JP6480237B2 - Method of manufacturing scorodite - Google Patents

Description

  The present invention relates to a method of manufacturing scorodite. In particular, it relates to a process for producing scorodite from intermediates produced in non-ferrous smelting processes.

Various impurities are mixed in non-ferrous smelting materials such as copper ore, and such impurities include arsenic (As). Arsenic is a toxic element, and in view of the influence on the surrounding environment, it is desirable to dispose it after converting it to a form that is chemically stable. In this regard, crystalline iron-arsenic compound scorodite (FeAsO ₄ · 2H ₂ O) is known to be chemically stable, it is also suitable for long-term storage.

  In the past, commonly used as a method for producing crystalline scorodite is the addition of divalent or trivalent iron to a pentavalent arsenic solution, and heat treatment at 80 ° C. or higher under acidic conditions to obtain crystalline scorodite. It is a method to generate. This technique is disclosed, for example, in Japanese Patent No. 3756687, "Method of removing and fixing arsenic from arsenic-containing solution", Japanese Patent Application Laid-Open No. 2005-161123, "Method of removing arsenic from smoke and ash", Japanese Patent Application Laid-Open No. 11-277075, "Sulfuric acid The details are described in a method of removing and fixing arsenic present in an iron solution, and in Japanese Patent No. 4185541 "Production method of iron-arsenic compound with good crystallinity". These documents disclose Fe / As at the time of scorodite synthesis as follows.

  In patent 3756687, it is referred to as Fe / As = 1.5-2.0. It is required to improve the crystallinity of the formed arsenic compound and to suppress the elution of arsenic. If scorodite is synthesized at a molar ratio other than this, the crystallinity is significantly reduced and arsenic is likely to be eluted. In the example, “3 L of an iron-containing solution of 40 g / L of Fe is added to 6 L of this arsenic-containing solution so that the Fe / As (molar ratio) is 1.8, sealed in an autoclave and raised to 165 ° C. It is said that it is warm.

Although it is set as Fe / As = 1.0-1.5 by Unexamined-Japanese-Patent No. 2005-161123, the reason is not disclosed. In the example, “a leaching solution of pH 1.0 obtained by leaching arsenic from smoke ash using a sulfuric acid solution and filtering it, an aqueous solution of ferric sulfate pH 1.0 (iron ion (Fe ³⁺ ) concentration 80 g / L ) Is added so that the molar ratio of iron to arsenic is 1 to 1.5, and the mixture is heated to 95.degree. C. under an arsenic concentration of 10 g / L or more to form amorphous iron arsenate. Of ferric sulfate is added so that the molar ratio of iron to arsenic is 1.3 to 1.5, and the mixture is 95 under the condition of an arsenic concentration of 15 g / L. C. to crystallize amorphous iron arsenate. "

  In JP-A-11-277075, “The compound of iron and arsenic has a slower rate of precipitation in the region of 3 <Fe / As <10, so in order to obtain a sufficient arsenic precipitation rate, preferably 1 < It mixes with it so that it may become Fe / As <3 or Fe / As> 10 ". In Examples, Fe / As was 4 (Example 1), 1.3 (Example 2), and 4.5 (Example 3).

Japanese Patent No. 4185541 publication, the ratio of "Iron and arsenic keep the excess slightly equal to the molar ratio of scorodite _{(FeAsO 4 · 2H 2 O)} , or iron. Specifically Fe / As ratio molar ratio In the process control, it is preferable to set the value to 0.9 or more and 1.5.about.0.2.

Patent No. 3756687 gazette JP, 2005-161123, A Japanese Patent Application Laid-Open No. 11-277075 Patent No. 4185541

  From the viewpoint of long-term storage of scorodite, it is desirable to reduce the storage volume because the storage cost can be reduced. However, there is not enough discussion about the volume of scorodite conventionally. If the volume per unit weight of scorodite is small (in other words, bulk density is large), the volume of the storage place can be reduced. For this reason, it would be advantageous to develop techniques to reduce the volume per unit weight of scorodite.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a scorodite having a small volume per unit weight.

In the prior art, the Fe / As molar ratio in producing scorodite was set to be equal to or higher than one. This is considered to be in consideration of not leaving unreacted As because Fe / As molar ratio is 1 in FeAsO ₄ .2H ₂ O which is a chemical formula of scorodite. However, according to the study results of the present inventor, it was found that the volume per unit weight of the obtained scorodite is reduced when synthesizing the scorodite with the Fe / As molar ratio less than 0.9.

  However, when scorodite is synthesized with an Fe / As molar ratio of less than 0.9, there is a problem that unreacted As remains due to lack of Fe. Therefore, when scorodite synthesized with an Fe / As molar ratio of less than 0.9 is used as a seed crystal, even if it is reacted with an Fe / As molar ratio of 0.9 or more, the scorodite having a small volume per unit weight continues It turned out that it synthesizes.

  The present invention has been completed based on the above findings, and in one aspect, it is a method of producing scorodite seed crystals from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions. This is a method of producing scorodite seed crystals by reacting a part of the As ions while maintaining the cumulative Fe / As molar ratio below 0.9.

  In one embodiment of the method for producing a scorodite seed crystal according to the present invention, a portion of the As ion is reacted to maintain the scorodite seed crystal while maintaining the cumulative Fe / As molar ratio at 0.7 or less. Manufacture.

  In another embodiment of the method of producing a seed crystal of scorodite according to the present invention, the initial pentavalent As ion concentration in the acidic aqueous solution is 2 g / L or more.

  In still another embodiment of the method of producing scorodite seed crystals according to the present invention, the reaction is continued until the average particle size of the seed crystals becomes 20 μm or more.

  In another aspect, the present invention is a method of producing scorodite by using the scorodite obtained by the method of producing a seed crystal of scorodite according to the present invention as a seed crystal.

  In still another aspect, the present invention is a method of producing scorodite from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions, wherein the cumulative Fe / As molar ratio is Step 1 of producing scorodite seed crystals by reacting a part of the As ions while maintaining the concentration to less than 0.9, and then adjusting the cumulative Fe / As molar ratio to 0.9 or more. And D. reacting the remainder of the As ion in the presence of a seed crystal to produce scorodite.

  In one embodiment of the method of producing scorodite according to the present invention, step 1 is continued until the average particle size of the seed crystals is 20 μm or more.

  In another embodiment of the process for producing scorodite according to the invention, the cumulative Fe / As molar ratio is obtained by additionally adding a source of divalent and / or trivalent Fe ions to the aqueous acid solution. Adjust to 0.9 or more.

  In still another embodiment of the method of producing scorodite according to the present invention, the source of divalent and / or trivalent Fe ions is additionally added in multiple times.

  In still another embodiment of the method of producing scorodite according to the present invention, the addition amount per addition of divalent and / or trivalent Fe ions to be added is 5 g or less per 1 L of acidic aqueous solution. , And an additional source of Fe ions.

  In yet another embodiment of the method of producing scorodite according to the present invention, the additional addition of the divalent and / or trivalent Fe ion source is from the point when the temperature of the acidic aqueous solution exceeds 50 ° C. The first operation is carried out after 2 hours or more, and the addition is further carried out 2 hours or more after the last addition.

  In yet another embodiment of the method of producing scorodite according to the present invention, in step 2, the cumulative Fe / As molar ratio is adjusted to 1.0 or more.

  In yet another embodiment of the method of producing scorodite according to the present invention, the pH at the reaction end exceeds 1.2.

The present invention, in still another aspect, is a crystalline scorodite having a volume per gram of 0.7 cm ³ or less.

  In one embodiment of the crystalline scorodite according to the present invention, it is in the form of secondary particles in which primary particles of polyhedral shape are aggregated.

  In another embodiment of the crystalline scorodite according to the present invention, the average particle size is 30 μm or more.

  According to the present invention, a scorodite having a small volume per unit weight can be manufactured. By using a small volume per unit weight scorodite as a seed crystal, it is possible to produce a small volume per unit weight scorodite, preferably without leaving unreacted As in the reaction solution. In addition, by changing the Fe / As molar ratio from less than 0.9 to 0.9 or more in the process of scorodite production, the scorodite having a small volume per unit weight can be continuously removed without separating and recovering the seed crystal. It is also possible to produce

It is an example of the SEM photograph of the seed crystal of the invention example 1. FIG. It is an example of the SEM photograph of the crystal grown using the seed crystal of the invention example 1. FIG.

In the present invention, the "cumulative Fe / As molar ratio" refers to the total As molar amount from the As ion source added to the reaction solution (acidic aqueous solution) from the start of the scorodite synthesis reaction to the molar ratio measurement time, Synthesis of scorodite It is defined as the ratio of the total molar amount of Fe from the Fe ion source added to the reaction liquid from the start of the reaction of the scorodite to the point of molar ratio measurement.
Also, “Fe / As molar ratio at reaction initiation time” means the reaction solution at reaction initiation time relative to the total As molar amount from As ion source in the reaction solution (acidic aqueous solution) at the synthesis reaction initiation time of scorodite It is given as the ratio of the molar amount of Fe from in the Fe ion source in
Also, “Fe / As molar ratio for each divided addition” refers to the total molar amount of As from the As ion source added to the reaction solution (acidic aqueous solution) from the start of the synthesis reaction of scorodite to the time point of molar ratio measurement. It is given as the ratio of the molar amount of Fe from the Fe ion source to be added per one step when the Fe ion source is added stepwise to the reaction solution.

(1. Production of seed crystal)
In one aspect of the present invention, a method is provided for producing scorodite seed crystals from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions. Pentavalent As can be exemplarily given in the form of arsenate (H ₃ AsO ₄ ) or the like. Arsenic acid is contained in a sulfuric acid leaching solution after sulfuric acid leaching of electrolytically precipitated copper, which is an intermediate produced in the copper smelting process. Therefore, the said sulfuric acid leaching solution can also be used as a raw material. The divalent and / or trivalent Fe can be exemplarily given in the form of iron oxide, iron sulfate, iron chloride, iron hydroxide and the like. Polyferrous sulfate and polyferric sulfate can also be used. The Fe ions in the acidic aqueous solution may be in the form of either divalent or trivalent and may be present in the form of a mixture thereof. However, since the valence of Fe in scorodite is trivalent, divalent Fe ions are oxidized to trivalent during the reaction. The acidic aqueous solution can be provided as an aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, etc. In the case of producing scorodite from As in arsenic acid contained in electrolytically precipitated copper generated in the copper smelting process, the aqueous solution of sulfuric acid acid is preferable because the solution after synthesis of scorodite can be returned to the copper electrolytic cell.

  From the viewpoint of suppressing the volume per unit weight of scorodite seed crystals, a part of the As ions are reacted while maintaining the cumulative Fe / As molar ratio in the acidic aqueous solution to less than 0.9, It is important to produce scorodite seed crystals. The effect of reducing the volume per unit weight of the scorodite seed crystals is that the smaller the cumulative Fe / As molar ratio in the acidic aqueous solution is, the cumulative Fe / As molar ratio is preferably 0.8 or less , More preferably 0.7 or less, still more preferably 0.6 or less, still more preferably 0.5 or less, still more preferably 0.4 or less, still more preferably 0 .3 or less. However, since the amount of seed crystals formed decreases if the cumulative Fe / As molar ratio is too small, the cumulative Fe / As molar ratio is preferably 0.05 or more, more preferably 0.1 or more. More preferably, it is 0.2 or more.

In FeAsO ₄ · 2H ₂ O is a chemical formula of scorodite, Fe: As = 1: As can be seen from a 1, in the present invention, to produce seed crystals of scorodite in a state in which Fe is insufficient. Therefore, if the synthesis of seed crystals progresses and all the Fe contained in the reaction solution is consumed for the synthesis of scorodite, As will remain in the reaction solution. That is, only a part of As in the reaction solution is consumed for producing scorodite seed crystals.

  Since the solubility of crystalline scorodite increases rapidly at pH less than 0.3, the pH of the acidic aqueous solution is preferably maintained at 0.3 or more from the initiation of the reaction to the termination of the reaction, preferably at 0.6 or more. It is more preferable to maintain 0.9 or more, more preferably 1.2 or more, and still more preferably 1.25 or more. In addition, when the pH of the acidic aqueous solution exceeds 2.2, the added iron precipitates as iron hydroxide and the iron is not used effectively for synthesizing scorodite, so the pH of the acidic aqueous solution is set to It is preferable to maintain at 2.2 or less, more preferably at 1.9 or less, and still more preferably at 1.6 or less from the time of the reaction to the end of the reaction.

  When synthesizing scorodite under atmospheric pressure without seed crystals, the pentavalent As ion concentration at the reaction initiation time is preferably 2 g / L or more, because scorodite can not be synthesized without a certain concentration. More preferably, it is 5 g / L or more.

  Seed crystals of scorodite can be produced by heating the above-mentioned acidic aqueous solution to, for example, 60 to 95 ° C. under atmospheric pressure. From the viewpoint of reaction promotion, it is preferable to stir the acidic aqueous solution during the reaction. Crystalline scorodite is chemically stable and suitable for long-term storage. The seed crystals can be recovered by solid-liquid separation into a residue containing seed crystals of the scorodite and the post-arsenic solution. However, if the reaction rate is too high, a large amount of independent crystals will be generated and the seed crystals will not be large. Therefore, it is preferable to cause the scorodite synthesis reaction under a mild oxidizing atmosphere. Specifically, air atmosphere is preferable to oxygen atmosphere.

In one embodiment, the scorodite seed crystals of the present invention are provided in a low volume per unit weight aspect. Since the small volume requires less storage space, storage space can be easily secured and storage costs can be reduced, which is economically advantageous. Specifically, the volume per 1g can be 0.9 cm ³ or less, further may be a 0.8 cm ³ or less, for example, the volume per 1g and 0.7～0.9Cm ³ be able to. In the present invention, the volume per 1 g of scorodite is determined by the following procedure. After the scorodite to be measured is dried for at least 24 hours in a 40 ° C. dryer, 2.5 g of the scorodite is gently poured into a 15 mL centrifuge tube (φ about 1 cm) using a funnel, and this is set in a centrifuge And rotate for 5 minutes at an acceleration of 13,420 g (g is the acceleration of gravity = 9.8 m / s ² ). Then, the volume per gram is measured from the volume of scorodite in the centrifuge tube taken out of the centrifuge.

  Moreover, the seed crystal of scorodite according to the present invention has a polyhedral shape in one embodiment. In the polyhedral shape, each surface is smooth, so the specific surface area is smaller than in the case of scorodite having many irregularities. This is considered to be effective in reducing the elution risk of As. Further, among polyhedral shapes, it is preferable from the viewpoint of reducing the specific surface area to be a shape close to a sphere.

  In one embodiment, scorodite seed crystals according to the present invention are provided with a large average particle size. The larger the average particle size, the smaller the volume per unit weight can be. This is because the scorodite seed crystal according to the present invention is typically in the form of a secondary particle formed by the aggregation of primary particles of polyhedral shape, and a plurality of primary particles have almost a gap between faces. It aggregates in such a close state as it can not form secondary particles. For this reason, the fact that secondary particles are large means that scorodite having a reduced number of voids per unit volume is produced. In addition, when the average particle size is large, an advantage that the water content can be easily reduced and an advantage that the filterability is improved can be obtained. Therefore, it is desirable to use a seed crystal having a large grain size because it easily grows into scorodite having a large grain size.

  In one embodiment, the seed crystal of scorodite according to the present invention can have an average particle size (D50) of at least 20 μm, preferably at least 25 μm, as measured by a laser diffraction / scattering particle size distribution measuring device. More preferably, it can be 30 micrometers or more, More preferably, it can be 35 micrometers or more, for example, can be 20-40 micrometers. In the present invention, the average particle size (D50) of scorodite is a particle size value of 50% integrated value calculated based on the volume distribution (the same applies hereinafter).

(2. Production of scorodite in the case of using a separately prepared seed crystal)
When using scorodite seed crystals according to the present invention, even if scorodite is produced in a reaction system in which As / Fe is increased at the start of the reaction, it is possible to synthesize scorodite in which the properties of the seed crystal are maintained. For this reason, as described above, when scorodite is produced in a state of insufficient iron, unreacted As remains, but once the seed crystal is used, the Fe / As molar ratio at the start of the reaction is 0.9 or more. Even if scorodite is produced from the acidic aqueous solution, a small volume of scorodite per unit weight can be produced while reducing unreacted As.

  In the method of producing scorodite using seed crystals, from the viewpoint of reducing unreacted As, it is preferable to set the cumulative Fe / As molar ratio in the acidic aqueous solution to 0.9 or more, The cumulative Fe / As molar ratio is more preferably set to 1.0 or more, and still more preferably 1.2 or more. In addition, if there is too much Fe, the crystal can not be grown while maintaining the shape of the seed crystal on the crystal, and there is a possibility that an independent crystal body may be generated, and from the viewpoint of eliminating unnecessary cost for Fe. The cumulative Fe / As molar ratio in the acidic aqueous solution is preferably set to 1.8 or less, more preferably 1.5 or less. The Fe / As molar ratio may be achieved at the start of the reaction or may be achieved by stepwise adjustment during the reaction.

  Therefore, in one embodiment of the method for producing scorodite according to the present invention, an acidic aqueous solution containing pentavalent As ion and divalent and / or trivalent Fe ion in the coexistence of the seed crystal according to the present invention Produce scorodite from The conditions for producing scorodite at this time are the same as those described in the description of the method for producing a seed crystal except that the cumulative Fe / As molar ratio is set to 0.9 or more.

  The amount of seed crystals to be added is preferably as large as possible with respect to the weight of the solution because it can be processed quickly to adsorb and grow arsenic in the solution on the surface of the seed crystals. Specifically, the content is preferably 0.05% or more, more preferably 0.2% or more, and still more preferably 0.8% or more based on the weight of the acidic aqueous solution.

  The crystalline scorodite thus obtained can be grown while maintaining the form of the seed crystal, so that the primary particles are in close contact with each other in a state of close aggregation to increase the particle size, and accordingly the volume per unit weight Becomes even smaller. In one embodiment, the scorodite obtained by using the seed crystal of scorodite according to the present invention has an average particle size (D50) of secondary particles measured by a laser diffraction / scattering particle size distribution measuring device of 30 μm or more. , Preferably 35 μm or more, more preferably 40 μm or more, still more preferably 45 μm or more, still more preferably 50 μm or more, for example 30 to It can be 60 μm.

Furthermore, the scorodite obtained using a seed crystal of scorodite of the present invention in one embodiment, the volume per 1g can be 0.7 cm ³ or less, also further to 0.6 cm ³ or less For example, the volume per 1 g can be 0.4 to 0.7 cm ³ .

(3. Production of scorodite when the seed crystal is not prepared separately)
In the manufacturing method of scorodite using the seed crystal mentioned above, the method of preparing a seed crystal separately and adding this to a reaction system was employ | adopted. However, even if seed crystals are not prepared at the start of the reaction, it is possible to produce the small volume scorodite per unit weight targeted in the present invention. Specifically, a method of producing scorodite from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions, wherein the cumulative Fe / As molar ratio is less than 0.9 Step 1 of producing a seed crystal of scorodite by reacting a part of the As ion while maintaining it, and then adjusting the cumulative Fe / As molar ratio to 0.9 or more, and the presence of the obtained seed crystal And 2. reacting the remainder of the As ion below to produce scorodite.

  In step 1, seed crystals are produced in situ by the same method as the seed crystal production method described above. Conditions such as the preferred cumulative Fe / As molar ratio are similar. Immediately after the start of the reaction, the chemical reaction proceeds with the cumulative Fe / As molar ratio being less than 0.9, thereby forming scorodite having a small volume per unit weight as a seed crystal. However, if the reaction is continued as it is, unreacted As will remain due to the lack of Fe. Therefore, at a stage where a seed crystal is generated to a certain extent, the cumulative Fe / As molar ratio is changed to adjust to 0.9 or more, and the remaining As ions are reacted. As described above, even if the cumulative Fe / As molar ratio is changed to 0.9 or more on the way, scorodite to be synthesized after that already has a small volume of scorodite per unit weight as a seed crystal in the reaction system. Therefore, it is possible to continue to take over the properties of the seed crystal. Therefore, according to the said method, even if it does not prepare a seed crystal separately, a scorodite with a small volume per unit weight can be manufactured, reducing unreacted As.

  The timing to adjust the cumulative Fe / As molar ratio to 0.9 or more is preferably 50% or more of the pentavalent As ion initially contained in the acidic aqueous solution, because it is not necessary to use Fe unnecessarily. It is preferable that 80% or more, more preferably 90% or more be consumed for producing scorodite seed crystals.

  As a method of adjusting the cumulative Fe / As molar ratio to 0.9 or more, there is no limitation, for example, a method of additionally adding a source of divalent and / or trivalent Fe ions to the acidic aqueous solution Can be mentioned. As the source of the ions, iron oxide, iron sulfate, iron chloride, iron hydroxide and the like mentioned in the explanation of the seed crystal can be used similarly. Polyferrous sulfate and polyferric sulfate can also be used.

  The source of the additionally added divalent and / or trivalent Fe ions may be added in multiple times. Since the amount of Fe to be added at one time can be suppressed by dividing and adding it in plural times, the advantage that the Fe ion concentration in the reaction liquid can be suppressed can be obtained. By suppressing the Fe ion concentration in the reaction solution, it is believed that it is difficult to form crystal nuclei that grow independently, and it is easy to grow crystals on species that already exist. Specifically, the additive amount per additional addition of divalent and / or trivalent Fe ions is 5 g / L (the mass of Fe ions added per liter of reaction solution) or less. To be preferably 4 g / L or less, more preferably 3 g / L or less, still more preferably 2 g / L or less, for example, 0.1 to 5 g / L Thus, it is desirable to add a source of Fe ions.

  In addition, a source of divalent and / or trivalent Fe ions to be additionally added is added after the divalent and / or trivalent Fe ion concentration in the acidic aqueous solution is generally consumed for the synthesis of scorodite. It is desirable to do so as to suppress the Fe ion concentration in the reaction solution. Specifically, the additional addition of the divalent and / or trivalent Fe ion source is preferably 2 hours or more, preferably 2.5 hours or more after the temperature of the acidic aqueous solution exceeds 50 ° C. It is desirable to carry out the first operation more preferably after 3 hours or more. After that, it is desirable to carry out each after 2 hours or more since the last addition time point, preferably 2.5 hours or more, more preferably 3 hours or more.

  From the viewpoint of reducing unreacted As, it is preferable to adjust the cumulative Fe / As molar ratio in the acidic aqueous solution finally to 1.0 or more, and more preferably to 1.2 or more. In addition, if the amount of Fe is too large, the crystals can not be grown while maintaining their shape on the crystals, and there is a possibility that independent crystals may be generated, and from the viewpoint of eliminating the unnecessary cost for Fe, the acidic aqueous solution It is preferable to adjust the cumulative Fe / As molar ratio to 1.8 or less, and more preferably to 1.5 or less.

  Even after changing the accumulated Fe / As from less than 0.9 to 0.9 or more, the conditions for producing scorodite are the same as described in the description of the method for producing a seed crystal. That is, various conditions such as pH, atmosphere and temperature may be maintained. The properties of the finally obtained scorodite are also similar to those of the seed crystals.

  The crystalline scorodite thus obtained can be grown while maintaining the form of the seed crystal produced in situ, so that the primary particles are in close contact with each other in a state in which they are aggregated to increase the particle size, and accordingly the unit weight The hit volume is further reduced. In one embodiment, the scorodite obtained by using the seed crystal of scorodite according to the present invention has an average particle size (D50) of secondary particles measured by a laser diffraction / scattering particle size distribution measuring device of 30 μm or more. , Preferably 35 μm or more, more preferably 40 μm or more, still more preferably 45 μm or more, still more preferably 50 μm or more, for example 30 to It can be 60 μm.

Furthermore, the scorodite obtained using a seed crystal of scorodite of the present invention in one embodiment, the volume per 1g can be 0.7 cm ³ or less, also further to 0.6 cm ³ or less For example, the volume per 1 g can be 0.4 to 0.7 cm ³ .

  The following examples illustrate the present invention, but these examples are presented to better understand the present invention and its advantages, and are not intended to limit the present invention.

(Comparative example 1)
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid and acidic water to prepare an aqueous solution (pH = 1.5) in which the concentration of divalent iron ions is 10 g / L and the concentration of pentavalent As ions is 5 g / L (Fe at the start of the reaction) / As molar ratio = 2.7). Thereafter, under atmospheric conditions, the aqueous solution was heated to 70 ° C., and scorodite seed crystals were synthesized for 6 days while stirring. The pH at the end of the reaction was 1.29. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of synthesis of scorodite seed crystals, suction filtration was carried out using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 99.3%. As for the yield, the immobilization rate was calculated from the difference in liquid concentration before and after the treatment with As, and this was taken as the yield (the same applies hereinafter). When the amount of Fe added was small relative to the amount of As, the immobilization rate was calculated with the amount of As that should be scorodite synthesized 1: 1 with the added Fe as 100%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

Next, reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) are prepared, and these are each 500 mL of volume In a flask, it mixed with 200 mL of sulfuric acid acidic water to prepare an aqueous solution (pH = 1.5) in which the concentration of divalent iron ions is 2 g / L and the concentration of pentavalent As ions is 2 g / L (initial Fe / As molar ratio = 1.34). Thereafter, 0.8 g of the seed crystal obtained above was added, and the aqueous solution was heated to 70 ° C. under atmospheric conditions, and scorodite was synthesized for 6 days while stirring. The pH at the end of the reaction was 1.26. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 75.2%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

(Comparative example 2)
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 10 g / L and a pentavalent As ion concentration of 10 g / L (Fe / As at the start of the reaction) Molar ratio = 1.34). Thereafter, under atmospheric conditions, the aqueous solution was heated to 70 ° C., and scorodite seed crystals were synthesized for 6 days while stirring. The pH at the end of the reaction was 1.16. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of synthesis of scorodite seed crystals, suction filtration was carried out using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of scorodite obtained was 99.4%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

Next, reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) are prepared, and these are each 500 mL of volume In a flask, it mixed with 200 mL of sulfuric acid acidic water, and prepared an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 2 g / L and a pentavalent As ion concentration of 2 g / L (at the start of the reaction) Fe / As molar ratio = 1.34). Thereafter, 0.8 g of the seed crystal obtained above was added, and the aqueous solution was heated to 70 ° C. under atmospheric conditions, and scorodite was synthesized for 6 days while stirring. The pH at the end of the reaction was 1.27. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 75.3%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

(Comparative example 3)
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid and acidic water to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 10 g / L and a pentavalent As ion concentration of 10 g / L (Fe at the start of the reaction) / As molar ratio = 1.34). Thereafter, while actively aerating oxygen gas, the aqueous solution was heated to 70 ° C., and scorodite seed crystals were synthesized for 6 days while stirring. The pH at the end of the reaction was 1.08. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of synthesis of scorodite seed crystals, suction filtration was carried out using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of scorodite obtained was 99.8%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

Next, reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) are prepared, and these are each 500 mL of volume In a flask, it mixed with 200 mL of sulfuric acid acidic water, and prepared an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 2 g / L and a pentavalent As ion concentration of 2 g / L (at the start of the reaction) Fe / As molar ratio = 1.34). Thereafter, 0.8 g of the seed crystal obtained above was added, and the aqueous solution was heated to 70 ° C. under atmospheric conditions, and scorodite was synthesized for 6 days while stirring. The pH at the end of the reaction was 1.26. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 76.8%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

(Comparative Example 4: Continuous production of scorodite)
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 20 g / L and a pentavalent As ion concentration of 20 g / L (Fe / As at the start of the reaction) Molar ratio = 1.34). Thereafter, the aqueous solution was heated to 70 ° C. under atmospheric conditions, and scorodite synthesis was performed for 7 hours while stirring. The pH at the end of the reaction was 0.91. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 76.5%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed.

Invention Example 1: Production of scorodite using separately produced seed crystals
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid acidic water to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 5 g / L and a pentavalent As ion concentration of 10 g / L (Fe at the start of the reaction) / As molar ratio = 0.67). Thereafter, under atmospheric conditions, the aqueous solution was heated to 70 ° C., and scorodite seed crystals were synthesized for 6 days while stirring. The pH at the end of the reaction was 1.18. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of synthesis of scorodite seed crystals, suction filtration was carried out using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 100%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed. In addition, when the obtained scorodite seed crystals were observed by SEM, as shown in FIG. 1, crystals of the secondary particle form in which the primary particle faces of the polyhedron were closely aggregated were observed.

Next, reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) are prepared, and these are each 500 mL of volume In a flask, it mixed with 200 mL of sulfuric acid acidic water, and prepared an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 2 g / L and a pentavalent As ion concentration of 2 g / L (at the start of the reaction) Fe / As molar ratio = 1.34). Thereafter, 0.8 g of the seed crystal obtained above was added, and the aqueous solution was heated to 70 ° C. under atmospheric conditions, and scorodite was synthesized for 6 days while stirring. The pH at the end of the reaction was 1.26. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 72.2%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed. Further, when the obtained scorodite was observed by SEM, crystals of a secondary particle form in which the primary particle faces of the polyhedron were closely aggregated as shown in FIG. 2 were observed.

(Inventive Example 2: Continuous production of scorodite)
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask The mixture was mixed with 200 mL of sulfuric acid and acidic water to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 2 g / L and a pentavalent As ion concentration of 10 g / L (Fe at the start of reaction). / As molar ratio = 0.27). Thereafter, under atmospheric conditions, the aqueous solution was heated to 70 ° C., and scorodite was synthesized for 19 days while stirring.

The Fe in the acidic aqueous solution is consumed by the reaction with As, 3 days (second time), 7 days (third time), 11 days (fourth time), and 13 days after the temperature of the acidic aqueous solution exceeds 50 ° C. The amount of Fe added the reagent of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) in acidic aqueous solution after 2 days (fifth time) 2 g / L (Fe / As in each divided addition = 0.27 Finally, a reagent of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) is added so that the total Fe amount is 10 g / L, and the cumulative Fe The / As molar ratio was 1.34. The pH at the end of the reaction was 1.31. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation. During the reaction of synthesis of scorodite, seed crystals having an average particle size of 20 μm or more were already formed immediately before performing the fourth addition of Fe (that is, cumulative Fe / As = 0.81).

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 99.2%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed. Moreover, when this seed crystal was observed by SEM, the crystal | crystallization of the secondary particle form which the surfaces of the primary particle of the polyhedron aggregated closely was observed.

(Inventive Example 3: Continuous production of scorodite)
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid acidic water to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 5 g / L and a pentavalent As ion concentration of 20 g / L (Fe at the start of the reaction) / As molar ratio = 0.34). Thereafter, under atmospheric conditions, the aqueous solution was heated to 70 ° C. and scorodite synthesis was performed for 6 days while stirring.

The Fe in the aqueous solution is consumed by the reaction with As, and after 3.5 hours (second time), 22 hours (third time) and 30.5 hours after the temperature of the aqueous solution exceeds 50 ° C. (second time) The amount of Fe added with the reagent of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) in the reaction solution at the 4th time) is 2 g / L per time (Fe / As in each divided addition = 0. 34) and finally adding ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) reagent so that the total Fe amount is 20 g / L, and The Fe / As molar ratio was 1.36. The pH at the end of the reaction was 1.31. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation. During the reaction of synthesis of scorodite, seed crystals having an average particle size of 20 μm or more were already formed immediately before performing the third addition of Fe (that is, cumulative Fe / As = 0.68).

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 99.2%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed. Moreover, when this seed crystal was observed by SEM, the crystal | crystallization of the secondary particle form which the surfaces of the primary particle of the polyhedron aggregated closely was observed.

Invention Example 4: Production of scorodite using separately produced seed crystals
Prepare reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) respectively in a 500 mL volumetric flask Mixed with 200 mL of sulfuric acid acidic water to prepare an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 2 g / L and a pentavalent As ion concentration of 5 g / L (Fe at the start of the reaction) / As molar ratio = 0.54). Thereafter, under atmospheric conditions, the aqueous solution was heated to 70 ° C., and scorodite seed crystals were synthesized for 5 days while stirring. The pH at the end of the reaction was 1.33. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of synthesis of scorodite seed crystals, suction filtration was carried out using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed. Moreover, when the seed crystal of the obtained scorodite was observed by SEM, the crystal | crystallization of the secondary particle form which the surfaces of the primary particle of the polyhedron aggregated closely was observed.

Next, reagents of ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) and disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O) are prepared, and these are each 500 mL of volume In a flask, it mixed with 200 mL of sulfuric acid acidic water, and prepared an aqueous solution (pH = 1.5) having a divalent iron ion concentration of 2 g / L and a pentavalent As ion concentration of 2 g / L (at the start of the reaction) Fe / As molar ratio = 1.34). Thereafter, 0.4 g of the seed crystal obtained above was added, and the aqueous solution was heated to 70 ° C. under atmospheric conditions, and scorodite was synthesized for 6 days while stirring. The pH at the end of the reaction was 1.34. During heating, water was appropriately added and maintained at 200 mL so that the amount of liquid was not reduced by evaporation.

  After completion of scorodite synthesis, suction filtration was performed using PTFE filter paper with a pore size of 1 μm. Then, the scorodite after filtration was again washed with pH 4 sulfuric acid acidified water and suction filtered in the same manner. Thereafter, it was dried in a drier at 40 ° C. for 24 hours or more. The yield of the obtained scorodite was 74%. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed. In addition, when the obtained scorodite was observed by SEM, crystals of a secondary particle form in which the primary particle faces of the polyhedron were closely aggregated were observed.

(Measurement of average particle size)
The average particle size (D50) of each scorodite obtained in the above test was measured by a laser diffraction / scattering particle size distribution measuring apparatus (model MT3300EXII manufactured by Nikkiso Co., Ltd.). The results are shown in Table 1.

(Measurement of volume per 1 g)
Using a funnel, gently pour 2.5 g of each scorodite obtained in the above test into a 15 mL centrifuge tube (φ about 1 cm), and use this in a centrifuge (KUBOTA 7780 II manufactured by Kubota Corp.) It set, and it was made to rotate for 5 minutes by the acceleration of 13,420 g (g is gravity acceleration = 9.8 m / s < ² >). The volume per unit weight was determined from the volume of scorodite in the centrifuge tube removed from the centrifuge. The results are shown in Table 1.

Claims (16)

A method of producing scorodite seed crystals from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions, wherein the cumulative Fe / As molar ratio is maintained at less than 0.9. A method of producing scorodite seed crystals by reacting a part of the As ions until the average particle size of the seed crystals reaches 20 μm or more .   The method according to claim 1, wherein a portion of the As ions are reacted to produce scorodite seed crystals while maintaining the cumulative Fe / As molar ratio at 0.7 or less.   The method according to claim 1 or 2, wherein the initial pentavalent As ion concentration in the acidic aqueous solution is 2 g / L or more. A method for producing scorodite seed crystals from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions, wherein the cumulative Fe / As molar ratio is less than 0.9 until the reaction is completed. A method of producing scorodite seed crystals by reacting a part of the As ions while maintaining at. 5. The method according to claim 4, wherein scorodite seed crystals are produced by reacting a part of the As ions while maintaining a cumulative Fe / As molar ratio of 0.7 or less. The method according to claim 4 or 52, wherein the initial pentavalent As ion concentration in the acidic aqueous solution is 2 g / L or more. The method of manufacturing scorodite by using the scorodite obtained by the method as described in any one of Claims 1-6 as a seed crystal. A method for producing scorodite from an acidic aqueous solution containing pentavalent As ions and divalent and / or trivalent Fe ions , wherein the seed is produced while maintaining the cumulative Fe / As molar ratio to less than 0.9. Step 1 of producing scorodite seed crystals by reacting a part of the As ions until the average particle size of the crystals becomes 20 μm or more, and then adjusting the cumulative Fe / As molar ratio to 0.9 or more And 2. reacting the remainder of the As ion in the presence of the obtained seed crystals to produce scorodite. The method according to claim 8 , wherein the cumulative Fe / As molar ratio is adjusted to 0.9 or more by additionally adding a source of divalent and / or trivalent Fe ions to the acidic aqueous solution. 10. The method according to claim 9 , wherein the source of divalent and / or trivalent Fe ions is additionally added in multiple portions. The method according to claim 9 or 10 , wherein a source of Fe ions is additionally added such that the amount of divalent and / or trivalent Fe ions to be added is 5 g or less per 1 L of the acidic aqueous solution. the method of. The additional addition of the divalent and / or trivalent Fe ion source is performed the first time 2 hours or more after the temperature of the acidic aqueous solution exceeds 50 ° C., and if further addition, immediately before the addition The method according to any one of claims 9 to 11 , which is carried out two hours or more after the time point. The method according to any one of claims 8 to 12 , wherein in step 2, the cumulative Fe / As molar ratio is adjusted to 1.0 or more. The method according to any one of claims 8 to 13 , wherein the pH at the reaction end point exceeds 1.2. Volume per 1g is Ri der 0.7 cm ³ or less, der an average particle size of more than 30μm Ru crystal scorodite. The crystalline scorodite according to claim 15 , in the form of secondary particles in which primary particles of polyhedral shape are aggregated.