Method for producing polycrystalline silicon from phosphorus slag

Abstract

The utility model relates to the field of chemical technology and industrial ecology, namely, to methods for producing polycrystalline silicon and methods for processing slags. The method includes preliminary addition of magnesium carbonate to the phosphorus slag in an amount of 25 - 45% of the amount introduced into the molten phosphorus slag, aluminum, removing the alloy of silicon with aluminum and magnesium formed during aluminothermic reduction, cooling it, grinding it, introducing it into a vacuum unit in which it is treated with an aqueous solution of hydrochloric acid, directing the silane released in this process into distillation columns for its purification, thermal decomposition and deposition on heated silicon rods or on wafers prepared for further assembly of solar cells, capture or combustion of the released hydrogen, periodic depressurization of the vacuum unit, removal of the precipitate rich in valuable magnesium and sending it to the beginning of the technological process, use of the material remaining in the melt, which crumbles after cooling, as high-alumina cement and collection in cylinders, the phosphine released in the process. What is new is that aluminum is added to the molten slag in a ratio of 1: 3, and the silicon floating on top of the melt is removed, cooled, crushed, introduced into a vacuum unit through which dry hydrogen chloride is passed, and the trichlorosilane and silicon tetrachloride released in this process are sent to distillation columns located in the same vacuum system for purification, after which the purified trichlorosilane and silicon tetrachloride enter the reactors located under vacuum, where hydrogen is supplied for hydrogen reduction and simultaneous deposition of polycrystalline silicon on heated silicon rods, the hydrogen chloride released in the process is captured and sent to a vacuum unit