WO2024182705A1

WO2024182705A1 - Calcium bentonite wet process slurry for linerboard

Info

Publication number: WO2024182705A1
Application number: PCT/US2024/018082
Authority: WO
Inventors: John Hockman; Ari-Pekka LAAKSO; Don Eisenhour
Original assignee: Specialty Minerals (Michigan) Inc.
Priority date: 2023-03-02
Filing date: 2024-03-01
Publication date: 2024-09-06

Abstract

A method for making a wet slurry containing calcium bentonite filler for a linerboard making process can include mixing calcium bentonite ore with water to form an initial slurry; screening the initial slurry to remove aggregates having a particle size of greater than 250 microns; milling the initial slurry until a d50 particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns is less than 5 wt% based on the total weight of the slurry; and screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry.

Description

CALCIUM BENTONTE WET PROCESS SLURRY FOR LINERBOARD

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The benefit of priority to U.S. Provisional Patent Application No. 63/488,170 filed March 2, 2023, is hereby claimed and the disclosure is incorporated herein in its entirety.

FIELD

[0002] The disclosure relates to a method of incorporating calcium bentonite filler into linerboard using a wet slurry.

BACKGROUND

[0003] Linerboard is generally any grade of paper product suitable for making corrugated packaging materials and containers. Given its application in corrugated packaging, linerboard is designed to have high tensile, burst, and compression strength. Linerboard is generally made in an acid-based process, utilizing wood fibers as the primary component of the pulp. Unlike other grades of paper, the use of mineral fillers in acid papermaking environments, such as linerboard manufacturing processes, is limited. Additionally, the use of mineral fillers, as done in other papermaking processes, requires the removal of fiber from the furnish to maintain key properties like bulk and basis weight. While this is advantageous for reducing the amount of costly fiber needed in such processes; for linerboard making, the replacement of fiber has been viewed as detrimental to maintaining the strength properties needed for linerboard.

SUMMARY

[0004] There is a need in the linerboard manufacturing industry for effective methods of incorporation of mineral fillers in linerboard, without adversely affecting the strength properties of the linerboard. Fiber is becoming supply limited and expensive to produce compared to minerals. The linerboard market is expected to grow at 2.3% CAGR globally (2.1% in the U.S.). Methods of the disclosure can advantageously provide a method of extending fiber uses and reducing costs to meet this globally growth.

[0005] In accordance with embodiments, a method for making a wet slurry containing calcium bentonite filler for a linerboard making process can include sizing calcium bentonite ore, for example, raw or as-mined calcium bentonite ore, to an average particle size of about 2 cm to about 8 cm; mixing the sized calcium bentonite ore with water to form an initial slurry having a solids content of about 10% to about 30%; screening the initial slurry to remove aggregates having a particle size of greater than 250 microns; milling the initial slurry until a dso particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns is less than 5 wt% based on the total weight of the slurry; and screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry, wherein the final slurry has a solids content of about 10% to about 20%.

[0006] In accordance with embodiments, a method for making a wet slurry containing calcium bentonite filler for a linerboard making process can include sizing calcium bentonite ore, for example raw or as-mined calcium bentonite, to a particle size of about 2 cm to about 8 cm; mixing the sized calcium bentonite ore with water and a dispersant to form an initial slurry having a solids content of at least about 10%; screening the initial slurry to remove aggregates having a particle size of greater than 250 microns; milling the initial slurry until a dso particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns is less than 5 wt% based on the total weight of the slurry; and screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry, wherein the final slurry has a solids content of at least about 10%.

[0007] Depending on the incoming size of the mineral ore, the sizing step can be omitted. For example, if the mineral ore is as-mined, obtained, or otherwise provided into the process at with an average particle size of about 2 cm to about 8 cm, the size step can be omitted or optionally performed.

[0008] A method for making linerboard in accordance with the disclosure can include incorporating the final slurry formed by the methods of making a wet slurry of the disclosure into a furnish comprising fiber for making linerboard, wherein the furnish comprises about 2 wt% to about 20 wt% mineral based on the total weight of the furnish, and forming the linerboard from the furnish

[0009] In accordance with the disclosure, a linerboard made by the method of the disclosure or containing an additive made by the method of the disclosure is also disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a graph of Horiba particle size distribution showing the particle size distributions for a precursor (initial) slurry (dispersed and passing 60M).

[0011] Figure 2 is a graph of Horiba particle size distribution showing the particle size distribution of a final slurry prepared by a method of the disclosure.

[0012] Figure 3 is a schematic illustration of a process flow diagram of a method of the disclosure. [0013] Figure 4 is a schematic illustration of a dispersion unit in accordance with the disclosure.

[0014] Figures 5A and 5B are graphs of strength testing of a handsheet formed using a filler and methods of the disclosure.

DETAILED DESCRIPTION

[0015] Methods of the disclosure advantageously provide calcium bentonite as a slurry to allow easier dispersion into the existing furnish. To be successful, it was also determined that the calcium bentonite should be retained in the paper product in an amount greater than 75% and not wear the equipment used in forming the wet paper sheet. Further, to be an economically viable process, 20% or less, preferably 15% or less of the calcium bentonite ore used in forming the slurry should be discarded in forming the slurry. As used herein “calcium bentonite” refers to a montmorillonite in which the primary divalent cation is calcium.

[0016] The slurry of the disclosure can have a high solids content of about 10% to about 20%. The slurry can be used directly in the linerboard manufacturing process as an additive to the furnish to supply the calcium bentonite filler in amounts greater than previously used in the linerboard industry. For example, the linerboard making process can include calcium bentonite filler in an amount of about 2 wt% to about 20 wt%, based on the weight of the furnish. It has advantageously been found that the methods of the disclosure can form a slurry with high calcium bentonite solids content that can use calcium bentonite ore directly received from a mining site, regardless of moisture content and ore size. Calcium bentonite ore can be used in the processes of the disclosure as it is mined and without further refining prior to use in the process. Ore in the “as-mined” state generally has starting particles sizes of about 20 cm to about 45 cm. Ore can be sized as part of the process of the disclosure. Alternatively, if the ore is processed, mined, or otherwise obtained in a size range of about 2 cm to about 8 cm, the sizing step can be omitted. Further, the slurries produced by the methods of the disclosure can be used directly in the papermaking process and supply an effective calcium bentonite filler content to linerboard without detrimentally affecting the strength properties of the linerboard or causing harmful abrasion to the equipment or sheet during the papermaking process. For example, linerboard produced with about 12% calcium bentonite filler was found to have acceptable strength properties, which is within 15 to 20% the strength of the linerboard produced without the filler. This advantageously allows for linerboard to be produced with a reduced amount of fiber and without sacrificing the needed strength. [0017] It has been determined that linerboard mills would require about 40,000 tpy to 75,000 tpy of calcium bentonite to meet capacity needs. The methods of the disclosure can advantageously meet these needs in a cost-effective manner by allowing the calcium bentonite slurry to be produced on-site and avoid costly shipping of slurry to the production site. However, it is also contemplated herein that the slurry can be produced in facilities removed from the linerboard mill and be transported to the mill.

[0018] A method of producing a wet slurry of calcium bentonite filler for the linerboard making process can include sizing the calcium bentonite ore to reduce the calcium bentonite to an average particle size of about 2 cm to about 8 cm. After sizing, the calcium bentonite ore is admixed with water to produce a slurry. The slurry is then screened to remove large aggregates. Sizing the calcium bentonite can be omitted if the ore is provided or otherwise obtained with an average particle size of about 2 cm to about 8 cm. In such cases the as- obtained ore can be screened to remove larger aggregates before mixing with water to produce the initial slurry. Large aggregates removed by the screening can optionally be collected and resized to reduce the amount of waste ore generated in the process. For example, the larger aggregates can be milled and then introduced back into the method of the disclosure for forming the initial slurry or the larger aggregates can be milled to particle sizes of less than 45 microns and then introduced into the final slurry. For example, after milling, the particles that pass through a 45 micron screen can be introduced into the final slurry.

[0019] After screening, the slurry is milled to reduce the particle size of the calcium bentonite in the slurry to values acceptable for abrasion and wear performance in the process. The milled slurry is then screened to remove aggregates. The resulting slurry can be pumped directly into the linerboard making process to be used in the furnish as a calcium bentonite filler.

[0020] Sizing the calcium bentonite ore can include reducing the particle size to passing 8 cm. For example, the calcium bentonite ore can be sized using a shredding machine.

[0021] The initial slurry formed after sizing can have a solids content of at least about 10%. For example, the initial slurry can have a solids content of about 10% to about 70%, about 30% to about 60%, about 10% to about 30% solids content, about 15% to about 25%, or about 17% to about 20%. For example, the slurry can have a solids content of about 20%. The slurry can be formed by mixing the sized calcium bentonite with water under conditions sufficient to form the slurry.

[0022] The slurry can be made with or without the need for added dispersant while maintaining a suitable viscosity. For example, it has been observed that a slurry having a solids content of up to 30% can be achieved without a dispersant while maintaining a Brookfield 100 rpm viscosity of less than 660 cps.

[0023] Optionally, the initial slurry can be formed using a dispersant. For example, for high solids contents above 30% and up to about 70% solids content, use of a dispersant can facilitate formation of the slurry. For example, the dispersant can be or can include phosphate salts. For example, the dispersant can be or can include sodium silicates. For example, the dispersant can include or be a sodium silicate in which the N₂O:SiO2 ratio is from 1 :1 to 1 :3.3. Examples of dispersants include, but are not limited to, sodium hexametaphospate, sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP), sodium polyacrylate, sodium silicates, and combinations thereof. The dispersant can be included in an amount of about 0.1 to about 5.0 percent, based on the total dry component weight of the slurry.

[0024] For example, the sized calcium bentonite, water and optional dispersant can be mixed for about 5 min to about 1 hour, about 10 min to about 20 min, about 15 min to about 30 min, or about 20 min to about 45 min. Other suitable mixing times include about 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60 min, or any values therebetween or ranges defined by any of these values.

[0025] The slurry can be formed by mixing at a speed of about 1000 fpm to about 5000 fpm, about 3000 fpm to about 4000 fpm, or about 3500 fpm to about 4500 fpm. For example, the mixing speed can be about 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, or 5000 fpm or any values there between or any ranges defined by these values. The slurry can be formed in a dispersion system as disclosed herein. It has been advantageously found that the dispersion system in accordance with the disclosure can impart high shear to form the slurry while minimizing viscosity and blade wear.

[0026] For example, the slurry can be formed using about 50 kilowatts/short ton (kw/ston) to about 150 kw/ston mixing energy. Other suitable mixing energies include about 80 kw/ston to about 120 kw/ston, about 100 kw/ston to 150 kw/ston, about 50 kw/ston toa bout 75 kw/ston or about 60 kw/ston to 110. For example, the slurry can be formed with a mixing power of about 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 kw/ston or any values there between or any ranges defined by these values. Mixing can impart sufficient energy into the slurry to break down the mineral in the slurry to substantially minus 60 mesh (60M), which is a slurry having particle sizes of substantially 250 microns or less. [0027] Screening the slurry to remove larger aggregates can be done to remove particles having a Horiba Particle size greater than 250 microns. For examples, the sizing can remove particles having a Horiba particle sizes of greater than 250 microns and up to about 595 microns. For example, the screening can be used to remove +30M to +60M size aggregates. Unless specified otherwise, particle sizes herein will be made with reference to Horiba particle sizes. The larger aggregates removed by the screening can be milled and reintroduced into the processes to reduce an amount of waste mineral generated by the processes. For example, the larger aggregates can be milled and then introduced back into the method of the disclosure for forming the initial slurry or the larger aggregates can be milled to particle sizes of less than 45 microns and then introduced into the final slurry.

Particles screened from the re-milled larger aggregates can be introduced at the initial stage of the method, for example, for forming the initial slurry.

[0028] After screening, the slurry is milled to reduce the dso particle size of the calcium bentonite to 10 microns or less. The milling can also be performed to reduce the amount of particles having a Horiba particles size of greater than 45 microns from 1 wt% to about 10 wt%. The slurry can be media milled for example. Milling can be performed, for example, with an energy input of about 20 kw/ston to about 80 kw/ton, about 30 kw/ton to about 70 kw/ton, about 40 kw/ton to about 60 kw/ton, or about 20 kw/ton to about 50 kw/ton. Other suitable milling energy input can be about 20, 30, 40, 50, 60, 70, or 80 kw/ston, or any values there between or any ranges defined by these values.

[0029] It was observed that particles in a calcium bentonite ore having particle sizes greater than 45 microns can be abrasive in downstream processing. Accordingly, reducing or removing particles in this size range and reducing the concentration of particles of this size in the slurry can aid in reducing or preventing abrasive wear both during processing of the slurry and caused by the filler during linerboard making.

[0030] After milling, the slurry can then be screened again to remove aggregates. For example, particles having a Horiba particle size greater than 44 microns can be removed. For example, aggregates, which have Horiba particle sizes of greater than 44 microns and up to 53 microns can be removed. For example, aggregates or grit that is plus 325M to plus 280M can be removed. For example, the dispersion can be performed such that the final slurry screening has less than 1% to 20% of the aggregates to be removed. For example, the final slurry can have less than 10% of the aggregates removed during final screening. The larger aggregates removed by the screening can be milled and reintroduced into the processes to reduce an amount of waste mineral generated by the processes. For example, the larger aggregates can be milled and then introduced back into the method of the disclosure for forming the initial slurry. For example, the larger aggregates can be milled to sub-44 micron size particles, screened, and introduced into the final slurry.

[0031] Methods of the disclosure can also include processing the calcium bentonite ore to remove high abrasive minerals, such as quartz. For example, calcium bentonite ore is about 70% montmorillonite clay by Xray diffraction. The other mineral species present can include quartz and mica. Removal of the abrasive minerals mixed with the ore can minimize abrasion and wear by the slurry on the ceramic and polymer cloths used in the linerboard process.

[0032] It has been observed that reduction and/or complete elimination of the abrasive minerals, as well as limiting the mineral filler particle size to a dso of less than 10 microns results in a mineral slurry that is suitable for use in the linerboard process and avoids degradation or destruction of ceramic and polymer cloths used in the linerboard process. Referring to Figure 1 , precursor calcium bentonite as well as the starting ore was found to have a significant percentage of particles with a size of 45 microns, which drives up the dso and dg₀. Figure 2 illustrates the calcium bentonite after processing with the method of the disclosure to reduce the dso and dg₀ particle size. A correlation between the higher particle sizes in the unprocessed system to abrasion and wear was observed during abrasion and wear testing of these two mineral compositions.

[0033] The final slurry formed by the method of the disclosure can have a Brookfield 100 spd viscosity of about 50 cps to about 600 cps, about 200 cps to about 600 cps, or about 50 cps to about 150 cps and any values therebetween and ranges defined by such values. Such viscosities can advantageously allow the slurry to be pumped into the linerboard making process. For example, a slurry production facility can be provided on site of the linerboard manufacturing facility such that calcium bentonite ore, for example, as-mined, can be brought to the facility to be produced onsite into the slurry of calcium bentonite filler and directly pumped into the linerboard making process. It is also contemplated herein that the slurry is made off-site of the linerboard making process and transported to the linerboard manufacturing facility.

[0034] A facility for the production of a wet slurry of calcium bentonite filler for use in linerboard production can include a calcium bentonite ore receiving sizing unit for sizing the calcium bentonite ore to an ore size of about 2 cm to about 8 cm. The facility further includes a dispersion unit for mixing the sized calcium bentonite ore and water to form an initial slurry having a solids content of about 10% to about 30%. The facility also includes a first screening unit for screening the initial slurry to remove aggregates having a particle size greater than 250 micron. A milling unit is included for milling the initial slurry until a dso particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns is less than 5 wt% based on the total weight of the slurry. The facility also includes a second screening unit for screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry. Figure 3 shows one possible configuration for the production facility.

[0035] The facility can be present at a linerboard mill such that the slurry can be directly pumped or otherwise transported to the linerboard manufacturing unit for incorporation into the furnish. For example, the wet slurry facility can include a wet slurry storage unit that is in fluid communication with the unit for processing the linerboard furnish to directly pump the calcium bentonite slurry into the furnish to supply the needed calcium bentonite filler.

[0036] Alternatively, the facility for producing the wet slurry can be separated from the linerboard manufacturing unit and storage units containing wet slurry can be transported to the linerboard mill for use as the calcium bentonite filler.

[0037] The calcium bentonite ore can contain auxiliary minerals, such as mica, quartz, opal, and feldspar. It has been found that the wet slurry process of the disclosure can advantageously reduce the presence of auxiliary minerals significantly more than through a dry process. For example, quartz can be included as an auxiliary mineral in the ore and can be removed in a screening step to remove grit. Remaining auxiliary minerals can be removed/reduced through the milling and screening steps of the process. The final slurry can include a reduced amount of auxiliary minerals as compared to the calcium bentonite ore such that the mineral present in the final slurry is greater than 80% calcium bentonite.

[0038] Dispersion systems in accordance with the disclosure can advantageously allow for formation of the calcium bentonite slurries of the disclosure with high shear while minimizing viscosity and blade wear. The dispersion system includes a dispersion tank having a ratio of the tank height to diameter of about 1 .0 to about 2.5. For example, the ratio of tank height to diameter can be about 1 .5. Such a ratios were advantageously found to allow for a high number of contacts of the slurry components with the blade. The dispersion system further includes a blade arranged inside the tank. The blade is sized such that the ratio of the dispersion tank diameter to the blade diameter is about 1 .75 to 2.5. It was observed that this sizing allowed for a high number of blade impacts. Figure 4 shows one possible design for a successful disperser using the invention.

[0039] The blade can be made of a highly wear resistant material, such as urethane or tungsten carbide coated metals.

[0040] Dispersion systems of the disclosure are capable of maintaining tip speeds of about 2,000 to 5,000 fpm for mixing times of up to 1 hour, for example, 10 min to 20 min. EXAMPLE

[0041] Calcium bentonite slurries for use as mineral fillers in a linerboard process were made by the method of the disclosure for different loads of as-mined calcium bentonite ore. The resulting wet slurry properties are shown in Table 1 . For each of these samples, the ore was processed by sizing the ore to minus 3 inches with a shredding machine, combining the sized ore with enough water to produce a 20% solids slurry using the dispersion system of the disclosure. The slurry was mixed for 10 min at 4000 fpm. The slurry was then screened to remove +60M aggregates. The resulting slurry was media milled until the 45 micron particle size peak of the particle size distribution was less than 5 wt% and the dso particle size was below 10 micros. A final screen was performed to remove +325M aggregates.

Table 1 shows the reduction in particle size with each unit operation culminating in a successful final product.

[0042] Handsheets using the slurry of the disclosure were formed and showed acceptable strength losses at 10% ash target with similar losses to the standard clay product produced through traditional means. The handsheets were produced in an 8” Box and Noble former targeting a standard linerboard formulation with 2#/ton Alum and 4#/ton retention aid. The retention of the calcium bentonite product was above 75% and among the best of the clays. Figure 5 shows the current invention performs equal in handsheets for key strength properties when compared to the more expensive other clay products.

[0043] Calcium bentonite was observed to have good retention properties at particle sizes of 8-10 microns dso due to its high surface area. Without intending to be bound by theory, it is believed that calcium bentonite in this particle size range has a specific surface area of about 60 m²/g, which allows it to interact well with polymer retention aids in the furnish. [0044] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the disclosure may be apparent to those having ordinary skill in the art.

[0045] All patents, patent applications, government publications, government regulations, and literature references cited in this specification are hereby incorporated herein by reference in their entirety. In the case of conflict, the present description, including definitions, will control.

[0046] Throughout the specification, where the compounds, compositions, methods, and/or processes are described as including components, steps, or materials, it is contemplated that the compounds, compositions, methods, and/or processes can also comprise, consist essentially of, or consist of any combination of the recited components or materials, unless described otherwise. Component concentrations can be expressed in terms of weight concentrations, unless specifically indicated otherwise. Combinations of components are contemplated to include homogeneous and/or heterogeneous mixtures, as would be understood by a person of ordinary skill in the art in view of the foregoing disclosure.

References

U.S. 4,797,158

U.S. 11 ,447,395

U.S. 5,055,161

U.S. 8,512,850

EP 0017353

DE3306478A

Claims

What is claimed is:

1 . A method for making a wet slurry containing calcium bentonite filler for a linerboard making process, comprising: mixing calcium bentonite ore with water to form an initial slurry having a solids content of about 10% to about 30%, wherein the calcium bentonite ore has an average particle size of about 2 cm to about 8 cm; screening the initial slurry to remove aggregates having a particle size of greater than 250 microns; milling the initial slurry until a dso particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns or greater is less than 5 wt% based on the total weight of the slurry; and screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry, wherein the final slurry has a solids content of about 10% to about 20%.

2. The method of claim 1 , wherein the initial slurry is free of dispersant.

3. The method of claim 1 or 2, wherein the final slurry is free of dispersant.

4. A method for making a wet slurry containing calcium bentonite filler for a linerboard making process, comprising: mixing calcium bentonite ore with water and a dispersant to form an initial slurry having a solids content of at least about 10%, wherein the calcium bentonite ore has an average particle size of about 2 cm to about 8 cm; screening the initial slurry to remove aggregates having a particle size of greater than 250 microns; milling the initial slurry until a dso particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns or greater is less than 5 wt% based on the total weight of the slurry; and screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry, wherein the final slurry has a solids content of at least about 10%

5. The method of claim 4, wherein the dispersant comprises a phosphate salt.

6. The method of claim 4, wherein the dispersant is one or more of sodium hexametaphospate, sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP), sodium polyacrylate, and sodium silicate.

7. The method of claim 4, wherein the dispersant comprises a sodium silicate where a ratio of N₂O:SiO2 is about 1 :1 to 1 :3.3.

8. The method of claim 4 or 5, wherein the dispersant is present in the initial slurry in an amount of about 0.1 to about 5.0 percent based on the total dry component weight of the initial slurry.

9. The method of any one of the preceding claims, wherein the initial slurry is milled by media milling.

10. The method of any one of the preceding claims, wherein 20% or less of the calcium bentonite ore is discarded in producing the final slurry.

11 . The method of claim 10, wherein 15% or less of the calcium bentonite ore is discarded in producing the final slurry.

12. The method of any one of the preceding claims, further comprising screening the calcium bentonite ore to at least partially remove grit, wherein the grit comprises quartz.

13. The method of any one of the preceding claims, wherein the calcium bentonite ore comprises one or more auxiliary minerals and the final slurry comprises a reduced amount of auxiliary minerals as compared to the calcium bentonite ore such a mineral content present in the final slurry is greater than 80% calcium bentonite.

14. The method of claim 13, wherein the auxiliary minerals comprise one or more of mica, quartz, opal, and feldspar.

15. The method of any one of the preceding claims, wherein mixing is performed for about 5 min to about 1 hour.

16. The method of any one of the preceding claims, wherein mixing is performed in a dispersion unit with a tip speed of about 1000 fpm to about 5000 fpm.

17. The method of any one of the preceding claims, wherein mixing is performed with a mixing energy input of about 50 kw/ston to about 150 kw/ston.

18. The method of any one of the preceding claims, wherein a Brookfield viscosity at 100spd of the initial slurry is about 100 cps to about 800 cps.

19. The method of any one of the preceding claims, wherein a Brookfield viscosity at 10Ospd of the final slurry is about 50 cps to about 600 cps.

20. The method of any one of the preceding claims, further comprising sizing the calcium bentonite ore to an average particle size of about 2 cm to 8 cm before mixing with water to form the initial slurry.

21 . The method of any one of the preceding claims, wherein the calcium bentonite is as-mined.

22. The method of any one of the preceding claims, further comprising collecting the aggregates having a particle size of greater than 250 microns removed during screening of the initial slurry, milling the aggregates, and recycling the aggregates into the mixing step for forming the initial slurry.

23. The method of any one of the preceding claims, further comprising collecting the particles having a particle size greater than 44 microns removed from the milled slurry, milling the particles having a particle size greater than 44 microns to a particle size less than 44 microns, and mixing with the final slurry.

24. The method of any one of the preceding claims, wherein milling is performed with an energy input of about 20 kw/ston to about 80 kw/ston.

25. A method for making linerboard comprising incorporating the final slurry made by the method of any one of the preceding claims into a furnish comprising fiber for making linerboard, wherein the furnish comprises about 2 wt% to about 20 wt% calcium bentonite based on the total weight of the furnish, and forming the linerboard from the furnish.

26. A linerboard made by the method of claim 25.

27. A facility for the production of a wet slurry of calcium bentonite filler for use in linerboard production, comprising: a calcium bentonite ore receiving sizing unit for sizing the calcium bentonite ore to a particle size of about 2 cm to about 8 cm; a dispersion unit for mixing the sized calcium bentonite ore and water to form an initial slurry having a solids content of at least about 10%; a first screening unit for screening the initial slurry to remove aggregates having a particle size greater than 250 microns; a milling unit for milling the initial slurry until a dso particle size of the slurry is 10 microns or less and a weight percent of particles having a particle size of 45 microns is less than 5 wt% based on the total weight of the slurry; and a second screening unit for screening the milled slurry to remove particles having a particle size greater than 44 microns to thereby produce a final slurry.

28. The facility of claim 27, further comprising a final slurry storage unit in fluid communication with a linerboard manufacturing unit.

29. The facility of claim 27 or 28, wherein the initial slurry has a solids content of about 10% to about 30%.

30. The facility of claim 27 or 28, wherein the initial slurry further comprises a dispersant and has a solids content of up to 70%.

31 . A dispersion system for forming a wet slurry of calcium bentonite filler for linerboard, comprising: a dispersion tank and a blade disposed in the dispersion tank, wherein the dispersion tank has a tank height and a tank diameter and a ratio of the tank height to the tank diameter is about 1 .0 to about 2.5, and the blade has a blade diameter and a ratio of the tank diameter to the blade diameter is about 1.75 to 2.5.

32. The dispersion system of claim 31 , wherein the blade is formed of a high shear material.

33. The dispersion system of claim 32, wherein the blade is formed of urethane or tungsten carbide coated metal.