No abstract

Refining of metallurgical-grade silicon was studied using a process sequence of slag treatment, controlled cooling, and acid leaching. A slag of the Na 2 O-CaO-SiO 2 system was used. The microstructure of grain boundaries in the treated silicon showed enhanced segregation of impurities, and the formation of CaSi 2 and other Ca-rich phases. Boron and phosphorus were found in the grain boundary phases of silicon after the slag treatment and were successfully removed together with most of the metallic impurities by acid leaching. The interaction between silicon and slag and the distribution of impurities are discussed. A novel mechanism of the refining approach is proposed, based on the microstructure of silicon and the analysis of impurities at each refining step. Parallel processes of slag refining, segregation, and solvent refining were observed, which explains the relatively high efficiency of the proposed refining technology. The investigated combination of refining processes followed by acid leaching has great potential as an efficient and cost-saving route for upgrading metallurgical-grade to solar-grade silicon.

No abstract

The efficiency of acid leaching as a low-cost refining method of metallurgical grade silicon (MG-Si) is determined by the microstructure of silicon. In the present work the influence of microstructure of MG-Si on its leaching behaviour was studied in order to explore the potential of this method in achieving solar grade purity of silicon. The microstructure of silicon was modified by alloying with 3-10 wt-% of calcium, and the influence of the concentration of alloying elements and the solidification conditions on the leaching efficiency was evaluated. It was shown that the major impurity and its location determine the preferred leaching agent. A mechanism of removal of metallic and non-metallic impurities was proposed. Control of the alloying process resulted in enhanced removal of the major part of the impurities, including phosphorus.

No abstract