MXPA97002649A

MXPA97002649A - Joint production of potassium sulphate and so sulphate

Info

Publication number: MXPA97002649A
Application number: MXPA/A/1997/002649A
Authority: MX
Inventors: Shalom Lapmert
Original assignee: Dead Sea Works Ltd
Priority date: 1994-11-28
Filing date: 1997-04-11
Publication date: 1998-02-01

Abstract

The present invention relates to a process for producing potassium sulfate or potassium sulfate and sodium sulfate from potash and a source of sodium / water sulfate, comprising the steps of: a) subjecting a source of sodium sulfate to conversion with potash, in an aqueous medium, to provide precipitate of glaserite and a first mother liquor, b) to convert the precipitate of glaserite, with potash and water to produce a precipitate of potassium sulfate and a second mother liquor; the second mother liquor of step (a) d) evaporate the first mother liquor so that a mixture of sodium chloride and anhydrous sodium sulfate is precipitated in a third mother liquor, e) subject the solids from step (b) to a source of sodium sulfate / water to produce anhydrous sodium sulfate, and f) returning the third mother liquor to its conversion into potassium salts

Description

JOINT PRODUCTION OF POTASSIUM SULPHATE AND SODIUM SULFATE FIELD AND BACKGROUND OF THE INVENTION The present invention relates to processes for producing sodium and potassium sulfate, and more particularly, to processes for producing sodium sulfate and potassium sulfate from potassium sulfate and hydrated sodium.

Production of Sodium Sulphate Several processes are known for making sodium sulfate from hydrated sources of sodium sulfate. The high quality commercial grades of sodium sulfate have normally been produced from the Glauber salt (Na SO4 * 10H2?). There are natural deposits of Glauber's salt ("mirabilita") in cold climates. Glauber's salt can also be obtained by cooling a natural brine, or a solution obtained from mining solutions or a process stream. Cooling is carried out in tanks or in crystallizers (surface-cooled or vacuum-cooled). The anhydrous sodium substrate is typically produced from the Glauber salts by crystallization by evaporation in a mechanical evaporator of INT. MEX. 87/38 recompression of vapor or multiple effect (MVR), by dehydration in a rotary dryer or by melting followed by saline displacement with sodium chloride. Glauber's salt normally contains insoluble material that is unacceptable in high-grade anhydrous sodium sulfate, since dissolution, filtration (and auxiliary separation methods such as de-loosening), and crystallization by evaporation are necessary to obtain this material. . Alternatively, the Glauber salts may be melted to produce a low grade "salt cake" sodium sulfate. The saturated mother liquor is filtered and subsequently evaporated to produce high-grade sodium sulfate.

Production of Potassium Sulphate In the production of potassium sulphate from potash and sodium sulfate, the economic thermodynamic restrictions require that potassium sulphate be produced in two stages. In conventional processes, these steps consist of: 1) production of glaserite (K3Na (S04) 2) from sodium sulfate, potash and the mother liquor from Step 2; 2) production of potassium sulphate from potash, water and glaserite from Step 1; The mother liquor produced in Step 1 contains INT. MEX. 87/38 substantial quantities of dissolved sulphate and potassium that, in general, guarantee a recovery operation. The processes that are currently known differ mainly in the scheme used for the recovery of these values of sulphate and potassium. Several processes (Type I) take advantage of the different solubility behaviors of potassium chloride, sodium chloride and sodium sulphate / Glauber's salt, at high and low temperatures. The effluent from Step 1, of composition "a" (at 25 ° C) (see Figure lb) is cooled to approximately 0 ° C (Figure 1), precipitating Glauber's salt for reuse and, possibly, a certain amount of sodium chloride, depending on the water balance in the system. The potassium values are concentrated in the aqueous phase. After separation, the solution is evaporated at high temperature producing sodium chloride and also concentrating the potassium ions in the solution. Sodium chloride is removed as a byproduct of the process and a hot liquor is cooled, precipitating potassium as KCl and / or glaserite, which is essentially returned to the reaction stages. Alternatively, the hot brine is reacted with Glauber's salt recovered from the crystallization step in order to produce a suspension of glaserite, which is returned to Step 1.

INT. MEX. 87/38 Other cyclic processes ("Type II") use the behaviors of different solubility of potassium chloride and sodium chloride at high temperatures. The amount of water added to the reaction steps is adjusted so that the glaserite and solution "b" (at 25 ° C) are produced in Step 1 (Figure lb). The glaserite is then reacted with potash and water to produce the potassium sulfate product and a liquor of composition "c". The liquor is returned to Stage 1. The effluent liquor from Stage 1 is evaporated at high temperatures (75-110 ° C), producing pure NaCl and the final liquor is returned to Stage 1. It should be emphasized that the production of potassium sulphate from potash and sodium sulfate is a process to which little value is added, even though the byproduct of sodium chloride It can be commercialized. The multi-stage processes described above require both a large amount of capital and a large amount of energy. Type I processes are particularly complex, and require a large number of unit operations. These include 4 to 6 stages of filtration, not including filtration of washed potassium sulfate product. In addition, the crystallization by cooling is used to bring the temperature of the effluent from Step I to 0 ° C. The heat of crystallization of Glauber's salt, INT. MEX. 87/38 which is substantial (18.4 Kcal / m), should also be removed at low temperatures. The cooling and heating costs associated with this stage, together with expensive equipment (crystallizers, heat exchangers, refrigerant systems, etc.), represent a serious disadvantage. Type II processes do not have cooling stages below environmental conditions. However, the processes have an exaggeratedly long recirculation current (~ 10 tons per ton of K2SO4 produced), which increases the energy consumption. The low proportion of the evaporated water with respect to the performance in the crystallization stage by evaporation drastically reduces the density of the natural suspension, requiring large crystallizers and / or more sophisticated crystallization technology. Although Glauber's salt is a relatively inexpensive source of sodium sulfate, the additional water from the Glauber's salt decreases the conversion in the reaction stages and increases the sulfate composition of the effluent from Stage 1. Some cyclic processes can not operate using Glauber's salt while others require additional unit operations (eg, evaporation). To date, no process using salt has been used commercially.

INT. MEX. 87/38 Glauber. Another unexpected source of sodium sulfate is aqueous sodium sulfate. However, the ratio of water to sodium sulfate in aqueous sodium sulfate is higher than that of Glauber's salt, so that the problem of excess water worsens considerably. No cyclic process using aqueous sodium sulfate with the raw material has been invented to date. Therefore, there is a widely recognized need for a process to produce potassium sulfate from sodium sulfate, which is much more efficient and more economical than those known to date and which is quite advantageous.

SUMMARY OF THE INVENTION According to the present invention there is provided a process for producing potassium sulfate or potassium sulfate and sodium sulfate from potash and a source of sodium / water sulfate, comprising the steps of: (a) to submit a source of sodium sulfate to conversion with potash in an aqueous medium to give precipitate of glaserite and a first mother liquor, (b) to convert the precipitate of glaserite, with potash and water to produce a potassium sulphate precipitate and a second liquor mother; (c) returning the second mother liquor to step (a); (d) evaporate the first INT. MEX. 87/38 mother liquor so that a mixture of solids of sodium chloride and anhydrous sodium sulfate is precipitated in a third mother liquor; (e) subjecting the solids from step (b) to a source of sodium sulfate / water to produce anhydrous sodium sulfate; and (f) return the third mother liquor for the conversion of the potassium salts. According to a further feature in the preferred embodiments of the invention described below, the source of sodium sulfate is Glauber's salt, semi-anhydrous sodium sulfate, ie a mixture of sodium sulfate and Glauber's salt or sulfate of partially hydrated sodium or any sodium sulphate solution capable of yielding sodium sulphate in the presence of sodium chloride, for example, vanthoffite solution. The present invention allows the use of sodium sulfate sources that are cheap and available. The invention takes advantage of the fact that the solubility behavior of potassium chloride differs to a large extent from the solubility behaviors of sodium chloride and sodium sulfate with changes in temperature. As the temperature increases, the solubility of potassium chloride increases greatly, while the solubility of sodium chloride rises only slightly and that of sodium sulfate decreases or remains constant. The present invention also makes use of the fact INT. MEX. 87/38 that the solubility of sodium sulfate decreases with increasing concentration of sodium chloride. Thus, the sodium chloride / sodium sulfate solids mixture produced at high temperatures can be added to the sodium sulphate feed source, so that sodium chloride dissolves completely. This decreases the solubility of sodium sulfate, whereby the anhydrous sodium sulfate is precipitated from the solution as the only stable solid phase. In this form, the raw material is converted to anhydrous sodium sulfate and the sodium sulphate from the evaporation stage is recovered. Sodium sulfate can be used to produce potassium sulfate and any excess material is a valuable co-product.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described herein by way of example only with reference to the accompanying drawings, in which: Figures la, lb and le are solution phase diagrams for the Na2S04 / 2NaCl / K2S04 system / 2KCl / H2? at 0 °, 25 ° and 100 ° C, respectively; Figure 2 is a block diagram schematically illustrating the processes according to the invention.

INT. MEX. 87/38 DESCRIPTION OF THE PREFERRED MODALITIES The present invention relates to processes for the coproduction of potassium sulfate and sodium sulfate.

The operating principles of the processes according to the present invention may be better understood in relation to the drawings and the accompanying description. Referring now to the drawings, Figure 2 illustrates various embodiments of the present invention. The proposed processes are carried out in the following way: the conversion of potash 10 and sodium sulfate 46 and / or 76 in potassium sulfate 42 is carried out in two stages. In the first stage or stage of glaserite production, 14, the reaction can be carried out at 15-100 ° C. But, while the kinetics of the reaction and the speed of crystal growth improve with increasing temperature, the equilibrium data shows a decrease in the conversion as the temperature increases, and energy costs increase. As a result, operating at conditions close to environmental conditions (20-40 ° C) is optimal. Potash 10, sodium sulfate 46 and / or 76, stream 28 from the recovery stage (described below) and brine 40 from the decomposition stage of glaserite (described below) INT. MEX. 87/38 introduce. The source of sodium sulfate is primarily or exclusively anhydrous sodium sulfate, but some Glauber's salt and / or aqueous sodium sulfate (not shown) may be added. The term "potash" refers to any material that contains potassium chloride and includes, for example, sylvinite. In the first step 14 the sodium sulphate and the potash dissolve, generating a supersaturation with respect to the glaserite, so that the glaserite is precipitated. The system may also be supersaturated with respect to sodium chloride, so that some of the sodium chloride co-precipitates. The suspension is drained and supplied in 20 to the decomposition stage of glaserite 16. The mother liquor 26 has the following composition in weight%: potassium: 2.5-6; sodium: 7.5-10; chloride 10-17; Sulfate 1.3-8; Water: the rest. The mother liquor composition corresponds to the points on the NaCl / glaserite equilibrium line or above it, or to the points that are on and / or to the right of the equilibrium line Na2S04 / glaserite. The mother liquor, which contains considerable amounts of potassium and sulfate, is processed in the recovery stage described below. The decomposition step of glaserite 16 is carried out at 15-60 ° C, the preferred temperature range is 20-40 ° C due to the same considerations INT. MEX. 87/38 delineated in the first stage. The potash 10 and the water 18 are introduced together with the stream 20 obtained from the first stage 14. The potash and the glaserite solids are dissolved, generating a supersaturation only in relation to the potassium sulfate, so that the potassium sulfate precipitates selectively. The maximum conversion is obtained when the mother liquor approaches the invariant point KCl / K2S04 / glaserite / H20. The potassium sulfate suspension 52 is drained and washed in 22. The wet product 42 is dried. The mother liquor 40 is removed from the reactor of the decomposition stage of glaserite 16 and returned to the production stage of glaserite 14; the spent washing water 50 can be used, however, in the decomposition stage of glaserite 16. Some or all of the steps 14, 16 and 22 can be carried out in a single countercurrent differential contact. The brine 26 produced in the production of glaserite 14 is evaporated at 60 to 70-130 ° C, the preferred range is 95-110 ° C, to remove water in 62. If necessary, the brine can be filtered (not shown) ) before evaporation to remove any insoluble material. Evaporation of the water produces a supersaturation of the sodium salts (sodium sulfate, sodium chloride, or both, depending on the operating temperature, feed brine composition, and INT. MEX. 87/38 amount of water evaporated per feeding unit). Care should be taken not to over-evaporate. When the over-evaporation occurs, the additional precipitation of the sodium salts drives the composition of the mother liquor to reach the invariant point NaCl / Na2S04 / glaserite / H20, where the undesirable co-precipitation of glaserite occurs. After a solid / liquid separation, the brine enriched with potassium 28 is cooled to 70 and returned to the decomposition stage of glaserite 14. The sodium salts produced during the crystallization by evaporation are subjected, in a suitable vessel 72, to a source of sodium sulfate of low quality and / or containing water, 12, such as, for example, aqueous sodium sulfate, Glauber's salt, vanthoffite or the like, with the addition of the necessary water. Each of the aforementioned components, alone or in combination, will henceforth be referred to simply or collectively as the "source of sodium / water sulfate". Vanthoffite can be easily obtained by reacting sodium chloride with astrakanite. In order to have a high quality anhydrous sodium sulfate product, the aqueous source of sodium sulfate can be filtered to remove insoluble impurities. Glauber's salt crystallized from the brine INT. MEX. 87/38 Clear, in general, is free of these impurities and can be added directly in 33 to the container 72. Alternatively, a Glauber's salt containing impurities 35 can first be melted in a suitable melting apparatus 34, with the aqueous phase 74, being filtered before entering the stream 30, and the concentrated solids 76 are used to produce the glaserite in the first reaction stage 14. Another alternative is to feed all or part of the solid phase 76 directly to the filtering and washing container 82. Solid sodium chloride from stream 30 is not in equilibrium in the sulfate-rich 72 medium, and dissolves. Dissolved sodium chloride reduces the solubility of sodium sulfate, so that sodium sulfate precipitates. The suspension of sodium sulphate 44 is filtered and washed in 82, vigorously, with water or clear solution of sodium sulfate 56 in a countercurrent form to obtain a product of sodium sulfate of low chloride content 84, which is then dry The spent wash 86 is fed to the container 72. The effluent liquor 80 from the container 72, which contains less than 20 mol% of the sulfate, is discharged and used in another process, or processed to produce high grade sodium chloride and sodium sulfate. While the invention has been described in INT. MEX. 87/38 in relation to a limited number of modalities, it will be appreciated that many variations, modifications and other applications of it can be made.

INT. MEX. 87/38

Claims

CLAIMS; A process for producing potassium sulfate or potassium sulfate and sodium sulfate from potash and a source of sodium / water sulfate, comprising the steps of: (a) subjecting a source of sodium sulfate to conversion with potash, in an aqueous medium, to provide a precipitate of glaserite and a first mother liquor; (b) converting the precipitate of glaserite, with potash and water to produce a precipitate of potassium sulfate and a second mother liquor; (c) returning the second mother liquor to step (a); (d) evaporating the first mother liquor so that a mixture of sodium chloride and anhydrous sodium sulfate is precipitated in a third mother liquor, - (e) subjecting the solids from step (b) to a source of sodium sulfate / water to produce anhydrous sodium sulfate; and (f) returning the third mother liquor for conversion into potassium salts.
2. A process according to claim 1, further comprising: (g) returning the required amount of the anhydrous sodium sulfate to step (a) as raw material, and INT. MEX. 87/38 any excess material is removed in the form of a co-product.
3. A process according to claim 1, wherein the source of the sodium / water sulfate includes aqueous sodium sulfate.
4. A process according to claim 1, wherein the source of sodium / water sulfate includes Glauber's salt.
5. A process according to claim 1, wherein the source of sodium / water sulfate includes semi-anhydrous sodium sulfate.
6. A process according to claim 1, wherein the source of sodium / water sulfate includes vanthoffite.
7. A process according to claim 1, wherein the aqueous sodium sulfate is obtained by melting the Glauber's salt or the semi-anhydrous sodium sulfate, wherein the solid sodium sulfate, produced in the melting device, is being used. as raw material for step (a).
8. A process according to claim 1, wherein the aqueous sodium sulfate is obtained by melting the Glauber's salt with the produced solids that are being removed as by-products, and the solid sodium sulfate produced from the aqueous sodium sulfate. used INT. MEX. 87/38 as a raw material for step (a).
9. A process according to claim 1, wherein at least one of the sources of the sodium sulfate source used in step (a) is a low-grade salt cake, such that at least part of the sulfate Sodium of higher grade produced can be removed as a co-product.
A process according to claim 1, wherein the third mother liquor is subjected to conversion with Glauber's salt, wherein the reaction mixture is substantially cooled and wherein the glaserite is precipitated in a fourth mother liquor and recovered in step (a), and where the fourth mother liquor evaporates subsequently according to step (b).
11. A process according to claim 1, wherein the conversion of the third mother liquor is effected and in situ in step (a) with the addition of Glauber's salt, so that the glaserite is precipitated in the first mother liquor and recover in step (b), and where the first mother liquor is subsequently evaporated according to step (d).
12. A process according to claim 1, wherein the evaporation includes crystallization by evaporation. INT. MEX. 87/38