Rapid uptake of gold ions by sulfonated humic acid modified phenolic resin with high adsorption capacity and selectivity

It is of great significance to develop an adsorbent with fast adsorption rate for gold ions to ensure high adsorption capacity and selectivity. Here, we report two humic acid modified phenolic resin (SHAR and NSHAR) using sulfuric acid and sodium sulfite as sulfonating agents respectively, which were prepared by a simple two-step method using water as solvent. They can recover Au(III) quickly and efficiently from mixed metals (Fe(III), Mn(II), Cu(II), Cr(III), Mg(II), Ni(II), Sn(II), Co(II), Pb(II) and Zn(II)). Adsorption behavior and mechanism of Au(III) on SHAR and NSHAR were studied. The Freundlich isotherm model and the Pseudo-second-order kinetic model are suitable for the description of Au(III) behavior meaning that the process belongs to multi-molecular chemical adsorption. Furthermore, adsorption thermodynamic study indicates that the adsorption of Au(III) on SHAR and NSHAR is endothermic and spontaneous. Different from conventional adsorbents, Au(III) are reduced to zero valent gold and deposited on the adsorbent. NSHAR takes only 10 min to reach adsorption equilibrium, and the adsorption capacity is up to 927 mg·g-1 (SHAR needs 50 min with capacity of 1440 mg·g-1). This research provides a new scheme and idea for quickly and efficiently recovering gold.