JP7571501B2 - Method for obtaining chlorine leachate from platinum group metal-containing material - Google Patents

Description

The present invention relates to a method for subjecting a platinum group element-containing material containing gold as an impurity element to chlorine leaching and then obtaining a chlorine leachate by solid-liquid separation treatment, and more specifically, to a method for obtaining a chlorine leachate in which the gold content has been effectively reduced.

Conventionally, methods for recovering precious metal elements from copper electrolytic slime have centered on removing copper from the copper electrolytic slime using a wet method, separating selenium, antimony, lead, tin, bismuth, tellurium, etc. using a dry method, and finally obtaining an alloy of gold, silver, and platinum group metals, which is then electrolyzed. However, such conventional methods have problems such as a long time until the precious metals are recovered, resulting in a large interest burden during the retention period in the system, a large amount of energy consumption, difficulty in automating the process because solid materials must be transported for each process, pollution of the work environment due to exhaust gases, and a low ability to adapt to slime compositions and compound forms.

In response to this, for example, Patent Document 1 proposes a method for selectively recovering gold, platinum group elements, selenium, and tellurium in high yields from copper electrolytic slime using only simple wet processing. The method disclosed in Patent Document 1 can effectively solve the problems of conventional methods.

As an improvement over the method disclosed in Patent Document 1, Patent Document 2 proposes a method in which, after recovering most of the gold, a process is added in which the platinum group elements are concentrated using an ion exchange resin to obtain a platinum group element concentrate (hereinafter also referred to as "PGM concentrate"; PGM: Platinum Group Metals), and the platinum group elements are preferentially recovered.

Specifically, the method involves using PGM concentrate as the starting material, carrying out chlorine leaching under conditions that facilitate the leaching of platinum group elements, and obtaining a PGM leachate (hereinafter also referred to as "chlorine leachate") and a residue (leach residue) in a solid-liquid separation process. Since the platinum group elements have been preferentially leached out of the obtained PGM leachate by the chlorine leaching, the platinum group elements can be effectively recovered by further processing in a post-process.

JP 2001-207223 A JP 2013-104064 A

In the method disclosed in the above-mentioned Patent Document 2, it is known that the PGM leachate obtained by chlorine leaching contains a small amount of gold, for example, about 0.2 g/L or less. This is because most of the gold is recovered in the PGM concentrate, which is the starting material, and gold inevitably remains in the PGM leachate obtained by leaching the PGM concentrate. For this reason, gold has traditionally been extracted in a post-process using a solvent extraction method (Au.Sb-SX). The extracted gold is recovered as reduced gold powder by reduction stripping from an organic solvent, and is then repeatedly processed in the pre-process, the copper electrolytic slime leaching process.

However, depending on the raw material conditions, the PGM concentrate may contain more gold than before, and with conventional operations, for example, 2 to 4 g/L of gold (more than 10 times the conventional amount) may remain in the PGM leachate. This may increase the load on the downstream processing step using solvent extraction, resulting in reduced operational efficiency. For example, the amount of processing liquid per unit time may be as low as one-tenth, which is beyond the range that can be resolved by adjusting the solvent extraction conditions, and may require an additional solvent extraction unit, increasing operational costs.

The present invention has been proposed in light of these circumstances, and aims to provide a method that can effectively reduce the amount of gold contained in the leachate obtained by chlorine leaching of a platinum group element-containing material that contains at least gold as an impurity element, and can prevent, for example, a decrease in the operational efficiency of the solvent extraction process in the subsequent process.

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, they discovered that by subjecting a platinum group element-containing material, including gold, to chlorine leaching, and then adding a reducing agent to the resulting slurry prior to solid-liquid separation treatment to reduce the gold, it is possible to efficiently precipitate and remove the reduced gold, effectively reducing the gold content in the leachate, and thus completed the present invention.

(1) The first aspect of the present invention is a method for subjecting a platinum group element-containing material containing gold as an impurity element to chlorine leaching, and then obtaining a chlorine leachate by solid-liquid separation treatment, in which a reducing agent is added to the slurry obtained by the chlorine leaching before the solid-liquid separation treatment to reduce the gold contained in the slurry, and the chlorine leachate is separated from a leach residue containing a precipitate of reduced gold by the solid-liquid separation treatment.

(2) The second aspect of the present invention is the method according to the first aspect, in which the reducing agent includes hydrazine.

(3) The third invention of the present invention is the method of the second invention, in which the hydrazine is added in a fixed amount in the range of 0.1% by volume to 0.3% by volume per 1000 L of the supernatant liquid of the slurry.

(4) The fourth aspect of the present invention is the method according to the first aspect, in which the reducing agent contains sodium sulfite.

(5) The fifth aspect of the present invention is the method of the fourth aspect, in which the amount of sodium sulfite added is controlled based on the redox potential of the slurry.

According to the present invention, it is possible to effectively reduce the gold content in the resulting leachate. This also makes it possible to prevent a decrease in the operational efficiency of the solvent extraction process in the subsequent process.

FIG. 1 is a process diagram showing an example of the flow of a method according to the present embodiment.

A specific embodiment of the present invention (hereinafter also referred to as "the present embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and can be implemented with appropriate modifications within the scope that does not change the gist of the present invention.

The method according to this embodiment involves subjecting a platinum group element-containing material, which contains gold as an impurity element, to chlorine leaching, and then obtaining a chlorine leachate by solid-liquid separation.

The platinum group element-containing material is not particularly limited, and may be a platinum group element concentrate (hereinafter referred to as "PGM concentrate") containing various impurity elements obtained from by-products of non-ferrous metal smelting such as copper, nickel, cobalt, and various used waste catalysts such as automobile exhaust gas treatment catalysts. The PGM concentrate used in this method contains at least gold as an impurity element. Other impurity elements include main metals such as copper, nickel, cobalt, and iron, and other constituent elements such as silver, lead, tin, selenium, tellurium, arsenic, antimony, and bismuth. An example of such a platinum group element-containing material containing at least gold as an impurity element is a product obtained by treating anode slime to concentrate precious metals (PGM conc.).

For example, as disclosed in Patent Document 2, in the separation and recovery of platinum group elements, a PGM concentrate is subjected to chlorine leaching to obtain a leachate from which the platinum group elements have been leached (PGM leachate, chlorine leachate).

In operations to obtain PGM leachate from such PGM concentrate as a starting raw material, the gold content in the PGM leachate obtained by chlorine leaching may be high, for example, when the copper electrolytic slime contains a high gold content, or when the PGM concentrate is mixed with miscellaneous raw materials such as residues or solids containing platinum group elements recovered from other processes. The reason why the gold content in the copper electrolytic slime is high is because there is a business requirement to increase gold production, which may increase the gold content in the gold ore, which is the raw material for copper smelting. Similarly, there is a business requirement to recover platinum group elements from miscellaneous raw materials, which may contain high concentrations of gold.

Conventionally, the gold content in the PGM leachate obtained by chlorine leaching is about 0.2 g/L, and gold has been separated and recovered by a subsequent solvent extraction process. However, due to the above-mentioned circumstances, if the gold content in the PGM leachate increases to about 2-4 g/L, the load required to separate the gold in the solvent extraction process (Au-Sb-SX) will exceed the limit. In other words, there is too much gold and it cannot be processed by solvent extraction, and measures such as reducing the amount of processing liquid will be required.

It is easy to imagine that the solution to this problem would be to reduce the gold concentration in the PGM leachate, but due to the business requirements mentioned above, it is not possible to choose a method that reduces the gold in the raw materials upstream of the process. Therefore, appropriate measures must be taken in the process after chlorine leaching of the PGM concentrate (which may contain a mixture of miscellaneous raw materials). One possible method for reducing the gold concentration in the liquid phase (supernatant) of the slurry immediately after chlorine leaching is to suppress the degree of leaching of the PGM concentrate, but this method is not an option because it would also reduce the leaching rate of the platinum group elements. Therefore, it is necessary to effectively reduce the gold content in the resulting PGM leachate under conditions that allow the platinum group elements to be preferentially leached to the maximum extent from the PGM concentrate.

Therefore, in the method according to the present embodiment, a platinum group element-containing material containing gold as an impurity element is subjected to chlorine leaching, and then a chlorine leachate is obtained by solid-liquid separation. In this method, a reducing agent is added to the slurry obtained by chlorine leaching to reduce the gold contained in the slurry (the leachate in the slurry).

Figure 1 is a process diagram showing the flow of the method according to this embodiment. As shown in the process diagram in Figure 1, after the chlorine leaching process (chlorine leaching process), a reducing agent is added to the slurry obtained by the leaching process (slurry containing a liquid phase leachate and leach residue) to reduce the gold (de-gold removal process). After that, the slurry is subjected to a solid-liquid separation process by filtration or the like to separate the chlorine leachate from the leach residue containing precipitates of reduced gold (solid-liquid separation process). Note that "reduced gold" refers to gold (gold powder) produced by reducing the gold ions in the slurry.

As described above, even if the gold concentration in the liquid phase of the slurry immediately after chlorine leaching becomes high, for example, to about 2 to 4 g/L or more due to raw material conditions, the gold content in the resulting PGM leachate can be effectively reduced by adding a reducing agent to the slurry to reduce the gold (de-gold treatment). In addition, a decrease in the operational efficiency of the solvent extraction process in the subsequent process can be effectively prevented.

Here, as a demetalization process for reducing the gold content in the PGM leachate, it is possible to separate the slurry (leach slurry) obtained by chlorine leaching into solid and liquid, and treat the leachate recovered by separating it from the leach residue. In addition, in the case of a method in which a reducing agent is added to the leachate after such solid-liquid separation, compared to a case in which a reducing agent is added to the leach slurry for treatment, the reducing agent acts only on the liquid phase, which has the advantage of saving the amount of reducing agent consumed by the leach residue when the reducing agent is added to the slurry containing the leach residue.

However, in the case of a method in which a reducing agent is added to the separated and recovered leachate after solid-liquid separation to perform demetalization, the reduction reaction produces gold-containing precipitates in the leachate, making it necessary to separate the leachate into solid and liquid again (requiring a separate solid-liquid separation process). This increases processing costs even more than the increased amount of reducing agent used, and can also cause a significant drop in operating efficiency.

For this reason, the method according to the present embodiment is characterized in that the slurry obtained by chlorine leaching is the target of the demetalization process, and a reducing agent is added to the slurry before the solid-liquid separation process (before the solid-liquid separation step) to reduce the gold. This method makes it possible to carry out efficient processing without the need to provide a new solid-liquid separation step to remove the precipitate, the main component of which is reduced gold, that is generated as a result of the effective reduction of the gold concentration in the leachate.

The reducing agent to be added in the degold removal process is not particularly limited, but it is preferable to use hydrazine, sodium sulfite, etc. These reducing agents are particularly inexpensive and readily available, so they can effectively reduce gold while achieving economically efficient processing.

For example, the reducing agent hydrazine is not only an inexpensive and easily available reducing agent as described above, but also a reducing agent that is stable in a liquid state within the treatment temperature range. In this respect, by using a reducing agent containing hydrazine, stable treatment can be performed without causing blockage of the supply path when supplying the reducing agent to the treatment tank holding the slurry.

On the other hand, however, in the treatment using a reducing agent containing hydrazine, the change in the oxidation-reduction potential (ORP) of the slurry accompanying the addition of hydrazine is gradual. Therefore, when treatment is performed while monitoring the ORP of the slurry, the amount of hydrazine added tends to increase. Since the PGM leachate obtained by chlorine leaching of the PGM concentrate naturally contains the platinum group elements to be separated and recovered, the excessive addition of hydrazine leads to the reduction of the platinum group elements platinum (Pt) and palladium (Pd), and these platinum group elements are distributed to the leach residue (leach residue containing precipitates produced by reduction) and become losses, which can also cause a decrease in the recovery rate of the platinum group elements.

For this reason, in demetalization treatment using a reducing agent containing hydrazine, it is preferable to add a fixed amount of hydrazine rather than controlling the amount of reducing agent added based on the ORP of the slurry. Specifically, the amount of hydrazine to be added is not particularly limited, but it is preferable to add a fixed amount in the range of 0.1% to 1.2% by volume, and more preferably 0.2% to 0.5% by volume, per 1000 L of the supernatant liquid (liquid phase) of the slurry. By adding a fixed amount in such a range, gold can be preferentially reduced and precipitated, and effective treatment can be achieved while suppressing the reduction of platinum group elements contained in the slurry.

If the amount of hydrazine added is less than 0.1% by volume, the amount of reducing agent may be too small to effectively reduce the gold contained in the liquid phase of the slurry. On the other hand, if the amount of hydrazine added is more than 1.2% by volume, the amount added may be excessive, and platinum group elements such as platinum and palladium may also be reduced, resulting in a decrease in the recovery rate of platinum group elements.

For example, the reducing agent sodium sulfite is an inexpensive and easily available reducing agent as described above, and can be easily applied to the treatment process, effectively reducing gold while achieving economically efficient treatment. Sodium sulfite is also an excellent reducing agent in terms of reactivity and responsiveness, and the ORP of the slurry responds appropriately with the addition of sodium sulfite, stabilizing in a short period of time.

For this reason, in demetalization processing using a reducing agent containing sodium sulfite, it is preferable to monitor the ORP of the slurry and control the amount of sodium sulfite added based on changes in the oxidation-reduction potential. This allows gold to be preferentially reduced and precipitated, while preventing excessive addition of reducing agent, suppressing the reduction of platinum group elements such as platinum and palladium, and preventing a decrease in the recovery rate of these platinum group elements. In addition, since the amount of reducing agent added can be controlled based on the ORP, the processing can also be automated.

However, since sodium sulfite is a sodium salt, it has the tendency to crystallize, and when supplying a reducing agent containing sodium sulfite, there is a possibility that the pipes that make up the supply path may become clogged, so it is advisable to take care in this regard.

When adding the above-mentioned reducing agents such as hydrazine and sodium sulfite, for example, the optimal amount to be added only to the liquid phase of the slurry may be determined in advance, and the amount added may be adjusted appropriately while monitoring the amount of gold recovered (the amount of gold removed from the liquid).

There are no particular limitations on the method for the solid-liquid separation process (solid-liquid separation process) of the slurry after the demetalization process (after the demetalization process), as long as it effectively separates the leachate that constitutes the liquid phase (supernatant) of the slurry from the leachate residue that contains the precipitate of reduced gold obtained by reduction. For example, this can be done by a process such as filtration.

As described above, the demetalization process is performed on the leaching slurry obtained by chlorine leaching, so the precipitate of reduced gold, which is the reduction product, can be separated by a solid-liquid separation process that separates the leaching residue in the same manner as in the past. For example, compared to when the demetalization process is performed on the PGM leachate recovered after solid-liquid separation process, a separate solid-liquid separation process to separate the precipitate of reduced gold is not required, making operation more efficient.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Common conditions]
Slurry (leached slurry) was collected immediately after chlorine leaching from a site where PGM concentrate was leached during operation, and the supernatant of the slurry (liquid phase only) was used as the original liquid for the treatment test. The slurry was collected at three different times selected from those when the gold concentration in the PGM concentrate was high, and the original liquid shown in Table 1 below was used. Table 1 shows the component composition of the liquid phase (no residue) after chlorine leaching and the oxidation-reduction potential (ORP) as a property.

1000 L of the liquid after degassing was collected as the original liquid to be treated, and a batch test was conducted using the supernatant without any residue. In the degassing process, steam was blown into the original liquid to remove acidic gases. Next, steam was blown into the original liquid to adjust the liquid temperature to about 60°C.

In the demetallization treatments in Examples 1 to 7, either the reducing agent [1] or the reducing agent [2] was used and added to the original solution in the amounts shown below.
Reducing agent [1]:
(Type) Sodium sulfite (powder, anhydrous sodium sulfite) (manufactured by Shinshu Chemical Industry Co., Ltd.)
(Amount added): Monitor the ORP and add until it reaches 560 mV or less.
Reducing agent [2]:
(Type) Hydrazine (liquid, hydrazine hydrate 60%) (manufactured by Otsuka MGC Chemical Co., Ltd.)
(Amount added) 0.2, 0.4, 0.6, and 0.8 vol% (= 0.2, 0.4, 0.6, and 0.8 mL, respectively) were added to 100 mL of liquid phase.

Analysis of metal components in the leachate was performed using ICP-AES (measuring device: Agilent, model number 5100).

[Example 1]
In Example 1, original liquid A was subjected to a demetalization treatment using sodium sulfite as a reducing agent [1], and the reducing agent was added until the ORP reached 560 mV while monitoring, thereby reducing the gold (Au) contained in original liquid A and generating a precipitate of reduced gold which was then removed. Table 2 below shows the results of component analysis of the liquid after the demetalization treatment (post-gold-removal liquid) and the removal rate.

As shown in Table 2, the Au concentration in the demetallized solution was less than 0.2 g/L (removal rate of 96.7%), effectively reducing Au. In addition, the removal rate of platinum (Pt) and palladium (Pd) contained in original solution A was low at less than 1.5%, resulting in almost no loss of platinum group elements due to the demetallization process.

In addition, no problems occurred during the subsequent solvent extraction process of the degold removal liquid, including an increase in the processing load.

[Example 2]
In Example 2, the same treatment as in Example 1 was carried out, except that in the demetalization treatment, a reducing agent was added until the ORP reached 540 mV. Table 3 below shows the results of component analysis of the liquid after demetalization and the removal rate.

As shown in Table 3, the Au concentration in the demetallized solution was less than 0.2 g/L (removal rate of 99.9%), effectively reducing Au. In addition, the removal rate of Pt and Pd contained in original solution A was low at less than 1.7%, and there was almost no loss of platinum group elements due to the demetallization process.

In addition, no problems occurred during the subsequent solvent extraction process of the degold removal liquid, including an increase in the processing load.

[Example 3]
In Example 3, original liquid B was subjected to a degold removal treatment using hydrazine as a reducing agent [2], adding 0.2% by volume (2 L) to the volume (1000 L) of original liquid B, reducing the Au contained in original liquid B and generating precipitates of reduced gold which were then removed. Table 4 below shows the results of the component analysis of the liquid after degold removal and the removal rate.

As shown in Table 4, the Au concentration in the demetallized solution was less than 0.2 g/L (removal rate of 98.8%), effectively reducing Au. In addition, the removal rate of Pt and Pd contained in original solution B was low at less than 3.5%, and there was almost no loss of platinum group elements due to the demetallization process.

In addition, no problems occurred during the subsequent solvent extraction process of the degold removal liquid, including an increase in the processing load.

[Example 4]
In Example 4, the same treatment as in Example 3 was carried out, except that 0.4% by volume (4 L) of the reducing agent was added to the volume (1000 L) of the original liquid B. Table 5 below shows the results of the component analysis of the liquid after gold removal and the removal rate.

As shown in Table 5, the Au concentration in the demetallized solution was 0 g/L (100% removal rate), effectively reducing Au. In addition, the removal rate of Pt and Pd contained in original solution B was low at less than 3.5%, and there was almost no loss of platinum group elements due to the demetallization process. Furthermore, since the Au removal rate was 100%, it can be seen that there is no need to add any further reducing agent.

In addition, no problems occurred during the subsequent solvent extraction process of the degold removal liquid, including an increase in the processing load.

[Example 5]
In Example 5, the original liquid C was used and the same treatment as in Example 3 was carried out on the original liquid C. Table 6 below shows the results of component analysis of the liquid after degold removal and the removal rate.

As shown in Table 6, the Au concentration in the demetallized solution was less than 0.2 g/L (removal rate of 99.7%), effectively reducing Au. In addition, the removal rate of Pt and Pd contained in the original solution C was low at less than 3.0%, and there was almost no loss of platinum group elements due to the demetallization process.

In addition, no problems occurred during the subsequent solvent extraction process of the degold removal liquid, including an increase in the processing load.

[Example 6]
In Example 6, the same treatment as in Example 5 was carried out, except that 0.4% by volume (4 L) of the reducing agent was added to the volume (1000 L) of the original liquid C. Table 7 below shows the component analysis results and removal rate of the liquid after gold removal.

As shown in Table 7, the Au concentration in the demetallized solution was 0 g/L (100% removal rate), effectively reducing Au. In addition, the removal rate of Pt and Pd contained in original solution C was low at less than 3.6%, and there was almost no loss of platinum group elements due to the demetallization process. Furthermore, since the Au removal rate was 100%, it can be seen that there is no need to add any further reducing agent.

In addition, no problems occurred during the subsequent solvent extraction process of the degold removal liquid, including an increase in the processing load.

[Example 7]
In Example 7, the same treatment as in Example 6 was carried out, except that original liquid D was used and hydrazine, a reducing agent, was added in small amounts up to 0.66 volume % relative to the volume (1000 L) of original liquid D. Table 7 below shows the component analysis results and removal rates of the resulting post-gold removal liquids (post-gold removal liquids 1 to 5) for each amount of hydrazine added in small amounts.

As shown in Table 8, the Au concentration in the post-demetalization solution could be reduced further by increasing the amount of hydrazine added. For example, when the amount of reducing agent added was 0.3 vol%, the Au concentration was less than 0.1 g/L (removal rate of 98%), while the Pt removal rate was kept at 6.5%.

In addition, no problems, including an increase in processing load, occurred in the subsequent solvent extraction process for the demetalized liquid obtained by processing with either amount of additive.

[Comparative Example 1]
In Comparative Example 1, the demetalization treatment was not performed (the demetalization step was not provided), and the original liquid A was subjected to the solvent extraction treatment. As a result, a problem occurred in that the solvent extraction treatment took five times longer than the solvent extraction treatments in Examples 1 and 2, possibly due to the Au contained in the original liquid A.

Claims (5)

A method for obtaining a chlorine leachate by subjecting a platinum group element-containing material obtained from copper electrolytic slime, which contains gold as an impurity element, to chlorine leaching and then subjecting the material to solid-liquid separation, comprising the steps of:
a reducing agent is added to the slurry obtained by the chlorine leaching and having a gold content of 2 g/L or more before the solid-liquid separation treatment to reduce the gold contained in the slurry;
The chlorine leachate is separated from a leach residue containing precipitates of reduced gold by the solid-liquid separation treatment, and the chlorine leachate is subjected to a step of extracting gold by a solvent extraction method.
method. The reducing agent includes hydrazine.
The method of claim 1. The hydrazine is added in a quantitative amount in the range of 0.1% by volume to 0.3% by volume per 1000 L of the supernatant of the slurry.
The method of claim 2. The reducing agent includes sodium sulfite.
The method of claim 1. The amount of sodium sulfite added is controlled based on the oxidation-reduction potential of the slurry.
The method according to claim 4.

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