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Adsorption of chromium from aqueous solution on treated sawdust

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Adsorption of chromium from aqueous solution on treated sawdust
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  Adsorption of chromium from aqueous solution on treated sawdust V.K. Garg  a,* , Renuka Gupta  a , Rakesh Kumar  a , R.K. Gupta  b a Department of Environmental Science and Engineering, Guru Jambheshwar University, Hisar 125001, India b Department of Applied Chemistry, Guru Jambheshwar University, Hisar 125001, India Received 20 March 2003; received in revised form 6 June 2003; accepted 10 July 2003 Abstract The adsorption of Cr(VI) from aqueous solutions on formaldehyde treated sawdust (SD) and sulphuric acid treated sawdustcarbon (SDC) of Indian Rosewood, a timber industry waste, was studied at varying Cr(VI) concentrations, adsorbent dose, pH andagitation time. Similar experiments were conducted with commercially available coconut based activated carbon to compare theresults. The Cr(VI) adsorption efficiency on SDC was higher than SD. The adsorption followed first order rate expression andLagergren equation. An initial pH of 3.0 was most favorable for Cr(VI) removal by both the adsorbents. Maximum Cr(VI) wassequestered from the solution within 60 min after the beginning for every experiment. It is proposed that SDC and SD can bepotential adsorbents for Cr(VI) removal from dilute solutions.   2003 Elsevier Ltd. All rights reserved. Keywords:  Cr(VI); Formaldehyde; Sulphuric acid; Sawdust; Adsorption; Batch mode 1. Introduction Chromium, in its hexavalent form, is one of the un-desirable heavy metals because it affects human physi-ology accumulates in the food chain and cause severalailments (Park and Jung, 2001). The main industrialsources of chromium pollution are leather tanning,electroplating, metal processing, wood preservatives,paint and pigments, textile, dyeing, steel fabrication andcanning industry (Raji and Anirudhan, 1997). Accord-ing to Indian standards, the permissible limit of Cr(VI)for industrial effluents to be discharged to surface wateris 0.1 mg/l. So the removal of Cr(VI) from industrialeffluents is important before discharging them intoaquatic environments or on to land. A wide range of physical and chemical processes is available for the re-moval of Cr(VI) from wastewater. However thesemethods are ineffective for Cr(VI) concentrations lowerthan 100 mg/l and prohibitively costly (Matheichal et al.,1997).Adsorption on activated carbon (ACR) has beenfound to be an effective process for Cr(VI) removal, butit is too expensive. Consequently numerous low costalternatives have been studied including  Casurina  leaves(Ranganathan, 2000), leaf mould (Sharma and Forster,1994), moss peat (Sharma and Forster, 1995), green al-gae (Gupta et al., 2001), activated carbon fibers (Parkand Jung, 2001) coconut waste (Selvi et al., 2001), rub-ber wood (Raji and Anirudhan, 1997) etc. New eco-nomical, easily available and highly effective adsorbentsare still needed. Saw dust is a waste by-product of thetimber industry that is either used as cooking fuel or apacking material. The objective of this work was toevaluate the adsorption capacity of Cr(VI) from aque-ous solutions by sawdust of Indian Rosewood pre-treated with formaldehyde and sulphuric acid byvarying Cr(VI) concentration, adsorbent dose, pH andcontact time and desorption. 2. Methods  2.1. Preparation of formaldehyde treated sawdust (SD) Sawdust of Indian Rosewood ( Dalbergia sissoo ) col-lected from a local saw mill was dried in sunlight andground to a fine powder. To immobilize the colorand water-soluble substances the ground powder wastreated with 1% formaldehyde in the ratio of 1:5 * Corresponding author. Fax: +91-1662-276240. E-mail address:  vinodkgarg@yahoo.com (V.K. Garg).0960-8524/$ - see front matter    2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2003.07.004Bioresource Technology 92 (2004) 79–81  (SD:formaldehyde, w/v) at 50   C for 4 h. The sawdustwas filtered out, washed with distilled water to removefree formaldehyde and activated at 80   C in a hot airoven for 24 h. The resulting material was ground fol-lowed by sieving in the size range of 20–50 mesh ASTM.The material was placed in an airtight container forfurther use.  2.2. Preparation of sulphuric acid treated sawdust carbon(SDC) One part of dried SD was mixed with one part of concentrated sulphuric acid and heated in a muffle fur-nace for 24 h at 150   C. The heated material was washedwith distilled water and soaked in 1% sodium bicar-bonate solution overnight to remove residual acid. Thematerial was dried in an oven at 105   C for 24 h, groundand sieved in the size range of 20–50 mesh ASTM andused for the further study. The various physico-chemicalcharacteristics of SDC were: apparent density ¼ 1.45 g/ml; ash content ¼ 1.68%; moisture content ¼ 3.80%;CEC ¼ 0.68 meq/g; water-soluble matter ¼ 1.68%; acidsoluble matter ¼ 9.34% and EC ¼ 0.10 mS/cm. All ad-sorbents were dried at 110   C overnight before the ad-sorption experiments.Commercially available ACR was supplied by S.D.Fine Chemicals, Mumbai, India and used as suchwithout further grinding and sieving.  2.3. Preparation of Cr(VI) solution An accurately weighed quantity of the K 2 Cr 2 O 7  wasdissolved in double-distilled water to prepare a stocksolution (1000 mg/l). Experimental solutions of the de-sired concentrations were obtained by successive dilu-tions. Experiments were carried out at initial pH valuesranging from 2.0 to 10.0; initial pH was controlled byaddition of dilute HCl or NaOH solutions.  2.4. Adsorption experiments In each adsorption experiment, 100 ml of Cr(VI) so-lution of known concentration and pH value was addedto 400 mg of SD, SDC or ACR in a 250 ml roundbottomed flask at room temperature (26±1   C) and themixture was stirred on a rotary orbital shaker at 160rpm. The samples were withdrawn from the shaker atthe pre-determined time intervals, and adsorbent wasremoved from the solution by centrifugation at 4500rpm for 5 min. The residual Cr(VI) concentration insupernatant was estimated calorimetrically with 1,5-diphenylcarbazide at 540 nm. The experiments weredone by varying the amount of adsorbent (0.2–1.0 g/100ml); Cr(VI) concentration in the solution (25–200 mg/l)at initial pH of 3.0 at different time intervals. 3. Results and discussion 3.1. Effect of pH on Cr(VI) removal  Initial pH of Cr(VI) solution was increased after theequilibrium time (3 h). The pH increase was lesser atlower initial pH values. It may be due to hydrolysis of the adsorbent in water, which will create positivelycharged sites (Dakiky et al., 2002). Percentage removalof Cr(VI) was maximum at the initial pH of 3.0 (99.7%,86.6% and 62.2% by ACR, SDC and SD respectively)and decreased at lower and higher initial pH values (Fig.1). At initial pH of 3.0, the adsorbent surfaces might behighly protonated which favor the uptake Cr(VI) in thepredominant anionic form (HCrO  4  ) (Srinivas Rao et al.,1992). With increase in pH from 3 to 10, the degree of protonation of carbon surfaces reduced gradually andhence removal was decreased. 3.2. Effect of initial Cr(VI) concentration and contacttime The effect of Cr(VI) concentration on the adsorptionby ACR, SDC and SD was investigated by varying theinitial Cr(VI) concentration (25, 50, 100, 150 and 200mg/l) at initial pH of 3.0 for different time intervals.Cr(VI) removal by ACR was 100% at all the studiedconcentrations. Percent Cr(VI) removal efficiency of SDC and SD reduced with increase in Cr(VI) concen-tration. Cr(VI) uptake was reduced for SDC from 99.8%to 74.8% and for SD from 87.8% to 36.2% as concen-tration was increased from 25 to 200 mg/l. Adsorptionand initial Cr(VI) concentration correlation was expo-nential in nature for SDC and SD. Though the per-centage removal was decreased with increase in Cr(VI) 0204060801001200 1 2 3 4 5 6 7 8 9 10 11 pH    P  e  r  c  e  n   t   C  r   (   V   I   )  r  e  m  o  v  a   l ACRSDCSD Fig. 1. Effect of pH on Cr(VI) removal by ACR, SDC and SD (initialCr(VI) concentration ¼ 100 mg/l, adsorbent dose ¼ 0.4 g/100 ml, tem-perature ¼ 26   C, contact time ¼ 180 min).80  V.K. Garg et al. / Bioresource Technology 92 (2004) 79–81  concentration but the actual amount of Cr(VI) adsorbedper unit mass of the adsorbent was increased. This ac-cords well with the findings of other investigator(Ranganathan, 2000). The equilibrium was establishedquickly within 15 min by ACR. However SDC and SDtook  @ 60 and  @ 180 min respectively for equilibrium at-tainment. The results also indicated that the time takento reach equilibrium was longer at higher concentra-tions. 3.3. Effect of adsorbent dose and contact time The effect of adsorbent dose on Cr(VI) uptake wasinvestigated by varying the adsorbent dose (0.2, 0.4, 0.6,0.8 and 1.0 g/100 ml) at initial pH of 3.0 for differenttime intervals. The percent adsorption increased from65.4% to 100%, as the SDC dose was increased (0.2–1.0g/100 ml) after equilibrium time (3 h). For SD adsorp-tion increased from 50.7% to 92.2% with similar doses.ACR had 100% adsorption at all the studied doses. In-crease in adsorption with dose can be attributed to in-creased surface area and the availability of moreadsorption sites. For SDC, unit adsorption density wasdecreased from 3.7 to 10.0 mg/g as the dose was in-creased from 0.2 to 1.0 g/100 ml in the solution. Thismay be due to aggregation of adsorption sites resultingin decrease in total adsorbent surface area of carbonparticles available to Cr(VI) and an increase in diffusionpath length. For SD, the adsorption density was lesser(25.4–9.2 mg/g) than SDC with similar doses. Equilib-rium time was lesser at higher adsorbent doses.The specific rate constants,  K  ad , for the adsorption of Cr(VI) on SDC and SD were determined using thepseudo-first order Lagergren equation. The straight-lineplot of log ð q e    q Þ  versus   t  ’ at different adsorbent dosesconfirmed the validity of the Lagergren equation andalso explained that process followed the pseudo-firstorder kinetics. The values of   K  ad , calculated from theslopes of the plots were 0.026 and 0.038 min  1 for SDC;and 0.019 and 0.023 min  1 for SD at 0.2 and 0.4 g dosesper 100 ml. These values showed that adsorption wasfaster at the higher adsorbent doses. 3.4. Desorption of Cr(VI) Desorption studied are helpful to explore the possi-bility of recycling the adsorbents and recovery of metalresource. From SDC and SD used for 100 mg/l Cr(VI)solution, 48% and 42% Cr(VI) was desorbed by 1 NNaOH Æ HCl was used to desorb the remaining Cr(VI).The total Cr(VI) released was 72% and 66% for SDCand SD respectively. 4. Conclusion New alternative adsorbents for Cr(VI) removal havebeen explored by making simple chemical modificationsof sawdust by formaldehyde and sulphuric acid. Thisstudy showed that SDC and SD had lower adsorptionefficiency than ACR at higher Cr(VI) concentrations.Initial pH of 3.0 was optimum for maximum Cr(VI)removal by SDC and SD. At higher and lower initial pHvalues than 3.0, adsorption of Cr(VI) was decreasedsharply. Higher removal by SDC and SD was possibleprovided the Cr(VI) concentration was low in the solu-tion. SD is easily available in the countryside, so can beused by small scale industries having low concentrationsof Cr(VI) in wastewater using batched or stirred-tankflow reactors after treating it with formaldehyde orsulphuric acid. References Dakiky, M., Khamis, M., Manassra, A., Mer’eb, M., 2002. Selectiveadsorption of chromium (VI) in industrial wastewater using lowcost abundantly available adsorbents. Adv. Environ. Res. 6, 533– 540.Gupta, V.K., Shrivastava, A.K., Jain, N., 2001. Biosorption of chromium (VI) from aqueous solutions by green algae spirogyraspecies. Water Res. 35 (17), 4079–4090.Matheichal, J.T., Yu, Q., Feltham, J., 1997. Cu(II) binding by  E.radiata  biomaterial. Environ. Technol. 18, 25–34.Park, S., Jung, W.Y., 2001. Removal of chromium by activated carbonfibers plated with copper metal. Carbon Sci. 2 (1), 15–21.Raji, C., Anirudhan, T.S., 1997. Chromium (VI) adsorption bysawdust: kinetics and equilibrium. Indian J. Chem. Technol. 4,228–236.Ranganathan, K., 2000. Chromium removal by activated carbonsprepared from  Casurina equisatifolia  leaves. Bioresour. Technol.73, 99–103.Selvi, K., Pattabhi, S., Kadirvelu, K., 2001. Removal of Cr(VI) fromaqueous solution by adsorption onto activated carbon. Bioresour.Technol. 80, 87–89.Sharma, D.C., Forster, C.F., 1994. The treatment of chromiumwastewater using the sorptive potential of leaf mould. Bioresour.Technol. 49, 31–40.Sharma, D.C., Forster, C.F., 1995. Column studies into the adsorptionof chromium (VI) using sphagnum moss peat. Bioresour. Technol.52, 261–267.Srinivas Rao, P., Shashikant, R., Munjunatha, G.S., 1992. Kineticstudies on adsorption of chromium by coconut shell carbonsfrom synthetic effluents. J. Environ. Sci. Health A 27 (8), 2227– 2241. V.K. Garg et al. / Bioresource Technology 92 (2004) 79–81  81
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