JP2011177651A - Arsenic-containing solution treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an arsenic-containing solution treatment method which can inhibit generation of a precipitate of arsenic compounds, which has low stability as an arsenic compound and is difficult to be separated from an arsenic-containing solution containing other elements including iron because of small particle diameter thereof. <P>SOLUTION: In the arsenic-containing solution treatment method, an oxidizing agent is added to the acidic arsenic-containing solution which contains pentavalent arsenic and trivalent iron, and is under the atmospheric pressure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  This is a method for treating a solution containing arsenic generated in various processes.

  When processing an arsenic-containing solution, a method is known in which arsenic and iron are reacted to form a compound such as scorodite. Therefore, it has been proposed in the industry to fix arsenic by treating arsenic in arsenic-containing solutions generated in various processes into a stable compound such as scorodite.

  Here, when arsenic and iron are reacted and immobilized, a certain control is required for the concentration in the solution and the reaction time of both. However, in particular, the arsenic-containing solution generated in the non-ferrous smelting process contains elements such as iron derived from ores and additives. For this reason, in the treatment of the arsenic-containing solution, an inadvertent and spontaneous reaction between arsenic and iron occurs. In order to avoid a spontaneous reaction between the arsenic and iron, remove the iron in the arsenic-containing solution in advance, or design a process in which iron is not mixed into the arsenic-containing solution, and then control the process. There was a need.

  On the other hand, a technique is disclosed in which scorodite can be generated by controlling the molar ratio of iron and arsenic in an arsenic-containing solution. For example, Patent Document 1 proposes that iron arsenate is generated by adding a basic sodium in an arsenic-containing solution containing arsenic and iron, with a low iron molar ratio. is doing.

  In addition, there is a method of generating scorodite by reacting arsenic and iron in an autoclave at a high temperature of 175 ° C. under a pressurized atmosphere.

JP 2008-231478 A

As described above, a method for advancing the scorodite production reaction has been proposed for arsenic-containing solutions under various conditions in which arsenic and iron coexist.
On the other hand, it is conceivable to immediately treat the arsenic-containing solution generated in various steps to generate, for example, scorodite and stabilize it. However, arsenic-containing solutions generated in various processes often have various components, properties, and the like, although each generation amount is small. In such a case, it takes a lot of work steps to immediately treat each arsenic-containing solution that is generated, for example, to generate and stabilize scorodite. Therefore, it is conceivable that these arsenic-containing solutions are stored and stored for a predetermined period of time to increase the batch amount and stabilize at once.

  However, according to the study by the present inventors, each of the generated arsenic-containing solutions contains various elements including trivalent iron in addition to arsenic. For this reason, arsenic-iron compound precipitation is generated by the spontaneous arsenic-iron reaction that is neither desired nor controlled in the storage and storage processes for the predetermined period. Most of these naturally occurring arsenic-iron compound precipitates have problems of low stability as arsenic compounds and a large amount of arsenic elution, and operability because of their small particle size and difficulty in separation from solution. I have the problem of being bad.

  The present invention has been made under the above circumstances, and the problem to be solved is that the arsenic compound has low stability as an arsenic compound solution containing other elements including iron. An object of the present invention is to provide a method for treating an arsenic-containing solution capable of suppressing the formation of a precipitate of an arsenic compound that has a small particle size and is difficult to separate from a solution.

In order to solve the above-mentioned problems, the present inventors have conducted intensive research.
As a result, even when the arsenic-containing solution (pentavalent arsenic-containing solution) further contains various elements such as trivalent iron, an oxidant is added to the arsenic-containing solution. The present invention was completed by discovering that the formation of arsenic-iron compound precipitates due to the spontaneous arsenic-iron reaction that is not controlled can be suppressed.
Further, for example, by adding a predetermined amount of divalent iron and an oxidizing agent to the arsenic-containing solution in which the generation of precipitates of the naturally occurring arsenic-iron compound is suppressed, the particle size is increased and the arsenic elution amount is increased. Of small scorodite.

That is, the first means for solving the above-mentioned problem is
A method for treating an arsenic-containing solution, comprising adding an oxidizing agent to an acidic arsenic-containing solution containing pentavalent arsenic and trivalent iron at atmospheric pressure.

The second means is
The method for treating an arsenic-containing solution according to the first means, wherein the pH value of the arsenic-containing solution is set to 1 or less when the oxidizing agent is added.

The third means is
The method for treating an arsenic-containing solution according to the first or second means, wherein the value of (number of moles of trivalent iron / number of moles of pentavalent arsenic) of the arsenic-containing solution is 1 or more. is there.

The fourth means is
Adding an oxidizing agent to an acidic arsenic-containing solution containing pentavalent arsenic and trivalent iron and under atmospheric pressure;
And a step of adding divalent iron and an oxidizing agent to the arsenic-containing solution to which the oxidizing agent has been added.

The fifth means is
The arsenic-containing solution containing the pentavalent arsenic and the trivalent iron and subjected to the step of adding an oxidizing agent to the acidic arsenic-containing solution under atmospheric pressure is stored for a predetermined period, and then the divalent iron and the oxidizing agent are added. The method for treating an arsenic-containing solution according to the fourth means, characterized in that the step of charging is performed.

The sixth means is
The post-reaction liquid obtained in the step of adding the divalent iron and the oxidizing agent is added as a divalent iron source, and is added again in the step of adding the divalent iron and the oxidizing agent. A method for treating an arsenic-containing solution described in the fourth or fifth means.

The seventh means is
Adding the oxidant means blowing at least one selected from oxygen gas, air, oxygen-containing gas, air diluted with nitrogen, etc., ozone into the arsenic-containing solution, or excess The method for treating an arsenic-containing solution according to any one of the first to sixth means, wherein hydrogen oxide water is added to the arsenic-containing solution.

  According to the method for treating an arsenic-containing solution according to the present invention, even when the arsenic-containing solution contains other elements such as trivalent iron, a naturally occurring arsenic-iron compound precipitate is generated. Can be suppressed.

  In practicing the present invention, the arsenic in the arsenic-containing solution is preferably pentavalent arsenic. If the arsenic contained is trivalent arsenic, it is preferably oxidized beforehand to pentavalent arsenic. However, trivalent arsenic can be oxidized to pentavalent arsenic during implementation of the present invention by increasing the amount of oxidizing agent added during implementation of the present invention.

  In practicing the present invention, in the elements including iron contained in the arsenic-containing solution, iron is desirably a trivalent iron compound or a trivalent iron ion. This is because, when the iron compound is divalent iron or divalent iron ions, the divalent iron is oxidized to trivalent iron during the above-described oxidation of arsenic, so that the consumption of the oxidizing agent increases. However, there is no particular problem when the increase in consumption of the oxidizing agent can be tolerated or when the amount of divalent iron is small.

The oxidant used in the process of suppressing the formation of naturally occurring arsenic-iron compound precipitates is oxygen gas, air, gas containing oxygen, gas containing air, air diluted with nitrogen, One or more selected from either ozone or hydrogen peroxide water can be used.
The oxidant may be added by blowing into an arsenic-containing solution in the case of at least one selected from oxygen gas, air, gas containing oxygen, air diluted with nitrogen, etc., ozone, Water may be added directly to the arsenic-containing solution.
However, it is easier to control the degree of oxidation when the gas is oxidized, blown or added, and the equipment cost is low.
The amount of the oxidizing agent blown and the amount added may be appropriately determined according to the liquid amount and various concentrations, and the stirring may be performed simultaneously. Specifically, while observing the state of the arsenic-containing solution, an oxidizing agent is blown and added, and it is confirmed that no spontaneous arsenic-iron compound precipitate is generated.

When the oxidant is blown into the arsenic-containing solution and added, the arsenic-containing solution can be placed under atmospheric pressure, so that the equipment can be simple.
In addition, when the oxidizing agent is blown into the arsenic-containing solution and added, the pH value of the arsenic-containing solution is preferably 1.5 or less, more preferably 1.0 or less. By controlling the pH value, spontaneous arsenic-iron compound precipitate formation in the arsenic-containing solution being stored can be further suppressed. As the pH adjuster, magnesium hydroxide, sulfuric acid and the like are suitable.

Furthermore, when the oxidizing agent is blown into the arsenic-containing solution and added, it is preferable that the ratio value of (number of moles of trivalent iron / number of moles of pentavalent arsenic) in the arsenic-containing solution is 1 or more. By controlling the ratio of the ratio of the number of moles of trivalent iron to the number of moles of pentavalent arsenic to be 1 or more, spontaneous precipitation of arsenic-iron compounds in arsenic-containing solutions during storage can be achieved. Further suppression can be achieved. If the number of moles of trivalent iron in the arsenic-containing solution to be treated is insufficient, a necessary amount of trivalent iron salt may be further supplemented.
The upper limit of the ratio value (number of moles of trivalent iron / number of moles of pentavalent arsenic) is not particularly limited, but iron is also a useful metal, so reducing the amount used reduces the production cost. Therefore, 3 or less is appropriate.

The arsenic-containing solution into which the oxidizing agent is blown can be stored. This is because the spontaneous formation of arsenic-iron compound precipitates during storage of the arsenic-containing solution is suppressed.
Industrially, various arsenic-containing solutions generated in each process are stored in a state where the above-mentioned treatment is performed to suppress the formation of spontaneous arsenic-iron compound precipitates. When the fixed amount is accumulated, the arsenic in the arsenic-containing solution can be treated by making it scorodite or the like.
The arsenic-containing solution treatment method generates scorodite having large crystal particles and low arsenic solubility from a predetermined amount of arsenic-containing solution in which the formation of spontaneously generated arsenic-iron compound precipitates is suppressed. This is effective from the viewpoint of reducing processing costs and suppressing the production of difficult-to-process products.

  Hereinafter, an example of a treatment method suitable for generating scorodite from the stored arsenic-containing solution in a predetermined amount will be described. However, other processing methods can be applied as desired.

  After the step of suppressing the formation of the spontaneously generated arsenic-iron compound precipitate, the lower the temperature of the arsenic-containing solution before the step of generating the scorodite, the lower the naturally occurring arsenic. -Generation | occurrence | production of the precipitate of an iron compound can be suppressed. On the other hand, at the time of producing scorodite, a liquid temperature of 70 ° C. or higher is desired.

  Moreover, when producing | generating a scorodite, it is desirable to adjust the arsenic density | concentration in the arsenic containing solution before production | generation reaction to 10 g (As conversion) / L or more. This is because the higher the arsenic concentration, the higher the productivity of scorodite and the easier the formation reaction. More preferably, the arsenic concentration is 20 to 40 g (as conversion) / L.

The oxidizing agent used in the step of generating scorodite is also one selected from oxygen gas, air, oxygen-containing gas, air-containing gas, air diluted with nitrogen, ozone, and hydrogen peroxide water The above can be used. However, if the form is a gas, the degree of oxidation is easier to control, and the equipment cost is lower. What is necessary is just to add the hydrogen peroxide water whose form is a liquid directly in an arsenic containing solution.
The amount of the oxidizing agent blown or added may be appropriately determined according to the amount of the arsenic-containing solution and the concentration of various components contained, and stirring may be performed simultaneously.

  The end of the scorodite production reaction can be determined, for example, by monitoring the arsenic concentration in the raw material solution or sampling every predetermined time, and when the arsenic concentration falls below a predetermined value. Furthermore, if the process is stable, it is possible to determine a reaction completion time and determine the end of the reaction with the passage of the time.

  Further, if desired, the pH value of the raw material solution may be increased to a new predetermined value from the beginning in the latter half of the scorodite formation reaction (after the second half of the total reaction time, or when the arsenic concentration has decreased by 70% or more). After the resetting, control may be performed so as to maintain the reset within the predetermined range of the predetermined pH value (± 0.1 of the predetermined pH value). By adopting a configuration in which the pH value is reset in the latter half of the reaction, crystallization of the generated scorodite is promoted, and arsenic concentration is reduced by consuming arsenic in the raw material liquid.

  On the other hand, most of arsenic in the raw material liquid is stabilized, and most of trivalent iron is used for stabilizing arsenic. As a result, the obtained post-reaction solution is almost a divalent iron solution, and the post-reaction solution can be added again as a new divalent iron source solution to the step of generating scorodite. The said structure is a preferable structure from a viewpoint of reduction of raw material cost.

As described above in detail, according to the present invention, when arsenic and iron coexist in the solution, the arsenic-iron spontaneous reaction, which is neither desired nor controlled, is fine, It is possible to suppress the formation of a precipitate of an iron-arsenic compound that has a large arsenic elution value.
The solution can be stably stored while arsenic and iron are dissolved in the solution coexistingly.
Furthermore, when desired, a crystalline scorodite having a large particle size and little arsenic elution could be produced from the stored solution. Moreover, the crystalline scorodite particles produced have good filterability and excellent handling in actual operation.

  Moreover, it is preferable that the present invention can be implemented with an inexpensive drug and a simple device. In addition, the arsenic-containing solution produced in the process of carrying out the present invention can be stored very easily and does not generate a product that requires secondary treatment such as residue. Therefore, the inhibitory effect of the arsenic-iron reaction between arsenic and trivalent iron due to the addition of the oxidizing agent is very useful industrially.

In an actual industrial process, since an arsenic-containing solution is a drainage or a residue, it is difficult to keep the liquid composition at a certain quality. However, if an attempt is made to manage and store arsenic-only and iron-only solutions for each individual composition, a separation process for each composition is required, resulting in high costs.
However, by implementing the present invention, first, when managing and storing the arsenic-containing solution, the cost is overwhelmingly reduced by suppressing the reaction between the contained arsenic and trivalent iron. When desired, by adding an oxidizer, divalent iron, and optionally trivalent iron to the arsenic-containing solution that is managed and stored, the crystallinity is large and the arsenic solubility is small. It enables the generation of scorodite.

Hereinafter, the present invention will be described with reference to examples.
Example 1
1) Test unit and test scale A 1 L beaker was used as a test container. The stirring apparatus installed in the test vessel was a four-stage baffle plate, two-stage turbine blade, and a rotation speed of 600 rpm.
The total amount of arsenic and iron mixed solution per batch was 650 mL. In each of the examples including Example 1, the treatment was performed at room temperature under atmospheric pressure (normal pressure). Pressure control is not performed even in containers such as beakers.

2) Preparation of trivalent iron solution
Reagent iron sulfate (trivalent) n hydrate (21.6% as Fe grade) 1,815 g was weighed and put into a 5 L beaker, and pure water was added to make the liquid volume 1,900 mL. And the said solution was heated at 80 degreeC and the said iron sulfate (trivalent) was dissolved, stirring.
After dissolution of iron sulfate (trivalent), the solution was allowed to cool to room temperature, and pure water was supplemented so that the liquid volume became 2,000 mL. Thus, trivalent iron solutions according to Example 1 and each Example were obtained.
As a result of the analysis, it was found that the Fe concentration of the trivalent iron solution was 196 g / L.

3) Preparation of Arsenic and Iron Mixed Solution A reagent 60% arsenic acid solution was prepared as pentavalent arsenic.
The trivalent iron solution of 2) described above was prepared as the trivalent iron.
Here, arsenic in which a pentavalent arsenic reagent 60% arsenic acid solution, a trivalent iron solution, and water are mixed to give 0.9 times equivalent (0.9 times mole) of trivalent iron to the total amount of pentavalent arsenic. A mixed solution of iron and iron was produced.
Specifically, 32.5 mL of the reagent 60% arsenic acid solution and 55.8 mL of the trivalent iron solution of 2) described above were mixed, and water was added to make the total amount 650 mL.
The mixed solution of arsenic and iron thus obtained had an arsenic concentration of 25.0 g / L and a trivalent iron concentration of 16.8 g / L.

4) pH adjuster In this example, a reagent manufactured by Kishida Chemical Co., Ltd., magnesium hydroxide Mg (OH) ₂ (assay min 95%) was used as a pH adjuster.

5) Addition of oxidizing agent The above-mentioned mixed solution of arsenic and iron is heated to 95 ° C. At this time, in order to prevent the pH value of the mixed solution from exceeding 1 when reaching 95 ° C., sulfuric acid was added to the mixed solution during heating. Then, the amount of sulfuric acid to be added was adjusted so that the pH value of the mixed solution became 1 when the liquid temperature of the mixed solution reached 95 ° C.
After confirming that the liquid temperature of the mixed solution was 95 ° C. and pH 1, addition of the oxidizing agent was started and the reaction was started. The oxidant was added by blowing oxygen gas into the solution from the start of the reaction.
Specifically, oxygen gas was blown from the bottom of the beaker through a glass tube at 1 L / min, and the blowing was continued for 180 minutes until the end of the reaction.

6) Reaction Although the pH value of the mixed solution was 1.0 at the beginning of the reaction, Mg (OH) ₂ was added as a pH adjuster in the form of powder, and the pH value of the solution during the reaction was adjusted to 0.94 to 0.94. Control between 0.98. After completion of the reaction, the reaction product was filtered and the liquid component was analyzed by ICP.
Table 1 shows the arsenic concentration and iron concentration at the beginning of the reaction, the values of arsenic concentration and iron concentration after the completion of the reaction, and the reduction rates of the arsenic concentration and iron concentration before and after the reaction according to Example 1.

(Example 2)
The same operation as in Example 1 was performed except that the ratio of (number of moles of trivalent iron / number of moles of pentavalent arsenic) was 1.15.
Table 1 shows the arsenic concentration and iron concentration at the beginning of the reaction according to Example 2, the values of arsenic concentration and iron concentration after the completion of the reaction, and the reduction rates of the arsenic concentration and iron concentration before and after the reaction.

(Comparative Example 1)
The same operation as in Example 1 was performed except that oxygen addition was not performed.
In addition, stirring was made weak stirring so that air | atmosphere might not be involved in a solution.
Table 1 shows the arsenic concentration and iron concentration at the beginning of the reaction according to Comparative Example 1, the values of arsenic concentration and iron concentration after the completion of the reaction, and the reduction rates of the arsenic concentration and iron concentration before and after the reaction.

From the results in Table 1, the arsenic reduction rate was less than 10% when the oxidant was added to the arsenic-containing solution containing trivalent iron and stirred. On the other hand, when the arsenic-containing solution containing trivalent iron was stirred, the reduction rate of arsenic was 23% or more despite the weak stirring.
That is, it has been found that the reaction between arsenic and trivalent iron can be suppressed by adding an oxidizing agent to the arsenic-containing solution containing trivalent iron. That is, it was found that an arsenic-containing solution containing the trivalent iron can be produced while suppressing the generation of a naturally occurring arsenic-iron compound precipitate.
I can do it.

(Example 3)
1) Preparation of test unit arsenic-iron mixed solution A reagent 60% arsenic acid solution was prepared as pentavalent arsenic.
The trivalent iron solution of 2) described above was prepared as the trivalent iron.
The reagent iron sulfate (divalent) heptahydrate was prepared as divalent iron.

Here, a mixture of arsenic and trivalent iron in which the concentration of pentavalent arsenic is 42 g / L and trivalent iron is present 0.75 times equivalent (0.75 times mol) to the total molar amount of pentavalent arsenic A solution was prepared.
Specifically, 72 mL of a 60% arsenic acid solution, 103 mL of the trivalent iron solution of 2) described above, and 670 mL of pure water were mixed.
The mixed solution of pentavalent arsenic and trivalent iron thus obtained had an arsenic concentration of 42.6 g / L and a trivalent iron concentration of 23.9 g / L.
Next, 0.75 times equivalent (0.75 times mol) of divalent iron was added to the mixed solution.
Specifically, 100 g of the reagent iron sulfate (divalent) heptahydrate was added to the mixed solution and completely dissolved and mixed.
The mixed solution of pentavalent arsenic, trivalent iron and divalent iron thus obtained has a pentavalent arsenic concentration of 40.4 g / L, a trivalent iron concentration of 22.7 g / L, and a divalent iron concentration of 22.6 g / L. Met. The mixed solution of pentavalent arsenic, trivalent iron and divalent iron was used as a raw material solution for producing scorodite.

pH adjuster In this example, a reagent manufactured by Kishida Chemical Co., Ltd., magnesium hydroxide Mg (OH) ₂ (assay min 95%) was prepared as a pH adjuster.

2) Scorodite formation reaction
The raw material liquid mentioned above is heated to 95 ° C. At this time, in order to set the pH value of the mixed solution to 1 when reaching 95 ° C., a pH adjuster (magnesium hydroxide) was added to the raw material solution during heating.

  After confirming that the liquid temperature of the raw material liquid was 95 ° C. and pH 1, the addition of the oxidizing agent was started to start the scorodite production reaction. Note that oxygen gas was used as the oxidizing agent, and the oxygen gas was blown through the glass tube from the bottom of the beaker at 1 L / min.

The pH value of the raw material liquid was 1.0 at the beginning of the reaction, but during the reaction, a pH adjuster (magnesium hydroxide) was added as a powder, and the pH value of the solution was adjusted to 0.93 to 0.99. Controlled in between. Then, 120 minutes after the start of the reaction, the pH value of the solution was raised to 2.0, and the pH value was controlled between 1.96 and 2.0 for an additional 60 minutes. Eventually, the scorodite production reaction time was 3 hours in total.
After completion of the reaction, the product was filtered to obtain a post-reaction solution and a product residue (scorodite). In this example, the filtration proceeded very smoothly and was completed in a few seconds instead of 10 seconds.

Table 2 shows the concentration of each element for each reaction time of the liquid component according to this example and the decreasing rate of each element in the post-reaction liquid with respect to the raw material liquid.

From the results of Table 2, it was found that 99% of arsenic in the original arsenic-iron mixed solution was stabilized by the present invention. It was also found that 99% of the trivalent iron in the original arsenic-iron mixed solution was used for arsenic stabilization. On the other hand, it was found that 34% of the divalent iron in the original arsenic-iron mixed solution was used.
From the results, it was also found that the obtained post-reaction solution is almost a divalent iron solution, and that the post-reaction solution can be added again to the step of generating scorodite as a new divalent iron source solution. .

3) Evaluation of produced scorodite The filtrate obtained at the end of the reaction was washed with pure water and then subjected to X-ray diffraction measurement to evaluate the scorodite production status. From the X-ray diffraction results, a sharp peak indicating a scorodite (FeAsO ₄ .2H ₂ O) crystal was confirmed in a wide diffraction angle range in the filtrate at the end of the reaction. From this, the obtained filtrate was identified as scorodite crystals.
The obtained scorodite had a particle size of 20 μm.

Claims (7)

  A method for treating an arsenic-containing solution, which comprises adding an oxidizing agent to an acidic arsenic-containing solution containing pentavalent arsenic and trivalent iron at atmospheric pressure.   The method for treating an arsenic-containing solution according to claim 1, wherein the pH value of the arsenic-containing solution is set to 1 or less when the oxidizing agent is added.   The method for treating an arsenic-containing solution according to claim 1 or 2, wherein the value of (number of moles of trivalent iron / number of moles of pentavalent arsenic) of the arsenic-containing solution is 1 or more. Adding an oxidizing agent to an acidic arsenic-containing solution containing pentavalent arsenic and trivalent iron and under atmospheric pressure;
And a step of introducing divalent iron and an oxidizing agent into the arsenic-containing solution to which the oxidizing agent has been added.   The arsenic-containing solution containing the pentavalent arsenic and the trivalent iron and subjected to the step of adding an oxidizing agent to the acidic arsenic-containing solution under atmospheric pressure is stored for a predetermined period, and then the divalent iron and the oxidizing agent are added. The method for treating an arsenic-containing solution according to claim 4, wherein a step of charging is performed.   The post-reaction liquid obtained in the step of adding the divalent iron and the oxidizing agent is added again in the step of adding the divalent iron and the oxidizing agent as a divalent iron source. Item 6. A method for treating an arsenic-containing solution according to Item 4 or 5.   Adding the oxidant means blowing at least one selected from oxygen gas, air, oxygen-containing gas, air diluted with nitrogen, etc., ozone into the arsenic-containing solution, or excess The method for treating an arsenic-containing solution according to claim 1, wherein hydrogen oxide water is added to the arsenic-containing solution.