Sustainable industrial technology for recovery of Al nanocrystals, Si micro particles and Ag from solar cell wafer production waste

Solar cell wafer industry is classified as one of the most complex electronic industries that produces a significant proportion of waste in the form of broken/damaged cells or cells having some defects in their chemical composition that can generally be called Rejected Solar Cell Wafers (RSCWs). Although these wastes contain valuable metals (e.g. Silver (Ag), Aluminum (Al), and Silicon (Si)), unfortunately there is currently no obvious strategy for recovery of these metals and landfilling is considered the primary option for their disposal what can lead to serious soil contamination and human health risks if the waste is not treated properly. This research aims to develop an integrated technology to recover all these metals as high added value nano/micro products with total recovery rate > 98%, thus achieving the sustainability and goals of circular economy. Milling process was used as a pretreatment to break the chemical and mechanical bonds between Ag electrodes, Al electrode, and Si layer of RSCW samples to increase the surface area for reaction. The pretreatment was followed by leaching process using Nitric Acid (HNO3) with concentration > 60% to dissolve Ag and break the chemical bonds between spherical Al microparticles in the Al paste layer. Thus the particles were separated and only a small amount of the Al was dissolved from the surface of the particles since due to the high concentration of HNO3 passivation of Al occurred, forming a thin layer from Aluminum Oxide (Al2O3) that prevented the further dissolution of Al. Under the effect of soundwaves, the separated particles began splitting further and exfoliate into Al nanocrystals. After that, micro-filtration process was used to extract Si microparticles from the leached solution and the extracted particles were purified by etching process using Hydrofluoric acid (HF) to remove Silicon Nitride contamination. Centrifugal process was used to separate Al nanocrystals from the leached solution. Finally, Hydrochloric acid (HCl) was added to the remaining saturated solution to recover AgCl. SEM-EDS, FTIR, ICP, XRD, and TEM were used to analyze and examine the selected wafers and recovered materials. Also, the economic performance, sustainability, and CO2 emissions of the advanced technology were evaluated.