JP7525340B2 - How to recover precious metals - Google Patents

Description

The present invention relates to a method for recovering precious metals.

In Patent Document 1,
A method for selectively recovering lead and silver, comprising the steps of:
a) A hydrometallurgical residue containing at least lead and silver is subjected to oxidative leaching in the presence of sulfuric acid, a chloride brine solution and an oxidizing agent, which selectively dissolves lead and silver as soluble chloride compounds. The sulfuric acid dissolves lead as lead sulfate salt by reaction with sodium chloride (claim 1 of JP 2003-233663).

Patent Document 1 also describes that the above step a) is carried out at an oxidation-reduction potential (Ag/AgCl) of 100 to 350 mV, more preferably 300 mV, and at a pH of 0.5 to 4, more preferably a pH of 4.

Patent Document 1 also discloses a technology in which the hydrometallurgical residue consists of sulfates, and the sulfates are dissolved in a brine solution.

Special table 2016-532011 publication

As described in Patent Document 1, when leaching metals starting from sulfates, it is sometimes difficult to sufficiently leach silver, for reasons unknown, and it is particularly difficult to control the leaching rate of precious metals.

The object of the present invention is to provide a method for recovering precious metals (especially Au) from precious metal-containing compounds.

The first aspect of the present invention is a method for producing a cellular membrane comprising the steps of:
1. A method for recovering precious metals from a precious metal-containing compound, comprising:
The method for recovering precious metals includes a leaching step of causing a precious metal-containing compound and an oxidizing agent to be present in a brine solution having a Cl concentration of 100 g/L or more, setting the ORP (3.3 M KCl-Ag/AgCl) to 700 mV or more, and leaching the precious metal from the precious metal-containing compound into the brine solution.

A second aspect of the present invention is the invention according to the first aspect,
The pH of the brine solution is greater than 2 and less than or equal to 5.

A third aspect of the present invention is the method according to the first or second aspect,
The noble metal includes at least Au.

A fourth aspect of the present invention is the invention according to any one of the first to third aspects,
The method further includes a pre-leaching step of subjecting the precious metal-containing compound to an acid leaching treatment prior to the leaching step.

A fifth aspect of the present invention is the invention according to any one of the first to fourth aspects,
The method further comprises a post-leaching step in which the residue after the leaching step is subjected to a reducing leaching treatment.

According to the present invention, it is possible to recover precious metals (especially Au) from precious metal-containing compounds.

FIG. 1 is a flowchart of the precious metal recovery method according to this embodiment.

In this specification, the term "to" refers to a value greater than or equal to a given value and less than or equal to a given value.
The present embodiment will be described below. Fig. 1 is a flow chart of the method for recovering precious metals according to the present embodiment. The present invention relates to a method for leaching a precious metal-containing compound, particularly a gold-containing metal compound, in a solution with a high chlorine concentration by adjusting the oxidation-reduction potential and pH, and freely controlling the leaching of gold or other metals.

In this embodiment, "precious metal" refers to a rare metal that is difficult to form a compound with, and specifically refers to at least one of gold (Au), silver (Ag), palladium elements such as ruthenium (Ru), rhodium (Rh), and palladium (Pd), and platinum elements such as osmium (Os), iridium (Ir), and platinum (Pt).

In this embodiment, the "precious metal-containing compound" is not limited as long as it is a compound that contains a precious metal. In this embodiment, the residue generated in metal smelting (particularly zinc smelting) is exemplified. In addition, the residue as the precious metal-containing compound may contain a precious metal, and may also contain at least one of Zn (zinc), Pb (lead), Cu (copper), Sn (tin), Cd (cadmium), arsenic, and silicon in the form of a metal, intermetallic compound, or oxide.

There is no particular limit to the amount of precious metal contained in the precious metal-containing compound, but it can be, for example, 0.1 to 5000 ppm.

An example of the composition of the noble metal-containing compound (dry) is as follows.
Au: 0.1-15g/t (ppm)
Si: 1 to 50% by mass
Cu: 0.01 to 1% by mass
Sn: 0.01 to 10% by mass
Ag: 0.005 to 0.5% by mass
Pb: 0.1 to 50% by mass

One of the major features of this embodiment is that it includes a leaching step in which precious metals are leached from a precious metal-containing compound into a brine solution under predetermined conditions. The details of the predetermined conditions are as follows.
- The Cl concentration of the brine solution should be 100 g/L or more.
-Adjust the pH to 1-5.
A precious metal-containing compound and an oxidizing agent are present in the brine solution.
ORP (3.3M KCl (internal solution)-Ag/AgCl (reference electrode)) is set to 700 mV or higher.

In this embodiment, it is preferable to set the Cl concentration in the brine solution to 100 g/L or more (preferably 180 g/L or more, more preferably 200 g/L or more). It may be even higher, such as 300 g/L or 400 g/L. It may also be set according to the saturation concentration of metals dissolved in the solution.

The brine may be prepared as follows:
The total halogen concentration of the brine solution may be set to 100 g/L or more (preferably 180 g/L or more, more preferably 200 g/L or more), while the Br concentration is less than 100 g/L and the Cl concentration exceeds 1/3 of the total halogen concentration. Preferably, the Cl concentration is set to exceed 1/2 of the total halogen concentration, more preferably, the Cl concentration is set to be equal to the total halogen concentration. Also, preferably, the Br concentration is set to 10 g/L or less, more preferably, the Br concentration is set to 1 g/L or less.

The halogen source is not limited, and examples thereof include sodium chloride (NaCl), calcium chloride (CaCl ₂ ) or its hydrate, hydrochloric acid (HCl), etc., which have high solubility in water. When Br is also used as the halogen, examples thereof include sodium bromide (NaBr), etc.

The oxidizing agent is not limited as long as it can leach precious metals from the precious metal-containing compound, and examples include hypochlorous acid (HClO) or its salts (e.g., NaClO) or its hydrates, potassium permanganate ( _KMnO4 ), oxygen ( _O2 ) or ozone ( _O3 ), and/or hydrogen peroxide ( _H2O2 ), particularly NaClO and/ _{or KMnO4} .

In the present invention, ORP (3.3M KCl-Ag/AgCl) is +199 mV (vs. SHE, 25°C) against the standard electrode, which is the so-called oxidation-reduction potential (vs. Ag/AgCl). In other words, the ORP value may be achieved by adding the above-mentioned oxidizing agent. By satisfying the above conditions and setting the ORP to 700 mV or more (preferably 800 mV or more, more preferably 950 mV or more, and even more preferably 1000 mV or more), the precious metals can be leached into the brine solution, and thus the precious metals can be recovered. As a result, if there is a halogen with Cl as the main component of the brine solution and the above-mentioned oxidizing agent, the precious metals can be recovered.

The pH of the brine solution is preferably between 1 and 5. If the pH of the brine solution is 5 or less, the precious metals can be leached more effectively.

The preferred range of the pH of the brine solution will be explained in more detail. It is more preferable that the pH of the brine solution is greater than 2 and less than 5. As shown in the Examples section below, by adopting the technical concept of the present invention, even if the pH of the brine solution is relatively high (a pH greater than 2 and less than 5, more specifically 3 to 5, and even more specifically 4 to 5), it becomes possible to leach precious metals that would not be easily leached. For example, even Au, which is one of the precious metals (hereinafter, precious metals that contain at least Au, are exemplified), can be leached under conditions of about pH 4, as shown in the Examples section below. This is an extremely advantageous effect in terms of cost, simplification of equipment specifications, reduction in the amount of neutralizing agent used in wastewater treatment, and work efficiency of leaching.

There is no particular limit to the temperature of the brine during the leaching process, but a temperature of 60 to 95°C is preferred, and 90 to 95°C is more preferred.

When the precious metal-containing compound is a metal smelting residue, the precious metal (e.g., Au) is present in a silicic acid ( _SiO2 ) compound or miscellaneous metal compounds, and the form of Au is unknown. Nevertheless, by adopting the technical concept of the present invention, it is possible to leach even a small amount of Au from the precious metal-containing compound.

The above means that precious metals can be recovered even when the silicate content in the precious metal-containing compound is 2% by mass or more, or even 10% by mass or more.

<Treatment process design>
The leaching of various metals in precious metal-containing materials may be carried out in a multi-stage process. For example, the precious metal leaching process described above is the main leaching, and there are treatment processes in which leaching is carried out before and after the main leaching, pre-leaching, main leaching, and repetition of these. Leaching is carried out on each residue generated after each leaching. If filtration is inserted between the two, the filtrate after filtration may be subjected to a liquid recovery process such as neutralization, and the residue fixed in the liquid recovery process or the residue after filtration may be the target of leaching in each process.

In this embodiment, the reason for providing a staged process of pre-leaching and main leaching is that by dividing the leaching into multiple stages, it becomes easier to separate and recover each metal according to its solubility. Therefore, whether to separate and recover each metal by leaching, or to perform a single leaching step followed by subsequent separation treatment (neutralization, etc.) is determined according to the leaching target.

Since pre-leaching is a preliminary leaching with acid, the potential and pH may be set depending on the metal to be leached in pre-leaching. In addition to brine, mineral acids (sulfuric acid, nitric acid, hydrochloric acid) may be used as the leaching solution. If the leaching solution is the same for pre-leaching and main leaching, the contents of pre-leaching may be carried out during main leaching. The pH may be a strong acid of 1 or less. For example, copper and iron may be leached with a potential of 500 mV or less. Even if the pre-treatment is a strong acid or low potential, it is possible to efficiently leach precious metals if the conditions for main leaching are met. The nature of the residue changes due to pre-treatment, but in the case of smelting residues, internal compounds rarely recombine, and even a small amount of precious metal will ultimately remain in the residue.

The pre-leaching process primarily leaches out metals other than precious metals (e.g. Pb) in advance, and the role of the pre-leaching process is to expose or increase the reactivity of the target precious metal (e.g. Au) during the main leaching process. Note that precious metals (e.g. Ag) may also be leached in the pre-leaching process. An example of an application is when the precious metal-containing compound is zinc smelting residue, and there is lead-silver residue containing lead, silver, silicon and other metals.

As a specific example of the method of this leaching process, a precious metal-containing compound is placed in a weakly acidic (e.g. pH = 3-5, e.g. 4) brine solution, and an oxidizing agent (e.g. sodium hypochlorite, i.e. NaClO solution) is added to set the ORP (3.3 M KCl-Ag/AgCl) to 600-1300 mV (e.g. 700 mV), and this leaching process is carried out. In this leaching process, a brine solution is used, and an oxidizing agent is added to increase the ORP, making it possible to leach Au (gold) at a relatively high pH, which is in the weak acid range.

In a preferred embodiment of the present invention, the precious metal (Au) can be leached within the pH range of the weak acid. This means that the pH of the brine in the main leaching process can be made equivalent to the pH of the weak acid in the pre-leaching process, which means that there is no need to take the trouble of preparing strong acid-compatible equipment just for the main leaching process, which in turn means that there is an advantage in terms of cost.

As shown in the Examples section below, this leaching process results in a leaching rate of the precious metal (Au) of 50% or more (preferably 55% or more, and particularly 90% or more when NaClO is used as the oxidizing agent). The "leaching rate" is a value that indicates how much of the precious metal (Au) in the precious metal-containing compound is leached into the brine solution by mass.

After the main leaching process, it is preferable to carry out a post-leaching process on the residue that remains. In this case, it is preferable to carry out a reductive leaching process to further leach selected metals (e.g. Sn, Pb) from the residue and to stabilize the residue.

As a specific method for the post-leaching process, a known method for reductive leaching may be adopted. As an example, the residue after the main leaching process may be put into a separate brine solution, and a pH adjuster (HCl, NaCl, etc.) and a reducing agent (known reducing agents can be used, for example iron powder) may be added to the brine solution to carry out the post-leaching process. The conditions of the brine solution and the conditions such as the liquid temperature during leaching may be the same as those for the main leaching process.

After this leaching process, a recovery process (e.g., electrolytic deposition process) may be carried out to recover precious metals from the brine solution. The specific method of the recovery process may be any known method. For example, the brine solution (containing Au, etc.) after this leaching process may be neutralized to increase the pH, and Fe, Cu, etc. may be precipitated and separated, after which Au may be recovered by electrolytic deposition, etc.

Pb, Ag, etc. may be recovered from the brine after the pre-leaching step.
Sn, Pb, etc. may be recovered from the brine after the post-leaching step.
The brine solution after the pre-leaching step and the brine solution after the post-leaching step (particularly the brine solution after the pre-leaching step) may be combined with the brine solution after the main leaching step to recover metals present in the solution, or metals may be recovered from each brine solution separately.
The final residue after the post-leaching step may be washed and transferred to existing metal smelting processes.

The technical scope of the present invention is not limited to the above-described embodiments, but includes forms with various modifications and improvements within the scope that can derive specific effects obtained by the constituent elements of the invention and their combinations.

The present invention will now be described in detail with reference to examples. The present invention is not limited to the following examples. Any content not described below is the same as that described in this embodiment.

<Noble metal-containing compounds used in Examples 1 and 2 and Comparative Example 1>
A precious metal-containing compound (metal smelting residue containing a composite oxide) having the following composition was prepared. The following composition was measured by chemical analysis in a solution. The results are shown in Table 1 below.

<Examples 1 and 2>
The above-mentioned precious metal-containing compound and the oxidizing agent shown in Table 2 were present in a brine solution (halogen was Cl only) formed from a halogen source shown in Table 2, and this leaching process was carried out to leach Au from the precious metal-containing compound into the brine solution at the pH value and ORP (3.3M KCl-Ag/AgCl) value shown in Table 2. HCl was used as a pH adjuster to set the above pH value. The temperature of the brine solution was 90°C, the PD (slurry concentration) was 100g/L, and the leaching time was 180 minutes. The stirring blade was a two-stage disk turbine. All of the brine solutions shown in Table 2 were aqueous solutions.

<Comparative Example 1>
The above-mentioned precious metal-containing compound was present in a brine solution formed from a halogen source shown in Table 2, and a leaching step was carried out in which Au was leached from the precious metal-containing compound into the brine solution at the pH and ORP (3.3M KCl-Ag/AgCl) values shown in Table 2. HCl was used as a pH adjuster to set the above pH value. The temperature of the brine solution was 90°C, the PD (slurry concentration) was 100g/L, and the leaching time was 180 minutes. An inclined paddle was used for stirring.

<Examples 3 to 5>
A pre-leaching step was carried out on the same precious metal-containing compound as that used in Examples 1 and 2 and Comparative Example 1. The details of the pre-leaching step were the same as those in Comparative Example 1.
The leaching process was then carried out according to the details in Table 2. The stirring was carried out using an inclined paddle. The other details were the same as in Example 1.

Example 6
A pre-leaching step was carried out on the same precious metal-containing compound as that used in Examples 1 and 2 and Comparative Example 1. The details of the pre-leaching step were the same as those in Comparative Example 1.
The leaching process was then carried out according to the details in Table 2. The stirring was carried out using an inclined paddle. The other details were the same as in Example 1.

<Results>
The leaching results in Examples 1 to 6 and Comparative Example 1 are shown in Table 3 below. The leaching results were obtained by analyzing the brine after the leaching process using an ICP analyzer (iCAP6000 manufactured by Thermo Scientific). The leaching rate is a value calculated from the leaching amount, with the content of the above-mentioned precious metal-containing compound as the standard (100 mass%).

In Examples 1 to 5, the leaching rates were 72.2 to 97.7% by mass for silver (Ag), 0 to 99.1% by mass for lead (Pb), 0 to 63% by mass for tin (Sn), 0 to 4.3% by mass for silicon (Si), and 57.1 to 100% by mass for gold (Au). Of the elements, it was found that gold and silver could be highly leached at over 90% depending on the conditions. Furthermore, the leaching rates for tin and silicon could be suppressed to 0%.

In Examples 1 to 6, it was found that by using a high chlorine concentration solution in which the potential, pH, and type of oxidizing agent were controlled, it was possible to achieve a high level of leaching rate of various metals and also to control the leaching of various metals.

When processing raw materials containing multiple metal components, it was found that it is possible to control the leaching of various metals, and in particular, it is possible to separate and recover gold and silver from other metal components.

As shown in Table 3, the Au leaching rate was higher in Examples 1 to 6 than in Comparative Example 1. In addition, even though silicic acid was present in the precious metal-containing compounds of Examples 1 and 2 at 13.13 mass%, and silicic acid was present in the precious metal-containing compound of Example 3 at 23.19 mass%, the Si leaching rate was extremely low. The Sn leaching rate was also extremely low.

In Examples 3, 5, and 6, Au could be leached even though the pH was relatively high (corresponding to a weak acid) at 4 or 5 in the pre-leaching process and main leaching process. The leaching rate of Au was high (30% or more). The leaching rate of Ag was 70% or more. This shows that by using the method of the present invention, the precipitation separation operation by controlling the pH and the leaching process can be performed simultaneously, making it possible to easily separate metals other than gold, etc.

As described above, it has become clear that this embodiment can recover precious metals (especially Au) from precious metal-containing compounds. In particular, it has become clear that, as in Examples 3, 5, and 6, precious metals such as Au can be leached even at a pH of 3 to 5.

Claims (5)

1. A method for recovering precious metals from a precious metal-containing compound, comprising:
The method includes a leaching step of causing a precious metal-containing compound and an oxidizing agent to be present in a brine solution having a Cl concentration of 100 g/L or more, setting an ORP (3.3 M KCl-Ag/AgCl) to 700 mV or more, and leaching a precious metal from the precious metal-containing compound into the brine solution,
The brine solution contains at least one of sodium chloride, calcium chloride, or a hydrate thereof as a halogen source, and has a pH of 1 or more and 5 or less.
How to recover precious metals. The method for recovering precious metals according to claim 1, wherein the pH of the brine solution is greater than 2 and less than or equal to 5. The method for recovering precious metals according to claim 1 or 2, wherein the precious metals include at least Au. The method for recovering precious metals according to any one of claims 1 to 3, further comprising a pre-leaching step in which the precious metal-containing compound is subjected to an acid leaching treatment prior to the leaching step. The method for recovering precious metals according to any one of claims 1 to 4, further comprising a post-leaching step in which a reductive leaching treatment is performed on the residue after the leaching step.

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