MXPA97008036A - Method for processing sulfurated auriferal minerals including the preparation of unconcentrate of sulfu - Google Patents

Abstract

The present invention relates to a method for processing an auriferous mineral material containing a sulphide mineral with which the gold is associated, comprising the steps of: a) providing a particulate gold ore material comprising gold and a sulfur mineral said gold is associated and from which said gold can be difficult to recover, said mineral material also comprising a non-sulfurized material as gangue, b) subjecting said mineral material to flotation with a flotation gas to separate said mineral material in at least two fractions, a first fraction being a flotation concentrate, collected from the flotation foam, enriched in said sulphided mineral and said gold and a second fraction consisting of a flotation tail enriched in said non-sulfurized and exhausted material in said gold, said flotation gas comprising oxygen gas no more than about 155 by volume; being so that the pyrrhotite, when present in said mineral material, could be collected from the flotation broth and could be concentrated in said flotation concentrate. Method for using various air streams separated from the air to assist in the processing of an auriferous mineral material containing a sulphide mineral to which the gold is associated, comprising the steps of: a) separating an amount of air into at least two streams of gas, a first stream being a gas stream enriched in nitrogen gas with respect to said air and said second stream being a gas stream enriched in oxygen gas with respect to said air, b) providing a supply of material particulate gold ore comprising a sulphided mineral with which said gold is associated, said mineral material also comprising non-sulfided materials, c) subjecting at least a portion of said mineral material to a flotation treatment to separate said mineral material into At least two fractions, a first fraction being a flotation concentrate enriched in said mineral, and said gold in relation to said mineral material in said feed and a second fraction being a flotation glue enriched in said non-sulfurized material and exhausted in said gold in relation to said mineral material of said feed, said flotation consisting of at least a portion of said feed to a flotation gas that includes at least a portion of said first gas stream enriched in nitrogen gas, and d) oxidative treatment of at least a portion of said mineral material, said oxidative treatment comprising contacting said portion of the mineral material with at least a portion of said second gas stream enriched in oxygen gas, to oxidize at least a portion of the sulfur sulfur in said sulfurized mineral and produce an oxidized material in which less part of said gold is released to its association with said sulphide mineral, facilitating the possible Subsequent recovery of the gold from said oxidized material

Description

METHOD FOR PROCESSING AURÍFEROS SULFURADOS MINERALS INCLUDING PREPARATION OF A CONCENTRATE OF SULFURS The present invention relates to a method for processing sulfur-bearing gold minerals that facilitates the recovery of gold from sulphided minerals. In particular, the present invention relates to a process of flotation of sulphide gold minerals in combination with an oxidative treatment, for example with oxidation under pressure, and the use of the gaseous by-product of an oxygen plant to supply oxygen gas for oxidative treatment. .

BACKGROUND OF THE INVENTION Significant amounts of gold are found in sulphide minerals in which gold is associated with the sulfur mineralogy. Gold is difficult to recover from said sulfur minerals because it is typically linked to the sulfur mineral grains in such a way that the mineral becomes refractory to many traditional gold recovery techniques, such as direct gold cyanidation. Therefore, sulphide minerals are generally treated in order to chemically alter the sulphide ore and allow gold to dissolve during subsequent gold recovery operations.

One technique to treat a sulphide gold ore and prepare it for gold recovery is to subject the ore to an oxidative treatment to oxidize the sulfur sulfur in sulphide minerals, making gold more susceptible to recovery. A method to treat a sulphide mineral by oxidation is oxidation under pressure, in which a slurry of the ore is subjected to a treatment with gaseous oxygen in an autoclave at elevated temperature and pressure to decompose the sulphide ore and release the gold for its subsequent Recovery . Other oxidative methods include the calcination and bio-oxidation of the ore in the presence of air or gaseous oxygen. The treatment of whole minerals by oxidation under pressure or by oxidative calcination is expensive. Part of said cost is due to the energy consumed to heat the non-auriferous material of the gangue in the whole ore, and especially to the energy required to heat the water used to make the slurry with the gangue material in the case of the oxidation under pressure. In addition, the dimensions of the equipment used for the treatment of whole minerals must be adapted to fit the entire gangue, in addition to the product of the sulfur-bearing gold minerals, which significantly increases the cost of the equipment of the process. In addition, collateral reactions may occur in which the material of the gangue participates and which may impair the oxidation treatment or produce hazardous materials that require special handling.

One way to reduce the high energy costs and processing equipment associated with the oxidative treatment of a complete mineral, as well as the possibilities of problems related to collateral reactions, would be to eliminate the ore gangue before submitting it to the oxidation treatment. For example, one method that has been used to eliminate the gangue of sulfur-bearing gold ores is flotation. In flotation, air is injected through a slurry of mineral particles that have been treated with reagents and mineral particles that are less hydrophilic tend to rise with air bubbles, allowing separation of the mineral into two fractions . Flotation has been used to prepare concentrates of sulphide-free gold minerals from the gangue material. However, one problem with the flotation of many sulfur-bearing gold ores is that often a significant amount of sulfur-bearing gold ore is incorporated into the wrong fraction during flotation and thus a significant amount of gold is lost.

It is therefore perceived a need to have an improved method of processing many sulfur-bearing gold ores, in which the high costs related to the oxidative treatment of the complete minerals are avoided without a significant loss of gold, as it happens with the concentration of sulfur minerals by flotation.

COMPENDIUM OF THE INVENTION The present invention relates to a method for processing sulfur-bearing gold minerals that facilitates the recovery of gold without the inconvenience of having to oxidize under pressure or calcining the entire mineral and without experiencing the substantial losses of gold that occur with the preparation of a concentrate. of the ore by conventional flotation treatment. It has been found that air, which is used as a flotation gas in conventional flotation, impairs flotation separation of sulfur-bearing gold ores, and that better flotation performance can be obtained by keeping the sulphide ore in a substantially free environment. of air until a desired final concentrate is obtained. It is believed that the oxygen gas present in the air tends to oxidize the surface of certain sulfurized gold particles, with the consequent reduction of the flotation of said particles of sulphide ore, resulting in a significant amount of sulfur mineral not floating during flotation. and therefore remains in the bargain. Using a flotation gas that is deficient in oxygen gas in relation to air, however, problems related to the use of air can be reduced. The result is a greater recovery of sulfur materials in the concentrate, and, therefore, an increase in gold recovery in the concentrate. In one embodiment, the sulfur-bearing gold minerals of a sulphide ore are maintained in a substantially oxygen-free environment, beginning with the grinding of the ore and ending with the recovery of a final sulfur mineral concentrate desired. An oxygen-deficient gas may be introduced before or during grinding to displace air that may be present in the ore feed and to prevent air from entering during grinding. In this way it is prevented that the oxygen that would be present in the air during the grinding oxidizes the newly exposed surfaces of the sulphide mineral created during the grinding. In one aspect, the present invention includes the advantageous use of gases that can be separated from air in the processing of sulfur-bearing gold ores. In one embodiment, a flotation operation conducted substantially in the absence of gaseous oxygen is combined with the oxidative treatment to decompose the sulphided minerals, releasing the gold for subsequent dissolution with a gold leach, such as cyanide. Oxidation under pressure is the preferred oxidation treatment, although alternative oxidation treatments such as oxidative calcination can also be used. Such oxidative treatment generally requires a source of purified oxygen gas, which is often produced by air separation in an oxygen plant. A byproduct of oxygen plants is gas deficient in oxygen and nitrogen-rich gas. The gaseous by-product is, therefore, an ideal source of gas to be used during the grinding and / or flotation of a sulfur-bearing gold ore. This gaseous by-product is usually vented to the atmosphere in current gold processing operations and, therefore, is wasted.

BRIEF DESCRIPTION OF THE DRAWINGS In Figure 1 a flow diagram of an embodiment of the present invention is presented; In Figure 2 a flow diagram of another embodiment of the present invention is presented; In Figure 3 a flow diagram of another embodiment of the present invention is presented. In Figure 4 a graph of the law of the concentrate recovered by means of the flotation as a function of the size of the particles is presented (Examples 1-6); In Figure 5 a graph of the law of the tails of the flotation according to the size of the particles of Examples 1 -6 is presented. In Figure 6 a graph of the weight percentage of concentrate recovered in the flotation according to the size of the particles of Examples 1-6 is presented.

In Figure 7 a graph of the gold recovered in the flotation concentrate as a function of the size of the particles of Examples 1-6 is presented; In Figure 8 a flow diagram of an embodiment of the present invention related to the pilot plant of Example 7 is presented. Figure 9 shows a graph of the gold recovery in the flotation concentrate as a function of the size of the the particles of Examples 8-15.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY The present invention provides a method for processing a sulphide gold ore material, to facilitate the recovery of gold from the ore. The method includes the preparation of a flotation concentrate in a manner that reduces the problems associated with conventional flotation. Surprisingly, it has been found that the problems related to the concentration of a sulphided gold ore by means of conventional flotation methods can be significantly reduced by using a flotation gas comprising a lower volumetric fraction of oxygen gas than that found in the air. of the environment Preferably, the flotation gas should be substantially free of oxygen gas. When air is used as the flotation gas, the oxygen gas in the air appears to impair the buoyancy of sulfur minerals. This may be due to a superficial oxidation of the sulfur mineral particles caused by the presence of oxygen gas. Surface oxidation will tend to depress sulphide ore particles during flotation. In addition, the damaging effects of oxygen gas can be reduced by keeping the ore in an environment that is substantially free of oxygen during grinding, mixing, pumping, and all other steps of the process until the final flotation concentrate is obtained. For example, when multiple flotation steps are used, it is desirable to maintain the mineral in an environment that is substantially free of oxygen gas between the flotation steps. By reducing the seemingly damaging effects of oxygen gas, it is possible to recover a higher amount of the sulphided ore in the flotation concentrate. The present invention, therefore, facilitates the recovery of gold from the sulphide ore of the flotation concentrate. The present invention, therefore, facilitates the recovery of gold from sulphide ore that previously could have been discarded as waste, either with the gangue in a flotation tail or as a low grade ore that was previously considered uneconomic for the recovery of gold. One embodiment according to the present invention is that shown in Figure 1. With reference to said Figure 1, a feed of gold ore material 102 is provided for processing. The ore feed 102 can be any gold material comprising one or more sulfur minerals with which the gold is predominantly associated, and of which gold is difficult to recover. The sulfurized material could include one or more materials including pyrite, larcasite, arsenopyrite, pyrite arsenose and pyrrhotite. Mineral feed 102 is typically a crude ore, but may be the residue of the other processes or a previously discarded glue. The ore feed 102 is subjected to grinding 104 to obtain a particulate mineral 106 with mineral particles of a size suitable for flotation. The particulate material 106 preferably has a dimension such that at least 80% by weight of the particles of the particulate mineral are less than 100 mesh, more preferably less than about 150 mesh, and more preferably less than 200 mesh. by which 80% of the material passes is generally called P80. For grinding, any suitable grinding operation 104 can be used. Wet grinding operations are generally preferred because of their relative ease and low cost compared to dry operations. The grinding 104 is conducted in the presence of a cover gas 104 which is obtained from a gas source 1 10. During the grinding 104, or before it, the ore feed 102 is mixed with the cover gas 108, with an oxygen gas content, if it contains it, of a volumetric fraction lower than that which is present in the ambient air, to reduce problems which could be caused by the presence of air during the grinding 104. During the grinding 104, it is preferable to maintain a positive pressure of the cover gas 108 in any grinding apparatus that is used to help mix the ore 102 with the cover gas 108, and to displace the air that may be present with the ore feed 102. After the grinding 104, the particulate mineral 106 is floated 1 12 to separate the sulfide minerals - with which the gold is associated - of the bargain of non-sulfur materials. During flotation, a slurry of particulate mineral material 106 is injected with a flotation gas 1 14 from a gas source 1 10. Any suitable apparatus for flotation 1 12, such as one or more between a flotation cell, can be used. conventional or a flotation column. Preferably, however, the flotation apparatus is such that a reduced positive pressure of the flotation gas 14 can be maintained in the apparatus to prevent the entry of air into the apparatus. The content of oxygen gas in the flotation gas 14, if it has one, in a reduced volumetric fraction with respect to the volume fraction of oxygen gas in the ambient air, to reduce the problems related to the use of air as a gas. floatation. Although this is not mandatory, the flotation gas 14 will normally have substantially the same composition as the cover gas 108 used in the grinding 104. In addition, normal reagents may be added during flotation 12 or before it, to assist separation by flotation. Such reagents may include foaming agents, activators, harvesters, depressants, modifiers and dispersants. Preferably, the flotation 12 is conducted at room temperature and the mineral produces a natural pH. Operating conditions such as pH may, however, be adjusted as desired to optimize flotation separation of any particular mineral material. Leaving flotation 1 12 a flotation concentrate 16 is obtained which is recovered from the flotation foam and which is enriched in sulfur minerals and consequently also enriched in gold. Also coming out of the flotation 1 12 a flotation tail 18 is obtained, enriched in non-sulfurized gangue materials, and which consequently contains reduced levels of gold. The flotation concentrate 1 16 can be further processed to recover the gold by any suitable technique, if desired. As an alternative, the flotation concentrate 1 16 can be sold as a valuable product for processing by third parties to recover the gold. As noted above, the flotation gas 14 and the cover gas 108 have a respective content of oxygen gas, if they contain it, in a volumetric fraction that is lower than the volumetric fraction of oxygen gas in the ambient air. However, preferably the amount of oxygen gas in the flotation gas 14 and / or the cover gas 108 is less than about 15 volume%, and more preferably less than about 5 volume%. More preferably, both the flotation gas 114 and the cover gas 108 are substantially free of oxygen gas. To help understand the present invention, but not wishing to theorize, it is believed that oxygen gas, if present in an appreciable amount, tends to oxidize the surface of the particles of certain sulfur-bearing gold minerals, which may have effect of depressing the flotation of sulfur-bearing gold ore particles during flotation 112. Reducing the amount of oxygen gas that comes in contact with a mineral, it is believed that any surface oxidation effect is reduced, resulting in a greater flotation of the sulphide ore particles and a corresponding increase in the amount of sulphide, and therefore gold, that is recovered from the flotation concentrate. Therefore, it is preferred that the flotation gas 114 and the cover gas 108 consist essentially of components that can not oxidize the surface of the sulphided gold ore particles. It is preferred that the flotation gas 114 and the cover gas 108 predominantly comprise one or more gases other than oxygen gas. Suitable gases include nitrogen, helium, argon and carbon dioxide. Preferably, one or more of these gases should comprise more than about 95% by volume of the flotation gas 114 and the cover gas 108, and more preferably more than 98% by volume. More preferably, the cover gas 108 and the flotation gas 14 consist essentially of one or more of these gases. Nitrogen gas is particularly preferred because of its relatively low cost. Carbon dioxide is less preferred because it forms an acid when it is dissolved in water, which could corrode the process equipment or produce conditions less favorable to optimal flotation. The cover gas 108 and / or the flotation gas 14 may be introduced into the process apparatus in any suitable manner. Such gases can be fed under positive pressure or they can be induced into the interior of the apparatus creating a suction that makes the gas enter. Preferably, however, the apparatus is designed to substantially prevent the introduction of air into the grinding and flotation apparatus. In one embodiment, the possible detrimental effects of any surface oxidation of sulfide mineral particles that may be present in a mineral feed can be counteracted by the addition of a sulfurizing agent or at least partially replacing the oxidized coating with a sulfide coating . Any material capable of reacting and forming the desired sulfur coating on the mineral particle can be used. Suitable sulfurizing agents include alkali metal sulphides and bisulfides, such as Na 2 S, NaHS, etc. Such sulfurizing agents could be added immediately before or during any step of the flotation 1 12. With the present invention, more than about 90% by weight of the sulfurized minerals of the particulate material 106 can be recovered in the flotation concentrate 16 and preferably more about 90% by weight of said sulfurized minerals are recovered in the flotation concentrate 1 16. An important advantage of the process of the present invention is that, in addition to allowing a high recovery of sulfur-containing gold minerals in the flotation concentrate 1 16, it allows a high degree of rejection of the material of the gangue in flotation glue 1 18. With respect to the use of air as flotation gas, the present invention allows obtaining the same recovery of gold in a concentrate of lower weight. This provides a significant economic advantage because less gangue material appears in the concentrate from which the gold must eventually be separated to produce a purified gold product, if desired. The gas source 1 10 can be any source that provides a suitable flotation gas 1 14 and cover gas 108. A preferred source of gas 1 10 is a plant in which the nitrogen gas is separated from the air, using the nitrogen gas separated as cover gas 108 and flotation gas 1 14. Certain processes are known for separating nitrogen from air, including cryogenic separation and membrane separation. A particularly preferred gas source 1 10 is an oxygen plant that is generally found in facilities where sulfur-containing gold ores are processed. For example, an oxygen plant is typically needed when a pressure oxidation operation or an oxidative calcination operation is used in the processing of sulfur-bearing gold ores. In the oxygen plant, the oxygen is separated from the air, for example by cryogenic separation or membrane separation, and the separated oxygen gas is used in the oxidation under pressure or in the oxidative calcination operation. A by-product of said oxygen plant is a tributary stream of gas enriched in nitrogen gas which is suitable for use as cover gas 108 and / or flotation gas 1 14. This by-product stream was previously vented to the atmosphere and therefore wasted In the present invention, however, the by-product stream can be advantageously used to produce the flotation concentrate 1 16, in addition to using the oxygen gas stream for pressure oxidation or oxidative calcination operation. Figure 2 shows an embodiment of the present invention in which both the oxygen gas stream and the by-product stream of an oxygen plant are both used to process sulfur-bearing gold material. With respect to Figure 2, the particulate material 1 10 is subjected to the flotation operation 1 12 to produce the flotation concentrate 1 16 and the flotation tail 1 18, as described above. Flotation gas 1 14 is a by-product stream enriched in nitrogen gas from an oxygen plant 130, in which air 132 is separated into a gas stream enriched in oxygen and a gas stream enriched in nitrogen. Flotation concentrate 1 16, which is enriched in sulfur-bearing gold ores, is subjected to pressure oxidation 124 to decompose sulphided ores, producing an oxidized material 126 from which gold could be recovered by dissolution using any suitable gold leach, such as for example a cyanide. Pressure oxidation 124 includes treating a slurry of the flotation concentrate 1 16 in an autoclave at a temperature greater than about 150 ° C and an elevated pressure in the presence of an overpressure of a treatment gas 128 which is rich in oxygen. It should be noted that other steps of oxidative treatment could be used in place of pressure oxidation 124. For example, an oxidative calcination or bio-oxidation could be used to produce the oxidized material 126 using the treatment gas 128. In the Figure 3 an additional embodiment according to the present invention is shown. In it the product and by-product streams of an oxygen plant are used to process a sulfur-containing gold material supplied through two independent feed streams. With respect to Figure 3, a first feed of particulate mineral 138 is subjected to flotation operation 1 12 to produce flotation concentrate 1 16 and flotation tail 1 18, as described above. The flotation gas 14 is a stream of nitrogen enriched gas from the oxygen plant 130. A second feed of particulate material 140 is combined with the flotation concentrate 16 in a mixing step 142. The combined stream 144, in slurry form, is subjected to oxidation under pressure 124 to produce the oxidized material 126, from which the gold can be recovered. An advantage of the modality shown in Figure 3 is that it allows the processing of multiple minerals of different characteristics. For example, the first ore feed 138 may comprise a sulphide gold ore of lower grade than the second ore feed, which may comprise a higher grade sulphide gold ore. The higher grade ore may be suitable for pressure oxidation over the entire ore, while the lower grade ore must be transferred to a concentrate form to be suitable for pressure oxidation treatment. Alternatively, the second ore feed may comprise sulphided gold ore having a significant amount of carbonate material that would consume acid produced during pressure oxidation 124, and which, therefore, could adversely interfere with the correct operation of the oxidation pressure 124. However, a high sulfur content of the sulfide in the flotation concentrate 1 16 tends to produce additional acid during oxidation under pressure to at least partially compensate for the acid consumption effect of the carbonate material in the second mineral feed. Almost all the carbonate material that could have been present in the first mineral feed, would normally have been eliminated during flotation 112. The present invention is further described through the following examples, which are intended to be merely illustrative and which are not intended to limit the scope of the present invention. »EXAMPLES Examples 1-6 Examples 1-6 demonstrate the use of nitrogen gas as a flotation gas during the flotation of a sulphide gold ore, to produce a concentrate enriched in sulfur that can be further processed to recover the gold. For each of Examples 1-6, a sample was obtained from the Lone Tree mine in Nevada, from the Santa Fe Pacific Gold Corporation. Samples of sulphided metalliferous ore are of low gradation, so they would not be suitable for the conventional pressure oxidation process in its full mineral form. A representative test of a mineral sample is shown in Table 1.

TABLE 1 For each example, the sample of metalliferous ore was crushed to the desired size. A first portion of the ore sample was floated in a flotation cell on a laboratory scale using air as the flotation gas. A second portion of the ore sample was floated under the same conditions, except that a flotation gas consisting essentially of nitrogen gas was used. During the flotation test modality, flotation foam was collected from the upper part of the flotation cell to recover a flotation concentrate in sulphided minerals and, therefore, was also enriched in gold. The material of the flotation glue is that which is not collected with the foam. For each flotation test, the conditions were substantially the following: natural pH and aggregate of potassium amylxanthate and mercaptobenzothiazole as harvesters, copper sulphate to activate sulfides and M I BC as foaming agent. The flotation periods varied between 20 and 30 minutes.

The results of Examples 1-6 are seen in Table 1. These results have also been plotted in the graphs of Figures 4-7 and reveal significant increases in the amount of gold recovered in the concentrate when nitrogen gas is used as the flotation gas, especially when the particles are small in size.

TABLE 2 (1) 80% by weight of the material passes through the indicated mesh (2) ounces of gold per short ton of concentrate (3) ounces of gold per short ton of tail material (4)% by weight of metalliferous ore included in the concentrate (5)% gold of the metalliferous ore sample included in the concentrate Fig. 4 graphically shows the law of the flotation concentrate (measured in ounces of gold per short ton of concentrate material) as a function of the particle size of the crushed material. As seen in Fig. 4, no identifiable effect is observed in the law of the concentrate by the use of nitrogen gas with respect to the use of air in the flotation. However, Fig. 5 shows that, when the ore particles are smaller in size, the flotation tail contains significantly less gold when nitrogen gas is used than when air is used as the flotation gas. For this reason, when nitrogen gas is used, more gold sulfide minerals are recovered in the concentrate, apparently without detrimental effect on the law of the recovered concentrate. Fig. 6 shows that the amount of material recovered in the concentrate can be significantly higher when nitrogen gas is used for flotation than when air is used, especially when the particles are smaller in size. Fig. 7 shows that the recovery of gold in the concentrate can be increased by almost 15% with a P80 grinding for 270 mesh when nitrogen gas is used for flotation instead of air, without being observed here, harmful effects in the law of concentrated recovered. It will be verified that with 100 mesh P80 grind, no significant difference in flotation performance is observed using nitrogen gas instead of air as the flotation gas. Therefore, it is surprising and unexpected that the yield increases so markedly with respect to air in small grain mills. Characteristically, the flotation performance is expected to increase with small grain particles due to a more complete release of sulfurized minerals from the non-sulfuric material of the gangue. As seen in the graph of Fig. 7, however, the recovery of gold in the concentrate using air as the flotation gas is invariable at best. On the other hand, when nitrogen gas is used, the recovery of gold generally increases as the grinding size decreases, as a result of a greater release of sulfur mineral particles, as would normally be expected. One explanation that contributes to the understanding of the unexpectedly poor performance of the use of air in the present invention, without pretending to theorize, is that harmful chemical processes can occur when air is used as the flotation gas, which would counteract the normal beneficial effects in small particle grinds It has been observed that when air is used as the flotation gas, the pH of the slurry inside the flotation cell drops rapidly for several minutes, sometimes up to 0.5-2 pH units. It would seem that the oxygen in the air oxidizes the surface of the sulphide ore particles producing sulfuric acid and reducing the pH of the slurry. Said surface oxidation of the sulphide ore particles can make them less sensitive to flotation. When the particle size is smaller, the surface available for the oxidation of sulphided minerals increases significantly and consequently, the beneficial effect of a more complete release of the sulphided ore is counteracted by a greater surface of oxidation, which also depresses the flotation of the particles of sulphide ore. Moreover, the nitrogen gas will not oxidize the surface of the sulfur minerals, thus allowing a better flotation of the particles, which, when the particle size is smaller, results in a recovery of sulfide minerals higher than what could be expected. nominally.

Example 7 This Example also demonstrates the beneficial use of nitrogen gas in the flotation of sulfur-bearing gold ores and the use of a coarse separation-wash-purification flotation arrangement to increase concentrate recovery. A flotation pilot plant is operated using low grade sulfide ore from the Lone Tree mine, as already described in Examples 1-6. The diagram of the pilot plant is shown in Fig.8. With reference to Fig.8, the ore sample 166 is subjected to grinding 168 in a ball mill to obtain particles of size P80 for 270 mesh. The ground metalliferous ore, in a slurry 170, is introduced in a step of coarse separation flotation 172. In this step 172 an initial separation is performed, a coarse separation concentrate 174 being collected in the flotation foam and a coarse separation tail 176 which is sent to a washing flotation stage 178, the material collected in the flotation foam of the washing flotation stage 178 is reintroduced, in the form of slurry 179, into a purification float stage 180, in which a final separation flotation is carried out to produce a concentrate of the purification flotation 182 from the foam and a tail of the purification float 184. The tail of the purification float 184 is combined with the water flotation tail. end 186 of the wash flotation stage 178, to produce a final tail 188. The thick separation flotation concentrate 174 and the purification flotation concentrate 182 combine to form a final concentrate 190. In this example, the Coarse separation flotation stage 172 is accomplished in a double compartment flotation cell, the wash flotation stage 178 is accomplished in a series of three double float cells and the purification float stage 180 is accomplished in a series of three double compartment flotation cells. As seen in Fig. 8, nitrogen gas 192 is supplied from a tank 194 and fed in the grinding step 168, in the thick separation float stage 172, in the wash flotation stage 178 and to the stage Purification Flotation 180. Nitrogen gas 192 is used as a flotation gas in each of the flotation stages and as a cover gas to prevent air from oxidising the ore particles during crushing 168. The nitrogen gas is also Use to protect all the rest of the process equipment (not shown), such as pumps and mixing tanks. The sulfur-bearing gold minerals of the metalliferous ore sample 166 are therefore maintained in a substantially air-free environment throughout the pilot plant, until the sulphided gold-bearing minerals have been recovered in a desired concentrate product. The results of the pilot plant are shown in Table 3, where it is observed that the final concentrate 190 of the pilot plant is of superior quality than the concentrates of Examples 1-6. Adding the wash flotation stage 178 and the purification float stage 180 in the pilot plant significantly improves the law of the concentrate that is finally recovered, without appreciable loss of gold recovery.

TABLE 3 (1) 80% by weight of the material passes through the indicated mesh (2) ounces of gold per short ton of concentrate (3) ounces of gold per short ton of tail material (4)% by weight of ore sample in the concentrate (5)% gold in the concentrate in relation to the feed of the respective flotation step Example 8 Laboratory tests were performed on samples of low grade gold sulfide ore containing gold from Twin Creeks Mine, Nevada, of the Santa Fe Gold Corporation. Table 4 shows a representative analysis of a sample of the mineral. For each test, a sample was crushed to an appropriate size and a portion of each sample was then floated using air as the flotation gas and another portion was subjected to flotation using nitrogen gas as the flotation gas. The same flotation conditions as those described for Examples 1-6 were used substantially TABLE 4 The results of Example 8 are shown graphically in Fig. 9, which presents a gold recovery diagram in the concentrate according to the size of the particles. As seen in Fig.9, the use of nitrogen gas translates, in general, into a significantly greater recovery of gold in the concentrate than when air is used as the flotation gas. The present invention has been described with reference to specific modal forms thereof. However, according to the present invention, any of the aspects presented in any of the forms of modality may be combined in any way with any other aspect of any other form of modality. For example, any of the aspects presented in any of Figs. 1-3 and 8 may be combined with any other aspect of any of said figures. In addition, different forms of modality of the present invention having been described in detail, art connoisseurs will be able to introduce modifications and adaptations thereof. It is noted that said modifications and adaptations are within the scope of the present invention, which is described in the following claims.

Claims (38)

1. CLAIMS 1 .- Method for processing an auriferous mineral material containing a sulphide mineral with which the gold is associated, comprising the steps of: (a) providing a particulate gold ore material comprising gold and a sulfur mineral to which said gold is added; gold is associated and from which said gold can be difficult to recover, said mineral material also comprising a non-sulfurized material as gangue; (b) subjecting said mineral material to flotation with a flotation gas to separate said mineral material into at least two fractions, a first fraction being a flotation concentrate, collected from the flotation foam, enriched in said sulfurized mineral and said gold and a second fraction consisting of a flotation tail enriched in said non-sulfurized material and exhausted in said gold; said flotation gas comprising oxygen not more than about 15% by volume; said flotation being such that the pyrrhotite, when present in said mineral material, could be collected from the flotation broth and could be concentrated in said flotation concentrate.
2. 2 - The method according to claim 1, wherein said flotation gas comprises a gaseous by-product, enriched in nitrogen gas with respect to air, of an oxygen plant in which oxygen enriched gas is produced from the air.
3. 3. The method according to claim 1, wherein said flotation gas comprises less than about 5 vol.% Oxygen gas.
4. 4. The method according to claim 1, wherein said flotation gas is substantially free of oxygen gas.
5. 5. The method according to claim 1, wherein said flotation gas comprises more than about 85 vol.% Nitrogen gas.
6. 6. The method according to claim 1, wherein said flotation gas comprises more than about 95 vol.% Nitrogen gas.
7. 7 - The method according to claim 1, wherein said flotation gas is substantially free of components capable of oxidizing, during said flotation, the sulfur of the sulfide in said sulfurized mineral.
8. 8. The method according to claim 1, wherein said flotation gas comprises more than about 95 volume% of gas selected from the group consisting of nitrogen gas, helium gas, argon gas, carbon dioxide gas and combinations thereof.
9. 9. The method according to claim 1, wherein said step of providing a particulate gold mineral material comprises grinding a raw gold mineral material in the presence of a cover gas comprising not more than about 15% by volume of oxygen gas.
10. 10. The method according to claim 1, wherein said step of providing a particulate gold mineral material comprises grinding an auriferous mineral material in an environment that is substantially free of oxygen gas. 1.
11. The method according to claim 1, wherein subsequent to said flotation, at least a portion of said flotation concentrate is subjected to an oxidative treatment in the presence of a treatment gas enriched in oxygen gas in relation to with ambient air, to oxidize at least a portion of the sulfur sulfur in said sulfurized mineral, to assist in the release of at least a portion of said gold from its association with said sulphide mineral and to facilitate the possible subsequent recovery of said gold.
12. 12. The method according to claim 1, wherein said flotation gas comprises an oxygen deficient gaseous byproduct of an oxygen plant that produces an oxygen enriched gas from air; and in said oxidative treatment step, said treatment gas comprises at least a portion of said oxygen enriched gas of said oxygen plant.
13. 13. The method according to claim 1, wherein said oxidative treatment comprises the oxidation under pressure of a slurry of said sulfurized mineral at an elevated temperature and an elevated pressure in the presence of said treatment gas.
14. 14. The method according to claim 1, wherein said oxidative treatment comprises calcining said sulfurized mineral at an elevated temperature in the presence of said treatment gas.
15. 15. The method according to claim 1, wherein subsequent to said flotation step, at least a portion of said flotation concentrate is bonded to the entire mineral, comprising a sulphide mineral to form a mixture.; and said mixture is subjected to said oxidative treatment.
16. 16. - The method according to claim 1, wherein said oxidative treatment comprises oxidation under pressure of a slurry of said sulfurized mineral at an elevated temperature and an elevated pressure in the presence of said treatment gas; said complete mineral comprises carbonate material that consumes acid during said oxidation under pressure; and said flotation concentrate is enriched in sulfur sulfur which, during said pressure oxidation, contributes in the production of sulfuric acid which at least compensates for the acid consumption of said carbonate material.
17. 17. The method according to claim 1, wherein after said oxidative treatment, the gold that has been released from the association with said sulfurized mineral during the oxidation under pressure, is recovered by dissolving in a washing solution that It comprises a leach for gold.
18. 18. The method according to claim 1, wherein said flotation concentrate comprises more than about 80% by weight of said sulphide mineral of said ore material.
19. 19. The method according to claim 1, wherein said flotation concentrate comprises more than about 90% by weight of said mineral material.
20. 20.- Method for processing an auriferous mineral material containing a sulphide mineral with which the gold is associated, comprising the steps of: (a) providing a crude material of particulate gold ore comprising gold and a sulphide mineral to which said gold is associated, said mineral material also comprising a non-sulfurized material as gangue; (b) mixing a covering gas with said mineral material; (c) crushing said crude mineral material in the presence of said cover gas to form a particulate gold mineral material; (d) subjecting said mineral material to a flotation process, with a flotation gas to separate said mineral material in at least two fractions, a first fraction, collected from the flotation foam, being a flotation concentrate enriched in said mineral sulfur and said gold, and a second fraction a flotation tail enriched in said non-sulfurized material and exhausted in said gold; said cover gas comprising oxygen gas not greater than about 15% by volume.
21. 21. The method according to claim 20, wherein during said mixing, said cover gas displaces the air in the vicinity of said raw mineral material.
22. 22. The method according to claim 20, wherein said cover gas comprises less than about 5 volume% oxygen gas.
23. 23. - The method according to claim 20, wherein said cover gas comprises more than about 95 volume% of nitrogen gas.
24. 24. The method according to claim 20, wherein said cover gas and said flotation gas have substantially the same gas composition.
25. 25.- Method for using different air streams separated from the air to collaborate in the processing of an auriferous mineral material that contains a sulfur mineral to which the gold is associated, which comprises the steps of: (a) separating an amount of air in at least two gas streams, a first stream being a gas stream enriched in nitrogen gas with respect to said air and said second stream being a gas stream enriched in oxygen gas with respect to said air; (b) providing a feed of particulate gold mineral material comprising a sulfide mineral with which said gold is associated, said mineral material also comprising non-sulfided materials. (c) subjecting at least a portion of said mineral material to a flotation treatment to separate said mineral material into at least two fractions, a first fraction being a flotation concentrate enriched in said sulfurized mineral and said gold in relation to said mineral. mineral material in said feed, and a second fraction being a flotation tail enriched in said non-sulfurized material and exhausted in said gold in relation to said mineral material of said feed; said flotation consisting in subjecting at least a portion of said feed to a flotation gas that includes at least a portion of said first gas stream enriched in nitrogen gas; and (d) oxidative treatment of at least a portion of said mineral material, said oxidative treatment comprising contacting said portion of the mineral material with at least a portion of said second gas stream enriched in oxygen gas, to oxidize at less a portion of the sulfur sulfur in said sulfurized mineral and produce an oxidized material in which at least part of said gold is released from its association with said sulphide mineral, facilitating the possible subsequent recovery of the gold from said oxidized material.
26. 26. The method according to claim 25, wherein said step of providing said feed of particulate mineral material comprises grinding a raw mineral material in the presence of at least part of said first gas stream enriched in nitrogen gas.
27. 27. The method according to claim 25, wherein at least a portion of said mineral material, which is subjected to said oxidative treatment step, comprises at least a portion of said flotation concentrate.
28. 28. The method according to claim 25, wherein at least a portion of said mineral material, which is subjected to said oxidative treatment step, comprises at least a portion of said feed mixed with at least a portion of said flotation concentrate.
29. 29. The method according to claim 25, wherein said oxidative treatment comprises the oxidation under pressure of a slurry of said sulfurized mineral at an elevated temperature and an elevated pressure in the presence of said second stream of gas enriched in oxygen gas.
30. The method according to claim 25, wherein said oxidative treatment comprises the oxidative calcination of said mineral material at an elevated temperature in the presence of said second gas stream enriched in oxygen.
31. The method according to claim 25, wherein said first gas stream comprises more than about 95 vol.% Nitrogen gas.
32. 32.- Method of processing an auriferous mineral material with sulfide mineral with which said gold is associated, comprising the steps of: (a) providing, in at least two portions, particulate auriferous mineral material with a first portion feeding said mineral material with a first average concentration of gold and a second feeding portion of said mineral material with a second average concentration of gold that is lower than the first average concentration of gold; each of said first feed portion and said second feed portion comprising a sulphide mineral with which the gold is associated and from which the gold is difficult to recover, and further comprising said first feed portion and said second portion of feed. feed a non-sulfurized material; (b) oxidative treatment of said first feed portion, said oxidative treatment comprising contacting said first feed portion with a treatment gas comprising oxygen gas, to oxidize at least a portion of the sulfur sulfur in said sulphided ore and producing an oxidized material in which at least part of said gold is released from its association with said sulfurized mineral; and (c) subjecting said second feed portion, but not the first feed portion, to flotation, which comprises treating a liquid slurry of said second feed portion with a flotation gas to separate said second feed portion at minus two fractions, a first fraction being a flotation concentrate enriched in said sulphided mineral and said gold, and a second fraction being a flotation tail enriched in said non-sulfurized mineral and exhausted in said gold; said float gas comprising not more than 15% by volume.
33. 33. The method according to claim 32, wherein said flotation gas comprises less than about 5% by volume of oxygen gas.
34. 34. The method according to claim 32, wherein said flotation gas comprises more than about 95 vol.% Nitrogen gas.
35. The method according to claim 32, wherein at least a portion of said flotation concentrate is mixed with said first feed portion prior to said oxidative treatment step.
36. 36 - The method according to claim 32, wherein said oxidative treatment comprises at least one of: (i) oxidation under pressure of a slurry of said first feed portion of said mineral material in the presence of said treatment gas at elevated temperature and high pressure, (ii) oxidative calcination of said first feed portion in the presence of said treatment gas at elevated temperature, and (iii) bioxidation of said first feed portion in the presence of said treatment gas.
37. 37.- The method according to claim 1, wherein: said oxidation treatment comprises bio-oxidation of said sulfurized material.
38. 38. The method according to claim 10, wherein: said sulfurized material is maintained in an environment that is substantially free of oxygen between and during said crushing and flotation. 39.- The method according to claim 1, wherein: said flotation concentrate is enriched with, and said flotation tail is depleted of, said gold and at least one of pyrite, marcasite, arsenopyrite, pyrite, arsenose and pyrrhotite. .