OA16959A - Enrichment of metal sulfide ores by oxidant assited froth flotation. - Google Patents

Abstract

The present invention is directed to methods that can be used in the enrichment of metal sulfide ores in desired minerals in cases where the ores have sulfide-containing gangues. The method involves adding an oxidant such as hydrogen peroxide to slurries prepared from the ores during, or immediately prior to froth flotation.

Description

Enrichment of Métal Sulfîde Ores by Oxidant Assisted Froth Flotation

Field of the Invention

The présent invention is directed to a method of improving the grade and recovery of desired base minerais, espccially copper. from métal sulfîde ores that hâve a sulfidecontaining gangue.

Background οΓ the Invention

The most common means of recovering a desired minerai from a métal sulfîde ore is 10 by a procedure that includes froth flotation (Froth Flotation: A Century of Innovation. Fuerstenau, et al. eds., Soc. Mining, Metallurgy and Exploration, 2007). Typically, ores are suspended in water and ground using milling equipment to the libération size, Le., the largest particle size which exposes the desired minerai to the action of flotation reagents (usually about 50 · 200 pm). The ground ore forms a pulp which is fed to flotation cells that 15 are typically arranged In banks of roughers, scavengers and cleaners.

During froth flotation, air is introduced into the pulp as fine bubbles which provide a surface for the attachment of relatively hydrophobie minerais. These minerais then rise with the bubbles to the surface of flotation cells and are removed. The hydrophilic gangue 20 particles are less attracted to the air bubbles and therefore tend to be left behind in the pulp. Frothers (such as pine oil, polyglycols and polyoxyparafins) and pH modifiers (such as CaO, NajCOj, NaOH or H2SO4, HCl) may be used to improve séparations. Collectors (e.g., xanthates, carbonates and fatty acids) may also be introduced to help promote the attachment of minerais to air bubbles. In more compllcated flotation circuits, the minerais may be either 25 collected with the froth product (known as the overflow) or with the tall, or underflow. tn addition, scavenger, cleaner, and re-cleaner cells, with or without an interrnediate re-grinding step, may also be employed.

The proper oxygénation of pulp is an important parameter in the flotation of complex métal sulfîde ores (Surface Chemistrv of Froth Flotation, Jan Leja, Plénum Press ( 1982)). For example, it has been reported that conditioning of ore slurries with oxidants such as hydrogen peroxide can be used as part of a process to separate a desired copper minerai from unwanted

Iron sulfîde, as well as from other copper-conlaining minerais (US 5,110,455 and

US 5,295385). However, incorrect oxygen levels may adversely affect séparations and recovery. Thus, the conditions under which oxygénation is performed is important to the ultimate success of these enrichment procedures.

Summary οΓ the Invention

The présent invention is directed to the addition of oxidants, preferably hydrogen peroxide, during froth Dotation of a métal sulfide ore to improve the séparation of a desired minerai from an unwanted sulfide-containing gangue. The grinding, pH adjustment, and addition of other chemicals (frothers and coliectors) may be performed prior to the addition 10 of the oxidant and the entry of pulp into the Dotation ceils. However, it is important to avoid conditioning ore pulp with Η₂Ο₂ (or any other oxidant) prior to Dotation as this may adverse! y affect recovery.

The proper amount of oxidant to be used may be determined for a given ore by using 15 varying amounts of oxidant and measuring the dissolved oxygen content (DO) in the Dotation feed. By plotting the resulting DO against the concentration of the oxidant, it is possible to détermine the optimum amount of said oxidant that shouid be added. SpeciDcaliy, încreasing amounts of oxidant should lead to a point where a sharp increase in DO occurs, i.e., where there is a substantial increase in the slope of the DO vs. ln [oxidant] curve (see e.g., figure 10 20 for hydrogen peroxide as oxidant). Between about 0.5 and 10 times of the oxidant addition at this point is the amount of oxidant that can most favorably be used in the processes described herein. Once process parameters hâve been determined, these may be used in the future processing of the same ore.

In its first aspect, the invention is directed to a process for treating a métal sulfide ore to separate a desired minerai from a sulfide-containing gangue. The desired minerai may be any that is of value, however copper ores and copper/gold ores are preferred. A typical sulfide-containing gangue to be removed would be iron sulfide, în particular pyrite (FeSî). The process involves forming a pulp by suspending the ore in water and then millîng it to 30 form small particles, typically 50 - 200 μm in diameter. Using procedures well known in the art, the pulp is then enriched in the desired minerai by froth Dotation. This is a procedure in which oxygen or air is bubbled through the pulp and a concentrate enriched în the desired minerai is collected. In order to improve séparations, on oxidant is added to the pulp immédiate]y prior to (i.e., within 30 seconds) or, preferably, directly during froth flotation. Preferably, the desired minerai is enriched in froth formed by the froth flotation. Avoiding the conditioning of pulp is important in optimizing the results. In addition, the procedure may be performed without adjusting the pH of the pulp with agents such ns lime.

The most preferred oxidant îs hydrogen peroxide. Other oxidants that may be used inciude sodium nitrate, sodium hypochlorite, potassium dichromate and sodium peroxodîsulfate. The oxidant should, most preferably, be added continuously during the froth flotation procedure and, to avoid reduced recoveries due to localized décomposition of the oxidant, should be added in a diluted form. For example, hydrogen peroxide is preferably added at a concentration of 0.5 - 20 % by weight, more preferably at 0.5 - 5 % by weight, and stili more preferably at 0.5 -1 % by weight. The continuous addition of low concentrations of oxidant during froth flotation may be used not only for the process described herein but in other procedures for enriching ores as weil.

The amount of oxidant that should be added to the pulp will vary depending on the type of ore being processed. As suggested above, one way to détermine the optimum amount is to perform assays mcasuring changes in the dissolved oxygen content of the slurry after various amounts of oxidant hâve been added. The objective of these assays is to détermine the amount of oxidant at an inflection point, i.e., a point where the curve of lhe amount of dissolved oxygen plotted against the Iogarithm of the concentration of added oxidant évidences a sudden increase in slope (see e.g.. Figure 10). The amount of oxidant added should be between half of this amount and 10 times this amount. In the case of hydrogen peroxide, typically, 0.01 - 0.5 kg (and more specifïcally 0.03 - 0.3 kg) of hydrogen peroxide will be used per ton of ore milled (weights of hydrogen peroxide refer to 100 % hydrogen peroxide).

Although the hydrogen peroxide may be added as one or more batches, it is most preferably added continuously during the froth flotation process. Typically, the rate of addition should bc between 0.03 kg per ton of ore and 0.5kg/t and, more specifïcally, between 0.03 kg/t and 0.3 kg/L The rate of addition per ton of ore processed will be largely dépendent on the composition of the ore and the rate at which the mili processes the ore.

Frothers and collectors may be added to slurries prier to froth flotation in order to împrove séparations and recoveries. Examples of frothers that may be used include pine oil. polyglycols, and polyoxyparafins. Examples of collectors that may be used include xanthates, carbonates, and fatty acids.

ln another aspect, the invention is directed to an improvement in processes for enriching métal sulfide ores in a desired minera! (partîcularly ores with sulfide-containing gangue). The processes are characterized by the steps of: a) suspending the ore in water and milling it (typically by grinding to a particle size of 50 - 200 μ m) to form a pulp; b) 10 performing froth flotation by bubbling oxygen or air through a pulp to which hydrogen peroxide has been added and collecting a concentrate composition enriched in the desired minera! from the pulp surface. The improvement comprises adding an aqueous hydrogen peroxide solution comprising 0.5 - 20 % by weight hydrogen peroxide to the pulp during froth flotation, or immedlately before (within 30 seconds of) froth flotation. The hydrogen 15 peroxide solution preferably comprises 0.5 - 5 % by weight, and more preferably at 0.5 -1 % by weight hydrogen peroxide. The hydrogen peroxide solution is preferably added continuously during froth flotation.

The parameters used in the improved procedure are essentially the same us those 20 discussed above. Oxidant should be added without any condltioning of the slurry and it is not necessary to adjust pH by adding lime or some other similar pH adjusting agents. Although oxidant can be added in one or more ïndividual batches, k should preferably be added continuously in the concentration ranges discussed above. Typically, the rate of addition should be between 0.01 kg per ton of ore and 0.5 kg/t and, more specifically, between 25 0.03 kg/t and 0.3 kg/t. The rate of addition per ton of ore processed is dépendent on the composition of the ore and on the rate at which the mill processes the ore. Preferred minerais for enrichment are copper suifides and gold and a typical sulfide-containing gangue that will be separated by the process is iron sulfide, in particular pyrite (FeS₂). Besides the bénéficiai effect on an increased grade or recovery in the desired base métal, the procedure may also 30 hâve the effect of removing unwanted, or potcntially harmful, impurities such as arsenic. Optionally. frothers and/or collectors, such as those listcd above, may be added to slurries to Împrove séparations.

In another aspect, the invention is directed to n method of incrcasing the hydrophilicity of a sulfïde-containing gangue during froth flotation of a métal sulfide ore slurry, using the methods described above. This modification may then be used to help ’ facîlitate séparation of a gangue from a desired minerai.

Brlef Description of the Drawings

Figure I: Figure i shows curvcs in which the copper grade (y-axis) is plotted against the recovery of copper (x-axis) for flotation expérimenta described in exemples i, 2 and 4. The figure présents curves obtained under standard conditions in the absence and in the 10 presence of 100 g/t and 200 g/t HjOj. The préparations were not conditioned with hydrogen peroxide.

Figure 2: Figure 2 shows curves In which the copper grade (y-axis) is plotted against the recovery of copper (x-axis) for flotation experiments described in exaniples 1, 3 and 5. 15 The figure présents curves obtained under standard conditions in the absence and in the présence of 100 gA and 200 g/t H2O2. Préparations that contained the hydrogen peroxide were conditioned with this agent for 15 minutes prior to the flotation process.

Figure 3: Figure 3 is a graph in which the recovery of iron sulfide (IS, y-axis) is 20 plotted against the recovery of copper (x-axis) for an ore processed in examples 1, 2 and 4 under standard conditions in the absence and in the presence of 100 g/t and 200 g/t H2O2. Processing was performed without conditioning.

Figure 4: Figure 4 is a graph in which the recovery of non-sulfide gangue (NSG, 25 y-axis) is plotted against the recovery of copper (x-axis) for an ore processed in examples 1,2 and 4 under standard conditions in the absence and in the presence of 100 g/t and 200 g/t Η₂Ο₂. Processing was performed without conditioning.

Figure 5: Figure 5 is a graph in which the recovery of arsenic (y-axis) is plotted against the recovery of copper (x-axis) for an ore processed in exaniples 1, 2 and 4 under standard conditions in the absence and in the presence of 100 g/t and 200 g/l H₂O₂.

Processing was performed without conditioning.

Figure 6: Figure 6 is a graph în which the concentration of dissolved oxygen (DO, y-axis) is plotted against the logarithm of the nmount of added H₂O₂ (in g/t of minerai, x-axis) for the experiments of ndding H2O2 to aqueous si unies of pure pyrite and pure chalcopyrite described in experiments 7-10 and 12-15.

Figure 7: Figure 7 Is a graph in which the copper grade (y-axls) is plottcd against the recovery of copper (x-axis) for flotation experiments described in examples 16 - 20. The figure présents curves obtained under standard conditions in the absence and in the presence of 50 - 200 g/t H2O2. The préparations were not conditioned with hydrogen peroxide.

Figure 8: Figure 8 shows curves in which the copper grade (y-axis) is plotted against the recovery of copper (x-axis) for flotation experiments described in examples 24 - 29 using various oxidants applied at the same molar O¹' dosage rate.

Figure 9: Figure 9 shows curves in which the copper grade (y-axis) is plotted against the recovery of copper (x-axis) for flotation experiments described in examples 30 - 36. The figure présents curves obtained under standard conditions in the absence and in the presence of 75 to 240 g/t H2O2. The préparations were not conditioned with hydrogen peroxide.

Figure 10: Figure 10 is n graph in which the concentration of dissolved oxygen (DO, y-axis) is plottcd against the natural logarithm of the amount of H2O2 (in kg/t ore, x-axis) added in examples 30 - 36.

Définitions lhe following définitions are provided to facilitate an understanding of the invention.

They appiy to the terms used herein unless there is an indication to lhe contrary either expressly or by context.

Ore

A naturally occurring minerai from which a métal and certain other éléments (e.g.

phosphorus) can be extracted, usually on a commercial basis. Metals may be présent in ores in clcmental form, but more commonly they occur combined as oxides, sulfides, sulfates or silicates.

Conner/Gold Ore

An orc containing sufficient copper and gold to make economically feasible the extraction of the metals from the ore.

Minerai

A minera! is a naturelly occurring solid material found in ore and having a charecteristic structure and spécifie physical properties. A minerai may be a métal or a nonmétal, such os a métal sulfïde.

Froth Flotation

Froth flotation is a method for separating various minerais in a feed by utüising différences in their surface properties. Séparation is achieved by passing air bubbles through the minerai pulp. By adjusting the chemistry of the pulp using various reagents, valuable 15 minerais can be made aerophiüc (air-avid) and gangue minerais aerophobic (water avid). Séparation occurs by the valuable minerais adhering to the air-bubbles which form the froth floating on the surface of the pulp.

Frother

A frother is a compound or composition added to a minerai pulp which increases the amount and stability of froth formed upon passing air bubbles through the minera] pulp.

Collector

A collector is a compound or composition added to a minerai pulp which increases the 25 amount οΓ a desired minerai that attaches to air bubbles passing through the minerai pulp.

Dep restant

A depressant is a compound or composition added to a minerai pulp which reduces the amount of gangue that attaches to air bubbles passing through the minerai pulp.

Ore Concentration

Ore concentration is the process of separating millcd orc into two streams; a concentrate enriched in a desired minera! and Tailings of waste material. Ore concentration is

a vital économie step in production processes because it reduces the volume of material which must be transported to, and processed in, a smelter and refinery.

Condifianine of Ore Slurry

Conditionîng of ore sluny refers to treating ore slurry with reagents, such as depressants, frothers, activators, collcctors, pH regulators, etc. for a given time period before entering the flotation cells in order to improve séparation.

Ganeue

Gangue is a material in an ore other than a desired minerai. Gangues usually hâve

Utile or, esscntially, no économie value.

Grade

Grade is the mass of a desired material in a given mass of ore.

Milline

Typically, in an initia) stage of minerai processing, ore from a mine is mechanically reduced in size to improve the efficiency of a concentration process. In general, two types of mills are used. Autogenous mills simply tumble the ore to achieve a desired grain size, 20 whcreas other mills use an additional medium, such as steel balls or rods, to aid milling.

Puln

Ground ore and water arc mixed to form a pulp. For the purposes of the présent invention, the terms slurry, ore sluny, pulp and ore pulp are ali used interchangeably.

Recovery

The amount of desired minerai obtained as the resuit of a froth flotation process relative to the amount orïginally présent is the recovery. In order to minimîze the volume of material that needs to be handlcd, the grade of rccovered material should be as high as 30 possible.

Bv-r>roduct

A by-product is a material of some économie value produced in a process which is focused on extracting another material. For example gold may be produced as a by-product of copper mining.

Tailings are fine grain romains of ore once most of the valuable material has been removed in a concentration process.

Detailed Description of the Invention

The présent invention is directed lo an improvement în froth flotation procedures by sélective alteration of the surface chemistry of sulfide-containing gangues in métal sulfidc ores using oxidants such as hydrogen peroxide. The métal sulfide ore is preferably a copper 15 ore, containing copper sulfide minerais, or a copper/gold ore, containing copper sulfide minerais and associated gold. Tlie sulfide-containing gangue ln such ores is typically an iron sulfide such as pyrite. Without being held to any particular theory, it is believed that the oxidant alters the surface of gangue sulfidc compounds to make them more hydrophilic. This is illustrated below for the oxidation of pyrite (FeS₂) by hydrogen peroxide.

FeS₂ + 7.5H₂O₂ -* FeO(OH) H₂O + 2 H₂SO₄ +4 H₂O

As oxidant is added to the pulp, the first iron sulfide to hâve its surface chemistry altered will typically be pyrite, the most common of the sulfide minerais. Should the oxidant 25 concentration be further increased, oxidation reactions will continue with other iron sulfide species such as arsenopyrite and pyrrhotite. Continued addition of the oxidant will ultimately change the surface chemistry of these métal sulfides to make them more hydrophilic and less prône to be présent in the concentrate recovered in the froth. Addîng too much oxidant can lead to surface modification of a desired métal sulfide minerai, such as chalcopyrite, which 30 will increase loss of this minerai to the tailings. The addition of oxidant may also change the surface chemistry of arsenic and bismuth compounds, such as e.g. arsenopyrite, présent in the ore to make them more hydrophilic and less prone to be présent in the concentrate recovered in the froth.

An especially important characteristic of the présent invention is that there is no, or essentially no, conditioning of ore préparations with oxidant prior to froth flotation as this may adversely affect recovery. Conditioning by lhe incubation of lhe ore slurry in lhe 5 presence of olhcr agents, e.g., frolhers or collectors, may still occur, but oxidants such as hydrogen peroxide should not be présent Although a pH modifier such as lime can be used lo condition lhe slurry, it is not necessary to include such agents and the cost of ore processing can be reduced if they are omitted.

Preferably, lhe oxidant is added directly to flotation cells while oxygen or air is bubbled through lhe slurry and there ts no prior conditioning of lhe slurry with lhe oxidant. However, less desirably, addition may take place immediately prior to (within 30 seconds of) froth flotation. The oxidant is preferably added continuously during froth flotation. Grinding, pH adjustment (if used), and addition of other chemicals (frolhers and collectors) may be 15 performed prior to the addition of oxidant Ail of these other steps, including the production of slurries of ore appropriate for minerai enrichment, are carried oui using methods that are well known in the mining arts. Preferably, no frolher, coHector, additional depressant or pH modifier is added after addition of oxidant Most preferably, lhe oxidant is added after addition of other flotation aids, such as frolher, collecter, additional depressant or pH 20 modifier.

The preferred oxidant is hydrogen peroxide. Other oxidants that may be used include sodium nitrate, sodium hypochlorile, potassium dichromate and sodium peroxodisulfate. The oxidant is preferably not molecular oxygen. The oxidant should, most preferably, be added 25 continuously during the froth flotation procedure and, to avold reduced recoveries due to localized décomposition of lhe oxidant, should be added in a diluted form. For example, hydrogen peroxide is preferably added at a concentration of 0.5 - 20 % by weight, more preferably at 0.5 - 5 % by weight, and still more preferably at 0.5 -1 % by weight.

The amount of oxidant to add to ore slurries is an important factor în determining the degree of enrichment achieved. For example, 0.01 - 0.5 kg of hydrogen peroxide per ton of ore would bc expected to produce generally positive results. However, the optimal amount of oxidant to add will vary depending on the components making up the ore. (n order to estimate

the amount of oxidant to add for a given orc, the ore should be processed by froth Dotation in the presence of increasing amounts of oxidant while measuring the dissolved oxygen content of the slurry. Plotling the results should provide a curve such as that shown in figure 10 for the addition of hydrogen peroxide. It can be seen from the figure that, as the amount of added 5 hydrogen peroxide increases, an inflection point is reached where there is a sudden increase in the slope of the curve. For convcnience, the inflection point is defined herein as being the point in the curve where there Is at least a doubling in slope. Expressing the amount of oxidant în the slurry at this point as x, the preferred amount of oxidant to use is between 0.5 x and 10 x. This can be arrived at by either adding the required amount of oxidant to the 10 slurry in one or more balches or by adding the oxidant in a continuous manner during froth flotation. It should be noted that once a preferred range is arrived at, this can then be applied to the processing of similarly prepared slurry from the same ore. If the composition of the ore changes, the procedure can be repeated to détermine a new optimum amount of oxidant.

If desired, the tailings from the initial processing step can be further treated by froth flotation în an attempt to recovcr additional minerai. Since the tailings will be of a lower grade than the initial ore, the preferred range of hydrogen peroxide to add should be separately determined using the procedure described above.

Examples

Exemples 1 to 5

A porphyry copper/gold ore was ground in the presence of water to a particle size

P80 of 200 pm using a laboraiory Magotteaux® mill. A head assay of the ore gave the following resuit: 0.84 % Cu, 20.9 % Fe, 562 ppm As, 0.40 ppm Au, 147 ppm Mo and 4.1% S.

The resulting ore pulp was transferred to a flotation cell and mixed for two minutes to homogenize. Xanthate collector (2:1 potassium amyt xanthate and sodium isobutyl xanthate) was added al 5 grams per ton as well as a 1 % by weight aqueous hydrogen peroxide solution 30 at 100 or 200 g hydrogen peroxide (100%) per Ion. The pulp was then condilioned for 0 or 15 minutes. Five drops of OTXI40 frolher from Cytec (sodium diisobutyl dithiophosphate) was added and pH was maintaîned at nominally 10.8 via addition of lime. Four limed concentrâtes were collected over intervals of 30 seconds, 1.5, 2.0 and 4.0 minutes, for a total flotation time of 8 minutes. Each concentrate was collected by hand scraping the froth from

the surface of the pulp once every 10 seconds. pH, redox potenlial Eh, dissolved oxygen content and température of the pulp were monîtored throughout the tests.

Results for Examples 1-5 are shown in Tables 1 and 2 below and in Figures 1-5.

Data points in Figures 1 - 5 refer to the combined timed concentrâtes obtained by flotation. As can be seen, a significant improvement in coppcr grade can be attributed to improved copper selectivity against iron sulfïdes (pyrite). Overali, the addition of hydrogen peroxlde improved conccntrate copper grade. Specifically, at 85 % copper recovery, the improvement In concentrais copper grade was as much as 3.7 % higher than without hydrogen peroxide 10 (Table l and Figure 1). Also, copper grade/recovery curves show that copper flotation rates increase with unconditîoned hydrogen peroxide addition, while conditioning the pulp prior to flotation had a négative effect on the copper flotation response.

Hydrogen peroxide, in addition to improving concentrai grade, was also bénéficiai 15 with respect to copper recovery. Specifically, at 8 % concentrate copper grade, copper recovery was significantly higher for ali the hydrogen peroxide tests compared to the standard (Table 2).

Although the addition of hydrogen peroxide improved coppcr selectivity against iron 20 sulfidcs, there was a conccm that gold recovery might be redueed as a significant proportion of the gold in this ore (and in many other ores) is associated with iron suicides. However, hydrogen peroxide addition without conditioning improved gold recovery with respect to the standard test, and Tables 1 and 2 illustrate similar gold grade compared to standard.

Iron sulfide rccoverics were lower for ail hydrogen peroxide tests, with respect to the standard test. However, conditioning in conjunction with 100 g and 200 g H₂O₂ addition per ton of pulp was associated with an increased tendency to recover sulfïdes (copper vs. iron sulfide selectivity is shown in Figure 3).

Besides improved selectivity toward iron sulfide, hydrogen peroxide treatment during flotation also results in lower non-sulfïde gangue (NSG) at any given copper recovery (see Figure 4).

Arsenopyrite (FcAsS) is lhe most common arsenic minerai in ores and is also a byproduct assoctaled with copper, gold, silver, and lead/zinc mining. Arsenic occurs at varying levels in some copper ore bodies and is a significant environmental hazard in the copper smeltering process when émissions are released into lhe atmosphère. The arsenic in lhe ore is 5 contained in coppcr-arscnic sulfide minerais, such as enargite and tennanite. High arsenic levels may reduce lhe value of the concentrate and therefore its removal is highly désirable. Table 1 and Figure 5 show a substantial arsenic réduction at 85 % copper recovery.

Table 1: Copper and gold concentrate grades and gold and diluent recoverles, 10 at 85 % copper recovery

Ex ample	HiOi added, Conditioning time	Grade	Recovery
Cu %	Au PPm	Au %	Mo %	As %	IS %	NSG %
t» Standard	0 g/ton, 15 min	7.9	3.2	69.4	43.8	63.4	76.0	2.6
2	100 g/ton, 0 min	11.6	4.4	72.7	34.2	31.4	40.7	1.8
3*	100 g/ton, 15 min	10.7	3.9	68.4	40.2	29.0	43.4	2.2
4	200 g/ton, 0 min	8.8	3.9	77.3	41.0	42.3	58.6	2.9
5*	200 g/ton, 15 min	9.8	3.7	68.1	36.2	33.4	45.4	2.7

Noie: *not according lo lhe invention, IS = iron su!Ode, NSG = non-su!Ode gangue

Table 2: Copper and gold recoverles and concentrate gold and diluent grades, at 8 % concentrate copper grade

Example	Η2Ο2 added, Conditioning time	Recovery	Grade
Cu %	Au %	Au ppm	Mo ppm	As ppm	IS %	NSG %
1* Standard	0 g/ton, 15 min	82.8	67.5	3.2	670	3812	49.8	26.3
2	100 g/ton, 0 min	91.7	84.2	3.2	664	2261	29.5	46.9
3.	100 g/ton, 15 min	91.0	78.7	3.0	756	1983	28.8	47.7
4	200 g/ton, 0 min	90.7	83.7	3.5	685	2635	37.2	39.1
5*	200 g/ton, 15 min	90.6	76.9	3.1	661	2116	29.9	46.5

Note: *not according lo the Invention, IS s Iran sulfide, NSG n non-sulfïdc gangue

Examples 6 to 15

An oxidation treatment with hydrogen peroxide was applied to pure minerais pyrite and chalcopyrite. pH was maintained at a target value of 11 via addition of lime. The aim of 10 this approach was to isolate the behavior of each minerai tested to various concentrations of oxidation treatment. Examples 6 -15 in Tables 3 and 4 illustrate that pyrite consumes much more oxidant than chalcopyrite before hydrogen peroxide addition leads to an increase in dissolved oxygen.

Figure 6 shows that pure pyrite ore requires more hydrogen peroxide to get oxidized compared to chalcopyrite. Chalcopyrite only requires about 0.34 g/ton of H₂O₂ for DO to drastically increase (thereby making it morehydrophilic), whereas the pyrite minerai required a much higher amount (3.4 g/ton of H2O2) in the slurry to producc a similar effect. This différence in DO suggests that it should be possible to separate these species, by floating chalcopyrite and rcmoving pyrite tn tailings.

Table 3: Pure Pyrite Minera! treated with Hydrogen Peroxide

Example	H2O2 added g/t	DO ppm	pH	Eh mV	Température °C
6	0	0.46	10.9	148	20.8
7	0.034	0.53	lt.0	86	19.1
8	0.34	0.52	ü.o	153	18.3
9	3.4	0.53	10.8	119	21.3
10	34	3.01	10.8	211	22.8

Note; DO = dissolved oxygen. Eh »= redox potential

Table 4: Pure Chalcopyrite Minerai treated with Hydrogen Peroxide

Example	H2O2added g/t	DO ppm	pH	Eh mV	Température °C
u	0	0.49	10.9	132	24.1
12	0.034	0.59	11.0	125	18.8
13	0.34	0.57	11.1	124	22.2
14	3.4	1.28	10.9	181	21
15	34	1.99	10.8	214	25.2

Note: DO = dissolved oxygen, Eh = redox potential

Exemples 16 to 20

Examples 16-20 were carried out as described for examples 1 - 5 using a different ore and adding varying amounts of hydrogen peroxide without conditioning time. They are designed to examine hydrogen peroxide in amounts sufficient to over oxidize the ore. in other words, the highest amounts of peroxide used should also oxidize chalcopyrite and thereby 15 make it hydrophîlic with lhe other sulfides. At 50, 80,120, and 200 g/ton of peroxide, copper grade reached ils maximum with 120 g/ton H₂O₂ and 200 g/t provided inferior results indicating that over-oxidation took place (see Tables 5 and 6, Figure 7).

Table 5: Copper and gold concentrate grades and gold and diluent recoveries, at 86 % copper recovery

Example	H2O2 added g/t	Grade	Recovery
Cu %	Au PPm	Au %	Mo %	As %	IS %	NSG %
16*	0	9.3	3.4	67.8	32.7	41.0	53.8	2.6
17	50	11.0	4.0	69.3	29.0	30.7	42.9	1.9
18	80	10.8	3.6	63.7	26.5	24.9	34.8	2.7
19	120	11.0	4.0	66.5	32.8	26.3	35.0	2.5
20	200	8.8	3.9	77.3	41.0	42.3	58.6	2.9

Note: ’not according to the Invention, IS b iron sulfide, NS G a non-sulfide gangue

Table 6: Copper and gold recoveries and concentrate gold and diluent grades, at 8 percent concentrate copper grade

Examplc	H2O2added βΛ	Recovery	Grade
Cu %	Au %	Au Ppm	Mo ppm	As PPm	IS %	NSG %
16*	0	89.6	74.4	3.0	629	2783	37,7	38.6
17	50	90.3	78.5	2.9	546	2118	30.8	45.6
18	80	90.7	74.8	2.8	507	1733	25J	51.2
19	120	90.7	77.0	3.0	609	1864	25.5	51.0
20	200	90.7	83.7	3.5	685	2635	37.2	39.1

Note: *nol according to the Invention, IS = iron sulfide, NSG = non-sulfide gangue

Exemples 21 to 23:

Examples 21-23 were carried oui as described for exemples 1-5, using a different copper/gold ore following grinding using forged steel media. Sodium ethyl xanthatc was used 15 as collecter and added after grinding at 15 grams per ton of ore. The pulp was transferred to the flotation cell and conditioned for two minutes. The slurry was then further condilioned

wtth 35 grams of sodium ethyl xanthate and 30 grams per ton of POLYFROTH® H27 frother from Huntsman. The desired concentration of hydrogen peroxide (0, 50 and 100 grams per Ion) was added to lhe Dotation feed and Dotation commenced immediately. During this set of tests, no lime to adjust pH was added. Flotation took place at the natural pH of 8.1. Results 5 are shown in Tables 7 and 8 below.

The addition of hydrogen peroxide increased dissolved oxygen in the Dotation feed as well as the response of the ore lo Dotation in general. Cumulative copper and gold recovery increased by 2.6 and 7.0 %, respectively. Also copper grade increased by 1.5 %.

At 73 % copper recovery and 50 g/t H₂O₂₁ copper grade increased by 3.5 % and arsenic and iron suIDdes recovery decreased by 3 and 0.7 %, respectively. At 18 % copper grade and 50 g/t H₂O₂, copper recovery increased by 4.5 % and gold recovery increased by 9.4%.

Tnble 7: Copper and gold grade, gold, molybdenum and diluents recovery at 73 % copper recovery

Example	H2O2 added g/t	Grade	Recovery
Cu %	Au PPm	Au %	Mo %	As %	S %	IS %	NSG %
21* Standard	0	17.4	5.3	59.1	11.3	12.7	69.5	68.2	4.4
22	50	20.9	6.5	62.7	9.7	9.7	68.9	67.5	2.2
23	100	22.1	6.6	55.8	8.9	11.1	69.0	67.5	2.1

Note: *noi according lo lhe invention, IS = iron sultide. NSG non-sulflde gangue

Table 8: Copper and gold recovery, gold, molybdenum and diluents grade at 18 % copper grade

Example	H2Oj added g/t	Recovery	Grade
Cu %	Au %	Au PPm	Mo ppm	As ppm	S %	IS %	NSG %
21* Standard	0	72.2	58.1	5.5	78	125	15.0	19.6	57.8
22	50	76.7	67.5	5.7	84	110	15.1	19.7	57.8
23	100	77.8	61.5	5.5	89	131	14.8	19.1	583

Note: *not according lo the Invention, IS b Iron sulfide. NSG = non-sulfide gangue

Examples 24 to 29:

Examples 24 - 29 were carried out as described for examples 1 - 5, using different oxidants and a different copper/gold ore following grinding using forged steel media. The 10 ground pulp was transferred from the laboratory mill to a 5 litre flotation cell and mixed for two minutes to homogenize the pulp. The slurry was then aerated for 12 minutes at 101/min to match the plant oxygen demand prior to flotation. The pulp was then conditioned for 2 minutes with 16.5 g/t of a blend of sodium isopropyl ethyl thionocarbamatc and dithiophosphate and 5 drops of iF52 frolher (isobutyl methyl carbinol), both from Chemical 15 & Min in g Services Pty. Four timed concentrâtes were collected over intervals of 30 seconds,

1.5, 3.0 and 5.0 minutes, for a total flotation time of 10 minutes. Each concentrate was collected by hand scraping the froth from the surface of the pulp once every 10 seconds. Oxidants H2O2, NaNOj, Na2S₂O8, KjCrjO? and NaOCI were used at the same molar 02dosage rate, assuming the following 02-equivalents for the oxidants: H₂O₂ = 0.5, NaNOj = 20 0.5, NajSjOg = 0.5, K₂Cr₂O7 = I and NaOCI = 0.25. Oxidants were added to the flotation feed and flotation commenccd immedia tel y. Flotation was performed at natural pH of 8.0. without addition of lime. Results are shown in Table 9 and Figure 8.

Overall, the addition of oxidants improved concentrate copper grade. At 85 % copper recovery, the improvement in concentrate copper grade was as much as 5.0 % higher than without oxidant.

Table 9 also illustrâtes improved gold grade of up to 5.1 ppm. While copper and gold concentrate grades at 85 % copper recovery improved, iron sulfide recoveries were substantially lower for ail oxidants tested. Besides improved seleclivity toward iron sulfide, oxidant addition during Dotation also results in lower non-sulfide gangue (see Table 9).

Table 9: Copper and gold concentrate grades and gold and diluent recoveries, at 85 % copper recovery

Example	Oxidant	Grade	Recovery
Cu %	Au ppm	Au %	S %	IS %	NSG %
24*	None	16.9	23.7	57.0	50.2	14.4	3.5
25	h2o2	19.1	26.6	48.4	49.4	6.6	3.0
26	NaNOj	20.4	28.4	29.7	46.6	10.4	2.0
27	Na2S20n	21.9	28.9	53.0	49.1	13.7	1.5
28	K2Cr2O7	21.9	26.8	51.2	49.7	13.6	1.6
29	NaOCl	18.8	28.4	58.4	51.2	19.1	2.2

Noie: *not according lo the invention, IS iron sulfide. NSG » non-sulfide gangue

Examples 30-36:

Examples 30 — 36 were carrîed out as described for examples 1-5, using a different ore following grinding using forged steel media. Prior to the reagent addition the Doat feed was aeraled for 7 minutes to simulate plant conditions. Sodium ethyl xanthate was used as collector and added after grinding at 21 grams per tone of ore. The pulp was transferred to the Dotation cell and conditioned for two minutes. The sluny was mixed with 5 grams per ton of POLYFROTH® H27 frother from Huntsman. During this set of tests, lime was added lo adjust the pH to a value of 9.7. The desired amount of hydrogen peroxide (0,7.5, 15,30,60, 120 and 240 grams per ton) was added to the Dotation feed and Dotation commenced îmmediately. Results are shown in Tables 10 and 11 and Figure 9.

At 120 g/t of hydrogen peroxide the copper grade increased by 1.8 percentage points at a constant recovery of 96 % vs. the example with no addition, while at 15 % copper grade

the recovery rose by 0.9 percentage points. Copper grade reached its maximum with an addition of 120 g/t HiOi and further increasing the amount of H₂O₂ to 240 g/t provided inferior results.

Table 10: Copper concentrate grades and diluents recovery at 96 % Copper recovery

Example	HiOj added g/t	Grade	Recovery
Cu %	Zn %	Fe %	S %	IS %	NSG %
30*	0	12.9	78.4	26.7	34.1	15.5	9.5
3i	7.5	13.7	67.4	27.2	32.5	18.5	8.3
32	15	13.8	67.8	26.9	33.5	15.5	8.9
33	30	13.5	64.4	26.6	33.2	16.4	9.0
34	60	13.7	72.0	27.8	33.6	14.9	9.2
35	120	14.7	71.8	27.2	33.2	15.7	6.5
36	240	13.5	67.4	27.0	32.5	14.0	8.6

Note: *not according to the invention, IS » iron sulfide, NSG = non-sulfide gangue

Table 11: Copper recoveries and diluents grade at 15 % Copper grade

Exemple	H2O2 added g/t	Recovery	Grade
Cu %	Zn %	IS %	NSG %
30*	0	95.9	0.37	19.5	31.8
31	75	95.6	0.32	24.4	30.3
32	15	96.0	0.33	21.3	31.7
33	30	96.0	0.32	22.9	32.3
34	60	96.1	0.34	18.9	33.3
35	120	96.8	0.33	20.4	33.7
36	240	95.9	0.34	19.7	33.2

Note: *not according to the invention. IS = iron sulfïde. NSG = non-sulfidc gangue

Figure 10 shows a plot of dissolved oxygen 030) concentration against the natural logarithm of the amount of added hydrogen peroxide in kg/t of ore. lhe slope is relatively fiat up to 0.12 kg/t and then becomes much steeper as the amount of added HiO₂ increascs.

Ail référencés cited herein are fully incoiporated by reference. Having now fully described the invention, it will be understood by those of sktll in the art that the invention may be practiced within a wtde and équivalent range of conditions, parameters and the like, without affecting the spirit or scope of the invention or any embodiment thereof.

Claims (32)

1. What is Claimed is:

   1. A process for treating a métal su] fi de ore ta separate a desired minerai from a sulfide-containing gangue, comprising:

   a) forming a pulp by suspending the ore in water and milling said ore; and

   b) enriching the pulp in said desired minerai by froth flotation, wherein oxidant 1s added to said pulp immediately prior to, or during, the bubbling of oxygen or air into said pulp.
2. 2. The process of claim 1, wherein said oxidant is added continuously during froth flotation without prior conditioning of the pulp with said oxidant
3. 3. The process of claim 1, wherein no frother, collector, additional depressant or pH modifier is added after addition of oxidant
4. 4. The process of daim 1, wherein said oxidant is selected from the group consisting of: sodium nitrate, sodium hypochlorite, potassium dichromate and peroxodisulfate.
5. 5. The process of daim 1 wherein said oxidant is hydrogen peroxide.
6. 6. The process of daim 5, wherein, prior to addition to said pulp, said hydrogen peroxide is in an aqueous solution at a concentration of 0.5-20 % by weight.
7. 7. The process of claim 5, wherein, prior to addition to said pulp, said hydrogen peroxide is in an aqueous solution at a concentration of 0.5-5 % by weight
8. 8. The process of claim 5, wherein prior to addition to said pulp, said hydrogen peroxide îs in on aqueous solution at a concentration of 0.5-1 % by weight
9. 9. The process of claim 1, wherein said oxidant is added without adjustment of pH.
10. 10. The process of claim 1, wherein said desired minerai is enriched in froth formed by the froth flotation.

    H. The process of any one of daims 1 to 10, wherein satd desired minerai is a copper sulfide.
11. 12. The process of daim 11, wherein said sulfide-containing gangue is iron sulfide.
12. 13. Tlie process of claim 11, wherein undesirable minerais such as arsenic and bismuth are reduced in said conccntrate pulp as a resuit of lhe froth flotation procedure.
13. 14. The process of any one of daims 1 to 10, wherein lhe amount of oxidant added is

    5 0.01-0.5 kg/t of ore.
14. 15. The process of claim 14, wherein lhe amount of oxidant added is 0.03-0.3 kg/t of ore.
15. 16. The process of claim 14, wherein said desired minerai is a copper sulfide.
16. 17. The process of claim 16, wherein said sulfide-containing gangue is iron sulfide.

    10
17. 18. The process of any one of daims 1 to 10, wherein an optimum amount of oxidant added Is determined based upon measurements of the dissolved oxygen content of lhe pulp.
18. 19. The process of daim 18, wherein lhe optimum amount of oxidant is determined by plotting lhe dissolved oxygen content against lhe natural logarilhm of lhe amount of

    15 oxidant added.
19. 20. The process of daim 19, wherein lhe optimum amount of oxidant is 0.5 to 10 times lhe amount of oxidant added at lhe inflection point of lhe plot

    2 !. The process of daim 18, wherein said desired minerai is a copper sulfide.
20. 22. The process of claim 2!, wherein said sulfide-containing gangue is iron sulfide.

    20
21. 23. The process of daim 18 wherein said oxidant is hydrogen peroxide.
22. 24. The process of daim 23, wherein said hydrogen peroxide is added wilhout adjustment ofpH.
23. 25. In a process for treating a métal sulfide ore to separate a desired minerai from a sulfide-containing gangue by:

    25 a) forming a pulp by suspending lhe ore in water and milling lhe ore; and

    b) adding hydrogen peroxide to said pulp and cnriching lhe pulp in said desired minerai by froth flotation;

    the improvement comprising adding an aqueous hydrogen peroxide solution comprising 0.5-20% hydrogen peroxide by weight to said pulp during or immediately before frolh notation.
24. 26. The improvement of claim 25, wherein said hydrogen peroxide solution comprises 0.5-5 % hydrogen peroxide by weighL
25. 27. The improvement of claim 25, wherein said hydrogen peroxide solution comprises 0.5-1 % hydrogen peroxide by weighL
26. 28. The improvement of claim 25, wherein said hydrogen peroxide solution is added continuously during frolh notation.
27. 29. The improvement of claim 25, wherein said hydrogen peroxide is added to said pulp without prior conditioning of the pulp with an oxidant.
28. 30. The improvement of claim 25, wherein no frolher, collector, additional depressant or pH modifier is added after addition of oxidant.
29. 31. The improvement of claim 25, wherein said desired minerai is enriched in frolh formed by the frolh notation.
30. 32. The improvement of any one of claims 25 to 31, wherein said desired minerai is a copper sulfide.
31. 33. The improvement of claim 32, wherein said sulfidc-containing gangue is iron sulfide.
32. 34. The improvement of claim 33, wherein said hydrogen peroxide is added wilhout adjustment of pH.