Purification of Silicon Through a Hydrometallurgical Process

Abstract

The demand for cleaner energy is rising because of the global warming and because of the access of fossil energy one day will come to an end. For encounter this demand, solar cells have a huge potential. Today the market for solar PV cells is rising quickly, and the need for silicon as production material is rising accordingly. Today most of the silicon is produced through an energy intensive process with large consumption of toxic chemicals, in addition to that the silicon produced is purer than required for solar cells. For production of silicon it has therefore been found that a metallurgical refining route will be less energy consuming and environmentally friendly. A metallurgical refining route often consist of several methods, where one of them can be acid leaching. Acid leaching is a method good upon removal of most metallic impurities found in silicon, but the process has also showed potential for removal of boron and phosphorous when the silicon is alloyed with a refiner element before leaching. In this study MG-Silicon and Silgrain was alloyed with magnesium, and the effect of refiner element, leaching conditions and double allying were studied. It was found that the Mg worked good as refiner element for removal of P in addition to all the metallic impurities: Fe, Al, Ti, Ca... The leaching process was found to be dependent on the leaching conditions, were 10 % HCl was found to be the optimal acid and concentration, and the removal degree increased with temperature and leaching time. It was also found that a double alloying process with 10 hours leaching time removed the metallic impurities very well, and the content of P is close to the requirement of SoG-Si. The removal of P was observed to be up to ~91%, with an overall purification up to ~99%.