SU1386567A1 - Method of producing cryolite - Google Patents

Abstract

The invention relates to methods for producing cryolite with a higher modulus, which can be used for the electrolytic production of aluminum, and allows for increasing the filtration rate while simplifying the process. Aluminum fluoride is treated with sodium fluoride at a concentration of 1.5-3% at a temperature of 80-120 ° C to obtain low modulus cryolite, which is then treated with sodium fluoride solution at a temperature T: W of 1: 50-60; a cryolite product with a size of 50-60 µm in an amount of 40-60% by weight of the solid phase, the product is separated by filtration and dried. The filtration rate of the suspension is 8.8-9.7 m / m h. 1 C. f-ly.

Description

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The invention relates to methods for the production of cryolite with a twisted module (2.0-2.4), which can be used for the electrolytic production of aluminum.

The purpose of the invention is to increase the filtration rate while simplifying it by eliminating one stage of filtration.

The method is carried out as follows.

To the heated solution of aluminum fluoride with a concentration of 2, .5– 7 wt.%, Add a solution of sodium fluoride with a concentration of 1.5–3 wt.%. The resulting pulp is stirred to obtain a suspension of cryolite with a modulus of 1.3-1.5 and the suspension without separation of the solid phase is treated with sodium fluoride solution of 1.5 wt.% To T: W 1: 50-60. When heated to 90-100 ° C, the mixture is stirred until cryolite crystals of 25- 60 µm (commodity fraction) are formed in the amount of 40-60% by weight of the solid phase. Target product. module 2.0-2.4 is filtered off and dried at a temperature of about 250 ° C;

The filtration rate depends on the size of the crystals and their amount in the cryolite suspension fed to the filtration. The size and quantity of these crystals depends on the conditions in which they are formed at all stages of the process. The processing of a cryolite suspension with a low modulus to a certain T: G allows crystals to be larger and more easily filtered, and their content in the suspension, coming in or filtered, must be strictly defined to maintain a high filtration rate.

Example 1. To 96 ma.h. a solution of aluminum fluoride with a concentration of 2.5 wt.%, heated to 95 ° C, was added 120 mash. 1.5% sodium fluoride solution. The resulting pulp is stirred for 25 minutes. The result is a cryolite module 1.5. Then, the resulting pulp is treated with 80 m. Ch. 1.5% sodium fluoride solution at T: F 1:55. The mixture is stirred for 2.5 hours at 95 ° C. The result is a product containing the cryolite fraction 25-60 µm in an amount of 60% of the solid mass (fraction up to 25 µm 20%, more than 60 µm 20%). The product is filtered and dried at

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250 C. Filtration rate 9.7 Target product yield 5.3 mas. module 2.05.

The dependence of the filtration rate of the suspension of high modulus cryolite (6.15, 8.83; 9.70; 9.08, 7.44 m / m, h) on the ratio of the solid and liquid phases (1: 48j 1:50; 1: 55; 1: 60J 1:62 respectively) at the stage of processing the suspension of low-modular cryolite. Test conditions: the temperature at the stage of processing the suspension with a solution of sodium fluoride 95 ° C, stirring time 2.5 hours.

When the liquid phase decreases below 50, the filtration rate decreases due to the formation of small crystals, while increasing it to above 60, the filtration rate also decreases due to a decrease in the driving force of the crystallization process, which leads to the formation of small crystals.

The dependence of the filtration rate of a suspension of high modulus cryolite (6.85; 9.32, v 9.47; 9.61, 7.04) on the number of crystals 25–60 µm in size (DL; 40 {50i 60; 70%) is calculated. respectively)..

The filtration rate drops from a decrease in the fraction size of 25-60 µm below 40% due to the fact that the number of small crystals increases and they clog the pores of the filter cloth, and an increase of it above 60% is also impractical, since the resulting crystals due to their fragility and agglomeration also clogs the filter and reduces filtration performance.

Using the proposed method allows to increase the filtration rate from 6.9 to 8.8-9.7 m / m h and to simplify the process by eliminating one filtration stage. The method allows to obtain cryolite module 2.0-2J4, which satisfies the requirements of electrical aluminum production, from technical solutions of sodium fluoride and Florida aluminum, obtained from hydrofluoric hydrofluoric acid - waste production of mineral fertilizers.

Claims (2)

1. A method of obtaining cryolite, including the interaction of solutions of aluminum fluoride and sodium fluoride at a PP-100 ° C to obtain a suspension of cryolite module 1.3-1.5, processing the latter with a solution of sodium fluoride at 90-100 s, separating the resulting target product module 2 , 0-2.4 by filtration and drying it, characterized in that, in order to keep the filtration rate at the same time simplifying the process, the cryolite suspension is treated with sodium fluoride solution 6567 T: W 1: 50-60 ten and the process is carried out until a fraction with a crystal size of 25-60 µm is obtained in an amount of 40-60% by weight of the solid phase in a suspension of cryolite. 2. The method according to claim 1, wherein the solution is that the sodium fluoride solution is fed to the interaction stage at a concentration of 1.5-3% by weight, and at the processing stage of the cryolite suspension - at a concentration of 1, 5 wt.X.