JP2011195367A - Method for producing iron arsenate compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an iron arsenate compound, by which the reaction of depositing an iron arsenate compound having high crystallinity and low elution concentration of arsenic from an arsenic solution can be finished in a short time and an adhesion amount of copper on the iron arsenate compound can be reduced.SOLUTION: The method includes a step of adding a ferrous ion into an arsenic solution and adding an oxidizing agent so as to oxidize the ferrous ion to react during stirring, wherein the step includes a step of adding a copper-containing material after a crystalline iron arsenate is produced.

Description

  The present invention relates to a method for producing an iron arsenate compound, and particularly to a method for obtaining an iron arsenate compound in which arsenic is hardly eluted by appropriately treating an arsenic solution.

  In non-ferrous smelting, smelting raw materials and smelting intermediates contain precious metals, main valuable metals such as copper, and accompanying elements such as arsenic. Arsenic is mainly immobilized and processed safely.

  Conventionally, as immobilization of arsenic contained in non-ferrous smelting intermediates, divalent iron ions were added to a solution containing pentavalent arsenic with a molar ratio of iron arsenic set at a pH of 2 or lower and atmospheric pressure, There has been proposed a method in which an oxidant is added, the temperature is raised while stirring and the reaction is performed, and then the solid content obtained by solid-liquid separation is dried (see, for example, Patent Document 1). In this method, scorodite having a very small arsenic elution concentration can be recovered by treating a high concentration arsenic solution.

  Moreover, when processing an arsenic solution, the method of performing precipitation reaction using cheap air as an oxidizing agent by coexisting copper ion in a liquid is proposed (for example, patent document 2, nonpatent literature 1). reference).

JP 2008-119690 A JP 2008-143741 A

T. Fujita et al., "Effects of zinc, copper and sodium ions on ferric arsenate precipitation in a novel atmospheric scorodite process.", Hydrometallurgy, July 2008, Vol. 93, No. 1-2, p.30-38

  However, when performing the precipitation reaction of an iron arsenate compound than the methods described in Patent Documents 1 and 2, in order to synthesize an iron arsenate compound with good crystallinity and low arsenic elution concentration, comparison of air, oxygen, etc. Since it is desirable to oxidize with a weak oxidant, there is a problem that the reaction rate becomes slow. Patent Document 2 only discloses an example in which copper ions are allowed to coexist in the pre-reaction solution before the addition of the oxidizing agent, and when the present inventor conducted a test, copper ions were allowed to coexist in the pre-reaction solution. In such a case, the deposited iron arsenate compound adheres so as to accompany a large amount of copper, and there is a problem that the recovery rate of copper as a valuable metal decreases. Further, Non-Patent Document 1 describes that scorodite has a spindle shape in the presence of copper. In general, a scorodite crystal in which elution of arsenic is suppressed is generally considered to have a crystal plane that is difficult to elute on the surface. However, if copper is attached to the crystal, the crystal lattice may be deteriorated due to defects in the crystal lattice, and the crystal shape may change from an orthorhombic shape to a spherical shape or a spindle shape. There is a risk that an unstable and easily eluted crystal plane is formed on the surface.

  Therefore, in view of such a conventional problem, the present invention can complete a reaction for precipitating an iron arsenate compound having a high crystallinity and a low elution concentration of arsenic from an arsenic solution in a short time, And it aims at providing the manufacturing method of the iron arsenate compound which can reduce the adhesion amount of the copper to an iron arsenate compound.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors added a divalent iron ion to a solution containing pentavalent arsenic, added an oxidizing agent, and allowed to react with stirring. Is added after the crystalline iron arsenate compound is formed, so that an iron arsenate compound having good crystallinity and a low elution concentration of arsenic can be synthesized in a short time without impairing the precipitation rate of arsenic, Moreover, it discovered that the amount of copper adhering to an iron arsenate compound could be reduced, and came to complete this invention.

  The method for producing an iron arsenate compound of the present invention is a method for producing an iron arsenate compound comprising a step of causing an iron arsenate compound to react with an oxidizing agent under normal pressure using an arsenic solution and divalent iron. In the step of depositing the iron arsenate compound, the copper-containing material is added after the crystalline iron arsenate compound is formed.

  In this method for producing an iron arsenate compound, the copper-containing substance is preferably added after 1 hour at the start of the reaction and 1 hour before the end of the reaction. Moreover, it is preferable that a copper containing material is added with respect to a process liquid so that it may become 0.5-4.0 g / L in copper concentration. Furthermore, it is preferable that the copper concentration in the treatment liquid before the addition of the copper-containing material is less than 0.5 g / L. The copper-containing material is preferably one or more of metallic copper, copper oxide, and copper sulfate.

  According to the present invention, the copper-containing substance is formed after the crystalline iron arsenate compound is formed in the step of using an arsenic solution and divalent iron to react with an oxidizing agent under normal pressure to precipitate the iron arsenate compound. Can be synthesized in a short time without impairing the precipitation rate of arsenic, and it is possible to synthesize copper arsenate compound with good crystallinity and low elution concentration of arsenic from arsenic solution. The amount of adhesion can be reduced.

  The method for producing an iron arsenate compound of the present invention is a method for producing an iron arsenate compound comprising a step of causing an iron arsenate compound to react with an oxidizing agent under normal pressure using an arsenic solution and divalent iron. The step of precipitating the iron arsenate compound is characterized by adding a copper-containing substance after the crystalline iron arsenate compound is formed. By having such a structure, the arsenic solution has good crystallinity and elution of arsenic. An iron arsenate compound having a low concentration can be synthesized in a short time without impairing the precipitation rate of arsenic, and the amount of copper adhering to the iron arsenate compound can be reduced. .

  As the arsenic solution to be treated, various smelting intermediates generated by non-ferrous smelting or the like can be used. When the arsenic concentration in the arsenic solution is low, the particles tend not to coarsen during the growth process from the precipitation of the iron and arsenic compound, and therefore it is preferably 10 g / L or more. Further, it is more preferable that the arsenic concentration is 20 g / L or more, because the amount of arsenic that can be processed at one time is increased and productivity is improved. Moreover, in order to avoid formation of an amorphous iron arsenate compound, the pH of the arsenic solution is preferably 2 or less. Arsenic ions are preferably pentavalent in the solution. That is, it is sufficient that pentavalent arsenic ions are present during the reaction, and how they are present may be appropriately selected by utilizing an oxidation-reduction reaction.

A divalent iron ion is added to this arsenic solution to prepare a pretreatment solution. As a salt which becomes a divalent iron ion supply source, for example, soluble iron (II) sulfate heptahydrate (FeSO ₄ · 7H ₂ O) can be used. The molar ratio of iron to arsenic (Fe / As) in the pretreatment liquid for the reaction is approximately equal to the molar ratio of scorodite (FeAsO ₄ .2H ₂ O), or iron is kept slightly excessive. Specifically, it is 1 or more, and preferably 1.0 to 1.5. Since iron and arsenic react at approximately equal equivalents, the molar ratio must be 1 or more to react all arsenic, and even if the molar ratio of iron to arsenic in the solution is greater than 1.5. This is because excessive iron source addition leads to iron loss. However, the molar ratio here may be set as appropriate.

  Next, an oxidizing agent is added to the pretreatment liquid for reaction to react with divalent iron ions to precipitate an iron arsenate compound. Any oxidizing agent capable of oxidizing divalent iron ions can be used as the oxidizing agent, but an oxidizing agent capable of controlling the oxidation rate is preferable, and examples thereof include a gas containing oxygen.

  In the present invention, after the addition of the oxidizing agent is started, the addition of the copper-containing material is started after the crystalline iron arsenate compound is formed. It is advantageous for increasing the precipitation growth rate of the iron arsenate compound to start adding the copper-containing material before or simultaneously with the addition of the oxidizing agent and before the crystalline iron arsenate compound is formed. However, the rapid progress of the oxidation reaction dominates the generation of nuclei, and there is a risk of forming fine crystal or amorphous. In order to avoid this, it is preferable to wait for the addition of the copper-containing compound until the formation of a certain amount of crystalline iron arsenate compound is confirmed. By adding the copper-containing substance after a lapse of time from the start of the reaction to the extent that the formation of the crystalline iron arsenate compound can be confirmed, the reaction rate can be improved without impairing the crystallinity. The state of formation of the iron arsenate compound can be roughly grasped by visual observation because the liquid color and the like change when fine particles of about several μm are generated in the liquid. As the actual timing, management and operation are simple if the time from the start of the reaction is measured. For example, when the reaction start time is set at the start of addition of the oxidant, the addition of the copper-containing substance is performed for a period of 1 hour before the end of the iron arsenate compound synthesis process after 1 hour from the start of the addition of the oxidant. It is desirable. This is because, in order to shorten the reaction time, the effect of the present invention is relatively diminished if it is too close to the end time. The time management level is sufficient in minutes.

As the copper-containing material, tampan (CuSO ₄ .5H ₂ O), copper oxide (CuO), metal copper (for example, copper powder), which is copper sulfate, or the like can be used. In the case of adding copper oxide or metallic copper, there is an effect of consuming the free acid generated by the reaction by neutralization, and the precipitation rate of arsenic and iron is slightly improved.

  In order to sufficiently obtain the effect of shortening the reaction time, the copper-containing substance is preferably 0.5 g / L or more in terms of copper concentration with respect to the solution after adding the oxidizing agent to the pre-reaction treatment solution. . On the other hand, excessive copper addition increases the amount of copper adhering to the iron arsenate compound. Therefore, the amount of copper-containing material added is preferably limited to 4.0 g / L or less in terms of copper concentration. In addition, in order to reduce the copper loss to an iron arsenate compound, it is preferable to make the copper concentration in the process liquid before addition into less than 0.5 g / L. The addition may be made appropriately by dividing the predetermined amount by a single number. When the addition is divided into a plurality of times, the addition amount may be increased or decreased at each time. There are gradual decrease and gradual increase.

  The reaction temperature may be appropriately selected so as not to cause a change in shape such as a spherical shape or a spindle shape, or to make the particles finer, which deteriorates the arsenic elution value of the produced iron arsenate compound.

  In the step of precipitating the iron arsenate compound, the precipitation reaction of iron and arsenic can be further advanced by stirring the solution using a predetermined device.

  The iron arsenate compound thus obtained has a very low arsenic elution concentration with respect to the standard value of 0.3 mg / L of the Japanese Environmental Agency Notification No. 13 method, and can be discarded, deposited or stored. it can. In addition, some arsenic and added copper remain in the post-reaction solution after adding scorodite by adding copper. These can be easily recovered by a substitution reaction such as sulfurization reaction or zinc dust, and the precipitated copper arsenic compound can be treated in the same manner as the smelting intermediate raw material. That is, finally, all arsenic contained in the smelting intermediate raw material can be immobilized as an iron arsenate compound by these processes.

[Example 1]
As a starting material, arsenic was used by diluting a solution of As = 500 g / L (pentavalent) with pure water in an arsenic solution of a commercially available reagent (manufactured by Wako Pure Chemical Industries, Ltd.). The iron salt used was a ferrous sulfate heptahydrate FeSO ₄ · 7H ₂ O (reagent (manufactured by Wako Pure Chemical Industries, Ltd.)).

  These substances and pure water were mixed to prepare 0.7 L of an arsenic / iron-containing liquid having an arsenic concentration of 50 g / L and an iron concentration of 55.91 g / L. The Fe / As molar ratio of this liquid is 1.5. This liquid was transferred to a 2 L glass beaker, a two-stage turbine stirring blade and four baffle plates were set, and heated to 95 ° C. with strong stirring at a rotational speed of 1000 rpm. At this time, a very small amount of the liquid was sampled, and after cooling the sample liquid to 60 ° C., the pH and ORP of the liquid were measured. The pH was measured using a glass electrode, and the ORP was measured using an Ag / AgCl electrode. Its pH was 1.25. The liquid after the measurement was returned to the reaction vessel.

While maintaining this pre-reaction solution at 95 ° C., 99% purity oxygen gas was blown into the container while stirring. The oxygen gas flow rate was 0.35 L / min. One hour after the start of blowing oxygen gas (copper-containing substance addition timing: 1.0 hour), copper powder (manufactured by Junsei Chemical Co., Ltd.) was added at 1.0 g / L to the solution. The stirring state, temperature, and gas flow rate were maintained for 4 hours from the start of oxygen gas blowing. On the way, the liquid was sampled every hour to measure pH and ORP. The liquid after the measurement was returned to the container.
In addition, when the addition of copper powder was started, precipitation of the iron arsenate compound which seems to be a scorodite crystal nucleus could be visually confirmed in the liquid. It was confirmed in the same manner in other examples.

After 4 hours from the injection of oxygen gas, the reaction was completed, and after the temperature of the liquid (mixed slurry of solution and precipitate) was lowered to 70 ° C., a pressure filter made by Advantech with a filtration area of 0.01 m ² ( It filtered using model number: KST-142). In the filtration, air was used as a pressurized gas, and the applied pressure (gauge pressure) was 0.4 MPa. The liquid after filtration was subjected to composition analysis. At that time, the precipitation rate of arsenic was calculated from the ratio between the arsenic concentration remaining in the liquid after filtration and the arsenic concentration in the pre-reaction liquid. The filtered solid content was a wet cake, which was repulped with pure water at a pulp concentration of 100 g / L for 1 hour and then filtered again.

The solid content after washing and filtration was dried at 60 ° C. for 18 hours. The dried solid content was subjected to composition analysis, dissolution test, particle size measurement with a particle size distribution meter, and crystal particle shape observation with an electron microscope.
The dissolution test was carried out by a method according to Notification 13 of the Environment Agency. That is, the solid content and water of pH = 5 were mixed at a ratio of 1:10, and the mixture was stirred for 6 hours with a centrifugal machine, followed by solid-liquid separation and composition analysis of the filtered liquid.

  The obtained copper content of the solid content was 1000 ppm. The arsenic precipitation rate calculated from the initial arsenic concentration before the reaction and the arsenic concentration in the liquid after the filtration was 95.74%, and a high precipitation rate was achieved in the reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.05 mg / L, which sufficiently cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

[Example 2]
The reaction was conducted in the same manner as in Example 1 except that the copper-containing substance addition timing was 1.5 hours.

  The obtained copper content of the solid content was 662 ppm. The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 94.78%, and a high precipitation rate was achieved with a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.12 mg / L, which sufficiently cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

Example 3
The reaction was carried out in the same manner as in Example 1 except that the copper-containing substance addition timing was set to 2.0 hours.

  The copper content of the obtained solid content was 577 ppm. The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 95.08%, and a high precipitation rate was achieved in a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.06 mg / L, which sufficiently cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

Example 4
The reaction was carried out in the same manner as in Example 1 except that 0.5 g / L of copper powder was added to the solution.

  The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 95.26%, and a high precipitation rate was achieved with a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.07 mg / L, which sufficiently cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

Example 5
The reaction was carried out in the same manner as in Example 1 except that the addition timing of the copper-containing substance was 2.0 hours, and 2.0 g / L of copper powder was added to the solution.

  The obtained copper content of the solid content was 1090 ppm. The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 95.28%, and a high precipitation rate was achieved with a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.07 mg / L, which sufficiently cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

Example 6
The reaction was performed in the same manner as in Example 1 except that the addition timing of the copper-containing substance was 2.0 hours and that 4.0 g / L of copper powder was added to the solution.

  The obtained copper content of the solid content was 2130 ppm. The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 96.56%, and a high precipitation rate was achieved with a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.09 mg / L, which sufficiently cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

Example 7
Other than adding copper (II) sulfate pentahydrate grains (manufactured by Wako Pure Chemical Industries, Ltd.) in place of copper powder, so that the copper concentration in the solution is 1.0 g / L. Was reacted in the same manner as in Example 1.

  The obtained copper content of the solid content was 613 ppm. The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 95.12%, and a high precipitation rate was achieved in a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.22 mg / L, which cleared the dissolution standard of 0.3 mg / L. When observed by SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was generated.

[Comparative Example 1]
It was made to react by the method similar to Example 1 except not having added copper powder.

  The precipitation rate of arsenic obtained by dividing the arsenic concentration of the solution after the reaction filtration by the arsenic concentration of the pre-reaction solution was 85.26%. As a result of the dissolution test, the dissolution amount of arsenic was 0.33 mg / L. When observed with an SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was produced.

[Comparative Example 2]
The reaction was carried out in the same manner as in Example 1 except that the addition timing of the copper-containing material was set before the addition of the oxidizing agent.

  The obtained copper content of the solid content was 2400 ppm. The arsenic precipitation rate calculated from the arsenic concentration of the liquid after filtration was 95.28%, and a high precipitation rate was achieved with a reaction time of 4 hours. As a result of the dissolution test, the dissolution amount of arsenic was 0.23 mg / L, which cleared the dissolution standard of 0.3 mg / L. When observed with an SEM (electron microscope), it was orthorhombic and it was confirmed that crystalline scorodite was produced.

As shown in Table 1, according to the methods of Examples 1 to 7 according to the present invention, the arsenic precipitation rate at the reaction time of 4 hours is equivalent to that of the comparative example, and the arsenic elution amount is small. It can be seen that an iron arsenate compound having a low elution concentration of arsenic can be synthesized from an arsenic solution in a short time and that the amount of copper adhering to the iron arsenate compound can be reduced. The deterioration of the shape of the iron oxide compound appears in the form of an increase in the amount of arsenic eluted. Although the arsenic elution amount of the comparative example shows a higher value than that of the example, the elution value is 0. It is an extremely low value of about several mg / L. At such a low value, it can be said that the crystallinity is good, and in the examples, the elution value is extremely low, so that the crystallinity is even better. However, such a comparison at a low value is difficult to say with a simple explanation of crystallinity alone. Rather, it can be said that the present invention has an effect of suppressing arsenic elution in addition to improving crystallinity.

According to the present invention, in the step of adding an oxidizing agent to the reaction pretreatment solution to react with divalent iron ions, after adding the oxidizing agent, after adding the copper-containing substance after the crystalline iron arsenate compound is formed As a result, an iron arsenate compound having good crystallinity and a low elution concentration of arsenic can be synthesized from the arsenic solution in a short time, and the amount of copper adhering to the iron arsenate compound can be reduced.
The above-described invention recovers an iron and arsenic compound having a very low arsenic elution concentration from an arsenic solution obtained by treating an arsenic-containing substance containing various elements other than arsenic, such as a smelting intermediate It can be used as a method.

Claims (5)

In the method for producing an iron arsenate compound, the method comprising reacting an arsenic solution and divalent iron with an oxidizing agent under normal pressure to precipitate an iron arsenate compound,
The step of precipitating the iron arsenate compound comprises adding a copper-containing substance after the crystalline iron arsenate compound is formed.   The method for producing an iron arsenate compound according to claim 1, wherein the copper-containing substance is added after 1 hour at the start of the reaction and 1 hour before the end of the reaction.   The said copper containing substance is a manufacturing method of the iron arsenate compound of Claim 1 or 2 added so that it may become 0.5-4.0 g / L as a copper concentration with respect to a process liquid.   The method for producing an iron arsenate compound according to claim 1, wherein the copper concentration of the treatment liquid before adding the copper-containing substance is less than 0.5 g / L.   The method for producing an iron arsenate compound according to any one of claims 1 to 4, wherein the copper-containing substance is at least one of metallic copper, copper oxide, and copper sulfate.