All 3 waste products, Si-kerf from wafer sawing, graphite from crystallisation furnaces, and silica from melting containers, are recovered with a rate >95%. A continuous drying equipment has been successfully commissioned and tested at RESITEC (pilot A) as an alternative to the current batch drying process for silicon kerf filter cake, yielding moisture levels < 1 wt% with capacity ranging 876-2600 t/y, removing particularly aluminium, nickel and iron impurities. 4 pilot campaigns at SINTEF were conducted in the submerged arc furnace (SAF) with capacity of 250 t/y converting Si-kerf waste in the form of briquettes, silica waste in the form of self-reducing briquettes and in the form of lumps into metallurgical grade silicon. The produced silicon has a purity and characteristics close to the metallurgical grade silicon, commercial traded commodity “metal silicon #553”, that has a current market value of 1585 USD/metric tons (ex. VAT). Thus, the material could directly enter the metallurgical and chemical route (Siemens process) to be further processed into solar-grade and electronic grade polysilicon, respectively. A combined system, based on powder feeding, melting, solidification, and granulation has been developed and commissioned at ROSI. The powder feeding unit has a capacity of 500 t/y, the melting and granulation unit a capacity of 50 t/y. The granulation unit includes the continuous production of liquid silicon droplets thanks to a silicon-specific drip nozzle design. Production of recycled silicon from kerf at a flow rate of 1 kg/h has been demonstrated, offering 4N purity level and a drastic reduction in C and O concentration (respectively 110 and 15 ppm wt.).
A chemical reactor converting Si-kerf and other silicon waste types with a capacity of 87 t/y was successfully commissioned at LUX producing silica (waterglass) and green hydrogen with suitable properties entering different market applications. Besides Si-kerf, alternative sources from EOL-PV and the semiconductor industry are also considered to be valuable waste sources. For every kg of cell scrap, 11 grams of silver can be recovered, with a current value of around €9!
