JPH11277075A - Method for removing/fixing arsenic existing in iron sulfate solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the loss of valued metals and to be adapted to a practical wet zinc smelting process by removing/fixing arsenic existing in an iron sulfate solution as an iron-arsenic compound which is stable, crystalline, and inelutable. SOLUTION: A reducing agent, i.e., the metal powder of zinc. iron, or the like is added into an iron sulfate solution containing arsenic for the removal and concentration of arsenic. In this process, arsenic is basically precipitated in the form of iron and iron arsenide and/or a simple substance of arsenic, and is precipitated preferentially as copper arsenide in the presence of copper. The reaction is preferably carried out while the oxidation-reduction potential is being controlled. In the concentration of arsenic, a sulfide such as hydrogen sulfide gas can be used in place of the metal powder reducing agent. In thin case, arsenic is precipitated in the form of arsenic sulfide. Next, iron is added to arsenic-concentrated pulp, mixing is done to be a prescribed Fe/As ratio, the temperature is increased to a prescribed value, oxygen is added to be a prescribed oxygen partial pressure to fix the arsenic as a crystalline, stable iron-arsenic compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for removing and fixing arsenic present in an iron sulfate solution.

[0002]

2. Description of the Related Art Conventionally, many techniques have been proposed and implemented as a method for removing arsenic present in an iron sulfate solution. The main methods are (1) coprecipitation and / or adsorption with iron sulfate or iron hydroxide. (2) Copper arsenide precipitation method by electrolysis or substitution in the presence of copper ions. (3) A sulfide precipitation method using a sulfide agent such as hydrogen sulfide or sodium sulfide.

The method (1) is further roughly classified into the following two methods. (A) A method in which a neutralizing agent such as slaked lime is added to an iron sulfate solution containing arsenic to form an arsenic iron compound precipitate under atmospheric pressure.

(B) A solution or solid containing arsenic and a solution or solid containing iron are charged into an autoclave,
A thermodynamic precipitation method in which the temperature is raised to about 200 ° C. to precipitate a crystalline iron-arsenic compound and simultaneously leaching elements such as zinc and copper into a liquid.

The above method (a) is very general,
A neutralizing agent is added to an iron sulphate solution containing arsenic to adjust the pH to 4 or more, and is removed by coprecipitation with iron arsenate or iron hydroxide and / or adsorption. At this time, when arsenic is not pentavalent and / or iron is divalent, the oxidation treatment is performed using air, oxygen and / or an oxidizing agent.

According to this method, arsenic is effectively removed, but there is a problem that the amount of the final residue becomes enormous with the use of the neutralizing agent. Also, the processing of the artifacts generated by this method is very costly.

[0007] Next, (b) is a method for making the apparatus more compact, and is a method in which the fixing of arsenic and the recovery of valuable metals can be performed simultaneously and with a simple process.

However, in the case of an actual iron sulfate solution, for example, an iron sulfate solution obtained from SO ₂ reduction or high-temperature high-acid leaching of a zinc leaching residue in a wet zinc smelting, the arsenic contained is overwhelmingly overwhelming. It usually contains a large amount of iron, and it was not possible to directly separate and fix arsenic using this method.

In the above method (2), copper ions coexisting with arsenic present in the acidic solution are precipitated and removed as copper arsenide by reduction. Not only a large amount of copper but also valuable metals such as indium and gallium are simultaneously precipitated.

The method (3) is also the same as the method (2). In the case of this method, a technique for preventing arsenic elution described in Japanese Patent Publication No. 56-69627 upon disposal of the final product has been proposed, but the problem of valuable metal loss has not been solved.

In recent years, there has been a proposal of the above-mentioned technology due to increasing interest in so-called environmental problems. However, no example has been known in which the technology for removing arsenic and fixing arsenic has been incorporated into actual operation. Although each of the above processes is an excellent technique under each predetermined condition, it is extremely difficult to implement them industrially due to differences in initial conditions or economic problems.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has been developed by using iron sulfate solution,
For example, arsenic present in an iron sulfate solution obtained from SO ₂ reduction or high-temperature high-acid leaching of zinc leaching residue in wet zinc smelting is removed from the system without losing valuable metals such as indium and gallium, and concentrated. Further, a method of fixing the compound as a stable crystalline compound with iron has been established, and a technique that can be adapted to an actual wet zinc smelting process is proposed.

[0013]

The first invention is characterized in that arsenic present in an iron sulfate solution is removed as a stable crystalline and non-elutable iron / arsenic compound with iron and fixed. And removing and fixing arsenic present in the iron sulfate solution.

According to a second aspect of the present invention, there is provided a first step of removing arsenic by adding a dearsenic agent to an arsenic-containing iron sulfate solution, and an Fe / As ratio, a temperature and an oxygen content of the arsenic-enriched pulp obtained in the first step. By adjusting the pressure to a predetermined condition, it is possible to
And a second step of fixing arsenic as an arsenic compound. A method for removing and fixing arsenic present in an iron sulfate solution, comprising the steps of:

In the above invention, the arsenic removing agent is a metal powder such as zinc dust and iron powder, or a sulfide agent such as sodium hydrogen sulfide and hydrogen sulfide. When the solution temperature is 40 to 100 ° C and the oxidation-reduction potential is -150
It is preferably adjusted to mV, and in the case of a sulfurizing agent, the oxidation-reduction potential of the liquid is preferably about 150 mV.

In the above invention, it is preferable to use a copper source leached in a solution obtained from the second step of fixing arsenic as a copper source used as necessary.
The / As ratio is 1 to 3 or 10 or more, and the iron source used is preferably an iron sulfate solution obtained from SO ₂ reduction leaching of a zinc leaching residue in wet zinc smelting.

The reaction temperature in the second step in the above invention is 150 to 200 ° C., and the oxygen partial pressure is 1.8 in total oxygen added pressure.
It is preferable that the iron sulfate solution is a solution containing arsenic obtained from SO ₂ reduction leaching of a zinc leaching residue in wet zinc smelting.

[0018]

Hereinafter, the present invention will be described in more detail. The present invention is composed of the following two steps, FIG. 1 is a conceptual diagram showing a basic flow according to the present invention, FIG. 2 is a conceptual diagram when a metal powder reducing agent is used as a dehydration reagent according to the present invention, FIG. 3 is a flow chart in the case where the present invention is applied to a zinc leaching residue treatment method by SO ₂ reduction or high temperature high acid leaching and hematite method.

First step: Arsenic removal and concentration step There are two methods in this step, and either method can be used. Since the produced residue has excellent sedimentation filtration properties in both methods, it can be easily concentrated and separated using a thickener or the like.

(A) To remove arsenic, a reducing agent, that is, a metal powder such as zinc powder or iron powder is used. It is not particularly necessary when only dearsenic is intended, but in this step, if it is not desired to precipitate valuable metals such as indium and gallium, the molar ratio of copper sulfate required for the production of copper arsenide (copper / It is better that two or more, preferably three or more, of arsenic) are present.

Arsenic basically precipitates in the form of iron and iron arsenide and / or simple arsenic, and preferentially precipitates as copper arsenide in the presence of copper. The pH of the reaction may be any low pH of pH 3 or less, unless the use of the reducing agent is increased.
Although the reaction proceeds at room temperature, the reaction rate is extremely slow at 40 ° C. or lower.
0 ° C.

It is preferred that the reaction proceed while adjusting the oxidation-reduction potential. The reaction is carried out at a saturation silver chloride electrode at -150 mV or less, preferably -200 to -210 mV.

(B) For arsenic concentration, a sulfide such as hydrogen sulfide gas may be used instead of the metal powder reducing agent. At this time, arsenic precipitates in the form of arsenic sulfide. When a sulphide is used, the reaction is preferably allowed to proceed at a potential of about 150 mV with a saturated silver chloride electrode.

Second Step: Arsenic Fixation and Copper Leaching Step The second step is common to the two methods of the first step. That is, divalent or trivalent iron is added as an iron source and mixed so that the molar ratio of iron to arsenic (hereinafter, referred to as Fe / As or arsenic ratio) becomes 1 or more. However, the compound of iron and arsenic slows down the formation of precipitates in the region of 3 <Fe / As <10. Therefore, in order to obtain a sufficient arsenic precipitation ratio, it is preferable that 1 <Fe / As <3 or Fe / As. As
Mix so that> 10.

Further, the temperature is raised to about 150 to 200 ° C., preferably to 200 ° C., oxygen is added, and the total pressure is adjusted to be approximately 1.8 to 2.0 MPa (megapascal). The supply of oxygen is used for oxidizing iron and arsenic, and is not necessary when both are Fe (III) and As (V). By this reaction, arsenic forms a stable crystalline compound with iron, which can be easily separated by filtration.

At the same time, elements other than arsenic and iron, such as zinc and copper, are leached into the liquid. Also, when it is easy to continuously supply a copper source for arsenic removal, for example, in an iron sulfate solution obtained from SO ₂ reduction or high-temperature high-acid leaching of zinc leaching residue particularly in wet zinc smelting. In this case, it is easy to recover copper from the liquid after the arsenic fixation, and the copper may be repeatedly used as a copper source in the arsenic removal step without performing recovery.

The flow when the copper source is used repeatedly is as follows:
This is clearly shown in FIG. 2 (conceptual diagram of using a metal powder reducing agent).
Next, embodiments of the present invention will be described with reference to examples and drawings.

[0028]

Embodiment 1 This embodiment is an embodiment using zinc powder as a dearsenic reagent. In particular, the adjustment of the copper concentration in the liquid was not performed, and this is an example of the basic flow of the present invention. An arsenic-containing iron sulfate solution (a solution after the one-stage neutralization in the process of iron treatment by the SO ₂ reduction leaching of the wet zinc residue and the hetamite method) is continuously supplied to a 2 liter glass beaker with an overflow tube by a quantitative pump and stirred. A zinc powder was added while the oxidation-reduction potential of the solution was kept constant at −210 mV with a saturated silver chloride electrode, and a dehydration test was continuously performed. The liquid temperature is 60 ° C
The test was conducted under the condition of pH 2.7. Under the conditions of this test, the molar ratio of copper to arsenic in the solution was 1.84, and the amount of copper was not sufficient to precipitate arsenic as copper arsenide. In the test, the liquid supply amount was adjusted such that the residence time of the liquid in the beaker was 1 hour, and sampling was performed 2 hours after the liquid started to overflow from the final beaker.
The analysis was performed on the filtrate by separating the overflow pulp by filtration. Table 1 shows the test results. Sufficient arsenic removal from the solution was achieved. On the other hand, the precipitation rate of indium is high, and adaptation to the step of recovering such rare metals may be problematic.

[0029]

[Table 1]

After an appropriate amount of arsenic-deposited pulp obtained by repeating the above-mentioned reaction is collected, an iron sulfate solution (one step in the process of iron leaching of a wet zinc residue by SO ₂ reduction and hetamite method) is used as an iron source. (Neutralized solution) was added, and mixed sufficiently so that the arsenic ratio became approximately 4. The mixed pulp was continuously supplied to a 20-liter autoclave with a metering pump, pressurized at 3 kg / cm ² with stirring, heated to 200 ° C., and continuously subjected to an arsenic test. The residence time of the autoclave was 1.5 hours, and after 3 hours from the start of continuous discharge, the discharged liquid was sampled, the pulp after the reaction was separated by filtration, and the filtrate was analyzed. Table 2 shows the results. Iron and arsenic were sufficiently precipitated by the reaction, and at the same time, copper, which was a valuable metal, could be leached into the liquid.

[0031]

[Table 2]

Example 2 This example is an example in which zinc powder is used as a dearsenic reagent and a sufficient amount of copper is present. An iron sulfate solution containing arsenic (a solution after the one-stage neutralization in the process of iron leaching by the SO ₂ reduction leaching of the wet zinc residue and the hetamite method) is quantitatively poured into the tank from the thickener overflow in the process, and The liquid residence time was adjusted to be one hour. In addition, a copper sulfate solution was continuously added as a copper source using a metering pump so that the concentration of copper in the reaction solution was approximately 3.0 g / l. This is because in the SO ₂ reduction or high temperature and high acid leach, intentionally can leave copper in the liquid by not added elemental sulfur or zinc concentrate, the copper concentration in this case is 2.5 This is because it has been confirmed to be about 3.0 g / l. While stirring the solution, zinc powder was added so that the oxidation-reduction potential was kept constant at -210 mV with a saturated silver chloride electrode, and a dehydration test was continuously performed.

The test source solution was at 70 ° C. at the time of addition and did not require heating during the reaction. In this reaction, the pH was kept almost constant at 2.0, and no particular adjustment was required. In this test, the ratio of copper to arsenic in the original solution was 3.6, and a sufficient amount of copper to precipitate arsenic as copper arsenide was confirmed. Table 3 shows the test results. Sufficient arsenic removal from the solution was achieved. At the same time, the indium precipitation rate could be sufficiently suppressed. This is because sufficient copper for copper arsenide generation is ensured in the liquid, and in such a case, it is possible to prevent the formation of indium precipitate due to a local potential drop near the zinc dust. is there. Therefore, in a process involving recovery of rare metals such as indium, it is better that sufficient copper is present in the original solution as in this embodiment.

[0034]

[Table 3]

An iron sulfate solution (a solution after the two-stage neutralization in the process of iron leaching by the SO ₂ reduction leaching of the wet zinc residue and the hetamite method) was added to the above dearsenic residue so that the arsenic ratio became approximately 1.3. Then, 3.5 l of the mixed pulp was fed into a 5 l autoclave, heated to 200 ° C. while stirring, and reacted for 3 hours while adding oxygen so that the oxygen partial pressure was kept constant at 5 kg / cm ² . The pulp after the reaction was separated by filtration and the filtrate was analyzed. Table 4 shows the results. Iron and arsenic were sufficiently precipitated by this reaction, and at the same time, copper, a valuable metal, could be leached into the liquid. Further, the solution after the reaction is a high-concentration copper sulfate solution, and it can be seen that this solution can be economically satisfied even if this solution is used again as a copper source in the arsenic removal step.

[0036]

[Table 4]

Example 3 This example is an example showing that a sulfurizing agent can be used as a dearsenic reagent. One liter of an iron sulfate solution containing arsenic (a solution after one-stage neutralization in a process of iron leaching of a wet zinc residue by SO ₂ reduction and a hetamite method) was collected in a glass beaker, and the oxidation-reduction potential of the solution was saturated with stirring. Hydrogen sulfide gas was blown through a glass ball filter so as to be constant at 150 mV with a silver chloride electrode, and a dehydration test was performed. After the reaction in the above-mentioned beaker for 1 hour, sampling was performed. The analysis was performed on the filtrate by separating the pulp by filtration after the reaction. The test was performed under the conditions of a liquid temperature of 60 ° C. and a pH of 2.7. Table 5 shows the test results.

[0038]

[Table 5]

The above test was repeated, and an iron sulfate solution (a solution after one-step neutralization in the process of iron leaching of a wet zinc residue by SO ₂ reduction and hetamite method) was added to an appropriate amount of the dearsenic residue obtained. The mixture was adjusted and mixed so that the arsenic ratio was approximately 4.5, and 3.5 liters of the mixed pulp were fed into a 5-liter autoclave, heated to 200 ° C. with stirring, and then subjected to an oxygen partial pressure of 9 kg / cm ² . The reaction was carried out for 1.5 hours while adding oxygen so as to be constant. The pulp after the reaction was separated by filtration and the filtrate was analyzed. Table 6 shows the results. Iron and arsenic were sufficiently precipitated by this reaction, and at the same time, copper, a valuable metal, could be leached into the liquid. As in this example, the present invention can be applied even when a sulfide agent is used as a dearsenic (arsenic enrichment) reagent.

[0040]

[Table 6]

Example 4 In order to ensure the environmental safety of the insoluble crystalline solids containing arsenic and iron obtained in Examples 1 to 3, a dissolution test was conducted in accordance with the criteria for landfill disposal established in Japan. Was done. An insoluble crystalline solid containing arsenic and iron and pure water are mixed at a weight / volume ratio of 10%.
1 or more was used as a sample solution, which was shaken at room temperature (about 20 ° C.) and normal pressure (about 1 atm) for 6 hours using a shaker in advance. After the test, the analysis was ICP-MASS
(Inductively coupled plasma mass spectrometer). As a result, the arsenic elution value Tr of 0.07 mg / l and the standard value of 0.
15 mg / 1 was satisfied.

[0042]

Among the many arsenic removal and fixation methods, there is no report of a method which has a possibility of being applied to this field and which is particularly cost-effective. However, for a solution that is difficult to remove and fix as arsenic as it is in a zinc leaching residue treatment solution in a wet zinc smelting process, if the dearsenic technology developed according to the present invention is also positioned as an arsenic enrichment technology, In terms of cost, the process can be established. For example, as shown in FIG. 3, the process can be easily incorporated into the process as shown in FIG. 3 even in the process of SO ₂ reduction or high-temperature high-acid leaching of the wet zinc residue and the iron treatment by the hetamite method.

[Brief description of the drawings]

FIG. 1 is a basic conceptual diagram of a processing step diagram according to the present invention.

FIG. 2 is a conceptual diagram in a case where a metal powder reducing agent is used for dearsenic in the treatment process chart according to the present invention.

FIG. 3 is a flowchart showing an example in which the method of the present invention is applied to a hematite method.

Continued on the front page (72) Inventor Kaoru Saruta 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Akita Smelting & Refining Co., Ltd. (72) Ryoichi Taguchi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Akita-made Refining Co., Ltd.

Claims (11)

[Claims] 1. An arsenic present in an iron sulfate solution, wherein arsenic present in the iron sulfate solution is removed as a stable crystalline and non-elutable iron-arsenic compound with iron and fixed. Removal and fixing method. 2. A first step in which an arsenic-removing agent is added to an arsenic-containing iron sulfate solution to remove and concentrate arsenic, and the Fe / As ratio, temperature and oxygen partial pressure of the arsenic-enriched pulp obtained in the first step are determined. A method for fixing arsenic as an iron-arsenic compound having stable crystallinity by adjusting to predetermined conditions, comprising the steps of: removing arsenic present in an iron sulfate solution; 3. The removal and fixation of arsenic present in an iron sulfate solution according to claim 2, wherein the arsenic removing agent is a metal powder such as zinc dust or iron powder or a sulfide agent such as sodium hydrogen sulfide or hydrogen sulfide. Method. 4. The method according to claim 2, wherein the metal powder in the first step is added to adjust the liquid temperature during the dearsenic reaction to 40 to 100 ° C. and the oxidation-reduction potential to -150 mV or less with a saturated silver chloride electrode. A method for removing and fixing arsenic present in an iron sulfate solution as described above. 5. The method according to claim 2, wherein a redox potential at the time of dearsenic reaction by adding a sulfurizing agent in the first step is about 150 mV at a saturated silver chloride electrode. Removal and fixing method. 6. The arsenic-enriched pulp in the second step, Fe
The iron source for adjusting the Fe / As ratio is an iron sulfate solution obtained from SO ₂ reduction leaching of a zinc leaching residue of wet zinc smelting, wherein the / As ratio is 1 to 3 or 10 or more. 4
A method for removing and fixing arsenic present in an iron sulfate solution as described above. 7. The reaction temperature in the second step is 150 to 2
00 ° C, and the oxygen partial pressure is 1.8 to
The method for removing and fixing arsenic present in an iron sulfate solution according to claim 2 or 6, wherein the pressure is 2.0 MPa. 8. The method for removing and fixing arsenic present in an iron sulfate solution according to claim 2, wherein the arsenic fixing reaction in the second step is performed in an autoclave. 9. The iron sulfate solution according to claim 1, wherein the iron sulfate solution is a solution containing arsenic obtained from SO ₂ reduction or high-temperature high-acid leaching of a zinc leaching residue in wet zinc smelting. How to remove and fix arsenic. 10. The copper source used as required in the first step can be secured by not performing SO ₂ reduction of a zinc leaching residue in wet zinc smelting or decoppering during high-temperature high-acid leaching. 10. The method for removing and fixing arsenic present in an iron sulfate solution according to items 9 to 9. 11. The iron sulfate solution according to claim 1, wherein the copper source used as needed in the first step uses copper leached in the solution obtained from the second step of fixing arsenic. How to remove and fix arsenic present.