An Integrated Thermal and Hydrometallurgical Process for the Recovery of Silicon and Silver from End-of-Life Crystalline Si Photovoltaic Panels.

This work proposes an integrated process flowsheet for the recovery of pure crystalline Si and Ag from end of life (EoL) Si photovoltaic (PV) panels consisting of a primary thermal treatment, followed by downstream hydrometallurgical processes. The proposed flowsheet resulted from extensive experimental work and comprises the following unit operations: Shredding the PV modules to − 4 mm, after the removal and recovery of aluminum frames, junction boxes and copper cables. Delamination of the Si cells from the front soda-lime protective glass, through a thermal treatment at 550 °C for 15 min, in excess of air, in order to disintegrate the encapsulating organic material (ethylene vinyl acetate (EVA)) and the polyvinyl fluoride (PVF) polymer backsheet (Tedlar®). Separation of the detached Si flakes from the front glass and the "ash residue" and classification via mechanical screening by a perforated trommel rotary screen equipped with square wire mesh sieves. Further grinding of the recovered Si flakes by ball milling to − 90 μm, in order to increase the specific surface area, prior to the downstream hydrometallurgical process. Quantitative leaching of Ag and Al from the Si flakes in one stage by HNO₃ at ambient temperature. Alternatively, acid leaching in two stages can be applied: initially by H₂SO₄ for Al quantitative extraction and subsequently by HNO₃ for Ag quantitative extraction at ambient temperature. In order to remove the anti-reflection coating, etching of the leached Si flakes by 2.5 M NaOH has been proven efficient and crystalline silicon of high purity was recovered. Separation and precipitation of Ag as AgCl or alternatively, Ag electrowinning from nitrate solutions and Al precipitation via solution neutralization. [ABSTRACT FROM AUTHOR]