Methods for separating arsenic

Abstract

To provide a method for selectively separating arsenic from a material containing arsenic and lead. [Solution] A method for separating arsenic from a material containing arsenic and lead. The material is leached under basic conditions to separate it into a leached solution containing arsenic and a residue containing lead. The leached solution is sulfurized to precipitate and remove the lead inevitably contained in the leached solution as an insoluble sulfide. Next, a calcium compound is added to the leached solution to precipitate and remove the arsenic contained in the leached solution as an insoluble calcium compound.

Description

[Technical Field]

[0001] The present invention relates to a method for separating arsenic from a material containing arsenic and lead. [Background technology]

[0002] During the metal smelting process, various by-products are produced, including intermediates containing different metals, molten fly ash, slime, and volatile dust. These by-products may contain arsenic, for example. Since arsenic is a metal with a high environmental impact, it is necessary to separate and immobilize it to prevent its release into the environment.

[0003] A known conventional technique for the separation and immobilization of arsenic is described in Patent Document 1. This document describes an oxidative leaching process in which an alkaline solution and an oxidizing agent are added to copper arsenide-containing slime generated during the electrolytic refining of copper to extract arsenic. The leached residue is then separated into solid and liquid phases to recover an alkaline arsenate solution. Slaked lime is added to this alkaline arsenate solution to produce calcium arsenate, and then solid and liquid phases are performed to separate and immobilize the arsenic as calcium arsenate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-115196 [Overview of the project] [Problems that the invention aims to solve]

[0005] The inventors further investigated the technology described in Patent Document 1 and discovered that when lead is present in addition to arsenic in the material to be treated, some of the lead is unintentionally incorporated into the calcium arsenate. In calcium arsenate containing lead, the lead is in an unstable state and easily leaches into the environment. Therefore, it is desirable to avoid mixing lead into calcium arsenate. Therefore, the object of the present invention is to provide a method for selectively separating arsenic from a material containing arsenic and lead. [Means for solving the problem]

[0006] The present invention relates to a method for separating arsenic from a material containing arsenic and lead, The material to be treated is subjected to leaching under basic conditions to separate it into an arsenic-containing leaching solution and a lead-containing residue. The leached solution is subjected to sulfidation treatment to precipitate and remove the lead inevitably contained in the leached solution as an insoluble sulfide, and then This invention provides a method for separating arsenic, which involves adding a calcium compound to the leaching solution to precipitate and remove the arsenic contained in the leaching solution as an insoluble calcium compound. [Effects of the Invention]

[0007] According to the present invention, arsenic can be selectively separated from a material containing arsenic and lead. [Modes for carrying out the invention]

[0008] The present invention will be described below based on its preferred embodiments. The present invention relates to a method for separating arsenic from a material containing arsenic and lead. The method of the present invention can be broadly divided into the following three steps. [Process 1] The material to be treated is leached under basic conditions to separate it into an arsenic-containing solution and a lead-containing residue. [Process 2] The arsenic-containing solution is subjected to sulfidation treatment to precipitate and remove the lead, which is inevitably present in the arsenic-containing solution, as an insoluble sulfide. [Step 3] A calcium compound is added to a solution containing arsenic to precipitate and remove the arsenic from the solution as an insoluble calcium compound. The following details each step.

[0009] [Process 1] The object to be processed in this project contains arsenic and lead. Examples of the object to be processed containing arsenic and lead include, but are not limited to, intermediates generated as by-products in the process of metal smelting, molten fly ash, slime, and volatile dust. In particular, the object to be processed is preferably a secondary raw material generated in the non-ferrous metal smelting process. The secondary raw material refers to intermediate products (such as slag and slime) generated in the non-ferrous metal smelting process, molten fly ash, volatile dust, etc. In contrast to the secondary raw material, the primary raw material mainly means ore raw materials. There are no particular restrictions on the state of existence of arsenic and lead in the object to be processed. For example, arsenic and lead can exist in the form of oxides respectively. Alternatively, arsenic and lead can exist, for example, in the form of complex oxides. The object to be processed may contain other metal elements in addition to arsenic and lead. For example, when the object to be processed is slime generated as a by-product in the non-ferrous metal smelting process, copper, zinc, bismuth, antimony, etc. may be contained in the object to be processed.

[0010] The amount of arsenic contained in the object to be processed depends on how the object to be processed is obtained, but generally it is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, and even more preferably 2.0 mass% or more. There is no particular restriction on the upper limit value of the amount of arsenic, but generally it is 10 mass% or less. Similarly, the amount of lead contained in the object to be processed also depends on how the object to be processed is obtained, but generally it is preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less. The lower limit value of the amount of lead contained in the object to be processed is generally 1.0 mass% or more. When the object to be processed contains other metal elements in addition to arsenic and lead, for example, when copper, zinc or antimony is contained, the amounts of these metal elements are preferably 0.1 mass% or more and 80.0 mass% or less independently.

[0011] In this process, the material to be treated is leached under basic conditions. Leaching the material under basic conditions has the advantage of selectively leaching arsenic without leaching lead contained in the material. For leaching under basic conditions, for example, aqueous solutions of alkali metal hydroxides and alkaline earth metals can be used. Examples of alkali metal hydroxides include, but are not limited to, sodium hydroxide and potassium hydroxide.

[0012] When using an aqueous solution of, for example, an alkali metal hydroxide for leaching under basic conditions, the concentration of the aqueous solution is preferably 0.25 mol / L or higher, more preferably 0.5 mol / L or higher, and even more preferably 0.75 mol / L or higher, from the viewpoint of successfully carrying out the leaching. On the other hand, from the viewpoint of suppressing lead leaching and reprecipitation, the concentration of the aqueous solution of alkali metal hydroxide is preferably 1.5 mol / L or less, more preferably 1.25 mol / L or less, and even more preferably 1.0 mol / L or less.

[0013] The amount of alkali metal hydroxide aqueous solution used relative to the amount of material to be treated can be appropriately adjusted according to the amount of arsenic contained in the material to be treated. For example, when the concentration of the alkali metal hydroxide aqueous solution is within the above range, it is preferable to use 100g or more of the material to be treated per 1L of alkali metal hydroxide aqueous solution, more preferably 150g or more, and even more preferably 200g or more. Furthermore, it is preferable to use 400g or less of the material to be treated per 1L of alkali metal hydroxide aqueous solution, more preferably 350g or less, and even more preferably 300g or less.

[0014] The leaching treatment may be carried out at room temperature without heating, or it may be carried out under heating. When the leaching treatment is carried out under heating, from the viewpoint of efficient leaching, it is preferable to raise the liquid temperature to 40°C or higher, more preferably to 50°C or higher, and even more preferably to 60°C or higher.

[0015] There are no particular restrictions on the leaching time; it should be continued until most of the arsenic contained in the material being treated has leached into the solution. The elution reaction of arsenic when, for example, an aqueous sodium hydroxide solution is used for the leaching treatment is expressed by the following formula. As2O5+ 4NaOH → Na2HAsO4+ H2O

[0016] By leaching the material to be treated under basic conditions, arsenic can be selectively leached without leaching lead contained in the material. Lead is contained in the leaching residue. Therefore, arsenic can be separated from lead by solid-liquid separation of the leaching solution and the leaching residue, and by recovering the leaching solution. If the material to be treated contains other non-ferrous metals in addition to arsenic and lead, such as zinc, zinc is contained in the leaching residue along with lead. Therefore, zinc, like lead, is separated from arsenic in the leaching solution.

[0017] At the completion of step 1, the concentration of arsenic in the leached solution is preferably 1.0 g / L or more, more preferably 2.0 g / L or more, and even more preferably 3.0 g / L or more, from the viewpoint of successfully generating an insoluble arsenic compound by adding a calcium compound to the solution. The upper limit of the concentration of arsenic in the leached solution is generally 20.0 g / L or less.

[0018] [Process 2] Under basic conditions, leaching of the material to be treated selectively extracts arsenic into the leaching solution, but some lead may inevitably leach out. In other words, the leaching solution may contain both arsenic and lead. Therefore, in this process, the arsenic-containing leaching solution is subjected to sulfidation treatment to precipitate and remove the lead inevitably present in the leaching solution as an insoluble sulfide. Through sulfidation treatment, lead becomes lead sulfide, an insoluble sulfide in water, and precipitates in the leaching solution. In contrast, arsenic does not become a sulfide and remains dissolved in the leaching solution. In the following explanation, the leaching solution containing arsenic and lead and subjected to sulfidation treatment will also be referred to as "arsenic-lead solution."

[0019] The lead concentration in a lead arsenic solution is generally 40.0 g / L or less, but may also be 20.0 g / L or less, or 10.0 g / L or less. The lower limit for the lead concentration in a lead arsenic solution is generally 1.0 g / L or higher.

[0020] For the sulfidation treatment of lead contained in the arsenic lead solution, metal sulfides can be used, for example. Examples of metal sulfides include alkali metal sulfides and alkaline earth metal sulfides. Examples of alkali metal sulfides include sodium sulfide and potassium sulfide. Examples of alkaline earth metal sulfides include magnesium sulfide and calcium sulfide. These sulfides can be used individually or in combination of two or more.

[0021] In this process, it is preferable to use alkali metal sulfides for the sulfidation treatment, and to use the same alkali metal as the alkali metal hydroxide used in the leaching treatment in the first step as the alkali metal sulfide used in the sulfidation treatment. For example, it is preferable to use sodium hydroxide in the leaching treatment in the first step and sodium sulfide in the sulfidation treatment in the second step. By doing so, the number of ionic species contained in the lead arsenic solution can be reduced. Reducing the number of ionic species is advantageous because it makes the reaction in the solution less complex and easier to control. Furthermore, as will be described later, there is also the advantage that it becomes easier to manage when the alkaline solution obtained in step 3 is reused in the leaching treatment in step 1.

[0022] The aforementioned metal sulfide can be added to the lead arsenide solution in solid particulate form. The amount of metal sulfide added can be appropriately adjusted according to the amount of lead contained in the lead arsenide solution. Specifically, from the viewpoint of reliably sulfidizing the lead contained in the lead arsenide solution, the amount of metal sulfide added can be adjusted according to the number of moles of lead (M) contained in the lead arsenide solution. Pb The number of moles of metal sulfide relative to M S The ratio M S / M PbIt is preferable that the value be 1.0 or greater, and even more preferable that it be 1.2 or greater. Furthermore, in order to facilitate management when the alkaline solution obtained in step 3 is reused in the leaching treatment of step 1, M S / M Pb The value of is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

[0023] The sulfidation treatment may be carried out at room temperature without heating, or it may be carried out with heating. When the sulfidation treatment is carried out with heating, from the viewpoint of efficiently performing sulfidation, it is preferable to raise the liquid temperature to 40°C or higher, more preferably to 50°C or higher, and even more preferably to 60°C or higher.

[0024] There are no particular restrictions on the sulfidation time; it should be continued until most of the lead in the arsenic lead solution has been sulfided and precipitated. The sulfidation reaction of lead when sodium sulfide is used for the sulfidation treatment is expressed by the following equation. Pb 2+ + Na2S → PbS + 2Na 2+

[0025] By sulfidating the lead arsenide solution, the lead contained in the solution can be selectively sulfided. The lead sulfide produced by sulfidation precipitates. On the other hand, arsenic is not sulfided and remains in the solution. Therefore, by recovering the solution separated by solid-liquid separation, arsenic can be completely separated from lead. This solution contains arsenic but does not contain lead. Therefore, in the following explanation, this solution will also be called the "arsenic solution." The pH of the arsenic solution (at 25°C) is generally between 11 and 14.

[0026] [Step 3] In this step, the arsenic contained in the arsenic solution obtained in step 2 is converted into a water-insoluble compound, precipitated, and removed from the solution. For this purpose, a calcium compound is added to the arsenic solution in this step.

[0027] The concentration of arsenic in the arsenic solution is preferably 1.0 g / L or more, more preferably 2.0 g / L or more, and even more preferably 3.0 g / L or more from the viewpoint of successfully forming an insoluble compound of arsenic by adding a calcium compound to the solution. Also, the concentration of arsenic is generally 15.0 g / L or less.

[0028] In the formation of the insoluble calcium compound of arsenic in this step, as the calcium compound, for example, calcium hydroxide, calcium oxide, calcium chloride, etc. can be used, but not limited thereto. These calcium compounds can be used alone or in combination of two or more.

[0029] The calcium compound can be added to the arsenic solution in a solid particulate state. The addition amount of the calcium compound can be appropriately adjusted according to the amount of arsenic contained in the arsenic solution. Specifically, from the viewpoint of surely converting the arsenic contained in the arsenic solution into an insoluble compound, the number of moles M As of calcium compound with respect to the number of moles M Ca of arsenic contained in the arsenic solution, the ratio of M Ca / M As is preferably 1.7 or more, more preferably 2.0 or more, and even more preferably 4.0 or more. M Ca / M As There is no particular limitation on the upper limit value of, but generally it is preferably 8.0 or less.

[0030] The insolubilization treatment of arsenic may be carried out without heating near room temperature or may be carried out under heating. When carrying out the insolubilization treatment under heating, from the viewpoint of efficiently carrying out the insolubilization, it is even more preferable to set the liquid temperature to 50°C or more and 70°C or less.

[0031] There is no particular limitation on the insolubilization time, and it may be carried out until almost all of the arsenic contained in the arsenic solution is insolubilized and precipitated. The arsenic insolubilization reaction when using, for example, calcium hydroxide in the insolubilization treatment is represented by the following formula. 3Na2HAsO4+ 5Ca(OH)2→ 6NaOH + As3Ca5O 13 H↓ + 3H2O

[0032] By recovering the arsenic-insoluble calcium compound through solid-liquid separation, arsenic can ultimately be separated from the treated material. The arsenic-insoluble calcium compound also has the advantage of suppressing elution because the arsenic is immobilized within it. To further suppress arsenic elution, the arsenic-insoluble calcium compound may be mixed with glass powder, and the mixture heated and melted to produce an arsenic-containing vitrified body. As the glass powder, for example, a vitrification material containing iron, silica, and an alkali component, as described in Patent Document 1, can be used.

[0033] [Other steps 1] It is preferable to add an alkali metal hydroxide to the arsenic solution obtained in step 2 after removing the insoluble lead sulfides by the sulfidation treatment in step 2, and before adding the calcium compound in step 3. Hereinafter, this step will also be referred to as the "alkali addition step." The technical significance of performing the alkali addition step between step 2 and step 3 is described below. The solubility of the calcium compound added in step 3, such as calcium hydroxide, decreases as the basicity of the solution increases. This is unfavorable from the standpoint of reacting the calcium compound with arsenic to produce an insoluble arsenic product. However, surprisingly, the inventors' research has revealed that if the calcium compound is added in step 3 after the lead has been removed from the solution by sulfidation treatment in step 2 and the basicity of the solution has been increased, the reaction between the calcium compound and arsenic is promoted, and the insoluble arsenic product can be successfully produced.

[0034] From the above perspective, examples of alkali metal hydroxides to be added to the arsenic solution obtained in step 2 include sodium hydroxide and potassium hydroxide. These alkali metal hydroxides can be used individually or in combination of two or more. In particular, it is advantageous that the alkali metal hydroxide used in the leaching treatment of step 1, the alkali metal sulfide used in the sulfidation treatment of step 2, and the alkali metal hydroxide used in the alkali addition step are all a common alkali metal, as this simplifies the reaction in solution and makes it easier to control the reaction. From this perspective, it is preferable that the common alkali metal is sodium.

[0035] Generally, the concentration of basic substances in aqueous solutions is often controlled by pH. In contrast to this, the inventors' research has shown that in the alkali addition step, it is advantageous to control the amount of alkali metal hydroxide added to the arsenic solution obtained in step 2 by the conductivity of the arsenic solution. This is because even if the amount of alkali metal hydroxide added to the arsenic solution in the alkali addition step is so small that a clear pH change cannot be measured in the complex reaction system in the solution, the insolubilization reaction of arsenic in step 3 is promoted. In contrast to the pH value, even if the amount of alkali metal hydroxide added is so small that a clear pH change cannot be measured in the complex reaction system in the solution, the conductivity of the arsenic solution changes sufficiently.

[0036] In the alkali addition step, it is preferable to add an amount of alkali metal hydroxide such that the conductivity of the arsenic solution obtained in step 2 is greater than 7 mS / cm, from the viewpoint of further promoting the arsenic insolubilization reaction in step 3. From the viewpoint of making this advantage even more pronounced, it is even more preferable to add an amount of alkali metal hydroxide in the alkali addition step such that the conductivity of the arsenic solution obtained in step 2 is greater than 9 mS / cm. The upper limit of conductivity is generally 30 mS / cm or less. In this specification, conductivity refers to the value measured at 60°C.

[0037] The alkali metal hydroxide added to the arsenic solution in the alkali addition step may be in a solid state or an aqueous solution, as long as the conductivity described above is controlled.

[0038] [Other steps 2] The solution obtained after precipitating and removing the insoluble calcium compound of arsenic from the arsenic solution in step 3 (hereinafter referred to as the "arsenic-removed solution") contains dissolved alkali metal hydroxides added in step 1 and, if necessary, in the alkali addition step. Since the arsenic-removed solution is highly basic, using this solution for the leaching treatment in step 1 can reduce the amount of basic substances used in step 1. This is extremely advantageous from an economic standpoint in this method. The arsenic-removed solution can be used in step 1 as is. Alternatively, it may be used in step 1 after adjusting its degree of basicity.

[0039] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiments, it is essential that the workpiece contains arsenic and lead, but there is no prejudice to the inclusion of other metals. Furthermore, prior to subjecting the material to be treated to step 1, the material may be crushed as needed to adjust its particle size to one suitable for leaching.

[0040] With regard to the embodiments described above, the present invention further discloses the following method for separating arsenic. <1> A method for separating arsenic from a material containing arsenic and lead, The material to be treated is subjected to leaching under basic conditions to separate it into an arsenic-containing leaching solution and a lead-containing residue. The leached solution is subjected to sulfidation treatment to precipitate and remove the lead inevitably contained in the leached solution as an insoluble sulfide, and then A method for separating arsenic, comprising adding a calcium compound to the leaching solution to precipitate and remove the arsenic contained in the leaching solution as an insoluble calcium compound. <2> Alkali metal hydroxide is used in the aforementioned leaching treatment. <1> The separation method described above. <3> In the aforementioned sulfidation treatment, an alkali metal sulfide is used. The alkali metal used in the alkali metal sulfide for the sulfidation treatment is the same type of alkali metal used in the alkali metal hydroxide for the leaching treatment. <2> The separation method described above. <4> The leaching treatment is performed under the condition that the concentration of the alkali metal hydroxide is 1.5 mol / L or less. <2> The separation method described above. <5> After removing the insoluble sulfide by the aforementioned sulfidation treatment, and before adding the calcium compound, alkali metal hydroxide is added to the leached solution. <1> or <4> The separation method described in any one of the following. <6> The amount of hydroxide added is controlled based on the conductivity of the leaching solution. <5> The separation method described above. <7> The leached solution, after removing the insoluble calcium compound, is used for the leaching treatment of the object to be treated. <1> or <6> The separation method described in any one of the following. <8> The material to be processed is a secondary raw material produced in the smelting process of non-ferrous metals. <1> or <7> The separation method described in any one of the following. [Examples]

[0041] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0042] [Example 1] [Process 1] A material containing arsenic, lead, and zinc was prepared. This material was a secondary raw material produced in the smelting process of non-ferrous metals. The proportion of arsenic in the material was 5.24%, the proportion of lead was 10.20%, and the proportion of zinc was 65.20%. A 1.07 mol / L sodium hydroxide aqueous solution heated to 60°C was mixed with the pulverized material to be treated and stirred for 60 minutes. 2 L of sodium hydroxide aqueous solution was used. 400 g of the material to be treated was used. This leached out the arsenic from the material. The leached solution containing arsenic and the leached residue containing lead and zinc were separated by solid-liquid separation, and the leached solution was recovered. Elemental analysis revealed that the leached solution contained 8.62 g / L of arsenic and 6.71 g / L of lead.

[0043] [Process 2] The leached solution obtained in step 1 was heated to 60°C, and sodium sulfide powder was added to the leached solution to carry out lead sulfidation. The amount added was such that the Na2S / Pb molar ratio was 1.2. The reaction time was 30 minutes. The arsenic solution was recovered by solid-liquid separation of the arsenic solution and the precipitate containing lead sulfide. Elemental analysis revealed that the arsenic solution contained 8.52 g / L of arsenic. The amount of lead was 0.02 g / L. The pH of the arsenic solution (at 25°C) was 12.1.

[0044] [Alkali addition process] A 400 g / L sodium hydroxide aqueous solution was added to the arsenic solution obtained in step 2. The amount of sodium hydroxide aqueous solution added was such that the conductivity after addition increased by 10.0 mS / cm compared to the conductivity of the solution before addition.

[0045] [Step 3] The arsenic solution after the alkali addition step was heated to 60°C, and calcium hydroxide powder was added to precipitate the arsenic-insoluble calcium compound. The number of moles of arsenic in the arsenic solution was M. As The number of moles of calcium compound M Ca Ratio M Ca / M As The value was set to 4.0. The reaction time was set to 120 minutes. The precipitate was separated into solid and liquid components to recover the liquid (hereinafter referred to as "arsenic-removed solution") and the residue. The arsenic and lead content of the arsenic-removed solution and the residue was measured by elemental analysis. Furthermore, an elution test was performed on the residue in accordance with Ministry of the Environment Notification No. 13. The results are shown in Table 1 below. The elution standard values ​​for arsenic and lead are less than 0.3 mg / L.

[0046] [Example 2] [Process 1] A material containing arsenic, lead, and zinc was prepared. This material was a secondary raw material produced in the smelting process of non-ferrous metals. The proportion of arsenic in the material was 2.42%, the proportion of lead was 3.24%, and the proportion of zinc was 65.65%. A 0.93 mol / L sodium hydroxide aqueous solution heated to 60°C was mixed with the pulverized material to be treated and stirred for 60 minutes. 2 L of sodium hydroxide aqueous solution was used. 400 g of the material to be treated was used. This leached out the arsenic from the material. The leached solution containing arsenic and the leached residue containing lead and zinc were separated by solid-liquid separation, and the leached solution was recovered. Elemental analysis revealed that the leached solution contained 5.12 g / L of arsenic and 6.53 g / L of lead.

[0047] [Process 2] The leached solution obtained in step 1 was heated to 60°C, and sodium sulfide powder was added to the leached solution to carry out lead sulfidation. The amount added was such that the Na2S / Pb molar ratio was 1.2. The reaction time was 30 minutes. The arsenic solution was recovered by solid-liquid separation of the arsenic solution and the precipitate containing lead sulfide. Elemental analysis revealed that the arsenic solution contained 4.73 g / L of arsenic. The amount of lead was 0.17 g / L. The pH of the arsenic solution (at 25°C) was 12.3.

[0048] [Alkali addition process] A 400 g / L sodium hydroxide aqueous solution was added to the arsenic solution obtained in step 2. The amount of sodium hydroxide aqueous solution added was such that the conductivity after addition increased by 12.0 mS / cm compared to the conductivity of the solution before addition.

[0049] [Step 3] The arsenic solution after the alkali addition step was heated to 60°C, and calcium hydroxide powder was added to precipitate the arsenic-insoluble calcium compound. The number of moles of arsenic in the arsenic solution was M. As The number of moles of calcium compound M Ca Ratio M Ca / M As The value was set to 5.0. The reaction time was set to 120 minutes. The precipitate was separated into solid and liquid phases to remove arsenic, and the resulting solution and residue were recovered. The arsenic and lead content of the arsenic-removed solution and residue was measured by elemental analysis. The results are shown in Table 1 below.

[0050] [Example 3] In the alkali addition step of Example 2, the amount of sodium hydroxide aqueous solution added was set to an amount that increased the conductivity of the solution after addition by 20.8 mS / cm compared to the conductivity of the solution before addition. The rest of the procedure was the same as in Example 2, and in step 3, the arsenic-removed solution and residue were collected. The arsenic and lead content of the arsenic-removed solution and residue was measured by elemental analysis. The results are shown in Table 1 below.

[0051] [Example 4] In Example 2, the alkali addition step was omitted. Otherwise, the procedure was the same as in Example 2, and in step 3, the arsenic-removed solution and residue were recovered. The arsenic and lead content of the arsenic-removed solution and residue was measured by elemental analysis. The results are shown in Table 1 below.

[0052] [Example 5] [Process 1] A material containing arsenic, lead, and zinc was prepared. This material was a secondary raw material produced in the smelting process of non-ferrous metals. The proportion of arsenic in the material was 5.62%, the proportion of lead was 12.02%, and the proportion of zinc was 56.45%. A 0.93 mol / L sodium hydroxide aqueous solution heated to 60°C was mixed with the pulverized material to be treated and stirred for 60 minutes. 2 L of sodium hydroxide aqueous solution was used. 400 g of the material to be treated was used. This leached out the arsenic from the material. The leached solution containing arsenic and the leached residue containing lead and zinc were separated by solid-liquid separation, and the leached solution was recovered. Elemental analysis revealed that the leached solution contained 5.62 g / L of arsenic and 5.50 g / L of lead.

[0053] [Process 2] The leached solution obtained in step 1 was heated to 60°C, and sodium sulfide powder was added to the leached solution to carry out lead sulfidation. The amount added was such that the Na2S / Pb molar ratio was 1.2. The reaction time was 30 minutes. The arsenic solution was recovered by solid-liquid separation of the arsenic solution and the precipitate containing lead sulfide. Elemental analysis revealed that the arsenic solution contained 5.39 g / L of arsenic. The amount of lead was 0.03 g / L. The pH of the arsenic solution (at 25°C) was 10.9.

[0054] [Alkali addition process] A 400 g / L sodium hydroxide aqueous solution was added to the arsenic solution obtained in step 2. The amount of sodium hydroxide aqueous solution added was such that the conductivity after addition increased by 11.0 mS / cm compared to the conductivity of the solution before addition.

[0055] [Step 3] The arsenic solution after the alkali addition step was heated to 60°C, and calcium hydroxide powder was added to precipitate the arsenic-insoluble calcium compound. The number of moles of arsenic in the arsenic solution was M. As The number of moles of calcium compound M Ca Ratio M Ca / M As The value was set to 5.0. The reaction time was set to 120 minutes. The precipitate was separated into solid and liquid phases to remove arsenic, and the resulting solution and residue were recovered. The arsenic and lead content of the arsenic-removed solution and residue was measured by elemental analysis. Furthermore, an elution test was performed on the residue in accordance with Ministry of the Environment Notification No. 13. The results are shown in Table 1 below.

[0056] [Comparative Example 1] In Example 5, steps 2 and alkali addition were omitted. Otherwise, the procedure was the same as in Example 5. The arsenic-removed solution and residue obtained in step 3 were measured in the same manner as in Example 5. The results are shown in Table 1.

[0057] [Table 1]

[0058] As is clear from the results shown in Table 1, the method of the examples shows that arsenic can be selectively separated without containing lead. Furthermore, it can be seen that the arsenic is immobilized and its elution is suppressed. In particular, as is clear from the comparison between Examples 1 to 3 and 5, in which an alkali addition step was performed between steps 2 and 3, and Example 4, in which no alkali addition step was performed, the arsenic concentration in the arsenic-removed solution obtained in step 3 decreased when the alkali addition step was performed, indicating that the formation of calcium arsenate was promoted.

Claims

1. A method for separating arsenic from a material containing arsenic and lead, The material to be treated is subjected to leaching under basic conditions to separate it into an arsenic-containing leaching solution and a lead-containing residue. The leached solution is subjected to sulfidation treatment to precipitate and remove the lead inevitably contained in the leached solution as an insoluble sulfide, and then A method for separating arsenic, comprising adding a calcium compound to the leaching solution to precipitate and remove the arsenic contained in the leaching solution as an insoluble calcium compound.

2. The separation method according to claim 1, wherein an alkali metal hydroxide is used in the leaching treatment.

3. In the aforementioned sulfidation treatment, an alkali metal sulfide is used. The separation method according to claim 2, wherein the alkali metal used in the alkali metal sulfide for the sulfidation treatment is of the same type as the alkali metal used in the alkali metal hydroxide for the leaching treatment.

4. The separation method according to claim 2, wherein the leaching treatment is performed under the condition that the concentration of the alkali metal hydroxide is 1.5 mol / L or less.

5. The separation method according to claim 1 or 2, wherein an alkali metal hydroxide is added to the leached solution after the insoluble sulfide has been removed by the sulfidation treatment and before the calcium compound is added.

6. The separation method according to claim 5, wherein the amount of hydroxide added is controlled based on the conductivity of the leaching solution.

7. The separation method according to claim 1 or 2, wherein the leached solution obtained after removing the insoluble calcium compound is used for leaching the material to be treated.

8. The separation method according to claim 1 or 2, wherein the material to be treated is a secondary raw material generated in the smelting process of non-ferrous metals.

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