Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
  • F26B5/005—Drying solid materials or objects by processes not involving the application of heat by dipping them into or mixing them with a chemical liquid, e.g. organic; chemical, e.g. organic, dewatering aids
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B2200/00—Drying processes and machines for solid materials characterised by the specific requirements of the drying good
  • F26B2200/18—Sludges, e.g. sewage, waste, industrial processes, cooling towers

Definitions

• Dewatering can be achieved by either mechanical methods (e.g., filtration and centrifugation) or thermal drying. In general, the former is cheaper than the latter. However, mechanical dewatering becomes inefficient with finer particles. Dewatered products contain high moistures, often requiring thermal drying to meet specifications.
• ⁇ ⁇ p 2 ⁇ ⁇ cos ⁇ r , in which ⁇ p is the pressure of the water inside a capillary (formed between the particles present in a filter cake), r is the capillary radius, ⁇ is the surface tension of water, and ⁇ is the contact angle of the particles in the cake.
• the contact angle is a measure of the hydrophobicity (water-hating property) of the particles.
• Eq. [1] shows that the pressure required to blow the water out of a capillary increases with decreasing capillary radius. Considering that finer particles form smaller capillaries, one can see the difficulty in dewatering fine particles.
• Eq. [1] suggests also that capillary pressure should decrease with decreasing surface tension and increasing contact angle.
• Various surfactants are used to decrease the surface tension.
• Most of the dewatering aids used for this purpose is ionic surfactants with high hydrophile-lipophile balance (HLB) numbers.
• HLB hydrophile-lipophile balance
• Singh Filtration and Separation, March, 1977, pp. 159-163 ) suggested that the former is an ideal dewatering aid for coal because it does not adsorb on the surface, which in turn allows for the reagents to be fully utilized in lowering surface tension.
• 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 can actually cause an increase in moisture in dewatering hydrophobic materials such as coal. Due to the high polarity of its head group, high HLB surfactants adsorb on hydrophobic surfaces with inverse orientation, i.e., with hydrocarbon tails in contact with the surface and the polar heads pointing toward the aqueous phase. Such an adsorption mechanism should decrease the hydrophobicity and, hence, cause an increase in cake moisture. Most of the flocculants used as dewatering aids also dampen the hydrophobicity, and cause an increase in moisture.
• the U.S. Patent No. 5,670,056 teaches a method of using non-ionic low HLB surfactants and polymers as hydrophobizing agents that can increase the contact angle above 65° and, thereby, reduce the cake moisture.
• Monounsaturated 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 tat can be dewatered using these reagents.
• the U.S. Patent No. 2,864,765 teaches a method of using a polyoxyethylene other 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 .
• methods of using linear or branched alkylethoxylated alcohols as dewatering aids were disclosed.
• the U.S. Patent No. 5,048,199 disclosed a method of using a mixture of a non-ionic surfactant, a sulfosuccinate, and a deforming 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 C 8 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 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.
• the U.S. Patent No. 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 of 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 to 150 kg/t (300 lb/ton) of additives and uses very large amounts (45 to 55% by volume of a coal to be cleaned) 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 very 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.
• 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 so low that no thermal drying is necessary.
• Yet another object of the invention is the provision of methods of controlling the frothing properties of the flotation product.
• the particles are hydrophobized in two steps. Initially, surfactants, preferably of high hydrophile-liphophile balance (HLB) numbers, or collectors are used to render a particulate material moderately hydrophobic.
• HLB hydrophile-liphophile balance
• collectors preferably of high hydrophile-liphophile balance (HLB) numbers, or collectors are used to render a particulate material moderately hydrophobic.
• the material is subsequently treated with a lipid, which is a naturally occurring hydrophobic substance, to further enhance its hydrophobicity close to or above the water contact angle of 90°. This will greatly weaken the bonds between the water molecules and the surface of the particulate material and, thereby, 'liberate' the surface water.
• the liberated surface water is then removed from
• hydrophobicity enhancement step The key to the methods of dewatering described in the present invention disclosure is the hydrophobicity enhancement step.
• a relatively small increment in hydrophobicity (above the level that can normally be achieved using a high HLB surfactant in the first hydrophobization step) can bring about a large decrease in capillary pressure and, hence, a large decrease in surface moisture.
• lipids used in the second hydrophobization step of the instant invention are insoluble in water; therefore, they are used as solutions in appropriate solvents, which include but not limited to light hydrocarbon oils and short-chain alcohols.
• appropriate solvents include but not limited to light hydrocarbon oils and short-chain alcohols.
• lipid molecules may act as nonionic surfactants that can greatly enhance the hydrophobicity of the particulate material to be dewatered. Since lipids are naturally occurring reagents, their use offers a low cost means of improving mechanical dewatering processes.
• the dewatering methods disclosed in the instant invention are capable of not only reducing the final cake moistures but also of increasing the kinetics of dewatering substantially. By virtue of the latter, the instant invention can greatly increase the throughput of a dewatering device. 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 surfaces of minerals and coal so that the plant water does not contain significant amounts of residual reagents.
• the difficulty in removing water from the surface of fine particles may be attributed to the fact that water molecules are held strongly to the surface via hydrogen bonding. It is possible to break the bonds and remove the water by subjecting the wet particles to intense heat, highpressure filters and high-G centrifuges. However, the use of such brute forces entails high energy costs and maintenance problems. A better solution would be to destabilize the surface water by appropriate chemical means, so that it can be more readily removed by using mechanical dewatering devices with minimum energy and maintenance requirements.
• the state of the water adhering to a surface may be best represented by the hydrophobicity (water-hating property).
• a more traditional measure of surface hydrophobicity is water contact angle. In the cessile drop technique, contact angles are measured by placing droplets of water on the surface of the solids of interest. The contact angle, which is measured through the aqueous phase, increases with increasing hydrophobicity.
• the particulate materials in a slurry are hydrophobized in two steps.
• an appropriate surfactant or collector is added to the slurry, so that it can adsorb on the surface of the particles and render them moderately hydrophobic.
• hydrophilic particles such as silica and clay
• ionic surfactants of high HLB numbers may be used for the initial hydrophobization.
• short-chain thiols may be used. These reagents adsorb on the surface with their polar heads in contact with the surface and their hydrocarbon tails directed toward the aqueous phase.
• hydrocarbon oils and short-chain alcohols may be used to enhance the hydrophobicity.
• a lipid dissolved in an appropriate solvent or a mixture of solvents is added to the slurry to further increase the hydrophobicity of the particulate materials, so that the surface water can be removed more readily by mechanical dewatering processes of low energy consumption.
• the contact angle of the particulate material to be dewatered is increased to the range of 25° to 60°. It is difficult, but not impossible, to obtain contact angles above this range using a high HLB surfactant alone.
• High HLB surfactants and thiols adsorb only on specific surface sites. The population of the surface sites, at which the adsorption can occur, is usually well below what is needed to form a close-packed monolayer of the adsorbed surfactant molecules.
• the reagents added in the second hydrophobization step i.e., the lipids dissolved in appropriate solvents, may adsorb in between the sparsely populated hydrocarbon tails of the high HLB surfactants and thiols, so that the surface is more fully covered by a close-packed monolayer of hydrophobes. This will increase the contact angle over 60° and more desirably close to or over 90°, so that water can be readily removed from the capillaries formed between finer particles.
• Lipids are naturally occurring organic molecules that can be isolated from plant and animal cells (and tissues) by extraction with nonpolar organic solvents. Large parts of the molecules are hydrocarbons (or hydrophobes); therefore, they are insoluble in water but soluble in organic solvents such as ether, chloroform, benzene, or an alkane. Thus, the definition of lipids is based on the physical property (i.e., hydrophobicity and solubility) rather than by structure or chemical composition. Lipids include a wide variety of molecules of different structures, i.e., triacylglycerols, steroids, waxes, phospholipids, sphingolipids, terpenes, and carboxylic acids.
• the hydrolysis products of olive oil consist of 80% oleic acid. Waxes can also be hydrolyzed, while steroids cannot.
• Vegetable fats and oils are usually produced by expression and solvent extraction or a combination of the two. Pentane is widely used for solvent, and is capable of extracting 98% of soybean oil.
• Some of the impurities present in crude oil, such as free fatty acids and phospholipids, are removed from crude vegetable oils by alkali refining and precipitation. Animal oils are produced usually by rendering fats.
• the lipids may act as natural surfactants that can enhance the hydrophobicity of the particles to be dewatered.
• Each triacylglycerol for example, consists of one head group, i.e., glycerol, and three hydrocarbon tails.
• hydroxyl groups may act as polar head, while the ester linkages serve as the head groups with waxes.
• They may act effectively as nonionic surfactants of low hydrophile-lipophile balance (HLB) numbers.
• HLB numbers of soybean oil and corn oil are 6 and 8, respectively, while that of castor oil is 14. They may adsorb in between or on top of the hydrocarbon chains of the surfactants and thiols that are present on the surface of fine particles as a result of the first hydrophobization step and, thereby, enhance the hydrophobicity.
• the lipids have low HLB numbers, they are used as solutions of appropriate solvents including but not limited to short-chain alcohols and light hydrocarbon oils.
• appropriate solvents including but not limited to short-chain alcohols and light hydrocarbon oils.
• one part by volume of a lipid which may be termed as active ingredient(s) is dissolved in two parts of a solvent before use. The two may be mixed in different ratios. As an example, three parts of an active ingredient may be mixed with one part of a solvent. In another, one part of an active ingredient may be mixed with 20 parts of a solvent.
• selected mineral (or coal) constituents of an ore (or coal) are selectively hydrophobized using appropriate reagents (e.g., high HLB surfactants, thiols, light hydrocarbon oils and short-chain alcohols) and floated away from hydrophilic mineral constituents as a means of separation and upgrading.
• appropriate reagents e.g., high HLB surfactants, thiols, light hydrocarbon oils and short-chain alcohols
• the particulate material to be dewatered must be moderately hydrophobic for the second hydrophobization step disclosed in the instant invention to work. Otherwise, the hydrophobic lipids disclosed cannot adsorb on the surface via hydrophobic attraction and enhance its hydrophobicity.
• the naturally hydrophobic materials or mineral concentrates become considerably less hydrophobic by the time they reach the dewatering step due to superficial oxidation, aging, or exposure to plant water containing hydrophilic polymers.
• they may be re-hydrophobized using the high HLB surfactants and other reagents noted above before adding the reagents identified in the instant invention for the second hydrophobization step.
• the second hydrophobization step is essential to reduce the cake moisture beyond the levels usually achieved using the currently available dewatering aids and methods.
• the use of lipids in the second hydrophobization step provides a low-cost means of increasing the contact angle close to or above 90°.
• parts of the surface must be more hydrophobic than the rest.
• a lipid as dewatering aid, most of the molecules may adsorb on the more hydrophobic parts of the surface, thereby increasing the packing density of hydrophobes on the surface and further increasing its hydrophobicity.
• the driving force for the adsorption mechanism may be one of hydrophobic attraction.
• some of the lipid molecules may adsorb on less hydrophobic parts of the surface, with the oxygens in the head groups in contact with the less hydrophobic parts of the surface, possibly via acid-base interactions, while the hydrocarbon tails are pointed toward the aqueous phase.
• the light hydrocarbon oils used as solvents for lipids may also adsorb on the surface of the particulate material to be dewatered via hydrophobic interaction, and further enhance its hydrophobicity.
• the lipid molecules may act as nonionic surfactants and help spread the light hydrocarbon oils on the surface by modifying the interfacial tensions involved.
• the lipid molecules should increase the interfacial tension at the solid/water interface, as a consequence of rendering the surface more hydrophobic, while causing a decrease in the interfacial tensions at the oil/water and solid/oil interfaces.
• Improved spreading of the light hydrocarbon oil should contribute to enhancing the surface hydrophobicity close to or above 90°.
• all of the reagents used in the present invention may also serve as surface tension lowering agents.
• the surface tensions of the lipids, hydrocarbon oils and short-chain alcohols are substantially lower than that of water. Their presence at the air-water interface by virtue of their hydrophobicity should reduce the surface tension, and thereby help reduce cake moistures according to the Laplace equation.
• a hydrophilic material such as silica and kaolin was hydrophobized in two steps: first using a high HLB surfactant to render the surface moderately hydrophobic and then using a lipid to further enhance its hydrophobicity. Since lipids are insoluble in water, they were used after dissolution in suitable solvents. When sulfide mineral concentrates were received from abroad, they were superficially oxidized and became hydrophilic.
• 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 or 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 surfaces. Lipids adsorb on the surface and enhance its hydrophobicity. To minimize the problems concerning oxidation, some of the tests were conducted using coarse dense-medium products. They were crushed, pulverized, wet-ground in a ball mill, and floated using kerosene and MIBC. The float product was placed in a container and agitated.
• standard flotation reagents such as kerosene and MIBC.
• a known volume of the slurry was removed and transferred to an Elenmeyer flask. After adding known amounts of reagent(s), the flask was hand-shaken for 2 minutes. The conditioned slurry was poured into a filter to initiate a dewatering test. After a preset drying cycle time (usually 2 minutes), the product was removed from the filter, dried in an oven for overnight, and then weighed to determine the cake moisture. In each test, cake formation time and cake thickness were recorded. The cake formation time is defines as the time it takes for bulk of the water is drained and a cake is formed on a filter medium. For vacuum filtration, a 6.35 cm (2.5-inch) diameter Buchner funnel with a medium porosity glass frit was used.
• the height of the Buchner filter was extended.
• a 6.35 cm (2.5-inch) diameter air pressure filter with a cloth fabric medium was used. It was made of Plexiglas so that the cake formation time could be determined by visual observation.
• a fine silica sample from Tennessee was wet-ground in a ball mill and screened to obtain a 0.074 mm x 0 fraction. It was subjected to two sets of vacuum filtration tests, using varying amounts of a lipid (sunflower oil) with and without the first hydrophobization step. Dodecylammonium hydrochloride was used in the amount of 0.2 kg/t (0.4 lb/ton) at pH 9.5 for the initial hydrophobization. The sunflower oil was used as a 33.3% solution in diesel. All tests were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel at 1.143 cm (0.45 inches) of cake thickness, 2 minutes of drying cycle time, and a vacuum pressure of 635 mm (25-inches) Hg.
• Tests were also conducted with a finer (0.034 mm x 0) silica sample.
• a control test gave a cake moisture of 26.4% and a cake formation time of 161 seconds.
• High-brightness kaolin clays are produced by reverse flotation, i.e., colored impurities are hydrophobized by appropriate collectors and floated away from the clay which remain hydrophilic.
• the product is usually in the form of 25 to 35% solids, and is dewatered by vacuum filtration to obtain a cake containing 50-55% moisture. Part of the filter cake is thermally dried and then mixed with the remaining wet cake to further reduce the moisture to 25 to 30% range.
• a series of filtration tests were conducted on a Middle Georgia kaolin clay (60% finer than 2 ⁇ m) to demonstrate that the method of dewatering as described in the instant invention disclosure can dewater clay by vacuum filtration to a desired level without thermal drying. All tests were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel at 635 mm (25 inches) Hg, 0.41 cm (0.16 inches) cake thickness, and 3 min drying cycle time.
• bituminous coal sample from Blackwater Mine, Australia was subjected to a series of laboratory vacuum filtration tests.
• the sample was a flotation product and was received in the form of slurry. Since bituminous coals are naturally hydrophobic, the tests were conducted without the initial hydrophobization. However, the moisture reduction was relatively poor, most probably due to the superficial oxidation Of the sample during transportation.
• the coal sample was wet-ground for 1.5 minutes and re-floated using a standard reagent package (i.e., 0.5 kg/t (1 lb/ton) of kerosene as collector and 0.1 kg/t (0.2 lb/ton) methylisobutylcarbinol (MIBC) as frother).
• a standard reagent package i.e., 0.5 kg/t (1 lb/ton) of kerosene as collector and 0.1 kg/t (0.2 lb/ton) methylisobutylcarbinol (MIBC) as frother.
• MIBC methylisobutylcarbinol
• the floatation product was then conditioned for two minutes with various reagents that can further increase its hydrophobicity and, thereby, improve dewatering.
• various reagents were used as hydrophobicity enhancing reagents and the results are compared. These include a vegetable lipid (soybean oil), diesel oil, and mixtures of the two.
• the coal sample was subjected to a series of vacuum filtration tests using a 6.35 cm (2.5-inch) diameter Buchner funnel at 635 mm (25 inches) Hg vacuum pressure 1.14 cm (0.45-inch) cake thickness, and 2 min drying cycle time. Table 3 compares the results.
• the performance of 0.5 kg/t (1 lb/ton) of the mixture should be compared with the performance of 1.5 kg/t (3 lb/ton) of soybean oil alone or diesel oil alone.
• the soybean oil-diesel oil mixtures outperformed either soybean oil or diesel oil individually even when they were compared on the basis of total amounts of the reagents used in the filtration experiments.
• the use of 0.5 kg/t (1 lb/ton) soybean oil and 1 kg/t (2 lb/ton) diesel oil mixture gave 17.1% moisture
• 1.5 kg/t (3 lb/ton) of soybean oil alone and diesel oil alone gave 20.5 and 20.1% cake moistures, respectively.
• triacylglycerols present in the soybean oil act as large surfactant molecules with one head group (glycerol) and three hydrocarbon tails. Since they are water insoluble, it will form large globules in water and would act as a hydrocarbon oil just like diesel oil. When soybean oil and diesel oil were used together, however, the latter serves as a solvent for triacylglycerols and help distribute them evenly on the surface of the coal particles. Triacylglycerols may adsorb on the surface of coal via hydrophobic interaction, and enhance its hydrophobicity. The contact angles may be increased close to or over 90°, which is conducive to achieving high degrees of moisture reduction.
• triacylglycerols present in soybean oil facilitate the spreading of diesel oil on coal. This can be achieved if the surfactant can reduce the interfacial tensions at the diesel oil/water and oil/coal interfaces, while increasing the interfacial tension at the solid/water interface.
• the net results of the two possible mechanisms are the same, that is, the hydrophobicity of coal increases by the combined use of a lipid of vegetable origin and a light hydrocarbon oil.
• a coarse Pittsburgh coal sample from a dense-medium separator was pulverized by means of a jaw crusher and a roll crusher, and then wet-ground in a ball mill.
• the advantage of using a freshly pulverized coal sample may be that the harmful effect of surface oxidation is minimized.
• the ball mill product was screened at 0.5 mm, and the screen underflow was floated using 0.5 kg/t (1 lb/ton) kerosene and 0.1 kg/t (0.2 lb/ton) MIBC.
• the process of flotation may be considered to be the first hydrophobization step disclosed in the instant invention.
• the product was subjected to a second hydrophobization step, in which a lipid (soybean oil) was used as a hydrophobicity-enhancing reagent. Since lipids are water insoluble, it may be beneficial to use them in conjunction with various solvents. In this example, several light hydrocarbon oils and a short-chain alcohol were used as solvents. The filtration tests were conducted using a 6.35 cm (2.5-inch) vacuum filter at 1.14 cm (0.45-inch) cake thickness, 2-minute drying cycle time, and 635 mm (25-inch) cake thickness. The results are given in Table 4. With the particular coal sample used in this example, mineral oils gave better results than butanol. Soybean oil dissolves better in the former.
• the sample was superficially oxidized during transportation. It was, therefore, wet-ground in a ball mill for 1.5 minutes and re-floated using 0.5 kg/t (1 lb/ton) of kerosene and 0.1 kg/t (0.2 lb/ton) MIBC.
• the flotation product was conditioned with a lipid of animal origin (fish oil) to enhance its hydrophobicity. The lipid was used as a 33.3% solution in diesel oil.
• the conditioned coal sample was subjected to a series of filtration tests at 200 kPa air pressure and 2 min drying cycle time. The results are given in Table 5.
• Table 6 shows the results of the vacuum filtration tests conducted on a Pittsburgh coal sample using fish oil as a dewatering aid. It was used as a 1:2 mixture by volume with diesel oil.
• the coal sample was a dense-medium product, which was pulverized, ball-mill ground and screened at 0.5 mm.
• the screen underflow was floated using 0.5 kg/t (1 lb/ton) kerosene and 0.1 kg/t (0.2 lb/ton) MIBC before filtration.
• the filtration tests were conducted using a 6.35 cm (2.5-inches) diameter Buchner funnel at 635 mm (25-inches) Hg of vacuum pressure and 1.14 cm (0.45 inches) of cake thickness. At 1.5 kg/t (3 lb/ton) of fish oil, moisture was reduced from 28.2 to 15.4%.
• the filtration tests were conducted using a 6.35 cm (2.5-inch) diameter pressure filter at 100 kPa air pressure and 2 min drying cycle time. The tests were conducted at various dosages of a lipid (fish oil) and cake thicknesses. One part by volume of fish oil was mixed with 2 parts of diesel oil before use. At 1.5 kg/t (3 lb/ton) fish oil, the moisture reductions were 46, 43 and 41% at 0.51 (0.2), 0.76 (0.3) and 1.52 cm (0.6 inches) of cake thicknesses, respectively. At 2.5 kg/t (5 lb/ton), the moisture reductions did not improve significantly further.
• soybean oil was used as dewatering aid for copper (chalcopyrite) concentrate (150 mm x 0).
• the lipid was used as a 33.3% solution in diesel oil.
• the sample was a flotation product, which was superficially oxidized during transportation.
• the sample was wet-ground in a ball mill and re-floated using 0.05 kg/t (0.1 lb/ton) sodium isopropyl xanthate and 55 g/t (50 g/ton) MIBC.
• the flotation product was subjected to vacuum filtration tests using a 6.35 cm (2.5-inch) Buchner funnel at 635 mm (25-inches) Hg and 2 min drying cycle time.
• the %moisture reductions were 55, 43, and 43.4% at 0.38 (0.15), 0.76 (0.3) and 1.52 cm (0.6 inches) of cake thickness, respectively. Reagent additions above 1.5 kg/t (3 lb/ton) did not significantly further the moisture reduction. These results are comparable to those obtained in the plant using a highpressure filter followed by a thermal dryer.
• Example 9 (not an example of the present invention)
• Table 9 shows a set of vacuum filtration tests conducted on a bituminous coal sample (0.6 mm x 0) from Elkview Mine, British Columbia, Canada. The sample was received in the form of slurry and used as received. The tests were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel at 635 mm (25 inches) Hg of vacuum pressure with 2 min drying cycle time and 1.02 cm (0.4 inches) of cake thickness. Three different vegetable oils were used as dewatering aids, and the results are compared. These oils were used as 10% solutions in butanol. Both sesame oil and peanut oil reduced the cake moisture by nearly 50% at 1 kg/t (2 lb/ton) of reagent addition.
• 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 0.1 kg/t (0.2 lb/ton) MIBC. Varying amounts of coconut oil were used at different cake thicknesses. It was used as a 1:2 mixture with diesel oil. The moisture reductions were 64.7, 58.5, and 51.2% at 0.51 (0.2), 1.02 (0.4) and 2.03 cm (0.8 inches) cake thicknesses, respectively.
• the dewatering aids disclosed in the present invention works well with hydrophobic particles.
• Talc is a naturally hydrophobic mineral that is used for a variety of applications including paper coating and removal of sticky materials from wood pulp.
• Table 11 shows the results obtained in a series of filtration tests conducted using sunflower oil as a dewatering aid. The reagent was used as a 33.3% solution in diesel oil. 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 sample was received from Luzenac America, and was floated using 0.1 kg/t (0.2 lb/ton) MIBC just before filtration. Better than 50% moisture reductions were achieved at 0.51 (0.2) and 1.02 cm (0.4 inches) cake thicknesses.
• a clean spiral product was wet-ground in a ball mill.
• the fines fraction (0.85 mm x 0) was floated using 0.5 kg/t (1 lb/ton) kerosene and 0.1 kg/t (0.2 lb/ton) MIBC as a means of initial hydrophobization.
• the hydrophobicity of the flotation product was enhanced using a lipid of animal origin (lard) and then subjected to filtration tests. Two sets of tests were conducted at 100 and 200 kPa of air pressures. Varying amounts of the lipid were used as 25% solutions in diesel oil. The tests were conducted using a 6.35 cm (2.5-inch) diameter filter at 2 min drying cycle time.
• lard oil works well as a dewatering aid.
• the moisture reduction improves with increasing reagent dosage and air pressure. Moisture reductions of 50 to 60% were obtained at lower cake thicknesses and at the higher air pressure. Even at the thicker cake, moisture reductions approaching 50% were obtained at higher reagent dosages.
• sorbitan monooleate Span 80
• diesel oil used as dewatering aid.
• the HLB number of sorbitan monooleate is 4.3; therefore, it blends well with the other two components.
• Dewatering tests were conducted on a bituminous coal sample from Massey Coal Company, West Virginia. It was a dense-medium product, which was crushed, ground, and screened to obtain 0.6 mm x 0 fraction, which was floated using 0.5 kg/t (1 lb/ton) kerosene and 110 g/t (100 g/ton) MIBC.
• Dewatering tests were conducted using a 6.35 cm (2.5-inch) diameter pressure filter at 150 kPa air pressure at 2 min drying cycle time and 1.27 cm (0.5 inches) cake thickness. The tests were conducted by varying the reagent dosage.
• the coal sample was a dense-medium product, which was crushed, ground and floated using 0.5 kg/t (1 lb/ton) kerosene and 0.1 kg/t (0.2 lb/ton) MIBC.
• the filtration experiments were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel at 635 mm (25-inch) Hg vacuum pressure. An ultrasonic probe was placed at the conical part of the Buchner funnel during the 5 minute drying cycle time. When the vibration was applied without the dewatering aid, the cake moisture was reduced from 22.6 to 19.2%. When 1 kg/t (2 lb/ton) of the dewatering aid was used in conjunction with the vibration, the cake moisture was reduced to 9.2% at 1.02 cm (0.4-inch) cake thickness.
• the flotation product was conditioned with varying amounts of a lipid (sunflower oil) prior to filtration.
• the filtration tests were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel at 635 mm (25-inch) Hg vacuum pressure, 2-min drying cycle time, and 1.65 cm (0.45-inch) cake thickness.
• the spray technique reduced the cake moisture by 4 to 5% beyond what can be achieved using the lipid as a hydrophobicity-enhancing reagent.
• the technique of using lipids and butanol spray provides a means of achieving deep moisture reductions. Any other surface tension lowering reagents may be sprayed in place of the butanol used in this example.
• the filtration tests were conducted using a 6.35 cm (2.5-inch) diameter Buchner funnel with a 16.5 cm (6.5-inch) height at a 635 mm (25-inch) Hg vacuum pressure and 2-min drying cycle time.
• the control test which was conducted on the flotation product without lipid and butanol spray, gave 25.8% cake moisture as shown in Table 16.
• the cake moisture was reduced from 25.8 to 13%.

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