CA2073709A1 - Separation of fine sulphide minerals by froth flotation - Google Patents

Abstract

Abstract of the Disclosure:
A process is disclosed which is capable of improving selectivity and recovery in subsequent mineral processing by flotation of fine sulphidic minerals of copper, lead, zinc, nickel, molybdenum, gold, silver, and the platinum group minerals. The process comprises:
providing a high shear conditioner consisting of a pulp holding tank, a high shear impeller, and a motor and drive capable of providing power draw for the impeller in the 5 to 150 kW/m3 range; and imparting to the pulp a high energy input ranging from 1 to 100 kWh/m3 of pulp, depending on the volume of the tank.

Description

20737~9 SFPARATION OF FINF SULPHIDF MIN~RALS BY FRO~H FLOTATION
This invention relates to the separation of sulphidic minerals by froth flotation in a mineral separation process. More particularly this invention relates to a new conditioning process to improve the separation by differential froth flotation of ultrafine sulphidic minerals present in polymetallic sulphides.
Froth flotation is a well-known mineral processing operation for obtaining mineral concentrates of a desired compound or element. In this process a collector agent is added to the aqueous slurry of the ground ore. Mixing is usually achieved in a mixing tank called a conditioner or directly in the flotation cells.
The collector agent for a particular mineral is preferentially adsorbed on the surface of the mineral particles containing the desired compound, thereby rendering the surface hydrophobic (non-wetting by water).
In a flotation device and in the presence of a frothing agent, air bubbles will be attached to the particles of the desired mineral thereby lifting them to the surface of the slurry. The froth in most instances is collected by mechanical means. The separated froth is usually dried or dewatered, and the concentrate is treated in subsequent steps to recover the desired compound or element.
In addition to collector and frothing agents being added to an ore slurry in the mineral separation process, it is usual to add depressant agents, which will be adsorbed on the surface of particles containing unwanted compounds. Depressants can be added to the same conditioner as the collector, or to a different one. The surface of the particles are thereby rendered wettable, i.e. hydrophillic and hence not floatable. The unwanted minerals may contain minerals bearing certain compounds which are to be recovered by subsequent flotation process steps, by means of additions of a collector agent specific to such a mineral. When two or more flotation circuits are operated sequentially to selectively separate desired compounds present in ores, the process is referred to as differential flotation.
The usual practice of differential flotation is to treat the ore pulp similarly to a single flotation circuit but with reagents which will permit the flotation of only one of the desired minerals by preventing or minimizing flotation of other minerals. The residue from the first flotation stage is then treated in a conditioner with one or more chemical reagents to bring about flotation and concentration of a second mineral. In the second flotation process the desired minerals contained in the froth will provide a concentrate of minerals which have been separated from the minerals contained in the concentrate of the first flotation step. The residue or tailing of the second flotation process step thus will contain the unwanted minerals separated from the two desired minerals originally present in the ore. Of course, more than two flotation process circuits may be introduced sequentially to result in more than two concentrates of compounds and minerals which are of use to the mineral processor.
The concentrates obtained still contain unwanted compounds, but have been substantially enriched in the desired compound or element, thereby reducing the cost of further recovery steps. It is customary to refer to the compound of metals in an ore which are to be recovered from the ore under treatment as value metals.
Massive sulphidic ores can contain sulphides of three or more metals which are to be separated and recovered by separate process steps; they usually contain also sulphides which are intimately mixed and disseminated throughout the ore. The iron sulphides, quartz and silicates are usually of no value to the metallurgist and are to be separated from the value metals and discarded.
In most massive sulphides ores, the various sulphidic value metals and the iron sulphides are so finely disseminated and intimately mixed to require very fine grinding or regrinding i.e. below 30 micrometers.

Although the fine grinding is technically feasible, the separation by froth flotation of the various metal values from a very finely ground ore (i.e. minus 30 micrometers) is difficult. Two major problems are usually encountered.
5The first problem is related to the recovery of the very finely ground sulphidic metal values. It has been well known in the industry that the recovery of minus 10 micrometer sulphidic minerals is much lower than the recovery of the plus 10 micrometer sulphidic minerals. In 10other words, it has been often proven that the major fraction of the sulphidic metal value losses in the flotation tailings from milling operations using very fine grinding (or regrinding) is generally contained in the finest fraction of the tailing. Using conventional 15methods for processing finely ground sulphidic material, a large proportion of the finest fraction of the value metal escapes the process and is definitively lost to the tailings.
In addition to the loss of values due to the low 20recovery of the fine sulphidic minerals, there is also a second problem related to the poor selectivity observed during the froth flotation of ultrafine minerals. It is also well known from current operations processing very finely divided sulphidic minerals that the finest (smaller 25than 10 micrometers) fraction of a final concentrate is significantly lower grade than the coarsest fraction. The grade of the global concentrate is therefore quite lower, and so its metallurgical value.
In the conventional froth flotation plants processing sulphide ores, the conditioners (or S conditioning tanks) are designed to blend various pulp streams and to mix them with suitable chemical reagents such as collectors, activators, depressants, modifiers.
The size of the conditioning tank is determined based on the time required for the various chemical agents to achieve full efficiency; in some cases, the action of the chemical agent is so rapid that no conditioning time is required; other chemical agents need a certain time to perform their task, and they will be added to the ground ore pulp in conditioners large enough to provide the required contact time between the chemicals and the pulp.
Conditioners are tanks equipped with a motor driven impeller to allow for proper suspension of the pulp.
There are a variety of impeller types which are currently used in the industry in standard conditioner units: propellers (marine type), turbines (pitched blade turbine PBT), hydrofoils. In the last 8-10 years the low shear, high flow, hydrofoil has become the standard mixing impeller for slurry applications in all solid concentrations. The hydrofoil replaced the pitched blade turbine (PBT) due to its high efficiency (low shear) characteristics in these solid suspension cases. The pitched blade turbine imparts too much shear and turbulence to the slurry and too little axial flow when compared to the hydrofoil. This high efficiency impeller coupled with impeller diameter to tank diameter ratios (D/T ratio) in the range of 0.25 to 0.30 have resulted in the most efficient combination for solid suspension.
The design of the standard conditioner units is based on minimizing the power draw of the conditioners while ensuring complete agitation of the pulp and avoiding settling of the coarsest particles. Installed power in standard conditioners used in froth flotation plants processing sulphide ores typically lies in the 0.04 to 1.5 kW/m3 range.
A new process has been developed to enhance the recovery of ultrafine metal sulphides contained in finely ground sulphide ores. Sulphidic ores that could be successfully processed using the new conditioning process of this invention include those of copper, lead, zinc, nickel, molybdenum, gold, silver, and the platinum group minerals (PGM).
The new process, called high intensity conditioning, consists in modifying the conditioning stage prior to flotation in such a way as to cause flocculation/agglomeration of the ultrafine metal sulphides in the conditioner; the flocs/agglomerates so formed can then be recovered as usually in the subsequent flotation stage. To be effective, the new process (High intensity conditioning) requires:
a) the use of a different conditioner unit (called high intensity conditioner), significantly different from the standard conditioners used to process sulphide minerals and briefly described above. The high intensity conditioner consists of:
- a holding tank, usually fully baffledi however baffle design is not critical to the conditioning process - a high shear impeller - a motor and drive capable of providing power draw for the impeller in the 5 to 150 kW/m3 range b) imparting to the pulp the appropriate amount of energy sufficient to overcome t h e e n e r g y b a r r i e r f o r flocculating/agglomerating the ultrafine metal sulphide. The optimum energy required has to be determined in each specific case since it will depend on the type of sulphide minerals present in the pulp, their size and the reagents in the pulp. In general, the energy requirements for high intensity conditioning are in the 1 to 10 k~/m3 range for the larger units (>25m3~, in the 20 to 70 kWh/m3 range for the smaller units (1-10 m3), and up to 100 kWh/m3 for the laboratory unit (2-30 liters). For comparison, energy requir~ments in standard conditioners larger than 25 m3 are usually in the 0.01 to 0.04 kWh/m3 range. Various impeller designs could be used for high intensity conditioning. An impeller suitable to be used for high intensity conditioning can be characterized by:
- one to three turbines mounted on the same shaft. The turbines could be opposed or not.
- at least one turbine comprises 3-6 blades.
- the ratio of the impeller diameter to the tank diameter, or the D/T ratio, ranges between 0.3 and 0.6; such a high ratio would be considered inefficient by conventional solid suspension requirements.
- the impeller, called HIC, differs from the radial flow impeller also because of the pitch ~40 to 70~ to the 20737~9 blades. This develops an axial component to the flow ensuring top to bottom turnover of the slurry preventing any stagnant zones. The HIC impeller has a lowwer blade width (W) to diameter (D) ratio compared to conventional impellers, as shown in Table 1.
Table 1: W/D ratio for Various Impellers Impeller Type PBT Radial HIC
W/D Ratio 0.19-0.25 0.15-0.19 0.10-0.20 Due to its design, the HIC impeller imparts more shear and turbulence to the pulp as compared to other impellers; the HIC impeller develops a high power draw, or high power number. It is believed that high shear is necessary to achieve selective agglomeration and/or flocculation of ultrafine particles in the pulp. These flocs or agglomerates then respond similar to coarse particles in the subsequent s~paration process of froth flotation resulting in good selectivity and recoveries.
Those skilled in the art will recognize that specific power requirements ~kW/m3) for processes involving mixing, in particular flotation and conditioning, significantly decrease with increase of the unit volume. This is also the case for the conditioner in this invention.

20737~9 Small high intensity conditioning units (less than 1 m3) could require specific power inputs larger than 100 kW/m3 to achieve the turbulent mixing needed to produce the desired results. Intermediate units (1 - 10 m3) could require a power input comprised between 25 and 100 kW/m3, while larger units (larger than 25 m3) could require power inputs in the 5 - 25 kW/m3 range.
The minimum power requirement to obtain the desired effect depends on the ore treated, the pulp density, the pulp viscosity, the reagents added to the conditioner and the tank volume. The number of impellers and their particular design will also depend on the tank height since it is necessary to achieve violent, turbulent conditioning throughout the entire vessel.
This invention will now be disclosed by way of example with reference to the accompanying drawings in which:
Figures la and lb illustrate side and plan views, respectively, of an impeller design suitable to be used in high intensity conditioning.
Figure 2 is a copper-lead-silver rougher and cleaner flotation flowsheet with no high intensity conditioning; and Figure 3 is a flowsheet as shown in Figure 2 with the addition of high intensity conditioning.
Referring to Figures la and lb, there is shown an impeller design comprising three, six blade turbines 10 mounted on a shaft 12 suspended in a tank 14. In this particular example, the laboratory turbine used had the following dimensions: D = 10.2 cm, W = 1.8 cm and a = 35.
Three such turbines were mounted on the same shaft although less than three turbines may be used in some applications. The tank was a fully baffled cylindrical tank (8L nominal volume) with a diameter L of 20.3 cm and a height of 25 cm. Installed power was 190 watts.
A detailed description of this invention and its application for the treatment of fine sulphide minerals will be provided herein below with reference to working examples.
ExamDle 1:
A massive sulphidic ore from Canada, which is treated in a commercial operation for the recovery of copper, lead, silver and zinc as major value metals, was treated in a laboratory flotation circuit using the same flotation reagents as used in the plant. The major difficulty in treating this ore is that the sulphide minerals are so disseminated that a very fine grinding is necessary to achieve liberation; however, using the standard flotation practice, low grade concentrates are produced at a low recovery.
In this example, two laboratory tests were conducted on pulp samples taken directly from the plant in 20737~9 the copper-lead-silver circuit. In the first test, the standard plant conditions were simulated, i.e. the collectors and frother were added directly to the flotation cell. In this test, collector agents A343, A355 and R2~1 (American Cyanamid) were added as well as the frothing agent MIBC (methyl isobutyl carbinol). In the second test, the same dosage of the same reagents was added to another sample of the same pulp, which was then treated for 20 minutes in the high intensity conditioner described above, before being submitted to the same froth flotation procedure.
The results obtained for these two tests are summarized in Table 2.
Table 2 Te6t Products Weigh~ Assays %, gtt 9'o Distribution % Cu Pb Ag Cu Pb A8 No bigb Copper-lead-silvorCone I 17.95 1.40 14.24 436 59.6 64.7 58.8 intensity Copper-lead-silvor Cone 2 5.20 0.78 7.91 259 9.6 10.4 10.1 conditioner Copper-lead-silvor Cone 3 1.89 0.54 7.60 233 2.4 3.6 3.3 2 0 Copper-lead-silver Tail 74.96 0.16 1.12 49A 28.4 21.3 27.8 Hoad (Cale~ 100.00 0.42 3.95 133 100.0 100.0 100.0 20rnimrb Coppor-lesd-silver Cone 1 12.44 2.28 23.86 685 67.8 77.6 70.3 high Copper-lead-silvor Cone 2 2.28 05~5.08 180 2.8 3.0 3A
inbnsiq Copper-lead-silvor Cone 3 2.56 0.28 3.70 115 1.7 25 2.4 2 5 condi~nin~ Copper-lesd-silver Tail 82.72 0.14 0.78 35.0 27.7 16.9 23.9 Head (Calc) 100.00 OA2 3.82 121 100.0 100.0 100.0 By comparing the flotation test results shown in Table 2, it is clearly observed that the use of the high 207~709 intensity conditioning of this invention significantly improves both the grade and the recovery of the copper, lead and silver minerals.
Ex~m~le 2:
Two other pulp samples were taken from the same plant as discussed in Example 1 and were used in two laboratory tests. In the first test, standard plant practice was simulated; no high intensity conditioning was carried out and the flowsheet illustrated in Figure 2 was followed.
In the second test, the same general flowsheet and reagents were used but the pulp was treated in the laboratory high intensity conditioner for 30 minutes before rough flotation, and the crude concentrate after regrinding was treated for 10 minutes in the high intensity conditioning before being submitted to cleaning stages. The flowsheet used during the second test is illustrated in Figure 3.
The results obtained during these two tests are summarized in Table 3.

Tabl e 3 Test Products Weigbt Assays %. g/t % Dis~ributio~
% Cu Pb Ag Cu Pb Ag No higb Copper-lead-silver Cl Conc8.79 2.68 27.32 694 67.7 67.8 58.7 intensity Copper-lead-silver Ro Conc20.45 1.31 13.28 351 77.2 76.7 69.0 conditioner Copper-lead-silver Ro Tail 79.55 0.10 1.04 40.5 22.8 23.3 31.0 Head (Calc) 100.00 0.35 3.54 104 100.0 100.0 100.0 high Copper-lead-silver Cl Conc8.36 3.12 32.73 786 71.2 76.1 65.4 intensi~y Copper-lead-silver Ro Conc18.44 1.54 16.06 402 77.7 82.3 73.8 0 conditioning Copper-lead-silver Ro Tail 81.56 0.10 0.78 32.2 22.3 17.7 26.2 Head (Calc) 100.00 0.37 3.60 100.5 100.0 100.0 100.0 From the results in Table 3, it is clearly seen that the introduction of high intensity conditioning after primary grind (before rougher flotation) and after regrinding (before cleaner flotation) has greatly increased the grade of the concentrates, and recovery kinetics as well as selectivity (due to a better rejection of iron sulphides) were improved due to the new invention.
~xam~le 3:
A massive sulphide ore originating in Quebec (Canada) containing copper, silver and zinc as major value metals was treated in a laboratory batch flotation circuit. Plant pulp samples from the zinc circuit were used. Two rougher flotation tests were conducted on the plant pulp.
In the first test, standard plant reagents were conditioned for 10 minutes in the flotation cell before zinc rougher flotation. In this case, copper sulphate, lime and collector were added to the cell.
In the second test, the pulp was treated with the same reagents for 20 minutes in the high intensity conditioner before being submitted to zinc rougher flotation.
The results obtained during these two tests are summarized in Table 4.
Table 4 Test Products Weight Assays % % Dis~ibulion % Zn Zn No high Zn Rougher Conc 1 2.54 30.10 44.9 intensiiy ZnRoqgberCooc 2 1.75 27.00 27.7 conditioning Zn Rougher Conc 3 1.70 13.60 13.6 Zn Total Rougher Conc 6.00 24.51 B6.2 Zn Rougher Tail 94.00 0.25 13.8 Head (Calc) 100.00 1.70 100.0 High in~ensity Zn Rougher Conc 1 4.71 31.0 85.2 conditioning Zn Rougher Conc 2 1.32 9.9 7.6 (20 minutes) Zn ~ougber Conc 3 2.11 1.53 1.9 2 0 Zn Total Rougher Conc 8.14 19.96 94.6 Zn Rougher Tail 91.86 0.10 5A
Hoad (Calc) 100.01.72 100.0 By comparing the flotation test results in Table 4, it is clear that the use of high intensity conditioning 25of this invention has greatly improved the selectivity and kinetics of zinc rougher flotation: the concentrate produced after 3 minutes of flotation assayed 31% Zn and contained 85% of the zinc in the feed when the high intensity conditioner of this invention was used, while it 30assayed 30.1~ Zn and contained only 44.9% of the zinc in 1~
the feed, when the high intensity conditioner was not used.
~xam~le 4:
A massive sulphide ore originating in British Columbia (Canada), containing copper as major value metal was treated in a laboratory batch flotation circuit. The major gangue minerals in the ore were iron sulphides (pyrrhotite and pyrite). Three laboratory rougher flotation tests were conducted on this ore using identical conditions and reagent scheme except for the conditioning before copper rougher flotation.
In the first test, the ground pulp and appropriate reagents were not conditioned before rougher flotation. In the second test, the ground pulp and the same appropriate reagents were conditioned for 20 minutes in the high intensity conditioner before rougher flotation. In the third test, the ground pulp and the same appropriate reagents were conditioned for 20 minutes in the flotation cell before rougher flotation.
The results of the three flotation tests are summarized in Table 5.

20737~9 Table 5 Test Products Weight Assays % % Distribution % Cu Cu No high Cu Rougher CODC I 7.97 8.59 32.9 intensity Cu Tolal Rougher Conc 31.25 5.94 89.1 conditioning Cu Rougber Ta~ 68.75 0.33 10.9 Head (Calc) I00.0 2.08 100.0 High intensity Cu Rougher CODC I 8.87 17.60 74.2 conditioning Cu Tot~ Rougher Conc 23.94 8.15 92.8 (20 ~ninutes) Cu Rougher Ta~ 76.06 0.20 7.2 Head (C~c) I00.00 2.10 100.0 20 rninute Cu RougheT Conc 1 14.13 5.87 38.8 conditioning Cu Tot~ Rougher Conc 36.00 5.41 91.0 in the Denver Cu Rougher Ta~ 64.00 0.30 9.0 Head (Calc) 100.00 2.14 1000 By comparing the results of the two first flotation tests in Table 5, it is again seen that the introduction of high intensity conditioning greatly increases the kinetics of copper flotation and the selectivity versus iron sulphides.
By comparing the results of the two last flotation tests in Table 5, it is also clearly seen that the beneficial effect observed when introduciny high intensity conditioning cannot be attributed to prolonged conditioning times but to the high shear developed in the pulp by the high intensity conditioning unit itself.
It has been shown by numerous examples conducted on a number of different massive sulphide ores that the high intensity conditioning of this invention is highly efficient in improving the froth flotation separation of 20737~9 ultrafine metal sulphides.
Although the present invention has been described with reference to the preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.

Claims (6)

1. A process capable of improving selectivity and recovery in subsequent mineral processing by flotation of fine sulphidic minerals of copper, lead, zinc, nickel, molybdenum, gold, silver, and the platinum group minerals, said process comprising:
a) providing a high shear conditioner consisting of a pulp holding tank, a high shear impeller, and a motor and drive capable of providing power draw for the impeller in the 5 to 150 kW/m3 range; and b) imparting to the pulp a high energy input ranging from 1 to 100 kWh/m3 of pulp, depending on the volume of the tank.

2. A process as defined in claim 1, wherein the holding tank is fully baffled.

3. A process as defined in claim 1, wherein the impeller comprises one to three turbines on the same shaft, at least one turbine with 3 to 6 blades with a steep pitch between 40 and 70° and the impeller diameter to tank diameter ratio (D/T) being between 0.3 and 0.6.

4. A process as defined in claim 1, wherein the high intensity conditioner was used to improve the recovery of ultrafine sulphidic minerals of copper, lead and silver.

5. A process as defined in claim 1, wherein the high intensity conditioner was used to improve the recovery of ultrafine sulphidic minerals of copper.

6. A process as defined in claim 1, wherein the high intensity conditioner was used to improve the recovery of ultrafine sulphidic minerals of zinc.