JP2023024269A - Pretreatment method of gold ore, and gold recovery method - Google Patents

Abstract

To provide a pretreatment method of a gold ore which can easily recover gold even when a sulfide or a carbonaceous component is contained in the gold ore, and a gold recovery method having a high gold recovery rate.SOLUTION: A pretreatment method includes a bio-oxidization step of bringing a gold ore containing a sulfide into contact with iron-oxidizing bacteria, and holding them for a predetermined time. A gold recovery method includes a pretreatment step of pretreating the gold ore by a pretreatment method, a leaching step of leaching gold from the gold ore to obtain a leaching solution, an adsorption step of adsorbing the gold in the leaching solution in active carbon, and an elution step of eluting the gold from the active carbon, and obtaining a gold solution. The sulfide confining the gold particles is subjected to oxidizing decomposition by action of the iron-oxidizing bacteria, which separates the gold particles into elements to facilitate recovery of gold. As a result, a gold recovery rate can be increased.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gold ore pretreatment method and a gold recovery method. More particularly, the present invention relates to a method for pretreating gold ore containing sulfides and a method for recovering gold using the pretreated gold ore.

Patent Document 1 discloses a CIP (Carbon In Pulp) method as a method for recovering gold from gold ore. Gold recovery by the CIP method is performed in the following procedure. First, a dilute cyanide solution of an alkali metal or an alkaline earth metal and an alkali are added to finely ground gold ore to elute gold in the gold ore as a gold cyanide ion complex (Au(CN) ₂ ⁻ ). Next, the slurry containing the ore and the gold complex and the activated carbon are brought into contact with each other in a countercurrent flow to adsorb the gold complex to the activated carbon. Next, a hot cyanide solution is allowed to act on the activated carbon separated from the slurry to desorb the gold complex from the activated carbon. The gold is then recovered by subjecting the cyanide solution in which the gold complex is concentrated to electrowinning.

JP-A-03-030834

Gold is often contained as a simple substance in metal sulfide ores. Minerals of this type may have gold particles trapped in sulfides, resulting in low gold recovery rates. Moreover, when the gold ore contains a carbonaceous component, part of the gold leached from the gold ore is adsorbed by the carbonaceous component in the ore. As a result, the gold remaining in the ore increases and the gold recovery rate decreases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for pretreating gold ore that facilitates the recovery of gold even if the gold ore contains sulfides or carbonaceous components.
Another object of the present invention is to provide a method for recovering gold, which achieves a high recovery rate of gold even if the gold ore contains sulfides or carbonaceous components.

A gold ore pretreatment method of the first invention is a pretreatment method performed before gold is leached from a sulfide-containing gold ore, wherein the gold ore and iron-oxidizing bacteria are brought into contact with each other for a predetermined period of time. It is characterized by comprising an oxidation step.
A method for pretreating gold ore according to a second aspect of the invention is characterized in that, in the first aspect, after the biological oxidation step, a hydrochloric acid washing step of washing the gold ore with hydrochloric acid to remove iron components is provided.
A method for pretreating gold ore according to a third aspect of the present invention is a pretreatment method according to the first or second aspect, which is performed before leaching gold from the gold ore further containing a carbonaceous component, wherein the gold ore and phenol oxidase are used together. It is characterized by comprising an enzymatic treatment step of contacting and holding for a predetermined time.
A gold recovery method of a fourth invention comprises a pretreatment step of pretreating the gold ore by any one of the methods of the first to third inventions, and after the pretreatment step, leaching gold from the gold ore. It is characterized by comprising a leaching step of obtaining a leaching solution, an adsorption step of adsorbing gold in the leaching solution to activated carbon, and an elution step of eluting gold from the activated carbon to obtain a gold solution.

According to the first invention, the sulfide enclosing the gold particles is oxidatively decomposed by the action of the iron-oxidizing bacteria, so that the gold particles are separated into individual particles, facilitating recovery of the gold.
According to the second invention, since the trivalent iron ions remaining on the surface of the gold ore are removed, the trivalent iron ions are granulated with the silicate in the gold ore to capture the separated gold particles. can be suppressed.
According to the third invention, the surface of the carbonaceous component is modified by the action of phenol oxidase, and the ability of the carbonaceous component to adsorb gold is reduced.
According to the fourth invention, the recovery rate of gold can be increased.

1 is a process diagram of a gold recovery method according to an embodiment of the present invention; FIG. It is the XRD pattern of each sample in the example. TG-DTA measurement results of each sample in Examples. FIG. (A) is a graph showing the gold concentration and gold leaching rate of the leaching solution when Sample 2 was leached with thiourea. FIG. (B) is a graph showing the oxidation-reduction potential (based on the standard hydrogen electrode) of the leachate when sample 2 was leached with thiourea.

Next, an embodiment of the present invention will be described based on FIG.
[Pretreatment method]
A gold ore pretreatment method according to an embodiment of the present invention is performed as a pretreatment for a process of recovering gold from gold ore. As mentioned above, sulfide or carbonaceous components in the gold ore make it difficult to recover the gold by leaching. Therefore, pretreatment is performed before gold is leached from the gold ore to increase the recovery rate of gold from the gold ore.

Gold ore is an aggregate of minerals containing gold. Gold is often contained as a single element in metal sulfide ores such as chalcocite, bornite, copper indigo, chalcopyrite, pyrite, arsenopyrite, and arsenopyrite. Gold ores include ores of this type. In general, after obtaining a gold concentrate whose gold grade has been raised by a treatment such as flotation, a treatment for recovering gold is performed. Gold ores also include such gold concentrates.

If a metal sulfide ore is used as the gold ore, the gold ore will contain sulfides. The pretreatment according to this embodiment is effective for gold ore containing such sulfides. The gold ore may also contain carbonaceous components. Among carbonaceous components, activated carbon is known to have a high ability to adsorb cyanide ions. The pretreatment according to the present embodiment is effective for gold ore containing carbonaceous components, particularly activated carbon or carbonaceous components having properties similar to activated carbon.

Gold ore is preferably pulverized in advance. Also, the gold ore may be washed in advance. By washing the surface of the gold ore, oxides and deposits caused by aged deterioration etc. are removed. In addition, the gold concentrate whose gold grade has been raised by flotation is washed to remove residual surfactant used for flotation. For example, gold ore can be washed by washing with ethanol, washing with nitric acid, and washing with water in this order.

(Biological oxidation process)
Pretreatment includes a biooxidation step. The biological oxidation step is carried out by contacting the gold ore with the iron-oxidizing bacteria and maintaining them for a predetermined period of time. Contact between gold ore and iron-oxidizing bacteria can be achieved by various methods. For example, gold ore may be immersed in a liquid containing iron-oxidizing bacteria, or a liquid containing iron-oxidizing bacteria may be sprayed on gold ore. A gold ore slurry may be produced by pulverizing gold ore in advance and adding a culture solution or water, and iron-oxidizing bacteria or a liquid containing iron-oxidizing bacteria may be added to the gold ore slurry. Alternatively, a liquid containing iron-oxidizing bacteria may be sprayed on bulk gold ore.

Iron-oxidizing bacteria are bacteria that obtain energy for carbonic acid assimilation by oxidizing ferric ions to ferric ions with molecular oxygen. Examples of iron-oxidizing bacteria include the genus Gallionella, the genus Leptothrix, the genus Siderocapsa, the genus Acidianus, and the like. Also, A.brierleyi, for example, is known as an iron-oxidizing bacterium belonging to the genus Acidianus.

The amount of iron-oxidizing bacteria added, the pH and temperature of the liquid containing the iron-oxidizing bacteria, and the contact time between the gold ore and the iron-oxidizing bacteria may be appropriately adjusted according to the type of iron-oxidizing bacteria used.

When the gold ore is brought into contact with iron-oxidizing bacteria, sulfide (iron sulfide) contained in the gold ore is oxidatively decomposed by the action of the iron-oxidizing bacteria. Since the sulfide enclosing the gold particles is oxidatively decomposed, the gold particles are isolated. As a result, the gold is easily leached from the gold ore in the subsequent gold recovery treatment, and the recovery of the gold is facilitated.

After the biooxidation step, solid-liquid separation is performed as required. By removing the liquid portion, the gold ore after biological oxidation can be obtained.

(Hydrochloric acid washing step)
After the biooxidation step, the gold ore is preferably washed with hydrochloric acid to remove iron components. When the sulfide (iron sulfide) contained in the gold ore is oxidatively decomposed, trivalent iron ions and sparingly soluble jarosite are present on the surface of the gold ore. Trivalent iron ions present on the surface of the gold ore may be granulated with silicates contained in the gold ore, and may recapture the separated gold particles. In addition, sparingly soluble jarosite consumes the cyanide used for gold leaching.

Since the trivalent iron ions remaining on the surface of the gold ore are removed by washing with hydrochloric acid, it is possible to prevent the trivalent iron ions from granulating with the silicate in the gold ore and trapping separated gold particles. In addition, excessive consumption of cyanide compounds can be suppressed by removing sparingly soluble jarosite. Furthermore, since the iron hydroxide adhering to the gold ore surface can be removed, the enzyme can easily act in the enzymatic treatment step described later. The carbon content decomposed by the enzymatic treatment also forms granules with aluminum and silicates contained in the gold ore through intervening iron ions. By removing iron ions before the enzymatic treatment, such granulation can be prevented and the loss of gold recovery can be reduced. As a result, the gold recovery rate in the subsequent gold recovery process can be increased.

(Enzyme treatment step)
When the gold ore contains a carbonaceous component, it is preferable to carry out enzymatic treatment. The enzymatic treatment step is performed by bringing the gold ore and phenol oxidase into contact with each other for a predetermined period of time. Contacting gold ore with phenol oxidase can be achieved by various methods. For example, the gold ore may be immersed in an enzyme solution containing phenol oxidase, or the enzyme solution may be sprayed on the gold ore. A gold ore slurry may be produced by pulverizing gold ore in advance and adding water, and phenol oxidase or an enzyme solution containing phenol oxidase may be added to the gold ore slurry. Alternatively, an enzyme solution containing phenol oxidase may be sprayed on bulk gold ore.

Phenol oxidase is an enzyme that has the ability to oxidize phenol. Phenol oxidases include laccase, tyrosinase, white rot fungi-secreted enzymes, and the like. Examples of enzymes secreted by white rot fungi include lignin peroxidase and manganese peroxidase.

The amount of phenol oxidase to be added, the pH and temperature of the enzyme solution containing phenol oxidase, and the contact time between the gold ore and phenol oxidase may be appropriately adjusted according to the type of phenol oxidase used.

When gold ore is brought into contact with phenol oxidase, the surface of the carbonaceous component is modified by the action of phenoloxidase, and the ability of the carbonaceous component to adsorb gold decreases. As a result, when the gold is leached from the gold ore in the subsequent gold recovery process, the adsorption of the leached gold to the carbonaceous component in the ore can be suppressed.

After the enzymatic treatment step, solid-liquid separation is performed as necessary. By removing the liquid component, the gold ore after enzyme treatment can be obtained.

After the enzymatic treatment step, the gold ore may be washed. The surface of the carbonaceous component contained in the gold ore is modified by an enzymatic reaction, resulting in a decrease in the ability to adsorb gold. At the same time, fine decomposition products of carbonaceous components may be produced. Degradation products can adsorb gold in subsequent gold recovery processes. By washing the gold ore to remove the decomposition products, adsorption of the leached gold to the decomposition products can be suppressed in the gold recovery process.

In addition, washing the gold ore can remove phenol oxidase adhering to the surface of the gold ore. Therefore, it is possible to prevent the enzymatic reaction from lowering the gold adsorption capacity of the activated carbon added in the subsequent gold recovery treatment.

A washing method is not particularly limited. For example, the gold ore may be taken out by solid-liquid separation after adding a washing liquid to the enzyme-treated gold ore and stirring. The addition of the washing liquid and the solid-liquid separation may be performed multiple times. As a washing liquid, an organic solvent can be used in addition to water. Decomposition products of carbonaceous components may be insoluble in water. In this case, it is preferable to use an organic solvent as the cleaning liquid.

[Gold collection method]
Gold can be recovered from the gold ore by performing the steps described below following the pretreatment step by the method described above.

(Leaching process)
In the leaching process, gold is leached from the gold ore to obtain a leachate. For example, a cyanide compound is added to a slurry containing pulverized gold ore, and leaching is performed while blowing air. Cyanide includes sodium cyanide, potassium cyanide, calcium cyanide and the like. Other gold leaching agents such as thiourea, ethylenethiourea, thiosulfuric acid, and halogen gas may be used instead of the cyanide. When thiourea is used as the gold leaching agent, it is preferable to add a reducing agent such as sodium sulfite.

Here, since the gold ore is subjected to pretreatment, the gold particles are isolated and the gold is easily leached. In addition, since the ability of the carbonaceous component contained in the gold ore to adsorb gold is reduced, the amount of gold contained in the leachate adsorbed to the carbonaceous component can be reduced. Therefore, the recovery rate of gold can be increased.

(adsorption process)
In the adsorption step, the leachate and activated carbon are brought into contact to adsorb gold in the leachate to the activated carbon. Here, it is preferable to adjust the holding time so that most of the gold in the leachate is adsorbed on the activated carbon. The gold-adsorbed activated carbon is separated from the leachate.

The type of activated carbon to be used is not particularly limited, but one having a high gold adsorption capacity is preferred. Further, in the adsorption step, activated carbon is generally added to the leachate and stirred. Since the activated carbons collide with each other due to agitation, activated carbons that are not easily crushed or pulverized are preferred. Examples of such activated carbon include coconut shell activated carbon.

It is preferable to wash the activated carbon with hydrochloric acid or the like before supplying it to the next step. Activated carbon may have attached copper, calcium, etc. derived from gold ore. By removing this in advance, the concentration of impurities in the gold solution obtained in the next step can be reduced.

(Elution step)
In the elution step, gold is eluted from the activated carbon after the adsorption step to obtain a gold solution. For example, the activated carbon is contacted with a heated alkaline cyanide solution to elute the gold from the activated carbon. Instead of the cyanide solution, an alkali solution such as sodium hydroxide may be used to elute gold.

Electrolytic gold can then be recovered by electrowinning using a gold solution. It is preferable to reactivate the activated carbon after gold has been eluted and use it repeatedly.

Next, an example will be described.
The gold ore was pulverized into a powder having a sieve undersize of 100 μm or less.

(pre-cleaning)
The crushed gold ore was washed by the following procedure. Powdered gold ore was immersed in 100% ethanol, stirred for 5 minutes, and then subjected to ultrasonic treatment for 30 seconds. The solid content obtained by filtration was immersed in 1M nitric acid, stirred for 5 minutes, and then subjected to ultrasonic treatment for 60 seconds. The solid content obtained by filtration again was immersed in ultrapure water, stirred for 5 minutes, and then subjected to ultrasonic treatment for 60 seconds. After repeating washing with ultrapure water three times, the solid content obtained by filtration was dried. The washed gold ore is referred to as Sample 1.

The mineral ratio of the gold ore before and after washing was analyzed with an MLA device (manufactured by FEI, model number: MLA650F). Table 1 shows the results.

From Table 1, the ratio of minerals with high possibility of containing gold (feldspar, quartz, muscovite, orthoclase) did not decrease, and the ratio of minerals with low possibility of containing gold (pyrite, anchorite) decreased. I know there is. From this, it was confirmed that the gold loss can be sufficiently suppressed by the cleaning method described above.

(biological oxidation)
Using a 2 L beaker, 16 g of washed gold ore (Sample 1) was mixed with 800 mL of medium to prepare a mineral slurry having a solid concentration of 2% by weight. 1.0×10 ⁷ cells of iron-oxidizing bacteria (A.brierleyi) were added to 1 mL of the mineral slurry. 1M sulfuric acid was added to the mineral slurry to adjust the pH to 1.5. Also, the liquid temperature of the mineral slurry was maintained at 70°C. The mineral slurry was stirred at 150 rpm for 6 days using a stirring device (Bioshaker, model number: BR-40LF, hereinafter the same) manufactured by TAITEC. After that, solid-liquid separation was performed to obtain 12 g of solid content. The biological oxidation described above was repeated to obtain the required amount of gold ore in the post-process. Sample 2 is the gold ore after biological oxidation.

Table 2 shows the composition of the medium used for biological oxidation.

The composition of the ABS medium (before dilution) in Table 2 is as shown in Table 3.

The composition of trace elements (before dilution) in Table 2 is shown in Table 4.

(Cleaning with hydrochloric acid)
Using a beaker with a volume of 1 L, 30 g of gold ore after biological oxidation (Sample 2) was immersed in 300 mL of 1 M hydrochloric acid and stirred at 500 rpm for 24 hours using a magnetic stirrer. 100 mL of ultrapure water was added to the solid content obtained after filtration and centrifuged to remove hydrochloric acid. Specifically, the solid content and 100 mL of ultrapure water were placed in a 250 mL centrifuge bottle, and the centrifuge bottle was set in a centrifuge (Suprema 21, manufactured by TOMY). It was centrifuged at 10,000 rpm for 5 minutes while maintaining the liquid temperature at 25°C. Only the solid content remained in the bottle, ultrapure water was added again, and centrifugation was repeated. After repeating centrifugation seven times, the solid content was freeze-dried using a freeze-drying device (manufactured by Tokyo Rikaki Co., Ltd., model number: FDU-120) to obtain 24 g of solid content. The above hydrochloric acid washing was repeated to obtain the required amount of gold ore in the subsequent process. The gold ore after washing with hydrochloric acid is referred to as sample 3.

(enzyme treatment)
Using a flask with a volume of 2 L, 25 g of gold ore after biological oxidation (sample 2) that had not been washed with hydrochloric acid was mixed with 500 ml of the enzyme solution. The pH was adjusted to 4 by adding 1M sodium hydroxide to the enzyme solution. In addition, while maintaining the enzyme solution at 30° C., it was stirred at 125 rpm using a stirrer. Every three days, the enzyme solution in the flask was solid-liquid separated, only the solid content was returned to the flask, and a new enzyme solution was added. After performing this treatment 6 times (18 days), a solid content was obtained by solid-liquid separation. A sample 4 is obtained by enzymatically treating the sample 2 with gold ore.

Enzymatic treatment was performed on the gold ore (sample 3) after washing with hydrochloric acid by the same procedure. A gold ore obtained by enzymatically treating sample 3 is referred to as sample 5.

An enzyme solution was prepared by the following procedure. A white rot fungus (P. chrysosporium) was cultured using the medium. Here, the pH of the medium was set to 4.0, the liquid temperature was set to 37° C., and the mixture was stirred at 80 rpm using a stirrer. Thereafter, the liquid obtained by filtering the culture medium was used as the enzyme liquid. During the period of enzymatic treatment (18 days), the medium of white rot fungi was renewed every 3 days. Enzymes that decompose wood (lignin) released by white rot fungi (lignin peroxidase, manganese peroxidase, etc.) are known to be classified as phenol oxidases.

Table 5 shows the composition of the medium used for culturing white rot fungi.

The composition of trace elements in Table 5 is as shown in Table 6.

(Leaching 1)
Cyanide leaching was performed on each of samples 1-5. Specifically, the sample was mixed with a 2.5 mM potassium cyanide solution to prepare a mineral slurry having a solid concentration of 5% by weight. The pH was adjusted to 12 by adding 1M potassium hydroxide to the mineral slurry. The liquid temperature of the mineral slurry was set to room temperature, and the mixture was stirred at 134 rpm for 24 hours using a stirring device. After that, solid-liquid separation was performed to obtain a leachate and a leach residue.

The amount of gold in the leachate was measured by ICP-MS (manufactured by Agilent Technologies, model number: Agilent 7500C, hereinafter the same). Also, the amount of gold in the liquid obtained by dissolving the leaching residue with acid was measured by ICP-MS. Then, the gold leaching rate was obtained based on the following formula (1).
R=A/(A+B) (1)
Here, R is the gold leaching rate [%], A is the amount of gold in the leaching solution, and B is the amount of gold in the leaching residue.

Table 7 shows the results.

(adsorption)
100 mg of activated carbon (activated carbon, powder, Wako special grade manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 200 mL of the leaching solution of each sample. While maintaining the liquid temperature of the slurry at 30° C., the slurry was stirred at 128 rpm for 3 days to adsorb gold onto the activated carbon.

(Elution)
10 mg of activated carbon after gold adsorption was added to 4.0 mL of cyano-gold solution. While maintaining the liquid temperature of the slurry at 25° C., the slurry was shaken at 120 rpm for 24 hours. After that, the Au(CN) ^2- concentration of the liquid obtained by solid-liquid separation was measured. It was confirmed that the Au(CN) ^2- concentration of each sample had the same tendency as the gold leaching rate shown in Table 7.

From Table 7, the gold leaching rate of sample 2 subjected to biological oxidation is approximately 1.5 times that of sample 1 subjected to pre-cleaning only. From this, it was confirmed that the gold leaching rate was improved by performing biological oxidation. Further, the gold leaching rate of sample 3, which was washed with hydrochloric acid, is higher than that of sample 2. From this, it was confirmed that the gold leaching rate was improved by washing with hydrochloric acid.

In addition, sample 4 subjected to enzyme treatment has a higher gold leaching rate than sample 2. From this, it was confirmed that the gold leaching rate was improved by enzymatic treatment. Further, the gold leaching rate reached 84.9% for sample 5, which was subjected to all of biological oxidation, hydrochloric acid washing, and enzymatic treatment. This is about twice the gold leaching rate of sample 1, which was pre-cleaned only. From this, it was confirmed that the gold leaching rate can be sufficiently increased by performing all of biological oxidation, hydrochloric acid washing, and enzymatic treatment.

FIG. 2 shows the XRD patterns of samples 1 to 5 measured with an XRD device (Rigaku, Ultima IV). It can be seen that there is a difference in the observation results of jarosite in each sample. While jarosite is not confirmed in sample 1, jarosite is confirmed in samples 2-5. From this, it can be seen that jarosite is generated by biological oxidation.

Further, when focusing particularly on the region of 2θ=15 to 18°, it can be seen that sample 5 has a weaker jarosite peak than samples 2 and 4. Further, when the iron contents of samples 2 and 3 were measured by chemical analysis, it was confirmed that the iron content of sample 3 was lower than that of sample 2 by 20.7%. These results show that iron components such as jarosite are removed by hydrochloric acid washing.

Considering this together with the results of the gold leaching rate, it can be said that the gold leaching rate is improved due to the removal of the iron component from the gold ore. This is presumed to be the result of suppressing granulation of trivalent iron ions with the silicate in the gold ore and capture of isolated gold particles. In addition, it is presumed that iron hydroxide adhering to the gold ore surface was removed, making it easier for the enzyme to act during the enzymatic treatment.

FIG. 3 shows the results of measuring samples 1 to 5 with a TG-DTA device (2000-SA, manufactured by Bruker). Focusing on the endothermic reaction peak of sulfides around 450° C., it can be seen that the endothermic peak of sample 3 is smaller than the endothermic peak of sample 2. This means that sample 3 has less sulfide than sample 2. Pyrite (FeS ₂ ) corresponds to sulfide in the composition of the gold ore used in this example. It is considered that pyrite was removed by washing with sulfuric acid.

(Leaching 2)
Sample 2 was leached with thiourea. The leachate contains 4.975 mM thiourea and 4.7 μM iron(III) sulfate. Also, the leachate contains sodium sulfite. Five infusions were prepared with sodium sulfite concentrations of 0, 1, 2, 5 and 10 mM. Sample 2 and each leachate were mixed to prepare a mineral slurry having a solid content concentration of 1.25% by weight.

The liquid temperature of the mineral slurry was adjusted to 60°, and the pH was adjusted to 1. The mineral slurry was sampled at various times from the start of leaching to determine the gold concentration and gold leaching rate of the leaching solution. In addition, the redox potential of the leachate was measured. FIG. 4A shows the gold concentration and gold leaching rate of the leaching solution. In addition, FIG. 4B shows the oxidation-reduction potential of the exudate.

As can be seen from FIG. 4(A), the gold leaching rate is low when sodium sulfite is not added. This is probably because Fe ³⁺ adsorbed on the surface of the gold ore of sample 2 oxidized thiourea, and a complex between thiourea and gold was no longer formed. On the other hand, the addition of sodium sulfite to the leaching solution increases the gold leaching rate. In particular, the gold leaching rate is high when the concentration of sodium sulfite is in the range of 5 to 10 mM. The gold leaching rate at this time is comparable to the gold leaching rate of 62.6% when sample 2 is leached with cyanide (see Table 1). As can be seen from FIG. 4(B), the addition of sodium sulfite to the leachate lowers the redox potential. That is, sodium sulfite acts as a reducing agent. It is believed that sodium sulfite reduces Fe ³⁺ and prevents the decomposition of thiourea, resulting in higher gold leaching rates.

From the above, it can be said that it is preferable to add a reducing agent such as sodium sulfite when leaching gold ore having a high iron content with thiourea. Addition of a reducing agent suppresses the decomposition of thiourea and increases the gold leaching rate.

Iron-oxidizing bacteria are bacteria that obtain energy for carbonic acid assimilation by oxidizing ferric ions to ferric ions with molecular oxygen. Examples of iron-oxidizing bacteria include the genus Gallionella, the genus Leptothrix, the genus Siderocapsa, the genus Acidianus , and the like. Also, A.brierleyi , for example, is known as an iron-oxidizing bacterium belonging to the genus Acidianus.

The composition of the ABS medium (before dilution) in Table 2 is as shown in Table 3.

The composition of trace elements in Table 5 is as shown in Table 6.

(Elution)
10 mg of activated carbon after gold adsorption was added to 4.0 mL of cyano-gold solution. While maintaining the liquid temperature of the slurry at 25° C., the slurry was shaken at 120 rpm for 24 hours. After that, the Au(CN) ₂ ^- concentration of the liquid obtained by solid-liquid separation was measured. It was confirmed that the Au(CN) ₂ ^- concentration of each sample had the same tendency as the gold leaching rate shown in Table 7.

Claims (4)

A pretreatment method prior to leaching gold from a sulfide-containing gold ore, comprising:
A method for pretreating gold ore, comprising a biological oxidation step in which the gold ore and iron-oxidizing bacteria are brought into contact with each other for a predetermined period of time. 2. The gold ore pretreatment method according to claim 1, further comprising a hydrochloric acid washing step of washing the gold ore with hydrochloric acid to remove iron components after the biological oxidation step. Furthermore, a pretreatment method performed before leaching gold from a gold ore containing a carbonaceous component,
2. The method for pretreating gold ore according to claim 1, further comprising an enzymatic treatment step in which the gold ore and phenol oxidase are brought into contact with each other for a predetermined period of time. a pretreatment step of pretreating the gold ore by the method according to any one of claims 1 to 3;
After the pretreatment step, a leaching step of leaching gold from the gold ore to obtain a leaching solution;
an adsorption step of adsorbing gold in the leachate to activated carbon;
and an elution step of eluting gold from the activated carbon to obtain a gold solution.

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