JPWO2014038236A1 - Method for leaching gold from gold ore containing pyrite - Google Patents

Abstract

Gold leaching method from gold ore containing pyrite without toxic chemicals such as cyan, thiourea, thiosulfuric acid and halogen gas, and further suppressing the generation of sulfur dioxide while leaching gold To improve. Step 1 for preparing a gold ore containing pyrite, and heating the gold ore to 450 ° C. or higher in a non-oxidizing atmosphere to thermally decompose the pyrite in the gold ore into iron (II) sulfide and elemental sulfur. A pretreatment including step 2 and not including an oxidation roasting step and a gold ore after the pretreatment step are brought into contact with a gold leachate containing chloride ions, bromide ions, and iron ions under supply of an oxidizing agent. And a step 3 of leaching a gold component in the ore.

Description

  The present invention relates to a method for leaching gold from gold ore containing pyrite.

  A technique using a wet method is known as a method for recovering gold from a sulfide mineral containing gold. Traditionally, leaching of gold in sulfide minerals into solutions has been performed by using chemicals such as cyanide, thiourea, thiosulfuric acid, and halogen gas. Recently, as a less toxic leachant, chloride ions, iron ions, as described in JP-A-2008-106347 (Patent Document 1) and JP-A-2009-235525 (Patent Document 2), It has also been proposed to use a gold leaching solution utilizing copper ions and bromide ions.

  Further, as a pretreatment for facilitating leaching of gold from sulfide minerals, a method of oxidizing and roasting sulfide minerals is known, and in recent years, a pretreatment combining oxidation roasting with other processes has also been proposed. . For example, in Japanese Patent Application Laid-Open No. 2010-235999 (Patent Document 3), copper sulfide mineral is leached at a temperature below the melting point of sulfur, and sulfur obtained as fine particles from the obtained leaching residue and remains without leaching. Sulfide particles are levitated by utilizing the difference in hydrophobicity from other iron oxides and gangue components, while iron oxide and gangue components are settled or separated as sedimentation to separate them in the leach residue. Concentrate the gold contained in the. After that, the concentrated gold-containing component is oxidized and roasted after removing sulfur to convert the iron component to iron oxide (hematite), and then dissolved using sulfuric acid to recover the gold-enriched residue. Is done.

  Or, for pyrite only, it is known that when heated to 550 ° C or higher in a non-oxidizing atmosphere, it decomposes into acid-soluble pyrrhotite and sulfur, and this reaction is used to leach copper sulfide ore containing pyrite. JP 2005-042155 A (Patent Document 4) proposes a method of removing pyrite from the residue, increasing the content ratio of the noble metal contained therein, and concentrating it.

JP 2008-106347 A JP 2009-235525 A JP 2010-235999 A JP 2005-042155 A

  In the method described in JP2009-235525A (Patent Document 2), gold can be easily leached without using chemicals such as highly toxic cyanide, thiourea, thiosulfuric acid, and halogen gas. Although it is very practical for gold leaching, the gold leaching rate is insufficient when it is applied to pyrite.

Therefore, sulfur is removed in advance by performing pretreatment using oxidation roasting performed by supplying oxygen as described in JP 2010-235999 A (Patent Document 3) to facilitate iron leaching. A method is also conceivable.

However, if the method of oxidizing and roasting sulfide minerals including the method described in Patent Document 3 is adopted, 2CuS + 2O ₂ → 2CuO + SO ₂ , 2CuFeS ₂ + 6O ₂ → CuO + 4SO ₂ + Fe ₂ O ₃ , and 4FeS ₂ + 11O ₂ → 2Fe _Since a chemical reaction such as ₂ O ₃ + 8SO ₂ occurs preferentially, the problem that sulfur dioxide (SO ₂ ) known as an environmental pollutant is generated is inevitable.

  Patent Document 4 is a process based on the premise that the noble metal is recovered by a dry process in view of the problem in the method of recovering the noble metal by a wet method, and it is assumed that the noble metal is leached by a wet process. (See paragraphs 0007 to 0008, 0078, etc. of Patent Document 4). In addition, there is no suggestion of what effect can be obtained by wet processing.

  In any case, the method of pretreating pyrite by thermal reaction can produce iron soluble in acid by removing sulfur, but harmful gas is generated during thermal reaction or dissolution of iron. In addition, pyrite is leached and removed, which contributes to the improvement of the gold quality of the raw material, but it is necessary to smelt gold separately.

  The present invention has been made in view of the above circumstances, and in the method of leaching gold from gold ore containing pyrite, without using chemicals such as highly toxic cyanide, thiourea, thiosulfuric acid, halogen gas, and the like. An object of the present invention is to provide an efficient gold leaching method by improving the gold leaching rate while suppressing the generation of sulfur dioxide.

  The present inventor has intensively studied to solve the above problems, and after performing a pretreatment of pyrite pyrolyzing into iron (II) sulfide in a non-oxidizing atmosphere, halide ions and trivalent iron are performed. It has been found that when gold leaching is performed using a gold leaching solution containing ions, the gold leaching rate is dramatically improved while suppressing the generation of sulfur oxide.

The present invention has been completed on the basis of the above knowledge, and in one aspect, Step 1 for preparing gold ore containing pyrite, and heating the gold ore to 450 ° C. or higher in a non-oxidizing atmosphere, Including a step 2 of thermally decomposing pyrite in gold ore into iron (II) sulfide and elemental sulfur, and a pretreatment not including an oxidation roasting step;
Contacting the gold ore after the pretreatment step with a gold leaching solution containing halide ions and iron ions under supply of an oxidizing agent, and leaching the gold component in the ore; and
This is a gold leaching method.

  In one embodiment of the gold leaching method according to the present invention, the gold leaching solution contains chloride ions and bromide ions.

  In another embodiment of the gold leaching method according to the present invention, the gold leaching in step 3 is performed under the condition that the oxidation-reduction potential (reference electrode is silver / silver chloride) is maintained at 550 mV or more.

  In still another embodiment of the gold leaching method according to the present invention, the thermal decomposition in step 2 is performed under the condition that the gold ore is held at 600 to 750 ° C. for 5 to 60 minutes.

  In still another embodiment of the gold leaching method according to the present invention, the content of pyrite in the gold ore is 5 to 80% by mass.

  In yet another embodiment of the gold leaching method according to the present invention, the gaseous elemental sulfur generated in step 2 is removed from the gold ore by solid-gas separation.

  In yet another embodiment of the gold leaching method according to the present invention, the iron (II) sulfide and elemental sulfur generated in step 2 are cooled and recovered together in solid form and brought into contact with the gold leaching solution together. To carry out the gold leaching process.

  In yet another embodiment of the gold leaching method according to the present invention, the gold leaching step is carried out while maintaining the pH of the gold leaching solution at 1.9 or lower.

  Gold ore containing pyrite is drastically improved while suppressing the generation of harmful sulfur oxides by performing gold leaching using a specific gold leaching solution after performing the pretreatment method according to the present invention. Gold leaching rate can be obtained. That is, according to the present invention, it is possible to provide an extremely practical gold leaching method that is excellent in safety and environmental conservation.

It is a graph which shows the relationship between leaching time and Au quality in a residue about an Example and a comparative example. It is a TG / DTA curve when the pyrite concentrate after the milling used in Example 1 is subjected to thermal analysis in a nitrogen atmosphere.

  The present invention will be described in detail below.

1. Pretreatment step In one embodiment of the pretreatment method for gold ore according to the present invention, step 1 for preparing gold ore containing pyrite, and heating the gold ore to 450 ° C or higher in a non-oxidizing atmosphere, Including the step 2 of thermally decomposing pyrite in the gold ore into iron sulfide (II) and elemental sulfur, and not including the oxidation roasting step.

(1) Step 1
In step 1, gold ore containing pyrite is prepared. This is because the purpose of the present invention is to increase the gold leaching rate in pyrite, which is hardly soluble and has a low gold leaching rate. However, other requirements such as the concentration of gold in the ore are not important. The gold ore to be treated in the present invention may be subjected to a conventional beneficiation process such as flotation or specific gravity sorting. Grinding can reduce the particle size of the ore so that the gold leachate can easily come into contact with the gold inside the ore. The gold concentration in the gold ore is typically about 0.1 to 100 ppm by mass, and more typically about 1 to 20 ppm by mass.

  In addition to containing pyrite, the gold ore may contain chalcopyrite, galena, sphalerite, arsenite, kyanite, pyrrhotite, etc., but in an exemplary embodiment of the present invention pyrite Is used, and in a more typical embodiment of the present invention, a gold ore containing 30% by mass or more of pyrite is used. By using such gold ore, the effect of the pretreatment according to the present invention is remarkably exhibited. The content of pyrite in the gold ore is not particularly limited, and may be 100% by mass, but typically 80% by mass or less.

  Moreover, in this invention, it is one of the characteristics that an oxidation roasting process is not included. In the prior art, oxidation roasting was performed in the presence of oxygen or air, so sulfur in the sulfide mineral was combined with oxygen to produce sulfur oxide. In the present invention, such an oxidation roasting step is not performed.

(2) Step 2
In step 2, the gold ore is heated to 450 ° C. or higher in a non-oxidizing atmosphere, and pyrite in the gold ore is thermally decomposed into iron sulfide (II) and elemental sulfur. The chemical reaction at this time is represented by the following formula: FeS ₂ → FeS + S. Theoretically, there is no generation of sulfur oxide, but it is actually difficult to completely block oxygen. Further, in actual operation, sulfuric acid production equipment for treating the sulfur oxide is not necessary as long as it does not cause a substantial adverse effect even if sulfur oxide is generated, and may be called a non-oxidizing atmosphere. Therefore, in the present invention, it is allowed that oxygen in such a degree that it is inevitably mixed in the non-oxidizing atmosphere is present in the reaction system. For example, when the molar ratio of the oxygen supply amount to pyrite is oxygen: pyrite = 1: 5 or less, it is acceptable, and more preferably 1:10 or less. The gold ore after undergoing the thermal decomposition has a marked improvement in solubility in the gold leachate described below. Compared to the case without thermal decomposition, the gold leaching rate can be increased by about 10 times. Since the pyrolysis method performed in the present invention did not change pyrite (FeS ₂ ) to hematite (Fe ₂ O ₃ ), the gold leaching rate seemed to be insufficient, and thus such a result was obtained. That was extremely surprising.

  Non-oxidizing atmospheres when carrying out thermal decomposition include inert atmospheres such as ammonia, carbon monoxide, hydrogen sulfide, rare gas atmospheres such as argon and helium, nitrogen atmospheres and carbon dioxide atmospheres. Although an atmosphere is mentioned, an inert atmosphere is preferable from the viewpoint of preventing an unexpected reaction. Or you may circulate and use the exhaust gas used for thermal decomposition. If oxygen is contained in the atmosphere, the gold ore is oxidized and roasted to generate sulfur dioxide, which is not adopted in the present invention because there is a concern about the influence on the environment.

  It is necessary to keep the temperature of the gold ore at 450 ° C. or higher during pyrolysis. This is because the pyrolysis of pyrite hardly proceeds at less than 450 ° C. Preferably, the thermal decomposition is preferably carried out while maintaining the temperature of the gold ore at 550 ° C. or higher, more preferably at 650 ° C. or higher. The thermal decomposition is preferably continued for 5 minutes or more, and more preferably for 30 minutes or more. This is because the thermal decomposition reaction proceeds sufficiently. However, if the temperature of the gold ore is excessively increased, the energy required for the temperature increase and the treatment time may be increased. Therefore, the holding temperature is preferably 800 ° C. or less, and more preferably 750 ° C. or less. Similarly, the time for maintaining the holding temperature is also preferably 120 minutes or less, and more preferably 60 minutes or less.

  Although there is no restriction | limiting in particular in the kind of heating furnace for implementing pyrolysis, For example, a tubular furnace and a rotary kiln can be used.

  Since elemental sulfur generated by pyrolysis is gasified in a high-temperature furnace, it can be separated from gold ore by solid-gas separation. Then, it can be sent to the exhaust system together with the atmospheric gas. However, when single sulfur is sent to the exhaust system, sulfur is deposited with a decrease in temperature to cause problems such as blockage of the gas passage. Therefore, it is desirable to recover with a wet scrubber or the like. Alternatively, the gasified elemental sulfur can be cooled together with the iron (II) sulfide generated in step 2 and recovered together in a solid state and sent together to the gold leaching step. In the gold leaching process, elemental sulfur is separated as a leaching residue without hindering gold leaching. In this case, a wet scrubber is unnecessary, which is economically advantageous.

2. Gold leaching step In one embodiment of the gold leaching method according to the present invention, the gold ore after the pretreatment step is brought into contact with a gold leaching solution containing halide ions and iron ions under supply of an oxidizing agent, and the ore Step 3 of leaching the gold component therein is performed.

  Gold leaching proceeds as the eluted gold reacts with halide ions to form a gold halogen complex.

  The halide ion in the gold leachate may be chloride ion alone, but preferably contains bromide ion in addition to chloride ion. By using bromide ions in combination, a complex is formed at a lower potential, so that the gold leaching efficiency can be improved.

In addition, the dissolution of iron sulfide produced by the pretreatment proceeds simultaneously with the gold leaching. Therefore, in the original ore, gold contained in pyrite also comes into contact with the leachate and dissolves. Iron ion is a trivalent iron ion oxidized under the supply of an oxidant or a trivalent iron ion from the beginning to oxidize gold and to immediately oxidize hydrogen sulfide produced by reaction with acid to sulfur. do. Fe ²⁺ generated when iron sulfide is dissolved is also oxidized to Fe ³⁺ under the supply of an oxidizing agent.

The gold leachate preferably contains copper ions. This is because copper ions are not directly involved in the reaction, but the presence of copper ions increases the oxidation rate of iron ions.

  The method for contacting the leachate with the gold ore is not particularly limited, and there are methods such as spreading and dipping. From the viewpoint of reaction efficiency, a method of dipping the residue in the leachate and stirring is preferred.

  The supply source of chloride ions is not particularly limited, and examples thereof include hydrogen chloride, hydrochloric acid, metal chloride, and chlorine gas. In consideration of economy and safety, supply in the form of metal chloride is preferable. . Examples of the metal chloride include copper chloride (cuprous chloride, cupric chloride), iron chloride (ferrous chloride, ferric chloride), and alkali metals (lithium, sodium, potassium, rubidium, cesium, francium). Chlorides and chlorides of alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, radium) can be mentioned, and sodium chloride is preferable from the viewpoint of economy and availability. Moreover, since it can utilize also as a supply source of copper ion and iron ion, it is also preferable to utilize copper chloride and iron chloride.

  The source of bromide ions is not particularly limited, but examples include hydrogen bromide, hydrobromic acid, metal bromide and bromine gas. In consideration of economy and safety, the form of metal bromide is used. It is preferable to supply. Examples of the metal bromide include copper bromide (cuprous bromide, cupric bromide), iron bromide (ferrous bromide, ferric bromide), alkali metals (lithium, sodium, potassium, Examples thereof include bromides of rubidium, cesium, and francium) and bromides of alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, and radium), and sodium bromide is preferable from the viewpoint of economy and availability. Moreover, since it can utilize also as a supply source of copper ion and iron ion, it is also preferable to utilize copper bromide and iron bromide.

Copper ions and iron ions are usually supplied in the form of these salts. For example, they can be supplied in the form of halide salts. From the viewpoint that it can also be used as a source of chloride ions and / or bromide ions, copper ions are preferably supplied as copper chloride and / or copper bromide, and iron ions are preferably supplied as iron chloride and / or iron bromide. As copper chloride and iron chloride, it is preferable to use cupric chloride (CuCl ₂ ) and ferric chloride (FeCl ₃ ) from the viewpoint of oxidizing power, respectively, but cuprous chloride (CuCl) and ferric chloride are preferable. Even if (FeCl ₂ ) is used, supplying an oxidizing agent to the leachate will oxidize to cupric chloride (CuCl ₂ ) and ferric chloride (FeCl ₃ ), respectively, so there is no significant difference.

  The concentration of chloride ions in the gold leachate used in step 3 is more preferably 30 g / L to 180 g / L. The concentration of bromide ions in the gold leachate used in step 3 is preferably 1 g / L to 100 g / L from the viewpoint of reaction rate and solubility, and 10 g / L to 40 g / L from the viewpoint of economy. More preferably. The total concentration of chloride ions and bromide ions in the gold leaching solution is preferably 80 g / L to 200 g / L.

  The oxidation-reduction potential (vs Ag / AgCl) of the leaching solution at the start of step 3 is preferably 550 mV or more, more preferably 600 mV or more from the viewpoint of promoting gold leaching.

Further, from the viewpoint of increasing the gold leaching rate, it is preferable to maintain the pH of the gold leaching solution at 2.0 or less. However, the higher the oxidation rate of iron, the higher the pH of the gold leaching solution. More preferably, it is maintained at 5 to 1.9. The temperature of the gold leachate is preferably 45 ° C. or higher from the viewpoint of increasing the gold leach rate, and more preferably 60 ° C. or higher. However, if it is too high, the leachate will evaporate and the heating cost will increase. It is preferable to set it as follows, and it is more preferable to set it as 85 degrees C or less.

  Accordingly, in a preferred embodiment of the present invention, at least one of hydrochloric acid and bromic acid, and chloride chloride are selected on the condition that the gold leachate in step 3 is selected to contain both chloride ions and bromide ions. A mixed liquid containing at least one of dicopper and cupric bromide, at least one of ferric chloride and ferric bromide, and at least one of sodium chloride and sodium bromide can be used.

  The gold leaching step of step 3 is performed while supplying an oxidizing agent, thereby managing the oxidation-reduction potential. If an oxidizing agent is not added, the redox potential is lowered in the middle, and the leaching reaction does not proceed. Although there is no restriction | limiting in particular as an oxidizing agent, For example, oxygen, air, chlorine, a bromine, hydrogen peroxide, etc. are mentioned. An oxidant with an extremely high redox potential is not necessary and air is sufficient. Air is also preferable from the viewpoint of economy and safety.

After carrying out the pretreatment and before carrying out the gold leaching step 3, various treatments for removing impurities in the gold ore can also be carried out. For example, elemental sulfur can separate gold and elemental sulfur by heating the gold ore after pretreatment to a temperature sufficient for elemental sulfur to melt and separating it. Iron sulfide (FeS) is made by contacting pre-treated gold ore with various mineral acids such as sulfuric acid and hydrochloric acid, as well as with aqueous solutions of Fe ³⁺ salts such as iron sulfate and iron chloride. It can be removed by liquid separation.

  After the gold leaching reaction, gold can be recovered from the gold solution obtained by solid-liquid separation. Although there is no restriction | limiting in particular as a collection | recovery method of gold | metal | money, Activated carbon adsorption | suction, electrowinning, solvent extraction, reduction | restoration, cementation, ion exchange, etc. can be utilized. The S component exists in the form of sulfate, sulfide and elemental sulfur in the solution after leaching, but these can be separated from gold by solvent extraction.

It is also an effective technique to increase the gold leaching rate by reducing the gold concentration in the leaching reaction solution by collecting gold during the leaching reaction. This can be done, for example, by introducing activated carbon or activated carbon and lead nitrate into the gold leaching solution during the leaching reaction.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these. In addition, the analysis method of the metal used in the Example was performed by ICP-AES. However, in the analysis of gold, gold in the sample was deposited by the ash blowing method, and then quantitative analysis was performed by ICP-AES.

<Comparative Example 1>
Pyrite concentrate (Papua New Guinea domestic) was prepared. It was 17 mass% when content of the pyrite in this pyrite concentrate was calculated by XRD and chemical analysis. The pyrite concentrate was pulverized and ground with a ball mill, and the particle size (d80) at which the cumulative weight was 80% in the cumulative weight particle size distribution curve was adjusted to 24 μm. d80 is an average value when measured three times with a laser diffraction particle size distribution measuring apparatus (model SALD2100 manufactured by Shimadzu Corporation). Next, the pyrite concentrate (200 g) after milling was subjected to a leaching treatment for 90 hours at a liquid temperature of 85 ° C. with a pulp concentration of 100 g / L using a hydrochloric acid acidic gold leachate having the composition shown in Table 1. It was. During the leaching treatment, air blowing (0.1 L / min with respect to 1 L of concentrate) and stirring were continued, and the oxidation-reduction potential (ORP: vs Ag / AgCl) was maintained at 530 mV or higher. During the leaching, hydrochloric acid was appropriately added so that the pH of the gold leaching solution was maintained at 1.0 to 1.1.

During the leaching test, samples of the leaching residue were taken periodically, and the Au quality in the residue was measured. FIG. 1 shows the relationship between the leaching time and the Au quality in the residue obtained from the results of the test (see the plot “FeS ₂ no thermal decomposition” in FIG. 1). From this result, it can be seen that it takes 90 hours for the Au quality in the residue, which was initially about 6 g / t, to be reduced to 0.9 g / t.

<Example 1>
The same pyrite concentrate (1.5 kg) after milling as in Comparative Example 1 was charged into a tubular furnace and heated to 700 ° C. (temperature increase rate = 10 ° C./min) over 1 hour in a nitrogen atmosphere. Heated for 1 hour. After cooling to room temperature, the XRD analysis before and after the heat treatment confirmed that the FeS ₂ peak contained in the original ore disappeared and the FeS peak was generated. The elemental sulfur produced by the heat treatment was not particularly removed.
Subsequently, the pyrite concentrate after the heat treatment was subjected to a leaching treatment for 18 hours at a liquid temperature of 85 ° C. using a hydrochloric acid acidic gold leaching solution having the same composition as Comparative Example 1 to a pulp concentration of 100 g / L. During the leaching process, air blowing (0.1 L / min with respect to 1 L of concentrate) and stirring were continued, and the oxidation-reduction potential (ORP: vs Ag / AgCl) was maintained at 400 mV or higher. During the leaching, hydrochloric acid was appropriately added so that the pH of the gold leaching solution was maintained at 1.0 to 1.1.

During the leaching test, samples of the leaching residue were taken periodically, and the Au quality in the residue was measured. FIG. 1 shows the relationship between the leaching time and the Au quality in the residue obtained from the results of the test (see the “FeS ₂ thermal decomposition” plot in FIG. 1). From this result, it can be seen that the Au quality in the residue, which was about 6 g / t at the beginning, decreased to 0.6 g / t in just 12 hours.

<Peak changes of FeS ₂ and FeS in XRD given by thermal decomposition conditions>
Diffraction intensity of FeS ₂ and FeS in XRD analysis when holding temperature and holding time are changed as shown in Table 1 for pyrite concentrate (1.5 kg) after milling used in Example 1 The change was investigated. The experiment was performed using a tubular furnace under a nitrogen atmosphere. Elemental sulfur produced by pyrolysis was evaporated and removed by a nitrogen stream. The heating rate was all 10 ° C./min. Cooling was allowed to cool to room temperature. For the XRD analysis, RIG2200 model RINT2200 ultimate was used. FeS ₂ has characteristic peaks at 2θ = 32.98 ° and 56.15 °, and FeS has characteristic peaks at 2θ = 43.67 ° and 33.78 °, so attention was paid to these incident angles. The results are shown in Table 2.

  From the results in Table 2, it can be seen that the pyrite-derived peak disappears reliably when heated to 600 ° C. or higher, which indicates that the crystalline pyrite was thermally decomposed, and the holding temperature and holding time were 650 ° C. and higher, respectively. When the condition is longer than 60 minutes, a clear FeS peak appears, which is most preferable.

<Example 2>
The same pyrite concentrate (1.5 kg) after milling as in Comparative Example 1 was charged into a tubular furnace and heated to 700 ° C. (temperature increase rate = 10 ° C./min) over 1 hour in a nitrogen atmosphere. Heated for 1 hour. After cooling to room temperature, the pyrite concentrate after heat treatment was subjected to a leaching treatment at a liquid temperature of 85 ° C. with a hydrochloric acid acidic gold leaching solution having the composition shown in Table 3 at a pulp concentration of 100 g / L. During the leaching treatment, air blowing (0.1 L / min with respect to 1 L of concentrate) and stirring were continued, and the oxidation-reduction potential (ORP: vs Ag / AgCl) was maintained at 600 mV or higher. However, NaBr was not added to NaBr, and other components were leached under the same conditions. Sampling was performed at regular intervals to quantify the gold concentration in the liquid. During the leaching, hydrochloric acid was appropriately added so that the pH of the gold leaching solution was maintained at 1.0 to 1.1.

<Comparative example 2>
The same pyrite concentrate (1.5 kg) after milling as in Comparative Example 1 was leached at a liquid temperature of 85 ° C. using a hydrochloric acid acidic gold leachate having the same composition as in Example 3 to a pulp concentration of 100 g / L. It was. During the leaching treatment, air blowing (0.1 L / min with respect to 1 L of concentrate) and stirring were continued, and the oxidation-reduction potential (ORP: vs Ag / AgCl) was maintained at 600 mV or higher. However, NaBr was not added to NaBr as in Example 2, and other components were leached even under the same conditions. Sampling was performed at regular intervals to quantify the gold concentration in the liquid. During the leaching, hydrochloric acid was appropriately added so that the pH of the gold leaching solution was maintained at 1.0 to 1.1.

  Table 4 shows the leaching time and leaching rate of gold in Example 2 and Comparative Example 2.

As described above, when gold ore containing pyrite is leached with Fe ³⁺ and Cu ²⁺ in a chloride bath (Table 4, Comparative Example 2), the gold leaching rate is insufficient. However, according to the present invention, as can be seen from the results of Example 2, the gold leaching rate is greatly improved, and even when the leaching solution does not contain bromide ions, a relatively high gold leaching rate can be obtained in a short time. I understand.

<Example 3: Temperature at which thermal decomposition occurs>
The pyrite concentrate after milling used in Example 1 was examined for weight change and endothermic-exothermic heat at each temperature by thermal analysis in a nitrogen atmosphere (model TG / DTA6300 manufactured by Seiko). The heating rate was 20 ° C. per minute. The results are shown in FIG. The decrease in mass begins at 450 ° C, and at the same time heat generation is seen, indicating that the decomposition of pyrite has started. In a nitrogen atmosphere, pyrolysis of pyrite will not occur unless the temperature is raised to at least 450 ° C. However, from the above-mentioned XRD analysis results, it is considered that the thermal decomposition takes a long time at around 450 ° C., and the heat treatment at 600 ° C. or higher is desirable.

The present invention has been made in view of the above circumstances, the leaching method of gold from gold ore containing pyrite, highly toxic cyan, thiourea, without the use of chemicals say Chio硫acid, further An object of the present invention is to provide an efficient gold leaching method by improving the gold leaching rate while suppressing the generation of sulfur dioxide.

Claims (8)

Step 1 for preparing a gold ore containing pyrite, and heating the gold ore to 450 ° C. or higher in a non-oxidizing atmosphere to thermally decompose the pyrite in the gold ore into iron (II) sulfide and elemental sulfur. A pretreatment including step 2 and not including an oxidation roasting step;
Contacting the gold ore after the pretreatment step with a gold leaching solution containing halide ions and iron ions under supply of an oxidizing agent, and leaching the gold component in the ore; and
Including gold leaching method.   The gold leaching method according to claim 1, wherein the gold leaching solution contains chloride ions and bromide ions.   3. The gold leaching method according to claim 1, wherein the gold leaching in step 3 is performed under a condition in which an oxidation-reduction potential (a reference electrode is silver / silver chloride) is maintained at 550 mV or more.   The gold leaching method according to claim 1 or 2, wherein the thermal decomposition in step 2 is performed under a condition in which the gold ore is held at 600 to 750 ° C for 5 to 60 minutes.   The gold leaching method according to any one of claims 1 to 3, wherein a content of pyrite in the gold ore is 5 to 80% by mass.   The method of leaching gold according to any one of claims 1 to 4, wherein gaseous single sulfur generated in step 2 is removed from the gold ore by solid-gas separation.   The iron (II) sulfide and elemental sulfur generated in step 2 are cooled and recovered together as a solid, and the gold leaching step is performed by bringing them into contact with the gold leaching solution together. The gold leaching method described in 1.   The gold leaching method according to any one of claims 1 to 6, wherein the gold leaching step is carried out while maintaining the pH of the gold leaching solution at 1.9 or lower.

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