Effect of salinity and temperature on the adsorption of Hg(II) from aqueous solutions by a Ca-montmorillonite

Use of clay minerals for removing mercury is an effective technology for the treatment of industrial wastewaters and can become an effective tool for the remediation of coastal ecosystems polluted with this metal. Calcic montmorillonite was employed for adsorbing Hg(II) ions from aqueous solutions at different conditions of salinity (0, 20 and 35 g NaCl L-1), temperature (15, 25 and 35 C), and initial concentrations (0.25, 0.50, 1.00, 2.50, 5.00 and 10.00 mg Hg L-1). It was observed that 0.4 g dry weight of montmorillonite removed from 0.02 mg g-1 (at 0.25 mg L-1 of Hg(II)) to 0.68 mg g-1 (at 10.0 mg L-1 of Hg(II)) at 25 C, salinity of 0 g NaCl L-1 and pH of 6. The initial concentration of Hg(II) and salinity had an effect on the behaviour of the adsorption process, which was temperature independent. The data fit well the Freundlich adsorption isotherm, indicating that heterogeneous conditions prevail in this process.