JP2005305265A - Method for removing iodine from salt water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing iodine from salt water to such an extent that regenerated salt can be utilized as a salt starting material for electrolysis in the soda industry when salt is regenerated from salt water including iodine. <P>SOLUTION: In the method for removing iodine from salt water, the oxidation-reduction potential of salt water containing Na, Cl and I is set to be 400 mV or less (SHE), the salt water is brought into contact with anion exchange resin while retaining iodine in the state of iodide ion, thereby the iodide ion in the salt ion is removed by the anion exchange resin. When the method is applied to the salt water generated in a gas treatment system upon gasification reforming of waste under a reductive atmosphere, an Fe removal process, a Zn removal process, a salt water concentration process and a salt crystallization/separation process are provided prior to the ion exchange treatment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for removing iodine from a cleaning liquid containing iodine obtained by cleaning gas generated when heat treating municipal waste and industrial waste containing chlorine and iodine.

  Conventionally, when municipal waste or industrial waste containing chlorine is incinerated, chlorine is mainly reacted with slaked lime, removed in the form of calcium chloride, and landfilled at landfill sites. However, such a disposal method requires a landfill site, and in recent years, it has become very difficult to secure such a disposal site. In addition, in the long term, there is a risk that salts eluted from the landfilled waste by washing out due to rainfall, etc. may cause environmental pollution, and in municipal waste and industrial waste. There is also a problem that these useful resources are not used even though useful metal resources are included.

Therefore, it has been attempted to produce sodium chloride salt from wastewater obtained by incinerating municipal waste and industrial waste and washing exhaust gas.
In the conventional method, a method has been proposed in which chlorine contained in municipal waste or industrial waste is crystallized by incineration in an oxygen-rich atmosphere, hydrogen chloride, neutralization with sodium hydroxide, and so on. .

  In Non-Patent Document 1, the leachate from the final disposal site is subjected to advanced treatment such as electrodialysis and reverse osmosis to desalinate the leachate and regenerate salt (Na salt, Ca salt, etc.) Although it is described that it is obtained, there is a problem that this method is expensive because it performs advanced processing.

  In Patent Document 1, heavy metals in the cleaning wastewater are removed by coagulating sedimentation treatment and adsorption treatment with a chelate resin on the wastewater from the exhaust gas discharged from the incinerator, and the cleaning wastewater after the heavy metals are removed is heated. It is described that sodium chloride is concentrated and recovered by crystallization and then separated, and the separated mother liquor after the crystallization and separation is cooled to recover sodium sulfate by crystallization and separation.

  However, even if the salt is recovered by such a method, conventionally, the recovered salt has not been used in large amounts as an electrolytic raw material salt in the soda industry. This is because the purity of the salt is not sufficient to use a large amount of the salt recovered by heat treating the waste as an electrolytic raw material. In particular, when the iodine ion concentration in the salt is high, the electrolyte membrane is adversely affected, the life of the electrolyte membrane is shortened, and the economic efficiency of electrolysis is deteriorated. Therefore, when using the regenerated salt as an electrolytic raw material salt in the soda industry, it is necessary to prevent iodine ions from being contained in the regenerated salt. Patent Document 1 and Non-Patent Document 1 do not describe iodine.

  And depending on these processes, when the waste containing iodine is processed, iodine is mixed in the sodium chloride salt. In particular, in systems that incinerate with excess oxygen, iodine in waste tends to take the form of iodic acid, and it is difficult to produce sodium chloride salt with reduced iodine in systems that incinerate and wash waste. is there.

On the other hand, various methods have been proposed for removing iodine ions contained in an aqueous alkali metal solution.
For example, in Patent Document 2, in order to purify an alkali metal chloride aqueous solution containing iodine, iodine is oxidized to periodate with active chlorine such as hypochlorite, and then this periodate is converted into a base. It is described that the precipitate is removed in an acidic medium.

    Patent Document 3 describes that in order to purify an alkali metal chloride aqueous solution containing iodine, iodine ions are oxidized to iodine by active chlorine, and the iodine is removed with a basic halogenated anion exchange resin. ing.

  Patent Document 4 describes a method for purifying an aqueous sodium chloride solution containing iodine, in which iodine in a sodium chloride solution is oxidized into molecular iodine and adsorbed and removed by a pre-oxidized activated carbon bed. Has been.

JP-A-57-119897 Japanese Patent Publication No. 6-88777 JP-A-7-237919 Japanese Patent Publication No. 7-91666

  An object of the present invention is to provide a method for removing iodine from salt water to the extent that the regenerated salt can be used as an electrolytic raw material salt in the soda industry when salt is regenerated from salt water containing iodine.

As a result of intensive studies on the method for achieving the above object, the present inventors heat treated waste containing chlorine and iodine in a state where oxygen is insufficient, and brought the reducing atmosphere gas into contact with an aqueous solution and neutralized with sodium chloride. When salt water is used, it is found that iodine is obtained in the form of iodine ions instead of iodic acid, and by removing the iodine ions, a salt suitable as an electrolytic raw material having a low iodine content is recovered. Completed the method.
That is, the present invention has a configuration as described below.

(1) A method for removing iodine from salt water containing Na, Cl and I, wherein iodine in the salt water is removed with an ion exchange resin so that the redox potential of the salt water is 400 mV (SHE) or less. A method for removing iodine from salt water.
(2) A method for removing iodine from salt water containing Na, Cl, Fe, I, wherein the salt water is once oxidized, and then the redox potential of the salt water is 400 mV (SHE) or less. A method for removing iodine from salt water, wherein iodine in the salt water is removed by an ion exchange resin.
(3) The salt water is gasified and reformed in a reducing atmosphere of waste, melted and gasified and reformed in a reducing atmosphere of waste, or in a reducing atmosphere of incinerated ash of waste. The method for removing iodine from salt water according to the above (1) or (2), wherein the salt water is generated in a gas treatment system in a melt treatment.

(4) The salt water is subjected to gasification reforming treatment in a reducing atmosphere of waste, melt gasification reforming treatment in a reducing atmosphere of waste, or in a reducing atmosphere of incineration ash of waste. A salt water generated in a step of producing a salt from a salt water containing Na, Ca, Fe, Zn, Cl, and I generated in a gas treatment system in a melt treatment, and the step of producing the salt includes at least Fe removal Process, Zn removal process, salt water concentration process, salt crystallization process, separation process, Fe and Zn are removed by Fe removal process and Zn removal process before making salt water into salt slurry in salt crystallization The method for removing iodine from salt water according to (3) above, wherein iodine ions are removed by ion exchange from a solution obtained by redissolving the solid salt separated in the separation step.
(5) From a part or all of the separation liquid after separating the solid salt in the separation step, iodine ions in the separation liquid are removed by an ion exchange resin, and the separation liquid from which the iodine ions have been separated is subjected to a salt crystallization step. Alternatively, the method for removing iodine from salt water according to (4) above, wherein the process is returned to the step before salt crystallization.
(6) The above (4), wherein the step of removing iodine ions by ion exchange from a solution obtained by re-dissolving the solid salt separated in the separation step at another site (5) A method for removing iodine from salt water.
(7) The above (1), wherein the Fe removal step is a step of oxidizing Fe of divalent iron in the brine to trivalent iron by an oxidizing agent to remove Fe as ferric hydroxide. The iodine removal method from the salt water of (6).
(8) The method for removing iodine from salt water according to the above (1) to (7), wherein the ion exchange resin is a strongly basic anion exchange resin.

The object of treatment of the method of the present invention is salt water containing sodium (Na), chlorine (Cl), and iodine (I).
Examples of such salt water include cleaning water obtained by cleaning a gas discharged in a processing step as described below.
(1) Process of gasifying and reforming waste in a reducing atmosphere (2) Process of melting and gasifying and reforming waste in a reducing atmosphere (3) Incineration obtained by incineration of waste Melting process of ash in reducing atmosphere

  In the method for removing iodine from the salt water of the present invention, the redox potential of the salt water is set to 400 mV (SHE) or less, more preferably 300 mV (SHE) or less, so that iodine in the salt water is in the form of iodine ions. Is treated with an ion exchange resin to remove iodine ions.

  The present invention is applied to the gas reforming incineration facility of (1) above, in which municipal waste and industrial waste are heat-treated in a reducing atmosphere to recover fuel gas mainly composed of hydrogen and carbon monoxide. This will be described below as an example.

As an incineration facility using a gas reforming method, for example, there is a waste gasification melting process based on a Kawatetsu thermoselect method having a process flow as shown in FIG.
For example, the process flow shown in Fig. 1 is a gas reforming incineration facility that heats municipal waste and industrial waste under reducing conditions and recovers fuel gas mainly composed of hydrogen and carbon monoxide. There is a waste gasification and melting process by the Kawatetsu Thermo Select method.
The gasification reforming method shown in FIG. 1 includes the following processes.

1. Press / degas channel (1) Waste compression, (2) Drying and pyrolysis 2. High-temperature reactor / homogenization furnace (3) Gasification and melting, (4) Slag homogenization, (5) Gas reforming Gas purification (6) Gas quenching (quenching, acid cleaning, acid cleaning), (7) Gas purification (alkali cleaning, desulfurization, dehumidification)
4). Water treatment (8) Water treatment (precipitation, desalination, etc.)

This method will be described along the flow as follows.
Wastes such as municipal waste containing chlorine and iodine accumulated in the pits are compressed by a press machine, then heated and distilled by indirect heating in a dry pyrolysis step, and sent to a high temperature reactor. A burner is disposed at the lower part of the high-temperature reactor, and fuel gas and oxygen are introduced into the furnace by the burner, and the oxygen gas gasifies carbon in the dry distillate to produce carbon monoxide and carbon dioxide. In addition, when high-temperature steam is present, a water gasification reaction occurs between carbon and steam to generate carbon monoxide and hydrogen. Further, the organic compound is thermally decomposed to generate carbon monoxide and hydrogen.
As a result of the above reaction, the crude synthesis gas is discharged from the top of the high temperature reactor.

  On the other hand, the melt produced in the lower part of the high temperature reactor flows out from the high temperature reactor to the homogenization furnace. This melt contains carbon, trace amounts of heavy metals, and the like, and carbon is gasified with sufficient oxygen and water vapor in a homogenization furnace to generate carbon dioxide, carbon monoxide, and hydrogen. In the homogenization furnace, the metal melt has a large specific gravity and therefore accumulates in the lower part of the slag. The melt flows down to the granulation system and is cooled and solidified, and the metal-slag mixture is separated into metal and slag by magnetic separation.

The crude synthesis gas discharged from the high temperature reactor is rapidly cooled from about 1200 ° C. to about 70 ° C. by injecting acidic water with a quenching device to prevent the formation of dioxins. At this time, the gas is washed with acidic water, and heavy metal components such as Zn and Pb and chlorine contained in the crude synthesis gas are dissolved in the washing liquid.
The acid-cleaned synthesis gas is further acid-washed if necessary, and then alkali-washed, and the remaining acidic gas such as hydrogen chloride gas is neutralized and removed. Next, hydrogen sulfide in the gas is converted into sulfur by a desulfurization washing apparatus and discharged as a sulfur cake. Next, the synthesis gas is used as a refined fuel gas after moisture is removed in a low temperature dehumidification process.

On the other hand, the wash water collects metal components such as iron and zinc in the waste water treatment apparatus, but the present invention is characterized by a configuration for obtaining salt water not containing iodine from the wash water as described above.
In a system that recovers fuel gas mainly composed of hydrogen and carbon monoxide by heat-treating waste containing chlorine and iodine as described above (reducing atmosphere) under oxygen-deficient conditions, When sulfur is contained, it is converted to hydrogen sulfide, but hardly absorbs hydrogen sulfide as long as it is washed with a relatively acidic solution. Further, iodine is not excessively oxidized and is recovered in the absorbed solution in the form of iodine ions together with chlorine ions, not in the form of iodic acid.
FIG. 2 is a flowchart showing the processing steps of the cleaning liquid.

  Washing water generated in the rapid cooling / acid washing step is added with an oxidizing agent such as hydrogen peroxide in the iron removing step, and then an alkaline agent such as NaOH is added to adjust the pH to 4 to 7, thereby oxidizing the iron ions. The resulting precipitate is separated into a solid and a liquid, and iron hydroxide is separated and recovered as a solid. This iron hydroxide can be recycled to the high-temperature reaction tower and recovered and reused as metal and slag.

In the above, the reason for adding the oxidizing agent is as follows. In other words, when the waste is heat treated by reduction, the iron content in the cleaning liquid is ferrous ions (Fe ²⁺ ). If it is left as it is, it cannot be separated by precipitation unless it is alkaline, and the iron content can be selectively separated. However, when oxidized with hydrogen peroxide or the like, ferrous ions (Fe ²⁺ ) become ferric ions (Fe ³⁺ ), which can be removed by precipitation at an acidic pH 5 level. This is because the zinc concentration of the metal hydroxide can be increased by precipitating and collecting zinc ions (Zn ⁻ ) as metal hydroxide with sodium hydroxide.

Further, when oxidizing ferrous ions to ferric ions with an oxidizing agent such as hydrogen peroxide, the oxidation-reduction potential of the solution is measured so as not to add an excessive oxidizing agent.
This is to prevent iodine ions from being oxidized and converted to iodate ions,
For this reason, the oxidation-reduction potential of the solution is controlled to be 0 mV to 400 mV, more preferably 100 mV to 300 mV.

  In addition, when the salt water is alkaline, iodine ions are likely to be converted to iodate ions. Therefore, even when treatment is performed in an alkaline region, the oxidation-reduction potential is measured, and the oxidizing agent is excessive. It is preferable to manage the oxidation-reduction potential so that it becomes 400 mV or less, more preferably 300 mV or less.

  The step of separating iron hydroxide is performed to improve the purity of zinc and lead. However, when obtaining a refining raw material for reducing Yamamoto containing zinc and lead in a form containing iron. This step can be omitted.

Next, the separated water from which the iron hydroxide obtained from the iron content removing step is separated is subjected to the treatment by adding an alkaline agent such as NaOH in the zinc content removing step to raise the pH of the water to be treated to about 8-12. Zinc ions in the treated water are selectively precipitated as zinc hydroxide, and the resulting precipitate is subjected to solid-liquid separation to recover a solid content containing zinc hydroxide.
When ammonia is mixed, since the heavy metal forms an ammonia complex, it is preferable to perform the above treatment after removing ammonia. In order to further remove the remaining heavy metal, it is preferable to treat the separation liquid using an ion exchange resin for heavy metal.

The separated water obtained from the zinc content removal step precipitates and separates the Ca content as calcium carbonate by blowing carbon dioxide in the Ca content removal step.
The separated water from which the Ca content has been removed is evaporated and concentrated using an evaporator in the salt production process to crystallize a salt mainly composed of sodium chloride, and then separated into a solid salt and a separated liquid in the separation process.
The separation liquid is returned to the salt crystallization step or the previous step by removing iodine ions with an ion exchange resin. This is to prevent the iodine ion concentration in the crystallization mother liquor from increasing, but this step is performed as necessary.

Next, the solid salt obtained in the separation step is dissolved in water, brought into contact with the ion exchange resin, and iodine ions are ion-exchanged on the ion exchange resin to be removed from the salt water.
However, when iodine ions are removed with an ion exchange resin, it is preferable to remove the water by reverse osmosis membrane, electrodialysis, or evaporation to increase the salt concentration and then treat with the ion exchange resin.

Sodium chloride salt can be recovered by crystallization from a sodium chloride solution from which iodine ions have been removed, and can be used as an electrolytic raw material.
In order to use a salt as an industrial raw material, it is preferable to remove impurities as much as possible. Where salt is used, for example, when it is used as a raw material for electrolysis, also in the purification of salt water used as a raw material for electrolysis, impurities are generally removed after dissolving rock salt, solar salt, etc. in water to form salt water. . If the salt is rich in impurities, not only will this process be difficult, but waste will be generated.

  Therefore, as described above, the salt production process comprises at least an iron content removal process, a zinc content removal process, and a salt water concentration / crystallization / separation process, whereby salt water is made into a salt slurry in the salt crystallization / separation process. It is preferable to previously remove Fe and Zn in the iron removal step and the zinc removal step.

  On the other hand, by removing impurities before salt production in waste treatment, the separated and recovered zinc, etc., is reduced to the slag, metal, or metal hydroxide as zinc raw material, etc. It is preferable for social construction.

  The iodine removal step is preferably performed at a site different from the salt production step. In other words, the iodine removal process is performed at another site for the salt water discharged from the salt water concentration / crystallization / separation process, thereby facilitating its control and management and further reducing the amount of iodine in the salt water. Can do. In addition, there is a facility that can be shared by adding an iodine removal process site to the electrolysis facility. Moreover, since salt water from a plurality of salt production sites can be collected and processed, there is a merit of scale.

  The ion exchange resin applied to the present invention is a basic resin comprising a fixed cation portion and an anion portion capable of ion exchange with a halogen anion. The immobilized cation moiety is a quaternary ammonium salt bonded to a copolymer of styrene and divinylbenzene, and the anion portion that can be ion-exchanged with a halogen anion is usually available as a chloride ion. As this type of resin, commercially available general-purpose strong basic ion exchange resins and weak basic ion exchange resins can be used. More preferably, it is a strongly basic ion exchange resin, and the quaternary ammonium salt moiety has a general-purpose structure such as trimethylammonium salt or dimethylhydroxyethylammonium salt.

  Further, either a gel type or a macroporous type classified according to the surface condition may be used. For example, Diaion (registered trademark) SA10 series, SA20 series, PA300 series, PA400 series, and Diaion (registered trademark) NSA100 manufactured by Mitsubishi Chemical Corporation can be used. The apparatus type can be either a fluidized bed or a fixed bed, and can be batch processing or continuous. As these methods, known methods can be arbitrarily applied.

[Examples 1 and 2]
The municipal waste containing chlorine and a small amount of iodine was gasified and reformed, and the gas mainly composed of hydrogen and carbon monoxide was washed with acid. Iodine was present in the form of iodine ions. The washing solution was converted to ferric ions with hydrogen peroxide, adjusted to pH 5 with sodium hydroxide, and the iron content was removed as ferric hydroxide. The redox potential of the solution was 190 mV. Further, heavy metals were removed at pH 9 level, and calcium ions were removed as calcium carbonate with carbon dioxide at pH 10 level. The redox potential of the liquid was 210 mV. Further, concentration and crystallization gave a 95% sodium chloride salt. The form of iodine in the salt was iodine ion alone, and its concentration was 14 mg-I / kg. The salt was dissolved in water to obtain salt water having a predetermined sodium chloride concentration. 10g of Mitsubishi Chemical basic ion exchange resin PA318 was added to 100g of this liquid, and it stirred at 20 degreeC for 3 hours. Thereafter, salt water was sampled, and iodine ions were analyzed by ion chromatography. In the case of analyzing iodic acid, as a pretreatment, it was reduced with sodium sulfite under sulfuric acid acidity, and the total iodine ion was obtained by subtracting the original iodine concentration. As a result, the iodine concentration in the salt water was as shown in Table 1.

[Example 3]
The municipal waste containing chlorine and a small amount of iodine was gasified and reformed, and the gas mainly composed of hydrogen and carbon monoxide was washed with acid. Iodine was present in the form of iodine ions. The cleaning solution was converted to ferric ions with hydrogen peroxide and adjusted to pH 5 level with sodium hydroxide, and iron was removed as ferric hydroxide. The redox potential of the solution was 190 mV. Further, heavy metals were removed at pH 9 level, and calcium ions were removed as calcium carbonate with carbon dioxide at pH 10 level. The oxidation-reduction potential of the liquid was 190 mV. The iodine contained in the liquid was present in the form of iodine ions. Further, after concentration, crystallization was performed to obtain a salt containing 95% sodium chloride. The separation liquid in the crystallization process was blown, iodine ions were removed with an ion exchange resin, and the iodine ion concentration in the crystallization mother liquid was adjusted so as not to increase. The iodine concentration in the salt was 0.5 mg-I / kg. The form of iodine was iodine ion. The salt was dissolved in water to obtain a salt water having a sodium chloride concentration of 25% by weight. The iodine ion concentration in the liquid was 0.13 ppm. 10g of Mitsubishi Chemical basic ion exchange resin PA318 was added to 100g of this liquid, and it stirred at 20 degreeC for 3 hours. Thereafter, salt water was sampled, and iodine ions were analyzed by ion chromatography. In the case of analyzing iodic acid, as a pretreatment, it was reduced with sodium sulfite under sulfuric acid acidity, and the total iodine ion was obtained by subtracting the original iodine concentration. As a result, the iodine concentration in the salt water was as shown in Table 2.

  According to the present invention, a regenerated salt containing no iodine can be produced from salt water discharged from a waste treatment process, and this regenerated salt can be effectively used as an electrolytic raw material salt in the soda industry.

It is a figure which shows an example of the process flowchart in the case of processing a waste material by a gasification reforming system. It is a figure which shows each process for enforcing the method of removing an iodine from the salt water of this invention.

Claims (8)

  A method for removing iodine from salt water containing Na, Cl, and I, wherein iodine in the salt water is removed with an ion exchange resin so that the redox potential of the salt water is 400 mV (SHE) or less. A method for removing iodine from salt water.   A method for removing iodine from salt water containing Na, Cl, Fe, I, wherein the salt water is once oxidized, and then the salt water has a redox potential of 400 mV (SHE) or less. A method for removing iodine from salt water, characterized in that the iodine is removed with an ion exchange resin.   In the gasification reforming treatment in the reducing atmosphere of waste, the melt gasification reforming treatment in the reducing atmosphere of waste or the melting treatment in the reducing atmosphere of the incinerated ash of waste The method for removing iodine from salt water according to claim 1, wherein the salt water is generated in a gas treatment system.   In the gasification reforming treatment in the reducing atmosphere of waste, the melt gasification reforming treatment in the reducing atmosphere of waste or the melting treatment in the reducing atmosphere of the incinerated ash of waste Salt water generated in a step of producing a salt from salt water containing Na, Ca, Fe, Zn, Cl, and I generated in a gas treatment system, and the step of producing the salt includes at least an Fe removal step, Zn It includes a removal process, a salt water concentration process, a salt crystallization process, and a separation process, and Fe and Zn are removed by the Fe removal process and the Zn removal process before salt water is made into a salt slurry by the salt crystallization, and the separation. 4. The method for removing iodine from salt water according to claim 3, wherein iodine ions are removed by ion exchange from a solution obtained by redissolving the solid salt separated in the step.   From a part or all of the separation liquid after separating the solid salt in the separation step, iodine ions in the separation liquid are removed by an ion exchange resin, and the separation liquid from which the iodine ions have been separated is converted into a salt crystallization step or a salt crystal. The method for removing iodine from salt water according to claim 4, wherein the process is returned to the step before the analysis.   The method for removing iodine from salt water according to claim 4, wherein the step of removing iodine ions by ion exchange from a solution obtained by re-dissolving the solid salt separated in the separation step in water is performed at another site.   The Fe removal step is a step of oxidizing Fe of divalent iron in the brine to trivalent iron by an oxidizing agent to remove Fe as ferric hydroxide. A method for removing iodine from salt water.   The said ion exchange resin is a strongly basic anion exchange resin, The iodine removal method from the salt water in any one of Claims 1-7 characterized by the above-mentioned.

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