Recovering Palladium from Chloridizing Leaching Solution of Spent Pd/Al2O3 Catalyst by Sulfide Precipitation

Abstract

The recovery of palladium from the chloridizing leaching solution of spent Pd/Al2O3 catalyst was studied mainly by the sulfide precipitation tests and chemical composition analysis, and the relevant mechanism was also investigated in this paper. Results showed that when NaOH was previously added to adjust the leaching solution to pH increasing from 1.21 to 4, the recovery of palladium was nearly 100% whilst the dosage of precipitant Na2S decreased by 75% comparing with direct precipitating by Na2S solution without previously adjusting the initial pH. However, at pH > 11.0, the excessive addition of NaOH resulted in the formation of some Pd(OH)2 from [PdCl4]2−, then the recovery rate of palladium was 98.18%. When the palladium lixivium concentration is too low or the sodium sulfide concentration is overhigh or the adding rate of sodium sulfide solution is too fast, [PdCl4]2− could be transformed into soluble [PdS2]2− because of partial over-dosage of sodium sulfide. Under the appropriate control of the above three factors, nearly 100% of palladium could be recovery successfully.