Adsorption characteristics of noble metal ions onto modified straw bearing amine and thiol groups

Abstract

Wheat straw was chemically modified by introducing amine and thiol groups in order to improve its adsorption capacity and selective adsorption ability towards noble metal ions. The removal of Au³⁺ and Pt⁴⁺ ions from aqueous solutions was assessed by using a batch sorption technique. The maximum adsorption amount for Au³⁺ and Pt⁴⁺ ions reached as high as 450 and 380 mg g⁻¹, and the adsorption equilibrium could be achieved within 120 min. The adsorption mechanism studied by X-ray photoelectron spectroscopy (XPS) revealed that the sorption of noble metal ions was realized by ion-exchange, coordination and redox reactions. The selectivity studies suggested that the quantitative removal and determination of Au³⁺ and Pt⁴⁺ ions could be achieved even in the presence of an excess of interfering ions. The desorption efficiency of adsorbed precious metals was studied by using various concentrations of HCl, NaOH, thiourea and thiourea–HCl solutions. It was indicated that the 0.8 mol L⁻¹ thiourea–0.5 mol L⁻¹ HCl solution could effectively desorb Au³⁺ and Pt⁴⁺ ions from the modified straw.