| A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized for this purpose. These include purification of SF, reduction by magnesium, and post-reduction acid leaching. SF is first subjected to an initial leaching with HCl to remove soluble impurities. Reduction was carried out successfully in a sealed reaction chamber with varying Mg/SF ratios, temperature and time. Mg/SF ratio, temperature and time affected the production of silicon from SF with the intermediate compounds Mg2Si and Mg2SiO 4 also forming. Suitable reduction conditions were found to be within the temperature range 750-850°C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels particularly low boron content can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon. |
