Fluorspar/Iodide process for reduction,purificatioin, and crystallization of silicon

Abstract

Method and apparatus for producing molten purified crystalline silicon from low-grade siliceous fluorspar ore, sulfur trioxide gas, and a metallic iodide salt. Method involves: (1) initially reacting silicon dioxide-bearing fluorspar ore and sulfur trioxide gas in sulfuric acid to create silicon tetrafluoride gas and fluorogypsum; (2) reacting the product gas with a heated iodide salt to form a fluoride salt and silicon tetraiodide; (3) isolating silicon tetraiodide from impurities and purifying it by washing steps and distillation in a series of distillation columns; (4) heating the silicon tetraiodide to its decomposition temperature in a silicon crystal casting machine, producing pure molten silicon metal ready for crystallization; and pure iodine gas, extracted as liquid in a cold-wall chamber. The system is batch process-based, with continuous elements. The system operates largely at atmospheric pressure, requiring limited inert gas purges during batch changes.

Dependencies are inferred from the claim text.