Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

Abstract

Abstract The adsorption of cadmium and zinc ions on natural bentonite heat‐treated at 110°C or at 200°C and on bentonite acid‐treated with H 2 SO 4 (concentrations: 0·5 mol dm −3 and 2·5 mol dm −3 ), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities ( X m ) and the apparent equilibrium constants ( K a ) of the samples; X m and K a values range respectively for 4·11 mg g −1 and 1·90 dm 3 g −1 for the sample acid‐treated with 2·5 mol dm −3 H 2 SO 4 [(B)‐A(2·5)] up to 16·50 mg g −1 and 30·67 dm 3 g −1 for the natural sample heat‐treated at 200°C [B‐N‐200], for the adsorption process of cadmium, and from 2·39 mg g −1 and 0·07 dm 3 g −1 , also for B‐A(2·5), up to 4·54 mg g −1 and 0·45 dm 3 g −1 [B‐N‐200], for the adsorption process of zinc. X m and K a values for the heat‐treated natural samples were higher than those corresponding to the acid‐treated ones. The removal efficiency ( R ) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B‐A(2·5)] up to 100% and 19·9% [B‐N‐200], for adsorption of cadmium and zinc.