Method of manufacturing thallium compound

Abstract

To provide a method of manufacturing a thallium compound efficiently and with high purity from a solution containing thallium, cadmium, and impurities.SOLUTION: A method of manufacturing a thallium compound from a raw material solution containing thallium, cadmium, and impurity elements includes a sulfurizing process of subjecting the raw material solution to sulfurization treatment by adding 2.5-4.0 equivalent of sulfurizing agent to a total amount of thallium, and cadmium to obtain a mixed sulfide of thallium sulfide, and cadmium sulfide, a leaching process of leaching thallium at pH of 0.5-1.5 by adding sulfuric acid to the mixed sulfide, and a thallium-manufacturing process of obtaining thallium from a leachate. In the thallium-manufacturing process, a crystallization process of crystallizing thallium chloride is performed by adding 5.5-8.0 equivalent of a chloride ion amount to a thallium amount. Alternatively, an oxidizing process of generating thallium oxide is performed by adding 1.0-2.0 equivalent of an oxidant for a thallium amount to the leachate to control pH to 2.0-4.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thallium compound from a raw material solution containing thallium, cadmium, and an impurity element. [Background technology]

[0002] Zinc oxide ore, which is obtained by separating and recovering impurities from crude zinc oxide ore, is widely used as a raw material for zinc ingots in zinc smelters. Crude zinc oxide can be obtained, for example, from steel dust generated in steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry through a reduction roasting process. From the viewpoint of promoting resource recycling, it is desirable to reuse the crude zinc oxide as a zinc raw material for steel dust.

[0003] On the other hand, crude zinc oxide derived from steel dust contains high proportions of impurities such as halogens such as chlorine and fluorine, as well as cadmium, in addition to its main component, zinc oxide. Of these impurities, cadmium in particular is a toxic metal, so separation and recovery of cadmium is commonly carried out at zinc oxide manufacturing plants. On the other hand, cadmium is also an important useful metal in electronics materials, as it is used as the anode material for nickel-cadmium batteries.

[0004] Cadmium can be separated and recovered by a wet treatment process that combines multiple treatments, such as a neutralization treatment and a zinc cementation treatment, on a leachate obtained by acid leaching crude zinc oxide to extract cadmium. However, crude zinc oxide contains a trace amount of thallium, which gradually accumulates in the wet treatment process without being removed from the system. Therefore, if thallium continues to accumulate in the wet treatment system, thallium separation becomes insufficient, which may adversely affect the quality of metallic cadmium.

[0005] As a method for discharging thallium from a hydrometallurgical treatment system, for example, a method is known in which a neutralization treatment solution generated in a neutralization treatment is subjected to a sulfiding treatment to produce a smelting intermediate, and thallium is discharged from the system via the smelting intermediate. However, the smelting intermediate contains cadmium in addition to thallium, and when the smelting intermediate is discharged from the system, not only thallium but also cadmium is discharged, which is not economical. If cadmium could be separated from the smelting intermediate and thallium could be recovered, it would be possible to discharge only thallium from the system, which would be an economical and more advantageous method.

[0006] An example of a method for recovering thallium from a smelting intermediate is the method disclosed in Patent Document 1, which makes it possible to recover thallium from a smelting intermediate. However, the method disclosed in Patent Document 1 requires complex processing steps, such as sulfuric acid leaching while blowing air or nitrogen gas into the smelting intermediate, then adding zinc dust to reduce and precipitate sponge thallium, and then subjecting the sponge thallium to multiple further sulfuric acid leaching and neutralization treatments, and is therefore not an efficient method.

[0007] Therefore, the method disclosed in Patent Document 2 has been proposed as a method for more efficiently recovering thallium from smelting intermediates. Specifically, the method disclosed in Patent Document 2 is a method for separating and recovering thallium using a mixed sulfide containing thallium sulfide and cadmium sulfide as a starting material, and is composed of a leaching step in which the mixed sulfide is leached with acid, and a thallium recovery step in which thallium is separated and recovered from the leachate as a precipitate of thallium chloride. This method makes it possible to efficiently recover thallium without undergoing complicated processing steps.

[0008] However, there is room for further improvement in the recovery of thallium. Furthermore, thallium itself is a valuable metal used in various industrial fields, and if a high-quality thallium compound could be produced, high-quality metallic thallium could be efficiently produced from the thallium compound. Therefore, from the viewpoint of industrial application, a method for more efficiently producing a high-quality thallium compound from a solution containing at least thallium, cadmium, and impurity elements as described above is desired. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 122722 / 1983 [Patent Document 2] Japanese Patent Publication No. 2022-43470 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been proposed in view of the above circumstances, and has as its object to provide a method that enables more efficient and high-quality production of thallium compounds from a solution containing thallium, cadmium, and impurity elements. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have completed the following invention.

[0012] (1) The present invention is a method for producing thallium from a raw material solution containing thallium, cadmium, and impurity elements, comprising: a sulfurization step in which a sulfiding agent is added to the raw material solution in an amount of 2.5 to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide; a leaching step in which sulfuric acid is added to the mixed sulfide and thallium is leached from the mixed sulfide while controlling the pH within a range of 0.5 to 1.5; and a crystallization step in which chloride or a solution containing chloride ions that liberates chloride ions is added to the leachate containing thallium in an amount such that the amount of chloride ions is 5.5 to 8.0 equivalents relative to the amount of thallium contained in the leachate, thereby precipitating thallium chloride.

[0013] (2) The present invention also provides a method for producing thallium from a raw material solution containing thallium, cadmium, and impurity elements, comprising: a sulfurization step in which a sulfiding agent is added to the raw material solution in an amount of 2.5 to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide; a leaching step in which sulfuric acid is added to the mixed sulfide and thallium is leached from the mixed sulfide while controlling the pH in the range of 0.5 to 1.5; and an oxidation step in which an oxidizing agent is added to the leachate containing thallium in an amount of 1.0 to 2.0 equivalents relative to the amount of thallium in the leachate while controlling the pH in the range of 2.0 to 4.0, thereby producing thallium oxide.

[0014] (3) The present invention also relates to a method for producing a thallium compound according to the above (1) or (2), wherein the sulfurization step comprises adding a sulfurizing agent to the raw material solution in an amount of 1.8 equivalents to 2.1 equivalents relative to the total amount of thallium and cadmium in the raw material solution to perform a first sulfurization treatment, and then adding a sulfurizing agent to the post-sulfurization solution obtained in the first sulfurization treatment in an amount of 2.5 equivalents to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution to perform a second sulfurization treatment.

[0015] (4) The present invention also relates to a method for producing a thallium compound according to the above (1) or (2), wherein the raw material solution contains at least zinc and / or lead as the impurity elements, and the raw material solution is subjected to a neutralization step prior to the sulfurization step, in which a pH adjuster is added to the raw material solution to adjust the pH to a range of 7.0 to 9.0 inclusive to perform a first neutralization treatment to produce a precipitate consisting of hydroxides of zinc and / or lead contained in the raw material solution, and then the precipitate is separated and removed, and a pH adjuster is added to a filtrate obtained by the first neutralization treatment to adjust the pH to a range of higher than the pH adjusted in the first neutralization treatment and 11.0 inclusive to produce a precipitate consisting of hydroxides of cadmium, and the neutralized liquid obtained by separating and removing the precipitate produced in the second neutralization treatment is subjected to the sulfurization step. [Effects of the Invention]

[0016] According to the present invention, it is possible to more efficiently produce a high-quality thallium compound using a solution containing thallium, cadmium and impurity elements as a raw material solution. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a graph showing the results of examining the transition of thallium and cadmium concentrations in the solution after sulfurization treatment when sulfurization treatment was carried out with different amounts of sulfurizing agent solution added in Test Example 1. [Figure 2] FIG. 10 is a graph showing the results of the leaching rate of each element when a sulfuric acid solution was added to a mixed sulfide in Test Example 2 and a leaching treatment was carried out while controlling the pH in the range of 1.5 to −0.5. [Figure 3] FIG. 1 shows the results of thallium precipitation rate when a solution containing chloride ions was added to the thallium leaching solution in a range of 1.0 equivalent to 7.0 equivalents relative to the amount of thallium in the leaching solution and a crystallization treatment was carried out in Test Example 3-1. [Figure 4]This figure shows the relationship between the thallium precipitation rate and the oxidation-reduction potential (reference electrode: silver / silver chloride electrode) when an oxidation treatment was carried out in Test Example 3-2 by adding an oxidizing agent to the thallium leaching solution in a range of 0 to 1.5 equivalents relative to the amount of thallium in the leaching solution. DETAILED DESCRIPTION OF THE INVENTION

[0018] Specific embodiments of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. Note that in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "at least X and at most Y."

[0019] The method according to the present embodiment is a method for recovering thallium by efficiently separating cadmium and impurity elements from a raw material solution containing thallium (Tl), cadmium (Cd), and impurity elements. As will be described in detail later, thallium can be recovered in the form of thallium chloride or thallium oxide compounds. Furthermore, the obtained thallium compound can be subjected to a known acid leaching treatment or reduction treatment to obtain metallic thallium.

[0020] Therefore, the method according to this embodiment can be defined as a method for producing a thallium compound, in which a thallium compound is produced from a raw material solution containing thallium, cadmium, and impurity elements.

[0021] Specifically, as a method according to one embodiment, this method comprises a sulfurization step in which a sulfiding agent is added to a raw material solution containing thallium, cadmium, and impurity elements to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide; a leaching step in which sulfuric acid is added to the mixed sulfide to leach thallium; and a crystallization step in which chloride ions are added to the leachate containing thallium to precipitate thallium chloride.

[0022] In addition, a method according to another embodiment includes a sulfurization step in which a sulfurizing agent is added to a raw material solution containing thallium, cadmium, and impurity elements to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide; a leaching step in which sulfuric acid is added to the mixed sulfide to leach thallium; and an oxidation step in which an oxidizing agent is added to the leachate containing thallium to produce thallium oxide.

[0023] Furthermore, in these methods, although it is not an essential step, when the raw material solution contains zinc and / or lead as impurity elements, a neutralization step can be provided prior to the sulfurization step, in which the raw material solution is subjected to a neutralization treatment to separate and remove these impurity elements.

[0024] As described above, the raw material solution is a solution containing thallium, cadmium, and impurity elements. Examples of impurity elements contained in the raw material solution include zinc (Zn), lead (Pb), iron (Fe), nickel (Ni), copper (Cu), magnesium (Mg), manganese (Mn), and calcium (Ca). Specific examples of the raw material solution include waste liquid containing thallium, cadmium, and impurity elements that is generated in the process of producing zinc oxide ore from steel dust from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry.

[0025] Each step will be described below. The following description will first explain in detail the common steps of the sulfurization step, leaching step, and neutralization step prior to the sulfurization step. Then, as a thallium compound production process, the crystallization step of precipitating thallium as thallium chloride and the oxidation step of producing thallium as thallium oxide will be described in detail.

[0026] [Sulfurization process] The sulfurization step is a step in which a sulfurizing agent is added to a raw material solution containing thallium, cadmium, and impurity elements to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide. By performing such a sulfurization treatment, the thallium and cadmium contained in the raw material solution are transferred into a precipitate consisting of sulfides, while the impurity elements that do not form sulfides are left in the solution (liquid phase), thereby enabling effective separation of thallium and cadmium. The thallium and cadmium separated as a precipitate exist mainly as thallium sulfide and cadmium sulfide. The mixed sulfide refers to the precipitate containing the produced thallium sulfide and cadmium sulfide.

[0027] In particular, in the method according to the present embodiment, the sulfurization treatment is carried out by adding a sulfurizing agent in an amount of 2.5 equivalents or more relative to the total amount of thallium and cadmium in the raw material solution, thereby allowing most of the thallium and cadmium in the raw material solution to precipitate as sulfides.

[0028] Furthermore, by carrying out the sulfurization treatment by adding a sulfurizing agent preferably in an amount of 3.3 equivalents or more, the efficiency of the sulfurization reaction can be further increased, and almost all of the thallium and cadmium in the raw material solution can be transferred into a sulfide precipitate (solid phase).

[0029] By adding a sulfurizing agent in an amount of 2.5 equivalents or more to perform the sulfurization treatment, the oxidation-reduction potential (ORP) of the reaction solution using a silver / silver chloride electrode as the reference electrode becomes approximately −175 mV or less, as will be shown in the Examples described later.

[0030] The upper limit of the amount of sulfurizing agent added is preferably 4.0 equivalents or less relative to the total amount of thallium and cadmium in the raw material solution. Addition of a sulfurizing agent in an amount exceeding 4.0 equivalents does not substantially increase the amount of precipitate produced.

[0031] Thus, in the sulfurization step, it is preferable to carry out the sulfurization treatment by adding a sulfurizing agent in an amount of 2.5 equivalents to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution. On the other hand, taking into account operational considerations, the sulfurization treatment may be carried out by adding a sulfurizing agent in an amount of 2.5 equivalents to 2.8 equivalents, which allows thallium and cadmium to precipitate as sulfides and reduces the amount of remaining sulfurizing agent, making it easier to suppress the generation of hydrogen sulfide gas in the subsequent steps.

[0032] Furthermore, the sulfurization step may be performed in two stages: a first sulfurization treatment and a second sulfurization treatment. Specifically, the first sulfurization treatment is performed by adding a sulfurizing agent to the raw material solution in an amount that is 1.8 equivalents or more and 2.1 equivalents or less relative to the total amount of thallium and cadmium in the raw material solution, which is the starting liquid. Thereafter, the second sulfurization treatment is performed by adding a sulfurizing agent to the post-sulfurization solution (post-first sulfurization treatment solution) obtained by the first sulfurization treatment in an amount that is 2.5 equivalents or more and 4.0 equivalents or less relative to the total amount of thallium and cadmium in the raw material solution.

[0033] By carrying out such a two-stage sulfurization treatment, the cadmium contained in the raw material solution can be sulfurized in the first sulfurization treatment and mutually separated from thallium, and then the thallium can be effectively sulfurized in the second sulfurization treatment, thereby efficiently increasing the purity of thallium in the resulting sulfide.

[0034] The sulfurizing agent used in the sulfurization treatment is not particularly limited as long as it can convert thallium and cadmium in the raw solution into sulfides. For example, in addition to sodium hydrogen sulfide (NaHS) used in the above-mentioned test example, sodium sulfide (NaS) and hydrogen sulfide (HS) can also be suitably used.

[0035] [Leaching process] The leaching step is a step of adding sulfuric acid to the mixed sulfide containing thallium sulfide and cadmium sulfide obtained through the sulfurization step to perform a leaching treatment to leach thallium from the mixed sulfide. By performing such a leaching treatment, thallium can be selectively leached from the mixed sulfide, and thallium can be separated from cadmium and recovered.

[0036] In the leaching process, sulfuric acid is added to the mixed sulfide and the pH is controlled to between 0.5 and 1.5. This allows thallium to be preferentially leached from the thallium sulfide that makes up the mixed sulfide into the sulfuric acid solution, thereby increasing selectivity. Meanwhile, cadmium is distributed in the form of cadmium sulfide to the leaching residue.

[0037] Furthermore, by carrying out the leaching treatment while controlling the pH in the range of 0.5 to 1.5 in this way, it is possible to suppress an increase in the amount of free acid contained in the treatment solution obtained after separating thallium in the production process of a thallium compound, which will be described later. As a result, when the treatment solution is recycled as a raw material solution for producing metallic cadmium, for example, the amount of alkali used in the recycling plant can be reduced.

[0038] Regarding temperature conditions, the higher the temperature, the more selectively leaching of thallium improves, and the more easily it can be separated from cadmium. However, as long as the temperature is within the range of 10°C to 80°C, there is no need to make any special temperature adjustments.

[0039] The solid phase obtained through the leaching step can be separated from the leachate containing thallium by applying a solid-liquid separation method such as settling separation or filtration as a leach residue, or industrially, a solid-liquid separation method such as pressure filtration, suction filtration, centrifugation, etc. The separated leach residue has a sufficiently reduced thallium content, and therefore can be recycled as a raw material for producing, for example, metallic cadmium or zinc oxide ore.

[0040] [Neutralization process] Although not an essential aspect, a neutralization step of neutralizing the raw material solution may be performed prior to the sulfurization step described above. In particular, when the raw material solution contains impurity elements including zinc and / or lead, the neutralization step can effectively separate and remove these impurity elements, thereby obtaining a solution in which thallium is concentrated.

[0041] As described above, the neutralization step is carried out prior to the sulfurization step, and the neutralized liquid obtained by separating and removing precipitates of impurity elements through the neutralization treatment is subjected to treatment in the sulfurization step.

[0042] Specifically, the neutralization step can include, for example, a step of performing a first neutralization treatment on the raw material solution (first neutralization step) and a step of performing a second neutralization step on the filtrate obtained in the first neutralization step (second neutralization step).

[0043] (First neutralization step) In the first neutralization step, a pH adjuster is added to a raw material solution containing thallium, cadmium, and at least zinc and / or lead, to adjust the pH to a range in which the impurity elements zinc and / or lead form hydroxides and precipitate. The treatment in the first neutralization step is also referred to as the first neutralization treatment. This first neutralization treatment produces a first neutralized slurry consisting of a precipitate of zinc and / or lead hydroxides and a neutralized liquid (liquid phase). The first neutralized slurry is then subjected to solid-liquid separation, which removes the precipitate of zinc and / or lead hydroxides from the system, yielding a first neutralized liquid (filtrate) containing thallium and cadmium.

[0044] The pH range to be adjusted is not particularly limited, as long as it is within a range in which the zinc and / or lead contained in the raw solution form hydroxides and precipitate. Preferably, the pH is adjusted to a range of 7.0 or higher and 9.0 or lower. This allows most of the zinc and / or lead to be distributed in the hydroxide precipitate (solid phase) while most of the cadmium and almost all of the thallium remain in the liquid phase, thereby enabling more effective and efficient separation and removal of impurity elements. More preferably, the pH is adjusted to a range of 7.5 or higher and 8.5 or lower. This allows the precipitation rate of zinc to be 90% or higher and the precipitation rate of lead to be 80%, enabling more effective separation and removal of impurity elements.

[0045] The pH adjuster can be any alkali hydroxide that is industrially usable, such as calcium hydroxide, sodium hydroxide, magnesium hydroxide, and potassium hydroxide.

[0046] (Second neutralization step) In the second neutralization step, a pH adjuster is added to the filtrate obtained through the first neutralization step to adjust the pH to a range in which the cadmium contained in the filtrate forms hydroxide and precipitates. The treatment in the second neutralization step is also referred to as the second neutralization treatment. This second neutralization treatment produces a second neutralized slurry consisting of a cadmium hydroxide precipitate and a neutralized liquid (liquid phase). The second neutralized slurry is then subjected to solid-liquid separation, which allows the cadmium hydroxide precipitate to be removed from the system, yielding a second neutralized liquid (filtrate) containing thallium at a high purity.

[0047] In this way, by treating the raw material solution in the first neutralization step and then treating the resulting filtrate in the second neutralization step, zinc and / or lead, as well as most of the cadmium, are removed, and a neutralized solution containing almost all of the thallium in the raw material solution can be obtained.

[0048] The cadmium hydroxide separated through the second neutralization step has almost all of the thallium removed, and it is possible to obtain, for example, 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.

[0049] The pH range to be adjusted is not particularly limited, as long as it is within a range in which cadmium contained in the filtrate forms cadmium hydroxide and precipitates, while thallium does not precipitate. Preferably, the pH is adjusted to a range higher than the pH adjusted in the first neutralization treatment and not exceeding 11.0. For example, the pH is adjusted to a range of 8.5 or higher and 11.0 or lower. This allows for more effective and efficient precipitation and separation of cadmium.

[0050] Regarding the pH adjustment range, by adjusting the pH to a range higher than the pH adjusted in the first neutralization treatment, preferably to a pH of 8.5 or higher, the cadmium precipitation rate can be 10% or higher, thereby improving the efficiency of cadmium precipitation separation. More preferably, by adjusting the pH to 9.5 or higher, the cadmium precipitation rate can be 50% or higher, which is even more effective. Note that if the pH is adjusted to be equal to or lower than the pH adjusted in the first neutralization treatment, cadmium may not be precipitated. On the other hand, if the pH is adjusted to a range exceeding 11.0, thallium may precipitate, resulting in a loss of thallium recovery.

[0051] As with the pH adjuster used in the first neutralization treatment, any alkali that is commercially available can be used, such as calcium hydroxide, sodium hydroxide, magnesium hydroxide, and potassium hydroxide.

[0052] [Manufacturing process of thallium compounds] The thallium compound production process is a process for producing thallium compounds from a leachate containing thallium obtained through a leaching process. The produced thallium compounds can be subsequently subjected to known acid leaching or reduction treatment to produce metallic thallium.

[0053] In one embodiment of the thallium compound production process, a crystallization step is carried out to precipitate thallium as thallium chloride, or in another embodiment, an oxidation step is carried out to produce thallium as thallium oxide.

[0054] (Crystallization process) In the crystallization step, either a chloride that liberates chloride ions or a solution containing chloride ions is added to the leachate containing thallium obtained through the leaching step to precipitate crystals of thallium chloride. In this way, thallium chloride can be produced by treating the leachate containing thallium in the crystallization step.

[0055] Examples of chlorides that can be added to the leaching solution and liberate chloride ions include sodium chloride, and examples of solutions containing chloride ions include aqueous solutions of sodium hypochlorite.

[0056] In this case, the amount of chloride or chloride ion-containing solution added to the leaching solution to liberate chloride ions is such that the amount of chloride ions is in the range of 5.5 equivalents to 8.0 equivalents relative to the amount of thallium contained in the leaching solution. By adding an amount within this range, thallium can be effectively distributed in a solid form to precipitate thallium chloride, and other elements can be distributed in the solution. Specifically, a high proportion of the thallium contained in the leaching solution, approximately 80% or more, can be converted into the form of thallium chloride, allowing the production of a thallium compound containing high-quality thallium.

[0057] The thallium chloride thus obtained can be separated and recovered from the liquid by applying a solid-liquid separation method. Since the treated liquid from which thallium chloride has been separated has a sufficiently reduced thallium content, it can be recycled as a raw material solution for producing, for example, metallic cadmium or zinc oxide ore.

[0058] (oxidation process) In the oxidation step, an oxidizing agent is added to the leachate containing thallium obtained through the leaching step to generate thallium oxide. In this way, thallium oxide can be produced by treating the leachate containing thallium in the oxidation step.

[0059] An example of an oxidizing agent that can be added to the leachate is sodium hypochlorite.

[0060] In this case, an oxidizing agent is added to the leachate in an amount of 1.0 equivalent to 2.0 equivalents relative to the amount of thallium in the leachate to carry out the oxidation treatment. By adding an oxidizing agent in this range, thallium can be effectively distributed in a solid form to produce thallium oxide, while other elements can be distributed in the solution. Specifically, a high proportion of the thallium contained in the leachate, approximately 80% or more, can be converted into the form of thallium oxide, allowing the production of a thallium compound containing high-quality thallium.

[0061] Preferably, the oxidizing agent is added in an amount of 1.5 to 2.0 equivalents relative to the amount of thallium in the leaching solution, which allows thallium to be more effectively distributed in a solid form to produce thallium oxide, while allowing other elements to be distributed in the solution.

[0062] By adding an oxidizing agent in an amount of 1.0 equivalent or more and 2.0 equivalents or less to carry out the oxidation treatment, the oxidation-reduction potential (ORP) of the reaction solution using a silver / silver chloride electrode as the reference electrode becomes approximately 800 mV or more, as will be shown in the examples described later.

[0063] In addition, in the oxidation treatment, the pH of the leachate is controlled within the range of 2.0 or more and 4.0 or less. If the pH is less than 2.0, thallium may be eluted from the produced thallium oxide, resulting in a reduced recovery amount. Furthermore, when sodium hypochlorite is used as the oxidizing agent, for example, a low pH of less than 2.0 may result in the generation of chlorine gas harmful to the human body. On the other hand, if the pH exceeds 4.0, a precipitate of impurity elements remaining in the leachate is formed, making it difficult to produce high-quality thallium oxide. Furthermore, when sodium hypochlorite is used as the oxidizing agent, for example, a high pH of more than 4.0 may weaken the oxidizing power.

[0064] The thallium oxide thus obtained can be separated and recovered from the liquid by applying a solid-liquid separation method. Since the treated liquid from which thallium oxide has been separated has a sufficiently reduced thallium content, it can be recycled as a raw material solution for producing, for example, metallic cadmium or zinc oxide ore. [Example]

[0065] EXAMPLES The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples.

[0066] [Test Example 1: Sulfurization Process] A sulfurization treatment was carried out by adding a sulfurizing agent solution prepared by diluting 25% sodium hydrogen sulfide (NaHS) 10 times to 200 mL of the raw material solution (starting solution) shown in Table 1 below. Specifically, the amount of sulfurizing agent solution added to the starting solution was varied, and the changes in the concentrations of thallium and cadmium in the liquid phase (post-sulfurization solution) were investigated. The oxidation-reduction potential (ORP) was also measured using a silver / silver chloride electrode as the reference electrode.

[0067] [Table 1]

[0068] The results are shown in Figure 1 and Table 2 below. The elemental analysis of the liquid phase was performed quantitatively using ICP atomic emission spectroscopy. Table 2 also shows the amount of sulfiding agent solution added relative to the total amount of thallium and cadmium in the starting solution.

[0069] [Table 2]

[0070] The results shown in Figure 1 and Table 2 indicate that adding a sulfurizing agent in an amount equal to or greater than 2.5 equivalents of the total amount of thallium and cadmium in the starting raw solution during the sulfurization treatment results in almost no thallium or cadmium remaining in the liquid phase, with almost all of the thallium and cadmium being transferred to a sulfide precipitate (solid phase). For example, the thallium concentration in the liquid phase was reduced to 0.3 mg / L or less, and the cadmium concentration to 0.1 mg / L or less. The ORP at this time was below -200 mV.

[0071] Table 3 below shows the composition of a mixed sulfide containing thallium sulfide and cadmium sulfide obtained by sulfurization treatment using a sulfiding agent solution added in an amount equivalent to 3.3 relative to the total amount of thallium and cadmium in the starting raw solution. The composition of the mixed sulfide was quantitatively analyzed using ICP atomic emission spectroscopy. The ORP at this time was -300 mV. As shown in Table 3, a mixed sulfide containing thallium sulfide and cadmium sulfide as the main components and having a low content of impurity elements was obtained.

[0072] [Table 3]

[0073] [Test Example 2: Leaching process] Next, a 20% sulfuric acid solution was added to 20 wet-g of the mixed sulfide having the composition shown in Table 3 above, and a leaching treatment was carried out while controlling the pH within the range of 1.5 to -0.5, and the leaching rate of each element contained in the mixed sulfide was investigated.

[0074] The results are shown in Figure 2 and Table 4 below. The leaching rate was calculated based on the analytical values ​​obtained by analyzing the element contents in the obtained leachate by ICP atomic emission spectroscopy. Table 4 also shows the content of each element in the leachate (thallium leachate) obtained by leaching treatment under conditions of a liquid temperature of 60°C and a pH of 1.5.

[0075] [Table 4]

[0076] The results shown in Figure 2 and Table 4 indicate that by controlling the pH between 1.5 and -0.5 during leaching, thallium in the mixed sulfide was preferentially leached into the sulfuric acid solution, while cadmium remained in the solid phase as leaching residue. Furthermore, it can be seen that the leaching rate of cadmium increased when the pH was lower than -0.5, and the leaching rate of thallium decreased when the pH was higher than 1.5.

[0077] Furthermore, referring to the graph in Figure 2, it can be seen that a leaching treatment under conditions of a liquid temperature of 60°C and a pH of 1.0 or less can achieve a thallium leaching rate of 80% or more. Furthermore, it can be seen that by controlling the pH to 0 or more, it is possible to leave almost all of the impurity element lead in the solid phase. Furthermore, it can be seen that by controlling the liquid temperature to around 60°C, the selectivity of thallium can be further improved, making it possible to efficiently leach thallium.

[0078] [Test Example 3: Manufacturing process of thallium compound] (Test Example 3-1: Crystallization process) Next, saturated sodium chloride (NaCl) water as a solution containing chloride ions was added to 150 mL of the leaching solution (thallium leaching solution) having the composition shown in Table 4 above in an amount of 1.0 to 7.0 equivalents relative to the amount of thallium in the leaching solution, and crystallization was carried out while maintaining the solution temperature at 20°C. Figure 3 shows the resulting thallium precipitation rate.

[0079] The results shown in Figure 3 show that by adding an amount of chloride ions that results in 5.5 equivalents or more, approximately 90% or more of the thallium in the leaching solution can be converted to thallium chloride.

[0080] (Test Example 3-2: Oxidation Process) In addition, an oxidation treatment was performed by adding sodium hypochlorite (NaClO) as an oxidizing agent in the range of 0 to 1.5 equivalents relative to the amount of thallium in the leachate to 150 mL of the leachate (thallium leachate) with the composition shown in Table 4 above, and sodium hydroxide (NaOH) as a pH adjuster to maintain a pH of 4.0. The oxidation-reduction potential (ORP) was measured using a silver / silver chloride electrode as the reference electrode. Figure 4 shows the relationship between the thallium precipitation rate and ORP as a function of the amount of oxidizing agent added.

[0081] The results shown in Figure 4 indicate that adding an oxidizing agent in an amount of 1.0 equivalent or more can convert approximately 80% or more of the thallium in the leachate into thallium oxide. The ORP at this time was 800 mV or more.

[0082] Table 5 below shows the grades of thallium chloride and thallium oxide obtained through the crystallization step of Test Example 3-1 and the oxidation step of Test Example 3-2. The elemental grades were analyzed by ICP atomic emission spectroscopy. The thallium recovery rate was calculated by comparing the amount of thallium in the starting leachate with the amount of thallium in the resulting thallium compound. Table 5 shows the content (mass%) of thallium (Tl) in the entire compound, and the grades (ppm) of the other elements (Cd, Zn, Pb, Ni).

[0083] [Table 5]

[0084] As shown in Table 5, in all cases where thallium compounds were produced, the content of impurity elements was reduced and thallium compounds containing a high content of thallium were obtained. Furthermore, the thallium recovery rate was 83% or more, indicating that thallium was recovered at a high recovery rate. Metallic thallium can be produced from such thallium compounds. In this case, high-quality metallic thallium can be produced efficiently without complex processing steps. Furthermore, since the treated solution from which the thallium compounds have been separated has a sufficiently reduced thallium content, the problem of thallium accumulation can be avoided even when the treated solution is recycled as a raw material solution for producing, for example, metallic cadmium or zinc oxide ore.

Claims

1. A method for producing thallium from a raw material solution containing thallium, cadmium, and an impurity element, comprising: a sulfurization step in which a sulfurizing agent is added to the raw material solution in an amount of 2.5 equivalents to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide; a leaching step of adding sulfuric acid to the mixed sulfide and leaching thallium from the mixed sulfide while controlling the pH within a range of 0.5 to 1.5; a crystallization step of adding a chloride or a solution containing chloride ions that liberates chloride ions to the leachate containing thallium in an amount such that the amount of chloride ions is 5.5 equivalents to 8.0 equivalents relative to the amount of thallium contained in the leachate, thereby precipitating thallium chloride; A method for producing a thallium compound, comprising:

2. A method for producing thallium from a raw material solution containing thallium, cadmium, and an impurity element, comprising: a sulfurization step in which a sulfurizing agent is added to the raw material solution in an amount of 2.5 equivalents to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution to perform a sulfurization treatment, thereby producing a mixed sulfide containing thallium sulfide and cadmium sulfide; a leaching step of adding sulfuric acid to the mixed sulfide and leaching thallium from the mixed sulfide while controlling the pH within a range of 0.5 to 1.5; an oxidation step of adding an oxidizing agent to the leachate containing thallium in an amount of 1.0 equivalent to 2.0 equivalents relative to the amount of thallium in the leachate and controlling the pH to a range of 2.0 to 4.0 to produce thallium oxide; A method for producing a thallium compound, comprising:

3. In the sulfurization step, a first sulfurization treatment is carried out by adding a sulfurizing agent to the raw material solution in an amount of 1.8 equivalents to 2.1 equivalents relative to the total amount of thallium and cadmium in the raw material solution; Thereafter, a second sulfurization treatment is carried out by adding a sulfurizing agent to the sulfurized solution obtained in the first sulfurization treatment in an amount of 2.5 equivalents to 4.0 equivalents relative to the total amount of thallium and cadmium in the raw material solution. The method for producing the thallium compound according to claim 1 or 2.

4. the raw material solution contains at least zinc and / or lead as the impurity element, Prior to the sulfurization step, a neutralization step is performed on the raw material solution, In the neutralization step, a first neutralization treatment is carried out by adding a pH adjuster to the raw material solution to adjust the pH to a range of 7.0 to 9.0, thereby generating a precipitate composed of hydroxides of zinc and / or lead contained in the raw material solution; Then, a second neutralization treatment is carried out by adding a pH adjuster to the filtrate obtained by separating and removing the precipitate to adjust the pH to a range higher than the pH adjusted in the first neutralization treatment but not exceeding 11.0, thereby producing a precipitate consisting of cadmium hydroxide; The neutralized liquid obtained by separating and removing the precipitate formed in the second neutralization treatment is subjected to the sulfurization step. The method for producing the thallium compound according to claim 1 or 2.

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