JP6329939B2 - Gold ore pretreatment method - Google Patents

Description

  The present invention relates to a gold ore pretreatment method for recovering gold from a gold ore containing pyrite by wet treatment.

  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, when adopting the method of oxidizing roasting sulfide minerals including the method described in Patent Document _{3, 2CuS + 3O 2 → 2CuO} + 2SO 2 _{and, 4CuFeS 2 + 13O 2 → 4CuO} + 8SO 2 + 2Fe 2 O 3, and 4FeS ₂ + 11O ₂ → 2Fe _Since a chemical reaction such as ₂ O ₃ + 8SO ₂ occurs preferentially, sulfur dioxide (SO ₂ ) known as an environmental pollutant is generated. In particular, when the pyrite content in the gold ore is high, the amount of sulfur dioxide generated is enormous, so that there is still a problem in terms of practicality.

  Pretreatment to increase the gold leaching rate is reduced from the viewpoint of safety and environment, sulfur dioxide generated in the mineral treatment process for gold leaching is reduced, safety is increased, and the impact on the environment is low. It is desirable to make it. And if it is a pretreatment applicable also to the gold ore containing a large amount of pyrite that has been considered difficult to put into practical use, it is thought that it will greatly contribute to the progress of gold mine development.

  In this regard, 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. It is not assumed (see paragraphs 0007 to 0008 and 0078 of Patent Document 4). In addition, there is no suggestion of what effect can be obtained by wet processing.

  The present invention has been made in view of the above circumstances, and is a gold ore pretreatment method for recovering gold from a gold ore containing pyrite by wet treatment, suppressing generation of sulfur dioxide, and It is an object of the present invention to provide a pretreatment method capable of improving the gold recovery rate.

In one aspect, the present invention is a pretreatment method for recovering gold contained in a gold ore containing pyrite (FeS ₂ ) by wet treatment, wherein the pyrite in the gold ore is converted into a hydrochloric acid-soluble iron compound. It is the pre-processing method including the process to convert.

In one embodiment of the pretreatment method according to the present invention, the solubility of hydrochloric acid contained in the gold ore after the pretreatment with respect to the total Fe content (Fe _all ) contained in the gold ore after the pretreatment. It includes a step of converting pyrite so that the Fe content (Fe _sol ) is 0.6 or more.

  In another embodiment of the pretreatment method according to the present invention, the hydrochloric acid-soluble iron compound in the gold ore after the pretreatment is a sulfide.

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

  In still another embodiment of the pretreatment method according to the present invention, S (mass%) / Au (mass ppm) in the gold ore before the pretreatment is 1 to 20.

  In yet another embodiment of the pretreatment method according to the present invention, the pretreatment involves heat treatment.

  In yet another embodiment of the pretreatment method according to the present invention, the heat treatment includes heating the gold ore to 450 ° C. or higher in a non-oxidizing atmosphere.

  In still another embodiment of the pretreatment method according to the present invention, the heat treatment is performed under a condition in which the gold ore is held at 600 to 750 ° C. for 5 to 60 minutes.

  By performing a wet treatment after applying the pretreatment method according to the present invention to gold ore containing pyrite, it is possible to obtain an improved gold recovery rate while suppressing the generation of harmful sulfur oxides. . In particular, the improved gold leaching rate is dramatic when a specific gold leaching solution is used. 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 In one embodiment of a pretreatment method for recovering gold contained in gold ore containing pyrite (FeS ₂ ) according to the present invention by wet treatment, pyrite in the gold ore is converted into hydrochloric acid-soluble iron. Converting to a compound. In a preferred embodiment of the pretreatment method for gold ore according to the present invention, hydrochloric acid contained in the gold ore after pretreatment with respect to the total Fe content (Fe _all ) contained in the gold ore after pretreatment. It includes a step of converting pyrite so that the content of soluble Fe (Fe _sol ) is 0.6 or more.

(1) Gold ore The present invention is intended for gold ore containing pyrite. 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, gold ore containing pyrite in an amount of 10% by mass or more, and further 30% by mass or more is used. In such gold ore, the concentration of sulfur content (S / Au) with respect to the gold content in the ore increases, and it is generally difficult to efficiently recover gold. Therefore, the effect of the pretreatment according to the present invention is remarkably exhibited by using such gold ore with a high pyrite concentration. Specifically, S (mass%) / Au (mass ppm) is 1 to 20, preferably 1.5 to 20, and more preferably 1.5 to 10. 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.

(2) Conversion process In the prior art, since oxidation roasting was performed in the presence of oxygen or air, sulfur in the sulfide mineral was combined with oxygen to produce sulfur oxide. In the present invention, such oxidation roasting is not substantially performed. In the present invention, from the viewpoint of suppressing the generation of sulfur oxides, it is preferable to convert pyrite into iron sulfides that are soluble in hydrochloric acid, while preserving pyrite in iron sulfides. If the iron in the ore is an iron sulfide that is soluble in hydrochloric acid and exceeds a specific amount, an improved gold leaching rate can be obtained significantly in the leaching step of the next step.

Pyrite (FeS ₂ ) is sparingly soluble in hydrochloric acid, while iron sulfides soluble in hydrochloric acid are expected to improve the recovery rate during gold recovery by wet processing, especially for certain leachates. It was found to show a dramatic effect. The specific leachate will be described later in “2. Wet treatment process”.

According to the inventor's research, “more than a specific amount” means that the total Fe content in the pretreated gold ore is Fe _all , and the hydrochloric acid soluble Fe contained in the pretreated gold ore. When the content of Fe _sol is Fe _sol , Fe _sol / Fe _all is 0.6 or more, and Fe _sol / Fe _all is preferably 0.8 or more, more preferably 0.9 or more. The upper limit of Fe _sol / Fe _all is 1.0 when pyrite is completely converted.

In the present invention, the Fe _all amount is calculated by the following procedure. 0.2 g of gold ore after pretreatment, 4 g of sodium peroxide, and 1 g of sodium carbonate are put in a zirconium crucible, and are sprinkled with a gas burner and alkali-melted. After cooling the crucible with water, 30 mL of 35% hydrochloric acid is put into the crucible and the melt is leached. The solution after leaching is measured by ICP-AES (in the examples, model SPS4000 manufactured by Hitachi High-Technologies Corporation (former SII) was used). The Fe _all amount is calculated from the liquid amount and the ore amount based on the measured Fe concentration. Specifically, Fe _all amount = Measured Fe concentration (g / L) × Liquid amount (30 mL) ÷ Ore amount (0.2 g).

In the present invention, Fe _sol is calculated by the following procedure. 50 g of the gold ore after the pretreatment is leached in 1 L of hydrochloric acid (1.0 mol / L) containing 1 mol / L of Fe ³⁺ while stirring at 85 ° C. for 180 minutes, and then filtered off. The concentration of Fe in the filtrate is measured by ICP-AES (in the examples, model SPS4000 manufactured by Hitachi High-Technologies Corporation (formerly SII) was used) (Fe included in hydrochloric acid from the beginning is excluded) .) Based on the measured Fe concentration, Fe _sol is calculated from the liquid amount and the ore amount. Specifically, Fe _sol amount = (Measured Fe concentration−Initial Fe concentration) (g / L) × Liquid amount (1 L) ÷ Ore amount (50 g).

  In the step of converting pyrite, it is desirable that the pyrite after the pretreatment is a sulfide. When converting pyrite into oxides, the generation of sulfur oxides is unavoidable, and the amount thereof is not a simple removal means such as a shower tower, and an apparatus capable of sufficiently removing is required. . Heat treatment is required so that the pyrite after pretreatment remains in the sulfide.

  The conversion step can be performed by heat treatment. From the viewpoint of suppressing the generation of sulfur oxides, the conversion step is preferably performed under conditions (non-oxidizing atmosphere) in which mixing of oxygen is suppressed. In the present invention, the condition in which the mixing of oxygen is suppressed indicates that the molar ratio of the oxygen supply amount to pyrite is oxygen: pyrite = 1: 2 or less. The non-oxidizing atmosphere means that the molar ratio of the oxygen supply amount to pyrite is oxygen: pyrite = 1: 5 or less, and the molar ratio of the oxygen supply amount to pyrite is preferably 1:10 or less.

  Under the condition that the mixing of oxygen is suppressed, the amount of sulfur oxide generated is small, and it is not necessary to install a separate sulfuric acid production facility in order to treat it. It can be removed sufficiently with a shower tower. If it is a non-oxidizing atmosphere, installation of a shower tower may be unnecessary.

  Compared to the case where the gold ore after the conversion step is not subjected to the conversion step, the solubility in the gold leaching solution described later can be remarkably improved, and the gold leaching rate can be increased by about 10 times. It was very surprising that such a result was obtained.

  Non-oxidizing atmosphere for carrying out the conversion step includes 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.

  In the conversion step, in order to promote thermal decomposition of pyrite, it is desirable to maintain the temperature of the gold ore at 450 ° C. or higher, preferably 550 ° C. or higher, and more preferably 650 ° C. or higher. preferable. Moreover, it is preferable that a conversion process continues holding temperature for 5 minutes or more, and it is more preferable to continue for 15 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 a conversion process, For example, a tubular furnace and a rotary kiln can be used.

  Since elemental sulfur generated by pyrolysis of pyrite 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. As an alternative method, it is also possible to cool the gasified elemental sulfur together with the pyrotite generated in the conversion process, collect them together in a solid state, and send them together to the gold leaching process. 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.

  Depending on operational restrictions, it may be possible to mix the gold ore that has undergone the pyrolysis process with the gold ore that has not undergone the pyrolysis process to perform the iron leaching process and the subsequent processes. However, since gold ore that has undergone at least a pyrolysis step is included, such an embodiment also belongs to the technical scope of the present invention.

2. Wet treatment step The gold ore after the pretreatment exhibits the effect of the present invention by collecting gold by a wet treatment. Examples of the wet treatment include, but are not limited to, gold leaching with a cyan bath combined with autoclave treatment or gold leaching with an acid bath.

In gold leaching using a cyan bath, gold ore containing pyrite is generally reacted with water and oxygen at high temperature and high pressure (eg, 200 ° C, 30 atm) in a pressure-resistant vessel to convert iron sulfide into iron oxide. After leaching gold. This is called autoclave treatment because an autoclave is used for the pressure-resistant container.
In the case of gold ore without pretreatment, the oxidation reaction of iron sulfide is represented by the following formula.
4FeS ₂ + 15O ₂ + 8H ₂ O → 2Fe ₂ O ₃ + 8H ₂ SO ₄ ― (1)
On the other hand, in the case of gold ore that has been subjected to pretreatment, sulfuric acid is generated by oxidation of sulfides, and an iron compound that is soluble in acid can be leached with the generated sulfuric acid, so that the reaction time can be reduced.

  In addition, in the leaching of gold in an acid bath, it is generally important to bring the leaching solution into contact with gold locked in iron sulfide. When the pretreatment according to the present invention is carried out, the pyrite in the gold ore can be converted into an iron sulfide that is soluble in acid, so that the leachate can be brought into contact with the gold in the iron sulfide earlier.

  Both wet treatments can shorten the time of wet treatment after pretreatment, but gold leaching with acidic leachate can be performed under mild operating conditions (at atmospheric pressure, less than 100 ° C), toxicity This is advantageous because it does not use high cyan. Gold leaching in an acid bath is described in detail below.

  The type and process of acid when gold is leached with an acid bath to the gold ore after pretreatment is not limited, but as an effective gold leaching process, gold containing halide ions, copper ions and iron ions is used. Examples include a gold leaching step including a step of leaching a gold component in the gold ore by bringing the leaching solution into contact with the oxidant under supply.

  Gold leaching proceeds by the elution of gold reacting with halide ions, particularly chloride ions or bromide ions, to form gold halide complexes, particularly gold chloride complexes or gold bromide complexes. Chloride ions alone may be used as halide ions in the gold leaching solution. By using chloride ions and bromide ions in combination, a complex is formed at a lower potential, thereby improving gold leaching efficiency. be able to. Further, the iron ions function to oxidize gold by trivalent iron ions oxidized under the supply of an oxidizing agent or trivalent iron ions from the beginning. 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.

  There are no particular restrictions on the source of chloride ions, but examples include hydrogen chloride, hydrochloric acid, metal chloride, and chlorine gas. In consideration of economy and safety, the supply source is chloride metal salt. preferable. Examples of metal chloride salts include copper chloride (cuprous chloride, cupric chloride), iron chloride (ferrous chloride, ferric chloride), and 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 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, and examples thereof include hydrogen bromide, hydrobromic acid, metal bromide, bromine gas, and the like. In consideration of economy and safety, the form of metal bromide salt It is preferable to supply by. Examples of metal bromide salts include copper bromide (cuprous bromide, cupric bromide), iron bromide (ferrous bromide, ferric bromide), and alkali metals (lithium, sodium, potassium). And bromides of alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, radium), and sodium bromide is preferred 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 leaching solution used in the gold leaching step is more preferably 30 g / L to 180 g / L. The concentration of bromide ions in the gold leaching solution used in the gold leaching step 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. It is more preferable that The total concentration of chloride ions and bromide ions in the gold leaching solution is preferably 120 g / L to 200 g / L. From the viewpoint of gold leaching efficiency, the weight concentration ratio of bromide ions to chloride ions in the gold leaching solution is preferably 1 or more.

  The oxidation-reduction potential (vs Ag / AgCl) of the leachate at the start of the gold leaching process (immediately before contacting the leachate with the ore) is preferably 550 mV or more, and preferably 600 mV or more from the viewpoint of promoting gold leaching. More preferred. Further, it is preferably maintained at 550 mV or more during gold leaching, and more preferably maintained at 600 mV or more. From the viewpoint of promoting the leaching of gold by allowing trivalent iron to be present in the leaching solution, the pH of the gold leaching solution is preferably maintained at 2.0 or less, and more preferably 1.8 or less. The temperature of the gold leaching solution is preferably 45 ° C. or higher from the viewpoint of increasing the gold leaching rate, and more preferably 60 ° C. or higher. It is preferable to set it as follows, and it is more preferable to set it as 85 degrees C or less.

  Therefore, in a preferred embodiment, at least one of hydrochloric acid and bromic acid and cupric chloride are selected on the condition that the gold leaching solution in the gold leaching step is selected to contain both chloride ions and bromide ions. And at least one of 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 process is performed while supplying the oxidizing agent, thereby managing the redox 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, it is also possible to carry out various treatments for removing impurities in the gold ore. 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.

  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 sulfur component is present in the form of sulfate, sulfide, elemental sulfur, etc. in the solution after leaching, but can be separated during solid-liquid separation after gold leaching reaction or gold recovery operation.

  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 gold analysis, gold in the sample was precipitated by the ash blowing method (JIS M8111), and then quantitative analysis was performed by ICP-AES.

<Comparative Example 1>
Pyrite concentrate (produced in Papua New Guinea) was prepared as gold ore. It was 17 mass% when content of the pyrite in this pyrite concentrate was calculated by XRD and chemical analysis. S (mass%) / Au (mass ppm) in the concentrate was 1.4. Further, when Fe _sol / Fe _all was measured according to the method described above, it was 0.

  On the other hand, 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 distribution curve of the cumulative weight particle size was adjusted to 50 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. Elemental sulfur produced by heat treatment was naturally removed from pyrite concentrate by solid-gas separation.

Further, the pyrite concentrate after heat treatment was measured according to the method previously described the Fe _sol / Fe _all, was 0.98.

  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. When a gold leaching solution containing no bromide ions was used, although the leaching rate of Au was slower than that containing bromide ions, almost the same results were obtained.

<Changes in Fe _sol / Fe _all given by pyrolysis conditions>
For the pyrite concentrate (1.5 kg) after milling used in Example 1, the change in Fe _sol / Fe _all when the holding temperature and holding time were changed as shown in Table 2 was investigated. . The value of Fe _sol / Fe _all was determined by the same procedure as in Example 1. Further, Fe / S was also measured according to the method described above. 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. The results are shown in Table 2.

From the results of Table 2, it can be seen that when the holding temperature and holding time are 650 ° C. or more and 60 minutes or more, Fe _sol / Fe _all approaches 1 and is most preferable.

<Example 2: 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.

Claims (5)

A pretreatment method for leaching gold contained in a gold ore containing pyrite (FeS ₂ ) with an acidic bath, wherein the total Fe content (Fe _all ) contained in the gold ore after the pretreatment On the other hand, including a step of converting pyrite so that the content of Fe soluble in hydrochloric acid (Fe _sol ) contained in the gold ore after pretreatment is 0.6 or more,
The hydrochloric acid-soluble iron compound in the gold ore after pretreatment is sulfide,
A pretreatment method , wherein the converting step is performed by heat treatment in a non-oxidizing atmosphere.   The pretreatment method of gold ore according to claim 1, wherein the content of pyrite in the gold ore before pretreatment is 5 to 80% by mass.   The gold ore pretreatment method according to claim 1 or 2, wherein S (mass%) / Au (mass ppm) in the gold ore before pretreatment is 1 to 20.   The gold ore pretreatment method according to any one of claims 1 to 3, wherein the heat treatment includes heating the gold ore to 450 ° C or higher in a non-oxidizing atmosphere.   The gold ore pretreatment method according to claim 4, wherein the heat treatment is performed under a condition in which the gold ore is held at 600 to 750 ° C for 5 to 60 minutes.

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