JP5290918B2 - Process for producing alkali metal chloride and alkali metal hydroxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high-purity alkaline metal chlorides from by-product salts generated when acid components in an exhaust gas from an incinerator for city waste or industrial waste is subjected to a dry neutralization treatment. <P>SOLUTION: Fly ash is separated and removed from an exhaust gas from an incinerator for city waste or industrial waste; thereafter, a sodium carbonate powder is sprayed and produced by-product salts are separated from the exhaust gas; and water or an aqueous solution of an alkaline metal chloride is added to the by-product salts in an amount of water or solution capable of dissolving substantially all amount of at least one water-soluble inorganic salt other than alkaline metal chlorides and not dissolving all the amount of the by-product salts to dissolve substantially all the amount of at least one water-soluble inorganic salt other than alkaline metal chlorides; and an obtained slurry is solid-liquid separated to recover the alkaline metal chlorides as solid components. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a purified alkali metal chloride and alkali metal hydroxide that can be used, for example, as an industrial product from a by-product salt mainly composed of an alkali metal chloride derived from waste incineration. .

  For example, sodium chloride is used as a raw material for producing sodium hydroxide and sodium carbonate, and as a snow melting agent, brine and the like. Sodium hydroxide is used to produce sodium hydroxide by electrolysis using an ion exchange membrane as a diaphragm (hereinafter referred to as IM electrolysis), and electrolysis using mercury as an electrode (hereinafter referred to as mercury). And electrodialysis. Examples of a method for producing sodium carbonate using sodium chloride include an ammonia soda method and an ammonium chloride soda method.

Sodium chloride is required to have few impurities when used as a raw material for producing sodium hydroxide or sodium carbonate.
For example, when producing sodium carbonate by the ammonia soda method, etc., in order to improve the quality of the product and prevent the scale from adhering to the equipment in each step, high purity with a low content of calcium, magnesium, SO ₄ ²⁻ Sodium chloride is required.

Further, in the production of sodium hydroxide by the IM electrolysis method, higher purity sodium chloride is required in order to prevent deterioration of the ion exchange membrane and to maintain the quality of the product sodium hydroxide. Specifically, calcium, magnesium, strontium, aluminum, iron, lead, mercury, copper, nickel, chromium, cobalt, vanadium, tungsten, manganese, zinc, titanium, molybdenum, tin, tantalum, barium, hafnium, silver, cadmium , Other than gallium, bismuth, cerium, lithium, potassium, sulfur (SO ₄ ²⁻ , HSO ₃ ^−, etc.), fluorine, iodine, bromine, boron, phosphorus, selenium, arsenic, silicon (such as silica), or chloride ions Chlorine compounds (ClO ₃ ^— etc.) and sodium chloride with a very low content of organic substances are required.

  Even when sodium chloride aqueous solution is evaporated to obtain sodium chloride crystals, it is necessary to reduce impurities in the sodium chloride aqueous solution in order to affect the quality of sodium chloride and prevent deposits on the evaporator. Similarly to the purification of sodium chloride, it is necessary to increase the purity of potassium chloride, which is a raw material for obtaining potassium carbonate, potassium hydroxide, and the like.

  Conventionally, acidic gases such as hydrogen chloride and sulfur oxides generated during incineration of municipal waste and industrial waste are often removed using calcium hydroxide as a neutralizing agent. However, in this case, it is very difficult industrially to produce calcium hydroxide from the generated calcium chloride and recycle it. In addition to calcium hydroxide, sodium compounds and potassium compounds are also used as neutralizing agents. In particular, sodium compounds are inexpensive and easily available. In particular, hydrogen carbonates and carbonates generally have low deliquescence and are excellent as neutralizing agents. Specific examples include sodium hydroxide, sodium carbonate, sodium sesquicarbonate, and sodium bicarbonate, and these can be used as synthetic products or natural products.

  In this case, the gas treatment produces a by-product salt mainly composed of sodium chloride and mixed with salts such as sodium sulfate, potassium chloride and sodium iodide. By-product salt (mainly sodium chloride) is purified and concentrated and solidified by chelate method, precipitation method that precipitates by sulfide or hydroxide, ultrafiltration method, electrodialysis method, ion exchange membrane method, etc. Impurities include metal sulfate, potassium chloride, iodide, heavy metal, fly ash, activated carbon used for dioxin removal, and the like. Therefore, because it is very difficult to refine and recycle as sodium chloride, the obtained solid by-product salt cannot be reused and is disposed of in landfills. Since the remaining capacity of final disposal sites for goods is decreasing, the disposal method has become a major social problem in recent years.

Therefore, it is preferable to generate an alkaline compound again using such a by-product salt as a raw material and to recycle it.
When removing impurities in by-product salts, conventionally, for example, SO ₄ ²⁻ is removed by adding calcium chloride to solid-liquid separation as calcium sulfate, or adding barium to separate solid-liquid as barium sulfate. The way is done. For removing heavy metals, iodine and the like, a method of increasing the pH in the liquid and precipitating as a hydroxide, a method of removing using an ion exchange resin, and the like are used.

  However, these methods alone cannot remove, for example, potassium chloride and iodine contained in a large amount in the by-product salt from the garbage incineration plant. Therefore, even if it can be used for sodium carbonate production by the ammonia soda method, ammonium chloride It cannot be used for the production of sodium carbonate by the soda method, the production of sodium hydroxide by the mercury method, the production of sodium hydroxide by the IM electrolysis method, or the production of sodium hydroxide by the electrodialysis method.

  In addition, in these manufacturing processes, the waste liquid is returned to the raw material and circulated, except for the removal of the product. Therefore, the amount of liquid in the system increases and increases when water enters from outside the manufacturing process. It is necessary to drain the liquid. For this reason, solid sodium chloride is required. However, in the above conventional method, sodium chloride is treated as an aqueous solution, so it cannot be used as it is, and a large amount of energy must be consumed to evaporate moisture and solidify it. .

That is, the by-product salt is carried in solid form, but in the case of the above method, the by-product salt must be once dissolved in water and treated as an aqueous solution, and further applied to a process using solid sodium chloride as a raw material. Must be evaporated to dryness again after purification. Further, in the operation of removing SO ₄ ²⁻ with calcium chloride or barium chloride, there is a problem that solid waste such as solid calcium sulfate or barium sulfate is newly generated.

As a method for solving such a problem, the present inventors previously made by-product salt obtained by spraying sodium carbonate powder into exhaust gas from an incinerator for municipal waste or industrial waste. Adding water or an aqueous solution of sodium chloride in an amount that can dissolve substantially all of one or more of the other water-soluble inorganic salts and does not dissolve the total amount of sodium chloride, A method for purifying sodium chloride is disclosed, wherein one or more salts are dissolved in substantially the entire amount, and the resulting slurry is subjected to solid-liquid separation to recover a solid component (see Patent Document 1).
In this method, separation of alkali metal chlorides such as a combination of sodium chloride and potassium chloride is performed well, and water-soluble metal sulfates such as sodium sulfate are removed without being generated as new solid waste. In addition, sodium chloride purified from by-product salts, particularly high purity to industrially can be used as a raw material for the IM electrolysis process, by successfully removing substances with extremely low permissible concentrations such as iodide. This is a method for obtaining sodium chloride.

JP 2002-167218 A (Claims)

Thereafter, the present inventors have found that it may be desired to further remove hydrogen chloride in the exhaust gas from the garbage incineration plant, further collect sodium chloride from this, purify it and recycle it. It was.
Therefore, the present invention provides a method for producing a purified alkali metal chloride more easily than in the previously proposed method by solving the above-mentioned problem of impurities based on fly ash. In particular, an object of the present invention is to provide a method for producing a highly purified alkali metal chloride that can also be used as a raw material for IM electrolysis.
The present invention also provides a method for producing an alkali metal hydroxide characterized by electrolyzing an aqueous solution of an alkali metal chloride obtained as described above using an ion exchange membrane as a diaphragm. With the goal.

  The present invention first separates fly ash contained in the exhaust gas, collects the secondary salt obtained by spraying the alkali metal carbonate powder on the separated exhaust gas, and then collects the secondary salt into the secondary salt. On the other hand, the above object is achieved by applying specific means.

  That is, the purified alkali metal chloride production method of the present invention separates and removes fly ash contained in the exhaust gas from the incinerator for municipal waste or industrial waste, and then removes the alkali metal into the exhaust gas after separation. By-product containing one kind of alkali metal chloride produced by spraying carbonate powder and reacting alkali metal carbonate powder with acidic components in the exhaust gas and other water-soluble inorganic salts A method for producing the alkali metal chloride purified by separating and recovering the salt from the exhaust gas, and separating and removing a water-soluble inorganic salt other than the alkali metal chloride in the by-product salt, Water or alkali metal chloride in an amount that can dissolve substantially all of one or more water-soluble inorganic salts other than the alkali metal chloride in the by-product salt and does not dissolve the by-product salt in its entirety. An aqueous solution of the alkali metal chloride Substantially to the total amount dissolved singly outside the water-soluble inorganic salts, separating the solid and the resulting slurry solution, and recovering the alkali metal chloride as a solid component.

  Moreover, in the manufacturing method of the refine | purified alkali metal chloride of this invention, it is preferable that an alkali metal carbonate particle is 30 micrometers or less by an average particle diameter. The average particle size is more preferably 20 μm or less, and particularly preferably 10 μm or less.

  In a preferred embodiment of the method for producing a purified alkali metal chloride of the present invention, one or more water-soluble inorganic salts other than the alkali metal chloride are a water-soluble metal sulfate, a water-soluble metal iodide, and the alkali. It is one or more selected from the group consisting of chlorides of alkali metals different from metal chlorides.

In another preferred embodiment of the method for producing a purified alkali metal chloride of the present invention, the alkali metal chloride is sodium chloride, and the water or the aqueous solution of the alkali metal chloride is sodium sulfate with respect to water. So that the concentration becomes 12 mass% or less in terms of SO ₄ , or the potassium chloride concentration becomes 35 mass% or less in terms of potassium chloride, or sodium iodide becomes 5 mass% or less in terms of iodine. And by-product salt.

  In another preferred embodiment of the method for producing a purified alkali metal chloride of the present invention, the alkali metal chloride is sodium chloride, and the by-product salt is sodium sulfate as another water-soluble inorganic salt. 0.15 times mol or less with respect to the metal chloride, or 1.0 mol or less with respect to the alkali metal chloride as the other water-soluble inorganic salt, or other water-soluble inorganic salt It is characterized by containing sodium iodide 0.01 mol or less with respect to the alkali metal chloride.

  In another preferred embodiment of the method for producing a purified alkali metal chloride according to the present invention, the solid component obtained by solid-liquid separation of the slurry is dissolved in water again, and then solid-liquid separation is performed again to form water. Impurities that are not dissolved are removed, and the alkali metal chloride is recovered as an aqueous solution.

  Moreover, in the manufacturing method of the alkali metal hydroxide of this invention, an alkali metal hydroxide can be manufactured by electrolyzing the aqueous solution of said alkali metal chloride using an ion exchange membrane.

  According to the present invention, when recycling by-product salt obtained from waste incineration waste gas, etc., impurities caused by fly ash, which is difficult to remove by conventional techniques or complicated in the removal process, can be efficiently and easily removed. Can be removed. Furthermore, after separating and removing fly ash from the waste gas from the incinerator of municipal waste or industrial waste, it can be used in the IM electrolysis method from by-product salt generated by spraying sodium carbonate powder. A highly pure alkali metal chloride can be obtained.

The figure which shows the dry-type neutralization process process of the waste gas in this invention. The figure which shows the refinement | purification process process of the byproduct salt in this invention.

  In the present invention, after the fly ash contained in the exhaust gas from the incinerator of municipal waste or industrial waste is separated and removed, alkali metal carbonate powder is sprayed on the exhaust gas after separation to obtain alkali metal carbonate. Separating and recovering from the exhaust gas a by-product salt containing one kind of alkali metal chloride produced by reacting the salt powder with the acidic component in the exhaust gas and another water-soluble inorganic salt; Using the by-product salt, water or an aqueous solution of an alkali metal chloride, utilizing the mutual solubility between the recovered alkali metal chloride and another water-soluble inorganic salt, one or more other water-soluble substances to be removed The inorganic inorganic salt is dissolved substantially in the entire amount of the aqueous solution, and the alkali metal chloride is partially dissolved in the aqueous solution.

  In the present invention, as an alkali metal carbonate for generating a by-product salt by neutralizing an acid gas containing hydrogen chloride in a combustion gas from a municipal waste incineration plant or an industrial waste incineration plant, an acid gas component For example, sodium carbonate, sodium sesquicarbonate, sodium hydrogen carbonate, etc. can be mentioned because of their high reactivity with the product, availability on an industrial scale, stability during storage, etc., and these can be used for both synthetic and natural products. . Although there is a difference in the production process of the by-product salt depending on the type of the alkali metal carbonate, the by-product salt basically has the same composition as the acid gas and the unreacted remaining alkali amount are different. These alkali metal carbonates react with acidic gas in the gas by a dry gas treatment facility to produce by-product salts in which sodium chloride, sodium sulfate, and the like are mixed. This by-product salt usually contains potassium chloride and metal iodide as impurities.

  Here, separation of the fly ash contained in the exhaust gas from the incinerator of municipal waste or industrial waste from the exhaust gas or spraying the alkali metal carbonate powder to the exhaust gas after the separation, the alkali metal carbonate powder The by-product salt containing one kind of alkali metal chloride produced by reacting the body with an acidic component in the exhaust gas and another water-soluble inorganic salt from the exhaust gas is separated from known gases. It can be performed by means for removing dust, and is not particularly limited. Examples include bag filters, electrostatic precipitators, cyclones, etc. Among them, bag filters have high separation performance, and alkali metal carbonate particles trapped on the filter cloth contribute to the reaction with acid gas. This is preferable because of its high removal efficiency.

  First, fly ash is separated and removed from the exhaust gas from the incinerator of municipal waste or industrial waste, and then the alkali metal carbonate powder is sprayed on the exhaust gas after separation to obtain the alkali metal carbonate powder and the exhaust gas. By-product salt generated by reacting with acidic components in the gas is separated, and the separated by-product salt is subjected to the following treatment using an aqueous solution of water or an alkali metal chloride, thereby producing fly ash. In addition, it is possible to sufficiently reduce the mixing of impurities other than the acidic component as the main component.

  In addition, it is necessary for the recovered alkali metal chloride to dissolve substantially the entire amount of one or more other water-soluble inorganic salts to be removed in the treatment operation using the aqueous solution of water or alkali metal chloride. This refers to dissolving the water-soluble inorganic salt to the extent that the target purity is reached. Next, the slurry is subjected to solid-liquid separation by filtration or the like, and preferably washed with a liquid substantially free from the other water-soluble inorganic salt (such as water), the solid component is substantially free from the other water-soluble inorganic salt. Contains no alkali metal chloride.

Here, the alkali metal chloride to be recovered is not a mixture of two or more kinds of alkali metal chlorides but a chloride composed of one kind of alkali metal and chlorine, and therefore, as other water-soluble inorganic salts to be removed, Alkali metal chlorides other than the alkali metal chloride are also subject to removal. For example, when one kind of alkali metal salt is sodium chloride, potassium chloride is also an object to be removed. That is, according to the method of the present invention, a purified alkali metal chloride can be obtained by easily separating different alkali metal chlorides, which has been difficult in the past.
In the present invention, addition of water or an aqueous solution of alkali metal chloride for forming a slurry can also be performed in divided portions. That is, when the operations of slurry formation and solid component recovery are repeatedly performed, the purity of the alkali metal chloride can be increased. In particular, it is effective to repeat the removal of water-soluble inorganic salts having a low concentration in the original mixture and a very low target allowable concentration in the alkali metal chloride.

  In the following, after separating and removing fly ash contained in exhaust gas from incinerators for municipal waste or industrial waste, alkali metal carbonate powder is sprayed into the exhaust gas after separation, and alkali metal carbonate is discharged. As a by-product salt containing one kind of alkali metal chloride produced by reacting salt powder with acidic components in the exhaust gas and other water-soluble inorganic salts, sodium chloride is the main component and removed. An example of a secondary salt containing sodium sulfate, potassium chloride and water-insoluble components as impurities to be described will be described, but the one alkali metal chloride in the present invention is limited to sodium chloride. is not.

  Removal of potassium chloride is necessary to suppress an increase in potassium concentration in sodium hydroxide obtained when sodium chloride is used in the IM electrolysis method. Usually, the operation performance is not deteriorated by mixing a small amount of potassium into the ion exchange membrane, but the potassium concentration in the obtained sodium hydroxide correlates if the potassium concentration in the raw material supplied to the electrolytic cell increases. And get higher.

  First, the by-product salt is mixed with water or an aqueous sodium chloride solution (hereinafter collectively referred to as water or the like). Here, the sodium chloride aqueous solution may be seawater, or may be dilute salt water (hereinafter referred to as light salt water) flowing out from the anode side in the IM electrolysis method. In the case of using a sodium chloride aqueous solution, it is preferable that the aqueous solution does not contain the impurities as much as possible in order to increase the operation efficiency.

  At this time, the amount of water (or water in the above aqueous solution) is not an amount capable of dissolving all of the by-product salt, but considering the mutual solubility of sodium chloride, sodium sulfate, and potassium chloride. It is preferable that the total amount can be dissolved, or a slightly larger amount, for example, 1 to 2 times the amount. Adjusting the amount of water in this way minimizes the sodium chloride recovery loss. Next, when this is solid-liquid separated, the solid component of the slurry contains sodium chloride which is supersaturated and does not dissolve, and sodium chloride (solid matter) substantially free of sodium sulfate and potassium chloride is obtained. Sodium sulfate, sodium chloride, and potassium chloride are present in the liquid.

  As a solid-liquid separation method, centrifugation, vacuum filtration, pressure filtration, sedimentation separation, or the like can be employed. Moreover, since the mother liquid (liquid in the slurry) is attached to the solid component obtained by solid-liquid separation, if the mother liquid is removed by washing with water etc., the solid component that does not contain potassium chloride or sodium sulfate is removed. Sodium chloride is preferable because it can be obtained. Here, the mutual solubility of sodium chloride when other water-soluble inorganic salts coexist is usually lower than the solubility of sodium chloride when only sodium chloride and water are present. This is advantageous for recovering sodium chloride as a solid.

Next, when the obtained solid component is dissolved in water or the like, a sodium chloride aqueous solution from which impurities insoluble in water are removed is obtained by solid-liquid separation. The obtained sodium chloride aqueous solution can produce high purity sodium chloride crystals by evaporating the solvent.
The sodium chloride aqueous solution can also be used as a raw material for producing sodium carbonate by an ammonia soda method or an ammonium chloride soda method.

In particular, the method of the present invention is a main method for producing sodium hydroxide, and can be suitably used for the IM electrolysis method capable of producing a high-purity product. In the IM electrolysis method, the fresh salt water flowing out from the anode after electrolysis is recycled and reused as a solution for dissolving sodium chloride, and the waste solution is operated so as to reduce it as much as possible. Therefore, if water is brought into the process system separately, the water in the system will increase unnecessarily, and the water in the system will increase, and the salt water containing sodium chloride, which is the raw material, will be unnecessarily discarded outside the system. Since it will disappear, solid sodium chloride is used as a raw material.
Sodium chloride obtained as a solid by removing other water-soluble inorganic salts by the method of the present invention is mixed with fresh salt water and dissolved, then solid-liquid separated to remove solid impurities, and then the existing method Can be used for IM electrolysis.

In the operation of dissolving by-product salt separated from the exhaust gas into water or fresh salt water (hereinafter simply referred to as water or the like), the concentration of sodium sulfate in the aqueous solution is 12 mass in terms of SO ₄ ^{2− with} respect to water. It is preferable to add water or the like so as to be not more than%, particularly not more than 9% by mass, because almost the entire amount thereof is dissolved. Further, it is preferable to add water or the like so that the concentration of potassium chloride in the aqueous solution is 35% by mass or less, particularly 15% by mass or less with respect to water, because almost all of the potassium chloride is dissolved. Further, in order to increase the speed and effect of this operation, the by-product salt may be crushed in advance before the treatment.

In the present invention, in order to effectively remove sodium sulfate from a by-product salt containing sodium chloride and sodium sulfate, the molar ratio of sodium sulfate to sodium chloride in the by-product salt is 0.15 sodium sulfate / sodium chloride. Hereinafter, it is particularly preferably 0.10 or less. When the above molar ratio exceeds 0.15, the amount of sodium chloride is too small to sufficiently remove sodium sulfate, and most of the sodium chloride is dissolved in the solution, resulting in a low sodium chloride recovery rate. . On the other hand, when the molar ratio is less than 0.001, it can be used in the IM electrolysis method without removing sodium sulfate, so that this removal operation is not so necessary.
Similarly, in order to effectively remove potassium chloride from a by-product salt containing sodium chloride and potassium chloride, the molar ratio of potassium chloride to sodium chloride in the by-product salt, potassium chloride / sodium chloride is 1. It is preferably 0 or less, particularly 0.7 or less. When the molar ratio exceeds 1.0, the amount of sodium chloride is too small to sufficiently remove potassium chloride, and most of the sodium chloride is dissolved in the solution, resulting in a low sodium chloride recovery rate. . Since it is preferable that the concentration of potassium chloride in the by-product salt is as low as possible, it is effective to perform this removal operation when the by-product salt contains even a small amount of potassium chloride (the above molar ratio exceeds 0). .

  As described above, when the water-soluble inorganic salt is a two-component system of sodium chloride and sodium sulfate or a two-component system of sodium chloride and potassium chloride, the molar ratio of the other water-soluble inorganic salt for improving the purity of sodium chloride Although the preferred range has been described, for example, when sodium chloride is produced in a three-component system of sodium chloride, potassium chloride and sodium sulfate, it is determined in consideration of the mutual solubility of the three components.

In addition, when the by-product salt is dissolved in water or an aqueous sodium chloride solution, when sodium sulfate is contained, 0 to 50 ° C., particularly 15 to 35 ° C. is less precipitated sodium sulfate, It is preferable because the recovery rate of sodium chloride is high.
This temperature range is determined in consideration of the temperature dependence of the mutual solubility of the desired salt and impurity, and the optimum temperature range varies depending on the combination of the desired salt and impurity. Sodium chloride and sodium sulfate are preferable because the solubility of sodium sulfate in water is high in the above temperature range.

When removing potassium chloride and sodium sulfate from the by-product salt mainly composed of sodium chloride to increase purity, in the present invention, the amount of water or the like is adjusted so as to completely remove potassium chloride, and the total amount of sodium sulfate is reduced. It can also be removed using conventional desulfurization techniques without removal. That is, in consideration of the recovery cost and the like of sodium chloride, potassium chloride was removed by the present invention, it kept to be less than 1.0 wt% of by-product salts total mass sodium sulfate present invention, a conventional SO ₄ ^{2 -} it may be used in combination with a technique for removing.
That is, a compound having low solubility in water by reacting with sulfate such as calcium hydroxide, barium chloride, calcium chloride, heavy metal, calcium or magnesium in an aqueous solution obtained by dissolving the by-product salt after removing potassium chloride in water. By adding one or more substances to be produced and performing solid-liquid separation, SO ₄ ²⁻ is removed, and a high-purity sodium chloride aqueous solution is obtained.
Further, by bringing the sodium chloride aqueous solution to be treated into contact with the chelate resin, calcium, magnesium, strontium, barium, mercury and the like can be reduced, so that a higher purity sodium chloride aqueous solution can be obtained.

In the above, the means for removing sodium sulfate and potassium chloride from sodium chloride has been specifically described. However, the present invention is not limited to these means, and according to the present invention, various water-soluble substances that are mixed little by little. Inorganic components can be removed simultaneously. That is, bromine compounds such as heavy metal chlorine compounds and sodium bromide, iodine compounds, fluorine compounds, sodium carbonates such as sodium chlorate, etc., which were difficult to remove by the conventional calcium chloride addition method and ion exchange resin method The water-soluble inorganic component can be removed.
In particular, when sodium chloride is applied to the IM electrolysis method, the allowable concentration of iodine in sodium chloride is extremely low. However, according to the present invention, water-soluble metal iodide can be removed to a very low concentration, which is preferable.

Hereinafter, the case where the water-soluble metal iodide is sodium iodide will be specifically described.
When removing sodium iodide from by-product salt containing sodium chloride, by-product salt and water etc. are mixed, sodium chloride is partially dissolved, and other water-soluble inorganic salts are dissolved in substantially all amounts. In addition, it is preferable to add water or the like so that sodium iodide is 5% by mass or less, particularly 2% by mass or less with respect to water in terms of iodine. By adjusting the amount of water and the like in this way, almost all of sodium iodide is dissolved. The molar ratio of sodium iodide to sodium chloride in the by-product salt, sodium iodide / sodium chloride, is preferably 0.01 or less, particularly preferably 0.005 or less. In order to use sodium chloride as a raw material in the IM electrolysis method, it is generally required that iodine is 1 mass ppm or less. Therefore, when the content of iodine in the by-product salt is large, this operation in the present invention needs to be repeated a plurality of times, particularly when the molar ratio exceeds 0.01, it is necessary to repeat five or more times. Takes time. Depending on the content of water-soluble metal iodide in the by-product salt and the content of other components, conventional operations such as removing water-soluble metal iodide in this operation and removing it with a chelating resin, etc. You may use together with the technique to do. The concentration of sodium iodide in the by-product salt is preferably as low as possible. Therefore, when the by-product salt contains even a small amount of sodium iodide (the molar ratio exceeds 0), this operation of the present invention is performed. Is valid.

  Furthermore, in the present invention, when the by-product salt to be treated contains impurities that are insoluble in water, the solid sodium chloride obtained by the above treatment is dissolved in water and separated into solid and liquid again. A sodium chloride aqueous solution from which water-insoluble impurities are removed can be obtained.

In the above, sodium chloride has been illustrated and described. However, the present invention is based on the same principle, and other alkali metal chlorides such as potassium chloride and lithium chloride, SO ₄ ²⁻ , heavy metals, Applicable for removing impurities.
For example, contamination of sodium in potassium chloride can be reduced so that potassium chloride can be used for the production of potassium hydroxide by the IM electrolysis method.

  Solid sodium chloride obtained by the present invention is produced by the production of sodium hydroxide by electrolysis in the IM electrolysis method, mercury electrolysis method or electrodialysis method, the production of sodium chloride crystals by evaporation of sodium chloride aqueous solution, or the ammonia soda method, It can be used for the production of sodium carbonate by the ammonium chloride soda method. Further, even when the aqueous solution of sodium hydroxide having restrictions on iodine concentration is used for production by the IM electrolysis method, equipment using a deiodine ion exchange resin or the like is unnecessary or the scale of the equipment can be reduced. That is, the equipment cost and running cost can be reduced as compared with the conventional method.

Next, the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an exhaust gas dry neutralization treatment step in which, for example, an exhaust gas generated in a municipal waste incineration plant is neutralized by a dry method to obtain a by-product salt. The gas G1 generated from the waste pyrolysis furnace 11 is combusted in the melting furnace 12, recovered by heat through the waste heat boiler 13, and then sent to the exhaust gas cooling tower 14. After the exhaust gas G2 is cooled below the synthesis temperature of dioxins in the exhaust gas cooling tower 14, fly ash is removed by the first bag filter 15. The removed fly ash 16 is recycled to the melting furnace 12. The powder neutralizer 17 and activated carbon added as necessary are sprayed into the exhaust gas from which the fly ash has been removed. A powder neutralizer (such as sodium carbonate, sodium bicarbonate, or sesquicarbonate) reacts with hydrogen chloride, sulfur oxides, and the like in the exhaust gas G2 to generate by-product salt 19. The produced by-product salt 19 is separated from the exhaust gas by the second bag filter 18, and the separated exhaust gas is discharged from the chimney through the induction fan. When activated carbon is added, dioxins are removed from the exhaust gas by activated carbon. In addition, calcium hydroxide or the like may be used in combination with the powder neutralizer.

FIG. 2 shows, for example, a step of purifying the by-product salt 19 (S2) produced by the process of FIG. 1 to the extent that it can be applied to a manufacturing process by an IM electrolysis method of an aqueous sodium hydroxide solution, It is an embodiment of the present invention and is a diagram showing a purification process of by-product salt. First, the by-product salt S2 is sent to the mixing tank 41, and an aqueous solution containing sodium chloride such as water or fresh salt water is added thereto to obtain a slurry SL1 in which the by-product salt S2 is partially dissolved. In the slurry SL1, only sodium chloride is present as a solid component among the water-soluble inorganic salts, and the other water-soluble inorganic salts are almost dissolved in the liquid.
Next, the slurry SL1 is solid-liquid separated by the filter 42 and further washed as necessary. In order to perform this solid-liquid separation operation industrially, as the filter 42, a horizontal belt filter (vacuum filter), a cylindrical vacuum filter, a filter press, a basket-type centrifuge, etc., which can have a washing function An apparatus is preferred.

SO ₄ ²⁻ , potassium, iodine and the like are contained in the liquid L3 and removed by solid-liquid separation here. The process of slurrying and solid-liquid separation so far can be repeated as shown by the broken line in FIG.
On the other hand, the roughly purified salt S3 separated as a solid is sent to the dissolution tank 43, dissolved in an aqueous solution containing sodium chloride such as water or fresh salt water supplied to the dissolution tank 43, and then converted into water by the filtration equipment 44. The insoluble solid S4 is separated and removed. Furthermore, sodium hydroxide, sodium carbonate, a chelating solution, and a polymer flocculant are added to the filtrate of the filtration equipment 44 in the reaction tank 45 to form a precipitate S5 such as a hydroxide such as calcium, magnesium, or heavy metal. Subsequently, it is sent to the clarification tank 46, where the precipitate S5 is removed.
Here, instead of the clarification tank 46, a filtration facility such as a filter press or a vacuum filter may be installed. The clarified liquid L4 from the clarification tank 46 is sent to the filtration equipment 47 to remove the solid matter contained in a trace amount. Next, calcium, magnesium, strontium and the like are removed to a higher degree in the chelate resin tower 48 to obtain highly purified brine L5. As the filtration equipment 44 and the solid-liquid separation equipment 47, a sand filter, a precoat filter, a cartridge filter, a filter press, or the like can be used.
Since this highly purified salt water L5 has a purity applicable to the IM electrolysis method, it can be supplied to an ion exchange membrane electrolytic cell to obtain a high-purity sodium hydroxide aqueous solution by the IM electrolysis method.

EXAMPLES Next, the present invention will be specifically described with reference to examples of the present invention, but the present invention is not limited to the following examples.
[Example 1]
The gasification melting furnace process and the purification process shown in FIGS. 1 and 2 were performed.
After the gas generated from the waste pyrolysis furnace 11 is combusted in the melting furnace 12, the heat is recovered through the waste heat boiler 13, and then sent to the exhaust gas cooling tower 14. After the exhaust gas is cooled below the synthesis temperature of dioxin by the exhaust gas cooling tower 14, the fly ash is separated and removed by the first bag filter 15. The removed fly ash is recycled to the melting furnace 12.
Sodium hydrogen carbonate having an average particle diameter of 9 μm is sprayed as a powder neutralizer (desalting agent) of acidic components in the exhaust gas into the exhaust gas from which the fly ash has been removed. Sodium bicarbonate reacts with hydrogen chloride, sulfur oxides, etc. in the exhaust gas to produce by-product salts. The produced by-product salt is separated from the exhaust gas by the bag filter 18.

30 kg of the by-product salt thus obtained was mixed with 37.5 kg of pure water in the mixing tank 41 to obtain a slurry in which the by-product salt was partially dissolved. At this time, the SO ₄ equivalent concentration of sodium sulfate with respect to pure water as a solvent at this time is 1.8%, the concentration of potassium chloride is 0.046% (as potassium chloride equivalent), and the iodine equivalent concentration of the water-soluble metal iodide is 0.004. %Met. The slurry is filtered with a Nutsche (filter) 42 using 5A filter paper, and 18 kg of a 25% by weight saturated aqueous solution in which reagent-grade sodium chloride is dissolved in water is sprayed on the filter layer. Was washed and removed. The solid was recovered from the filter paper and 13 kg of salt (hereinafter referred to as crude purified salt) was recovered. 16 kg of the crudely purified salt was dissolved in 48 kg of pure water in the dissolution tank 43, and solid sodium sulfate was added so that the concentration of SO ₄ ²⁻ in the liquid was about 0.2% by mass (hereinafter, crude Called purified brine).

Next, 43 kg of roughly purified salt water was filtered with a Nutsche (filtering equipment) 44 using 5A filter paper to separate solids, and then a chelating solution (trade name: Aclean M, Asahi Glass Engineering Co., Ltd.) in the reaction tank 45. 17.2 g and 11 g of iron chloride were added and stirred for 30 minutes. A cationic polymer flocculant (trade name: Crifix CP-933, manufactured by Kurita Kogyo Co., Ltd.) was added to this and clarified, filtered through a Nutsche (clarification tank 46) using 5A filter paper, and purified brine ( Hereinafter, it was referred to as primary purified brine).
Next, 40 kg of the primary purified brine is taken, to which 33 g of sodium hydroxide, 8 g of sodium carbonate and a polymer flocculant (trade name: Aquaric, manufactured by Nippon Shokubai Co., Ltd.) are added, and then 5C filter paper is used. And filtered with Nutsche to obtain purified brine (hereinafter referred to as secondary purified brine).

Next, 52 kg of this secondary purified brine was fractionated, and a first small column packed with 140 g of an aminophosphate type ion exchange resin (trade name: DUOLITE C467, manufactured by Sumitomo Chemical Co., Ltd.) was used. The liquid was passed so as to be 10 m / h. Here, the liquid superficial velocity is a value obtained by dividing the liquid flow rate (m ³ / h) by the cross-sectional area (m ² ) of the column. The liquid that passed through the first small column is then applied to a second small column packed with 140 g of a styrene-based macroporous ion exchange resin (trade name: DUOLITE A161TRSO4, manufactured by Sumitomo Chemical Co., Ltd.) to remove iodine. The solution was passed through to obtain purified brine (hereinafter referred to as tertiary purified brine). Table 1 shows analysis values of by-product salt, crude purified salt, primary purified brine, secondary purified brine, and tertiary purified brine. In this example, the target value of the purity of the sodium chloride aqueous solution to be applied to the IM electrolysis method is as shown in Table 1.

  From Table 1, it was confirmed that the tertiary purified brine has a purity sufficient for use in the IM electrolysis method. It was also found that primary purified brine can be used sufficiently for the production of sodium carbonate by the ammonia soda method and the ammonium chloride soda method.

Next, it applied to IM electrolysis method using the said tertiary purified brine. That is, an ion exchange membrane (trade name: Flemion F-795, manufactured by Asahi Glass Co., Ltd.) is installed in a monopolar electrolytic cell having an electrolysis area of 5 cm in length and 5 cm in width, a current density of 3 kA / m ² , a temperature of 85 ° C., a cathode The above-mentioned tertiary purified brine was used as sodium hydroxide concentration of 32% by mass in the chamber and sodium chloride in the anode chamber, and the sodium chloride concentration was 210 g / L. Table 2 shows the relationship between elapsed days and current efficiency. The current efficiency did not decrease even after 90 days.

ここで、ガス化溶融プロセスを使用する。

Here, a gasification melting process is used.

  DESCRIPTION OF SYMBOLS 11 Pyrolysis furnace 12 Melting furnace 13 Waste heat boiler 14 Cooling tower 15 Bag filter 16 Fly ash 17 Sodium hydrogen carbonate 18 Bag filter 19 Byproduct salt 41 Mixing tank 42 Filter machine 43 Dissolution tank 45 Reaction tank 46 Clarification tank 47 Filtration equipment 48 Chelate resin tower

Claims (5)

After the fly ash contained in the waste gas from the incinerator of municipal waste or industrial waste is separated and removed by the first bag filter, the alkali metal carbonate powder is sprayed on the separated waste gas, By-product salt containing one kind of alkali metal chloride produced by reacting salt powder with acidic components in the exhaust gas and other water-soluble inorganic salt is removed by the second bag filter into the exhaust gas. A method for producing the alkali metal chloride purified by separating and recovering from the product and separating and removing a water-soluble inorganic salt other than the alkali metal chloride in the by-product salt, the alkali metal chloride Is sodium chloride, and the other water-soluble inorganic salt is one or more selected from the group consisting of sodium sulfate, potassium chloride and sodium iodide, and the following (a) to (c) ) Adding an amount of water or an aqueous solution of sodium chloride that satisfies any one or more of the conditions and does not dissolve the by-product salt in total, and separates the resulting slurry into solid and liquid to recover sodium chloride as a solid component. A method for producing a purified alkali metal chloride characterized by the following.
(A): The concentration of sodium sulfate with respect to water is 12% by mass or less in terms of SO ₄ .
(B): The concentration of potassium chloride with respect to water is 35% by mass or less in terms of potassium chloride.
(C): The concentration of sodium iodide with respect to water is 5% by mass or less in terms of iodine.   The by-product salt is, as the other water-soluble inorganic salt, 0.15 times or less of sodium sulfate relative to sodium chloride, 1.0 times or less of potassium chloride relative to sodium chloride, and sodium chloride. The manufacturing method of the refine | purified alkali metal chloride of Claim 1 containing 1 or more types chosen from the group which consists of sodium iodide of 0.01 times mole or less.   The method for producing a purified alkali metal chloride according to claim 1 or 2, wherein the alkali metal carbonate particles are sodium hydrogen carbonate particles having an average particle diameter of 30 µm or less.   The solid component obtained by solid-liquid separation of the slurry is again dissolved in water, and then solid-liquid separation is performed again to remove impurities not dissolved in water, and sodium chloride is recovered as an aqueous solution. The manufacturing method of the refine | purified alkali metal chloride in any one.   A method for producing an alkali metal hydroxide, comprising electrolyzing the aqueous solution of sodium chloride according to claim 4 using an ion exchange membrane.

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