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recovering precious metals from three-way catalysts

     

The main components of three-way catalysts (TWCs) are as follows: aluminum oxide (Al₂O₃) accounts for over 98% of the total mass, with palladium (Pd) content ranging from 3000 to 10000 grams per ton of catalyst, platinum (Pt) at 150–1000 g/t, and rhodium (Rh) at 150–600 g/t.

There are generally two conventional processes for recovering rare and precious metals from spent (deactivated) three-way catalysts in existing industrial technologies:

1、Pyrometallurgical Process: The spent TWCs are first ball-milled into powder, mixed with lead fume dust and lead-silver slag for granulation, then charged into a blast furnace for smelting and enrichment to obtain crude lead. The crude lead then undergoes cupellation, which yields a Ag-Pd-Pt-Rh alloy. Next, silver and palladium are dissolved from the alloy using nitric acid, and the two metals are separated from the leachate via precipitation. The remaining undissolved solid is treated with aqua regia to leach platinum, which is subsequently extracted from the solution, while the solid residue insoluble in aqua regia is rhodium powder.

2、Hydrometallurgical Process: The spent TWCs are ball-milled into powder and fed into a reaction kettle, where leaching is carried out via aqueous chlorination in a hydrochloric acid medium, and the obtained leachate is processed using the sodium nitrite complexation method.

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