Chemically modified silica gel with thiol group as an adsorbent for retention of some toxic soft metal ions from water and industrial effluent

In this study, functionalized silica with mercaptopropyl groups were synthesized. These materials have been characterized by powder X-ray diffraction and FT-IR spectroscopy. We have shown that silica gel (SG) particles with a surface functionalization of thiol group (S–H) are an effective adsorbent material for toxic soft metal ions such as Hg2+, Pb2+ and Cd2+, which effectively bind to the thiol ligands. The ability of the thiol modified silica gel (TMSG) to remove heavy metal ions was studied by the method of continuous variation of two process variables: Initial heavy metal concentration (mg L−1) in distilled water and the contact time of adsorbent and solutions in water and industrial effluent. The experimental data were fitted into three kinetic models: Lagergren, pseudo-second order and Elovich. The experimental isotherm data were analyzed using Langmuir, Freundlich, Sips, Redlich–Peterson and Temkin isotherms. Six error functions were used to treat the adsorption data using nonlinear optimization techniques for evaluating the fit of the model equations. Error analysis showed that the Langmuir and Redlich–Peterson isotherms best fit the ions adsorption data on TMSG and the pseudo-second order kinetic model described the adsorption process.