JP2005199221A - Detoxicating processing method for sludge or soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detoxicating processing method for sludge or soil containing mercury compounds produced in a hot spring or a geothermal power station, or the like. <P>SOLUTION: After the sludge or soil containing mercury compounds is washed with water to remove water-soluble sulfur compounds, detoxicating treatment is performed by adding a heavy metal treating agent thereto. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for detoxifying sludge or soil containing a mercury compound generated in a geothermal power plant or a hot spring.

  Mercury compounds are highly toxic, so if they are contained in waste, some treatment is required. For example, the amount of mercury contained in the wastewater is determined to be a certain value or less by the Water Pollution Control Law. For this reason, detoxification treatment methods such as sulfide generation-aggregation precipitation method and adsorbent method are performed on wastewater containing mercury compounds. (For example, refer nonpatent literature 1).

  Moreover, harmful metals contained in the garbage are concentrated in the fly ash generated when the garbage is incinerated. When landfilling fly ash, the amount of harmful heavy metals to be eluted (mercury, lead, cadmium, hexavalent chromium, arsenic, selenium) is determined to be a certain value or less. To insolubilize heavy metals contained in fly ash, organic chelate heavy metal treatment agent and water are added to fly ash and kneaded to perform detoxification, or cement and water are added to fly ash and solidified. There is a way to do. (For example, refer nonpatent literature 2.)

In facilities that use high-temperature steam and hot water from underground such as geothermal power plants and hot springs, in some areas, the steam and warm water contain trace amounts of harmful heavy metals such as mercury, arsenic, and selenium. There is a case. In these facilities, sludge and soil enriched with mercury, arsenic, selenium and the like need to be generated and disposed of over a long period of time. In such sludge or soil, the elution of mercury may exceed the regulation value, and as it is, final disposal at the landfill site cannot be performed, so treatment with organic chelate heavy metal treatment agent or solidification treatment with cement etc. Has been done. However, there are cases where a sufficient treatment effect cannot be obtained even if treatment is performed, and such an effective treatment method for sludge or soil has been desired.
Four revisions and pollution prevention technologies and regulations [Water quality], Japan Association for Industrial Environmental Management, 1994, P249-255 Chemical Equipment April 1999 Issue, Industrial Research Committee, P59-64

  The problem to be solved by the present invention is to provide a method for efficiently insolubilizing a mercury compound contained in sludge or soil generated in a geothermal power plant or a hot spring in the background described above.

The inventors of the present invention, as a result of intensive investigations to find a method for efficiently insolubilizing mercury in sludge or soil generated in geothermal power plants and hot springs, etc., in these sludge or soil, Compared to ordinary waste, sulfur components derived from hydrogen sulfide from the ground are contained in a large amount, and some sulfur components are sulfur ions (S 2− ) or thiosulfate ions (S 2 O 3 2-) are contained in the form of it, larger polysulfide mercury relatively solubility for these reducing sulfur ion (S 2-) or thiosulfate (S 2 O 3 2-) It has been found that it is present as a product ion (HgS 2 2− etc.) and is difficult to undergo insolubilization treatment with an organic chelate heavy metal treating agent or the like. Furthermore, by washing these sludge and soil, sulfur ions (S 2− ) and thiosulfate ions (S 2 O 3 2− ) can be removed, and the sludge and soil from which these are removed are treated with heavy metals. It has been found that mercury can be insolubilized by adding an agent, and the present invention has been completed.

  That is, the present invention relates to a sludge or soil detoxification method comprising adding a heavy metal treating agent after washing a sludge or soil containing a mercury compound with water.

  ADVANTAGE OF THE INVENTION According to this invention, the sludge or soil containing a mercury compound which was difficult by the conventional method can be detoxified more effectively.

  Hereinafter, the present invention will be described in detail.

  The sludge or soil containing a mercury compound that is the subject of the present invention is, for example, sludge generated in a cooling tower of a geothermal power plant, or the nearby soil from which hot water such as a hot spring springs out. It is contaminated with various harmful metals including the trace amount of mercury contained. When these sludges or soils are brought to landfill sites for final disposal, it is necessary that the elution of heavy metals be less than the value stipulated by law. As a result of investigations by the present inventors, mercury is very easily eluted from these sludges and soils, and even if an organic chelate heavy metal treating agent is added to the sludges or soils as it is, the mercury elution is suppressed. I found it extremely difficult.

As a result of further investigation, these sludges and soils contain several times more sulfur than fly ash and incinerated ash, and these sulfur are contained in water vapor and warm water from the ground. It is considered that hydrogen sulfide is used as a source, part of which is contained in the form of reducing ions such as sulfur ions (S ²⁻ ) and thiosulfate ions (S ₂ O ₃ ²⁻ ), sludge or soil It has been found that mercury contained therein is contained as polysulfide ions (HgS ₂ ²⁻ etc.) having relatively high solubility.

  The mercury compound in the present invention is “Ministry Ordinance for Establishing Judgment Criteria for Industrial Waste Containing Metals, etc .: Prime Minister's Ordinance No. 5 on February 17, 1973” Method (Environment Agency Notification No. 13 Test: Ministry of the Environment is the Environment Agency at the time) ”means a water-soluble mercury compound that elutes into the test solution when it is prepared. Means.

In the present invention, it is essential to wash the sludge or soil described above and remove reducing sulfur compounds such as sulfur ions (S ²⁻ ) and thiosulfate ions (S ₂ O ₃ ²⁻ ) from the sludge or soil. . The washing method at this time is not particularly limited, and either a batch method or a continuous method can be used, and any method known industrially can be used. Specifically, after adding water to the sludge and stirring for a predetermined time, decantation is performed to separate the cleaning liquid and sludge, and industrially known filtration and cleaning devices (for example, belt filters, filter presses, drum filters) Examples of the method used can be exemplified, and all of these can be suitably used. Moreover, in order to improve the cleaning efficiency of sludge at the time of washing, a flocculant can be used at the same time, and all flocculants can be suitably used regardless of inorganic or organic polymer.

  Sludge or soil water washing conditions vary depending on the amount and type of reducing sulfur compounds contained in them and the washing method, but cannot be specified unconditionally, but if the amount of water used for washing is too small, This is not preferable because the removal of the sulfur compound becomes insufficient and the effect of the heavy metal treating agent to be added subsequently decreases, and it is not preferable if the amount of water used for washing is too large, because the disposal cost of the washing water increases. As washing conditions, for example, water can be used in an amount of 1 to 1000 times, preferably 5 to 100 times, more preferably 10 to 50 times the amount of sludge or soil. It is further preferable to obtain optimum cleaning conditions. Examples of the laboratory test method include a method for obtaining the washing condition from the amount of the sulfur compound in the washing liquid, and a method for obtaining the washing condition from the condition when the amount of the sulfur compound contained in the sludge is measured and the decrease stops.

  The sludge or soil cleaning liquid contains harmful heavy metals as well as water-soluble sulfur compounds. Therefore, it is necessary for the cleaning liquid to remove hazardous heavy metals in the wastewater treatment process and discard it. However, the method is not particularly limited, and any known wastewater treatment method may be used. If it is a power plant, it can be disposed of directly using a reduction well.

By washing the sludge or soil with the above method, sulfur ions (S ²⁻ ) and thiosulfate ions (S ₂ O ₃ ²⁻ ) contained therein can be removed, and a heavy metal treatment agent Mercury detoxification treatment becomes possible by adding. As the heavy metal treating agent used at this time, for example, dithiocarbamic acid using amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, piperazine, propipylenediamine, butylenediamine, hexamethylenediamine as raw materials. A heavy metal treating agent such as an organic chelate heavy metal treating agent containing Na salt or K salt as a main component is preferable, and these form an insoluble chelate compound with mercury, lead, and cadmium to detoxify sludge or soil. The amount of the heavy metal treatment agent added at this time cannot be determined unconditionally because it varies depending on the composition of the sludge or soil. It is preferable to add by multiplying by a coefficient.

  Moreover, it does not specifically limit as addition conditions of a heavy metal processing agent, What kind of method can be used if it is the method used until now for the fly ash process by a heavy metal processing agent, for example. Specifically, after adding a predetermined amount of heavy metal treatment agent to the sludge or soil after washing in the present invention, using a kneader (a kneader, a mix muller, a vibration mixer) or the like known at room temperature. A method of performing a kneading treatment for several minutes can be exemplified, and by this operation, mercury in the sludge or soil reacts with the heavy metal treating agent and is rendered harmless. Moreover, in order to perform a detoxification process more completely, you may perform curing after kneading | mixing as needed.

  By the above operation, mercury in the sludge or soil is detoxified by the heavy metal treating agent. Since the detoxified mercury acts as a heavy metal treating agent, the elution is suppressed in a wide range of pH from weakly acidic to alkaline.

Examples Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these examples. In addition, each measuring method in an Example is as follows.

  Analysis of main component of sludge: The content (wt%) as an element was determined using an energy dispersive fluorescent X-ray (JSX-3200) manufactured by JEOL Ltd.

  Analysis of trace toxic heavy metals in sludge: The content (mg / kg) as an element was determined according to the bottom sediment investigation method (September 8, 1988, ring water tube No. 127).

  Analysis of sludge and components eluted from sludge after treatment: In accordance with the test method for metals contained in industrial waste (Test No. 13 of the Notification by the Environment Agency on February 17, 1973) The content (mg / L) was determined.

  As a result of the compositional analysis of the sludge generated in the cooling tower of the geothermal power plant, the main components are Si: 18.4 wt%, Ca: 11.4 wt%, Al: 8.9 wt%, and elemental sulfur is 7 It was found to contain 9 wt%. Further, analysis of trace harmful heavy metals in the sludge revealed that mercury contained 52 mg / kg, selenium 150 mg / kg, and lead 500 mg / kg. 50 g of this sludge was placed in a 1000 ml polyethylene container, 500 g of water was further added, and the mixture was shaken for 30 minutes and washed with water. After the water washing, in order to separate the sludge and the water washing liquid, a polymer flocculant (manufactured by Organo Corporation, trade name Olflock AP-1) was added and mixed with the sludge at 5 ppm. After separating the washing solution by decantation, a part of the sludge was sampled and the composition was analyzed. As a result, the amount of elemental sulfur in the sludge was 4.7 wt%. To the sludge after washing, 4% of an organic chelate heavy metal treating agent (trade name TS-500, manufactured by Tosoh Corporation) containing sodium dithiocarbamate as a main component was added and kneaded for detoxification. Table 1 shows the analysis results of the eluted components from the sludge after the detoxification treatment.

  The water washing operation similar to Example 1 was implemented twice with respect to the sludge used in Example 1. The amount of elemental sulfur in the sludge after washing with water was 4.6 wt%. The sludge after washing was subjected to the same detoxification treatment as in Example 1. Table 1 shows the analysis results of the eluted components from the sludge after the detoxification treatment.

Comparative Example 1

  The sludge used in Example 1 was analyzed for elution components without any treatment. The results are shown in Table 1.

Comparative Example 2

  The sludge used in Example 1 was added with 10 wt% of humidified water and 4 wt% of an organic chelate heavy metal treating agent (trade name TS-500, manufactured by Tosoh Corporation), kneaded, and detoxified. Table 1 shows the analysis results of the eluted components from the sludge after the treatment.

Comparative Example 3

  The water washing operation similar to Example 1 was implemented twice with respect to the sludge used in Example 1. The sludge after washing was analyzed for the eluted components without any treatment. The results are shown in Table 1.

実施例１の結果、スラッジからの有害な重金属類の溶出量はすべて基準値以下であり、水洗を行なうことにより重金属処理剤による無害化処理が行なわれていることがわかる。また、実施例１と実施例２の比較より、水洗が良好であるほど重金属処理剤による無害化処理が行なわれやすいことがわかる。比較例１の結果より、無害化処理を行なわなかった場合のスラッジからは、水銀が基準値（０．００５０ｍｇ／Ｌ）以上溶出するとともに、基準値以下であるが鉛の溶出が見られることがわかる。また、比較例２の結果より、硫黄元素を大量に含んだスラッジを直接重金属処理剤で処理しようとしても水銀の無害化処理が困難であることがわかる。さらに、比較例３の結果よりこのスラッジは、水洗を２回行なっても水銀の溶出量が基準値以上であり、水洗操作だけによる完全な無害化処理は困難であることがわかる。

As a result of Example 1, it can be seen that the amount of harmful heavy metals eluted from the sludge is less than the standard value, and the detoxification treatment with the heavy metal treating agent is performed by washing with water. Moreover, it turns out that the detoxification process by a heavy metal processing agent is easy to be performed, so that washing with water is favorable from the comparison of Example 1 and Example 2. From the results of Comparative Example 1, mercury eluted from the sludge when no detoxification treatment was performed, and the elution of lead was observed although it was below the reference value (0.0050 mg / L) and below the reference value. Understand. In addition, the results of Comparative Example 2 show that mercury detoxification is difficult even when sludge containing a large amount of elemental sulfur is directly treated with a heavy metal treating agent. Furthermore, it can be seen from the results of Comparative Example 3 that this sludge has a mercury elution amount equal to or higher than the reference value even if it is washed twice, and it is difficult to completely detoxify it only by the washing operation.

  INDUSTRIAL APPLICABILITY The present invention can detoxify sludge or soil containing mercury compounds generated in geothermal power plants, hot springs, etc., and is extremely useful.

Claims (5)

A method for detoxifying sludge or soil, comprising washing a sludge or soil containing a mercury compound with water and then adding a heavy metal treating agent. The method for detoxifying sludge or soil according to claim 1, wherein the mercury compound is mercury sulfide. The sludge or soil contains one or more heavy metals selected from the group consisting of lead, cadmium, hexavalent chromium, arsenic and selenium in addition to mercury compounds. The method for detoxifying sludge or soil according to 2. The method for detoxifying sludge or soil according to any one of claims 1 to 3, wherein the heavy metal treating agent is an organic chelate heavy metal treating agent. The method for detoxifying sludge or soil according to claim 4, wherein the organic chelate heavy metal treating agent is a heavy metal treating agent mainly composed of sodium dithiocarbamate and / or potassium dithiocarbamate.