Retention of lead from an aqueous solution by use of bentonite as adsorbent for reducing leaching from industrial effluents

The adsorptive properties of bentonite, which was made homoionic by exchangeable mono-, di- and trivalent cations (Na+, Li+, K+, Ca2+, Mg2+, Al3+ and Fe3+), in lead-rich aqueous environment have been studied. The results show an increase in the final pH values of the recuperated suspension after exchange of homoionic bentonites with lead aqueous solution prepared at pH 5. The alkaline and alkaline earth metals located in the exchangeable sites of homoionic bentonites are replaced with Pb2+ cations present in the prepared aqueous solution. The higher amounts of lead adsorbed seems to be more than cation exchange capacity (CEC) of homoionic bentonites. The higher final pH values of the residual suspension may explain formation of lead hydroxyl species which participate to the adsorption or precipitation onto the bentonites. Only potassium ions suppressed the lead adsorption to bentonite, probably by collapsing the clay lattices and preventing the expression of the interlayer derived cation-exchange capacity, however the amount of lead adsorbed by bentonite made potassium homoionic and reached the value of CEC.