NOVELTY - Sulfur trioxide gas is bubbled into dilute sulfuric acid (S1) to produce 70 wt.% concentrated sulfuric acid. Milled fluorspar ore or fluorspar tailings is mixed with sulfuric acid to produce a liquor of dilute sulfuric acid and fluosilicic acid, and insoluble product calcium sulfate. The obtained concentrated sulfuric acid is mixed with the obtained liquor of sulfuric acid and fluosilicic acid, to obtain silicon tetrafluoride gas and dilute sulfuric acid (S1).    USE - Production of silicon tetrafluoride gas used for producing silicon tetraiodide gas for producing high-purity iodine gas, molten high-purity silicon (all claimed) for manufacturing photovoltaic solar cell, and in aluminum industry and chemical industry.    ADVANTAGE - The silicon tetrafluoride gas enables manufacture of high-purity crystalline silicon with high productivity, without requiring carbon fuels and producing carbon-containing waste gas. The silicon metal obtained using the silicon tetrafluoride gas enables economical manufacture of photovoltaic solar cell.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) production of silicon tetraiodide gas, which involves introducing the silicon tetrafluoride gas into a container with heated iodine-containing salt, capturing silicon tetraiodide from the mixed gas using a cold trap, collecting the product salt, and separating into fluoride-bearing byproduct and iodine-bearing salt for reuse; and    (2) production of molten high-purity silicon and high-purity iodine gas in batches from purification and thermal decomposition of crude silicon tetraiodide gas from separate batch sources, which involves liquefying crude silicon tetraiodide gas, repeatedly adding and removing nonreactive liquid-washing chemicals such as alkane mixtures including hexane, heptane, and octane, to separate impurities by boiling and freezing the crude silicon tetraiodide material mixture into a less crude silicon tetraiodide material and more crude silicon tetraiodide material, subjecting less crude silicon tetraiodide material to fraction distillation, producing pure silicon tetraiodide material and impure silicon tetraiodide material, introducing pure silicon tetraiodide material to a heated crystallization furnace, producing molten silicon metal and iodine gas, collecting iodine gas from the furnace in a cold trap, crystallizing melt of sufficient size, producing semiconductor-grade ingots, sheets, or boules for wafering and further processing.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of apparatus for producing crude silicon tetrafluoride gas.    Mixing tank (10)    Conduits (11,15)    Gypsum (16)    Mixing column (30)    Bubbler (40)