EP1333905B1 - Verfahren zur verbesserung der entwässerung feiner teilchen - Google Patents

Verfahren zur verbesserung der entwässerung feiner teilchen Download PDF

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EP1333905B1
EP1333905B1 EP00967227A EP00967227A EP1333905B1 EP 1333905 B1 EP1333905 B1 EP 1333905B1 EP 00967227 A EP00967227 A EP 00967227A EP 00967227 A EP00967227 A EP 00967227A EP 1333905 B1 EP1333905 B1 EP 1333905B1
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Prior art keywords
dewatering
cake
coal
surfactants
hydrophobic
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French (fr)
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EP1333905A1 (de
EP1333905A4 (de
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Roe-Hoan Yoon
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Yoon Roe-Hoan
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Yoon Roe-Hoan
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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
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/001—Flotation agents
    • B03D1/004—Organic compounds
    • B03D1/008—Organic compounds containing oxygen
    • 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
    • B03D1/001—Flotation agents
    • B03D1/004—Organic compounds
    • B03D1/006—Hydrocarbons
    • 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
    • B03D1/001—Flotation agents
    • B03D1/004—Organic compounds
    • B03D1/01—Organic compounds containing nitrogen
    • 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
    • B03D1/001—Flotation agents
    • B03D1/004—Organic compounds
    • B03D1/016—Macromolecular compounds
    • 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
    • B03D2201/00—Specified effects produced by the flotation agents
    • B03D2201/02—Collectors
    • 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
    • B03D2203/00—Specified materials treated by the flotation agents; specified applications
    • B03D2203/02—Ores
    • B03D2203/04—Non-sulfide ores
    • B03D2203/08—Coal ores, fly ash or soot

Definitions

  • nin-of-the-mine (ROM) ores are crushed and pulverized to detach (or liberate) the valuable components from waste rocks.
  • ROM coal is rarely crushed, a significant portion is present as fine coal.
  • the pulverized ores and fine coal are then separated using appropriate methods.
  • One of the most widely used methods of separation is froth flotation.
  • a pulverized ore (or fine coal) is mixed with water to form a slurry, to which surfactants known as collectors are added to render selected constituent(s) hydrophobic.
  • collectors for the case of processing higher-rank coals such as bituminous and anthracite coals, which are naturally hydrophobic as mined, no collectors may be necessary.
  • the concentrates are dewatered before they can be further processed or shipped to consumers, while the tailings (or refuse) are discarded with or without extensive dewatering.
  • the dewatering process consists of several steps. In the first step, a slurry is thickened to 35 to 75% solids in a large settling tank, while free water is removed from the top and recycled back to the plant. In the second step, the thickened pulp is subjected to a mechanical dewatering process, such as filtration or centrifugation, to further remove the water.
  • a mechanical dewatering process such as filtration or centrifugation
  • the moisture content in the dewatered product increases with decreasing particle size, which indicates that the residual moisture is mostly due to the surface water, i.e., the water molecules that are strongly adhering to the surface.
  • the filtered products contain typically 12 to 18% moisture by weight.
  • the residual moistures are higher (20 to 30% by weight) due to its low specific gravity.
  • thermal drying which may be an option for high-priced materials.
  • it is not so for low-priced commodities such as coal.
  • elimination of the third step has significant economic and environmental advantages.
  • coal producers are blessed in that the fines fractions constitute only 5 to 20% of their product streams. In countries where coals are more friable, the fines fractions can be in the 20 to 50% range. In this case, coal producers can no longer afford to discard the fines. It is unfortunate that there are no technologies available today, other than the costly thermal drying, to lower the moisture of coal fines.
  • a filter cake consists of a series of capillaries of different radii, from which water is removed during the process of vacuum or pressure filtration.
  • the water can be removed only when the pressure drop applied across the filter cake exceeds the pressure of the water present inside the capillaries.
  • the capillary wall is made of the surfaces of the particles in the cake, and the effective capillary radius decreases with decreasing particle size.
  • the contact angle is the most widely used measure of particle hydrophobicity (water-hating property).
  • the term contact angle used in the present invention refers to the water contact angle, which increases with increasing surface hydrophobicity.
  • the moisture of a filter cake should be determined by the amount of the water trapped in the capillaries smaller than the critical capillary radius.
  • Eq. [1] suggests three ways of achieving low cake moistures during filtration. These include i) surface tension lowering, ii) capillary radius enlargement, and iii) contact angle increase.
  • Various chemicals dewatering aids
  • One group of reagents is the surfactants that can lower the surface tension.
  • Most of the dewatering aids used for this purpose are ionic surfactants with high hydrophile-lipophile balance (HLB) numbers.
  • HLB hydrophile-lipophile balance
  • Sodium laurylsulfate and sodium dioctylsulfosuccinate, whose HLB numbers are 40 and 35.3, respectively, are typical examples. Sing ( Filtration and Separation, March, 1977, pp.
  • the U.S. Patent No. 5,346,630 teaches a method of pressure spraying a solution of a dewatering aid from a position within the filter cake forming zone of a filter just prior to the disappearance of the supernatant process water. This method, which is referred to as torpedo-spray system, ensures even distribution of the dewatering aid without becoming significantly diluted by the supernatant process water.
  • high HLB surfactants are also used as wetting agents for hydrophobic materials such as coal. Recognizing that dewatering is essentially a de-wetting process, it is difficult to see how one type of reagents can be used for both. It is well known that high HLB surfactants adsorb on hydrophobic non-wetting surfaces with inverse orientation, i.e., with hydrocarbon tails in contact with the surface and the polar heads pointing toward the aqueous phase. Thus, high HLB surfactants can lower the surface tension, but they can also dampen the hydrophobicity and decrease the contact angle. For this reason, the high HLB surfactants used as dewatering aids can actually cause an increase in moisture content. Furthermore, the reagents remaining in filtrate eventually return to the flotation circuit and cause adverse effects.
  • Various polymeric flocculants are used as dewatering aids.
  • the role of these reagents is to increase the effective size of the particles in the filter cake, so that the pore radii are enlarged. This will greatly reduce the capillary pressure and, hence, increase the filtration rate.
  • most of the flocculants used as dewatering aids are hydrophilic. Therefore, their adsorption dampens the hydrophobicity of the mineral or coal concentrates that are mildly hydrophobic by virtue of collector adsorption or by nature.
  • the particles form small capillaries within each floc created by organic flocculants. Therefore, the method of using polymeric flocculants for dewatering has limitations. It has been reported that flocculants are capable of reducing dewatering rate but not necessarily the final cake moisture ( Meenan, Proceedings of the Industrial Practice of Fine Coal Processing, Society of Mining Engineers, pp. 223-229,1988 ).
  • the U.S. Patent No. 5,670,056 teachers a method of using non-ionic (or neutral) low HLB surfactants and water-soluble polymers as hydrophobizing agents that can increase the contact angle above 65° and, thereby, facilitate dewatering processes.
  • Mono-unsaturated fatty esters, fatty esters whose HLB numbers are less than 10, and water-soluble polymethylhydrosiloxanes were used as hydrophobizing agents.
  • the fatty esters were used with or without using butanol as a carrier solvent for the low-HLB surfactants.
  • This invention disclosure lists a group of particulate materials that can be dewatered using these reagents.
  • the low HLB surfactants are the reaction products of one mole equivalent of a primary alcohol containing 6 to 13 carbons with 2 to 7 mole equivalents of methylene oxide.
  • the U.S. Patent No. 2,864,765 teaches a method of using another nonionic surfactant, a polyoxyethylene ether of a hexitol anhydride partial long chain fatty acid ester, functioning alone or as a solution in kerosene.
  • the disclosure does not mention that the nonionic surfactant increases the hydrophobicity of moderately hydrophobic particles.
  • the compounds disclosed are essentially not adsorbed upon the solid surface of the ore particles and remain in the filtrate, as noted in the U.S. Patent No. 4,156,649 . In the latter patent and also in the U.S. Patent No.
  • the U.S. Patent No. 5,048,199 disclosed a method of using a mixture of a non-ionic surfactant, a sulfosuccinate, and a defoaming agent.
  • the U.S. Patent No. 4,039,466 disclosed a method of using a combination of nonionic, surfactant having a polyoxyalkylene group and an anionic surfactant.
  • the U.S. Patent No. 5,215,669 teaches a method of using water-soluble mixed hydroxyether, which is supposed to work well on both hydrophobic (coal) and hydrophilic (sewage sludge) materials.
  • the U.S. Patent No. 5,167,831 teaches methods of using non-ionic surfactants with HLB numbers of 10 to 14.
  • This process is useful for dewatering Bayer process alumina trihydrate, which is hydrophilic.
  • the U.S. Patent No. 5,011,612 disclosed methods of using Cg to C 20 fatty acids, fatty acid precursors such as esters or amides, or a fatty acid blend. Again, these reagents are designed to dewater hydrophilic alumina trihydrate.
  • the U.S. Patent No. 4,206,063 teaches methods of using a polyethylene glycol ether of a linear glycol with its HLB number in the range of 10 to 15 and a linear primary alcohol ethoxylate containing 12 to 13 carbon atoms in the alkyl moiety. These reagents were used to dewater mineral concentrates in conjunction with hydrophobic alcohols containing 6 to 24 carbon atoms. The composition of this invention was preferably used in conjunction with polymeric flocculants. Similarly, the U.S. Patent No. 4,207,186 disclosed methods of using a hydrophobic alcohol and a non-ionic surfactant whose HLB number is in the range of 10 to 15.
  • 5,256,169 teaches a method to treat a slurry of fine coal with an emulsifiable oil in combination with an elastomeric polymer and an anionic and nonionic surfactant, dewatering the slurry and drying the filter cake, where the oil reduces the dissemination of fugitive dusts.
  • the U.S. Patent No. 5,405,554 teaches a method of dewatering municipal sludges, which are not hydrophobic, using water-in-oil emulsions stabilized by cationic polymers.
  • 5,379,902 disclosed a method of using heavy oils in conjunction with two different types of surfactants, floating the coal-emulsion mixture, dewatering the flotation product and drying them for reconstitution.
  • the U.S. Patent No. 4,969,928 also teaches a method of using heavy oils for dewatering and reconstitution.
  • the U.S. Patent No. 4,770,766 disclosed methods of increasing the hydrophobicity of oxidized and low-rank coals using additives during oil agglomeration.
  • the main objective this process is to improve the kinetics of agglomeration and ultimately the separation of hydrophilic mineral matter from coal.
  • the additives disclosed in this invention include a variety of heavy oils and vegetable oils, alcohols containing 6 or more carbon atom, long-chain fatty acids, etc. When these additives were used, the product moisture was lower than would otherwise be the case.
  • the process requires up 300 lb/ton of additives and uses 45 to 55% by volume of an agglomerant, which is selected from butane, hexane, pentane and heptane.
  • the U.S. Patent Nos. 5,458,786 disclosed a method of dewatering fine coal by displacing water from the surface with a large amount of liquid butane. The spent butane is recovered and recycled.
  • the U.S. Patent No. 5,587,786 teaches methods of using liquid butane and other hydrophobic liquids for dewatering other hydrophobic particles.
  • one obvious object of the present invention is the provision of novel methods of decreasing the moisture of fine particulate materials during mechanical methods of dewatering processes such as vacuum and pressure filtration and centrifugation.
  • Another important objective of the invention is the provision of improving the rate at which water is removed so that given dewatering equipment can process higher tonnages of particulate materials.
  • An additional objective of the present invention is the provision of novel fine particle dewatering methods that can reduce the moisture to a level that no thermal drying is necessary.
  • Still another object of the instant invention is the provision of a novel dewatering method that creates no adverse effects on up- and downstream processes when the water removed from the dewatering processes disclosed in the present invention is recycled.
  • the invention relates to a process according to claim 1.
  • the instant invention discloses methods of rendering the particulate materials suspended in water hydrophobic and/or enhancing the hydrophobicity of the materials, so that the process of removing the water by mechanical processes such as filtration and centrifugation are improved.
  • the improvements will result in lower product moisture and/or higher throughput.
  • the essence of the invention is to render the particles reasonably hydrophobic in the first place by suitable means and, then, add non-ionic low HLB surfactants to significantly enhance the hydrophobicity of the particulate materials, so that the pressures required to expel the moisture from smaller capillaries are reduced substantially. This will greatly increase the rate of dewatering and reduce the cake moisture.
  • the hydrophobicity enhancing reagents disclosed in the present invention have HLB numbers below 15, and are insoluble in water. Therefore, appropriate solvents such as light hydrocarbon oils and short-chain alcohols may be used in conjunction with the low-HLB surfactants.
  • the light hydrocarbon oils which should also be considered as HLB surfactants, may also act as hydrophobicity enhancing agents.
  • the packages of the reagents used in the instant invention are capable of lowering surface tension. Also, the particles coagulate owing to the increased hydrophobicity and, thereby, increase the capillary radius.
  • the reagent compositions disclosed in the present invention is capable of increasing contact angle, lowering surface tension, and enlarging capillary radius, all of which should contribute to decreasing capillary pressure and improving dewatering.
  • the instant invention also discloses reagent dosage by adding cations, and achieving substantial moisture reduction by spraying reagents to filter cake and applying mechanical vibration during drying cycle time.
  • the present invention discloses methods of destabilizing the surface water by rendering the particles substantially more hydrophobic than usually required for the flotation of minerals and coal using appropriate surfactants and combinations thereof.
  • dewatering can be represented as a process in which a solid/liquid interface, whose interfacial tension is ⁇ 12 , is displace by an air/water interface, whose interfacial tension is ⁇ 13 .
  • the process of flotation is also based on hydrophobizing mineral particles.
  • Appropriate collectors are used to render the surface hydrophobic so that air bubbles can displace the water that has become labile due to the hydrophobization from the surface and establish a three-phase contact.
  • ⁇ G ⁇ 12 - ⁇ 13 - ⁇ 23 ⁇ 0
  • collectors In flotation, various collectors are used to render selected mineral constituents hydrophobic.
  • the collectors adsorb on the surface with normal mode of orientation, i.e., with their polar heads in contact with the surface and their hydrocarbon tails pointing toward the aqueous phase.
  • the collector molecules effectively coat the surface with hydrocarbon tails (or hydrophobes) that are hydrophobic.
  • the hydrocarbon tails do not usually form a close-packed monolayer at the dosages normally employed in flotation practice. Even at high dosages, the hydrocarbon tails of collector molecules do not form close-packed monolayers. The reason is that the interaction between the polar heads and the surface are site specific and the number of reactive sites available on mineral surfaces are less than those required to form close-packed monolayers.
  • the number of negative charge sites available on mica surface is approximately one half of what is needed for dodecylammonium ions to form a close-packed monolayer.
  • collector molecules usually form monolayers of sparsely populated hydrocarbon tails, the spaces between them being filled with water molecules. In such cases, contact angles are usually well below 90°. Such moderate hydrophobicity may be sufficient for flotation but not for spontaneous dewatering.
  • various non-ionic surfactants are used to increase the contact angle close to or above 90°, so that the efficiency of dewatering fine particulate materials is greatly improved.
  • This is achieved by using various neutral (or nonionic) low HLB surfactants that may be useful for producing more complete monolayers.
  • Part of the surfactants may adsorb in between the sparsely populated hydrocarbon tails and thereby increase the hydrocarbon chain density on the surface, which is conducive to hydrophobicity enhancement.
  • Some of the surfactants may adsorb on top of the first monolayer of hydrophobes, which should also increase the hydrophobicity.
  • the low HLB surfactants disclosed in the instant invention may adsorb with their polar parts in contact with the surface, possibly via acid-base interactions. Such an adsorption mechanism will have the hydrocarbon tails point toward the aqueous phase, and thereby convert the less hydrophobic sites to more hydrophobic ones by covering the sites with hydrophobes.
  • the nonionic surfactants disclosed in the instant invention have HLB numbers below 15. These include fatty acids, fatty esthers, phosphate esters, hydrophobic polymers, ethers, glycol derivatives, sarcosine derivatives, silicon-based surfactants and polymers, sorbitan derivatives, sucrose and glucose esters and derivatives, lanolin-based derivatives, glycerol esters, ethoylated fatty esters, ethoxylated amines and amides, ethoxylated linear alcohols, ethoxylated tryglycerides, ethoylated vegetable oils, ethoxylated fatty acids, etc.
  • reagents are insoluble in water; therefore, they are normally used in appropriate solvents, which are light hydrocarbon oils and short-chain alcohols whose carbon atom numbers are less than eight.
  • the light hydrocarbon oils include diesel oil, kerosene, gasoline, petroleum distillate, turpentine, naphtanic oils, vegetable oils, etc.
  • the light hydrocarbon oils may also act as hydrophobicity enhancing reagents.
  • both the light hydrocarbon oils and short chain alcohols may act as added surfactants that can lower the surface tension of water. This is possible because the surface tensions of the solvents used in the instant invention are in the range of 20 to 30 mN/m.
  • the use of a low HLB surfactant in conjunction with a proper solvent addresses two of the three parameters that are important for improving dewatering, namely, contact angle increase and surface tension lowering. It seems that the dewatering in the instant invention also cause particles to coagulate by virtue of increased hydrophobicity. This phenomenon, known as hydrophobic coagulation, should increase the capillary radius and help dewatering.
  • hydrophobic coagulation causes the capillary radius to increase, which is beneficial for dewatering
  • metal ions are added to coagulate particles, which has been found to drastically reduce the amount of the surfactants required to achieve a desired moisture reduction.
  • Various metal ions can be used for this purpose.
  • the higher the valence of the cations the smaller the amount of the amount of the reagents needed to obtain beneficial effects.
  • the reagents can be added before, during or after the addition of the dewatering aids disclosed in the present invention.
  • contact angle is increased by using low HLB surfactants in conjunction with light hydrocarbon oils and short-chain alcohols.
  • the driving force for the adsorption mechanism is the hydrophobic attraction. Since the hydrophobic attraction exists only between two hydrophobic entities, it is necessary that the particles to be dewatered be rendered hydrophobic prior to or during the addition of the low HLB surfactants. For hydrophilic particles such as untreated silica and clay, they are hydrophobized by adsorbing appropriate surfactants on the surface. After the initial hydrophobization step, a low HLB surfactant can be added to further enhance the hydrophobicity for improved dewatering.
  • the surfactants that can be used for the initial hydrophobization step are usually high HLB surfactants whose polar head groups can interact with the surface via coulombic attraction, chemical bonding, electron-transfer, or acid-base interactions, while their non-polar tails are directed toward the aqueous phase. If a mineral concentrate from flotation processes is aged or oxidized during storage and transportation, it is necessary that the surface is re-hydrophobized using appropriate amount of collectors (or other high HLB surfactants) before adding the low HLB surfactants.
  • the instant invention also discloses a method of decreasing the final cake moisture by applying appropriate vibration to the filter cake. It is possible that the vibration improves the transportation of the water that has become labile by increasing the hydrophobicity of the particulate materials to be dewatered. This technique is particularly useful for lowering the moisture from thicker cakes.
  • the instant invention discloses still another method of decreasing cake moisture.
  • This technique involves spraying light hydrocarbon oils and short-chain alcohols on a filter cake, which is particularly useful for achieving low cake moisture with thick cakes. It is believed that these reagents decreases the surface tension of the residual water left in the filter cake. This technique is efficient in lowering the surface tension of the water that is most difficult to remove. Spraying low HLB surfactant on to a filter cake is also effective in achieving low cake moistures using very little incremental reagent consumption.
  • dewatering aids disclosed in the present invention An added benefit of using the dewatering aids disclosed in the present invention is that the kinetics of mechanical dewatering is substantially improved, which will greatly increase the throughput of dewatering devices. Furthermore, the dewatering aids of the present invention have the characteristics of anti-forming agents, which is very important for processing the particulate materials produced from flotation processes. Also, most of the reagents added as dewatering aids and blends thereof adsorb on the surface of the particulate materials, so that the water removed from the dewatering process can be recycled without creating problems at the upstream processes.
  • coal samples were used as received. Most of the tests were conducted, however, after re-flotation using standard flotation reagents such as kerosene and MIBC. When a sample became hydrophilic due to aging and superficial oxidation during transportation, it was wet-ground in a ball mill for a short period of time to remove the oxidation products and regenerate fresh, moderately hydrophobic surface. This procedure helped the low HLB surfactants work better, indicating that they do not adsorb on hydrophilic surfaces. In order to eliminate the problems concerning oxidation, many tests were conducted using coarse coal products from the dense-medium circuit. These samples were crushed, pulverized, wet-ground in a ball mill, and floated using kerosene and MIBC.
  • the flotation product was placed in a container and agitated continually. A known volume of the slurry was transferred to an Elenmeyer flask. A known amount of a dewatering aid was added to the flask before shaking it for 2 minutes. The conditioned slurry was then poured into a filter to initiate a filtration test. After a preset drying cycle time, the product was removed from the filter, dried in an oven for overnight, and then weighed to determine the cake moisture. During each test, cake formation time, which is the time it took for bulk of the water is drained, was recorded along with the cake thickness. For vacuum filtration, a 6.35cm (2.5-inch) diameter Buchner funnel with medium porosity glass frit was used.
  • sorbitan monooleate (Span 80), whose HLB number is 4.3, was used as a dewatering aid. Since the surfactant is insoluble in water, it was dissolved in a suitable solvent before use.
  • dewatering tests were conducted with the surfactant dissolved in five different solvents, which included diesel oil, kerosene, fuel oil, gasoline, and butanol. Each test was conducted using one part by volume of the active ingredient dissolved in two parts of a solvent.
  • a 6.35 cm (2.5-inch) diameter Buchner funnel with medium porosity glass frit was used at 6.35mm (2.5-inch) Hg vacuum pressure with 2 minute drying cycle time and 1.143cm (0.45-inch) cake thickness.
  • the tests were conducted on a Pittsburgh coal sample. It was a dense-medium clean coal product, which was crushed, ground, and screened to obtain a 0.5 mm x 0 fraction.
  • the fine coal sample prepared as such was floated using a laboratory flotation machine using 0.5 kg/t (1 lb/ton) of kerosene as collector and 82.7 g/t (75 g/ton) of MIBC as frother.
  • the flotation product was used as a feed to filtration tests.
  • Table 1 shows the results of the fiitration experiments. Diesel oil and kerosene gave the best results. In general, mineral oils gave considerably better results than butanol, which was used as a solvent for mono-unsaturated fatty esters whose HLB numbers are less than 10 in the U.S. Patent No. 5,670,056 . At 1.5 (3) to 2.5 kg/t (5 lb/ton) sorbitan monooleate, the moisture reductions where nearly 50%. Such results are far superior to what can be achieved using conventional dewatering aids that are designed to control surface tension.
  • Sorbitan monooleate was used as a dewatering aid in the filtration of coal sample using diesel oil as a solvent.
  • One part of the surfactant by volume was dissolved in two parts of the solvent before use.
  • the coal sample used in this example was a 0.6 mm x 0 flotation product from Blackwater coal preparation plant, Australia, which was received in the form of slurry. It was found, however, that the sample was considerably oxidized during transportation.
  • the coal sample was wet-ground in a ball mill for 1.5 minutes, and re-floated using 0.5 kg/t (1 lb/ton) kerosene and 82.7 g/t (75g/ton) MIBC.
  • the process of regenerating fresh surface and re-floating the pulverized coal rendered the coal surface moderately hydrophobic, which appeared to be a prerequisite for the dewatering aids disclosed in the present invention to work more effectively.
  • the pressure filtration tests were conducted at different reagent additions, cake thicknesses, and air pressures. In each test, 2 minutes of conditioning time and 2 minutes of drying cycle time were employed. The results are given in Table 2.
  • the reagent dosages given in this table refer to the active ingredient only. In general, the moisture reduction improves with increasing reagent dosage, decreasing cake thickness, and increasing air pressure. At 200 kPa of air pressure, the cake moisture was reduced by nearly 50% at 2.16 cm (0.85 inches) of cake thickness and 2.5 kg/t (5lb/ton) sorbitan monooleate.
  • Sorbitan monooleate was also tested as a dewatering aid for zinc (sphalerite) concentrate.
  • the sample (0.105 mm x 0) was a flotation product, which was oxidized, however, during transportation.
  • the sample was wet-ground in a ball mill for 1.5 minutes and re-floated using 55.1 g/t (50 g/ton) sodium isopropyl of xanthate (NaIPX) and 55.1 g/t (50 g/ton) MIBC.
  • the flotation product was subjected to pressure filtration tests using a 6.35 cm (2.5-inch) diameter filter at 100 kPa of air pressure and 2 minutes of drying cycle time.
  • the cake thickness was varied by changing the volume of the slurry, used in the filtration tests.
  • the results are given in Table 3.
  • the %moisture reductions were 64.1, 54.8, and 52.8% at 0.508 (0.2), 0.762 (0.3) and 1.524 cm (0.6 inches) of cake thicknesses, respectively, at 1.5 kg/t (3 lb/ton) sorbitan monooleate. Moisture reduction did not further increase significantly at 2.5 kg/t (5 lb/ton).
  • Ethyl oleate is another low HLB number surfactant, which was tested as a dewatering aid in the present invention. This reagent was also used as a dewatering aid in the U.S. Patent No. 5,670,056 , in which butanol was used as a carrier solvent.
  • ethyl oleate was tested for the vacuum filtration of a 0.5 mm x 0 Pittsburgh coal using mineral oils as solvents. The method of preparing the coal sample and the procedures employed for the filtration experiments were the same as described in Example 1. The results obtained with four different mineral oils are given in Table 4 and are compared with those obtained using butanol as a solvent. As shown, mineral oils produced considerably better results than butanol.
  • Ethyl oleate was used as a dewatering aid for the vacuum filtration of a bituminous coal sample from Elkview Mine, British Columbia, Canada.
  • the sample was a 0.21 mm x 0 flotation product, which was received as a slurry. It was oxidized during transportation; therefore, the sample was wet-ground in a ball mill for 15 minutes and re-floated using 0.5 kg/t (1 lb/ton) kerosene and 82.7 g/t (75 g/ton) MIBC before filtration.
  • a 6.35 cm (2.5-inch) diameter Buchner funnel was used at a vacuum pressure of 635 mm (25 inches) Hg and 2 min drying cycle time.
  • Ethyl oleate was tested as dewatering aid for a lead concentrate (0.074 mm x 0) received from a flotation plant in Europe.
  • One part by volume of the surfactant was dissolved in 2 parts of diesel oil before use.
  • the sample which was received as thickened slurry, was oxidized during transportation. To generate fresh, hydrophobic surface, the sample was wet-ground for 1.5 minutes and re-floated using 55.1 g/t (50 g/ton) NaIPX and 55.1 g/t (50 g/ton) MIBC before filtration.
  • a 6.35 cm (2.5-inch) diameter Buchner funnel was used for filtration at a vacuum pressure of 63.5 cm (25-inch) Hg and at a drying cycle time of 2 minutes.
  • Sorbitan monooleate with 20 polyoxyethlene (POE) groups is a nonionic surfactant with its HLB number at 15, which is higher than those of other non-ionic surfactants disclosed in the present invention. Nevertheless, the reagent was not completely soluble in diesel. Therefore, one part by volume of the surfactant was mixed with two parts of diesel oil and one part of butanol before use. The nonionic surfactant dissolved in the mixed solvent was used as a dewatering aid for a bituminous coal (0.84 mm x 0) from Massey Coal Company, West Virginia, using a 6.35 cm (2.5-inch) diameter pressure filter.
  • the coal sample was a spiral product, which was wet-ground in a ball mill and floated using 0.5 kg/t (1 lb/ton) kerosene and 110.2 g/t (100 g/ton) MIBC.
  • the filtration experiments were conducted at 200 kPa air pressure by varying reagent addition and cake thickness at 2 min drying cycle time. The best results were obtained at 0.5 (1) and 1 kg/t (2 lb/ton). At 1 kg/t (2 lb/ton) Tween 80 and 2.032 cm (0.8 inches) cake thickness, the moisture reduction was 54.9%. At smaller cake thicknesses, higher levels of moisture reductions were achieved.
  • the moisture reduction deteriorates at higher reagent dosages, which may be due to the inverse orientation of the surfactant molecules with their polar heads (BO groups) pointing toward the aqueous phase.
  • Such orientation should make the surface less hydrophobic, which is detrimental to dewatering.
  • the inverse orientation is possible with a nonionic surfactant with a relatively high HLB number, particularly with EO groups.
  • Phosphate esters constitute an important group of low HLB surfactants. They can also be used as dewatering aids for coal and other mineral concentrates that are moderately hydrophobic. Table 9 shows the results obtained using tridecyldihydrogen phosphate (TDDP) (a phosphoric acid mono-tridecyl ester) as a dewatering aid in the vacuum filtration of a Pittsburgh coal (0.5 mm x 0) sample.
  • TDDP tridecyldihydrogen phosphate
  • Various mineral oils and butanol were used as solvents for the low HLB surfactant. Mineral oils, particularly diesel oil and kerosene, gave better results than butanol. With diesel oil, the moisture reduction was 50%.
  • the sample preparation and the experimental procedures employed were the same as described in Example 1.
  • the reagent addition caused an increase in contact angle and a decrease in surface tension, both of which are conducive to improved dewatering. It is interesting that contact angle increased from 12° to 90° at 1.5 kg/t (3 lb/ton). Thermodynamically, water should recede spontaneously from a solid surface when its contact angle exceeds 90°. The fact that water is still left in the cake at such high contact angle may be a reflection of the slow kinetics of transporting the water 'liberated' from the surface through filter cake.
  • the primary role of the low HLB surfactants is to help liberate the water molecules adhering on the surface of coal by further increasing its hydrophobicity. Both the nonionic surfactant and the solvent may have contributed to the surface tension lowering.
  • One part by volume of the reagent was dissolved in two parts of diesel oil before use.
  • the tests were conducted using a 6.35 cm (2.5-inch) diameter pressure filter at 200 kPa air pressure and 2 min drying cycle time.
  • the coal sample was a flotation product (0.21 mm x 0) received as a slurry.
  • the sample was re-floated using 0.5 kg/t (1 lb/ton) kerosene and 82.7 g/t (75 g/ton) MIBC as a means of regenerating fresh, hydrophobic surfaces.
  • ionic surfactants are used as dewatering aids for fine coal dewatering. Brooks and Bethel (1984) used cationic surfactants (amines) to obtain significant improvements in fine coal dewatering. It would, therefore, be of interest to compare the performance of the low HLB surfactants used in the present invention with those obtained using amines.
  • Table 12 compares the results of the vacuum filtration tests conducted on a bituminous coal from the Middle Fork coal preparation plant, Virginia, using two different cationic surfactants (diaminecyclohexane and dodecylammonium chloride) of high HLB numbers and two different low HLB No. nonionic surfactants (sorbitan monooleate and TDDP).
  • the coal sample was a dense-medium product, which was crushed and ground to obtain a 0.6 mm x 0 fraction. All tests were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel at 6.35 mm (25-inches) Hg vacuum pressure, 2 min drying time, and 1.143 cm (0.45-inches) cake thickness.
  • Table 12 show that the low HLB surfactants used in the manner disclosed in the present invention are substantially more efficient than the high HLB surfactants.
  • Example 10 it is one thing to liberate the water molecules from the surface of the particles to be dewatered using low-HLB surfactants, but it is another to transport the liberated water droplets through a filter cake. The latter problem becomes more serious with thicker cakes.
  • One way to minimize the second problem is to apply vibration during filtration. Therefore, a bituminous coal (0.6 mm x 0) from Massey Coal Company was subjected to a series of vacuum filtration experiments, in which a 6.35 cm (2.5-inch) Buchner funnel was vibrated during the 5 min drying cycle time. The feed to the filtration tests was prepared in the same manner as described in Example 8. The vibration was created by placing an ultrasonic probe at the bottom part of the funnel.
  • Varying amounts of sorbitan monooleate were used as dewatering aid at 0.635 (0.25) and 1.27 cm (0.5 inches) of cake thicknesses.
  • One part by volume of the surfactant was dissolved in two parts of diesel oil before use.
  • the results, given in Table 13, show that very low levels of cake moisture can be achieved by combining the methods of using low HLB surfactants and mechanical vibration.
  • Table 14 shows the results obtained by spraying approximately 1 kg/t (2 lb/ton) of butanol, ethanol, and diesel oil at the beginning of 2 min drying cycle time.
  • the surface tensions of n-butanol and ethanol are 20.6 and 22.77 mN/m, respectively, at 20°C.
  • the surface tension of diesel oil should also be low, as most other hydrocarbon liquids are. Therefore, spraying these reagents should lower the surface tension of the water left in filter cake and help reduce the moisture.
  • the filtration experiments were conducted on a 0.6 mm x 0 bituminous coal sample from Middle Fork, Virginia, at 1.143 cm (0.45 inch) cake thickness.
  • the fine coal was floated using 0.5 kg/t (1 lb/ton kerosene) and 110.2 g/t (100 g/ton) MIBC to obtain a feed to the filtration experiments.
  • the tests were conducted at varying amounts of TDDP and 5 minutes of drying cycle time. It can be seen that the combined use of i) low HLB surfactant in diesel oil, ii) butanol spray, and iii) mechanical vibration achieved very low moistures at an industrial cake thickness of 3.048 cm (1.2 inches).
  • Table 16 shows the results of a series of vacuum filtration tests conducted using TDDP in the presence of aluminum chloride, chromium chloride, and copper nitrate. Before filtration, each coal sample (0.2 mm x 0 flotation product) was conditioned with a known amount of electrolyte for 5 minutes. A known amount of TDDP dissolved in diesel oil (in 1:2 volume ratio) was then added and conditioned for another 2 minutes.
  • the conditioned coal slurry was poured into a 63.5 cm (2.5-inch) diameter Buchner funnel for filtration experiments at 63.5 cm (25-inch) vacuum pressure, 2 min drying cycle time, and 1.016 cm (0.4 inch) cake thickness.
  • the coal sample was received from Massey Coal Company, West Virginia.
  • the objective of this example is to demonstrate that combination of several different methods disclosed in this invention can be used to achieve high levels of moisture reduction at a cake thickness of approximately 2.54 cm (1 inch).
  • a series of vacuum filtration experiments were conducted using different combinations of i) a low HLB surfactant (sorbitan monooleate) mixed with an appropriate carrier solvent, ii) an electrolyte 11.02 g/t (10 g/ton) aluminum chloride), iii) spray of a surface tension lowering reagent (1.0-1.5 kg/t (2-3 lb/ton) butanol), and/or iv) mechanical vibration.
  • the tests were conducted on a flotation product (0.6 mm x 0) using a specially designed Buchner funnel that can handle large volumes of coal slurry, as described in Example 15.
  • the coal sample was a dense-medium product from the Middle Fork coal preparation plant. It was crushed, ground, and floated using 0.5 kg/t (1 lb/ton) kerosene and 110.2 g/t (100 g/ton) MBIC. results, given in Table 17, show that almost any level of cake moisture can be achieved at an industrial cake thickness by combining the various methods disclosed in the present invention.
  • 14.2% cake moisture can be achieved using only 0.125 kg/t (0.25 lb/ton) sorbitan monooleate, 11.02 g/t (10 g/ton) aluminum chloride, 1.0 to 1.5 kg/t (2 to 3 lb/ton) butanol, and mechanical vibration.
  • Example 7 It has been shown in Example 7 that the use of PMCH dissolved in a suitable solvent such as diesel oil gives superior results as compared to the case of using it directly. It will be shown that the use of PMCH in vegetable oils further improves its performance.
  • a series of filtration tests were conducted on a bituminous coal from Massey coal company, West Virginia, using a 6.35 cm (2.5-inch) pressure filter at 100 kPa of air pressure.
  • the coal sample was a flotation product (0.5 mm x 0) obtained directly from an operating plant. It contained considerable amount of clay and other ash-forming minerals that have not been completely removed. Also, the sample was oxidized to some extent.
  • the tests were conducted at a 1.27 cm (0.5-inch) cake thickness and a 2 min drying cycle time using: i) soybean oil dissolved in diesel oil in 1:2 volume ratio, ii) PMCH dissolved in diesel oil in the same manner, and iii) PMCH dissolved in soybean oil and diesel oil.
  • the molecular weight of the PMCH used in this example was 2,900.
  • the results given in Table 18 show that the combined use (Case iii) exhibited a synergistic effect in that the results are superior to the Case i or ii.
  • the role of PMCH is a hydrophobizing agent that can reduce the capillary pressure and facilitate the process of dewatering. It is possible that the triacylglycerols present in the vegetable oil may act as additional hydrophobizing agents.
  • the first series of tests were conducted using various amounts of sorbitan monooleate (Span 80) dissolved in diesel oil. These reagents were used as a 1:2 mixture by volume. In the absence any dewatering aid, the cake moisture was 26.1% and the cake formation time was 158 seconds. At 1 kg/t (2 lb/ton) Span 80, the moisture was reduced to 20.9% and the cake formation time increased to 179 seconds. The moisture reduction is not as good as those obtained in other examples with hydrophobic particles. Probably, the relatively small moisture reduction is due to the surface tension lowering. The next series of tests were conducted on the silica sample floated using 220.5 g/t (200 g/ton) of dodecylammonium hydrochloride as collector at pH.9.5.
  • the hydrophobization by the collector coating reduced the cake moisture from 26.1 to 18.9% and the cake formation time from 158 seconds to 27 seconds.
  • the low HLB surfactant was added to the flotation product, the moisture was further reduced.
  • the cake moisture was reduced to 8.4% and the cake formation time to 18 seconds.
  • the improved dewatering brought about by the low HLB surfactants is most likely due to the hydrophobicity enhancement.
  • the pH was adjusted to 9.3 using lime.
  • the flotation product was subjected to vacuum filtration tests using a 6.35 cm (2.5-inch) diameter Buchner funnel at 63.5 cm (25 inches) Hg, 0.914 cm (0.36 inches) cake thickness and 3 min drying cycle time. As shown in Table 20, the cake moisture was 50.4% and the cake formation time was 39.4 minutes, when no dewatering aid was used. At 3.5 kg/t (7 lb/ton) sorbitan monooleate (Span 80), the moisture content was reduced to 28.6%, and the cake formation time was reduced to 18.4 minutes.

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Claims (18)

  1. Verfahren zur Entwässerung einer Aufschlämmung von feinem teilchenförmigen Material, das im Durchmesser kleiner als 2 mm ist, wobei das Verfahren die Schritte umfasst:
    i) moderates Hydrophobieren des feinen teilchenförmigen Materials durch Verwendung geeigneter oberflächenaktiver Substanzen und Sammler, so dass der Wasserkontaktwinkel des Materials auf einen Wert von erheblich unterhalb 90° erhöht wird, in einem anfänglichen Hydrophobierungsschritt,
    ii) Hinzufügen einer nichtionischen oberflächenaktiven Substanz mit einem Hydrophilie-Lipophilie-Gleichgewicht (HLB-Wert) von weniger als 15, die in einem geeigneten Lösungsmittel oder einer Mischung von Lösungsmitteln gelöst ist,
    iii) Rühren der Aufschlämmung, um die oberflächenaktiven Moleküle an die Oberfläche des moderat hydrophoben Materials adsorbieren zu lassen, so dass seine Hydrophobie erhöht wird und sein Berührungswinkel auf nahezu oder oberhalb von 90° vergrößert wird, und dann
    iv) Unterziehen der konditionierten Aufschlämmung, die das teilchenförmige Material, dessen Wasserberührungswinkel vergrößert worden ist, enthält, einem geeigneten mechanischen Verfahren zur Entwässerung.
  2. Verfahren nach Anspruch 1, wobei das feine teilchenförmige Material, das zu entwässern ist, ein Material ist, dessen Oberfläche aufgrund von Alterung oder Oberflächlichenoxidation weniger hydrophob geworden ist.
  3. Verfahren nach Anspruch 1, wobei das feine teilchenförmige Material Mineralien, Kohle, Kunststoffe, Metalle, Metallpulver, Flugasche und biologische Stoffe umfasst.
  4. Verfahren nach einem der vorstehenden Ansprüche, wobei dieses geeignete mechanische Verfahren zur Entwässerung Vakuumfiltration, Druckfiltration, Zentrifugalfiltration und Zentrifugation umfasst.
  5. Verfahren nach einem der vorstehenden Ansprüche, wobei die nichtionische oberflächenaktive Substanz ausgewählt ist aus Fettsäuren, Fettsäureestern, Phosphatestern, hydrohoben Polymeren, Ethern, Glykolderivaten, Sarcosinderivaten, oberflächenaktiven Substanzen und Polymeren auf Siliciumbasis, Sorbitanderivaten, Sucrose und Glukoseestern und -derivaten, Derivaten auf Lanolinbasis, Glycerinestern, ethoxylierten Fettsäureestern, ethoxylierten Aminen und Amiden, ethoxylierten linearen Alkoholen, ethoxylierten Triclyceriden, ethoxylierten Pflanzenölen und ethoxylierten Fettsäuren.
  6. Verfahren nach Anspruch 5, wobei die nichtionische oberflächenaktive Substanz mit einem Pflanzen-, Fisch- oder Tieröl vermischt wird, das Triacylglycerine enthält, um synergistische Verbesserung bei der Entwässerung des feinen teilchenförmigen Materials zu erzielen.
  7. Verfahren nach einem der vorstehenden Ansprüche, wobei dieses geeignete Lösungsmittel leichte Kohlenwasserstofföle und kurzkettige Alkohole umfasst.
  8. Verfahren nach Anspruch 1, wobei diese geeigneten oberflächenaktiven Substanzen oberflächenaktive Substanzen mit hohem HLB-Wert sind, deren polare Köpfe mit der Oberfläche der teilchenförmigen Materialen wechselwirken können.
  9. Verfahren nach Anspruch 1, wobei diese Sammler Thiole für Sulfidminerale und Metalle sind.
  10. Verfahren nach Anspruch 1, wobei diese Sammler Kohlenwasserstofföle sind und das teilchenförmige Material Kohle oder eine andere natürlich hydrophobe Substanz ist.
  11. Verfahren nach einem der vorstehenden Ansprüche, wobei ein Elektrolyt oder eine Mischung von Elektrolyten, ausgewählt aus Salzen von monovalenten, divalenten und trivalenten Kationen und Anionen, nach dem anfänglichen Hydrophobierungsschritt (i) und vor Schritt (ii) zugegeben wird.
  12. Verfahren nach Anspruch 11, wobei diese Elektrolyte die Salze von Aluminiumionen sind.
  13. Verfahren nach Anspruch 11 oder 12, wobei die Reagenzien, die in Schritt (i) und Schritt (ii) verwendet werden, und dieser Elektrolyt oder diese Mischung von Elektrolyten in einem einzigen Schritt zugegeben werden können.
  14. Verfahren nach einem der Ansprüche 1 bis 10, wobei das geeignete mechanische Verfahren zur Entwässerung ein Filtrationsprozess ist, in welchem der Filterkuchen geeigneten vibrierenden Mitteln ausgesetzt wird, so dass ein höherer Grad an Feuchtigkeitsreduzierung bei einer gegebenen Kuchendicke erreicht wird.
  15. Verfahren nach Anspruch 14, wobei die geeigneten vibrierenden Mittel Ultraschall-, mechanische und akustische Mittel umfassen.
  16. Verfahren nach einem der Ansprüche 1 bis 10, wobei das geeignete mechanische Verfahren zur Entwässerung ein Filtrationsprozess ist, in welchem ein geeignetes Reagenz zur Verringerung der Oberflächenspannung zu dem Filterkuchen in Form von feinem Nebel oder Spray gegeben wird, so dass ein höherer Grad an Feuchtigkeitsreduktion bei einer gegebenen Kuchendicke erreicht wird.
  17. Verfahren nach Anspruch 16, wobei das geeignete Mittel zur Verringerung der Oberflächenspannung aus kurzkettigen Alkoholen, leichten Kohlenwasserstoffölen und oberflächenaktiven Substanzen ausgewählt ist.
  18. Verfahren nach einem der Ansprüche 11 bis 13, wobei das geeignete mechanische Verfahren zur Entwässerung ein Filtrationsprozess ist, in welchem ein geeignetes Reagenz zur Verringerung der Oberflächenspannung zu dem Filterkuchen in Form von feinem Nebel oder Spray gegeben wird und gleichzeitig der Filterkuchen geeigneten vibrierenden Mitteln ausgesetzt wird, so dass eine wesentliche Feuchtigkeitsreduktion bei hohen Kuchendicken unter Verwendung minimaler Mengen von Reagenzien erreicht wird.
EP00967227A 2000-09-28 2000-09-28 Verfahren zur verbesserung der entwässerung feiner teilchen Expired - Lifetime EP1333905B1 (de)

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US4561953A (en) * 1983-06-16 1985-12-31 Battelle Memorial Institute Solid-liquid separation process for fine particle suspensions by an electric and ultrasonic field
US5814210A (en) * 1988-01-27 1998-09-29 Virginia Tech Intellectual Properties, Inc. Apparatus and process for the separation of hydrophobic and hydrophilic particles using microbubble column flotation together with a process and apparatus for generation of microbubbles
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