RU2215717C1 - Method for preparing dust-removed potassium fertilizer - Google Patents

Abstract

FIELD: inorganic chemistry, fertilizers. SUBSTANCE: invention relates to technology for preparing potassium chloride from sylvinite ores with reduced content dust fractions in it. Method involves dissolving ore, crystallization of potassium chloride from forming hot saturated solution in multiple-step vacuum- crystallizing unit to yield suspension with saturation degree of liquid phase up to 0.98 by sodium chloride, classification of suspension solid phase for large-crystalline and small-crystalline fractions of potassium chloride, drying and dust-removing of large-crystalline fraction. Then filtered-off moisture small-crystalline fraction of potassium chloride is subjected for storage at environment temperature, drying and dust-removing with addition of isolated dust-like fraction to moisture solid phase feeding to the storage. After storage moisture small- crystalline fraction of potassium chloride is dried in common with large-crystalline fraction of the main flow or separately. Method allows preparing dust-removed potassium fertilizer potassium chloride with simultaneous simplification of process due to exclusion of technological stages of dissolving small-crystalline fraction and crystallization of potassium chloride and reduction of consumptions also. EFFECT: improved preparing method. 2 cl, 1 tbl

Description

 The invention relates to techniques for producing potassium chloride with a reduced content of pulverulent fractions therein.

 Widely known are methods for producing potassium chloride from sylvinite ores by hot dissolution, separation of sodium chloride, clarification of solutions, their cooling in a vacuum crystallization unit, separation of crystallizate, followed by drying and separation of dust fractions. It is proposed that dust fractions be either returned to the process or granulated (see ME Pozin. Technology of Mineral Salts, Vol. 1, Khimiya Publishing House, 1970, pp. 154-159).

 As practice has shown, the known methods do not allow to obtain the target product with a reduced content of pulverulent fractions (less than 100 microns) or are difficult and require large energy costs.

A known method of producing dedusted potash fertilizers (see AS USSR 781194, class C 05 D 1/04, Bull. 43, 1980) by processing sylvinite ores with subsequent separation of potassium chloride from the clarified solution by multi-stage vacuum crystallization at a degree of saturation solution according to sodium chloride 0.97-0.98, followed by classification of the solid phase into coarse-grained and fine-grained product, drying, dedusting and processing of the dust fraction with water with the return of the solution along with the wash water from the coarse fraction to the crista process lizatsii, processing the crystalline product with water and hot steam to obtain a suspension with a temperature of 90-100 ^o With the supply of the latter in solution before vacuum crystallization. The known method allows to obtain the target product with a reduced content of dust fractions, but differs in complexity associated with the need to adjust the water balance of the dissolution-crystallization process when introducing a suspension of dust fractions, the proportion of which reaches 30% of the crystallizate stream, and requires large energy consumption for heating the suspension to 90 -100 ^o C, and then cooling the solution in a vacuum crystallization unit.

 A known method of producing dedusted potash fertilizers from sylvinite ores is a prototype (see A.S. USSR 990757, class C 05 D 1/04, Bull. 3, 1983) by dissolving them, including crystallization of potassium chloride from the resulting hot saturated solution in multistage vacuum crystallization unit to obtain a suspension with a degree of saturation of the liquid phase in sodium chloride to 0.98, the classification of the solid phase of the suspension into coarse and fine fractions, their separation from the suspension, washing, drying and dust removal large ristallicheskoy fractions followed by mixing fine-grained and dusty fractions with 15-20% hot saturated solution, cooling under vacuum and joining the main flow suspension entering the classification. The method is notable for the complexity associated with the need to adjust two crystallization streams of potassium chloride, as well as the water balance of the dissolution-crystallization process, and requires energy consumption for the processes of dissolution of the fine crystalline fraction and crystallization of the target product from the resulting suspension.

 The objective of the invention is to obtain dedusted potash fertilizer - potassium chloride - while simplifying the process and reducing energy consumption.

 A positive effect is achieved by the fact that, in contrast to the known method, including the dissolution of sylvinite ores, crystallization of potassium chloride from the resulting hot saturated solution in a multi-stage vacuum crystallization unit to obtain a suspension with a degree of saturation of the liquid phase in sodium chloride to 0.98, classification of the solid phase suspensions for coarse-grained and fine-grained fractions of potassium chloride, drying and dedusting of coarse-grained fractions, according to the proposed method, a filter bathroom wet fine crystals of potassium chloride fraction is subjected to storage at ambient temperature, dried and dedusted adding dust fraction extracted to a wet solid phase flowing to storage. The filtered wet fine-grained fraction of potassium chloride after storage is dried separately or combined with the coarse-grained fraction of potassium chloride of the main stream.

 A positive effect in the production of dust-free potassium chloride by the proposed method is expressed in simplifying the process by eliminating the complicated technological operations of dissolving the fine crystalline fraction and crystallizing potassium chloride, as well as in reducing energy consumption for heating and cooling suspensions.

 The essence of the method is as follows. In contrast to the known method according to the proposed method, the filtered wet fine-grained fraction of potassium chloride is subjected to storage at ambient temperature. The solubility of potassium chloride is highly temperature dependent. Fine crystalline potassium chloride has a developed surface, which is in contact with the liquid phase contained in the filtered potassium chloride.

 When the ambient temperature changes at different times of the day, dissolution-crystallization processes occur intensively on the surface of the crystals with the formation of numerous phase contacts, which leads to the growth of crystals and their surface leveling. The process of recrystallization of potassium chloride is particularly intense with high polydispersity of finely crystalline potassium chloride at the points of contact of crystals with the formation of agglomerates and in the mass of wet filtered potassium chloride under the influence of static loads.

 At the same time, the presence in the filtered potassium chloride of up to 10% of the liquid phase does not lead to drying of the salts in bulk and the caking of potassium chloride during storage is negligible. Storage of wet potassium chloride can be carried out in covered warehouses and in open piles. In the latter case, drainage and the use of the liquid phase formed from precipitation are necessary.

 The table shows the change in the particle size distribution of wet potassium chloride depending on the duration of its storage in an indoor warehouse.

 It can be seen from the table that during storage of fine crystalline potassium chloride in the wet state, the product coarsens due to its recrystallization with the gradual disappearance of dust fractions - less than 0.2 mm.

 When filtering fine crystalline potassium chloride obtained by hydroclassification of a crystallized suspension, the moisture content of the filtered potassium chloride reaches 12% (usually 8-10%), when dry cyclone dust is added to it, the moisture content decreases to 6-9%. During storage of such a product, there is a gradual decrease in salt moisture in the upper layer of the collar (up to ~ 4%) and migration of the mother liquor deep, which helps to reduce the caking of potassium chloride, which is under a static load in the lower part of the collar.

 Potassium chloride after storage is dried separately or combined with a coarse-grained fraction of potassium chloride of the main stream. Cyclone dust is sent for mixing with a filtered wet fine-grained fraction of potassium chloride, the resulting mixture is sent for storage at ambient temperature.

 From the above description of the essence of the method, it can be seen that the proposed method allows to obtain dedusted potassium fertilizer - potassium chloride with the simultaneous simplification due to the elimination, in comparison with the prototype of the complex technological operations of the technological operations of the dissolution of the fine crystalline fraction and crystallization of potassium chloride, as well as reducing energy consumption for heating and cooling suspensions.

 The method is as follows.

 Sylvinite ore is subjected to dissolution with a hot working solution with separation from a solution of sodium chloride and sludge. Potassium chloride is crystallized from the clarified solution in a multi-stage vacuum crystallization unit to obtain a suspension with a degree of saturation of the liquid phase in sodium chloride to 0.98. The suspension is classified, for example, on hydrocyclones into coarse and fine crystalline fractions of potassium chloride. The classification in accordance with the requirements of consumers is preferably in the class of ± 0.2 mm. The suspension of large and small fractions of potassium chloride is filtered separately and washed on the filter. The fractions of coarse crystalline potassium chloride are dried to obtain the desired product, and the fine crystalline potassium chloride is stored at ambient temperature and then dried.

 Wet fine crystalline potassium chloride is stored either in covered warehouses or in open areas. In the latter case, the quality of the product is improved due to its additional washing with atmospheric precipitation, however, this requires drainage of the wash water and their subsequent use in the main cycle.

 The duration of storage of wet potassium chloride for specific conditions is determined experimentally depending on the volume of the warehouse, the climatic conditions of the region, the season and the requirements for the final content of small classes in the wet product.

 Dust removal of the target product is usually combined with drying, for example, in a fluidized bed apparatus in which classes less than 0.2 mm are blown off and removed through a system of cyclones. Cyclone dust is added in the mixer to the filtered wet fine-grained fraction of potassium chloride.

 The wet fine-grained fraction of potassium chloride after storage is dried together with the coarse-grained fraction of potassium chloride of the main stream or separately.

 Examples of the method.

EXAMPLE 1
100.00 parts by weight of sylvinite ore having a composition (parts by weight,%): KCl - 26.52; NaCl - 69.12; MgCl ₂ - 0.08; CaSO ₄ - 2.18; but. - 1.72; H ₂ O — 0.38; treated with 199.63 parts by weight of a circulating solution having a composition (parts by weight,%): KCl — 11.50; NaCl - 19.33; MgCl ₂ - 0.50; CaSO ₄ 0.47; H ₂ O - 68.20 and 17.71 parts by weight of water at a temperature of ~ 100 ^o C.

After separation of the insoluble part of the ore and clarification of the saturated solution from clay sludge particles, 232.77 parts by weight of clarified solution were obtained having a temperature of 95 ^{° C.} and the following composition (parts by weight,%): KCl - 19.86; NaCl - 16.84; MgCl ₂ 0.43; CaSO ₄ - 0.42; H ₂ O, 62.45. The degree of saturation of the clarified solution in KCl is 0.95, the degree of saturation in NaCl is 1.

The clarified saturated solution was cooled in vacuo to a temperature of 30 ^{° C.} , during the cooling, 11.07 wt. parts of water. The result was a suspension consisting of 23.28 parts by weight of the solid phase composition (parts by weight,%): KCl - 99.00; NaCl - 1.00; MgCl ₂ - 0; CaSO ₄ - 0; n about. - 0; H ₂ O — 0 and 201.66 parts by mass of the mother liquor having the composition (mass percent,%): KCl — 11.50; NaCl - 19.33; MgCl ₂ - 0.50; CaSO ₄ 0.47; H ₂ O, 68.20. The degree of saturation of the mother liquor in KCd is 1, the degree of saturation in NaCl is 0.98.

 The crystallizate suspension was hydroclassified according to the ± 0.2 mm class.

A suspension of crystallizate with a particle size of more than 0.2 mm was filtered; it was obtained 12.80 parts by weight of a filtered crystallizate having the following composition (parts by weight,%): KCl - 93.87; NaCl - 2.07; MgCl ₂ - 0.03; CaSO ₄ - 0.03; n about. - 0; H ₂ O - 4.00, which was dried to obtain 12.31 parts by weight of dust-free product of the following composition (parts by weight,%): KCl - 97.58; NaCl - 2.16; MgCl ₂ - 0.03; CaSO ₄ - 0.03; but. - 0; H ₂ O - 0.20. In this case, the product had the following particle size distribution, mass fraction of fractions,%: +1 mm - 1.8; -1 - +0.2 mm - 95.3; -0.2 - +0.1 mm - 2.6; -0.1 mm - 0.3.

A suspension of crystallizate with a particle size of less than 0.2 mm was filtered separately; it was obtained 12.51 parts by weight of a filtered crystallizate having the following composition (mass fraction,%): KCl-90.02; NaCl - 2.88; MgCl ₂ - 0.05; CaSO ₄ - 0.05; but. - 0; H ₂ O - 7.00.

 The mother liquor, separated by filtration of a suspension of large and small fractions of the crystallizate, was combined (a total of 199.63 parts by weight of the mother liquor) and returned to the dissolution stage of sylvinite ore.

 A crystallizate with a particle size of less than 0.2 mm was mixed with 1.14 parts by weight of cyclone dust generated during subsequent drying of the crystallizate.

The resulting mixture was kept at ambient temperature for 20 days in a covered warehouse with a maximum daily temperature difference of ~ 6 ^° C, after which it was dried with dedusting of 0.2 mm class. As a result, 11.66 parts by weight of a dust-free product of the following composition were obtained (parts by weight,%): KCl - 96.60; NaCl - 3.10; MgCl ₂ - 0.05; CaSO ₄ - 0.05; but. - 0; H ₂ O — 0.20, and 1.14 parts by weight of cyclone dust, which was returned to the process. The resulting product had the following particle size distribution, wt. fraction fraction,%: +1 mm - 0; -1 - +0.2 mm - 98.2; -0.2 - +0.1 mm - 1.8; -0.1 mm - 0.

EXAMPLE 2
The method was carried out in accordance with example 1, but with 12.51 wt. parts of the filtered crystallizate with a particle size of less than 0.2 mm were kept at ambient temperature for 20 days, after which they were combined with 12.80 parts by weight of the filtered crystallizate with a particle size of more than 0.2 mm. The combined crystallizate was mixed with 2.34 parts by weight of cyclone dust generated during subsequent drying of the crystallizate. The mixture was dried to obtain 23.97 parts by weight of dust-free product of the following composition (parts by weight,%): KCl - 97.11; NaCl - 2.61; MgCl ₂ - 0.04; CaSO ₄ - 0.04; but. - 0; H ₂ O - 0.20.

 Granulometric composition of dust-free product, mass fraction of fractions,%: +1 mm - 1.0; -1 - +0.2 mm - 97.2; -0.2 - +0.1 mm - 1.8; -0.1 mm - 0.

EXAMPLE 3
The method was carried out in accordance with example 1, but the product was stored in an open pile.

 After storage and drying, a product was obtained in which the mass fraction of KCl increased to 97.10%. A drainage liquid phase was used instead of water at the dissolution stage of sylvinite ore.

Claims (2)

 1. A method of producing dedusted potash fertilizer from sylvinite ores, including their dissolution, crystallization of potassium chloride from the resulting hot saturated solution in a multi-stage vacuum crystallization unit to obtain a suspension with a degree of saturation of the liquid phase in sodium chloride to 0.98, classification of the solid phase of the suspension on coarse-grained and fine-grained fractions of potassium chloride, drying and dedusting of coarse-grained fractions, characterized in that the filtered wet m lkokristallicheskuyu potassium chloride fraction is subjected to storage at ambient temperature, dried and dedusted adding dust fraction extracted to a wet solid phase flowing to storage.  2. The method according to p. 1, characterized in that the filtered wet fine-grained fraction of potassium chloride after storage is dried together with the coarse-grained fraction of the main stream.

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