).
B. Sen Gupta et al. / Journal of Environmental Management 90 (2009) 954–960 957
reactions. At lower pH (that is under acidic condition), the func-tionality of these groups is not changed. At higher pH, this groupbegins to neutralize changing their activity, binding properties. Theprobable binding mechanism with various functional groups isshown in Fig. 3. Although the release of Hþ by these reactionsshould reduce the pH of the final solution, as noted earlier the re-leased Hþ ions interacted with the surface, and, thus, are removedfrom the solution increasing the solution pH.
3.2. Equilibrium adsorption isotherms of copper and nickel on peat
The equilibrium adsorption isotherms of copper and nickel onpeat were determined in the concentration range of 5 mg/L–100 mg/L. As mentioned in the previous section, peat moss pro-vided best capacity for Cu2þ and Ni2þ ions at pH 4.5 without anyprecipitation of Cu2þ and Ni2þ from the solution. Therefore, theequilibrium isotherm experiments were carried out at a pH of 4.5.The uptake of copper and nickel by the peat as a function of time atvarious concentrations of the solution is shown in Fig. 4a–b. Almost60% of Cu2þ and Ni2þ were adsorbed during the first 60 min ofa run, and then the equilibrium was attained monotonically at240 min in most of the runs. The adsorption isotherm data obtainedat pH 4.5 showed Type I behaviour (Figs. 5 and 6). This suggestsa monolayer adsorption of copper and nickel ions on the peatsurface.
Although the Langmuir equation provided a reasonable fit to theequilibrium adsorption data, the pH dependence could not becorrelated using this model. The pH dependence of the metal ions’adsorption can be explained by a competitive adsorption of copper,nickel, and Hþ ions as follows.
4
5
31
2
Fig. 8. A schematic diagram of the fixed-bed column system. (1) Feed storage, (2)pump (3) rotameter (4) column and (5) sample collector.
�� SH 4 ��S þ HþðkHÞ (2)
�� S þ M 4 ��SMðkm;M is a metal ionÞ (3)
q [qmakm½M�1Dakm½M�
(4)
where, qm is the maximum adsorption capacity of ion (expressed interms of mg/g), and
a [kH
kHDhHDiZ (5)
where Z is the ionic concentration in the solution.In Fig. 2, the pH dependence of both copper and nickel ions’
adsorption showed an inflection point between pH 3 and 5. Thissuggests that there are more than one metal binding sites inthe peat. Also, as mentioned earlier, surface binding sites otherthan –S�Hþ are involved in the adsorption of copper and nickel. Hoand Mckay (1999a,b) noted that both copper and nickel may adsorbonto the polar groups present in the peat surface. In such case, totaluptake can be obtained as the sum of the amounts adsorbed by allthese sites. In this work, we applied Langmuir two-site model to fitthe data. The two-site model can be written as
q [qm1a1km1½M�1Da1km1½M�
Dqm2a2km2½M�1Da2km2½M�
(6)
A non-linear regression method was used to obtain the constantsand is presented in Table 2. The two-site Langmuir isotherm plotsare shown in Figs. 5 and 6 as the amount of copper and nickeladsorbed on the peat as a function of concentration. The predicted
00.10.20.30.40.50.60.70.80.91
0 20 40 60 80 100 120 140 160 180Bed Volume
C/C
0
Fig. 9. Breakthrough curves for (B) copper and (-) nickel from a column packed withpeat (inlet influent concentration¼ 90 mg/L, flow rate¼ 3 mL/min).
00.10.20.30.40.50.60.70.80.91
0 20 40 60 80 100Bed Volume
C/C
0
Fig. 10. Breakthrough curves for copper (B) and nickel (-) from their binary mixturefrom a column packed with peat (inlet influent concentration of copper and nickel(50:50)¼ 100 mg/L; flow rate¼ 3 mL/min).
0
20
40
60
80
100
0 20 40 60 80Time (hr)
% C
op
per D
eso
rb
ed
Fig. 12. Desorption efficiencies of copper using (C) EDTA (2 mM), (6) HCl (pH 1.0),and (,) deionized water.
B. Sen Gupta et al. / Journal of Environmental Management 90 (2009) 954–960958
adsorption capacities from Eq. (6) are compared with the experi-mental data for copper and nickel in Figs. 5 and 6, respectively.From the two-site model a sharp increase in copper and nickeladsorption onto peat was observed, which was followed by a slowincrease towards the equilibrium amount. In Figs. 4 and 5, thecontribution of first and second terms of Eq. (6), which may beconsidered as adsorption on site 1 and site 2, respectively, was alsoplotted. It may be noted that the site 1 adsorbed significant amountof both copper and nickel. However, the amount of nickel adsorbedon site 2 was negligible, but amount of copper adsorbed was higherthan that of nickel. This result indicates that the adsorption ofcopper occurred on both site 1 (strong adsorption sites) and site 2(weak adsorption sites) on the peat surface simultaneously,whereas most of nickel adsorption occurred mainly on site 1.
3.3. Adsorption of copper and nickel from binary mixtures
Since the peat had a maximum adsorption capacity at a pH of 4.5,equilibrium adsorption capacity of peat copper and nickel fromtheir binary mixtures was determined at pH 4.5 and 298 K. Theinitial concentrations of copper in the solution were 10%, 25%, 50%,and 90% of the total metal content and the rest was nickel. The finalmetal concentration in the solution was 100 mg/L in all the exper-iments. The amount of copper and nickel uptake by peat is de-termined by Eq. (1). Fig. 7 shows that the equilibrium uptakecapacity of peat for copper is higher than nickel from their binarymixture. It was observed that the amount of copper and nickeluptake was 7.5 mg/g and 5.95 mg/g of peat, respectively, when theinitial concentration ratio of copper and nickel was 50:50. Homa-tidis et al. (2000) observed that peat has great affinity for copperthan nickel ions. Ho et al. (1995) also observed a similar trend formetal removal by sphagnum moss peat and concluded that
0
500
1000
1500
2000
2500
3000
0 10 20 30 40Bed
Co
pp
er co
ncen
tratio
n (m
g/L
)
Fig. 11. Regeneration of column following adsorption of copp
although peat moss could be a suitable adsorbent for nickel re-moval, its removal for other metals could be even higher. As notedearlier, copper can get adsorbed on both sites 1 and 2, whereas,nickel is primarily adsorbed on site 1. In a binary mixture, bothcopper and nickel are expected to compete for site 1, but there is nocompetition for site 2. Therefore, the affinity or amount of copperadsorbed from its binary mixture with nickel is expected to behigher.
3.4. Breakthrough curves
A continuous flow fixed-bed column was designed and built forstudying breakthrough characteristic of copper and nickel from thebed. A schematic diagram of the system is shown in Fig. 8. Thecolumn was constructed from perspex, and was approximately30 cm in length and 2.54 cm in diameter. Retort stands and clampssupported the column vertically. The bed contained a wire gaugefitted at the bottom of the column. In order to overcome the hy-drostatic pressure and to facilitate a steady flow rate, tubing andclips were attached to the tap outlet of a 5-L tank. The column wasopen at the top end where the liquid stream was fed.
As can be seen from Fig. 9, approximately 60 bed volume ofcopper sulphate solution percolated through the column beforebreakthrough started, when the inlet concentration was 90 mg/Land the flow rate was 3 mL/min through the bed. The saturation ofthe bed occurred after 48 h or after treating 154 bed volume ofcopper sulphate solution.
The nickel breakthrough occurred after 53 bed volume undersimilar conditions. About 100 bed volumes of additional nickelsulphate solution was needed to saturate the bed at which point theoutlet concentration became same as the inlet concentration of90 mg/L. In this experiment, the breakthrough time for both copper
50 60 70 80 90 Volume
er using (,) EDTA, (A) deionized water, and (6) HCl.
0
200
400
600
800
1000
1200
1400
1600
0 10 20 30 40 50 60 70 80 90Bed Volume
Nickel co
ncen
tratio
n (m
g/L
)
Fig. 13. Regeneration of column following adsorption of nickel using (,) EDTA, (A) deionized water, and (6) HCl.
B. Sen Gupta et al. / Journal of Environmental Management 90 (2009) 954–960 959
and nickel was found to be fairly same, although several re-searchers indicated that peat has greater affinity for copper thannickel ions (Homatidis et al., 2000).
Fig. 10 shows the breakthrough for copper and nickel from theirbinary mixture. The concentration of both copper and nickel in thesolution was 50 mg/L. As can be seen from Fig. 10, nickel brokethrough after 25 bed volumes, whereas the copper concentration inthe outlet begun to increase slowly after 40 bed volumes.
3.5. Regeneration study
The copper or nickel laden peat was regenerated using eitherHCl or EDTA solutions. Deionized water was also tested for re-generation of the bed.
The pH of HCl solution was 1.0 and the concentration of EDTAwas 2 mM. The initial pH of the EDTA solution was 4.7. The con-centration profiles for copper desorption using various regenerat-ing solutions are shown in Fig. 11. It can be seen that copperdesorption using deionized water and HCl was fast compared toEDTA. In the case of the deionized water, equilibrium was reachedwithin 2 bed volume, and it was 3 bed volumes when using HCl. Inthe case of EDTA, almost 15 bed volumes were required to reach thedesorption equilibrium. However, it was noted that a greateramount of copper could be removed by using EDTA compared todeionized water or HCl. The desorption efficiency was calculatedusing the following expression.
Desorption efficiencyð%Þ
[Amount of metal desorbedðmmolÞ
Amount of metal loadedðmmolÞ 100%
Desorption efficiencies for copper calculated from the aboveequation were 41%, 55%, and 58% when using deionized water, HCl,
0102030405060708090100
0 20 40 60 80Time (hr)
% N
ic
kel D
eso
rb
ed
Fig. 14. Desorption efficiency of nickel from peat bed using (>) deionized water, (,)EDTA, and (6) HCl.
and EDTA, respectively. Cumulative amounts of copper removed bythese three solutions are compared in Fig. 12 as a function of time.
The desorption of heavy metals from a biomass, such as peat, byacidic solutions comprises three steps. (1) The desorption of themetal ions from the binding sites of the sorbent, (2) diffusion ofmetal ions from inside to the surface of the sorbent, and (3) diffu-sion of metal ions across a stationary liquid film surrounding thesorbent particles and into the bulk liquid.
In general the mass transfer process controls the overall kineticsof the metal desorption process. The resistance to mass transferthrough the liquid film is proportional to the thickness of the liquidlayer for the solution system, which in turn, is controlled by agi-tation in the bulk solution. Strong stirring, therefore, will actuallydecrease the thickness of the film, eliminating the effect of the filmresistance and ultimately affecting the overall desorption process.Based on these findings and the findings of previous studies, de-sorption experiments should be carried out under agitatedconditions.
Contact time is an important parameter during desorption. Thecontact time for 2 mM EDTA equivalent to 15 bed volumes shouldbe sufficient to achieve the equilibrium. Tan (1999) noted that thedesorption equilibrium could be achieved at this equivalent bedvolume, and the desorption efficiencies obtained for the samedesorbents were substantially higher. Desorption efficiencies of95%, 91%, and 80% for 2 mM EDTA, HCl at pH 1.0, and HCl at pH 2.0were achieved, respectively. This difference is due to the fact thatthe initial concentration of metal loading in Tan’s, study (w390 mg/L, 1.57 mM Cu2þ) was substantially lower than the metal loading inthis present study (6352 mg/L Cu2þ). About 80 bed volume ofregenerating solution was employed for all subsequent desorptionexperiments to ensure that equilibrium was achieved.
As shown in Fig. 13, nickel desorption using all three solutionswas relatively fast. Desorption equilibrium for deionized water,EDTA and HCl, was reached with 6, 4, and 2 bed volumes, re-spectively. Despite the relatively fast desorption equilibrium, de-sorption efficiencies for all three solutions were substantially lowercompared to desorption efficiency for copper. Desorption efficien-cies for nickel with deionized water, EDTA and HCl were found to be3%, 28%, and 25%, respectively (Fig. 14).
4. Conclusions
The adsorption characteristics of copper and nickel on peat mosswere studied at pH range of 2.0–6.0. The favourable pH range wasfound to be 4.0–4.5. The batch adsorption data for copper andnickel were successfully correlated with a two-site Langmuirmodel. Breakthrough data from a column showed that the de-sorption of copper was comparatively more efficient than nickelfrom peat surface. The adsorbed copper and nickel could be
B. Sen Gupta et al. / Journal of Environmental Management 90 (2009) 954–960960
removed completely from the bed by using either deionized water,HCl solution, or 2 mM EDTA solution, however, the amount of so-lution necessary for complete regeneration varied.
Acknowledgement
B. Sen Gupta and M. Curran would like to thank S. J. Allen for hissupport.
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