The method of cleaning the recovery of cryolite from sodium sulfate

 

The invention relates to the metallurgy of aluminum and can be used to obtain the recovery of cryolite of gases from electrolytic cells. Cleaning the recovery of cryolite from sodium sulfate is carried out by hot water in one stage, but cryolite load in the solution is not all at once, and occasionally with an initial weight ratio W: T equal to 10-16: 1, and after at least two periodic downloads of cryolite it reduced to 3-6: 1. The invention improves the performance recovery of cryolite. table 1.

The present invention relates to the field of metallurgy of aluminium and can be used to obtain the recovery of cryolite of gases from electrolysis cells.

One of the impurities in the cryolite, adversely affecting the process of electrolysis is sodium sulfate, which is mainly adsorbed on the surface of the crystals svezheosazhdennoi cryolite.

The presence of sodium sulfate in the recovery cryolite increases the alkalinity of cryolite, causing increased consumption of aluminum fluoride or fresh cryolite for adjusting module of the electrolyte, leads to loss of aluminum due restored the result is evil in the method (1), whereby regeneration cryolite is loaded into the reactor with hot water, mix and dehydrate the product. Moreover, the best results are obtained in the case when cryolite is subjected to 2-3-fold washing with W:T = 3:6-1, T=85-90oWith intensive stirring.

The greatest difficulty from the point of view of industrial development known process necessitates the implementation of 2-3 washes, the implementation of which in practice is unlikely because of the necessary use of large amounts of equipment (stirrers, thickeners, vacuum filter, and so on).

Object of the present invention is to improve the technical and economic indicators of obtaining the recovery of cryolite.

The technical result is to reduce the complexity of the cleaning process the recovery of cryolite from sodium sulfate.

The technical result is achieved in that in the method of cleaning the recovery of cryolite from sulfates, including filling of the reactor with hot water, loading the regeneration cryolite, stirring and dehydration of the product, the process is conducted in one stage, while in the beginning the weight ratio W: T establish 10-16:1, and after at least two pokedude in the following.

At the present time in offices and shops regeneration aluminium smelters, the ratio of the quantity of cryolite and volume of the tank of the apparatus is such that the achievable ratio W:T is within 3-6:1.

The greatest difficulty from the point of view of industrial process necessitates the implementation of 2-3 leaching of cryolite. This circumstance is due to the need of the use of large equipment (stirrers, thickeners, vacuum filters).

In practice, the implementation of even a two-stage leaching of cryolite unlikely.

If cryolite in the wash water to load immediately, but periodically, portions of several techniques, the result of washing in one stage can improve the cleaning efficiency of cryolite by 5-10% compared to single-stage washing of cryolite, loaded at once.

Starting weight ratio W:T is 10-16:1, and as the load in the wash water of new portions of cryolite ratio W:T reduced to 3-6:1.

Deeper cleaning from sodium sulphate occurs in the initial period when loading the first portions of cryolite, which is explained by the concentration process peculiarities, gatorcountry W:So

It is found experimentally that when the reduction ratio W:T in the process of cleaning due to the loading of the subsequent portions of cryolite, the reverse process, i.e. the transition of the sodium sulfate from the leaching solution washed cryolite, is not observed.

Comparative analysis of the proposed solution with the prototype shows that the proposed solution differs from the well-known fact that: - the process is conducted in one stage; in the beginning of the process, the weight ratio W:T set equal to 10-16: 1; - weight ratio W:T reduce by using at least two consecutive downloads of cryolite.

Therefore, the proposed solution meets the condition of patentability "novelty."

Analysis of the known technical solutions in this and related fields has shown that the sign of the weight ratio W:T equal to 3-6:1, known at wash recovery of cryolite in 2-3 stage, and cryolite in a known way download immediately and completely.

In the proposed method, cryolite washed in one stage, but not load immediately, and consistently with the initial weight ratio W:T equal to 10-16:1, and the final - 3-6:1.

However, the identified characteristic, similar to distinguishing the claimed invention, on the relatively well to do, and previously unknown, reduces the complexity of the process and the volume of process equipment, i.e. to get the specified technical result.

Thus, the proposed solution meets the condition of patentability "inventive step".

The possibility of implementation of the method is confirmed by the following examples.

An example of a Mixer with a capacity of ~20 m3fill with hot water at a temperature of 80-90oC and a mass of ~11 so In the trough drum filter located above the agitator, pump the thickened pulp regeneration of cryolite. KEK cryolite from the filter is fed into the mixer for leaching. Per load for washing served ~ 1000 kg of cryolite with a humidity of ~25 wt.%. The number of downloads of cryolite wash - 4.

If necessary, carry out heating of the pulp in the mixer with live steam.

The ratio of W:T in the pulp is controlled by the gravimetric method.

The results of the other examples carried out according to a similar method presented in the table.

As follows from the table, compared with the prototype, the proposed method provides a reduction of the mass fraction of sodium sulfate in single-stage washing of cryolite and two-stage cleaning of the prototype with almost novogo ratio W:T = (10-16: 1) above the claimed limit practically does not improve the cleaning of cryolite, however, increases the volume of the leaching solution and, therefore, the process equipment.

Reducing the lower limit of the initial weight ratio W:T = (10-16: 1) reduces the purification rates of cryolite from sodium sulfate.

Change the upper limit of the final weight ratio W:T = (3-6:1) above the proposed limit, despite the improvement in the purification of cryolite, economically impractical because it leads to increased leaching solution.

Reducing the lower limit of the final weight ratio W:T = (3-6:1) reduces the purification rates of cryolite from sulfates.

Sources of information 1. S. Y. Gouze, P., Baranov. The production of cryolite, aluminum fluoride and sodium fluoride. M., "metallurgy", 1964, S. 208.

Claims

The method of cleaning the recovery of cryolite from sodium sulfate, including the filling of the reactor with hot water, booting him in the recovery of cryolite, stirring and dehydration of the product, wherein the process is conducted in one stage, while the first process, the weight ratio W:T establish 10-16:1, and after at least two consecutive downloads of cryolite it reduces to 3

 

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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.

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SUBSTANCE: method comprises charging cryolite in rinsing water, washing it at stirring, and dehydration of washed product. Washing is continued until content of sodium sulfate achieves 45-65% that in initial cryolite, which requires time from 5 to 60 min at rinsing water temperature 25 to 70°C and water-to-cryolite weight ratio (3-10):1.

EFFECT: reduced mechanical loss of cryolite due to lesser degree of particle grinding at maximum possible degree of sodium sulfate removal.

4 tbl, 2 ex

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1 tbl

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SUBSTANCE: cryolite is obtained by mixing aluminium oxide, sodium chloride and ammonium hydrodifluoride or fluoride in stoichiometric ratio, taken in excess of up to 20% of the stoichiometric ratio. The obtained mixture is heated at the first stage to 240°C and kept at this temperature until complete separation of ammonia gas and water, and at the second stage - to 400°C and kept until complete subliminal removal of ammonium chloride.

EFFECT: invention allows for obtaining cryolite and ammonium chloride at the same time.

2 ex

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SUBSTANCE: proposed method washing off of regeneration cryolite pulp in condensate formed in heating of cryolite in pulping reactor. Duration of washing-off makes 30-60 minutes, temperature of condensate used for purifying if regeneration cryolite of sulfur compounds makes 50-80°C, volume ratio of used condensate to purifying pump makes (5÷8):1.

EFFECT: reduced costs, high quality.

4 cl, 1 dwg

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1 tbl, 5 ex

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3 cl, 1 tbl, 2 ex

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5 cl, 1 tbl, 1 ex

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