JP2011168467A - Method for producing crystalline scorodite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing crystalline scorodite by which crystalline scorodite particles having high crystallinity and low elution of arsenic can be easily produced in a short period of time from a various solutions including arsenic and further arsenic concentration in a post-reaction solution produced after reaction can be reduced. <P>SOLUTION: In the method for producing the crystalline scorodite, ferrous ions are made to coexist in a pentavalent arsenic-containing solution, the solution is set to ≥70°C liquid temperature and ≤2.0 pH value and then an oxidizing agent is added thereto to produce crystalline scorodite. When producing the crystalline scorodite, alkali is used as a pH adjuster and addition amount of the pH adjuster is controlled so that the pH value of the solution is controlled within a variation range of a predetermined pH value ±0.1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for separating and recovering arsenic present in various liquids as a stable arsenic compound from the liquid, and in particular, arsenic existing in various liquids as scorodite which is a stable arsenic compound. The present invention relates to a technique for separating and recovering from the liquid.

In non-ferrous smelting, arsenic is an associated element contained in ore. As a result, when non-ferrous smelting processing is performed, arsenic is also processed. In other words, the arsenic treatment is an important and inevitable technical element in the nonferrous smelting business. Therefore, in running a non-ferrous smelting business, it is desired that the arsenic treatment be performed by a treatment method that is appropriate and cost-effective.
For example, Patent Documents 1 and 2 have been proposed for the arsenic treatment.

The proposal of Patent Document 1 uses an acidic solution to leach arsenic from non-ferrous smelting smoke ash into a leachate, and ferric sulfate (Fe ³⁺ ) is added to the leachate to convert arsenic into amorphous iron arsenate. Crystallize. In the crystallization step, a seed crystal of scorodite is further added, and the amorphous iron arsenate is converted into crystalline scorodite by allowing it to stand at atmospheric pressure and high temperature for a predetermined time.

  The proposal of Patent Document 2 is a method for producing crystalline scorodite from an acidic aqueous solution containing pentavalent arsenic and trivalent iron. Then, by adding a basic sodium compound to the acidic aqueous solution so that the sodium concentration in the acidic aqueous solution is more than 0 g / L and 4 g / L or less, high production efficiency and arsenic concentration rate can be obtained. It is supposed to be.

JP 2005-161123 A JP 2008-231478 A

  The present inventors examined a method for producing scorodite from an arsenic-containing solution according to the conventional technique. As a result, the method described in Patent Document 1 required a long time of at least 10 hours, usually 20 hours or more in order to obtain crystalline scorodite. Further, the method described in Patent Document 2 requires a long reaction time of 24 hours in order to increase the concentration rate of arsenic that is a crystalline substance. With the methods described in Patent Documents 1 and 2, it has not been sufficient to reduce the arsenic concentration in the post-reaction solution generated after the reaction in a short time.

  The present invention has been made under the circumstances described above, and the problem to be solved is to easily and shortly convert crystalline scorodite particles having high crystallinity and low arsenic elution from various solutions containing arsenic. Another object of the present invention is to provide a method for producing crystalline scorodite capable of reducing the arsenic concentration in the post-reaction liquid produced after the reaction and further after the reaction.

In order to solve the above-described problems, the present inventors have conducted intensive research.
Then, divalent iron ions are allowed to coexist in the solution containing arsenic, the pH value of the solution is set to a predetermined value of 2.0 or less at a high temperature, and crystalline scorodite is added to the solution while adding an oxidizing agent. When the crystalline scorodite is produced, an alkali is used as a pH adjusting agent so that the pH value of the solution is controlled within a fluctuation range of ± 0.1 from the predetermined value pH value, and the pH adjusting agent is added. I came up with a configuration to control the amount.

That is, the first invention for solving the above-described problem is
A divalent iron ion is allowed to coexist in a solution containing pentavalent arsenic, the solution temperature is set to a predetermined value of 70 ° C. or higher and a pH value is set to 2.0 or lower, and crystallinity is added while an oxidizing agent is added to the solution. The scorodite is generated, and when the crystalline scorodite is generated, the pH is adjusted using an alkali as a pH adjusting agent so that the pH value of the solution is controlled within a fluctuation range of ± 0.1 from the predetermined value pH value. It is a method for producing crystalline scorodite characterized by controlling the amount of the agent added.

The second invention is
The method for producing crystalline scorodite according to the first invention, wherein copper having a copper concentration of 50 mg / L or more is further added to the arsenic-containing solution.

The third invention is
A pH adjuster is added to the solution having the predetermined pH value while adding an oxidizing agent, and the amount of the pH adjuster added is controlled, so that the variation of the solution pH value is ± 0 of the predetermined pH value. The pH of the crystalline scorodite according to the first or second invention is reset in the second half of the reaction for generating the crystalline scorodite while being within the range of .1. It is a generation method.

The fourth invention is:
The method for producing crystalline scorodite according to any one of the first to third inventions, wherein an alkali of an alkaline earth metal is used as the pH adjuster.

The fifth invention is:
The crystalline scorodite according to any one of the first to fourth inventions, wherein at least one of oxygen, air, oxygen-containing gas, air dilution gas, and hydrogen peroxide is used as the oxidant. It is a generation method.

  According to the method for producing crystalline scorodite according to the present invention, since the reaction time is short, the crystalline scorodite can be produced with high time efficiency and high productivity. Furthermore, the arsenic concentration in the post-reaction liquid produced after the crystalline scorodite reaction could be greatly reduced. As a result, the post-process load in the arsenic treatment process is greatly reduced and the process is stabilized.

It is a process flow figure showing an example of a production method of crystalline scorodite concerning the present invention.

  As described above, the present inventors have made trial and error to find a production method that can easily produce crystalline scorodite particles having high crystallinity and low arsenic elution from various solutions containing arsenic in a short time. Went. As a result, divalent iron (a divalent iron salt compound) was added to a pentavalent arsenic-containing solution, and conditions were found to enable scorodite to be produced with high productivity and low cost.

The conditions for enabling scorodite to be manufactured with the high productivity and low cost will be described.
First, a divalent iron salt is added to and mixed with the arsenic-containing solution, and further a pH adjuster is added to obtain a raw material liquid with a pH value at room temperature of 2.0 or less (for example, 1.0), for example. . Then, while stirring the raw material liquid, the temperature is raised to a predetermined temperature of 70 ° C. or higher, and when the predetermined temperature is reached, addition of an oxidizing agent is started to start a scorodite production reaction.

  The pH value of the raw material liquid has risen to, for example, around 1.6 when the predetermined temperature is reached, but decreases as the scorodite production reaction starts and progresses. Then, when the pH value of the raw material liquid is lowered to a predetermined value set in advance, the alkali is added as a pH adjuster, and the reaction is performed while controlling the raw material liquid at the predetermined value. To continue. Here, the predetermined pH value is set in a range of pH 2.0 or less, but a more preferable setting range of the predetermined value of pH value is 0.8 or more and 2.0 or less. In addition, when the predetermined pH value is higher than the pH value at the time when the raw material liquid reaches the predetermined temperature, alkali is added as a pH adjuster, and the pH of the raw material liquid is adjusted to the predetermined pH value in advance. It is good to start the reaction.

  As described above, acid or alkali is used as the pH adjuster. As the acid, sulfuric acid, hydrochloric acid, and nitric acid are preferable. In the case of an alkali, alkalis such as alkaline earth metals and alkali metals, or salts thereof are preferable.

As a method for adding the oxidizing agent, one or more selected from oxygen gas, air, oxygen-containing gas, air dilution gas blowing, and hydrogen peroxide charging can be used.
In the present invention, the oxygen-containing gas refers to a gas in which an inert gas such as nitrogen gas and oxygen gas are mixed and the oxygen-containing composition is greater than 21% (air-containing oxygen content) and less than 100%. The air dilution gas refers to a gas in which an inert gas such as nitrogen gas and air are mixed and the oxygen-containing composition is greater than 0% and less than 21% (air-containing oxygen amount).
As the addition method, in the case of gas, a method of blowing directly into the raw material liquid is simple and preferable. In the case of liquid, direct injection is possible. The amount of the oxidant to be charged may be determined appropriately depending on the state of the scorodite production reaction.

During the scorodite production reaction, if no pH adjustment operation is performed on the raw material liquid and the reaction proceeds in a so-called “successful” manner, the pH value of the raw material liquid changes in a decreasing direction. In the present invention, a predetermined value of the pH value is determined, and the pH adjustment is performed in order to keep the fluctuation of the pH value of the raw material solution during the reaction within the range of control width 0.2 (± 0.1) from the predetermined value. An appropriate amount of the agent is added.
By controlling the pH value, crystalline scorodite can be produced with high time efficiency and high productivity.

The control range of the pH value described above is preferably narrow from the viewpoint of promoting particle growth of the scorodite crystal, and more preferably controlled by a control range of 0.1 (± 0.05).
In order to realize the control range of the pH value, for example, water is added to Mg (OH) ₂ powder which is one of alkalis of alkaline earth metals to form a high pulp concentration liquid and then added to the raw material liquid. Thus, a method of ensuring wetness to the raw material liquid and facilitating diffusion into the raw material liquid is effective.

As described above, alkalis such as alkaline earth metals and alkali metals can be suitably used as the alkaline pH adjuster. Among these, Mg (OH) ₂ is preferable for the pH adjuster. This is because MgSO ₄ produced after adjusting the pH of the arsenic-containing solution using the pH adjusting agent is easily soluble, and Mg ions do not adversely affect the scorodite production reaction in the subsequent step.

For example, Ca (OH) ₂ is also preferable as a pH adjuster other than Mg (OH) ₂ . However, when pH is adjusted using Ca (OH) ₂ , hardly soluble gypsum (CaSO ₄ .2H ₂ O) is generated. Accordingly, gypsum is mixed in the scorodite collected after the reaction is completed.

Furthermore, as other pH adjusting agents, for example, NaOH and KOH are also preferable. However, NaOH and KOH have high raw material costs. In addition, it is required to pay attention to the added concentration and not to form jarosite during the reaction of NaOH or KOH with arsenic. Accordingly, when NaOH or KOH is used as the pH adjuster, it is preferable to suppress the use amount to a small amount by using it together with Mg (OH) ₂ or Ca (OH) ₂ .

If desired, it is also preferable to add copper to the raw material liquid. In some cases, the addition of copper can further reduce the arsenic concentration in the post-reaction solution. Moreover, the elution value of arsenic from the generated scorodite described later may be reduced.
As the copper to be added, any metal such as metallic copper or copper oxide that can be dissolved and supplied with copper ions under predetermined conditions can be used. Especially, it is preferable to add in the form of copper sulfate, copper oxide, metallic copper (including powder) and copper hydroxide. Moreover, the addition effect of copper can confirm the addition effect, if the copper concentration in the raw material liquid after the said addition shall be 50 mg / L or more. What is necessary is just to determine the upper limit of the addition amount of copper from raw material cost.

  At the end of the scorodite production reaction, for example, the arsenic concentration in the raw material solution can be monitored or sampled every predetermined time, and can be determined by the arsenic concentration being below a predetermined value. Furthermore, if the process is stable, a reaction completion time can be determined, and it can be determined that the reaction has ended by the passage of the time. However, in normal cases, the reaction time is 2 to 6 hours.

  While adding the oxidizing agent to the raw material liquid having a predetermined pH value as described above, a pH adjuster is added, and the fluctuation of the pH value of the raw material liquid is within ± 0.1 of the predetermined pH value. It is also preferable to reset the pH value higher than the predetermined pH value in the second half of the reaction for generating crystalline scorodite while controlling to maintain the pH (at the stage where the generation of crystalline scorodite is almost completed). It is. By resetting the pH value in the latter half of the reaction with this configuration, the arsenic concentration in the reaction solution can be reduced without affecting the crystal formation reaction of the generated scorodite.

This is because the arsenic concentration in the raw material liquid decreases to 30% or less in 1.5 to 2 hours from the start of the reaction. After the time point when the concentration of arsenic in the raw material liquid decreases, the latter half is regarded as the second half, and the predetermined pH value is increased to reset the higher predetermined pH value.
When the second half of the reaction is grasped and set as the reaction elapsed time, it becomes the second half of the total reaction time (50 to 90% elapsed time in the total reaction time). It is preferable to reset the set value of the pH value in the latter half to a value that is at least 0.2 or higher than the initial set value. If the reset value is higher than the control range of the predetermined pH value, the effect of resetting the pH value can be obtained. However, from the viewpoint of maintaining the crystallinity of the generated scorodite, the pH value is preferably maintained at 3 or less.

  By observing the conditions, it became possible to produce crystalline scorodite particles from various solutions containing arsenic in a short time using a divalent iron salt. The produced crystalline scorodite particles have a small arsenic elution value. Further, the produced crystalline scorodite particles have good filterability and are excellent in handling in actual operation. Moreover, the implementation of the present invention does not require a large-scale capital investment.

Hereinafter, the present invention will be described in detail with reference to examples.
Example 1
1) Test unit and test scale A 1 L beaker was used as a test container. The stirrer installed in the test vessel was equipped with four baffle plates and two-stage turbine blades, and reacted under strong stirring after the start of oxygen blowing.
At this time, the processing amount of the pentavalent arsenic base solution per batch was 800 mL. All tests were performed under atmospheric pressure.

2) Preparation of pentavalent arsenic base solution 72 mL of a 60% arsenic acid solution was weighed and diluted to 800 mL with pure water to obtain a pentavalent arsenic base solution according to Example 1.
As a result of analysis, the arsenic concentration of the pentavalent arsenic base solution was 45.0 g / L.

3) Addition of divalent iron In this example, the ferrous sulfate reagent (FeSO ₄ · 7H ₂ O) was used as the addition source of divalent iron.

4) Addition amount of divalent iron to pentavalent arsenic base solution
The chemical formula of scorodite is represented by FeAsO ₄ .2H ₂ O. Accordingly, in terms of reaction stoichiometry, the formation reaction of scorodite is an equimolar reaction in which the molar ratio of iron and arsenic in which 1 mol of iron reacts with 1 mol of arsenic is 1.0.
Therefore, in Example 1, the addition amount of the divalent iron salt is 1.5 times equivalent to the total molar amount of arsenic in the pentavalent arsenic base solution as the pure iron content, and the molar ratio of iron and arsenic is 1. .5. Specifically, it is 200 g as a reagent ferrous sulfate.

  The ferrous sulfate was completely dissolved in the pentavalent arsenic base solution. Sulfuric acid was added as a pH adjuster to the solution at a liquid temperature of 30 ° C. and adjusted to pH 1.0 to prepare a raw material solution.

5) pH adjuster In Example 1, sulfuric acid is used as the acid as the pH adjuster as described above, and Mg (OH) ₂ is used as the alkali as the pH adjuster of the raw material liquid used during the reaction. And a reagent manufactured by Kishida Chemical Co., Ltd., magnesium hydroxide Mg (OH) ₂ (assay min 95%) was prepared.

  As described above, the parts 1) to 5) in Example 1 are the same in Examples 2 to 9 described later.

6) Scorodite production reaction A flow chart of the scorodite production reaction according to Example 1 of the present invention is shown in FIG. Hereinafter, a description will be given with reference to FIG.
Add pure water to 72 mL of reagent 60% arsenic acid solution to prepare 800 mL of pentavalent arsenic base solution, add 200 g of ferrous sulfate salt and dissolve completely, then add sulfuric acid as a pH adjuster, to 30 ° C. The pH was adjusted to 1.0 to obtain a raw material solution. Next, the raw material liquid was heated to 95 ° C., and the temperature was maintained. The pH value of the raw material liquid at this time was 1.6.

  Here, while vigorously stirring the raw material liquid, oxygen gas was introduced from the bottom of the beaker through a glass tube by a bubbling method to initiate the reaction. The amount of oxygen gas introduced was 950 ml / min, and the reaction time was measured with the start of oxygen gas introduction as the start of the scorodite production reaction and the end of introduction as the end of the scorodite production reaction.

As the reaction started, the pH value of the raw material solution naturally decreased with the scorodite production reaction, and after about 30 minutes, the pH value decreased to a predetermined value of pH 1.0.
Here, during the scorodite production reaction, an appropriate amount of Mg (OH) ₂ powder was added as the pH adjuster described above.
Specifically, the pH value of the raw material liquid is controlled within the range of more than 0.9 and less than 1.1, and the reaction proceeds while maintaining the liquid temperature of 95 ° C. Ended. And the reaction product after the said reaction completion was filtered, and the filtrate and the post-reaction liquid were obtained.

7) Measurement of As concentration in liquid after completion of reaction The arsenic concentration in the post-reaction liquid obtained after the completion of the reaction for producing scorodite was measured by ICP.

8) Evaluation of generated scorodite The filtrate after completion of the formation reaction of the obtained scorodite was washed with pure water and then subjected to X-ray diffraction measurement. As a result, it was identified as crystalline scorodite.
Moreover, the elution value of arsenic from the produced scorodite was measured by subjecting it to an elution test based on Environmental Notification No.13. The test solution after elution was filtered through a filter made by MCE (Mixed Cellulose Ester) having a pore size of 0.2 μm. Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 2)
The same operation as in Example 1 was performed except that 355 mg of reagent copper sulfate (CuSO ₄ .5H ₂ O) was added to the raw material solution and dissolved, and the Cu concentration in the raw material solution was adjusted to 100 mg / L.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 3)
The same operation as in Example 1 was performed except that the predetermined value of the pH of the raw material liquid was set to 1.2.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

Example 4
The same operation as in Example 3 was performed except that 355 mg of reagent copper sulfate (CuSO ₄ .5H ₂ O) was added and dissolved in the raw material solution, and the copper concentration in the raw material solution was adjusted to 100 mg / L.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 5)
The same operation as in Example 1 was performed except that the predetermined value of the pH of the raw material liquid was set to 1.4.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 6)
The same operation as in Example 1 was performed except that the predetermined value of the pH of the raw material liquid was 1.4 and the reaction time was 7 hours.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 7-1)
355 mg of reagent copper sulfate (CuSO ₄ · 5H ₂ O) is added and dissolved in the raw material solution, the copper concentration in the raw material solution is 100 mg / L, the predetermined value of the pH of the raw material solution is 1.4, and the reaction time is 2 hours The same operation as in Example 1 was performed except that.
Here, Example 7-1 and Example 7-2 and Example 7-3, which will be described later, are a series of related examples. Specifically, in Example 7-1, the reaction was terminated at the elapse of 2 hours, the generated scorodite was sampled, and the elution value of the scorodite was evaluated. The purpose is to confirm the formation and properties of scorodite at that time.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 7-2)
The same operation as in Example 7-1 was performed except that the reaction time was 3 hours.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 7-3)
The same operation as in Example 7-1 was performed except that the reaction time was 7 hours.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Example 8)
The reaction was performed in the same manner as in Example 7-1 for 2 hours, and then the same operation as in Example 1 was performed, except that the reaction was further performed for 2 hours at a predetermined pH value of 2.0.
Note that, even at the predetermined values of both pHs, the fluctuation range was kept within a range of ± 0.1 from the predetermined value.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

Example 9
The raw material liquid to the reagent copper sulfate _(CuSO 4 · _5H 2 O) was dissolved 355mg addition, the copper concentration of the raw material solution and 100 mg / L, warmed the raw material solution 95 ° C. (pH value at this point 1.6), then Mg (OH) ₂ was added, the same operation as in Example 1 was performed, except that the predetermined pH value was 2.0 and the reaction time was 6 hours.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Comparative Example 1)
The same operation as in Example 1 was performed except that Mg (OH) ₂ which is a pH adjusting agent was not added to the raw material liquid, pH control was not performed, and the process was left to work.
The pH value at the end of 4 hours of reaction was 0.57.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

(Comparative Example 2)
The same operation as in Example 1 was performed, except that Mg (OH) ₂ as a pH adjusting agent was not added to the raw material liquid, pH control was not performed, and the reaction time was 7 hours.
The pH value at the end of reaction 7 hours was 0.53.
Table 1 shows the arsenic concentration of the obtained post-reaction solution and the arsenic elution value from the generated scorodite.

From the results shown in Table 1, when control was performed to maintain the pH value of the raw material solution within a range of ± 0.1 from each predetermined value that is 2.0 or less, the arsenic concentration in the post-reaction solution was 1100-50 mg / L or less. The obtained crystal was a good crystalline scorodite having an elution value in an arsenic elution test of 0.3 mg / L or less, which is an environmental standard. In other words, it was found that the arsenic concentration in the solution after the reaction was drastically reduced to 1/40 or less of the raw material solution, and a stable crystalline scorodite having a low elution value was obtained.
In the second half of the reaction (when 50% of the total reaction time has elapsed), a high effect can also be obtained by resetting the predetermined pH value to a range higher than the initial value, further reducing the arsenic concentration in the solution after the reaction. It also turned out to be.

Claims (5)

  A divalent iron ion is allowed to coexist in a solution containing pentavalent arsenic, the solution temperature is set to a predetermined value of 70 ° C. or higher, and a pH value is set to 2.0 or lower. The scorodite is generated, and when the crystalline scorodite is generated, the pH is adjusted using an alkali as a pH adjusting agent so that the pH value of the solution is controlled within a fluctuation range of ± 0.1 from the predetermined value pH value. A method for producing crystalline scorodite, characterized in that the addition amount of the agent is controlled.   The method for producing crystalline scorodite according to claim 1, wherein copper having a copper concentration of 50 mg / L or more is further added to the arsenic-containing solution.   A pH adjuster is added to the solution having the predetermined pH value while adding an oxidizing agent, and the amount of the pH adjuster added is controlled, so that the variation of the solution pH value is ± 0 of the predetermined pH value. The method for producing crystalline scorodite according to claim 1 or 2, wherein the pH value higher than the predetermined value is reset in the latter half of the reaction for producing crystalline scorodite while being within the range of 0.1. .   The method for producing crystalline scorodite according to any one of claims 1 to 3, wherein an alkaline agent of an alkaline earth metal is used as the pH adjuster.   The method for producing crystalline scorodite according to any one of claims 1 to 4, wherein at least one of oxygen, air, oxygen-containing gas, air dilution gas, and hydrogen peroxide is used as the oxidant. .

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