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Italian scientists have used hydrometallurgical and electrochemical processes to recover pure silver from solar cells. The proposed technique also uses a method known as electrodeposition-redox substitution, which reportedly increases the silver recovery rate.
Researchers at the University of Camerino in Italy have developed a novel way of recovering silver from solar cells at the end of their useful life.
By combining hydrometallurgical and electrochemical processes, they have been able to recover pure silver with an efficiency of 98%. Hydrometallurgical, or leaching, processes use aqueous solutions to extract metals, while electrochemical processes refer to the use of electrical currents to drive reactions in metals.
“Raw material recovery is crucial for multiple reasons,” the academics explain. “Conventional metal extraction techniques, such as open-pit mining, can inflict substantial damage on the environment and neighbouring ecosystems. Therefore, employing a metal recovery process based on industrial waste can mitigate the environmental impact associated with metal production. In addition, metal recovery typically requires less energy than metal extraction from ore, resulting in reduced energy consumption and carbon emissions, especially if the recovery rate is comparable or higher than that of traditional extraction methods.”
Due to the close values ??of the standard reduction potential of silver and copper, leaching silver particles from PV waste is a challenge. To overcome this, the researchers proposed a combination of base-activated persulfate and ammonia, where the persulfate acts as an oxidizing agent, while the system itself generates a protective, hermetic layer of copper(II) oxide that prevents its own leaching.
To test the proposed process, the researchers performed an experiment consisting of varying the parameters of the leaching process. These were the concentration of ammonia (NH3) in a solution, measured in moles per liter (mol/L); the photovoltaic waste sample, in grams per liter (g/L); potassium persulfate (PPS), in mol/L; and the reaction time, in minutes. The temperature was maintained at 25 ºC and the stirring speed at 300 rpm during all experiments.
“The following conditions were chosen as the best: 0.5 M NH3, 0.2 mol/L PPS, S/L ratio at 50 g/L, and reaction time set at 60 min,” the academics explained. “Two additional experiments were performed under these conditions to assess reproducibility. When combined with the two previous tests of the experimental design, a mean of 85.0±2.6% with a confidence interval of 95% was achieved.”
Despite these good results, the 85% of pure silver recovered was considered insufficient by the research group, which decided to start the electrochemical process. Namely, the electrodeposition-redox substitution (EDRR) approach using a pulsed electrodeposition method. “This technique, previously described in the literature, makes it possible to recover high-purity metallic silver from hydrometallurgical leachates containing copper ions,” the team explained.
The best conditions for silver recovery were obtained with the EDRR method, which achieved an efficiency of 98.7%. “It is noteworthy that this approach proves to be selective in its silver recovery and does not require any chemical additions. This unique feature makes this methodology competitive compared to conventional processes,” the scientists conclude.
The novel method and the results of the experiments were presented in “ Silver recovery from silicon solar cells waste by hydrometallurgical and electrochemical technique ,” ??published in Environmental Technology & Innovation . The study was conducted in collaboration with ORIM, an Italian company specialized in the recovery of metals from solid waste. |
