FLOTATION TEST APPARATUS

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method of and apparatus for testing the floatability of ore particles particularly so that the floatability can be related accurately to size, grade, mineralogy and chemical treatment.

[0002] A primary small-scale test used for flotation involves the operation of a single batch flotation cell. A more advanced test is the "sequential batch test", wherein concentrate material from one single-cell batch test is used as starting material for a subsequent single-cell batch test. Another advanced test is a "locked cycle test", which comprises a series of batch tests in which material is recycled between individual batch tests to simulate a continuous operation. Other methods use trees of batch tests and continuously operated small-scale flotation circuits.

[0003] A more advanced and larger-scale flotation test makes use of a "Flotation Characterisation Test Rig", or FCTR. Relatively large flotation cells (e.g. perhaps each 50-litres in capacity) are configured to operate continuously in a manner similar to an industrial-type flotation circuit with a number of stages. The FCTR circuit is operated in a continuous manner, with flows of feed, tailings and concentrate streams and, in essence, produces a split of feed ore into two products giving one operating point on a grade-recovery curve for every steady-state test operation.

[0004] A "grade-recovery curve" is an important representation of how a flotation plant does or could operate. By allowing the concentrate to be a smaller or larger part of the initial material, flotation can usually be adjusted by operational parameters to give a higher grade and lower recovery, or a lower grade and higher recovery, respectively. A grade-recovery curve gives a graphical representation of this process.

[0005] The flotation of an ore is commonly modelled by the use of flotation "rate constants", which characterise relative flotation rates of different ore components. When a flotation cell is operated, different components of ore float at different rates, thus producing a concentrate that is richer in more floatable components and less rich in less floatable components. A further mechanism that occurs in flotation is the entrainment of particles in water that goes to the concentrate stream.

[0006] Unfortunately, a single stage of flotation does not partition ore efficiently according to its different floatabilities. In the processing of results from a batch flotation test, this problem is addressed by the back-calculation of one or more flotation rates that would conform to the experimental results. The test does not efficiently split the material into distinct groups by floatabilities so that physical properties (such as mineralogy, size and liberation) can be directly associated with floatability. A major disadvantage of this is that models based on physical properties need to be derived from test results by back-calculation, but these models are usually degenerate and under-specified.

[0007] A flotation plant normally comprises a network of flotation stages, configured to provide an efficient separation of the ore particles according to their flotation rate constants. These networks are generally designed to operate continuously. A network of this kind gives sharp separations to yield two products at a time, but does not give sharp separations into many fractions on the basis of floatability.

[0008] The invention is concerned with a flotation test which allows for the collection of fractions of material wherein the particles in each fraction are separated physically on the basis of their flotation rate constants.

SUMMARY OF THE INVENTION

[0009] The invention provides apparatus for conducting a flotation test on a slurry which includes a movable support, a plurality of differently sized flotation units which are mounted on the support, each unit including a respective vessel with a froth exit point, a froth entry point, a tailings exit point and a tailings entry point, the units being interconnected so that froth from the froth exit point of a first unit is directed to the froth entry point of a second adjacent unit, and so that tailings from the tailings exit point of the second unit are directed to the tailings entry point of the first unit, and a mechanism for moving the support thereby to control the level of the slurry in each vessel.

[0010] The support may be movable in any appropriate way and preferably is pivotally movable.

[0011] Each froth exit point may include an overflow weir.

[0012] Each unit may include means for inducing slurry flow and froth breakage within the respective vessel, the means being selected at least from the following: an impeller; an air stream; a slurry pump, optionally with a venturi; a water spray; and a water jet.

[0013] Slurry down-flow may be induced in each respective vessel.

[0014] Each vessel may include a baffle which defines a region in which slurry down- flow is induced. This may be achieved by means of a suitable impeller. The froth entry point may be positioned in an upper locality of the region.

[0015] A deflector may be located at a lower end of the region and may be positioned to direct downwards slurry flow to a second impeller located more or less at a central location of the vessel.

[0016] The invention also provides a method of conducting flotation tests on a slurry which includes the steps of separating a first sample of slurry into a froth concentrate and into tailings, directing the froth concentrate into a second sample of slurry and the tailings into a third sample of slurry, separating the second sample of slurry into a froth concentrate, and into tailings which are directed into the first sample of slurry, and separating the third sample of slurry into a froth concentrate which is directed into the first sample of slurry, and into tailings.

[0017] The invention further extends to a method of conducting flotation tests on a slurry which includes the steps of separating slurry, in a first vessel, into a froth concentrate at an overflow of the first vessel and into tailings at a lower side of the first

vessel, directing the froth concentrate into an upper region of a second vessel and directing the tailings into a lower region of a third vessel, and altering the orientation of the vessels to control the slurry level in each vessel,

[0018] Preferably the slurry in the second vessel is separated into a froth concentrate which is directed to an upper region of a fourth vessel, and into tailings which is directed into a lower region of the first vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention is further described by way of example with reference to the accompanying drawings in which : Figure 1 illustrates in cross section and from one side apparatus for carrying out flotation tests in accordance with the principles of the invention; and

Figure 2 is a curve of recovery versus grade of a slurry treated with the apparatus of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENT

[0020] Figure 1 of the accompanying drawings illustrates, in cross section and from one side, flotation test apparatus 10 according to the invention.

[0021] The apparatus 10 includes a plurality of flotation units or cells designated 12A, 12B ... 12N which are different sizes and which are positioned, from right to left in the drawing, in a descending size order. The flotation units are substantially identical to each other and the construction of a single unit 12 is described.

[0022] The unit includes a vessel 14 of any appropriate cross section e.g. circular or rectangular. A baffle 16 is positioned to one side of the vessel to define a relatively small region 18. A first impeller 20 is located in the region 18 and is operable to produce downward slurry flow as is indicated by means of an arrow 22.

[0023] A deflector 24 is located at a lower side of the region 18 and is orientated so as to direct slurry flow, induced by the impeller 20, towards a central region 26 of the vessel, A second impeller 28 is located in this central region and has provision for the distribution of air bubbles into the slurry.

[0024] Except, possibly, for the first unit 12A each vessel includes a froth entry point 30 and a froth exit point or overflow weir 32. Each unit includes a tailings entry point 34 and a tailings exit point 36. Entry and exit flow passages 38 and 40 are connected to the points 34 and 36 respectively. The exit passage of one unit is connected by a suitable flange arrangement 42 to the entry passage 38 of an adjacent unit, as is shown in Figure 1.

[0025] At least the first unit 12A has control valves 44 and 46 connected to the entry passage 38A and the exit passage 4OA respectively.

[0026] The flotation units 12 are connected in a cascaded series configuration. The froth exit point 32 of one vessel is connected directly to the froth entry point 30 of an adjacent vessel. Similarly the tailings exit point 36 of a vessel is connected to the tailings entry point 34 of an adjacent vessel.

[0027] The final flotation unit, 12N, in the series, has a water inlet conduit 48.

[0028] The flotation units are mounted to supporting structure 50 which in turn is fixed to a pedestal 52 via a controllable pivot connection 54.

[0029] The various units are shown as being distinct from one another. This is not necessarily the case for the apparatus 10 may be of complex construction and the various units may include vessels 14 or other components in common with adjoining units.

[0030] The operation of the apparatus 10, for a batch flotation test, is as follows: the valves 44A and 46A on the first unit 12A are closed. The various impellers 20 and 26 are turned on but without aeration. A chemically conditioned feed slurry, which is to be tested, is introduced into the largest vessel 14A. Water, with added frother if required, is introduced into the vessels of the remaining flotation units. The valve 44 is opened and the assembly of flotation units is pivoted about the point 54 to obtain satisfactory initial levels of slurry and water inside the various vessels. Generally the smallest unit 12N is highest, at least initially, even though the vessel 12N does not necessarily contain water.

[0031] Aeration is then started at the various impellers 26 and, within each vessel, froth concentrate 60 is produced at an upper surface of the slurry and tailings are produced in a lower region of the vessel.

[0032] The froth concentrate which overflows at the froth exit point 32 of a first vessel enters a second adjacent vessel (i.e. to the left in Figure 1) at the froth entry point 30 of the second vessel. This froth is broken down and mixed with slurry by the action of the

respective impeller 20, which induces a downward flow of slurry in the region 18. The deflector 24 directs the slurry flow from the impeller 20 towards the main impeller 26. The deflector also acts to prevent bubbles produced in the slurry by the aerated impeller from entering the region.

[0033] Froth 60 accumulates at the upper end of the second vessel and overflows at the froth exit point 32 into a third adjacent vessel (i.e. to the left in Figure 1). Tailings exit the second vessel through the tailings exit point 34 and flow via the corresponding tailings entry point 36 into an adjacent vessel (i.e. to the right in Figure 1).

[0034] The overall function of each unit is to separate particles in the slurry in the unit's vessel which comprises the initial contents of the vessel, the froth feed from an adjacent unit to the right (in Figure 2) and the tailings stream from an adjacent unit to the left (in Figure 1), into a froth concentrate stream and a tailings stream. These streams are directed in different directions from the vessel in question.

[0035] Two regulatory actions are applied to the apparatus 10, either manually or by automated means. Firstly the apparatus is tilted about the point 54 to ensure a steady flow of concentrate froth over the final weir 32N. Secondly, with respect to the unit 12A, water is introduced at the point 48 to control the level 70 of the interface between the slurry and froth to be a relatively small distance 72 below the entry level of the exit weir 32 A.

[0036] Final concentrates are collected at the overflow weir 32N in a series of sampling vessels, not shown, over a suitable series of time periods. Each successive sample of

the concentrate collected in this way corresponds to material with successively smaller flotation rate constants. The material that remains unfloatable is then collected. Particles from all the samples can be sized, assayed for grades and subjected to mineralogical tests fro mineral composition and liberation.

[0037] In Figure 1 the flotation units are arranged in a substantially linear array. This array could however be curved or follow a different configuration to achieve different separation characteristics. Another variation is that the required flow and breakage of froth can be induced, not by using a mechanical impeller, but by making use of an air stream or water jet or spray, or pumped slurry, optionally in combination with a venturi device.

[0038] The water which is introduced into the smallest flotation unit 12N, at the point 48, reduces entrainment of particles in the concentrate and maintains a suitable pulp level in the largest unit 12A.

[0039] In a variation of the invention the apparatus 10 is operated as a continuous flotation plant and slurry is introduced at an internal unit and not at the large end unit 12A. The final tailings are extracted via the exit passage 38A. Water can optionally be added through the point 48 or at an upper surface of the region 18N to reduce entrainment relative to flotation.

[0040] Figure 2 is a curve of percentage recovery versus grade produced by the use of the apparatus of the invention on a copper-containing slurry. The test was run over 100 seconds and ten samples were extracted at intervals of 10 seconds. The first sample is

at the end of the curve on the right, and the last sample (barring the residue) is at the end of the curve on the left. The mass of each sample, and the accumulated mass of the samples, are given in columns 1 and 3 respectively of Table 1. The grade and actual copper content of each sample are given in columns 4 and 5 respectively. Columns 6, 7 and 8 give the copper recovery figures in different formats.

[0041] Table 1 :

[0042] It is evident that the apparatus provides a full grade-recovery curve in a short time period.

[0043] The test provides a good experimental technique to facilitate the study of floatability as a function of particle size, composition, mineral liberation and chemical conditioning. This eliminates inaccurate back-calculations in respect of experimental samples containing particles of mixed floatabilities and impracticable procedures requiring many sequential flotation test stages.

[0044] The test apparatus can be made portable for convenient transport and tests at operating plants. The physically separated ore particles can then be returned to a

centralised laboratory for assays and mineralogical investigations. Tests can be done on samples from the feed, concentrate, tailings and other streams of plants. A test on the feed stream indicates the ideal grade-recovery relationship which is possible for the ore being processed. A test on the tailings stream can indicate if there is any valuable floatable material that is being lost. The test on the concentrate stream can indicate the floatabilities of gangue materials that are,' lowering the concentrate grade. Together, these tests provide direct indications of problem areas and opportunities. A poor separation by floatability indicates that the design or operation of the plant should be changed. Unwanted aspects of the plant operation could be identified and corrected by appropriate measures e.g. by adding more flush-water to stop too much fine slow- floating gangue from going to the concentrate.

[0045] In the case of an ore body being considered for processing by flotation, a drill- core sample could be subjected to the test procedure to establish a grade-recovery curve which could be obtained by a well-designed full-scale flotation plant. An economic cut-off grade could be determined. The compositions of the fast-floating fractions of material could be measured and this information could be used in the conceptual design of a downstream treatment process. For example there might be a fast-floating mineral present that would cause problems with smelting.

[0046] In all these cases, the tests could be done with differing chemical treatments by reagents. Comparative physical separations by flotation rates would then give direct evidence on how flotation of the different particles is affected by changes in reagents

and reagent conditionings. Similarly, comparative tests could be done with feed ore ground to different extents or by different grinding methods.

[0047] The test can provide standard results that reflect only the floatabilities of particles which facilitates the characterisation of many ores in useful databases. Such results are usable directly in flotation simulators for process design and optimisation.