JP2007319755A - Method for fixing arsenic compound in contaminant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for fixing arsenic compounds in contaminants which can certainly and uniformly fix and detoxify arsenic compounds in contaminants covering a diversity of the contaminants on the spot when a chemical agent is used particularly fixing for the arsenic compounds in the contaminants. <P>SOLUTION: The method for fixing the arsenic compounds in the contaminants by adjusting pH of the contaminants through adding an iron-based chemical agent, an alkaline agent and water to the contaminants containing the arsenic compounds adjusts the pH of the contaminant to 9 or more and then cures the contaminants for 24 hr or longer under the air environments. The iron-based chemical agent is preferably at least one compound selected from a group consisting of ferric chloride, ferric sulfate and a polyferric sulfate. The alkaline agent adjusting pH is preferably calcium hydroxide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for immobilizing arsenic compounds in contaminants.

  Conventionally, when an immobilization process using a drug is performed on an arsenic compound in a contaminant, an iron-based drug is often used as the drug. In this case, many iron-based chemicals have acidity, and it is usual to add an alkaline agent such as calcium hydroxide or sodium hydroxide as an auxiliary agent.

Here, the patent documents relating to the conventional method for immobilizing arsenic compounds in contaminants include the following.
JP, 2001-121131, A The detoxification processing method of soil or industrial waste currently indicated by patent documents 1 is soluble mercury, hexavalent chromium, trivalent chromium, lead, cadmium, copper, zinc, manganese, arsenic Insoluble and detoxified heavy metals in soil or industrial waste containing heavy metals such as ferrous sulfate and water added to the soil or industrial waste containing soluble heavy metals, and then added calcium compound Thus, the pH is adjusted to an appropriate range.

  However, when the immobilization treatment is performed on the arsenic compound in the pollutant using a drug, what is important is the amount of iron-based drug added and the pH of the pollutant. On the other hand, the amount of alkaline agent added as an auxiliary agent varies depending not only on the amount of iron-based chemical added, but also on the type of contamination and the degree of contamination, and the amount of alkaline agent required at the same contamination site is not constant. In addition, it was economically disadvantageous to perform a dissolution test for each unit treatment and measure pH.

  In Patent Document 1, soluble metals, hexavalent chromium, trivalent chromium, lead, cadmium, copper, zinc, manganese, arsenic and other heavy metals contained in soil or industrial waste are simultaneously insolubilized and rendered harmless. However, when immobilization treatment is performed using chemicals on arsenic compounds, especially in arsenic compounds, the non-uniformity of on-site contaminants is covered to ensure reliable and uniform contamination. The method for immobilizing and detoxifying the arsenic compound was not described at all.

  The object of the present invention is to solve the above-mentioned problems of the prior art, and to cover the non-uniformity of on-site contaminants when performing immobilization treatment using chemicals on contaminants, particularly arsenic compounds. It is an object of the present invention to provide a method for immobilizing and treating arsenic compounds in contaminants, which can achieve reliable and uniform immobilization / detoxification treatment of arsenic compounds in contaminants.

  As a result of intensive studies in view of the above points, the present inventor added an iron-based chemical to a contaminant containing an arsenic compound, added an alkaline agent, and water to adjust the pH of the contaminant. In addition, by adjusting the pH of the pollutant to 9 or more and then curing the pollutant in an air environment for 24 hours or more, the pH of the pollutant becomes pH 7-8 necessary for arsenic immobilization, and in the field The present inventors have found that it is possible to reliably cope with the difference in the contaminant pH depending on the position of the above, and have completed the present invention.

  In order to achieve the above object, the invention of the method for immobilizing arsenic compounds in pollutants according to claim 1 adds an iron-based chemical, an alkaline agent, and water to a pollutant containing an arsenic compound. The method of fixing the arsenic compound in the pollutant by adjusting the pH of the pollutant, the pH of the pollutant being adjusted to 9 or more, and then the pollutant in the air environment for 24 hours or more It is characterized by curing.

  Here, the pH of the contaminant refers to the pH of an aqueous solution containing 10% by weight of the contaminant.

  In the method for immobilizing an arsenic compound in a contaminant of the present invention, the iron-based drug is at least one selected from the group consisting of ferric chloride, ferric sulfate, and polyferric sulfate. One compound is preferred.

  Moreover, it is preferable that the alkaline agent which adjusts pH is calcium hydroxide.

  The present invention is a treatment for fixing an arsenic compound in a contaminant by adding an iron-based chemical agent to a contaminant containing an arsenic compound, adding an alkaline agent and water, and adjusting the pH of the contaminant. A method for adjusting the pH of a pollutant to 9 or more, and then curing the pollutant in an air environment for 24 hours or more. According to the present invention, a chemical is used for pollutants, particularly arsenic compounds. When performing the immobilization process using, it is possible to cover the non-uniformity of on-site pollutants and achieve a reliable and uniform immobilization / detoxification process for arsenic compounds in the pollutants. Play.

  In the method for immobilizing an arsenic compound in a contaminant of the present invention, the iron-based drug is at least one selected from the group consisting of ferric chloride, ferric sulfate, and polyferric sulfate. One compound is used. Thereby, specifically, the above-described effect can be produced. In this case, the alkaline agent for adjusting the pH is preferably calcium hydroxide.

  Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

  In the method for immobilizing an arsenic compound in a contaminant according to the present invention, the contaminant containing the arsenic compound is kneaded together with humidified water, a fixing agent, and an alkali agent by a kneader such as a pan-type kneader or a biaxial kneader. The pH of the contaminant is adjusted to 9 or more.

  Here, about the arsenic contaminant in a contaminant, the arsenic density | concentration in a contaminant is measured by prior investigation, and the addition amount of fixing agents, such as an iron-type chemical | medical agent, is determined. Moreover, the alkali addition amount for making contaminant pH 9 or more is calculated | required by a prior test.

  In addition, the pH of a contaminant refers to the pH of the aqueous solution containing 10 weight% of a contaminant.

  The discharge from the kneader is cured for 24 hours or more in a form that easily comes into contact with air to obtain an immobilization treatment product.

  In the method for immobilizing an arsenic compound in a contaminant of the present invention, the iron-based agent is at least one compound selected from the group consisting of ferric chloride, ferric sulfate, and polyferric sulfate. It is preferred to use.

  Moreover, it is preferable that the alkaline agent which adjusts pH is calcium hydroxide.

  Here, when the immobilization treatment is performed using a chemical on the arsenic compound in the contaminant, what is important is the amount of iron-based chemical added and the pH of the contaminant. According to the test by the present inventors, it was found that the arsenic fixing effect is high when the pH of the contaminant is pH 6 to 8 and pH 12 or more. Therefore, the amount of the alkaline agent may be adjusted and added so as to reach this value. However, when the treatment is performed so that the pH of the contaminant is 12, the contaminant is introduced into the air after the treatment. When exposed, the pH drops, so basically the pH adjustment is targeted at pH 6-8.

  On the other hand, the amount of alkaline agent added as an auxiliary agent varies depending not only on the amount of iron-based chemical added, but also on the type of contamination and the degree of contamination, and the amount of alkaline agent required at the same contamination site is not constant. In addition, it is economically disadvantageous to conduct a dissolution test for each unit treatment and measure pH.

  Therefore, the present inventor added an iron-based chemical to a contaminant containing an arsenic compound, added an alkaline agent and water, and adjusted the pH of the contaminant by 9 or more when adjusting the pH of the contaminant. After that, by curing the contaminants in the air environment for 24 hours or more, the pH of the contaminants becomes pH 7-8 necessary for arsenic immobilization, and the difference in contaminant pH depending on the position in the field It has been found that it is possible to respond reliably.

  According to the method for immobilizing an arsenic compound in a contaminant according to the present invention, when the immobilization treatment is performed using a chemical on the arsenic compound, particularly in the contaminant, the in-situ contaminants are not uniform. It is possible to achieve a reliable and uniform treatment for fixing and detoxifying arsenic compounds in contaminants.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1
To contaminated soil with an arsenic content of 780 mg / kg, 3% by weight of polyferric sulfate is added to the soil, and then calcium hydroxide is adjusted to a pH of 4.5 to 12.4 during the soil elution test. Further, 40% by weight of ion-exchanged water was added to the soil and kneaded with a glass rod for about 5 minutes. Immediately after kneading, a soil elution test was performed to measure the contaminant pH and the arsenic concentration in the elution test solution. In addition, the soil elution test was performed based on the test method by the Ministry of the Environment Notification No. 18 in 2003. The obtained results are shown in Table 1 below.

  As is clear from the results in Table 1 above, it can be seen that arsenic immobilization is highly effective at pH 5.5 to 9.2 and pH 12 or higher. In addition, when treated soil having a pH of 7 or more immediately after kneading is cured in the air, even if it is highly alkaline immediately after kneading, it will be in the range of pH 7 to 8 after curing, and arsenic immobilization is promoted. I understood. Furthermore, when the pH immediately after kneading was 12.1 or higher, curing in the air for 24 hours did not lead to sufficient neutralization. Even in such a case, it was found that the arsenic immobilization can be achieved in the range of pH 7 to 8 after curing for 72 hours or more.

Example 2
At the site A where arsenic-contaminated soil is present, five soils were collected and mixed, and these were used as the average soil at the site A. To this average soil, 3% by weight of polyferric sulfate is added to the soil, followed by calcium hydroxide, and then 40% by weight of ion-exchanged water, and about 5 minutes with a glass rod. Kneaded. Immediately after kneading, a soil elution test was performed to measure the pH of the contaminants. In addition, the soil elution test was performed based on the test method by the Ministry of the Environment Notification No. 18 in 2003. This test was carried out by changing the amount of calcium hydroxide, and the amount of calcium hydroxide was calculated so that the pH of the contaminant was pH 7, pH 8, pH 9, and pH 10.

Next, 50 samples of soil at the site A were randomly sampled at equal intervals as much as possible, and the amount of calcium hydroxide calculated previously was used to elution the pollutants at pH 7, pH 8, pH 9, and pH 10. A test was conducted. The obtained results are shown in Table 2 below.

  As is apparent from the results in Table 2 above, the percentages of contaminants tested for pH 7 and pH 8 at a pH of 6 or higher were 74% and 96%, respectively, Then, it was found that there was locally low pH soil. However, when the target pH was set to 9 or higher, the pH of all 50 contaminants was 6 or higher.

  Here, when immobilizing arsenic contaminants with iron-based chemicals, it is important to adjust the pH of the contaminants to 6-8. It is possible to make the pH of the pollutant uniformly 6 or more by covering the non-uniformity of the on-site pollutant, and then further in the air. By curing for a period of time, preferably 72 hours or more, the pH of the contaminant can be adjusted to 7 to 8, and a reliable and uniform immobilization / detoxification treatment of the arsenic compound in the contaminant can be achieved.

Claims (3)

  A treatment method for fixing an arsenic compound in a contaminant by adding an iron-based chemical to a contaminant containing an arsenic compound, adding an alkaline agent and water, and adjusting the pH of the contaminant. A method for immobilizing an arsenic compound in a contaminant, wherein the pH of the contaminant is adjusted to 9 or more, and then the contaminant is cured in an air environment for 24 hours or more.   The pollutant according to claim 1, wherein the iron-based drug is at least one compound selected from the group consisting of ferric chloride, ferric sulfate, and polyferric sulfate. A method for immobilizing arsenic compounds.   The method for immobilizing an arsenic compound in a contaminant according to claim 1 or 2, wherein the alkaline agent for pH adjustment is calcium hydroxide.