The use of a rotating cylinder electrode to selective recover palladium from acid solutions used to manufacture automotive catalytic converters

Abstract

The reduction of palladium, rhodium and neodymium ions at concentrations of 0.94, 0.97 and 0.69 mol dm-3, respectively was studied in 1 mol dm-3 HNO3 or 1 mol dm-3 HCl, at a stainless steel and a vitreous carbon electrode, at 25 ºC. At a vitreous carbon electrode in a solution containing rhodium and palladium ions in 1 mol dm-3 HCl electrolyte, the reduction of metal ions occurred at a similar potential to the formation of hydrogen gas, which impeded selective separation of the two metals. At a stainless steel cathode in 1 mol dm-3 HNO3, palladium deposition occurred at a potential ? 0.35 V less negative than that of rhodium allowing the selective recovery of palladium. Neodymium ions were not electroactive in acidic chloride or nitrate media at pH 0. Using a solution obtained from a catalytic converter manufacturer containing palladium, rhodium and neodymium ions in 1 mol dm-3 HNO3, palladium ions were preferentially removed at 0.15 V vs. SHE at an average cumulative current efficiency of 57 %

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ORCID for Carlos Ponce de Leon: orcid.org/0000-0002-1907-5913

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