JP2008247647A - Manufacture method of sodium chloride aqueous solution for industrial use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the amount of sludge generated when purifying the aqueous solution of a byproduct salt, and to make heavy metals in the sludge reclaimable in soil. <P>SOLUTION: During the process of purification of a solution containing the byproduct salt which is recovered by adding sodium bicarbonate to a combustion exhaust gas, carbonate group dissolved in the solution is reacted with hydrochloride for removal by decomposition until the pH reaches less than 8; sulfurate group remained in the solution where carbonate group is removed is insolubilized; heavy metals remained in the solution where sulfurate group is insolubilized is reacted with a chelating agent added to the solution to insolubilize the heavy metals and then these insolubilized products are separated from the solution to be discarded. The insolubilization of the sulfurate group is performed by making the sulfate group into calcium sulfate, and the remaining sulfate group is insolubilized as barium sulfate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an industrial aqueous sodium chloride solution.

  As a method of removing hydrogen chloride contained in waste incineration exhaust gas, powdered sodium hydrogen carbonate (hereinafter referred to as baking soda) is added to the combustion exhaust gas and reacted with hydrogen chloride, and the solid produced by this reaction A technique for collecting and recovering sodium chloride (by-product salt) with a dust collector is known.

  On the other hand, attempts are being made to dissolve sodium chloride recovered in the treatment of the combustion exhaust gas in water to form an aqueous solution, and industrially regenerate and use this aqueous solution. For example, in the electrolytic soda industry, an aqueous solution of sodium chloride is used as a raw material for producing caustic soda, chlorine, sodium carbonate, sodium hypochlorite and the like.

  However, solid sodium chloride recovered from an exhaust gas treatment facility contains impurities (for example, heavy metals, sulfate radicals derived from sulfur oxides in exhaust gas, carbonate radicals derived from unreacted sodium bicarbonate, etc.). It does not meet the standards required for sodium chloride as an industrial raw material. Therefore, in order to reuse an aqueous solution of sodium chloride as an industrial raw material, it is necessary to purify the aqueous solution to remove impurities.

  On the other hand, for example, a solid product recovered by adding sodium bicarbonate to combustion exhaust gas is dissolved in water, the solution is adjusted to pH 8 to 14, and polyvalent metals in the solution are precipitated and removed as hydroxides. Then, the soluble polyvalent metal is adsorbed on the chelate resin and separated and removed, while the calcium chemical is added to the solution, and the sulfate radical and carbonate radical are precipitated and removed as calcium sulfate and calcium carbonate, respectively. A technique for reusing the obtained sodium chloride aqueous solution as an industrial raw material is disclosed (see Patent Document 1).

Japanese Patent No. 3390433

  By the way, as mentioned above, when recycling the product collect | recovered when processing combustion exhaust gas, the impurity contained in a product is isolate | separated from a refinement | purification process, and a normal landfill process is carried out.

  However, as in Patent Document 1, when separating polyvalent metal as a hydroxide and recovering it, there is a problem that landfill disposal cannot be performed as it is because heavy metals do not satisfy the landfill standard. In addition, the solution from which the hydroxide has been separated is adsorbed and separated from the polyvalent metal remaining in the solution in the chelate resin tower, and therefore, for example, operations for pH adjustment and solid-liquid separation increase, and the process is complicated. become.

  In addition, since a large amount of calcium chemicals is required to precipitate and remove carbonate and sulfate radicals in the solution, there is a problem that a large amount of sediment sludge is generated.

  On the other hand, waste combustion exhaust gas contains, for example, hydrogen fluoride and the like, and hydrogen fluoride reacts with sodium bicarbonate and exists as an impurity of a fluorine compound in the byproduct salt. In other words, in order to industrially reuse the sodium chloride aqueous solution, it is necessary to remove impurities such as a fluorine compound, while Patent Document 1 does not discuss this point at all.

  An object of the present invention is to reduce the amount of sludge generated when purifying an aqueous solution of by-product salt recovered by treating combustion exhaust gas with baking soda, and to make it possible to landfill and dispose of heavy metals in the sludge. It is in providing the manufacturing method of sodium chloride aqueous solution.

  In order to solve the above problems, the present invention is a method for producing a sodium chloride aqueous solution in which a product produced by adding sodium bicarbonate to combustion exhaust gas is dissolved in water, and the solution is purified to produce a sodium chloride aqueous solution. 1, a first step in which carbonate radicals dissolved in the solution are reacted with hydrochloric acid to decompose and remove until pH is less than 8, and a sulfuric acid dissolved in the solution from which carbonate radicals have been removed by the first step A second step of insolubilizing the root; and a heavy metal remaining in the solution in which the sulfate radical is insolubilized by the second step and a chelating agent added in the solution are reacted to insolubilize the heavy metal. A third step, a second step, and a fourth step of separating and removing the insolubilized material insolubilized by the third step from the solution, wherein the second step comprises sulfate radical After insoluble as calcium sulfate, and the sulfate radical remaining lysates, which is the insolubilization treatment characterized in that to insolubilize as barium sulfate.

  Thus, after sequentially treating the carbonate and sulfate radicals dissolved in the solution, the polyvalent metal remaining in the solution is continuously reacted with the chelating agent in the solution to insolubilize, for example, In addition, it is possible to reduce pH adjustment and solid-liquid separation, and to simplify the operation method and equipment configuration. Moreover, since the heavy metal chelate compound separated and recovered from the dissolved solution stably fixes the polyvalent metal, it can satisfy the landfill standard and can be directly landfilled.

  In the present invention, since the sulfate radical is insolubilized after decomposing the carbonate radical in the solution, the agent used for this treatment is only derived from the removal of the sulfate radical. The sulfate radicals can be removed efficiently without receiving. Thereby, the usage-amount of a chemical | medical agent and sludge generation amount can be decreased.

  Furthermore, by adding calcium chemicals to the solution from which carbonate radicals have been removed, the sulfate radical in the solution is insolubilized as calcium sulfate, and the fluorine compound dissolved in the solution is insolubilized as calcium fluoride. be able to. Then, for example, by adding barium chloride to the solution, the separation efficiency of sulfate radicals can be further improved. This is based on the fact that the solubility in 100 g of water is 0.298 g for calcium sulfate, whereas 0.000115 g for barium sulfate.

In this case, in the third step, in addition to reacting the heavy metal remaining in the solution with the chelating agent, a part of the heavy metal is converted into sodium sulfide (Na ₂ S) or sodium hydrosulfide (NaHS). It is preferable to react with a sodium compound such as Thus, by adding sodium compounds to the solution, some heavy metals react preferentially with sodium compounds over chelating agents and are insolubilized as sulfides, so heavy metals are removed with high accuracy. can do. In addition, the heavy metal sulfide produced | generated here satisfy | fills a landfill standard.

  The chelating agent used in the present invention is preferably a liquid or powder chelating agent having a dithiocarbamic acid group or a thiol group.

  ADVANTAGE OF THE INVENTION According to this invention, the generation amount of the sludge collect | recovered when refine | purifying the aqueous solution of by-product salt can be decreased, and the landfill standard of the heavy metals in sludge can be satisfy | filled.

  The present embodiment relates to a process for producing a sodium chloride aqueous solution to be used as an industrial raw material by refining by-product salt recovered from an incineration facility that is treated by adding baking soda to combustion exhaust gas. Hereinafter, an example of the manufacturing method of the industrial sodium chloride aqueous solution to which this invention is applied is demonstrated using drawing.

  FIG. 1 is a system diagram of a sodium chloride aqueous solution manufacturing system to which the present invention is applied. The manufacturing system of the sodium chloride aqueous solution of the present embodiment includes a dissolution tank 1, an adjustment tank 2, a first reaction tank 3, a second reaction tank 4, a coagulation tank 5, a precipitation tank 6, a storage tank 7, a sand filtration tower 8, and activated carbon. A tower 9, a recovery tank 10, a concentration tank 11, and a dehydrator 12 are provided.

  In incineration facilities such as household waste and municipal waste, exhaust gas discharged from the incinerator contains fly ash, harmful acidic components, heavy metals (for example, mercury, lead, etc.) and the like. For this reason, when the exhaust gas discharged from the incinerator first passes through a first-stage bag filter (not shown), most of the fly ash and heavy metal are collected on the filter cloth. Subsequently, fine powder baking soda that is air-transported through an air transport pipe is added to the exhaust gas that has passed through the first-stage bag filter. The baking soda added to the exhaust gas is deposited, for example, on the filter cloth surface of a second stage bag filter (not shown) installed on the downstream side to form an exhaust gas treatment layer. As a result, acidic gas such as hydrogen chloride and sulfur oxide in the exhaust gas reacts with the fine powder sodium bicarbonate when passing through the exhaust gas treatment layer, and is neutralized, and the by-product salt generated here is recovered.

  Next, a process for treating by-product salt will be described. The by-product salt recovered from the second-stage bag filter is introduced into, for example, a plurality of dissolution tanks 1 and water is added to form the by-product salt as a solution. The solution in the dissolution tank 1 is fed into the adjustment tank 2 and becomes uniform raw water. Next, an appropriate amount of raw water in the adjustment tank 2 is fed to the first reaction tank 3, and hydrochloric acid (HCl) is introduced thereto by the hydrochloric acid supply means 31.

By introducing hydrochloric acid into the first reaction tank 3, the raw water in the tank is adjusted to a pH of less than 8, preferably to a pH of 6-8. Here, carbonate radicals (for example, sodium carbonate: Na ₂ CO ₃ ) present in the raw water are decomposed by reacting with hydrochloric acid, and at the same time, sodium chloride (NaCl) is generated (Formula 1). In this reaction, the decomposition efficiency of carbonate radicals is improved by using stirring means such as aeration.

Na ₂ CO ₃ + 2HCl → 2NaCl + H ₂ O + CO ₂ ↑ (Formula 1)
Subsequently, an appropriate amount of, for example, a calcium chloride (CaCl ₂ ) aqueous solution adjusted to 35 wt% is introduced into the raw water by the calcium agent supply means 32. As a result, sulfate radicals (for example, sodium sulfate: Na ₂ SO ₄ ) and fluorine compounds (for example, sodium fluoride: NaF) in the raw water react with calcium chloride, and calcium sulfate (CaSO ₄ ) and calcium fluoride, respectively. While being insolubilized as (CaF ₂ ), sodium chloride is generated (Formula 2 and Formula 3).

Na ₂ SO ₄ + CaCl ₂ → 2NaCl + CaSO ₄ ↓ (Formula 2)
2NaF + CaCl ₂ → 2NaCl + CaF ₂ ↓ (Formula 3)
Next, the raw water containing the precipitate in the first reaction tank 3 is sent to the second reaction tank 4, and, for example, an appropriate amount of a liquid chelating agent is added, so that heavy metals remaining in the raw water, that is, The valent metal reacts with the chelating agent and is fixed as a chelate compound, that is, insolubilized. Subsequently, an appropriate amount of barium chloride (BaCl ₂ ) aqueous solution adjusted to, for example, 25 wt% is introduced into the second reaction tank 4 by the barium chloride supply means 33. Thereby, barium chloride reacts with, for example, a sulfate radical suspended in raw water and a sulfate radical released from calcium sulfate dissolved in the raw water, and becomes insoluble as barium sulfate (BaSO ₄ ).

  The raw water containing the precipitate in the second reaction tank 4 is sent to the coagulation tank 5, and an appropriate amount of PAC (polyaluminum chloride), for example, is introduced into the coagulant supply means 34 there. Subsequently, an appropriate amount of, for example, an anionic polymer flocculant is introduced into the flocculation tank 5 by the polymer flocculant supply means 35. Thereby, calcium sulfate, calcium fluoride, barium sulfate, heavy metal chelate compounds, etc. remaining in the raw water are agglomerated and separated from the raw water. The raw water containing the agglomerates is sent to the settling tank 6, where these agglomerates are discharged from the bottom as sludge.

  Next, the supernatant liquid from the sedimentation tank 6 from which the sludge has been removed is sent to the storage tank 7 and temporarily stored, and then sent to the sand filtration tower 8 as appropriate, and aggregates remaining in the liquid. Is collected in the filter. The supernatant liquid that has passed through the sand filtration tower 8 is sent to the activated carbon tower 9, where SS (floating particulate matter), organic matter, etc. remaining in the liquid are adsorbed and removed by the activated carbon. The treatment liquid from which impurities have been removed by the activated carbon tower 9 is stored in a recovery tank 10 and recovered as a purified industrial sodium chloride aqueous solution.

  On the other hand, the concentrated water containing high-concentration aggregates extracted from the bottom of the precipitation tank 6 is introduced into the concentration tank 11 and then sent to the dehydrator 12 for dehydration. Here, the dewatered sludge remaining after the dehydration process is discharged from the dehydrator 12, while the dehydrated liquid is collected in the adjustment tank 2.

  In this system, industrial water is supplied from a water source via two supply water channels 21 and 22. The supply water supplied from the supply path 21 is used as backwash water for the sand filtration tower 8 and the activated carbon tower 9. On the other hand, the backwash water discharged from the sand filtration tower 8 and the activated carbon tower 9 joins the supply water supplied from the supply path 22 and is supplied to the dissolution tank 1.

  In the present embodiment, the raw water in which the by-product salt is dissolved is decomposed in the first reaction tank 3 so that the carbonate radical is decomposed and the sulfate radical and the fluorine compound are insolubilized. The raw water treated here is fed to the second reaction tank 4 as it is, and the polyvalent metal in the raw water reacts with the chelating agent added to the second reaction tank 4 to be insolubilized. These insolubilized materials are separated from the supernatant in the precipitation tank 6. As described above, in this embodiment, when the impurities are insolubilized, expensive removal equipment such as a chelate resin tower is not necessary, and in addition, operations such as pH adjustment and solid-liquid separation need only be performed once. The operability is good and the equipment configuration is simple, which is very economical. Moreover, since the polyvalent metal is stably bound to the chelate compound separated and recovered from the raw water, the landfill standard can be satisfied and the landfill treatment can be performed as it is. Here, the chelating agent used in this embodiment is preferably a liquid or powder chelating agent having a dithiocarbamic acid group or a thiol group.

  In addition, in this embodiment, after processing a carbonate radical, a sulfate radical, etc., it is made to add a chelating agent to raw water, but the timing which adds a chelating agent is not limited to this, for example, If it is a powder chelate, it may be added directly to the by-product salt before the by-product salt is dissolved in water.

  In this embodiment, before treating the sulfate radical, hydrochloric acid is added to the raw water in advance to adjust the pH to the neutral range, and the carbonate radical is decomposed with hydrochloric acid, so that the second reaction tank 4 When the sulfate radical is insolubilized, the sulfate radical can be efficiently removed with simple equipment without being affected by the carbonate radical that suppresses the insolubilization of the sulfate radical. In addition, the calcium chemicals used for the insolubilization treatment of sulfate radicals are not limited to sulfate radicals, but also react with fluorine compounds in raw water to insolubilize them as calcium fluoride. Can be improved. Furthermore, since the calcium chemical | medical agent does not need to be used for the insolubilization of a carbonate radical, and is used only for the insolubilization of a sulfate radical and a fluorine compound, the usage-amount of a calcium chemical | medical agent and sludge generation amount can be reduced.

  In this embodiment, the sulfate radical in the raw water is insolubilized as calcium sulfate, and then the sulfate radical remaining in the raw water and the sulfate radical released from the calcium sulfate are reacted with barium chloride, respectively, so that the solubility is higher than that of calcium sulfate. Insoluble as small barium sulfate. Thereby, it is possible to separate and remove sulfate radicals with high accuracy without performing a high-level purification treatment.

  On the other hand, fluorine compounds and other impurities dissolved in raw water are insolubilized using calcium chemicals, and then transferred to the coagulation tank 5 where PAC for separation and aggregation and polymer coagulant are added and separated. Therefore, separation and removal can be performed with high accuracy. Here, as the aggregating and separating agent, a neutral or anionic polymer flocculant may be used alone, but it is preferable to use the polymer flocculant and PAC in combination as in this embodiment.

  Furthermore, in this embodiment, the polyvalent metal dissolved in the raw water is reacted with the chelating agent to insolubilize it. In combination with this, for example, sodium sulfide is added to the raw water to dissolve the heavy metals. A part of may be insolubilized as a sulfide. That is, some heavy metals react preferentially with sodium sulfide over the chelating agent and are insolubilized as sulfides, so that heavy metals can be removed with high accuracy. Moreover, since the reaction between sodium sulfide and heavy metal proceeds, for example, under the condition of pH 7, it is not necessary to adjust pH, and the removal efficiency of heavy metal can be improved by a simple method. In addition, the heavy metal sulfide produced | generated here satisfy | fills a landfill standard.

  As described above, according to the present invention, the carbonate radical in the solution in which the by-product salt is dissolved is decomposed, the sulfate radical and the fluorine compound are insolubilized, and then the chelating agent is added to the solution. Since the polyvalent metal therein is fixed and separated and removed by coagulation precipitation, a high-purity sodium chloride aqueous solution can be produced with a simple equipment configuration and treatment method. Further, by fixing the polyvalent metal in the solution with a liquid or powder chelating agent, the recovered chelating agent can be landfilled as it is. Moreover, since the sulfate radical and the fluorine compound are insolubilized after decomposing the carbonate radical in the solution, the amount of chemical used for the insolubilization treatment and the amount of sludge generated can be reduced.

It is a systematic diagram of a sodium chloride manufacturing system to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dissolution tank 2 Adjustment tank 3 1st reaction tank 4 2nd reaction tank 5 Coagulation tank 6 Precipitation tank 7 Storage tank 8 Sand filtration tower 9 Activated carbon tower 10 Recovery tank 11 Concentration tank 12 Dehydrator 31 Hydrochloric acid supply means 32 Calcium agent supply means 33 Barium chloride supply means 34 Flocculant supply means 35 Polymer flocculant supply means

Claims (3)

In a method for producing a sodium chloride aqueous solution, a product produced by adding sodium bicarbonate to combustion exhaust gas is dissolved in water, and the solution is purified to produce a sodium chloride aqueous solution.
A first step in which carbonate radicals dissolved in the solution are reacted with hydrochloric acid to decompose and remove until pH is less than 8,
A second step of insolubilizing the sulfate radical dissolved in the solution from which the carbonate radical has been removed by the first step;
A third step of insolubilizing the heavy metal by reacting the heavy metal remaining in the solution in which the sulfate radical has been insolubilized by the second step and the chelating agent added in the solution;
And a fourth step of separating and removing the insolubilized material insolubilized by the third step from the solution.
The second step comprises insolubilizing the sulfate radical as calcium sulfate, and then insolubilizing the sulfate radical remaining in the insolubilized solution as barium sulfate. Production method.   2. The method for producing an industrial sodium chloride aqueous solution according to claim 1, wherein in the third step, a part of heavy metals remaining in the solution is reacted with a sodium compound.   The method for producing an industrial sodium chloride aqueous solution according to claim 1 or 2, wherein the chelating agent is a liquid or powder chelating agent having a dithiocarbamic acid group or a thiol group.

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