Process for the complete material utilization of the valuable components of polymineralic hard salts with a high clay content

Abstract

A process for the complete material utilization of polymineralic hard salts with a high clay content by hot leaching of the chloride minerals, including sodium chloride, and the soluble sulfate minerals with water for several hours. This yields a KCl-MgSO4-NaCl solution and, by solid-liquid separation, a solvent residue consisting of sulfate and clay minerals. After drying and calcination, the solvent residue produces a clay-containing, chloride-free K-Mg-Ca-SO4 fertilizer granulate with soil-improving properties. Magnesium chloride solution is generated as a byproduct and can be used as a raw material for magnesium as well as for magnesium compounds such as MgCl2·6H2O and Mg(OH)2, which can be produced using known methods.

Description

[0001] The invention relates to a process for the complete utilization of all valuable components of multi-component polymineral potash raw salts (hard salts) with a high proportion of polysulfate minerals and a high proportion of clay minerals. Such polymineral hard salts with high impurities of insoluble material in the form of clay minerals contain a variety of mineral components suitable for the production of fertilizers. Such raw salts are mainly typical of potash deposits in the Carpathian foothills. Both clay-rich and clay-poor polymineral potash raw salts consist, in addition to rock salt (halite), of potassium-containing minerals (kainite, sylvite, langbeinite, polyhalite), sulfate minerals (kieserite, anhydrite), and, in the case of the Carpathian foothills deposits, of up to 20 percent further insoluble components in the form of various clay minerals and other silicates.The production of potassium sulfate from such multi-component mineral mixtures has not yet been achieved on an industrial scale. Despite accepting significant environmental damage and substantial losses in the processing, only the extraction of the potassium and magnesium components of the minerals sylvite (KCl), kainite (KCl · MgSO4 · 2.75 H2O), and kieserite (MgSO4 · H2O) contained in the raw salt has been possible so far in a hot dissolution process. In this process, the minerals langbeinite and polyhalite, along with halite (NaCl) and clay, were generated as dissolution residues and sludge, resulting not only in unusable materials but also in severe environmental pollution.

[0002] The product obtained via an intermediate stage was the double salt Schönite (K2SO4 · MgSO4 · 6 H2O) and after its thermal calcination a K2SO4-MgSO4 mixture which, after press granulation, yielded a K-Mg fertilizer with 30% K2O and 10% MgO (Kalimag40) as a marketable product.

[0003] The relatively low utilization rate of potassium and magnesium in the overall process, the generation of a residue-sludge mixture with high proportions of unrecoverable sulfate minerals, sodium chloride, and clay, and the inability to adapt the process to fluctuations in the raw salt composition and changing market conditions are significant disadvantages of existing methods for such multi-component polymineral hard salts, which, in addition to their diverse mineral components, also contain considerable amounts of clay and silicates. Even flotation separation yielded only a K₂O concentrate of 18 to 20% with approximately 50% potash loss. Since a clay content of 15 to 20% in the raw potash salt severely and negatively impacts mineral separations, resulting in very high losses of valuable materials and environmental pollution from clay sludge, it has been proposed to significantly reduce the clay content of the raw salt through its dry separation.DE 3613 672 A1 describes such a process for separating clays from salts using a permanent magnet separator in a high-field magnetic separator. Unfortunately, this separation method only achieves acceptable separation results with multi-component raw salts in the range of medium grain sizes from 1 to 4 millimeters and requires field strengths of over 3 Tesla or the use of superconducting magnetic systems. Even slight material moisture content significantly disrupts the separation process, and even under optimal conditions, a considerable residue of clay minerals always remains in the raw salt being processed. The production of chloride-free potash fertilizers as potassium sulfate from raw salts containing KCl and MgSO4 is currently only feasible if the minerals are present as sylvite, kieserite, and halite, as is the case in Germany, without clay content. These conditions exist in potash mines in Thuringia and Hesse, but are not applicable to raw salts with high clay and polysulfate content.

[0004] It is also possible to produce chloride-free potash products if the potash and magnesium component is present as the double salt kainite only next to rock salt, as is the case in some deposits in Sicily or in the USA.

[0005] DBP 1086 220 describes a process for the continuous production of potassium sulfate from kainite by a hot dissolution process followed by cooling of the solution from 100 °C to 20 °C, yielding schönite as a crystallizate and ultimately potassium sulfate from it. Further process proposals for kainitic potash crude salts are presented in DBP 1140 914 and DBP 1210 427. Process proposals suitable for crude kainite are also the subject of DE 1215 667, 1467 240, and DDWP 43613. These processes require either natural clay-free crude salts without significant proportions of sulfate minerals other than kainite or kainite-containing crystallizates from processing potassium- and sulfate-containing solutions.

[0006] None of the proposed processes are suitable for producing potassium sulfate from raw salts that simultaneously contain the potassium component as sylvite, kainite, langbeinite, and polyhalite, as well as sodium chloride in the form of rock salt and significant amounts of clay minerals. A new approach for the production of potassium chloride and sulfate end products is described in DE 10 2009 041 456 A1 / 2011.03.24 as a process for producing high-percentage potassium chloride from polymineralic, magnesium sulfate-rich potash raw salts. The claimed process, which is also suitable for processing raw salt with a high clay content, avoids recirculating the mother liquor and instead employs a hot dissolution process of the raw salt at approximately 85 °C using hot water as the solvent. This results in the sodium chloride also being dissolved in the raw salt.The solvent residue, consisting of polyhalite, anhydrite and clay minerals, is removed after washing and pressure filtration using a filter press, thus representing waste and would be the cause of a considerable environmental problem (slag heap or sludge pond).

[0007] The invention aims to obtain virtually all valuable components from multi-component and significantly clay-containing polymineral potash raw salts, including the contained halite (NaCl) as well as the insoluble sulfate minerals such as polyhalite and the clay, in the form of marketable products.

[0008] The object of the invention is to realize a process path after mining, raw salt extraction and raw salt grinding which is able to decompose the ground raw salt into all chloride and sulfate raw salt components and a residue consisting of clay and the sparingly soluble sulfate minerals and subsequently obtain these in a usable form.

[0009] This problem is solved by eliminating, analogous to DE 10 2009 041 456 A1, the need to separate potassium-containing mineral components from the non-potassium-containing raw salt components by processing methods that aim to obtain rock salt, sulfate minerals, and clay as a repulsive byproduct. The process according to the invention successively isolates the soluble, primarily chloride-containing, raw salt components by dissolution, thereby avoiding the separation of halite as an insoluble, repulsive residue and also foregoing the separation of clay minerals for disposal. Instead, a multi-component fertilizer containing K₂O, MgO, and CaO is obtained from the potassium and magnesium content of the undissolved polysulfate minerals, and the clay minerals are also incorporated into this mixture. The main products, however, are potassium sulfate and magnesium sulfate, as well as marketable NaCl.

[0010] By using undissolved polysulfate minerals and incorporating the insoluble clay minerals into an additional marketable product, the process according to the invention differs significantly from the known process of DE 10 2009 041 456 A1, but works in approximately the same way as already described therein.Characteristically, polymineralic magnesium sulfate-rich potash crude salts with up to 20% insoluble content are extracted by hot dissolution with water at dissolution temperatures between +80 and +95°C, without recycling and reusing the mother liquor as a solvent. From this, Glauber's salt (Na2SO4·10H2O) is obtained by cooling to temperatures <0°C, followed by evaporation to obtain NaCl crystallizate, and by cooling to obtain KCl crystallizate, which are then processed into high-percentage potash fertilizer, table salt, and anhydrous sodium sulfate using known processes. The preferred target product potassium sulfate is obtained from the KCl crystallizate obtained by evaporation of the solution and the Glauber's salt or anhydrous sodium sulfate, as already claimed in patent application DE 10 2009 041 456 A1, according to methods also known beforehand.

[0011] The process according to the invention, like those known before it, uses hot water as a solvent and therefore dissolves all water-soluble minerals, thereby obtaining potassium and sodium chloride as solutions, as well as the magnesium component of water-soluble Mg mineral salts. The clay / silicate component contained in the raw salt, which is usually considered a contaminant or waste component in polymineralic hard salts, is not disposed of in environmentally damaging sludge ponds as is customary, but is processed into a practically chloride-free multi-nutrient fertilizer containing the nutrients potassium, magnesium, calcium, and sulfur as a byproduct. This fertilizer consists of approximately 50% harmless clay substrate and is obtained in granular form. Clays do not cause problems as a component of fertilizer granules during application or in the topsoil and generally even have positive soil-improving effects in podzol soils and even in normal soils.A typical polymineralic potash crude salt from the deposits of the Precarpathians consists of minerals whose diversity differs from that of usual potash crude salts and is furthermore characterized by a considerable range of mineral composition and, above all, by a considerable clay content, for which the process according to the invention can produce marketable products.

[0012] In accordance with the claimed method of DE 10 2009 041 456 A1 “Process for the production of high-percentage potassium chloride from polymineralic magnesium sulfate-rich potash crude salts”, such a separation was achieved in the dissolution process according to the invention and, with a dissolution time of a maximum of three hours, an extract solution with the components KCl, NaCl, MgSO4, MgCl2 and H2O as well as an undissolved crude salt fraction as a dissolution residue was obtained, which contains the mineral components clays and silicates, anhydrite (CaSO4), polyhalite (K2SO4 · MgSO4 · 2 CaSO4 · 2 H2O) and partial amounts of kieserite (MgSO4 · H2O) and langbeinite (K2SO4 · 2 MgSO4).

[0013] Hot water (condensate) at approximately 60 °C has proven to be the preferred solvent.

[0014] The suspension obtained after the dissolution process can be separated using known methods and equipment. This includes pressure filters and filter presses as well as continuous solid-walled screw centrifuges. This process yields both solution and insoluble solid. The solution obtained as a filtrate or through a prior clarification and thickening process is decomposed into crystallizes by dehydration and temperature variations, utilizing the known solution equilibria of the K-Na-Mg-Cl-SO4-H2O system. The crystallizes occur in the following sequence: Na2SO4 · 10 H2O - KCl - NaCl - MgSO4 · 7 H2O, ultimately yielding MgCl2 as a concentrated solution.

[0015] The filtered mixture of clay minerals and sparingly soluble sulfate minerals is dried to remove the water. First, the adhering water is removed, and then, at a higher temperature, the water contained as water of crystallization is removed.

[0016] This calcined mineral mixture forms a hard mass containing approximately 50% clay and 50% sulfate minerals, but very little chloride. According to the invention, this hard mixture is ground and the 2-5 mm particle size fraction is then isolated by sieving. Surprisingly, this mixture has excellent soil-improving and fertilizing properties, as neither the clay content nor the small residual chlorides are detrimental. It was found that after application to arable land, the otherwise practically insoluble polyhalite decomposes due to precipitation and the extremely long dissolution times in the soil itself. This causes its components K₂SO₄, MgSO₄, and CaSO₄ to dissolve slowly and completely, and the clay content not only does not cause problems but actually improves the soil quality.

[0017] The invention is explained in more detail by means of an example. Example (See Fig. 1)

[0018] 100 tons of crude potash salt, crushed to < 5 millimeters and composed of 22% kainite, 5% sylvite, 35% halite, 5% kieserite, 9% langbeinite, 3% anhydrite, 9% polyhalite and 15% clay minerals, are heated at 60 °C with 160 ± 10 m 3The mixture is stirred in hot water for 2 to 2.5 hours and then separated by pressure filtration. The minerals kainite, sylvite, and halite are completely dissolved, while kieserite and langbeinite are largely dissolved. Polyhalite, clay, and anhydrite remain as an insoluble residue-sludge mixture, which, after separation from the solution, consists of approximately 30% polyhalite, 5% langbeinite, 9% kieserite, 30% clay, and about 25% adhering solution, resulting in a chloride content of only about 3%. This moist product contains approximately 27% total water, which can be completely removed by heating to over 350 °C. This yields a rock-hard dry material that can be ground. From this, a granulate with a grain size of 2-5 mm and the fertilizer-effective components 8% K2O, 5-8% MgO, 8% CaO, 20% SO3 can be obtained by sieving, which contains a maximum of 3% chloride.

[0019] From the extract solution with the typical composition 70 g / l KCl, 105 g / l MgSO4, 120 g / l NaCl, 0-5 g / l Na2SO4, 0.3 g / l CaSO4 and a density of 1.22 g / ml, the following substances are obtained by known processes of cooling and evaporation crystallization: Na2SO4 · 10 H2O, KCl, NaCl, MgSO4 · 7 H2O, and from these, potassium sulfate (K2SO4) and further NaCl can be produced by also known processes, such as the Glaserite process, as well as anhydrous MgSO4 and a magnesium chloride solution by calcination.

[0020] The process allows the complete conversion of the components potassium chloride and sodium sulfate from the extract solution to potassium sulfate via the intermediate of the double salt glaserite (3 K2SO4 · Na2SO4) in a manner known per se.

[0021] 15 t of K₂SO₄ result from 12.8 t each of KCl and Na₂SO₄ reacted with 40 t of water at 25 °C. The water introduced into the process must be removed from the glassy mother liquor by evaporation, yielding 10 t of NaCl as crystals. The conversion process of 2 moles of KCl and 1 mole of Na₂SO₄ requires almost exactly 1 t of Na₂SO₄ for every 1 t of KCl. However, this ratio is generally not present in typical polymineralic crude potash salts; instead, there is usually an excess of soluble sulfate, which is obtained as Glauber's salt or can also be recovered as Epsom salt (MgSO₄ · 7 H₂O).

[0022] The excess sulfate obtained through cooling, for which no corresponding amount of KCl is available, can be easily produced as anhydrous magnesium sulfate or sodium sulfate as a by-product using known methods and removed from the process.

[0023] Further soluble sulfate present in the extract solution accumulates in parallel with the MgCl2 content in the solution during the further course of the process and can be removed by cooling the solution as Epsom salt (MgSO4 · 7 H2O).

[0024] From 100 tons of raw potash salt, the following totals are obtained: • 15 t potassium sulfate (> 95% K2SO4) • 10 t magnesium sulfate (> 95% MgSO4) or 20 t MgSO4 · 7 H2O • 35 t sodium chloride (> 95% NaCl) • 25-30 t K · Mg CaSO4 - Granules with approx. 50% clay + 50% sulfate minerals • 20 t MgCl2 solution (32% MgCl2), so-called MgCl2 final solution Reference symbol list

[0025] (to Fig. 1) Raw materials A 1 Raw salt A 1.1 Sylvin (soluble) A 1.2 Syngenit (sparingly soluble) A 1.3 Halite (soluble) A 1.4 Kieserite (soluble) A 1.5 Langbeinit (soluble) A 1.6 Polyhalite (sparingly soluble) A 1.7 clay (insoluble) A 2 Water B Intermediates B 1.1 Leaching residue B 1.2 Leasing solution B 2.1 crystallized NaCl B 2.2 evaporated solution B 3.1 crystallized MgSO4 B 3.2 Solution B 4.1 crystallized K2SO4 B 4.2 MgCl2 solution C Process stages C 1 leaching C 2 Evaporation with NaCl crystallization C 3 Cooling with MgSO4 crystallization C4 double reaction with K2SO4 crystallization D products D 1 NaCl, >99% D 2 MgSO4, as Epsom salt or anhydrous D 3 Potassium sulfate, D 4 MgCl2 solution, 30 - 33 % MgCl2 D 5 K-Mg-Ca fertilizer, chloride-free, granulated QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 3613 672 A1

[0003] DE 1215 667, 1467 240

[0005] DE 10 2009 041 456 A1 [0006, 0009, 0010, 0012]

Claims

[1] Method for the complete material utilization of the valuable components of polymineralic hard salts with a high clay content as a chloride-free fertilizer potassium sulfate (K2SO4) and sodium chloride in evaporated salt quality, magnesium sulfate (MgSO4 or MgSO4 · 7 H2O), a K-Mg-Ca-SO4 fertilizer containing clay, and a magnesium chloride solution suitable for flushing processes or material utilization, characterized by, that the water-soluble chloride minerals, including halite, and the soluble sulfate minerals are extracted from the mined, ground polymineralic raw salt by means of hot water in a dissolution process lasting several hours in a previously known manner, in the form of a KCl-NaCl-MgSO4-MgCl2-containing extract solution, and that the solvent residue, consisting of clay minerals and sulfate minerals that are not or not completely dissolved, is dried and calcined after its separation, and a chloride-free multi-component fertilizer with potassium, magnesium, sulfate and clay is produced from it. [2] Method according to claim 1, characterized by , that in the dissolving process the amount of raw salt and the amount of water are used in a ratio of 1 : 1.4 to 1 : 1.8, preferably 1 : 1.6, and the duration of the leaching from the raw salt ground to a grain size < 5 mm is preferably 2 ± 0.5 hours and the dissolving temperature is preferably 60 °C. [3] Method according to claims 1 and 2, characterized by, that the residue separated from the hot extract solution by filtration or centrifugation is washed to be approximately chloride-free, thermally dried and then calcined at 350 to 400 °C. [4] Method according to claims 1 to 3, characterized by , that all magnesium chloride produced is obtained as a concentrated, preferably 32 to 33 percent MgCl2 final solution and this is exported as a further usable by-product from the processing process.

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