Adsorption of silver from aqueous solution onto raw vermiculite and manganese oxide-modified vermiculite

In this work, the manganese oxide-modified vermiculite (Mn-MV) was prepared from raw vermiculite (RV) and characterized chemically and morphologically. The adsorption surface of RV was increased about 10 times after the modification due to the increase in negative charge onto the sorbent surface. The adsorption performance of RV and Mn-MV sorbents in the removal of silver (Ag(I)) ions from aqueous solution was examined using batch method. The effects of initial pH of solution, contact time, adsorbent concentration, initial silver ion concentration, modifying agent concentration and temperature of solution on the adsorption efficiency were investigated systemically. The maximum adsorption capacity of RV and Mn-MV sorbents was found as 46.2 and 69.2 mg g^-1, respectively. The calculated adsorption energy (9.6 kJ mol^-1) from the Dubinin-Radushkevich (D-R) model indicated that the adsorption process onto modified sorbent was taken place mainly by chemical ion exchange. A 95% portion of the Ag(I) ions adsorbed was desorbed successfully from the sorbent surface by using 0.5 M 10 mL HCl. The Mn-MV sorbent had good reusability performance after 10 adsorption-desorption cycles. The calculated thermodynamic parameters showed that the adsorption of Ag(I) onto Mn-MV sorbent process was feasible, spontaneous and exothermic. The kinetic evaluation also suggested that the adsorption process followed well the pseudo-second-order kinetic model.