Sorption of heavy metal cations on rhyolitic and andesitic bentonites from Central Slovakia

The main purpose of this work was to determine adsorption characteristics of heavy metal cations on two Slovak bentonites. Adsorption of Pb(2+), Zn(2+), Cu(2+) and Cd(2+) on Jelsovy Potok (JP) and Lieskovec (L) bentonites was studied by the batch equilibration technique using solutions of different concentrations. Higher smectite content (81 mass %) and higher cation exchange capacity (CEC) (105 mmol M(+)/100 g) of JP bentonite cause higher adsorption of all heavy metals in comparison with L bentonite. JP adsorbed heavy metals in the order Pb(2+)>>Cd(2+)>Zn(2+)>Cu(2+) while sorption on L was slightly different, Pb(2+)>>Cd(2+)>Cu(2+)>= Zn(2+). The Freundlich model of adsorption is more appropriate for adsorption of Pb(2+) and Cd(2+) while lower uptake of Cu(2+) and Zn(2+) is better described by the Langmuir model. Negative A G values indicate that the adsorption process of all cations on both bentonites is feasible, spontaneous and exothermic. The decrease in the d(001) spacings from 14.8-14.9 angstrom in natural dominantly Ca(2+)-saturated samples to 13.2-12.6 angstrom for both bentonites saturated with four heavy metal cations shows the effect of less hydrated exchangeable cations on interlayer spacing. Jelsovy Potok bentonite of higher montmorillonite content and greater CEC is the more effective candidate for removal of Pb(2+), Zn(2+), Cu(2+) and Cd(2+) from waste water than Lieskovec bentonite.