JP7359059B2 - Method for producing cadmium hydroxide - Google Patents

Description

The present invention relates to a method for producing cadmium hydroxide from a solution containing cadmium.

Zinc oxide ore obtained by separating and recovering impurities from crude zinc oxide and the like is widely used as a raw material for zinc ingots in zinc smelters. This crude zinc oxide can be obtained, for example, from steel dust generated from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry through reduction roasting treatment. Reuse as a resource is desirable.

Such crude zinc oxide derived from steel dust contains high proportions of halogen components such as chlorine and fluorine, and impurities such as cadmium, in addition to its main component, zinc oxide. Among these impurities, cadmium in particular has properties as a toxic metal, and in zinc oxide manufacturing plants, it is essential to separate and recover cadmium.

On the other hand, cadmium is used as a negative electrode material in nickel-cadmium batteries, making it an important useful metal as an electronic material.
By the way, as a method for separating and recovering cadmium, for example, a method is generally used in which impurities are roughly separated by wet treatment and then purified by dry treatment.

However, dry processing has the problem of high environmental and energy burden due to the use of fossil fuels and electricity. Therefore, there is a need for the development of a wet processing technology that can further improve the separation of impurities and suppress the use of fossil fuels and electricity in the dry process that follows the wet process.

In a wet processing technique that includes a wet process in which a target metal is precipitated by a cementation method or an electrowinning method, it is important to suppress the incorporation of impurities other than the target metal in advance during the precipitation process. Therefore, impurities other than the target metal are roughly separated in advance from the solution that becomes the precipitation mother liquor.

For example, the technology disclosed in Patent Document 1 is a wet processing technology in which impurities are roughly separated from a cadmium solution leached from dust with sulfuric acid using a purifying solution, and metallic cadmium is obtained using the roughly separated cadmium solution as a precipitation mother liquor. However, although liquid purification is performed through a complicated process using multiple agents such as oxidizing agents, alkaline agents, and carbonating agents, the amount of cadmium contained in the precipitated mother liquor is only 4.7 g/L. On the other hand, the impurity zinc contained 18.4 g/L, which is approximately four times the amount of cadmium, the target metal, and was poorly separated.
Against this background, there have been expectations for a wet processing technique for producing a cadmium solution containing highly purified and highly concentrated cadmium.

Patent No. 3762047

In order to solve these problems, the purpose of the present invention is to develop a wet processing technology for producing a high-purity cadmium solution, and specifically, to develop a method for producing a high-purity cadmium water as a starting material for producing the cadmium solution. An object of the present invention is to provide a method for producing an oxide.

As a result of extensive research to achieve the above object, the present inventors have found that a solution containing cadmium is used as a raw material solution, and the pH of the raw material solution is adjusted in a first pH adjustment step and a second pH adjustment step. The inventors have discovered that highly pure cadmium hydroxide can be produced by adjusting and treating in two steps, and have completed the present invention.

A first aspect of the present invention is to add a pH adjuster to a raw material solution containing cadmium so that zinc and lead in the raw material solution form a hydroxide and become a precipitate. After adjusting the pH to form a first slurry consisting of the precipitate and the filtrate from the raw material solution, the first slurry is subjected to a solid-liquid separation treatment to obtain the filtrate and the precipitate. and a pH adjusting agent is added to the filtrate obtained in the first pH adjusting step so that the pH is higher than the pH adjusted in the first pH adjusting step, and the cadmium contained in the filtrate is cadmium water. A second slurry containing the cadmium precipitate is prepared by adjusting the pH of the filtrate to a range where the formation of thallium precipitate is suppressed while forming an oxide to become the cadmium precipitate containing the cadmium hydroxide. After the cadmium hydroxide is produced, the second slurry is subjected to a solid-liquid separation treatment to obtain a cadmium precipitate containing the cadmium hydroxide.

A second invention of the present invention is a method of producing cadmium hydroxide according to the first invention, characterized in that the pH of the first pH adjustment step is adjusted to a range of 7.0 or more and 9.0 or less. This is the manufacturing method.

A third invention of the present invention is a method of producing cadmium hydroxide according to the first invention, characterized in that the pH in the first pH adjustment step is adjusted to a range of 7.5 or more and 8.5 or less. This is the manufacturing method.

A fourth invention of the present invention is a cadmium-based cadmium ion-coating method according to the first to third inventions, characterized in that the pH in the second pH adjustment step is adjusted to be 8.5 or more and 11.0 or less. This is a method for producing hydroxide.

A fifth invention of the present invention is a cadmium-containing compound according to the first to third inventions, characterized in that the pH in the second pH adjustment step is adjusted to be 9.5 or more and 10.5 or less. This is a method for producing hydroxide.

A sixth invention of the present invention is that in the first to fifth inventions, the cadmium-containing raw material solution contains 0.005% by mass or more of cadmium, 0.3% by mass or less of zinc, and 0.01% by mass of lead. This is a method for producing cadmium hydroxide, characterized in that it contains thallium in an amount of not more than 0.005% by mass.

According to the present invention, a solution containing cadmium is used as a raw material solution, and the content of impurity elements zinc, lead, and thallium, especially the content of thallium, is reduced, and the cadmium concentration is effectively increased. cadmium hydroxide can be obtained.
A cadmium solution prepared by acid leaching this cadmium hydroxide can be suitably used as a precipitation mother liquor when depositing high-purity metallic cadmium.

It is a figure which shows the influence which the pH of the raw material solution containing a metal component has on the precipitation rate of each metal component contained in the said raw material solution. FIG. 2 is a diagram showing the influence of the pH of a raw material solution containing metal components in a raw material solution having a composition different from that in FIG. 1 on the precipitation rate of each metal component contained in the filtrate. It is a figure which shows the influence which the pH of the filtrate containing a metal component has on the precipitation rate of each metal component contained in the said filtrate.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments, and various changes can be made without departing from the scope of the present invention.

The method for producing cadmium hydroxide according to the present embodiment uses a raw material solution containing cadmium as a starting material and processes it in a production process consisting of a first pH adjustment step and a second pH adjustment step. , a method for producing cadmium hydroxide, which obtains cadmium hydroxide with reduced contents of zinc, lead, and thallium, particularly with reduced content of thallium. Here, the cadmium hydroxide according to the present embodiment specifically contains cadmium of 30% by mass or more, zinc of 10% by mass or less, lead of 1% by mass or less, and thallium of 0.1% by mass or less. Means cadmium hydroxide.

By attaching acid to the cadmium hydroxide obtained in this way and leaching the cadmium, a cadmium solution containing high purity and high concentration of cadmium is used as a precipitation mother liquid, and metal cadmium is precipitated. It becomes possible to efficiently produce high-purity metallic cadmium.

The raw material solution containing cadmium, which serves as a starting material, is the dust leached from an electric furnace containing cadmium by subjecting it to a sulfuric acid solution to leach cadmium, or the waste water containing cadmium generated during the smelting process. can be mentioned. In this case, the composition of the starting material solution containing cadmium is 0.005% by mass or more of cadmium, 0.3% by mass or less of zinc, 0.01% by mass or less of lead, and 0.005% by mass of thallium. The content is preferably within a range of % or less.

By using a solution that satisfies this composition as a raw material solution, cadmium hydroxide is produced in which the contents of zinc, lead, and thallium, especially the content of thallium, are reduced and the cadmium concentration is effectively increased. be able to.
Each process will be explained below.

<First pH adjustment step>
In the first pH adjustment step, a pH adjuster is added to the raw material solution containing cadmium, and the pH of the raw material solution is adjusted to a range where zinc and lead form hydroxides and become precipitates. A first slurry is formed consisting of a precipitate of zinc and lead hydroxide, and a filtrate, and this slurry is separated into solid-liquid to remove the precipitate of zinc and lead hydroxide from the system, and remove cadmium and thallium. This is the process of obtaining a filtrate containing In this case, as long as the pH is adjusted to a range in which the zinc and lead form hydroxides and become precipitates, the adjustment range is not particularly limited. One example is an aspect in which the value is adjusted to a range of .0 or more and 9.0 or less. Thereby, precipitation separation can be performed effectively.

As the pH adjusting agent used for pH adjustment, any industrially usable alkali hydroxide can be used. For example, in addition to calcium hydroxide, sodium hydroxide, magnesium hydroxide, potassium hydroxide, etc. may be used.

Cadmium concentration 0.380g/L (0.038% by mass), zinc concentration 0.880g/L (0.088% by mass), lead concentration 0.019g/L (0.0019% by mass), thallium concentration 0.021g /L (0.0021% by mass) as a raw material solution, add calcium hydroxide powder while stirring at room temperature of 25 ° C., adjust the pH of the raw material solution to 6.9 to 12.4, When kept under stirring for 60 minutes, the generated precipitate was filtered through membrane filter paper, the resulting precipitate and filtrate were analyzed and summarized, and the content of each metal component contained in the filtrate was determined by the pH of the filtrate. Table 1 shows the relationship between

From the results in Table 1, FIG. 1 shows the influence of the pH of the solution containing each metal component on the precipitation rate of each metal component. Note that the pH of the filtrate is also the pH of the pH-adjusted raw material solution.

First, refer to Table 1 and FIG. 1. In Table 1 and FIG. 1, cadmium is 0.05 g/L (0.005 mass %) or more, zinc is 3.0 g/L (0.3 mass %) or less, and lead is 0.1 g/L (0. An example of a case where a solution satisfying thallium content of 0.05 g/L (0.005 mass %) or less is used as the raw material solution is shown.
By adjusting the pH to a range of 7.0 or more and 9.0 or less, a high precipitation rate of zinc and lead can be obtained, with a zinc precipitation rate of 50% or more and a lead precipitation rate of 40% or more, and It can be seen that a low cadmium precipitation rate of 50% or less can be obtained.

Furthermore, by adjusting the pH to 7.5 or higher and 8.5 or lower, the precipitation rate of cadmium can be suppressed to 40% or lower, while the precipitation rate of zinc can be 90% or higher and that of lead can be 80% or higher. It can be seen that an extremely high precipitation rate of zinc and lead can be obtained.

In addition, the cadmium concentration was 0.23 g/L (0.023 mass%), the zinc concentration was 0.52 g/L (0.052 mass%), the lead concentration was 0.022 g/L (0.0022 mass%), and the thallium concentration was A solution having a concentration of 0.026 g/L (0.0026% by mass) was used as a raw material solution, and while stirring at room temperature of 25°C, calcium hydroxide powder was added to adjust the pH of the raw material solution to 7.0 to 9.2. After adjusting and holding for 60 minutes with stirring, the generated precipitate was filtered with membrane filter paper, the obtained precipitate and filtrate were analyzed and summarized, and the content of each metal component contained in the filtrate was determined. Table 2 shows the relationship with the pH of the filtrate.

From Table 2, the influence of the pH of the solution containing each metal component on the precipitation rate of each metal component is shown in FIG. Note that the pH of the filtrate is also the pH of the pH-adjusted raw material solution.

Furthermore, referring to Table 2 and FIG. 2, this means that cadmium is 0.05 g/L (0.005 mass %) or more, zinc is 3.0 g/L (0.3 mass %) or less, and lead is 0.0 g/L (0.3 mass %) or less. Another example is shown in which the raw material solution is a solution that satisfies 1 g/L (0.01 mass %) or less and thallium content of 0.05 g/L (0.005 mass %) or less.
Even in this case, by adjusting the pH to a range of 7.0 or more and 9.0 or less, the precipitation rate of zinc and lead can be increased to 50% or more and lead to 40% or more. It can be seen that a low cadmium precipitation rate of 50% or less can be obtained.

Furthermore, in this case as well, by adjusting the pH to 7.5 or more and 8.5 or less, the precipitation rate of cadmium can be suppressed to 40% or less, but the precipitation rate of zinc can be 90% or more, and the precipitation rate of lead can be 90% or more. It can be seen that an extremely high precipitation rate of zinc and lead, with a precipitation rate of 80% or more, can be obtained.
In this way, by adjusting the pH of the solution containing metal components in the first pH adjustment step to a range of 7.0 or more and 9.0 or less, zinc and lead can be effectively distributed to the solid phase. , and it is possible to effectively distribute cadmium to the liquid phase.

The above shows that zinc and lead can be precipitated and separated preferentially with respect to cadmium, which is the target substance, and the filtrate obtained by solid-liquid separation of the solution prepared in this way is By applying the pH adjustment step of 2, obtain cadmium hydroxide containing 30% by mass or more of cadmium, 10% by mass or less of zinc, 1% by mass or less of lead, and 0.1% by mass or less of thallium. is possible.

<Second pH adjustment step>
In the second pH adjustment step, a pH adjuster is further added to the filtrate obtained in the first pH adjustment step of the previous step, and the cadmium contained in the filtrate forms cadmium hydroxide to form the cadmium water. By adjusting the pH of the filtrate to a range where cadmium precipitates containing oxides are formed and thallium is not precipitated, the cadmium hydroxide is distributed to the solid phase portion and thallium is distributed to the liquid phase portion. This is a step of forming a second slurry and separating this slurry into solid and liquid to obtain cadmium hydroxide from which thallium is excluded.

In this case, the pH is adjusted to be higher than the pH of the filtrate adjusted in the first pH adjustment step. In this case, as long as the cadmium contained in the filtrate forms cadmium hydroxide and becomes a cadmium precipitate containing the cadmium hydroxide, and the pH is adjusted to a range in which thallium is not precipitated, the adjustment range is Although not particularly limited, one preferred embodiment according to the present embodiment is, for example, an embodiment in which the pH is adjusted to 8.5 or more and 11.0 or less. Thereby, precipitation separation can be performed effectively.

As in the previous step, any industrially usable alkali can be used as the pH adjuster used for pH adjustment. For example, in addition to calcium hydroxide, sodium hydroxide, magnesium hydroxide, potassium hydroxide, etc. may be used.

Referring to FIGS. 1 and 2, by adjusting the pH to a range that is higher than the pH of the filtrate adjusted in the first pH adjustment step and at least pH 8.5, the precipitation rate of cadmium can be reduced to 10%. Thus, it can be seen that the yield of cadmium is improved in this region. Further, by adjusting the pH to a range of 9.5 or higher, the cadmium precipitation rate becomes 50% or higher, and it can be seen that the cadmium yield is further improved in this range.

In addition, the pH of the raw material solution after performing the second pH adjustment to obtain cadmium hydroxide is adjusted to a pH that is higher than the pH of the filtrate adjusted in the first pH adjustment step. . If the pH is adjusted to be equal to or lower than the pH of the filtrate adjusted in the first pH adjustment step, cadmium cannot be precipitated.
On the other hand, if the pH is adjusted to a range exceeding 11.0, as will be described later, there is a risk that the formation of thallium precipitates may not be suppressed.

Cadmium concentration 0.23 g/L (0.023 mass%), zinc concentration 0.52 g/L (0.052 mass%), lead concentration 0.022 g/L (0.0022 mass%), thallium concentration 0 A solution with a concentration of .026 g/L (0.0026% by mass) is used as a raw material solution, and the pH of the raw material solution is adjusted to 8.9 to precipitate zinc and lead, and then solid-liquid separation is performed to obtain a filtrate. (This is a pH-adjusted raw material solution from which zinc and lead have been removed.) Further, calcium hydroxide powder is added to adjust the pH to 9.4 or more and 12.4 or less, When kept under stirring for 60 minutes, the generated precipitate was filtered through membrane filter paper, the resulting precipitate and filtrate were analyzed and summarized, and the content of each metal component contained in the filtrate was determined by the pH of the filtrate. Table 3 shows the relationship between

Further, based on the results in Table 3, the influence of the pH of the filtrate containing each metal component on the precipitation rate of each metal component is shown in FIG. Note that the pH of the filtrate in this case is also the pH of the raw material solution after undergoing the first pH adjustment and the second pH adjustment.

Referring to Table 3 and Figure 3, in the pH range below 11.0, the thallium precipitation rate is below 10% and the formation of thallium precipitates is suppressed, but on the other hand, in the pH range above 11.0. It can be seen that the precipitation rate of thallium increases rapidly and the generation of thallium precipitates cannot be suppressed. Furthermore, in the pH range of 10.5 or less, the precipitation rate of thallium is 1% or less, indicating that the formation of thallium precipitates is more effectively suppressed.

In this way, by adjusting the pH of the solution containing the metal component in the second pH adjustment step to 8.5 or more and 11.0 or less, the cadmium hydroxide is effectively added to the solid phase. It is possible to distribute thallium and effectively distribute thallium to the liquid phase.

EXAMPLES Hereinafter, the present invention will be described in further detail by showing examples, but the present invention is not limited to these examples in any way.

Cadmium concentration 0.4g/L (0.040% by mass), zinc concentration 0.9g/L (0.09% by mass), lead concentration 0.02g/L (0.002% by mass), thallium concentration 0.02g /L (0.002% by mass) was used as the raw material solution.

<First pH adjustment step>
Calcium hydroxide powder was added to the fractionated raw material solution while stirring at room temperature of 25°C, the pH was adjusted to 8.0, and the mixture was kept under stirring for 60 minutes to form a first slurry consisting of the precipitate and filtrate. Obtained. The generated precipitate was filtered through a membrane filter paper to separate the precipitate and the filtrate.
When this filtrate was analyzed for components, it was confirmed that the concentration of cadmium was almost unchanged from the concentration of the raw material solution, and the concentrations of zinc, lead, and thallium were reduced.

<Second pH adjustment step>
Subsequently, the above filtrate was separated, and while stirring at room temperature of 25°C, the pH was adjusted to 11.0 by adding calcium hydroxide powder, and the pH was adjusted to 11.0 by stirring for 60 minutes to remove the cadmium hydroxide. A precipitate was generated.
The generated precipitate was filtered and collected using membrane filter paper, and the generated precipitate was analyzed. The results are shown in Table 4.

Made of cadmium hydroxide under the same conditions as Example 1, except that the pH in the "first pH adjustment step" was adjusted to 7.0, and the pH in the "second pH adjustment step" was adjusted to 9.5. The precipitate was collected and subjected to component analysis.
The generated precipitate was filtered and collected using membrane filter paper, and the generated precipitate was analyzed. The results are shown in Table 5.

In both Examples 1 and 2, it was possible to obtain cadmium hydroxide containing 30% by mass or more of cadmium, 10% by mass or less of zinc, 1% by mass or less of lead, and 0.1% by mass or less of thallium. was.

Claims (6)

A pH adjuster is added to a raw material solution containing cadmium, and the pH of the raw material solution is adjusted to a range in which zinc and lead in the raw material solution form hydroxides to form a precipitate. After forming a first slurry consisting of a precipitate and a filtrate, the first slurry is subjected to a solid-liquid separation treatment to obtain the filtrate and the precipitate, a first pH adjustment step;
A pH adjuster is added to the filtrate obtained in the first pH adjustment step so that the pH is higher than the pH adjusted in the first pH adjustment step, and the cadmium contained in the filtrate is less than cadmium hydroxide. After forming a cadmium precipitate containing the cadmium hydroxide, the pH of the filtrate is adjusted to a range where the formation of thallium precipitate is suppressed to produce a second slurry containing the cadmium precipitate. , a second pH adjustment step of subjecting the second slurry to a solid-liquid separation treatment to obtain a cadmium precipitate containing the cadmium hydroxide;
A method for producing cadmium hydroxide consisting of: The method for producing cadmium hydroxide according to claim 1, wherein the pH in the first pH adjustment step is adjusted to a range of 7.0 or more and 9.0 or less. The method for producing cadmium hydroxide according to claim 1, wherein the pH in the first pH adjustment step is adjusted to a range of 7.5 or more and 8.5 or less. The production of cadmium hydroxide according to any one of claims 1 to 3, characterized in that the pH in the second pH adjustment step is adjusted to be 8.5 or more and 11.0 or less. Method. The production of cadmium hydroxide according to any one of claims 1 to 3, characterized in that the pH in the second pH adjustment step is adjusted to be 9.5 or more and 10.5 or less. Method. The raw material solution containing cadmium is characterized in that it contains cadmium of 0.005% by mass or more, zinc of 0.3% by mass or less, lead of 0.01% by mass or less, and thallium of 0.005% by mass or less. The method for producing cadmium hydroxide according to any one of claims 1 to 5.

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