JP2018192462A - Heavy metal immobilize method in fly ash - Google Patents

Abstract

To provide a heavy metal immobilize method which can suppress elution of heavy metals, especially mercury, without adding abundant chelate agent even if fly ash is highly alkaline, and to provide an agent composition therefor.SOLUTION: A heavy metal immobilize method includes a step of adding a chelate agent for heavy metal immobilizing, water for humidifying and polymer coagulant to fly ash caused by incineration disposal or gasification fusion processing of non-industrial wastes or industrial wastes, mixing them and kneading them. The polymer coagulant is anionic, nonionic or amphoteric polymer coagulant.SELECTED DRAWING: None

Description

  The present invention relates to a method for immobilizing heavy metals contained in fly ash generated due to incineration or gasification melting treatment of general waste or industrial waste. The present invention also relates to a pharmaceutical composition for immobilizing heavy metals contained in fly ash, related to such a method for immobilizing heavy metals.

  In general, waste is broadly classified into general waste such as municipal waste and industrial waste such as waste plastic. When any of these general wastes or industrial wastes is processed, it is subjected to incineration processing or gasification melting processing in an incineration processing facility or gasification melting processing facility.

  In the case of incineration, incineration main ash that accumulates at the bottom of the incinerator and incineration fly ash that floats in the air together with gas components generated by incineration are generated. Incineration fly ash is collected by an exhaust gas dust collector outside the incinerator. Incineration main ash and incineration fly ash have the same generation factors, and the components are substantially the same, and the same processing is required. Will be referred to as “flying ash”.

  Further, the gasification melting process is a combination of the gasification process and the melting process, and a gas component, a molten slag, and fly ash floating in the air together with the gas component are generated. The fly ash present together with the gas component is collected by an exhaust gas dust collector installed outside the gasification melting furnace as in the case of the incineration process described above.

  Furthermore, there is also known an ash melting facility that melts fly ash generated by incineration or gasification melting as described above into slag by melting it at a high temperature. Are collected by the exhaust gas dust collector.

  Fly ash produced by any of the above treatments contains harmful heavy metals. Various methods are known as a method for treating this harmful heavy metal, and examples include a method for immobilizing heavy metal. Among them, a treatment method using a chelating agent is frequently used because facilities are simple and the amount of elution of heavy metals can be fixed to a low level.

  However, in this heavy metal immobilization treatment with a chelating agent, there may be a phenomenon in which the elution of mercury exceeds the regulation value set by the Ministry of the Environment when the amount of chelate added is large or when the treatment is performed in a high alkali region.

  Patent Document 1 discloses a water washing step in which waste containing chlorine and heavy metals and water are mixed to elute chlorine and heavy metals in the waste to form a waste-containing eluent, and chlorine and heavy metals in the waste. A solid-liquid separation process for separating the waste from which salt has been desalted from the chlorine-containing eluate from which chlorine and heavy metals have been eluted, and adding a chelating agent and an anionic polymer flocculant to the chlorine-containing eluate, A chlorine-containing waste treatment method is described which includes an agglomeration step for agglomerating chlorine and heavy metals into an agglomerate, and a removal step for removing the agglomerate by filtration. In this document, before adding a chelating agent and an anionic polymer flocculant to a chlorine-containing eluate, the pH of the chlorine-containing eluate is adjusted to 8-11, most preferably to a pH of 9-10.5. The components are precipitated as hydroxides, the unreacted heavy metals are aggregated by a chelating agent, and these aggregates are further aggregated and separated by an anionic polymer flocculant. Since most of the heavy metals are converted into hydroxides by pH adjustment, the amount of chelating agent used can be reduced.

  However, many heavy metal hydroxides remain in the fly ash (demineralized cake), and there is a concern that heavy metals may be re-eluted due to the influence of pH fluctuations when landfilled in the final disposal site. Moreover, many chemical | medical agents are needed for pH adjustment.

JP 2014-237114 A

  The present invention has been made in view of the circumstances listed above, and even if fly ash is highly alkaline, heavy metals, particularly heavy metals that can suppress elution of mercury without adding a large amount of chelating agent. It is an object to provide an immobilization method and a pharmaceutical composition for the immobilization method.

  In order to solve the above problems, the present inventors have made various studies.

  Fly ash produced by incineration or gasification and melting treatment of general waste or industrial waste may vary depending on its origin, but when processing such high alkali fly ash Although it is necessary to add an excessive amount of chelating agent, mercury (Hg) may re-elute if the amount of the chelating agent added is excessive.

  This is because (1) the chelate compound becomes water-soluble by leaving an excess of the functional group of the chelating agent that is originally water-soluble by having a polar functional group without forming a chelate with the metal, (2) It is conceivable that it is colloidalized as mercury polysulfide and moves to the filtrate side (measured as the amount of elution) without being captured as filtrate during filtration in the elution test.

  In order to devise a solution to suppress mercury elution based on the possible causes as described above, we examined the mercury capture experiment using a highly alkaline mercury aqueous solution. The knowledge from the following three document descriptions was referred in advance.

(1) "About heavy metal wastewater treatment with polymer heavy metal scavenger" (PPM-1987 / 9, p35-55)
In the case of Hg ²⁺ in a single metal ion aqueous solution, a solubilization phenomenon is observed when the treatment pH is 6 or more and the removal efficiency is deteriorated by addition of one equivalent or more of the drug.

(2) Physics and Chemistry Dictionary: Colloidal particles and colloidal ions Colloidal particles are in the range of 0.1 to 1 μm in diameter when the particles are spherical in the dispersed state of the substance. In general, including particles that are not spherical, the particle is defined as a particle composed of 10 ³ to 10 ⁹ atomic groups. It is roughly classified into molecular colloid (polymer or macromolecule), micelle colloid and associating colloid according to its internal structure. The presence of these colloids cannot be confirmed with an optical microscope, but is observed with an electron microscope. These colloidal particles pass through ordinary filter paper, but their diffusion rate is significantly slower than low molecular weight particles.

  The colloidal ions are called charged colloidal particles having a diameter of about 1 to 0.001 μm, but are also called colloidal ions. They are called colloidal cations and colloidal anions according to the positive and negative charges, and move to the cathode and anode in electrophoresis, respectively. When an ion having the same kind of charge as a colloid ion (not a colloid) exists in the solution, this is called a side ion. The colloidal ion is considered to be surrounded by the counterion, and the counterion may be fixed in the colloid.

(3) Pollution Prevention Technology and Regulations (Water Quality Edition) 5th revision Mercury sulfide has excessive S ²⁻ , and when the pH rises, redissolution progresses due to the purification of mercury polysulfide. This requires the presence of a small excess of S ²⁻ .

In the actual wastewater treatment, the mercury concentration in the wastewater fluctuates, and sodium sulfide for fixing mercury matches the maximum mercury concentration. Therefore, when the mercury concentration is low, S ²⁻ becomes excessive and redissolution occurs. As an improvement measure, addition of iron (II) or iron (III) is used in combination. Iron sulfide is more soluble than mercury sulfide and can hold S ²⁻ in a small excess relative to HgS.

  In actual wastewater, iron may form iron polysulfide and the treated water may become cloudy. This white turbidity is a colloidal substance that cannot be separated by a filter and adsorbs mercury. Heavy metal scavengers have been used to remedy this drawback.

  Based on the above findings, colloid capture experiments were conducted by adding a chelating agent and a polymer flocculant to a highly alkaline mercury (Hg) aqueous solution, or by further adding an inorganic flocculant. Confirmed that it will be.

  The present inventors have applied the method for adding a polymer flocculant obtained as described above to the treatment of high alkali fly ash, which can suppress the elution of mercury, resulting in the completion of the present invention. .

  That is, the present invention is a heavy metal immobilization method for immobilizing heavy metals contained in fly ash generated due to incineration processing or gasification melting processing of general waste or industrial waste, The fly ash is added with a chelating agent for fixing heavy metals, water for humidification, and a polymer flocculant, and the polymer flocculant is anionic, nonionic, or amphoteric. It is a polymer flocculant.

  In the heavy metal immobilization method in fly ash of the present invention, it is preferable to further add an inorganic flocculant in the kneading step.

  In the method for immobilizing heavy metals in fly ash according to the present invention, the polymer flocculant is preferably added in an amount of 0.001 part by weight or more based on the total weight of the fly ash. .

  The present invention also provides a pharmaceutical composition for fixing heavy metals contained in fly ash, comprising a chelating agent for fixing heavy metals and a polymer flocculant.

  The pharmaceutical composition of the present invention preferably further includes an inorganic flocculant.

  The heavy metal immobilization method of the present invention includes a step of kneading a fly ash to be treated with a chelating agent for immobilizing heavy metal, water for humidification, and a polymer flocculant, and kneading the polymer The agent is an anionic, nonionic or amphoteric polymer flocculant, and even if the fly ash to be treated is highly alkaline, the action of the polymer flocculant promotes the aggregation of heavy metals, particularly mercury, The total mercury elution amount according to Notification No. 13 of the Ministry of the Environment can be suppressed below the standard value.

It is a graph which shows the measurement result of the residual Hg density | concentration in a filtrate at the time of using potassium diethyldithiocarbamate as a chelating agent for heavy metal fixation. It is a graph which shows the measurement result of the residual Hg density | concentration in a filtrate at the time of using tetra (dithiocarboxy) tetraethylene pentamine sodium as a chelating agent for heavy metal fixation. It is a graph which shows the measurement result of the residual Hg density | concentration in a filtrate at the time of using dipotassium = piperazine-1, 4- dicarbodithioate as a chelating agent for heavy metal fixation.

  Hereinafter, according to one embodiment of the present invention, a heavy metal immobilization method for immobilizing heavy metals contained in fly ash generated due to incineration processing or gasification melting processing of general waste or industrial waste This will be described in detail.

  In the method of the present invention, the fly ash to be treated includes a step of adding a chelating agent for fixing a heavy metal, water for humidification, and a polymer flocculant, and kneading the polymer flocculant, It is an anionic, nonionic or amphoteric polymer flocculant.

  Here, general waste means waste other than industrial waste in Article 2, Paragraph 2 of the Law on Waste Disposal and Cleaning, and household general waste that is waste discharged from general households. And industrial general waste that is waste other than industrial waste discharged by business operators. General waste includes, for example, what are called municipal waste and household waste.

  In addition, industrial waste refers to the waste generated by business activities in the law on waste treatment and cleaning, and waste disposed of by husk, sludge, waste oil, waste acid, waste alkali, waste plastics and other government ordinances. Means goods or imported waste.

  Fly ash generated by incinerating or gasifying and melting these general waste or industrial waste, or fly ash generated by ash melting that slags fly ash generated by these processes It exhibits a high alkalinity of pH 10 or higher, more specifically pH 12 or higher.

  In a conventional method not according to the present invention, that is, a method of treating from a chemical such as a chelating agent alone, mercury exceeding the reference value (0.005 mg / L) due to the high alkalinity of fly ash ( Several cases of Hg) eluting have been reported. For the purpose of preventing mercury elution, separation of fluorescent lamp tubes containing mercury, mercury thermometers, mercury sphygmomanometers, etc. has been strengthened. In the present situation, heavy metals are inevitably mixed in general waste or industrial waste.

  The method according to the present invention can immobilize heavy metals without increasing the amount of the chelating agent added even if fly ash is highly alkaline, and in particular, can suppress elution of mercury below a specified value.

  Here, the fly ash to be treated according to the present invention, for example, blows an alkali chemical (for example, slaked lime) into the upstream of the bag filter and reacts with the acidic gas (HCl, SOx, etc.) in the exhaust gas to collect dust. Collected fly ash (such as fly ash after dry desalination) is also included. In addition, if it contains a heavy metal, it will not be restricted to the fly ash mentioned above. For example, combustion ash may be used.

  The method according to the present invention can suppress the elution of mercury even when the fly ash has a pH of 10 or higher, more specifically 12 or higher, but for some reason. Thus, even if the fly ash has a pH of 12 or less, elution of mercury can be similarly suppressed.

  The chelating agent for immobilizing heavy metals used in the method of the present invention may be any as long as it can immobilize heavy metals, but is preferably a chelating agent having a carbamic acid group. Examples of such chelating agents include sodium tetra (dithiocarboxy) tetraethylenepentamine, potassium diethyldithiocarbamate, and dipotassium = piperazine-1,4-dicarbodithioate.

  In the present invention, the heavy metal to be fixed means all heavy metals that may be included in fly ash and are subject to regulation, and specifically, mercury (Hg), cadmium (Cd). Lead (Pb), chromium (Cr), arsenic (As), and selenium (Se). These heavy metals are immobilized by forming a chelate with a chelating agent.

  The humidifying water used in the method of the present invention is applied to such a degree that the fly ash can be made into a slurry state without any hindrance and a mixture such as a polymer flocculant can be kneaded in the kneading step. In addition, it is added in order to promote chelate formation between a heavy metal and a chelating agent, and is added in an amount that can achieve such a purpose. Moreover, even if it adds at once before performing the kneading | mixing process, it may be added in multiple times during the kneading | mixing process. Specifically, it is added at a weight ratio of 30 to 50 with respect to the total weight of fly ash.

  The polymer flocculant used in the method of the present invention is an anionic, nonionic or amphoteric polymer flocculant. As these polymer flocculants, in addition to these, cationic ones are known. As shown in Reference Example 11 described later, this type of polymer flocculant is effective in mercury fixation experiments. Since it was not obtained, it was excluded from the polymer flocculant used in the method of the present invention. Examples of the anionic polymer flocculant include sodium polyacrylate and polyacrylamide. Nonionic polymer flocculants include, for example, polyacrylamide.

  In general, particles repel each other when the surface charges are all anions or cations and remain colloidal. When anionic, nonionic, or amphoteric polymer flocculants are used, the results show that they are effective for coagulation precipitation, so that the heavy metal chelate complex is in the cationic state and anionic, nonionic, or amphoteric It is considered that the addition of the polymer flocculant causes the colloidal state to collapse and the aggregation proceeds, whereby the chelate complex is captured by the filter paper.

  The polymer flocculant is preferably added in an amount of 0.001 part by weight or more based on the total weight of the fly ash. This is because when the present inventors actually conducted a dissolution test in the treatment of fly ash, an aggregation effect was obtained with addition of 0.001 part by weight (corresponding to 1 ppm when the dissolution test was performed) or more. Is. Although there is no restriction | limiting in particular about an upper limit, It is thought that 0.01 weight part or less is enough from a viewpoint that a required amount for acquiring the effect of mercury elution suppression is enough, and a viewpoint of cost.

  In the above method, an inorganic flocculant may be further added in terms of further improving the mercury elution suppression effect.

  The inorganic flocculant means a flocculant containing an inorganic compound as a main component, and any flocculant having a heavy metal aggregating action may be used. For example, an aluminum-based or iron-based flocculant may be used. Can be mentioned. The reason for this is that inorganic aggregating agents such as aluminum and iron produce hydroxide colloids in aqueous alkaline solutions, and these colloids are called hydrophobic colloids and are sparingly soluble in water. (Plus charge). The addition of anionic, nonionic and amphoteric polymer flocculants is believed to have a superior agglomeration effect on this inorganic colloid.

  The aluminum-based aggregating agent means an aggregating agent mainly composed of an aluminum compound or made of an aluminum compound. Examples of such an aluminum compound include polyaluminum chloride.

  The iron-based flocculant means a flocculant mainly composed of an iron compound or made of an iron compound. Examples of such an iron compound include basic ferric sulfate (generic name: polyiron). Is mentioned.

  In the kneading step in the above-described method of the present invention, the chelating agent, the humidified water, the polymer flocculant, and the optional inorganic flocculant added to the fly ash to be kneaded are added simultaneously. Alternatively, it may be added step by step. The time required for the kneading process is not particularly limited because it varies depending on the type of kneading machine and the way of kneading, but it may be about several tens of seconds if it is a biaxial kneader for fly ash treatment. The temperature conditions at that time are not particularly limited, and may be room temperature. The chelation reaction between the heavy metal and the chelating agent is considered not to be usually overheated because the amount of heavy metal in the fly ash is very small as a whole.

(Example)
In the following, the heavy metal immobilization method according to the present invention will be specifically described using examples, and a comparative example for comparison with the examples and a reference example for reference will be shown. Further, the present invention is not limited to those shown in the examples.

  First, a heavy metal immobilization test according to the prior art was performed on gasified molten fly ash.

(Comparative Example 1)
In Comparative Example 1 below, a heavy metal immobilization test was performed on gasified molten fly ash. The gasified molten fly ash used had a pH of 12.2 to 12.4.

  To 100 parts by weight of the gasified molten fly ash, 6 parts by weight of tetra (dithiocarboxy) tetraethylenepentamine sodium, which is a pentamine sodium salt chelating agent, and 39 parts by weight of humidified water were added and kneaded well. About the obtained kneaded material, the elution test by Ministry of the Environment notification No. 13 was conducted.

  An outline of the dissolution test by Ministry of the Environment Notification No. 13 will be given.

  Using a shaker at normal temperature (generally 20 ° C.) and normal pressure (generally 1 atm) (with a shaking frequency adjusted to about 200 times per minute and a shaking width of 4 cm or more and 5 cm or less) Shake horizontally for hours.

  The results of the dissolution test are shown in Table 1 below.

  Calculation of the amount of heavy metal elution was similarly performed according to the method described in Ministry of the Environment Notification No.13.

  Specifically, 20 to 100 g (a gram) of the kneaded product is accurately applied to a flat balance bottle (with a capacity of 50 mL or more and previously dried) or an evaporation pan (with a capacity of 100 mL or more and previously dried). Evaporate to dryness, taking care not to boil, dry at 105-110 ° C. for 2 hours, and then allow to cool in a desiccator for 30 minutes. As a result, the weight (b gram) of the substance remaining in the flat balance or the evaporating balance is accurately obtained, and this is determined as the weight of the solid part and obtained by the following formula.

    Weight ratio of solid component (%) = b / a × 100

(Comparative Example 2)
The heavy metal immobilization test was conducted in the same manner as in Comparative Example 1 except that the chelating agent tetra (dithiocarboxy) tetraethylenepentamine sodium was 10 parts by weight and the humidified water was 35 parts by weight.

  The obtained results are shown in Table 1 below.

  In Table 1 above, T-Hg represents the total amount of mercury, that is, the total amount of alkali mercury compound and mercury or a compound thereof.

  As shown in Table 1, the elution amount of T-Hg exceeded the standard (0.005 mg / L or less) defined by the Prime Minister's Ordinance that defines the judgment standard related to industrial waste containing metals and the like.

(Test using mercury-containing solution)
The present invention includes a step of adding a chelating agent for immobilizing heavy metal, water for humidification, and a polymer flocculant to fly ash containing heavy metal, and adding a specific polymer flocculant. In order to preliminarily confirm the effect of immobilizing heavy metals, a test using a mercury-containing solution was conducted. Hereinafter, each test is shown as a reference example.

(Reference Example 1)
In this Reference Example 1, three kinds of heavy metal fixing chelates of potassium diethyldithiocarbamate, tetra (dithiocarboxy) tetraethylenepentamine sodium, and dipotassium = piperazine-1,4-dicarbodithioate were added to moles of mercury nitrate. In this case, the relationship between the pH of the solution and the concentration of mercury remaining in the solution was confirmed.

  For example, in order to conduct a test of 0.5 equivalent of potassium diethyldithiocarbamate, a 200 mL beaker is charged with 100 mL of 1 ppm Hg mercury nitrate aqueous solution and an amount of potassium diethyldithiocarbamate equivalent to 0.5 equivalents with respect to mercury nitrate in the aqueous solution. Was added. The pH of the initial mercury nitrate aqueous solution was 4. After stirring for 10 minutes, the total amount was filtered using glass fiber filter paper having a pore diameter of 1 μm, and the residual Hg concentration in the filtrate was measured.

  In the same manner, the residual Hg concentration at pH 6-14 was measured.

  Further, the residual Hg concentration at pH 4 to 14 was measured in the same manner in the case of 1 equivalent and 1.5 equivalent of potassium diethyldithiocarbamate.

  The results obtained by sequentially performing the above operations are shown in the graph of FIG.

  According to the same operation, when the chelating agent for fixing heavy metal was tetra (dithiocarboxy) tetraethylenepentamine sodium, dipotassium = piperazine-1,4-dicarbodithioate, the pH and residual Hg concentration at each equivalent Are shown in FIGS. 2 and 3, respectively.

  As shown in FIGS. 1 to 3, it was found that when the number of equivalents of the chelating agent to mercury is 1 or more, re-elution of mercury is observed on the high alkali side.

(Reference Example 2)
In this Reference Example 2, the residual Hg concentration was determined in the case where the pH of the solution was 12 and no chelating agent for fixing heavy metals was added, as a reference to the following Reference Examples 3 to 10.

  A 200 mL beaker was charged with 100 mL of a 1400 ppm Hg mercury chloride aqueous solution, adjusted to pH = 12 with an aqueous NaOH solution while stirring at a stirring speed of 150 rpm, and slowly stirred at a stirring speed of 50 rpm for 10 minutes. Then, it filtered using the glass fiber filter paper of the hole diameter of 1 micrometer, and measured the residual Hg density | concentration in a filtrate. Since no chelating agent for fixing heavy metals was used, naturally, a high residual Hg concentration of 1400 ppm was obtained.

(Reference Example 3)
A 200 mL beaker is charged with 100 mL of an aqueous solution containing 1400 ppm of mercury chloride. Here, a tetralium (dithiocarboxy) tetraethylenepentamine nanolium salt, which is a chelating agent for fixing heavy metals, is added to 2.0 equivalents of mercury. The corresponding amount was added and the pH was adjusted to 12 with an aqueous NaOH solution while stirring at a stirring speed of 150 rpm, and then slow stirring was performed at a stirring speed of 50 rpm for 10 minutes. Then, it filtered using the glass fiber filter paper of the hole diameter of 1 micrometer, and carried out similarly to the reference example 2, and measured the residual Hg density | concentration in a filtrate. That is, this reference example 3 shows a case where a chelating agent is added but a polymer flocculant is not added, and the difference in effect from the case where the polymer flocculants of the following reference examples 4 to 14 are used is compared. It was made to serve as a reference for doing so. The obtained residual Hg concentration was 48 ppm. In the following Reference Examples 4 to 14, a value that is at least smaller than this value is a criterion that should be regarded as having an effect of adding a polymer flocculant.

(Reference Example 4)
In the same manner as in Reference Example 2, 100 mL of an aqueous solution containing 1400 ppm of mercury chloride was put into a 200 mL beaker, and the nanolium salt of tetra (dithiocarboxy) tetraethylenepentamine, which is a chelating agent for fixing heavy metals, was converted into mercury. On the other hand, it was added in an amount corresponding to 2.0 equivalents and adjusted to pH = 12 with an aqueous NaOH solution while stirring at a stirring speed of 150 rpm. Thereafter, an anionic polymer flocculant (UF-105 manufactured by Unitika) was added to this so as to be 0.5 ppm with respect to 100 mL of the aqueous solution, followed by slow stirring at a stirring speed of 50 rpm for 10 minutes. The solution was filtered using a glass fiber filter having a pore diameter of 1 μm, and the residual Hg concentration in the filtrate was measured in the same manner as in Reference Example 2. The obtained residual Hg concentration was 35 ppm.

(Reference Example 5)
The residual Hg concentration was measured in the same manner as in Reference Example 4 except that anionic polymer flocculant (UF-105 manufactured by Unitika) was added to 1.0 ppm with respect to 100 mL of the aqueous solution. The obtained residual Hg concentration was 14 ppm.

(Reference Example 6)
The residual Hg concentration was measured in the same manner as in Reference Example 4 except that anionic polymer flocculant (UF-105 manufactured by Unitika) was added to 2.0 ppm with respect to 100 mL of the aqueous solution. The obtained residual Hg concentration was 5.8 ppm.

(Reference Example 7)
The residual Hg concentration was measured in the same manner as in Reference Example 4, except that anionic polymer flocculant (UF-105 manufactured by Unitika) was added to 3.0 ppm with respect to 100 mL of the aqueous solution. The obtained residual Hg concentration was 3.8 ppm.

(Reference Example 8)
After adding and stirring potassium dithiocarbamate, which is a chelating agent for fixing heavy metals, aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) (also referred to as sulfuric acid band), which is an inorganic flocculant, is adjusted to 100 ppm with respect to 100 mL of an aqueous solution. The residual Hg concentration was measured in the same manner as in Reference Example 5 except that it was added as described above. The obtained residual Hg concentration was 0.11 ppm.

(Reference Example 9)
The residual Hg concentration was measured in the same manner as in Reference Example 8 except that polyferric sulfate was used in place of the sulfate band as the inorganic flocculant. The obtained residual Hg concentration was 0.10 ppm.

(Reference Example 10)
The residual Hg concentration was measured in the same manner as in Reference Example 6 except that nonionic polymer flocculant (UF-250 manufactured by Unitika) was used as the polymer flocculant. The obtained residual Hg concentration was 15 ppm.

(Reference Example 11)
Residual Hg concentration was measured in the same manner as in Reference Example 6 except that a cationic polymer flocculant (UF-340 manufactured by Unitika) was used as the polymer flocculant. The obtained residual Hg concentration was 51 ppm.

(Reference Example 12)
The residual Hg concentration was measured in the same manner as in Reference Example 6 except that the amphoteric polymer flocculant (UF-715 manufactured by Unitika) was used as the polymer flocculant. The obtained residual Hg concentration was 37 ppm.

(Reference Example 13)
The residual Hg concentration was measured in the same manner as in Reference Example 8 except that nonionic polymer flocculant (UF-250 manufactured by Unitika) was used as the polymer flocculant. The obtained residual Hg concentration was 0.33 ppm.

(Reference Example 14)
The residual Hg concentration was measured in the same manner as in Reference Example 9 except that nonionic polymer flocculant (UF-250 manufactured by Unitika) was used as the polymer flocculant. The obtained residual Hg concentration was 0.32 ppm.

  Table 2 summarizes the concentration and conditions of each reagent introduced and the obtained effect (residual Hg concentration) for each of Reference Examples 2 to 14.

  As shown in Table 2, Reference Examples 4 to 7 to which an anionic polymer flocculant is added can suppress the mercury elution action as compared with Reference Example 3 to which no polymer flocculant is added. It was. Further, as apparent from the results of Reference Examples 4 to 7, the effect of fixing mercury was increased as the amount of the anionic polymer flocculant added was increased.

  Moreover, it became clear by comparing Reference Example 5 with Reference Examples 8 and 9 that the effect of suppressing mercury elution is significantly improved by further adding an inorganic flocculant.

  Further, as is clear from Reference Example 10, the effect of fixing mercury was also observed when a nonionic polymer flocculant was used.

  On the other hand, as apparent from Reference Example 11, the cationic polymer flocculant could not obtain the effect of mercury fixation.

  Further, as apparent from Reference Example 12, the effect of mercury fixation was obtained by using an amphoteric polymer flocculant.

  As is apparent from comparison between Reference Example 10 and Reference Examples 13 and 14, even when a nonionic polymer flocculant and an inorganic polymer flocculant are used, the remarkable effect of mercury fixation is remarkable. Improved.

(Test using gasified molten fly ash)
Based on the result obtained by the mercury immobilization test according to Reference Examples 1 to 14 using a mercury-containing solution, the immobilization test for heavy metals contained in the gasified molten fly ash was performed. That is, in the following examples, a heavy metal immobilization test was performed using a chelating agent and an anionic polymer flocculant.

Example 1
The test object is the same gasified molten fly ash as used in Comparative Examples 1 and 2. For 100 parts by weight of the gasified molten fly ash, 6 parts by weight of tetra (diethylcarboxy) tetraethylenepentamine sodium (hereinafter also referred to as pentamine Na salt) as a chelating agent, 39 parts by weight of humidified water, After adding 0.002 part by weight (UF-105 manufactured by Unitika) as a molecular flocculant, it was kneaded well. About the kneaded material, the elution test by Ministry of the Environment Notification No. 13 similar to that described in Comparative Example 1 was performed, and the elution amount was calculated for each heavy metal.

(Example 2)
In the kneading, the amount of the polymer flocculant added was 0.001 part by weight (halved), and 0.05 part by weight of polyiron sulfate as an inorganic flocculant was further added. Same as above.

  In Examples 1 and 2, the addition amount of the polymer flocculant and the inorganic flocculant was such that the flocculant concentration in the filtrate during the elution test of the treated ash was 2 ppm as the polymer flocculant in Example 1. In Example 2, it was added so as to be 50 ppm as polyiron sulfate and 1 ppm as a polymer flocculant.

  The results of the heavy metal elution test of the kneaded products obtained in Examples 1 and 2 are shown in Table 3 below.

  As can be seen from Table 3 above, a chelating agent for fixing heavy metals, humidified water, and a polymer flocculant are added to the gasified molten fly ash to be treated as in Example 1 and kneaded. As a result, aggregation of mercury was promoted, and its filterability was improved. As a result, residual Hg in the filtrate could be reduced.

  Further, as in Example 2, the residual Hg in the filtrate could be further reduced by further adding an inorganic flocculant.

Claims (5)

A heavy metal immobilization method for immobilizing heavy metals contained in fly ash resulting from incineration processing or gasification melting processing of general waste or industrial waste,
Including a step of adding a kneading agent for fixing heavy metal, water for humidification, and a polymer flocculant to the fly ash to be treated, and kneading the polymer flocculant, anionic, nonionic, Alternatively, a method for immobilizing heavy metals in fly ash, which is an amphoteric polymer flocculant.   The method for immobilizing heavy metal in fly ash according to claim 1, wherein an inorganic flocculant is further added in the kneading step.   The method for immobilizing heavy metals in fly ash according to claim 1 or 2, wherein the polymer flocculant is added in an amount of 0.001 parts by weight or more based on the total weight of the fly ash.   A pharmaceutical composition for fixing heavy metals contained in fly ash, comprising a chelating agent for fixing heavy metals and a polymer flocculant. The pharmaceutical composition for fixing heavy metals contained in fly ash according to claim 4, further comprising an inorganic flocculant.

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