A unique sustainable chemical method for the recovery of pure silicon from waste crystalline silicon solar panels

The present work suggests a unique approach for recovering pure silicon from end-of-life silicon solar panels by a direct treatment which does not involve the use of Hydrofluoric Acid (HF). Firstly, the better alkaline treatment between NaOH and KOH was determined. Then, effects of HF etching time and concentration were studied by comparing different etching treatments. Metal impurities such as Ag, Sn, and heavy metal Pb decreased considerably during the acid leaching studies with suitable concentrations. The major impurity Aluminium was reduced significantly by a two-step chemical treatment which ensures minimal silicon loss. Although it is possible to recover 4 N pure silicon by both (with and without HF etching) methods, direct treatment is preferred since the process eliminates potential human health and environmental concerns associated with HF. The recovered silicon samples were analysed by ICP-OES to detect impurity concentration, by XRD for phase identification and SEM analysis for surface morphology. The critical doping impurities, boron and phosphorous dropped considerably to 18.7 ppm and ND in direct treatment. Thus, the study not only provides an alternative way for recovering pure silicon without the use of harmful chemicals such as HF, but it also recommends a 6 M nitric acid leaching treatment before the etching procedure to lower the concentration of metallic impurities. The results are based on treatments with commercial grade chemicals which ensures the scalability of the process at commercial batch. The profit analysis of the recoverable metals was carried out and estimated to be nearly $19 for an 18 kg c-Si module.