JPH10296229A - Method for recovering mercury from contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it easy to perform a use cycle of natural resources by adding a reaction promoter to a mercury-contaminated soil, then thermally stirring and both promoter and soil at a lower temperature than the boiling point of mercury and heating a mercury compound produced in a heated vapor again at a higher temperature than the boiling point of the mercury to recover the mercury compound as metallic mercury. SOLUTION: A sample 2 obtained by stirring and mixing a soil contaminated by a mercury compound such as mercury sulfide with a reaction promotion additive, is placed in a heating reaction furnace 1. Next, the sample 2 is heated at temperatures of about 250-300 deg.C which are lower than the boiling point of mercury to adequately remove the concentration of the mercury contained in the contaminated soil. This removed mercury and a sulfur component are heated at 100 deg.C or higher using a ribbon heater 6 and then are guided into a reheating reaction pipe 3 heated at about 500 deg.C with a heated exhaust through a heat-retaining conduit. Further, the mercury compound is thermally decomposed to be recovered as metallic mercury. Thus it is possible to facilitate a use cycle of natural resources and thereby simplify the recovery process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The applicant of the present invention discloses a method for purifying mercury-contaminated soil, using a transition element compound such as iron as an additive, mixing and stirring the contaminated soil, and using a rotary kiln or the like to carry out mixing and stirring at 250 ° C. to 300 ° C. A method for removing mercury in contaminated soil by evaporating it at low temperatures has already been applied for a patent. (Japanese Patent Application No. 7-203805) The present invention is a further improvement of this method patent, and is a method of recovering mercury vaporized and diffused.

[0002]

2. Description of the Related Art Methods for collecting mercury from contaminated soil The following methods have been proposed so far for collecting mercury produced by heating and purifying mercury-contaminated soil. <B> This method has been widely used as a scythe technique for mercury ore, but the ore is heated to a high temperature of about 600 to 800 ° C, and the mercury in the ore is heated and vaporized as mercury vapor.
A method of condensing and precipitating mercury by rapidly cooling steam. <B> A method of heat-treating mercury-contaminated soil instead of ore at the same high temperature as described above. In this method, evaporating mercury is collected in a wet oxidation absorbing solution by an acid solution of potassium permanganate and sulfuric acid (commonly called chameleon solution). Or,
A method of simply removing by adsorption with activated carbon.

[0003]

The conventional mercury recovery method described above has the following problems. <B> It is possible to remove mercury from the gas phase by physical or chemical adsorption, but when it is in the form of a compound, physical adsorption is the main component, and therefore, it does not exhibit sufficient removal performance. Not exclusively. <B> In the case of a chameleon solution, most mercury compounds can be oxidized and collected even if they are mercury or mercury compounds. However, although chemically possible, some compounds are easy to collect and some are not, given the ability and speed of collection. For example, it is difficult to collect mercury sulfide and the like. In addition, the operation is complicated, for example, a processing process for recovering mercury alone requires adding a reducing agent to the chameleon solution again and heating. <C> Since activated carbon has a mercury adsorption limit, it must be replaced as appropriate. In the case of a chameleon solution, the potassium permanganate in the solution reacts with oxygen in the air over time and is auto-oxidized, so the solution must be changed periodically. As described above, a great amount of maintenance work is required during operation.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and provides a method for recovering mercury from contaminated soil, in which resource recycling is easy, the recovery process is simple, and the initial cost is low. The purpose is to do.

[0005]

That is, according to the present invention, a reaction accelerator is added to soil contaminated with mercury, the mixture is heated at a temperature lower than the boiling point of mercury, and the mixture is stirred and mixed. The method is characterized by a method of recovering mercury from contaminated soil, in which the incoming mercury compound is heated again at a temperature higher than the boiling point of mercury, and the mercury compound is pyrolyzed and recovered as metallic mercury.

[0006]

Embodiments of the present invention will be described below.

<A> Outline of mercury removal method A reaction-promoting additive is stirred and mixed into soil contaminated with a mercury compound such as mercury sulfide, and a temperature lower than the boiling point of mercury, for example, about 250 ° C. to 300 ° C. Heat at a temperature of This reduces the concentration of mercury in contaminated soil.

<Mouth> Additives There are some examples of reaction promoting additives. Here, the case where iron sulfide is used will be described. The additive may be one containing divalent iron as a main component. As the component, iron sulfide and the like are applicable. By mixing and heating iron sulfide to the mercury-contaminated soil, a sufficient removal rate can be obtained. In this case, the mercury removed by this heating reaction is generated by the heat denaturation of the mercury vapor and iron sulfide removed in the gas phase into oxides as the heated exhaust air is cooled. The generated sulfur causes a chemical reaction and is removed and discharged in the form of mercury sulfide.

<C> Method of reheating By mixing and heating the additive, the removed mercury and sulfur components move from the soil to the gas phase, but the conduit leading to the chameleon solution is 100 ° C or less. At this level, the mercury component in the gas phase becomes mercury sulfide. To prevent this reaction, the conduit to the reheating reaction tube 3 was
Heat to 0 ° C or more and keep it warm. The heated exhaust gas is led into a reheating reaction tube 3 heated to about 500 ° C. through a conduit heated and maintained at 100 ° C. or more. By filling the inside of the reaction tube 3 with partition walls, glass beads 31 and the like, the heating reaction time is reduced, and the combustion oxidation proceeds smoothly. By reheating the heated exhaust gas to about 500 ° C., the sulfur component present in the gas phase is burned and oxidized to form sulfur dioxide gas. As a result, the sulfur component does not react with the mercury vapor, and the mercury and the sulfurous acid gas are directly transferred to the collecting solution. As a heat source for reheating, a method utilizing waste heat generated when heating the rotary kiln can be adopted. Alternatively, heating can be performed using another energy such as electricity, gas, or oil.

[0010]

EXAMPLE An example of an experiment for removing mercury by heating using iron sulfide will be described below.

<A> Experimental apparatus An experiment was conducted using a heating experimental system shown in FIG. This experimental system simulates the structure of a rotary kiln with a reheating device. The air can flow laterally while heating the experimental system at a pressure slightly lower than the atmospheric pressure while heating. In the figure, 1 is a heating reactor, 2 is a sample, 3 is a reheating reactor, 4 is a mercury absorption reactor, and 5 is activated carbon for removing trace amounts of mercury. Reagents and soil: Mercury sulfide Quartz sand Heating time: 60 minutes Simulated contaminated soil concentration of 2000 mg / kg dry soil (20
00PPm)

<B> Contaminated soil The simulated contaminated soil with quartz sand used in the experiment was prepared by adding and mixing 12 mg of mercury sulfide to 5 g of quartz sand. After the preparation, iron sulfide (FeS) was mixed at a weight ratio of about 2% (0.1 g) and subjected to a heating experiment.

<C> Experimental progress The heating rate was set to about 5 to 10 minutes at a heating rate of up to 300 ° C. The air during the heating and heating was also ventilated, and the reduced pressure in the apparatus was maintained. After reaching 300 ° C, the mercury concentration in the chameleon solution was measured four times every 15 minutes, and the change over time was observed. As a result, mercury migrated into the chameleon solution and was sufficiently collected by heating and mixing as compared with the experimental result of heating the simulated contaminated soil with iron sulfide. (Fig. 2)

[0014]

As described above, according to the present invention, a method for recovering mercury from contaminated soil can recover mercury in contaminated soil as metallic mercury. Therefore, resource recycling is possible. Further, according to the method of the present invention, mercury can be recovered only by cooling the heated exhaust gas, so that the recovery process is simplified. Therefore, the initial cost of the processing plant can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing an experimental apparatus for confirming a method of recovering by heating mercury.

FIG. 2 is a graph showing a change over time in a mercury collection rate due to reheating.

Claims (5)

[Claims] Claims 1. A reaction accelerator is added to soil contaminated with mercury, heated at a temperature lower than the boiling point of mercury, and mixed by stirring. The mercury compound generated in the heated steam is again converted into mercury. A method for recovering mercury from contaminated soil by heating at a temperature higher than the boiling point to thermally decompose mercury compounds and recover them as metallic mercury 2. The method for recovering mercury from contaminated soil according to claim 1, wherein the mercury compound generated in the heated steam is heated again to about 500 ° C. 3. The method for recovering mercury from contaminated soil according to claim 1, wherein the method is performed by using a sulfide of iron as a reaction accelerator. 4. The method for recovering mercury from contaminated soil according to claim 1, wherein the method is performed using another energy such as electricity, gas or oil as a heat source for reheating. 5. The method for recovering mercury from contaminated soil according to claim 1, wherein waste heat generated when the rotary kiln is heated is used as a heat source for reheating.