Equilibrium studies for the sorption of zinc and copper from aqueous solutions using sugar beet pulp and fly ash

Abstract

In the present work, the abilities of native sugar beet pulp (SBP) and fly ash (FA) to remove copper (Cu 2+) and zinc (Zn 2+) ions from aqueous solutions were compared. The SBP and FA, an industrial by-product and solid waste of sugar industry, were used for the removal of copper and zinc from aqueous water. Batch adsorption experiments were performed in order to evaluate the removal efficiency of SBP and lignite-based FA. The effect of various operating variables, i.e. initial pH, adsorbent dose, initial metal ion concentration, and time on adsorption of copper and zinc onto the SBP and FA, has been studied. The sorption process was relatively fast and equilibrium was reached after about 60 min of contact. As much as 60–97% removal of copper and zinc for SBP and FA are possible in about 60 min, respectively, under the batch test conditions. Uptake showed a pH-dependent profile. The overall uptake for the SBP is at a maximum at pH 5.5 and gives up to 30.9 mg g −1 for copper and at pH 6.0 and gives 35.6 mg g −1 for zinc for SBP, which seems to be removed exclusively by ion exchange and physical sorption. Maximum adsorption of copper and zinc occurred 7.0 and 7.84 mg g −1 at a pH value of 5.0 and 4.0 for FA, respectively. A dose of 8 g l −1 of SBP and 8 g l −1 FA were sufficient for the optimum removal of both the metal ions. The sorption data were represented by the Freundlich for SBP and the Langmuir and Freundlich for FA. The sorption data were better represented by the Langmuir isotherm than by the Freundlich one for FA in the adsorption of zinc ion, suggesting that the monolayer sorption, mainly due to ion exchange. The presence of low ionic strength or low concentration of Na and Cl ions does not have a significant effect on the adsorption of these metals by SBP and FA. The SBP and FA are shown to be effective metal adsorbents for these two metals.