AU2018340945B2

AU2018340945B2 - Gold leaching method and gold recovery method

Info

Publication number: AU2018340945B2
Application number: AU2018340945A
Authority: AU
Inventors: Kazuhiro Sekine; Ryosuke TATSUMI; Akira Yoshimura
Original assignee: JX Nippon Mining and Metals Corp
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2017-09-26
Filing date: 2018-06-08
Publication date: 2021-05-27
Anticipated expiration: 2038-06-08
Also published as: JP2019059984A; WO2019064709A1; AU2018340945A1; CL2020000774A1; JP6953258B2; PE20201046A1

Abstract

Provided is a gold leaching method for leaching gold included in raw material that includes sulfide minerals or gold and sulfur as a refining intermediate obtained by refining treatment of sulfide minerals, wherein the gold leaching method includes: a first leaching step for leaching part of the gold in the raw material and obtaining a leaching residue having a gold residue and including sulfur; a sulfur elimination step for eliminating the sulfur in the leaching residue; and a second leaching step for leaching at least part of the residual gold in the leaching residue that has passed through the sulfur elimination step.

Description

GOLD LEACHING METHOD AND GOLD RECOVERY METHOD TECHNICAL FIELD

[0001] The present invention relates to a method for leaching gold that can be contained in sulfide minerals and refining intermediates, and a method for recovering gold using the same. More particularly, it proposes a technique that will contribute to improvement of a recovery rate of gold.

BACKGROUND ART

[0002] For example, it is known to use a hydrometallurgical process as a gold recovery technique for recovering gold contained in ores such as chalcopyrite or other sulfide minerals and/or silica minerals or gold contained in refining intermediates which are leached residues obtained such as by leaching copper in copper sulfide minerals or leaching iron in iron pyrite. With regard to such a hydrometallurgical process, to leach gold contained in the sulfide minerals or the refining intermediates in a solution, chemicals such as cyanides, thiourea, thiosulfuric acid and halogen gases have been conventionally used. However, the use of cyanide, among these chemicals, is often limited because of its toxicity, and so the use of such a chemical is not desired.

[0003] In such circumstances, it has been recently proposed to leach gold contained in the sulfide minerals or like using a halogen bath of an aqueous acidic solution containing a copper ion or the like as a cation, and a chloride ion and a bromide ion as anions, as described in Patent Documents 1 and 2, for example. According to a gold leaching step of the proposed technique, gold can be easily leached as a polysulfide-type complex or the like, without using the cyanide that are toxic. In addition, gold leached in the aqueous acidic solution can be recovered by adsorbing gold on activated carbon and then eluting it with sodium hydroxide.

[0004] Here, the gold contained in the sulfide minerals is generally exposed on the surfaces, covered with sulfide, or covered with a gangue component such as SiO 2 , or the like. Among them, the exposed gold in the sulfide minerals or the like can be dissolved by forming a halogen complex in the gold leaching step.

[0005]

For the gold covered with sulfide, as described in Patent Document 1, prior to the gold leaching step, a calcination step is carried out by heating sulfide minerals or the like in a non-oxidizing atmosphere to thermally decompose iron disulfide into iron (II) sulfide and sulfur, as well as after the calcination step, a deironing step is carried out under substantially the same leaching conditions as those of the gold leaching step to leach and remove iron (II) sulfide, whereby the gold can be dissolved in the subsequent gold leaching step. Although a miner amount of gold covered with SiO2 or the like in the sulfide minerals is present, it would be difficult to leach the gold.

CITATION LIST Patent Literatures

[0006] Patent Document 1: WO 2014/038236 Al Patent Document 2: Japanese Patent Application Publication No. 2009-526912 A

SUMMARY OF INVENTION Problem to be Solved by the Invention

[0007] It have been found that the leaching rate of gold actually leached through the calcination step, the deironing step, the gold leaching step, and the like as described above is lower than a theoretical leaching rate obtained by analysis of a form of gold present in raw materials such as sulfide minerals and refining intermediates. That is, it is believed that not only gold covered with gangue components such as Si02 in sulfide minerals but also gold present in other forms are not sufficiently leached by the conventional gold leaching method. Thus, the prior arts have room for improvement in terms of further leaching of gold.

[0008] An object of the present invention is to solve such problems of the prior arts. The object of the present invention is to provide a gold leaching method that can increase a leaching rate of gold contained in sulfide minerals and/or refining intermediates and contribute to improvement of the recovery rate of gold, and to provide a gold recovery method using the same.

Means for Solving the Problem

[0009] As a result of intensive studies on the reason why gold that otherwise could be leached is not leached, the present inventors have found that in the middle of the gold leaching step, a sulfur fraction of the sulfides contained in the sulfide minerals and/or refining intermediates remain in a certain form such as elemental sulfur, and the sulfur having a slower dissolution rate in an acid becomes present around gold, thereby inhibiting the leaching of the gold. This is a major problem because it is more difficult to leach the gold as an amount of such sulfur generated increases, although not limited to such a theory.

[0010] Under such findings, the gold leaching method according to the present invention is a method for leaching gold contained in raw materials containing gold and sulfur, as sulfide minerals or refining intermediates obtained by subjecting the sulfide minerals to a refining treatment, the method comprising: a first leaching step of leaching a part of gold in the raw materials to obtain a leached residue containing sulfur and remaining gold; a sulfur removing step of removing sulfur in the leached residue; and a second leaching step of leaching at least a part of the remaining gold in the leached residue after the sulfur removing step.

[0011] In the gold leaching method according to the present invention, it is preferable that the gold in the leached residue is exposed by removing the sulfur in the leached residue in the sulfur removing step. The gold leaching method according to the present invention is particularly effective when the leached residue containing sulfur, at least a part of the sulfur being in the form of elemental sulfur, is obtained in the first leaching step.

[0012] In the gold leaching method according to the present invention, it is preferable that the sulfur in the leached residue can be removed by bringing the leached residue into contact with an alkaline solution in the sulfur removing step. In this case, it is preferable that the alkaline solution to be brought into contact with the leached residue in the sulfur removing step has a pH of 10 or more.

[0013] Alternatively, in the gold leaching method according to the present invention, in the sulfur removing step, the leached residue can be heated to remove sulfur in the leached residue as a gas.

[0014] In the gold leaching method according to the present invention, it is preferable that a sulfur removal rate in the sulfur removing step is preferably 10% or more, and more preferably 25% or more.

[0015] In the gold leaching method according to the present invention, it is preferable that in the first leaching step, the raw materials are brought into contact with an acidic aqueous solution containing a copper ion, an iron ion and a halide ion while feeding an oxidizing agent.

[0016] The gold recovery method according to the present invention is a method for recovering gold from raw materials using any one of the gold leaching methods described above.

Effects of the Invention

[0017] According to the present invention, after the first leaching step, the sulfur removing step is carried out by removing sulfur in the leached residue, and subsequently a second leaching step is further carried out by leaching at least a part of the remaining gold in the leached residue after the sulfur removing step, whereby the gold from which the surrounding sulfur has been removed in the sulfur removing step can be effectively leached in the second leaching step. As a result, the leaching rate of gold contained in sulfide minerals and/or refining intermediates is further increased, so that it can contribute to improvement of the recovery rate of gold.

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a flowchart showing a gold leaching step according to an embodiment of the present invention. FIG. 2 is a graph showing changes in gold quality and gold leaching rate in a residue over time when a leaching step is carried out after a non-oxidizing calcination step in Example. FIG. 3 is a graph showing a relationship between a sulfur removal rate and a gold recovery rate based on results of Example and Comparative Example.

MODES FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail. As shown in FIG. 1, a method for leaching gold according to an embodiment of the present invention uses raw materials as sulfide minerals or refining intermediate obtained by subjecting the sulfide minerals to a refining treatment, which contain gold and sulfur, and leaches the gold contained in the raw materials from the raw materials. This method includes at least: a first leaching step of leaching a part of the gold in the raw materials to obtain a leached residue containing sulfur and remaining gold; a sulfur removing step of removing sulfur in the leached residue; and a second leaching step of leaching at least a part of the remaining gold in the leached residue after the sulfur removing step, thereby obtaining a leached solution containing gold.

[0020] The gold leaching method according to this embodiment can be applied to a certain gold recovery method. Examples of such a gold recovery method include a method including subjecting raw materials containing gold and sulfur resulting from sulfide minerals and/or refining intermediates to a pretreatment step, a first leaching step, a sulfur removing step, a second leaching step, an adsorption step, a washing step, and an elution step in this order to obtain a concentrated gold solution. Detailed descriptions thereof will be as follow.

[0021] (Raw Materials Containing Gold and Sulfur) The sulfide minerals and the refining intermediates can be, for example, sulfide minerals containing gold and sulfur, such as sulfide minerals and silica minerals including one or more selected from chalcocite, bornite, covellite, chalcopyrite, pyrite, enargite, arsenopyrite, galena, sphalerite, arsenical pyrite, stibnite and pyrrhotite, or intermediates obtained by subjecting those sulfide minerals to a refining process (also referred to as "refining intermediates"). As used herein, the refining process refers to, for example, a process for leaching copper with a certain leaching solution for copper sulfide minerals, or a process for leaching iron with a certain leaching solution for pyrite. Leached residues obtained by such a process can be the refining intermediates.

[0022] The sulfide minerals and the refining intermediates may be optionally refined ores which has undergone a conventional ore dressing treatment such as ore flotation and gravity concentration of ores. Further, they may be those which have the particle size decreased by grinding and milling the ores such that the aqueous acidic solution in the gold leaching step is easily contacted with gold inside the ores and the like.

[0023] The above sulfide minerals and refining intermediates can be raw materials containing gold and sulfur to be leached in the present invention. More particularly, the raw materials containing gold and sulfur are, for example, the sulfide minerals themselves or the refining intermediates obtained by the predetermined refining treatment as described above. The concentration of gold in the raw materials thus obtained is typically from about 1 to 500 ppm by mass, and more typically from about 10 to 50 ppm by mass.

[0024] (Pretreatment Step) When a calcination step is carried out as a pretreatment step, in this calcination step, the raw materials containing gold and sulfur are heated in a reducing atmosphere such as ammonia, carbon monoxide and hydrogen sulfide, a rare gas atmosphere such as argon and helium, an inert atmosphere such as a nitrogen atmosphere and a carbon dioxide atmosphere, or other non-oxidizing atmosphere at a temperature of from about 450 °C

to 800 °C for about 30 to 120 minutes to thermally decompose pyrite in the raw materials into iron (II) sulfide and elemental sulfur. The chemical reaction at this time is represented by FeS 2 - FeS + S. The non-oxidizing atmosphere may contain oxygen to such an extent that substantially no adverse effect is produced even if sulfur oxide is generated. For example, it is acceptable if a molar ratio of the oxygen fed to the raw materials is oxygen: pyrite = 1/5 or less, and preferably 1/10 or less. Here, various furnaces such as a tubular furnace and a rotary kiln furnace can be used. The pretreatment step is an optional step and can be omitted.

[0025] (First Leaching Step) In the first leaching step, the above raw materials as it is without the pretreatment step or after the pretreatment step are brought into contact with a certain acidic aqueous solution while feeding an oxidizing agent to leach iron and gold. Here, it is preferable to use an acidic aqueous solution containing a copper ion, an iron ion and a halide ion such as a chloride ion and a bromide ion. The iron (II) sulfide converted from iron disulfide in the above calcination step can be leached and removed by the reaction of FeS - Fe + S. This can allow gold covered with the sulfide in the raw materials to be exposed and the gold to be leached.

[0026] When the predetermined sulfide minerals are targeted, due to exposed gold covered with sulfide in the raw materials, in the first leaching step, a leaching rate of gold of 99.9% should be theoretically obtained except for gold covered with gangue components such as SiO 2 in the raw materials. According to the results of the analysis of the gold form present in the raw materials, the remaining 0.1% corresponds to the gold covered by the gangue components, and it is difficult to leach the gold. However, it is found that an actual leaching rate of gold is 94%, indicating that nearly 6% of gold is not leached. As a result of intensive studies, the present inventors have found reasons why gold that otherwise could be leached remains in the leached residue, as follows. That is, when a sulfide (such as iron sulfide) that inhibits gold leaching is leached in the first leaching step, the metal component of the sulfide is dissolved, but the sulfur component generally remains as elemental sulfur (simple sulfur) or the like in the leached residue. Most of the sulfur such as elemental sulfur is present on the gold particles so as to surround them, and inhibits the leaching of gold due to a slower rate dissolved in the acid. Therefore, the present inventors have considered that the remaining gold can be effectively leached by a sulfur removing step of removing sulfur in the leached residue after the first leaching step, and a second leaching step of leaching at least a part of the remaining gold in the leached residue after the sulfur removing step. Details of the sulfur removing step and the second leaching step will be described later.

[0027] The leaching of gold in the first leaching step proceeds by reacting the leached gold with the chloride ion or bromide ion to generate a complex of gold with chloride or a complex of gold with bromide. In particular, by using the bromide ion, the complex is formed in a lower potential state, so that the leaching efficiency of gold can be improved. Further, for the iron ion, a trivalent iron ion oxidized under the feeding of the oxidizing agent or an initial trivalent iron serves to oxidize gold. The acidic aqueous solution preferably contains a copper ion. This is because the copper ion does not directly participate in the reaction, but the presence of the copper ion increases an oxidation rate of the iron ion.

[0028] The halide ion in the acidic aqueous solution can be only the bromide ion. Alternatively, the chloride ion may be further contained in addition to the bromide ion. In this case, a lower chloride ion concentration is preferable. The concentration of the bromide ion in the aqueous acid solution may be preferably 50 g/L or more, and more preferably 80 g/L or more, and particularly 150 g/L or more, in terms of further improving the leaching rate of gold. Although there is no particularly preferred upper limit of the bromide ion concentration, but it may be preferably less than or equal to the solubility of a metal bromide to be added. On the other hand, the concentration of the chloride ion may be preferably 40 g/L or less, and more preferably 25 g/L or less. Furthermore, it is still more preferable that the halide ion in the aqueous acidic solution is only the bromide ion, so that no chloride ion is present in the aqueous acidic solution.

[0029] The concentration of the iron ion in the aqueous acidic solution may be 50 g/L or less, and preferably from 0.01 g/L to 10 g/L. Furthermore, the concentration of the copper ion may be preferably 1 g/L or more, and more preferably 5 g/L or more, but from the economical viewpoint, any excessively high concentration is not required and the concentration of the copper ion in the aqueous acidic solution may be generally 30 g/L or less, and preferably 20 g/L or less. In addition, each concentration of the bromide ion, chloride ion, copper ion and iron ion means the concentration in the aqueous acidic solution before bringing the aqueous acidic solution into contact with the raw material.

[0030] The supply sources of the bromide ion include, but not limited to, hydrogen bromide, hydrobromic acid, metal bromides, a bromine gas and the like, and the bromide ion is preferably supplied in the form of metal bromide in terms of economy and safety. Examples of the metal bromides include bromides such as copper bromides (copper (1) bromide, copper (II) bromide), iron bromides (iron (1) bromide, iron (II) bromide), bromides of alkali metals (lithium, sodium, potassium, rubidium, cesium, francium), bromides of alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, radium), and sodium bromide is preferable in terms of economy and availability. In addition, the copper bromide and the iron bromide are preferably used because they can also be used as the supply sources for the copper ion and the iron ion.

[0031] If the chloride ion is contained, the supply sources include, but not limited to, for example, hydrogen chloride, hydrochloric acid, metal chlorides, a chlorine gas and the like, and they are preferably supplied in the form of metal chloride in view of economy and safety. Examples of the metal chlorides include copper chlorides (copper (1) chloride, copper (II) chloride), iron chlorides (iron (1) chloride, iron (II) chloride), chlorides of alkali metals (lithium, sodium, potassium, rubidium, cesium, francium), and chlorides of alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, radium), and sodium chloride is preferred in terms of economy and availability. Moreover, it is also possible to use the copper chloride and the iron chloride because they can also be utilized as sources for the copper ion and the iron ion.

[0032] The copper ion and the iron ion are usually supplied in the form of their salts, for example they can be supplied in the form of halide salts. The copper ion is preferably supplied as copper bromide and/or copper chloride, and the iron ion is preferably supplied as iron bromide and/or iron chloride, because these can be also used as sources for the chloride ion and/or the bromide ion. Examples of the copper chlorides and the iron chlorides that can be used include copper (II)chloride (CuCl2), copper (1) chloride (CuCI), iron (II) chloride (FeCl 3 ), iron (1) chloride (FeCl 2) and the like. Examples of the copper bromides and the iron bromides that can be used include copper (II)bromide (CuBr 2), copper (1) bromide (CuBr), iron (II) bromide (FeBr 3), iron (1) bromide (FeBr 2) and the like.

[0033] For example, the aqueous acidic solution may be a mixed solution which contains at least one of hydrochloric acid and bromic acid, and at least one of copper (II)bromide and copper (II) chloride, and at least one of iron (II) bromide and iron (II) chloride, and at least one of sodium chloride and sodium bromide.

[0034] The method of bringing the aqueous acidic solution into contact with the raw materials is not limited, and includes methods such as spraying and immersing, but a method of immersing the raw materials in the aqueous acidic solution and then stirring them is preferred in terms of efficiency of the reaction.

[0035] A redox potential (vs. Ag/AgCI) of the acidic aqueous solution at the start of the first leaching step is preferably 500 mV or more, and more preferably 600 mV or more, in terms of promoting the gold leaching. Further, a pH of the acidic aqueous solution is preferably maintained at 2.0 or less in terms of enhancing the leaching rate of gold, but the pH of the acidic aqueous solution is more preferably maintained at 0.5 to 1.9 because a higher pH will further facilitate the oxidation rate of iron.

[0036] The first leaching step is carried out while feeding an oxidizing agent to manage the redox potential. If the oxidizing agent is not added, the redox potential will decreases in the middle of the step and the leaching reaction will not proceed. The oxidizing agent includes, but not limited to, for example oxygen, air, chlorine, bromine, hydrogen peroxide and the like. No oxidizing agent with extremely high redox potential is needed, and air is sufficient.

[0037] In addition, a higher pulp concentration of the acidic aqueous solution containing the raw materials is preferable because the leaching of copper can be suppressed. However, if it is too high, a leaching speed of gold will be reduced. From this viewpoint, the pulp concentration is preferably 200 g/L or less, and more preferably from 15 g/L to 50 g/L. The pulp concentration means a ratio of dry weight (g) of the raw materials to a volume (L) of the acidic aqueous solution.

[0038] Although the redox potential is not particularly adjusted during the leaching of gold, the redox potential (ORP) of the gold leaching solution after sufficiently performing the gold leaching may be generally from approximately 450 to 600 mV, and typically from approximately 500 to 580 mV.

[0039] An increase in ORP indicates a decrease in a monovalent copper ion in the gold leached solution. The monovalent copper is known as a very soft element, and has high affinity to the activated carbon and competes with the adsorption of the gold complex. By such a decrease in the monovalent copper, the adsorption active sites in the activated carbon increase the selectivity for gold, so that efficient recovery of gold can be achieved.

[0040] Such a first leaching step can be terminated when the leaching rate of iron from the raw materials reaches, for example, 5% or more, preferably 15% or more, and more preferably 30% or more, depending on the type of ores. Further, the first leaching step can be terminated when the leaching rate of iron from the raw materials reaches the above rate and the leaching rate of copper from the raw materials reaches, for example, 5% or more, preferably 15% or more. At this time, the leaching rate of gold from the raw materials is preferably 85% or more, and more preferably 90% or less, and particularly preferably 95% or less.

[0041] It should be noted that in addition to the leaching conditions as described above, leaching can also be carried out under the conditions as described in Japanese Patent Application Publication No.2005-523992A. That is, under the conditions, gold in the raw materials is dissolved by leaching gold while feeding an oxygen-containing gas under atmospheric pressure conditions using an aqueous copper (II)chloride-sodium chloride solution. Here, the redox potential can be less than 650 mV, and preferably from 530 mV to 620 mV, and the pH can be maintained in the range of from 1 to 3. In the leaching under these conditions, most of the iron component and sulfur component in the raw materials are not dissolved, but a certain amount of the sulfur component is converted into elemental sulfur to remain in the leached residue, which may inhibit the leaching of gold as described above. Therefore, even if the leaching is carried out under those conditions, it is effective to carried out the sulfur removing step and the second leaching step as described below, in terms of further improvement of the recovery rate of gold.

[0042] (Sulfur Removing Step) The leached residue obtained in the first leaching step is subjected to a sulfur removing step for removing sulfur contained in the leached residue. The sulfur removing step is carried out as a separate step from the leaching in the first leaching step. This exposes the gold covered with sulfur such as elemental sulfur in the leached residue, such that it will be able to be effectively leached in the second leaching step as described later. The sulfur removing step can include heating the leached residue in a certain atmosphere to remove sulfur in the leached residue as a gas, or washing the leached residue with an alkaline solution to dissolve and remove the sulfur.

[0043] For the sulfur removal by heating, the leached residue can be heated and maintained at, for example, a temperature of 450 °C or higher, which is a boiling point of sulfur, to remove sulfur in the leached residue as a gas. If the maintaining temperature during heating is too high, an energy required for heating increases. Therefore, the temperature can be 1000 °C or lower in terms of suppressing an increase in processing cost. More preferably, the maintaining temperature of the leached residue is from 500°Cto700°C. A time for maintaining the temperature is preferably from 30 minutes to 180 minutes, and more preferably from 30 minutes to 60 minutes. An atmosphere during the heating may be an inert atmosphere including a rare gas atmosphere such as argon or helium, a nitrogen atmosphere, a carbon dioxide atmosphere, or the like. In this case, sulfur is removed as a sulfur gas. Alternatively, an oxidizing atmosphere such as an air can be used. In this case, the gas is removed as SO 2 gas. Various furnaces such as a tubular furnace and a rotary kiln furnace can be used for the heating.

[0044] In the case of sulfur removal by washing with an alkaline solution, an alkaline solution having a pH of preferably from 10 to 14, and more preferably from 10 to 12, can be used. Specific examples of the alkaline solution include a sodium hydroxide solution, sodium oxide, sodium carbonate and the like. If the pH of the alkaline solution is too high, a large amount of alkali is required for raising the pH, as well as a large amount of acid is required during the next second leaching step or during a treatment of a washed solution having dissolved sulfur, which would increase costs. Further, gold may be dissolved in alkali in the form of a thiosulfate complex or the like. In this case, the gold can be recovered using activated carbon. However, if the pH is higher, a large amount of sodium will be contained, whereby adsorption of gold to and elution of gold from the activated carbon may be inhibited. On the other hand, if the pH is too low, the pH further decreases due to effects of sulfur dissolution and hydrolysis of components in the solution. In particular when the pH is 7 or less, a hydrogen sulfide gas may be generated although it depends on the redox potential The solution temperature during washing with the alkaline solution can be from 20 (room temperature) °C to 90 °C, and more preferably from 50 °C to 80 °C. If the solution temperature is too low, the sulfur dissolution rate may decrease, and if the solution temperature is too high, the heating cost may increase. The washing time can be, for example, from 60 minutes to 360 minutes, and preferably from 60 minutes to 180 minutes. If the washing time is too short, sulfur in the leached residue may not be sufficiently removed, while if the washing time is too long, the processing efficiency is reduced.

[0045] In the sulfur removal by heating, as described above, the heating is carried out in the non-oxidizing atmosphere to remove a sulfur gas, or the heating is carried out in the oxidizing atmosphere to remove a S02 gas. Here, when the heating is carried out in the non-oxidizing atmosphere, it is necessary for the temperature to be 450 °C or higher, as well as it is necessary for sulfur in the exhaust gas to be dissolved and recovered in an alkaline solution using a scrubber. In this case, an alkaline waste fluid having dissolved sulfur is generated. Since such an alkaline waste fluid is the same as the case where the leached residue is directly washed with the alkaline solution as described above. From this viewpoint, the washing with the alkaline solution is more preferable, because it does not require heating at elevated temperature and can be carried out at a lower temperature. On the other hand, when the heating is carried out in the oxidizing atmosphere, a sulfuric acid production plant must be securely installed, which cases a disadvantage that the equipment scale and cost increase. For these reasons, in the sulfur removing step, it is preferable to wash the leached residue with the alkaline solution to dissolve and remove the sulfur.

[0046] The sulfur removing step as described above can be carried out to remove sulfur from the leaching residue by preferably 10% or more, and more preferably 25% or more. In this case, the removal of sulfur even if it is in a miner amount can allow gold to be further leached in the second leaching step as described later, leading to improvement of the leaching rate of gold.

[0047] (Second Leaching Step) After removing sulfur in the leached residue through the sulfur removing step, a second leaching step for leaching gold in the leached residue is carried out to leach gold again. The second leaching step can be carried out under substantially the same conditions as those of the first leaching step as described above. However, here, the sulfur covering gold remaining in the leached residue after the first leaching step is removed to expose the gold, which can be effectively leached.

[0048] The components, pH, redox potential and other conditions of the acidic aqueous solution in the second leaching step are substantially the same as those in the first leaching step, and so descriptions thereof are not repeated. By the second leaching step, the leaching rate of gold from the leached residue can be preferably 10% or more, and more preferably 30% or more.

[0049] (Adsorption Step) After the leaching of gold, it can be recovered from the gold-leached solution obtained by solid-liquid separation using activated carbon adsorption. The contacting of gold with the activated carbon can be carried out in a batchwise manner or by continuously feeding an acidic leaching solution to an adsorption towerfilled with the activated carbon.

[0050] In the case of the batchwise manner, the stirring speed is not particularly limited, and the activated carbon is added such that the amount of the activated carbon added is from 50 to 10000 times the weight of gold. In the case of the manner of continuous feeding of the acid leaching solution, the rate of feeding the solution is not particularly limited (generally SV1 to 25). However, as an adsorption amount of gold per a unit weight of the activated carbon reaches 20000 to 30000 g/t, a decrease in adsorption capacity of the activated carbon may be observed. Therefore, the stripping of gold and regenerating of the activated carbon can be carried out on the basis of such an adsorption amount. The regenerating of the activated carbon can be carried out by various approaches such as sulfur compounds and nitrogen compounds that are generally known in the art, or acids.

[0051] (Washing Step) A washing step can be then carried out by washing the activated carbon having the gold adsorbed in the adsorption step with an acidic solution or an alkaline solution as a washingagent. In the washing with the alkaline solution such as NaOH, sulfur that may be adsorbed on the activated carbon can be effectively removed. In the washing with the acidic solution such as hydrochloric acid, copper or iron that may be adsorbed on the activated carbon can be effectively removed. One or both of the acid washing and the alkali washing may be carried out, or the washing step may not be carried out without performing both.

[0052] (Elution Step) Gold adsorbed on the activated carbon is eluted by an alkaline solution, preferably NaOH or a mixed solution of NaOH and Na 2S. Here, if the alkali concentration is low, elution of gold becomes difficult, and if the alkali concentration is high, there is a risk of heat generation during preparation. From this point of view, when using NaOH, its concentration may be preferably from 0.05 to 1 M, and more preferably from 0.1 to 0.5 M. Further, an amount of Na 2 S used is preferably as low as possible because of its cost and difficulty of handling of this substance, but a decreasing concentration of Na 2 S will decrease the effect of eluting gold. On the other hand, if the concentration of Na 2 S is too high, no further effect will be expected, and the processing load of Na 2 S will be further increased. From such a viewpoint, when using the mixed solution of NaOH and Na 2 S, the amount of Na 2S added is preferably 0.1 to 10 mol times the amount of NaOH, and more preferably 0.5 to 1.5 mol times.

[0053] In addition, the elution may be carried out in a batchwise manner or by continuously feeding the solution. However, when the elution is carried out in the batchwise manner, any vigorous stirring preferably should not be performed in order to avoid losing a charge due to oxidation of the sulfide with oxygen and re-adsorbing gold on the activated carbon or depositing gold onto a reactor. When stirring is necessary, air is replaced with a non oxidizing gas and stirred. Alternatively, an increased amount of sodium sulfide added is set, or sodium sulfide is timely added. Further, the elution is preferably carried out under atmospheric pressure.

[0054] A concentrated gold solution can be obtained by elution from the activated carbon. The concentrated gold solution refers to a solution containing from 50 to 5000 mg/L of gold. A method for producing gold by reduction from the concentrated gold solution includes a chemical reduction method by reduction with sodium oxalate or chemical reduction method with sulfur dioxide, or solvent extraction-electrolytic extraction method.

Elemental gold can be obtained by using both methods.

EXAMPLES

[0055] Next, the gold recovery method according to the present invention was experimentally conducted and its effects were confirmed as described below. However, the descriptions herein are only for the purpose of illustration and are not intended to be limited thereto.

[0056] (Gold Form in Raw Material and Gold Leaching Rate) The gold form present in the sulfide minerals mainly based on pyrite was confirmed by Diagnostic Leach Test, and results shown in Table 1 were obtained. When the sulfide is leached by carrying out the non-oxidizing calcination step and one leaching step, an assumed leaching rate of gold should be 99.9%, but in an actual test, the leaching rate of gold was only 94%, as shown by the graph in FIG. 2. Therefore, it is found that in the conventional leaching method, residual about 6%of gold is not leached although it should have been leached.

[0057]

[Table 1]

Percentage 1) Exposed Au 79.9 2) Au Covered with Sulfide 20.0 3) Au Covered with Si02 0.1

[0058] (Comparative Example) After subjecting the sulfide minerals to the non-oxidizing calcination step and the first leaching step, the resulting leached residue was subjected to the second leaching step without carrying out the sulfur removing step. Here, in the second leaching step, using an acidic aqueous solution having a composition of 18 g/L of Cu, 2 g/L of Fe, 40 g/L of Cl, and 80 g/L of Br and having a pH of 1, the leaching was carried out at a temperature of 85 °C for 6 hours. Table 2 shows quality of each leached residue before and after the second leaching step. The quality as shown in Table 2 is an amount of each element when the above leached residue used in the second leaching step is 100 g. In Table 2, "S-0" means elemental sulfur. Also, table 3 shows percentages of the sulfur removal rate and the gold leaching rate calculated from a change in an amount of each component before and after the second leaching step, respectively. The analysis of each component was performed by high frequency inductively coupled plasma emission spectroscopy (ICP-AES).

[0059]

[Table 2]

Cu Fe S-0 Au g g g mg Residue according to Conventional Method 0.48 0.98 71.00 5.80 Residue after Leaching without Washing 0.28 0.73 63.84 5.11

[0060]

[Table 3]

S Removal Rate 10.1 Au Leaching Rate 12.0

[0061] As can be seen from Table 3, the leaching rate of gold in the second leaching step was 12%, which was lower. This would be because the sulfur removal rate was only 10% and the dissolution rate of sulfur which inhibited the leaching of gold was slower, so that gold was in a state of being covered with sulfur.

[0062] (Example) The quality of each leached residue before the sulfur removing step and after the second leaching step, as well as the removal rate of sulfur and the leaching rate of gold were measured and calculated in the same manners as those of Comparative Example, with the exception that before the second leaching step, the sulfur removing step was carried out by washing with an alkaline solution. Results are shown in Tables 4 and 5. Here, the washing in the sulfur removing step was carried out using a NaOH solution as an alkaline solution for a washing time of 3 hours, and at a temperature during washing was 60 °C.

[0063]

[Table 4]

Cu Fe S-0 Au g g 9 mg Residue before Washing 0.31 0.80 70.00 5.60 Residue after Washing + Releaching 0.16 0.63 15.89 0.58

[0064]

[Table 5]

S Removal Rate 77.3 Au Leaching Rate 89.7

[0065] As can be seen from Table 5, about 77% of sulfur was removed by the sulfur removing step, whereby the leaching rate of gold in the second leaching step was about 90%.

[0066] FIG. 3 shows a graph plotting a relationship between the gold recovery rate (gold leaching rate) and the sulfur removal rate for Comparative Example and Example as described above. As can be seen from FIG. 3, the relationship between the gold recovery rate and the sulfur removal rate is linear with a slope of approximately 1 and an intercept of 0. Therefore, the removal of sulfur even if it is in a minor amount can increase the recovery rate of gold, and the recovery rate of gold can increase by an amount of removed sulfur.

[0067] In view of the foregoing, it was found that according to the present invention, by removing sulfur, gold that has inhibited the leaching by the sulfur can be effectively leached.

Claims

What is claimed is:

1. A method for leaching gold contained in raw materials containing gold and sulfur, as sulfide minerals or refining intermediates obtained by subjecting the sulfide minerals to a refining treatment, the method comprising: a first leaching step of leaching a part of gold in the raw materials to obtain a leached residue containing sulfur and remaining gold; a sulfur removing step of removing sulfur in the leached residue; and a second leaching step of leaching at least a part of the remaining gold in the leached residue after the sulfur removing step, wherein an acidic aqueous solution containing a copper ion, an iron ion, and a halide ion is used in the first leaching step and the halide ion in the acidic aqueous solution is only a bromide ion, and wherein in the sulfur removing step, the sulfur in the leached residue is removed by bringing the leached residue into contact with an alkaline solution and the alkaline solution to be brought into contact with the leached residue in the sulfur removing step has pH or 10 or more.

2. The method according to claim 1, wherein the gold in the leached residue is exposed by removing the sulfur in the leached residue in the sulfur removing step.

3. The method according to claim 1 or 2, wherein the leached residue containing sulfur, at least a part of the sulfur being in the form of elemental sulfur, is obtained in the first leaching step.

4. The method according to any one of claims 1 to 3, wherein in the sulfur removing step, the leached residue is heated to remove the sulfur in the leached residue as a gas.

5. The method according to any one of claims 1 to 4, wherein a sulfur removal rate in the sulfur removing step is 10% or more.

6. The method according to claim 5, wherein the sulfur removal rate in the sulfur removing step is 25% or more.

7. The method according to any one of claims 1 to 6, wherein in the first leaching step, the raw materials are brought into contact with an acidic aqueous solution containing a copper ion, an iron ion and a halide ion while feeding an oxidizing agent.

8. A method for recovering gold from raw materials using the method according to any one of claims 1 to 7.

FIG.1 1/3 2018340945 08 Jun 2018