RU2500620C1 - Method of obtaining potassium chloride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to field of chemistry. Potassium chloride is obtained from sylvinite ores by their dilution in heated circulating mother liquor, clarification of discharge of solvents - hot solution, saturated with potassium chloride and sodium chloride, from clay-saline sludge, crystallisation of clarified solution under vacuum and separation of crystallisate from mother liquor, heating mother liquor and its returning for dilution. Excess mother liquor is evaporated on countercurrent evaporation installation with obtaining suspension, liquid phase of which is saturated with potassium chloride and sodium chloride at temperature of its boiling. Suspension is combined with discharge of solvents, combined concentrated saline sludge is output from the process, and combined condensed saline sludge is supplied to crystallisation. Combined saline sludge is discharged into sludge-storage or washed and/or filtered with return of liquid phase into the process.

EFFECT: invention makes it possible to increase extraction of target product with obtaining potassium chloride from sylvinite ores and reduce pollution of environment due to liquidation of liquid wastes of production.

2 cl, 1 tbl, 4 ex

Description

The invention relates to techniques for producing potassium chloride from sylvinite ores by the method of dissolution-crystallization.

Known methods for producing potassium chloride from sylvinite ores, including their dissolution in a heated reverse mother liquor, clarification of the discharge of solvents - a hot solution saturated with potassium chloride and sodium chloride, from clay-salt sludge, crystallization of the target product from a clarified solution in vacuum crystallization plants ( VKU), separating the crystallizate from the mother liquor, heating the mother liquor and returning it to dissolve sylvinite ores - see, for example, M.E. Pozin, Technology of Mineral Salts, Part 1, Ed. “Chemistry”, L.O., 1970, p. 154-159; A.B. Zdanovsky, Galurgia, Publ. "Chemistry", L.O., 1972, S. 466-469; O.D. Kashkarov, I.D. Sokolov, Technology of potash fertilizers, Ed. “Chemistry”, L.O., 1978, p. 38-43.

In all known methods, upon receipt of high-quality potassium chloride containing 98-99% KCl, and if water balance is disturbed, during periods of planned production shutdowns or with regular washing of equipment upon receipt of 96-97% of the product, excess solutions with a high content of potassium chloride and chloride are formed sodium, the discharge of which leads to loss of extraction of the target product from sylvinite ores and to environmental pollution by chlorides.

Widely known methods for processing solutions containing sodium chloride, potassium salts, sulfates and other impurities by evaporation of solutions - see, for example, A.S. No. 186991, Method for producing table salt, class. CO1D 3/06, Publ. 11.X.1966, Bull. No. 20. However, all of them are aimed at obtaining sodium chloride of various grades and do not provide for the use of technical solutions aimed at increasing the extraction of potassium from sylvinite ores, i.e. do not match the proposed method for technical essence.

A known method of producing potassium chloride from sylvinite ores, including their dissolution in a heated working mother liquor, clarification of the discharge of solvents - a hot solution saturated with potassium chloride and sodium chloride, from clay-salt sludge, crystallization of the target product from a clarified solution under vacuum, separation of the crystallizate from stock solution, heating the stock solution and returning it to dissolve sylvinite ores - prototype - see Mining Journal, No. 8, 2007, ISSN 0017-2278, www.rudmet.ru, Production technology of halurga potassium chloride in Russia and Belarus, pp. 25-30. The known method also does not exclude the formation of excess solutions, which leads to losses in the extraction of potassium chloride from sylvinite ores and to environmental pollution by chlorides.

The task of the invention is to increase the extraction of the target product upon receipt of potassium chloride from sylvinite ores and reduce environmental pollution by eliminating liquid waste products.

This goal is achieved in that, in contrast to the known method for producing potassium chloride from sylvinite ores, including their dissolution in a heated reverse mother liquor, clarification of the discharge of solvents - a hot solution saturated with potassium chloride and sodium chloride, from clay-salt sludge, crystallization of the target product from the clarified solution under vacuum, separating the crystallizate from the mother liquor, heating the mother liquor and returning it to dissolution, according to the proposed method, excess mother liquor The solution is evaporated on a countercurrent evaporator to obtain a suspension, the liquid phase of which is saturated with potassium chloride and sodium chloride at its boiling point. The suspension is combined with the discharge of solvents, the combined thickened saline sludge is removed from the process, and the combined clarified solution is fed to crystallization. Another difference is that the combined saline sludge is discharged into the sludge storage or washed and / or filtered to return the liquid phase to the process.

The essence of the method as a technical solution is as follows.

In contrast to the known method for producing potassium chloride from sylvinite ores, including their dissolution in a heated reverse mother liquor, clarification of the discharge of solvents - a hot solution saturated with potassium chloride and sodium chloride, from clay-salt sludge, crystallization of the target product from the clarified solution under vacuum, separation of the crystallizate from the mother liquor, heating the mother liquor and returning it to dissolution, according to the proposed method, the excess mother liquor is evaporated on a counterflow In a slurry production plant, the liquid phase of which is saturated with potassium chloride and sodium chloride at its boiling point, the suspension is combined with a drain of solvents, the combined thickened saline sludge is removed from the process, and the combined clarified solution is fed to crystallization. At the same time, the combined salt sludge is discharged into the sludge storage or washed and (or) filtered with the return of the liquid phase into the process.

As the experience of the concentration plants processing sylvinite ores by dissolution-crystallization method with the production of high-quality potassium chloride, for example, with a content of 98% KCl, shows, in accordance with the regulatory documentation for 1 ton of finished products, 0.2185 tons of excess mother liquor saturated with potassium chloride is formed and sodium chloride at a temperature of 30-40 ° C, which entails losses in the extraction of the obtained component from the ore into the target product and the discharge of the liquid phase into the sludge storage.

With a production volume of ~ 3 million tons of potassium chloride per year, for example, at the 4 Bereznikovsky potash mine department of OJSC Uralkali, these discharges will amount to 655,500 tons, and taking into account atmospheric precipitation (up to 500 mm / year) the amount of liquid waste increases, which causes a noticeable harm to the environment. The construction of large section chambers for liquid waste disposal entails large capital investments and an increase in the cost of finished products. In the production of 96% potassium chloride, in accordance with the water balance, excess mother liquors are not formed, however, they are almost always present due to scheduled and unscheduled shutdowns of equipment, flushing of VKU, pumps and pipelines, mechanical losses and other operations.

According to the proposed method, the excess mother liquor, saturated with potassium chloride and sodium chloride, at a temperature of 30-40 ° C is subjected to evaporation on a 2-4-body countercurrent vacuum evaporation unit - VVU, the first body of which operates at atmospheric pressure and is heated with hot steam, and the rest - under vacuum and are heated with secondary steam from previous buildings. Evaporation of the evaporated solution is carried out from the first housing, where the suspension temperature is 106-110 ° C, while the evaporation process in the first housing of the VVU is completed upon reaching the degree of saturation of the solution with potassium chloride at the indicated temperatures of 0.98-1.00 to avoid crystallization into solid potassium chloride phase.

The mother liquor is fed into the last VVU casing, operating under vacuum, which reduces the risk of incrustation of heating surfaces with gypsum. The number of IVU hulls is chosen for economic reasons, depending on the production volume of potassium chloride and, as a rule, 3-4-body HVUs are used.

Table 1 shows the approximate chemical composition of the excess mother and evaporated solutions, which may vary depending on fluctuations in the water balance of potassium chloride production.

Table 1 No. p / p Name of solution Temperature ° C Chemical composition, % KCl NaCl CaSO ₄ MgCl ₂ H ₂ O one Uterine discharge thirty 11.39 19.47 0.48 0.68 67.98 2 solution 40 12.83 18.88 0.47 0.68 67.14 3 One stripped off solution 106 21.69 15.74 0.43 1.28 60.86 four 110 22.19 15.60 0.42 1.33 60.46 5 Drain solvents - liquid phase with a degree of saturation according to KCl - 0.95 92 19.47 16,99 0.62 0.62 62.48 6 97 20.02 16.88 0.43 0.63 62.04

To eliminate liquid waste according to the proposed method, it is necessary to evaporate the excess mother liquors “to dryness” to obtain potassium chloride in the form of a crystallizate at the VKU and sodium chloride contaminated with calcium sulfates in the form of saline sludge. At the same time, the excess mother liquor is evaporated to obtain a suspension, the liquid phase of which is saturated with potassium chloride, i.e. has a saturation degree of Kl 0.98-1.00, while only part of the water needed to be removed from the system is removed. Therefore, to remove water from the mother liquor in an amount equivalent to its content in the excess mother liquor, the amount of mother liquor supplied to the residue is increased by a factor K equal to:

, $$K=C_{H_{2}Om}\cdot \frac{C_{KCly}}{\mathrm{one\; hundred}\cdot \left(C_{KCly}-C_{KClm}\right)}$$

,

where C _H2Om is the water content in the excess mother liquor,%;

C _KClу - the content of potassium chloride in the liquid phase of one stripped off suspension,%;

With _KClm - the content of potassium chloride in the excess mother liquor,%.

Consequently, an excess mother liquor is fed for evaporation at a rate multiplied by the correction factor given.

Considering that the additional flow of the liquid phase circulates only in the cycle: thickener - VKU - VVU, there are no changes in the flow rate of the mother liquor entering the dissolution, and the amount of excess mother liquor entering the evaporation is automatically determined by the level of the solution in the reserve tanks, virtually without additional calculations, which are necessary only at the stage of selection and calculation of VKU.

The solid phase in the evaporated solution is represented by sodium chloride with impurities of ~ 2.2% CaSO ₄ , and its content in the suspension is ~ 13.3% (L: T ~ 4.4).

According to the proposed method, the resulting suspension is combined with a drain of solvents - a hot solution with a temperature of 92-98 ° C, saturated with sodium chloride, and with a degree of saturation of potassium chloride of 0.93-0.97 containing clay-salt sludge, and the resulting suspension is clarified. Thanks to this operation, all of the potassium chloride contained in the excess mother liquor enters the target product in the form of a crystallizate with VKU, which is formed by cooling the clarified combined solution under vacuum. In addition, combining the evaporated solution with the drain of the solvent leads to an increase in the temperature and degree of saturation of the combined solution with potassium, which makes it possible to increase the yield of crystallizate in the first VKU buildings and improve its particle size distribution by increasing its residence time in the VKU and also reduce water consumption prevent contamination of the crystallizate with sodium chloride, and therefore, reduce the volume of circulating solutions.

According to the proposed method, the combined salt sludge condensed in the thickener to a liquid to solid ratio - L: T = 1.5-2.5, is removed from the process. After dilution, this sludge can be sent to the sludge store or washed, for example, with an excess mother liquor and filtered by known methods, for example, on a filter press, and sent, for example, to the working open spaces together with a halite dump. Condensed sludge can be filtered without rinsing. The filtrate and wastewater are returned to the process, for example, added to the drain of solvents.

Thanks to the implementation of the present invention in the production of, for example, 98% potassium chloride with the utilization of 0.2185 t / t KCl excess solutions, the degree of extraction of KCl from sylvinite ores in the finished product increased by 2.44%.

Thus, the problem of the invention is solved - the production of potassium chloride from sylvinite ores with an increase in the extraction of the target product and reduction of environmental pollution due to the elimination of liquid production waste.

The method was carried out as follows.

Sylvinite ore was subjected to dissolution in a heated reverse mother liquor. Solvent drain - a hot solution with a temperature of 92-98 ° C, saturated with sodium chloride and potassium chloride with a saturation degree of KCl 0.93-0.97 and containing clay-salt sludge, represented by clay compounds, anhydrite, sodium chloride and traces of sylvinite ore , combined with one stripped off excess mother liquor, saturated with potassium chloride and sodium chloride at a boiling point of 106-110 ° C and containing sodium chloride and calcium sulfate in the solid phase. The resulting suspension was clarified on a thickener. The combined clarified solution was cooled in a vacuum crystallization unit to a temperature of 30-40 ° C, followed by crystallization by centrifugal filtration and filtration, and then drying to obtain the finished product with a content of at least 98.2% potassium chloride. The mother liquor was heated in the first part of the VKU, and then in surface heaters to a temperature of 114-116 ° C and fed to the dissolution of sylvinite ore. An excess mother liquor in an amount of 0.2185 t / t on average 92.2% KCl was evaporated in a countercurrent 3-case vacuum evaporator to obtain a suspension, the liquid phase of which was saturated with potassium chloride and sodium chloride at a boiling point of 106-110 ° C, and the solid phase is represented by sodium chloride with impurities of 2.2% CaSO ₄ .

The thickened combined sludge with W: T = 1.5-2.5 from the thickeners was sent to the sludge dump. The sludge was also filtered on a filter press to obtain a cake containing up to 30% moisture and a filtrate, which was added to the drain of the solvent. In another embodiment, the sludge was washed with a mother liquor heated to 60 ° C, and then concentrated to W: T = 2 and filtered on a vacuum filter.

The filtered cake was sent for mixing with a halite blade and for storage of the mixture. The degree of extraction by the proposed method was 88.61%, which is 2.44% higher compared to the prototype. At the same time, there was no liquid waste, since all excess solutions were processed.

Examples of the method

Example 1

In accordance with the prototype, sylvinite ore was subjected to dissolution in a heated circulating mother liquor. Solvent drainage - a hot solution with a temperature of 95 ° C, saturated with sodium chloride and potassium chloride with a KCl saturation degree of 0.96, and containing clay-salt sludge, was clarified on a thickener, cooled in a 7-case vacuum crystallization unit to 30 ° C. The resulting crystallizate suspension was separated by thickening and filtration. The crystallizate was dried to obtain the desired product - 98.2% potassium chloride. The mother liquor was heated in the first part of the VKU, and then in surface heaters to a temperature of 115.2 ° C and fed to the dissolution of sylvinite ore. In this case, 0.2185 t / t 98.2% KCl of the excess mother liquor was formed, which was discharged into the sludge dump.

The thickened clay-salt sludge with W: T = 2.1 from the thickener was dumped into the sludge dump.

The degree of extraction of KC1 from sylvinite ore into the target product was 86.17%.

Example 2

In accordance with example 1, sylvinite ore was dissolved to obtain 0.2185 t / t 98.2% KCl of the excess mother liquor composition: KO - 11.39%, NaCl - 19.47%, CaSO ₄ - 0.48%, MgCl ₂ - 0.68%; H ₂ O - 67.98%.

To obtain salts in a "dry" form from the system during evaporation, it is necessary to remove 0.6798 tons of water from 1 ton of excess solution. However, when the excess solution is evaporated until it is saturated with potassium chloride at the boiling point, a smaller amount of water will be removed, therefore, to remove water in an amount equivalent to its content in the excess solution, we will determine the correction factor for the mother liquor flow to the evaporation:

, $$K=C_{H_{2}Om}\cdot \frac{C_{KCly}}{\mathrm{one\; hundred}\cdot \left(C_{KCly}-C_{KClm}\right)}$$

,

where C _H2Om is the water content in the excess mother liquor, 67.98%;

C _KClу - the content of potassium chloride in the liquid phase of one stripped off suspension, 22.19%;

C _KClм - the content of potassium chloride in the excess mother liquor, 11.39%.

The liquid phase composition of the stripped off suspension: KCl - 22.19%, NaCl - 15.60%, MgCl ₂ - 1.33%, CaSO ₄ - 0.42%, H ₂ O - 60.46%. K = 1.4. Therefore, the flow rate of the mother liquor entering the residue is 0.305 t / t 98.2% KCl.

This flow rate was determined automatically by the level of the solution in the reserve tanks, increasing or decreasing the consumption of excess solution for evaporation during level fluctuations in the tanks.

The solid phase of the suspension is represented by sodium chloride with a content of 2.21% CaSO ₄ .

The resulting suspension was combined with the drain of the solvent and clarified on a thickener to obtain a clarified solution with a temperature of 95 ° C and with a KCl saturation of 0.98, and then it was cooled in VKU to 30 ° C, crystallized was isolated from the cooled suspension and dried to obtain 98, 2% potassium chloride.

The mother liquor, in accordance with the prototype, was directed to the dissolution of sylvinite ore, and the excess mother liquor to the residue. The combined clay and salt sludge was thickened to W: T = 2.1 and dumped into the sludge dump.

The degree of extraction of KCl from sylvinite ore into the target product was 88.61%, with no discharge of excess mother liquor.

Example 3

The method was carried out in accordance with example 2, but the thickened combined clay and salt sludge was filtered on a filter press to obtain cake with a moisture content of 30% and returning the filtrate to the solvent drain.

Example 4

The method was carried out in accordance with example 2, but the thickened combined clay-salt slurry was washed with a mother liquor at a temperature of 60 ° C, then dried to W: T = 2, filtered on a vacuum filter and the filtrate and washings were combined with the mother liquor.

Claims (2)

1. A method of producing potassium chloride from sylvinite ores, including their dissolution in a heated reverse mother liquor, clarification of the discharge of solvents - a hot solution saturated with potassium chloride and sodium chloride, from clay-salt sludge, crystallization of the target product from a clarified solution under vacuum, separation of crystallizate from the mother liquor, heating the mother liquor and returning it to dissolution, characterized in that the excess mother liquor is evaporated on a countercurrent evaporator to obtain suspension, the liquid phase of which is saturated with potassium chloride and sodium chloride at its boiling point, the suspension is combined with the discharge of solvents, the combined thickened saline sludge is removed from the process, and the combined clarified solution is fed to crystallization. 2. The method according to claim 1, characterized in that the combined salt sludge is discharged into the sludge storage or washed and (or) filtered to return the liquid phase to the process.