Method for preparing high-purity ammonium fluosilicate

Abstract

The invention discloses a method for preparing high-purity ammonium fluosilicate. The method comprises the following steps of: (1) feeding fluorosilicic acid of which the concentration is not less than 10 percent and liquid ammonia into a reaction tank for neutral reaction, when a pH value of a reaction system reaches 3 to 5, reaction is finished; (2) pumping a reaction liquid into a low-temperature flash evaporation concentration system to perform low-temperature flash evaporation in a vacuum state, removing a large amount of water in a neutral liquid of the ammonium fluosilicate, concentrating to a saturated state, and then precipitating crystal, wherein steam generated during flash evaporation is subjected to despumation and is discharged to atmosphere air; (3) introducing a solution after flash evaporation into a setting tank, and discharging a material containing ammonium fluosilicate crystal from the setting tank; and (4) filtering the discharged material, and thus obtaining a high-purity ammonium fluosilicate product with purity over 90 percent, wherein a filtering liquid is returned to the reaction tank of neutral reaction for recovery. According to the method, the ammonium fluosilicate crystal product with purity over 90 percent can be produced, energy consumption of a process is low, operation is safe and reliable, continuous production is easy to realize, and the method is applicable for comprehensive utilization of a fluorine resource of a large-scale phosphate fertilizer enterprise.

Description

technical field [0001] The invention relates to fluorine-containing compounds, in particular to fluosilicic acid, and in particular to a preparation method of ammonium fluosilicate. Background technique [0002] As we all know, a large amount of fluorine-containing gas will be produced in the process of production and processing in the phosphorus chemical industry, which exists in the form of silicon tetrafluoride and hydrogen fluoride. If these substances are not recycled, they will cause serious environmental pollution and cause waste of fluorine resources. . Studies have shown that although the fluorine content in phosphate rock is low, the total amount is huge, and it is an important fluorine resource. At present, most of the fluorine-containing gas produced when phosphate rock is used as raw material to produce wet-process phosphoric acid fertilizers is absorbed by water to obtain fluosilicic acid. The recycling of this part of fluorosilicic acid is not only beneficia...

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Problems solved by technology

This process has the following disadvantages: (1) Since the absorption liquid is ammonium fluorosilicate crystallization liquid, when the absorption liquid reaches a certain concentration, it needs to be discharged from the system for the next cooling and crystallization process, and the continuous process is difficult; (2) During the absorption process of fluorine-containing gas, a large amount of silica will inevitably be produced. Due to its difficulty in filtration, it will be doped in a large amount in the ammonium fluorosilicate product, seriously affecting the quality of the ammonium fluorosilicate product; (3) process energy consumption Large, because the temperature of the ammonium fluorosilicate absorption liquid can reach above 80°C when the reaction is saturated, cooling it to below 30°C for crystallization will consume a lot of energy, thereby increasing production costs

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