Researchers at France’s Alternative Energies and Atomic Energy Commission (CEA) have developed a leaching route that strips base metals from end-of-life solar cell waste in under 10 minutes while leaving the silver behind, avoiding the nitric acid used in most current recovery processes.
The process combines selective leaching with density-based separation and recovers more than 98% of the silver at laboratory scale, the researchers said. It produces a silver and silver chloride composite of 97.2% purity, and the team has validated it in a 20-liter pilot reactor.
Most hydrometallurgical routes dissolve silver in nitric acid and then precipitate it as silver chloride, a method that generates nitrogen oxides and nitrate-rich effluents, the researchers said. Alternatives such as methanesulfonic acid perform comparably but face high reagent costs and complex regeneration. Because the CEA process leaves the silver undissolved, the leachate can be reused over several cycles.
The leaching step uses 3 M hydrochloric acid with 10% hydrogen peroxide at 80 C. It dissolves more than 98% of the aluminum, copper, lead and zinc in the waste. Rather than dissolving, the silver forms an insoluble silver chloride shell around a metallic core, which shields it from further attack and limits silver losses during leaching to 1.7%. A density-based separation step at a 10% solid-to-liquid ratio then separates the silver from the silicon, leaving residual impurities below 0.5% by weight.
The feedstock is a metal-rich powder produced by sanding delaminated end-of-life modules layer by layer, a mechanical process the group described in a separate paper.
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