Chemical Treatment of Copper and Aluminum Derived from Waste Crystalline Silicon Solar Cell Modules by Mixed Acids of HNO₃ and HCl

In this study, copper (Cu) and aluminum (Al) particles derived from waste crystalline silicon solar cell modules were etched with mixed acid containing HNO₃ and HCl, and the optimal mixing conditions were examined for the purpose of recovering silicon with high yield. The crushed particles of waste silicon solar cells were used after sieving between 450 and 600 μm particle size. The Cu etching rate decreased with the increasing HCl concentration in the region of HNO₃/HCl ≧ 3.36, whereas it increased at HNO₃/HCl < 3.36. The Al etching rate increased when HCl was added, although it was almost independent of the amount of HNO₃. 99.6% silicon purity was achieved at the treatment time of 30 min. The rate-determining step of Cu and Al etchings was represented by the volume reaction model instead of the surface reaction model. The CuCl coating was observed on the residuals of Cu. The increasing HCl blocked the Cu etching, but the excess Cl⁻ promoted the dissolution of CuCl due to complex formation, corresponding to the regions of HNO₃/HCl ≧ 3.36 and HNO₃/HCl < 3.36, respectively. In the region of HNO₃/HCl < 3.36, the spontaneous complete etching time of Cu and Al was achieved with higher HNO₃ concentration of 8.5–10 mol/L.