JP2019037929A - Method for treating selenium-containing soil and rock - Google Patents

Abstract

To provide a method for treating selenium-containing soil and rock in which the selenium content in soil and rock can be reduced.SOLUTION: [1] A method of treating selenium-containing soil and rock characterized in comprising an extraction process in which an oxidizing agent is brought into contact with particles of soil or rock containing selenium to yield a selenium-containing extract. [2] A method of treating selenium-containing soil and rock according to [1] characterized in that the soil or rock contains a sulfur constituent, and the contact of the sulfur constituent with the oxidizing agent produces sulfuric acid, and selenium is extracted by the sulfuric acid. [3] The method for treating selenium-containing soil and rock according to [1] or [2] characterized in that, in the soil or rock, selenium is in solid solution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating selenium-containing soil / rock.

  Naturally occurring selenium that exceeds the elution amount standard (0.01 mg / L) of the soil pollution control method may be detected from rocks such as soil and mudstone / shale excavated during the construction of mountain tunnels. Usually, the total content value of selenium contained in soil and rocks is about 0.5 to 1 mg / kg, and the elution amount of selenium by rainwater or the like is about 0.01 to 0.05 mg / L.

  Soil and rocks containing selenium above the standard value cannot be disposed of as construction generated soil and must be disposed of as contaminated soil. As a conventional disposal method, landfill in a designated disposal site is performed, but since the disposal site is tight, there is a concern that it is difficult to continue the same disposal in the future (Non-patent Document 1). , 2).

Supervised by Masafumi Kamon and Takeshi Katsumi, edited by the Civil Engineering Research Institute, Civil Engineering Research Center, Ground Pollution Control Technology Review Committee, Handbook for soil containing natural heavy metals, etc. generated during construction work, "Introduction", "Superscript" Company, 2015 Kitaoka Yuki, Global Environment, Vol.15, No.1, p.23-30, 2010.

  As a result of intensive studies by the present inventors, the amount of selenium eluted from naturally derived soil and rocks exceeds the reference value as described above, but it can be sufficiently reduced if appropriate chemical treatment is performed. it was thought.

  The present invention provides a method for treating selenium-containing soil / rock that can reduce the selenium content in soil or rock.

[1] A method for treating selenium-containing soil or rock, comprising an extraction step of contacting an oxidant with soil or rock particles containing selenium to obtain an extract containing selenium.
[2] The selenium-containing soil according to [1], wherein the soil or rock contains a sulfur component, sulfuric acid is generated by contact between the sulfur component and the oxidizing agent, and selenium is extracted by the sulfuric acid.・ Method of processing rocks.
[3] The method for treating selenium-containing soil / rock according to [1] or [2], wherein selenium is dissolved in the soil or rock.
[4] The selenium-containing soil / rock treatment according to any one of [1] to [3], wherein the selenium-containing soil / rock according to any one of [1] to [3] has a crushing step of obtaining the particles by crushing soil or rock containing selenium. Method.
[5] First, an extract containing sulfate ions and selenate ions is obtained, and barium ions are added to the extract to produce barium sulfate, thereby obtaining a primary treatment solution in which the concentration of free sulfate ions is reduced. And a second step of obtaining a secondary treatment solution in which the concentration of the selenate ion is reduced by bringing the selenate ion into adsorption by bringing the primary treatment solution into contact with the akaganeate to adsorb the selenate ion to the akaganeate. The method for treating selenium-containing soil / rock as described in [2].

  According to the method for treating selenium-containing soil / rock according to the present invention, it is possible to obtain a purified soil in which the selenium content contained in the selenium-containing soil / rock generated by excavation in construction is reduced. The purified soil can be disposed of in the same way as conventional construction-generated soil.

It is a mimetic diagram of an example of a processing system applicable to processing of selenium content soil and rock. It is a schematic diagram of an example of the water treatment system applicable to the treatment of selenium wastewater. It is a schematic diagram showing the tunnel structure of an akaganate. It is an adsorption isotherm of the selenate ion in three types of iron oxide minerals. It is an experimental result showing that desorption of chloride ions occurs with the adsorption of sulfate ions in akaganeate.

《Selenium-containing soil and rock treatment method》
The first aspect of the present invention is a method for treating selenium-containing soil / rock, which comprises an extraction step of contacting an oxidant with soil or rock particles containing selenium to obtain an extract containing selenium.
In this processing method, you may have the crushing process which obtains the said particle | grain by crushing the soil or rock in which selenium is contained.

The soil includes coarse particles or clay (sticky soil) -like inorganic substances generated by weathering rocks, organic substances derived from living organisms, and the like, and is generally called soil.
The rock is a mineral or a mixture thereof, and may contain a metal component, a natural glass component, or the like. In this specification, soil and rock may be collectively referred to as soil / rock.

[Crushing process]
The size of soil and rocks discharged from construction sites is usually a few centimeters to several tens of centimeters. These lumps are made into fine particles in the crushing step. For example, by using a known crusher such as a jaw crusher or a rod mill, the long diameter (particle diameter) of the particles is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 2 mm or less. .
If it is finely crushed below the above particle size, the extraction efficiency of selenium by the oxidizing agent can be increased, and the amount of selenium remaining inside the mass can be reduced. The lower limit value of the particle diameter is not particularly limited, but if it is too small, it becomes difficult to handle and collect, so it is preferably 10 μm or more, for example. Usually, when soil and rock are crushed by a known crusher, the upper limit value is relatively easy to control, but it is difficult to keep the particle diameter constant. For this reason, the crushed material obtained by a crushing process turns into a mixture of various particle diameters.
In the present specification, the term “crushing” is synonymous with “crushing”.

[Extraction process]
Examples of the method of bringing an oxidant into contact with the particles contained in the crushed material obtained in the crushing step include a method of dropping or spraying a solution containing an oxidant on the crushed material, and the crushing into an oxidant solution. The method of throwing things in is mentioned.
When the oxidizing agent contacts the particles, selenium is extracted from the particles by a chemical reaction. That is, selenium contained in the particles is released from the particles and dissolved or dispersed in the extract. The extracted selenium may be selenium alone (metal selenium) or a compound containing selenium.

The form in which the soil / rock contains selenium may be a form in which free selenium or a compound containing selenium is adsorbed on the soil / rock, or a compound containing selenium or selenium in the mineral constituting the soil / rock. It may be in the form of a solid solution or may be included as an element constituting a mineral. Here, the fact that selenium is solid-solved in the minerals constituting soil and rocks should be confirmed by elemental analysis using EDS (energy dispersive X-ray spectrometer) or XPS (X-ray photoelectron spectroscopy). Can do.
Examples of minerals having selenium as a constituent element include sarknite (FeSe ₂ ), kurtaite (CuSe ₂ ), trotalite (CoSe ₂ ), penrose mineral {(Ni, Co, Cu) Se ₂ }, and the like.

The soil / rock preferably contains a sulfur component. When this sulfur component comes into contact with the oxidizing agent, sulfuric acid is generated, and the sulfuric acid further elutes selenium.
As soil and rocks containing a sulfur component, in addition to sulfur (S), for example, pyrite (FeS ₂ ), pyrrhotite (Fe _1-x S _x ; x = 0.09 to 0.17), pyroxenite ( MoS ₂ ), chalcopyrite (CuFeS ₂ ), galena (PbS), howell ore (MnS ₂ ), base ore (NiS ₂ ), Katiel ore (CoS ₂ ), laura ore (RuS ₂ ), Elrichman ore ( Examples thereof include sulfide minerals such as OsS ₂ ), beramanin ore {(Cu, Ni, Co, Fe) S ₂ }, fukuchi (Cu ₃ FeS ₈ ), and cinnabar (HgS).
Of these, selenium contained in soil and rocks containing pyrite is particularly preferable because the selenium extraction efficiency by this method is high.

  The oxidizing agent is preferably an oxidizing agent capable of eluting selenium, for example, 1 selected from hydrogen peroxide, potassium nitrate, hypochlorite, chlorite, chlorate, and perchlorate. More than species are preferred. When these suitable oxidizing agents are used, it reacts with the sulfur component contained in the soil and rock to produce sulfuric acid, and selenium can be easily extracted. Moreover, you may use a sulfuric acid as an oxidizing agent.

  The amount of the oxidizing agent brought into contact with the particles contained in the crushed material may be an amount sufficient to elute selenium contained in the particles. As an example, the quantity which contacts sodium hypochlorite aqueous solution (effective chlorine concentration: 2-15%) with about 1-20 ml with respect to 1 g of pyrite is mentioned, for example.

  As for the temperature of the mixture at the time of mixing and contacting the said oxidizing agent and the said particle | grain, about 10-60 degreeC is mentioned, for example. Moreover, the extraction efficiency of selenium can be further increased by stirring the mixture.

Selenium extracted from soil and rock by the oxidizing agent can take the form of oxo acid of selenium. Here, as the oxo acid ion of selenium, selenate ion (SeO ₄ ²⁻ ), hydrogen selenate ion (HSeO ₄ ⁻ ), selenite ion (SeO ₃ ²⁻ ), hydrogen selenite ion (HSeO _3). ^- ).
The oxidizing agent can oxidize selenium oxo acid from tetravalent to hexavalent. Tetravalent selenium oxoacids are relatively strongly adsorbed as an inner sphere complex with respect to hydroxyl groups on the surface of soil and rock particles. On the other hand, the hexavalent selenium oxo acid is relatively weakly adsorbed as an outer sphere complex with respect to the hydroxyl groups on the surface of the soil and rock particles. For this reason, oxidizing the oxo acid of selenic acid from tetravalent to hexavalent with an oxidizing agent is advantageous in that the oxo acid of selenium is extracted from the oxidizing agent.

The time for extracting selenium by bringing the oxidant into contact with the particles can be made shorter as the particle size is smaller and the oxidant concentration is higher. As an example, for example, a particle diameter of 10 mm or less is preferably about 1 hour to 24 hours, and a particle diameter of 2 mm or less is preferably about 10 minutes to 2 hours.
As a guideline for completion of extraction, for example, the total content of selenium in the soil and rock after the extraction treatment is reduced to about 10 to 50% before the treatment, and the selenium elution amount is the elution amount reference value (0.01 mg / L ) It can be mentioned below.
The extraction management method is, for example, performing an extraction experiment in advance using the soil / rock to be treated, and the total content of selenium in the soil / rock after the extraction treatment is reduced to about 10-50% before the treatment. Or the oxidant addition rate that satisfies the purification target such that the selenium elution amount is less than or equal to the elution amount reference value (0.01 mg / L), the liquid-solid ratio of the extract and the soil / rock to be treated, the extract It is possible to determine the contact time between the soil and rock to be treated and the extraction treatment under the conditions determined in the extraction experiment. In this case, it is more reliable to analyze the soil and rock after extraction at a frequency of one specimen per 100 m ³ and perform a sampling inspection to confirm that the purification target is satisfied.

[Separation process]
After extraction, the extract is separated from the extract (soil / rock dispersion) containing soil / rock residues. As the separation method, although depending on the size of the particles contained in the residue, for example, a method of separating in steps from large particles to small particles can be mentioned.
Specifically, for example, it is passed through a sieve having an opening of about 2 mm in the first stage to remove soil particles (residues) up to a particle diameter of about 2 mm, and soil particles up to about 75 μm using a hydrocyclone in the second stage. In the third stage, a flocculant is added to the extract in the third stage to generate flocs containing the remaining fine soil particles, and then agglomerate and precipitate to remove them.

Since the particles removed in each of the above steps are clean particles from which selenium has been removed, after dehydration by returning the pH to a neutral range, the particles can be treated as waste with less environmental impact. A processing method is not specifically limited, For example, it can be set as the solidification material which has the intensity | strength of 200 kN / m < ² > or more by the well-known solidification process performed with respect to construction generation | occurence | production soil.

  The crushing process, the extraction process, and the separation process described above can be performed by, for example, the processing system illustrated in FIG.

《Selenium-containing soil and rock treatment system》
The processing system of FIG. 1 is used for the process for extracting selenium from soil and rock containing selenium, and has the following configuration. That is, a crusher 1 that crushes (crushes) soil / rock R1 containing natural selenium into fine particles, and an extraction tank 2 that contacts an oxidant with the crushed soil / rock particles to obtain an extract containing selenium. And the fluid 3 that separates soil and rock residues from the extract, the cyclone 4 that separates soil and rock particles from the extract that passed through the fluid 3, and the fine particles remaining in the extract that passed through the cyclone 4 Are separated by agglomerating with a flocculant to obtain an extract as a supernatant liquid excluding soil and rock, and a mud storage tank 6 for temporarily storing the precipitate recovered by the muddy water treatment apparatus 5 A dewatering device 7 such as a filter press for dewatering the sediment accumulated in the mud storage tank 6, a sand dewatering sieve 8 for dewatering the soil and rock particles collected by the cyclone 4, a sieve 3, a sand dewatering sieve 8, and Recovered with dehydrator 7 A mixer 9 that collects (aggregates) residues, particles, and precipitates derived from loam and rock, mixes them, adjusts the pH and moisture of the mixture, and sets the final purified soil R2; Yes.

The extraction tank 2 is connected to a crushed material supply unit 1 a that transfers crushed soil and rock particles from the crusher 1 to the extraction tank 2. Further, the extraction tank 2 is equipped with a stirring blade for mixing and stirring the received soil / rock and the oxidizer charged in the extraction tank 2 and a scrubbing machine for rubbing the soil / rock together. Yes.
The fluid 3 is connected to an extract first liquid feeding section 2 a that feeds an extract containing soil and rock residues after extraction from the extraction tank 2 to the fluid 3.
Connected to the cyclone 4 is an extract second feeding section 3 a for feeding an extract containing soil and rock particles that have passed through the sieve 3 to the cyclone 4 from the sieve 3.
The turbid water treatment device 5 is connected to an extract third liquid feeding section 4 a for feeding an extract containing fine particles of soil and rock that have passed through the cyclone 4 from the cyclone 4 to the turbid water treatment device 5. In addition, an extract liquid fourth liquid feeding section 5 b for feeding the extract liquid as a supernatant obtained in the muddy water treatment apparatus 5 to the outside (for example, a raw water tank 11 of the water treatment system 10 described later) is connected to the muddy water treatment apparatus 5. Has been.
The sediment storage tank 6 is connected to a sedimentation first transfer section 5 a that transports the precipitate collected by the turbid water treatment apparatus 5 from the turbid water treatment apparatus 5 to the mud storage tank 6.
The dewatering device 7 is connected to a second sedimentation transfer unit 6 a that transfers the sediment temporarily stored in the mud tank 6 from the mud tank 6 to the dewatering device 7. In addition, a drainage first liquid feeding unit 7 b that feeds the wastewater dehydrated by the dehydrating device 7 to the outside (for example, a raw water tank 11 of a water treatment system 10 described later) is connected to the dehydrating device 7.
The sand dewatering sieve 8 is connected to a first particle transfer unit 4 b that transfers the soil / rock particles collected by the cyclone 4 from the cyclone 4 to the sand dewatering sieve 8. Although not shown in FIG. 1, the second drainage unit for feeding the drainage dewatered by the sand dewatering sieve 8 to the outside (for example, a raw water tank 11 of the water treatment system 10 described later) is a sand dewatering unit. It is connected to the sieve 8.
The mixer 9 includes a residue transfer unit 3b for transferring the soil / rock residue separated by the sieve 3 from the sieve 3 to the mixer 9, and the soil / rock particles dehydrated by the sand dehydrating sieve 8 from the sand dehydrating sieve 8. The second particle transfer unit 8a that transfers to the mixer 9 and the third precipitation transfer unit 7a that transfers the sediment of fine particles of soil and rock dehydrated by the dehydrator 7 to the mixer 9 are connected. Has been.
Each part which performs said connection is comprised by well-known connection members, such as piping, a valve, and a pump.

By treating the extract containing selenium obtained by the selenium-containing soil / rock treatment method and treatment system described above with, for example, the water treatment method and water treatment system using akaganeite described below, Clean treated water (purified water) with reduced selenium content in the extract can be obtained.
Below, the said extract containing selenium may be called raw | natural water (process target water).
As a premise, raw water contains sulfate ions and anions of inorganic compounds other than sulfate ions. A representative example of this anion is an anion of selenium oxoacid (for example, selenate ion, selenite ion).

《Water treatment system》
As an example of the water treatment system, a water treatment system 10 is shown in FIG.
The water treatment system 10 includes a raw water tank 11 for introducing raw water containing sulfuric acid ions and anions of inorganic compounds other than sulfate ions, a barium tank 12 for holding a barium aqueous solution containing barium ions, and the barium aqueous solution. And a barium supply unit 12a for supplying the raw water tank 11 from the tank 12.
Moreover, the water treatment system 10 introduces a mixed solution of the raw water introduced into the raw water tank 11 and the barium aqueous solution mixed therewith, and contains barium sulfate and a first supernatant liquid contained in the mixed solution. A first turbid water treatment device 13 for separating the liquid, a first mixed liquid feeding portion 11a for feeding the mixed liquid from the raw water tank 11 to the first turbid water treatment device 13, and an adsorption tank for introducing the first supernatant liquid. 14 and a first supernatant liquid feeding part 13a for feeding the first supernatant liquid from the first muddy water treatment device 13 to the adsorption tank 14.
Further, the water treatment system 10 includes a chemical preparation tank 15 that holds a chemical liquid containing akaganate, and a chemical liquid supply unit 15 a that supplies the chemical liquid from the chemical preparation tank 15 to the adsorption tank 14.
The barium supply unit 12a, the first mixed liquid supply unit 11a, the first supernatant liquid supply unit 13a, and the chemical solution supply unit 15a are each configured by a known connection member such as a pipe, a valve, or a pump.

The water treatment system 10 includes a first storage tank 16 for storing a first aqueous solution containing iron (III) chloride to be supplied to the chemical preparation tank 15, and an alkali metal hydrogen carbonate to be supplied to the chemical preparation tank 15. A second storage for storing a second aqueous solution containing at least one salt (S) selected from carbonates, hydroxides, and alkaline earth metal hydrogen carbonates, carbonates and hydroxides A tank 17 is provided as an arbitrary configuration.
A first aqueous solution supply unit 16 a that supplies the first aqueous solution from the first storage tank 16 to the chemical preparation tank 15 is connected to the chemical preparation tank 15.
A second aqueous solution supply unit 17 a that supplies the second aqueous solution from the second storage tank 17 to the chemical preparation tank 15 is connected to the chemical preparation tank 15.

Furthermore, the water treatment system 10 introduces a mixed solution of the first supernatant liquid introduced into the adsorption tank 14 and the chemical liquid mixed therewith, and the akaganate and the second supernatant contained in the mixed liquid are introduced. A second muddy water treatment device 18 for separating the liquid is provided as an arbitrary configuration.
Connected to the second muddy water treatment device 18 is a second liquid mixture feeding portion 14 a for feeding the mixed solution containing akaganate from the adsorption tank 14 to the second muddy water treatment device 18.

  In addition to the above, the water treatment system 10 is supplied to the first turbid water treatment device 13 and the second turbid water treatment device 18, and a third storage tank 20 holding a flocculant for aggregating barium sulfate and akaganate, respectively, and the second From the discharge tank 19 for temporarily storing the second supernatant until it is discharged to the outside, and the barium sulfate precipitate from the first muddy water treatment device 13 and the second muddy water treatment device 18. A mud storage tank 21 for receiving sediment containing akaganate and a dewatering device 22 for dewatering the sediment are provided as optional configurations.

The first muddy water treatment device 13 is connected to a first coagulant supply unit 20 a that supplies the flocculant from the third storage tank 20 to the first muddy water treatment device 13.
The second muddy water treatment device 18 is connected to a second coagulant supply unit 20b that supplies the coagulant from the third storage tank 20 to the second muddy water treatment device 18.
Connected to the discharge tank 19 is a second supernatant liquid supply section 18 a for supplying the second supernatant liquid from the second muddy water treatment device 18 to the discharge tank 19.
Connected to the mud storage tank 21 is a first sediment transfer section 13 b for transferring the barium sulfate precipitate from the first muddy water treatment device 13 to the mud storage tank 21.
Connected to the mud storage tank 21 is a second sediment transfer section 18b for transferring a precipitate containing akaganate from the second muddy water treatment device 18 to the mud storage tank 21.
Connected to the dehydrator 22 is a third precipitate transfer section 21 a that transfers at least one of the barium sulfate precipitate and the akaganate-containing precipitate from the mud storage tank 21 to the dehydrator 22.
Each part which performs said connection is comprised by well-known connection members, such as piping, a valve, and a pump.

《Water treatment method using water treatment system》
The water treatment method illustrated here utilizes the water treatment system described above, and includes inorganic ions other than sulfate ions among sulfate ions and anions of inorganic compounds other than sulfate ions contained in raw water (treated water). This is a method for efficiently reducing anions with akaganate. By this water treatment method, clean treated water is obtained.
In addition, according to this method, since the primary treated water with reduced sulfate ion concentration is brought into contact with akaganeate, anions of inorganic compounds other than sulfate ion can be adsorbed to akaganeate without being subjected to competition by sulfate ion. . As a result, the amount of akaganate used can be reduced.
Below, the method using the water treatment system 10 is demonstrated.

First, raw water containing anions of inorganic compounds other than sulfate ions and sulfate ions is introduced into the raw water tank 11.
Next, the barium aqueous solution is supplied from the barium tank 12 to the raw water tank 11 via the barium supply unit 12a. By mixing the raw water and the barium aqueous solution in the raw water tank 11, barium sulfate is generated in the mixed solution. At this time, tap water may be supplied to the raw water tank 11 as necessary. Subsequently, the mixed liquid containing barium sulfate is introduced from the raw water tank 11 to the first muddy water treatment apparatus 13 through the first mixed liquid feeding section 11a.

  The said mixed liquid introduce | transduced into the water tank of the 1st muddy water treatment apparatus 13 is left still, and the precipitation containing a barium sulfate is settled. When a flocculant (for example, polyaluminum chloride, polymer flocculant, etc.) is supplied from the third storage tank 20 to the first muddy water treatment device 13 via the flocculant first supply unit 20a, sedimentation of the precipitate is promoted. Can do. After the sedimentation, the first supernatant liquid separated from barium sulfate is fed to the adsorption tank 14 via the first supernatant liquid feeding section 13a.

  The first supernatant liquid fed to the adsorption tank 14 still contains anions of inorganic compounds other than sulfate ions. On the other hand, since barium sulfate has low solubility in water, most barium sulfate is separated as a precipitate.

  The sediment containing the precipitated barium sulfate is treated as sludge and transferred from the first muddy water treatment device 13 to the mud storage tank 21 via the first sediment transfer section 13b and temporarily stored. Thereafter, the sludge is transferred from the mud storage tank 21 to the dewatering device 22 such as a filter press through the third sediment transfer section 21a, and the sludge is dehydrated to obtain a dehydrated cake containing barium sulfate. The dehydrated cake is properly disposed of by known methods.

  Moreover, the 1st aqueous solution containing iron (III) chloride from the 1st storage tank 16 and the 2nd storage tank 17 to the chemical | medical agent preparation tank 15 via the 1st aqueous solution supply part 16a and the 2nd aqueous solution supply part 17a, A second aqueous solution containing at least one salt (S) is supplied. By mixing the first aqueous solution and the second aqueous solution in the chemical blending tank 15, akaganeate is generated in the mixed solution. At this time, tap water may be supplied to the chemical compounding tank 15 as necessary.

  Next, a mixed liquid (chemical liquid) containing akaganate is introduced from the chemical preparation tank 15 to the adsorption tank 14 via the chemical liquid supply unit 15a, and the first supernatant liquid and the mixed liquid (chemical liquid) are mixed. . Thereby, in the adsorption tank 14, the negative ion of inorganic compounds other than a sulfate ion contacts and adsorb | sucks. Then, the liquid mixture containing akaganaate is transferred from the adsorption tank 14 to the second muddy water treatment device 18 through the second liquid mixture feeding part 14a.

  The said mixed liquid introduce | transduced into the water tank of the 2nd muddy water processing apparatus 18 is left still, and the precipitation containing an akaganate is settled. When the flocculant (for example, polyaluminum chloride, polymer flocculant, etc.) is supplied from the third storage tank 20 to the second muddy water treatment device 18 via the flocculant second supply unit 20b, sedimentation of the precipitate is promoted. Can do. After the precipitate containing akaganeate settles, the second supernatant liquid in which the anion concentration of inorganic compounds other than sulfate ions is reduced is transferred to the discharge tank 19 via the second supernatant liquid feeding section 18a. Are stored and discharged to the outside of the river etc. at an appropriate timing. Moreover, you may return a 2nd supernatant liquid to the raw | natural water tank 11 as needed.

  The sediment containing the settled akaganeate is treated as sludge and transferred from the second muddy water treatment device 18 to the mud storage tank 21 via the second sediment transfer section 18b and temporarily stored. Thereafter, the sludge is transferred from the mud storage tank 21 to the dewatering device 22 such as a filter press machine via the third sediment transfer section 21a, and the sludge is dehydrated to obtain a dehydrated cake containing akaganate. The dehydrated cake is properly disposed of by known methods.

  In the water treatment method described above, the sulfate ion removal method, the anion adsorption method, and the akaganeate synthesis method described below can be applied.

<Method of removing sulfate ion>
In the raw water tank 11, barium sulfate can be produced by bringing raw water containing sulfate ions and anions of inorganic compounds other than sulfate ions into contact with barium ions.
Examples of the method of bringing the raw water and barium ions into contact with the raw water tank 11 include a method of directly adding a barium salt and a method of adding a barium aqueous solution containing a barium salt.

Examples of the barium salt include one or more barium salts selected from barium chloride and barium hydroxide.
These barium salts are less likely to interfere with the adsorption of the anions of the inorganic compounds by akaganate. Here, the anion of the inorganic compound is preferably an anion other than the counter anion constituting the barium salt.

  Of the above barium salts, barium chloride is particularly preferred. Chloride ions inherently constitute akaganate, and the adsorptive power of chloride ions to akaganate is lower than other anions, such as inorganic oxoacid ions. For this reason, in the adsorption of anions to akaganeate, competition by chloride ions hardly occurs, and barium ions can be added to the aqueous solution.

  The density | concentration of the said barium salt contained in the said barium aqueous solution is not specifically limited, For example, it can be set as about 0.1-3.0M.

The pH of the barium aqueous solution is not particularly limited as long as it is a pH at which barium sulfate is generated when mixed with raw water, and examples thereof include pH 1 to 7. Within this pH range, the pH of the mixed solution obtained by mixing with raw water and the first supernatant is likely to be 1 to 7, and the anion adsorption efficiency by the subsequent akaganeate is increased, which is preferable.
The method for adjusting the pH of the raw water is not particularly limited, and examples thereof include a method of adding hydrochloric acid and sodium hydroxide.

The temperature of the barium aqueous solution when mixed with the raw water is not particularly limited, and examples thereof include 10 to 40 ° C.
The amount of the barium aqueous solution to be mixed with the raw water is not particularly limited, and may be set according to the concentration of sulfate ions contained in the raw water. It is preferable to mix. That is, it is preferable to mix the barium aqueous solution with the raw water so that the barium ion / sulfate ion molar ratio is 1 or more. When barium ions are mixed in the above amounts, most of the sulfate ions contained in the raw water can be removed as barium sulfate.

  The object of generating barium sulfate can be achieved even when a method of adding a barium salt directly to the raw water tank 11 is employed instead of the method of adding the barium aqueous solution as described above. However, the operation is easier when the barium salt is added as a barium aqueous solution than when it is added as a solid. Furthermore, it is preferable because undissolved barium salt in the raw water tank 11 is prevented and the concentration of the barium salt in the raw water tank 11 is easily controlled.

<Anion adsorption method>
In the adsorption tank 14, the anion can be adsorbed to the akaganate by bringing the first supernatant liquid containing anions of inorganic compounds other than sulfate ions into contact with the akaganate.

  Examples of the inorganic compound include inorganic compounds containing inorganic elements such as selenium, arsenic, chromium, fluorine, and phosphorus. Specific examples include selenium, arsenic, chromium oxo acid, hydrofluoric acid (hydrofluoric acid), phosphoric acid, and the like.

The inorganic compound is preferably an oxo acid from the viewpoint of exhibiting a high adsorptive power to akaganate, and more preferably a monovalent or divalent inorganic oxo acid ion containing the inorganic element.
Here, the oxo acid is an inorganic compound in which a hydroxyl group (—OH) and an oxo group (═O) are bonded to one inorganic atom, and a proton of the hydroxyl group can be eliminated. Oxo acid can be an oxo acid ion from which the proton is eliminated in water.

As the oxo acid, selenium oxo acid is preferable from the viewpoint of exhibiting a high adsorption power to akaganeate, and selenium oxo acid ions include selenate ion (SeO ₄ ²⁻ ) and selenate hydrogen ion (HSeO ₄ ⁻ ). , Selenite ions (SeO ₃ ²⁻ ), and hydrogen selenite ions (HSeO ₃ ⁻ ).

  The anion of the inorganic compound contained in the raw water and the first supernatant may be one type or two or more types.

Akaganeite used as an anion adsorbent in the present method is an iron oxide mineral represented by the chemical composition β-Fe ³⁺ (O (OH, Cl)). The crystal system is monoclinic, and the crystallographic data of space group I2 / m, unit cell: a = 10.600, b = 3.0339, c = 10.513, β = 90.24 ° are academic. It is described in a paper “Post JE, Buchwald VF, American Mineralogist, 76 (1991) p.272-277, Crystal structure refinement of akaganeite”. It is also described that the crystal structure of akaganeate clarified in this paper has a tunnel structure that retains chloride ions, and a hydroxyl group is pushed out from the tunnel wall toward the center.

  FIG. 3 is a diagram schematically showing the tunnel structure. In the figure, gray circles represent oxygen atoms, white circles represent hydrogen atoms, the circle at the center of the octahedron represents iron atoms, and the black circles in the tunnel represent the same occupation ratio (50 :)).

  In this method, when the first supernatant is brought into contact with akaganate, the anion of the inorganic compound contained in the first supernatant is considered to be trapped and adsorbed by the tunnel structure of the akaganate. As a result of this adsorption, chloride ions pre-existing in the tunnel structure are replaced with the anions and desorbed (see Test Example 2).

When akaganeate is added to purified water, the pH of the purified water tends to be acidic. Therefore, even when akaganeate is added to the first supernatant, the pH of the first supernatant tends to be low.
The pH of the first supernatant liquid (akaganate dispersion) during treatment when akaganate is added to the first supernatant liquid and the target anion is adsorbed to the akaganate is preferably 10 or less, more preferably 2 or more and 9 or less. 3 or more and 7 or less are more preferable, and 4 or more and 6 or less are particularly preferable.
When the pH of the first supernatant during the treatment is 9 or less, the decomposition of akaganate can be prevented, and the adsorption power of the target anion by akaganate can be increased.
The lower the pH of the first supernatant during processing, the more protons that bind to the hydroxyl groups that point towards the center of the tunnel structure of the akaganeate. As a result, the tunnel structure can be prevented from being negatively charged, and the target anion can be more easily adsorbed in the tunnel structure. Therefore, from the viewpoint of increasing the target anion adsorptive power, the pH of the first supernatant during the treatment is preferably pH 2 to 5, more preferably pH 2 to 4, and still more preferably pH 2 to 3.
It is preferable that the pH of the first supernatant during the treatment is 4 or more and 6 or less from the viewpoint of easy aggregation of akaganates and easy recovery of akaganates.
The method for adjusting the pH of the first supernatant is not particularly limited, and examples thereof include a method of adding hydrochloric acid and sodium hydroxide.

The temperature of the 1st supernatant liquid at the time of making a 1st supernatant liquid and akaganate contact is not specifically limited, For example, 4-60 degreeC is preferable, 15-50 degreeC is more preferable, and 30-40 degreeC is further more preferable.
When the temperature is within the above range, the adsorption force of the target anion by akaganate can be enhanced. When the temperature is not less than the lower limit of the above temperature range, the diffusion rate of the target anion in the first supernatant is increased, and the efficiency of adsorbing in contact with the akaganate is further increased. When the temperature is not more than the upper limit of the above temperature range, it is possible to further reduce the desorption of the anion once adsorbed from the akaganeate.

The amount of akaganeate in contact with the first supernatant liquid is not particularly limited with respect to the content of the target anion contained in the first supernatant liquid. What is necessary is just to set to the quantity confirmed that it can fully adsorb | suck.
Usually, when the amount of akaganeate to be brought into contact is increased, the amount of anions that can be adsorbed also increases. For example, the adsorption amount of inorganic oxoacid ions by akaganeate is 0.3 to 0.5 mol / kg.

  Examples of the method for recovering the akaganeate adsorbed with the anion from the first supernatant include a precipitation method and a filtration method. Examples of the precipitation method include, for example, a method in which the first supernatant liquid is allowed to settle, a method in which a sulfuric acid band, PAC, a polymeric polymer flocculant, and the like are added to the first supernatant liquid to cause aggregation to precipitate, A method of aggregating akaganates by adjusting the pH of one supernatant to 4-6 is exemplified.

《Synthesis of akaganate》
In the chemical compounding tank 15, the method of generating akaganeate by mixing the first aqueous solution containing iron (III) and the second aqueous solution containing one or more salts (S) has an adsorption power. It is preferable because an excellent high-quality akaganeate can be obtained.

The one or more salts (S) are preferably easily soluble in water from the viewpoint of synthesizing akaganeate in high yield, and for example, salts containing the following cations are preferable.
The alkali metal is a Group 1 element of the periodic table, and sodium and potassium are preferable.
The alkaline earth metal is a Group 2 element of the periodic table, and magnesium, calcium, and barium are preferable.

By mixing the first aqueous solution and the second aqueous solution in the chemical compounding tank 15, ions ionized in the aqueous solution react spontaneously to produce akaganate. More specifically, hydroxide ions are generated when the one or more salts (S) are dissolved in water. The hydroxide ions and iron ions react in an acidic aqueous solution in which a large amount of chloride ions are dissolved, thereby producing akaganeate.
The aqueous solution (reaction solution) may be heated to about 40 to 100 ° C. in order to promote the formation reaction of akaganeate.

The pH of the reaction solution for producing akaganeate is preferably less than 7, more preferably less than 4, and still more preferably 1 to 3.
If the pH is less than 7, akaganeate is easily produced in the presence of chloride ions.
When the pH is less than 4, particularly when the pH is 3 or less, akaganeate can be produced in a high yield in the presence of chloride ions. In addition, although akaganate is easily formed even at pH 4-6, if it is within this pH range, the akaganate being produced may aggregate and unreacted iron chloride (III) or salt (S) may be taken in. is there. On the other hand, when the pH is alkaline, there is a high possibility that iron oxide minerals having different structures (for example, goethite, scumite, etc.) are generated.

  In adjusting the pH of the reaction solution when producing akaganeate, it is preferable to adjust in advance at least one of the first aqueous solution and the second aqueous solution before mixing the first aqueous solution and the second aqueous solution. However, if the pH of the reaction solution obtained by mixing the first aqueous solution and the second aqueous solution is alkaline, iron oxide minerals other than akaganate may be generated. Therefore, it is preferable to adjust the pH of at least one of the first aqueous solution and the second aqueous solution to acidity immediately after mixing the first aqueous solution and the second aqueous solution, or to maintain the acidic pH.

  The method of adjusting the pH of the first aqueous solution and the second aqueous solution is preferably a method of dropping hydrochloric acid. If hydrochloric acid is used, it is possible to prevent adsorbing an anion by adding an anion (for example, sulfate ion) other than the chloride ion useful for the production of an akaganeate to the reaction solution. It is also preferable to adjust the pH of the reaction solution using sodium hydroxide.

The ratio of mixing the first aqueous solution and the second aqueous solution is preferably such that the amount of iron (III) chloride in the resulting mixed liquid (reaction liquid) is, for example, 0.01 to 3 mol / L. Moreover, it is preferable to mix a 1st aqueous solution and a 2nd aqueous solution in the ratio from which the total amount of the said 1 or more types of salt (S) in the said liquid mixture becomes 0.01-3 mol / L, for example.
The method of mixing the first aqueous solution and the second aqueous solution when preparing the reaction solution is not particularly limited, but the second aqueous solution is added to the first aqueous solution in order to maintain the pH of the reaction solution acidic. The method is desirable.

In the reaction solution, the molar ratio of Fe ³⁺ produced by iron (III) chloride and OH ⁻ produced by the one or more salts (S) is 1: 1 to 1: 3. Is more preferable, and 1: 1.5 to 1: 2.5 is more preferable, and 1: 1.8 to 1: 2.2 is more preferable. Theoretically, a molar ratio of 1: 2 is most preferred.
When the molar ratio is in the above range close to 1: 2, the positive charge amount of Fe ³⁺ in the reaction solution and the negative charge amount of OH ⁻ are in a suitable balance for the production of akaganate, and iron chloride ( Almost all of the Fe ³⁺ derived from III) can be consumed in the reaction to produce akaganate easily in high yield.

Specifically, for example, in a 1 L aqueous solution in which 0.1 mol of sodium hydrogen carbonate is dissolved, an apparent acid dissociation constant pKa ₁ = 6.3 (influence of equilibrium with carbon dioxide) of carbonic acid. When the solution pH is 1 or more lower than pKa ₁ and pH 5.3 or less, the hydroxide ion concentration (carbonic acid molecule concentration) generated in the aqueous solution is 0.09 to 0.1 mol / L. It is thought to be about. Based on this, the concentration of iron (III) chloride in the reaction solution is preferably 1/3 to 1 times the concentration of 0.09 to 0.1 mol / L, more preferably 1/2 to 1 times the concentration. preferable.
In addition, for example, in a 1 L aqueous solution in which 0.1 mol of sodium carbonate is dissolved, in consideration of the acid dissociation constant pKa ₂ = 10.3 of carbonic acid and the apparent acid dissociation constant pKa ₁ = 6.3, When the solution pH is 5.3 or lower, the hydroxide ion concentration (carbonic acid molecule concentration) generated in the aqueous solution is considered to be about 0.18 to 0.2 mol / L. Based on this, the concentration of iron (III) chloride in the reaction solution is preferably 1/3 to 1 times the concentration of 0.18 to 0.2 mol / L, more preferably 1/2 to 1 times the concentration. preferable.
In addition, for example, in a 1 L aqueous solution in which 0.1 mol of sodium hydroxide is dissolved, water generated in the aqueous solution in an acidic region where the solution pH is 7 or less in consideration of the acid dissociation constant pKa = 13. The oxide ion concentration is considered to be approximately 0.1 mol / L. Based on this, the concentration of iron (III) chloride in the reaction solution is preferably 1/3 to 1 times the concentration of 0.1 mol / L, more preferably 1/2 to 1 times the concentration.

When using any bicarbonate, carbonate, or hydroxide salt, if the pH of the aqueous solution is 1 or more lower than the pKa _{1 of} the salt, it is about 0.9 to 2 times the molar concentration of the dissolved salt. Of hydroxide ions are formed. Therefore, iron (III) chloride is about 0.3 to 2 times the molar concentration of the dissolved one or more salts (S) in the above pH range (1/3 of the hydroxide ion concentration to be generated). It is preferable to dissolve at a concentration of 1 time), and more preferable to dissolve at a concentration of 0.45 to 1 time (1/2 times the concentration of hydroxide ions to be generated).

Moreover, considering the above comprehensively, in the reaction solution for producing akaganeate, the molar ratio of iron (III) chloride to the one or more salts (S) is 2: 1 to 1: 3. Is preferred.
When the molar ratio is within the above range, the charge balance between Fe ³⁺ and OH ^{− in} the reaction solution becomes good, and akaganate can be easily produced in a high yield.

The completion of the reaction for producing akaganate in the reaction solution can be judged empirically based on the fact that the reaction solution has changed from dark brown to reddish brown.
The time required for the reaction to complete once after the start of the reaction for producing akaganate is about 3 to 5 minutes at 10 to 25 ° C., depending on the concentration of the produced akaganate.

After the akaganate is formed, the akaganate can be aggregated by adjusting the pH of the reaction solution to 4 or more and 6 or less. At this time, it is preferable to carry out at a temperature range that does not prevent aggregation, for example, at 10 to 40 ° C. The time required for adjusting the pH to aggregate the akaganeate is, for example, about 5 to 10 minutes at 10 to 25 ° C.
Here, as a method of adjusting the pH of the reaction solution to 4 or more and 6 or less, a method of adding the one or more salts (S) in addition to the reaction solution is preferable. By using the one or more salts (S), it is possible to prevent extra anions (for example, sulfate ions, etc.) from being mixed into the reaction solution and adsorbed on the akaganate.

  According to the above method for synthesizing akaganate, when the yield when all of the iron atoms introduced as iron (III) chloride become akaganate is 100% on a molar basis, the yield is 90 to 99%. It can be obtained by collecting akaganate.

  As described above, akaganeate is generated in the reaction liquid in which the first aqueous solution and the second aqueous solution are mixed in the chemical preparation tank 15. The chemical liquid containing this akaganate is supplied from the chemical preparation tank 15 to the adsorption tank 14 via the chemical liquid supply unit 15a. With this configuration, the amount of akaganate supplied to the adsorption tank 14 can be easily controlled according to the amount of target anions contained in the first supernatant.

  The sulfate ion removal method, the anion adsorption method, and the akagane synthesis method described above can be applied to the water treatment method described below.

《Water treatment method》
The water treatment method exemplified here is a primary treatment in which the concentration of free sulfate ions is reduced by adding barium ions to raw water containing inorganic ions other than sulfate ions and sulfate ions to produce barium sulfate. A first step of obtaining a liquid, and contacting the primary treatment liquid with akaganate to adsorb the anion of the inorganic compound to the akaganeate to obtain a secondary treatment liquid in which the concentration of the anion of the inorganic compound is reduced. A second step.

  By obtaining a primary treatment liquid having a reduced free sulfate ion concentration in the first step, the anion of the inorganic compound is adsorbed on the akaganeate without being competed by sulfate ions in the second step. Thereby, the amount of akaganate used in the second step can be reduced. In other words, since sulfate ions have a relatively high adsorptive power to akaganate, if sulfate water is contained in the water to be treated, akaganate will be consumed by sulfate ions. However, in this water treatment method, the amount of akaganate used in the second step can be reduced by removing sulfate ions in the first step in advance.

[First step]
The raw water in the first step is the same as the raw water in the water treatment method using the water treatment system described above.
Examples of the method of adding barium ions to the raw water include a method of directly adding the barium salt exemplified in the above-described sulfate ion removing method and a method of adding the above-described barium aqueous solution containing the barium salt.

The amount of barium ions added to the raw water is preferably 50 parts by mole or more, more preferably 70 parts by mole or more, and more preferably 120 parts by mole or more relative to 100 parts by mole of the sulfate ion contained in the raw water. preferable.
If it is at least the lower limit of the above range, barium sulfate can be easily formed, and the free sulfate ion concentration in the raw water can be sufficiently reduced. The upper limit of the above range is not particularly limited, and may be, for example, about 200 parts by mole.

The pH of the raw water to which barium ions are added (primary treated water) is not particularly limited as long as it is a pH at which barium sulfate is generated, and can be performed in the range of pH 3 to 8, for example.
The method for adjusting the pH of the aqueous solution to the above range is not particularly limited, and examples thereof include a method of adding hydrochloric acid, sodium hydroxide or the like to raw water or primary treated water.

  The temperature of the raw water (primary treated water) to which barium ions have been added is not particularly limited as long as it is a temperature at which barium sulfate is generated, and can be performed, for example, in the range of 4 to 60 ° C.

  Barium sulfate is produced by adding barium ions to the raw water. Since the solubility of barium sulfate in water is low, precipitation of barium sulfate occurs. The presence of barium sulfate hardly interferes with the adsorption of the anion of the inorganic compound to the akaganeate in the second step. For this reason, the primary treatment liquid used in the second step may or may not contain barium sulfate, but from the viewpoint of increasing the dispersibility of the akagane added to the primary treatment liquid, Is preferably removed.

  Examples of the method for removing barium sulfate from the primary treatment liquid include a precipitation method and a filtration method. Examples of the precipitation method include a method in which the aqueous solution is allowed to stand, and a method in which a sulfate band, PAC, a high molecular weight polymer flocculant, and the like are added to the aqueous solution to cause aggregation to precipitate.

[Second step]
By bringing the akaganeate into contact with the primary treatment liquid, the anion of the inorganic compound contained in the primary treatment liquid can be adsorbed on the akaganeate. This adsorption method is the same as the case of the anion adsorption method described above. When the anion of the inorganic compound is adsorbed on the akaganeate, the akaganeate adsorbing the anion is dispersed in the secondary treatment liquid in which the anion concentration is reduced.

  The method for bringing the primary treatment liquid into contact with the akaganate is not particularly limited. Can be mentioned.

In the case of employing an adsorption method in which akaganate powder is introduced into the primary treatment liquid and stirred, the akaganeate adsorbed with the anion of the inorganic compound can be recovered from the dispersion (secondary treatment liquid).
Examples of the method for recovering the akaganeate powder from the secondary treatment liquid include a precipitation method and a filtration method. Examples of the precipitation method include a method in which the secondary treatment liquid is allowed to settle, a method in which the secondary treatment liquid is agglomerated by adding a sulfate band, PAC, a polymer flocculant, and the like, and a secondary treatment. Examples include a method in which the pH of the liquid is adjusted to 4 to 6 to aggregate the akaganeates. Thereafter, the secondary treatment liquid is obtained as a supernatant liquid of precipitated akaganate or a filtrate obtained by filtering the precipitated akaganate.

  When an adsorption method is adopted in which the akaganate powder is packed in a column and the primary treatment liquid is allowed to flow into this column, the secondary treatment liquid in which the anion of the inorganic compound is adsorbed by the akaganate and the anion is removed. From the column.

  In the above water treatment method, an anion adsorbent having akaganeate as a main component of the adsorbent can be used. Here, “main component” means a component having the largest adsorption amount when the adsorption amount of the target anion between the components of the adsorbent is compared. This anion adsorbent may further have a holding member for holding an adsorbent (akaganate).

  As the shape of the akaganeate as the adsorbent, for example, a shape such as powder, gravel, lump, or plate can be easily used. The powdered akaganate obtained by chemical synthesis may be used as an adsorbent as it is, or may be formed into a larger shape by binding this powder. As a method for binding powdered akaganate, for example, a known method used when forming a porous body (for example, electrode, deodorant) by binding carbon particles with a polymer is adopted. can do. In addition, a lump obtained by pressing or sintering may be used as it is, or the lump may be formed by crushing or cutting the lump to an appropriate size.

  Examples of the holding member include containers, columns (cylinders), baskets, nets, and the like that hold akaganate inside. Also, a holding member capable of fixing akaganate to the surface can be adopted, and for example, a form in which akaganate is fixed to the surface of the plate material can be mentioned.

  The total Se content in the samples used in the following was measured by “67. Selenium hydride generation ICP emission spectroscopy” of JIS K0102: 2013.

[Example 1]
An aqueous solution of hydrogen peroxide (H ₂ O ₂ ) having a concentration of 30% was used as an oxidizing extractant.
The rock discharged from the construction site was crushed to obtain selenium-containing soil particles having a particle size of 0.075 mm to 0.150 mm. The total Se content of the selenium-containing soil particles was 0.52 mg / kg.
To 100 g of the selenium-containing soil particles obtained above (total Se content = 0.052 mg), 1000 g of an oxidizing extractant was added and stirred. By this stirring, the sulfide contained in the soil particles and hydrogen peroxide (oxidant) reacted to generate sulfuric acid. Selenium contained in the soil particles was extracted with sulfuric acid and eluted as selenium oxoacid ions.
360 minutes after the start of stirring, the dispersion of soil particles was centrifuged and the resulting supernatant water was filtered through a membrane filter having a pore size of 0.45 μm to obtain a final extract containing selenate ions.
The total Se content in the final extract was 0.038 mg in total, and 73% of Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

[Example 2]
A Se extraction test was performed in the same manner as in Example 1 except that the concentration of the hydrogen peroxide aqueous solution added to the selenium-containing soil particles was changed to 10%. As a result, the total Se content in the final extract was 0.037 mg in total, and 71% of Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

[Example 3]
The Se extraction test was conducted in the same manner as in Example 1 except that the concentration of the hydrogen peroxide aqueous solution added to the selenium-containing soil particles was changed to 3%. As a result, the total Se content in the final extract was 0.030 mg in total, and 58% of Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

[Comparative Example 1]
A Se extraction test was performed in the same manner as in Example 1 except that the hydrogen peroxide aqueous solution was changed to the same amount of distilled water in the selenium-containing soil particles. As a result, the total Se content in the final extract was 0.017 mg in total, and 33% of Se contained in the treated selenium-containing soil particles was recovered in the final extract. That is, as compared with Example 1, the amount of selenium contained in the final extract was clearly less.

[Example 4]
To 100 parts by volume of distilled water, 100 parts by volume of a sodium hypochlorite (NaClO) aqueous solution having an effective chlorine concentration of 5.7 wt% and 0.23 parts by volume of hydrochloric acid (HCL) were added to obtain an oxidizing extractant. .
The rock discharged from the construction site was crushed to obtain selenium-containing soil particles having a particle diameter of 1 mm to 2 mm. The total Se content of the selenium-containing soil particles was 0.51 mg / kg.
To 100 g of the selenium-containing soil particles obtained above (Se total content = 0.051 mg), 1000 g of an oxidizing extractant was added and stirred. By this stirring, the sulfide contained in the soil particles reacted with hypochlorous acid (oxidant) neutralized with hydrochloric acid to produce sulfuric acid. Selenium contained in the soil particles was extracted with sulfuric acid and eluted as selenium oxoacid ions.
After 360 minutes from the start of stirring, the supernatant water obtained by centrifuging the dispersion of soil particles was filtered through a membrane filter having a pore size of 0.45 μm to obtain a final extract containing selenate ions.
The total Se content in the final extract was 0.039 mg in total, and 76% of Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

[Example 5]
Five Se extraction tests were performed in the same manner as in Example 4 except that the stirring time was changed to 240 minutes, 120 minutes, 60 minutes, 30 minutes, and 10 minutes instead of 360 minutes. As a result, the total Se content in the final extract was 0.039 mg, 0.038 mg, 0.031 mg, 0.026 mg, and 0.024 mg, respectively, in total. Therefore, in each test, 76%, 75%, 61%, 51%, and 47% of Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

[Example 6]
3 parts by volume of hypochlorous acid (NaClO) and 0.23 parts by volume of hydrochloric acid (HCL) were added to 100 parts by volume of distilled water to obtain an oxidizing extractant. A Se extraction test was conducted in the same manner as in Example 4 except that this oxidizing extractant was used. As a result, the total Se content in the final extract was 0.042 mg in total, and 82% of the Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

[Example 7]
Five Se extraction tests were conducted in the same manner as in Example 6 except that the stirring time was changed to 240 minutes, 120 minutes, 60 minutes, 30 minutes, and 10 minutes instead of 360 minutes. As a result, the total Se content in the final extract was 0.040 mg, 0.037 mg, 0.032 mg, 0.037 mg, and 0.040 mg, respectively, in total. Therefore, in each test, 78%, 73%, 63%, 73%, and 78% of Se contained in the treated selenium-containing soil particles could be recovered in the final extract.

(Synthesis of akaganate)
To 1 L of 0.2 mol / L iron (III) chloride aqueous solution, 0.4 L / L sodium hydroxide (1 L) was added, and while stirring gently for 5 minutes, about pH 2 aqueous solution (Fe ³⁺ : OH ⁻ = about 1: 2) Akaganate was produced. Next, sodium hydroxide was further added to the suspension containing the produced akaganeate, adjusted to pH 4 to 5, and agglomerated with each other while gently stirring for 5 minutes. Aggregated akaganeate was collected by filtration to obtain a dried clay-like akaganeto lump. The akaganeate, which was crushed in a mortar and made into powder, was used in the following experiment.
When the yield when all of the iron ions added as iron (III) chloride became akaganate was assumed to be 100% on a molar basis, the akaganate was recovered and obtained at a yield of 95%.
When the synthesized akaganate was analyzed by XRD, a peak indicating akaganate was confirmed.

[Test Example 1]
A sodium selenate aqueous solution containing 10 mg / L of selenium was prepared. The following experimental procedure was performed using the akaganeate obtained by the above synthesis.
(1) 0.015, 0.025, 0.05, 0.1, 0.2, 0.5, 1.0 (unit: w) is added to the above-described aqueous solution containing selenate ions. / W%) at each concentration. After the aqueous solution adjusted to pH 6 was stirred at 20 ° C. for 1 hour, akaganeate was precipitated, the supernatant was recovered, and the selenate ion concentration was determined according to “67. Selenium hydride generation ICP emission spectroscopic analysis in JIS K0102: 2013. Method ".
(2) Green last was added to the aqueous solution containing selenate ions so as to have a weight ratio of 0.15 w / w% to 1.0 w / w%. After the aqueous solution at pH 6 was stirred at 20 ° C. for 1 hour, green last was precipitated, the supernatant was collected, and the selenate ion concentration was measured by the above method.
(3) To the above aqueous solution containing selenate ions, Schwertmannite is added to 0.015, 0.025, 0.05, 0.1, 0.2, 0.5, 1.0 (unit: w / w). %) At each concentration. After the aqueous solution adjusted to pH 6 was stirred at 20 ° C. for 1 hour, Schwertmannite was precipitated, the supernatant was collected, and the selenate ion concentration was measured by the above method.
By the above experiment, adsorption isotherms for selenate ions in iron oxide minerals of akaganeate, green last, and schbertmanite were obtained (FIG. 4).
From the results shown in FIG. 4, it is clear that the iron oxide mineral whose equilibrium concentration of dissolved selenate ion is not more than the environmental standard (0.01 mg / L) is only akaganate, and its adsorption amount is the highest.

[Test Example 2]
0.1, 0.5, 1.0, 2.0, 3.0 (units) of the akaganate synthesized above in an aqueous solution (pH 10) containing about 1200 mg / L (about 12.5 mmol / L) of sulfuric acid. : W / w%) at each concentration. After the aqueous solution adjusted to pH 6 was stirred at 20 ° C. for 1 hour, akaganeate was precipitated, the supernatant was collected, and the concentrations of sulfate ion and chloride ion were measured by ion chromatography.
As a result, as shown in the graph of FIG. 5, the chloride ion concentration in the aqueous solution increased in proportion to the amount of akaganate added, and the sulfate ion concentration decreased accordingly. The increased chloride ion concentration was approximately twice the reduced sulfate ion concentration. This result means that the charge amount of the chloride ion desorbed from the akaganeate and the charge amount of the sulfate ion adsorbed on the akaganeate are almost the same.
From the above results, it is considered that the chloride ion constituting the akaganeate is replaced when another anion is adsorbed.

[Test Example 3]
100 ml of pH 9 sodium selenate aqueous solution (raw water) containing 1200 mg / L of sulfate ion and 0.3 mg / L of selenium was prepared.
Barium chloride aqueous solutions A to C having a barium chloride dihydrate concentration of 1500 mg / L, 3000 mg / L, and 4500 mg / L were prepared. The raw water is mixed with each of the barium aqueous solution and the purified water for control to obtain a mixed solution a1 to a molar ratio of Ba ²⁺ / SO ₄ ²⁻ of 0, 0.5, 1.0, 1.5. d1 was obtained. The mixed solution a1 was transparent, and the other mixed solutions b1 to d1 were precipitated with barium sulfate and became cloudy.
The above mixed liquids a1 to d1 were stirred at 25 ° C. for 10 minutes, and then passed through filter paper to filter the barium sulfate precipitate, thereby obtaining transparent filtrates (first supernatant liquids) a2 to d2.
Subsequently, 0.5 w / w% of the brown akaganate synthesized above was added to each of the filtrates a2 to d2, and after stirring at 25 ° C. for 10 minutes, the powder (precipitate) of the akaganate was filtered through a filter paper, Transparent filtrates (second supernatants) a3 to d3 were obtained.

When the sulfate ion concentration contained in the filtrate (first supernatant liquid) a2 to d2 obtained after the barium sulfate filtration obtained above was measured by ion chromatography, a2 was about 1200 mg / L, b2 was about 600 mg / L, c2 And d2 was approximately 0 mg / L.
From this result, it was found that if the barium aqueous solution was added so that the molar ratio of Ba ²⁺ / SO ₄ ²⁻ was 1, sulfate ions in the raw water could be removed almost completely.

When the selenate ion concentration contained in the filtrate (second supernatant liquid) a3 to d3 obtained by filtration of the akaganeate obtained above was measured by the ICP emission spectroscopic analysis method, it was found that a3>b3> c3≈d3. It was.
From this result, it was found that by removing sulfate ions from the raw water in advance, the adsorption efficiency of selenic acid by the akaganeate in the latter stage is increased.
Moreover, the residual concentration (dissolved selenium concentration) of selenate ions in the second supernatants c3 and d3 was less than 0.01 mg / L of the environmental standard.
From this result, it is understood that wastewater containing selenium can be sufficiently treated by the present invention, considering that the concentration of selenium contained in the wastewater at the construction site is about 0.03 to 0.1 mg / L.

[Test Example 4]
In the same manner as in Test Example 3, after obtaining the mixed solutions a1 to d1, without removing the barium sulfate produced in each mixed solution by filtration, the brown akaganate synthesized above in the mixed solutions a1 to d1 was 0.5 w / Each w% was added and stirred at 25 ° C. for 10 minutes, and then passed through a filter paper to filter the barium sulfate precipitate and the akaganate powder (precipitate) to obtain transparent filtrates a4 to d4.
When the selenate ion concentration contained in the obtained filtrates a4 to d4 was measured by the ICP emission spectroscopic analysis method, the magnitude relationship was a4>b4> c4≈d4.
From this result, it is clear that barium sulfate does not hinder the adsorption of selenate ion of akaganeate.

  From the results of Test Examples 1 to 4, it is clear that treated water obtained by removing sulfate ions and anions of other inorganic compounds from raw water can be obtained by the water treatment system and the water treatment method described above.

  The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications of known configurations are possible without departing from the spirit of the present invention.

R1 ... soil / rock containing selenium, R2 ... purified soil, 1 ... crushing machine, 1a ... crushed material supply part, 2 ... extraction tank, 2a ... extract first liquid feed part, 3 ... fluid, 3a ... extract liquid first Two liquid feeding units, 3b ... residue transfer unit, 4 ... cyclone, 4a ... extract liquid third liquid feeding unit, 4b ... particle first transfer unit, 5 ... turbid water treatment device, 5a ... precipitation first transfer unit, 5b ... extraction 4th liquid feeding part, 6 ... Mud storage tank, 6a ... Second sedimentation transfer part, 7 ... Dehydration device, 7a ... Third sedimentation transfer part, 7b ... First drainage liquid feeding part, 8 ... Sand dewatering sieve, 8a DESCRIPTION OF SYMBOLS 2nd particle transfer part, 9 ... Mixer, 10 ... Water treatment system, 11 ... Raw water tank, 11a ... 1st liquid mixture feed part, 12 ... Barium tank, 12a ... Barium supply part, 13 ... 1st muddy water treatment Apparatus, 13a ... first supernatant liquid feeding part, 13b ... first sediment feeding part, 14 ... adsorption tank, 14a ... second mixed liquid feeding part, 15 ... chemicals Combined tank, 15a ... Chemical solution supply unit, 16 ... First storage tank, 16a ... First aqueous solution supply unit, 17 ... Second storage tank, 17a ... Second aqueous solution supply unit, 18 ... Second muddy water treatment device, 18a ... First Two supernatant liquid feed sections, 18b ... second sediment transfer section, 19 ... release tank, 20 ... third storage tank, 20a ... flocculant first supply section, 20b ... flocculant second feed section, 21 ... storage Mud tank, 21a ... third sediment transfer section, 22 ... dehydration device

Claims (5)

  A method for treating selenium-containing soil or rock, comprising an extraction step of contacting an oxidant with soil or rock particles containing selenium to obtain an extract containing selenium.   2. The selenium-containing soil / rock according to claim 1, wherein the soil or rock contains a sulfur component, sulfuric acid is generated by contact between the sulfur component and the oxidizing agent, and selenium is extracted by the sulfuric acid. Processing method.   The selenium-containing soil / rock treatment method according to claim 1 or 2, wherein selenium is dissolved in the soil or rock.   The selenium-containing soil / rock treatment method according to any one of claims 1 to 3, further comprising a crushing step of obtaining the particles by crushing soil or rock containing selenium. A first step of obtaining the above-mentioned extract containing sulfate ions and selenate ions, adding barium ions to the extract to produce barium sulfate, and obtaining a primary treatment solution having a reduced concentration of free sulfate ions; ,
And a second step of obtaining a secondary treatment liquid in which the concentration of the selenate ion is reduced by bringing the primary treatment liquid into contact with the akaganeate to adsorb the selenate ion to the akaganeate. The processing method of the selenium containing soil and rock of Claim 2.