Controlled-release potassium chloride fertilizer

Abstract

The present invention relates to a process for producing a controlled-release fertilizer for potassium chloride, which comprises the following steps: a. providing compacted KCl having a sphericity of below 0.87; b. dry polishing the KCl in a high-intensity mixer-type device comprising a container and at least one set of stirring elements, such that the KCl has a sphericity between 0.88 and 0.92; c. providing a coating on the polished KCl. In the case of a 6 pph coating, the polished and coated compacted KCl may exhibit a release of about 18% after 7 days when measured using a water leaching test at 21°C. The polished and coated compacted KCl may have one or more of the following release properties: a release of about 20% or less at 10 days; and / or a release of 40% or less at 30 days; and / or a release of 50% or less at 50 days.

Description

[0001] The present invention relates to a controlled-release potassium chloride fertilizer. Background Art

[0002] The concept of controlled-release fertilizers (CRFs) is well known in the art. These CRFs are typically manufactured by applying a coating to a substrate (matrix) fertilizer in a reaction vessel such as a rotating drum or pan to form a coated mixture and curing the coated mixture (i.e., forming a coated fertilizer having a layer of coating). Additional coating layers can be applied by the same process (i.e., coating and curing in a reaction vessel).

[0003] For example, U.S. Patent No. 3,223,518 discloses granular, particulate, or pelletized fertilizers encapsulated with a water-insoluble, non-hygroscopic organic resinous coating. U.S. Patent No. 3,285,223 discloses coating and encapsulating particulate materials with multiple coatings using a specially designed apparatus that provides heating, blowing, and rotating means in a single vessel.

[0004] U.S. Patent Nos. 4,772,490 and 7,722,696 describe resins that can be cured at room temperature. Specifically, the resin is a combination of polyols, cardanol, cashew phenol, their derivatives or oligomers, and polyisocyanates or isocyanates. The resin is cured or encapsulated on the fertilizer by activation with an amine catalyst.

[0005] The granular fertilizers available on the market as substrates for coatings to produce CRFs differ in composition, size, and shape. These fertilizers are manufactured by different methods such as granulation, compaction, prilling, etc. The manufacturing method selected depends on the nature of the fertilizer, the target market, and the production cost.

[0006] The shape of the granular fertilizer has a great influence on their performance as a substrate for coatings to produce CRFs. For CRFs, a fertilizer substrate composed of perfectly spherical granules is preferred because it allows the production of a layer with a uniform thickness and, therefore, uniform release. For example, prilling or granulation of fertilizers can produce nearly spherical particles, which are very advantageous for applying a thin and uniform coating. Urea is a well-known fertilizer that is widely available as a prilled or granulated product.

[0007] KCl has been obtained as a pelleted product, but pelletizing KCl is relatively expensive. Therefore, the most widely available KCl fertilizers are obtained from a compaction process. It is known that compacted KCl has a very irregular shape. However, pelleted KCl is relatively small, includes pinholes and a hollow core, and the hollow core is disadvantageous for controlled-release fertilizers because it increases the dissolution of KCl.

[0008] The irregular shape of compacted KCl has many drawbacks. If the fertilizer is used as a pure granule, during transportation and handling, the sharp edges will cause the formation of dust. To reduce the formation of dust during transportation and handling, it is not uncommon to apply a polishing step. The polishing of fertilizers (e.g., after compaction) is a process that uses a rotating drum in a so-called "dry" process, or - more often - adds water in a wet process, where the water dissolves the sharp edges and then the water is evaporated. The latter process has the disadvantage of increasing energy consumption, but the dust in the product is reduced.

[0009] CN101381263 describes the specific application of this common polishing knowledge to CRF. This reference describes the use of a rotating barrel / drum polishing machine. This equipment is equivalent to the type commonly used in the fertilizer manufacturing industry as described above. According to this reference, a polishing time of 45 - 60 minutes is required for each batch.

[0010] Another example is the paper published by Lu et al. in Sci Rep 10,5763 (2020), which describes a water polishing pretreatment, resulting in increased sphericity (decreased angle of repose). The results of the increased sphericity are described as allowing a lower coating weight.

[0011] The two polishing methods described for CRF are both aimed at smoothing the rough surfaces of already relatively spherical granules. No mention is made of highly irregular-shaped, non-spherical substrates.

[0012] Due to multiple problems, these prior art polishing methods based on rotating drum equipment have not been found to be widely applied to improving the substrates to be coated for producing CRF. The first problem is the generation of dust. The polishing action generates a certain amount of small particles and dust, and the more dust generated, the more irregular the product. The presence of dust in the substrate is considered harmful to coating, causing defects in the coating layer and loss of expensive polymers when coating small particles. The second problem is cost. The polishing step is an additional step in the process of manufacturing CRF, so for high efficiency, it needs to be carried out in equipment that involves low investment, low operating costs (avoiding the use of water, heat, etc.) and has the highest possible production volume (or if not continuous, shorter batch times). If possible, polishing is avoided by using more spherical products; however, for some fertilizers, such products are not available or are too expensive.

[0013] Accordingly, there is a need for effective and cost - effective methods that can improve irregular fertilizers for use as substrates for controlled - release fertilizers. Additionally, a specific objective of the present invention is to provide a process for polishing irregularly compacted KCl such that good slow - release properties are obtained, where the amount of coating is comparable to the amount of coating used for more spherical pellets. Summary of the Invention

[0014] The present invention provides a process for producing a slow - release fertilizer of KCl, which comprises the following steps:

[0015] a. Providing compacted KCl having a sphericity of less than about 0.87;

[0016] b. Dry - polishing the KCl in a high - intensity mixer - type device comprising a container vessel and at least one set of agitation elements rotating relative to static elements in the container such that the KCl has a sphericity between 0.88 and 0.94;

[0017] c. Providing a coating on the polished KCl.

[0018] The agitation elements of the high - intensity mixer - type device generally maintain a certain gap between the rotating elements and the static elements. For example, the container may contain a rotating element on a central axis that has a certain gap from the static elements on the container wall. The distance is preferably between about 1 mm and about 5 cm, more preferably between about 5 mm and about 3 cm.

[0019] The agitation elements generally move at a certain circumferential tip speed. Preferably, the circumferential tip speed is from about 0.3 m / s to about 5 m / s, more preferably about 1 m / s to 3 m / s.

[0020] This process is a dry process. Thus, little or no water is used.

[0021] Preferably, the compacted KCl has a d50 between 2 - 4 mm, preferably between 2.5 mm and 3.5 mm. The d90 is generally less than 5.5 mm, preferably less than 5 mm. The d50 is the size of the pellet where 50% of the pellet weight is less than the d50 value and 50% is greater than the d50 value. The d90 defines the size of the pellet where 10% by weight is greater than the size and 90% by weight is less than the size.

[0022] The process according to the present invention allows for an effective and low - cost polishing step. Preferably, the polishing process step is completed within 1 hour, preferably within 30 minutes, and an effective process seems to be achievable within 20 minutes (such as for example about 10 minutes).

[0023] The present invention also relates to a polished and coated compacted potassium chloride controlled release fertilizer obtainable by using the process according to the present invention. The polished and coated granular fertilizer has a slower release profile than unpolished compacted KCl, pelletized KCl or dry drum polished compacted KCl, and has the following characteristics: lower release on the first day and a more gradual and slower increase in the first weeks.

[0024] The present invention also relates to a polished and coated compacted potassium chloride controlled release fertilizer, wherein the KCl has a sphericity between 0.88 and 0.92 and shows a release of less than 18%, preferably about 15% or less, on the 7th day in a standard test at 21 °C at 6 pph (parts per hundred) (6 parts by weight of coating, calculated as solids, relative to 100 parts by weight of potassium chloride granules).

[0025] Preferably, the polished and coated granular KCl according to the present invention has a d50 between 3 - 4 mm and a d90 below 5.5 mm.

[0026] The present invention also relates to the use of a high - intensity mixer - type device comprising a container and at least one set of stirring elements rotating relative to a static element in the container for treating granular material before coating the granular material to produce a controlled release granular material. Description of the Drawings

[0027] Figure 1 Photographs of untreated compacted KCl and dry - polished compacted KCl according to the present invention.

[0028] Figure 2 Graph showing various release profiles of the coated KCl product. Detailed Description

[0029] Generally, compacted KCl has a sphericity below 0.87, such as for example about 0.86. This substrate reflects the common irregular (non - spherical) shape of compacted (also called compacted and granulated) KCl, similar to commercially available agricultural KCl. Other fertilizer products can be obtained in a more spherical shape, see for example the table below.

[0030]

[0031] A sphericity above 0.9 generally allows good release properties and generally requires little polishing. However, for compacted KCl, it seems more difficult to achieve a good release profile. Thus, dry polishing or wet polishing using a standard drum can be applied. The sphericity and release properties of various KCl reference products are given in the table below:

[0032]

[0033] Standard KCl and the dry tumble polished KCl in the standard tumbler showed a rapid initial release and a very flat release curve after about 10 - 15 days.

[0034] The release of the unpolished compacted KCl was clearly quite unacceptable. The dry polishing of the standard tumbler treated KCl required a relatively long time (more than 2 hours), and even when reasonable sphericity was achieved, the release of the coated pellets did not really meet the standard. The wet polished KCl showed better release properties after standard coating, but had a long processing time and was relatively expensive due to energy use and water evaporation.

[0035] The present invention allows polishing in a relatively short time with a low energy input, and a low amount of coating results in an even improved release curve compared to the coated pelletized KCl with the same coating weight (e.g., 6 pph).

[0036] According to the present invention, common compacted and pelletized KCl can be used. The compacted and pelletized KCl is also simply referred to as compacted KCl. Common KCl contains at least 90%, preferably about 95% or more, of KCl. Other components are generally sodium chloride (2 - 3 wt%) and other impurities. The amount of water is generally less than 0.5 wt%, such as for example 0.2 wt%.

[0037] The compacted potassium chloride (KCl) generally has a d50 between 2 - 4 mm, preferably between 2.5 mm and 3.5 mm. The d90 is generally below 5.5 mm, preferably below 5 mm. The compacted KCl generally has a sphericity below 0.87, such as for example between 0.85 and 0.87, about 0.86.

[0038] The base fertilizer form and particle size distribution of the product can be analyzed by a RETSCH Camsizer via Particle Size and Particle Shape Analysis with Dynamic Image Analysis. The main form parameter for evaluating the base fertilizer is the sphericity (SPHT), which is defined as:

[0039]

[0040] Where P is the measured perimeter of the particle projection and A is the area covered by the particle projection. For an ideal sphere, SPHT = 1. The higher the sphericity, the rounder the granular material, and the better the CRF manufactured with this substrate. The measured parameter is the sphericity at d50, named SPHT3 at Q3[%]50 in the software of the RETSCH Camsizer equipment used.

[0041] The polishing device comprises a container containing the material to be treated, and a stirring element rotating relative to the static element in the container transfers energy to the material bed provided for mixing. For example, the container may contain a rotating element on a central axis, which has a certain gap from the static element on the container wall. Similarly, the container housing with the stirring element may rotate while the static element is attached to the central axis of the high-intensity mixer.

[0042] The rotating element and the static element can be, but are not limited to, paddles, blades, belts and pins. The rotating element and the static element are attached to one or more shafts or axles, or to the inner side of the container housing.

[0043] The rotating elements maintain a certain gap distance between them and the static elements to avoid excessive breakage of the granular material, and at the same time operate at a tip circumferential speed high enough to provide sufficient polishing effect. This distance is generally about 1 mm or more, but preferably about d90 or more, such as about 5 mm or more. Generally, this distance is about 5 cm or less, because otherwise lower efficiency will be achieved. Preferably, this distance is about 3 cm or less. Suitable distances are for example 8 mm, 1 cm, 1.5 cm or 2 cm.

[0044] The tip circumferential speed is the speed of the blade tip, which is the point on the mixing element closest to the wall or the point farthest from the axis of rotation. The tip speed is generally between 0.3 and 5 m / s. A relatively low tip speed can lead to an increase in processing time and more dust generation, and is therefore less preferred. Therefore, a tip speed of about 1 m / s or higher is preferred. An excessively high tip speed can lead to a high energy input, and a tip speed of about 3 m / s is preferred.

[0045] The effect of the polishing pretreatment according to the present invention is not only to remove the sharp edges of the granular material, but also to incorporate part of the dust generated by friction into the cracks on the surface of the granular material at the same time, providing an excellent substrate for being coated into the controlled-release fertilizer.

[0046] The device can be operated batchwise or continuously. Since the residence time required for polishing is short, it can be incorporated upstream of the fertilizer coating line without negatively affecting the production capacity of the equipment.

[0047] In a batch process, on an industrial scale, the apparatus can handle at least one ton or more, preferably 2 tons or more, per batch, such as for example 3, 4 or 5 tons per batch.

[0048] The polished potassium chloride has a sphericity of 0.88 or greater. Generally, the sphericity is about 0.92 or less, and preferably about 0.9 or less. More preferably, the sphericity is between 0.88 and 0.90, and even more preferably between 0.88 and 0.89, since such sphericity can be sufficient to provide appropriate release properties of the controlled-release fertilizer and allow for an efficient process. As explained above, the presence of small dust granules in the (small) cavities of the potassium chloride granules is believed to contribute to achieving such a favorable release profile.

[0049] The presence of small dust particles can also be observed on the micrographs, as Figure 1 shown in Figure 1 A is a photograph of unpolished compacted KCl, while Figure 1 B shows a picture of compacted KCl polished by a blender (dry blender) according to the present invention. In Figure 1 B, white dust patches are visibly incorporated on the surface. It is believed that the dust incorporated on the surface of the granules of the polishing material provides surprisingly improved performance. Accordingly, the present invention also relates to polished compacted KCl granules ready for coating, having a sphericity between 0.88 and 0.92 and having dust patches visible under a microscope at 15x magnification.

[0050] The polymer coating step can be a conventional coating step. The amount of the polymer coating is determined by the desired properties. More coating is needed to make the controlled release of the fertilizer last longer (longer life), which is required for some applications. However, more coating means higher cost. Typically, for a life of about 6 - 7 months, the amount of the polymer coating is about 6 pph (parts per hundred) (6 parts by weight of coating, in solid form, relative to 100 parts by weight of potassium chloride granules). However, other amounts can also be applied to provide different lifetimes for different applications. For example, the coating can be applied in an amount of 3 - 10 pph.

[0051] Other types of coatings, such as coatings based on elemental sulfur, will also benefit from the use of such polishing materials. The typical coating weight of the sulfur coating is significantly higher than that of the polymer coating. Typically, about 15 - 25 pph or even higher, up to 50 pph, is applied, since the performance of sulfur as a barrier is inferior to that of the polymer coating and since cost is not a problem due to the low cost of elemental sulfur.

[0052] Figure 2Shows a comparison of the release of different KCl fertilizers (unpolished (pelletized or compacted) and polished by different methods) in a water leaching test. All products were coated with a 6 pph polyurethane polymer coating. It can be clearly seen from the figure that unpolished compacted and coated KCl (“compacted standard KCl”) shows a release of about 50% of KCl in about 10 days in a standard test (described below in the experimental section). After about 20 days, the release is relatively slow, resulting in a release of about 65% at 30 days and 70% at 50 days. Pelletized and coated KCl (“pelletized KCl”), like standard drum polished KCl (“drum polished KCl”), shows a release of about 30% at 10 days, about 50% at 30 days and 55% at 50 days. KCl polished according to the present invention (“blender polished KCl”) shows a release of only 10% at 10 days, about 25% at 30 days and about 40% at 50 days. The figure shows that the polished KCl according to the present invention allows a controlled release fertilizer with improved controlled release compared to prior art type products.

[0053] The preferred controlled release fertilizer according to the present invention shows a release of about 18 wt% or less, preferably about 15 wt% or less, at 7 days. As explained above, the release in the first week is very indicative of the controlled release behavior, and a slow initial release is considered important.

[0054] The preferred controlled release compacted KCl fertilizer according to the present invention preferably shows a release of about 20% or less, preferably about 15% or less, at 10 days; and / or 40% or less, preferably 35% or less, at 30 days; and / or 50% or less, preferably 45% or less, at 50 days. Even more preferably, at 20 days, the release is about 30% or less. Even more preferably, the KCl fertilizer meets the release percentages as described above at all time points.

[0055] Examples:

[0056] Materials and Methods

[0057] The KCl used in the examples was granular KCl from ICL (Iberpotash). The composition was: 95% KCl, 2.3% NaCl, 0.2% H2O (moisture). The bulk density was 1 ton / m 3 . The particle size distribution of the material is shown in the table below.

[0058]

[0059] The maximum diameter was defined as d90, which is the diameter under which 90% by weight of the sample is contained. In this case, d90 was 4.71 mm.

[0060] The device for pretreatment according to the present invention is a paddle mixer. It has a working capacity of approximately 300 liters (approximately 50 cm in diameter and 150 cm in length). It is equipped with a control panel with a frequency converter for speed control of the blades. It has a single shaft with 12 arms vertically mounted to it (completed by adjustable blades). The distance from the edge of the blade to the wall can be adjusted in the range of 1 to 30 mm.

[0061] CRFs were prepared using the fertilizers pretreated in the mixing device to compare their performance. In these examples, CRFs were prepared by coating the fertilizers with a polyurethane-based resin, which was made by reacting a liquid polyol and a liquid diisocyanate in a similar manner as described in U.S. Patent No. 7,722,696. The coating level for all examples was 6 parts per 100 parts of fertilizer of solid coating (6 pph). Samples were prepared in a drum containing 1.5 kg of fertilizer and equipped with a heating system to maintain the fertilizer at a temperature between 60 °C and 80 °C.

[0062] Analysis

[0063] The amount of dust was determined by sieving a representative sample through a standardized sieve with a 2.36 mm opening. All materials passing through the sieve (<2.36 mm) were considered dust and needed to be removed before coating. Therefore, this dust was considered waste and needed to be restricted.

[0064]

[0065] The morphology and particle size distribution of the base fertilizer in the >2.36 mm fraction were analyzed by RETSCH Camsizer via particle size and particle shape analysis with dynamic image analysis. The main morphological parameter used to evaluate the base fertilizer was sphericity (SPHT), defined as:

[0066]

[0067] where P is the measured perimeter of the particle projection and A is the area covered by the particle projection. For an ideal sphere, SPHT = 1. The higher the sphericity, the rounder the granule, and the better the CRF made from this base material. The parameter measured was the value of sphericity at d50, called SPHT3 at Q3[%]50 in the software of the Camsizer device.

[0068] The performance of the coated fertilizer was measured by the rate of nutrient release from the granule when in contact with water. A slower release rate indicates a longer lifespan of the product in releasing its nutrients over time. The industrial standard for determining the release characteristics of the product includes the water leaching release test.

[0069] In the water leaching release test, the produced CRF was placed in water at 21 °C and tested at different time intervals (24 hours, 7 days and in some cases longer times) (e.g., for making Figure 2 ). Specifically, 20 g of the coated fertilizer was placed into a flask with 400 mL of demineralized water. The flask containing the sample was inverted three times to allow mixing and kept at 21 °C. After a 24-hour time period, the flask was inverted three times and samples were taken to determine the amount of nutrients (K 2 O) in the water. The water was replaced and renewed with 400 mL of fresh demineralized water. The measurement was repeated again after 7 days. Additional measurement points were obtained to be able to plot the release curve of the controlled-release fertilizer during the working time. After the last measurement, the remaining pellets were ground, dissolved to a known volume and analyzed to check the closure of the mass balance of each component. The results were given as the weight % of the nutrient K 2 O released into the solution at different time intervals.

[0070] Examples with different clearances between the opposing walls.

[0071] Settings: load 300 kg, time 30 min, circumferential speed 1.64 m / s (70 Hz), coating level: 6 pph (parts per hundred of coating per hundred parts of fertilizer)

[0072]

[0073] Examples with different speeds

[0074] Settings: load 300 kg, time 30 min, clearance between opposing walls 30 mm, coating level: 6 pph (parts per hundred of coating per hundred parts of fertilizer)

[0075]

[0076] Comparison of treated vs. untreated

[0077] Polishing settings: load 300 kg, time 30 min, clearance between opposing walls 30 mm, circumferential speed 1.64 m / s (70 Hz)

[0078] Coating weight: 6 pph (parts per hundred of coating per hundred parts of fertilizer)

[0079]

[0080] Comparison of treated vs. cleaned treated

[0081] Polishing produces fine dust that adheres to the fertilizer. Generally, the presence of dust is considered harmful to coating. The dust was removed from the untreated and polished fertilizer by hexane washing treatment and their performance was compared.

[0082] Polishing settings: load 300 kg, time 30 min, clearance to the wall 30 mm, circumferential speed 1.64 m / s (70 Hz); coating weight: 6 pph (parts per hundred of fertilizer)

[0083] Release increased by washing At 1 day At 7 days Untreated 14％ 6％ Polished 106％ 154％

[0084] For the untreated samples, the performance largely remained the same, while for the polished samples, the dust-free samples surprisingly performed considerably worse. This indicates that the presence of the dust generated by this novel dry polishing process is beneficial for coating. The conventional drum polishing and water polishing known in the art for CRF would not have this beneficial dust.

Claims

1. A process for a controlled-release fertilizer for the production of potassium chloride, which comprises the following steps: a. Providing compacted KCl with a sphericity below 0.87; b. Dry polishing the KCl in a high-intensity mixer-type device comprising a container and at least one set of stirring elements rotating relative to static elements in the container, such that the KCl has a sphericity between 0.88 and 0.92; c. Providing a coating on the polished KCl.

2. The process according to claim 1, wherein the stirring elements maintain a certain gap between them and the static elements, where the distance is between 1 mm and 5 cm.

3. The process according to claim 1, wherein the stirring elements maintain a certain gap between them and the static elements, where the distance is between 5 mm and 3 cm.

4. The process according to any one of claims 1-3, wherein the stirring elements move at a certain circumferential tip speed, where the circumferential tip speed is between 1 and 5 m / s.

5. The process according to any one of claims 1-3, wherein the stirring elements move at a certain circumferential tip speed, where the circumferential tip speed is between 1 m / s and 3 m / s.

6. The process according to any one of claims 1-3, wherein the stirring elements are rotating stirring elements on a central axis, and wherein the static elements are parts inside the container wall.

7. The process according to any one of claims 1-3, wherein the compacted KCl has a d50 between 2–4 mm and a d90 below 5.5 mm.

8. The process according to claim 7, wherein the compacted KCl has a d50 between 2.5 mm and 3.5 mm.

9. The process according to claim 7, wherein the compacted KCl has a d90 below 5 mm.

10. The process according to any one of claims 1-3, wherein the polishing process step is completed within 1 hour.

11. The process according to any one of claims 1-3, wherein the polishing process step is completed within 30 minutes.

12. The process according to any one of claims 1-3, wherein the polishing process step is completed within 20 minutes.

13. The process according to any one of claims 1-3, wherein the coating is a polymer coating applied to the polished KCl in an amount between 3 pph and 10 pph.

14. The process according to any one of claims 1-3, wherein the coating is a polymer coating applied to the polished KCl in an amount between 4 pph and 7 pph.

15. The process according to any one of claims 1-3, wherein the coating is a sulfur coating applied to the polished KCl in an amount between 15 pph and 50 pph coating.

16. The process according to any one of claims 1-3, wherein the coating is a sulfur coating applied to the polished KCl in an amount between 15 pph and 25 pph coating.

17. Prepared polished compacted KCl particulate material for coating, having a sphericity between 0.88 and 0.92 and having dust patches visible under a microscope at 15x magnification.

18. A polished and coated particulate material obtainable by the process according to any one of claims 1 - 16.

19. The coated and polished KCl material according to claim 18, and which has a release of 18% or less at 7 days when measured using a water leaching test at 21°C at 6 pph or less.

20. The coated and polished KCl material according to claim 18, wherein it has a release of 15% or less at 7 days when measured using a water leaching test at 21°C at 6 pph or less.

21. Coated and polished compacted KCl, having a sphericity between 0.88 and 0.92 and having a release of 18% or less at 7 days when measured using a water leaching test at 21°C in the case of 6 pph coating.

22. The coated and polished compacted KCl according to claim 21, wherein it has a release of 15% or less at 7 days when measured using a water leaching test at 21°C in the case of 6 pph coating.

23. The coated and polished compacted KCl according to claim 21, having one or more of the following release properties: a release of 20% or less at 10 days; and / or a release of 40% or less at 30 days; and / or a release of 50% or less at 50 days.

24. The coated and polished compacted KCl according to claim 23, wherein the release at 10 days is 15% or less.

25. The coated and polished compacted KCl according to claim 23, wherein the release at 30 days is 35% or less.

26. The coated and polished compacted KCl according to claim 23, wherein the release at 50 days is 45% or less.

27. The coated and polished compacted KCl according to any one of claims 18 - 26, wherein the polished and coated compacted KCl has a d50 between 3 - 4 mm and a d90 below 5.5 mm.

28. Use of a high - intensity mixer - type device comprising a container and at least one set of mixing elements rotating relative to a static element in the container for treating particulate material before coating the particulate material to produce a controlled - release particulate material.

Images