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

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Description/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 %