Adsorption and desorption behavior of silver ions onto valonia tannin resin

Valonia tannin (VT) was gelated through polymerization with formaldehyde to prepare an adsorbent, which was found effective to remove Ag from aqueous solution. The adsorption–desorption behaviors of valonia tannin resin (VTR) were investigated under various initial Ag concentrations, solution temperatures, pH values etc. The applicability of empirical kinetic models was also studied. The pseudo-second-order model studies revealed the Ag sorption was very rapid. VT and VTR were characterized using FTIR and SEM before and after adsorption. The Ag biosorption on VTR increased with a rise in initial concentration of Ag and with a decrease in temperature. Desorption experiments were conducted at low pH values and the solutions of H2SO4, HNO3 and HCl were used for desorption. The VTR shows high adsorption capacity to Ag in a wide pH range of 2.0−7.0, and a maximum adsorption capacity of 97.08 mg/g was obtained at pH 5.0 and 296 K when the initial concentration of Ag was 100.0 mg/L. Ag ion desorption could reach 99.6% using 1 mol/L HCl+1% thiourea (NH2CSNH2) solution. By utilizing such characteristics of VTR, it is expected that it can be applied to recovering Ag efficiently and simply with low cost.