Uptake and Recovery of Gold from Simulated Hydrometallurgical Liquors by Adsorption on Pine Bark Tannin Resin

Cr-Based MOF for Efficient Adsorption of Au at Low Concentrations

The efficient enrichment and selection of Au are crucial for gold recovery. The adsorption technology is considered to have potential due to the advantages of operation simplicity and green processability. Nevertheless, the poor Au selectivity at low concentrations in complex solutions limits the further application of the adsorption technology. In this work, a novel Cr-based MOF adsorbent was successfully synthesized using 1,2,4-triazole and 4-aminobenzoic acid as ligands. Benefitting from the surface positive charge and extensive chelation and reduction sites, the novel Cr-based MOF exhibited a total adsorption capacity of up to 357 mg/g and excellent adsorption selectivity toward Au(III) in the complex metal mixed solutions, such as simulated sewage ash waste liquid and actual e-waste leachate. Furthermore, the adsorption kinetics, isotherms, and thermodynamics were discussed in depth for investigating the adsorption mechanisms of the MOF. The PXRD and XPS analyses reveal that the adsorption process involves complexation, redox, and electrostatic interactions. We believe that this study of novel Cr-based MOF adsorbents for efficient Au adsorption is meaningful for further application in the gold recovery technology from e-waste.

Recovery of Au from dilute aqua regia solutions via adsorption on the lyophilized cells of a unicellular red alga Galdieria sulphuraria: A mechanism study

The high electrical conductivity, chemical stability, and low toxicity of elemental Au make it a highly valuable resource. However, wastewater produced during the mining, utilization, and disposal of Au inevitably contains small amounts (10-40 mg L^-1) of Au, thus posing environmental risks. It is too acidic to be treated with inexpensive and eco-friendly bioadsorbents previously studied for the remediation of less acidic effluents. Herein, lyophilized Galdieria sulphuraria cells are shown to directly adsorb Au from simulated Au-containing wastewater with a total acid concentration of 4 M, achieving an adsorption capacity of 35 ± 2.5 mg g^-1 Au after 30-min exposure and a selectivity that exceeds that of an ion-exchange resin and is comparable to that of activated carbon. Additionally, Au adsorbed on these cells is more easily eluted than that adsorbed on the ion-exchange resin or activated carbon. Detailed characterizations reveal that Au accumulates on the surface of lyophilized cells, where it is mainly present as AuCl₄^- and not as Au⁰, in contrast to a previously proposed adsorption mechanism. Thus, our work provides valuable insights into the mechanism of Au adsorption on biomaterials and paves the way to the cheap and eco-friendly recovery of Au from acidic wastewater.