Gold recovery from ammonia-thiosulfate leaching solution assisted by PEI-functionalized magnetite nanoparticles

Abstract

This work describes a novel process for gold recovery from ammonia-thiosulfate leaching solution utilizing polyethylenimine (PEI) coated magnetite nanoparticles (PEI-MNPs). In this process, PEI-MNPs were synthesized by electro-oxidation method and in situ surface coverage of magnetite with PEI. Characterization of the material produced was then carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal analysis (TGA), zeta potential measurements, and Raman and infrared spectroscopies. PEI-MNPs developed a surface electric charge of +21.5 mV at pH = 9, which allowed the Au(S2O3)23− complex anion to be caught from the gold/ammonia-thiosulfate solution by coulombic attraction. At the last stage, the adsorbed gold complex was chemically reduced to metallic gold and desorbed from the PEI-MNPs by an ascorbic acid solution. Finally, the PEI-MNPs and metallic gold could be separated from each other by the action of an external magnetic field. The integrity of the PEI-MNPs was preserved after the process, indicating that the magnetic material is ideally suited for recycling without additional regeneration steps.