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Method for recycling hydrofluoric acid from wastewater containing fluorosilicic acid

A technology of hydrofluoric acid and fluorosilicic acid, applied in hydrogen fluoride, fluorine/hydrogen fluoride, silicon oxide and other directions, can solve the problems of waste of fluorine resources, heavy environmental protection pressure, etc., and achieve the effects of low recovery cost, good working environment and easy operation.

Inactive Publication Date: 2016-12-07
CENT SOUTH UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

At present, besides the fluosilicic acid by-product of dehumidification phosphoric acid and superphosphate process can be comprehensively utilized, most of the fluosilicic acid wastewater produced in other industries is treated by lime precipitation, resulting in a large amount of fluorine-containing solid waste, causing heavy Environmental pressure and serious waste of fluorine resources

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0034] Take 2.5m of fluorine-containing silicic acid wastewater generated during the tantalum and niobium smelting process 3 , 45°C, stirring and adding concentrated ammonia water with a concentration of 6mol / L to adjust the pH of the solution to 9, after reacting for 2.5h, filter to obtain SiO-containing 2 filter cake and containing NH 4 Filtrate of F. The obtained filtrate presses the F - converted to MgF 2 Add MgSO to 1.03 times the theoretical amount of precipitation 4 ·6H 2 O, stirred at room temperature for 2.5h, and filtered to obtain the magnesium fluoride precipitate and the liquid after defluorination. The resulting magnesium fluoride precipitate is decomposed into MgSO 4 1.05 times the theoretical amount, stir and add concentrated sulfuric acid with a concentration of 98%, and decompose it at 210°C for 1.5 hours, so that the fluorine in it is volatilized in the form of HF, and the gas containing HF is condensed and absorbed to obtain hydrofluoric acid, and the...

Embodiment 2

[0037]Take 1.5m of waste gas eluent from a smelter 3 , stirred at room temperature and introduced ammonia gas, adjusted the pH to 8.5, continued to stir for 2 hours, and filtered to obtain SiO-containing 2 filter cake and containing NH 4 Filtrate of F. The obtained filtrate presses the F - Form MgF 2 Add anhydrous magnesium sulfate obtained in Example 1 to 1.02 times the theoretical amount of precipitation, stir at 60° C. for 1 hour, and filter to obtain magnesium fluoride precipitate and defluoridated liquid. The resulting magnesium fluoride precipitate is decomposed into MgSO 4 1.01 times of the theoretical amount is stirred and added with sulfuric acid with a concentration of 93%, and evaporated at 230°C for 1 hour, so that the fluorine in it is volatilized in the form of HF, and the gas containing HF is condensed and absorbed to obtain hydrofluoric acid. The obtained evaporation residue-anhydrous magnesium sulfate is returned to the magnesium fluoride precipitation pr...

Embodiment 3

[0040] Get 2.5L of fluosilicic acid by-product of the phosphate fertilizer plant, w(H 2 SiF 6 )=24.1%, add ammonium bicarbonate according to 1.05 times of the theoretical amount of ammonium fluoride converted from fluosilicic acid, stir at 35-80°C for 3.5h, and filter to obtain SO 2 filter cake and containing NH 4 Filtrate of F. Gained filtrate according to wherein F - converted to MgF 2 Add magnesium oxide to 1.2 times the theoretical amount of precipitation, stir at room temperature for 2 hours, and filter to obtain magnesium fluoride precipitate and defluoridated liquid. The obtained magnesium fluoride precipitate is dried to obtain magnesium fluoride product, and the liquid is directly evaporated to recover ammonia after defluorination.

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Abstract

The invention provides a method for recycling hydrofluoric acid from wastewater containing fluorosilicic acid. Ammonia or ammonium is added into the wastewater containing the fluorosilicic acid and the fluorosilicic acid is decomposed into sediments of ammonium fluoride and silicon dioxide; magnesium sulfate is added into a solution containing the ammonium fluoride and fluorine in the solution is precipitated and separated out in a magnesium fluoride form; the solution is filtered to obtain magnesium fluoride and a fluoride precipitation post-solution; then the magnesium fluoride is thermally decomposed by sulfuric acid; thermally decomposed steam is condensed and absorbed to obtain the hydrofluoric acid; residues of thermal decomposition are returned back to a fluoride precipitation and separation procedure and are circularly utilized. Lime is added into the fluoride precipitation post-solution, stirring and a mixed solution is evaporated to recycle the ammonia; the recycled ammonia is returned back to a fluorosilicic acid ammonolysis procedure for circular utilization; the method has the advantages of simple process, simplicity and convenience for operation, high fluorine recovery rate, low recovery cost, good working environment and the like.

Description

technical field [0001] The invention belongs to the fields of chemical industry and metallurgy, and in particular relates to a method for recovering hydrofluoric acid from fluorine-containing silicic acid wastewater. Background technique [0002] Hydrofluoric acid is an important chemical raw material, and hydrofluoric acid is usually prepared from fluorspar (fluorite) and sulfuric acid. The used hydrofluoric acid waste liquid usually contains impurities such as fluorosilicic acid, fluoroferric acid, and fluorotitanic acid. People have made a lot of attempts to recover hydrofluoric acid from fluorosilicic acid, including the lime proposed by the US Bureau of Mines. The silica method, the pyrolysis method proposed by the bus company, and the concentrated sulfuric acid decomposition method adopted by Wellman Electric Gas Company, etc. [0003] Lime silica method: first mix lime, silica and fluosilicic acid in a certain proportion. The resulting calcium fluoride and silica pr...

Claims

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Application Information

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IPC IPC(8): C01B7/19C01B33/12
CPCC01B7/193C01B33/12
Inventor 王学文王明玉孟钰麒
Owner CENT SOUTH UNIV
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