Scientific-Technical Center “Silicon” of “Polysilicon plant “Crystall” LLC, Yelabuga, Russia:

V. A. Kozhemyakin, Leading Researcher, e-mail: kozhemyakin_va@mostovik.ru
A. M. Chapygin, Leading Researcher

“Giredmet” JSC, Moscow, Russia:
A. N. Pochtarev, Head of Laboratory

This article describes the results of laboratory researches of absorption of silicon tetrachloride by soda solution. The absorption process simulates the neutralization of waste gases (“abgases”) of production of silicon tetrachloride and polycrystalline silicon. “Abgases” are the mixture of silicon tetrachloride and technical argon vapours, which is fed in a vessel (barboter) with soda solution. Partial pressure of silicon tetrachloride in the vapours-gas mixture is 150–380 mm HG. Initial concentration of the soda solution is 15.2–16.2% of Na₂CO₃. The absorption of silicon tetrachloride by soda solution is finished at the value of pH = 7. Resulted suspend is separated by filtration into two parts: sodium chloride brine (~20% of NaCl) and silica hydrotation sediment [Si(OH)₄]·nH₂O. The sediment contains 73.5–84.5% of Н₂О. The silica sediment is filtered under vacuum (antigravity) from initial solution (sodium chloride brine). The speed of filtration of initial solution is 0.56–1.5 m³/m² per hour. In order to remove solubility salts (NaCl, NaHCO₃), the sediment is washed by distillated water. The speed of filtration of the wash water is 0.27–0.55 m³/m² per hour. The physical-chemical properties of powder of silicon dioxide, dried up at 105 ^oC, corresponds to the following grades of silica white: BS-100 (БС-100), BS-120 (БС-120) (State Standard 18307–78). The dry powder includes the following substances: 86.2–87.5% of SiO₂; 0.09–0.16% of Cl^– and 0.2–0.8% of Na₂O. Gravimetric density of silicon dioxide is 90–115 g/dm³ (not densed) and 130–195 g/dm³ (densed). The sodium chloride (solid salt or brine), received from the waste product of gas purification, is suitable as raw materials for electrolytic manufacturing of chlorine for recycling in production of synthesis of HCl-gas, chlorine, thrichlorsilane and polycrystalline silicon.

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