[en] Alumothermic reduction of silica from the wastes of a phosphorus industry is suggested. The slag composition consists of four main components, SiO/sub 2/, CaO, Al/sub 2/O/sub 3/ and MgO as well as a few percents of P/sub 2/O/sub 5/, CaF/sub 2/ and other impurities. The presence of fluorine makes favorable conditions for the process because it causes a decreasing of the viscosity and the melting temperature of the slag up to 1200-1300 deg. C. The process is beneficial in energy saving due to exothermic nature of the reaction. The yield of the silicide-contained alloy from this process is about 80% of the weight of a metal reluctant. There are two different ways to get purified semiconductor silicon from the silicide-contained alloy. Those are the chemical refining and silane synthesis followed by the commonly used pyrolysis process. (author)