Removal of Cd(II) from Aqueous Solution Using Blue Pine Sawdust: Equilibrium, Kinetics and Thermodynamic Studies

Amjad Farooq, Syed Moosa Hasany, Muhammad Mansha Chaudhary, Nasseem Irfan
2007 Main Group Metal Chemistry  
The adsorption of Cd(II) ions onto sawdust has been investigated in detail as a function of equilibration time (1-120 min), dosage of adsorbent (0.025-0.5 g)/10 ml, concentration of Cd(II) (9-1780 μΜ) and of nature (pH 1-10). Maximum adsorption (ca. 95.3%) is achieved from deionised water in 30 minutes at pH 7 using 0.2 g adsorbent/10 ml adsorbate solution. The adsorption data follow Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms over the entire range of Cd(II) ions concentration
more » ... ions concentration examined and their characteristic constants have also been evaluated. The variation of adsorption with temperature has yielded ΔΗ, AS and AG values for the 18μΜ cadmium concentration. The kinetics of adsorption obeys Morris-Weber and Lagergren equations. The first order rate constant and the intraparticle diffusion rate have also been estimated. Sawdust appears to have potential to remove Cd(II) ions from aqueous solutions at trace or subtrace concentration, to preconcentrate or treat industrial wastewater. and monitor the tolerance levels of cadmium concentration in the environment. Failure to do so may cause certain physiological disorders and diseases in humans and animals. Several techniques like ion exchange, chemical precipitation, solvent extraction, reverse osmosis and adsorption have been used to remove cadmium from industrial effluents and to bring its concentration to a safer limit in aqueous medium 13/. An effective, easy to operate, economical and rapid method to remove metal ions is adsorption /4/. In general, an adsorbent abundant in nature, or as a by-product or waste material from another industry that requires little processing, is called a low cost adsorbent /4/. The adsorption profile of a number of agricultural and waste materials has been investigated for the removal of toxic and heavy metal ions including cadmium from aqueous medium. These include coconut husk 151, corncob 161, pinus sylvestris sawdust 111, juniper fiber /8/, sugarcane bagasse pith 191, tea industry waste /10/, groundnut husk /ll/, papaya wood /12/, juniper bark and wood /13, 14/, poplar wood sawdust /15/, lignite 13/, beach sand /16/, olive cake IM I and Haro river sand /18/ for cadmium; sawdust l\9l, polyurethane foam /20/, sunflower stem /21 / and coconut husk 1221 for mercury; coconut husk 1231, used tyres and sawdust /24/, fly ash 1251, feldspar 1261, tea factory waste 1211, modified oak sawdust /28/ and sawdust 129, 30/ for chromium; rice husk /31 /, papaya wood /12/, poplar wood sawdust /15/, lignite 131 and Haro river sand 1321 for zinc; papaya wood /12/, lignite 131, modified oak sawdust /28/, sawdust /29/, poplar wood sawdust /15/, tea industry waste /10/, oil shale waste 1331 and fly ash /34/ for copper; pyrite fine for arsenic /35/; polyurethane foam for silver /36/; lichen biomass/37/ and groundnut husk /11/, pinus sylvestris sawdust Π, 38/, caladium bicolor biomass 139, 40/, blast furnace sludge /41/, lichen biomass /37/ and beach sand /42/ for lead. No study was undertaken to monitor the adsorption behaviour of Cd(II) ions onto sawdust (Pinus Wallichiana) from aqueous media; therefore this investigation is carried out. This communication reports the results of the adsorption of cadmium(II) ions onto sawdust. MATERIALS AND METHODS Reagents/Buffers and Materials: All reagents used were of analytical grade and procured from Fluka Chemical Co. or E. Merck, Germany. Throughout this investigation deionised water was used. All glassware used was of Pyrex, Germany, and repeatedly washed with deionised water followed by drying. Stock solution of cadmium was made by adding small amount (1 ml) of nitric acid (14.53 M) to 1 g of cadmium metal (Merck) and subsequent heating to dryness. Nitric acid (14.53 M) was again added (0.5 ml) and heated till evaporation. The residual white precipitate was quantitatively transferred to a 100 ml flask and the volume was made up with deionised water. This gave a 10 mg/ml clear stock solution of cadmium. The samples of required concentration were made by appropriate dilution of the stock solution. The buffers of pH 1-3, 4-6 and 7-10 were made by mixing 0.2 Μ of potassium chloride + hydrochloric acid, acetic acid + sodium acetate and boric acid + sodium hydroxide solutions respectively. Ail solutions for the study were made in deionised water. Removal of Cd(Il) from Aqueous Solution Using Blue Pine Sawdust Influence of common ions on the adsorption: The common anions, cations and complexing agents also influence the adsorption of metal ions in aqueous solution. Thus investigation was carried out to monitor their effect on the adsorption of Cd(Il) ions (18 μΜ) onto sawdust. The anions were added as their sodium or potassium salts, whereas cations were included as their chlorides or nitrates. The concentration of additional ions was kept at 0.01 Μ (555 times more than Cd(II) ions). The results are listed in Tables 3 and 4 . Thiosulphate, EDTA, carbonate, sulphide and citrate reduced the adsorption below 30% whereas percent adsorption was reduced below 20% in the presence of Ca(II), Ba(II), Fe(III), Al(III), Ni(II), Co(II), Zn(II), Mg(II), Sr(II) and Pb(II). The ions of acetate and Chromate cause substantial increase in the adsorption of Cd(II) ions. The addition of anions or cations may change the properties of interfacial layer (surface double layer). The reduction in the adsorption of Cd(II) ions in the presence of additional ions may be ascribed to the formation of anionic complexes of Cd(ll) ions, which are not adsorbed onto the adsorbent surface to the same extent as Cd(II) ions. The reduction in the presence of cations may also be attributed to the preferential adsorption of other metal ions on the surface. As a consequence, adsorption sites may be blocked and may not be available for Cd(Il) ions adsorption. Mostly divalent metals caused reduction in the adsorption of Cd(II) ions. The enhancement of Cd(II) ions adsorption in the presence of acetate and Chromate may be interpreted as their higher adsorption affinity onto the adsorbent surface than Cd(II) ions themselves. The ions which caused a reduction must be absent from the adsorption system, otherwise low adsorption yields would be expected. Strong complexes of Cd(II) with EDTA and thiosulphate have been reported in the literature /58, 59/. Table 3 The effect of anions on the retention ofCd(II) ions (18 raM) onto sawdust (0.2 g/10 mL) after 30 min equilibration time
doi:10.1515/mgmc.2007.30.6.345 fatcat:3s77adqxonhohnj6verpxngdne