Method for producing potassium chloride granular materials

Abstract

A method for producing potassium chloride granular materials from a crystalline potassium chloride raw material, wherein, before the granulation process, the potassium chloride raw material is treated with at least one alkali metal carbonate and at least one metaphosphate additive in the presence of water.

Claims

1. A process for producing potassium chloride granules from a crystalline potassium chloride raw material, the process comprising: treating the crystalline potassium chloride raw material, prior to granulating, with at least one alkali metal carbonate in an amount of from 0.05 to 0.7 wt. % and at least one alkali metal metaphosphate in an amount of from 0.025 to 0.4 wt. %, in the presence of water, the weight percentages based on solid constituents of the crystalline potassium chloride raw material, to obtain a treated potassium chloride material; and subsequently, granulating the treated potassium chloride material, the granulating comprising compression agglomeration of the treated potassium chloride material, wherein the at least one alkali metal carbonate is selected from the group consisting of a potassium carbonate, a sodium carbonate, and a mixture thereof, wherein a counterion of the at least one alkali metal metaphosphate is at least one selected from the group consisting of sodium and potassium, and wherein at least 90 wt. % of the potassium chloride granules have a particle size or particle diameter in a range of from 0.5 to 8 mm.

2. The process of claim 1, wherein the amount of the at least one alkali metal carbonate is in a range of from 0.1 to 0.7 wt.

3. The process of claim 1, wherein the amount of the at least one alkali metal metaphosphate is in a range of from 0.07 to 0.4 wt. %.

4. The process of claim 1, wherein, during the treating, water is present in a range of from 2 to 15 wt. %, based on the solid constituents of the crystalline potassium chloride raw material.

5. The process of claim 1, wherein the at least one alkali metal carbonate is used in a form of a powder and/or in a form of an aqueous solution.

6. The process of claim 1, wherein the at least one alkali metal metaphosphate is used in a form of a powder and/or in a form of an aqueous solution.

7. The process of claim 1, wherein the crystalline potassium chloride raw material comprises magnesium salt(s), calcium salt(s), or mixture thereof, in an amount of from 0.01 to 1.0 wt. %, based in each case on KCl and calculated as MgCl.sub.2 and CaCl.sub.2 respectively.

8. The process of claim 1, further comprising: adding the at least one alkali metal carbonate and the at least one alkali metal metaphosphate to a moist potassium chloride raw material having a water content of at least 2 wt. %, based on the solid constituents of the potassium chloride raw material.

9. The process of claim 8, further comprising: drying the moist potassium chloride raw material, after the adding, prior to the granulating.

10. The process of claim 1, further comprising: adding at least one micronutrient to the crystalline potassium chloride raw material before or during the granulating.

11. Potassium chloride granules, obtained by the process of claim 1.

12. A method for reducing moisture absorption and/or increasing fracture resistance or cracking resistance of potassium chloride granules exposed to high air humidity, the method comprising: bringing a combination of at least one alkali metal carbonate in an amount of from 0.05 to 0.7 wt. %, at least one alkali metal metaphosphate additive in an amount of from 0.025 to 0.4 wt. %, and water, into contact with a crystalline potassium chloride raw material, the weight percentages based on solid constituents of the crystalline potassium chloride raw material, to obtain a treated potassium chloride material; and subsequently, granulating the treated potassium chloride material, to obtain the potassium chloride granules, wherein the potassium chloride granules, when having a grain size in a range of from 2.5 to 3.15 mm have a reduced moisture absorption, based on mass measurement after 24 hours at 20° C. under relative humidity in a range of from 70 to 71%, and/or an increased fracture resistance or cracking resistance, based on mean cracking resistance measured with an ERWEKA® TBH 425D tablet hardness tester on 56 individual agglomerates of different particle size in a 2.5 to 3.15 mm fraction, relative to otherwise identically made potassium chloride granules, using only one of the alkali metal carbonate and the metaphosphate in an identical mass to a total mass of the alkali metal carbonate and the metaphosphate, wherein the at least one alkali metal carbonate is selected from the group consisting of a potassium carbonate, a sodium carbonate, and a mixture thereof, wherein a counterion of the at least one alkali metal metaphosphate is at least one selected from the group consisting of sodium and potassium, wherein the granulating comprises compression agglomeration of the treated potassium chloride material.

13. The method of claim 12, which increases the fracture resistance or cracking resistance of the potassium chloride granules.

14. The method of claim 12, which reduces the moisture absorption of the potassium chloride granules.

15. The method of claim 12, which reduces the moisture absorption of the potassium chloride granules and increases the fracture resistance or cracking resistance of the potassium chloride granules.

16. The method of claim 12, wherein, during the treating, water is present in a range of from 2 to 15 wt. %, based on the solid constituents of the crystalline potassium chloride raw material.

17. The method of claim 15, wherein, during the treating, water is present in a range of from 4 to 9 wt. %, based on the solid constituents of the crystalline potassium chloride raw material.

18. The method of claim 1, wherein, during the area water is in a range of from 4 to 9 wt. %, based on the solid constituents of the potassium chloride raw material.

19. The method of claim 12, wherein, during the treating, water is in a range of from 4 to 9 wt. %, based on the solid constituents of the potassium chloride raw material.

Description

LABORATORY EXPERIMENTS

(1) The potassium chloride raw material (fine salt) used was a crystalline material obtained by hot leaching. The potassium content of the potassium chloride was around 60% by weight, calculated as K.sub.2O and based on solid constituents. The Mg content, calculated as MgCl.sub.2, and the Ca content, calculated as CaCl.sub.2, totaled around 0.13% by weight, based on solid constituents. The grain size of the potassium chloride raw material (fine salt) was generally was 0.01 to 2 mm. The water content of the moist potassium chloride raw material (moist fine salt) was 4-9% by weight, especially 8% by weight, based on the solid constituents prior to the drying.

(2) The alkali metal carbonate and metaphosphate additive used in each case were a commercial pulverulent anhydrous sodium carbonate and hexasodium metaphosphate with a water content of 0.01% by weight.

(3) Production of test specimens for the determination of fracture resistance:

(4) For this purpose, 3 kg of the potassium chloride of the above-stated specification, with addition of 240 g of water, were mixed with the respective additive in powder form in an intensive mixer for 1 min. The moist potassium chloride raw material/additive mixture was dried in a drying cabinet at 105° C. for 24 h and then deagglomerated with a disk mill to a grain size of <0.8 mm. For the “dry” comparative experiments, the additives were mixed together after the drying and after the deagglomeration.

(5) For the determination of fracture resistance, this material was used to produce cuboidal test specimens of dimensions 50×50×8 mm. The production of the test specimens (laboratory experiments) was effected by means of a hydraulic ram press (K50 model from Komage) at a compression force of about 290 kN, as shown in schematic form in FIG. 1.

(6) Determination of fracture resistance (point load) of the test specimens:

(7) The unweathered test specimens were analyzed immediately after they had been produced.

(8) For weathering, the freshly produced test specimens were weighed and then weathered as follows: The test specimens were fixed vertically in sample holders and stored in a climate-controlled cabinet at 20° C. and 70% relative air humidity for 72 h.

(9) Immediately after they had been removed from the climate-controlled cabinet, the test specimens thus weathered were weighed again to determine water/moisture absorption and then fracture resistance was determined immediately.

(10) The determination of fracture resistance via a point load was in accordance with ASTM D5731:2008 (Point load strength index). For this purpose, the square test specimens (2) were fixed at both sides in the u-shaped sample holder (3) of the tester shown schematically in FIG. 1 in such a way that the test tip (R5) was directed to the middle of the square test specimen (2). Then the test tip was pressed onto the test specimen at a speed of 1 mm/min and the force exerted on the test specimen was determined by means of a load cell. The maximum stress value on the test specimen immediately prior to the fracture of the test specimen is ascertained, which is indicated by a drop in the force to zero. The test tip was conical with a cone angle of 60°. The tip has a radius of 5 mm (cf, FIG. 1).

(11) 10 test specimens (weathered/unweathered) were measured in each case. The values for the compressive strengths (point load) reported in table 1 are averages from 10 measurements.

(12) TABLE-US-00001 TABLE 1 Compressive strengths of test specimens composed of potassium chloride raw material and the additives anhydrous sodium carbonate and SHMP, laboratory experiments (square test specimens): Moisture Point loads Point loads- absorption # Additives unweathered weathered** at 70% RH** 1* 0.16% by wt. A11 + 0.38 kN 0.34 kN 0.12% 0.4% by wt. P931 2* 0.16% by wt. A11 + 0.32 kN 0.28 kN 0.21% 0.2% by wt. P931 3* 0.16% by wt. A11 + 0.33 kN 0.25 kN 0.30% 0.1% by wt. P931 4* 0.16% by wt. A11 + 0.33 kN 0.20 kN 0.40% 0.05% by wt. P931 5* 0.16% by wt. A11 + 0.39 kN 0.33 kN 0.26% 1.0% by wt. P931 V6 0.16% by wt. A11 0.35 kN 0.19 kN 0.65% (dry) + 0.4% by wt. P931 (dry) V7* 0.4% by wt. P931 0.34 kN 0.23 kN 0.29% V8* 0.2% by wt. P931 0.33 kN 0.21 kN 0.50% V9* 0.1% by wt. P931 0.35 kN 0.22 kN 0.57% V10* 0.05% by wt. P931 0.33 kN 0.19 kN 0.64% V11 0.4% by wt. P931 0.35 kN 0.20 kN 0.71% dry V12* 0.13% by wt. A11 0.33 kN 0.19 kN 0.41% V13 0.16% by wt. A11 0.33 kN 0.15 kN 0.68% dry V14* Potassium chloride 0.34 kN 0.17 kN 0.63% raw material (here: 60er MOP fein) without additive *each with 8% by weight of water; **weathered 72 h, 20° C., 70% RH; # = experiment number; V = comparative experiment; A11 = anhydrous sodium carbonate; P931 = hexasodium metaphosphate (SHMP); 60er MOP fein = fine potassium chloride salt with a potassium content of at least 60.0% K.sub.2O

(13) Factory Operation Experiment:

(14) For production of potassium chloride granules in a factory operation experiment, moist potassium chloride raw material (i.e. moist fine salt) having a residual moisture content of 2-15% by weight was sent to the drying stage, optionally via a mixer. The additives of the invention were added, for example, in the installed mixer and the mixture was homogenized. The treated fine salt was then sent to the drying stage and subsequently introduced into the presses, optionally together with the compression reject material in the granulation. After classification/comminution, the material of the correct size is obtained, the saleable potassium chloride granules. One name given to these granules, provided that the potassium chloride content is at least 60.0% K.sub.2O, is commercial “60er MOP-Gran”.

(15) For the compression agglomeration, in production, multiple roll presses with reject material circulation were used. The individual roll presses are constructed as follows: two rolls rotating counter to one another have waffle profiling on the roll surface (typical roll diameter 1000 mm, typical working width 1000 mm, gap width typically about 15 mm). The press was run with a linear force of around 60 kN/cm and a roll speed of 18 rpm. The fine salt was generally fed in by means of a central chain conveyor and the stuffing screws arranged above the presses.

(16) The slugs obtained in the roll press were comminuted by means of an impact mill. Subsequently, the material was classified with a conventional sieving apparatus, the fraction with grain size 2-4 mm (product) was separated off, the fraction with grain size <2 mm was recycled to the feed (fines), and the fraction with grain size >4 mm (oversize) was ground up and sieved again.

(17) For the determination of the cracking resistance of the granules, a test fraction (test granules) with a grain size of 2.5-3.15 mm was sieved out.

(18) The unweathered test granules were analyzed parallel to the weathered granules.

(19) For weathering, about 9 g of the test granules produced were introduced into a petri dish and weighed. For conditioning, the petri dish was stored in a climate-controlled cabinet at 20° C. and relative air humidity 70% or 71% for 24 h. Immediately after it had been removed from the climate-controlled cabinet, the petri dish containing test granules was weighed again to determine water absorption and then the fracture resistance of the granules was determined immediately by the method that follows.

(20) The mean cracking resistances were ascertained with the aid of the TBH 425D tablet hardness tester from ERWEKA on the basis of measurements on 56 individual agglomerates of different particle size (2.5-3.15 mm fraction), and the average was calculated. The force required to break the granule between the ram and plate of the fracture resistance tester was determined. Granule particles having a cracking resistance >400 N and those having a cracking resistance <4 N were not included in the formation of the average.

(21) In the factory operation experiment detailed in tab. 2, potassium chloride raw material having the following specification was used: KCl content around 61% K.sub.2O. MgCl.sub.2/CaCl.sub.2 content about 0.2% by weight, the residual moisture contents of the (moist) potassium chloride raw material were generally 5.7-6.2% by weight. The amounts processed run to around 90 t/h potassium chloride raw material.

(22) TABLE-US-00002 TABLE 2 Factory operation experiments: potassium chloride granules with anhydrous sodium carbonate and SHMP made from filter- moist potassium chloride (KCl) raw material* (cracking resistances in N and moisture absorption in %) # Additives unweathered 1 d/70% RH 1 d/71% RH 15* 0.26% by wt. A11 + 80N 47N  26N 0.07% by wt. P931 0.14% 0.55% V16* 0.12% by wt. P931 70N 18N <10N 1.10% 2.75% V17* KCl raw material 62N 14N <10N (no additive) 1.34% 3.14% # = experiment number; 1 d/70% RH = storage at 70% relative humidity for 1 day 1 d/71% RH = storage at 71% relative humidity for 1 day *each with about 6% by weight of water; A11 = anhydrous sodium carbonate; P931 = hexasodium metaphosphate (SHMP)

(23) Table 2 shows the in comparison the particular effect of the combination of the additives anhydrous sodium carbonate with SHMP, for example compared to SHMP. The potassium chloride granules from experiment 15 show distinctly better cracking resistances even in the case of higher relative air humidities—than the products from comparative experiment V16 and V17. Moisture absorption after one day is 0.14% (70% rel. humidity) and 0.55% (71% rel. humidity).

(24) TABLE-US-00003 TABLE 3 Laboratory experiments with potassium chloride granules with the additives anhydrous sodium carbonate and SHMP and micronutrients** Point loads - Point loads - Moisture # Additives unweathered weathered absorptionn 18* 0.16% by wt. A11 + 0.34 kN 0.39 kN 0.26% 0.4% by wt. P931 + 0.5% by wt. B # = experiment number; *with 8% by weight of water; **for comparative experiments see No. 1 and V14 A11 = anhydrous sodium carbonate; P931 = hexasodium metaphosphate (SHMP), B = anhydrous borax, calculated as boron