Efficient platinum cementation via galvanic interactions promoted by physically interconnected zinc-graphite plates in an acidic HClO4-HCl medium

Cementation using aluminum or zinc powders is the predominant technique for depositing platinum group metals (PGMs) from concentrated solutions, which are obtained by leaching natural ores or secondary raw materials with a combination of strong acids. Nevertheless, the efficiency of PGMs cementation tends to decline when alternative lixiviants are employed. This study introduces a simple yet highly effective technique for recovering platinum (Pt) ions through cementation, utilizing galvanic interactions between interconnected zinc-graphite plates in an acidic medium comprising HClO₄ (perchloric acid) and diluted HCl (hydrochloric acid) while varying operational conditions. The results indicate that Pt recovery significantly improves when temperature and concentrations of dissolved Pt and HClO₄ are increased to 15–50 °C, 5–15 ppm, and 0.1–0.5 M, respectively. Additionally, the findings reveal that at 50 °C, Pt recovery exceeds 95 %, with approximately 15 min needed to reach this peak recovery. The cementation reaction exhibited pseudo-first-order kinetics, with the rate-determining step being predominantly chemically controlled, as evidenced by activation energies exceeding 36 kJ/mol. Morphological analyses of the studied deposits confirmed successful Pt cementation on the surfaces of the graphite plates, revealing a consistent relationship between the size of the cemented areas and the percentage of Pt recoveries. Finally, energy dispersive X-ray spectroscopy (EDX) analyses indicated a high Pt metal content within these deposits, reaching nearly 90 % without washing and over 96 % when graphite plates are washed with deionized water after the cementation experiments. Additionally, X-ray photoelectron spectroscopy (XPS) analyses confirmed the effective cementation of Pt on the graphite plates.