AU2022203563A1 - Methods for separating and dewatering fine particles - Google Patents

Abstract

A process for cleaning and dewatering hydrophobic particulate materials is presented. The process is performed in in two steps: 1) agglomeration of the hydrophobic particles in a first hydrophobic liquid/aqueous mixture; followed by 2) dispersion of the agglomerates in a second hydrophobic liquid to release the water trapped within the agglomerates along with the entrained hydrophilic particles. 18751764 1 (GHMatters) P98786.AU.3

Description

METHODS FOR SEPARATING AND DEWATERING FINE PARTICLES

This application is a divisional application of Australian Application No. 2020201982 the

original disclosure of which is incorporated herein by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

[001] This application is a continuation in part of U.S. Provisional Application No. 13/576,067,

filed January 17, 2013, which is a U.S. National Phase Application of PCT/US2011/023161,

filed January 31, 2011, which claims the priority of U.S. Provisional Application No.

61/300,270, filed February 1, 2010; and U.S. Provisional Application No. 61/658,153, filed June

11, 2012; which are incorporated herein by reference.

FIELD OF THE INVENTION

[002] The instant invention pertains to methods of cleaning fine particles, particularly

hydrophobic particles such as coal, of its impurities in aqueous media and removing process

water from products to the levels that can usually be achieved by thermal drying.

BACKGROUND OF THE INVENTION

[003] Coal is an organic material that is burned to produce heat for power generation and for

industrial and domestic applications. It has inclusions of mineral matter and may contain

undesirable elements such as sulfur and mercury. Coal combustion produces large amounts of

ash and fugitive dusts that need to be handled properly. Therefore, run-of-the mine coal is

cleaned of the mineral matter before utilization, which also helps increase combustion

efficiencies and thereby reduces C02 emissions. In general, coarse coal (50 x 0.15 mm) can be

1 12183923_1 (GHMatters) P98786.AU.2 cleaned efficiently by exploiting the specific gravity differences between the coal and mineral matter, while fine coal (approximately 0.15 mm and smaller) is cleaned by froth flotation.

[004] In flotation, air bubbles are dispersed in water in which fine coal and mineral matter are

suspended. Hydrophobic coal particles are selectively collected by a rising stream of air bubbles

and form a froth phase on the surface of the aqueous phase, leaving the hydrophilic mineral

matter behind. Higher-rank coal particles are usually hydrophobic and, therefore, can be attracted

to air bubbles that are also hydrophobic via a mechanism known as hydrophobic interaction. The

hydrophobic coal particles reporting to the froth phase and subsequently to final product stream

are substantially free of mineral matter but contain a large amount of process water. Wet coal is

difficult to handle and incurs high shipping costs and lower combustion efficiencies. Therefore,

the clean coal product is dewatered using various devices such as cyclones, thickeners, filters,

centrifuges, and/or thermal dryers.

[005] Flotation becomes inefficient with finer particles. On the other hand, low-grade ores often

require fine grinding for sufficient liberation. In mineral flotation, its efficacy deteriorates rapidly

below approximately 10 to 15 m, while coal flotation becomes difficult below approximately

44 m. Furthermore, it is difficult to dewater flotation products due to the large surface area and

the high-capillary pressure of the water trapped in between fine particles. Flotation also becomes

inefficient when particle size is larger than approximately 150 m for minerals and 500 m for

coal.

[006] Many investigators explored alternative methods of separating mineral matter from fine

coal, of which selective agglomeration received much attention. In this process, which is also

referred to as oil agglomeration or spherical agglomeration, oil is added to an aqueous

2 12183923_1 (GHMatters) P98786.AU.2 suspension while being agitated. Under conditions of high-shear agitation, the oil breaks up into small droplets, collide with particles, adsorb selectively on coal by hydrophobic interaction, form pendular bridges with neighboring coal particles, and form agglomerates. The high-shear agitation is essential for the formation of agglomerates, which is also known as phase inversion.

Nicol et al. (U.S. Patent No. 4,209,301) disclose that adding oil in the form of unstable oil-in

water emulsions can produce agglomerates without intense agitation. The agglomerates formed

by these processes are usually large enough to be separated from the mineral matter dispersed in

water by simple screening. One can increase the agglomerate size by subjecting the slurry to a

low- shear agitation after a high-shear agitation.

[007] In general, selective agglomeration gives lower-moisture products and higher coal

recoveries than froth flotation. On the other hand, it suffers from high dosages of oil.

[008] The amounts of oil used in the selective agglomeration process are typically in the range of

to 30% by weight of feed coal (S,C. Tsai, in Fundamentals of Coal Beneficiation and

Utilization, Elsevier, 2982, p. 335). At low dosages, agglomerates have void spaces in between

the particles constituting agglomerates that are filled-up with water, in which fine mineral matter,

e.g., clay, is dispersed, which in turn makes it difficult to obtain low moisture- and low-ash

products. Attempts were made to overcome this problem by using sufficiently large amounts of

oil so that the void spaces are filled-up with oil and thereby minimize the entrapment of fine

mineral matter. Capes et al. (Powder Technology, vol. 40, 1 84, pp. 43-52) disclose that the

moisture contents are in excess of 50% by weight when the amount of oil used is less than 5%.

By increasing the oil dosage to 35%, the moisture contents are substantially reduced to the range

of 17-18%.

3 12183923_1 (GHMatters) P98786.AU.2

[009] Keller et al. (Colloids and Surfaces, vol. 22, 1987, pp. 37-50) increase the dosages of oil to

5 - 5 6 % by volume to fill up the void spaces more completely, which practically eliminated the

entrapment problem and produced super-clean coal containing less than 1-2% ash. However, the

moisture contents remained high. Keller (Canadian Patent No. 1,198,704) obtains 40% moisture

products using fluorinated hydrocarbons as agglomerants. Depending on the types of coal tested,

approximately 7- 3 0 % of the moisture was due to the water adhering onto the surface of coal,

while the rest was due to the massive water globules trapped in the agglomerates (Keller et al.,

Coal Preparation, vol. 8, 1990, pp.1-17).

[0010] Smith et al (U.S. Patent No. 4,244,699) and Keller (U.S. Patent No. 4,248,698; Canadian

Patent No. 1,198,704) use fluorinated hydrocarbon oils with low boiling points (40-159°F) so

that the spent agglomerants can be readily recovered and be recycled, These reagents are known

to have undesirable effect on the atmospheric ozone layer. Therefore, Keller (U.S. Patent No.

4,484,928) and Keller et al. (U.S. Patent No, 4,770,766) disclose methods of using short chain

hydrocarbons, e,g., 2-methyl butane, pentane, and heptane as agglomerants. Like the fluorinated

hydrocarbons, these reagents have relatively low boiling points, which allowed them to be

recovered and recycled.

[0011] Being able to recycle an agglomerant would be a significant step toward eliminating the

barrier to commercialization of the selective agglomeration process. Another way to achieve this

goal would be to substantially reduce the amount of the oils used. Capes (in Challenges in

Mineral Processing, ed. by K.V.S. Sastry and M.C. Fuerstenau, Society of Mining Engineers,

Inc., 1989, pp. 237-251) developed the low-oil agglomeration process, in which the smaller

agglomerates (<1 mm) formed at low dosages of oil (0.5-5%) are separated from mineral matter

by flotation rather than by screening. Similarly, Wheelock et al., (U.S. Patent No. 6,632,258) 4 12183923_1 (GHMatters) P98786.AU.2 developed a method of selectively agglomerating fine coal using microscopic gas bubbles to limit the oil consumption to 0.3-3% by weight of coal.

[0012] Chang et al. (U.S. Patent No. 4,613,429) disclose a method of cleaning fine coal of

mineral matter by selective transport of particles across the water/liquid carbon dioxide interface.

The liquid C02 can be recovered and recycled. A report shows that the clean coal products

obtained using this liquid carbon dioxide (LICADO) process contained 5-15% moisture after

filtration (Cooper et al., Proceedings of the 25th Intersociety Energy Conversion Engineering

Conference, 1990, August 12-17, 1990, pp. 137-142).

[0013] Yoon et al. (U.S. Patent No. 5,459,786) disclose a method of dewatering fine coal using

recyclable non-polar liquids. The dewatering is achieved by allowing the liquids to displace

surface moisture. Yoon et al. report that the process of dewatering by displacement (DBD) is

capable of achieving the same or better level of moisture reduction than thermal drying at

substantially lower energy costs, but do not show the removal of mineral matter from coal.

[0014] As noted above, Keller (Canadian Patent No. 1,198,704) attributed the high moisture

contents of the clean coal products obtained from his selective agglomeration process to the

presence of massive water globules. Therefore, there remains a need for a process that can be

used to clean hydrophobic particles, especially coal, of hydrophilic impurities with low water

content.

SUMMARY OF THE INVENTION

[0015] The instant invention may provide methods for cleaning hydrophobic particulate

materials of hydrophilic contaminants. The instant invention may provide a clean hydrophobic

5 12183923_1 (GHMatters) P98786.AU.2 fine particulate material that contains moisture levels that is substantially lower than can be achieved by conventional dewatering methods. In this invention, the particulate materials include, but are not limited to, minerals and coal particles smaller than about 1 mm in diameter, preferably smaller than about 0.5 mm, more preferably smaller than about 0.15 mm. Significant benefits of the present invention can be best realized with the ultrafine particles that are difficult to be separated by flotation.

[0015A] In the instant invention, there is provided a process of upgrading low-rank coal particles

comprising the steps of:

a. adding water to the low-rank coal particles to form an aqueous slurry;

b. hydrophobizing the low-rank coal particles;

c. adding a first hydrophobic liquid to the slurry;

d. agitating the slurry to form agglomerates of hydrophobized low-rank coal particles;

e. separating the agglomerates of hydrophobized coal particles from the aqueous slurry;

and

f. dispersing the agglomerates in a second hydrophobic liquid to liberate the water

molecules entrapped within the agglomerate structure along with the hydrophilic mineral matter

dispersed in the water, thereby removing water and mineral matter from the low-rank coal and

increasing its heating value.

[0015B] Also disclosed herein is a process of upgrading a low-rank coal comprising the steps of

a. heating said low-rank coal in a hydrothermal reactor in the presence of C0 2 ;

b. displacing the water released during the hydrothermal process with liquid C0 2 ; and

c. transporting the dewatered coal under a C02 atmosphere, thereby minimizing the

possibility of spontaneous combustion.

6 12183923_1 (GHMatters) P98786.AU.2

[0016] In the instant invention, a hydrophobic liquid is added to an aqueous medium, in which a

mixture (or slurry) of hydrophobic and hydrophilic particles are suspended. The hydrophobic

liquid is added under conditions of high-shear agitation to produce small droplets. As used

herein, "high shear", or the like, means a shear rate that is sufficient to form large and visible

agglomerates, which is referred to phase inversion. As noted above, under conditions of high

shear agitation, oil breaks up into small droplets, which collide with the fine particles, and

selectively form pendular bridges with neighboring hydrophobic particles, and thereby produce

agglomerates of hydrophobic particles. The intensity of agitation required to form the

agglomerates should vary depending on particle size, particle hydrophobicity, particle shape,

particle specific gravity (S.G.), the type and amounts of hydrophobic liquid used, etc. Ordinarily,

agglomerate formation typically occurs at impeller tip speeds above about 35 ft/s, preferably

above about 45 ft/s, more preferably above about 60 ft/s. In certain embodiments, the aqueous

slurry is subjected to a low-shear agitation after the high-shear agitation to allow for the

agglomerates to grow in size, which will help separate the agglomerates from the hydrophilic

particles dispersed in the aqueous phase.

[0017] The agglomerated hydrophobic particles are separated from the dispersed hydrophilic

particles using a simple size-size separation method such as screening. At this stage, the

agglomerates are substantially free of the hydrophilic particles, but still contain considerable

amount of the process water entrapped in the interstitial spaces created between the hydrophobic

particles constituting the agglomerates. The entrapped water also contains dispersed hydrophilic

particles dispersed in it.

[0018] To remove the entrained water, a second hydrophobic liquid is added to the agglomerates

to disperse the hydrophobic particles in the liquid. The dispersion liberates the entrapped process 7 12183923_1 (GHMatters) P98786.AU.2 water and the hydrophilic particles dispersed in it from the agglomerates. The hydrophobic particles dispersed in the second hydrophobic liquid are then separated from the hydrophobic liquid. The hydrophobic particles obtained from this final step are practically free of surface water and entrained hydrophilic particles. Typically, the amount of hydrophilic particles associated with the clean hydrophobic particles are less than 10 % by weight, preferably less than about 7 %, more preferably less than about 3 %; and less than about 10 % water, preferably less than about 7 % water, more preferably less than about 5 % water. Importantly, the present invention is able to remove over 90 % of hydrophilic particles from the hydrophobic particles, preferably 95 %,more preferably 98%; and 95 % of water from the hydrophobic particles, preferably 95 ,more preferably 99 %.

[0019] The invention may separate hydrophobic particles from hydrophilic particles and

simultaneously remove the water from the product using a hydrophobic liquid. The hydrophobic

hydrophilic separation (HHS) process described above can also be used to separate of one type

of hydrophilic particles from another by hydrophobizing a selected component using an

appropriate method. The invention, for example, may be practiced with different types of coal

including without limitation bituminous coal, anthracite, and subbituminous coal.

[0020] This invention may further reduce the moisture of clean coal product to the extent that

they can be dried without using excessive heat, and thus energy.

[0021] The invention may recover the spent hydrophobic liquid for recycling purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

8 12183923_1 (GHMatters) P98786.AU.2

[0022] Figure 1 is a graph showing the contact angles of n-alkanes on a hydrophobic coal

immersed in water (Yoon et al., PCT Application No. 61/300,270, 2011) that are substantially

larger than those (~65°) of water droplets on most hydrophobic coal (Gutierrez-Rodriguez, et al.,

Colloids and Surfaces, 12, p.1, 1984).

[0023] Figure 2 is a schematic of one embodiment of the process as disclosed in the present

invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention provides methods of separating a mixture of hydrophobic fine

particulate materials suspended in water. The present invention may also provide a method to

dewater at least one of the products to a level that is substantially lower than can be achieved by

conventional dewatering methods. In this invention, the fine particulate materials include but not

limited to minerals and coal particles, smaller than about 1 mm in diameter, preferably smaller

than about mm, more preferably smaller than about 0.5 mm more preferably less than about 0.15

mm. The hydrophobic particulate materials amenable to the present invention include, but are

not limited to, coal, base-metal sulfides, precious metallic minerals, platinum group metals, rare

earth minerals, non-metallic minerals, phosphate minerals, and clays.

[0025] The present invention provides a method of separating hydrophobic and hydrophilic

particles from each other in two steps: 1) agglomeration of the hydrophobic particles in a first

hydrophobic liquid/aqueous mixture; followed by 2) dispersion of the agglomerates in a second

hydrophobic liquid to release the water trapped within the agglomerates along with the entrained

hydrophilic particles. The second hydrophobic liquid can be the same as the first hydrophobic

liquid in many cases. Essentially, the agglomeration step removes the bulk of hydrophilic 9 12183923_1 (GHMatters) P98786.AU.2 particles and the water from the fine hydrophobic particles by selectively agglomerating the latter; and the dispersion step removes the residual process water entrapped within the structure of the agglomerates.

[0026] In the agglomeration step, a hydrophobic liquid is added to an aqueous medium, in which

a mixture (or slurry) of fine hydrophobic (usually the product of interest) and hydrophilic (the

contaminants) particles are suspended. The hydrophobic liquid is added under conditions of

high-shear agitation to produce small droplets. The agitation must be sufficient to induce

agglomeration of the hydrophobic particles. In general, the probability of collision between oil

droplets and fine particles increases with decreasing droplet size. Further, the high-shear

agitation helps prevent and/or minimize the formation of oil-in-water emulsions stabilized by

hydrophobic particles. The hydrophobic liquid is chosen such that its contact angle (0) on the

surface, as measured through aqueous phase, is larger than 90. Use of such a liquid allows it to

spontaneously displace the moisture from the surface. High shear agitation produces small oil

droplets that are more efficient than larger droplets for collecting the hydrophobic fine particles

and forming agglomerations of those particles. The hydrophilic particles (usually undesired

material) remain in the aqueous phase.

[0027] When oil and water are mixed in the presence of spherical particles, water-in-oil

emulsions are formed when 0 > 90°, and oil-in-water emulsions are formed when 0 < 900 (Binks,

B.P., Current Opinion in Colloid and Interface Science, 7, p.21, 2002). The former is likely the

case when using the hydrophobic liquids that give contact angles greater than 900. In the instant

invention, this problem is eliminated and/or minimized by adding a hydrophobic liquid to

aqueous slurry under conditions of high-shear agitation.

10 12183923_1 (GHMatters) P98786.AU.2

[0028] While high-shear agitation can minimize the formation of water-in-oil emulsions, it may

not prevent the residual process water from being entrapped in the interstitial spaces created in

between the particles constituting agglomerates. In the dispersion step, the entrapped water can

be removed by breaking the agglomerates and dispersing the hydrophobic particles in a

hydrophobic liquid. The hydrophobic particles readily disperse in a hydrophobic liquid due to the

strong attraction between hydrophobic particles and hydrophobic liquid. On the other hand,

water has no affinities toward either the hydrophobic particles or the hydrophobic liquid;

therefore, it is released (or liberated) from the agglomerates and are separated from the

hydrophobic particles. During the dispersion step, the hydrophilic particles in the entrained water

are also removed, providing an additional mechanism of separating hydrophobic and hydrophilic

particles from each other.

[0029] The bulk of the hydrophobic liquid used in the instant invention is recovered for recycle

purpose without involving phase changes by using appropriate solid-liquid separation means

such as settling, filtration, and centrifugation. Only the small amount of the residual hydrophobic

liquid adhering onto the surface of hydrophobic particles can be recovered by vaporization and

condensation. Thermodynamically, the energy required to vaporize and condense the recyclable

hydrophobic liquids disclosed in the instant invention is only a fraction of what is required to

vaporize water from the surface of hydrophobic particulate materials.

[0030] In floatation, for a bubble to collect a hydrophobic particle on its surface, the thin liquid

film (TLF) of water (or wetting film) formed in between must thins and ruptures rapidly during

the short time frame when the bubble and particle are in contact with each other. In a dynamic

flotation cell, the contact times are very short typically in the range of tens of milliseconds or

less. If the film thinning kinetics is slow, the bubble and particle will be separated from each 11 12183923_1 (GHMatters) P98786.AU.2 other before the film ruptures. It has been shown that the kinetics of film thinning increases with increasing particle hydrophobicity (Pan et al., Faraday Discussion, 146, p.325, 2010). Therefore, various hydrophobizing agents, called collectors, are used to increase the particle hydrophobicity and facilitate the film thinning process.

[0031] At the end of a film thinning process, the film must rupture to form a three-phase. A

wetting film can rupture when the following thermodynamic condition is met,

where ys is the surface free energy of a solid (or particle) in contact with air, whileysw and Tw

are the same at the solid/water and water/air interfaces, respectively. The term on the left, i.e.,

ys - ysw, is referred to as wetting tension. Eq. [1] suggests that a particle can penetrate the TLF

and from a three-phase contact if the film tension is less than the surface tension of water. The

free energy gained during the film rupture process (AG) is given by ys - ysw - yw; therefore, the

lower the wetting tension, the easier it is to break the film.

[0032] It follows also that for a wetting tension to be small, it is necessary thatysw be large.

According to the acid-base interaction theory (van Oss, C.J., Interfacial Forces in Aqueous

Media, CRC Taylor and Francis, 2"dEd., p. 1 60), the solid/water interfacial tension can be

calculated by the following relation,

YY" =Y + ". -[2]

where yf is the Lifshitz-van der Waals component of ys and yL is the same of yw; ys+ and ys

are the acidic and basic components of ys, respectively; and y' and y-, are the same for water.

12 12183923_1 (GHMatters) P98786.AU.2

Essentially, the acidic and basic components represent the propensity for hydrogen bonding.

According to Eq. [2], it is necessary to keep y,+ and y,- small to increase ysw, which can be

accomplished by rendering the surface more hydrophobic. When a surface becomes more

hydrophobic, ys decreases also, which helps decrease the wetting tension and hence improve

flotation.

[0033] In the present invention, a hydrophobic liquid (oil), rather than air, is used to collect

hydrophobic particles. In this case, oil-particle attachment can occur under the following

condition,

r"1- Z-ov 131

where yso represents the interfacial tension between solid and oil. According to the acid-base

theory,

where the subscript 0 represents hydrophobic liquid phase. The hydrophobic liquids that can be

used in the instant invention include, but are not limited to, n-alkanes (such as petane, hexane,

and heptanes), n-alkenes, unbranched and branched cycloalkanes and cycloalkenes with carbon

numbers of less than eight, ligroin, naphtha, petroleum naptha, petroleum ether, liquid carbon

dioxide, and mixtures thereof. The acidic and basic components of these hydrophobic liquids,

i.e., y- and y', are zero as they cannot form hydrogen bonds with water, which makes the last

two terms of Eq. [4] to drop out. Since 7o is nonzero, one may be concerned thatyso > ys.

However, the value of the third term of Eq. [4], i.e., 2 ySLWyLW, is substantial. For n-pentane

interacting with Teflon, for example, 7o = 16.05 mJ/m 2 and 7s = 17.9 mJ/m 2. Since both of

13 12183923_1 (GHMatters) P98786.AU.2 these substances are completely non-polar, yo = yowand ys= WFromthosevalues,one obtains the fourth term to be -33.9 mJ/m 2 , the magnitude of which is larger than that ofyo.

Therefore, in reality yso < ys and hence,

Ko- Y'I , - Yv[5]

which suggests that the wetting film formed between n-pentane and a hydrophobic surface can

more readily rupture than the same formed between air bubble and a hydrophobic surface.

[0034] According to the inequality of Eq. [5], an oil droplet placed on a hydrophobic surface

immersed in water should give a higher contact angle than an air bubble can. Figure 1 shows the

contact angles of various n-alkane hydrocarbons placed on a hydrophobic coal. As shown, all of

the contact angles are larger than 90 and increase with decreasing hydrocarbon chain length. In

comparison, the maximum contact angles of the air bubbles adhering on the surface of the most

hydrophobic bituminous coal placed in water is approximately 65 (Gutierrez-Rodriguez, et al.,

Colloids and Surfaces, 12, p.1, 1984). The large differences between the oil and air contact

angles supports the thermodynamic analysis presented above and clearly demonstrates that oil is

better than air bubble for collecting hydrophobic particles from an aqueous medium.

[0035] When an air bubble encounters a particle during flotation, it deforms and causes a change

in curvature, which in turn creates an excess pressure (p) in the wetting film. The excess pressure

created by the curvature change (peur) can be predicted using the Laplace equation; therefore, it is

referred to as Laplace pressure or capillary pressure. The excess pressure causes a wetting film to

drain. When its film thickness (h) reaches -200 nm, the surface forces (e.g., electrical double

layer and van der Waals forces) present at the air/water and bitumen/water interfaces interact

with each other and give rise to a disjoining pressure (II). A pressure balance along the direction

14 12183923_1 (GHMatters) P98786.AU.2 normal to a film shows that the excess pressure becomes equal to the Laplace pressure minus disjoining pressure, i.e., p = pcur - H. Under most flotation conditions, both the double-layer and van der Waals forces are repulsive (or positive) in wetting films, causing the excess pressure to decrease and hence the film thinning process be retarded.

[0036] The disjoining pressure can become negative when the particle becomes sufficiently

hydrophobic by appropriate chemical treatment. In this case, the excess pressure (p) in the film

will increase and hence accelerate the film thinning process. It has been shown that the negative

disjoining pressures (H < 0) are created by the hydrophobic forces present in wetting films. In

general, hydrophobic forces and hence the negative disjoining pressures increase with increasing

particle hydrophobicity or contact angle (Pan et al., Faraday Discussion, vol. 146, 325-340,

2010).

[0037] Thus, it is essential to render a particle sufficiently hydrophobic for successful flotation.

An increase in particle hydrophobicity should cause the wetting film to thin faster, while at the

same time cause the wetting tension to decrease. If the wetting tension becomes less than the

surface tension of water, then the wetting film ruptures, which is the thermodynamic criterion for

bubble-particle attachment.

[0038] A fundamental problem associated with the forced air flotation process as disclosed by

Sulman et al. (U.S. Patent No. 793,808) is that the van der Waals force in wetting films are

always repulsive, contributing to positive disjoining pressures which is not conducive to film

thinning. When using oil to collect hydrophobic particles, on the other hand, the van der Waals

forces in wetting films are always attractive, causing the disjoining pressures to become

negative. As discussed above, a negative disjoining pressure causes an increase in excess

15 12183923_1 (GHMatters) P98786.AU.2 pressure in the film and hence facilitates film thinning. For the reasons discussed above, oil agglomeration should have faster kinetics and be thermodynamically more favorable than air bubble flotation. An implication of the latter is that oil agglomeration can recover less hydrophobic particles, has higher kinetics, and gives higher throughput.

[0039] In the instant invention, the hydrophobic liquid is dispersed in aqueous slurry. In general,

the smaller the air bubbles or oil droplets, the higher the probability of collision, which is a

prerequisite for bubble-particle or oil-particle attachment. At a given energy input, it would be

easier to disperse oil in water than to disperse air in water. The reason is simply that the

interfacial tensions at the oil-water interfaces are in the range of 50 mJ/m 2, while the same at the

air/water interface is 72.6 mJ/m2

[0040] In the instant invention, hydrophobic liquid, rather than air, is used to collect hydrophobic

particles to take advantage of the thermodynamic and kinetic advantages discussed above. On the

other hand, hydrophobic liquid is generally more expensive than air to use. Further, oil flotation

products have high moistures. In the instant invention, the first problem is overcome by using

hydrophobic oils that can be readily recovered and recycled after use, while the second problem

is addressed as discussed below.

[0041] There are three basic causes for the high moisture content in oil agglomeration products

(the agglomerated fine particles recovered by hydrophobic/hydrophilic separation). They include

i) the film of water adhering on the surface of the hydrophobic particles recovered by oil

flotation; ii) the water-in-oil emulsions (or Pickering emulsions) stabilized by the hydrophobic

particles; and iii) the water entrapped in the interstitial void spaces created by the hydrophobic

particles constituting agglomerates. In the instant invention, the water from i and ii are removed

16 12183923_1 (GHMatters) P98786.AU.2 in the agglomeration stage by selecting a hydrophobic liquid with contact angle greater than 90.

The surface moisture (mentioned in i) is removed by using a hydrophobic liquid that can displace

the water from the surface. Thermodynamically, the surface moisture can be spontaneously

displaced by using a hydrophobic liquid whose contact angles are greater than 90°.

[0042] The water entrainment in the form of water-in-oil emulsions (mentioned in ii) is

eliminated by not allowing large globules of water to be stabilized by hydrophobic particles. This

is accomplished by subjecting aqueous slurries to high-shear agitation. Preferably, the high shear

agitation produces hydrophobic liquid droplet sizes to be smaller than the air bubbles used in

flotation, which allows the process of the instant invention to be more efficient than flotation.

Typically, the droplet sizes are in the range of 0.1 to 400 tm, preferably 10 to 300 tm, more

preferably 100 to 200 tm. The agitation can be accomplished by using a dynamic mixer or an

inline mixer known in the art. In-line mixers are designed to provide a turbulent mixing while

slurries are in transit.

[0043] Under conditions of high-shear agitation, hydrophobic particles can be detached from oil

water interface and, thereby, destabilize water-in-oil emulsions or prevent them from forming.

The amount of energy (E) required to detach hydrophobic particles from the interface can be

calculated by the following relation (Binks, B.P., Current Opinion in Colloid and Interface

Science, 7, 2002, p.21),

= wr'y,(1 ±cos8) [61

where yo/w is the interfacial tension, r is particle radius, and 0 is the contact angle. The sign

inside the bracket is positive for removal into hydrophobic phase and is negative for removal into

water phase. Therefore, the higher the contact angle, the easier it is to remove particles to the 17 12183923_1 (GHMatters) P98786.AU.2 hydrophobic phase. Conversely, the lower the contact angle, the easier it is to remove particles to water phase. Thus, the high-shear agitation employed in the instant invention offers a mechanism by which less hydrophobic particles are dispersed in water phase, while more hydrophobic particles are dispersed in oil phase. Eq. [6] suggests also that the smaller the particles, the easier it is to detach particles from the oil- water interface and achieve more complete dispersion.

[0044] The interstitial water trapped in between hydrophobic particles (mentioned in iii) is

removed by dispersing the agglomerates in a second hydrophobic liquid. Upon dispersion, the

trapped interstitial water is liberated from the agglomerates and are separated from the

hydrophobic particles and subsequently from the hydrophobic liquid. As has already been noted

in conjunction with Eq. [6], the smaller the particles and the higher the contact angles, the easier

it is to disperse agglomerates into the hydrophobic liquid in which the hydrophobic particles are

dispersed. The second hydrophobic liquid (used for dispersion) can be the same of different from

the hydrophobic liquid used in the agglomeration step. The second hydrophobic liquid can be,

but is not limited to, n-alkanes (such as petane, hexane, and heptanes), n-alkenes, unbranched

and branched cycloalkanes and cycloalkenes with carbon numbers of less than eight, ligroin,

naphtha, petroleum naptha, petroleum ether, liquid carbon dioxide, and mixtures thereof.

[0045] The hydrophobic liquid recovered from the process is preferably recycled. The

hydrophobic particles obtained from the solid/liquid separation step are substantially free of

surface moisture. However, a small amount of the hydrophobic liquid may be present on the coal

surface, in which case the hydrophobic particles may be subjected to a negative pressure or

gentle heating to recover the residual hydrophobic liquid as vapor, which is subsequently

condensed back to a liquid phase and recycled.

18 12183923_1 (GHMatters) P98786.AU.2

[0046] Figure 2 shows an embodiment of the instant invention. A mixture of hydrophobic and

hydrophilic particulate materials dispersed in water (stream 1) is fed to a mixing tank 2, along

with the hydrophobic liquid recovered downstream (stream 3) and a small amount of make-up

hydrophobic liquid (stream 4). The aqueous slurry and hydrophobic liquid in the mixing tank 2 is

subjected to a high-shear agitation, e.g. by means of a dynamic mixer as shown to break the

hydrophobic liquid into small droplets and thereby increase the efficiency of collision between

particles and hydrophobic liquid droplets. As noted above, collision efficiency with fine particles

should increase with decreasing droplet size. Further, high-shear agitation is beneficial for

preventing entrainment of water into the hydrophobic liquid phase in the form of water-in-oil

emulsions. Upon collision, the wetting films between oil droplets and hydrophobic particles thin

and rupture quickly due to the low wetting tensions and form agglomerates of the hydrophobic

particulate material, while hydrophilic particles remain dispersed in water. The agitated slurry

flows onto a screen 5 (or a size separation device) by which hydrophilic particles (stream 6) and

agglomerated hydrophobic particles (stream 7) are separated. The latter is transferred to a tank 8,

to which additional (or a second) hydrophobic liquid 9 is introduced to provide a sufficient

volume of the liquid in which hydrophobic particles can be dispersed. A set of vibrating meshes

installed in the hydrophobic liquid phase provides a sufficient energy required to break the

agglomerates and disperse the hydrophobic particles in the hydrophobic liquid phase. Vibrational

frequencies and amplitudes of the screens are adjusted by controlling the vertical movement of

the shaft 11 holding the screens. Other mechanical means may be used to facilitate the breakage

of agglomerates. The hydrophobic particles dispersed in hydrophobic liquid (stream 12) flows to

a thickener 13, in which hydrophobic particles settle to the bottom while clarified hydrophobic

liquid (stream 14) is returned to the mixer 2 (in this case, the hydrophobic liquids in the

19 12183923_1 (GHMatters) P98786.AU.2 agglomeration and dispersion steps are the same). The thickened oily slurry of hydrophobic particles 15 at the bottom of the thickener 13 is sent (stream 15) to a solid-liquid separator 16, such as centrifuge or a filter. The hydrophobic particles (stream 17) exiting the solid-liquid separator 16 are fed to a hydrophobic liquid recovery system consisting of an evaporator 18 and/or a condenser 19. The condensate is recycled back to the mixer 2. The hydrophobic particles (stream 20) exiting the evaporator 18 are substantially free of both moisture and of hydrophilic impurities. The hydrophilic particles recovered from the screen 5 and the disperser 8 may be rejected or recovered separately.

[0047] The hydrophobic liquids that can be used in the process described above include shorter

chain n-alkanes and alkenes, both unbranched and branched, and cycloalkanes and cycloalkenes,

with carbon numbers less than eight. These and other hydrophobic liquids such as ligroin (light

naphtha), naphtha and petroleum naphtha, and mixtures thereof have low boiling points, so that

they can be readily recovered and recycled by vaporization and condensation. Liquid carbon

dioxide (C02 ) is another that can be used as a hydrophobic liquid in the instant invention. When

using low-boiling hydrophobic liquids, it may be necessary to carry out the process described in

Figure 2 in appropriately sealed reactors to minimize the loss of the hydrophobic liquids by

vaporization.

[0048] When processing high-value fine particulate materials, such as precious metals, platinum

group metals (PGM), and rare earth minerals, it may not be necessary to recycle the spent

hydrophobic liquids. In this case, hydrocarbons of higher carbon numbers, such as kerosene,

diesel, and fuel oils may be used without provisions for recycling. When using those

hydrophobic liquids, the instant invention can be similar to the conventional oil agglomeration

20 12183923_1 (GHMatters) P98786.AU.2 process, except that agglomeration products are dispersed in a suitable hydrophobic liquid to obtain lower-moisture and lower-impurity products.

[0049] In the process diagram presented in Figure 2, a hydrophobic particulate material (e.g.,

high-rank coals) is separated from hydrophilic materials (e.g., silica and clay), with the resulting

hydrophobic materials having very low surface moistures.

[0050] The processes as described in the instant invention can also be used for separating one

type of hydrophilic materials from another by selectively hydrophobizing one but not the

other(s). For example, the processes can be used to separate copper sulfide minerals from

siliceous gangue minerals by using an alkyl xanthate or a thionocarbamate as hydrophobizing

agents for the sulfide minerals. The hydrophobized sulfide minerals are then separated from the

other hydrophilic minerals using the process of the present invention.

[0051] Further, the process disclosed in the instant invention can be used for further reducing the

moisture of the hydrophobic particulate materials dewatered by mechanical dewatering methods.

For example, a filter cake consisting of hydrophobic particles can be dispersed in a hydrophobic

liquid to remove the water entrapped in between the void spaces of the particles constituting the

filter cake, and the hydrophobic liquid is subsequently separated from the dispersed hydrophobic

particles and recycled to obtain low-moisture products.

[0052] In addition, the process disclosed in the instant invention can be used for dewatering low

rank coals. This can be accomplished by heating a coal in a hydrothermal reactor in the presence

of C02. The water derived from the low-rank coal is displaced by liquid C02 in accordance to

the DBD and the HHS mechanisms disclosed above. The product coal obtained from this novel

21 12183923_1 (GHMatters) P98786.AU.2 process will be substantially free of water and can be transported under C02 atmosphere to minimize the possibility of spontaneous combustion.

[0053] Further, low-rank coals can be dewatered and upgraded by the present invention by

derivatizing the low-rank coal to make it hydrophobic. It is well known that low-rank coals are

not as hydrophobic as high-rank coals, such as bituminous coal and anthracite. Some are so

hydrophilic that flotation using conventional coal flotation reagents, such as kerosene and diesel

oils do not work. Part of the reasons is that various oxygen containing groups such as carboxylic

acids are exposed on the surface. When a low-rank coal is upgraded in accordance to the present

invention, it is preferably derivatized to render the surface hydrophilic surface hydrophobic. In

one embodiment, the low-rank coal is first esterified with an alcohol, e.g. methanol, ethanol, and

the like, using methods known in the art. The esterification renders the low-rank coal more

hydrophobic (than before esterification). The reaction between the carboxyl groups (R-COOH)

of the low-rank coal and alcohol (R-OH) is indicated as follows:

0 Ht -0H~

CH O-R

The reaction produces esters (R-COOR) on the surface of the low-rank coal and water.

Preferably, the reaction takes place at about 25-75°C, more preferably about 45-55°C, and most

preferably at about 50°C. A catalyst, such as H' ions may also be used for the esterification. The

production of water by the condensation reaction represents a mechanism by which "chemically

bound" water is removed, while the substitution of the hydrophilic carboxyl groups with short

hydrocarbon chains (R) renders the low-rank coal hydrophobic. Once esterified, the low-rank

coal can be subjected to the HHS process disclosed in the instant invention to remove the

22 12183923_1 (GHMatters) P98786.AU.2 residual process water and the entrained hydrophilic mineral using the agglomeration/dispersion steps as disclosed in the present invention.

[0054] Without further description, it is believed that one of ordinary skill in the art can, using

the preceding description and the following illustrative examples, make and utilize the present

invention. The following examples are given to illustrate the present invention. It should be

understood that the invention is not to be limited to the specific conditions or details described in

the examples.

Example 1

[0055] A sample of rougher concentrate was received from a chalcopyrite flotation plant

operating in the U.S. The sample assaying 15.9 %Cu was wet ground in a laboratory ball mill for

12.5 hours to reduce the particle size to 80% finer than 20 m. The mill product was subjected to

a standard flotation test, and the results were compared with those obtained from an oil

agglomeration test. In each test, a 100 g mill product was treated with 4 lb/ton of potassium amyl

xanthate (KAX) to selectively hydrophobize chalcopyrite.

[0056] The flotation test was conducted using a Denver laboratory flotation cell. The oil

agglomeration test was conducted using a kitchen blender with 100 g mill product, 80 ml n

pentane, and 400 ml tap water. The mixture was subjected initially to a high-shear agitation for

s and subsequently to a low-shear agitation for another 40 s. Here, the dividing line between

the high- and low-shear agitations is the impeller speed that can create agglomerates of

hydrophobic (and/or hydrophobized) particles, which is referred to as phase inversion. For the

case of bituminous coal, the phase inversion occurs at the rotational speeds above approximately

8,000 r.p.m. The slurry in the blender was then poured over a screen to separate the 23 12183923_1 (GHMatters) P98786.AU.2 agglomerated hydrophobized chalcopyrite particles from the dispersed hydrophilic siliceous gangue. The agglomerates recovered as screen overflow were then dispersed in n-pentane, while being agitated by means of an ultrasonic vibrator to assist dispersion. The hydrophobized chalcopyrite particles dispersed in pentane were then separated from pentane and analyzed for copper and moisture.

[0057] As shown in Table 1, oil agglomeration gave 92.3% copper recovery, as compared to

55.4% recovery obtained by flotation. The large improvement can be attributed to the differences

in wetting tensions and the nature of the van der Waals forces present in the respective wetting

films. On the other hand, the oil agglomeration test gave a little lower copper grade than the

flotation test.

[0058] A problem associated with the oil agglomeration process was that the moisture content of

the agglomerates was high (48.6%) due to the presence of the water trapped within the

agglomerate structure. It was possible, however, to overcome this problem by dispersing the

agglomerates in a hydrophobic liquid (n-pentane) and thereby liberating the residual process

water entrapped within the agglomerate structure. The moisture content of the chalcopyrite

concentrate obtained in this manner was only 0.6 %, as shown in Tale 1.

Table 1

Copper Moisture twt} Recovery Grade Agglomerates Dispersed N (%]:U) Flotation 554 - •

Agglomeration 92.3 23.1 48.6 0.6

24 12183923_1 (GHMatters) P98786.AU.2

[0059] This example shows that oil droplets are more efficient than air bubbles for the recovery

of ultrafine hydrophobic particles from aqueous media, and that that the HHS process can be

used to overcome the high moisture problem associated with the oil agglomeration process.

Example 2

[0060] In this example, the process of the present invention was compared with flotation. The

copper rougher concentrate assaying 15.9 %Cu was wet ground in a ball mill using tap water.

The grinding times were varied to obtain mill products of different particle sizes, and the

products were subjected to both flotation and HHS tests.

[0061] Table 2 compares the flotation and HHS test results obtained on a mill product with a

particle size distribution of 80% finer than 22 m. Each test was conducted using -250 g samples

with 17.6 lb/ton potassium amyl xanthate (KAX) as a selective hydrophobizing agent (collector)

for the copper mineral (chalcopyrite). As shown, flotation gave a concentrate assaying 28.0

% Cu with a 67.4 % copper recovery, while the HHS process gave a concentrate assaying 23.1

% Cu with a 91.9 % recovery. In the latter, the mill product was first agglomerated with pentane in

a kitchen blender, which provided a high-shear agitation, and the agglomerates were

subsequently separated from dispersed materials by means of a screen. The agglomerates were

then dispersed in pentane so that the residual process water entrapped within the agglomerate

structure is liberated from the agglomerates. A gentle mechanical agitation facilitated the

dispersion by breaking the agglomerates.

25 12183923_1 (GHMatters) P98786.AU.2

Table2

weight Assays {%wt] Copper Product rams % wt CIi Moistur Recovery Concentrate 151.1 68. 28.0 - 67.4 Rotation Tailing 692 31.4 8.4 - Feed 220.3 100.0 15.9 - Hydrophobfc- Concentrate 238.2 983 23.1 0.14 91.9 Hydrophilic Tailing 4.0 1.7 3.5 - Separation (HRS) Feed 242.2 100.0 15.9

[0062] The results presented in the table demonstrated that the present invention is more efficient

in recovering fine particles. That the present process gave a slightly lower copper grade than the

flotation process can be attributed to high recovery. Since the droplets of hydrophobic liquid

(pentane) are more efficient than air bubbles in collecting hydrophobic particles, the former can

recover composite particles that are less hydrophobic than fully liberated chalcopyrite particles,

resulting in a lower-grade product. When the present process (HHS) was conducted at lower

dosages of xanthate, the concentrate grade was improved.

Example 3

[0063] Monosized silica spheres of 11 m in diameter were hydrophobized and subjected to oil

agglomeration, followed by a dispersion step as described in the foregoing examples. The silica

particles were hydrophobized by immersing them in a 0.002 moles/liter octadecyltrichlorosilane

(OTS) solution. After a 10 minute immersion time, the particles were washed with toluene and

subsequently with ethanol to remove the residual OTS molecules adhering on the surface.

[0064] An aqueous suspension containing 50 g of the hydrophobized silica at 10% solids was

placed in a kitchen blender and subjected to a high-shear agitation for 40 s in the presence of 20

26 12183923_1 (GHMatters) P98786.AU.2 ml of n-pentane, followed by 40 s of low-shear agitation. The agglomerates showed 19.5% moisture by weight.

[0065] The agglomerates were then dispersed in n-pentane while being agitated mechanically to

facilitate the breakage of the agglomerates and thereby release the water trapped in between

hydrophobic particles. The mechanical device that was used to help break the agglomerates was

a set of vibrating meshes located in the pentane phase. The tiny water droplets liberated from the

agglomerates fall to the bottom, while the hydrophobic particles remain dispersed in the organic

phase. The hydrophobic particles separated from the organic phase were practically dry

containing only 0.7% by weight of moisture. This example clearly demonstrates that the process

of the present invention is efficient for recovering and dewatering ultrafine particles.

Example 4

[0066] Fundamentally, dewatering is a process in which solid/water interface is replaced by

solid/air interface. For hydrophobic solids, the interfacial free energies at the solid/oil interface

(yso) is lower than the same at the solid/air interface (ys) as discussed in view of Eqs. [4] and [5].

It should, therefore, be easier to displace the solid/water interface with solid/oil interface than

with solid/air interface.

[0067] In this example, 200 ml of tap water and 50 g of monosized silica particles of 71 m were

agitated in a kitchen blender for a short period of time to homogenize the mixture. A known

volume of a cationic surfactant solution, i.e., 4x10-6 M dodecylaminium hydrochloride (DAH),

was then added to the mixture. The slurry was agitated for 3 minutes at a low speed to allow for

the surfactant molecules to adsorb on the surface and render the silica surface hydrophobic. A

volume of n-pentane (25 ml) was then added before agitating the slurry at a high speed for 40 s, 27 12183923_1 (GHMatters) P98786.AU.2 followed by another 40 s of agitation at a low speed. The agitated slurry was poured over a screen to separate the agglomerates, formed in the presence of the hydrocarbon oil, from the water. The agglomerates were analyzed for surface moisture after evaporating the residual n pentane adhering on the silica surface. The tests were conducted at different DAH dosages, with the results being presented in Table 3. As shown, the moisture of the agglomerates decreased with increasing DAH dosages. Nevertheless, the moistures remained high due to the presence of the water trapped in between the particles constituting the agglomerates.

Table 3 DAH Dosage Moisture (%wt)

(lb/ton) Agglomerate Dispersed 212 24,20 7

44 23.67 0.9 is 22.5 0.06

[0068] Another set of agglomeration tests were conducted under identical conditions. In this set

of experiments, the agglomeration step was followed by another step, in which the agglomerates

were added to a beaker containing 100 ml of n-pentane. After a gentle agitation by hand, the

hydrophobic silica particles dispersed in pentane was transferred to a Buchner filter for solid

liquid separation. Additional pentane was added to ensure that most of the entrapped water was

displaced by the hydrophobic liquid. The filter cake was analyzed for moisture after evaporating

the residual n-pentane from the surface. As shown in Table 3, the moisture contents of the

filtered silica were substantially lower than those of the agglomerates.

Example 5

28 12183923_1 (GHMatters) P98786.AU.2

[0069] Screen-bowl centrifuges are widely used to dewater clean coal products from flotation.

However, the process loses ultrafine particles smaller than 44 m as effluents. In this example, a

screen-bowl effluent received from an operating bituminous coal cleaning plant was first

subjected to two stages of flotation to remove hydrophilic clay, and the froth product was

dewatered by vacuum filtration. The cake moisture obtained using sorbitanmonooleate as a

dewatering aid was 20.2% by weight. The filter cake was then dispersed in a hydrophobic liquid

(n-pentane) while the slurry was being agitated by sonication to facilitate the breakage of the

agglomerate. Since the bituminous coal particles are hydrophobic, they can readily be dispersed

in the hydrophobic liquid, while the water droplets trapped in between the particles were released

and fall to the bottom. The ultrafine coal particles dispersed in the hydrophobic liquid phase

contained only 2.3% moisture, as analyzed after appropriately separating the n-pentane from the

coal. The results obtained in this example showed that most of the moisture left in the filter cake

was due to the water trapped in the void spaces in between the particles constituting the cake,

and that it can be substantially removed by the method disclosed in the instant invention.

Example 6

[0070] Recognizing the difficulty in cleaning and dewatering ultrafine coal, many companies in

the U.S. remove ultrafine coal by cyclone prior to flotation and subsequently dewater the froth

product using screen -bowl centrifuges. A sample of cyclone overflow containing particles finer

than 400 mesh (37 m) and 53.6% ash was subjected to a series of selective agglomeration tests

using n-pentane as agglomerant. The tests were conducted by varying oil dosages, agitation

speed, and agitation time. As shown in Table 4, low-shear agitation resulted in high-ash and

high-moisture products. Combination of high- and low-shear agitation gave better results. In

general, selective oil agglomeration did an excellent job in ash rejection. However, product 29 12183923_1 (GHMatters) P98786.AU.2 moistures were high due to the entrapment of water within the structure of the agglomerates as has already been discussed.

Table 4

Product (%wt] Combuotible Oil Dosage Agitation Speed

& Moisture Ash Recovery (K wt) (%w) Time (min) 61.2 19.1 74.1 25 low shear(2) 24.8 11.1 67.0 50 high shear (0.5) & low shear (2) 43.1 10.4 66.1 30 high shear (0.5) & low shear (2)

50.9 11.0 72.2 20 high shear (0.5] & low shear (2)

45.2 13.2 75.8 10 high shear (0.5) & low shear (2)

[0071] The same coal sample was subjected to a series of oil agglomeration tests as described

above. The amount of n-pentane used in each test was 20% by weight of feed, and the mixture

was agitated for 30 s at a high speed and then for 2 min at a low speed. The results presented in

Table 5 show that the moistures of the clean coal products were substantially reduced further

from those obtained in the agglomeration tests (Table 4). The improvements can be attributed to

the liberation of the interstitial water by dispersing the agglomerates in a hydrophobic liquid.

Note also that by releasing the interstitial water, the mineral matter dispersed in it was also

removed, resulting in a further reduction in ash content beyond what was obtainable using the

selective agglomeration process alone. Thus, the process of the instant invention can improve

both moisture and ash rejections.

30 12183923_1 (GHMatters) P98786.AU.2

Table 5

Product (% wt) Combustible Moisture Ash Recovery M% wt) 3A 2.3 78.8 3.5 3.9 84.7 3. 2.9 83.4 10.6 3.0 78.8 10.0 2.5 78.7 4A 3.0 80.1 !.1 3.7 86.7

Example 7

[0072] A sample of screen bowl effluent was received from a metallurgical coal processing plant

and used for the process of the present invention. The effluent, containing 11% ash, was

processed at 5% solids as received without thickening. The procedure was the same as described

in the preceding examples. The amount of n-pentane used was 20% by weight of feed, and the

slurry was agitated for 20 s in a kitchen blender at a high agitation speed. The results presented

in Table 6 show that low-moisture and low-ash products were obtained from the screen bowl

effluent. Since the coal was very hydrophobic, it was not necessary to have a low-shear agitation

after the high- shear agitation.

[0073] The fourth column of Table 6 gives the %solids of the coal dispersed in n-pentane. The

data presented in the table show that product moistures become higher at higher %solids.

However, other operating conditions such as the amount of mechanical energy used to break

agglomerates and facilitate dispersion also affected the moisture. In this example, the mechanical

energy was provided by a set of two vibrating meshes moving up and down in the pentane phase.

31 12183923_1 (GHMatters) P98786.AU.2

The solid content in dispersed phase is important in continuous operation, as it affects throughput

and product moisture.

Table 6 Product (% wt) Ieject Ash %Solid Combustible Moisture Ash (% wt) Pentane Recovery% 8.1 2.3 84.0 7.1 98.0 6.1 2.0 $4.3 63 98.0 6.8 2.7 83.8 7.3 98.1 2.8 2.2 $3.0 1.7 97.8

Example 8

[0074] A bituminous coal processing plant is cleaning a 100 mesh x 0 coal assaying

approximately 50% ash by flotation. Typically, clean coal products assay 9 to 11% ash. A coal

sample was taken from the plant feed stream and subjected to the method of the present

invention. As shown in Table 7, the process produced low-ash (3.2 to 4.2%) and low-moisture(

1%) products with approximately 90% combustible recoveries. Without the additional dispersion

step, the agglomerates assayed 37.2 to 45.1% moistures.

Table 7

Feed Product Moisture (% wt) Ash (%wt) Combustible Ash (%wt Agglomerate Dispersed Clean Coal Reject Recovery (%)

51,0 45.1 1. 4.2 90.0 88.9 52.5 45.2 01 3.5 91.4 89.9 52.6 37.2 1.0 16 91.7 90.3

Example 9

32 12183923_1 (GHMatters) P98786.AU.2

[0075] Two different bituminous coal samples were subjected to continuous process of the

present invention, n-pentane was used as a hydrophobic liquid. The process was substantially the

same as described in Figure 2, except that an ultrasonic vibrator rather than a set of vibrating

mesh was used to break the agglomerates and facilitate dispersion in n-pentane. As shown in

Table 8, the oil agglomeration followed by a dispersion step reduced the ash content of a

metallurgical coal from 51 to 3.6% ash with a 92% combustible recovery. With another coal

sample assaying 40.4% ash, the ash contents were reduced to 3.3 to 5.0% with combustible

recoveries in the neighborhood of 80%.

[0076] The bulk of the spent pentane was recycled without phase changes. However, a small

amount of the hydrophobic liquid adhering onto coal surfaces was recycled by evaporation and

condensation. The amount of n-pentane that was lost due to adsorption or incomplete removal

from coal was in the range of 1.5 to 4 lb/ton of clean coal. The energy cost for evaporating n

pentane is substantially less than that for water in view of the large differences in boiling points

(36.1°C vs. 100°C) and heats of vaporization (358 kJ/kg vs. 2,257 kJ/kg) for pentane and water.

Table8 Feed Product [%wt) Reject Combustrble Ash (%wt) Moistur Ash Ash (%wt] Recovery (%wt) 51.0 2.9 3.6 92.6 92.0 40.4 l. 5.0 80.6 84.8 40.4 3.9 3.3 801 839

Example 10

[0077] In this example, a subbituminous coal (-1.18 + 0.6 mm) from Wyoming was dry

pulverized and hydrophobized in water using sorbitanmonooleate (Reagent U) in the presence of

33 12183923_1 (GHMatters) P98786.AU.2 water. The coal sample assayed 28% moisture by weight of as-received moisture, 8.5% ash, and

8,398 Btu/lb. As shown in Table 9, the process of the present invention substantially reduced the

moisture and hence increased the heating values. In general, the moisture reductions were higher

at higher reagent dosages and longer agitation times. As has been the cases with bituminous

coals, the hydrophobized subbituminous coal also formed agglomerates in the presence of a

hydrophobic liquid (n-pentane) but the agglomerate moistures were high due to the entrapment

mechanism discussed in the foregoing examples. When the agglomerates were dispersed in

n-pentane, however, the moisture contents were substantially reduced and the heading values

increased accordingly.

Table 9

ReagentU Agglomerale Product Dosage Agtn. Time Moisture Mosture Ash Heating Value (lb/ton) (min) {%Wt)t) (%wt) (BlulAb) 33.3 15 44.6 38.2 8.2 7,562 333 30 27.1 208 5.8 9,814 50 5 48.2 6.0 5.8 11,560 50 30 28.1 4.1 6.0 11,759

Example 11

[0078] In this example, a Wyoming coal sample was hydrophobized by esterification with

ethanol and then subjected to the process of the present invention. The reaction took place at

°C in the presence of a small amount of H' ions as a catalyst. As has already been discussed,

the esterification reaction removes the chemically bound water by condensation and renders the

coal hydrophobic. The hydrophobized coal sample was then subjected to the process of the

present invention (HHS) as discussed above to remove the water physically entrapped within the

34 12183923_1 (GHMatters) P98786.AU.2 agglomerate structure and the capillaries of low-rank coals. As is well known, much of the

'inherent moistures' in low-rank coals is due to the water trapped in macropres (Katalambula and

Gupta, Energy and Fuels, vol. 23, p. 3392, 2009).

[0079] The ethanol molecules may be small enough to penetrate the pore structures and remove

the water by condensation and the displacement mechanisms involved in the HHS process. A

strong evidence for this possibility may be that even the coarse particles were readily dewatered

as shown in Table 10. Also shown in that table is that the hydrophobized low-rank coals form

agglomerates, which trap large amount of moistures. When they were dispersed in n-pentane,

however, the moisture was substantially reduced.

Table 1D

Top Size of Agglomerate HHS Product Coal Sarnples Moisture Moisturs Ash Heating Value (mM) MV) (%wA (%wt) (Btulb) 0.350 40.3 3.20 9.92 10,827 0.600 25.62 3.20 9,82 11,01a 1.1BO 28.34 2.87 8.4 11,216 6.300 37.63 2.30 6.27 11,529

[0080] Table 11 shows the results obtained with different alcohols for esterification. As shown,

the shorter the hydrocarbon chains of the alcohols, the lower the moistures of the Wyoming coal

samples treated by the HHS process. This finding suggests that smaller molecules can more

readily enter the pores and remove the chemically-bound water by the mechanisms discussed

above.

35 12183923_1 (GHMatters) P98786.AU.2

Table 11

Agglomerate HHS Product Alcohol Moisture Moisture Ash Heating Value (%Wt) (%wtt) (%wt) (BuAb) Methanol 25.39 8.32 2.35 11,625 Elhanol 30.92 9-14 3.20 11,125 2-Propanol 29.82 10.12 0.93 10,693 1-Pentanol 31.5 15.12 3.8 10,092

[0081] Although certain presently preferred embodiments of the invention have been specifically

described herein, it will be apparent to those skilled in the art to which the invention pertains that

variations and modifications of the various embodiments shown and described herein may be

made without departing from the spirit and scope of the invention. Accordingly, it is intended

that the invention be limited only to the extent required by the appended claims and the

applicable rules of law.

[0082] It is to be understood that, if any prior art publication is referred to herein, such reference

does not constitute an admission that the publication forms a part of the common general

knowledge in the art, in Australia or any other country.

[0083] In the claims which follow and in the preceding description of the invention, except

where the context requires otherwise due to express language or necessary implication, the word

"comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e.

to specify the presence of the stated features but not to preclude the presence or addition of

further features in various embodiments of the invention.

36 12183923_1 (GHMatters) P98786.AU.2

Claims (18)

What is claimed is:

1. A process of upgrading low-rank coal particles comprising the steps of: a. adding water to the low-rank coal particles to form an aqueous slurry; b. hydrophobizing the low-rank coal particles; c. adding a first hydrophobic liquid to the slurry; d. agitating the slurry to form agglomerates of hydrophobized low-rank coal particles; e. separating the agglomerates of hydrophobized coal particles from the aqueous slurry; and f. dispersing the agglomerates in a second hydrophobic liquid to liberate the water molecules entrapped within the agglomerate structure along with the hydrophilic mineral matter dispersed in the water, thereby removing water and mineral matter from the low-rank coal and increasing its heating value.

2. The process of claim 1, wherein the low-rank coal particles are hydrophobized with a surfactant.

3. The process of either of claims 1 or 2, wherein the low-rank coal particles are hydrophobized by esterification.

4. The process of any one of claims I to 3, wherein the low-rank coal particles are hydrophobized by adding an alcohol.

5. The process of any one of claims 1 to 4, wherein said alcohol from the group consisting of: methanol, ethanol, 2-propanol and 1-pentanol.

6. The process of any one of the preceding claims, wherein said first or second hydrophobic liquid is selected from the group consisting of n-alkanes, n-alkenes, unbranched and branched cycloalkanes and cycloalkenes with carbon numbers of less than eight, ligroin, naphtha, petroleum naptha, petroleum ether, liquid carbon dioxide, and mixtures thereof.

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7. The process of any one of the preceding claims, wherein said first hydrophobic liquid is selected from gasoline, kerosene, diesel fuel, and heating oils.

8. The process of any one of the preceding claims, wherein at least one of the first hydrophobic liquid and the second hydrophobic liquid is recycled.

9. The process of any one of the preceding claims, wherein the coal is smaller than 1 mm in diameter.

10. The process of any one of the preceding claims, further comprising the step of evaporating any hydrophobic liquid attached to the hydrophobic particles substantially free of hydrophilic contaminant and water produced in step d.

11. The process of any one of the preceding claims, wherein step a produces hydrophobic droplet sizes ranging from about 0.1 m to about 400 [m.

12. The process of any one of the preceding claims, wherein step c also includes agitation to promote dispersion.

13. The process of claim 12, wherein the agitation is selected from the group consisting of sonication, ultrasonic vibration, agitation with a dynamic mixer, agitation by a static mixer, and vibrating screens.

14. The process of any one of the preceding claims, wherein step e is accomplished by sedimentation, vacuum filtration, pressure filtration, centrifugal filtration, or centrifugation.

15. The process of any one of the preceding claims, wherein the hydrophobic particles substantially free of hydrophilic contaminant and water have a water content of about 0.1% to about 10%.

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16. The process of any one of the preceding claims, wherein the hydrophobic particles substantially free of hydrophilic contaminant and water have a hydrophilic particulate material content of about 1% to about 10%.

17. The process of any one of the preceding claims, wherein step c is accomplished by creating an upward current of the second hydrophobic liquid to keep heavy minerals in suspension.

18. The process of any one of the preceding claims, wherein agglomerates formed with the first hydrophobic liquid are washed with the second hydrophobic liquid to recover the first hydrophobic liquid.

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