Resource comprehensive utilization method for recovering fluorine from wet-process phosphoric acid

Abstract

The invention relates to a resource comprehensive utilization method for recovering fluorine from wet-process phosphoric acid. The method comprises the following steps of: absorbing SiF4 and HF gases generated in the wet-process phosphoric acid by using water, and preparing the gases into a hydrofluosilicic acid solution of which the mass percent concentration is 10-35%; mixing one of four solids including solid sodium sulfate, solid potassium sulfate, solid sodium chloride and solid potassium chloride with the hydrofluosilicic acid solution, and reacting for 0.1-2 hours at 30-80 DEG C under stirring to obtain a mixture; centrifugally separating the obtained mixture to obtain a solid and a filtrate; and washing the solid with water, and drying for 1-3 hours at 100-120 DEG C to obtain a sodium fluorosilicate or potassium fluorosilicate crystal. According to the method, a byproduct hydrofluosilicic acid in the wet-process phosphoric acid and sodium (potassium) sulfates or chlorides which are abundant and easily-available are used as raw materials, so that the cost is low, two products including sodium fluorosilicate and potassium fluorosilicate can be produced at the same time by using one set of equipment, and the maximum utilization ratio of the hydrofluosilicic acid can reach over 99%.

Description

technical field [0001] The invention relates to a resource comprehensive utilization method for recovering fluorine from wet-process phosphoric acid, and belongs to the technical field of inorganic chemical production. Background technique [0002] There are three main types of existing natural fluorine-containing ore resources: fluorite (the main component is CaF 2 ), containing 49% fluorine; natural cryolite (the main component is Na 3 AlF 6 ), containing 45% fluorine; fluoroapatite, (main component Ca 5 F(PO 4 ) 3 ), containing 3%~4% fluorine. Among them, fluorspar resources, especially acid-grade fluorspar, are facing depletion, so that the price is rising year by year. Many years ago, my country designated fluorspar as a strategic resource and imposed strict quota restrictions on the export of fluorspar, while the amount of natural cryolite is scarce. , does not have industrial application value. Although the fluorine content of fluoroapatite is low, more than 90%...

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Problems solved by technology

Chinese patent document CN95100688.6 discloses a method for preparing Na 2 SiF 6 The production process, that is, using fluorite as the main raw material, in NH 4 + Under the condition of being a catalyst, CaF 2 and SiO 2 react with dilute sulfuric acid to produce H 2 SiF 6 solution, and then react with sodium salt to produce Na 2 SiF 6 ; The limitations of this process are: the raw material is scarce fluorspar resources, the production cost is high and does not meet the sustainable development strategy; NH should be used in the reaction 4 + As a catalyst, the process is cumbersome and the operation is inconvenient; the prepared Na 2 SiF 6 The finished product particles are small, and the quality needs to be improved

Chinese patent document CN02137889.4, using sodium chloride or potassium chloride solution as raw material to react with fluosilicic acid for crystallization, the reaction mother liquor is discharged from the upper part of the reactor, and the crystals settle from the bottom, after being washed with water, they enter the thickener for washing and separation , and then the finished product is obtained after filtering and drying; the shortcoming of this process is that: the simple chloride salt solution of sodium or potassium is used as raw material, and the variety is relatively single; and the mother liquor of the first step reaction is directly discharged, and the salt solution is not fully The utilization of resources, to a certain extent, causes waste of resources, increases the amount of waste liquid discharged, and aggravates environmental pollution.

Chinese patent document CN101284669A (application number 200810018141.0) discloses a process for producing sodium fluorosilicate by sodium sulfate method, which specifically includes the following steps: (1) reacting fluorosilicic acid with a molar ratio of 1:1.0 to 1.2 and sodium sulfate solution Crystallization; (2) put solid sodium sulfate salt into the above reaction solution until the mass percent concentration of sodium sulfate is 15-20%; (3) separate sodium fluorosilicate; (4) mother liquor salt solution enters and circulates again Salt, reaction process; the disadvantage of this process is: purely using sodium or potassium chloride salt solution as raw material, the product variety is relatively single; in addition to the reaction raw materials, excessive sulfuric acid has been put into the reaction system in order to form circulating salt Sodium, which increases the salt concentration, affects the growth of crystals, and increases the cost; waste water is generated, and the environment is polluted

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