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 HNO 3 or 1 mol dm -3 HCl, at a stainless steel and a vitreous carbon electrode, at 25°C. 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 the selective separation of the two metals. At a stainless steel cathode in 1 mol dm -3 HNO 3 , 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 HNO 3 , palladium ions were preferentially removed at 0.15 V versus SHE at an average cumulative current efficiency of 57%.

Mass transfer at a rotating tubular packed bed of woven screens in relation to electrochemical and catalytic reactor design

“…The rotating cylinder electrochemical reactor is one of the most important reactors which has been used widely in practice for processing dilute solutions such as those encountered in waste water treatment and electroorganic synthesis where diffusion controlled reactions are involved [1][2][3][4][5][6][7][8][9][10][11]. The widespread use of the reactor is attributed to merits such as the high mass transfer coefficient, the uniform current and potential distribution, the low floor space occupied by the reactor and the possibility of continuous operation at low feed rate in order to increase the residence time, the high rate of mass transfer and the high residence time would increase the degree of conversion per pass.…”