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Hydrometallurgy for Three-Way Catalysts

     

The main components of three-way catalysts are as follows: alumina (Al₂O₃) accounts for over 98%, with a palladium (Pd) content of 3000–10000 g/t, platinum (Pt) content of 150–10000 g/t, and rhodium (Rh) content of 150–600 g/t.

The process proceeds as follows: the three-way catalyst is first ball-milled into powder, fed into a reaction vessel, and leached via the aqueous chlorination method in a hydrochloric acid medium; the obtained leachate is then treated via the sodium nitrite complexation process.

This process has multiple drawbacks: it requires secondary leaching, and an excessive volume of leachate will impair the recovery efficiency of precious metals. The leaching residue suffers from incomplete leaching, making it economically unviable to recover valuable components from the residue. The overall process is lengthy and cumbersome: the sodium nitrite complexation step requires multiple cycles to separate platinum, palladium and rhodium, leading to high labor intensity, high reagent costs, and large volumes of waste gas and wastewater. During the hydrolysis of base metals, precious metals are easily entrained in the hydrolysis products. During the separation of Pt, Pd and Rh, the obtained Pt and Pd fractions are often entrained with Rh, while the Rh product contains residual Pt and Pd. The process is difficult to regulate and poses high operational difficulty.

Although this method can directly recover and separate Pt, Pd and Rh, it suffers from low recovery rates, high costs, and a heavy workload for waste gas and wastewater treatment, which is not conducive to environmental protection.

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