IDENTIFICATION AND ANALYSIS OF SLAGS PRODUCED DURING SILICON MANUFACTURE

Methods for the identification and analysis of the components of silic on smelter slags are described. The silicon content was determined aft er removal of silica and aluminosilicates with hydrofluoric acid. The silicon carbide content was determined after removal of all other spec ies in the slag by digestion with an acid mixture of hydrochloric acid hydrofluoric acid, nitric acid, and perchloric acid, which also allow ed Sor the determination of the elemental analysis of the slag by indu ctively coupled plasma-atomic emission spectroscopy. The phases detect ed in the slags were silicon, alpha-silicon carbide, beta-silicon carb ide, alpha-quartz, alpha-cristobalite, anorthite, a magnesium silicate phase, Mg2.85Al5.7S10.3O32, and calcium carbonate, all in an amorphou s matrix. X-ray diffraction and scanning electron and optical microsco py were used to identify the phases and validate the steps in the anal ytical procedure. An accurate knowledge of the slag phase constitution is of particular importance in considering the economics of the recov ery of silicon from the slag.