ADSORPTION OF CADMIUM AND ZINC FROM AQUEOUS-SOLUTION ON NATURAL AND ACTIVATED BENTONITE

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110-degrees-C or at 200-degrees-C and on bentonite acid-treated with H2SO4 (concentrations: 0.5 mol dm-3 and 2.5 mo. dm-3), from aqueous solution at 30-degrees-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 calculate 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 dm3 g-1 for the sample acid-treated with 2-5 mol dm-3 H2SO4 [(B-A(2.5)] up to 16.50 mg g-1 and 30.67 dM3 g-1 for the natural sample heat-treated at 200-degrees-C [B-N-200], for the adsorption process of cadmium, and from 2.39 mg g-1 and 0.07 dm3 g-1, also for B-A(2-5), up to 4.54 mg g-1 and 0.45 dM3 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.