Recovery of platinum group metals from aqueous solution by iron-electrocoagulation

Abstract

The recovery of platinum group-metals (PGMs) has attracted increasing attention owing to their scarcity, economic importance, and criticality. Traditional techniques for PGM recovery often involve the use of toxic reagents and require strict extraction conditions, posing challenges for their implementation in complex environments. In this paper, a novel method based on iron electrocoagulation (Fe-EC) is proposed for PGM extraction. The Fe-EC process generates iron (hydr)oxide flocs in situ, which spontaneously and uniformly adsorb and reduce PGM ions. The selectivity of PGM recovery is attributed to the higher electronegativity and standard reduction potential of PGM ions compared to base metal ions. Efficient extraction of Pt, Pd, and Rh ions from aqueous solutions was achieved using Fe-EC, with extraction efficiencies of 81.26 %, 81.32 %, and 99.66 %, respectively. These results were obtained at a voltage of 2 V and residual concentrations of 0.3072, 0.0051 and 0.0049 mg L–1. TEM-EDS and XPS characterizations of the Fe-EC flocs showed that Pt, Pd, and Rh were present in the elemental form particles. The extraction performance of base metal such as Ni, Zn, Mg and Mn ions by Fe-EC was found to be poor, with minimal reduction to elemental form. Finally, the Fe-EC flocs were subjected to acid washing and filtration, resulting in the selective recovery of Pt, Pd, and Rh products with high purities of 97.43%, 97.12%, and 97.92%, respectively. This study presents a new and environmentally friendly method for the recycling of PGMs, offering a promising approach for sustainable PGM recovery.