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MAGNESIUM, TITANIUM, RARE METALS, SEMICONDUCTORS
ArticleName Salt crystallization with the gaseous waste utilization by the soda solution in production of trichlorosilane and polycrystalline silicon
ArticleAuthor Apanasenko V. V.
ArticleAuthorData
OJSC “Giredmet”
V. V. Apanasenko, Leading Researcher, e-mail: asla_new@rambler.ru
Abstract

There is considered the process of the waste gas purification by sodium carbonate solution in the range of temperatures from 0 to 60 oC. The waste gas contains the hydrogen chloride, trichlorosilane, silicon tetrachloride and dichlorosilane with 10 and 17% wt. It is established by the calculation, that the crystallization of obtained sodium hydrocarbonate might take place in the course of process. The amount of precipitated NaHCO3 grows with the increasing of Na2CO3 concentration in the initial solution and decreases with the growth of temperature and extremely depends on degree of soda use in the process of gas purifying. In the generated suspension, the peak value of weight of solid salts fraction reaches, when soda is half used. That means that sodium carbonate completely transforms into hydrocarbonate and makes up to 10,9% (conditions: 17% of soda solution, t = 0 oC, HCl is the only hazardous substance in waste gases). At the temperature 60 oC the maximum of salt crystallization decreases to 5,4% (other conditions are the same). There are computed the properties such as density and viscosity for obtained solutions and suspensions (when solid salt is precipitated). The flows' density and viscosity decreases, with increasing of soda use degree, which improves the mass exchange in a neutralization process. There is formed the precipitate of silicic acid, along with solid sodium hydrocarbonate in a purifying process of waste gases, which contain clorosilanes. The amount of this precipitate grows with the increase of the degree of soda use and thus increases the lump of precipitation. It is also shown that under the temperature less than 20 oC, Na2CO3·10H2O might precipitate as well. The amount of the precipitate of sodium carbonate decahydrate is calculated in terms of the temperature, soda concentration and degree of its use. The formation of solid salt phases might significantly complicate the utilization process of the waste gas in production conditions. It has to be taken into account in choosing the equipment for gas purifying system.

keywords Gaseous wastes, neutralization, utilization, gas purifying, trichlorosilane, chlorosilanes, hydrogen chloride, soda, sodium hydrocarbonate, crystallization
References

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