AUSTRALIA Regulation 3.2 Patents Act 1990 Complete Specification Standard Patent APPLICANT: JX Nippon Mining & Metals Corporation Invention Title: METHOD OF LEACHING GOLD FROM SULFIDE ORES The following statement is a full description of this invention, including the best method of performing it known to me: METHOD OF LEACHING GOLD FROM SULFIDE ORES BACKGROUND OF THE INVENTION Field of the Invention 5 [0001] The present invention relates to a method of leaching gold from sulfide ores. Alternatively, the present invention relates to a method of recovering gold from aqueous solution from which gold was leached. 10 Description of the Related Art [0002] In recent years, a technique of recovering copper from sulfide ore by using a hydrometallurgical process has been 15 attracting attention, as a substitute for a conventional pyrometallurgical process. Although the content is very small, sulfide ores often contain additional precious metals such as gold, so that there has been a need for economically recovering not only copper but also such 20 precious metals. [0003] Concerning for the issue, a known technique is to leach gold from the residue after copper leaching, using chloride and bromide of alkali metal or alkali earth metal, and chloride and bromide of copper and iron (Japanese Laid Open Patent Publication No. 2009-235519). According to the description, the method successfully leaches and recovers copper and gold contained in copper sulfide ores at high 5 leach rates, merely by making use of air, but without using any special oxidizing reagent. [00041 In connection with the above-described techniques, Japanese Laid-Open Patent Publication No. 2009-235525 10 describes that "leaching of gold in a copper concentrate requires a suitable oxidizing reagent, and a stabilizing reagent that prevents precipitation of metallic gold produced by the reduction of the leached gold" (paragraph 0014). It is also described that the concentration of 15 bromide ions used in the copper leaching reaction, which are required to form gold bromide and complexes with eluted gold, depends in part on the concentration of gold to be eluted. The bromide salt solubility, which is affected by the concentration of sodium chloride that is present 20 together, has its upper limit. In consideration of the solubility, the amount of the reagent may be 1 g/l to 80 g/l, and desirably about 10 g/l to 26 g/l from the viewpoint of economy (paragraph 0017) . The document also describes that bromide ions are added as sodium bromide, 2 and a higher concentration of bromide ions is desirable, however, the solubility is influenced by the concentration of co-existing chloride ions and the temperature. In practice, the concentration of bromide ions may be 1 g/l to 5 50 g/l, and preferably 10 g/l to 26 g/l (paragraph 0025). [00051 Furthermore, Japanese Patent Application Publication (Translation of PCT Application) No. 2009-526912 describes a method of leaching gold from a leaching residue or 10 intermediate product which is generated in the atmospheric chloride leaching of raw material of copper sulfide concentrate. The document proposes that the concentration of alkali bromides in the leaching solution will be 0.5 g/l to 30 g/l to enhance leaching. 15 [00061 Techniques described in the aforementioned documents propose that chlorine ions are mainly used as halogen ions contained in the leaching solution for gold leaching. The documents propose commercially operable techniques for the 20 method of recovering gold from sulfide ores in the hydrometallurgical process by supplementary adding bromine ions in addition to the chlorine ions. When gold leaching is processed by the conventional techniques, the gold concentration is high in a fresh leachate which is derived 3 after gold leaching. However, it has found that there has been a problem that gold concentration in the gold leachate decreases rapidly with time. In an actual operation of recovering gold from copper ores, gold recovering process 5 is not always performed immediately after the gold leaching process. In some cases, gold leaching process might be performed after retaining the gold leachate for about one to three days due to the time for the solid-liquid separation or operation schedules. Thus, a method for 10 maintaining gold concentration dissolved in the leachate as high as possible during the retaining has been expected. SUMMARY OF THE INVENTION [0007] 15 The present invention provides a method which can suppress degradation of concentration of gold in the leachate proceed with time after leaching gold from sulfide ores. [0008] 20 The present inventors have found out through their extensive investigations that gold will be stably kept in a dissolved state in the leachate if bromide ion concentration in the leachate which is consist of alkali chloride solution mainly is greatly elevated. 4 [0009] Accordingly, an aspect of the present invention provides a method of leaching gold contained in sulfide ores or a residue after leaching the sulfide ores 5 (hereinafter referred to as raw materials) which encompasses bringing an aqueous acidic solution which contains chloride ion, bromide ion, copper ion, and iron ion, into contact with the raw materials under supply of an oxidizing reagent, so as to leach gold contained in the raw 10 materials, and retaining the aqueous acidic solution from which gold was leached while keeping the concentration of bromide ion of 40 g/L or more and redox potential (vs Ag/AgCl) at 500 mV or above. [0010] 15 In an embodiment of the method of leaching gold according to the present invention, the bromide ion in the aqueous acidic solution is kept 80 g/L or more and the redox potential (vs Ag/AgCl) is kept at 480 mV or above. [0011] 20 In another embodiment of the method of leaching gold according to the present invention, a weight concentration ratio of bromide ion to chloride ion in the aqueous acidic solution is 1 or more. [0012] 5 In still another embodiment of the method of leaching gold according to the present invention, copper ion concentration in the aqueous acidic solution is 5 g/L or more and iron ion concentration in the aqueous acidic 5 solution is 1 g/L or more. [0013] Another aspect of the present invention inheres in a method of leaching gold from raw materials encompassing recovering gold from gold leachate which is obtained by 10 performing aforementioned method of leaching gold. [0014] In an embodiment of the method of leaching gold according to the present invention, a retention period from an end of the gold leaching process to a beginning of the 15 recovery process of gold is 24 hours or more. [0015] Another embodiment of the method of leaching gold according to the present invention encompassing increasing the concentration of the bromide ion in the gold leachate 20 during the retention period. [0016] According to the present invention, it becomes possible to suppress degradation of the gold concentration in the leachate proceed with time after leaching gold from 6 sulfide ores or the residue after leaching the sulfide ores and recovery rate of gold from sulfide ores will be enhanced. 5 BRIEF DESCRIPTION OF THE DRAWINGS [0017] Fig. 1 is a graph illustrating changes in the gold concentration dissolved in the leachate. 10 DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION [0018] (Leaching Process) In a gold leaching process, aqueous acidic solution (gold leaching liquid) containing chloride ion, bromide ion, 15 copper ion and iron ion is brought into contact with the raw materials under supply of an oxidizing reagent, so as to leach gold component contained in the raw materials. It is preferable to adjust chloride ion concentration of 5 g/L to 70 g/L, bromide ion concentration of 40 g/L or more, 20 copper ion concentration of 5 g/L ore more, iron ion concentration of 1 g/L or more in the aqueous acidic solution. Intended raw materials according to the present invention include sulfide ores or leaching residue which is obtained after leaching the sulfide ores. The sulfide ores 7 are typically exemplified by gold-containing primary copper sulfide ore (example: chalcopyrite), copper sulfide ore containing silicate ore containing gold, and pyrite containing gold, but not limited thereto. In addition, 5 intermediate products reproduced in the various treating process of sulfide ores are also treated as the sulfide ores. [0019] The gold leaching proceeds in such a manner that 10 leached gold reacts with chloride ion or bromide ion to produce gold chloride complex or gold bromide complex. By using bromide ion and chloride ion, the complexes can be formed at lower redox potential, and thereby reducing the time for leaching and enhancing the leaching efficiency of 15 gold, more specifically, the gold concentration of leachate can be improved. In the present embodiment, since bromide ion concentration in the gold leaching solution is greatly elevated, it will be possible that the leached gold can exist stably for a long period. 20 [0020] The redox potential of leaching solution also depends upon temperatures. If the solution temperature drops by 10 *C, the redox potential also drops by 10 mV. For this reason, if the leaching solution having general 8 leaching temperature of 80 0C is left without any operations, it becomes difficult to keep the dissolution of gold because the temperature of the leaching solution is lowered and the redox potential thereof is also decreased. 5 [0021] It will be enough that bromide ion concentration in the gold leaching solution may be 5g/L, from the view point of reaction rate and solubility only. However, it will be necessary that the bromide ion concentration in the gold 10 leaching solution may be 40 g/L or more to keep the gold in the leaching solution as the dissolved state and gold concentration thereof is kept 2 mg/L or more or to keep the gold in the leaching solution in the dissolved state even the temperature of the leaching solution is lowered to the 15 room temperature from general leaching temperature of 80 C. It will be more preferable that the bromide ion concentration in the gold leaching solution is 80 g/L or more, more preferably 100 g/L or more, and more preferably 120 g/L or more. Since the bromide ion concentration in the 20 gold leaching solution may be lowered from the view point of the cost, the bromide concentration may be preferably 80 to 100 g/L. [0022] Chloride ion concentration in the gold leaching 9 solution is preferably 5 g/L, and more preferably 15 g/L, from the view point of the generation of copper (I). However, too excess chloride ion concentration causes various kinds of precipitations as a result of the 5 saturation. Therefore, it may be 70 g/L or less, more preferably 20 to 40 g/L. [0023] Iron ions oxidize gold. All useful iron ions are ferric ion which is produced by the oxidizing reagent or 10 ferric compounds. Ion concentration of iron in the gold leaching solution will be preferably 1 g/L or more, more preferably 3 g/L or more. [0024] While copper ion does not directly take part in the 15 reaction, the presence of copper ion accelerates the oxidation by iron ion. Cupic ion in all copper ions acts to oxidize gold. Ion concentration of copper in the gold leaching solution will be preferably 5 g/L or more, more preferably 20 g/L or more. 20 [0025] Supply sources of chloride ion are typically exemplified by hydrogen chloride, hydrochloric acid, metal chloride and chlorine gas, without special limitation. Taking economy and safety into account, supply in the form 10 of metal chloride is preferable. The metal chloride is typically exemplified by copper chlorides (copper (I) chloride, copper (II) chloride), iron chlorides (iron (II) chloride, iron (III) chloride), chlorides of alkali metals 5 (lithium, sodium, potassium, rubidium, cesium, and francium), and chlorides of alkali earth metals (beryllium, magnesium, calcium, strontium, barium, and radium). From the viewpoint of economy and availability, sodium chloride is preferable. Also copper chloride and iron chloride are 10 preferably used, since they may be used also as supply sources of copper ion and iron ion, respectively. [0026] Supply sources of bromide ion are typically exemplified by hydrogen bromide, hydrobromic acid, metal 15 bromide and bromine, without special limitation. Taking economy and safety into account, it is preferably supplied in the form of metal bromide. The metal bromide is exemplified by copper bromides (copper (I) bromide, copper (II) bromide), iron bromides (iron (II) bromide, iron (III) 20 bromide), bromides of alkali metals (lithium, sodium, potassium, rubidium, cesium, francium), and bromides of alkali earth metals (beryllium, magnesium, calcium, strontium, barium, radium). From the viewpoint of economy and availability, sodium bromide is preferable. Also 11 copper bromide and iron bromide are preferably used, since they may be used also as supply sources of copper ion and iron ion, respectively. [0027] 5 Supply sources of copper ion and iron ion are supplied generally in the form of salts, and typically in the form of halides. Copper ion is preferably supplied in the form of copper chloride and/or copper bromide, and iron ion is preferably supplied in the form of iron chloride and/or 10 iron bromide, in view of using them also as supply sources of chloride ion and/or bromine ion. Copper chloride and iron chloride adoptable herein are preferably copper (II) chloride (CuCl 2 ) and iron (III) chloride (FeCl 3 ), respectively, in view of oxidizing power. It is, however, 15 of no difference if copper (I) chloride (CuCl) and iron (II) chloride (FeCl 2 ) are adopted, because they may be oxidized into copper (II) chloride (CuCl 2 ) and iron (III) chloride (FeCl 3 ), respectively, if any oxidizing agent is supplied to the leaching solution. 20 [0028] Accordingly, in a preferred embodiment of gold leaching process according to the present invention, a mixed solution containing at least either one of hydrochloric acid and hydrobromic acid; at least either one 12 of copper (II) chloride and copper (II) bromide; at least either one of iron (III) chloride and iron (III) bromide; and at least either one of sodium chloride and sodium bromide, may be used as the leaching solution, provided 5 that the selection is made so as to contain both of chloride ion and bromide ion. [0029] The pH of gold leaching solution is preferably 0 to 3, more preferably 0.5 to 2.0 to ensure the dissolution of the 10 trivalent ions. At the beginning of the gold leaching process, the redox potential (vs Ag/AgCl) in the leaching solution is preferably at 500 mV or above, more preferably at 550 mV or above, taking into consideration of the effect of the bromide ions. The temperature of the gold leaching 15 solution is preferably at 60 *C or more, in view of the leaching efficiency and materials of the apparatus, more preferably at 70 to 90 *C, in view of leaching rate. [0030] The gold leaching process is performed by supplying an 20 oxidizing reagent to control the redox potential. The oxidizing reagent is exemplified by oxygen, air, chlorine, bromine, and hydrogen peroxide, without special limitation. There is no necessity of using an oxidizing reagent having an extremely high redox potential, but air is good enough. 13 Air is also preferred from the viewpoints of economy and safety. [0031] Methods of bringing the gold leaching solution into 5 contact with the raw materials may be spraying, dipping and so forth, which are selectable without special limitation. From the viewpoint of reaction efficiency, it is preferable to dip the residue into the leaching solution and to stir. [0032] 10 (Recovery of Copper) The leachate obtained in copper leaching process contains a large amount of copper ion, so that copper may be recovered from the leachate. Recovery methods of copper may typically be solvent extraction, ion exchange, 15 cementation with a base metal, and electrowinning, without special limitation. While copper in the leachate exists as both cuporous and cupric ions, it is preferable to preliminarily oxidize the ions to entirely make them cupric, for smoothness of solvent extraction and ion exchange. 20 Methods of oxidation are not specifically limited, wherein a simple method may be employed by blowing of air or oxygen into the leachate. [0033] (Recovery of Gold) 14 The precious leached solution obtained by the gold leaching process contains gold dissolved therein, so that the gold may be recovered from the solution. Methods of recovery of gold may typically be adsorption on activated 5 carbon, electrowinning, solvent extraction, and ion exchange, without special limitation. The gold leaching rate may be improved by collecting gold on middle way of the leaching reaction so as to lower the concentration of gold in the leaching solution. 10 [0034] According to the present invention, since the stability of the gold dissolved in the leachate after gold leaching is high, the retention period from an end of the gold leaching process until a beginning of the gold 15 recovery process will be able to be prolonged. For example, the retention time can be prolonged for five days or one week or more. It may be preferable to retain the leachate within two days because keeping the leachate for a long time does not bring much benefit. 20 [0035] Bromide ion concentration in the gold leachate can be increased to keep the gold dissolved in the leachate stably for a long time. In particular, supply source of bromide ion can be added to the gold leachate within a day, 15 preferably within half a day, more preferably within six hours, more preferably within one hour after the end of the gold leaching process. The foregoing compound can be used as the supply source of the bromide ion. Sodium bromide 5 may be preferable from the viewpoint of economy and availability. [0036] During the period from the end of the gold leaching process until the beginning of the gold recovering process, 10 dissolution of gold can be kept by controlling the gold leachate of the redox potential (vs. Ag/Cl) at 500 mV or above and the temperature at room temperature (25 *C) or more, when the bromide ion concentration in the precious leached solution is 40 g/L or more. This value of the redox 15 potential is more than 40 mV lower than the redox potential in the fresh leachate derived immediately after leaching. It is also possible to manage the redox potential (vs. Ag/Cl) of the gold leachate at 480 mV or above and the temperature at room temperature (25 0C) or more, when the 20 bromide ion concentration in the precious leached solution is 80 g/L or more. There is no harm in keeping the redox potential at higher level, however, the cost becomes high if the redox potential is kept higher beyond necessity. It is preferable that the redox potential will be at 700 mV 16 (vs. Ag/Cl) or lower, more preferably, 600 mV (vs. Ag/Cl) or lower. [0037] In general, the redox potential decreases when 5 temperature decreases. The leaching solution having composition as described herein, degradation ratio of the temperature degradation and the redox potential degradation is about 1 mV/*C. That is to say, the control can be performed by decreasing the temperature of the leaching 10 solution about 40 *C. EXAMPLES [0038] In an experiment, gold was leached by using a residue 15 of the copper sulfide concentrate containing gold after copper leaching. The gold concentration of the residue was 26 g/t and copper concentration thereof was 1.2 %. Gold leaching was performed by adjusting the Cl ion concentration of 40g/t, Cu ion concentration of 20 g/L, Fe 20 ion concentration of 2 g/L, Br ion concentration of 20 to 120 g/L, supplying air and keeping the solution temperature at 80 *C. The redox potential at 80 *C was at 537 to 557 mV (vs.Ag/AgCl). [0038] 17 The leachate was left without any operations at room temperature (15 to 25 0C) and gold concentration dissolved in the precious leached solution on first to seventh days after leaching was measured. In order to eliminate the 5 influence of minute precipitate, sampled leaching solution was filtered with 0.1 micrometer membrane filter and subjected to the ICP analysis. The redox potential of the leachate which is in the retention period was measured after decreasing the solution temperature at 250C. 10 [0040] The results of the analysis were shown in Figure 1. In a case where the leachate having bromide ion concentration of 20 g/L was used, one day after, the gold concentration was decreased to 1 mg/L or lower. In a case where the leachate 15 having bromine ion concentration of 40 g/L was used, the gold concentration was kept at initial concentration for seven days if the redox potential was kept at 500 mV. In a case where the leachate having the redox potential at 480 mV and bromide ion concentration of 60 g/L was used, 20 one day after, the gold concentration was decreased less than half of the 60 g/L. In a case whrere the leachate having the bromine ion concentration of 80 g/L was used, the gold concentration was kept at initial concentration for five days. 18 [0041] In the specification the term "comprising" shall be understood to have a broad meaning similar to the term "including" and will be understood to imply the inclusion 5 of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. This definition also applies to variations on the term "comprising" such as "comprise" and "comprises." 10 [0042] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the referenced prior art forms part of the common general knowledge in Australia. 15 19