DE102009041456A1 - Producing high percentage potassium chloride from polymineralic, magnesium sulfate rich crude potassium salt or from crude salt fraction obtained during dry treatment of crude salt, comprises hot dissolution-cold crystallization process - Google Patents

Abstract

Producing high percentage potassium chloride from polymineralic, magnesium sulfate rich crude potassium salt or from crude salt fraction obtained during the dry treatment of the crude salt, comprises hot dissolution-cold crystallization process. The lye for dissolution in the hot dissolution process comprises heated water or a very dilute heated solution with low content of potassium chloride, magnesium chloride and magnesium sulfate. The recycling circulation of the solutions and reusing of potassium chloride saturated mother liquor as lye for dissolution is completely avoided. Producing high percentage potassium chloride from polymineralic, magnesium sulfate rich crude potassium salt or from crude salt fraction obtained during the dry treatment of the crude salt, comprises hot dissolution-cold crystallization process. The lye for dissolution in the hot dissolution process comprises heated water or a very dilute heated solution with low content of potassium chloride, magnesium chloride and magnesium sulfate. The recycling circulation of the solutions and reusing of potassium chloride saturated mother liquor as lye for dissolution is completely avoided. The recyclable material solution separated from insoluble components is evaporated after carrying out desulfation and thus the common salt crystallizes out and the potassium chloride-sodium chloride-crystallizate obtained by the cool crystallization process is worked up by known methods to obtain high percentage potassium chloride.

Description

The invention relates to a process for the preparation of high-percentage potassium chloride with ≥ 95% KCl content of polymineral Kalirohsalzen with a high proportion of soluble magnesium sulfate minerals in the form of individual salts or double salts by a hot-dissolving crystallization process. The method is applicable to naturally occurring crushed potash salts of polymineral composition degraded by mining processes, which in addition to sylvite (KCl), halite (NaCl), anhydrite (CaSO ₄ ), polyhalite (K ₂ SO _4. MgSO ₄ .2CaSO ₄ .2H ₂ O Soluble magnesium sulfate in the form of the minerals kieserite (MgSO ₄ .H ₂ O), kainite (KCl.MgSO ₄ .275 H ₂ O), langbeinite (K ₂ SO ₄ .2MgSO ₄ ), schoenite (K ₂ SO ₄ MgSO ₄ .6H ₂ O) and varying proportions insoluble. The process is applicable not only to a coarsely ground potash crude salt but also to fractions thereof, for example, dusting salt or tailings from a dry processing process of this crude salt. In addition to potassium chloride, sodium chloride and sodium or magnesium sulfate are obtained as further commercial products.

The production of potassium chloride from Kalirohsalzen by a hot-dissolving cooling crystallization process has long been known and generally feasible without difficulty if the Kalirohsalz to be processed consists either only of KCl, NaCl and insoluble minor constituents, such as anhydrite and / or polyhalite and low-clay constituents.

Soluble sulfates, such as kiesite or kainite, dissolve completely or partially during the hot-dissolving process and accumulate in the circulating solutions of the hot-dissolving process, unless counteracted by co-promotion of magnesium chloride in the form of carnallitic crude salts. The magnesium chloride and the magnesium sulfate dissolved in solution are continuously removed from the solution cycle, which can only be done by repulsion or a two-fold dissolving process, as in the case of Freiberger research book A654, Leipzig 1981, pp. 39-47 described is possible.

Dust salts or highly clay-containing crude salts can hitherto not be processed to high-percentage potash fertilizers by a hot-dissolving crystallization process with circulating circulating solutions. But also kieserit- / kainithaltige polymineral Hartsalze prepare when hot enormous difficulties, either in the stage of hot clarification or even in the cooling crystallization itself disruptive magnesium sulfate and calcium sulfate containing double salts arise that disturb the process sensitive or at least a production of high-potassic fertilizers (> 60% K ₂ O or> 95% KCl) impossible.

The cause of the difficulties arising from sulfate dissolution from the crude salt is the circulation of the mother liquor and its renewed use as a dissolving liquor after appropriate heating. Due to the continuous circulation, which is used in all common processing for sylvite and hard salts, in a nearly closed solution cycle in the circulating solutions accumulate all substances dissolved in the hot solution from the crude salt, if they do not like the sylvin KCl in cooling the solution crystallize.

Dissolved magnesium sulfate accumulates in the solution cycle until its solubility limit is exceeded, which usually happens above all as a potassium- and magnesium-containing double salt. This can lead to the fact that instead of potassium chloride in the vacuum cooling process, the double salt Schönit (K ₂ SO ₄ .MgSO ₄ .6H ₂ O) crystallizes next to NaCl, in particular if the liberated crude salt had a high kainite content with only a small amount of sylvite. It goes without saying that it is not possible to produce high-percentage potassium chloride as the end product under such conditions. However, even with polymineral crude salts with high sylvite content and high content of soluble MgSO ₄ minerals, high-percentage KCl is difficult or impossible to produce as an end product, especially if at the same time reactive calcium sulfate contained in the crude salt.

The object of the invention is the production of high-percentage potassium chloride from a polymineral Kalirohsalz, which contains in addition to KCl, NaCl, CaSO ₄ and double salts especially soluble MgSO ₄ as kieserite, kainite and langbeinite and larger amounts of clay. Another object of the invention is the processability of fractions of this type of crude salt to high-percentage potassium chloride, which are obtained in the preparation of this crude salt by dry sorting.

The invention must solve the problem of reliably avoiding the occurring before or during KCl crystallization crystallization of magnesium and sulfate-containing double salts and to separate a crystallization of potassium chloride temporally and spatially from the excretion of sulfates.

The invention solves this problem in that the reuse of the mother liquor as Löselauge and thus a circulation of process solutions, which is otherwise a characteristic feature of known hot-dissolving processes, is completely avoided.

This is no accumulation of dissolved from the crude salt out of magnesium and sulfate in the dissolving lye circuit possible and therefore no uncontrolled crystallization MgSO ₄ -containing double salts.

Instead of a solution cycle with heated mother liquor used as Löselauge of KCl crystallization to dissolve the valuable minerals from the crushed crude salt, the inventive method works with hot solvent, which is water in the simplest case or a very dilute solution with low content of KCl, MgCl ₂ and MgSO _4. Such Löselauge dissolves from shredded crude salt or from the obtained in the dry processing of crude salt crude salt fractions the valuable minerals, especially potassium chloride, but also kainite and depending on the temperature and duration of release and kieserite and langbeinite. However, because of the avoidance of recirculation of the solution, the resulting solution has such a low content of sulfate and total magnesium that precipitation of poorly soluble MgSO ₄ -containing double salts during cooling crystallization is reliably avoided. If the hot, clarified solutions formed during the hot-cooling are cooled, then only the alkali chlorides, but not MgSO ₄ -containing soil bodies, crystallize when their solubility limits are exceeded. At best, such hot solutions are in the existence of the Mg-free double salt glaserite (3K ₂ SO ₄ · Na ₂ SO ₄ ), which, however, does not interfere with the crystallization process of alkali chlorides due to its relatively lower crystallization rate. The crystallized alkali chlorides are separated if necessary after the cooling process at about 25 to 35 ° C. Since reuse of the mother liquor as Löselauge is excluded according to the invention, the mother liquor must be concentrated by an evaporation process to recover all the potassium chloride and sodium chloride contained therein as a product.

If this mother liquor, which is saturated with KCl and NaCl, contains no or only a small amount of magnesium chloride, but quite considerable amounts of magnesium sulfate, evaporate directly as such, a salt mixture of chlorides and sulfates which would be difficult to separate would not form from the pure high-percentage potassium chloride or can be won only with great effort. The process according to the invention therefore provides for desulfating the solution before it evaporates, expediently by the known crystallization of the magnesium-free alkali sulfate mirabilite (Na ₂ SO ₄ .10H ₂ O), which precipitates at very high crystallization rate and yield when the solution is up low, preferably below ± 0 ° C lying temperatures is cooled. After reheating the separated from the crystallized Mirabilit solution can be evaporated without interference from magnesium-containing or magnesium-free sulfates by known methods, with only the alkali chlorides crystallize KCl and NaCl. This KCl-NaCl mixture can be separated by known methods as well as the resulting in the primary cooling crystallization KCl-NaCl mixture and decomposed into the individual salts of potassium chloride and sodium chloride, for example by dissolution.

The end product resulting in addition to the target product potassium chloride with at least 60% K ₂ O content as a byproduct sodium chloride and sodium sulfate, which can be obtained from the mirabilite by dewatering. The magnesium chloride-rich, after evaporation and subsequent cooling of the solution resulting residual solution leaves the process and is recycled or disposed of without damage. The invention will be explained by the following embodiments.

Example 1 Hot dissolving of crude clay with high clay content

100 t of polymineral, clay-rich potash brine containing 10% sylvite, 8% kainite, 4% langbeinite, 1% anhydrite, 11% kieserite, 13% polyhalite, 31% halite, 18% clay and insoluble, are stored at 85 ° C with hot water Addition of the resulting in the sound washing saline wash water stirred for 30 to 40 minutes. The caliminerals sylvin (KCl), kainite (KCl · MgSO ₄ · 2.75H ₂ O) and halite (NaCl) completely dissolve. Kieserite also dissolves completely or mostly, Langbeinit partially. Completely undissolved remain polyhalite, anhydrite and clay minerals. After completion of the dissolution, the suspension is clarified hot with the aid of polyacrylamide as flocculant and the thickened insoluble residue separated by a filter press. The damp, containing material containing valuable clay sludge is washed with about 100-200 kg / t solid hot water and the resulting wash water is added to the dissolving water.

The hot material-containing solution is the starting point for obtaining the components potassium chloride and sodium chloride and the sulfate as sodium sulfate.

About 220 m ³ hot solution with a composition of 55-60 g / l KCl, 130-135 g / l NaCl, 80-85 g / l MgSO ₄ , 0.7-0.9 g / l CaSO ₄ and a density of 1.185 to 1.195 g / cm ³ .

The insoluble residue consists mainly of clay, polyhalite and some kieserite and anhydrite. After filtering and washing out the filter cake on a filter press, the moist residue is removed. By cooling the solution obtained to -5 to -7 ° C, the majority of the dissolved sulfate as Glauber's salt (Na ₂ SO ₄ · 10H ₂ O) crystallized out. The other components of the solution (KCl, NaCl and the magnesium chloride formed remain in solution. After separation of 35-37 t Na ₂ SO ₄ · 10H ₂ O has the re-heated solution has a composition of 55-60 g / l KCl, 130- 135 g / l NaCl, 50 g / l MgCl ₂ , 20 g / l MgSO ₄ at a density of 1.175 g / cm ³ .

This solution is evaporated by a known method, initially crystallized sodium chloride (NaCl). Because of the removal of sulfate as Glauber's salt, the solution does not form sulphate-containing double salts either during evaporation or during subsequent cooling. The evaporation is carried out taking advantage of the known differences in solubility of NaCl and KCl and the known crystallization delay of Langbeinits so that is first evaporated at 85 to 95 ° C to close to the KCl saturation. This is achieved at about 145 g / l MgCl ₂ . After removal of the hot crystallized sodium chloride (about 22 t NaCl), the solution is cooled to + 25 ° C, whereby the concentration in the solution of 175 g / l KCl to 90 g / l KCl decreases, while the NaCl concentration hardly changed. The KCl crystals (6.0 t) is separated and the solution is further concentrated by a new evaporation process, as long as at + 55 ° C the Leonite saturation is reached. In turn, only the alkali chlorides KCl and NaCl crystallize out. After cooling to turn 25 to 30 ° C falls after separating the alkali chloride, a residual solution with 240 to 260 g / l MgCl ₂ , 90 to 100 g / l MgSO ₄ , which still about 55-60 g / l KCl and about 40 g / 1 contains NaCl dissolved and has a density of about 1.31 g / cm ³ .

The solution evaporation reduced the volume from 220 to about 45 to 50 m ³ . The potassium yield of the process is about 80 percent. The yield of common salt is about 90 percent. The MgCl ₂ residual solution is run out of the process and either recycled or disposed of. The sodium chloride obtained by evaporation can after washing and drying to pure sodium chloride and crystallized on cooling potassium chloride can be further processed by cold washing or recrystallization to a sales product with ≥ 95% KCl on.

Example 2 Heat dissolving concentrate with reduced clay content

By prior separation of clay by magnetic separation is obtained from the mentioned in Example 1 crude salt with about 20 percent higher recyclable content and about 30 to 50 percent of the starting content depleted clay content.

The concentrate is treated analogously to Example 1 at about +80 to 90 ° C with hot water to give a solution having about 70 g / l KCl, 155 g / l NaCl, 100 g / l MgSO ₄ having a density of 1,21- 1.22 g / cm ³ is formed. After cooling to about -7 ° C Na ₂ SO ₄ · 10H ₂ O is crystallized out analogously to Example 1 and this solution is heated again after its separation and evaporated analogously to Example 1. The potassium and sodium yield of the process is about 85 percent for potassium and about 95 percent for sodium due to the higher input concentration.

Example 3 Hot dissolving of low toning polymineral potash crude salts

A polymineral crude salt from another deposit has the following mineral contents: 18% Sylvite KCl 1% carnallite 0.5% Kainit 6% langbeinite 11% polyhalite 14% Kieserit 3% anhydrite 45% Halite (NaCl) 0.5% volume 1.0% Moist and other

Dissolving 100 t with hot water at + 90 ° C produces about 250 m ^{3 of} hot solution with the following analysis: KCl: 70-75 g / l NaCl: 180 g / l MgSO _4: 55 g / l MgCl ₂ : 2-3 g / l Density: about 1.27-1.28 g / cm ³ the dissolution residue consisting essentially of polyhalite, anhydrite and clay is filtered off hot.

Thereafter, this solution is cooled to -5 ° C. Only Glauber's salt (25-26 t) crystallizes again and the reheated solution separated from Glauber's salt has approximately the following composition: KCl: 75-80 g / l NaCl: 180-190 g / l MgSO _4: 15-18 g / l MgCl ₂ : 30-35 g / l Density: 1.22 g / cm ³

After evaporation of the solution and crystallization of the alkali metal chlorides described in Example 1, the residual solution is evaporated to a MgCl ₂ content of 190 to 200 g / l MgCl ₂ . The potassium yield is about 80-83 percent, the sodium yield about 92 to 94 percent. After further desulfurization of the separated at about + 25 ° C residual solution by precipitation of the sulfate as CaSO ₄ or by freezing as epsomite (MgSO ₄ · 7H ₂ O) according to known methods, this solution can be further vaporized into the Carnallitgebiet and theoretically the Alkali chlorides gain nearly one hundred percent.

The Glauber's salt can be further processed according to procedures known per se to thenardite (Na ₂ SO ₄ ) or to potassium sulfate (K ₂ SO ₄ ).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Freiberg Research Book A654, Leipzig 1981, pp. 39-47 [0003]

Claims (8)

Process for the preparation of high-percentage potassium chloride from polymineral, magnesium sulphate-rich potash or the crude salt fractions resulting from the dry preparation of these crude salts by a hot-solution cooling crystallization process, characterized in that heated water or a very dilute heated solution with low contents of KCl, as a dissolving liquor for the hot dissolving process, MgCl ₂ and MgSO ₄ used, the circulation of the solutions and reuse of the KCl-saturated mother liquor is completely avoided as Löselauge and evaporated from the insoluble constituents Wertstofflösung after desulfurization, thereby crystallized sodium chloride (NaCl) and the KCl-NaCl recovered by cooling crystallization Crystals are worked up by known methods to high-percentage potassium chloride. A method according to claim 1, characterized in that the hot dissolution with water or dilute solutions at temperatures of +80 to + 95 ° C, preferably +85 to + 90 ° C and the proportions of crude salt and solvent are adjusted, which is a solution composition which does not lead to the existence of magnesium sulfate-containing double salts on cooling. A method according to claim 1 to 2, characterized in that the desulfurization of the solution to be evaporated by a cooling process to low temperatures, preferably -5 to -7 ° C, wherein the dissolved sulfate excreted as mirabilite (Na ₂ SO ₄ · 10H ₂ O) becomes. A method according to claim 1 to 3, characterized in that the evaporation of the desulfated solution in one or more stages is such that from the evaporation with subsequent cooling of the evaporated solution to +20 to + 40 ° C, preferably +25 to + 35 ° C. a consisting of the alkali metal chlorides KCl + NaCl sulfate-free crystals and a residual solution with MgCl ₂ contents between 180 and 260 g / l MgCl ₂ is formed, which leaves the process after the crystallization separation. A method according to claim 1 and 4, characterized in that the NaCl obtained by evaporation and the KCl crystals obtained in the cooling crystallization of the hot evaporated solution to +20 to + 35 ° C, preferably +25 to + 30 ° C according to known per se Cleaning process to salable saline (NaCl) and high-percentage potash fertilizer with ≥ 95% KCl further processed. Process according to Claims 1 to 5, characterized in that the mirabilite crystallizate obtained by desulfurization by solution cooling is dehydrated and anhydrous sodium sulphate is prepared therefrom. A method according to claim 1 to 6, characterized in that the concentrated to 180 to 260 g / l MgCl ₂ content residual solution is desulphurized and further concentrated by evaporation with further KCl and NaCl recovery. A method according to claim 1 to 7, characterized in that the Mirabilit crystals obtained in the solution cooling and the KCl crystals obtained in the solution evaporation are converted in equimolar amounts to potassium sulfate and sodium chloride.