WO2025163312A1

WO2025163312A1 - Selective pellet recirculation

Info

Publication number: WO2025163312A1
Application number: PCT/GB2025/050165
Authority: WO
Inventors: Rudolph Johannes FOUCHEE; Wesley Robin GOUNDER; Garry LONSDALE
Original assignee: Anglo American Woodsmith Ltd
Current assignee: Anglo American Woodsmith Ltd
Priority date: 2024-01-29
Filing date: 2025-01-29
Publication date: 2025-08-07
Anticipated expiration: 2026-07-29
Also published as: GB202401147D0; GB2637556A

Abstract

A method for forming an evaporite mineral product, the method comprising: grinding an evaporite mineral supply to form an evaporite mineral feedstock; separating the evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; grinding at least one of the first oversized fraction and the first undersized fraction to form further evaporite mineral feedstock; separating the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized fraction; and forming the evaporite mineral product from the first in-size fraction, and the second in-size fraction; wherein the evaporite mineral feedstock is formed by a first grinding device and the further evaporite mineral feedstock is formed by a second grinding device, the first grinding device being distinct from the second grinding device, the evaporite mineral product being an evaporite mineral powder.

Description

SELECTIVE PELLET RECIRCULATION

This invention relates to forming powdered evaporite minerals, for example for use as pellets in a fertiliser.

Polyhalite is an evaporite mineral. It is a complex hydrated sulphate of potassium, calcium and magnesium. Deposits of polyhalite occur in, amongst other countries, Austria, China, Germany, India, Iran, Turkey, Ukraine, the UK and the USA.

Polyhalite has the capacity to be valuable as a source of agricultural fertiliser. In some prior art processes, it has been proposed to decompose natural polyhalite to extract specific nutrients. See, for example, WO 2013/074328, US 1 ,946,068 and US 4,246,019. However, intact polyhalite is also usable as a fertiliser, being able to supply sulphur, potassium, calcium and magnesium to the soil.

Mineral polyhalite can be spread in raw, crushed or powdered form. That involves low material processing costs, but it has a number of agronomic disadvantages. Alternatively, polyhalite can be mixed with a binder and processed to form pellets. The pellets may have improved properties of polyhalite alone. Other evaporite minerals may also be spread in raw, crushed or powdered form, or mixed with a binder to be formed into pellets.

GB 2 533 490 and GB 2 530 757 disclose forming powdered polyhalite into pellets, the powder being bound by starch.

Figure 1 illustrates an example evaporite mineral powder grinding process 100. An evaporite mineral supply 111 may be fed into a first grinding device 101. The first grinding device 101 may produce an evaporite mineral feedstock 112 by roughly grinding the evaporite mineral supply 111. The evaporite mineral feedstock 112 may be fed into a second grinding device 102. The second grinding device 102 may produce an evaporite mineral powder 113 by further grinding the evaporite mineral feedstock 112. The evaporite mineral powder 113 may be fed into a screen 103. The screen 103 may separate the evaporite mineral powder 113 into an in-size fraction 114a, an oversized fraction 114b, 114c and an undersized fraction. The oversized fraction 114b, 114c and the undersized fraction may be returned for further grinding by the second grinding device 102. The initial grinding by the first grinding device 101 may be required to sufficiency reduce the size of the particles before they are grinded by the second grinding device 102, which have a maximum limit on particle size. However, requiring both grinding devices 101 , 102 to grind the entire evaporite mineral supply 111 can be energy inefficient.

There is a need for an improved process for powdering evaporite mineral supplies.

According to a first aspect of the present invention there is provided a method for forming an evaporite mineral product, the method comprising: grinding an evaporite mineral supply using a first grinding device to form an evaporite mineral feedstock; separating the evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; grinding at least one of the first oversized fraction and the first undersized fraction using a second grinding device to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; separating the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized fraction; and forming the evaporite mineral product from the first in-size fraction and the second in-size fraction.

According to a second aspect of the present invention there is provided a method for forming an evaporite mineral product, the method comprising: grinding an evaporite mineral supply using a first grinding device to form an evaporite mineral feedstock; separating the evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; grinding at least one of the first oversized fraction and the first undersized fraction using a second grinding device to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; separating the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized fraction; and forming the evaporite mineral product from the first in-size fraction and the second in-size fraction, the evaporite mineral product being an evaporite mineral powder. According to a third aspect of the present invention there is provided a method for forming an evaporite mineral product, the method comprising: grinding an evaporite mineral supply using a first grinding device to form an evaporite mineral feedstock; grinding the evaporite mineral feedstock using a second grinding device to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; separating the further evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and forming the evaporite mineral product from the first in-size fraction; wherein at least part of the first oversized fraction is outputted as a chip.

The first grinding device may be configured to grind larger particles than the second grinding device. The first grinding device may be a mineral sizer device. The second grinding device may be a high-pressure grinding roll (HPGR) device.

Separating the evaporite mineral feedstock may be carried out by a first screening device. Separating the further evaporite mineral feedstock may be carried out by a first screening device. Both the evaporite mineral feedstock and the further evaporite mineral feedstock may be separated by the first screening device.

The method may further comprise separating the first in-size fraction into an in-form fraction and an out-form fraction. The form may comprise at least one of size, and density. The method may further comprise forming the evaporite mineral product from the in-form fraction. Particles of the in-form fraction may comprise at least one of a size and a density falling within a predetermined in-form range. The predetermined inform range may comprise an upper limit of 1 mm to 2mm and a lower limit of 0.2mm to 0.6mm. Separating the first in-size fraction into the in-form fraction and the out-form fraction may be carried out by an air classifier.

The method may further comprise separating the out-form fraction into a further insize fraction and at least one of a further oversized fraction and a further undersized fraction. The method may further comprise grinding at least one of the further oversized fraction and the further undersized fraction to form more further evaporite mineral feedstock.

The method may further comprise separating the more further evaporite mineral feedstock into a third in-size fraction and at least one of a third oversized fraction and a third undersized fraction.

The method may further comprise forming the evaporite mineral product from the first in-size fraction, the second in-size fraction, and the third in-size fraction.

At least part of the first oversized fraction, the second oversized fraction and/or the third oversized fraction may be outputted as a chip. At least part of the further oversized fraction may be outputted as a further chip.

Separating the out-form fraction into the further in-size fraction and at least one of the further oversized fraction and the further undersized fraction may be carried out by a second screening device.

Separating the more further evaporite mineral feedstock may be carried out by the first screening device.

Grinding at least one of the further oversized fraction and the further undersized fraction to form more further evaporite mineral feedstock may be carried out by the high-pressure grinding roll (HPGR) device.

Particles of the first in-size fraction, the second in-size fraction, and/or the third in-size fraction may comprise a diameter falling within a predetermined in-size range. Particles of the further in-size fraction may comprise a diameter falling within a predetermined further in-size range. The predetermined in-size range may be lower than the predetermined further in-size range. The predetermined in-size range may comprise an upper limit of 1 mm to 2mm. The predetermined further in-size range may comprise an upper limit of 5mm to 8mm.

The evaporite mineral supply may comprise polyhalite. The method may further comprise processing the evaporite mineral product to form a pelletised evaporite material product.

The processing may comprise mixing the first in-size fraction and/or the in-form fraction with a binder and with a liquid to form a mixture, and optionally wherein the binder comprises starch and/or the liquid comprises water. The processing may comprise pelletising the mixture to form pellets. The processing may comprise drying the pellets to form dried pellets. The processing may comprise separating the dried pellets into a pellet in-size fraction and at least one of a pellet oversized fraction and a pellet undersized fraction. The processing may comprise comprises cooling the pellet in-size fraction to form cooled pellets. The processing may comprise coating the cooled pellets to form coated pellets. The processing may comprise outputting the coated pellets to form the pelletised evaporite mineral product.

According to a fourth aspect of the present invention there is provided a production facility for forming an evaporite mineral product, the production facility comprising: a first grinding device configured to grind an evaporite mineral supply to form an evaporite mineral feedstock; a separator configured to separate the evaporite mineral into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and a second grinding device configured to grind at least one of the first oversized fraction and the first undersized fraction to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; wherein the separator is further configured to separate the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized faction; and the evaporite mineral powder is formed from the first in-size fraction and the second in-size fraction.

According to a fifth aspect of the present invention there is provided a production facility for forming an evaporite mineral product, the production facility comprising: a first grinding device configured to grind an evaporite mineral supply to form an evaporite mineral feedstock; a separator configured to separate the evaporite mineral into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and a second grinding device configured to grind at least one of the first oversized fraction and the first undersized fraction to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; wherein the separator is further configured to separate the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized faction; and the evaporite mineral powder is formed from the first in-size fraction and the second in-size fraction, the evaporite mineral product being an evaporite mineral powder.

According to a sixth aspect of the present invention there is provided a production facility for forming an evaporite mineral product, the production facility comprising: a first grinding device configured to grind an evaporite mineral supply to form an evaporite mineral feedstock; a second grinding device configured to grind the further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; and a separator configured to separate the further evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and wherein the evaporite mineral product is formed from the first in-size fraction, and at least part of the first oversized fraction is outputted as a chip.

The present invention will now be described by way of example with reference to the accompanying drawings:

Figure 1 illustrates an example evaporite mineral powder grinding process.

Figure 2 illustrates a first evaporite mineral powder grinding process of the invention.

Figure 3 illustrates a second evaporite mineral powder grinding process of the invention.

Figure 4 illustrates a third evaporite mineral powder grinding process of the invention.

Figure 5 illustrates a fourth evaporite mineral powder grinding process of the invention.

Figure 6 illustrates an evaporite mineral pellet forming process of the invention. Figures 2 to 5 illustrate four processes 200, 300, 400, 500 for grinding an evaporite mineral supply 211 to output an evaporite mineral powder 221. The process 300 in Figure 3 may also output a chip 301. The process 400 in Figure 4 may also output a further chip 401. The processes 300 and 400 may be combined to output both the chip 301 and the further chip 401 . The remaining aspects of the processes 200, 300, 400 may be the same. The process 500 may output the chip 301 and/or the further chip 401. The evaporite mineral powder 221 , chip 301 , and/or the further chip 401 may provide an evaporite mineral product.

The evaporate mineral supply 211 may be prepared so that there are substantially no pieces having a dimension greater than a predetermined size. That predetermined size may, for example, be 150mm or thereabouts (i.e. a size of minus 150mm).

The evaporate mineral supply 211 may comprise polyhalite. The evaporite mineral powder 221 may be a polyhalite powder.

The evaporite mineral supply 211 may be grinded. The evaporite mineral supply 211 may be input into a first grinding device 201. The evaporite mineral supply 211 may be fed into the first grinding device 201 manually or by means of a feeding device. The first grinding device 201 may grind the evaporite mineral supply 211 . The first grinding device 201 may grind the evaporite mineral supply 211 to form an evaporite mineral feedstock 212. The evaporite mineral feedstock 212 may thus comprise smaller particles than the evaporite mineral supply 211 . The first grinding device 201 may be a mineral sizer device. The first grinding device 201 may initially grind the evaporite mineral supply 211 into the evaporite mineral feedstock 212. The evaporite mineral feedstock 212 may be ground down to a gravel-like size: for example to minus 20mm or thereabouts. The gravel-like Polyhalite may have substantially no pieces having a dimension greater than, e.g., 10mm, 15mm, 20mm, 25mm or 30mm. A proportion such as 70%, 80% or 90% by mass of the gravel-like Polyhalite may have a size greater than 200pm. In general, the grinding may produce a range of sizes and so the feedstock 212 may contain a range of sizes from powder up to a maximum dimension of, e.g., 10mm, 15mm, 20mm, 25mm or 30mm. Put another way, the first grinding device 201 may ‘crush’ large particles into smaller particles. The evaporite mineral feedstock 212 may be separated. The evaporite mineral feedstock 212 may be input into a first separator 203. The first separator 203 may be a first screening device 203. The evaporite mineral feedstock 212 may be fed into the first separator 203 manually or by means of a feeding device. Alternatively, the evaporite mineral feedstock 212 may fall from the first grinding device 201 into the first screening device 203. The first screening device 203 may separate the evaporite mineral feedstock 212. The evaporite mineral feedstock 212 may be separated into a first in-size fraction 213a. The evaporite mineral feedstock 212 may be separated into at least one of a first oversized fraction 213b,c and a first undersized fraction.

The particles of the first in-size fraction 213a may comprise a diameter which falls within a predetermined in-size range. If the only first out of size fraction is the first oversized fraction 213b, c, then the predetermined in-size range of the first in-size fraction 213a may only comprise an upper range limit. Put another way, any particles in the evaporite mineral feedstock 212 that comprise a diameter under the upper limit may fall through the screen of the first screening device 203 to form the first in-size fraction 213a. This example is illustrated in Figures 2, 3 and 4 in which the first in-size fraction 213a falls to the bottom of the first screening device 203.

Alternatively, if the only first out of size fraction is the first undersized fraction, then the predetermined in-size range of the first in-size fraction 213a may only comprise a lower range limit. Put another way, any particles in the evaporite mineral feedstock 212 that comprise a diameter above the lower limit may sit on the screen of the first screening device 203 to form the first in-size fraction 213a.

Alternatively, if there is the first oversized fraction 213b,c and the first undersized fraction, then the predetermined in-size range of the first in-size fraction 213a may comprise an upper and a lower range limit. In this case, the first screening device 203 may comprise two screens of sequentially reducing diameter. Any particles in the evaporite mineral feedstock 212 that comprise a diameter below the upper limit and above the lower limit may fall through the first screen and sit on the second screen of the first screening device 203 to form the first in-size fraction 213a. The first out of size fractions may be returned for further grinding. The first oversized fraction 213b,c may be returned for further grinding. This is shown in Figure 2. The first undersized fraction may be returned for further grinding. All of the first oversized fraction 213b,c and/or the undersized fraction may be returned for further grinding.

Alternatively, the first oversized fraction 213b,c may be outputted as a chip. Or, the first oversized fraction 213b,c may be separated so that at least part of the first oversized fraction 213b,c may be outputted as the chip. The first screening device 203 may separate the first oversized fraction 213b,c. The first oversized fraction 213b,c may be separated into a primary first oversized fraction 213b and a secondary first oversized fraction 213c. The primary first oversized fraction 213b may be outputted as the chip 301 . In this case, the first screening device 203 may comprise two screens of sequentially reducing diameter. Any particles in the evaporite mineral feedstock 212 that comprise a diameter below a chip upper limit and above a chip lower limit may fall through the first screen and sit on the second screen of the first screening device 203 to form the chip 301 . This is shown in Figure 3. The chip 301 may be used as a fertiliser in its raw form. The chip 301 may provide the evaporite mineral product.

The predetermined in-size range may comprise an upper limit of 5mm to 8mm. Preferably, the predetermined in-size range may comprise an upper limit of 5mm. The chip lower limit may be the same as the predetermined in-size range upper limit. The chip upper limit may be 20mm to 25mm. Preferably, the chip upper limit may be 20mm.

The first out of size fractions may be grinded. The first oversized fraction 213b, c and/or the first undersized fraction may be grinded. The first oversized fraction 213b,c and/or the first undersized fraction may be input into a second grinding device 202. The first oversized fraction 213b,c and/or the first undersized fraction may be fed into the second grinding device 202 manually or by means of a feeding device. Alternatively, the first oversized fraction 213b,c and/or the first undersized fraction may fall from the first screening device 203 into the second grinding device 202. The second grinding device 202 may grind the first oversized fraction 213b,c and/or the first undersized fraction. The second grinding device 202 may grind the first oversized fraction 213b,c and/or the first undersized fraction to form further evaporite mineral feedstock 214. The further evaporite mineral feedstock 21 may thus comprise smaller particles than the first oversized fraction 213b,c and/or the first undersized fraction. The second grinding device 202 may be a high-pressure grinding roll (HPGR) device. The second grinding device 202 may provide secondary grinding of the out of size fractions 213b, c. The second grinding device 202 may not significantly reduce the particle size of the first undersized fraction. However, grinding the first oversized fraction 213b,c along with the first undersized fraction can improve the efficiency of the HPGR. This may be because smaller particles help to fill the gaps around the larger particles in the HPGR, which can increase the pressure and grinding force on the larger particles. Put another way, the second grinding device 202 may ‘grind’ small particles into powder.

The first grinding device 201 and the second grinding device 202 may be distinct devices. As illustrated in Figures 2 to 4, the first grinding device 201 and the second grinding device 202 may not be sequential in the manufacturing apparatus pipeline. An intermediate device may be positioned in between the first grinding device 201 and the second grinding device 202 in the manufacturing apparatus pipeline. Outputs from the first grinding device 201 may not be directly inputted into the second grinding device 202. Outputs from the first grinding device 201 may pass through an intermediate device before being inputted into the second grinding device 202. The first grinding device 201 and the second grinding device 202 may be provided by different types of machines. The first grinding device 201 may be configured to grind larger particles than the second grinding device 202. The first grinding device 201 may be able to receive larger particles than the second grinding device 202. The first grinding device 201 may output larger particles on average than the second grinding device 202.

Alternatively, as shown in Figure 5, the first grinding device 201 and the second grinding device 202 may be sequential in the manufacturing apparatus pipeline. An intermediate device may not be positioned in between the first grinding device 201 and the second grinding device 202 in the manufacturing apparatus pipeline. Outputs from the first grinding device 201 may be directly inputted into the second grinding device 202. Outputs from the first grinding device 201 may not pass through an intermediate device before being inputted into the second grinding device 202. The further evaporite mineral feedstock 214 may be separated. The further evaporite mineral feedstock 214 may be input into the first screening device 203. The further evaporite mineral feedstock 214 may be fed into the first screening device 203 manually or by means of a feeding device. Alternatively, the further evaporite mineral feedstock 214 may fall from the second grinding device 202 into the first screening device 203. The first screening device 203 may separate the further evaporite mineral feedstock 214. Alternatively, the further evaporite mineral feedstock 214 may be separated by a different screening device to the first screening device 203. The further evaporite mineral feedstock 214 may be separated into a second in-size fraction 213a. The further evaporite mineral feedstock 214 may be separated into at least one of a second oversized fraction 213b,c and a second undersized fraction. The further evaporite mineral feedstock 214 may join the flow of the evaporite mineral feedstock 212. As a result, the second in-size fraction 213a and the at least one of the second oversized fraction 213b,c and the second undersized fraction may join the flow of the first in-size fraction 213a and the at least one of the first oversized fraction 213b, c and the first undersized fraction, respectively.

Put another way, any out of size particles from the first screening device 203 may be recirculated through the second grinding device 202 before being reintroduced into the flow of the evaporite mineral feedstock 212. In this way, the out of size particles may not be wasted, and can be grinded again until they are in-size. This can reduce material wastage.

Additionally, as shown in Figures 2 to 4, by initially feeding the evaporite mineral feedstock 212 into the first screening device 203 without first passing the evaporite mineral feedstock 212 through the second grinding device 202, this can allow any particles that are already in-size from the first grinding device 201 to be passed straight through. In this way, less of the flow of evaporite mineral feedstock 212 is passed through the second grinding 202. This can reduce the energy consumption.

Alternatively, as shown in Figure 5, the evaporite mineral feedstock 212 may be fed directly from the first grinding device 201 to the second grinding device 202, depending on the requirements. The first in-size fraction 213a may be separated. The first in-size fraction 213a may be input into an air classifier 204. The first in-size fraction 213a may be fed into the air classifier 204 manually or by means of a feeding device. Alternatively, the first in-size fraction 213a may fall from the first screening device 203 into the air classifier 204. The air classifier 204 may separate the first in-size fraction 213a. The first in-size fraction 213a may be separated into an in-form fraction 215a. The first in-size fraction 213a may be separated into an out-form fraction 215b.

The form may comprise at least one of size, and density. The particles of the in-form fraction 215a may comprise at least one of a size, and density which falls within a predetermined in-form range. The in-form fraction 215a may comprise all of the size, and density which fall within the predetermined in-form range. Put another way, each of the size, and density of the particles meet the criteria of the predetermined in-form range. The size requirement may be based on diameter.

The in-form fraction 215a may rise to the top of the air classifier 204. The out-form fraction 215b may fall to the bottom of the air classifier 204. As shown in Figures 2 to 5, the predetermined in-form range may comprise only an upper limit, and so larger particles may form the out-form fraction 215b. Alternatively, the predetermined in-form range may comprise only a lower limit, and so smaller particles may form the out-form fraction.

The upper limit may be a diameter of 1 mm to 2mm. Preferably, the upper limit may be a diameter of 1 mm. The lower limit may be a diameter of 0.2mm to 0.6mm. Preferably, the lower limit may be a diameter of 0.6mm. More preferably, the predetermined inform range may be a diameter in the range of 0.6mm to 1 mm.

The out-form fraction 215b may be separated. The out-form fraction 215b may be input into a second separator 205. The second separator 205 may be a second screening device 205. The out-form fraction 215b may be fed into the second screening device 205 manually or by means of a feeding device. Alternatively, the out-form fraction 215b may fall from the air classifier 204 into the second screening device 205. The second screening device 205 may separate the out-form fraction 215b. The out-form fraction 215b may be separated into a further in-size fraction 216a. The out-form fraction 215b may be separated into at least one of a further oversized fraction 216b,c and a further undersized fraction.

The particles of the further in-size fraction 216a may comprise a diameter which falls within a further predetermined in-size range. If the only further out of size fraction the further oversized fraction 216b, c, then the further predetermined in-size range of the further in-size fraction 216a may only comprise an upper range limit. Put another way, any particles in the out-form fraction 215b that comprise a diameter under the upper limit may fall through the screen of the second screening device 205 to form the further in-size fraction 216a. This example is illustrated in Figures 2, 3 and 4 in which the further in-size fraction 216a falls to the bottom of the second screening device 205.

Alternatively, if the only further out of size fraction the further undersized fraction, then the further predetermined in-size range of the further in-size fraction 216a may only comprise a lower range limit. Put another way, any particles in the out-form fraction 215b that comprise a diameter above the lower limit may sit on the screen of the second screening device 205 to form the further in-size fraction 216a.

Alternatively, if there is the further oversized fraction 216b, c and the further undersized fraction, then the further predetermined in-size range of the further in-size fraction 216a may comprise an upper and a lower range limit. In this case, the second screening device 205 may comprise two screens of sequentially reducing diameter. Any particles in the out-form fraction 215b that comprise a diameter below the upper limit and above the lower limit may fall through the first screen and sit on the second screen of the second screening device 205 to form the further in-size fraction 216a.

The further out of size fractions 216b, c may be returned for further grinding. The further oversized fraction 216b,c may be returned for further grinding. This is shown in Figure 2. The first undersized fraction may be returned for further grinding. All of the further oversized fraction 213b,c and/or the undersized fraction may be returned for further grinding. In the case shown in Figure 2, the further in-size fraction 216a is also returned for further grinding. Alternatively, the further oversized fraction 216b,c may be outputted as a chip. Or, the further oversized fraction 216b,c may be separated so that at least part of the further oversized fraction 216b, c may be outputted as the chip. The second screening device 205 may separate the further oversized fraction 216b,c. The further oversized fraction 216b,c may be separated into a primary further oversized fraction 216b and a secondary further oversized fraction 216c. The primary further oversized fraction 216b may be outputted as the further chip 401 . In this case, the second screening device 205 may comprise two screens of sequentially reducing diameter. Any particles in the out-form fraction 215b that comprise a diameter below a chip upper limit and above a chip lower limit may fall through the first screen and sit on the second screen of the second screening device 205 to form the further chip 401. This is shown in Figure 4. The further chip 401 may be used as a fertiliser in its raw form. The further chip 401 may provide the evaporite mineral product.

The further predetermined in-size range may comprise an upper limit of 1 mm to 2mm. Preferably, the further predetermined in-size range may comprise an upper limit of 1 mm. The chip lower limit may be the same as the predetermined in-size range upper limit. The chip upper limit may be 5mm to 8mm. Preferably, the chip upper limit may be 5mm.

The further predetermined in-size range may be lower than the predetermined in-size range. As a result, the in-size particles from the second screening device 205 may be smaller than the in-size particles from the first screening device 203. The first screening device 203 may form a coarse filter and the second screening device 205 may form a fine filter. In this way, the chip 301 from the first screening device 203 may be larger than the further chip 401 from the second screening device 205. This may be useful as different sized chips can be outputted, which may have different properties and/or uses.

As shown in Figure 5, both the chip 301 and the further chip 401 may be outputted. The chip 301 and/or the further chip 401 may be outputted, depending on the requirements. Figure 5 also shows the evaporite mineral feedstock 212 being directly fed from the first grinding device 201 into the second grinding device 202. In this embodiment, direct feeding of the evaporite mineral feedstock 212 may be combined with the production of the chip and/or the further chip 401 .

The further out of size fractions 216b,c may be grinded. The further oversized fraction 216b,c and/or the further undersized fraction may be grinded. The further oversized fraction 216b,c and/or the further undersized fraction may be input into the second grinding device 202. The further oversized fraction 216b,c and/or the further undersized fraction may be fed into the second grinding device 202 manually or by means of a feeding device. Alternatively, the further oversized fraction 216b,c and/or the further undersized fraction may fall from the second screening device 205 into the second grinding device 202. As explained herein, the further in-size fraction 216a may also be fed into the second grinding device 202 for grinding. The second grinding device 202 may grind the further oversized fraction 216b,c and/or the further undersized fraction. The second grinding device 202 may grind the further oversized fraction 216b,c and/or the further undersized fraction to form more further evaporite mineral feedstock 214. The more further evaporite mineral feedstock 214 may thus comprise smaller particles than the further oversized fraction 216b,c and/or the further undersized fraction. The second grinding device 202 may provide secondary grinding of the further out of size fractions 216b,c. The second grinding device 202 may not significantly reduce the particle size of the further undersized fraction. However, grinding the further oversized fraction 216b, c along with the further undersized fraction can improve the efficiency of the HPGR. This may be because smaller particles help to fill the gaps around the larger particles in the HPGR, which can increase the pressure and grinding force on the larger particles.

The four processes 200, 300, 400, 500 for grinding an evaporite mineral supply 211 may output an evaporite mineral powder 221 . The evaporite mineral powder 221 may provide an evaporite mineral product. The in-form fraction 215a may provide the evaporite mineral powder 221. The in-form fraction 215a may provide all the evaporite mineral powder 221 . This is illustrated in Figures 2, 3, 4 and 5. Additionally, the further in-size fraction 216a may provide the evaporite mineral powder 221 . Put another way, both the in-form fraction 215a and the further in-size fraction 216a in combination may be outputted as the evaporite mineral powder 221 (not shown in the Figures). Alternatively, the first in-size fraction 213a may provide the evaporite mineral powder 221. Put another way, the evaporite mineral powder 221 may be formed by the first grinding device 201 and the first screening device 203 (and optionally the second grinding device 202) without the need for the air classifier 204 and the second screening device 205. The first in-size fraction 213a outputted by the first screening device 203 may provide the evaporite mineral powder 221 .

Alternatively, a combination of the above options may be used. The evaporite mineral powder 221 may be provided by one or more of the first in-size fraction 213a, the inform fraction 215a, and the further in-size fraction 216a. Which options are used may depend on the selected screen sizes and air classifier set up, and the size requirements for the evaporite mineral powder 221 .

Figure 6 illustrates an evaporite mineral pellet forming process 600. The evaporite mineral powder 221 may be processed to form a pelletised evaporite material product 616. Although certain steps of the processing are shown in Figure 6, it will be appreciated that some steps may be removed, or added to, depending on the requirements for the pelletised evaporite material product 616.

The evaporite mineral powder 221 may be fed into a mixer 601 . The mixer 601 may be a ribbon blender. The mixer 601 may mix the evaporite mineral powder 221 with other components for forming the pellets. The evaporite mineral powder 221 may be mixed with a binder. The evaporite mineral powder 221 may be mixed with a liquid. The evaporite mineral powder 221 may be mixed with the binder and the liquid to form a mixture 611 . The evaporite mineral powder 221 may be first mixed with the binder and water added later. Alternatively, the binder and water may be premixed before the evaporite mineral powder 221 is added. The binder may comprise starch. The liquid may comprise water. The evaporite mineral powder 221 , binder and liquid may be mixed until the mixture 611 is homogeneous.

In the description below, the additions of water and binder are specified by mass with reference to the mass of the powder to which they are added. The amount of water to be added may depend on the inherent water content of the evaporite mineral powder 221 , such as polyhalite, and the nature of the subsequent processing steps. However, it has been found that when the binder is a starch-based binder such as starch itself or flour, acceptable results can be achieved by adding water in the range of 5% to 10%, more preferably between 7% and 8%. At a subsequent stage in the process excess water is removed from the formed pellets by drying. That can consume energy, so it is preferred to minimise the amount of water added, provided that is consistent with the production of an acceptably bound pellet product. The preferred amount of water can readily be determined by testing. The amount of binder to be added will depend on the qualities of the binder. For typical binders, e.g., starch or flour, the amount added may be in the range of 0.5% to 4%, preferably 0.5% to 3%, more preferably 0.5% to 1.5%. The binder may be a starch-based binder such as a purified starch or a flour, or an adhesive such as PVA.

One option as a binder is purified starch. This can be added in the range 0.5% to 1 .0%. Another option as a binder is flour. The flour may be formed by grinding a starchy vegetable base such as one or more types of vegetable root or seed. The flour may, for example be formed from the seeds of a cereal such as wheat, corn or rye or of a pulse such as pea. The flour may be a raw flour: that is a flour formed by the grinding of the base biological material with no substantial bleaching or refinement. The flour may be a wholegrain flour. The flour may be formed from material from which the germ and/or the bran has not been separated. The flour may comprise starch together with fat (e.g. oil) or protein or both. The germ is a significant source of fat. The flour may comprise greater than 1.0% or greater than 2.0% germ by mass. The flour may comprise greater than 0.05% or greater than 0.1 % or greater than 0.2% fat by mass or greater than 0.4% fat by mass. The bran is a significant source of protein. The flour may comprise greater than 8% or greater than 12% bran by mass. The flour may comprise greater than 0.5% or greater than 1 .0% or greater than 4.0% or greater than 8.0% or greater than 10% of protein by mass. The flour may comprise greater than 50% or greater than 55% or greater than 60% starch by mass. The flour may comprise less than 90% or less than 80% or less than 70% starch by mass. The flour may comprise greater than 1 % or greater than 2% lipids by mass. The flour may comprise greater than 0.2% or 0.4% fatty acids by mass. A suitable example composition of the flour is: lipids 3%, protein 7.5%, moisture 13.5%, fibre 3.6%, fatty acids 0.5%, ash 2.5%, starch 69.4%. The flour may comprise gluten. The flour may comprise greater than 5.0% or greater than 8.0% or greater than 10% gluten by mass. Flour has been found to be advantageous as a binder for the present process for a number of reasons:

1 . When a pelletised fertiliser bound with flour is introduced to a growing medium (e.g. soil) and breaks down, the protein and oil in flour can be released to the growing medium. The protein and potentially also the oil can attract and support the growth of mycorrhizal organisms. Those organisms can promote the growth of the target plants and supplement the nutrient-giving effects of the fertiliser composition itself.

2. Flour is typically less flammable than refined starch, which can even be explosive. This improves safety and makes flour less expensive to handle.

3. Flour is significantly cheaper than some alternative binders, such as refined starch.

4. The type of flour selected for use can depend on the availability of suitable starchy crops convenient to the pelletising plant, and may vary seasonally without significantly affecting pellet yield.

When the binder is starch or flour, it is convenient to mix it with water, and then subsequently to add the mixture of binder and water to the polyhalite powder. This can improve the intermixing of the binder and the mineral powder. Starch contained in the binder may be gelatinised prior to being mixed with the mineral powder. This may, for example be done by atmospheric cooking or by jet cooking. To this end the binder may be added to water at a temperature of greater than 55°C, more preferably greater than 80°C; or the binder may be added to water and the binder/water mixture heated to a temperature in that range. The binder may be added to the water in equal proportion to the intended additions of the same to the powder, or alternatively additional water may be added after the water/binder mix is added to the mineral powder. As part of the process of cooking the starch, water may be added to the binder in liquid form or in the form of steam. The process of cooking the starch may be performed at atmospheric pressure and/or at greater than atmospheric pressure. The cooking process may be completed before the binder mixture is added to the polyhalite powder.

The mixture 611 may be fed into a pelletiser 602. The pelletiser 602 may be a pan pelletiser. The pelletiser 602 may form the mixture 611 into pellets 612. The pelletiser 602 may be configured to output the pellets 612 as it operates, allowing it to run continuously. Alternatively, the pelletiser 602 may operate on a batch basis, with material being processed according to a defined programme and then expelled en masse.

Alternatively, a single device may provide the mixing and pelletising. An example of such equipment is an intensive mixer/granulator, e.g. as available from Maschinenfabrik Gustav Eirich GmbH & Co KG.

Before or after being expelled from the pelletiser 602, the formed pellets 612 may be coated with dry powder before subsequently being screened. This can help to resist them sticking or breaking up during later screening or related processing. Further polyhalite powder may be added to the pelletiser 602 towards the end of the pelletising process. The polyhalite powder may coat the pellets 612 with a dry coating which can assist with subsequent processing. The amount of polyhalite powder added at this stage may be between 5 and 15% by mass of the content of the pelletiser 602, more preferably between 8 and 12% by mass. The additional polyhalite may be added between 10 and 15 seconds prior to completion of the pelletising process. At completion of the pelletising process may be when the pellets are expelled from the pelletiser 602. Alternatively, no dry powder may be added.

The pellets 612 may be fed into a drying device 603. The drying device 603 may comprise a heater. The pellets 612 may be dried to form dried pellets 613. The pellets 612 may be dried by heating them with the heater. It has been found that a retention time of around 10 to 20 minutes in a drier capable of heating the pellets 612 to a temperature of around 130°C is sufficient to adequately dry the pellets 612. This can harden the pellets 612. Pellets manufactured using polyhalite powder and with flour as a binder can have a crush strength in excess of 4.0kgf and/or in excess of 5.0kgf. This compares favourably with a generally accepted lower limit of 2.5kgf for acceptable agricultural pellets of 2.36mm to 2.8mm. Moisture may be extracted from the dryer using a reverse jet air filter. The operating temperature and retention time in the dryer may be selected to provide dried pellets 613 of the desired strength for subsequent handling. The dried pellets 613 may be fed into a third screening device 604. The dried pellets 613 may be separated into a pellet in-size fraction 614b and at least one of a pellet oversized fraction 614c and a pellet undersized fraction 614a. The pellet in-size fraction 614b may fall within a pellet predetermined in-size range. The pellet predetermined in-size range may have an upper limit of 4mm and a lower limit of 2mm. Alternatively, other sizes may be chosen as appropriate to the desired application. The out of size pellets, the pellet oversized fraction 614c and the pellet undersized fraction 614a, may be recirculated. The pellet oversized fraction 614c may be ground and then returned to the mixer 601 . The pellet oversized fraction 614c may be ground in an auxiliary grinder (not shown in the Figures). The pellet undersized fraction 614a may be returned directly to the pelletiser 602.

Alternatively, the pellets 612 may be screened by the third screening device 604 before the pellets 612 are dried in the drying device 603. In this case, the pellet predetermined in-size range may be larger to account for shrinking during drying. Alternatively, the pellets 612 may be screen before and after the drying.

The dried pellet in-size fraction 614b may be fed into a cooling device 605. The cooling device 605 may comprise a refrigerator. The pellet in-size fraction 614b may be cooled to form cooled pellets 615. The pellets 615 may be cooled by cooling them with the refrigerator. The cooling device 605 is optional. The pellet in-size fraction 614b may air cool instead. This may be more energy efficient, but less time efficient. The pellet in-size fraction 614b may not be cooled at all.

The cooled pellets 615 may be fed into a coating device 606. The coating device 606 may coat the cooled pellets 615 in a coating. The coating device 606 may comprise a rotating drum. The coating may be added to the drum with the cooled pellets 615. Rotation of the drum may cause the cooled pellets to be coated in the coating. The coating device 606 may comprise a spray. The coating may be sprayed onto the cooled pellets 615. The coating may, for example, be a wax or wax-like coating. The coating may act as a moisture barrier and/or an anti-caking agent and/or a dust suppressant. The coating may comprise further fertiliser compositions. There may be more than one coating applied. A first coating may be applied by one of the rotating drum and the spray. A second coating may be applied by one of the rotating drum and the spray. The coating device 606 is optional. The cooled pellets 615 may not be coated at all.

Alternatively, the pellet in-size fraction 614b may be coated by the coating device 606 before the pellet in-size fraction 614b are cooled in the cooling device 605. In this case, the coating may be suitable for being applied at higher temperatures.

The processed pellets may be outputted as the pelletised evaporite mineral product 616. As explained herein, one or more of the processing steps may be optional. As such, the pelletised evaporite mineral product 616 may be the output of any of the devices 601 , 602, 603, 604, 605, 606. The pelletised evaporite mineral product 616 may provide the evaporite mineral product.

Other additives may be included in the pelletised evaporite mineral product 616. Such additives may one or more of the following, in any combination:

- a component having the effect of chemically and/or mechanically stabilising and/or preserving the pellets: for example to increase their shelf life, reduce their susceptibility to environmental contaminants or to reduce the likelihood of them being broken up during spreading;

- a component having the effect of enhancing the fertilising effect of the polyhalite: for example by accelerating or retarding the breakdown of the polyhalite in the field;

- a component having the effect of protecting or enhancing the growth of crops by means other than fertilising: for example a herbicide, fungicide, insecticide, rodenticide, hormone, plant stimulant or mycorrhizal fungus or spore;

- a seed: which may be a seed of an angiosperm and/or of a crop species (e.g. a cereal such as wheat, maize, rice, millet, barley, oats or rye);

- a further fertiliser composition in addition to the polyhalite: for example a source of nitrogen and/or phosphorus;

- a pigment;

- a component having the effect of altering soil pH: for example lime, sulphur or a sulphate.

Such a component may be added at various stages in the process, for example it could be combined with the polyhalite powder prior to or during the first mixing stage as described above, or with the binder prior to the first mixing stage as described above, or with the polyhalite/binder mix between the first and second mixing steps as described above, or during the second mixing step as described above, or it could be added to the pan pelletiser 602, or it could be sprayed or otherwise coated on to the pellets before or after drying.

The polyhalite content of the resulting pellets is preferably greater than 75% by weight, more preferably greater than 80% and most preferably greater than 90%. In the case of pellets that contain seeds this may optionally be varied such that the polyhalite content of the pellets excluding the weight of the seeds may be greater than 75% by weight, more preferably 80%, most preferably greater than 90%.

The pellets are preferably substantially spherical, and of substantially uniform volume and mass. The pellets may have a mean Wadell sphericity of greater than 0.85, 0.90 or 0.95. The pellets are preferably substantially free from voids, for example having not more than 1 %, 2% or 5% by volume of air.

The process as described above may be used for pelletising minerals other than polyhalite, and in particular for pelletising feedstocks composed principally of one or more evaporite minerals, especially other chloride minerals. These may include any one or more of Anyhdrite, Carnalite, Gypsum, Halite, Kainite, Kieserite, Langbeinite and/or Sylvite. The process is especially suitable for pelletising feedstocks composed principally of minerals that are substantially hygroscopic in recently powdered form and/or that have a Moh’s hardness in the range from 2 to 4. The resulting pellets may be used for purposes other than fertilisation.

The pelletised evaporite mineral product 616 may be packaged. For example, in 600kg bags or 25kg sacks, or shipped loose for use or further processing elsewhere.

The pelletised evaporite mineral product 616 can then be shipped for use as a fertiliser. The product may be used as a fertiliser by spreading the pellets on the surface of a growing medium such as soil, or by intermixing the pellets in the growing medium.

The processes 200, 300, 400, 500 and 600 may be carried out by a manufacturing apparatus. The manufacturing apparatus may comprise a manufacturing plant. The steps in the processes 200, 300, 400, 500 and 600 may be carried out at different sites. For example, the grinding processes 200, 300, 400 and 500 may be carried out at a first site, and the pelletising process 600 may be carried at a second site. The devices 201-205 and 601-606 may be located at the same or different sites. Conveyor belts, auger conveyors or other handling apparatus can be used to move the components between devices 201-205 and 601 -606. The processes 200, 300, 400, 500 and 600 may be automated such that human interaction is not required. The processes 200, 300, 400, 500 and 600 may be monitored by monitoring devices, such as cameras and sensors, so as to maintain quality. For example, after each device 201-205 and 601-606 the output may be checked. The quality checks may be manual or automated or a combination of both. The devices 201 -205 and 601-606 which are described herein as optional may be added to, and removed from, the manufacturing apparatus as required. The devices 201 -205 and 601-606 may be reconfigurable within the manufacturing apparatus.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1 . A method for forming an evaporite mineral product, the method comprising: grinding an evaporite mineral supply using a first grinding device to form an evaporite mineral feedstock; separating the evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; grinding at least one of the first oversized fraction and the first undersized fraction using a second grinding device to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; separating the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized fraction; and forming the evaporite mineral product from the first in-size fraction and the second in-size fraction, the evaporite mineral product being an evaporite mineral powder.

2. A method for forming an evaporite mineral product, the method comprising: grinding an evaporite mineral supply using a first grinding device to form an evaporite mineral feedstock; grinding the evaporite mineral feedstock using a second grinding device to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; separating the further evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and forming the evaporite mineral product from the first in-size fraction; wherein at least part of the first oversized fraction is outputted as a chip.

3. The method according to claim 1 or 2, wherein the first grinding device is configured to grind larger particles than the second grinding device.

4. The method according to any preceding claim, wherein the first grinding device is a mineral sizer device.

5. The method according to any preceding claim, wherein the second grinding device is a high-pressure grinding roll (HPGR) device.

6. The method according to any preceding claim when dependent on claim 1 , wherein the separating the evaporite mineral feedstock and separating the further evaporite mineral feedstock are both carried out by a first screening device.

7. A method according to any preceding claim, further comprising: separating the first in-size fraction into an in-form fraction and an out-form fraction, the form comprising at least one of size, and density; and forming the evaporite mineral product from the in-form fraction.

8. The method according to claim 7, wherein particles of the in-form fraction comprise at least one of a size and a density falling within a predetermined in-form range.

9. The method according to claim 8, wherein the predetermined in-form range comprises an upper limit of 1 mm to 2mm and a lower limit of 0.2mm to 0.6mm.

10. The method according to any of claims 7 to 9, wherein separating the first insize fraction into the in-form fraction and the out-form fraction is carried out by an air classifier.

11. The method according to any preceding claim, further comprising separating the out-form fraction into a further in-size fraction and at least one of a further oversized fraction and a further undersized fraction.

12. The method according to claim 11 , further comprising: grinding at least one of the further oversized fraction and the further undersized fraction to form more further evaporite mineral feedstock; and separating the more further evaporite mineral feedstock into a third in-size fraction and at least one of a third oversized fraction and a third undersized fraction; and forming the evaporite mineral product from the first in-size fraction, the second in-size fraction, and the third in-size fraction.

13. The method according to claim 10, wherein at least part of the first oversized fraction, the second oversized fraction and/or the third oversized fraction is outputted as a chip; and/or wherein at least part of the further oversized fraction is outputted as a further chip.

14. The method according to any of claims 11 to 13, wherein separating the out- form fraction into the further in-size fraction and at least one of the further oversized fraction and the further undersized fraction is carried out by a second screening device.

15. The method according to any of claims 12 to 14 when dependent on claim 6, wherein separating the more further evaporite mineral feedstock is carried out by the first screening device.

16. The method according to any of claims 12 to 15 when dependent on claim 5, wherein grinding at least one of the further oversized fraction and the further undersized fraction to form more further evaporite mineral feedstock is carried out by the high-pressure grinding roll (HPGR) device.

17. The method according to claim 12, wherein particles of the first in-size fraction, the second in-size fraction, and/or the third in-size fraction comprise a diameter falling within a predetermined in-size range.

18. The method according to any of claims 11 to 17, wherein particles of the further in-size fraction comprise a diameter falling within a predetermined further in-size range.

19. The method according to claim 18 when dependent on claim 17, wherein the predetermined in-size range is lower than the predetermined further in-size range.

20. The method according to any of claims 17 to 19, wherein the predetermined insize range comprises an upper limit of 1 mm to 2mm.

21. The method according to any of claims 18 to 20, wherein the predetermined further in-size range comprises an upper limit of 5mm to 8mm.

22. The method according to any preceding claim, wherein the evaporite mineral supply comprises polyhalite.

23. The method according to any preceding claim, wherein the method further comprises processing the evaporite mineral product to form a pelletised evaporite material product.

24. The method according to claim 23, wherein processing comprises mixing the first in-size fraction and/or the in-form fraction with a binder and with a liquid to form a mixture, and optionally wherein the binder comprises starch and/or the liquid comprises water.

25. The method according to claim 23 or 24, wherein processing comprises pelletising the mixture to form pellets.

26. The method according to claim 25, wherein processing comprises drying the pellets to form dried pellets.

27. The method according to claim 26, wherein processing comprises separating the dried pellets into a pellet in-size fraction and at least one of a pellet oversized fraction and a pellet undersized fraction.

28. The method according to claim 27, wherein processing comprises cooling the pellet in-size fraction to form cooled pellets.

29. The method according to claim 28, wherein processing comprises coating the cooled pellets to form coated pellets.

30. The method according to claim 29, wherein processing comprises outputting the coated pellets to form the pelletised evaporite mineral product.

31. A production facility for forming an evaporite mineral product, the production facility comprising: a first grinding device configured to grind an evaporite mineral supply to form an evaporite mineral feedstock; a separator configured to separate the evaporite mineral into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and a second grinding device configured to grind at least one of the first oversized fraction and the first undersized fraction to form further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; wherein the separator is further configured to separate the further evaporite mineral feedstock into a second in-size fraction and at least one of a second oversized fraction and a second undersized faction; and the evaporite mineral powder is formed from the first in-size fraction and the second in-size fraction, the evaporite mineral product being an evaporite mineral powder.

32. A production facility for forming an evaporite mineral product, the production facility comprising: a first grinding device configured to grind an evaporite mineral supply to form an evaporite mineral feedstock; a second grinding device configured to grind the further evaporite mineral feedstock, the second grinding device being distinct from the first grinding device; and a separator configured to separate the further evaporite mineral feedstock into a first in-size fraction and at least one of a first oversized fraction and a first undersized fraction; and wherein the evaporite mineral product is formed from the first in-size fraction, and at least part of the first oversized fraction is outputted as a chip.