containing an iron sulfide

Field of the Invention The present invention is directed to a method of recovering a copper sulfide concentrate from an ore containing an iron sulfide which provides an improvement in concentrate grade and recovery of copper sulfides and has a low consumption of processing chemicals.

Background of the Invention

The most common method for recovering a copper sulfide concentrate from an ore is by froth flotation. The ore is wet ground to form a mineral pulp, which is usually

conditioned with a collector compound that adsorbs to the surface of copper sulfide minerals and makes the surface of copper sulfide minerals more hydrophobic. A gas is then passed through the mineral pulp to form gas bubbles, hydrophobic particles of the mineral pulp attach

predominantly to the gas/liquid phase boundary of the bubbles and are carried with the gas bubbles to the froth that forms on top of the mineral pulp. The froth is removed from the liquid surface to recover a copper sulfide

concentrate . Most copper sulfide ores contain iron sulfides in addition to copper sulfides and one aims at achieving selective flotation of copper sulfides, with iron sulfides remaining in the flotation tailings.

US 5,110,455 discloses a method for separating copper sulfide from rimmed iron sulfide which uses conditioning of the mineral pulp with an oxidant that is preferably hydrogen peroxide. The document teaches to add an oxidant in an amount that raises the redox potential of the mineral pulp by 20 to 500 mV.

A Uribe-Salas et al . , Int. J. Miner. Process. 59 (2000) 69-83 describe an improvement in the selectivity for the flotation of chalcopyrite from an ore of pyrite matrix by raising the redox potential of the mineral pulp by 0.1 V through an addition of hydrogen peroxide before flotation. The amount of hydrogen peroxide added is adjusted to provide a constant redox potential.

Summary of the Invention

The inventors of the present invention have found that addition of small amounts of hydrogen peroxide to the conditioned mineral pulp before or during flotation, which do not raise the redox potential of the pulp but to the contrary effect a lower redox potential, surprisingly provide a substantial improvement in concentrate grade and recovery of copper sulfides. The present invention is therefore directed to a method for recovering a copper sulfide concentrate from an ore

containing an iron sulfide, which method comprises the steps of a) wet grinding the ore with grinding media to form a

mineral pulp, b) conditioning the mineral pulp with a collector

compound to form a conditioned mineral pulp, and c) froth flotation of the conditioned mineral pulp to

form a froth and a flotation tailing, separating the froth from the flotation tailing to recover a copper sulfide concentrate, wherein hydrogen peroxide is added to the conditioned mineral pulp between steps b) and c) or during step c) in an amount effective to lower the redox potential of the conditioned mineral pulp.

Brief Description of the Drawings

Figure 1 shows redox potential E _h plotted against the amount of added hydrogen peroxide for the experiments of example 1. Figure 2 shows curves for cumulated copper concentrate grade (y-axis) plotted against cumulated copper recovery (x-axis) for examples 2 and 3.

Figure 3 shows redox potential E _h plotted against the amount of added hydrogen peroxide for the experiments of example 4.

Figure 4 shows curves for cumulated copper concentrate grade (y-axis) plotted against cumulated copper recovery (x-axis) for examples 5 to 7.

Figure 5 shows redox potential E _h plotted against the amount of added hydrogen peroxide for the experiments of example 8.

Figure 6 shows curves for cumulated copper concentrate grade (y-axis) plotted against cumulated copper recovery (x-axis) for examples 9 and 10. Figure 7 shows redox potential E _h plotted against the amount of added hydrogen peroxide for the experiments of example 11.

Figure 8 shows curves for cumulated copper concentrate grade (y-axis) plotted against cumulated copper recovery (x-axis) for examples 12 and 13. Detailed Description of the Invention

The method of the invention recovers a copper sulfide concentrate from an ore containing an iron sulfide using three method steps.

In the first step of the method of the invention, the ore is ground with grinding media to form a mineral pulp, i.e. an aqueous suspension of ground ore. Suitable grinding media for grinding ores are known from the prior art.

Preferably, the grinding media comprise a grinding surface made of steel or cast iron having an iron content of at least 90 % by weight. Grinding can be carried out in any mill known from the art that uses grinding media. Suitable mills are ball mills using balls as grinding media or rod mills using rods as grinding media, with ball mills being preferred. The mill preferably has a lining of an abrasion resistant material.

The ore is wet milled to form a mineral pulp, i.e. an aqueous suspension of ground ore. The ore may be fed to the mill together with water. Alternatively, ore and water are fed separately. Milling is carried out typically to a median particle size of 50-200 ym. Preferably, the ore is ground to what is called the liberation size, i.e. the maximum median particle size where essentially all copper sulfide is exposed to the particle surface and essentially no copper sulfide remains encapsulated inside a particle.

In the second step of the method of the invention, the ore is conditioned with a collector compound to form a

conditioned mineral pulp. Collector compounds are compounds which after addition to the mineral pulp adsorb to the surface of copper sulfides and render the surface

hydrophobic. Collector compounds suitable for froth

flotation of copper sulfides are known from the prior art. Preferably, an alkali metal alkyl xanthate is used as collector, such as potassium amyl xanthate or sodium ethyl xanthate. Conditioning is typically carried out by adding the conditioner to the mineral pulp and mixing for a time period sufficient to achieve adsorption of the conditioner to the mineral surface, typically for less than 15 minutes. Preferably for 0.5 to 15 minutes. Alternatively, the collector is added in the first step of grinding and conditioning is carried out by retaining the mineral pulp for a corresponding time.

Further reagents, such as frothers, pH regulators,

depressants and mixtures thereof may be added in the grinding step, the conditioning step or in both steps.

Frothers are compounds that stabilize the froth formed in a froth flotation. Suitable frothers are commercially

available, e.g. from Huntsman under the trade name

Polyfroth®. Depressants are compounds that render the surface of unwanted minerals more hydrophilic. Polyamines known from the prior art, such as diethylenetriamine or triethylenetetraamine, may be used as depressants for iron sulfides. pH regulators, such as calcium oxide, calcium hydroxide or sodium carbonate, may be added to adjust the pH of the mineral pulp to a desired value, preferably to a value in the range from 7 to 11. In the third step of the method of the invention, the conditioned mineral pulp is subjected to froth flotation to form froth and a flotation tailing, with hydrogen peroxide being added to the conditioned mineral pulp during froth flotation or between the second step of conditioning the mineral pulp and the step of froth flotation. The froth is separated from the flotation tailing to recover a copper sulfide concentrate. Froth flotation may be carried out using equipment and procedures known to a person skilled in the art for the froth flotation of copper ores. Froth flotation may be carried out as a single stage flotation or as a multiple stage flotation, using e.g.

rougher, scavenger and cleaner stages. In a multiple stage froth flotation, hydrogen peroxide is preferably added before the first flotation stage or during the first flotation stage.

Hydrogen peroxide is added to the conditioned pulp in an amount that is effective to lower the redox potential of the conditioned mineral pulp. Preferably, hydrogen peroxide is added in an amount lowering the redox potential by at least 10 mV. When the ore is ground with grinding media comprising a grinding surface made of steel or cast iron with an iron content of at least 90 % by weight, the amount of hydrogen peroxide added is preferably adjusted to provide a maximum lowering of redox potential after

hydrogen peroxide addition. The redox potential of the mineral pulp can be determined with methods known from the prior art. Preferably, the redox potential is determined with a redox electrode that uses an electrochemical cell. The method of the invention requires only small amounts of hydrogen peroxide. In general, less than 100 g hydrogen peroxide per ton of ore are needed and preferably less than 50 g/t are used. The method can be carried out with as little as 2 g/t hydrogen peroxide per ton of ore and preferably at least 5 g/t are used.

When hydrogen peroxide is added between the step of conditioning the mineral pulp and the step of froth

flotation, the time period between addition of hydrogen peroxide and froth flotation is preferably less than

15 min, more preferably less than 3 min and most preferably less than 1 min. Limiting the time period between addition of hydrogen peroxide and froth flotation improves both concentrate grade and recovery of copper sulfides. In a preferred embodiment of the method of the invention, froth flotation is carried out continuously and hydrogen peroxide is added continuously during froth flotation.

Hydrogen peroxide is preferably added as an aqueous

solution comprising 0.5 to 5 % by weight hydrogen peroxide. Adding such a dilute hydrogen peroxide solution provides better concentrate grade and recovery than obtained with the same amount of a more concentrated hydrogen peroxide solution. Therefore, it is preferred to dilute a commercial hydrogen peroxide solution comprising 30 to 70 % by weight hydrogen peroxide to a dilute solution comprising 0.5 to 5 % by weight hydrogen peroxide before adding it in the method of the invention.

Usually there will be an optimum amount of hydrogen

peroxide per ton of ore that depends on the ore

composition. Increasing the amount of added hydrogen peroxide up to the optimum amount will lead to an increase in concentrate grade and recovery of copper sulfides, whereas increasing the amount of added hydrogen peroxide beyond the optimum amount will not lead to any further improvement, but in general will even lead to a reduced concentrate grade and recovery of copper sulfides.

The prior art teaches that hydrogen peroxide shall be added to a flotation process for copper sulfide ores in amounts increasing the redox potential of the ore in order to improve the recovery of copper sulfides. The inventors of the present invention have found that addition of hydrogen peroxide to the conditioned mineral pulp in small amounts that do not increase the redox potential of the mineral pulp, but effect a lowering of the redox potential,

surprisingly provides a substantial increase in the

concentrate grade and recovery of copper sulfides. Even more surprisingly, for most copper sulfide ores the

addition of hydrogen peroxide in an amount lowering the redox potential of the conditioned ore will lead to a better concentrate grade and recovery of copper sulfides than addition of a large amount of hydrogen peroxide that raises in the redox potential.

In addition to providing an improvement in the concentrate grade and recovery of copper sulfides, the method of the invention can also provide an improved recovery of gold from the ore and reduce the content of iron sulfides and arsenic minerals in the copper sulfide concentrate.

The following examples illustrate the invention, but are not intended to limit the scope of the invention.

Examples

In all flotation experiments, ores were ground to a

particle size Pso of 200 ym with a laboratory Magotteaux Mill® using 16*1 inch forged carbon steel rods as grinding media. The resulting mineral pulp was transferred to a laboratory flotation cell and mixed for two minutes to homogenize. Sodium ethyl xanthate was added as collector at 21 g per ton of ore, followed by 5 g per ton of POLYFROTH® H27 frother from Huntsman. The resulting mineral pulp was conditioned for 1 min before flotation was started by introducing air. Four timed concentrates were collected during flotation over intervals given in the examples. Each concentrate was collected by hand scraping the froth from the surface of the pulp once every 10 seconds. Concentrates were weighed and assayed and cumulated grades and

recoveries were calculated from these data. Grades were plotted against recovery and the values for grades at a specific copper recovery and recoveries at a specific copper grade given in the tables below were read from these curves . Examples 1 to 3

Flotation was carried out with a sedimentary copper/gold ore having a head assay of 1.74 % Cu, 9.95 % Fe, 3.27 ppm Au, 168 ppm Bi, and 3.21 % S. In example 1, varying amounts of hydrogen peroxide were added immediately before starting flotation and the redox potential (E _h ) was determined immediately after flotation was started. The results are summarized in table 1. Figure 1 shows the values of E _h plotted against the amount of added hydrogen peroxide. Figure 1 shows E _h decreasing upon addition of small amounts of hydrogen peroxide and

increasing upon addition of larger amounts.

Table 1

Variation of added hydrogen peroxide amount

In examples 2 and 3, flotation was carried out with concentrates collected over intervals of 0.5, 2, 5, and 10 minutes. No hydrogen peroxide was added in example 2. In example 3, a 1 % by weight aqueous hydrogen peroxide solution was added in an amount of 75 g/t ore immediately before starting flotation. Figure 2 shows the curves for cumulated copper concentrate grade plotted against cumulated copper recovery for examples 2 and 3. Tables 2 and 3 compare these results at 85 % copper recovery and at 18 % concentrate copper grade.

Table 2

Copper and gold concentrate grades and gold and diluent recoveries at 85 % copper recovery

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue

Table 3

Copper and gold recovery and concentrate gold and diluents grade at 18 % concentrate copper grade

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue

Examples 4 to 7

Flotation was carried out with a volcanogenic sulfide deposit ore having a head assay of 2.63 % Cu, 19.2 % Fe, and 15.9 % S.

In example 4, varying amounts of hydrogen peroxide were added immediately before starting flotation and the redox potential (E _h ) was determined immediately after flotation was started. The results are summarized in table 4. Figure 3 shows the values of E _h plotted against the amount of added hydrogen peroxide. Figure 3 shows E _h decreasing upon addition of small amounts of hydrogen peroxide and

increasing upon addition of larger amounts. Table 4

Variation of added hydrogen peroxide amount

In examples 5 to 7, flotation was carried out with

concentrates collected over intervals of 0.5, 2, 4, and 7 minutes. No hydrogen peroxide was added in example 5. In examples 6 and 7, a 1 % by weight aqueous hydrogen peroxide solution was added in amounts of 15 g/t ore and 240 g/t ore immediately before starting flotation. Figure 4 shows the curves for cumulated copper concentrate grade plotted against cumulated copper recovery for examples 5 to 7. Tables 5 and 6 compare these results at 90 % copper recovery and at 18 % concentrate copper grade. Table 5

Copper and iron concentrate grades and diluent recoveries at 90 % copper recovery

* Not according to the invention,

iron sulfides, NSG = non sulfide gangue

Table 6

Copper and iron recovery and concentrate diluents grade at 18 % concentrate copper grade

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue Examples 8 to 10

Flotation was carried out with a porphyry copper/gold ore having a head assay of 0.43 % Cu, 5.4 % Fe, 0.18 ppm Au and 5.0 % S. In example 8, varying amounts of hydrogen peroxide were added immediately before starting flotation and the redox potential (E _h ) was determined immediately after flotation was started. The results are summarized in table 7. Figure 5 shows the values of E _h plotted against the amount of added hydrogen peroxide. Figure 5 shows E _h decreasing upon addition of small amounts of hydrogen peroxide and

increasing upon addition of larger amounts.

Table 7

Variation of added hydrogen peroxide amount

H2O2 added Example 8

[g/t] E _h [mV]

0 224

7.5 203

15 186

30 199

60 190

120 201

180 210

240 225 In examples 9 and 10, flotation was carried out with concentrates collected over intervals of 0.5, 2, 4, and 9 minutes. No hydrogen peroxide was added in example 9. In example 10, a 1 % by weight aqueous hydrogen peroxide solution was added in an amount of 120 g/t ore immediately before starting flotation.

Figure 6 shows the curves for cumulated copper concentrate grade plotted against cumulated copper recovery for examples 9 and 10. Tables 8 and 9 compare these results at 70 % copper recovery and at 9 % concentrate copper grade.

Table 8

Copper and gold concentrate grades and gold and diluent recoveries at 70 % copper recovery

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue

Table 9

Copper and gold recovery and concentrate gold and diluents grade at 9 % concentrate copper grade

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue

Table 9 shows an additional improvement in the recovery of copper and gold.

Examples 11 to 13

Flotation was carried out with an iron oxide hosted

copper/gold ore having a head assay of 0.83 % Cu, 21.7 % Fe, 0.39 ppm Au, 568 ppm As, and 4.0 % S.

In example 11, varying amounts of hydrogen peroxide were added immediately before starting flotation and the redox potential (E _h ) was determined immediately after flotation was started. The results are summarized in table 10. Figure 7 shows the values of E _h plotted against the amount of added hydrogen peroxide. Figure 7 shows E _h decreasing upon addition of small amounts of hydrogen peroxide and

increasing upon addition of larger amounts. Table 10

Variation of added hydrogen peroxide amount

In examples 12 and 13, flotation was carried out with concentrates collected over intervals of 0.5, 2, 4, and 8 minutes. No hydrogen peroxide was added in example 12. In example 13 a 1 % by weight aqueous hydrogen peroxide solution was added in an amount of 50 g/t ore immediately before starting flotation. Figure 8 shows the curves for cumulated copper concentrate grade plotted against cumulated copper recovery for examples 12 and 13. Tables 11 and 12 compare these results at 80 % copper recovery and at 13 % concentrate copper grade . Table 11

Copper and gold concentrate grades and gold and diluent re ^¬ coveries at 80 % copper recovery

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue

Table 12

Copper and gold recovery and concentrate gold and diluents grade at 13 % concentrate copper grade

* Not according to the invention,

IS = iron sulfides, NSG = non sulfide gangue