Method for producing sodium fluoride and sodium silicate by utilizing fluorine-containing silicon slag

Abstract

The invention discloses a method for producing sodium fluoride and sodium silicate from fluorine-containing silicon slag, which comprises the following steps: adding silicon slag containing silicon dioxide and fluosilicic acid into a sodium carbonate solution, and reacting to generate a mixture of sodium fluoride crystals and silicon dioxide; adding a caustic soda solution into filter cake obtained by solid-liquid separation, reacting to generate sodium fluoride crystal and sodium silicate mixed slurry, and carrying out solid-liquid separation to obtain crude sodium fluoride and liquid sodiumsilicate; subjecting the liquid sodium silicate to concentration and filtration again to remove precipitated sodium fluoride impurities so as to obtain a liquid sodium silicate product with the required modulus and concentration; washing and refining the crude sodium fluoride by using dilute caustic soda liquid, removing sodium silicate impurities, and neutralizing residual sodium hydroxide attached liquid on the sodium fluoride by using hydrofluoric acid to generate sodium fluoride; drying the refined wet sodium fluoride to obtain a sodium fluoride product of which the purity is greater than98%. The method is mature in technology, good in product quality, low in cost, free of waste water and waste residues and capable of thoroughly converting fluorine-containing silicon slag solid wasteinto sodium fluoride and sodium silicate products.

Description

technical field [0001] The invention belongs to the technical field of chemical industry and relates to a method for producing sodium fluoride and sodium silicate by using fluorine-containing silicon slag. Background technique [0002] The use of fluosilicic acid, a by-product of phosphorus chemical industry, to produce hydrogen fluoride has a short process flow and low cost of raw materials. A large amount of wet silicon slag solid waste, its main chemical composition includes: silicon dioxide 25-40%; fluosilicic acid 10-25%; moisture 45-65%. Fluorosilicic acid in silicon slag is based on fluosilicic acid liquid and dihydrate crystal H 2 SiF 6 2H 2 The two states of O are attached to the surface of silica particles and in the pores formed by silica aggregates, making it very difficult to separate silica and fluosilicic acid for use separately, and become solid waste with no economic value, which can only occupy an area Stacking, causing environmental pressure, affecting...

AI Technical Summary

Problems solved by technology

This method can produce sodium fluoride and sodium silicate products, but the product quality is relatively poor and cannot meet the technical index requirements of qualified products

There are three reasons: First, in the sodium silicate system produced by the reaction of silicon dioxide and sodium hydroxide, the reaction of fluorosilicate dihydrate crystals with sodium hydroxide has hysteresis, and while most of the reactions generate sodium fluoride, Part of sodium fluorosilicate will be produced, which is not good for the stability of sodium silicate liquid, and will cause sodium silicate to precipitate out of silica gel and solidify, affecting storage and use; second, when the pH value of fluorosilicate and sodium hydroxide exceeds 9 React under the strong alkali state, the particle size of the generated sodium fluoride is very small, and the sodium fluoride itself has a solubility of 3-4.5%, when the sodium fluoride crystal is separated from the liquid sodium silicate, the fluorine entering the liquid sodium silicate There are many impurities in sodium fluoride, which affect the viscosity of sodium silicate and bring difficulties to the deep processing and direct use of sodium silicate; third, there is sodium silicate attached to the surface of sodium fluoride crystal, and sodium silicate is removed by washing with alkaline solution , can significantly reduce the silicon dioxide impurity content of sodium fluoride, but it is very difficult to remove free sodium oxide impurities by washing. In order to obtain sodium fluoride with a purity of more than 95%, a large amount of fresh water is required for washing. The water in the production process is unbalanced, the cost of wastewater treatment reaches or even exceeds the value of sodium fluoride itself, the product cost is too high, and there is no market survival space, so this technical method has no application value