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 hydrogen phosphate additive in the presence of water. The alkali metal carbonate is anhydrous sodium carbonate, sodium carbonate monohydrate or sodium carbonate decahydrate.

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 and at least one hydrogenphosphate additive in the presence of water.

2: The process as claimed in claim 1, wherein the at least one alkali metal carbonate is selected from the group consisting of anhydrous sodium carbonate, sodium carbonate monohydrate and sodium carbonate decahydrate.

3: The process as claimed in claim 1, wherein the at least one hydrogenphosphate additive is an alkali metal hydrogenphosphate.

4: The process as claimed in claim 1, wherein the at least one alkali metal carbonate is used in an amount of 0.05% to 1% by weight based on solid constituents of the crystalline potassium chloride raw material.

5: The process as claimed in claim 1, wherein the at least one hydrogenphosphate additive is used in an amount of 0.025% to 2% by weight based on solid constituents of the crystalline potassium chloride raw material.

6: The process as claimed in claim 1, wherein water content during the treating is in a range from 2% to 15% by weight based on solid constituents of the crystalline potassium chloride raw material.

7: The process as claimed in 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.

8: The process as claimed in claim 1, wherein the at least one hydrogenphosphate additive is used in a form of a powder and/or in a form of an aqueous solution.

9: The process as claimed in claim 1, wherein the crystalline potassium chloride raw material comprises 0.01% to 1.0% by weight of magnesium salts and calcium salts and mixtures thereof based in each case on KCl and calculated as MgCl.sub.2 and CaCl.sub.2 respectively.

10: The process as claimed in claim 1, wherein the granulating is carried out with a potassium chloride raw material in which at least 90% by weight of pulverulent potassium chloride raw material has a particle size in a region of less than 2 mm.

11: The process as claimed in claim 1, wherein the granulating comprises compression agglomeration of the crystalline potassium chloride raw material.

12: The process as claimed in claim 1, further comprising: adding the at least one alkali metal carbonate to a moist potassium chloride raw material.

13: The process as claimed in claim 1, further comprising: adding the at least one hydrogenphosphate additive to a moist potassium chloride raw material.

14: The process as claimed in claim 12, further comprising: drying the moist potassium chloride raw material, after the adding, prior to the granulating.

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

16: Potassium chloride granules obtainable by the process as claimed in claim 1.

17: A method for reducing moisture absorption of potassium chloride granules, the method comprising: bringing a combination of at least one alkali metal carbonate, at least one hydrogenphosphate additive and water into contact with the potassium chloride granules.

18: A method for increasing fracture resistance or cracking resistance of potassium chloride granules that are exposed to high air humidity, the method comprising: bringing a combination of at least one alkali metal carbonate, at least one hydrogenphosphate additive and water into contact with the potassium chloride granules.

19: The process as claimed in claim 13, further comprising: drying the moist potassium chloride raw material, after the adding, prior to the granulating.

Description

[0061] FIG. 1 shows an experimental setup for determination of fracture resistance for test specimens, comprising a test ram (1) having a conical test tip (R5) and a u-shaped test specimen holder (3) in which the test specimen (2) is fixed on both sides.

LABORATORY EXPERIMENTS

[0062] 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 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.

[0063] The alkali metal carbonate and hydrogenphosphate additive used in each case were a commercial pulverulent anhydrous sodium carbonate and disodium hydrogenphosphate with a water content of 0.01% by weight.

[0064] Production of test specimens for the determination of fracture resistance:

[0065] 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.

[0066] For the determination of fracture resistance, this material was used to produce cuboidal test specimens of dimensions 50508 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.

[0067] Determination of Fracture Resistance (Point Load) of the Test Specimens:

[0068] The unweathered test specimens were analyzed immediately after they had been produced. 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.

[0069] 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.

[0070] 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).

[0071] 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.

TABLE-US-00001 TABLE 1 Fracture resistances of test specimens made from potassium chloride raw material and the additives anhydrous sodium carbonate and anhydrous disodium hydrogenphosphate or anhydrous sodium dihydrogenphosphate, laboratory experiments (square test specimens): Moisture Point loads- Point loads- absorption at # Additives unweathered weathered** 70% RH** 1* 0.16% by wt. A11 + 0.37 kN 0.32 kN 0.08% 0.28% by wt. P954 2* 0.16% by wt. A11 + 0.36 kN 0.26 kN 0.13% 0.14% by wt. P954 3* 0.16% by wt. A11 + 0.35 kN 0.23 kN 0.26% 0.07% by wt. P954 4* 0.16% by wt. A11 + 0.34 kN 0.21 kN 0.23% 0.04% by wt. P954 V5* 0.28% by wt. P954 0.37 kN 0.28 kN 0.24% V6* 0.14% by wt. P954 0.33 kN 0.22 kN 0.49% V7* 0.07% by wt. P954 0.30 kN 0.21 kN 0.63% V8* 0.04% by wt. P954 0.33 kN 0.20 kN 0.72% V9 0.28% by wt. P954 0.32 kN 0.20 kN 0.25% dry V10* 0.13% by wt. A11 0.33 kN 0.19 kN 0.41% V11 0.16% by wt. A11 0.33 kN 0.15 kN 0.68% (dry) V12 0.16% by wt. A11 0.34 kN 0.19 kN 0.24% (dry) + 0.28% by wt. P954 (dry) V13* KCl raw material 0.34 kN 0.17 kN 0.63% without additive 14* 0.08% by wt. A11 + 0.35 kN 0.31 kN 0.13% 0.28% by wt. P954 15* 0.32% by wt. A11 + 0.38 kN 0.32 kN 0.11% 0.24% by wt. P951 *each with 8% by weight of water; **weathered 72 h, 20 C., 70% RH; # = experiment number; V = comparative experiment; A11 = anhydrous sodium carbonate; P954 = anhydrous disodium hydrogenphosphate; P951 = anhydrous sodium dihydrogenphosphate 60er MOP fein = fine potassium chloride salt with a potassium content of at least 60.0% K.sub.2O

Factory Operation Experiment:

[0072] For production of potassium chloride granules for the factory operation experiments, 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The unweathered test granules were analyzed parallel to the weathered granules.

[0077] 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%, 72%, 73% or 74% 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.

[0078] 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.

[0079] 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.

TABLE-US-00002 TABLE 2 Factory operation experiments: potassium chloride granules with anhydrous sodium carbonate and anhydrous disodium hydrogenphosphate made from filter-moist potassium chloride (KCI) raw material* with different weathering (cracking resistances in N and moisture absorption in %) un- 1 d/ 1 d/ 1 d/ 1 d/ # Additives weathered 70% RH 72% RH 73% RH 74% RH 16* 0.16% by wt. AA11 + 83 N 47 N 15 N <10 N 0.08% by wt. P954 0.1% 3.1% 7.0% 17* 0.16% by wt. A11 + 73 N 46 N 19 N 17 N 16 N 0.15% by wt. P954 0.1% 2.4% 4.3% 5.2% V18* 0.08% by wt. P954 61 N 13 N <10 N 1.1% 4.4% V19* 0.15% by wt. P954 85 N 24 N <10 N 0.6% 5.1% V20* 0.16% by wt. A11 85 N 37 N <10 N 0.2% 3.5% V21* KCI raw material 70 N <10 <10 <10 <10 (no additive) 2.1% 7.3% 12.0% 14.5% # = experiment number; 1 d/70% RH = storage at 70% relative humidity for 1 day 1 d/72% RH = storage at 72% relative humidity for 1 day 1 d/73% RH = storage at 73% relative humidity for 1 day 1 d/74% RH = storage at 74% relative humidity for 1 day *each with about 6% by weight of water; A11 = anhydrous sodium carbonate; P954 = anhydrous disodium hydrogenphosphate

[0080] Table 2 shows the in comparison the particular effect of the combination of anhydrous sodium carbonate with disodium hydrogenphosphate compared to the individual additives. The products from experiments 16 and 17 show much higher cracking resistanceseven in the case of higher relative air humiditiesthan the products from comparative experiments V18, V19, V20 and V21. Moisture absorption after one day is 0.1% or 0.1% (70% rel. humidity) and 3.1% or 2.4% (72% rel. humidity).

TABLE-US-00003 TABLE 3 Laboratory experiments with potassium chloride granules with the additives anhydrous sodium carbonate and anhydrous disodium hydrogenphosphate and micronutrients** Point loads- Point loads- Moisture Additives unweathered weathered absorption 22* 0.16% by wt. A11 + 0.34 kN 0.42 kN 0.19% 0.28% by wt. P954 + 0.5% by wt. B *with 8% by weight of water; **for comparative experiments see No. 1 and V12 A11 = anhydrous sodium carbonate; P954 = anhydrous disodium hydrogenphosphate, B = anhydrous borax, calculated as boron