Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B1/00—Conditioning for facilitating separation by altering physical properties of the matter to be treated
  • B03B1/04—Conditioning for facilitating separation by altering physical properties of the matter to be treated by additives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B5/00—Washing granular, powdered or lumpy materials; Wet separating
  • B03B5/28—Washing granular, powdered or lumpy materials; Wet separating by sink-float separation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B9/00—General arrangement of separating plant, e.g. flow sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B9/00—General arrangement of separating plant, e.g. flow sheets
  • B03B9/005—General arrangement of separating plant, e.g. flow sheets specially adapted for coal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L1/00—Liquid carbonaceous fuels
  • C10L1/32—Liquid carbonaceous fuels consisting of coal-oil suspensions or aqueous emulsions or oil emulsions
  • C10L1/324—Dispersions containing coal, oil and water
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L1/00—Liquid carbonaceous fuels
  • C10L1/32—Liquid carbonaceous fuels consisting of coal-oil suspensions or aqueous emulsions or oil emulsions
  • C10L1/328—Oil emulsions containing water or any other hydrophilic phase

Definitions

• 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.
• 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 CO 2 emissions. In general, coarse coal (50 x 0.15 mm) can be 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.
• Flotation becomes inefficient with finer particles.
• low-grade ores often require fine grinding for sufficient liberation.
• mineral flotation its efficacy deteriorates rapidly below approximately 10 to 15 ⁇ , while coal flotation becomes difficult below approximately 44 ⁇ .
• Flotation also becomes inefficient when particle size is larger than approximately 150 ⁇ for minerals and 500 ⁇ for coal.
• 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.
• the amounts of oil used in the selective agglomeration process are typically in the range of 5 to 30% by weight of feed coal (S,C. Tsai, in Fundamentals of Coal Beneficiation and Utilization, Elsevier, 2982, p. 335).
• 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.
• 6,632,258 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.
• 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
• 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.
• DBD dewatering by displacement
• hydrophobic particulate materials of hydrophilic contaminants It is also an object to provide a clean hydrophobic fine particulate material that contains moisture levels that is substantially lower than can be achieved by conventional dewatering methods.
• 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.
• 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.
• high shear or the like, means a shear rate that is sufficient to form large and visible agglomerates, which is referred to phase inversion.
• 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.
• 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.
• 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.
• a second hydrophobic liquid is added to the agglomerates to disperse the hydrophobic particles in the liquid.
• the dispersion liberates the entrapped process 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.
• 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.
• 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 %.
• hydrophobic-hydrophilic separation (HHS) process 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.
• Figure 1 is a graph showing the contact angles of w-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, ⁇ 2, p. ⁇ , 1984).
• Figure 2 is a schematic of one embodiment of the process as disclosed in the present invention.
• the present invention provides methods of separating a mixture of hydrophobic fine particulate materials suspended in water. It is also an object to dewater at least one of the products to a level that is substantially lower than can be achieved by conventional dewatering methods.
• 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.
• 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.
• 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.
• the agglomeration step removes the bulk of hydrophilic 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.
• 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.
• the probability of collision between oil droplets and fine particles increases with decreasing droplet size.
• 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 ( ⁇ ) 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.
• 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.
• 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.
• the hydrophilic particles in the entrained water are also removed, providing an additional mechanism of separating hydrophobic and hydrophilic particles from each other.
• 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.
• 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.
• TLF thin liquid film
• 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 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.
• a wetting film can rupture when the following thermodynamic condition is met
• ⁇ 8 is the surface free energy of a solid (or particle) in contact with air, while y sw and y w are the same at the solid/water and water/air interfaces, respectively.
• the term on the left, i.e., Ys ⁇ Ys 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 ⁇ 5 — Ys ? — ; therefore, the lower the wetting tension, the easier it is to break the film.
• ⁇ 8 is the Lifshitz-van der Waals component of y s and y w is the same of y ⁇ and are the acidic and basic components of -y s , respectively; and y*. and ) ⁇ % are the same for water.
• the acidic and basic components represent the propensity for hydrogen bonding. According to Eq. [2], it is necessary to keep y ⁇ and ⁇ small to increase ⁇ $$ >, which can be accomplished by rendering the surface more hydrophobic. When a surface becomes more hydrophobic, y s decreases also, which helps decrease the wetting tension and hence improve flotation.
• a hydrophobic liquid rather than air, is used to collect hydrophobic particles.
• oil-particle attachment can occur under the following condition,
• hydrophobic liquids that can be used in the instant invention include, but are not limited to, w-alkanes (such as petane, hexane, and heptanes), w-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 value of the third term of Eq. [4], i.e., 2 ⁇ ⁇ ⁇ ' ⁇ ⁇ , is substantial.
• ⁇ ⁇ 16.05 mJ/m 2
• FIG. 1 shows the contact angles of various w-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. l, 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.
• the disjoining pressure can become negative when the particle becomes sufficiently hydrophobic by appropriate chemical treatment.
• the excess pressure (p) in the film will increase and hence accelerate the film thinning process.
• the negative disjoining pressures ⁇ ⁇ 0 are created by the hydrophobic forces present in wetting films.
• 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).
• a fundamental problem associated with the forced air flotation process as disclosed by Sulman et al. 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.
• the van der Waals forces in wetting films are always attractive, causing the disjoining pressures to become negative.
• a negative disjoining pressure causes an increase in excess pressure in the film and hence facilitates film thinning.
• 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.
• the hydrophobic liquid is dispersed in aqueous slurry.
• 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.
• hydrophobic liquid rather than air, is used to collect hydrophobic particles to take advantage of the thermodynamic and kinetic advantages discussed above.
• hydrophobic liquid is generally more expensive than air to use. Further, oil flotation products have high moistures.
• 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.
• the agglomerated fine particles recovered by hydrophobic/hydrophilic separation 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.
• the water from i and ii are removed 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.
• a hydrophobic liquid that can displace the water from the surface.
• the surface moisture can be spontaneously displaced by using a hydrophobic liquid whose contact angles are greater than 90°.
• the water entrainment in the form of water-in-oil emulsions 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.
• 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.
• the droplet sizes are in the range of 0.1 to 400 ⁇ , preferably 10 to 300 ⁇ , more preferably 100 to 200 ⁇ .
• 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.
• hydrophobic particles 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.2l),
• the interstitial water trapped in between hydrophobic particles is removed by dispersing the agglomerates in a second hydrophobic liquid.
• the trapped interstitial water is liberated from the agglomerates and are separated from the hydrophobic particles and subsequently from the hydrophobic liquid.
• 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, w-alkanes (such as petane, hexane, and heptanes), w-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.
• w-alkanes such as petane, hexane, and heptanes
• w-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 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.
• 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.
• FIG. 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.
• collision efficiency with fine particles should increase with decreasing droplet size.
• high-shear agitation is beneficial for preventing entrainment of water into the hydrophobic liquid phase in the form of water-in-oil emulsions.
• 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 10 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 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.
• the hydrophobic liquids that can be used in the process described above include shorter-chain w-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 (C0 2 ) 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.
• the instant invention can be similar to the conventional oil agglomeration process, except that agglomeration products are dispersed in a suitable hydrophobic liquid to obtain lower-moisture and lower-impurity products.
• hydrophilic materials e.g., silica and clay
• 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).
• 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.
• 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.
• 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.
• 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 C0 2 .
• the water derived from the low-rank coal is displaced by liquid C0 2 in accordance to the DBD and the HHS mechanisms disclosed above.
• the product coal obtained from this novel process will be substantially free of water and can be transported under C0 2 atmosphere to minimize the possibility of spontaneous combustion.
• 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.
• 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:
• esters R-COOR
• 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.
• the low-rank coal can be subjected to the HHS process disclosed in the instant invention to remove the residual process water and the entrained hydrophilic mineral using the agglomeration/dispersion steps as disclosed in the present invention.
• 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 ⁇ .
• 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.
• 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 40 s and subsequently to a low-shear agitation for another 40 s.
• 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.
• 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 agglomerated hydrophobized chalcopyrite particles from the dispersed hydrophilic siliceous gangue.
• the agglomerates recovered as screen overflow were then dispersed in w-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.
• 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 (w-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.
• 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.
• Table 2 compares the flotation and HHS test results obtained on a mill product with a particle size distribution of 80% finer than 22 ⁇ . 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
• KAX 17.6 lb/ton potassium amyl xanthate
• 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.
• dewatering is a process in which solid/water interface is replaced by solid/air interface.
• the interfacial free energies at the solid/oil interface ⁇ 'ss
• the same at the solid/air interface 3 ⁇ 4 as discussed in view of Eqs.
• Screen-bowl centrifuges are widely used to dewater clean coal products from flotation. However, the process loses ultrafine particles smaller than 44 ⁇ as effluents.
• 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 (w-pentane) while the slurry was being agitated by sonication to facilitate the breakage of the agglomerate.
• 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.
• 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 w-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.
• 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.
• 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.
• other operating conditions such as the amount of mechanical energy used to break agglomerates and facilitate dispersion also affected the moisture.
• the mechanical energy was provided by a set of two vibrating meshes moving up and down in the pentane phase.
• the solid content in dispersed phase is important in continuous operation, as it affects throughput and product moisture.
• 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.
• the process of the present invention substantially reduced the moisture and hence increased the heating values.
• the moisture reductions were higher at higher reagent dosages and longer agitation times.
• the hydrophobized subbituminous coal also formed agglomerates in the presence of a hydrophobic liquid (w-pentane) but the agglomerate moistures were high due to the entrapment mechanism discussed in the foregoing examples.
• the agglomerates were dispersed in n- pentane, however, the moisture contents were substantially reduced and the heading values increased accordingly.
• 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 50 °C in the presence of a small amount of H + ions as a catalyst.
• 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 agglomerate structure and the capillaries of low-rank coals.
• HHS process of the present invention
• 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.
• 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 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.

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