China-based researchers have introduced a new eco-friendly method to extract valuable silver from retired solar panels without using toxic acids. The process dips solar cells into a molten mixture of sodium and potassium hydroxide salts. This molten salt weakens the coating on the silicon panel, allowing the silver wires to peel off intact as pure metal. Ningxia University researchers recovered up to 97% of the silver while limiting damage to the underlying silicon wafer to just 2.6%.“These findings clarify the mechanisms of acid-free, low-loss precious-metal recovery from crystalline silicon photovoltaic materials,” the team noted in the study paper.Molten salt recipeThe first generation of commercial solar panels is reaching the end of its 25- to 30-year lifespan. The aging infrastructure is a major trash problem, but also a massive treasure hunt. Silver accounts for less than 0.03% of a retired solar panel’s weight, but it drives nearly half of its monetary value. Recovering that precious metal hasn’t been eco-friendly.A Chinese team designed a cleaner alternative. The new laboratory-scale method uses a molten mixture of sodium hydroxide and potassium hydroxide to pop silver wires off dead solar cells. Usual solar recycling uses acid leaching. Nitric acid dissolves solid silver into silver ions, leaving recyclers with toxic nitrogen oxide emissions, acidic wastewater streams, and a complex chemical recovery process. The molten salt strategy skips that chemical detour entirely.The hot salt bath targets the solar cell’s silicon nitride (SiNx) passivation layer rather than dissolving the metal directly. It etches the layer, weakens the adhesive bond at the interface, and lets intact metallic silver wires slide off.Eco-friendly method The process is fast. At 230 °C for 150 seconds, the system recovered 94.34% of the cell’s silver while wiping away the SiNx coating. Under peak conditions, total silver recovery reached 97.11%.Protecting the underlying silicon wafer proved to be a difficult hurdle. Early molten salt methods failed to keep the salt bath from corroding the valuable silicon substrate. The research team limited this damage after identifying the exact chemical mechanism driving the corrosion.Hydroxide ions attack the exposed silicon as soon as the protective silicon nitride layer strips away. This reaction converts the silicon into soluble silicates, leaving behind tiny pits across the surface. Researchers limited total silicon loss to 2.62% at 230 °C for 100 seconds by precisely controlling the bath temperature and exposure time.“At 230 °C for 150 s, Ag recovery reached 94.34 %, and the SiNx passivation layer was effectively removed, maximum Ag recovery was 97.11 %,” the study reported. Although the process currently operates only at a lab scale, understanding the mechanics of direct silver detachment could provide a practical solution for green industrial recycling. It offers an acid-free, low-loss approach to recovering precious silver from retired silicon solar panels without damaging the underlying substrate.This approach arrives at a key moment, preparing the global solar market for the massive influx of panel waste expected in the coming years.The study findings were published in the Journal of Cleaner Production on October 28.