Cadmium manufacturing method

Abstract

To efficiently separate and recover cadmium from a "cadmium sulfide-containing material" by a simpler process than a conventionally known multi-stage wet process.SOLUTION: A cadmium production method is provided, comprising: a reduction roasting step S10 of roasting a cadmium sulfide-containing material together with other raw material containing zinc and chlorine in a reduction atmosphere; a wet step S20 of distributing cadmium chloride obtained in the reduction roasting step S10 into a liquid phase, and distributing a zinc oxide and a cadmium oxide into a solid phase, thereby separating both of them; a cementation step S30 of adding zinc powder to a cadmium solution obtained by distributing the cadmium chloride into the liquid phase in the wet step S20, thereby precipitating metal cadmium; and a dehydration step S40 of solid-liquid separating a slurry including the metal cadmium precipitated from the solution in the cementation step S30, thereby obtaining a metal cadmium-containing dehydrated cake.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing cadmium, which involves separating and recovering metallic cadmium from a raw material containing cadmium sulfide. [Background technology]

[0002] In many non-ferrous metal smelting processes, dehydrated cake containing cadmium sulfide is discharged as a smelting intermediate. As a method for recovering metallic cadmium as a valuable metal from this dehydrated cake containing cadmium sulfide, a production method has been proposed in which multiple hydroprocessing steps are performed while adding various chemicals (Patent Document 1).

[0003] However, the process disclosed in Patent Document 1 inevitably increases the cost of producing cadmium due to the increased processing time and labor required for the multi-stage wet treatment, such as the need to control the amounts of various types of chemicals added at each stage and to control the pH at each stage. Therefore, there has been a demand for a simpler process for separating and recovering metallic cadmium from a cadmium sulfide-containing raw material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-191782 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a "cadmium production method" that can efficiently separate and recover cadmium as a valuable metal by a process that is simpler than the conventionally known multi-stage wet processes, for example, a process for separating and recovering "metallic cadmium" from a "cadmium sulfide-containing raw material" such as a "dehydrated cake containing cadmium sulfide" that is discharged as a smelting intermediate in a non-ferrous metal smelting process such as copper refining. [Means for solving the problem]

[0006] The present inventors have newly discovered that the above-mentioned problems can be solved by a process in which a dehydrated cake containing cadmium sulfide is subjected to a pretreatment process in which the cake is subjected to a reduction roasting process together with other raw materials containing zinc and chlorine before being subjected to a wet process, and have thus completed the present invention. More specifically, the present invention provides the following.

[0007] (1) A method for producing cadmium by separating and recovering metallic cadmium from a cadmium sulfide-containing raw material, the method comprising: a reduction-roasting step in which the cadmium sulfide-containing raw material is roasted in a reducing atmosphere together with other raw materials containing zinc and chlorine; a wet step in which treated water is added to dust containing cadmium chloride obtained in the reduction-roasting step and zinc oxide and cadmium oxide reoxidized after reduction, thereby separating the cadmium chloride from the zinc oxide and cadmium oxide by distributing the cadmium chloride in a liquid phase and the zinc oxide and cadmium oxide in a solid phase; a cementation step in which zinc powder is added to the cadmium solution obtained in the wet step, in which the cadmium chloride is distributed in the liquid phase, thereby precipitating metallic cadmium; and a dehydration step in which a slurry containing metallic cadmium precipitated from the solution in the cementation step is subjected to solid-liquid separation to obtain a dehydrated cake containing metallic cadmium.

[0008] According to the cadmium production method (1), metallic cadmium can be efficiently separated and recovered from a "cadmium sulfide-containing raw material" such as a "dehydrated cake containing cadmium sulfide" by a process simpler than the conventionally known multi-stage wet process.

[0009] (2) The method for producing cadmium according to (1), further comprising a dry heating step of dry-heating a dehydrated cake containing cadmium oxide and chlorine distributed in the solid phase in the wet step, and an exhaust gas treatment step of treating exhaust gas discharged from the dry heating step, in which the exhaust gas-derived dust containing cadmium chloride recovered in the exhaust gas treatment step is returned to the wet step.

[0010] According to the cadmium production method (2), cadmium can be separated and recovered more efficiently with a higher separation and recovery rate than the cadmium production method described in (1).

[0011] (3) A method for producing metallic cadmium by acid leaching cadmium from the metallic cadmium-containing dehydrated cake obtained by the method for producing cadmium according to (1) or (2).

[0012] According to the method for producing metallic cadmium (3), high-quality metallic cadmium can be obtained very easily from the dehydrated cake containing metallic cadmium that can be obtained by the method for producing cadmium described in (1) or (2). [Effects of the Invention]

[0013] According to the present invention, there can be provided a "cadmium production method" which is a process for separating and recovering "metallic cadmium" from "cadmium sulfide-containing raw materials" and which is capable of efficiently separating and recovering cadmium as a valuable metal by a process simpler than the conventionally known multi-stage wet processes. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a flow chart showing an example of the flow of the "cadmium production method" of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] <Overall structure> As shown in FIG. 1, the "cadmium production method" of the present invention is a process in which a cadmium sulfide-containing raw material such as a "dehydrated cake containing cadmium sulfide" is introduced into a composite process that essentially includes a reduction roasting step S10, a wet process S20, a cementation step S30, and a dehydration step S40, to separate and recover "metallic cadmium."

[0016] Furthermore, the "cadmium production method" of the present invention is more preferably a process further including a dry heating step S50 and an exhaust gas treatment step S60 in addition to the above four steps, and is configured so that the exhaust gas-derived dust recovered in the exhaust gas treatment step S60 is repeatedly subjected to the wet step S20. The dry heating step S50 and the exhaust gas treatment step S60 are not necessarily essential constituent elements of the present invention, but below, an embodiment including six steps, namely, the reducing roasting step S10, the wet step S20, the cementation step S30, the dehydration step S40, the dry heating step S50, and the exhaust gas treatment step S60, will be described in detail as a preferred embodiment of the "cadmium production method" of the present invention.

[0017] Furthermore, according to the "cadmium production method" of the present invention, a dehydrated cake containing metallic cadmium at a sufficiently high quality ("metallic cadmium-containing dehydrated cake") can be obtained, and high-purity metallic cadmium can be easily obtained from the "metallic cadmium-containing dehydrated cake" obtainable by the "cadmium production method" of the present invention by a simple acid leaching treatment.

[0018] The composite process consisting of the reduction roasting step S10, the wet process S20, the cementation step S30, the dehydration step S40, the dry heating step S50, and the exhaust gas treatment step S60 can be implemented in an existing zinc oxide production facility that performs a process for recovering zinc oxide from steel dust via the reduction roasting step of the Welz process. However, in the zinc oxide production facility, cadmium, which is inevitably present in steel dust and other raw materials used in zinc oxide production, is strictly controlled to prevent its content from exceeding a certain level in the final product (iron-containing clinker) obtained in the reduction roasting step. Specifically, various efforts have been made to keep the cadmium content of the iron-containing clinker below 0.1%. Therefore, for those skilled in the art of zinc oxide production, the introduction of the above-mentioned "cadmium sulfide-containing raw material," primarily composed of cadmium sulfide, into the reduction roasting step of the Welz process was clearly an unexpected processing method.

[0019] <Reduction roasting process> The reducing roasting step S10 involves roasting the "cadmium sulfide-containing raw material" together with "other raw materials containing zinc and chlorine" in a reducing atmosphere. In this specification, the "cadmium sulfide-containing raw material" primarily refers to "dehydrated cake containing cadmium sulfide," which is a smelting intermediate product in non-ferrous metal smelting processes. However, the "cadmium sulfide-containing raw material" is not limited to the dehydrated cake and may be any other powder or slurry containing cadmium sulfide as a primary component. Furthermore, the "other raw materials containing zinc and chlorine" may be any material containing zinc or a zinc compound and chlorine or a chlorine compound, such as steel dust, which is widely used as a raw material for zinc oxide ore.

[0020] The reduction-roasting step S10 can be performed using a reduction-roasting rotary kiln (RRK), known as an apparatus for performing the reduction-roasting step of the Weltz process described above. In this rotary kiln (RRK), the zinc oxide (ZnO) contained in each of the raw materials is reduced and roasted, and the volatilized metallic zinc is then reoxidized in the exhaust gas to form powdered zinc oxide (ZnO). Similarly, most of the cadmium contained in each of the raw materials becomes a cadmium compound, primarily composed of cadmium chloride (CdCl). The zinc oxide (ZnO) and cadmium chloride (CdCl) are captured by a dust collector along with the exhaust gas from the rotary kiln and recovered as "dust containing cadmium chloride (CdCl) and zinc oxide (ZnO)."

[0021] <Wet process> The wet process S20 is a process in which the "dust containing cadmium chloride (CdCl2) and zinc oxide (ZnO)" recovered in the reduction roasting process S10 is subjected to wet processing, thereby distributing chlorides such as cadmium chloride (CdCl2) into a liquid phase and oxides such as zinc oxide (ZnO) and cadmium oxide (CdO) into a solid phase, thereby separating the two.

[0022] Specifically, the wet process S20 involves repulping the above-mentioned "dust containing cadmium chloride (CdCl2) and zinc oxide (ZnO)" with treatment water to form a slurry. This repulping process distributes water-soluble chlorides, such as cadmium chloride (CdCl2), in the dust into the treatment liquid. The treatment water used for this repulping can be fresh water or process water used in the process.

[0023] The repulping process distributes most of the cadmium components present as chlorides in the "dust containing cadmium chloride (CdCl2) and zinc oxide (ZnO)" into a liquid phase. Then, by performing solid-liquid separation in this state, the liquid phase containing the cadmium components at high concentrations can be separated and recovered. The specific equipment used for the dehydration process for solid-liquid separation can be appropriately selected from known dehydration equipment such as gravity-settling slurry concentrators, e.g., thickeners, and vacuum dehydrators.

[0024] <Cementation process> The cementation step S30 is a step in which metallic cadmium is precipitated by a cementation treatment in which zinc (Zn) powder is added to the cadmium solution obtained by distributing cadmium chloride (CdCl) in the liquid phase in the wet step S20, thereby causing the reaction (cadmium precipitation) shown in the following reaction formula (Formula 1). This cementation treatment can be carried out using, for example, any of various known reaction vessels equipped with a stirrer. CD 2+ +Zn → Cd+Zn 2+ ...(Formula 1)

[0025] <Dehydration process> The dewatering step S40 is a step in which the slurry containing metallic cadmium precipitated from the solution in the cementation step S30 is subjected to solid-liquid separation to obtain a dehydrated cake containing metallic cadmium (metallic cadmium-containing dehydrated cake). The specific method for the solid-liquid separation is not particularly limited, and various known methods can be selected. For example, a method in which the slurry is concentrated in a settling device called a calorcon and then the concentrated slurry is passed through a filter press can be mentioned.

[0026] <Dry heating process> The dry heating step S50 is a step in which the dehydrated cake containing the oxides distributed in the solid phase in the wet step S20 is fed into a dry heating apparatus and calcined, thereby removing the cadmium component contained in the dehydrated cake by volatilizing it as a chloride. A known dry heating rotary kiln (DRK) can be used as the dry heating apparatus for performing the dry heating step S50. After calcination and the recovery of the cadmium component, the calcined ore is used as crude zinc oxide, which is a raw material for a zinc smelter.

[0027] <Exhaust gas treatment process> The exhaust gas treatment step S60 is a step in which dust is separated and recovered from the exhaust gas discharged from the dry heating step S50. The dehydrated cake fed to the dry heating step S50 contains, in addition to zinc oxide, some of the cadmium fed to the reduction roasting step S10 that has been reduced and volatilized to form an oxide, as with zinc, and chlorine and other substances that are entrained in the moisture contained in the dehydrated cake. Therefore, the exhaust gas discharged from the dry heating step S50 contains cadmium chloride (CdCl2) that has been chlorinated and volatilized in the dry heating step S50. The exhaust gas-derived dust separated and recovered from the exhaust gas in the exhaust gas treatment step S60 contains the recovered cadmium chloride (CdCl2). Therefore, by using this exhaust gas-derived dust as a cadmium raw material and repeating it in the wet process S20, the recovery rate of metallic cadmium from a raw material primarily composed of cadmium sulfide can be further increased. This exhaust gas treatment step S60 can be carried out in a known exhaust gas treatment facility configured to include a wet electrostatic precipitator and the like.

[0028] <Method of manufacturing cadmium metal> High-quality metallic cadmium can be easily obtained by acid leaching cadmium or a cadmium compound from the "metallic cadmium-containing dehydrated cake" obtained by the "cadmium production method" of the present invention described above. [Example]

[0029] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0030] <Example> As an example, a test run was carried out under the following conditions to obtain metallic cadmium from a cadmium sulfide-containing raw material using the "cadmium production method" of the present invention. In this test run, the six steps of the reduction roasting step, wet process step, cementation step, dehydration step, dry heating step, and exhaust gas treatment step were carried out in the manner described above, and metallic cadmium was finally recovered by acid leaching from the dehydrated cake containing metallic cadmium (dehydrated cake containing metallic cadmium) obtained in this combined process.

[0031] The "cadmium sulfide-containing raw material" fed into the reduction roasting process was a sulfide containing 20% ​​by mass of cadmium and 20% by mass of zinc. Steel dust was used as the "other raw material containing zinc and chlorine." These raw materials were mixed with 200 t / day of steel dust at a rate of 2 t / day of the "cadmium sulfide-containing raw material," and the mixture was fed into a reduction roasting rotary kiln. The reduction roasting rotary kiln also contained reducing agents: 25% by mass of coke breeze relative to the steel dust, and 14% by mass of limestone breeze relative to the steel dust. The furnace temperature of the reduction roasting rotary kiln was set to 1400°C.

[0032] In the reduction roasting process performed under the above conditions, more than 98% of the cadmium in the "cadmium sulfide-containing raw material" was recovered, as shown in Table 1 below. The dust containing cadmium and zinc recovered in the reduction roasting process was then subjected to a wet process, a cementation process, and a dehydration process, resulting in a "metallic cadmium-containing dehydrated cake" that could be acid-leached. The dehydrated cake containing zinc oxide distributed to the solid phase in the wet process was then fed to a dry-heating process for dry-heat treatment. The exhaust gas discharged from this dry-heating process was sent to an exhaust gas treatment process, where the dust contained in the exhaust gas was separated and recovered as exhaust-gas-derived dust using a wet electrostatic precipitator. Metallic cadmium was recovered from the "metallic cadmium-containing dehydrated cake" obtained in this manner by acid leaching. The cadmium recovery rate from the "cadmium sulfide-containing raw material" throughout the above-mentioned processes was more than 97%, as shown in Table 1 below.

[0033] <Comparative Example> A comparative example was carried out under the same conditions as in the example except that no reducing agent (coke powder) was added. In the roasting step carried out without a reducing atmosphere, the recovery rate of cadmium in the "cadmium sulfide-containing raw material" was 10%, as shown in Table 1 below. Furthermore, the recovery rate of cadmium in the "cadmium sulfide-containing raw material" throughout the entire process described above was 9%, as shown in Table 1 below.

[0034] [Table 1]

[0035] From the results of the above test operations, it was confirmed that the recovery rate of cadmium from the cadmium sulfide-containing raw material is dramatically improved by performing a reducing roasting process, in which the cadmium sulfide-containing raw material is roasted in a reducing atmosphere together with other raw materials containing zinc and chlorine, prior to the wet process, and that if the roasting is not performed in a reducing atmosphere, the effect of improving the cadmium recovery rate is hardly manifested. [Explanation of symbols]

[0036] S10 Reduction roasting process S20 Wet process S30 Cementation Process S40 Dehydration process S50 Drying heating process S60 Exhaust gas treatment process

Claims

1. A method for producing cadmium by separating and recovering metallic cadmium from a raw material containing cadmium sulfide, comprising: a reducing roasting step of roasting the cadmium sulfide-containing raw material together with other raw materials containing zinc and chlorine in a reducing atmosphere; a wet process in which treated water is added to dust containing cadmium chloride obtained in the reduction roasting process and zinc oxide and cadmium oxide reoxidized after reduction, thereby distributing the cadmium chloride into a liquid phase and the zinc oxide and cadmium oxide into a solid phase, thereby separating the two; a cementation step in which zinc powder is added to the cadmium solution obtained by distributing the cadmium chloride in the liquid phase in the wet step, thereby precipitating metallic cadmium; a dehydration step of subjecting the slurry containing metallic cadmium precipitated from the solution in the cementation step to solid-liquid separation to obtain a dehydrated cake containing metallic cadmium; A method for producing cadmium, comprising:

2. the method further comprises a dry heating step of dry-heating a dehydrated cake containing the zinc oxide and the cadmium oxide distributed in the solid phase in the wet step, and an exhaust gas treatment step of treating exhaust gas discharged from the dry heating step, The cadmium chloride-containing dust derived from the exhaust gas recovered in the exhaust gas treatment step is returned to the wet process. The method for producing cadmium according to claim 1.

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