FIELD

[0001] The present invention relates to forming granules, and in particular, to methods for forming granules from powders.

BACKGROUND

[0002] Pelletizing, or granulating, refers to the process for producing solid granules from powder, slurry, or bulk material. For example, granulation processes can be useful to form granules from a combination of impurity-absorbing materials that are pulverized into a fine powder and then mixed together. The granules formed from such powders can be used for water filtration purposes. Some techniques used for granulating include compaction granulation, centrifugal granulation, melting granulation, spraying granulation, and extrusion pelletizing.

[0003] Centrifugal granulation begins with adding small starter granules onto a centrifugal plate, then spraying the powder and a liquid, such as water in a continuously alternating pattern. As the process continues, layers of the powder build up on the small starter granules. The process continues until enough of the powder has adhered to the small starter granules to produce granules of a desired average diameter.

Centrifugal granulation uses simple equipment and can produce high yields. However centrifugal granulation requires the small starter granules, which can be difficult to obtain. Centrifugal granulation may take a relative long period of time and produce nonuniform granules. Centrifugal granulation may also require the balancing of many process parameters, for example, the amount of small starter granules, the amount of water and the rate at which it is added, the amount of powder and the rate at which it is added, and the rotational speed of the centrifugal plate. Thus, production time and product quality produced by centrifugal granulation may be highly dependent upon the skill of the centrifugal granulator operator. SUMMARY

[0004] A method for forming substantially spherical granules of a desired diameter from a powder includes rotating a container including the powder and a liquid around a longitudinal axis of the container while also revolving the container around a centrifugal axis that is coplanar with the longitudinal axis.

[0005] Various embodiments concern a method for forming a plurality of substantially spherical granules of a desired diameter from a powder. The method includes placing the powder into a container having a longitudinal axis, adding a liquid into the container, rotating the container around the longitudinal axis, revolving the container around a centrifugal axis, and repeating the steps of adding the liquid, rotating the container around the longitudinal axis revolving the container around the centrifugal axis until the plurality of substantially spherical granules of the desired diameter forms from the powder. The powder is insoluble in the liquid. The centrifugal axis is coplanar with the longitudinal axis. The container rotates around the longitudinal axis at the same time that the container revolves around the centrifugal axis. In some

embodiments, the container rotates around the longitudinal axis at the same time that the container revolves around the centrifugal axis at a rotational speed between 1 ,500 revolutions per minute (RPM) and 3,500 RPM. In some embodiments, the container rotates around the longitudinal axis at the same time that the container revolves around the centrifugal axis for a time between 10 seconds and 60 seconds following each addition of the liquid. In some embodiments, the powder includes a filter material and a binder material. In some particular embodiments, the filter material includes iron oxyhydroxide, titanium dioxide, and manganese oxide. In some embodiments, the liquid includes water. In some embodiments, the powder has a median particle size between 0.050 microns and 100 microns. In some embodiments, the desired diameter of the granules is between 0.1 millimeters (mm) and 3 mm. In some embodiments, the container rotates around the longitudinal axis in a first direction and revolves around the centrifugal axis in a second direction, the second direction opposite the first direction. In some embodiments, the steps of adding the liquid, rotating the container around the longitudinal axis, and revolving the container around the centrifugal axis are repeated between 10 and 40 times. In some embodiments, adding the liquid into the container includes at least one of: spraying the liquid into the container, and drop-wise addition of the liquid into the container.

[0006] Various embodiments concern another method for forming a plurality of substantially spherical granules of a desired diameter from a powder. The method includes kneading together a powder and a liquid to form a damp powder, placing the damp powder into a container having a longitudinal axis, rotating the container around the longitudinal axis, and revolving the container around a centrifugal axis. The powder is insoluble in the liquid. The centrifugal axis is coplanar with the longitudinal axis. The container rotates around the longitudinal axis at the same time that the container revolves around the centrifugal axis to form the plurality of substantially spherical granules of the desired diameter from the powder. In some embodiments, the container rotates around the longitudinal axis at the same time that the container revolves around the centrifugal axis at a rotational speed between 1 ,500 revolutions per minute (RPM) and 3,500 RPM. In some embodiments, a diameter of the substantially spherical granules formed is a function of a weight percentage of liquid in the damp powder. In some embodiments, the powder includes a filter material and a binder material. In some particular embodiments, the filter material includes iron oxyhydroxide, titanium dioxide, and manganese oxide. In some embodiments, the liquid includes water. In some embodiments, the powder has a median particle size between 0.050 microns and 100 microns. In some embodiments, the desired diameter of the granules is between 0.1 millimeters (mm) and 3 mm. In some embodiments, the container rotates around the longitudinal axis in a first direction and revolves around the centrifugal axis in a second direction, the second direction opposite the first direction.

[0007] The above mentioned and other features of the invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic view of a centrifugal mixer configuration suitable for use with methods for forming substantially spherical granules from powder, according to embodiments of this disclosure.

[0009] FIG. 2 is a schematic view of another centrifugal mixer configuration suitable for use with methods for forming substantially spherical granules from powder, according to embodiments of this disclosure.

[0010] FIG. 3 is a schematic view of another centrifugal mixer configuration suitable for use with methods for forming substantially spherical granules from powder, according to embodiments of this disclosure.

[0011] FIG. 4 is a flowchart illustrating a method for forming a plurality of substantially spherical granules of a desired diameter from a powder, according to some embodiments of the disclosure.

[0012] FIG. 5 is a flowchart illustrating another method for forming a plurality of substantially spherical granules of a desired diameter from a powder, according to some embodiments of the disclosure.

DETAILED DESCRIPTION

[0013] As noted above, centrifugal granulation can be a time consuming process and the granules produced can be of uneven quality. Embodiments of the disclosure provide methods for forming substantially spherical granules of a desired diameter quickly, consistently, and of more uniform quality than centrifugal granulation. Methods according to embodiments of the disclosure can form granules directly from powder, without the need for small starter granules. Methods according to embodiments of this disclosure employ a centrifugal mixer that rotates a container containing the powder around its longitudinal axis while simultaneously revolving the container around a centrifugal axis that is coplanar with the longitudinal axis. Such centrifugal mixers are available from a variety of manufacturers and may be referred to as, for example, a Dual Asymmetric Centrifuge, a Dual Axis Centrifugal Mixer, a Planetary Centrifugal Mixer, or a Centrifugal Planetary Mixer. [0014] FIGS. 1 , 2, and 3 are schematic views of some centrifugal mixer configurations suitable for use with methods for forming substantially spherical granules from powder, according to embodiments of this disclosure. It is understood that the centrifugal mixer configurations are illustrative examples and not intended to limit the scope of the disclosure. FIG. 1 shows a centrifugal mixer 10 including a container 12, a rotating member 14, a revolving member 16, and a revolving axle 18. The container 12 has a longitudinal axis 20. The revolving axle 18 has a centrifugal axis 22. In some embodiments, the centrifugal axis 22 is coplanar with the longitudinal axis 20.

[0015] The container 12 can be formed of any durable material compatible powders and liquids to be used. The container 12 can be a cylindrical container as shown in FIG. 1. The rotating member 14 can be a rod to which the container 12 attaches, as shown in FIG. 1 , or a rotator cup within which the container 12 rests. The rotating member 14 is connected to a motor or other device (not shown) to cause the rotating member 14 to rotate. The container 12 and the rotating member 14 are aligned such that rotation of the rotating member 14 causes the container 12 to rotate around the longitudinal axis 20. The revolving member 16 can be a disk or an arm physically connecting the rotating member 14 to the revolving axle 18. In some embodiments in which the revolving member 16 is a disk, the rotating member 14 and the container 12 can be disposed at a periphery of the revolving member 16. In some other

embodiments in which the revolving member 16 is an arm, the rotating member 14 and the container 12 can be disposed at an end of the revolving member 16 distal from the revolving axle 18. The revolving axle 18 can be connected to a motor or device (not shown) to cause the revolving axle 18 to rotate. The container 12, the rotating member 14, the revolving member 16, and the revolving axle 18 are aligned such that rotation of the revolving axle 18 causes the container 12, the rotating member 14, and the revolving member 16 to revolve around the centrifugal axis 22.

[0016] In use, the rotating member 14 rotates the container 12 around the longitudinal axis 20 in a first direction D1 . At the same time, the revolving axle 18 rotates the revolving member 16, causing the rotating member 14 and the container 12 to revolve around the centrifugal axis 22 in a second direction D2. In some

embodiments, such as the embodiment shown in FIG. 1 , the second direction D2 is different from the first direction D1 . For example, in the embodiment of FIG. 1 , the first direction D1 is a counter-clockwise direction, while the second direction D2 is a clockwise direction.

[0017] As the container 12 revolves around the centrifugal axis 22, the

longitudinal axis 20 remains coplanar with the centrifugal axis 22. That is, as the container 12 revolves around the centrifugal axis 22, the longitudinal axis 20 is contained within one of the infinite number of vertical planes containing the centrifugal axis 22. In some embodiments, as shown in FIG. 1 , the longitudinal axis 20 can be disposed at an angle A with respect to the revolving member 16. In some

embodiments, the angle A can be as small as 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, or 40°, or as large as 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, or 90°, or any angle between any two of the preceding angles. For example, in some embodiments, the angle A range can from 0° to 90°, 10° to 80°, 20° to 70°, 30° to 60°, 35° to 55°, or 40° to 50°. In some embodiment, the angle A can be about 45°.

[0018] FIG. 2 shows another centrifugal mixer configuration suitable for use with methods for forming substantially spherical granules from powder, according to embodiments of this disclosure. FIG. 2 shows a centrifugal mixer 30. The centrifugal mixer 30 is similar to the centrifugal mixer 10 described above in reference to FIG. 1 , except that it further includes a second container 32 and a second rotating member 34 disposed at a diametrically opposed position on the revolving member 16. The second container 32 has a longitudinal axis 36. The second container 32 and the second rotating member 34 can be substantially identical to the container 12 and the rotating member 14 as described above. The second container 32 and the second rotating member 34 are aligned such that rotation of the second rotating member 34 causes the second container 32 to rotate around the longitudinal axis 36. Operation of the centrifugal mixer 30 is substantially the same as for the centrifugal mixer 10 described above, with the second rotating member 34 rotating the second container 32 around the longitudinal axis 36 in a first direction D1 . The addition of the second container 32 increases the capacity of the centrifugal mixer 30 compared to the centrifugal mixer 10, and can also provide a counterbalance to the container 12, providing for smoother operation. [0019] FIG. 3 shows yet another centrifugal mixer configuration suitable for use with methods for forming substantially spherical granules from powder, according to embodiments of this disclosure. FIG. 3 shows a centrifugal mixer 40 including a first container 42, a second container 44, a first rotating member 46, a second rotating member 48, and a revolving axle 50. The first container 42 has a first longitudinal axis 52. The second container 44 has a second longitudinal axis 54. The revolving axle 50 has a centrifugal axis 56. In some embodiments, the centrifugal axis 56 is coplanar with the first longitudinal axis 52 and the second longitudinal axis 54.

[0020] The each of the first container 42 and the second container 44 can be as described above for the container 12 in reference to FIG. 1 . The each of the first rotating member 46 and the second rotating member 48 can be as described above for the rotating member 14 in reference to FIG. 1 . The first container 42 and the first rotating member 46 are aligned such that rotation of the first rotating member 46 causes the first container 42 to rotate around the first longitudinal axis 52. The second container 44 and the second rotating member 48 are aligned such that rotation of the second rotating member 48 causes the second container 44 to rotate around the second longitudinal axis 54. The revolving axle 50 can be connected to a motor or device (not shown) to cause the revolving axle 50 to rotate.

[0021] The first rotating member 46 and the second rotating member 48 are physically connected to the revolving axle 50. In some embodiments, the first rotating member 46 and the second rotating member 48 are physically connected to

diametrically opposite sides of the revolving axle 50 to help balance forces acting on the revolving axle 50. The first container 42, the second container 44, the first rotating member 46, and the second rotating member 48 are aligned such that rotation of the revolving axle 50 causes the first container 42, the second container 44, the first rotating member 46, and the second rotating member 48 to revolve around the centrifugal axis 56. In the embodiment shown in FIG. 3, the first container 42, the second container 44, the first rotating member 46, and the second rotating member 48 project downward at an angle from the revolving axle 50.

[0022] In use, the first rotating member 46 rotates the first container 42 around the first longitudinal axis 52 in a first direction D1 and the second rotating member 48 rotates the second container 44 around the second longitudinal axis 54, also in the first direction D1 . At the same time, the revolving axle 50 causes the first container 42, the second container 44, the first rotating member 46, and the second rotating member 48 to revolve around the centrifugal axis 56 in a second direction D2. In some

embodiments, such as the embodiment shown in FIG. 3, the second direction D2 is different from the first direction D1 .

[0023] FIG. 4 is a flowchart illustrating a method 100 for forming a plurality of substantially spherical granules of a desired diameter from a powder, according to some embodiments of the disclosure. The method 100 is described with reference to the centrifugal mixer 10 of FIG. 1 , but it is understood that the method 100 may be used with any of the centrifugal mixers as described herein. The method 100 begins at step 102 by placing a powder into the container 12 having the longitudinal axis 20. In some embodiments, the container 12 may already be attached to the rotating member 14 in the centrifugal mixer 10 when the powder is added. In other embodiments, the powder is first placed within the container 12, and then the container 12 is connected to the rotating member 14.

[0024] Next, the container 12 is optionally rotated around the longitudinal axis 20 at step 104. At the same time, the container 12 is revolved around the centrifugal axis 22 at step 106. The rotating and revolving of container 12 at this point serves to mix the powder, which can be a combination of materials, as described below. In embodiments in which the powder is premixed, or a single material, steps 104 and 106 may be omitted.

[0025] As defined herein, the powder is a fine powder having a median powder particle size as small as 0.05 microns (pm), 0.1 pm, 0.2 pm, 0.3 pm, 0.5 pm, 1 pm, or 2 pm, or as large as 3 pm, 5 pm, 10 pm, 20 pm, 30 pm, 50 pm, or 100 pm, or between any two of the preceding values. For example, in some embodiments, the median powder particle sized can range from 0.05 m to 100 pm, 0.05 pm to 2 pm, 0.3 pm to 30 pm, 1 pm to 50 pm, 3 pm to 50 pm, or 10 pm to 20 pm. The median powder particle size can be determined by, for example, a dynamic light scattering system, as is known in the art. [0026] In some embodiments, the powder can be any of a variety of materials or mixtures of materials. Examples materials include zeolites, metal oxides, medicinal powders, wax powders, rubber powders, and polymer powders. For example, in some embodiments, the powder can be a filter material and a binder material. Together the filter material and the binder can be formed into filtering/absorbing granules for the removal of impurities, such as heavy metals, from water. In some embodiments, the filter material can include, for example, iron oxyhydroxide, titanium dioxide, and manganese oxide (e.g., in the form of manganese sand) that have each been

pulverized to form a fine powder, as described above. In some embodiments, the binder can be for example, a clay, such as attapulgite clay or montmorillonite clay that has been pulverized to form a fine powder, as described above.

[0027] Next, a liquid can be added into the container 12 at step 108. In some embodiments, the liquid can be added by spraying onto the powder within the container 12. In other embodiments, the liquid can be added by drop-wise addition into the container 12. The liquid is selected such that the powder is insoluble in the liquid. In some embodiments, the liquid can be a single component liquid. In other embodiments, the liquid can be a multiple component liquid as necessary to achieve desired properties in the resulting substantially spherical granules. Examples of component liquids can include, for example, water, isopropyl alcohol, toluene, dimethyl sulfoxide, ethylene glycol, silicone oil, and polyethers.

[0028] Next, the container 12 is rotated around the longitudinal axis 20 at step 1 10. At the same time, the container 12 is revolved around the centrifugal axis 22 at step 1 12 to begin formation of the substantially spherical granules without the use of small starter granules. Simultaneous steps 1 10 and 1 12 can be for a time as short as 10 seconds, 15 seconds, 20 seconds, or 25 seconds, or for a time as long as 35 seconds, 40 seconds, 50 seconds, or 60 seconds, or for any time between any of the preceding times. For example, in some embodiments steps 1 10 and 1 12 may be for a time ranging from 10 seconds to 60 seconds, 15 seconds to 50 seconds, 20 seconds to 40 seconds, or 25 seconds to 35 seconds.

[0029] In some embodiments, the container 12 can rotate around the longitudinal axis 20 at a speed as low as 1 ,500 revolutions per minute (RPM), 1 ,700 RPM, 1 ,900 RPM, 2, 100 RPM or 2,300 RPM, or as high as 2,700 RPM, 2,900 RPM, 3, 100 RPM, 3,300 RPM, or 3,500 RPM, or at a speed between any two of the preceding speeds. For example, in some embodiments, the container 12 can rotate around the longitudinal axis 20 at a speed ranging from 1 ,500 RPM to 3,500 RPM, 1 ,700 RPM to 3,300 RPM, 1 ,900 RPM to 3, 100 RPM, 2, 100 RPM to 2,900 RPM, or 2,300 RPM to 2,700 RPM. In some embodiments, the container 12 can rotate around the longitudinal axis 20 at a speed of about 2,500 RPM.

[0030] In some embodiments, the container 12 can revolve around the centrifugal axis 22 at a speed as low as 1 ,500 RPM, 1 ,700 RPM, 1 ,900 RPM, 2, 100 RPM or 2,300 RPM, or as high as 2,700 RPM, 2,900 RPM, 3, 100 RPM, 3,300 RPM, or 3,500 RPM, or at a speed between any two of the preceding speeds. For example, in some

embodiments, the container 12 can revolve around the centrifugal axis 22 at a speed ranging from 1 ,500 RPM to 3,500 RPM, 1 ,700 RPM to 3,300 RPM, 1 ,900 RPM to 3, 100 RPM, 2, 100 RPM to 2,900 RPM, or 2,300 RPM to 2,700 RPM. In some embodiments, the container 12 can rotate around the centrifugal axis 22 at a speed of about 2,500 RPM.

[0031] Next, the substantially spherical granules are examined at step 1 14 to determine if the substantially spherical granule diameter is correct. That is, the average diameter of the substantially spherical granules is as desired for the intended purpose. In some embodiments, the average granule diameter can be as small as 0.1 millimeters (mm), 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 .0 mm, 1.2 mm, or 1.4 mm, or as large as 1 .6 mm, 1 .8 mm, 2.0 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, or 3.0 mm, or of any diameter between any two of the preceding diameters. For example, in some

embodiments, the average granule diameter can range from 0.1 mm to 3.0 mm, 0.2 to 0.6 mm, 0.6 mm to 1 .2 mm, or 2.0 mm to 3.0 mm. The average diameter of the substantially spherical granules can be determined, for example, by sieve analysis, or passing the granules through a series of sieves of known mesh sizes. The average diameter can be the arithmetic mean of two sieves which can collect greater than 90% of the granules, by weight.

[0032] If the average granule diameter is not correct, then the process returns to step 108 and more liquid is added as describe above. Then the container 12 is simultaneously rotated and revolved at steps 1 10 and 1 12, and then the substantially spherical granules are once again examined at step 1 14. This process repeats until the average granule diameter is correct and the process concludes at step 1 16. In some embodiments, steps 108, 1 10, 1 12, and 1 14 may be repeated as few as 10 times, 14 times, 18 times, or 22 times, or as many as 28 times, 32 times, 36 times, or 40 times, or for as many times between any two of the preceding times. For example, in some embodiments, steps 108, 1 10, 1 12, and 1 14 may be repeated from 10 to 40 times, from 14 to 36 times, from 18 to 32 times, or from 22 to 28 times.

[0033] As defined herein, the substantially spherical granules are granules that have an aspect ratio between 0.8-1 .2. In some embodiments, the substantially spherical granules have an aspect ratio between 0.9-1 .1 . In some embodiments, the substantially spherical granules have an aspect ratio of about 1 .0, where about means plus or minus measurement error, as is known in the art.

[0034] It has been found by employing the method 100 described above, that for a given powder, the resulting average substantially spherical granule diameter can be a function of the total amount of liquid added as a weight percentage of the total powder and total liquid. That is, a known amount of powder and liquid can produce granules having a predictable average granule diameter. FIG. 5 is a flowchart illustrating another method 200 for forming a plurality of substantially spherical granules of a desired diameter from a powder, according to some embodiments of the disclosure. The method 200 uses the finding that the resulting average substantially spherical granule diameter can be a function of the total amount of liquid added as a weight percentage of the total powder and total liquid to produce substantially spherical granules without the need to depend on special skills of an operator.

[0035] The method 200 is described with reference to the centrifugal mixer 10 of FIG. 1 , but it is understood that the method 200 may be used with any of the centrifugal mixers as described herein. The method 200 begins at step 202 by kneading together a powder and a liquid to form a damp powder. The powder and the liquid can be as described above in reference to the method 100 of FIG. 4. The kneading may be done by any of several mechanical mixing machines known in the art, such as a kneader or a blender mixer. Next, the damp powder is placed into the container 12 at step 204. As with method 100 above, in some embodiments, the container 12 may already be attached to the rotating member 14 in the centrifugal mixer 10 when the damp powder is added. In other embodiments, the damp powder is first placed within the container 12, and then the container 12 is connected to the rotating member 14.

[0036] Next, the container 12 is rotated around the longitudinal axis 20 at step 206. At the same time, the container 12 is revolved around the centrifugal axis 22 at step 208 to form the substantially spherical granules without the use of small starter granules. Simultaneous steps 206 and 208 can be done for a time as short as 3 minutes, 6 minutes, or 9 minutes, or as long as 12, minutes, 15 minutes, 18 minutes, or 20 minutes, or for any length of time between any two of the preceding lengths of times. For example, in some embodiments, the steps 206 and 208 can be done

simultaneously for a length of time ranging from 3 minutes to 20 minutes, 6 minutes to 18 minutes, or 9 minutes to 15 minutes. In some embodiments, the simultaneous steps 206 and 208 can be done continuously for the entire length of time. In other

embodiments, entire length of time the simultaneous steps 206 and 208 can be done is broken up into short lengths of time, with pauses between to permit the container 12 to cool. In some embodiments, the short lengths of time can be as short as 10 seconds, 15 seconds, 20 seconds, or 25 seconds, or for a time as long as 35 seconds, 40 seconds, 50 seconds, or 60 seconds, or for any time between any of the preceding times, such as from between 10 seconds to 60 seconds, 15 seconds to 50 seconds, 20 seconds to 40 seconds, or 25 seconds to 35 seconds.

EXAMPLES

Example 1

[0037] Filter material powder consisting of iron oxyhydroxide, titanium dioxide, manganese sand, and zeolite 13X in a weight ratio of 1 : 1 : 1 :0.6 in the amount of 69 grams (g) and a binder consisting of 6 g of attapulgite clay powder were placed into a container. The container was compatible for use with a centrifugal mixer of a type as described above in reference to FIG. 1 (Speedmixer™ DAC 150.1 FVZ-K from FlacTek Inc., Landrum, South Carolina, U.S.). The powders were mixed by the centrifugal mixer twice at a rotational speed of 3,000 RPM for of 30 seconds each time. [0038] Water in an amount ranging from 0.5 to 2 grams was sprayed into the container and then stirred by the centrifugal mixer at 3,000 RPM for 30 seconds. After stirring the container was examined for formation of granules. The process of adding water, stirring, and examining for the formation of granules was repeated until substantially spherical granules were formed. The substantially spherical granules were found to have a diameter from 0.6 mm to 1 .2 mm when the total amount of water added was 1 1 g.

Example 2

[0039] Filter material powder consisting of iron oxyhydroxide, titanium dioxide, manganese sand, and zeolite 13X in a weight ratio of 1 : 1 : 1 :0.6 in the amount of 1000 g, a binder consisting of 125 g of Portland cement, and 200 g water were premixed in a mechanical kneader for 1 hour to form a damp powder. 70 g of the damp powder was placed into a container. The container was compatible for use with a centrifugal mixer of a type as described above in reference to FIG. 1 (Speedmixer™ DAC 150.1 FVZ-K from FlacTek Inc., Landrum, South Carolina, U.S.). The damp powder was mixed by the centrifugal mixer at a rotational speed of 3,000 RPM for of 8 minutes. 93% of the resulting substantially spherical granules were found to have diameters from 0.2 to 0.6 mm.

Example 3

[0040] HISIV 1000 absorbent powder (from UOP LLC, Des Plaines, Illinois, U.S.) in an amount of 20 g and a binder consisting of 3 g of montmorillonite powder were placed into a container. The container was compatible for use with a centrifugal mixer of a type as described above in reference to FIG. 1 (Speedmixer™ DAC 150.1 FVZ-K from FlacTek Inc., Landrum, South Carolina, U.S.). The powders were mixed by the centrifugal mixer twice at a rotational speed of 3,000 RPM for of 30 seconds each time.

[0041] Water in an amount ranging from 0.5 to 2 grams was added into the container by a dropper, and then stirred by the centrifugal mixer at 2,500 RPM for 30 seconds. After stirring the container was examined for formation of granules. The process of adding water, stirring, and examining for the formation of granules was repeated until substantially spherical granules were formed. The substantially spherical granules were found to have a diameter from 2 mm to 3 mm when the total amount of water added was 15.9 g.

[0042] While this invention has been described as relative to exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.