Abstract:
Platinum group metals in leach slag of spent auto- catalyst by aqueous chlorination residues up to 100-150 g/t,so it is of great practical significance to study the cause of excessive residue in the slag and the process parameters of secondary leaching.The secondary chlorination leaching study of the leaching slag was carried out through orthogonal experiment,and the effects of sulfuric acid concentration,hydrochloric acid concentration,sodium chlorate dosage and temperature on the leaching rate of Pt,Pd and Rh were investigated.The optimized leaching conditions were obtained,that is,the chlorination leaching temperature was 70 ℃,the sulfuric acid concentration was 5 mol/L,the hydrochloric acid concentration was 5.5 mol/L,the amount of sodium chlorate was 35% of the amount of leaching slag.Under the conditions of the process parameters,the leaching rates of platinum,palladium and rhodium were 63.88%,16.92% and 15.00%,respectively.The re-leaching of the primary leach residue indicates:a large proportion of precious metals are oxidized into insoluble metal oxides during catalytic purification process and the process of chlorination leaching of automobile exhaust purification catalyst,which is important reason for the excessive residue of platinum,palladium and rhodium in the primary leaching slag.