EP0246105B1 - Recovering coal fines - Google Patents

Recovering coal fines Download PDF

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Publication number
EP0246105B1
EP0246105B1 EP87304307A EP87304307A EP0246105B1 EP 0246105 B1 EP0246105 B1 EP 0246105B1 EP 87304307 A EP87304307 A EP 87304307A EP 87304307 A EP87304307 A EP 87304307A EP 0246105 B1 EP0246105 B1 EP 0246105B1
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Prior art keywords
slurry
weight
coal
froth flotation
hydrophobic
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EP87304307A
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German (de)
French (fr)
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EP0246105A3 (en
EP0246105A2 (en
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Gerald Frederick Brookes
Lynne Spencer
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Fospur Ltd
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Fospur Ltd
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B03SEPARATION 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
    • B03DFLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D3/00Differential sedimentation
    • B03D3/06Flocculation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B03SEPARATION 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
    • B03DFLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00Flotation
    • B03D1/001Flotation agents
    • B03D1/004Organic compounds
    • B03D1/006Hydrocarbons
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B03SEPARATION 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
    • B03DFLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00Flotation
    • B03D1/001Flotation agents
    • B03D1/004Organic compounds
    • B03D1/016Macromolecular compounds
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B03SEPARATION 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
    • B03DFLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00Flotation
    • B03D1/02Froth-flotation processes
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B03SEPARATION 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
    • B03DFLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D2201/00Specified effects produced by the flotation agents
    • B03D2201/04Frothers
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B03SEPARATION 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
    • B03DFLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D2203/00Specified materials treated by the flotation agents; Specified applications
    • B03D2203/02Ores
    • B03D2203/04Non-sulfide ores
    • B03D2203/08Coal ores, fly ash or soot
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02BINTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B3/00Engines characterised by air compression and subsequent fuel addition
    • F02B3/06Engines characterised by air compression and subsequent fuel addition with compression ignition

Definitions

  • This invention concerns recovering coal from aqueous slurries of coal fines also containing associated impurities as suspended fine solids and compositions of use in the recovery process.
  • Coal as mined contains a proportion of impurities (hereinafter called 'shale') and, in the case of the fine particles present, separation of the coal from the shale presents considerable problems.
  • 'shale' impurities
  • This fine 'coal' typically has a substantial coal content but also a substantial shale content so it is important to make use of the coal content but also to remove shale from it.
  • Modern coal preparation processes result in the fines (separated from coarser material) being in the form of aqueous slurries.
  • the usual separation technique applied to the aqueous slurry of fines is to pass the slurry through a hydrocyclone and then feed the hydrocyclone underflow to a screen having apertures of about 0.25 mm.
  • the "product" i.e. coal fines with a reduced proportion of shale fines is the matter retained by the screen whilst the hydrocyclone overflow and the matter passing through the screen are discarded.
  • a consequent disadvantage is that the significant proportion of the coal having particle sizes below 0.25 mm is lost.
  • coal fines are selectively agglomerated, with respect to shale fines, by use of an oil "binder" and the coal agglomerates are then separated from the shale fines by a screening or classification process.
  • the process has the disadvantage of requiring a substantial proportion of oil in relation to the solids in the slurry being treated.
  • An aqueous coal slurry is admixed with a surface treating mixture under polymerisation conditions and the resultant surface treated coal is rendered hydrophobic.
  • a method of recovering coal fines from an aqueous slurry also containing shale as suspended fine solids in which the coal fines are rendered hydrophobic the resulting mixture is agitated, gas is introduced into the slurry to form bubbles whereby flocs of coal fines formed are caused to float, and the underlying slurry containing shale is discarded characterised in that the coal fines are rendered hydrophobic by the addition to the slurry of a hydrophobic polyvinylether in a liquid organic carrier.
  • coal fines can be flocculated efficiently by use of hydrophobic polyvinylethers and that the flocculation is highly selective for coal fines in preference to shale fines.
  • flocs of coal fines are formed selectively in preference to flocs of shale fines and a high degree of selectivity can be achieved.
  • the agglomeration of the coal fines into flocs reduces the exposed surface area of the coal and thereby reduces entrainment of shale fines with the coal.
  • the coal fines can be formed into flocs of sufficient strength to survive vigorous agitation of the slurry and by agitation of the slurry the flocs of coal fines can be caused to 'extrude' shale fines and water that may initially have been entrained within the flocs.
  • the method of the invention should be performed as a froth flotation in a froth flotation cell, using, in addition to polyvinylether and carrier, a frother, as used in conventional froth flotation processes.
  • the organic liquid not only acts as a carrier for the polyvinylether but it also acts as a so-called collector in the conventional froth flotation sense.
  • the polyvinylether dosage may be as low as say 0.5 kg/tonne of slurry solids.
  • high yields are obtainable i.e. not only is the method highly selective as between coal fines and shale fines but also a high proportion of the coal fines, particularly those of very low particle sizes (less than about 50 microns) can be recovered.
  • Polyvinylethers have been found to be particularly satisfactory in the case of the more aliphatic coals e.g. steam coals.
  • Gas oil has been found to be a particularly satisfactory carrier for the polyvinylether.
  • examples of other carriers that may be used include diesel oil, and kerosene and other petroleum and coal-based distillates.
  • a co-solvent compatible with the carrier may be used.
  • co-solvents include toluene, xylenes and other aromatic solvents and hexane and other paraffinic solvents. Co-solvents may be particularly useful if the polyvinylether is of high molecular weight.
  • the efficiency of the method is dependent on the dosage rate of the polyvinylether in relation to the solids in the slurry.
  • some recovery of the coal fines may be achieved with a dosage rate as low as for example, 2.45 kg. polyvinylether/tonne of slurry solids but under the same conditions an almost double dosage rate of 4.71 gave far superior results.
  • the optimum dosage rate in any particular case is that just sufficient to cause effective flocculation of substantially all the coal fines. Whilst high selectivity may be retained with lesser rates, only partial recovery of the coal fines is then achievable. Rates higher than the optimum are simply wasteful of the polyvinylether.
  • an additive composition for use in the froth flotation method of the invention comprises 5 - 25% of hydrophobic polyvinylether, 5 - 25% of frother and 50 - 90% of liquid organic carrier, all by weight.
  • the frother may be as in the known froth flotation process, and may be for example methyl isobutyl carbinol or a mixture of polypropylene glycol ethers available under the tradename TEEFROTH G.
  • the composition is preferably used in an amount not greater than 10 kg per tonne of slurry solids, especially 0.5 - 5 kg per tonne.
  • the method of the invention gives rise to a secondary advantage in that the coal flocs formed are more readily filtered than coal fines which have not been flocculated. Moreover, not only can the filtration be carried out more quickly but also it gives rise to a coal residue having the advantage of a lower water content.
  • the method of the invention is applicable to coal/shale slurries of the types that in the past have been subjected to conventional froth flotation processes.
  • the size of the coal and shale particles is usually less than 500 microns and commonly up to 50% by weight of the particles can have sizes less than 50 microns.
  • Process I Three different treatment processes were applied to the slurry.
  • Process I the chosen additive was added to a sample of the slurry in a separating funnel and the mixture stirred at a low speed such that thorough mixing occurred but there was substantially no creation of air bubbles in the slurry.
  • the stirring was then discontinued, solids allowed to sediment out, the sediment separated from the slurry above and both the sediment and the overlying slurry collected, the sediment returned to the funnel, water added and the resultant mixture again stirred slowly, the stirring again discontinued and solids again allowed to sediment out and the sediment separated from the overlying slurry and both collected.
  • the sediment was filtered, dried and weighed (to determine the product yield of the process) and then burnt and reweighed (to determine the ash content of the product).
  • the two portions of collected separated slurry were separately filtered and the residues dried, weighed and burnt (to determine their ash contents).
  • Process II the above process was generally repeated but using high speed stirring such that numerous air bubbles were created in the slurry and caused solids to float rather than sediment out. Accordingly in this process on each of the two occasions the underlying slurry was separated from the floated-out solids rather than the sediment being separated from the overlying slurry.
  • Process III the chosen additive was added to a sample of the slurry and the mixture then subjected to froth flotation using froth flotation apparatus of the Leeds cell design.
  • the floated-out matter was separated from the underlying slurry and the latter collected and the former returned with added water to the Leeds cell which was then operated again.
  • the floated-out matter was again separated from the underlying slurry and both collected.
  • the floated-out matter was filtered, dried and weighed (to determine the product yield) and burnt and re-weighed (to determine the ash content of the product).
  • the two portions of collected separated slurry were separately filtered and the residues dried, weighed and burnt.
  • Example 1.6 in the Table is shown as being conducted according to Process II. However, although high speed stirring was used such that numerous air bubbles were created in the slurry, the solids sedimented out rather than floated and thus the separation steps were conducted in accordance with Process I rather than Process II.
  • Examples 1.1 and 1.2, which use Process I, are included only for comparison purposes.
  • the product ash contents are high, signifying a substantial proportion of shale in the product.
  • Example 1.3, which uses Process II, gives a much lower ash content but the yield is low.
  • Examples 1.5, again using Process II, gives a good yield of low ash content and the high ash contents of the tailings signify that little coal is lost in the tailings. The contrast with Example 1.2 using Process I but otherwise generally similar is very marked.
  • Example 1.6 is included only for comparison purposes and shows that Process II is not effective in the absence of the polyvinylether: whilst the product yield is high, the product has a high ash i.e. shale content.
  • Example 1.9 included only for comparison purposes, shows that if gas oil and frother are used in Process III without the polyvinylether a greatly reduced yield results.
  • Process IV which was the same as Process III described in Example 1 except that froth flotation was done once instead of twice, was carried out on an aqueous coal/shale slurry from a coal preparation plant using in one series of experiments an additive composition according to the invention and in another series of experiments the froth flotation oil in current use on the plant at the time.
  • the ash content of the solids in the slurry was 36.5% by weight, and of the solids 69% by weight were of particle size less than 53 microns.
  • the composition of the additive was, by weight:- 60% gas oil 20% mixture of polypropylene glycol ethers (TEEFROTH G) 20% polyvinyl ethyl ether (LUTONAL A25)
  • TEEFROTH G polypropylene glycol ethers
  • LUTONAL A25 polyvinyl ethyl ether
  • the results obtained using the additive composition are, over the range of dosages investigated, superior to those obtained using the conventional froth flotation oil, and particularly at high dosages are characterised by higher weight yields and lower product ash contents. For example at a dosage of 1.21 kg ash is reduced by 5.6% by weight and the yield increased by 2.8% by weight.
  • Process IV as described in Example 2 was carried out on a sample of particle size less than 105 microns screened from a run-of-mine coal/shale slurry in which the particle size of the solids was less than 500 microns.
  • the ash content of the solids in the sample was 45% by weight. 86% by weight of the solids in the sample had a particle size of less than 20 microns and an ash content of 46.4% by weight, and the remaining 14% by weight contained 30% by weight ash.
  • Example 2 The additive composition described in Example 2 was compared with a proprietary froth flotation oil used in a conventional froth flotation process.
  • a bulk feed sample of a coal/shale slurry was screened at 500 microns. Part of the sample was retained for normal froth flotation for comparison purposes and the remainder was classified in a 5 cm hydrocyclone.
  • the underflow was diluted with water to approximately 6% solids by weight and similar froth flotation treatments were carried out on portions of the diluted material to those carried out on the overflow material.
  • Froth flotation was also carried out on the retained screened feed sample using the froth flotation oil normally used to treat the particular coal/shale slurry in practice.
  • results demonstrate the benefits to be obtained by using a hydrocyclone to split the feed for a conventional froth flotation into one fraction containing fine particles of a size predominantly less than 50 microns (overflow) and another fraction containing relatively coarse particles of a size predominantly in the range of 50 - 500 microns (underflow) and then treating the fraction containing the fines by the method of the invention and the other fraction by a conventional froth flotation process.

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  • Extraction Or Liquid Replacement (AREA)

Description

  • This invention concerns recovering coal from aqueous slurries of coal fines also containing associated impurities as suspended fine solids and compositions of use in the recovery process.
  • Coal as mined (run-of-mine coal) contains a proportion of impurities (hereinafter called 'shale') and, in the case of the fine particles present, separation of the coal from the shale presents considerable problems. In the case of mines where modern, mechanical extraction techniques are used, typically a proportion as high as about 20% of the run-of-mine coal consists of particles smaller than 0.5 mm. This fine 'coal' typically has a substantial coal content but also a substantial shale content so it is important to make use of the coal content but also to remove shale from it. Modern coal preparation processes result in the fines (separated from coarser material) being in the form of aqueous slurries.
  • In the United Kingdom the usual way of separating coal fines from shale fines in aqueous slurries is by means of froth flotation followed by filtration. However, the efficiency of this process is seriously affected by the presence of ultra-fine (of less than about 50 microns) matter (both coal and shale), often present in significant proportions in the material requiring treatment.
  • When froth flotation is not used, the usual separation technique applied to the aqueous slurry of fines is to pass the slurry through a hydrocyclone and then feed the hydrocyclone underflow to a screen having apertures of about 0.25 mm. The "product" i.e. coal fines with a reduced proportion of shale fines is the matter retained by the screen whilst the hydrocyclone overflow and the matter passing through the screen are discarded. A consequent disadvantage is that the significant proportion of the coal having particle sizes below 0.25 mm is lost.
  • Another technique that has been proposed for separating coal fines from shale fines in aqueous slurries is oil agglomeration. In this process coal fines are selectively agglomerated, with respect to shale fines, by use of an oil "binder" and the coal agglomerates are then separated from the shale fines by a screening or classification process. However, the process has the disadvantage of requiring a substantial proportion of oil in relation to the solids in the slurry being treated.
  • EP-A-0166897 describes a process for beneficiating oxidised coal by froth flotation in which modified coal, produced by a subjecting coal having oxidised surfaces to high shear agitation in water and desliming the resulting aqueous coal mixture, is introduced to a surface treating mixture comprised of a polymerisable monomer having the formula XHC=CHX', a catalyst and a liquid organic carrier. An aqueous coal slurry is admixed with a surface treating mixture under polymerisation conditions and the resultant surface treated coal is rendered hydrophobic.
  • According to the present invention there is provided a method of recovering coal fines from an aqueous slurry also containing shale as suspended fine solids in which the coal fines are rendered hydrophobic, the resulting mixture is agitated, gas is introduced into the slurry to form bubbles whereby flocs of coal fines formed are caused to float, and the underlying slurry containing shale is discarded characterised in that the coal fines are rendered hydrophobic by the addition to the slurry of a hydrophobic polyvinylether in a liquid organic carrier.
  • It has been found in accordance with the invention that coal fines can be flocculated efficiently by use of hydrophobic polyvinylethers and that the flocculation is highly selective for coal fines in preference to shale fines. Thus in the above method flocs of coal fines are formed selectively in preference to flocs of shale fines and a high degree of selectivity can be achieved. The agglomeration of the coal fines into flocs reduces the exposed surface area of the coal and thereby reduces entrainment of shale fines with the coal. Moreover, the coal fines can be formed into flocs of sufficient strength to survive vigorous agitation of the slurry and by agitation of the slurry the flocs of coal fines can be caused to 'extrude' shale fines and water that may initially have been entrained within the flocs.
  • It has been found that if gas is not introduced into the mixture and bubbles formed causing flocs of coal fines formed to float, little separation of coal and shale is achieved and the sediment contains coal and shale fines in proportion not greatly different from the original ones and there is little distinction between different levels of the sediment. It is thought that the reason for this is that as the flocs of coal fines descend in the slurry they entrain shale fines and thus the benefit of selective flocculation of the coal fines is lost to a greater or lesser extent. The introduction of the gas e.g. air and formation of the bubbles may be effected by sufficiently vigorous agitation of the mixture or a specific device may be used to introduce gas into the mixture and form the bubbles.
  • It is much preferred that the method of the invention should be performed as a froth flotation in a froth flotation cell, using, in addition to polyvinylether and carrier, a frother, as used in conventional froth flotation processes. When the method is performed in this manner the organic liquid not only acts as a carrier for the polyvinylether but it also acts as a so-called collector in the conventional froth flotation sense. When the method is conducted in this manner high selectivity is easily retained but with the advantage that greatly reduced dosage rates of polyvinylether are effective. In the froth flotation form of the method, the polyvinylether dosage may be as low as say 0.5 kg/tonne of slurry solids. Moreover as with the method in general, high yields are obtainable i.e. not only is the method highly selective as between coal fines and shale fines but also a high proportion of the coal fines, particularly those of very low particle sizes (less than about 50 microns) can be recovered.
  • Polyvinylethers have been found to be particularly satisfactory in the case of the more aliphatic coals e.g. steam coals.
  • Gas oil has been found to be a particularly satisfactory carrier for the polyvinylether. Examples of other carriers that may be used include diesel oil, and kerosene and other petroleum and coal-based distillates. To aid solution of the polyvinylether in the liquid a co-solvent compatible with the carrier may be used. Examples of co-solvents that may be used include toluene, xylenes and other aromatic solvents and hexane and other paraffinic solvents. Co-solvents may be particularly useful if the polyvinylether is of high molecular weight.
  • The efficiency of the method is dependent on the dosage rate of the polyvinylether in relation to the solids in the slurry. In a simple form of the method (not involving froth flotation) some recovery of the coal fines may be achieved with a dosage rate as low as for example, 2.45 kg. polyvinylether/tonne of slurry solids but under the same conditions an almost double dosage rate of 4.71 gave far superior results. The optimum dosage rate in any particular case is that just sufficient to cause effective flocculation of substantially all the coal fines. Whilst high selectivity may be retained with lesser rates, only partial recovery of the coal fines is then achievable. Rates higher than the optimum are simply wasteful of the polyvinylether.
  • It has been found that it is not the liquid, organic carrier e.g. gas oil alone that yields the good results in the method of the invention. In general, if e.g. gas oil is used without a hydrophobic polyvinylether, the selectivity is largely lost and in the case of a froth flotation method, use of gas oil and a conventional frother but no hydrophobic polyvinylether results in a low yield i.e. the coal fines are not efficiently flocculated.
  • According to a further aspect of the invention, an additive composition for use in the froth flotation method of the invention comprises 5 - 25% of hydrophobic polyvinylether, 5 - 25% of frother and 50 - 90% of liquid organic carrier, all by weight. The frother may be as in the known froth flotation process, and may be for example methyl isobutyl carbinol or a mixture of polypropylene glycol ethers available under the tradename TEEFROTH G. The composition is preferably used in an amount not greater than 10 kg per tonne of slurry solids, especially 0.5 - 5 kg per tonne.
  • The method of the invention gives rise to a secondary advantage in that the coal flocs formed are more readily filtered than coal fines which have not been flocculated. Moreover, not only can the filtration be carried out more quickly but also it gives rise to a coal residue having the advantage of a lower water content. These effects are thought to result from the formation of relatively large coal flocs having fully hydrophobic surfaces and low shale content.
  • The method of the invention is applicable to coal/shale slurries of the types that in the past have been subjected to conventional froth flotation processes. In such slurries the size of the coal and shale particles is usually less than 500 microns and commonly up to 50% by weight of the particles can have sizes less than 50 microns.
  • The presence of substantial proportions of ultra-fine particles e.g. less than 50 microns seriously impairs the efficiency of the conventional froth flotation process. By use of a hydrocyclone a typical feed for a conventional froth flotation process can be split into two fractions, one containing particles of predominantly 50 microns and upwards and the other particlespredominantly less than 50 microns. The fraction containing the larger particles may then be treated by a conventional froth flotation process with increased efficiency whilst the method of the invention is especially well suited to the treatment of the fraction containing the smaller particles.
  • The invention is illustrated by the following examples, in which some of the processes described are not according to the invention and are included for comparison purposes.
  • EXAMPLE 1
  • Experiments were carried out on a synthetic aqueous coal/shale slurry containing equal weights of coal and shale fines and having a solids content of 5% by weight. The ash content of the solids was 46% by weight. Of the solids, 80% by weight were of particle sizes less than 63 microns.
  • Three different treatment processes were applied to the slurry. In Process I the chosen additive was added to a sample of the slurry in a separating funnel and the mixture stirred at a low speed such that thorough mixing occurred but there was substantially no creation of air bubbles in the slurry. The stirring was then discontinued, solids allowed to sediment out, the sediment separated from the slurry above and both the sediment and the overlying slurry collected, the sediment returned to the funnel, water added and the resultant mixture again stirred slowly, the stirring again discontinued and solids again allowed to sediment out and the sediment separated from the overlying slurry and both collected. The sediment was filtered, dried and weighed (to determine the product yield of the process) and then burnt and reweighed (to determine the ash content of the product). The two portions of collected separated slurry were separately filtered and the residues dried, weighed and burnt (to determine their ash contents).
  • In Process II the above process was generally repeated but using high speed stirring such that numerous air bubbles were created in the slurry and caused solids to float rather than sediment out. Accordingly in this process on each of the two occasions the underlying slurry was separated from the floated-out solids rather than the sediment being separated from the overlying slurry.
  • In Process I and II sodium hexametaphosphate was included in the initial slurry as shale dispersant at a concentration of 2.5% by weight.
  • In Process III the chosen additive was added to a sample of the slurry and the mixture then subjected to froth flotation using froth flotation apparatus of the Leeds cell design. The floated-out matter was separated from the underlying slurry and the latter collected and the former returned with added water to the Leeds cell which was then operated again. The floated-out matter was again separated from the underlying slurry and both collected. The floated-out matter was filtered, dried and weighed (to determine the product yield) and burnt and re-weighed (to determine the ash content of the product). The two portions of collected separated slurry were separately filtered and the residues dried, weighed and burnt.
  • The experimental date is given in Table 1.
    Figure imgb0001
  • In the Table 'A25' and '130' signify a polyvinyl ethyl ether and a polyvinyl isobutyl ether available under the tradenames Lutonal A25 and Lutonal 130 respectively from BASF United Kingdom Limited. These are hydrophobic polymers. In the Table 'frother' signifies the known frother methyl isobutyl carbinol. First and second 'tailings' in the Table refer to the solids respectively in the initially and subsequently separated slurries. In connection with the figures for 'yield', it should be noted that the theoretical maximum for the yield of coal is 50%, as half the weight of the initial slurry solids is coal and the other half shale.
  • Example 1.6 in the Table is shown as being conducted according to Process II. However, although high speed stirring was used such that numerous air bubbles were created in the slurry, the solids sedimented out rather than floated and thus the separation steps were conducted in accordance with Process I rather than Process II.
  • Examples 1.1 and 1.2, which use Process I, are included only for comparison purposes. The product ash contents are high, signifying a substantial proportion of shale in the product. Example 1.3, which uses Process II, gives a much lower ash content but the yield is low. Example 1.4, where the additive application rate is approximately doubled, gives a much higher yield but the ash content is still low. Examples 1.5, again using Process II, gives a good yield of low ash content and the high ash contents of the tailings signify that little coal is lost in the tailings. The contrast with Example 1.2 using Process I but otherwise generally similar is very marked.
  • Example 1.6 is included only for comparison purposes and shows that Process II is not effective in the absence of the polyvinylether: whilst the product yield is high, the product has a high ash i.e. shale content.
  • Examples 1.7 and 1.8, using Process III, give good yields with low ash contents and in comparison with Examples 1.4 and 1.5, using Process II and also using the same polyvinylethers and gas oil, the application rates of the polyvinylether and gas oil are very much lower.
  • Example 1.9, included only for comparison purposes, shows that if gas oil and frother are used in Process III without the polyvinylether a greatly reduced yield results.
  • EXAMPLE 2
  • Process IV, which was the same as Process III described in Example 1 except that froth flotation was done once instead of twice, was carried out on an aqueous coal/shale slurry from a coal preparation plant using in one series of experiments an additive composition according to the invention and in another series of experiments the froth flotation oil in current use on the plant at the time.
  • The ash content of the solids in the slurry was 36.5% by weight, and of the solids 69% by weight were of particle size less than 53 microns.
  • The composition of the additive was, by weight:-
    60% gas oil
    20% mixture of polypropylene glycol ethers (TEEFROTH G)
    20% polyvinyl ethyl ether (LUTONAL A25)
       A range of dosages comparable to normal practice was used for both the additive composition and the froth flotation oil, and in each experiment the flotation time was 180 seconds.
  • The results obtained are tabulated in Table 2 in which Combustible Recovery is defined as
    Figure imgb0002
    Figure imgb0003
  • The results obtained using the additive composition are, over the range of dosages investigated, superior to those obtained using the conventional froth flotation oil, and particularly at high dosages are characterised by higher weight yields and lower product ash contents. For example at a dosage of 1.21 kg ash is reduced by 5.6% by weight and the yield increased by 2.8% by weight.
  • EXAMPLE 3
  • Process IV as described in Example 2 was carried out on a sample of particle size less than 105 microns screened from a run-of-mine coal/shale slurry in which the particle size of the solids was less than 500 microns. The ash content of the solids in the sample was 45% by weight. 86% by weight of the solids in the sample had a particle size of less than 20 microns and an ash content of 46.4% by weight, and the remaining 14% by weight contained 30% by weight ash.
  • The additive composition described in Example 2 was compared with a proprietary froth flotation oil used in a conventional froth flotation process.
  • The results obtained are tabulated in Table 3. TABLE 3
    Additive Composition Froth Flotation Oil Froth Flotation Oil
    Dosage kg/tonne 0.25 0.25 0.65
    Flotation Time (secs) 120 360 120
    Product Ash (% wt) 17.0 19.6 20.6
    Yield (% wt) 54.0 34.0 45.2
    Tails Ash (% wt) 80.9 60.2 68.9
    Combustible Recovery (% wt) 83.6 51.0 67.0
  • Columns 2 and 3 of Table 3 represent optimum results for the additive composition and for the froth flotation oil respectively at a dosage level of 0.25 kg/tonne. The flotation time using the additive composition is lower but the additive composition also produces lower product ash and an appreciably higher yield. Column 4 shows that flotation time using the proprietary froth flotation oil can be reduced by increasing the amount of oil used. However, this results in an increase in the product ash, and the high yield value achieved using the additive composition is still not reached.
  • EXAMPLE 4
  • A bulk feed sample of a coal/shale slurry was screened at 500 microns. Part of the sample was retained for normal froth flotation for comparison purposes and the remainder was classified in a 5 cm hydrocyclone.
  • One part of the overflow from the cyclone was subjected to froth flotation using Process IV described in Example 2 and the additive composition described in Example 2, and another part of the overflow was similarly treated using the froth flotation oil normally used to treat the slurry in the mine.
  • The underflow was diluted with water to approximately 6% solids by weight and similar froth flotation treatments were carried out on portions of the diluted material to those carried out on the overflow material.
  • Froth flotation was also carried out on the retained screened feed sample using the froth flotation oil normally used to treat the particular coal/shale slurry in practice.
  • The results obtained are tabulated in Tables 4.1, 4.2 and 4.3. In the Tables AC signifies that the additive composition was used and FFO indicates that the froth flotation oil was used. TABLE 4.1
    UNDERFLOW - AFTER 45 SECS FLOTATION
    DOSAGE (kg/tonne) PRODUCT ASH (wt %) YIELD (wt %) COMBUSTIBLE RECOVERY (wt %)
    FFO 0.210 7.58 18.85 33.25
    AC 0.356 12.02 48.27 76.76
    FFO 0.360 9.47 47.78 74.88
    AC 0.551 13.66 54.76 86.39
    FFO 0.700 13.69 56.67 86.96
    AC 0.724 14.25 55.78 87.33
    FFO 0.860 18.30 56.77 88.78
    AC 1.047 14.21 60.90 91.09
    TABLE 4.2
    OVERFLOW - AFTER 45 SECS FLOTATION
    DOSAGE (kg/tonne) PRODUCT ASH (wt %) YIELD (wt %) COMBUSTIBLE RECOVERY (wt %)
    AC 1.080 25.82 21.54 53.02
    FFO 1.210 29.86 21.16 49.56
    AC 1.560 27.67 24.28 58.84
    FFO 1.600 30.92 23.15 53.56
    AC 1.890 28.51 23.42 56.14
    FFO 2.210 33.27 25.00 54.75
    AC 2.480 29.34 26.44 62.63
    FFO 2.750 32.58 25.81 57.95
    AC 3.560 32.91 31.53 67.51
    Figure imgb0004
  • The results demonstrate the benefits to be obtained by using a hydrocyclone to split the feed for a conventional froth flotation into one fraction containing fine particles of a size predominantly less than 50 microns (overflow) and another fraction containing relatively coarse particles of a size predominantly in the range of 50 - 500 microns (underflow) and then treating the fraction containing the fines by the method of the invention and the other fraction by a conventional froth flotation process.
  • For the underflow froth flotation using the additive composition of the invention gave similar results to the conventional froth flotation using the froth flotation oil except at a high dosage level (greater than about 0.8 kg/tonne) at which level the additive composition produced a lower ash product. For the overflow while product ash levels remained relatively high using either the additive composition or the froth flotation oil, the ash contents were up to 4% lower using the additive composition and weight yields were in general improved. The results in Table 4.3 show that the conventional froth flotation applied to the cyclone underflow i.e. feed slurry from which fine particles have been removed is more efficient at lower dosages of froth flotation oil than froth flotation applied to unclassified feed slurry.

Claims (13)

  1. A method of recovering coal fines from an aqueous slurry also containing shale as suspended fine solids in which the coal fines are rendered hydrophobic, the resulting mixture is agitated, gas is introduced into the slurry to form bubbles whereby flocs of coal fines formed are caused to float, and the underlying slurry containing shale is discarded characterised in that the coal fines are rendered hydrophobic by the addition to the slurry of a hydrophobic polyvinylether in a liquid organic carrier.
  2. A method according to Claim 1 characterised in that the hydrophobic polyvinylether is polyvinyl ethyl ether or polyvinyl isobutyl ether.
  3. A method according to Claim 1 or Claim 2 characterised in that the liquid organic carrier is gas oil, diesel oil or kerosene.
  4. A method according to any one of Claims 1 to 3 characterised in that a co-solvent compatible with the carrier is used to aid solution of polyvinyl ether.
  5. A method according to Claim 4 characterised in that the co-solvent is an aromatic solvent.
  6. A method according to Claim 5 characterised in that the aromatic solvent is toluene or xylene.
  7. A method according to Claim 4 characterised in that the co-solvent is a paraffinic solvent.
  8. A method according to Claim 7 characterised in that the paraffinic solvent is hexane.
  9. A method according to any one of Claims 1 to 8 characterised in that a frother is used and the method is performed as a froth flotation in a froth flotation cell.
  10. A method according to Claim 9 characterised in that the frother is methyl isobutyl carbinol or a mixture of polypropylene glycol ethers.
  11. A method according to Claim 9 characterised in that an additive composition comprising 5 - 25% by weight of hydrophobic polyvinyl ether, 5 - 25% by weight of frother and 50 - 90% by weight of liquid organic carrier is used at up to 10 kg per tonne of slurry solids.
  12. A method according to Claim 11 characterised in that the additive composition is used at 0.5 - 5 kg per tonne of slurry solids.
  13. An additive composition for use in a method of recovering coal fines according to Claim 9 characterised in that the composition comprises 5 - 25% by weight of hydrophobic polyvinyl ether, 5 - 25% by weight of frother and 50 - 90% by weight of liquid organic carrier.
EP87304307A 1986-05-14 1987-05-14 Recovering coal fines Expired - Lifetime EP0246105B1 (en)

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US5021165A (en) * 1987-06-10 1991-06-04 Conoco Specialty Products Oil and water separating system with hydrocyclone and floatation device
GB8726857D0 (en) * 1987-11-17 1987-12-23 Fospur Ltd Froth floatation of mineral fines
US5298167A (en) * 1992-12-10 1994-03-29 Arnold Kenneth E Method for separating immiscible liquid
JPH08511728A (en) * 1994-04-13 1996-12-10 フィリップス エレクトロニクス ネムローゼ フェンノートシャップ Method of heat-aggregating aqueous dispersion
RU2461426C2 (en) * 2006-12-06 2012-09-20 Шелл Интернэшнл Рисерч Маатсхаппий Б.В. Normal and isoparaffins with low content of aromatic compounds, sulphur and nitrogen as collector for foam flotation
CN101823025B (en) * 2010-04-01 2013-02-13 西安科技大学 Coal flotation agent and preparation method thereof
CN103394416B (en) * 2013-08-22 2014-11-26 陕西延长石油矿业有限责任公司 Coal flotation agent and preparation method thereof
CN105750092A (en) * 2016-03-10 2016-07-13 徐州工程学院 Novel coal preparation collecting agent and preparation method thereof
CN105728200A (en) * 2016-03-29 2016-07-06 江苏尧舜机械科技有限公司 Coal dressing composite reagent and preparing method thereof
CN111135960B (en) * 2020-01-16 2021-11-19 辽宁科技大学 Micro-bubble flotation machine for laboratory and working method thereof

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AU5856080A (en) * 1979-06-01 1980-12-04 Calgon Corporation Flotation circuit additive
US4304573A (en) * 1980-01-22 1981-12-08 Gulf & Western Industries, Inc. Process of beneficiating coal and product
US4466887A (en) * 1983-07-11 1984-08-21 Nalco Chemical Company Polymer collectors for coal flotation
US4532032A (en) * 1984-05-30 1985-07-30 Dow Corning Corporation Polyorganosiloxane collectors in the beneficiation of fine coal by froth flotation
US4605420A (en) * 1984-07-02 1986-08-12 Sohio Alternate Energy Development Company Method for the beneficiation of oxidized coal

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GB2190310A (en) 1987-11-18
DE3777448D1 (en) 1992-04-23
GB2225260B (en) 1990-08-29
EP0246105A3 (en) 1989-04-05
ZM1592A1 (en) 1992-11-30
GB8924001D0 (en) 1989-12-13
GB8611747D0 (en) 1986-06-25
ES2040251T3 (en) 1993-10-16
GB2225260A (en) 1990-05-30
EP0246105A2 (en) 1987-11-19
GB8711401D0 (en) 1987-06-17

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