Abstract: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.

Key words: biosorption; desorption; kinetics; silver; Ag⁺ ions; absorbent; valonia tannin; resin