In industrial HF production, there is the issue of hydrofluorosilicic acid as a by-product
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This post was last edited by *nyang3390 on 2011-1-14 07:08. In industrial HF production, SiF4 is absorbed using a diluted HF solution, resulting in the formation of fluorosilicic acid. However, in actual production processes, fluorosilicic acid tends to crystallize easily, causing blockages in the system; in severe cases, this can lead to environmental accidents. What is the concentration at which fluorosilicic acid is most stable, and are there any effective methods to prevent crystallization?
By the way, our unit’s standard approach is to use HF gas to purge the clogged exhaust tower; after clearing the blockage, the absorbent solution is prepared anew, with the concentration of fluorosilicic acid generally kept around 35%, yet blockages still occur. .
Theoretically, hydrogen fluoride reacts with silicon fluoride to form fluorosilicic acid, but this acid decomposes at room temperature. Fluorosilicic acid is most stable at around 13% concentration; however, if the concentration is only 13%, manufacturers might be reluctant to accept it for production purposes! Why do you have to use hydrogen fluoride for absorption? Is it planned to sell the by-products again? If it cannot be sold, sodium hydroxide can be used for absorption. For safety reasons, a secondary buffer tank should be employed, as sodium hydroxide ensures thorough hydrolysis!
Industrial production focuses on costs (after all, the by-product fluorosilicic acid is easy to sell), and using alkali for neutralization is too wasteful; no one wants 13% fluorosilicic acid – we usually use 35% concentration. Thank you, brother LS.
As a supplementary note, the crystalline substance is likely to be H2SiF6·2H2O. Crystallization of this substance is problematic; unless the HF concentration in the aqueous fluorosilicic acid solution is high, but that would be wasteful. I’m thinking about ways to prevent this substance from crystallizing. . . . . . . . . . . .
Help. . . . . . . . . . . . . . . . . . . . . . . .
The original poster asked a good question. What should I do if it has crystallized?