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 sodium salt selected from among sodium chloride, sodium sulphate, sodium sulphate hydrates, sodium hydroxide and mixtures thereof 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 sodium salts and glaserite and mixtures thereof 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

1-16. (canceled)

17. A process for producing potassium sulphate granulates, comprising: adding a sodium salt to the potassium sulphate during granulation, wherein said sodium salt is selected from the group consisting of sodium chloride, sodium sulphate, sodium sulphate hydrate, sodium hydroxide and mixtures thereof, wherein said sodium salt is added in a quantity of 0.1 wt % to 7.5 wt %, with respect to the used potassium sulphate.

18. The process according to claim 17, wherein the sodium salt is added in the form of a dust with a maximum particle size of 200 μm or in the form of an aqueous solution.

19. The process according to claim 17, wherein a fraction of the sodium salt is added in the form of a dust with a maximum particle size of 200 μm with the rest in the form of an aqueous solution.

20. The process according to claim 17, wherein the sodium salt is in the form of a dust having a bulk density of between 250 kg/m.sup.3 to 1300 kg/m.sup.3.

21. The process according to claim 17, wherein the sodium salt is sodium chloride.

22. The process according to claim 17, wherein a quantity of water added before or during a pressing process is in the range of 0.1 wt % to 2.5 wt % , and/or after the pressing process in the range of 0.1 wt % to 2.5 wt %, and the total quantity of added water is maximal 3.5 wt % with respect to anhydrous potassium sulphate.

23. The process according to claim 17, wherein during said granulation, compaction is performed as pressure agglomeration.

24. The process according to claim 23, wherein pressure agglomeration comprises the compaction of the mixture consisting of potassium sulphate, sodium salt and water using a roller press.

25. The process according to claim 24, wherein pressure agglomeration comprises the compaction of the mixture consisting of potassium sulphate, sodium salt and water using a roller press under a specific line load of between 30 kN/cm to 100 kN/cm, and a 1000 mm roller diameter and an average slug thickness of 10 mm.

26. The process according to claim 24, wherein compaction of the mixture of potassium sulphate, sodium salt and water is performed with a roller press and subsequent grinding and classification of slugs obtained by compaction.

27. The process according to claim 26, wherein the slugs are moistened with water after the pressing process.

28. The process according to claim 17, wherein the granulation is performed at a temperature of between 20° C. to 100° C.

29. A potassium sulphate granulate, obtained by a process according to claim 17.

30. The potassium sulphate granulate according to claim 29, comprising a sodium salt content in the range of 0.1 wt % to 7.5 wt %, based on the used potassium sulphate.

31. A method for improving a mechanical property of potassium sulphate granulates, said method comprising: adding a sodium salts selected from the group consisting of sodium chloride, sodium sulphate, sodium sulphate hydrates, sodium hydroxide and mixtures thereof to potassium sulphate during granulation.

32. The method according to claim 31, wherein the crack strength and/or the abrasion resistance of the granulates is increased compared to granulates comprising no sodium salt.

33. A potassium sulphate granulate, comprising: glaserite as binding agent.

Description

EXAMPLES

[0051] The process of the invention, the potassium sulphate used by the invention and the purpose of the invention are explained in more detail by way of the following examples. The following Table 2 presents a summary of the experiments performed as Examples 1 to 9 subject to type and quantity of the components used. Potassium sulphate appears under Materials as SOP (sulphate of potash) subject to the respective specification. Two SOP fine products from the company K+S Kali GmbH were used as potassium sulphate powder, which demonstrated differing specifications:

[0052] SOP fine product 1:

[0053] Potassium sulphate (K.sub.2SO.sub.4): 95.5 wt %

[0054] Other sulphates (MgSO.sub.4, CaSO.sub.4): 2.6 wt %

[0055] Other components, primarily crystallisation water: 0.9 wt %

[0056] Humidity: 0.2 wt % Grain size distribution: >0.85 mm 1 wt %; 0.5-0.85 mm 3%; 0.25-0.5 mm 12%; 0.15-0.25 mm 22%; 0.09-0.15 mm 29%; <0.09 mm 33%;

[0057] SGN: 12 (size-guide number)

[0058] SOP fine product 2:

[0059] Potassium sulphate (K.sub.2SO.sub.4): 93 wt %

[0060] Other sulphates (MgSO.sub.4, CaSO.sub.4): 4.1 wt %

[0061] Other components, primarily crystallisation water: 1.0 wt %

[0062] Humidity: 0.2 wt %

[0063] Grain size distribution: >0.85 mm 2 wt %; 0.5-0.85 mm 3%; 0.25-0.5 mm 12%; 0.15-0.25 mm 25%; 0.09-0.15 mm 31%; <0.09 mm 27%;

[0064] SGN: 13

[0065] Calculations show that there is a maximum water fraction in the obtained granulate of about 2.0 wt %. To determine the annealing loss, the substance is covered with lead oxide, heated in a muffle furnace to between 450° C. and 600° C. before the weight difference is measured gravimetrically.

[0066] Drying loss (at 105° C.) was measured by determining the residue and the water content according to DIN EN 12880.

[0067] To perform pressure agglomeration using roller compaction as in Examples 1 to 9, the potassium sulphate (SOP fine products) and the sodium salt, where appropriate, was fed into the compaction zone between the rollers and the powder/fine particles were then pressed into slugs between the counter-rotating rollers using a given force. Grinding and classification of the slugs obtained via compaction were then performed.

[0068] The roller press possesses the following properties and set parameters:

[0069] Feeder mechanism: screw feeder

[0070] Roller diameter: 800 mm

[0071] Operating width of the press rollers: 180 mm

[0072] Operating power of the press rollers: up to 160 kW

[0073] Specific line load between the rollers: up to 100 kN/cm

[0074] Roller rim speed: 0.13 m/s to 0.84 m/s

[0075] Roller material/roller cover: segments with waffle-like structure

[0076] The grinding unit was an impact mill from the Hazemag company with a rotor diameter of 460 mm and was fitted with 2 impact bars with a bar width of 340 mm as well as 2 impact plates.

[0077] Two vibrating sieve machines from the Rhewum company were used as classification units.

[0078] The sieving process produced the following grain band distribution of the granulate of the invention as presented, for example, by Table 1.

TABLE-US-00001 TABLE 1 Grain band distribution of the produced potassium sulphate granulate Grain class Residual amount/wt % >5.0 mm 0 >4.0 mm 0.4 >3.15 mm  32.6 >2.5 mm 81.5 >2.0 mm 96.7   >0 mm 100

[0079] According to X-ray powder diffractometry, the main component of the product is an “arcanite (K.sub.2SO.sub.4) phase”. Minor components are an aphthitalite phase (potassium-sodium-sulphate, K.sub.3Na(SO.sub.4).sub.2, also known as glaserite). It is suspected that the formation of the glaserite phase at the edges of the grains leads to improved and more permanent binding of the pressed particles of the potassium sulphate and therefore causes less, or helps to reduce, abrasion and leads to higher crack-resistance. The use of glaserite as a binding agent in potassium sulphate granulates, in particular to improve the mechanical properties of the granulate, is therefore an object of the invention.

[0080] As glaserite formation as a recrystallisation is also possible at room temperature, improvement to the crack-resistance and abrasion values can also be expected during structural granulation e.g. on a granulation dish, so long as sodium salts are present, either as solid or liquid, and homogeneously distributed with water/water vapour. In the case of structural granulation, e.g. in the fluidised bed coating, these can also be performed at higher temperatures mentioned above.

[0081] Table 2 presents the results for abrasion and crack-resistance. The admixture with the SOP fine products are included “Additives”.

[0082] During production of the granulates, breaking strength, abrasion and residual humidity are determined using the following methods: the average breaking strengths were determined using the tablet breaking strength tester model TBH 425D from the ERWEKA company on the basis of measurements on 56 individual agglomerates with particle sizes between 2.5 mm to 3.15 mm.

[0083] The values for abrasion were determined using the rolling drum process according to Busch. The abrasion compressive strength values were measured on granulates with fractions between 2.5 mm to 3.15 mm.

[0084] The residual moisture was determined using the halogen dryer model HR 73 from the Mettler company.

[0085] The measured values were determined directly after the experiment as well as after a maturity period, i.e. periods of 1, 7 and 14 days and are listed in the following in Table 2. During the curing period, the samples were stored at 22° C. and 65% relative air humidity. If water was added, then this sample, as given by Table 2, could be undertaken before the pressing process (called “untreated samples”) or after pressing process (called “post-treated samples”). The addition totalled around 2 wt % H.sub.2O. The samples post-treated with water were investigated once in a dry state.

TABLE-US-00002 TABLE 2 SOP granulation with sodium salts Example no.: 1* 2a 2b 2c Material SOP fine product 2 SOP fine product 1 SOP fine product 1 SOP fine product 1 Additive +H.sub.2O (reference +H.sub.2O + 3.5% NaCl +H.sub.2O + 3.5% NaCl +H.sub.2O + 3.5% NaCl experiment) [cyclone dust [cyclone dust [cyclone dust (evaporated salt)] (evaporated salt) (evaporated salt) Curing period (days) 0 1 7 14 0 1 7 14 0 1 7 14 0 1 7 14 Untreated samples Abrasion [%] 27 27 26 23 4 5 6 5 7 2.1 5 3.7 0.1 3.0 3.6 6 Crack strength [N] — 38 38 37 — 47 45 47 — 46 51 46 — 45 46 50 Post-treated with 2% H.sub.2O Not dried Abrasion[%] 1.3 7 8 0.5 3.0 1.0 0.2 2.8 2.9 1.8 2.9 5 Crack strength [N] 38 43 46 52 50 54 42 56 50 42 51 56 Example no.: 3 4 5 6 Material SOP fine product 1 SOP fine product 1 SOP fine product 2 SOP fine product 2 Additive +H.sub.2O + +H.sub.2O + 3.5% NaCl dust +H.sub.2O + +H.sub.2O + 1.8% NaCl dust 1.25% NaCl dust 1.75% NaCl dust Curing period (days) 0 1 7 14 0 1 7 14 0 1 7 14 0 1 7 14 Untreated samples Abrasion [%] 7 9 10 11 5 3.4 7 7 14 8 13 12 5 4 5 7 Crack strength [N] — 43 46 45 — 47 45 46 — 36 40 39 — 38 44 47 Post-treated with 2% H.sub.2O Not dried Abrasion [%] 1.6 2.6 4 Crack strength [N] 34 54 53 Example no.: 7 8 9 Material SOP fine product 2 SOP fine product 2 SOP fine product 2 Additive +H.sub.2O + 2.5% NaCl dust +H.sub.2O + 15% NaCl +H.sub.2O + 1% Na.sub.2SO.sub.4** solution + 1.7% NaCl dust**** Curing period (days) 0 1 7 14 0 1 7 14 0 1 7 14 Untreated samples Abrasion [%] 4 3.2 7 5 3.1 2.9 6 7 10 9 7 15 Crack strength [N] — 37 42 45 — 42 45 47 — 36 44 42 Post-treated with 2% H.sub.2O Not dried Abrasion [%] 1.6 3.0 2.8 0.6 2.5 2.2 4 6 7 Crack strength [N] 34 49 49 35 53 51 36 46 46 *Reference experiment 1 was also performed with SOP fine product 1 and led to comparable values for abrasion and crack strength as the reference experiment with SOP fine product 2. Abrasion values <4 are stated to one decimal place **Target value: 0.3% Na.sup.+-content in product; K.sub.20-content >50%; ***Potassium sulphate with <50% K.sub.20 can still be used. In principle and within certain bounds, a glaserite formation may also occur during granulation of langbeinite, leading therefore to an improvement in quality. ****With respect to SOP

Example 1

Reference Experiment 1

[0086] Example 1 is a reference experiment for the production of potassium sulphate granulate, so-called SOP granulates, whereby SOP-5 fine product 2 was used as the potassium sulphate powder and no additional sodium salt was added.

[0087] The potassium sulphate was preheated in a rotary pipe oven before the pressing process to a temperature of 80° C. For the addition of water before the pressing process, two mass percent with respect to the SOP mass used was added. In another version of the experiment, the samples were post-treated with 2% water after classification and investigated whilst in a non-dry state.

Examples 2a to 2c

[0088] In Examples 2a to 2c SOP fine product 1 is used in the production of potassium sulphate granulate and sodium chloride was added as sodium salt in the form of a dust from a crystallisation unit (cyclone dust) with the concentrations (3.5 wt %) given in Table 1. In comparison to Example 1, higher crack strength and improved abrasion values were achieved in Examples 2a to 2c (see untreated samples as well as post-treated samples with 2 wt % water 114 day curing period).

Examples 3 to 4

[0089] In Examples 3 to 4, SOP fine product 1 was used during production of potassium sulphate granulate and various doses of sodium chloride were added as sodium salt in the form of a dust from a rock salt such as those given in Table 2. With the addition of NaCl and water, higher crack strength and improved abrasion values were achieved.

Examples 5 to 7

[0090] In Examples 5 to 7, SOP fine product 2 was used during production of potassium sulphate granulate and various doses of sodium chloride were added as sodium salt in the form of a dust from a rock salt such as those given in Table 2. The results of Examples 3 and 4 were confirmed. With increasing NaCl dust quantity (0 days and also 14 days curing time) significantly better abrasion values were achieved.

Example 8

[0091] Analogously to Examples 5 to 7, NaCl was added in Example 8 in the form of a solution. In this series (5 to 8) it was shown that the addition of NaCl in the form of a solution before compaction allowed high granulate strength to be achieved. In a direct comparison of all samples with sodium chloride as sodium salt in the form of a dust from a rock salt, the best instantaneous abrasion values (0 days=3.1%) were achieved in Example 8. The abrasion and crack strength values were also very good after 14 days curing both without and with post-treatment.

Example 9

[0092] In Example 9, SOP fine product 2 was used during production of potassium sulphate granulate and sodium chloride was added as sodium salt in the form of a dust such as those given in Table 2. With the use of sodium sulphate, only the abrasion value of untreated granulate came in under the level of the reference experiment (i.e. is improved), the other values lay in the range of or exceeded the value of Comparison Example 1.

[0093] In summary, the data in Table 2 shows that the potassium sulphate granulate produced in the process of the invention with the addition of a sodium salt demonstrates significant improvements compared with the reference experiment as Example 1 with respect to both breaking strength and abrasion. The manufactured potassium sulphate granulates are therefore overall significantly more stable and demonstrate high mechanical stability and reduced dust formation, e.g. during transportation.

[0094] Large-scale implementation using a pressure roller with 1000 mm operational width and a diameter of 1050 mm confirmed these good results. In this case, an Na-content of 0.5 wt % to max. 1.4 wt %, preferentially under 1 wt % in the product achieved very good crack strength (approx. 55 N). With regard to abrasion, the values of the raw granulate were about 50% less than the comparison values (abrasion reduced from 30% to 15%), despite the fact that only solid sodium chloride salt was used here. Dust levels were reduced during transport such that no or less dust binding agent had to be used.

[0095] Additional experiments were performed for pressure agglomeration using a model L200/50 laboratory press from the Bepex company. Here too the good results, e.g. with sodium chloride or thenardite (Na.sub.2SO.sub.4) were confirmed.