The Study On Adsorption Performance Of Immobilized Biosorbents For The Removal Of Heavy Metal Copper

This study used Saccharomyces cerevisiae (S.cerevisiae) and orange peels as rawmaterials. After alkali treatment modification, they were immobilized by Na-alginateto form three biosorbents: Ca-alginate immobilized S.cerevisiae beads (SCA),Ca-alginate immobilized orange peel beads (OPCA), and Ca-alginate immobilizedorange peel and S.cerevisiae beads (OPSCA). The performance of them for theremoval of Cu(II) ions from aqueous solution was tested.Cu(II) removal by OPSCA, OPCA, and SCA was pH dependent and the optimumpH was5.0. Solution pH value effected the Cu(II) adsorption capacities by means ofimpacting on the formation of ion species in solutions, the degree of ionization ofsurface function groups of adsorbents, and the surface charges of the adsorbents. Atthe same conditions, the adsorption amounts of Cu(II) ions by the adsorbentsdecreased in this order: OPSCA＞OPCA＞SCA, which indicated that compositesorbent contained multi-component organism had a higher capacity to combine withCu(II) ions than the adsorbents contained only one kind of organism.The adsorption capacities of Cu(II) ions by OPSCA, OPCA, and SCA increasedwith the increase of initial concentration of solution, and tended to be saturated afterreached a certain degree. The maximum adsorption capacities of OPSCA, OPCA, andSCA were58.279,37.091, and29.962mg/g respectively, but the removal ratios ofCu(II) ions decreased with the increase of initial concentration of solution. Theequilibrium data of three kinds of sorbents adsorbing Cu(II) ions could be adequatelydescribed by Langmuir and Freundlich isotherm models, while Langmuir model wasshown the better description. It implied that monolayer adsorption and heterogeneousadsorption might coexist in adsorption process but monolayer adsorption wasdominant.The adsorption amounts of Cu(II) ions by three kinds of adsorbents increasedwith the increase of contact time, and almost reached equilibrium in approximately120min. The equilibrium adsorption capacities of OPSCA, OPCA, and SCA were12.309,7.733, and7.103mg/g. The adsorption kinetics data were in good agreementwith the pseudo-second-order model but not the pseudo-first-order model, indicatingthat the rate-limiting step of adsorption process was the chemisorption but not thephysisorption. The results of fitting intraparticle and film diffusion models showed that the adsorption process was controlled by both intraparticle diffusion and filmdiffusion.The results of Fourier transform infrared analysis indicated that–OH,–NH,–CH,C=O and–CN groups possibly all involved in Cu(II) adsorption onto OPSCA, OPCA,and SCA.The results of adsorption-desorption experiment demonstrated that Cu(II) ionscould be released from the Cu(II) loaded OPSCA, OPCA, and SCA using0.1mol/LHCl solutions, and the three adsorbents could be successfully regenerated andrepeatedly used without appreciable losses in their adsorption capacities anddesorption ratios.