French researchers have recovered silver, the most valuable material in end-of-life silicon PV modules, in two steps using a reusable leaching solution.
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. The composite still needs downstream refining, such as chemical reduction or electrowinning, to become metallic silver.
Silver makes up only 0.1% to 0.5% of the waste by weight but accounts for about 60% of a module’s economic value, the researchers said, citing earlier literature.
The work was funded by the European Union’s Horizon Europe EVERPV project, which CEA coordinates. The same research group recently reported a mild oxalic acid process for recovering indium from heterojunction cells. Silver has become the main driver of PV recycling economics, and a University of Newcastle team reported 97% silver recovery using froth flotation in January.
The scientists described their findings in “A simplified hydrometallurgical process for silver recovery from photovoltaic waste,” which was recently published in Hydrometallurgy.
Recyclers’ silver recovery rates have risen as the sector has scaled. In data compiled by the International Energy Agency’s Photovoltaic Power Systems Programme (IEA-PVPS), US recycler Solarcycle reports recovering nearly 92% of silver at commercial scale and Italian pilot-scale recycler 9-Tech 90%. Alongside the EU-funded Photorama project, EVERPV is among the EU projects developing multi-step pilot lines that target 95% to 98% metal recovery.
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