METHOD FOR THE PRODUCTION OF SULPHATE OF POTASH GRANULATES, SULPHATE OF POTASH GRANULATE OBTAINED THEREBY, AND USE THEREOF

Abstract

The invention relates to a method for producing sulphate of potash granulates, wherein 0.1 to 7.5 wt % of a potassium chloride are added to the sulphate of potash during the granulation process, the percentage by weight being in relation to the sulphate of potash used. In addition, 0.1 to 2.5 wt % of water are added prior to or during the granulation process. The invention also relates to the granulates obtained by said method as well as the use of potassium chloride for improving the mechanical properties of sulfate of potash granulates. The sulphate of potash granulates produced by the method of the invention have significantly greater bursting strength and significantly greater abrasion resistance than granulates known from the prior art.

Claims

1-13. (canceled)

14: A process for producing potassium sulphate granulates, comprising: adding potassium chloride to the potassium sulphate in a granulation process in a quantity of 0.1 to 7.5% by weight, based on the potassium sulphate used.

15: The process according to claim 14, wherein the potassium chloride is added in the form of a dust with a maximum particle size of 200 μm or in the form of an aqueous solution.

16: The process according to claim 14, wherein part of the potassium chloride added is in the form of a dust with a maximum particle size of 200 μm, and a remaining quantity of the potassium chloride is in the form of an aqueous solution.

17: The process according to claim 14, wherein a volume of water added before or during the pressing process is between 0.1 and 2.5% by weight, and/or wherein a volume of water added after the pressing process is between 0.1 and 2.5% by weight, with the total volume of the added water amounting to 3.5% by weight as a maximum, the weight % being based on the water-free potassium sulphate.

18: The process according to claim 14, comprising: compacting of the potassium chloride, potassium sulphate and water mixture; wherein said compacting is performed as pressure agglomeration.

19: The process according to claim 18, wherein the pressure agglomeration comprises compacting of the mixture of potassium sulphate, potassium chloride and water with a roller press.

20: The process according to claim 19, wherein the pressure agglomeration comprises compacting of the mixture of potassium sulphate, potassium chloride and water with a roller press at a specific line force ranging between 30 and 100 kN/cm, based on a roller diameter of 1000 mm and an average slug thickness of 10 mm.

21: The process according to claim 18, wherein the compacting of the mixture of potassium sulphate, potassium chloride and water is performed with a roller press and followed by a subsequent milling and grading of slugs obtained from the compacting.

22: The process according to claim 21, wherein the slugs are moistened with water after the pressing process.

23: The process according to claim 14, wherein the granulation is performed at a temperature ranging between 20 and 100° C.

24: A potassium sulphate granulate obtainable by a process according to claim 14.

25: The potassium sulphate granulate according to claim 24, comprising a potassium chloride content ranging between 0.1 and 7.5% by weight, based on the amount of the potassium sulphate used.

26: A method for improving mechanical properties of potassium sulphate granulates, comprising: adding potassium chloride to the potassium sulphate during a granulation process.

27: The method according to claim 26, wherein the burst strength and/or abrasion resistance of said potassium sulphate granulates is increased compared to potassium sulphate granulates which do not comprise potassium chloride.

Description

EXAMPLE

[0046] The inventive method, inventive potassium sulphate granulate and inventive use are explained in greater detail by the examples below. Table 1 shows an overview of the trials performed as examples 1 to 3, including the type and quantity of the components used. The potassium sulphate powder used was a fine SOP product from K+S Kali GmbH with the following characteristics:

Fine SOP product:
Potassium sulphate (K.sub.2SO.sub.4): 95.5% by weight
Other sulphates (MgSO.sub.4, CaSO.sub.4): 2.6 percent by weight
Other ingredients, mostly crystal water: 0.9% by weight
Moisture: 0.2% by weight
Grain size distribution: over 0.85 mm 1%; 0.5-0.85 mm 3%; 0.25-0.5 mm 12%; 0.15-0.25 mm 22%; 0.09-015 mm 29%; under 0.09 mm 33%;
SGN: 12 (size guide number)

[0047] It emerged that granulates with markedly improved mechanical properties could be obtained by the use of finely ground KCl and a 23% KCl solution in trial 3. The following table shows a summary of the most important results achieved so far. The settings of the laboratory roller press were identical in all three trials.

[0048] The following mixture variants were used: [0049] Trial no. 1: SOP without additives (reference trial) [0050] Trial no. 2: SOP with 1% water [0051] Trial no. 3: SOP with KCl and 23% aqueous KCl solution (objective: 2.5% maximum chloride content in granulate)

[0052] Trial 3 shows that the stability values are significantly increased over the comparison trials so far after one and/or seven days (burst strength: 55 N/56 N) as the KCl content in the base mix rises. Although the stability values can also be reduced again by storage (trial 2), there are first indications that even higher burst strengths yet are achievable by an after-treatment with water.

TABLE-US-00001 Trial no. 1 2 3 Mixture used SOP [g] 4000 4000 3831.8 KCl [g] — — 156.25 NaCl [g] — — — Water [g] — 40 — 23% NaCl solution [g] — — — 23% KCl solution [g] — — 51.95 After day 1 Burst strength [N] 18 33 55 Abrasion [%] 85 13 10 After day 7 Burst strength [N] 22 30 56 Abrasion [%] 50 18 10

[0053] The maximum water fraction arrived at mathematically amounts to ca. 2.0% by weight in the obtained granulate. The ignition loss was established by covering the substance with lead oxide, annealing it at 450-600° C. in a muffle furnace and determining the weight loss gravimetrically.

[0054] The breaking strength, abrasion and residual moisture of the produced granulates were determined by the following methods:

[0055] The average breaking strengths were determined with the help of the EWEKA tablet breaking resistance tester type TBH 425D based on measurements involving 56 individual agglomerates of 2.5 to 3.15 mm particle size.

[0056] The abrasion values were determined with the rolling drum method after Busch. The abrasion and compressive strength values were measured using granules of the 2.5 to 3.15 mm fraction.

[0057] The residual moisture was determined using a Mettler halogen dryer, type HR 73.

[0058] The measured values were determined directly after the trial and after a maturing period, i.e. a time span of 1 and 7 days. During the maturing period, the samples were stored at 22° C. and a humidity of 65%. If water was added, this could be done before or after the pressing process. The addition amounted to ca. 2% of H.sub.2O in each case.

[0059] The pressure agglomeration (trials 1 to 3) was performed using a Bepex laboratory press, type L200/50, with two counter-rotating drums featuring rod-shaped indentations in the roller surface (roller diameter 200 mm, working width 50 mm). The laboratory press was operated with a specific press force of up to 30 kN/cm and roller speed of 6.2 rpm. The applied press force was varied in a manner ensuring that the maximum value was reached, i.e. until the power consumption of the stuffing screw was near the limit preceding its malfunction.

[0060] The milling of the slugs obtained by the compacting with the laboratory press was performed with a Hazemag impact mill. The impact mill featured 2 impact elements and had a rotor diameter of 300 mm. The gap size of the front impact element was set to 10 mm and that of the back impact element to 5 mm. The impact mill was operated with a rotor circumferential speed of 15 m/s.

[0061] The potassium chloride used was KCl as a commercially available Merck laboratory chemical.