The present invention relates to a method of controlling one or more than one flotation cell for separating substances in a feed material in a froth flotation circuit.
The present invention relates particularly, although by no means exclusively, to a method of controlling one or more than one flotation cell in a froth flotation circuit for separating substances, for example minerals containing valuable material such as valuable metals such as nickel and copper, from a feed material in the form of an ore that contains the minerals and other material (hereinafter referred to as “gangue”).
The following description of the invention focuses on a froth flotation method for separating particles of valuable minerals from particles of gangue in a feed material in the form of mined ores, but the invention is not confined to this application.
Froth flotation is a process for separating valuable minerals from gangue by taking advantage of hydrophobicity differences between valuable minerals and waste gangue in a feed material. The purpose of froth flotation is to produce a concentrate that has a higher grade, i.e. a higher product grade, of a valuable material (such as copper) than the grade of the valuable material in the feed material. Performance is normally controlled through the addition of surfactants and wetting agents to an aqueous slurry of particles of the minerals and gangue contained in a flotation cell. These chemicals condition the particles and stabilise the froth phase. For each system (ore type, size distribution, water, gas etc), there is an optimum reagent type and dosage level. Once the surface of the solid phases has been conditioned they are then selectively separated with a froth that is created by supplying a flotation gas, such as air, to the process. A concentrate of the minerals is produced from the froth. Like the chemical additives, the separation gas used to generate the froth is a process reagent with an optimum dosage level. The optimum dose of gas is a complex function of many system and equipment factors but for a given flotation cell can be determined empirically by maximising the gas recovery point for the cell.
The performance quality of a flotation process can be measured with respect to two characteristics of a concentrate that is extracted from a flotation cell—namely product grade and product recovery. Product grade indicates the fraction of a valuable material in the concentrate as compared to the remainder of the material in the concentrate. Product recovery indicates the fraction of the valuable material in the concentrate as compared to the total amount of the valuable material in the original feed material that was supplied to the flotation cell.
A key aim of an industrial flotation process is to control operating conditions in order to achieve an optimal balance between grade and recovery, with an ideal flotation process producing high recovery of high grade concentrate.
International publication WO 2009/044149 in the name of Imperial Innovations Limited relates to an invention of a method of controlling operation of a froth flotation cell that forms part of a froth flotation circuit. The method is based on controlling flotation gas flow rate into a cell so that the cell operates at maximum gas recovery for the cell.
The maximum gas recovery for a cell is described as the “peak gas recovery” and the gas flow rate at the peak gas recovery is described as the “peak gas rate”. In a situation in which the flotation gas is air, the maximum gas recovery is described as the “peak air recovery” and the air flow rate at the peak air recovery is described as the “peak air rate”.
The International publication describes that there is a correlation between operating a flotation cell to maximise gas recovery and maximising the combination of concentrate grade and concentrate recovery. In particular, the International publication describes that maximum gas recovery, i.e. peak gas recovery, coincides with optimum metallurgical performance, where metallurgical performance includes concentrate grade and concentrate recovery.
The applicant has considered how to control a flotation cell and a froth flotation circuit that comprises a plurality of flotation cells to maximise gas recovery and, more particularly peak recovery in situations where the flotation gas is air.
The present invention is based on a realisation that it is not a straightforward exercise to continuously control the operation of such cells to maximise peak gas recovery. For example, variations in feed rate, froth level, solids composition, pulp pH, and chemical dosage rates can have a significant impact on the stability of cells.
The present invention is also based on a realisation that peak gas recovery for a cell coincides with a maximum froth stability (i.e. a peak froth stability) for the cell and that the peak froth stability is what drives the peak gas recovery.
The term “froth stability” is understood herein to mean the ability of bubbles in a froth to resist coalescence and bursting.
In broad terms, the present invention is a method of controlling a froth flotation cell in a froth flotation circuit for separating substances that includes controlling flotation gas flow rate to the cell based on changes in cell conditions to maintain the operation of the cell at a peak froth stability of the cell or closer to the peak froth stability of the cell than if the flotation gas flow rate was not changed.
According to the present invention there is provided a method of controlling a froth flotation cell in a froth flotation circuit for separating substances, the method including monitoring conditions of the cell and changing the flotation gas flow rate to the cell if there is a change in cell conditions in order to maintain the operation of the cell at a peak froth stability or closer to the peak froth stability of the cell than if the flotation gas flow rate was not changed.
The change in cell conditions may be a change in one selected cell condition or changes in a number of selected cell conditions. The change in cell conditions may be any change in conditions that is regarded as being a significant change from the viewpoint of operating the cell at the peak froth stability of the cell or closer to the peak froth stability of the cell. By way of example, the change in cell condition or conditions may be a predetermined change based on operational knowledge of the cell.
The cell condition or conditions may be monitored directly or indirectly. One example of indirect monitoring of a cell condition is monitoring data that is derived from or based on a cell condition. One specific example is set point data for a cell condition. Set point data is understood herein to mean data indicating a set point for a monitored cell condition wherein the cell condition is maintained at or close to the set point, usually by an automated control loop.
The term “gas flow rate” to the cell as used herein is understood to be interchangeable with the term “superficial gas velocity” within the cell.
The method may include changing the gas flow rate to the cell by a predetermined amount if there is a predetermined change in cell conditions.
The conditions may include any one or more of the following inputs to the cell: feed rate, solids concentration in the feed, particle size distribution of solids in the feed, pH of the feed, gas flow rate, chemical dosage rate, feed grade, feed type, and froth depth.
The conditions may include any one or more of the following outputs of the cell: concentrate grade, concentrate recovery, gas recovery, and gas hold-up.
The term “gas hold-up” in understood herein to mean the volume of gas in a pulp zone of a flotation cell. The volume of gas reduces the pulp volume and therefore decreases the residence time available for flotation. The gas hold-up depends on the amount of gas added to the flotation cell and is a strong function of pulp viscosity.
The method may include automatically changing the gas flow rate to the cell if there is a change in cell conditions.
The method may include determining the change in the gas flow rate for the cell required in any given situation by reference to data obtained by calibrating the cell. The data may relate to a range of different actual operating conditions for the cell and the gas flow rates required to operate at the peak froth stability of the cell across the range of actual operating conditions. The data may be part of a control system for the cell.
The method may include “matching” the shape of a froth stability/gas recovery versus gas flow rate curve generated from calibration data with cell conditions. As a set of cell conditions is likely to yield a uniquely shaped curve, curves generated from calibration data from a cell can be used to locate the peak gas rate for similar cell conditions. Two sets of cell conditions may yield the same peak gas rate, but different shaped froth stability/gas recovery curves or two sets of cell conditions may yield a different peak gas rate and different shaped curves. Two sets of cell conditions may also appear to yield the same shaped curve, but actually yield different peak gas rates.
The method may include carrying out a control routine to check the froth stability of the cell. The control routine may be carried out after changing the gas flow rate to the cell in response to monitored changes to cell conditions. The control routine may be carried out in parallel to monitoring the cell conditions and changing the gas flow rate to the cell in response to monitored changes to cell conditions.
The control routine may be as described in International application PCT/AU2011/001480 in the name of the applicant and may include changing the gas flow rate to the cell in a series of steps and assessing the froth stability at each gas flow rate and continuing the step changes in the gas flow rate until the froth stability is the peak froth stability or is within a predetermined range of the peak froth stability of the cell. The disclosure in the International application is incorporated herein by cross reference.
The method may include carrying out a control routine comprising changing the gas flow rate to the cell in a series of steps and assessing the froth stability at each gas flow rate and continuing the step changes in the gas flow rate so that the cell approaches the peak froth stability of the cell, wherein the cell conditions are monitored in-between making the steps and the flotation gas flow rate to the cell is changed if there is a change in cell conditions.
According to the present invention there is also provided a method of controlling a froth flotation circuit including a plurality of froth flotation cells for separating substances, the method including monitoring conditions in at least one cell and changing the flotation gas flow rate to the cell if there is a change in cell conditions in order to maintain the operation of the cell at a peak froth stability of the cell or closer to the peak froth stability of the cell than if the flotation gas flow rate was not changed.
The method may include changing the gas flow rate to the cell by a predetermined amount if there is a predetermined change in cell conditions.
The method may include automatically changing the gas flow rate to the cell if there is a predetermined change in cell conditions.
The method may include determining the change in the gas flow rate for the cell required in any given situation by reference to data obtained by calibrating the cell. The data may relate to a range of different actual operating conditions for the cell and the gas flow rates required to operate at the peak froth stability of the cell across the range of actual operating conditions. The data may be part of a control system for the cell. The data may be part of a control system for the circuit.
The method may include “matching” the shape of a froth stability/gas recovery versus gas flow rate curve generated from calibration data with cell conditions. As a set of cell conditions is likely to yield a uniquely shaped curve, curves generated from calibration data from a cell can be used to locate the peak gas rate for similar cell conditions. Two sets of cell conditions may yield the same peak gas rate, but different shaped froth stability/gas recovery curves or two sets of cell conditions may yield a different peak gas rate and different shaped curves. Two sets of cell conditions may also appear to yield the same shaped curve, but actually yield different peak gas rates.
The method may include carrying out a control routine to check the froth stability of the cell.
The method may include carrying out a control routine to check the froth stability after making the change to the gas flow rate to the cell, the control routine comprising changing the gas flow rate to the cell in a series of steps and assessing the froth stability at each gas flow rate and continuing the step changes in the gas flow rate until the froth stability is the peak froth stability or closer to the peak froth stability of the cell than if the flotation gas flow rate was not changed.
The control routine may be as described in International application PCT/AU2011/001480 in the name of the applicant.
The method may include carrying out a control routine including changing the gas flow rate to the cell in a series of steps and assessing the froth stability at each gas flow rate and continuing the step changes in the gas flow rate so that the cell approaches the peak froth stability of the cell, wherein the cell conditions are monitored in-between making the steps and the flotation gas flow rate to the cell is changed if there is a change in cell conditions.
The method may include periodically carrying out the control routine in a selected cell in the froth flotation circuit to maximise froth stability of the selected cell. Thereafter, the method may include periodically carrying out the control routine in other cells in the froth flotation circuit.
The method may include continuously carrying out the control routine in a selected cell in the froth flotation circuit to maximise froth stability of the selected cell.
The method may include periodically carrying out the control routine in all of the cells or a selection of cells or the “rougher” bank of cells in the froth flotation circuit.
The method may include continuously carrying out the control routine in all of the cells or a selection of cells or the “rougher” bank of cells in the froth flotation circuit.
The present invention is described further by way of example only with reference to the accompanying drawings, of which:
The basic froth flotation cell and the basic froth flotation circuit shown in
The circuit shown in
With reference to
The feed material to each cell 3 in the bank 5 of cells 3, which is commonly referred to as a “rougher” bank of cells, has a required particle size distribution and has been dosed appropriately with chemicals to facilitate flotation (such as chemicals that act as “collectors” and “conditioners”).
The feed material to the rougher bank 5 may be any suitable material. The following description focuses on a feed material in the form of an ore that contains valuable minerals. The valuable minerals are minerals that contain valuable material in the form of a valuable metal, such as copper. The feed material is obtained from a mined ore that has been crushed and then milled to a required particle size distribution.
The slurry of the feed material that is supplied to the cells 3 in the rougher bank 5 is processed in these cells 3 to produce froth and tailings outputs. The processing comprises introducing a suitable flotation gas, typically air, at a selected gas flow rate into a lower section of the cells 3 via an air control valve 2. Controlling the air control valve 2 controls the gas flow rate into the cell 3. The gas rises upwardly and suitably conditioned particles of the feed material attach to the gas bubbles. The gas bubbles form a froth.
The froth from the cells 3 in the rougher bank 5 is transferred via transfer lines 23 to a second bank 9 of cells 3, which is described as a “cleaner” bank of cells. The froth is processed in these cells 3 in the cleaner bank 9 as described above in relation to the cells 3 in the rougher bank 5 to produce froth and tailings outputs.
The tailings from the rougher bank 5 are transferred via a transfer line 19 to a third bank 7 of cells, which is described as a “scavenger” bank of cells. The tailings are processed in these cells 3 in the scavenger bank 7 to produce froth and tailings outputs.
The froth from the scavenger bank 7 is transferred via lines 25 and 35 to the rougher bank 5 and via line 27 to the cleaner bank 9.
The froth from the cleaner bank 9 is transferred via a transfer line 31 to downstream operations (not shown) for processing to form a concentrate. The concentrate is transferred to a downstream processing operation to recover the valuable metal from the concentrate.
The tailings from the scavenger bank 7 are transferred via a line 29 to waste disposal not shown.
The tailings from the cleaner bank 9 are returned via a transfer line 35 to the rougher bank 5.
The graph of valuable metal recovery in a concentrate from a froth flotation circuit versus valuable metal grade in the concentrate in
As is described above, the applicant has considered how to control a flotation cell and a froth flotation circuit that comprises a plurality of flotation cells to maximise gas recovery and, more particularly peak gas recovery in situations where the flotation gas is air, and the applicant has realised that such control is not a straightforward exercise.
As is described above, in general terms, the present invention is a method of controlling at least one froth flotation cell in a froth flotation circuit that is based on a feed forward control methodology whereby the flotation gas (such as air) flow rate for a cell is adjusted, for example automatically, and for example by a predetermined amount, if there is a change, for example a predetermined change, in a selected cell operating condition or conditions (which may be cell input and cell output conditions). Basically, the purpose of the flotation gas flow rate adjustment is to operate the cell at the peak gas rate and thereby maximise gas recovery and cell performance. The conditions may include any one or more of the following inputs to the cell: feed rate, solids concentration in the feed, particle size distribution of solids in the feed, pH of the feed, gas flow rate, chemical dosage rate, feed grade, feed type, and froth depth. The conditions may include any one or more of the following outputs of the cell: concentrate grade, concentrate recovery, gas recovery, and gas hold-up. The change in cell conditions may be a predetermined change in one selected cell condition or predetermined changes in a number of selected cell conditions.
The required change, such as the required predetermined change, in the gas flow rate is based on information obtained by calibrating the cell and compiling data on flotation gas flow rate that is required for each of a number of sets of cell operating conditions to obtain a peak froth stability (which the applicant has found drives a peak gas recovery) for each cell condition. This data is part of a control system for a cell and for a froth flotation circuit comprising a plurality of such cells.
In other words, this embodiment of the invention utilizes data, held for example in a system memory, from previous operations of a cell, to adjust, for example automatically, the gas flow rate for a given set of cell conditions. This reduces the time taken to set the peak gas rate for a cell and minimizes downstream disturbances caused by continued gas rate variation as the system searches to set the peak gas rate in the cell.
The method may include “matching” the shape of a froth stability/gas recovery curve versus flotation gas flow rate generated from calibration data with cell conditions. This is illustrated in
In one embodiment of the control system, a Peak Air Recovery (PAR) finder control routine is run periodically to check whether the froth stability of the cell is at or close to the peak froth stability for that cell. The control system wherein the PAR finder control routine is run periodically is described in more detail with reference to
In another embodiment of the control system, the Peak Air Recovery finder control routine runs continuously with periodic steps to check whether the froth stability of the cell is at or close to the peak froth stability for that cell. The control system wherein the PAR finder control routine is run continuously is described in more detail with reference to
The PAR finder control routine forms part of the control system.
One PAR finder control routine option, as described in International application PCT/AU2011/001480, comprises changing the gas flow rate to the cell in a series of steps and assessing the froth stability at each gas flow rate and continuing the step changes in the gas flow rate until the froth stability is a peak froth stability or is close to the peak froth stability, such as within a predetermined range of the peak froth stability of the cell.
The schematic diagram of
In this embodiment of the PAR finder control routine, froth stability is assessed by assessing the air recovery of the cell. The present invention is not limited to assessing froth stability via air recovery and extends to any options for assessing froth stability. Other options include, by way of example, assessing bubble collapse rate in froth in the cell and bubble coalescence rate in froth in the cell. Yet another example is using a forth stability column as described in International application PCT/AU2004/000311.
The example of the control routine shown in
The amount of the increase or decrease of the air flow rate to the cell may be the same or may vary in successive steps of the control routine. For example, the amount of the increase or decrease may be reduced as the difference between the air recoveries in successive steps decreases.
International application PCT/AU2011/001480 describes other embodiments of the control routine in a froth flotation cell. One of these other embodiments is described in relation to FIGS. 6-8 of the International application and assesses different gradients between sets of points on an air flow (addition) rate versus air recovery graph. The method is based on the understanding that the gradient of a tangent at the peak air recovery will be approximately zero.
Having at least two gradients on the graph provides information to enable an estimate of the air flow rate at peak air recovery.
In general terms, the steps of the method may be described by the following search algorithm:
Many more points may be taken to increase the accuracy of the prediction of the air flow rate at peak air recovery. In particular the gradients between previous sets of points may be used to predict the necessary change in air flow rate to establish a new point on the graph which forms part of a set of points having a gradient between them closer to zero.
The gas flow rate is adjusted by adjusting the air control valve 2 (see
The control system 60 is configured so that the air control valve 2 positions are adjusted depending on changes to the monitored cell conditions 62.
The control system 60 is configured so that any changes in the monitored cell conditions 82-88 will result in a change in the air control valve 2 positions to change air flow rate into the cell. The size of the change in air control valve 2 positions relative to a change in a monitored cell condition is set in the logic rules of the logic controller 64. The size of the change is adjustable by changing the gain value 90 in the user interface. As can be seen the gains 90 in interface 80 are set so that pulp level (gain 2.0) is the only monitored condition to have an effect on changing air valve position.
The data of the monitored cell conditions 82-88 may be real time variable data that changes as the conditions change in real time or may be set-point data. Set point data is data indicating the set point for the monitored cell condition wherein the cell condition is maintained at or close to the set point, usually by an automated control loop. In certain instances the set point data may be preferred for being more stable than the real time variable data, but remains an indication of the monitored cell condition.
The feed forward control steps for pulp level 82 is an example where the logic control 64 decreases the air rate for increases in pulp level to maintain the cell close to Peak Air Recovery. Conversely for a monitored decrease in pulp level the control system 60 increases the air rate.
Referring to
Referring to
The advantages of the present invention include the following advantages.
The above description of the invention with reference to the Figures focuses on individual cells in a froth flotation circuit comprising a plurality of such cells. The present invention also extends to froth flotation circuits per se. It can be appreciated that, if changes to the air flow rate for one cell are necessary so that the cell operates at or close to the peak froth stability for that cell, it may also be the case that changes to the air flow rates for other cells in the circuit may be required so that these cells operate at the peak froth stability for each cell. As a consequence, it may be appropriate to carry out the method of the invention on a selection or all of the cells in a circuit.
Many modifications may be made to the embodiments of the present invention described above without departing from the spirit and scope of the invention.
By way of example, whilst
Filing Document | Filing Date | Country | Kind |
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PCT/AU2013/000495 | 5/14/2013 | WO | 00 |
Number | Date | Country | |
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61646444 | May 2012 | US |