energies Article Size- and Surface-Dependent Solubility of Cadmium Telluride in Aqueous Solutions Renate Zapf-Gottwick 1,*, Matthias Zorn 1, Jessica Nover 1, Michael Koch 2, Carolin Feifel 2 and Jürgen H. Werner 1 1 Institute for Photovoltaics and Research Center SCoPE, University of Stuttgart, 70569 Stuttgart, Germany;
[email protected] (M.Z.);
[email protected] (J.N.);
[email protected] (J.H.W.) 2 Institute for Sanitary Engineering, Water Quality, and Solid Waste Management, University of Stuttgart, 70569 Stuttgart, Germany;
[email protected] (M.K.);
[email protected] (C.F.) * Correspondence:
[email protected]; Tel.: +49-711-685-69225 Abstract: Due to the toxicity of cadmium (Cd) and the scarcity of telluride (Te), CdTe-based photo- voltaic modules have been under discussion during the last few years. In particular, the stability of CdTe in aqueous solutions is under debate. Here we show that the stability of CdTe depends not only on the pH of water-based solutions but also on size and surface treatment of CdTe parti- cles. We compare milled module pieces with CdTe powders of different particle size. The leaching of CdTe is conditioned by the outdiffusion of Cd and Te at the interface between CdTe particles and the aqueous solution. The smaller the particle size, the faster the leaching. Therefore, milled module pieces decompose faster than CdTe powders with relatively large grains. We observe a dependence on time t according to t0.43. The room temperature diffusion coefficients are calculated as −17 2 −17 2 DCd ≈ 3 × 10 cm /s for Cd, and DTe ≈ 1.5 × 10 cm /s for Te in pH4.