RU2241669C2 - Soda-potash solution processing method - Google Patents

Abstract

FIELD: nonferrous metallurgy.

SUBSTANCE: invention relates to integrated processing of nepheline ores producing soda-potash solution. The latter, which has low molar potassium index and contains potassium sulfate impurities, is processed by concentrating evaporation of soda-potash solution followed by additional evaporation to precipitate soda monohydrate, isolation of potassium sulfate from soda monohydrate mother liquor in vacuum crystallizers, and isolation of anhydrous soda from potassium sulfate mother liquor purified in precipitating thickeners. Potassium sulfate mother liquor freed of potassium sulfate in precipitating thickeners, prior to isolation of anhydrous soda therefrom, is subjected to additional purification to remove potassium sulfate salts by performing control filtration on sheet filters followed by returning filtered off potassium sulfate crystals into stage of isolation of potassium sulfate from soda monohydrate mother liquor in vacuum crystallizers.

EFFECT: enabled production of anhydrous soda containing no more than one and half % potassium sulfate.

Description

The method relates to non-ferrous metallurgy, in particular, to the complex processing of nepheline ores, the processing of which produces a soda paste solution with a low molar index of potassium containing sodium sulfate salts.

There is a method of processing soda-paste solution, carried out on an industrial scale at the Achinsk Alumina Refinery in the complex processing of nepheline ores of the Kiya-Shaltyrsky deposit, in which up to 20% K ₂ SO ₄ (Varlamov M. L., Benkovsky S.V., Romanchikov I.V. et al. Production of soda ash and potash in the integrated processing of nepheline raw materials. - M.: Chemistry, 1977, p. 82-98).

According to this method, the initial soda-paste solution obtained from nepheline ore, after preliminary concentrating it to a predetermined density, is mixed with a reversible double salt (Na ₂ CO ₃ , K ₂ CO ₃ ), obtained at the next stage of the technological cycle. The mixed solution is then subjected to the second stage of evaporation, with the release of monohydrate soda from it at a density of one evaporated mother liquor of 1.38-1.39 t / m ³ .

The mother liquor purified in a soda cultivating thickener from monohydrate soda is mixed with the reverse mother liquor of anhydrous soda obtained at the next stage of the technological cycle until the molar index of potassium alkali in the mixed solution reaches 52-54%. The mixed solution is then diluted with water to reduce the density of the mixed solution to 1.4-1.42 g / m ³ and subjected to vacuum crystallization cooling to t-35-40 ° C with precipitation of crystals of commodity potassium sulfate. The mother liquor purified from crystals of potassium sulfate in precipitation thickeners is subjected to the third stage of evaporation until the density of the evaporated solution reaches 1.47-1.49 t / m ^3, and anhydrous soda is precipitated. Part of the mother liquor purified from anhydrous soda is returned to the stage of separation from the mixed soda-potash solution of potassium sulfate. Another part of the mother liquor is mixed with the circulating mother liquor in the potash isolation step. The mixed solution is subjected to the fourth stage of evaporation until the density of the evaporated solution reaches 1.64-1.65 t / m with the release of the reverse double soda-potash salt (Na ₂ CO ₃ , K ₂ CO ₃ ), which is returned to the head of the technological cycle for mixing with initial soda-liquor solution after concentrating evaporation before separation of monohydrate soda.

The mother liquor, purified from double soda potash salt, with a molar index of potassium alkali of 95-96%, is diluted with water to reduce the density of the solution to 1.55 t / m ³ and then subjected to vacuum-crystallization cooling of the solution to t-15-30 ° C with evolution salts of chloride and potassium sulfate concomitant in the solution precipitate.

The mother liquor purified from the accompanying salts is subjected to the fifth stage of evaporation until the density of the evaporated solution reaches 1.65-1.66 t / m ³ , the evaporated solution is cooled to t-40-45 ° С with precipitation of one and a half potash (K ₂ CO ₃ 1.5 H ₂ O).

The mother liquor purified from potash is returned back to the process at the stage of mixing with the mother liquor of anhydrous soda to isolate a double salt.

One of the significant drawbacks of the indicated technological scheme, operating at the Achinsk Alumina Refinery, is the low quality of the obtained anhydrous soda of the second and third grades, due to its contamination with potassium sulfate due to incomplete purification of the mother liquor of potassium sulfate from small crystals of potassium sulfate in precipitation thickeners.

An object of the invention is the purification of the obtained anhydrous soda from potassium sulfate to a level of not higher than 1.5%, which corresponds to the standard of the first grade soda, against the anhydrous soda with potassium sulfate content 3.5-5.0 obtained with the current technology at AGK %, corresponding to the standard of soda of the second and third grades.

This goal is achieved by a method of processing nepheline soda-potash solution with a low molar index of potassium and containing impurities of potassium sulfate, which includes a concentrated residue of soda-potash solution, its subsequent evaporation with the precipitation of monohydrate soda, the separation from the mother liquor of monohydrate soda potassium sulfate, in a vacuum crystallizer purified in precipitating thickeners mother liquor of potassium sulfate anhydrous soda. The mother liquor of potassium sulfate, purified from potassium sulfate salts in precipitating thickeners, is subjected to additional purification from potassium sulfate salts by separating the filtered crystals of potassium sulfate from the mother liquor to the stage of separation of potassium sulfate from the mother liquor prior to the isolation of anhydrous soda from it. in vacuum crystallizers.

As shown by laboratory and pilot tests, during the control filtration in leaf filters, the mother liquor, purified from potassium sulfate salts in precipitating thickeners, is additionally purified not only from the accompanying small crystals of potassium sulfate, but also additionally crystallized from the solution into the precipitate of potassium sulfate salt when percolating the mother liquor through a filtered layer of potassium sulfate crystals in leaf filters. So, as a result of control filtration in leaf filters, the content of potassium sulfate in the mother liquor decreased by 20-25%, the content of potassium sulfate in anhydrous soda decreased to 1.2-1.5%. The output of first-grade soda ash of the first grade increased by 10%, the yield of potassium sulfate increased by 5.0 thousand tons per year. With the current capacity of AGK OJSC for the production of soda 520 thousand tons per year, the expected annual effect from the implementation of new technology at the plant is:

1. From improving soda quality

520000 · 0.1 (1427-1260) = 8.684 million rubles,

where - 1427 and 1260 rubles. Soda prices of the first and second grades;

2. From increasing the yield of potassium sulfate

5000 (3150-1400) = 8.75 million rubles,

where 1400 and 3150 rubles. the prices of soda and potassium sulfate.

Implementation costs

7.5 million rubles. 0.15 = 1.125 million rubles.,

where 7.5 - the cost of construction and development of a filtration station for sulphate mother liquor;

0.15 - the normative ratio of capital investments.

The total expected annual effect is

8.684 + 8.75-1.125 = 16.309 million rubles.

Claims (1)

A method of processing a nepheline soda-potash solution with a low molar index of potassium and containing impurities of sulfuric acid potassium, including concentrating the residue of soda-potash solution, its subsequent evaporation with the precipitation of monohydrate soda, the separation from the mother liquor of monohydrate soda sulfuric acid potassium in vacuum crystallizers purified in precipitating thickeners mother liquor of sulfuric acid potassium anhydrous soda, characterized in that the mother liquor of sulfuric acid potassium, purified from potassium sulfate salts in precipitating thickeners before separation of anhydrous soda from it, is subjected to additional purification from potassium sulfate salts by means of its control filtration in leaf filters with the return of filtered crystals of potassium sulfate to the stage of separation of potassium sulfate from the mother liquor monohydrate soda in vacuum crystallizers.