Preparation process of prodan by sodium sulfate method

Abstract

The invention discloses a process for producing sodium fluosilicate by using sodium sulfate, which comprises the following steps: (1) subjecting the solution of hydrofluorosilicic acid and sodium sulfate with the mol ratio of 1:1.0 to 1.2 to reaction and crystallization; (2) adding solid sodium sulfate to the reaction solution for salt dissolution till the mass percent concentration of the sodium sulfate reaches 15 to 20%; (3) separating the sodium fluosilicate; (4) subjecting the mother solution slating liquid to a circulated process of salt dissolution and reaction. The method utilizes the water of the hydrofluorosilicic acid, saves a large part of water for the salt dissolution and reduces the production of sewage; the salt dissolution by the mother solution is to continue to add excess amount of salt so as to continue to enlarge the size of hydrofluorosilicic acid crystals and increase the precipitation quantity. The utilization rate of the hydrofluorosilicic acid can reach to above 96%, which is far higher than the level of around 80% by prior solution method.

Description

technical field [0001] The invention relates to a process for recovering fluorine in a phosphorus compound fertilizer plant and producing sodium fluorosilicate using sodium sulfate as a raw material, which belongs to the process improvement of the inorganic chemical product sodium fluorosilicate. technical background [0002] Since phosphate rock generally contains about 3% fluorine, in the production process of ordinary calcium, heavy calcium and wet-process phosphoric acid, in order to protect the environment, comprehensively select resources and improve the economic benefits of enterprises, it is necessary to treat the fluorine-containing exhaust gas, and the fluorine-containing waste gas must be treated. It is absorbed and converted into fluorosilicic acid, which is used to produce market-effective fluoride salt products. Among the fluoride salt products currently produced, sodium fluorosilicate is relatively common. (Fertilizer Engineering Series "Phosphoric Acid, Phos...

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Problems solved by technology

In fact, during the wet production of sodium sulfate, since the sodium sulfate solution is in a saturated state and its solubility changes significantly with temperature, attention must be paid to the heat preservation of the chemical salt and the pipeline of the conveying equipment, otherwise it may be precipitated at any time and block the equipment or pipeline. On the one hand, when the temperature of the mother liquor is high, the hydrolysis of sodium fluorosilicate in the acidic medium is accelerated, which not only increases the loss of sodium fluorosilicate, but also increases the amount of silica gel; in dry production, due to the rapid dissolution of sodium sulfate, it is difficult to control the feeding rate , in the crystallizer, it is easy to partially supersaturate the reaction solution and precipitate a large amount of fine sodium fluorosilicate, which is easy to be thrown out during centrifugation and causes losses (Xu Weiwen, using Na 2 SO 4 Process reform of producing sodium fluorosilicate instead of NaCl, Phosphate Fertilizer and Compound Fertilizer, No. 2, 1996)

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