JP5967397B2 - Methods for insolubilizing hazardous substances - Google Patents

Description

  The present invention relates to a method for insolubilizing a hazardous substance, which insolubilizes a harmful substance such as heavy metal distributed in a contaminated area in the ground in situ.

  Various toxic substances such as volatile organic chlorine compounds such as trichlorethylene, fuel oils and machine oils, dioxins, and heavy metals such as cadmium, lead, copper, zinc, nickel and chromium are found in the ground of the factory site. May be mixed.

  If the soil contaminated with such harmful substances is left as it is, the harmful substances will diffuse to the surrounding area and hinder the lives of the residents in the surrounding area. It may cause pollution. Therefore, the soil contaminated with the above-mentioned harmful substances is prevented from spreading to the environment by performing purification treatment or insolubilization treatment by various methods.

  In order to insolubilize harmful substances in the ground, if it is distributed on a small scale near the ground surface, a method of excavating the contaminated area in the ground and treating it with a plant can be adopted. In-situ processing without drilling is desirable in terms of cost. For example, it is used for soft ground improvement methods such as deep mixing machines used for horizontal blade mechanical stirring and shallow mixing machines used for vertical continuous mixing. A technique of stirring and mixing while injecting an insolubilizing material into a contaminated area of the ground using a heavy machine is employed.

  On the other hand, a method has been developed in which a liquid to which an insolubilizing material is added is prepared in advance as an insolubilizing material solution or an insolubilizing material slurry, and the insolubilizing material solution or the insolubilizing material slurry is injected into the ground through an injection well. Therefore, although applicable ground is limited to permeable ground, even if it is difficult to use heavy machinery because existing structures exist on the ground or near the ground surface, harmful substances in the ground can be removed. In addition to being able to insolubilize, it is possible to insolubilize harmful substances distributed in the contaminated area of the ground simply by installing an injection well regardless of the presence or absence of existing structures.

JP 2004-255376 A

  However, when the insolubilizing material slurry in which the powder insolubilizing material is suspended in water is injected into the ground, the insolubilizing material is agglomerated and settled while the insolubilizing material slurry penetrates the ground. The situation that the strainer of the injection well is clogged due to the aggregation of, and as a result, the insolubilized material can not penetrate into the contaminated area in the ground, the infiltration range is limited to the periphery of the injection well, Since the powder insolubilizing material is sparingly soluble in water, it has been difficult to produce a homogeneous insolubilizing material slurry in the first place.

  On the other hand, a method of dispersing the insolubilizing material using an inorganic type dispersing agent such as polyphosphate or a surfactant type dispersing agent is also conceivable, but adding these dispersing agents increases the pH of the insolubilizing material slurry, If it is an iron oxide type insolubilizing material, there exists a possibility that the adsorption | suction effect | action of heavy metal and by extension, insolubilization effect | action may fall.

  The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a method for insolubilizing harmful substances that can infiltrate the insolubilizing material into the contaminated area in the ground while maintaining the insolubilizing action. .

In order to achieve the above object, a method for insolubilizing a harmful substance according to the present invention comprises adding a powder insolubilizing material together with a dispersing agent to water as described in claim 1 so that the insolubilizing material is suspended in water. A method for insolubilizing a harmful substance, wherein the insoluble material slurry is infiltrated into a contaminated area of the ground contaminated with the harmful substance to insolubilize the harmful substance by an adsorption action. The dispersant is made of polyacrylate, polymethacrylate or a copolymer thereof, the weight average molecular weight Mw is 10,000 to 14000, and the harmful substances are cadmium, all cyan, lead, hexavalent chromium, Arsenic, total mercury, alkyl mercury, copper, selenium, fluorine or boron .

  The hazardous substance insolubilization method according to the present invention is a method in which the polyacrylate, polymethacrylate or a copolymer thereof is used as a monovalent salt.

  Further, in the method for insolubilizing a harmful substance according to the present invention, the insolubilizing material may be ferrous oxide, ferric oxide, ferric oxide, ferrous oxide, ferrous sulfate, or ferrous chloride. While making the iron oxide which oxidized the ferrous salt, the mass ratio of the said dispersing agent with respect to this insolubilization material shall be 0.05-1.

  Further, in the method for insolubilizing harmful substances according to the present invention, the mass ratio of the dispersing agent to the insolubilizing material is changed from 0.05 to 1 to 0.1-1.

In the method for insolubilizing harmful substances according to the present invention, a powder insolubilizing material is added to water together with a dispersant to produce an insolubilizing material slurry in which the insolubilizing material is suspended in water, and then the insolubilizing material slurry In order to insolubilize the harmful substance by adsorbing action by infiltrating the contaminated area of the ground contaminated with the harmful substance, the dispersant is composed of polyacrylate, polymethacrylate or a copolymer thereof, The weight average molecular weight Mw is set to 10,000 to 14,000, and the harmful substance is constituted as cadmium, all cyan, lead, hexavalent chromium, arsenic, total mercury, alkyl mercury, copper, selenium, fluorine or boron .

  If it does in this way, while the above-mentioned dispersing agent will not make an insolubilizing material aggregate, it will disperse | distribute reliably in an insolubilizing material slurry, and there is also no fear of reducing an insolubilizing effect by pH rise.

  For this reason, the insolubilized material slurry penetrates into the contaminated area in the ground without clogging at the infiltration start position (injection position) or coagulating sedimentation during infiltration, and while retaining the insolubilizing action of the insolubilizing material. To do.

  Moreover, the said dispersing agent also has the effect | action which suppresses the viscosity increase of an insolubilization material slurry by the high dispersibility. Therefore, the permeability of the insolubilized material slurry in the ground is improved, and the water permeability restriction required for the applicable ground is greatly relaxed.

  The means for infiltrating the insolubilizing material slurry into the contaminated area of the ground contaminated with harmful substances is optional, for example, using a method of using a head difference through an injection well or an injection method or injection pipe similar to the chemical injection method A method by pressure injection can be employed.

Hazardous substances are specified in the Environmental Agency Notification as a target of soil elution standards (Cadmium, All Cyan, Lead, Hexavalent Chromium, Arsenic, Total Mercury, Alkyl Mercury, Copper, Selenium, Fluorine, Boron) .

  A dispersing agent may be comprised only from polyacrylate or polymethacrylate, and may be comprised as those copolymers. Moreover, you may use these copolymers together.

  Here, the reason why the weight average molecular weight Mw is set to 10000 to 14000 is that sufficient dispersibility can be secured within the above range. Incidentally, the weight average molecular weight Mw is obtained on the basis of polystyrene by gel permeation chromatography (GPC).

  If the weight average molecular weight Mw is in the above range, the insolubilizing material can be surely dispersed in the insolubilizing material slurry, but the polyacrylate, polymethacrylate or copolymer thereof described above is particularly preferable. If a monovalent salt such as an alkali metal salt such as sodium salt, potassium salt or lithium salt or ammonium salt is used, a dispersion function can be obtained with a small amount of addition.

  The insolubilizing material can be appropriately selected from known substances that can trap harmful substances such as heavy metals by adsorption, and includes, for example, clay minerals such as bentonite, magnesium oxide, ferrous oxide, and second oxide. It is possible to employ iron oxide-based insolubilizing materials including iron oxides such as iron or iron tetroxide, and iron oxides obtained by oxidizing ferrous salts such as ferrous sulfate or ferrous chloride. .

  Here, the insolubilizing material, iron oxide made of ferrous oxide, ferric oxide or iron tetroxide, or iron oxide obtained by oxidizing ferrous sulfate or ferrous chloride made of ferrous chloride and In this case, the mass ratio of the dispersant to the insolubilizing material can be 0.05 to 10, preferably 0.05 to 1, more preferably 0.1 to 1, particularly preferably 0.1 to 0. 5 is good.

  This is because if the mass ratio of the dispersant to the insolubilizing material is less than 0.05, the dispersing action is insufficient, and if it exceeds 10, the pH becomes excessively high and the insolubilizing action may be lowered.

  On the other hand, if the mass ratio of the dispersant to the insolubilizing material is 0.1 or more, a good dispersing action can be secured. If it is 1 or less, the pH is kept lower than 9.5, and 0.5 or less. This is because the pH can be suppressed to about 9 or less.

Schematic which showed the implementation situation of the insolubilization method of the harmful substance which concerns on this embodiment. It is a graph showing the results of the demonstration test, (a) is a graph showing the relationship between the mass ratio of the test dispersant to the test insolubilized material and the residual ratio of the insolubilized material remaining in the supernatant of the test sample slurry, (b) shows the relationship between the mass ratio and the pH of the specimen slurry. FIG. 3 is a graph showing the results of a demonstration test, (a) is a graph showing a change with time of a water permeability coefficient, and (b) is a graph showing a change with time of a residual rate of an insolubilized material.

  Embodiments of the method for insolubilizing harmful substances according to the present invention will be described below with reference to the accompanying drawings.

  In the method for insolubilizing harmful substances according to this embodiment, first, an insolubilizing material slurry is prepared by adding and suspending the insolubilizing material together with a dispersant in water.

  The dispersant is made of polyacrylate, polymethacrylate or a copolymer thereof and has a weight average molecular weight Mw of 10,000 to 14,000. The polyacrylate, polymethacrylate or copolymer thereof is preferably a monovalent salt such as an alkali metal salt such as a sodium salt, a potassium salt or a lithium salt or an ammonium salt in order to enhance the dispersion function.

  As such a dispersing agent, it is preferable to use a dispersing agent for a stable liquid sold by Sanyo Kasei Kogyo Co., Ltd. under the trade name “SUPER SLURRY B”.

  The insolubilizing material may be appropriately selected according to the type of harmful substance to be insolubilized.For example, when cadmium, lead, hexavalent chromium, arsenic, mercury, selenium, or fluorine is a harmful substance, An iron oxide made of ferrous oxide, ferric oxide or triiron tetroxide, or an iron oxide obtained by oxidizing a ferrous salt made of ferrous sulfate or ferrous chloride can be selected.

  As such an insolubilizing material, for example, a material sold by Ishihara Sangyo Co., Ltd. under the trade name “Fixall” (registered trademark) may be used.

  In addition, arsenic, phosphorus, selenium, and hexavalent chromium are subject to insolubilization, and environmental purification materials sold by Sophia Co., Ltd. under the trade name “Azley S”, and arsenic, lead, hexavalent chromium, and selenium are subject to insolubilization. MSI-SH3 "heavy metal adsorbent sold by JFE Mineral Co., Ltd. or" TG Catch II "for insolubilization of hexavalent chromium, cadmium, arsenic, selenium, lead, fluorine and boron It is possible to use heavy metal high performance adsorbents sold by Technica GK.

  Here, when the insolubilizing material is iron oxide, the mass ratio of the dispersant to the insolubilizing material is 0.05 to 1, desirably 0.1 to 1, more desirably 0.1 to 0.5. It is good.

  This is because if the mass ratio of the dispersant to the insolubilizing material is less than 0.05, the dispersing action is insufficient, and if it exceeds 10, the pH becomes excessively high and the insolubilizing action may be lowered.

  On the other hand, if the mass ratio of the dispersant to the insolubilizing material is 0.1 or more, a good dispersing action can be secured. If it is 1 or less, the pH is suppressed to less than 9.5 and 0.5 or less This is because the pH can be further suppressed to 9 or less.

  Once the insolubilized material slurry is produced, the insolubilized material slurry is poured into the ground and allowed to penetrate into the contaminated area in which harmful substances to be insolubilized are distributed.

  In order to infiltrate the insolubilized material slurry into the contaminated area, as shown in FIG. 1 (a), in consideration of the flow of groundwater passing through the contaminated area 2 in the ground 1, the injection well is positioned upstream. 3 is excavated and formed in the ground 1, and the insolubilized material slurry is injected into the injection well.

  On the other hand, when it is difficult to place the contaminated area in a natural groundwater flow due to the fact that the contaminated area is distributed at a position shallower than the groundwater level, as shown in FIG. The groundwater level is raised in the contaminated area 2 by damming the groundwater with the underground water blocking wall, and the insolubilized material slurry is injected from the injection well 3 in such a state.

  Further, instead of the method shown in FIG. 6B, as shown in FIG. 6C, the water injection well 5 and the pumping well 8 are excavated to sandwich the contaminated area 2, and the water blocking walls 6 and By constructing the water blocking walls 7, injecting water from the injection well 5 and pumping it from the pumping well 8, artificially creating a groundwater flow from the injection well 5 to the pumping well 8, The insolubilized material slurry may be injected from the injection well 3 formed by excavation between the contaminated areas 2.

  When the insolubilized material slurry is injected into the ground 1 through the water injection well 3 in this way, the insolubilized material uniformly dispersed in the slurry by the dispersant does not clog the strainer (not shown) of the injection well 3. It flows to the outside of the injection well and does not coagulate and settle in the soil particle gap of the ground 1, reaches the contaminated area 2 in the form of being entrained in the groundwater flow described above, penetrates into the contaminated area and is harmful Insolubilize.

  As described above, according to the method for insolubilizing harmful substances according to the present embodiment, the polyacrylic acid salt, the polymethacrylic acid salt or a copolymer thereof is dispersed so that the weight average molecular weight Mw is 10,000 to 14,000. In addition, the dispersant is added to water together with the insolubilizing material to form an insolubilizing material slurry, so that the insolubilizing material does not cause clogging in the injection well and does not cause aggregation precipitation in the ground during infiltration. It reaches the contaminated area in the ground, penetrates into the contaminated area, does not raise the pH, and does not lower the insolubilizing action.

  Therefore, the insolubilizing material that has penetrated into the contaminated area surely insolubilizes harmful substances in the contaminated area, thus preventing the diffusion to the environment.

  In addition, according to the method for insolubilizing harmful substances according to the present embodiment, the above-described dispersant exhibits high dispersibility and suppresses the increase in viscosity of the insolubilized material slurry, so that the permeability of the insolubilized material slurry in the ground is improved. However, the water permeability restriction required for the applicable ground is also greatly eased.

  Next, a verification test was conducted on the method for insolubilizing harmful substances according to the present invention, which will be described below.

(a) Dispersion test "Fixall" (registered trademark) trade name of Ishihara Sangyo Co., Ltd. sold by Ishihara Sangyo Co., Ltd. The stabilizer for stabilizers sold by Sanyo Kasei Kogyo Co., Ltd. under the trade name is used as a test dispersant, and these test insolubilizer and test dispersant are added to water so that their mass ratios are different. A plurality of test specimen slurries are mixed to measure turbidity to obtain turbidity A, and after standing for 30 minutes, 30 mL of the supernatant is sampled from each test specimen slurry, and their turbidity is obtained. Was measured in the same manner as turbidity B, and then
Residual rate of insolubilized material (%) = (turbidity B / turbidity A) × 100
The change in turbidity due to standing was calculated as the residual ratio of the insolubilized material. The results are shown in FIG.

  As shown in the figure, when the mass ratio of the test dispersant to the test insolubilizer is 0.01, the residual ratio is about 2%, whereas the residual ratio is about 30 when the mass ratio is 0.05. The residual ratio was almost 100% at 0.1 or more.

  From these results, it was found that when the mass ratio of the dispersant to the insolubilizing material is 0.05 or more, preferably 0.1 or more, the insolubilizing material can be dispersed in the slurry at a certain level or more. If the ground has high water permeability, the penetration rate is fast. Therefore, it is sufficient to set the mass ratio of the dispersant to the insolubilizing material to 0.05 or more. Even if it exists, it means that the mass ratio may be set to 0.1 or more.

(b) Dissolution test A composite contaminated soil of arsenic, selenium and lead was prepared, and among the above-mentioned test slurry, a test slurry having a mass ratio of 0.2 was put into the composite contaminated soil and shaken for 6 hours. Thereafter, the pH of the filtrate was measured by solid-liquid separation, and the concentrations of arsenic, selenium and lead were measured. The results are shown in Table 1.

  As can be seen from the table, all hazardous substances were at concentrations below the elution standard. From this result, it was found that the insolubilization effect was not lowered even when the test dispersant was added at a mass ratio of 0.2 to the test insolubilized material.

(c) pH test The results of measuring the pH of the test specimen slurry are shown in FIG. As can be seen from the figure, in the case of the test dispersant according to the present invention, even when the mass ratio to the test insolubilizer becomes about 10, the pH is 9.5 and remains weak alkali, and the insolubilization action decreases. It was found that when the mass ratio was about 1 or less, the pH was suppressed to about 9 or less as well as being within an allowable range.

(d) Permeability test The sample slurry was infiltrated into the column-filled soil assuming sandy ground, and the permeation effect was examined.

  As a test procedure, first, a cylindrical column having a diameter of 10 cm is filled with silica sand No. 6 so as to have a height of 15 cm and 30 cm, and the water flow is stabilized by allowing water to flow with a constant head difference, and then the test is performed. Impregnated with a slurry of a test specimen to which 20 g / L of an insolubilizing material is added and 2 g / L of a test dispersant is added (mass ratio is 0.1). By measuring the degree, the change with time of the hydraulic conductivity was examined.

  FIG. 3 shows changes in the water permeability coefficient and changes in the insolubilized material remaining rate.

  As shown in the figure, in the case where the test dispersant was not added, the test insolubilized material adhered to the sand and clogged, and the water permeability decreased with time, whereas the test dispersant was added. In the case, it was found that the hydraulic conductivity hardly decreased.

  By the way, the residual rate was almost zero in the case where the test dispersant was not added, whereas in the case where the test dispersant was added, the residual rate was almost 100% over the test time, corresponding to the change in water permeability. The result was obtained.

  From the above results, it is presumed that the permeability coefficient is small only with the insolubilized material and it is difficult to penetrate into the contaminated area even in the sandy ground, but when the dispersant according to the present invention is used in combination, it is insolubilized. It seems that the insolubilized material can be surely infiltrated into the contaminated area if the water permeability coefficient of the material increases and at least sandy ground.

DESCRIPTION OF SYMBOLS 1 Ground 2 Polluted area 3 Injection well 4 Underground water barrier 5 Water injection well 6,7 Water blocking wall 8 Pumping well

Claims (4)

A powder insolubilizing material is added to water together with a dispersant to produce an insolubilizing material slurry in which the insolubilizing material is suspended in water, and then the insolubilizing material slurry is contaminated in the soil contaminated with harmful substances. A method of insolubilizing the harmful substance by adsorbing into the harmful substance by adsorbing, wherein the dispersing agent is made of polyacrylate, polymethacrylate or a copolymer thereof, and has a weight average molecular weight Mw 10000 to 14000, and the toxic substance is cadmium, total cyanide, lead, hexavalent chromium, arsenic, total mercury, alkylmercury, copper, selenium, fluorine or boron . Insolubilization method. The method for insolubilizing harmful substances according to claim 1 , wherein the polyacrylate, polymethacrylate or copolymer thereof is a monovalent salt. The insolubilizing material is iron oxide obtained by oxidizing ferrous oxide, ferric oxide or ferric tetroxide, or iron oxide obtained by oxidizing ferrous sulfate or ferrous chloride. The method for insolubilizing a harmful substance according to claim 1 or 2 , wherein a mass ratio of the dispersant to the insolubilizing material is 0.05 to 1. The method for insolubilizing a harmful substance according to claim 3 , wherein the mass ratio of the dispersant to the insolubilizing material is changed to 0.1 to 1 instead of 0.05 to 1.

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