JP6953258B2 - Gold leaching method and gold recovery method - Google Patents

Description

The present invention relates to a method for leaching gold that can be contained in sulfide minerals and smelting intermediates, and a method for recovering gold using the same, and particularly proposes a technique that contributes to improving the recovery rate of gold. ..

For example, gold contained in ores such as chalcopyrite and other sulfide minerals and silicate ores, and smelting intermediates that are leaching residues obtained by leaching copper in copper sulfide or leaching iron in pyrite. As a gold recovery technique for recovering the gold contained in the above, a method using a wet smelting method is known.
Regarding such hydrometallurgical methods, chemicals such as cyanide, thiourea, thiosulfuric acid, and halogen gas have been used before in leaching gold in sulfide minerals and smelting intermediates into a solution. However, it is not desirable to use such chemicals, especially cyan, as their toxicity often limits their use.

On the other hand, in recent years, as described in Patent Documents 1 and 2, for example, sulfurization is carried out by using a halogen bath with an acidic aqueous solution containing copper ions and the like as cations and chloride ions and bromide ions as anions. It has been proposed to leach gold contained in minerals and the like. According to the gold leaching step of the proposed technique, gold can be easily leached as a polysulfide type complex or the like without using toxic cyanide. The gold leached in the acidic aqueous solution can be recovered by adsorbing it on activated carbon and then eluting it with caustic soda.

Here, gold contained in sulfide minerals generally includes those exposed on the surface, those covered with sulfide, those covered with gangue components such as _{SiO 2, and the like.}
Of these, exposed gold in sulfide minerals and the like can be dissolved by forming a halogen complex in the above-mentioned gold leaching step.

For gold covered with sulfide, as described in Patent Document 1, iron disulfide is sulfided by performing a roasting step of heating sulfide minerals and the like in a non-oxidizing atmosphere prior to the gold leaching step. By thermally decomposing into iron (II) and sulfur, and by performing an iron removal step under almost the same leaching conditions as the gold leaching step after the roasting step, iron (II) sulfide is leached and removed. The gold can be dissolved in the subsequent gold leaching step. _{Although a small amount of gold covered with SiO 2} or the like is present in the sulfide mineral, it is considered difficult to leach it.

International Publication No. 2014/0382836 Special Table 2009-526912

By the way, the leaching rate of gold actually leached through the roasting step, the iron removal step, the gold leaching step, etc. as described above is determined by analyzing the gold presence form in the raw materials such as sulfide minerals and smelting intermediates. It was found that the leaching rate was lower than the theoretical leaching rate obtained. That is, it is considered _{that not only the gold covered with the gangue component such as SiO 2} in the sulfide mineral but also the other existing forms of gold are not sufficiently leached by the conventional gold leaching method. Therefore, the prior art has room for improvement in terms of further leaching of gold.

An object of the present invention is to solve such a problem of the prior art, and an object of the present invention is to increase the leaching rate of gold contained in sulfide minerals and smelting intermediates to increase the recovery rate of gold. It is an object of the present invention to provide a method for leaching gold that can contribute to improvement and a method for recovering gold using the method.

As a result of diligently investigating the reason why gold that should be able to be leached is not leached, the inventor found that the sulfur content of sulfide contained in sulfide minerals and smelting intermediates was elemental sulfur, etc. in the middle of the process of the gold leaching method. It has been found that the presence of this sulfur, which remains in a predetermined form and has a slow dissolution rate in acid, around the gold inhibits the leaching of the gold. This becomes a big problem because the larger the amount of such sulfur generated, the more difficult it is for gold to be leached out. However, the present invention is not limited to such a theory.

Based on such findings, the gold leaching method of the present invention is contained in a sulfide mineral or a raw material containing gold and sulfur as a smelting intermediate obtained by subjecting the sulfide mineral to a smelting treatment. This is a method of leaching gold, which is a first leaching step of leaching a part of gold in the raw material to obtain a leaching residue containing sulfur while remaining gold, and removing sulfur in the leaching residue. and sulfur removal step, seen including a second leaching step of leaching at least a portion of the remainder of the gold in the leach residue passed through a sulfur removal step, the sulfur removal step, the leach residue is contacted with an alkaline solution, leaching residue It removes the sulfur inside .

In the gold leaching method of the present invention, it is preferable that the gold in the leaching residue is exposed by removing the sulfur in the leaching residue in the sulfur removing step.
The gold leaching method of the present invention is particularly effective when a leaching residue containing sulfur, which is at least partially in the form of elemental sulfur, can be obtained in the first leaching step.

The gold leaching method of the present invention, in sulfur removal step, it is preferable that the pH of the alkaline solution contacting the leach residue 10 or more.

In the gold leaching method of the present invention, the sulfur removal rate in the sulfur removal step is preferably 10% or more, and even more preferably 25% or more.

In the gold leaching method of the present invention, it is preferable that the raw material is brought into contact with an acidic aqueous solution containing copper ions, iron ions and halide ions in the first leaching step under the supply of an oxidizing agent.

The gold recovery method of the present invention is to recover gold from a raw material by using any of the above gold leaching methods.

According to the present invention, after the first leaching step, a sulfur removing step of removing sulfur in the leaching residue is performed, and then at least a part of the gold residue in the leaching residue that has undergone the sulfur removing step is leached. By performing the second leaching step, the gold from which the surrounding sulfur has been removed in the sulfur removing step can be effectively leached in the second leaching step. As a result, the leaching rate of gold contained in sulfide minerals and smelting intermediates is further increased, which can contribute to the improvement of gold recovery rate.

It is a flow chart which shows the leaching step of gold which concerns on one Embodiment of this invention. It is a graph which shows the change of the gold grade and the gold leaching rate in the residue with the lapse of time when the leaching step is performed after the non-oxidizing roasting step in an Example. It is a graph which shows the relationship between the sulfur removal rate and the gold recovery rate based on the result of the invention example and the comparative example.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, the method for leaching gold according to one embodiment of the present invention is a sulfide mineral or a raw material as a smelting intermediate obtained by subjecting the sulfide mineral to a smelting treatment. This is a method of leaching the gold contained therein from the raw materials of those containing gold and sulfur. In this method, at least a part of gold in the raw material is leached to obtain a leaching residue in which gold remains and sulfur is contained, and a sulfur removing step of removing sulfur in the leaching residue. Including a second leaching step of leaching at least a part of the gold residue in the leaching residue that has undergone the sulfur removal step, thereby obtaining a gold-containing post-leaching liquid.

The gold leaching method of this embodiment can be applied to a predetermined gold recovery method. For example, as such a method for recovering gold, a pretreatment step, a first leaching step, a sulfur removing step, a second leaching step, etc. are used for raw materials containing gold and sulfur obtained from sulfide minerals and smelting intermediates. Some have a concentrated gold solution obtained by sequentially performing an adsorption step, a washing step, and an elution step. This will be described in detail below.

(Ingredients containing gold and sulfur)
Sulfide minerals and smelting intermediates are selected from, for example, bright copper ore, mottled copper ore, copper indigo, brass ore, yellow iron ore, arsenopyrite, arsenopyrite, astride ore, zinc flash ore, arsenopyrite, bright an ore, and magnetic arsenopyrite. Sulfide minerals containing at least one of these sulfide minerals, arsenopyrites containing gold and sulfur such as silicate ore, or intermediates obtained after smelting these sulfide minerals (also referred to as "smelting intermediates" here). Can be.
Here, the smelting treatment refers to, for example, a treatment of leaching copper with a predetermined leachate in the case of copper sulfide ore, or a treatment of leaching iron with a predetermined leachate in the case of pyrite. The leachate residue obtained in the above can be used as a smelting intermediate.

Sulfide minerals and smelting intermediates can be refined ores that have undergone conventional beneficiation treatments such as flotation, ore, and specific gravity sorting, if necessary. Further, the particle size of the ore may be reduced by crushing ore so that the acidic aqueous solution in the gold leaching step or the like can easily come into contact with the gold inside the mineral.

The above-mentioned sulfide minerals and smelting intermediates can be used as raw materials containing gold and sulfur, which are the targets of leaching in the present invention. Specifically, the raw material containing gold and sulfur is, for example, the sulfide mineral itself or a smelting intermediate obtained by subjecting a predetermined smelting treatment as described above.
The gold concentration in the raw material containing gold thus obtained is typically about 1 to 500 mass ppm, and more typically about 10 to 50 mass ppm.

(Pretreatment process)
When a roasting step is performed as a pretreatment step, in this roasting step, raw materials containing gold and sulfur are used in a reducing atmosphere such as ammonia, carbon monoxide and hydrogen sulfide, a rare gas atmosphere such as argon and helium, and nitrogen. Under an inert atmosphere such as an atmosphere or a carbon dioxide atmosphere or other non-oxidizing atmosphere, the pyrite in the raw material is heated at about 450 ° C. to 800 ° C. for about 30 minutes to 120 minutes, and the pyrite in the raw material is iron (II) sulfide and simple sulfur. Thermally decomposes into. The chemical reaction at this time is _{represented by FeS 2} → FeS + S.
The non-oxidizing atmosphere may contain oxygen to such an extent that substantially no adverse effect is exerted even if sulfur oxide is generated. For example, the molar ratio of oxygen supply to the raw material is oxygen: pyrite = 1. If it is / 5 or less, it is acceptable, and if it is 1/10 or less, it is preferable.
Here, various furnaces such as a tube furnace and a rotary kiln furnace can be used.
The pretreatment step is an arbitrary step and may be omitted.

(First leaching process)
In the first leaching step, the above-mentioned raw materials are brought into contact with a predetermined acidic aqueous solution under the supply of an oxidizing agent as they are without the pretreatment step or after the pretreatment step to leach iron and gold. Here, it is preferable to use an acidic aqueous solution containing copper ions, iron ions, and halide ions such as chloride ions and bromide ions. Iron (II) sulfide converted from iron disulfide in the above-mentioned roasting step can be leached and removed by the reaction of FeS → Fe + S. Thereby, the sulfide-covered gold in the raw material can be exposed and leached.

In the first leaching step, gold covered with sulfide in the raw material is exposed, so that when a predetermined sulfide mineral is targeted, it is theoretically covered with a gangue component such as _{SiO 2 in the raw material.} Excluding gold, a gold leaching rate of 99.9% should be obtained. According to the result of analysis of the existence form of gold as a raw material, the remaining 0.1% corresponds to gold covered with a gangue component, and it is difficult to leach this gold. However, the actual gold leaching rate was 94%, and it was found that nearly 6% of gold was not leached.
As a result of diligent studies, the inventor found the following factors regarding the reason why gold that should be able to leach remains in the leachate residue. That is, when a sulfide (iron sulfide, etc.) that inhibits the leaching of gold is leached in the first leaching step, the metal component of the sulfide is dissolved, but the sulfur component is generally leached residue as elemental sulfur (single sulfur) or the like. Remains in. Most of the sulfur such as elemental sulfur exists on the gold particles so as to surround the surroundings, and the slow dissolution rate in the acid inhibits the leaching of gold.
Therefore, the inventor has a sulfur removing step of removing sulfur in the leaching residue after the first leaching step, and a second leaching step of leaching at least a part of the gold residue in the leaching residue after the sulfur removing step. It was thought that the remaining gold could be effectively leached out by performing the above. Details of these sulfur removal steps and the second leaching step will be described later.

The leaching of gold in the first leaching step proceeds by reacting the eluted gold with chloride ions or bromide ions to form a gold chloride complex or a gold bromide complex. In particular, by using bromide ions, a complex is formed in a lower potential state, so that the leaching efficiency of gold can be improved. Further, as for iron ions, trivalent iron ions oxidized under the supply of an oxidizing agent or trivalent iron ions from the beginning act to oxidize gold. The acidic aqueous solution 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.

As the halide ion in the acidic aqueous solution, only the bromide ion can be used. Alternatively, it is possible to further contain chloride ions in addition to the bromide ions, but in this case, it is preferable that the chloride ion concentration is low.
The concentration of the bromide ion is preferably 50 g / L or more, more preferably 80 g / L or more, particularly 150 g / L or more, from the viewpoint of further improving the leaching rate of gold. There is no particularly preferable upper limit of the bromide ion concentration, but it is desirable that the concentration is equal to or less than the solubility of the metal bromide to be added. On the other hand, the concentration of chloride ions can be, for example, 40 g / L or less, and more preferably 25 g / L or less. Furthermore, it is even more preferable that the halide ion in the acidic aqueous solution is only the bromide ion and no chloride ion is present in the acidic aqueous solution.

The iron ion concentration in the acidic aqueous solution can be 50 g / L or less, preferably 0.01 g / L to 10 g / L. Further, the copper ion concentration is preferably 1 g / L or more, more preferably 5 g / L or more, but in consideration of economic efficiency, it is not necessary to make the concentration excessively high, and it is not necessary to make the concentration excessively high, and it is necessary to use it in an acidic aqueous solution. The concentration of copper ions is generally 30 g / L or less, preferably 20 g / L or less.
The above-mentioned concentrations of bromide ion, chloride ion, copper ion and iron ion mean the concentration in the acidic aqueous solution before the acidic aqueous solution is brought into contact with the raw material.

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

When chloride ions are contained, the source thereof is not particularly limited, but examples thereof include hydrogen chloride, hydrochloric acid, metal chloride and chlorine gas, and in the form of metal chloride in consideration of economy and safety. It is preferable to supply. Examples of metals chloride include copper chloride (ferrous chloride, ferric chloride), iron chloride (ferrous chloride, ferric chloride), and alkali metals (lithium, sodium, potassium, rubidium, cesium, franchium). Chlorides and chlorides of alkaline earth metals (berylium, magnesium, calcium, strontium, barium, radium) can be mentioned, and sodium chloride is preferable from the viewpoint of economy and availability. Further, since it can be used as a source of copper ions and iron ions, it is also possible to use copper chloride and iron chloride.

Copper ions and iron ions are usually supplied in the form of these salts, and can be supplied, for example, in the form of halogenated salts. From the viewpoint that it can also be used as a source of chloride ion and / or bromide ion, it is preferable that copper ion is supplied as copper bromide and / or copper chloride, and iron ion is supplied as iron bromide and / or iron chloride. As copper chloride and iron chloride, cupric chloride (CuCl ₂ ), cuprous chloride (CuCl), ferric chloride (FeCl ₃ ), ferrous chloride (FeCl ₂ ) and the like are used. As copper bromide and iron bromide, cupric bromide (CuBr ₂ ), cuprous bromide (CuBr), ferric bromide (FeBr ₃ ), ferrous bromide (FeBr ₂ ), etc. are used. Will be done.

For example, the acidic aqueous solution includes at least one of hydrochloric acid and bromic acid, at least one of ferric chloride and ferric bromide, at least one of ferric chloride and ferric bromide, sodium chloride and odor. A mixed solution containing at least one of sodium bromide can be used.

The contact method between the acidic aqueous solution and the raw material is not particularly limited, and there are methods such as sprinkling and dipping, but from the viewpoint of reaction efficiency, a method in which the raw material is immersed in the acidic aqueous solution and stirred is preferable.

The redox potential (vs Ag / AgCl) of the acidic aqueous solution at the start of the first leaching step is preferably 500 mV or more, and more preferably 600 mV or more, from the viewpoint of promoting gold leaching. Further, from the viewpoint of increasing the leaching rate of gold, it is preferable to maintain the pH of the acidic aqueous solution at 2.0 or less, but since the higher pH of iron is promoted, the pH of the acidic aqueous solution is 0. It is more preferable to maintain it at 5 to 1.9.

The redox potential is controlled by carrying out the first leaching step while supplying an oxidizing agent. If no oxidizing agent is added, the redox potential will drop on the way and the leaching reaction will not proceed. The oxidizing agent is not particularly limited, and examples thereof include oxygen, air, chlorine, bromine, and hydrogen peroxide. No oxidant with an extremely high redox potential is required, air is sufficient.

It is preferable that the pulp concentration of the acidic aqueous solution to which the raw material is added is high because the leaching of copper can be suppressed, but if it is too high, the leaching rate of gold is lowered. From this viewpoint, the pulp concentration is preferably 200 g / L or less, and more preferably 15 g / L to 50 g / L. The pulp concentration means the ratio of the dry weight (g) of the raw material to the volume (L) of the acidic aqueous solution.

The redox potential at the time of gold leaching is not particularly adjusted, but the redox potential of the liquid after leaching after sufficient gold leaching is about 450 to 600 mV, typically about 500 to 580 mV.

An increase in the redox potential indicates a decrease in monovalent copper ions in the liquid after gold leaching. Monovalent copper is known as a very soft element and has a high affinity for activated carbon and competes with the adsorption of gold complexes. Due to this decrease in monovalent copper, the adsorption active sites in the activated carbon are more selective with respect to gold, so that efficient recovery of gold can be realized.

Such a first leaching step is completed when the leaching rate of iron from the raw material is, for example, 5% or more, preferably 15% or more, more preferably 30% or more, although it depends on the type of ore. can do. Further, the first leaching step is terminated when the leaching rate of iron from the raw material becomes the above ratio and the leaching rate of copper from the raw material becomes, for example, 5% or more, preferably 15% or more. May be good.
At this time, the leaching rate of gold from the raw material is preferably 85% or more, more preferably 90% or less, and particularly preferably 95% or less.

In addition to the above-mentioned leaching conditions, leaching can also be performed under the conditions described in Japanese Patent Publication No. 2005-523992 and the like. That is, under this condition, gold in the raw material is dissolved by leaching while supplying an oxygen-containing gas using an aqueous solution of copper (II) chloride-sodium chloride under atmospheric pressure conditions. Here, the redox potential is set to less than 650 mV, preferably 530 mV to 620 mV, and the pH can be maintained in the range of 1 to 3. In leaching under this condition, most of the iron component and sulfur component in the raw material are not dissolved, but a certain amount of sulfur component becomes elemental sulfur and remains in the leaching residue, and gold leaching occurs as described above. May interfere. Therefore, even when leaching is performed under these conditions, it is effective to carry out the sulfur removing step and the second leaching step, which will be described later, from the viewpoint of further improving the gold recovery rate.

(Sulfur removal process)
The leaching residue obtained in the first leaching step is subjected to a sulfur removing step for removing sulfur contained in the leaching residue. This sulfur removal step is performed as a step different from the leaching step of the first leaching step. As a result, gold covered with sulfur such as elemental sulfur in the leaching residue is exposed, and this can be effectively leached in the second leaching step described later.
In the sulfur removal step, the leachate residue is heated in a predetermined atmosphere to remove the sulfur in the leachate residue as a gas, or the leachate residue is washed with an alkaline solution to dissolve and remove the sulfur. Can be mentioned.

In the case of sulfur removal by heating, the leachate residue can be heated and held at a temperature of 450 ° C. or higher, which is the boiling point of sulfur, for example, to remove the sulfur in the leachate residue as a gas. If the holding temperature during heating is too high, the energy required for heating increases, so that the temperature can be set to 1000 ° C. or lower from the viewpoint of suppressing an increase in processing cost. Particularly preferably, the holding temperature of the leachate residue is set to 500 ° C. to 700 ° C. The time for maintaining the temperature is preferably 30 minutes to 180 minutes, more preferably 30 minutes to 60 minutes.
The atmosphere during heating can be a rare gas atmosphere such as argon or helium, an inert atmosphere including a nitrogen atmosphere, a carbon dioxide atmosphere, and the like. In this case, sulfur is removed as sulfur gas. Alternatively, it can be an oxidizing atmosphere such as in the air, and in this case, it is removed as _{SO 2 gas.}
Various furnaces such as a tube furnace and a rotary kiln furnace can be used for this heating.

In the case of removing sulfur by washing with an alkaline solution, an alkaline solution having a pH of preferably 10 to 14, more preferably 10 to 12 can be used, and specifically, the alkaline solution is a sodium hydroxide solution or water. Examples thereof include sodium oxide and sodium carbonate. If the pH of the alkaline solution is too high, not only will a large amount of alkali be required to raise the pH so much, but also a large amount of acid will be generated during the second leaching step of the next step and the treatment of the post-cleaning solution in which sulfur is dissolved. It will be necessary and will lead to an increase in cost. In addition, gold may become a thiosulfate complex or the like and dissolve in alkali. In this case, the gold can be recovered by using activated carbon, but when the pH is high, a large amount of sodium is contained and the gold to the activated carbon is added. Adsorption and elution may be hindered. On the other hand, if the pH is too low, the pH is further lowered due to the effects of sulfur dissolution and the hydrolysis reaction of the components in the liquid, and especially when the pH is 7 or less, hydrogen sulfide gas depends on the redox potential. May occur.
The liquid temperature at the time of washing with an alkaline solution can be 20 (room temperature) ° C. to 90 ° C., and particularly preferably 50 ° C. to 80 ° C. If the liquid temperature is too low, the dissolution rate of sulfur may be lowered, and if the liquid temperature is too high, there is a concern that heating costs will be high.
The washing time can be, for example, 60 minutes to 360 minutes, preferably 60 minutes to 180 minutes. If the washing time is too short, there is a concern that sulfur in the leachate residue cannot be sufficiently removed, while if the washing time is too long, the treatment efficiency is lowered.

In the removal of sulfur by heating, as described above, it is heated in a non-oxidizing atmosphere to remove it as sulfur gas, or heated in an oxidizing atmosphere and removed as _{SO 2 gas.}
Here, when heating in a non-oxidizing atmosphere, it is necessary to set the temperature to 450 ° C. or higher, and sulfur in the exhaust gas is dissolved and recovered in an alkaline solution using a scrubber. Alkaline drainage is generated. Such alkaline drainage is similar to the case where the leachation residue is directly washed with an alkaline solution as described above. Therefore, from this viewpoint, washing with an alkaline solution that does not require high-temperature heating and can be performed at a low temperature can be performed. Can be said to be preferable.
On the other hand, when heating in an oxidizing atmosphere, it is necessary to surely install a sulfuric acid production plant, which has a drawback that the equipment scale and cost increase.
For these reasons, in the sulfur removal step, it is preferable to wash the leachation residue with an alkaline solution to dissolve and remove the sulfur.

By performing the sulfur removal step as described above, sulfur can be removed from the leachate residue by preferably 10% or more, more preferably 25% or more. If sulfur is removed even a little here, gold can be further leached in the second leaching step described later, which leads to an improvement in the leaching rate of gold.

(Second leaching process)
After removing the sulfur in the leaching residue through the sulfur removing step, a second leaching step for leaching the gold in the leaching residue is carried out, and the leaching of gold is performed again. The second leaching step can be made under substantially the same conditions as the first leaching step described above, but here, the sulfur covering the gold remaining in the leaching residue after the first leaching step is used. Since the gold is removed by the gold-sulfur removal step and the gold is exposed, it can be effectively leached.

Since the components, pH, redox potential and other conditions of the acidic aqueous solution in the second leaching step are almost the same as those in the first leaching step, the description thereof will be omitted again.
By the second leaching step, the leaching rate of gold from the leaching residue can be preferably 10% or more, more preferably 30% or more.

(Adsorption process)
After leaching of gold, gold can be recovered from the liquid after leaching gold obtained by solid-liquid separation by utilizing activated carbon adsorption. The contact of gold with the activated carbon can be performed by a batch batch method or by continuously passing an acidic leachate through an adsorption tower filled with activated carbon.

In the case of the batch type, the stirring speed is not particularly limited, and the amount of activated carbon added is 50 to 10000 times the weight of gold.
In the case of the continuous liquid passing method, the liquid passing speed is not particularly limited (generally SV1 to 25). However, when the amount of gold adsorbed per unit weight of activated carbon reaches 20000 to 30000 g / t, the activated carbon may be found to have a reduced adsorption capacity. Therefore, gold stripping and regeneration from activated carbon can be performed using this adsorption amount as a guide. The method for regenerating activated carbon can be carried out by various methods such as generally known sulfur compounds, nitrogen compounds, and acids.

(Washing process)
Next, a cleaning step can be performed in which the activated carbon on which gold is adsorbed in the adsorption step is washed with an acidic solution or an alkaline solution as a cleaning agent. Cleaning with an alkaline solution such as NaOH can effectively remove sulfur that may be adsorbed on activated carbon, and cleaning with an acidic solution such as hydrochloric acid can effectively remove copper that may be adsorbed on activated carbon. And iron can be effectively removed. The acid cleaning and the alkaline cleaning can be performed only by one of them, or both can be performed, and it is also possible that this cleaning step is not performed without performing either of them.

(Elution process)
Gold adsorbed on the activated carbon, an alkaline solution, preferably eluted with the mixed liquid of NaOH, or an NaOH and Na ₂ S. Here, if the alkali concentration is low, it becomes difficult to elute gold, and if the alkali concentration is high, there is a risk of heat generation during preparation. From this point of view, when NaOH is used, its concentration is preferably 0.05 to 1 M, more preferably 0.1 to 0.5 M. Further, Na ₂ S is preferably more amount is low the difficulty of price and handling, correspondingly decreases the eluting effect of gold the lower the concentration of Na ₂ S. On the other hand, if _{the concentration of Na 2} S is too high, no further effect can be expected, and the processing burden of _{Na 2 S also increases.} From this point of view, _{when a solution in which NaOH and Na 2} S are mixed is used, the _{amount of Na 2} S added is preferably 0.1 to 10 mol times the amount of NaOH, and is 0.5 to 1.5. It is more preferable to use a molar amount.

The elution can be performed by a batch batch method or a continuous water flow method, but in order to prevent the charge from being lost due to the oxidation of sulfide by oxygen and the gold being re-adsorbed on the activated carbon or deposited in the reactor. When elution is performed in a batch system, it is preferable not to stir vigorously. If stirring is required, replace the air with a non-oxidizing gas and stir. Alternatively, the amount of sodium sulfide added is set to a large amount, or the amount of sodium sulfide is added in a timely manner. Further, the elution is preferably performed under atmospheric pressure.

A concentrated gold solution can be obtained by elution from activated carbon. The concentrated gold solution means a solution containing 50 to 5000 mg / L of gold. As a method for producing gold by reduction from a concentrated gold solution, a reduction method using sodium oxalate, a chemical reduction method using sulfur dioxide, or a solvent extraction-electrowinning method is known. You can get money.

Next, the gold leaching method of the present invention was carried out on a trial basis and its effect was confirmed, which will be described below. However, the description here is for the purpose of mere illustration, and is not intended to be limited thereto.

(Gold form and gold leaching rate in raw materials)
When the existence form of gold in the sulfide mineral mainly composed of pyrite was confirmed by the Diagnostic Leach Test, the results shown in Table 1 were obtained. When sulfide is leached by performing a non-oxidizing roasting step and a single leaching step, the estimated gold leaching rate should be 99.9%, but in the actual test, the graph in Fig. 2 shows. As shown by, the leaching rate of gold was only 94%.
Therefore, it can be seen that with the conventional leaching method, the remaining 6% of gold is supposed to be leached but not leached.

(Comparison example)
After performing the non-oxidizing roasting step and the first leaching step on the above-mentioned sulfide mineral, the second leaching step was carried out on the leached residue without performing the sulfur removing step. Here, in the second leaching step, an acidic aqueous solution having a liquid composition of Cu: 18 g / L, Fe: 2 g / L, Cl: 40 g / L, Br: 80 g / L and pH: 1 was used, and the temperature was 85 ° C. The leaching was carried out for 6 hours.
Table 2 shows the grades of each leaching residue before and after the second leaching step. The grade shown in Table 2 is the amount of each element when the above-mentioned leaching residue used in the second leaching step is 100 g, and “S-0” in Table 2 means elemental sulfur. In addition, Table 3 shows the sulfur removal rate and the gold leaching rate calculated from the changes in the amount of each component before and after the second leaching step as percentages. The analysis of each component was performed by high frequency inductively coupled plasma emission spectroscopy (ICP-AES).

As can be seen from Table 3, the leaching rate of gold in the second leaching step was as low as 12%. It is considered that this is because the removal rate of sulfur is only 10% and the dissolution rate of sulfur that inhibits the leaching of gold is slow, so that the gold is covered with sulfur.

(Example of Invention)
The grade of each leaching residue before the sulfur removing step and after the second leaching step, and sulfur The removal rate and the leaching rate of gold were measured and calculated. The results are shown in Tables 4 and 5. Here, in the cleaning in the sulfur removing step, a NaOH solution was used as the alkaline solution, the cleaning time was set to 3 hours, and the cleaning temperature was set to 60 ° C.

As can be seen from Table 5, about 77% of sulfur was removed by the sulfur removing step, and as a result, the leaching rate of gold in the second leaching step was about 90%.

Further, FIG. 3 shows a graph plotting the relationship between the gold recovery rate (gold leaching rate) and the sulfur removal rate for the above comparative examples and invention examples. From FIG. 3, it can be seen that the relationship between the gold recovery rate and the sulfur removal rate is linear with a slope of 1 and an intercept of 0. Then, it can be said that if sulfur is removed even a little, the gold recovery rate will increase, and if sulfur is removed, the gold recovery rate will increase as much as the removal.

From the above, it was found that, according to the present invention, by removing sulfur, gold whose leaching was inhibited can be effectively leached.

Claims (8)

A method of leaching gold contained in gold and a raw material containing sulfur as a sulfide mineral or a smelting intermediate obtained by subjecting the sulfide mineral to a smelting treatment.
A first leaching step of leaching a part of gold in the raw material to obtain a leaching residue containing gold and sulfur remaining, a sulfur removing step of removing sulfur in the leaching residue, and a sulfur removing step were performed. a second leaching step of leaching at least a portion of the remainder of the gold in the leach residue seen including,
A method of leaching gold in which the leaching residue is brought into contact with an alkaline solution to remove sulfur in the leaching residue in the sulfur removing step. The method for leaching gold according to claim 1, wherein in the sulfur removing step, the gold in the leaching residue is exposed by removing the sulfur in the leaching residue. The method for leaching gold according to claim 1 or 2, wherein in the first leaching step, a leaching residue containing sulfur, which is at least partially in the form of elemental sulfur, is obtained. The method for leaching gold according to any one of claims 1 to 3, wherein the pH of the alkaline solution to be brought into contact with the leaching residue is 10 or more in the sulfur removing step. The method for leaching gold according to any one of claims 1 to 4 , wherein the removal rate of sulfur in the sulfur removal step is 10% or more. The method for leaching gold according to claim 5 , wherein the removal rate of sulfur in the sulfur removal step is 25% or more. The method for leaching gold according to any one of claims 1 to 6 , wherein in the first leaching step, the raw material is brought into contact with an acidic aqueous solution containing copper ions, iron ions and halide ions under the supply of an oxidizing agent. .. A method for recovering gold, which comprises recovering gold from a raw material by using the method for leaching gold according to any one of claims 1 to 7.

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