Recovery of Lead in Silicon Solar Modules

Silicon solar modules contain toxic lead (Pb) in the solder. To prevent contamination of the environment, it is imperative all the Pb is recovered from end-of-life silicon solar modules. In this study, acetic acid (AcOH) is shown as a successful leaching agent for Pb from solder and end-of-life silicon solar cells. Hydrogen peroxide (H2 O2) is used to facilitate Pb leaching. To quantify the effect of H2 O2, 3 g of virgin solder ribbon was leached for 24 hours using 16.5 mL of 10% v/v AcOH and different mole ratios of H2 O2 to Pb with and without stirring. It was observed that the amount of mass loss from the solder increases with H2 O2 amount. The leachate with a mole ratio of 1.5:1 H2 O2:Pb and no stirringwas electrowon using two half cells with a potassium chloride (KCl) salt bridge. Gray-colored dendrites were formed on a graphite working electrode by applying a potential of –0.8 V vs the silver/silver chloride (Ag/AgCl) reference electrode. Scanning electron microscopy (SEM) imaging shows large, flat Pb crystallites. Energy dispersive X-ray spectroscopy (EDS) of the dendrites confirms that they are metallic Pb. No tin (Sn) is found in the dendrites, and leaching studies of Sn in AcOH + H2 O2 confirm Sn does not leach into solution. Finally, Pb leaching from an end-of-life silicon solar cell was tested. 25 cm2 of solar cell was milled in liquid nitrogen, then leached in 178 mL of 10% v/v AcOH and 35 mL of H2 O2 for 80 hours with no stirring or heating. Inductively coupled plasma optical emission spectroscopy (ICP-OES) confirms 0.001 M Pb in the leachate, which suggests near complete leaching.