JP6551171B2 - Method for producing stabilized Schwartermanite - Google Patents

Description

  The present invention relates to a method of stabilizing by introducing silicic acid into the structure of Schwertmannite, which is known to sorb harmful anions such as arsenate ion, arsenite ion and fluoride ion. The present invention relates to a method for producing more easily than the conventional method, and to the stabilized schwertmannite obtained by the method.

  Since elements such as arsenic, selenium, fluorine, and chromium are harmful to human bodies and animals and plants if they are consumed in excess, their emissions from factories and the like are severely restricted. These elements are widely distributed in nature, and are often contained in soil, rocks, groundwater, hot spring water, and the like. Moreover, it may be contained in excavation debris such as rocks and soil generated in mines, tunnel constructions, etc., and rainwater may come into contact with such excavation debris and dissolve in rivers and groundwater. Thus, since the generation sources are diverse and widely distributed, countermeasures have been an issue. In addition, since the harmful element forms an anion, it is difficult to remove or insolubilize it by forming a slightly water-soluble hydroxide by increasing the pH, as is done in many heavy metals. .

Adsorption as a scientific term refers to a phenomenon in which a specific component is concentrated at a two-phase interface such as a solid-liquid interface. However, in the present invention, a specific substance such as a harmful ion is present only at the interface. Since it is taken up not only in the solid but also in the solid, sorption is used as a word meaning that harmful ions are trapped and difficult to release, including such phenomena.
Although ion exchange is considered to be the main mechanism when anions are incorporated into Schwertmannite in the present invention, these phenomena may also be considered particularly because they may be concentrated on the surface electrostatically. Explain using the term sorption without distinction.

  Further, in the present invention, silicic acid introduced to improve the stability of Schwertmannite also adheres to the surface or adheres by condensation when introduced by ion exchange with sulfate ions in the structure of Schwertmannite. In some cases, the sorption is expressed as including sorption. In addition, since silicate ions may be condensed and sorbed or condensed after sorption, hereinafter, in this specification, regardless of whether the silicate is in an ionic state, In some cases, ions are omitted as in sorption.

Schwertmannite is a low crystalline compound containing iron and sulfuric acid and is represented by the following chemical formula (1). The main structure is composed of a stack of units in which eight irons surround one sulfate ion in a ring, and the iron has a cylindrical structure, and it is said that sulfate ions exist inside the cylinder.
Fe ₈ O ₈ OH _8-2x (SO ₄ ) _x [1 ≦ x ≦ 1.75] (1)
This compound also exists in nature, and it is reported in Non-Patent Document 1 by Sato et al. That it takes in arsenic existing in nature and insolubilizes it, and is attracting attention as a sorbent and insolubilizer for arsenic and the like. Moreover, it is known that the sorption performance is high compared with other sorbents.

Schwertmannite has a more stable structure by replacing sulfate ions contained in the structure with arsenite ions containing trivalent arsenic and arsenate ions containing pentavalent arsenic. It is said to sorb compounds. For this reason, under conditions where the arsenic concentration is high or conditions where arsenic is continuously supplied, Schwartonite takes in and stabilizes arsenic.
However, it is known that Schwertomanite has low stability, and when it is left, it changes to more crystalline goethite, and its ability to sorb arsenic and the like is greatly reduced. For this reason, when the arsenic concentration is low, there is a concern that it may change to goethite to reduce the amount of sorbed arsenic compound before sorbing sufficient arsenic to make the structure stable. As a method of improving this, it is proposed in Patent Document 1 that a part of the sulfate ion in the structure of Schwertmannite is replaced with a silicate ion.

  In Patent Document 1, 1 g of Schwertmannite previously synthesized in 1 liter of an aqueous solution in which sodium silicate is dissolved is added at a rate of 1 g, shaken at room temperature for 24 hours, solid-liquid separated, and silicate ions Has been sorbed schbertmanite. In this method, it is described that when the silicate ion concentration is 0.6 mmol / l or more, the sorption amount of silicate ions to Schwermannite is saturated at about 0.4 mmol / g. Furthermore, from the powder X-ray diffraction pattern after leaving these stabilized schwertmannites in a saturated water vapor atmosphere at 50 ° C., it was confirmed that the goethite formation rate was reduced and stabilized compared to untreated schwertmannite. I'm sure.

  However, in the method of sorbing and stabilizing silicic acid on Schwbertmannite in Patent Document 1, the process of synthesizing Schwertmannite and Schwertmannite are carried out in order to mix the previously synthesized Schwertmannite and the silicic acid solution. In each process of sorbing silicic acid to knight, processes such as filtration, washing, and drying are required, and the process is long and complicated, resulting in an increase in waste liquid.

Patent No. 3859001

K Fukushi, M Sasaki, T Sato, N Yanase, H Amano and H Ikeda, Applied Geochemistry, 18 (8), 1267-1278, 2003.

  In view of the above situation, the present invention is a method for easily obtaining a stabilized Schwbertmannite by sorbing silicic acid, and a harmful anionic substance such as arsenic using the obtained stabilized Schwbertmannite. It is an object to provide a method for sorption removal or insolubilization.

As a result of diligent studies to solve the above-mentioned problems, the present inventor produced and precipitated Schwbertmannite by adjusting the pH of a solution in which iron ions and sulfate ions, which are raw materials for Schwbertmannite, were dissolved. By adding silicate ions to the dispersion (slurry), a schbertmanite with improved stability and sorbed silicic acid is obtained without going through a process of isolating and purifying schwertmannite that has not been treated with silicate. I found out.
In addition, it has been found that the amount of desorbed sulfuric acid is increased by raising the pH of the dispersion after adding schwert mannite before adding the silicate. Furthermore, the sorption amount of silicic acid can be controlled by adjusting the addition ratio of silicic acid relative to the deposited schwertmannite, and by combining the pH adjustment before adding silicic acid and the addition ratio of silicic acid, It has been found that the desorbed amount, that is, the ion exchange amount of sulfate ion and silicate ion in the Schwertmannite structure, and the total sorption amount of silicic acid can be arbitrarily controlled.

  Thus, the present inventor has found that, according to specific manufacturing conditions, it is possible to easily obtain a Schwertmannite that sorbs silicic acid and has improved stability, compared to the method described in Patent Document 1. Furthermore, the present inventors have found that the amount of silicate ion sorption can be controlled by adjusting the pH of the Schbertmannite dispersion immediately after synthesis before the addition of silicate, and the present invention has been completed.

  That is, claim 1 is characterized in that silicate ions are sorbed to Schwbertmannite by adding silicate ions to a dispersion in which Schwertmannite is precipitated from an aqueous solution in which iron ions and sulfate ions coexist. It is a manufacturing method of stabilized Schwertomanite.

  A second aspect of the present invention is the method for producing a stabilized schwertmannite according to the first aspect, wherein the silicate ion is added after adjusting the pH of the dispersion liquid in which the schbertmanite is precipitated to 4 to 10.

  Claim 3 is the method for producing a stabilized Schwermannite according to claim 1 or 2, wherein the silicate ion is added after adjusting the pH of the dispersion in which the Schwertmannite is precipitated to 6-8. is there.

  In Claim 4, the molar ratio of iron atoms to silicon atoms in Schwertmannite sorbed with silicic acid is 8.0: 0.4 to 3.0. It is a process for the preparation of the described stabilized Schwertomanite.

  Claim 5 is the molar ratio of iron atoms and sulfur atoms in Schwertmannite sorbed with silicic acid is 8.0: 0 to 1.3. This is a method for producing a stabilized schwertmannite.

  A sixth aspect of the present invention relates to an anionic hazard characterized by contacting the stabilized Schwermannite according to any one of the first to fifth aspects with a liquid or solid containing an anionic harmful substance. It is a method of sorption removal or insolubilization of substances.

  Claim 7 sorption-removes the anionic toxic substance according to claim 6, wherein the anionic toxic substance is an anionic toxic substance containing any one element of arsenic, selenium, fluorine, chromium and iodine. Or it is the method to insolubilize.

  The stabilized schwertmannite obtained by the method of the present invention can maintain excellent sorption properties against harmful ions including arsenic over a long period of time, and is extremely simple compared to conventional production methods. Can be manufactured at low cost, and can be used for sorption removal and insolubilization of hazardous substances in contaminated water, contaminated soil, waste and excavated sediment generated in civil engineering, incineration ash buried in disposal sites, industrial waste, etc. Being excellent as an agent, it is extremely useful as a material for treating harmful substances.

The relationship between the addition rate of silicic acid and the amount of silicic acid sorbed in Schwertmannite produced in each example and comparative example is shown. The relationship between the addition rate of silicic acid and the desorption amount of sulfate ions in Schwertmannite produced in each Example and Comparative Example is shown. The powder X-ray-diffraction pattern of the reference example Schwertmannite is shown. The powder X-ray-diffraction pattern of the Schwermannite of Example 1 is shown. The powder X-ray-diffraction pattern of the Schwertmannite of Example 4 is shown. The powder X-ray-diffraction pattern after leaving the reference example Schwertmannite for 7 days on the conditions of 50 degreeC relative humidity 98% is shown. The powder X-ray-diffraction pattern after leaving the Schbertmanite of Example 2 for 7 days on the conditions of 50 degreeC relative humidity 98% is shown.

  The stabilized schwertmannite according to the present invention comprises a first step for producing and precipitating schwertmannite and a second step for sorbing silicate ions and desorbing sulfate ions. After completion, the process of isolating and purifying Schwbertmannite is not required, and it is produced as a series of continuous processes.

The first step can apply known methods as they are. For example, reference 1 (Schwertmann, U, and Cornell, RM (1991) Iron Oxides in the Laboratory, VCH, Weinheim, 137 pp) and reference 2 (Akayuki Inoue and Tamaro Hatta "Clay Science" Vol. 45 No. 4 250 In this method, an aqueous iron nitrate solution is added to a heated aqueous solution of sodium sulfate as described in JP-265 (2006)), and pH is adjusted to precipitate Schwartermanite. In this method, a trivalent iron salt such as iron chloride can also be used as an iron source.
In addition, a method described in Japanese Patent No. 5362292, in which an aqueous iron sulfate solution is heated and a weak alkaline salt such as sodium hydrogen carbonate is added to adjust the pH to precipitate Schbertmanite, is also applicable.
Furthermore, there is also known a method of obtaining Schwertmannite by culturing iron-oxidizing bacteria in the coexistence of sulfate ions and divalent iron, simulating the formation process of Schwbertmannite in nature.

  In the first step, the ratio of the raw material and water is such that the deposited schwertmannite is 45% by mass or less, preferably 40% by mass or less in terms of solid content. When the solid content concentration is 40% by mass or less, it becomes liquid and can be easily stirred, but when it is 40 to 45% by mass, it becomes creamy and stirring becomes difficult. If it exceeds 45% by mass, the slurry viscosity is remarkably increased and the fluidity is almost lost, which is not preferable.

In the second step of the present invention, the silicate or its solution is added to the slurry dispersion in which the schbertmannite is deposited in the first step and stirred, so that the desorption of sulfate ions and the silicate ions are performed. Sorptive.
The second step can be carried out with warming as in the first step, but the reaction can be carried out sufficiently even at room temperature.
After completion of the second step, filtration, drying, etc. are performed to obtain a schbertmanite stabilized with silicic acid. However, the filtered schwertmannite contains extra substances when used to remove soil and water contamination. It is preferable to remove excess ions and the like by washing several times with water and the like before drying so as not to leach out and contaminate.

Schwertmannite keeps the temperature of the solution in which iron ions and sulfate ions co-exist at 50 to 70 ° C. and precipitates when the pH is adjusted to about 2 to 4, more preferably, to 2 to 3. In the slurry state after the above step, the pH of the liquid is relatively low, and if silicate is added in this state, silica gel is likely to be generated by the condensation reaction, which absorbs the liquid and swells, thus reducing the filterability. Productivity tends to deteriorate.
As a method of preventing this, it is preferable to set the pH of the obtained slurry to 4 or more before adding a silicate ion. At this time, as the pH is higher, there is an advantage that the replacement of the sulfate ion and the silicate ion present in the structure of Schwertmannite can be facilitated.
The pH of the dispersion at the end of the first step is preferably 4 to 10, more preferably 6 to 8. When the pH is less than 4, silicic acid is likely to condense, and the filterability tends to decrease. On the other hand, when the pH exceeds 10, it easily changes to an iron compound other than Schwertmanite.

  As described above, it is preferable to raise the pH after the completion of the first step and before adding silicic acid, but the slurry is filtered or the slurry is stopped and the product is allowed to settle, and the supernatant is removed by decantation. Even if it is removed, gelation of silicic acid can be suppressed. It is preferable to add water after this operation to impart fluidity. In this case, as in the first step, the solid concentration is 45% by mass or less, preferably 40% by mass or less. If the solid content concentration is 40% by mass or less, it becomes liquid and can be easily stirred, but if it is 40 to 45% by mass, it becomes creamy and stirring becomes difficult. When it exceeds 45% by mass, the viscosity of the slurry is significantly increased, and it is not preferable because the fluidity is almost lost.

  These operations remove much of the excess liquid with a low pH, thereby reducing the amount of the pH adjusting agent added in the second step, and without adding a pH adjusting agent, such as sodium silicate. Since the silicate itself is alkaline, the pH of the slurry immediately rises, and the purpose is to reduce the time that the silicate is exposed to a low pH immediately after the addition, so that excess water is completely removed. There is no need. Excess water may be removed completely, but when redispersed for the next step, lumps may be formed, making it difficult to redisperse.

As a silicate ion source used to stabilize Schwertmannite, salts such as sodium silicate and potassium silicate can be preferably used. Sodium silicate (also known as sodium silicate, water glass) is represented by the formula [Na ₂ O · nSiO ₂ · mH ₂ O], and n = 0.5 to 4 are industrially manufactured. It is distributed as solids such as powder and aqueous solutions. The same applies to potassium silicate. These can be used without particular limitation.

In the step of sorbing silicate ions in Schwertmannite, a silicate or an aqueous solution thereof is added to a dispersion in which Schwertmannite is formed and precipitated, and stirring is performed. As described above, in this step, the pH of the slurry may be adjusted to 4 to 10 before adding the silicate. After sorbing silicic acid, solid-liquid separation is performed by a method such as filtration or centrifugation, washed with water several times if necessary, and finally dried to obtain a stabilized Schwermannite.
In that case, what is obtained by adjusting pH to 4-10 before adding a silicic acid is favorable in terms of productivity, since filterability becomes good. In addition, if the pH is not adjusted before the addition of silicic acid, the amount of silicate ions sorbed without the ion exchange reaction between sulfate ions and silicate ions increases, which deteriorates the filterability. Although the treated silica gel scherutmanite also has a large amount of silicified silica and can be slightly different from the conventional method, it adsorbs arsenite etc. and is more stable than general schwert mannite. You can get something expensive.
Since sorption of silicic acid proceeds easily even at room temperature, there is no need for heating. Stirring at room temperature for several hours to a day almost completes the sorption of silica.

In this step, the molar ratio of Schwertmannite to silicic acid is important for controlling the amount of silicic acid sorption. In Patent Document 1, 1 liter (0.895 mmol) of Schwermanite is added to 1 liter of an aqueous solution having a silicate ion concentration (SiO ₂ conversion) of 0.2 to 1.0 mM, and shaken for 24 hours. Acid ions are sorbed. As a result, it is described that when the silicate concentration is 0.6 mM or more, the maximum sorbed amount of silicate ions is about 0.4 mmol / g and saturated. In this case, the silicate ion used is 0.22 to 1.11 times in molar ratio with respect to Schwertmannite. Incidentally, in Patent Document 1, schwertmannite the chemical formulas supra Fe ₈ O ₈ OH ₈ - to _2x (SO _{4) x} [1 ≦ x ≦ 1.75], the crystal water and x = 1.75 It is calculated on the assumption that the formula quantity is 1116.705 including 16.5.

  On the other hand, the present inventors have found that when the silicate ion is 1.5 times or more in molar ratio with respect to Schwertmannite, the sorption amount of silicic acid exceeds 0.4 mmol / g, Furthermore, when the addition rate of silicate ions is adjusted so that the sorbed silicate ions are 0.5 to 2.5 mmol / g, the stability to high temperature and high humidity conditions is remarkably improved. I found out.

  In Patent Document 1, schwertmannite once isolated and dried after synthesis is added to an aqueous silicate solution and stirred to sorb silicic acid. For this reason, the number of moles of schbertmannite used can be determined by dividing the weight used by the formula amount of the chemical formula. It can be calculated on the basis. Further, the sorption amount of silicic acid can be obtained by examining the silicon concentration in the filtrate after filtering the schwertmannite after completion of the silicate sorption operation and the silicate sorption operation before adding the schbertmanite. .

  On the other hand, in the method of the present invention, silicate is added to a slurry formed by synthesizing Schwertmannite, so that the silicic acid concentrations before and after the sorption process cannot be compared. For this reason, the silicic acid sorption amount and the sulfuric acid desorption amount of the obtained stabilized Schbertmanite were examined by determining the content of each element of iron, silicon, and sulfur by fluorescent X-ray analysis. In addition, it can investigate similarly by various elemental analysis. For schwertmannite synthesized by a conventional method and sorbed with silicic acid, the amount of silicic acid sorbed from the silicon concentration of the aqueous silicic acid solution before and after the sorption treatment operation and silicic acid sorption determined by fluorescent X-ray analysis When the amount was examined, it was confirmed that they were almost the same.

  When treating Schwertmannite with silicic acid, the addition ratio of silicic acid to Schwertmannite is important as described above, but in the method of the present invention, the formation of Schwertmannite at a stage before adding silicic acid. The quantity can not be measured accurately. Since the formation reaction of schwertmannite proceeds almost quantitatively if sulfate ions are sufficiently present relative to iron ions, the iron atom used in the synthesis is used when determining the addition multiple of silicic acid in the present invention. An 8 mole fraction is assumed to be 1 mole of Schwartermanite, which is a multiple of it.

  In the method of the present invention, it is assumed that 8 times the number of moles of iron used for the production of schwertmannite is 1 mol of schwertmannite, and how many times the amount of silicic acid is added is used. The inventor analyzed the schwertmannite after sorption of silicic acid with fluorescent X-rays and plotted the amount of silicic acid sorbed against the addition multiple of silicic acid. Furthermore, as described below, it was found that even if the pH of the slurry before addition of silicic acid was changed, it was plotted on almost a straight line regardless of the pH. That is, it was found that the sorption amount of silicic acid can be controlled by the amount of silicic acid added to iron regardless of the pH before silicic acid is added.

In the present invention, the preferable addition ratio of silicic acid is 0.4 to 10 moles of 8 moles of iron ions used in the synthesis of Schwertmannite, that is, 1 mole of Schwertmannite.
It is a molar ratio. More specifically, without adjusting the pH of the slurry, 1.5 to 10 when the pH is about 2 to 3, 1 to 10 when the pH of the slurry is about 4, 0 when the pH of the slurry is 6 or more 4 to 10 times. The higher the pH, the higher the utilization rate of the added silicic acid, so even with a small amount of silicic acid added, the necessary sorbed amount of silicic acid can be obtained. As a result, since the amount of silicic acid remaining in the waste water is reduced by selecting an appropriate amount of silicic acid added, it is preferable from the viewpoint of waste water treatment to increase the pH of the slurry. Even if the addition ratio of silicic acid is less than 0.4, the stability is improved as compared with untreated Schwertmanite, but it tends to be insufficient in practical use. On the other hand, if the addition ratio of silicic acid is high, not only the silicic acid is wasted, but the content of silicic acid in the waste water becomes high, which is not preferable in terms of waste water treatment cost.

According to Patent Document 1, by replacing part of the sulfate ions contained in the structure of Schwartermanite with silicate ions, the stability against wet heat conditions is increased. The amount of sulfate ions to be desorbed is important as an indicator of the amount of ion exchange with silicate ions. The amount of sulfate ions desorbed was analyzed by X-ray fluorescence analysis of the sulfur content in Schwertmannite that was synthesized using the same lot of raw material and was not sorbed with silicic acid, and all sulfur was assumed to be sulfate ions. Then, the value of x in the chemical formula of the following Schwbertmannite is obtained, and then the number of sulfur in the Schwertmannite that has undergone the silicic acid sorption step is similarly obtained and subtracted, and the amount of sulfuric acid desorbed per 1 g of Schwertmannite ( The unit was determined as mmol / g).
Chemical formula: Fe ₈ O ₈ OH _{8 -2x} (SO ₄ ) _x [1 ≦ x ≦ 1.75]

As a result of analyzing the silica sorbed schwert mannite obtained by the method of the present invention by fluorescence X-ray, the amount of desorbed sulfate ion increases as the added amount of silicic acid to iron used as the raw material, that is, schertzermanite is increased A trend was seen. Furthermore, it was found that the higher the pH of the slurry before the addition of silicic acid, the easier the sulfate ion was desorbed. When the sulfate ion is desorbed, it is considered to be ion-exchanged with the silicate ion, but as described above, the total sorbed amount of the silicate ion was not pH-dependent.
From these facts, it is thought that not only is the silicate ion substituted for the sulfate ion, but it is also sorbed around Schwertmannite. The ratio between the silicate ions introduced by ion exchange and the silicate ions adsorbed to the surroundings seems to change depending on the pH of the Schwermanite dispersion adjusted before adding the silicate, but surprisingly as described above. The total amount was not affected by pH.
That is, in the method of the present invention, it is possible to arbitrarily adjust the silicate ion sorption amount and the sulfate ion desorption amount by adjusting the addition amount of silicic acid to iron and the pH of the slurry before addition of silicic acid. is there.

The preferable amount of silicic acid sorbed in the silicic acid-treated Schwartmanite obtained by the method of the present invention is 0.4 to 3.0 moles per mole of Schwertmannite, that is, per 8 moles of iron atoms. This value can be obtained by converting the molar ratio obtained by dividing the weight ratio of iron and silicon by the respective atomic weights, obtained by elemental analysis means such as fluorescent X-ray analysis, to 1 mol of Schwermanite.
If the amount of silicic acid adsorbed per mole of Schwertmannite is less than 0.4 moles, the effect of improving the stability may not be obtained. On the other hand, when the silicic acid sorption amount is more than 3.0 mol, not only arsenic ions are hardly absorbed, but also the arsenite ion sorption property when left in a high temperature and high humidity environment is impaired. Sometimes.

  Furthermore, in order to obtain good sorption performance with respect to both arsenic acid and arsenite ions while imparting high stability to Schwertmannite, sulfur per mole of Schwertmannite, that is, per 8 moles of iron atoms. The molar ratio of is preferably 1.3 or less. Since it is considered that all sulfur in the silicic acid-treated Schwertmannite is present as sulfate ions, the molar ratio of sulfur may naturally be considered as the molar ratio of sulfuric acid. When the molar ratio of sulfur exceeds 1.3, only a little effect of improving the stability in a moist heat environment can be obtained. In order to obtain a sufficient effect, it is preferable to set it to 1.3 or less.

  Arsenic can take several valences, but what causes problems with water quality and soil contamination is mainly trivalent arsenite ions and pentavalent arsenate ions. There are two types of cases. These are likely to become arsenite under anaerobic conditions and arsenate ions under aerobic conditions. In this way, since the valence is likely to change due to oxygen concentration, bacteria, etc., trivalent and pentavalent coexist in many cases, and the ratio also changes due to environmental changes. For this reason, the arsenic sorbent also needs to correspond to both ions as needed. In some cases, one of the valences may be almost in an oxidizing atmosphere or a reducing atmosphere.

  The schwertmannite slurry that has undergone the above-described sorption process of silicic acid is subjected to solid-liquid separation operations such as filtration, centrifugation, decantation, etc., preferably washed with water, and then used after drying or in water. It can be used as a dispersed slurry. In the presence of water, Schwertmannite is likely to become goethite with poor arsenic sorption performance due to a change in crystal form, and the tendency becomes more pronounced at higher temperatures, but it is stabilized by sorbing silicic acid. Therefore, the usable time of the slurry is long and easy to handle.

The harmful substances to be targeted when using the stabilized Schwertomanite obtained by the method of the present invention as a sorbent or insolubilizing agent for harmful metals include fluoride ion, arsenous acid ion, arsenate ion, selenium Acid ions, selenite ions, chromate ions, dichromate ions, and the like that have been found to be sorbed by Schwertmannite, and iodate ions, chlorate ions, bromate ions, etc. However, it is not limited to these.
Among these, it is suitable for a method for sorption removal or insolubilization of an anionic harmful substance containing any element of arsenic, selenium, fluorine, chromium and iodine.

The stabilized Schbertmanite of the present invention is a sorbent removal agent for harmful substances from contaminated water containing harmful substances such as industrial wastewater, groundwater, hot spring water, contaminated soil, excavated soil generated in civil engineering, It can be used as a sorbent for intoxicating substances such as drilling waste, incineration ash, industrial waste and so on, and insolubilizer. Contaminated soil etc. usually contain water, but the stabilized Schwertomanite obtained in the present invention is stabilized when used in contaminated water because its stability is improved under moist heat conditions. It can be used for a long time as compared with no Schwartmanite, and can maintain its sorption performance for a long time while being mixed with an object such as a contaminated soil.
When using it as the sorption removal agent of the harmful | toxic substance from a contaminated water, a well-known method can be applied. For example, the stabilized Schwertmanite of the present invention may be packed in a filtration tower and the like, and waste water containing harmful substances may be supplied to the filtration tower to sorb harmful substances. Further, a method of adding the stabilized schwertmannite of the present invention to the contaminated water, stirring and solid-liquid separation can be used, and a flocculant may be used in combination as necessary.

Moreover, when using as an insolubilizing agent of the harmful | toxic substance contained in contaminated soil etc., a well-known method is applicable.
For example, mixing of contaminated soil and the stabilized Schbertmanite of the present invention can be carried out using a mixer used for ground improvement work, and a machine for improving contaminated soil in situ and improvement on the ground. Any machine can be used. In any case, the stabilized Schwertmannite of the present invention can be mixed with the contaminated soil in the form of a solid or in the form of a slurry to which water is added. In addition, it can be used as an adsorption layer such as an adsorption layer method, which is spread under the contaminated soil to prevent the diffusion of the pollutant to the surroundings.

Hereinafter, the present invention will be described more specifically with reference examples, examples and comparative examples.
<Reference example> Schertomanite not containing silica 93.7 g (0.23 mol) of iron nitrate (III) nonahydrate in a 2 L four-necked flask
) And 28.4 g (0.20 mol) of sodium sulfate were added, water was added to a total volume of 800 ml, and a stirrer, a thermometer and a Dimroth through cooling water were attached. The solution was set in a hot water bath, and while heating, the inside of the flask was stirred to dissolve uniformly, and the aqueous solution was maintained at about 60 ° C. At this time, the pH was 1.2. While stirring and keeping warm, sodium carbonate was added little by little, and when the pH of the aqueous solution reached 2.7, the addition of sodium carbonate was stopped. The amount of sodium carbonate added was 15.4 g. At this point, the liquid was a yellowish brown and opaque slurry. Stirring and warming were continued for 15 minutes, after which the heating of the water bath was stopped and the hot water of the water bath was replaced with water to cool to about room temperature.
Subsequently, the reaction mixture in which the product was dispersed was filtered using a Buchner funnel set with filter paper. 1 L of water was added to the obtained solid content to remove excess ions and the like, and after repeating the process of repeating filtration three times, it was taken out to a petri dish and vacuum dried overnight at 50 ° C. . In Table 1, the number of washing steps was counted as one step where the washing and filtration were repeated three times. The yield of the obtained yellow-brown dry solid was 25.1 g. This was ground in a mortar and used as a powder for sorption tests. When this powder was analyzed by powder X-ray diffraction, a typical Schwartermanite diffraction pattern shown in FIG. 3 was obtained, and it was confirmed that Schwartermanite was obtained.
Further, this powder was analyzed by fluorescent X-ray, and the mass ratio of iron: silicon: sulfur was 46.3: 0.00: 5.33 obtained from the X-ray intensity ratio. When this number is divided by each atomic weight to obtain the number of moles of each atom, and iron is converted to 8.0, the molar ratio of each atom is converted to iron: silicon: sulfur = 8.0: 0.0: 1. It was six. Therefore, the value of x in chemical formula (1) is 1.60 in the Schbertmanite obtained by this synthesis.
Fe ₈ O ₈ OH _8-2x (SO ₄ ) _x [1 ≦ x ≦ 1.75] (1)
The Schwartermanite was allowed to stand in a constant temperature and humidity chamber at 50 ° C. and a relative humidity of 98%, and the transition of the arsenic sorption characteristics was examined. The results are summarized in Table 3. According to this, it was found that the arsenous acid sorption performance after being left moist and heat was halved in about one week and extremely unstable. Moreover, the powder X-ray-diffraction pattern 1 week after moist heat leaving was shown in FIG. This diffraction pattern was a goethite pattern and was found to be significantly unstable compared to the other examples.

Example 1
93.7 g (0.23 mol) of iron nitrate (III) nonahydrate in a 2 L four-necked flask
) And 28.4 g (0.20 mol) of sodium sulfate, water was added until the whole became 800 ml, and a stirrer, thermometer, and a Dimroth through which cooling water was passed were attached. The solution was set in a hot water bath, and while heating, the inside of the flask was stirred to dissolve uniformly, and the aqueous solution was maintained at about 60 ° C. At this time, the pH was 1.2. While stirring and keeping warm, sodium carbonate was added little by little, and when the pH of the aqueous solution reached 2.7, the addition of sodium carbonate was stopped. The amount of sodium carbonate added was 15.4 g. Stirring and warming were continued for 15 minutes, after which the heating of the water bath was stopped and the hot water of the water bath was replaced with water to cool to about room temperature. Next, a sodium silicate aqueous solution prescribed in No. 3 in JIS K1408 as a sodium silicate source in this slurry-like mixed solution (manufactured by Aichi Sangyo Kogyo Co., Ltd., sodium silicate No. 3, containing 29% in terms of SiO ₂ ) The mixture was stirred at room temperature for 20 hours while adding 18.0 g corresponding to 3 times the number of moles of Schwertmanite, that is, 3 times the number of moles of iron nitrate.
Thereafter, the reaction mixture in which the product is dispersed is filtered using a Buchner funnel in which filter paper is set, and in order to remove excess ions, etc., 1 L of water is added to the obtained solid content, and the mixture is stirred and filtered. The process was repeated three times and the solids on the filter were vacuum dried overnight at 50 ° C. Filtration at this time was slightly slower than the reference example and was difficult to filter.
The obtained yellow-brown dry solid was 31.4 g. The product was ground in a mortar and used as a powder in sorption tests and the like. When this powder was analyzed by powder X-ray diffraction, the diffraction pattern shown in FIG. 4 was obtained, and it was confirmed that Schwartermanite was obtained. Among the diffraction patterns, it was presumed that the broad peak near 2θ = 26 ° was slightly larger than that in FIG. 3, and silica gel was formed from the position of the peak and the used raw material. The decrease in filterability is believed to be due to the swelling of the silica gel. This powder was analyzed by fluorescent X-ray, and when the molar ratio of iron, silicon, and sulfur atoms was determined when iron was set to 8 as in the reference example, iron: silicon: sulfur = 8.00: 2. 43: 1.15. Since the Schwbertmannite obtained in the Reference Example was iron: silicon: sulfur = 8.0: 0.0: 1.6, sulfate ion calculated by the difference in the molar ratio of sulfur per mole of Schwertmannite 0.45 mol was desorbed and 2.43 mol of silicic acid was sorbed.
Table 3 shows the results of examining the transition of the arsenic sorption characteristics by leaving this silicic acid-treated Schwermannite in a constant temperature and humidity chamber at 50 ° C. and 98% relative humidity. As compared with the reference example, it was found that the arsenous acid sorbability was less likely to decrease even under moist heat conditions.

  In all the examples, the synthesis from the synthesis of Schwertmannite to the stabilization by silicic acid sorption is carried out continuously using a single reaction vessel. The drying step was only performed one last time. In addition, since it is not taken out in the middle, the number of times of washing the reaction container is reduced, and there is no time for redispersion. Therefore, compared with a conventionally known method such as a comparative example, the time required for synthesis is greatly increased. It was found that the manufacturing cost could be greatly reduced because the amount of waste water could be reduced to half or less.

Examples 2 to 4
The same sodium silicate aqueous solution as in Example 1 was added 2 times in terms of silicic acid to Example 2 with respect to 1/8 of the number of moles of iron nitrate. The thing was made into Example 4, all the processes other than that were performed similarly to Example 1, and various evaluation was performed. The filterability was somewhat inferior to any of the reference examples. When these powder X-ray diffraction patterns were measured and the peaks around 2θ = 26 ° were compared, the peaks were larger as the amount of silicic acid added was larger. Be
The powder X-ray-diffraction pattern of Example 4 is shown as FIG. 5 as a representative example. Compared to Example 1, it can be seen that the peak around 2θ = 26 ° is further increased. Further, the molar ratio of atoms of silicon and sulfur when iron was 8 as calculated from fluorescent X-ray measurement was calculated in the same manner as in Example 1 and summarized in Table 2.
Furthermore, after standing on the moist heat condition, evaluation of arsenous acid sorption performance was performed, and the obtained results are summarized in Table 3.
From these results, it was found that high arsenite ion sorption property can be maintained after being left in a wet heat environment as compared with the reference example in which no silicic acid treatment was performed in the wet heat environment.

Example 5
The process until the precipitation of Schwertmannite was carried out in the same manner as in Example 1. When cooling to room temperature, the stirring was stopped, but the produced Schwertmannite precipitated, and the supernatant was removed by decantation. After this, the same amount of water as the removed supernatant was added and stirred again. At this time, the pH of the solution was 3.5. Next, in the same manner as in Example 4, the same sodium silicate aqueous solution as in Example 1 was added 5 times in terms of silicic acid to 1/8 of the molar number of iron nitrate. The subsequent steps were performed in the same manner as in Example 1 to obtain silicic acid-treated Schwermanite. In this example, the filterability was slightly improved as compared with Examples 1-4. Further, the molar ratio of silicon and sulfur when iron was 8 as calculated from fluorescent X-ray measurement was calculated in the same manner as in Example 1 and summarized in Table 2. The arsenite ion sorption performance was evaluated and the results obtained are summarized in Table 3.
As described above, it was found that the silicate-treated schwertmanite can be easily obtained as compared with the conventional method, and the stability under the moist heat environment can be similarly obtained. Moreover, it is thought that the filterability was improved as a result of adding the same amount of water after removing the supernatant once by decantation, thereby increasing the pH and making the silicic acid difficult to gel.
Compared to Example 4 using the same amount of sodium silicate in Table 2, the amount of silicic acid sorbed slightly decreased and the amount of sulfuric acid desorbed increased, so Example 5 compared to Example 4 It can be said that the ion exchange between sulfate ions and silicate ions occurs easily, and the amount of silicic acid taken into the structure of Schwertmannite increases, but the amount of silicic acid sorbed to the surroundings tends to decrease.

Example 6
The steps until precipitation of schwert mannite was performed in the same manner as in Example 1. After cooling to room temperature, sodium carbonate was added while stirring to adjust the pH to 4.0. Next, the same aqueous solution of sodium silicate as in Example 1 was added twice in terms of silicic acid to 1/8 of the number of moles of iron nitrate. The subsequent steps were performed in the same manner as in Example 1 to obtain silicic acid-treated Schwermanite. In this example, the filterability was improved as compared with Examples 1 to 4, and was similar to the reference example. Further, the molar ratio of silicon and sulfur when iron was 8 as calculated from fluorescent X-ray measurement was calculated in the same manner as in Example 1 and summarized in Table 2. The arsenite ion sorption performance was evaluated and the results obtained are summarized in Table 3.
As described above, it was found that the silicate-treated schwertmanite can be easily obtained as compared with the conventional method, and the stability under the moist heat environment can be similarly obtained. Moreover, after Example 4, it is thought that silicic acid became difficult to gelate by raising pH before adding sodium silicate. Further, as can be seen from FIG. 2, it was found that the higher the pH before adding the silicate, the more the amount of desorbed sulfuric acid with respect to the added amount of silicic acid.
On the other hand, as can be seen from FIG. 1, the total sorption amount of silicic acid with respect to the addition amount of silicic acid is not affected by pH, and the higher the pH before addition of silicic acid, the more sorbed silicic acid, It can be said that the rate of ion exchange with sulfate ions increases. That is, it can be said that the higher the pH is, the more efficiently the silica inside the structure contributing to the stabilization is sorbed. In addition, since it is possible to suppress a decrease in filterability considered to be caused by the gelation of silicic acid, it can be said that the method of increasing the pH before adding the silicate is extremely effective in the method of the present invention. It has been found that a remarkable effect can be obtained by the above.

Examples 7 to 16
The amount of sodium silicate added is 1 to 5 times the molar number of iron nitrate used in the synthesis, that is, the theoretical number of moles of Schwertmannite, and the pH adjustment before the addition of sodium silicate is 4 to 8 These combinations are summarized in Table 1. Except this, it carried out similarly to Example 1, and obtained the silicic acid processing Schwermanite. In all of these, the filterability was improved as compared with Examples 1 to 4, which was comparable to the reference example. Further, the molar ratio of silicon and sulfur when iron was 8 as calculated from fluorescent X-ray measurement was calculated in the same manner as in Example 1 and summarized in Table 2. The arsenite ion sorption performance was evaluated and the results obtained are summarized in Table 3.
As described above, it was found that the silicate-treated schwertmanite can be easily obtained as compared with the conventional method, and the stability under the moist heat environment can be similarly obtained. Moreover, it is thought that silicic acid became difficult to gelate by raising pH before adding sodium silicate.
Although the powder X-ray diffraction patterns of Examples 15 and 16 in which the pH before addition of silicic acid was adjusted to 8 were those of typical Schwertmannite, the color of the powder was different from that of other examples and comparative examples. It was reddish compared to. In an aqueous solution containing trivalent iron ions, it is known that goethite is formed when the pH is adjusted to about 12, and in the method of the present invention, if the pH is too high before stabilization with silicic acid, another iron is generated. Compounds can be formed.

Comparative Example 1
An aqueous solution having a sodium silicate concentration of 0.1 mol / L was prepared by dissolving 20.7 g of the same aqueous solution of sodium silicate as in Example 1 in water to make the whole 1 L. 165 ml of this aqueous solution was collected, and 0.016 g of sodium nitrate was added as a supporting electrolyte, and water was added to make the whole into 1.1 L, stirred and dissolved to obtain a 15 mmol / L silicic acid treatment aqueous solution in terms of SiO ₂ . 1 L of this aqueous solution and 5 g of Schwertmannite of Reference Example were weighed into a 2 L four-necked flask, a stirrer, a thermometer, and a Dimroth through which cooling water was passed, and stirred at room temperature for 20 hours. Next, the contents were filtered and solid-liquid separated. This filtrate was used to determine the sorption amount of silicic acid and the desorption amount of sulfuric acid. Next, the solid collected on the filter paper was put into 500 ml of water, stirred and filtered, and the washing step was repeated three times. The obtained solid was vacuum-dried at 50 ° C. to obtain Schwertmannite in which silicic acid was sorbed. The remaining unused aqueous solution for treatment and the filtrate after the treatment are filtered through a membrane filter having a pore size of 0.45 μm, and analyzed by silicon concentration ICP emission analysis in the solution. The silica adsorption amount per 1 g of untreated Schwertomanite used was 1.01 mmol / g as silicon. Further, the concentration of sulfate ion in the filtrate after treatment was analyzed by ion chromatography, and the amount of sulfate ion desorbed from schwertmannite was calculated to be 0.86 mmol / g. Separately, the obtained silicic acid-treated Schwermanite was analyzed by fluorescent X-ray, and the silicic acid sorption amount and the sulfuric acid desorption amount were calculated from the analytical values of silicon and sulfur. The amount of sulfuric acid desorption was 0.81 mmol / g, almost coincident with the analysis value of the treatment liquid. The arsenite ion sorption performance of the obtained silicate-treated schwert mannite was evaluated, and the obtained results are summarized in Table 3. From these results, it was found that the structural stability and high arsenous acid ion sorbability in a moist heat environment were exhibited as compared to the reference example not treated with silicic acid.
Therefore, it can be said that the silicic acid-treated Schwermanite obtained in Comparative Example 1 has high adsorption performance for arsenite ions and can stably maintain the performance even in a wet heat environment. However, it has the disadvantage that the synthesis is complicated and the amount of wastewater generated is large.

FIG. 1 shows the sorption amount of silicic acid obtained from the silicon analysis value of fluorescent X-ray, with the abscissa being the addition ratio of silicic acid with respect to the mole number of Schwartmanite used in the synthesis of each example and comparative example. The results of each Example and Comparative Example are plotted as In this case, in Comparative Example 1, the number of moles of Schwertmannite using a value obtained by dividing the weight of the actually used Schwbertmannite by the formula weight is set to 1/8 of the number of moles of iron nitrate used in the examples. The number of moles of Schwermannite using
In the examples, it was found that the addition ratio of silicic acid and the sorbed amount of silicic acid were plotted on one straight line regardless of the pH adjustment value before the addition of sodium silicate. This indicates that the sorbed amount of silicic acid can be controlled by the addition ratio of silicic acid regardless of pH. In the examples, even if the sulfuric acid was almost completely desorbed, the amount of silicic acid was increased, and as inferred from the powder X-ray analysis and filterability, the method of the example desorbed all the sulfuric acid. However, the silica sorption amount seems to increase due to the formation of silica gel and the sorption of silica to the outside of Schwartmanite.

FIG. 2 shows the addition rate of silicic acid relative to the number of moles of Schwermannite used in the synthesis of each example and comparative example on the horizontal axis, and the desorption amount of sulfate ion obtained from the sulfur analysis value of fluorescent X-rays on the vertical axis. It is a plot.
Unlike the case of FIG. 1, the behavior differs depending on the pH of the slurry before addition of silicic acid. After depositing Schwertmannite, the pH is not adjusted before adding the silicate, that is, in the slurry having a pH of about 2.7, desorption of sulfate ions occurs as compared with other examples in which the pH is increased. It can be understood that the higher the adjusted pH is, the more the sulfate ion is desorbed with the smaller amount of silicic acid added. In FIG. 2, the sulfate ion is more likely to be desorbed in the conventional method of Comparative Example 1 than in the case of pH about 2.7 without adjusting the pH of the slurry. This seems to be because, in the conventional method, Schwbertmannite was once washed and dried, so that acidic components such as nitrate ions were removed, and the pH of the reaction solution was increased compared to Examples 1-4. . Also, it is supported that Example 5 in which the acidic component is removed to some extent by decantation falls in between the conventional method and the example of unadjusted pH. Furthermore, when the pH before addition of silicic acid is 4, sulfate ions are more likely to be desorbed than in the conventional method, and at pH 5, 6 and 8, it is clearly easier to desorb than the conventional method. At pH 8, the addition of sodium silicate in a molar amount close to that of Schwermannite desorbs almost the entire amount of sulfate ions, so that it is preferred that silicate ions be taken into the interior of Schwertmannite by ion exchange. Conceivable. As the pH decreases, the desorption of sulfate ions is less likely to occur, but as mentioned above, the sorption of silica does not depend on pH, so as the pH is lowered, ion exchange with sulfate ions is performed. Therefore, it is considered that silicate ions sorbed on the outer side of Schwertmannite increase. For this reason, it is considered effective to set the pH of the slurry high in the sense that the excess silicic acid is reduced to obtain silicified schwert mannite similar to the conventional method.

  1 and 2, the sorption amount of silicic acid is determined by the amount of silicate added to Schwertmannite, while the desorption amount of sulfuric acid depends on the amount of silicate added and the pH before silicate addition. Therefore, the amount of silicic acid sorbed and the amount of sulfuric acid desorbed can be controlled by adjusting the amount of silicate added and the pH before the addition. Furthermore, by setting the pH as high as about 6-8, the proportion of silicic acid sorbed by ion exchange can be increased, and the same silicic acid-treated Schwermannite as in the conventional method can be obtained efficiently. In addition, it can be said that a structure in which silicic acid is sorbed inside and outside of Schwertmannite, which was difficult to synthesize by the conventional method, can be made separately. Further, when the pH is increased, the use efficiency of silicic acid is superior to the conventional method, and the residual amount of silicic acid in the wastewater is extremely reduced.

  FIG. 3 is a powder X-ray diffraction pattern of Schwartermanite obtained in Reference Example. This is a typical schwertmannite diffraction pattern, and when such a pattern was obtained, it was indicated as ◯ in Table 4.

  FIG. 4 is a powder X-ray diffraction pattern of Schwartermanite obtained in Example 1. Although it is a typical Schbertmanite pattern, the peak height around 2θ = 26 ° is slightly larger than that of the reference example. This is thought to be because the diffraction of silica gel formed by sorption of silicic acid on the outside of Schwertmannite overlapped.

  FIG. 5 is a powder X-ray diffraction pattern of Schwertmannite obtained in Example 4. As the amount of silicic acid used increases, the peak height near 2θ = 26 ° is even greater than that of Example 1. From this also, it is considered that diffraction in this vicinity is due to duplication of diffraction of silica gel. When the pH is not adjusted, the pH is low and the silicic acid is easily gelled, so it is considered that the silica gel patterns overlap.

  FIG. 6 is a powder X-ray diffraction pattern of the Schwertmannite obtained in the Reference Example after being left for 7 days under the condition of 50 ° C. and relative humidity of 98%. It can be seen that the diffraction pattern of Schwertmannite disappears and is goethite. In Table 4, when such a pattern was obtained, it was set as x in Table 4.

  FIG. 7 is a powder X-ray diffraction pattern of the Schwertmannite obtained in Example 2 after being left for 7 days at 50 ° C. and a relative humidity of 98%. This is a state in which the deterioration is slightly advanced in a diffraction pattern in which Schwermannite and goethite overlap. In Table 4, when such a pattern was obtained, it was set as (triangle | delta).

Evaluation of Silicic Acid Sorption and Sulfate Ion Desorption of Conventional Method For Comparative Example 1, an unused silicic acid treatment solution and a filtrate after silicic acid sorption operation were diluted with ultrapure water, and an ICP emission spectrometer It measured using (Spectro make, ARCOS SOP), and quantified silicon | silicone based on the analytical curve produced with the silicon standard solution. Further, this solution was separately measured by an ion chromatograph (Dionex ICS 3000, manufactured by Thermo Fisher Scientific Co., Ltd.) equipped with a column Dionex IonPac AS 19 manufactured by Thermo Fisher Scientific Co., Ltd. to determine the amount of sulfate ion. From this quantitative result and the elemental content ratio by fluorescent X-ray analysis described below, the results obtained by assuming that the total amount of silicon is silicate ions and the total amount of sulfur are sulfate ions showed close values as described above. .

Evaluation of Silicic Acid Sorption and Sulfate Ion Desorption by X-ray Fluorescence About Schwertmannite obtained in Examples, Reference Examples and Comparative Examples, using a scanning X-ray fluorescence analyzer ZSX Primus II manufactured by Rigaku Corporation The constituent elements were analyzed and quantified by the FP method. Since the quantitative value is a mass ratio, it was divided by the atomic weight to determine the molar ratio. Of these, silicon is present as silicic acid and sulfur as sulfuric acid. In addition, in the chemical formula of Schwertmannite, there is 8 moles of iron in 1 mole of Schwertmannite, so when the iron atom is 8 moles, the silicon is treated with silicic acid by determining the molar ratio of silicon and sulfur. The abundance ratio of sulfuric acid to silicic acid per mole of Schwarternite was determined. Regarding the desorption amount of sulfuric acid, the desorption amount was obtained by subtracting the sulfate ion amount in the silicic acid-treated product based on the amount of sulfate ion contained in the schwertmannite not treated with silicic acid.

Evaluation method (forced deterioration)
1 g of Schwertmannite obtained in Examples, Reference Examples and Comparative Examples was weighed into a wide-mouthed plastic bottle with a capacity of 50 ml, and was placed in a constant temperature and humidity chamber set at 50 ° C. and a relative humidity of 98% without a lid. I left for a while. The sample taken out of the constant temperature and humidity chamber was vacuum dried overnight at 50 ° C., and the powder X-ray diffraction pattern was measured, and the arsenate ion and arsenous acid ion sorption performance were evaluated. In addition, some samples were also evaluated for sorption characteristics of selenite ion, selenite ion, fluoride ion, and dichromate ion.

X-ray powder diffraction (XRD)
The powder X-ray diffraction pattern was measured using an X-ray diffractometer D8 ADVANCE manufactured by Bruker AXS, Inc., using CuKα rays as an X-ray source, and 2θ ranging from 10 to 80 °.

Sorption test Test solutions containing the toxic substances A to E shown in Table 5 were prepared. In a 100 ml polypropylene bottle, 0.1 g of each sorbent sample was weighed, and 50 ml of the test solution was added. Among these, only the sorption test using the test solution B was 0.05 g of each sorbent sample with respect to 50 ml of the test solution. These plastic bottles were set in a shaker equipped with a water bath and shaken at 40 ° C. for 24 hours. After completion of the shaking, the sorbent and the test solution were separated by a membrane filter having a pore size of 0.45 μm, and the harmful substance concentration in the filtrate was measured with ICP-AES (iCAP7600 manufactured by Thermo Fisher Scientific). Fluorine was measured by ion chromatography (column; IonPacTM AS12A (manufactured by DIONEX, φ4 mm × 200 mm). The harmful substance removal rate (%) of each sample was calculated, and the results are shown in Tables 3 and 6. .

Table 1 summarizes the synthesis conditions of each Example and Comparative Example, the filterability after the reaction, and the number of steps required to obtain the product. The amount of silicic acid used was stated as the molar excess of sodium silicate to Schwertmannite, ie the Si / Sch loading ratio. In the examples, 1⁄8 of the used iron nitrate was calculated as the number of moles of Schwertmanite. In the comparative example, since Schwertmannite synthesized in advance was used, the weight was divided by the molecular weight of Schwertmannite to calculate the number of moles, which was used for calculation of the feed ratio. In the examples, when pH was adjusted before silicic acid addition, the pH was described. Although Examples 1-4 did not perform pH adjustment before silicic acid treatment, pH before silicic acid addition was described as about 2.7 at the time of depositing Schwertomanite.
The filterability is ◎ if the filterability is equal to or higher than the reference example, and the one with clearly inferior filterability is △. Although it improved compared with the case of (triangle | delta), when it was inferior to the reference example, it evaluated as (circle).
In addition, according to the conventional method shown in Comparative Example 1, the number of steps required to obtain a product is temporarily performed by washing with water and drying after synthesis of Schwertmannite, but this example is not included in this example. As the number is halved, the amount of wastewater is also reduced, and steps such as cleaning of the reaction container are not required, so that the manufacturing cost can be significantly reduced.

  Table 2 summarizes the results obtained by fluorescent X-ray analysis for the Schwertmannite obtained in each Example and Comparative Example. The two columns on the left are summarized from the weight ratio of the constituent elements in terms of the molar ratio of silicon and sulfur when iron is 8 moles. The two columns on the right summarize the results of calculating the sorption amount of silicic acid and the desorption amount of sulfuric acid compared to the schwertmannite not treated with silicic acid.

  Table 3 shows the results of the arsenic sorption test for the samples obtained in each of the examples and comparative examples, which were left in a constant temperature and humidity chamber by the above-described method, and the samples before being left as they were. It summarized as an ion removal rate.

  Table 4 summarizes the results of the measured powder X-ray diffraction of the samples obtained in each of the examples and the comparative examples, and the samples left in the constant temperature and humidity chamber by the above-described method and the samples before the standing. . Before the standing test in a thermo-hygrostat, all the samples showed a Schbertmanite diffraction pattern. When such a Schwartmanite diffraction pattern was obtained, it was marked as ◯ in the table. On the other hand, when the diffraction pattern after being left in a thermo-hygrostat changed to goethite, it was marked as x. Moreover, it was set as (triangle | delta) when the diffraction pattern of Schwertmannite and goethite overlaps.

  Table 5 is a table summarizing the test solutions used for the sorption test.

表６は、ヒ素以外の有害元素を含むイオンの収着試験結果をまとめた。なお、表６において、初期は湿熱放置前、３０日後は５０℃９８％ＲＨの湿熱環境に３０日間放置した後に測定した値である。

Table 6 summarizes the sorption test results of ions containing harmful elements other than arsenic. In Table 6, the initial value is a value measured before leaving in a wet heat environment before leaving for 30 days after leaving in a wet heat environment of 50 ° C. 98% RH for 30 days.

Claims (7)

  Stabilized schbert characterized by sorbing silicate ions to schwertmannite by adding silicate ions to a dispersion in which schbertmannite is precipitated from an aqueous solution in which iron ions and sulfate ions coexist Method of manufacturing manite.   The method for producing a stabilized schbertmannite according to claim 1, wherein silicate ions are added after adjusting the pH of the dispersion in which schbertmannite is precipitated to 4 to 10.   The method for producing a stabilized Schwermannite according to claim 1 or 2, wherein the silicate ion is added after adjusting the pH of the dispersion in which the Schwertmannite is precipitated to 6-8.   The stabilized ratio according to any one of claims 1 to 3, wherein the molar ratio of iron atoms to silicon atoms in the Schwartmanite sorbed with silicic acid is 8.0: 0.4 to 3.0. Method of Schultermanite.   The stabilized Schwbert according to any one of claims 1 to 4, wherein the molar ratio of iron atoms to sulfur atoms in the Schwertmannite sorbed with silicic acid is 8.0: 0 to 1.3. Method of manufacturing manite.   6. Sorptive removal of anionic harmful substances, characterized in that the stabilized schwertmannite according to any one of claims 1 to 5 is brought into contact with a liquid or solid containing anionic harmful substances. Or a method to insolubilize.   The method for sorption removal or insolubilization of an anionic toxic substance according to claim 6, wherein the anionic toxic substance is an anionic toxic substance containing any element of arsenic, selenium, fluorine, chromium and iodine.

Images