Method of processing of sodium sulfate solution produced after a gas purification of the electrolysis bodies at aluminum production

FIELD: nonferrous metallurgy; processing of sodium sulfate solutions.

SUBSTANCE: the invention is pertaining to the field of nonferrous metallurgy, in particular, to processing of sodium sulfate solutions, which are released into a slime storage after a gas cleaning treatment electrolysis of bodies by production of aluminum. The method of processing of sodium sulfate solutions produced after the gas purification of the electrolysis bodies at production of aluminum provides for the gases purification from sulfuric oxides and fluorides by their sprinkling with a sodium sulfate solution in the washers, extraction from the solution after the gas purification of the fundamental quantity of sodium fluoride in the form of cryolite. The sodium sulfate solution purified from cryolite is in addition purified from sodium fluoride by its treatment at the temperature of 95-105°С within 1.5-2.0 hours with a lime milk injected into the sodium sulfate solution at the rate of stoichiometric binding of fluorine contained in the solution in CaF2. The sodium sulfate solution purified from fluorine is further subjected to a concentrating evaporation till achieving the density of a product solution of 1.37±0.02 g/l and extract a sodium sulfate from it into the sediment a in the form of berkeyit salt by introduction in the product solution of a carbonate soda till achieving the concentration of the titratabic alkali in the mother liquor of 215-230 g/l Na2Ot and the density of the solution in the suspension up to 1.35±0.02 g/l at stirring of the suspension at temperature of 95-100°С within 30-40 minutes. The invention ensures a more complete extraction of sodium sulfate from the product sodium sulfate solution in the form of berkeyit salt purified from sodium fluoride.

EFFECT: the invention ensures a more complete extraction of sodium sulfate from the product sodium sulfate solution in the form of berkeyit salt purified from sodium fluoride.

 

The method applies to non-ferrous metallurgy, specifically to processing sodality solutions discharged into the sludge after treatment electrolysis gas enclosures in aluminium production.

All aluminium smelters in the Russian Federation, working with the unfired anode exhaust gases from the electrolysis of buildings clear of sulfur and fluorine compounds in wet scrubbers, irrigated soda solution to achieve a working solution concentration of NaF 17-25 g/l, carbonate and bicarbonate of soda until 15-23 g/l and sodium sulfate to 60-75 g/l Of circulating sodalitates solution before returning to the gas cleaning allocate precipitated cryolite to reduce the concentration of sodium fluoride in it to 5-8 g/l to About 15% of the working sodalitates solution after separation from it of cryolite throw in the slurry tank (pit). In the remaining 85% of the working sodalitates solution is metered estimated amount spent on gas purification fresh soda before returning the circulating slurry back to the scrubber gas cleaning. With discharged into the slurry tank (pit sodalitates solution with the aluminum power plant 900 thousand tons of aluminum per year lost about 16,000 tons of Na2SO45,000 tons of soda, 2200 tons of sodium fluoride and inflict considerable ecological damage to the environment.

There is a method of separation of the Oia sodium sulfate from discharged into the slurry tank (pit sodalitates solution from the gas purification electrolysis buildings by A.S. No. 6485180 - 05.10.73, including exposure sodalitates solution for deep cooling to minus 5°emitting in the precipitate of sodium sulfate in the form of desativado Glauber's salt (Na2SO4·10H2O) with subsequent dehydration by melting and atomization in combustion units. The method in practice because of the complexity of its operation, large thermal power costs and contamination of the final product sodium fluoride.

The closest prototype of the proposed method is "a Method of processing waste of aluminium fluoride production" (ed. St. SU 789392 from 15.01.79), including the processing gases soda solution and solid waste alkaline solution, precipitation of cryolite from the resulting solution, separating the precipitate, followed by separation of the mother liquor into parts, one of which is directed to the treatment of exhaust gases, and the other caustification lime, followed by processing the resulting solution of solid waste, characterized in that, with the aim of increasing the fluoride content in the cryolite and the degree of extraction of sodium sulfate, after caustification of solution crystallized powerbuy salt and separate it. The main disadvantage of this method is the consumption of lime for caustification soda with the formation of a waste of carbonate of lime and the selection of sodium sulfate in the form of natiolnal Glauber's salt by cooling the mother liquor to minus 5 - minus 12°With that associated with high power costs for deep cooling of the mother liquor and high costs of fuel for drying of Glauber's salt,

The technical object of the present invention is to provide a deeper selection of sodium sulfate from one stripped off sodalitates solution and highlight it in the form of berkeiey salt, purified from sodium fluoride with a significant reduction of heat and energy costs of production and excretion of fluoride in water is calcium fluoride.

The goal is to reach the fact that in the method of processing sodalitates solution obtained after gas cleaning exhaust gases of electrolysis housings in aluminium production, including cleaning gas from sulfur oxides and fluoride compounds by their irrigation sodalitates solution in the wet subbaraj, the allocation from the solution after gas purification principal amount of sodium fluoride in the form of cryolite, sodality solution, purified from cryolite, is additionally clear of sodium fluoride by treatment with t - 95-105°C for 1.5-2 hours with lime milk dosing in sodality solution at a ratio of stoichiometric binding of fluorine contained in the solution in CaF2after which purified from fluorine sodality the solution is further subjected to concentrating the th residue to achieve a density of one stripped off solution to 1,37± 0.02 g/l and distributed from it to precipitate sodium sulphate in the form of the anhydrous berkeiey salt by introducing one stripped off the solution of carbonate of soda to achieve the concentration of titratable alkali in the mother solution to 215-230 g/l Na2Oτand the density of the solution in suspension up to 1.35±0.02 g/l with stirring the suspension at a temperature of 95-100°C for 30-40 minutes.

Dosage of lime in sodality the solution is less than required by stoichiometry for the formation of CaF2leads to incomplete cleaning sodalitates solution from fluorine and subsequent pollution emitted from it berkeiey salt is sodium fluoride. Excessive dosage of lime leads to deterioration allocated from the solution of calcium fluoride due to its contamination by calcium carbonate. Temperature reduction sodalitates solution below 95°and reducing the time from processing sotoportego solution with the milk of lime is less than 1.5 hours leads to insufficient cleaning sodalitates solution from sodium fluoride and subsequent pollution emitted from it berkeiey salt is sodium fluoride. The temperature rise sodalitates solution above 105°and With the increase in time more than two hours when processing sodalitates solution of lime milk leads to an increase in heat energy and other production costs is DSTV.

The decrease in the density sodalitates solution when it is concentrating the residue below 1.35 g/l and at the dosage of soda in one stripped off the solution below 1,33 g/l leads to a decrease in the release of berkeiey salt from sodalitates solution.

The increase in the density sodalitates solution when it is concentrating the residue above 1.39 g/l leads to occlusion of heating tubes of the evaporating battery sulphate salts. The increase of density one stripped off sodalitates solution at a dosage in him carbonate of soda above 1,37 g/l and the concentration of titratable alkali above 230 g/l NaOτleads to the pollution emitted into the sediment berkeiey salt carbonate soda. The temperature decrease one stripped off sodalitates solution at a dose of his soda below 95°C leads to a decline in the rate of release of berkeiey salt from sodalitates solution. The temperature rise at the dosage of his soda above 100°increases heat and power and other costs of production.

An example of the practical implementation of the processing sodalitates solution obtained in the gas cleaning electrolysis buildings proposed method in the production of 900 thousand tons of aluminum per year, shown in the accompanying balance sheet time material flow in the production cycle (drawing).

A method of processing sodalitates the solution, obtained after gas cleaning exhaust gases of electrolysis housings in aluminium production, including cleaning gas from sulfur oxides and fluoride compounds by their irrigation sodalitates solution in wet scrubbers, the allocation from the solution after gas purification principal amount of sodium fluoride in the form of cryolite, characterized in that sodality solution, purified from cryolite, is additionally clear of sodium fluoride by treatment with t 95-105°C for 1.5-2.0 hours with lime milk, entered in sodality solution at a ratio of stoichiometric binding of fluorine contained in the solution, CaF2after which purified from fluorine sodality the solution is further subjected to concentrating the residue to achieve a density of one stripped off solution to 1,37±0.02 g/l and separated from him in the precipitate sodium sulphate in the form of the anhydrous berkeiey salt by introducing one stripped off the solution of carbonate of soda to achieve the concentration of titratable alkali in the mother solution, 215-230 g/l Na2Otand the density of the solution in suspension up to 1.35±0.02 g/l and stirring the suspension at a temperature of 95-100°C for 30-40 minutes



 

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