WO 2008/000037 PCT/AU2007/000904 Title of the Invention A SEPARATION PROCESS AND SYSTEM Field of the Invention This present invention relates to a separation process and system for and in particular to a process and system for minerals separation, especially coal, using a froth 5 flotation process. The invention has been developed primarily for use in a froth flotation process to separate coal, and will be described hereinafter with reference to this application. However, it would be appreciated that the invention is not limited to this particular field of use. In particular, it is contemplated that the invention is applicable to a separation 10 process, wastewater treatment, flotation or aeration system where a frother or other chemicals are added to the system. The invention is also applicable for any mineral including aluminia, bauxite, iron ore, copper and lead. Background of the Invention Any discussion of the prior art throughout the specification should in no way be 15 considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field. Coal processing plants typically employ one or more minerals separation flotation cells to process fine coal. A slurry or pulp containing coal and gangue is fed into the flotation cell or cells, which separate the coal values or concentrates from the gangue by 20 inducing bubbles so that the values float to the surface of the pulp with the bubbles or "froth". The coal values are recovered by an overflow weir or launder as a product stream, whereas the gangue is drained from the lower part of the cell as a tailings stream. To facilitate separation and improve the productivity of the flotation cells, typically surfactants and wetting agents are used as "frother" to encourage the 25 production of bubbles or "froth" for transporting the coal values to the pulp surface. An example of a frother is methyl isobutyl carbinol (MIBC). Other chemicals known as ''collectors" may be added to assist separation by rendering the coal values hydrophobic and thus promote attachment to the air bubbles generated in the flotation cell. The WO 2008/000037 PCT/AU2007/000904 -2 gangue may also be conditioned to be hydrophilic and thus remain in the lower part of the cell for drainage and subsequent removal. Throughout this specification, the term "frother" means any chemical substance which encourages the production of froth, bubbles or foam, including any 5 agglomeration of thereof, in a fluid or liquid. Whilst frother assists in the flotation process, it acts as a contaminant in the tailings stream and poses an environmental pollutant if it is discharged into the tailings dam. Excess collector in the tailings stream also acts as a contaminant and an environmental pollutant. 10 Furthermore, the tailings stream is often recycled to obtain clarified water for use in the pumping system of the rest of the coal processing plant. The presence of too much frother in the tailings stream also contaminates the clarified water, since excess frother causes cavitations in the pumping system and "froths out" the coal processing plant. Flushing the frother out of the pumping system requires the shut down of the 15 entire plant and the associated down time spent in cleaning out the pumping system results in wasted labour and lost production. In this context, coal separation by flotation typically involves only 20% of the entire coal processing plant and is limited to the recovery of fine coal, whereas the rest of the plant produces the remaining 80% of the coal. Consequently, to avoid these 20 potential production losses and environmental hazards, it has been the practice to use substantially reduced amounts of frother in the floatation cells to minimise the presence of frother in the tailings stream. However, this reduces the efficiency of the flotation cells in recovering fine coal. Summary of the Invention 25 According to a first aspect of the present invention, there is provided a separation process, said process including the steps of: feeding a feed fluid into a separator; separating said feed fluid with a frother into a product stream and a tailings stream; WO 2008/000037 PCT/AU2007/000904 -3 treating said tailings stream with a flotation-type cell to substantially remove frother therefrom; and recycling at least a portion of said frother to said feeding step to increase the concentration of frother in said separator. 5 A second aspect of the present invention provides a separation system, said system including: a separator for receiving a feed fluid, wherein said separator separates said feed fluid with a frother into a product stream and a tailings stream; a flotation-type cell adapted for substantially removing frother from said tailings 10 stream; and a conduit for recycling at least a portion of said frother to said separator, thereby increasing the concentration of frother in said separator. A third aspect of the present invention provides a froth flotation process for minerals separation, said process including the steps of: 15 feeding a feed slurry, including at least one mineral and gangue, into a flotation cell; separating said feed slurry with a frother into a product stream and a tailings stream; treating said tailings stream in a flotation-type cell adapted to substantially 20 remove frother from said tailings stream; and recycling at least a portion of said frother to said feeding step to increase the concentration of frother in said flotation cell. A fourth aspect of the present invention provides a froth flotation system for minerals separation, said system including: 25 a flotation cell for separating a feed slurry, including at least one mineral and gangue, with a frother into a product stream and a tailings stream; a flotation-type cell adapted for substantially removing frother from said tailings stream; and .a conduit for recycling at least a portion of said frother to said flotation cell, 30 thereby increasing the concentration of frother in said flotation cell.
WO 2008/000037 PCT/AU2007/000904 -4 Preferably, said treating step is repeated one or more times to progressively remove the frother from said tailings stream. Preferably, at least 20% of said frother is recycled to the feeding step. Preferably, up to 80% of the frother is recycled to the feeding step. Preferably, the entire amount of 5 the frother is substantially recycled to the feeding step. Preferably, a portion of said frother is diverted to a further processing step. Preferably, the further processing step includes skimming a portion of the frother. Alternatively or additionally, a portion of said frother is diverted to the product stream. Preferably, the separating step includes a minerals separation flotation process. 10 Preferably, the process further includes the steps of treating said product stream to substantially remove frother therefrom and recycling at least a portion of said frother to said feeding step. Preferably, the treating step further includes substantially removing collector from said tailings stream. Preferably, the process further includes the step of recycling at 15 least a portion of said collector to said feeding step to increase the concentration of collector in the feeding step. Preferably, a portion of the collector is diverted to a further processing step. Preferably, the entire amount of the collector is substantially recycled to the feeding step. Preferably, said treating step is repeated one or more times to progressively remove the collector from said tailings stream. 20 In the system, it is preferred that the flotation-type cell is adapted to remove collector from said tailings stream. Preferably, at least a portion of said collector is recycled from said flotation-type cell to said separator or flotation cell to increase the concentration of collector in the separator or flotation cell. Preferably, at least 20% of said frother is recycled to the separator or flotation 25 cell. Preferably, up to 80% of the frother is recycled to the separator or flotation cell. Preferably, the entire amount of the frother is substantially recycled to the separator or flotation cell.
WO 2008/000037 PCT/AU2007/000904 -5 Preferably, a portion of said frother is diverted to a processing unit. Preferably, the processing unit includes a skimmer. Alternatively or additionally, a portion of said frother is diverted to the product stream of the separator or flotation cell. Preferably, a portion of the collector is diverted to a processing unit. Preferably, 5 the entire amount of the collector is substantially recycled to the separator or flotation cell. Preferably, the system includes a plurality of said flotation-type cells for treating said tailings stream. Preferably, the flotation-type cells are fluidly connected in series such that the frother is progressively removed from the tailings stream. Preferably, the 10 flotation-type cells progressively remove said collector from the tailings stream. Preferably, the system includes a further flotation-type cell adapted for substantially removing frother from the product stream and a conduit for recyling at least a portion of said frother to said separator or flotation cell. Preferably, the system includes a feed box for feeding said feed fluid into said 15 separator or flotation cell. Preferably, the feed box includes a pump to facilitate feeding of said feed liquid. Preferably, the conduit recycles the portion of frother to the feed box for feeding the separator or flotation cell. Preferably, the separator includes a flotation cell. By way of example only, the flotation cell may be a Jameson-type flotation cell. Preferably, the product stream is 20 obtained from the overflow launder of the flotation cell and the tailings stream is obtained from the drained lower part of said cell. Alternatively, the product stream is obtained from the drained lower part of said flotation cell and the tailings stream is obtained from the overflow launder of said cell. Preferably, the separator includes a thickener to separate clarified water from 25 gangue. Preferably, the product stream is obtained from the drained lower part of said thickener and the tailings stream is obtained from the overflow launder of the thickener. Preferably, the tailings stream includes clarified water. Preferably, the treated clarified water is recycled to a pumping system of an associated coal processing plant. Alternatively, the product stream is obtained from the overflow launder of said WO 2008/000037 PCT/AU2007/000904 -6 thickener and the tailings stream is obtained from the drained lower part of said thickener. Preferably, said feed fluid includes a liquid or semi-liquid. Preferably, said feed fluid is a slurry or pulp including at least one mineral and gangue. Preferably, said at 5 least one mineral includes coal, iron ore, copper or lead. Preferably, said frother includes a surfactant or wetting agent. Preferably, said frother includes MIBC, polyethylene glycols, polypropylene glycols, alcohols, pine oil, eucalyptus oil, other natural oils or a range of other frothers. Brief Description of the Drawings 10 Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic drawing illustrating the method according to one embodiment of the present invention; Figure 2 is a schematic drawing illustrating a system according to one 15 embodiment of the present invention; Figure 3 is a schematic drawing illustrating a system according to another embodiment of the invention; Figure 4 is a schematic drawing illustrating a system according to yet another embodiment of the invention; and 20 Figure 5 is a schematic drawing illustrating a system according to a further embodiment of the invention.
WO 2008/000037 PCT/AU2007/000904 -7 Preferred Embodiments of the Invention Referring to Figure 1, a process of separating a feed fluid includes the steps of 1 feeding the feed fluid into a separator and 2 separating the feed fluid with a frother into a product stream and a tailings stream. At step 3, the tailings stream is treated to 5 remove frother from the tailings stream and obtain a treatment stream including the frother. At step 4, the treatment stream, or at least a portion thereof, is then recycled by returning it to step 1 to increase the concentration of frother in the separator. The system according to one embodiment of the present invention is illustrated in Figure 2. The system 10 includes a separator 11 for receiving a feed fluid stream 12 and 10 a frother, the separator 11 being adapted to separate the feed fluid into a product stream 13 and a tailings stream 14. A treatment unit 15 is adapted to remove frother from the tailings stream 14 and obtain a treatment stream 16 including a high frother concentration and any residual values of a desired product, and a waste stream 17 containing waste and a lower concentration of frother. A conduit 18 recycles the 15 treatment stream 16, or at least a portion thereof, to the separator 11, thereby increasing the frother concentration in the separator 11. The waste stream 17 is either processed again by another treatment unit 15 to further reduce the amount of frother in the waste stream, discharged into a tailings dam, or recycled by a thickener to produce clarified water. In any event, the amount of 20 frother in the waste stream 17 is significantly reduced so that any residual frother has a minimal adverse impact as an environmental pollutant or as a contaminant in the processing plant. By recycling frother from the tailings stream 14, the process and system reduces the overall presence of frother in the gangue stream 17. Thus, the risk of contamination 25 in the pumping system of the processing plant and the tailings dam is substantially minimised. At the same time, the frother concentration is increased in the separator 11, increasing the yield that is obtained from the separator, and optimising the use of frother in the system 10. The process and system of Figures 1 and 2 are applicable to any separation 30 process employing frother, such as wastewater treatment, water clarification, aeration or WO 2008/000037 PCT/AU2007/000904 other flotation-type separation systems. Further embodiments of the system according to the invention will now be described in the application of the invention to a coal processing plant. Referring to Figure 3, where corresponding features have the same reference 5 numerals, the system 19 includes a feed box 20 for supplying a feed slurry containing coal values and gangue to a Jameson-type flotation cell 11 through a pump 21 and a conduit 22. Frother is added either into the feed box 20 or the flotation cell 11 directly. The flotation cell 11 separates the feed slurry into a product stream 13, containing coal values and a tailings stream 14 containing gangue. Both the product stream 13 and the 10 tailings stream 14 contain frother. A feed box 23 receives the tailings stream 14 and, using a pump 24 and a conduit 25, directs the tailings stream 14 into a flotation-type cell 15, which has been adapted for treating the tailings stream 14. The flotation-type cell may be called a "treatment cell" or a "frother stripping cell". In this embodiment, the treatment cell 15 is in the form of a modified Jameson-type flotation cell. This 15 treatment cell 15 is adapted to remove a substantial amount of frother and any residual coal values from the tailings stream 14 as a treatment stream 16, whereas the gangue and a small amount of frother exits the treatment cell 15 as a tailings stream 17. Generally, the main modification is to the operational parameters of the treatment cell 15 so that the maximum amount of froth is removed, for example, by reducing the froth 20 depth to a minimum level. In addition, the treatment cell 15 can have crowders fitted and operated at the lower froth depth, and the air and slurry feed rates altered. A conduit 18 recycles the treatment stream back to the feed box 20, thereby increasing the concentration of frother in the Jameson-type flotation cell 11. Alternatively, a portion of the treatment stream 16 (and thus a portion of the 25 frother) is returned to the feed box 20 to increase the concentration of frother in the flotation cell 11, and the remainder of the treatment stream is diverted to another device, such as a skimmer or dewatering device, for further processing. The tailings stream 17 from the treatment cell 15 is then disposed through a gangue outlet 26. Alternatively, the tailings stream 17 is fed into another modified 30 treatment cell adapted for removing any residual coal values and frother from the tailings stream 17 into another treatment stream that is recycled, in whole or in part, to WO 2008/000037 PCT/AU2007/000904 -9 the flotation cell 11. This frother removal and recycling process can be repeated using a number of reconfigured Jameson-type cells 15 connected in series or in parallel before disposal through the gangue outlet 26. Another embodiment of the system is shown in Figure 4, where corresponding 5 features have the same reference numerals. In this embodiment, the system 30 is used to remove frother from the clarifed water product stream of a thickener at the end of a coal separation flotation process. The system 30 has a pair of Jameson-type flotation cells 11 a, 1lb connected in series by a feed box 23, pump 24 and conduit 25. The feed box 20 supplies the feed 10 slurry containing coal values and gaugue by way of a pump 21 and a conduit 22 to the first Jameson-type flotation cell 11 a. As in the case of the first embodiment, frother is added to the feed slurry by way of the feed box 20 or directly into the flotation cell 11 a. The flotation cell 11 a separates the coal values into a product stream 13a and the gangue into tailings stream 14a, which is received by the feed box 23. The pump 24 and the 15 conduit 25 convey the tailings stream 14a into the second Jameson-type flotation cell 11 b, where any remaining coal values in the tailings stream 14a are separated from the gangue into a product stream 13b. The gangue exits the flotation cell 1 lb as a tailings stream 14b, which is received by a feed box 31. A pump 32 conveys the tailings stream 14b from the feed box 31 through a conduit 33 to a thickener 34 as a gravity feed. 20 Alternatively, a suitable pump may be used to feed the tailings stream 14b into the thickener 34 instead of a gravity feed. In the thickener 34, the gangue is allowed to settle at the bottom 35 of thickener while the clarified water exits the overflow launder of the thickener 34 as a product stream 36. The gangue is drained by a conduit 37 into a sump 38 and eventually 25 discharged into a tailings dam 39. In this system 30, a significant amount of frother may remain in the clarified water product stream 36. Consequently, the clarified water product stream 36 is conveyed into a new type of flotation cell 40 developed by the inventor. The detailed operation of the flotation cell 40 is described in more detail in co-pending Australian 30 Provisional Patent Application No. 2006903752 titled "Flotation Cell". For the WO 2008/000037 PCT/AU2007/000904 -10 purposes of the disclosure of this invention, the new flotation cell 40 is substantially similar to other flotation-type cells in that the flotation cell 40 induces bubbles so that the values float with the bubbles and are extracted as a product stream, while the gangue is drained as a tailings stream. This new flotation cell 40 has been adapted to operate as 5 a treatment cell in the same manner as described above, so as to remove frother, residual coal values and other impurities from the clarified water in the product stream 36. The treatment stream 41 of the treatment cell 40 substantially containing frother is recycled by a conduit 42 to the feed box 20 to increase the concentration of frother in the first flotation cell 11 a. Alternatively, a portion of the treatment stream 41 is 10 recycled by the conduit 42 to the feed box 20. Whilst a greater amount of recycled frother will be concentrated in the first flotation cell 11 a, a flow on effect will result in higher amounts of frother in the second flotation cell 1 lb as well. Thus, both flotation cells 11 a, 11 b will operate with improved efficiency due to the higher concentrations of frother. The tailings stream 43 from the treatment cell 40 substantially containing 15 clarified water is then conveyed by a conduit 44 to the pumping system of an associated coal processing plant (not shown). As discussed above, a portion of the frother in the treatment stream from the systems described in Figures 2 to 4 can be diverted to another processing unit. A further embodiment of the invention illustrating this variation is shown in Figure 5, 20 where corresponding features have been given the same reference numerals. In this embodiment, the treatment stream 16 of the treatment cell 15 is diverted through a skimmer 50, which is in the form of a cyclone or screen. The skimmer 50 skims off an amount of froth from the treatment stream 16 and the remainder of the treatment stream 16 is recycled back to the feed box 20 by the conduit 18. The skimmed froth, which 25 contains residual coal values, may then be added to the product stream. In other embodiments, the treatment stream 16 is divided, for example by separate conduits, so that a portion of frother is returned to the separator or flotation cell. Preferably, the portion of frother that is recycled to the separator or flotation cell is between 20% and 80%. However, it will be appreciated that smaller portions or the 30 entire treatment stream may be recycled back to the separator or flotation cell, as required. Alternatively or additionally, a portion of the frother from the treatment WO 2008/000037 PCT/AU2007/000904 - 11 stream may be returned to the product stream. In one preferred example, 20% of the treatment stream is returned to the product stream of the flotation cell or separator, whereas the remaining 80% of the treatment stream is returned to the separator or flotation cell to increase the concentration of frother and improve the efficiency of the 5 separator or flotation cell. The illustrated embodiments of the invention thus provide a process and system where the minimisation or complete removal of frother from the tailings stream substantially reduces the risk of frother contaminating the environment as a discharge into the tailings dam or contaminating clarified water recycled from the tailings stream 10 for use in the rest of the coal processing plant. In addition, the amount of frother is optimised in the flotation cells, thereby increasing the yield from the fine coals separation flotation process, and reducing the amount of frother used in the flotation process. Moreover, there is a reduced need to continually monitor and adjust the amount of frother that is added to the flotation cells. The invention is conveniently 15 implemented in existing coal processing plants, since any type of flotation cell can be suitably modified to act as the treatment unit. It will also be appreciated by one skilled in the art that the treatment cell can be any flotation-type cell that has been modified to remove frother and is not limited to the Jameson-type or the newly developed flotation cells described in each of the 20 embodiments. In addition, the modified Jameson-type cell could be used in the system 30 of Figure 4. Likewise, the new flotation cell 40 could be used in the systems described in Figures 3 and 5, as a flotation cell and/or a frother stripping cell. In other embodiments, the method and system are configured to additionally remove any excess collector contained in the tailings stream in the same way as frother. 25 Other embodiments employ a multiple number of treatment cells connected in series at the end of the separators or flotation cells to progressively remove frother from the tailings stream. A further embodiment has a multiple number of separators or flotation cells, connected in series, where the end tailings stream is connected to the treatment cell, or a plurality of treatment cells. A further embodiment replaces the pumps 30 between the separators/flotation cells and the treatment cells with a gravity feed system. In yet another embodiment, the product stream of the separator or flotation cell is WO 2008/000037 PCT/AU2007/000904 - 12 connected to an associated treatment cell to substantially remove frother from the product stream into a further treatment stream, which is then recycled to the feed of the separator or flotation cell. It is also contemplated that the invention is applicable to other mineral separation 5 processes other than a coal flotation separation process. For example, it is contemplated that the invention is applicable to any other flotation system and to other mineral ores such as aluminia, bauxite, iron ore, copper and lead. It is also contemplated that the invention is applicable to wastewater treatment systems to produce a final water product with reduced amounts of residual chemicals. 10 Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.