JP2016056031A - Method for producing greigite by solid-gas reaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means to safely and quickly produce Greigite.SOLUTION: This invention relates to a method for producing Greigite that comprises a Greigite formation step of forming Greigite by the solid-gas reaction between hydrogen sulfide and iron raw material in an enclosed reaction system.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing Greigite by a solid-gas reaction.

Greigite is a compound that is also referred to as Greigite or Greigite (common name by mispronunciation Japanese name). Greigite is a mixed-valence iron sulfide represented by the composition formula of Fe (III) ₂ Fe (II) S ₄ and has ferrimagnetism. Greigite has a [4Fe4S] cluster-like structure that is essential for life, as shown in (FeS ₂ ) ₂ (Fe ₄ S ₄ ). For this reason, Greigite is recognized as one of the minerals deeply involved in the chemical evolution of Earth life (Non-patent Documents 1 and 2). The [4Fe4S] cluster is not only used as an electron transfer component, but also as an enzyme active center (Non-Patent Document 3), or a translation control factor (Non-Patent Document 4), a transcriptional control factor (Non-Patent Document 5), or a radical utilization It plays an important function as a component of proteins (Non-Patent Documents 6 and 7).

  Greigite has ferrimagnetism. For this reason, Greigite generates heat by being given a magnetic field change. Because of these characteristics, Greigite is delivered to cancer in the body by being administered to cancer patients, and is used as a heat source for hyperthermia (thermotherapy), which kills cancer cells by heat induced by magnetic field changes. Promising (Non-Patent Document 8).

  Currently, iron used as an active ingredient in iron agents and iron supplements is soluble. For this reason, the danger of generating active oxygen is pointed out when an iron agent and an iron supplement are ingested excessively. On the other hand, Greigite is hardly soluble because it has a crystal structure, and it is difficult to generate active oxygen. Greigite is also known as a component of Indian black salt used in Ayurvedic therapy, one of the alternative medicines, and is expected to have medicinal properties.

  Greigite is expected to be applied to various uses as described above. Therefore, if a mass production method of Greigite is developed, Greigite may become useful as an active ingredient of pharmaceuticals, supplements or foods in the future.

  Various chemical synthesis methods are known as a production method of Greigite (Non-Patent Documents 9 to 13). For example, Non-Patent Document 9 describes a method of reacting a divalent iron salt and hydrogen sulfide in a solution of 100 ° C. or lower. Non-Patent Document 10 describes a method of reacting a divalent iron salt and a polysulfide in a solution of 100 ° C. or lower. Non-Patent Document 11 describes a method of synthesizing Greigite by reacting iron vapor and zinc sulfide at a temperature of 250 ° C. or higher using a high-temperature vacuum apparatus.

  A biological synthesis method is also known as a production method of Greigite. For example, Non-Patent Document 14 describes a method based on intracellular synthesis using magnetotactic bacteria, and Non-Patent Document 15 describes a method based on extracellular synthesis using sulfate-reducing bacteria.

Wachtershauser G (2006) From volcanic origins of chemoautotrophic life to Bacteria, Archaea and Eukarya. Phil Trans R Soc B 361: 1787-1808 Russell MJ, Martin W (2004) The rocky roots of the acetyl-CoA pathway.Trends Biochem Sci 29: 358-363 Lazazzera BA, Beinert H, Khoroshilova N, Kennedy MC, Kiley PJ (1996) DNA binding and dimerization of the Fe-S-containing FNR protein from Escherichia coli are regulated by oxygen.J Biol Chem 271: 2762-2768 Rouault T, Haile D, Downey W, Philpott C, Tang C, Samaniego F, Chin J, Paul I, Orloff D, Harford J, Klausner R (1992) An iron-sulfur cluster plays a novel regulatory role in the iron-responsive element binding protein. Biometals 5: 131-140 Spiro S, Guest JR (1990) FNR and its role in oxygen-regulated gene expression in Escherichia coli.FEMS Microbiol Lett 75: 399-428 Staples CR, Ameyibor E, Fu W, Gardet-Salvi L, Stritt-Etter AL, Schurmann P, Knaff DB, Johnson MK (1996) The function and properties of the iron-sulfur center in spinach ferredoxin: thioredoxin reductase: a new biological role for iron-sulfur clusters. Biochemistry 35: 11425-11434 Kamat SS, Williams HJ, Dangott LJ, Chakrabarti M, Raushel FM (2013) The catalytic mechanism for aerobic formation of methane by bacteria.Nature 497: 132-136 Chang Y-S, Savitha S, Sadhasivam S, Hsu C-K, Lin F-H (2011) Fabrication, characterization, and application of greigite nanoparticles for cancer hyperthermia.J Colloid Interface Sci 363: 314-319 Berner R (1964) Iron sulfides formed from aqueous solution at low temperatures and atmospheric pressure.J Geol 72: 293-306 Wada H (1977) The synthesis of greigite from a polysulfide solution at about 100 ℃. Bull Chem Soc Japan 50: 2615-2617 Bauer E, Man KL, Pavlovska A, Locatelli A, Mentes TO, Nino MA, Altman MS (2014) Fe3S4 (greigite) formation by vapor-solid reaction. J Mater Chem A 2: 1903-1913 Rickard D, Luther GW (2007) Chemistry of iron sulfides. Chem Rev 107: 514-562 Hunger S, Benning L (2007) Greigite: a true intermediate on the polysulfide pathway to pyrite.Geochem Trans 8: 1 Lefevre CT, Menguy N, Abreu F, Lins U, Posfai Mtl, Prozorov T, Pignol D, Frankel RB, Bazylinski DA (2011) A cultured greigite-producing magnetotactic bacterium in a novel group of sulfate-reducing bacteria. Science 334: 1720 -1723 Gramp JP, Bigham JM, Jones FS, Tuovinen OH (2010) Formation of Fe-sulfides in cultures of sulfate-reducing bacteria. J Hazard Mater 175: 1062-1067

  There were several problems with the prior art Greigite manufacturing method. For example, in the methods described in Non-Patent Documents 10 to 13, since reduced iron (divalent iron) is usually used to obtain Greigite, it takes 15 hours to several days. In the method described in Non-Patent Document 9, Greigite was obtained in a relatively short time of about 15 minutes, but in this method, highly toxic hydrogen sulfide gas is used. For this reason, the method described in Non-Patent Document 9 requires strict safety management.

In the prior art Greigite production method using polysulfide or hydrogen sulfide as a sulfur raw material, Mackinawite (Mackinawite, Fe (II) S), Greigite, and Pyrite (Pyrite, Fe (II) S ₂ ) as the reaction proceeds. ) Are sequentially formed (Non-Patent Documents 12 and 13). In the reaction, Greigite is converted to Pyrite before the entire amount of Mackinawite is converted to Greigite (Non-patent Document 13). For this reason, it is difficult to obtain only Greigite by the prior art Greigite manufacturing method in which Greigite is formed via Mackinawite. In addition, there is no known means for efficiently purifying and isolating the obtained Greigite from a reaction mixture containing Pyrite or the like.

  In addition, in the case of a production method of Greigite by a biological synthesis method, the reaction rate of the Greigite production reaction depends on the growth rate of the bacteria used, and therefore requires a long time of 2 weeks or more (Non-Patent Document 14 and 15).

  In view of the above problems, an object of the present invention is to provide means for manufacturing Greigite safely and quickly.

  As a result of various studies on means for solving the above problems, the present inventors have found that Greigite can be synthesized by solid-gas reaction between hydrogen sulfide and an iron raw material in a sealed reaction system. Based on the above findings, the present inventors have completed the present invention.

That is, the gist of the present invention is as follows.
(1) A method for producing Greigite, which includes a Greigite forming step of forming Greigite by solid-gas reaction between hydrogen sulfide and an iron raw material in a sealed reaction system.
(2) The method according to (1), wherein the iron raw material contains iron oxide.
(3) The method according to (2), wherein the iron oxide is at least one iron oxide selected from the group consisting of Hematite, amorphous FeO (OH), Goethite, Lepidocrocite, and Magnetite.
(4) The method according to (3), wherein the iron oxide is at least one iron oxide selected from the group consisting of Hematite and amorphous FeO (OH).
(5) The method according to any one of (1) to (4), further comprising a hydrogen sulfide forming step of reacting a sulfide with an acid in a sealed reaction system to form hydrogen sulfide.
(6) The method according to (5), wherein the sulfide is one or more alkali metal sulfides selected from the group consisting of sodium sulfide and potassium sulfide.
(7) The method according to (5) or (6), wherein the acid is one or more acids selected from the group consisting of sulfuric acid, hydrochloric acid, acetic acid, formic acid, nitric acid, and hydrobromic acid.
(8) The method according to (7), wherein the acid is sulfuric acid.

  According to the present invention, it is possible to provide a means for producing Greigite safely and rapidly.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

FIG. 1 is a photograph showing an outline of a solid-gas reaction in a gas phase in Example 1. FIG. 2 is a photograph showing an outline of the induction heating test of Greigite produced by the method of the present invention. FIG. 3 is an X-ray diffraction (XRD) spectrum of the product of Example 1. (A): Product after reaction for 15 minutes; (b): Product after reaction for 30 minutes; (c): Product after reaction for 1 hour. In the figure, the black square (■) indicates the peak attributed to Hematite, the black inverted triangle (▼) indicates the peak attributed to Greigite, and the black circle (●) indicates the peak attributed to Pyrite. Show. FIG. 4 is an X-ray diffraction (XRD) spectrum of the product of Example 2. In the figure, the black square (■) indicates the peak attributed to Hematite, the black inverted triangle (▼) indicates the peak attributed to Greigite, and the black circle (●) indicates the peak attributed to Pyrite. Show. FIG. 5 is an X-ray diffraction (XRD) spectrum of the product of Example 3. In the figure, open circles (◯) indicate peaks attributed to Mackinawite, and black inverted triangles (▼) indicate peaks attributed to Greigite. FIG. 6 is an X-ray diffraction (XRD) spectrum of the product of Example 4. In the figure, open circles (○) indicate peaks attributed to Mackinawite, black inverted triangles (▼) indicate peaks attributed to Greigite, and black circles (●) indicate peaks attributed to Pyrite. Show. FIG. 7 is an X-ray diffraction (XRD) spectrum of the product of Comparative Example 1. In the figure, open circles (◯) indicate peaks attributed to Mackinawite.

Hereinafter, preferred embodiments of the present invention will be described in detail.
<1: Greigite>
Greigite is a mixed-valence iron sulfide represented by the composition formula of Fe (III) ₂ Fe (II) S ₄ and has ferrimagnetism. Greigite identification includes, but is not limited to, for example, by measuring X-ray diffraction (XRD) and comparing the resulting XRD spectral data with a known database such as the Powder Diffraction File ™. Can be implemented.

  Greigite produced by the method of the present invention may be used as an active ingredient in pharmaceuticals, supplements or foods. The Greigite produced by the method of the present invention is, for example, hyperthermia (thermotherapy) that is delivered to a cancer part in the body by being administered to a cancer patient, and kills cancer cells by heat induced by a magnetic field change. ) May be used as a heat source. The fact that Greigite produced by the method of the present invention can be used as a heat source for thermotherapy can be confirmed, for example, by performing an induction heating test according to the following procedure. Greigite powder is put in water, and an alternating current is passed through a coil arranged to surround it. Thereby, a magnetic field change is formed around the coil, and an eddy current is generated in Greigite by the magnetic field change. Since the temperature of the water around Greigite rises due to the generated eddy current, the temperature change (temperature rise) of this water is measured.

<2: Greigite manufacturing method>
The present invention relates to a method for producing Greigite. The method of the present invention needs to include a Greigite forming step. Hereafter, each process of this invention is demonstrated in detail.

[2-1: Greigite formation process]
This step requires a solid-gas reaction between the sulfur raw material and the iron raw material in a sealed reaction system. In the present specification, the “solid-gas reaction” means a reaction that proceeds between a solid and a gas. Through this step, the sulfur raw material and the iron raw material can be subjected to a solid-gas reaction to form Greigite.

  The sulfur raw material used in this step needs to be hydrogen sulfide. Since hydrogen sulfide has a boiling point of -60.7 ° C. at 1 atm, it is a gas at normal temperature and normal pressure. Therefore, by using hydrogen sulfide, a solid-gas reaction can proceed with the iron raw material described below. Thereby, Greigite can be formed rapidly.

  The hydrogen sulfide used in this step may be obtained by purchasing one prepared in advance, or may be prepared each time by carrying out a hydrogen sulfide forming step described below. Either case is included in the embodiment of this step. Hydrogen sulfide is preferably prepared each time by carrying out a hydrogen sulfide forming step. In the case of the present embodiment, after the hydrogen sulfide formation step, the hydrogen sulfide formation step and this step can be continuously performed by performing this step in the same sealed reaction system as the hydrogen sulfide formation step. preferable. Thus, Greigite can be formed more safely by substantially avoiding leakage of highly toxic hydrogen sulfide from the reaction system. Moreover, by filling the sealed reaction system with hydrogen sulfide, the reaction system can be brought into a completely anaerobic condition by reacting oxygen and hydrogen sulfide in the reaction system.

  The iron raw material used in this step is usually in a solid form. The iron raw material is preferably in a powder form, and more preferably in a substantially uniform powder form. By using a solid form iron raw material, a solid-gas reaction can proceed with hydrogen sulfide. Thereby, Greigite can be formed rapidly. Moreover, the purity of Greigite can be improved by using an iron raw material in a substantially uniform powder form.

  The iron raw material used in this step may be obtained by purchasing one prepared in advance, or may be prepared each time by a method known in the technical field. Either case is included in the embodiment of this step. For example, an iron raw material in powder form can be prepared by preparing a desired iron raw material and then drying and pulverizing the obtained product. In the preparation, drying of the iron raw material product is preferably performed under air when the iron raw material is iron oxide and under completely anaerobic conditions when the iron raw material is reduced iron. Moreover, it is preferable to dry the product of the iron raw material at a temperature in the range of 20 ° C. or higher, for example, 20 to 60 ° C., preferably 30 to 50 ° C.

The present inventors have found that by using an iron raw material containing iron oxide, the oxidizing power necessary for the synthesis of Greigite is supplied from the iron raw material, and the Greigite production reaction proceeds rapidly. The reason why the method of the present invention has the above-described characteristics can be explained as follows. Note that the present invention is not limited to the following actions and principles. When Hematite (hematite, α-type iron oxide (III), α-Fe ₂ O ₃ ) is used as the iron oxide, for example, Hematite is reduced by hydrogen sulfide by a solid-gas reaction represented by the following reaction formula (I). As a result, amorphous FeS (amorphous iron sulfide) is formed. The formed amorphous FeS further reacts with the remaining Hematite and hydrogen sulfide by a solid-gas reaction represented by the following reaction formula (II) to form Greigite. The total reaction for forming Greigite from Hematite and hydrogen sulfide together with Reaction Formulas (I) and (II) is shown in the following Reaction Formula (III). The reaction represented by the reaction formula (III) includes, for example, the production of amorphous FeS as a reaction intermediate in this step, the absence of sulfur with oxidation number 0 in the product, the presence of hydrogen in the product, etc. It is supported by confirming. The presence of amorphous FeS in the reaction intermediate is determined, for example, by determination of Fe (II) and sulfide, and XRD measurement, and the absence of sulfur with oxidation number 0 in the product, for example, by measuring XRD. Can be confirmed. The presence of hydrogen can be confirmed, for example, by detection means such as a hydrogen detector usually used in the art.
Fe ₂ O ₃ + 3H ₂ S → 2FeS + H ₂ O + SO ₂ + 2H ₂ (I)
Fe ₂ O ₃ + FeS + 3H ₂ S → Fe ₃ S ₄ + 3H ₂ O (II)
3Fe ₂ O ₃ + 9H ₂ S → 2Fe ₃ S ₄ + 7H ₂ O + SO ₂ + 2H ₂ (III)

The iron raw material preferably contains iron oxide (trivalent iron) or reduced iron (divalent iron), more preferably contains iron oxide, and more preferably consists only of iron oxide. When the iron raw material contains iron oxide, the iron oxide includes Hematite, amorphous FeO (OH) (amorphous iron oxide hydroxide (III)), Goethite (goethite, α-type iron oxide hydroxide (III), α- 1 selected from the group consisting of FeO (OH),), Lepidocrocite (repidocrocite, γ-type iron oxide hydroxide (III), γ-FeO (OH)) and Magnetite (magnetite, magnetite, Fe ₃ O ₄ ) One or more types of iron oxide are preferable, and one or more types of iron oxide selected from the group consisting of Hematite and amorphous FeO (OH) are more preferable. When using an iron raw material containing Hematite, Greigite can be obtained rapidly without substantially forming Mackinawite, as compared with the prior art Greigite manufacturing method via Mackinawite. In addition, it can confirm that Mackinawite is not substantially formed in this process, for example by measuring XRD of a reaction intermediate or a product. When the iron raw material contains reduced iron, the reduced iron is preferably amorphous FeS. The iron raw material may be obtained by purchasing a material prepared in advance, or may be prepared by a method known in the art. Either case is included in the embodiment of this step. The iron raw material containing iron oxide can be used in any of the solid-gas reaction embodiments in the gas phase and in the liquid phase described below. Iron raw materials containing reduced iron can be used in embodiments of solid-gas reactions in the gas phase. By using the iron raw material containing iron oxide, it is possible to supply the oxidizing power necessary for the synthesis of Greigite from the iron raw material. Moreover, it is preferable that an iron raw material does not contain anions other than an oxygen atom substantially. When the iron raw material contains an anion other than an oxygen atom, the target Greigite may not be formed. Therefore, by using iron oxide as described above as an iron raw material, it is possible to synthesize target Greigite by supplying oxidizing power from the iron raw material.

  The ratio of hydrogen sulfide and iron raw material used in this step is preferably in the range of 10: 1 to 1: 1 as the molar ratio of sulfur and iron, and is in the range of 5: 1 to 1.5: 1. It is more preferable that the ratio is in the range of 3: 1 to 1.5: 1. Greigite can be obtained by subjecting hydrogen sulfide and the iron raw material to a solid-gas reaction at the above ratio.

This step needs to be performed in a sealed reaction system. The present inventors have found that Greigite is rapidly formed by causing a solid-gas reaction between hydrogen sulfide and an iron raw material in a sealed reaction system. Hydrogen sulfide used in this step reacts with oxygen in the reaction system. For this reason, when this step is performed in a sealed reaction system, the amount of hydrogen sulfide used is appropriately adjusted even if oxygen molecules (O ₂ ) are present in the reaction system at the start of this step. By doing so, when the formation of Greigite is confirmed, a condition in which oxygen molecules are not substantially present in the reaction system can be achieved. In the present specification, a condition in which oxygen molecules are not substantially present in the reaction system may be referred to as “complete anaerobic condition”. In this step, the gas phase of the reaction system preferably contains one or more inert gases such as nitrogen, helium or argon as a main component, and optionally one kind such as hydrogen or carbon dioxide. You may contain the above other gas as a further component. In this case, the inert gas has a concentration of 50 to 100% by volume, preferably 60 to 100% by volume, more preferably 80 to 100% by volume, as a sum of the inert gas with respect to the entire gas phase of the reaction system. The other gas has a concentration of 0 to 50% by volume, preferably 0 to 40% by volume, more preferably 0 to 20% by volume, as the sum of the other gases with respect to the entire gas phase of the reaction system. By carrying out this step in a sealed reaction system, hydrogen sulfide filled in the sealed reaction system reacts with oxygen in the reaction system, and the reaction system can be brought into a completely anaerobic condition. Thereby, Greigite can be rapidly formed using the oxidizing power of the iron raw material as a driving force for the reaction.

  When this process is carried out continuously after the hydrogen sulfide formation process described below, this process is carried out continuously in the same sealed reaction system as the reaction system used in the hydrogen sulfide formation process. It is preferable to do. In this case, it is preferable that the iron raw material used in this step is charged in advance into the sealed reaction system used in the hydrogen sulfide forming step in the hydrogen sulfide forming step. Thereby, the hydrogen sulfide formation process and the Greigite formation process can be continuously performed without opening the sealed reaction system. Examples of the sealed reaction system used in this step include, but are not limited to, an anaerobic workstation or a serum bottle sealed with a butyl rubber stopper and an aluminum seal. By carrying out this step in the sealed reaction system, hydrogen sulfide filled in the sealed reaction system reacts with oxygen in the reaction system, so that the reaction system can be brought into a completely anaerobic condition. Thereby, solid-gas reaction can be advanced under completely anaerobic conditions. Further, Greigite can be safely formed by substantially avoiding leakage of highly toxic hydrogen sulfide out of the reaction system.

In this step, the iron raw material may be allowed to undergo a solid-gas reaction by being brought into contact with hydrogen sulfide as it is, or may be caused to undergo a solid-gas reaction by being brought into contact with hydrogen sulfide in a state existing in the liquid medium. Good. Either case is included in the embodiment of this step. In the present specification, the former embodiment may be described as “solid-gas reaction in the gas phase”, and the latter embodiment may be described as “solid-gas reaction in the liquid phase”. Examples of the liquid medium include, but are not limited to, water. The liquid medium may optionally contain one or more components that do not participate in the reaction of this step, such as inert salts. In the case of the solid-gas reaction embodiment in the gas phase, the iron raw material may be in a state as it is, that is, in a state where it does not exist in the liquid medium. In embodiments with solid-gas reactions in the gas phase, a liquid medium may optionally be present in the reaction system. For example, when this step is continuously performed after the hydrogen sulfide forming step described below, the reaction medium for the hydrogen sulfide forming step may exist in the reaction system. Even in such a case, as long as the iron raw material is present in the reaction system in a state where it is not substantially in contact with the reaction medium in the hydrogen sulfide formation step, it is included in the embodiment of the solid-gas reaction in the gas phase. In the case of the embodiment, for example, the iron raw material and the reaction medium for the hydrogen sulfide formation step may be separately charged into the reaction system by means such as putting in a container separate from the container having the reaction medium for the hydrogen sulfide formation step. preferable. As a result, the iron raw material can be solid-gas reacted with hydrogen sulfide without substantially contacting the reaction medium in the hydrogen sulfide forming step. In the case of the solid-gas reaction embodiment in the liquid phase, the iron source is present in a substantially undissolved state in the liquid medium. In the present invention, the “state in which the iron raw material is not substantially dissolved in the liquid medium” is, for example, 90 to 100% by mass, preferably 95 to 100% by mass, based on the total mass of the iron raw material used. More preferably, it means that the iron raw material in the range of 98 to 100% by mass does not dissolve in the liquid medium but exists in a solid form (for example, suspended in the liquid medium). In the case of the solid-gas reaction embodiment in the liquid phase, hydrogen sulfide exists in an equilibrium state between gaseous hydrogen sulfide (H ₂ S) and hydrogen sulfide ions (HS ⁻ ) in the liquid medium. Therefore, in the case of the solid-gas reaction embodiment in the liquid phase, the iron raw material that is not substantially dissolved in the liquid medium comes into contact with the hydrogen sulfide dissolved in the liquid medium, and the solid-gas reaction proceeds. To do. For example, when this step is continuously performed after the hydrogen sulfide forming step described below, the iron raw material is substantially dissolved in the reaction medium of the hydrogen sulfide forming step present in the reaction system. It is preferable to put it into the reaction system in advance in the absence of the above. Thereby, after the hydrogen sulfide forming step, the formed hydrogen sulfide and the iron raw material existing in the liquid medium can be immediately solid-gas reacted. When the iron raw material used in this step contains iron oxide, this step may be any solid-gas reaction embodiment in the gas phase and in the liquid phase. When the iron raw material used in this step contains reduced iron, this step is preferably an embodiment of a solid-gas reaction in the gas phase. This step is more preferably an embodiment of a solid-gas reaction in the gas phase. By implementing this step in such an embodiment, Greigite can be obtained more rapidly.

  In this step, conditions for solid-gas reaction between hydrogen sulfide and the iron raw material can be appropriately set by those skilled in the art based on the type and / or amount of the hydrogen sulfide and iron raw material used. For example, the reaction time is preferably 1 minute or more, more preferably in the range of 1 minute to 72 hours, further preferably in the range of 1 minute to 24 hours, and in the range of 1 minute to 5 hours. It is particularly preferred that The reaction temperature is preferably 20 ° C. or higher, more preferably in the range of 20 to 150 ° C., further preferably in the range of 40 to 130 ° C., and particularly preferably in the range of 50 to 90 ° C. preferable. Usually, the higher the concentration of hydrogen sulfide used and / or the higher the reaction temperature, the shorter the reaction time. For example, when the reaction temperature is in the range of 40 to 130 ° C., the reaction time is in the range of 1 minute to 72 hours, preferably in the range of 1 minute to 24 hours, and more preferably in the range of 1 minute to 5 hours. When the reaction temperature is in the range of 50 to 90 ° C., the reaction time is in the range of 1 minute to 24 hours, preferably in the range of 1 minute to 5 hours. When this step is an embodiment of a solid-gas reaction in a liquid phase, the pH of the liquid medium is preferably in the range of 1.0 to 6.1, more preferably in the range of 3.0 to 6.0, and in the range of 5.4 to 5.9. It is particularly preferred that Greigite can be formed in a short time by setting the reaction time and / or reaction temperature to the lower limit value or more. By setting the reaction time and / or the reaction temperature to the upper limit value or less, formation of by-products such as Pyrite can be minimized and Greigite can be obtained. By making the pH less than 6, the equilibrium between hydrogen sulfide and hydrogen sulfide ions can be tilted to hydrogen sulfide (Snoeyink VL, Jenkins D. Water Chemistry. New York ,: John Wiley & Sons, 1980). Thereby, the progress of the solid-gas reaction between the iron raw material and hydrogen sulfide can be promoted. When this step is continuously performed after the hydrogen sulfide formation step described below, the reaction time means the total reaction time from the start of the hydrogen sulfide formation step to the end of the step. To do.

[2-2: Hydrogen sulfide formation process]
The method of the present invention may optionally include a hydrogen sulfide formation step in which sulfide and acid are reacted in a sealed reaction system to form hydrogen sulfide.

  The sealed reaction system used in this step is preferably the same as described above. By carrying out this step using the sealed reaction system, hydrogen sulfide can be formed while substantially avoiding leakage of highly toxic hydrogen sulfide out of the reaction system. Thereby, Greigite can be formed more safely.

  The component constituting the gas phase of the sealed reaction system used in this step is not particularly limited as long as it does not substantially inhibit the reaction between the sulfide and the acid. The component constituting the gas phase of the reaction system may be air, for example. Alternatively, the gas phase of the reaction system may contain the same components as the gas phase of the reaction system in the Greigite forming step described above. By carrying out this step using a sealed reaction system containing the above components, hydrogen sulfide filled in the sealed reaction system reacts with the oxygen in the reaction system to bring the reaction system to a completely anaerobic condition. be able to.

  The sulfide is preferably an alkali metal sulfide, more preferably one or more alkali metal sulfides selected from the group consisting of sodium sulfide and potassium sulfide, and further preferably sodium sulfide. . By carrying out this step using the sulfide, it is possible to substantially avoid leakage of highly toxic hydrogen sulfide out of the reaction system, and hydrogen sulfide can be formed in a sealed reaction system. Thereby, Greigite can be formed more safely.

  The acid is preferably at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid, acetic acid, formic acid, nitric acid and hydrobromic acid, and more preferably sulfuric acid. If the Greigite formation step described above is an embodiment in the gas phase, any of the acids may be used. In the case where the Greigite formation step described above is an embodiment in a liquid phase, if formic acid, nitric acid or hydrobromic acid is present in the liquid phase, an undesirable side reaction may proceed with the iron raw material. . For this reason, when the Greigite forming step is an embodiment in a liquid phase, the acid used is preferably one or more acids selected from the group consisting of sulfuric acid, hydrochloric acid and acetic acid. By carrying out this step using the acid, hydrogen sulfide having high toxicity can be substantially avoided from leaking out of the reaction system, and hydrogen sulfide can be formed in a sealed reaction system. Thereby, Greigite can be formed more safely.

  In this step, it is preferable to react sulfide and acid in a liquid medium. The liquid medium is preferably water. The liquid medium may optionally contain one or more components that do not participate in the reaction of this step, such as inert salts. In the case where both substances are reacted in an aqueous solution containing sulfide and acid, this step is performed, for example, in a sealed reaction system in an aqueous solution containing either sulfide or acid, and the other substance or its This can be done by adding an aqueous solution. It is preferable to carry out by adding an acid or an aqueous solution thereof to an aqueous solution containing sulfide in a sealed reaction system. By carrying out this step in the above-described manner, hydrogen sulfide can be formed safely.

  In this step, conditions for reacting the sulfide with the acid can be appropriately set by those skilled in the art based on the type and / or amount of the sulfide and acid used. For example, the reaction time is preferably 1 minute or more, more preferably in the range of 1 minute to 72 hours, further preferably in the range of 1 minute to 24 hours, and in the range of 1 minute to 5 hours. It is particularly preferred that The reaction temperature is preferably 20 ° C. or higher, more preferably in the range of 20 to 150 ° C., further preferably in the range of 40 to 130 ° C., and particularly preferably in the range of 50 to 90 ° C. preferable. Usually, the greater the amount of sulfide and acid used and / or the higher the reaction temperature, the shorter the reaction time. For example, when the reaction temperature is in the range of 40 to 130 ° C., the reaction time is in the range of 1 minute to 72 hours, preferably in the range of 1 minute to 24 hours, and more preferably in the range of 1 minute to 5 hours. When the reaction temperature is in the range of 50 to 90 ° C., the reaction time is in the range of 1 minute to 24 hours, preferably in the range of 1 minute to 5 hours. When the present step is an embodiment in which a sulfide and an acid are reacted in a liquid medium, the pH of the liquid medium is preferably in the range of 1.0 to 6.1, more preferably in the range of 3.0 to 6.0, A range of 5.4 to 5.9 is particularly preferable. By setting the reaction temperature to the lower limit value or more, hydrogen sulfide can be formed in a short time and the reaction time can be shortened. By making the pH less than 6, the equilibrium between hydrogen sulfide and hydrogen sulfide ions can be tilted to hydrogen sulfide (Snoeyink VL, Jenkins D. Water Chemistry. New York ,: John Wiley & Sons, 1980). Thereby, the amount of hydrogen sulfide used for the reaction in the Greigite formation step can be increased. When the Greigite formation step is continuously performed after this step, the reaction time means the total reaction time from the start point of this step to the end point of the Greigite formation step.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

<I: Preparation of iron raw material>
Hematite (purity ≧ 99.9%, particle size ≦ 0.3 μm; High Purity Chemical Laboratory, Saitama) was dried at 40 ° C. and subjected to the reaction. Amorphous FeO (OH) was prepared by the method described in the literature (Lovley DR, Phillips EJP (1986) Organic matter mineralization with reduction of ferric iron in anaerobic sediments. Appl Environ Microbiol 51: 683-689) and then with distilled water. It was washed 6 times, blown and dried at room temperature, and then ground in a mortar. Amorphous FeS is prepared by the method described in the literature (Brock TD, O'Dea K (1977) Amorphous ferrous sulfide as a reducing agent for culture of anaerobes. Appl Environ Microbiol 33: 254-256) and then anaerobic water (N Washed 6 times with ₂ bubbling), blown and dried in an anaerobic workstation (gas phase, N ₂ : H ₂ : CO ₂ = 80: 10: 10) and ground in a mortar. As for amorphous FeO (OH) and amorphous FeS, non-uniformity was not recognized before drying, but solidification occurred due to drying, and the non-uniformity was visually recognized.

<II: Synthesis of Greigite>
[II-1: Example 1: Solid-gas reaction in gas phase]
A solid-gas reaction in the gas phase was performed using Hematite as an iron raw material. Inside an anaerobic workstation (gas phase, N ₂ : H ₂ : CO ₂ (80:10:10)) into a 68 ml serum bottle, 1 ml of 1 M sodium sulfide (Na ₂ S) aqueous solution (not pH) Adjustment). A small test tube (outer diameter 10 mm, length 50 mm) containing a dry powder of Hematite containing 0.63 mmol of iron (Fe) was placed in the serum bottle. The serum bottle was sealed with a butyl rubber stopper and an aluminum seal, and the gas phase was replaced with argon (Ar). Next, by injecting 0.6 ml of 2 M sulfuric acid into 1 M aqueous sodium sulfide solution using a syringe, the following reaction formula (IV):
Na ₂ S + H ₂ SO ₄ → Na ₂ SO ₄ + H ₂ S (IV)
Based on this, hydrogen sulfide gas was generated in the serum bottle (Fig. 1). By keeping the serum bottle at 80 ° C. for a predetermined time, the hydrogen sulfide gas and the dry powder of Hematite were reacted. After completion of the reaction, the butyl rubber stopper of the serum bottle was opened, and the pH of the reaction solution was measured using a pH test paper. The pH was about 5.6. For comparison, 1 M sodium sulfide aqueous solution and 2 M sulfuric acid were mixed in 6 times the same volume ratio as described above, and the pH was measured with a pH meter to be pH 5.6.

[II-2: Example 2: Solid-gas reaction in liquid phase]
Hematite was used as an iron raw material to carry out a solid-gas reaction in the liquid phase. In Example 1, Greigite was synthesized in the same procedure and conditions as described above except that the dry powder of Hematite was directly suspended in a 1 M aqueous sodium sulfide solution and changed to solid-gas reaction conditions in the liquid phase.

[II-3: Example 3: Solid-gas reaction in liquid phase]
Using amorphous FeO (OH) as an iron raw material, a solid-gas reaction in a liquid phase was performed. As described above, amorphous FeO (OH) became non-uniform due to solidification when dried. For this reason, the sample before drying was used in this reaction. Greigite was synthesized in the same procedure and conditions as described above except that Hematite was changed to amorphous FeO (OH) in Example 2.

[II-4: Example 4: Solid-gas reaction in the gas phase using reduced iron as an iron raw material]
A solid-gas reaction in the gas phase was performed using amorphous FeS, which is reduced iron (divalent iron), as an iron raw material. Greigite was synthesized in the same procedure and conditions as described above except that Hematite was changed to a dry powder of amorphous FeS in Example 1.

[II-5: Example 5: Relationship between reaction time and reaction temperature in solid-gas reaction in the gas phase]
A solid-gas reaction in the gas phase was performed using Hematite (manufactured by Wako Pure Chemical Industries) as an iron raw material. In an anaerobic workstation (gas phase, N ₂ ), 1 ml of 1 M aqueous sodium sulfide solution (pH unadjusted) was placed in a 68 ml serum bottle. A small test tube (outer diameter 10 mm, length 50 mm) containing a dry powder of Hematite containing 0.63 mmol of iron was placed in the serum bottle. The serum bottle was sealed with a butyl rubber stopper and an aluminum seal, and the gas phase was replaced with argon. Next, hydrogen sulfide gas was generated in the serum bottle by dropping 0.6 ml of 2 M sulfuric acid into a 1 M aqueous sodium sulfide solution using a syringe. By keeping the serum bottle at 20, 40, 60, 80 or 130 ° C. for a predetermined time, the hydrogen sulfide gas and the dry powder of Hematite were reacted. After completion of the reaction, the butyl rubber stopper of the serum bottle was opened, and the pH of the reaction solution was measured using a pH test paper. The pH was about 5.6. For comparison, 1 M sodium sulfide aqueous solution and 2 M sulfuric acid were mixed in 6 times the same volume ratio as described above, and the pH was measured with a pH meter to be pH 5.6. After completion of the reaction, a magnet was brought close to the product, and the formation of Greigite was confirmed based on whether the product was attracted to the magnet.

[II-6: Comparative Example 1: Solid-gas reaction in a liquid phase using reduced iron as an iron raw material]
A solid-gas reaction in a liquid phase was performed using amorphous FeS, which is reduced iron (divalent iron), as an iron raw material. As described above, amorphous FeS became non-uniform due to solidification when dried. For this reason, the sample before drying was used in this reaction. In Example 2, the reaction was carried out in the same procedure and conditions as above except that Hematite was changed to amorphous FeS.

<III: Characteristics of Greigite>
[III-1: X-ray crystal structure analysis]
Samples of the products of Examples 1-4 and Comparative Example 1 were placed on a silicon non-reflective holder (SanyuShoko, Tokyo). The dried sample was used as it was, and the sample containing water was used for the measurement while being covered with vacuum grease and a polyimide film (Nilaco, Tokyo) so as not to trap air. A powder X-ray diffractometer (Ultima IV; Rigaku, Tokyo) was operated at an acceleration voltage = 40 kV and a current value = 30 mA. The sample was irradiated with CuK _α- ray, and the intensity of the diffraction line was measured for 2 seconds at each angle in the range of 2θ = 15-60 ° every 0.02 °. The resulting XRD spectra were compared to the Powder Diffraction File ™ database to identify minerals.

[III-2: Induction heating test]
A small test tube used for Greigite synthesis (containing a sample of the products of Examples 1-3 corresponding to 0.63 mmol Greigite) was charged with 0.5 ml of water. The small test tube was placed in the center of a dedicated coil arranged to surround the small test tube (FIG. 2). Using an induction heating device (SPW900 / 56 (900 kHz, 5.6 kW power supply); SA Japan Incorporated), a magnetic field change was formed by applying an alternating current to the coil. Due to this magnetic field change, an eddy current was generated in the sample to generate heat. The water temperature after heat generation was measured using a sheath thermocouple. In each sample, the time until the water temperature reached 46 ° C. (corresponding to the highest temperature used for hyperthermia for cancer treatment) was measured.

<IV: Results>
[IV-1: Synthesis of Greigite]
The reaction rate of a reaction between a solid and a gas (solid-gas reaction) is usually determined by the density (concentration) of gas molecules on the surface of the solid. However, the quantification of hydrogen sulfide gas is generally difficult because the provision and / or use of pure hydrogen sulfide preparations is restricted by law. For this reason, in the present Example, the density | concentration of the produced | generated hydrogen sulfide was computed based on the density | concentration and volume of the used sodium sulfide and sulfuric acid.

  In Example 1, an amount (1 mmol) of hydrogen sulfide that can be generated by 1 ml of 1 M aqueous sodium sulfide solution and 0.6 ml of 2 M sulfuric acid was used. When a solid-gas reaction in the gas phase was carried out for 15 minutes under the above conditions, the produced Grigite and Pyrite were detected in addition to unreacted Hematite, but Mackinawite was not detected (FIG. 3 (a)). . When the reaction time was extended to 30 minutes or 1 hour, Hematite disappeared and Pyrite increased, but Mackinawite was still not detected (FIGS. 3 (b) and (c)). From this result, Greigite synthesis by the method of the present invention is about 30 times faster than Greigite synthesis from divalent iron and polysulfide described in Non-Patent Document 10, for example, and unnecessary reaction like Mackinawite. It has been shown to have the advantageous feature of proceeding without going through an intermediate. Greigite was produced in the same manner as in Example 1 by changing the reaction time even under the reaction conditions of the amount of hydrogen sulfide other than those described in Example 1.

  In the case of Example 2, Hematite was suspended in 1 M sodium sulfide aqueous solution, and a solid-gas reaction was performed in the liquid phase. In the case of a reaction time of 30 minutes, unreacted Hematite, which is an iron raw material, was the main component, and although formation of Greigite was slightly confirmed, Pyrite was not detected (FIG. 4). From the comparison with the results of the same reaction time in the solid-gas reaction in the gas phase (Example 1, Fig. 3 (b)), the solid-gas reaction in the liquid phase is more effective than the solid-gas reaction in the gas phase. It was shown to be very slow. This result strongly suggested that the sulfide molecular species involved in the Greigite synthesis reaction was hydrogen sulfide. In the liquid phase, hydrogen sulfide exists in an equilibrium state between gaseous hydrogen sulfide and hydrogen sulfide ions. In addition, in the vicinity of pH 5.6, which is the pH of the reaction solution of this example, the equilibrium between hydrogen sulfide and hydrogen sulfide ions is greatly inclined to hydrogen sulfide, so that it is known that sulfide mainly exists as hydrogen sulfide. (Snoeyink VL, Jenkins D. Water Chemistry. New York ,: John Wiley & Sons, 1980). For this reason, also in the solid-gas reaction in the liquid phase of Example 2, it is presumed that Greigite was generated as a result of the reaction of hydrogen sulfide dissolved in the solution with Hematite.

  In Example 3, the amorphous iron oxide was blackened when suspended in a 1 M aqueous sodium sulfide solution. This result suggested the formation of iron sulfide. After that, sulfuric acid was added to 1 M sodium sulfide aqueous solution and reacted for 1 hour. As a result, Greigite was produced as the main component and a small amount of Mackinawite was produced as the subcomponent (FIG. 5). The progress of the known Greigite formation reaction via reduced iron (divalent iron) may be expected from the results of blackening (implying iron sulfide formation) and Mackinawite formation. When the above prediction is correct, the reaction rate can be improved by using amorphous FeS as an iron raw material. However, in Example 4, when a solid-gas reaction in a gas phase was performed using amorphous FeS as an iron raw material, a reaction time of 144 hours was required until Greigite was detected (FIG. 6). Mackinawite and Pyrite were also detected. On the other hand, in Comparative Example 1, when the solid-gas reaction in the liquid phase was carried out for 144 hours using amorphous FeS as the iron raw material, only Mackinawite was detected and Greigite was not detected (FIG. 7). The results of Examples 3 and 4 and Comparative Example 1 suggest that Greigite synthesis by the method of the present invention proceeds through a reaction route different from the known Greigite formation reaction via reduced iron (divalent iron). It was. Such consideration is consistent with the finding that oxidation power is required for the progress of the Greigite formation reaction via reduced iron (divalent iron) (Non-patent Document 9). For example, in the case of Example 3, the surface of amorphous FeO (OH) was covered with the formed iron sulfide, but the amorphous FeO (OH) remaining in the lower layer of the iron sulfide coating layer supplied the oxidizing power. It is guessed. From the above results, it was suggested that in the Greigite synthesis by the method of the present invention, it is preferable to use iron oxide having oxidizing power as an iron raw material.

Table 1 shows the relationship between the reaction temperature and reaction time of the hydrogen sulfide formation reaction and the Greigite formation reaction and the amount of Greigite formed in Example 5. In the table, the reaction time represents the total reaction time from the start time of the hydrogen sulfide formation reaction to the end time of the Greigite formation reaction. “-” Means that the product is black but not attracted to the magnet, “+” means that only the top is attracted to the magnet, and “++” means that the whole is weakly attracted to the magnet. "+++" represents the product that is strongly attracted to the magnet as a whole. Since Greigite is a compound having ferrimagnetism, “-” indicates that Greigite was not formed, “+” indicates that formation of Greigite began to be confirmed slightly, and “++” indicates that , “+++” means that the formation of Greigite was clearly confirmed. A blank represents that no experiment was conducted at the corresponding reaction temperature and reaction time.

  As shown in Table 1, when the reaction temperature was in the range of 20 ° C., the formation of Greigite started to be slightly confirmed in 24 hours, and after 64 hours of reaction time, the formation of Greigite was clearly confirmed. On the other hand, when the reaction temperature was raised to 60 ° C., the formation of Greigite started to be confirmed after the reaction time of 0.5 hour, and the formation of Greigite was clearly confirmed after the reaction time of 2 hours. . When the reaction temperature was further increased, the reaction time until Greigite was formed was further shortened.

  In the Greigite synthesis of this example, Hematite and amorphous iron oxide were used as a raw material for iron in a sealed reaction system, and at the same time, used as a supply substance for the oxidizing power necessary for the synthesis. The standard redox potential of Hematite / Fe (II) is -0.287 mV (Kappler A, Straub KL (2005) Geomicrobiological cycling of iron. Rev Mineral Geochem 59: 85-108). As described above, since Hematite is difficult to be reduced, it is presumed that the oxidizing power could be maintained even in the presence of hydrogen sulfide.

  The environment of the known Greigite production reaction via reduced iron (divalent iron) was an anaerobic environment, but was not an enclosed environment (Non-patent Document 9). Under such reaction conditions, trace amounts of oxygen can participate in the Greigite production reaction. For example, in the reaction described in Non-Patent Document 9, the reaction was not performed in a sealed container. For this reason, it is speculated that Greigite could be synthesized by supplying oxidizing power from oxygen in the air by hydrogen sulfide bubbling treatment of divalent iron. However, under such reaction conditions, a constant oxidizing power is not always supplied. For this reason, it is not specially noted as a Greigite production method, and the operation involves a danger due to the toxicity of hydrogen sulfide. In contrast, the Greigite synthesis of Examples 1 to 3 and 5 was carried out in a sealed reaction system using iron oxide having oxidizing power as an iron raw material. For this reason, it is estimated that Greigite could be manufactured safely and quickly.

[IV-2: Induction heating by Greigite]
The induction heating test was performed by suspending the powder of Greigite (reaction time: 30 minutes) prepared in Example 1 and Greigite (reaction time: 1 hour) prepared in Example 3 in 0.5 ml of water. . As a result, the water temperature was increased to 46 ° C. within 1 minute with Greigite prepared by any of the methods of Examples 1 and 3.

Claims (8)

  A method for producing Greigite, comprising a Greigite forming step in which Greigite is formed by a solid-gas reaction between hydrogen sulfide and an iron raw material in a sealed reaction system.   2. The method according to claim 1, wherein the iron raw material contains iron oxide.   3. The method according to claim 2, wherein the iron oxide is one or more iron oxides selected from the group consisting of Hematite, amorphous FeO (OH), Goethite, Lepidocrocite, and Magnetite.   4. The method according to claim 3, wherein the iron oxide is one or more iron oxides selected from the group consisting of Hematite and amorphous FeO (OH).   5. The method according to any one of claims 1 to 4, further comprising a hydrogen sulfide forming step of reacting a sulfide and an acid in a sealed reaction system to form hydrogen sulfide.   6. The method according to claim 5, wherein the sulfide is one or more alkali metal sulfides selected from the group consisting of sodium sulfide and potassium sulfide.   The method according to claim 5 or 6, wherein the acid is one or more acids selected from the group consisting of sulfuric acid, hydrochloric acid, acetic acid, formic acid, nitric acid and hydrobromic acid.   8. The method of claim 7, wherein the acid is sulfuric acid.

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