JP2006175389A - Cleaning method of cyanide contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and surely insolubilize a cyanide contained in soil and also collectively clean the complex contamination of cyanide with benzene or the like. <P>SOLUTION: Contaminated soil is charged in a soil hopper 2 of a soil cleaning system 1 and temporarily stored therein. The contaminated soil temporarily stored in the soil hopper 2 is quantitatively metered by a soil quantitative feeder 3 to be supplied to a mixer 5. A calcium oxide with the weight ratio of 10-20% to the contaminated soil is metered and supplied to the mixer 5 from a cleaning agent quantitative feeder 4. The supplied contaminated soil and the calcium oxide are mixed. After leaving the soil for a fixed time, it is recovered as mixed soil. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a soil purification method for purifying soil contaminated with a cyanide compound contained in waste water of a city gas manufacturing plant, a plating plant, a metal refining plant, etc., and suppressing the amount of cyan elution to a reference value or less. .

  Complex pollution with cyanide and benzene occurs on land in city gas manufacturing plants. This is because the factory that was operating before 1965 produced coal gas, but benzene was produced from the compounds in the coal during the production process, and cyanide was produced from carbon and ammonia. Is considered to have leaked and penetrated into the soil. As described above, cyanide contained in soil contaminated with cyanide contained in wastewater from city gas manufacturing plants, plating plants, metal refining plants, etc. is highly toxic and requires measures such as excavation and removal. . Various treatment methods are adopted as a purification treatment method for the cyan contaminated soil.

  For example, in the treatment method disclosed in Patent Document 1, the slurry liquid of soil containing free cyanide, complex cyanide and hardly soluble cyanide compound is adjusted to pH 10 to pH 13 with alkali, heated and stirred for 30 minutes or more, and then sodium hypochlorite is slurried. The solution is dividedly added to the solution and reacted with free cyanide, complex cyanide and a hardly soluble cyanide compound in the range of pH 10 to pH 13 and in the temperature range of 80 to 100 ° C. to decompose cyanic acid into carbon dioxide and nitrogen.

  In addition, the treatment method disclosed in Patent Document 2 is adjusted to pH 8 to pH 9 by adding polyaluminum chloride, divalent iron sulfate and water to soil containing a cyanide compound and a soluble heavy metal, and further adding a calcium compound. Treating part of soluble cyanide with divalent iron sulfate to make it an insoluble stable iron cyano complex and the other as ferrocyan ion to be adsorbed on polyaluminum chloride to suppress elution of soluble cyanide and soluble metal I have to.

  Furthermore, in the treatment method disclosed in Patent Document 3, the contaminated soil containing cyanide is indirectly heated in a range of 300 to 650 ° C. in an oxygen-deficient atmosphere to separate the cyanide from the soil as hydrogen cyanide gas. I am doing so. In the treatment method disclosed in Patent Document 4, soil contaminated with cyanide or an organic halogen compound is subjected to microbial decomposition treatment.

  The treatment method disclosed in Patent Document 1 cannot remove harmful components when the amount of sodium hypochlorite added is insufficient, and if the amount added is excessive, harmful residual chlorine is generated. Therefore, it is necessary to adjust the amount of sodium hypochlorite added according to the concentration of free cyanide and complex cyanide contained in the slurry liquid of cyan contaminated soil. There is a disadvantage that it is necessary to control while confirming, and processing is not easy.

  Further, the treatment method disclosed in Patent Document 2 also has a disadvantage in that it is necessary to determine the total cyan content in the contaminated soil to be treated and to set the addition amount of polyaluminum chloride, and the treatment is not easy. Furthermore, the treatment methods shown in Patent Document 1 and Patent Document 2 require a large-scale wastewater treatment facility, which increases the treatment cost. In addition, there is a disadvantage that fine particles having a concentration of, for example, 70 μm or less, which are concentrated in contamination, become waste.

The treatment method disclosed in Patent Document 3 requires a recovery device for the generated hydrogen cyanide gas, which requires a lot of equipment and operation, and increases the economic burden. In addition, the processing method disclosed in Patent Document 4 has a disadvantage that the processing takes a long time.
JP 2004-58011 A JP 2001-121132 A JP 2003-181438 A JP 2004-66195 A

  An object of the present invention is to provide a method for purifying cyan-contaminated soil, which solves the above disadvantages and easily and reliably insolubilizes cyanide compounds contained in the soil.

  The method for purifying cyan contaminated soil according to the present invention is characterized in that 10 to 20% by weight of powdered calcium oxide is added to and mixed with cyan contaminated soil.

  In the present invention, by adding 10 to 20% by weight of calcium oxide to the cyan contaminated soil and mixing, the amount of all cyan in the soil with an amount of all cyan exceeding 100 times the reference value can be reduced. It can be reduced below the reference value.

  In addition, since a certain amount of calcium oxide is added to and mixed with soil contaminated with cyanide to reduce the amount of elution, it can be processed at the excavation site using existing equipment, greatly reducing processing costs. can do.

  In addition, the amount of total cyanide can be reduced and volatile organic compounds such as benzene can be removed by the heat of hydration reaction of calcium oxide, and the combined contamination of cyanide and benzene can be purified at once. it can.

  FIG. 1 is a configuration diagram of a soil purification apparatus of the present invention. As shown in the figure, a soil purification device 1 for treating cyan-contaminated soil includes a sediment hopper 2, a sediment fixed amount supply device 3, a purification agent quantitative supply device 4 and a mixing device 5. The earth and sand hopper 2 temporarily stores contaminated soil and sends it out sequentially. The earth and sand fixed quantity supply device 3 is composed of, for example, a conveyor having a conveyor scale, measures the contaminated soil sent out from the earth and sand hopper 2, and supplies a certain amount of contaminated soil to the mixing device 5. The cleaning agent quantitative supply device 4 measures the calcium oxide used as the cleaning agent for the contaminated soil and supplies a certain amount of calcium oxide to the mixing device 5. The mixing device 5 is composed of, for example, a soil conditioner or a twin screw paddle mixer, and mixes the supplied contaminated soil and calcium oxide.

  A process when the soil contaminated with cyan is insolubilized by the soil cleaning apparatus 1 will be described with reference to the flowchart of FIG.

  First, the soil contaminated with excavated cyan has a vibrating screen with a mesh width of, for example, 40 mm, and the raw soil, which is contaminated soil, is given a particle size of 40 mm while preventing clogging by applying vibration and rotation to the screen surface. It puts into the dry classifier 6 which mechanically separates as a reference, and separates into earth and sand having a particle diameter of 40 mm or more and earth and sand having a particle diameter of less than 40 mm (steps S1 and S2). The separated soil having a particle size of 40 mm or more is collected as purified soil (step S8), and the soil having a particle size of less than 40 mm is put into the earth and sand hopper 2 of the soil washing apparatus 1 and temporarily stored (step S3). The contaminated soil having a particle size of less than 40 mm temporarily stored in the earth and sand hopper 2 is supplied to the earth and sand fixed quantity supply device 3, and is measured by the fixed quantity of earth and sand by a certain amount and supplied to the mixing apparatus 5 (step S4). On the other hand, the powdery calcium oxide used as the cleaning agent is metered and supplied to the mixing device 5 from the cleaning agent quantitative supply device 4 (step S5). The amount of calcium oxide supplied from the purification agent quantitative supply device 4 to the mixing device 5 is 10 to 20% by weight with respect to the contaminated soil quantitatively supplied from the earth and sand quantitative supply device 3. The mixing apparatus 4 mixes the supplied contaminated soil having a particle size of less than 40 m and calcium oxide (step S6). The mixed soil is recovered from the mixing device 5 and allowed to stand for a predetermined time, for example, 12 to 24 hours, and then recovered as mixed treated soil and used as backfill soil (step S7).

  The basis for insolubilizing soil contaminated with cyan by mixing 10 to 20% by weight of calcium oxide with contaminated soil having a particle size of less than 40 m will be described.

  The environmental standards for soil against contamination with cyanide stipulate that the total cyan elution amount is 0.1 mg or less per liter of test solution and the content is 50 mg or less of free cyanide per 1 kg of soil. From this reference value, the amount of elution of all cyan exceeding 100 times was mixed with 10% by weight of various calcium-based materials to soil having an elution amount of 11.0 mg / L, and the change in the elution amount was examined. The results are shown in FIG. As shown in FIG. 3, when calcium carbonate and calcium oxide, calcium hydroxide, calcium phosphate, calcium acetate and calcium citrate are used as the calcium-based material, it is possible to reduce the elution amount of all cyan in any case. However, when calcium oxide was mixed, there was the effect of reducing the amount of all cyan elution most, and the cyan contaminated soil could be reduced below the environmental standard value. Moreover, when calcium hydroxide was mixed, the amount of all cyan eluted could be reduced to 1/10.

  Therefore, the amount of calcium oxide and calcium hydroxide added to the soil was changed to 3%, 5%, 10%, and 20% by weight and mixed, and the change in the amount of elution and the content of free cyanide were investigated. It shows to Fig.4 (a), (b). 4A shows the case where calcium oxide is added and mixed, and FIG. 4B shows the case where calcium hydroxide is added and mixed. As shown in FIGS. 4 (a) and 4 (b), as the addition amount of calcium oxide and calcium hydroxide is increased, the elution amount of all cyan and the content of free cyanide are reduced, and the addition amount of calcium oxide is 10%. As a result, the total cyan elution amount was reduced to the standard value of 0.1 mg / L, and the content of free cyan was also reduced to 15 mg / kg or less. On the other hand, when calcium hydroxide was added and mixed, even if the addition amount was 20%, the elution amount of all cyan could not be reduced to the reference value.

  Thus, by adding calcium oxide and calcium hydroxide to cyan contaminated soil and mixing them, the cyanide ions in the soil react with the metal ions in the soil due to the presence of calcium, so that an insoluble metal cyanide complex such as an iron cyano complex is obtained. It is considered that free cyanide decreased and the amount of all cyan eluted was reduced. In addition, calcium oxide reacts with moisture in the soil and changes to calcium hydroxide. This heat of hydration promotes the formation of cyanide complexes, so when calcium oxide is added to the soil and mixed. It is considered that the effect of reducing the total cyan elution amount is greater.

  Therefore, when the soil contaminated with cyan is insolubilized by the soil washing apparatus 1, the addition amount of calcium oxide is mixed with the soil supplied from the sediment fixed quantity supply apparatus 4 at a weight ratio of 10 to 20%. Thus, by adding and mixing 10-20% by weight of calcium oxide with respect to the soil, the total cyan elution amount in the soil of the total cyan elution amount exceeding 100 times the standard value is below the standard value. It is possible to reduce the amount of leaching to less than the reference value, and the mixed treated soil can be used for backfilling.

  In addition, since a certain amount of calcium oxide is added to and mixed with soil contaminated with cyanide to reduce the amount of elution, it can be processed at the excavation site using existing equipment, greatly reducing processing costs. can do.

  Furthermore, by mixing calcium oxide into soil contaminated with cyanide, the amount of total cyanide dissolved can be reduced, and volatile organic compounds such as benzene can also be removed by the heat of hydration of calcium oxide. Combined contamination of cyanide and benzene at manufacturing plants can be purified at once.

It is a block diagram of the soil purification apparatus of this invention. It is process drawing which shows the insolubilization process of cyan contaminated soil. It is a change characteristic view of the total cyan elution amount when various calcium type materials are added to and mixed with cyan contaminated soil. It is a change characteristic figure of the total cyan elution amount and free cyan content when the addition amount of calcium carbonate and calcium hydroxide is changed.

Explanation of symbols

1; soil purification device, 2; earth and sand hopper, 3;
4; Cleaner quantitative supply device, 5; Mixing device, 6; Dry classifier.

Claims (1)

  A method for purifying cyan-contaminated soil, wherein 10 to 20% by weight of powdered calcium oxide is added to and mixed with cyan-contaminated soil.

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