JP5939328B1 - Compound treatment agent for acid gas and heavy metal, and method for treating acid gas and heavy metal - Google Patents

Abstract

[Problem] To solve the problem of the subsequent fly ash treatment process caused by excess and deficiency of acid gas treatment agent caused by changes in the properties of waste, sufficient alkalinity in the fly ash is achieved in a wide range of addition amount Can be reduced. An acid gas and heavy metal composite treatment agent according to the present invention is a single salt selected from a double salt comprising calcium hydroxide and magnesium hydroxide, and a chloride, sulfate and hydroxide. And the above compound (alkaliness reducing agent). Since both the material stability and the blending stability are excellent, it is preferable that the specific surface area of the double salt is 20 m 2 / g or more and the median diameter (d50) is less than 30 μm. The alkalinity reducing agent is one or more selected from magnesium sulfate, sulfate-containing aluminum hydroxide, zinc sulfate, copper sulfate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, zinc hydroxide, and copper hydroxide. It is preferable to contain. [Selection] Figure 3

Description

  The present invention relates to an acid gas and heavy metal composite treatment agent, and an acid gas and heavy metal treatment method. More specifically, the present invention relates to acid gases (hydrogen chloride, sulfur oxides, etc.) contained in exhaust gas generated in combustion facilities such as municipal waste waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories. And a composite treatment agent and a composite treatment method used for treatment of heavy metals contained in fly ash generated in this combustion facility.

  In general, exhaust gas containing hydrogen chloride or sulfur oxide is treated with an alkali agent such as calcium hydroxide and then discharged from a chimney via a dust collector such as a bag filter. On the other hand, the fly ash collected by the dust collector contains harmful heavy metals such as lead and cadmium. After being collected by the dust collector, the heavy metal is stabilized by the heavy metal fixing agent, and then landfilled. (See, for example, Patent Document 1).

JP-A-9-99215

  When the addition amount of the acid gas treatment agent varies greatly due to the change in the acid gas load caused by the change in the properties of municipal waste or industrial waste, an excess acid gas treatment agent can be supplied to the flue. In such a case, since the acid gas treating agent is alkaline, an alkaline compound remains in the fly ash collected by the dust collector, and a heavy metal fixing agent is applied to the fly ash collected by the dust collector. Even if supplied, this heavy metal fixing agent is consumed not only by immobilization of heavy metals contained in the fly ash, but also by neutralization reaction with the remaining acid gas treatment agent, and as a result, the heavy metals contained in the fly ash are suitably used. It may not be possible to suppress it.

  The present invention has been made in view of the above circumstances, and in order to solve the problem of the subsequent fly ash treatment process due to the excess or deficiency of the acid gas treatment agent caused by the change in the properties of the waste, The purpose is to sufficiently reduce the alkalinity in the fly ash in the added amount range.

  As a result of intensive research in order to achieve the above object, the present inventors have obtained a double salt comprising calcium hydroxide and magnesium hydroxide instead of the conventional acid gas treating agent including slaked lime. By using together with an alkalinity reducing agent, the acidity contained in the exhaust gas can be treated and the alkalinity of the fly ash collected by the dust collector can be reduced, and the fly ash after treatment with the heavy metal fixing agent The inventors have found that the amount of elution of heavy metals from can be suppressed, and have completed the present invention. Specifically, the present invention provides the following.

  (1) The present invention is an acid gas and heavy metal composite treatment agent containing a double salt containing calcium hydroxide and magnesium hydroxide and an alkalinity reducing agent.

(2) Moreover, this invention is a composite processing agent as described in (1) whose specific surface area of the said double salt is 20 m < ² > / g or more, and a median diameter (d50) is less than 30 micrometers.

  (3) Moreover, this invention is a composite processing agent as described in (1) or (2) whose said alkalinity reducing agent is 1 or more types of compounds selected from a chloride, a sulfate, and a hydroxide. It is.

  (4) In the present invention, the compound is selected from magnesium sulfate, sulfate-containing aluminum hydroxide, zinc sulfate, copper sulfate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, zinc hydroxide, and copper hydroxide. It is a composite processing agent as described in (3) containing 1 or more types.

  (5) Further, the present invention provides the composite treating agent according to any one of (1) to (4), wherein the acidic gas is an acidic gas contained in exhaust gas, and the heavy metal is a heavy metal contained in fly ash. It is.

  (6) Moreover, this invention collects fly ash after adding the double salt comprised including calcium hydroxide and magnesium hydroxide to exhaust gas, and adds an alkalinity reducing agent to the fly ash after dust collection. This is a method for treating acidic gas and heavy metals.

  According to the present invention, in addition to being able to treat the acidic gas contained in the exhaust gas suitably, the alkalinity of the fly ash can be reduced, and as a result, the amount of heavy metal elution from the fly ash after treatment with the heavy metal fixing agent can be suppressed.

The schematic structure of the simulation dust collector indoor evaluation apparatus used in the Example is shown. The relationship between the addition amount of the various processing agent which concerns on an Example and a comparative example, and the hydrogen chloride gas removal rate in the apparatus shown in FIG. 1 is shown. The relationship between the addition amount of the various processing agent which concerns on an Example and a comparative example, and the alkalinity of the residue obtained with the apparatus shown in FIG. 1 is shown.

  Hereinafter, although embodiment of this invention is described, this does not limit this invention.

<Compounding agent of acid gas and heavy metal>
The composite treatment agent according to the present invention includes a double salt containing calcium hydroxide and magnesium hydroxide, and an alkalinity reducing agent.

[Double salt]
The double salt contains calcium hydroxide and magnesium hydroxide as essential components. The method for producing the double salt is not particularly limited, but as an easy example, dolomite (dolomite, CaMg (CO ₃ ) ₂ ) is calcined, hydroxylated (digested), and dolomite hydroxide (Ca (OH ), and to obtain a _{2 · Mg (OH) 2)} .

  If the double salt does not contain calcium hydroxide, the acidic gas contained in the exhaust gas cannot be suitably treated, which is not preferable. If it does not contain magnesium hydroxide, the alkalinity of the double salt is high, and the double salt remaining in the system inhibits the fixation of heavy metals contained in the fly ash by the heavy metal fixing agent, and the heavy metals contained in the double salt are suitable. That may not be able to be suppressed, and the reaction product of calcium hydroxide and acid gas becomes passive and suppresses the suppression of the subsequent reaction. It may not be sufficiently reduced, which is not preferable.

Since the double salt contains not only calcium hydroxide but also magnesium hydroxide, the alkalinity can be suppressed lower than the case of not containing magnesium hydroxide. Alkalinity of the double salt is not particularly limited, it is preferable that 500MgCaCO ₃ / g or more 1000mgCaCO is ₃ / g or less, and more preferably 700MgCaCO ₃ / g or more 900MgCaCO ₃ / g or less. For reference, the alkalinity when the powder is calcium hydroxide alone is in the range of 1200 mgCaCO ₃ / g or more and 1350 mgCaCO ₃ / g or less.

In this specification, the alkalinity refers to a sample in which a sample (0.1 to 0.5 g) and 1,000 times the amount of pure water (100 to 500 ml) are put into a beaker and stirred for 1 hour with a magnetic stirrer. Take a predetermined amount (ml) with a micropipette, add a few drops of phenolphthalein indicator, mix, and then quickly titrate until 1 / 50N sulfuric acid changes color (to reach pH 8.3). The titration amount (ml) of sulfuric acid is recorded, and the value calculated by the following conversion formula is used.
(Conversion formula)
Alkalinity (mgCaCO ₃ / g)
= 0.02 {Titration sulfuric acid concentration (mol / L)} x A (ml) ÷ B (g) x C (ml) ÷ D (ml) x 100 ÷ 2
= A (ml) / B (g) x C (ml) / D (ml)

  In the conversion formula, A is a sulfuric acid titration amount (ml), B is a sample amount (g), C is a pure water addition amount (ml), and D is a preparative amount after stirring (ml). ml).

  The composite treatment agent according to the present invention contains a double salt composed of calcium hydroxide and magnesium hydroxide. Even if the composite treatment agent contains a mixed salt of magnesium hydroxide powder and calcium hydroxide powder, this mixture does not correspond to a double salt. Different. In a double salt, a calcium atom and a magnesium atom constitute a single salt, but in a mixed salt of simple salts, magnesium hydroxide powder and calcium hydroxide powder are in a state of being dispersed with each other. .

  In the double salt, (a) the double salt itself has an alkalinity reducing effect by making magnesium hydroxide an essential component in addition to calcium hydroxide, and (b) calcium hydroxide and acid gas. By suppressing the reaction product from being passive, the alkalinity reducing effect is considered to be able to take in the acidic gas to the inside of the particles, (c) sulfate, which is another component of the composite treatment agent The alkalinity reducing effect by one or more compounds selected from the above (alkalinity reducing agent) and (d) the alkalinity reducing effect by the reaction product with acidic gas can be obtained. It is presumed that the alkalinity of ash can be reduced to about ½, and as a result, the amount of elution of heavy metals from fly ash can be suppressed.

The specific surface area of the double salt is not particularly limited, it is preferably ^{20 m} 2 / g or more, more preferably ^{30 m} 2 / g or more, more preferably ^{40 m} 2 / g or more. If the specific surface area is too small, the contact area with the acidic gas (hydrogen chloride gas, sulfur oxide gas, etc.) may be small, and the acidic gas may not be suitably treated. Further, along with this, unreacted double salt increases and the alkalinity of the fly ash increases, and as a result, there is a possibility that the amount of heavy metal elution from the fly ash after treatment with the heavy metal fixing agent cannot be suitably suppressed.

  The median diameter (d50) of the double salt is not particularly limited, but is preferably 30 μm or less, and more preferably 20 μm or less.

  The lower limit of the median diameter is not particularly limited, but the median diameter of the double salt is preferably 5 μm or more.

  In the present specification, the “median diameter” refers to a particle diameter (d50) at which the integrated value of the number of particles in a particle size distribution on a volume basis obtained by a laser diffraction method is 50%.

  The ratio of calcium hydroxide to magnesium hydroxide is not particularly limited, but both the effect of treating acidic gas with calcium hydroxide and the effect of reducing the alkalinity of the double salt itself with magnesium hydroxide can be suitably obtained. In view of the above, it is preferable that the molar ratio is within the range of calcium hydroxide: magnesium hydroxide = 0.79: 1.0 to 3.15: 1.0, and 0.96: 1.0 to More preferably, it is in the range of 2.36: 1.0.

(Alkalinity reducing agent)
The composite treating agent according to the present invention contains a compound having an alkalinity reducing action such as chloride, sulfate, hydroxide and the like. Hereinafter, this compound is referred to as “alkalinity reducing agent” for convenience.

  When the composite treatment agent is supplied to the flue, the acid gas reacts with the above-described double salt (mainly the calcium hydroxide component). The reaction products and unreacted substances in this reaction are collected as fly ash by a dust collector. And when water is added to the collected fly ash, the alkali content derived from calcium hydroxide contained in the unreacted double salt reacts with the alkalinity reducing agent and the reaction product, and the alkalinity of the fly ash Is reduced.

  The alkalinity reducing agent is not particularly limited as long as it can reduce the alkali content derived from calcium hydroxide contained in the unreacted double salt, but is selected from chloride, sulfate and hydroxide. Those containing more than one kind of compound are preferred. Examples of chlorides include magnesium chloride, aluminum chloride, iron (II) chloride, iron (III) chloride, zinc chloride, copper chloride and the like. Examples of sulfates include magnesium sulfate, aluminum sulfate, sulfate-containing aluminum hydroxide, iron (II) sulfate, iron (III) sulfate, zinc sulfate, copper sulfate and the like. Examples of the hydroxide include magnesium hydroxide, aluminum hydroxide, iron (II) hydroxide, iron (III) hydroxide, zinc hydroxide, copper hydroxide and the like. Among them, since the stability of the substance itself is high and heat generation when supplying the alkalinity reducing agent can be kept low, the alkalinity reducing agent includes magnesium sulfate, sulfate-containing aluminum hydroxide, zinc sulfate, copper sulfate, water It is preferable to include at least one selected from magnesium oxide, aluminum hydroxide, iron hydroxide, zinc hydroxide, and copper hydroxide.

The ratio between the double salt and the alkalinity reducing agent is not particularly limited, but the treatment effect of acidic gas with calcium hydroxide contained in the double salt and the alkali of the double salt itself with magnesium hydroxide contained in the double salt In view of the fact that both the effect of reducing the degree of alkalinity and the effect of reducing the alkalinity of fly ash by the alkalinity reducing agent can be suitably obtained, in the mass ratio, double salt: alkalinity reducing agent = 10: 0.5-10 : Preferably in the range of 8, more preferably in the range of 10: 1 to 10: 6. Further, when setting the ratio of the powder and the alkalinity reducing agent, the alkalinity of the fly ash is preferably 100 mgCaCO ₃ / g or less, more preferably 70 mgCaCO ₃ / g or less, more preferably 50 mgCaCO ₃ / g. Make sure that:

[Other ingredients]
If it is a range which does not inhibit this invention, a composite processing agent may contain the other component different from a double salt and an alkalinity reducing agent. Examples of other components include activated carbon for treating dioxin contained in acid gas, diatomaceous earth used as a filter aid for bag filters, and the like. Further, the composite treatment agent may contain a heavy metal fixing agent. In this case, the mixing step of the heavy metal fixing agent can be omitted, which is an effective means.

[Method for producing composite treatment agent]
The composite treatment agent can be obtained by uniformly mixing the various components described above by a conventionally known method.

<Method of treating acid gas and heavy metal>
In the treatment method according to the present invention, the above-mentioned composite treatment agent is supplied to the flue to treat the acidic gas contained in the exhaust gas, and then the fly ash is collected, and the heavy metal contained in the fly ash after the dust collection is heavy metal. Treating with a fixative.

  The type of exhaust gas is not particularly limited. For example, hydrogen chloride and sulfur oxides generated in combustion facilities such as municipal waste waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, private factories, etc. Exhaust gas containing any acid gas.

  The timing for supplying the composite treatment agent is not particularly limited as long as the fly ash is not collected in the dust collector. For example, the timing for incinerating waste in an incinerator, flue gas generated by incineration Until the temperature reduction tower that reduces the temperature of the exhaust gas, and after the exhaust gas is cooled by the temperature reduction tower, the exhaust gas after cooling reaches the bag filter provided in front of the dust collector Timing etc. are mentioned.

  Although the supply amount of the composite treatment agent is not particularly limited, in order to avoid both becoming too small and becoming too large, the concentration of acid gas passing through the flue is monitored and adjusted as appropriate. It is preferable to supply so as to satisfy the management target value for each combustion facility.

  After supplying the composite treatment agent to the flue, fly ash containing the reaction product of the acid gas and the composite treatment agent and the unreacted material as components is collected. The fly ash may be collected by a known dust collector.

  Here, an example in which the exhaust gas is treated with the composite treatment agent has been described as an example. However, as a separate form, the double salt is supplied to the flue, the fly ash is collected, and the alkali level is added to the fly ash after the dust collection. You may take the form which adds a reducing agent. In addition, when adding a double salt and an alkalinity reducing agent separately, you may add an alkalinity reducing agent as aqueous solution or a slurry.

  In the present invention, (a) the double salt itself contains calcium hydroxide as well as magnesium hydroxide as an essential component, and the alkalinity reduction effect of the double salt itself; The alkalinity of the fly ash after dust collection is kept low by the unreacted content with the salt and, in some cases, the alkalinity reducing effect of the reaction product of the acidic gas and the double salt. Therefore, elution of heavy metals such as lead can be suppressed without treating heavy metals contained in fly ash after dust collection with heavy metal fixing agents. However, when a small amount of heavy metal is eluted or heavy metals other than lead are eluted, it is preferable to treat the heavy metal contained in the fly ash after dust collection with a heavy metal fixing agent.

  Examples of heavy metal fixing agents include generally used organic chelate-based and inorganic-based ones. Examples of inorganic heavy metal fixing agents include phosphoric acid compounds, silicon dioxide compounds, iron-containing compounds, and acidic neutralizers, and at least one selected from these can be used. Phosphoric acid compounds exhibit a long-term fixing effect of heavy metals at a disposal site, and are effective materials from the viewpoint of environmental protection. A phosphoric acid compound reacts with lead which is a heavy metal, for example, forms lead chloropyromorphite or lead pyromorphite, and can fix lead in the form of a mineral.

  Phosphoric acid compounds exhibit a long-term fixing effect of heavy metals at a disposal site, and are effective materials from the viewpoint of environmental protection. A phosphoric acid compound reacts with lead which is a heavy metal, for example, forms lead chloropyromorphite or lead pyromorphite, and can fix lead in the form of a mineral.

  The phosphoric acid compound can be used without particular limitation as long as it contains phosphoric acid, and may be a phosphate or a mineral. Specific examples include orthophosphoric acid (orthophosphoric acid), polyphosphoric acid, metaphosphoric acid, hypophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, superphosphoric acid, primary phosphoric acid soda, and secondary phosphoric acid. Soda, trisodium phosphate, primary potassium phosphate, dibasic potassium phosphate, tertiary potassium phosphate, primary calcium phosphate, secondary calcium phosphate, primary magnesium phosphate, secondary magnesium phosphate, primary phosphate Ammonium, dibasic ammonium phosphate, lime superphosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, potassium hexametaphosphate, sodium pyrophosphate, potassium pyrophosphate, sodium phosphite, potassium phosphite, hypophosphorous acid Examples thereof include sodium and potassium hypophosphite. Among these, minerals having the form of orthophosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, tripolyphosphate, hexametaphosphate, pyrophosphate, hydroxyapatite, especially apatite (apatite Compound) exhibits a good heavy metal fixing effect.

  Phosphoric acid compounds are particularly useful for immobilization of lead among heavy metals.

The silicon dioxide-containing compound has the effect of containing calcium metal in fly ash and silicon dioxide to produce calcium silicate mineral (3CaO · 2SiO ₂ · 3H ₂ O), and encapsulating heavy metals in the mineral, In addition, it is considered that the effect of fixing heavy metal can be obtained by silicon dioxide directly acting on heavy metal to form hardly soluble heavy metal silicate (PbSiO3 or the like). The heavy metal fixation of the silicon dioxide-containing compound is affected by the alkali content in the fly ash, and if the alkali content in the fly ash is large, the required addition amount increases. Therefore, according to the present invention, the required addition amount can be greatly reduced even in the silicon dioxide-containing compound.

The silicon dioxide-containing compound can be used without particular limitation as long as it is a compound having an SiO ₂ component, and may be silicon dioxide itself, a salt, or a mineral.

  Silicon dioxide-containing compounds include silicates containing alkali metals and alkaline earth metals such as sodium silicate and potassium silicate, silica fume, silica gel, activated clay, zeolite, bentonite, kaolinite, halloysite, antigolite, piolite. Wright, talc, montmorillonite, savonite, permiculite, muscovite, barragonite, illite, phlogopite, biotite, margarite, zansophylite, donpasite, sudite, clinochlore, chamosite, sepiolite, palygorskite, imogolite, allophane, and hychinguerite And silicate minerals.

  Silicon dioxide-containing compounds are particularly useful for immobilizing lead among heavy metals.

  The iron-containing compound only needs to contain iron, and examples thereof include ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, polyferric sulfate, and iron powder.

  Iron-containing compounds are particularly useful for immobilization of hexavalent chromium, arsenic, selenium and mercury among heavy metals.

  The acidic neutralizing agent has a role of reducing the elution amount of heavy metals. The acidic neutralizer is also affected by the alkali remaining in the fly ash, and if the alkali content in the remaining fly ash is large, the required addition amount increases. Therefore, according to the present invention, the necessary addition amount of the acidic neutralizer can be greatly reduced.

  Examples of the acidic neutralizer include hydrochloric acid, sulfuric acid, nitric acid, aluminum chloride, polyaluminum chloride, aluminum sulfate and the like.

  The acidic neutralizer may be used alone, but is preferably used in combination with the above-described inorganic heavy metal fixing agent from the viewpoint of further suppressing elution of heavy metals. Moreover, when an inorganic heavy metal fixing agent and an acidic neutralizing agent are used in combination, it is preferable in that the amount of the expensive inorganic heavy metal fixing agent can be reduced. Furthermore, the effect of the present invention can be obtained even when a neutralizing agent and a chelate heavy metal fixing agent are used in combination.

  Here, the pH of the eluate when the liquid-solid ratio of the fly ash after adding the inorganic heavy metal fixing agent and / or the acidic neutralizer is 10 is preferably 8.0 to 11.5, particularly More preferably, it is 9.0-10.5.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these.

<Screening for alkalinity reducing agents>
The alkalinity reducing agent is sufficient if it can reduce the alkali content derived from calcium hydroxide contained in the unreacted material, and includes one or more compounds selected from chloride, sulfate and hydroxide. There is no particular limitation.

  First, in order to confirm the effect of the alkalinity reducing agent, the presence or absence of the alkalinity reducing action was confirmed for various compounds shown in Table 1.

For the ash generated from the municipal waste waste incinerator A factory (alkalinity: 106 mg CaCO ₃ / g, lead content: 4290 mg / kg, lead elution amount: 127 mg / L), various alkalinities listed in Table 1 The reducing agent was added in the proportions listed in Table 1. And the alkalinity after alkalinity reducing agent supply was measured. The results are shown in Table 1. From Table 1, as a result, the alkalinity reducing action was confirmed for various compounds.

In addition, in order to find a more suitable alkalinity reducing agent in terms of the stability of the substance itself and the suppression of heat generation when supplying the alkalinity reducing agent, the alkalinity reducing agent was screened for various compounds listed in Table 2. It was.
Material stability was evaluated by allowing the alkalinity reducing agent to stand for 1 week at room temperature / humidity and confirming the appearance.
Compounding stability was determined by adding 70 parts by weight of a high specific surface area dolomite hydroxide, 30 parts by weight of an alkalinity reducing agent and 20 parts by weight of water, and stirring with a spatula. ) Was evaluated.
The results of screening are shown in Table 2.

  From Table 2, copper chloride, magnesium sulfate, zinc sulfate, copper sulfate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, zinc hydroxide and copper hydroxide are excellent in both material stability and compounding stability. It was confirmed that it is more suitable as an alkalinity reducing agent.

  Moreover, the relationship of the elution density | concentration of harmful lead when alkalinity was reduced was confirmed using the fly ash of B factory. At this time, magnesium sulfate was used as an alkalinity reducing agent. The elution concentration of lead was determined by an elution test based on a method for testing metals contained in industrial waste (environmental agency notification No. 13 in 1973). The results are shown in Table 3.

  From Table 3, it was confirmed that when the alkalinity is reduced, the lead elution amount is also reduced.

Furthermore, for conditions where the landfill reference value (0.3 mg / L) could not be satisfied, using a phosphate compound (75% normal phosphoric acid aqueous solution) as a heavy metal fixing agent, lead fixation was performed under the conditions shown in Table 4. Processed. As a result, it was found that the necessary addition rate of the heavy metal fixing agent is reduced by reducing the alkalinity.

<Preparation of composite treatment agent>
[Example 1]
High specific surface area dolomite hydroxide (compound containing calcium hydroxide and magnesium hydroxide, represented by Ca (OH) ₂ .Mg (OH) ₂ , specific surface area: 50 m ² / g, median diameter (d50) : 15 μm) 70 parts by weight and sulfate-containing aluminum hydroxide (product name: ashnite I-201, compound represented by the chemical formula Al _x (SO ₄ ) y (OH) _Z, etc., manufactured by Kurita Kogyo Co., Ltd.) The composite treating agent according to Example 1 was obtained.

[Example 2]
The composite according to Example 2 was prepared in the same manner as in Example 1 except that the sulfate-containing aluminum hydroxide was changed to magnesium sulfate (specific surface area: 5.8 m ² / g, median diameter (d50): 228 μm). A treating agent was obtained.

  In Examples and Comparative Examples, “specific surface area” is a specific surface area calculated by the BET method, and “pore volume” is a pore volume calculated by the BJH method. All of these can be measured by a measuring apparatus such as NOVA2000 manufactured by Quanta Chrome. The “median diameter (d50)” is a particle diameter (d50) at which the integrated value of the number of particles in the particle size distribution determined by the laser diffraction scattering method is 50%, and is measured by SALD-2100 manufactured by Shimadzu Corporation. It can be measured by the device.

[Comparative Example 1]
70 parts by weight of highly reactive slaked lime (specific surface area: 46 m ² / g, median diameter (d50): 7.9 μm, pore volume: 0.26 ml / g) and magnesium hydroxide (product) Name: Magnesium hydroxide 300, specific surface area: 35 m ² / g, median diameter 7 μm, manufactured by Kamishima Chemical Co., Ltd.) 30 parts by weight of a mixture, 70 parts by weight of the same sulfate-containing aluminum hydroxide as in the examples, Were mixed to obtain a composite treating agent according to Comparative Example 1.

[Comparative Example 2]
70 parts by weight of the same highly reactive slaked lime as in Comparative Example 1 and 30 parts by weight of the same sulfate-containing aluminum hydroxide as in the Example were mixed to obtain a treating agent according to Comparative Example 2.

[Comparative Example 3]
The same highly reactive slaked lime as in Comparative Example 1 was used as the treatment agent according to Comparative Example 3.

<Comparison of processing performance # 1>
Using the simulated dust collector indoor evaluation device shown in FIG. 1, the processing performance of various processing agents according to Examples and Comparative Examples was evaluated. In this apparatus, the test conditions were as follows.
Gas flow rate: 0.43 m ³ / min
Filtration area: 0.43 m ²
Filtration speed: 1 m / min
HCl concentration load; 350ppm
Dust collection chamber temperature: 180 ° C

  First, after adjusting the HCl concentration at the inlet of the dust collection chamber to 350 ppm, supply of various treatment agents according to Examples and Comparative Examples was started. Twenty minutes after the start of supply, an HCl meter (product name: HL-22, manufactured by Kyoto Electronics Co., Ltd.) was used to measure the outlet HCl concentration, and the average value of 30 minutes of data collected every other minute was measured under HCl under the test conditions. The outlet concentration was used. Then, the HCl removal rate was calculated from the inlet HCl concentration and the outlet HCl concentration. The results are shown in Table 5 and FIG.

  It was confirmed that the composite treatment agent according to the example can treat the acid gas suitably as in the case of various treatment agents so far. In the examples, the addition amount of the composite treatment agent necessary for achieving the HCl removal rate of 90% is 1.4 g / min, and there is a slight increase in the addition rate compared to the treatment agent according to the comparative agent. However, as described later, since the amount of heavy metal fixing agent added is optimized by reducing the alkalinity of fly ash, it is within a range that does not present any problem in terms of exhaust gas treatment and heavy metal treatment.

  Next, the alkalinity of the residue from which the filter cloth deposits were removed under each condition was measured. The results are shown in Table 6 and FIG.

When using a composite treating agent according to Examples 1 and 2, alkalinity remained the 170mgCaCO ₃ / g~180mgCaCO ₃ / g approximately, compared with treatment agent according to Comparative Examples 1 to 3, marked alkalinity reduction Indicates. Moreover, this tendency was confirmed in the wide range with the addition amount of a composite processing agent 0.8g / min-1.6g / min.

<Comparison of processing performance # 2>
In the above <Comparison of processing performance, part 1>, the residue after evaluating the processing performance of the various processing agents according to the examples and comparative examples was obtained from the C factory with the ash that was not blown with the acid gas processing agent. Then, 4 parts by weight of the first ash of the two-stage bag filter was mixed with 1 part by weight of the residue to prepare simulated fly ash. Table 7 shows the properties of ash obtained from Factory C and the properties of various simulated fly ash.

In this example, the lead content, eluate pH, and lead elution concentration are measured by the following methods.

Method for measuring lead content Fly ash is heated and concentrated with concentrated nitric acid and concentrated hydrochloric acid and allowed to cool. After standing to cool, pure water is added, and the heated and dissolved solution is filtered through a quantitative filter paper (Advantech, No. 6), and the lead concentration in the filtrate is measured by an atomic absorption photometer (Hitachi, Z-2000). Measured with

Method for Measuring Eluate pH After performing an elution test based on the Environmental Agency Notification No. 13 test method, the pH of the eluate was measured.

Method for measuring lead elution amount After conducting an elution test based on the Environmental Agency Notification No. 13 test method, the lead concentration in the eluate was measured with an atomic absorption photometer (manufactured by Hitachi, Z-2000).

Subsequently, for each simulated fly ash, lead fixing treatment was performed under the conditions shown in Table 8 using a phosphoric acid compound (75% normal phosphoric acid aqueous solution) which is a heavy metal fixing agent. In the lead fixation treatment, 20% by weight of pure water and a predetermined amount of various heavy metal fixatives (phosphate-based compounds, silicon dioxide-containing compounds, iron-containing compounds) are added to each fly ash sample. With thorough stirring. And while measuring the alkalinity and lead content of various samples after a lead fixation process, the elution test was done to Environment Agency Notification No. 13 test method, and eluate pH and lead elution concentration were measured. The results are shown in Table 8.

As can be seen from Table 8, with respect to Examples 1 and 2, the alkalinity was reduced, and accordingly, the amount of lead elution was reduced. Moreover, with the reduction in alkalinity, the addition rate of the phosphate heavy metal fixing agent for reducing the amount of lead elution to a landfill reference value or less was reduced.

Claims (6)

A double salt composed of calcium hydroxide and magnesium hydroxide, and an alkalinity reducing agent,
The alkalinity reducing agent includes one or more selected from magnesium sulfate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, zinc hydroxide and copper hydroxide,
The mass ratio of the said double salt and the said alkalinity reducing agent is the complex processing agent of an acidic gas and heavy metal which exists in the range of double salt: alkaliness reducing agent = 10: 0.5-10: 8. ^2. The composite treatment agent according to claim 1, wherein the double salt has a specific surface area of 20 m ² / g or more and a median diameter (d50) of less than 30 μm. The acidic gas is an acidic gas contained in exhaust gas,
The composite treatment agent according to claim 1, wherein the heavy metal is a heavy metal contained in fly ash. After adding double salt composed of calcium hydroxide and magnesium hydroxide to exhaust gas, collecting fly ash, adding an alkalinity reducing agent to the fly ash after dust collection,
The alkalinity reducing agent includes one or more selected from magnesium sulfate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, zinc hydroxide and copper hydroxide,
The mass ratio of the said double salt and the said alkalinity reducing agent exists in the range of double salt: alkalinity reducing agent = 10: 0.5-10: 8, The processing method of acidic gas and heavy metal.   A method for treating acidic gas and heavy metal, comprising collecting fly ash after adding the composite treating agent according to any one of claims 1 to 3 to exhaust gas. Heavy metal contained in the fly ash after dust collection , organic chelate, phosphate compound, silicon dioxide compound, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, polysulfuric acid ferric iron powder, hydrochloric acid, sulfuric acid, nitric acid, aluminum chloride, treatment with one or more heavy metal immobilizing agent selected from poly aluminum chloride and aluminum sulfate, Ru untreated der, according to claim 4 or 5 Acid gas and heavy metal treatment method.

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