Abstract
In the current study, platinum—present as a negligible component (below 1 ppb, the detection limit of the HR-ICP-MS at the dilutions used) in real industrial hydrometallurgical process solutions—was recovered by an electrodeposition–redox replacement (EDRR) method on pyrolyzed carbon (PyC) electrode, a method not earlier applied to metal recovery. The recovery parameters of the EDRR process were initially investigated using a synthetic nickel electrolyte solution ([Ni] = 60 g/L, [Ag] = 10 ppm, [Pt] = 20 ppm, [H2SO4] = 10 g/L), and the results demonstrated an extraordinary increase of 3 × 105 in the [Pt]/[Ni] on the electrode surface cf. synthetic solution. EDRR recovery of platinum on PyC was also tested with two real industrial process solutions that contained a complex multimetal solution matrix: Ni as the major component (>140 g/L) and very low contents of Pt, Pd, and Ag (i.e., <1 ppb, 117 and 4 ppb, respectively). The selectivity of Pt recovery by EDRR on the PyC electrode was found to be significant—nanoparticles deposited on the electrode surface comprised on average of 90 wt % platinum and a [Pt]/[Ni] enrichment ratio of 1011 compared to the industrial hydrometallurgical solution. Furthermore, other precious metallic elements like Pd and Ag could also be enriched on the PyC electrode surface using the same methodology. This paper demonstrates a remarkable advancement in the recovery of trace amounts of platinum from real industrial solutions that are not currently considered as a source of Pt metal.
Highlights
In hydrometallurgical industries, significant amounts of impurities[1−5] and some additives[6−8] are present in the base metal (Cu, Ni, Zn)-rich process solutions
The cyclic voltammograms using pyrolyzed carbon (PyC) electrode were determined before the electrodeposition−redox replacement (EDRR) measurements in order to study the characteristic oxidation and reduction peaks of Pt, Ag, and Cu as well as to determine the optimum deposition (E1) and cutoff (E2) potentials for Pt enrichment (Figures 1 and 2)
The EDRR parameters in synthetic solutions were optimized for Pt recovery, primarily E1, t1, and n
Summary
Significant amounts of impurities[1−5] and some additives[6−8] are present in the base metal (Cu, Ni, Zn)-rich process solutions. Most impurities are other base metals,[9,10] which subsequently end up in the process bleed solution or leach residue, and the recovery can be a challenge as processing consumes additional chemicals and energy.[11,12] In addition, noble metals like Pt, Pd, and Ag11 can be present in these types of solutions, albeit at much lower concentrations It is widely known[13] that minor amounts of noble elements can be found in the final products of hydrometallurgical processing like copper, nickel, or zinc cathodes; i.e., the noble metals are “diluted” within the bulk metal. According to circular economic principles, and more importantly due to the ever-increasing need for critical precious metals, it is essential that the loss of even minor amounts of noble elements into bulk metals be avoided
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