JP4079225B2 - Treatment method for heavy metal contaminated soil - Google Patents

Description

  The present invention stabilizes heavy metals in contaminated soil or sludge that is contaminated with heavy metals and may elute heavy metals, and prevents heavy metals from diffusing into the surrounding environment such as the ground, surface, and groundwater. The present invention relates to a method for treating contaminated soil.

  Soil originally has the function of purifying water quality and the function of recharging groundwater, but with the rapid industrialization in recent years, the soil itself is contaminated with harmful substances, and has the function of purifying water quality and the function of recharging groundwater. In addition to many cases, the pollution has been expanded to the surrounding environment, and many countermeasures have been reported as social problems.

  As a treatment method for contaminated soil that elutes heavy metals, a cement solidification method and a chemical insolubilization method have been widely used.

The cement solidification method is a method that incorporates heavy metals into the hydrated product of cement mineral and stabilizes the solidification. Generally, cement minerals such as Portland cement and contaminated soil are mixed and kneaded, and the soil is adhered to the cement mineral. It suppresses the elution of heavy metals by condensing the soil by the hydration reaction. However, due to the calcium hydroxide (Ca (OH) ₂ ) produced during the hydration reaction of the cement mineral, the pH in the soil rises to 12 or higher, so that among heavy metals, amphoteric elements such as lead increase the solubility, Has the problem of expanding pollution to the surrounding environment.

  In order to solve the above-mentioned problem of pH increase, Patent Document 1 proposes the use of a heavy metal elution inhibitor with a low alkaline cement having a pH of 11 or less, thereby stabilizing amphoteric elements such as lead. can do.

  However, in this method, since the cement is mixed, the soil is solidified and is difficult to regenerate as soil. In addition, cement is agglomerated when left unmixed, so workability is poor, such as the need to clean the equipment each time work is interrupted. Furthermore, cement is expensive, and if the amount of soil required for purification is large, a huge amount of processing costs are required.

  The insolubilization method using chemicals is a method in which soluble heavy metals are insolubilized by adding a chemical such as a heavy metal scavenger to a hardly soluble material by chemical reaction or adsorption. Therefore, it is necessary to select a plurality of drugs for soil eluting a plurality of heavy metals and to consider the influence of chemical reactions between the drugs.

  In addition, even if the insolubilization method using chemicals can insolubilize heavy metals in the short term, the sustainability of the insolubilization effect may be greatly impaired by changes in the external environment such as acid rain. It is not a sufficient processing method.

  On the other hand, Patent Document 2 proposes a method for preventing soil acidification and soil pH stabilization using alkaline materials such as blast furnace slag and converter slag, but the pH is adjusted to insolubilize as hydroxide. Because of this method, it is difficult to insolubilize arsenic that does not generate hydroxide or heavy metal whose solubility of hydroxide is not sufficiently low. In addition, alkaline materials with a maximum particle size of 30 mm are used, but when the particle size exceeds 10 mm, elution of alkali components becomes extremely slow, and a large amount of alkaline materials are required to adjust the target pH, which is economical. Absent.

As described above, in the prior art, an effective technique for stabilizing heavy metals with respect to contaminated soil containing heavy metals has not yet been obtained. The same applies to sludge containing heavy metals.
JP-A-10-258263 (Claims etc.) Japanese Patent Laid-Open No. 2000-282934 (Claims etc.)

  The present invention has been made in view of such circumstances, and is simple and inexpensive to contaminate soil or sludge containing heavy metals that elutes heavy metals, and further, has no adverse effect on the soil environment, and its effect. It aims at providing the processing method of the heavy metal contaminated soil which can be maintained over a long period of time.

  As a result of repeated studies on a method for treating heavy metal-contaminated soil that can solve the above-mentioned problems, the present inventors have found that for heavy metal-containing contaminated soil that elutes heavy metals, agricultural phosphate-based fertilizer or in addition to this By spraying or adding / mixing the calcium supply material, the soluble heavy metals present in the soil are made into a hardly soluble substance by phosphoric acid, which is a soluble component of phosphate fertilizer, and calcium supplied from the soil or the calcium supply material. The present inventors have found that it can be changed and stabilized over a long period of time, and have reached the present invention.

  The present invention is based on the outflow of heavy metals by insolubilizing heavy metals over a long period of time in so-called contaminated soil that contains heavy metals regardless of natural causes or artificial causes and may elute some of the heavy metals. It provides a method to prevent secondary contamination from spreading to surrounding soil and groundwater.

That is, the first invention, fluorine is heavy metals, mercury, and at least one in contaminated contaminated soil cadmium, superphosphate, triple super phosphate of lime, phosphate magnesia fertilizer,熔成- phosphate, calcined phosphate Only the phosphate fertilizer consisting of at least one of fertilizer, coated phosphate fertilizer, liquid phosphate fertilizer, processed phosphate fertilizer, processed mineral phosphate fertilizer, humic phosphate fertilizer, by-product phosphate fertilizer, mixed phosphate fertilizer is 0 for the contaminated soil .1-20% by mass application or addition / mixing treatment, causing the heavy metals contained in the contaminated soil to react with hydroxyapatite to produce hardly soluble apatite or fluoroapatite, A method for treating heavy metal contaminated soil is provided , wherein the heavy metal is insolubilized . This method is effective when the contaminated soil is alkaline and the soil contains 0.01% by mass or more of soluble calcium.

According to such a configuration, the phosphoric acid component effective for insolubilizing fluorine, mercury, and cadmium contained in the contaminated soil is eluted from the phosphate fertilizer by rainwater or the like, and calcium is eluted from the soil. And these eluted components react to produce the hydroxyapatite, fluorine contained in Oite contaminated soil in the process of penetrating the contaminated soil, mercury, and at least one and軟溶hydroxy apatite react cadmium Apatite or fluoroapatite is generated, and at least one of fluorine, mercury, and cadmium is insolubilized. In this case, since only a phosphate fertilizer is used, a complicated process is unnecessary. In addition, special equipment is not required for spraying, and addition and mixing can be performed only with equipment similar to agricultural cultivators according to the scale of the target soil. In addition, construction at a low cost is possible. In addition, since an agricultural phosphate fertilizer is used, not only does it have an adverse effect on the soil, but also it can stabilize heavy metals and add ingredients necessary for agricultural soil.

The second invention, fluorine is heavy metals, mercury, and at least one in contaminated contaminated soil cadmium, superphosphate, triple super phosphate of lime, phosphate magnesia fertilizer,熔成- phosphate, calcined phosphate Fertilizer, coated phosphate fertilizer, liquid phosphate fertilizer, processed phosphate fertilizer, processed mineral phosphate fertilizer, humic phosphate fertilizer, byproduct phosphate fertilizer, phosphate phosphate fertilizer consisting of at least one of mixed phosphate fertilizer and lime, slaked lime, limestone, bitter Calcium supply material consisting of at least one of soil lime, gypsum and steel slag is sprayed or added / mixed at a mass ratio of 0.05 to 10% with respect to the contaminated soil, and is contained in the contaminated soil. and said heavy metals and hydroxyapatite have to produce a sparingly soluble or fluorapatite is reacted, heavy metals, characterized in that insolubilize the heavy metals of the contaminated soil stain To provide a method of processing soil. This method is particularly effective when the contaminated soil is neutral or acidic.

  Since some phosphate fertilizers react with water and become acidic, the ability to neutralize the acidity of not only the calcium supply from the soil but also the calcium supply material helps neutralize the acid soil and make it alkaline. Contribute.

With such a configuration, a phosphoric acid component effective for insolubilization of fluorine, mercury, and cadmium contained in the contaminated soil is eluted from the phosphate fertilizer by rainwater or the like, and calcium is eluted from the soil or the calcium supply material. And these eluted components react to produce the hydroxyapatite, fluorine contained in Oite contaminated soil in the process of penetrating the contaminated soil, mercury, and at least one hydroxyapatite and react with each sparingly soluble cadmium Apatite or fluoroapatite is generated, and at least one of fluorine, mercury, and cadmium is insolubilized. In the second invention, the calcium fertilizer is only added to the phosphate fertilizer of the first invention, so that it can be sprayed or added / mixed in the same manner as in the first invention, and the same effect as the first invention can be obtained. Obtainable.

In the first and second inventions described above, stabilization can be promoted by spraying or adding / mixing water at a mass ratio of 1 to 50% with respect to the contaminated soil, and prevention of scattering of phosphate fertilizers Can do.

  In the present invention, the contaminated soil is a concept including sludge.

According to the present invention, to produce hydroxyapatite by chemical reaction with calcium eluted from the eluted phosphoric acid component and the soil or calcium supply material from phosphate fertilizer, contained in Oite contaminated soil in the process of penetrating the contaminated soil Hydroxyapatite reacts with at least one of fluorine, mercury, and cadmium that is produced to produce sparingly soluble apatite or fluoroapatite, so that fluorine, mercury, and cadmium in the contaminated soil become insoluble , and elution of fluorine, mercury, and cadmium occurs. Can be suppressed.

Embodiments of the present invention will be described below.
In the first embodiment of the present invention, a phosphate fertilizer is sprayed or added / mixed to contaminated soil contaminated with at least one of heavy metals such as fluorine, mercury and cadmium . As a result, the phosphoric acid component eluted from the phosphate fertilizer and the calcium eluted from the soil produce hydroxyapatite by a chemical reaction described later in the process of penetrating into the contaminated soil, and fluorine, mercury, and cadmium in the contaminated soil. Reacts with this hydroxyapatite to produce hardly soluble apatite or fluoroapatite , insolubilizes and stabilizes fluorine, mercury and cadmium in the contaminated soil, and suppresses elution of heavy metals.

Phosphate fertilizers, 0.1 to 20% of the mass ratio to the contaminated soil. If it is less than 0.1%, the stabilization of heavy metals may not be exhibited effectively, and if it exceeds 20%, the effect is saturated and the economy is impaired. In addition to these, it is preferable to spray or add / mix water at a mass ratio of 1 to 50% with respect to the contaminated soil. Stabilization can be promoted by adding water, and scattering of phosphate fertilizer and the like can be prevented. If the water content is less than 1%, the effect is not exhibited effectively. If the water content exceeds 50%, the soil becomes muddy and handling becomes difficult.

  Since the phosphate fertilizer is for agricultural use, it not only does not adversely affect the soil, but also stabilizes heavy metals and can add components necessary for agricultural soil. Phosphoric fertilizers are slow-acting, can exist in the soil for a long time, and have a long duration of effect.

  Phosphoric fertilizers include: superphosphate, heavy superphosphate, phosphoric acid clay fertilizer, molten phosphorous fertilizer, calcined phosphorous fertilizer, coated phosphoric fertilizer, liquid phosphoric fertilizer, processed phosphoric fertilizer, processed mineral phosphoric fertilizer, humic phosphate fertilizer By-product phosphate fertilizer and mixed phosphate fertilizer can be used, and at least one of these can be used. The phosphate fertilizer may be powder or granules (granular).

In the second embodiment of the present invention, a phosphate fertilizer and a calcium supply material are sprayed or added / mixed to contaminated soil contaminated with at least one of fluorine, mercury, and cadmium, which are heavy metals. As a result, the phosphoric acid component eluted from the phosphate fertilizer and the calcium eluted from the calcium supply material generate hydroxyapatite by a chemical reaction as described later in the process of permeating into the contaminated soil, and fluorine, mercury in the contaminated soil Then, cadmium reacts with this hydroxyapatite to produce hardly soluble apatite or fluoroapatite, and fluorine, mercury and cadmium in the contaminated soil are insolubilized and stabilized, and elution of heavy metals is suppressed.

Each of the phosphate fertilizer and the calcium supply material has a mass ratio of 0.05 to 10% with respect to the contaminated soil . If it is less than 0.05%, the stabilization of heavy metals may not be exhibited effectively, and if it exceeds 10%, the effect is saturated and the economic efficiency is impaired. Also in this embodiment, in addition to these, it is preferable to further spray or add / mix water at a mass ratio of 1 to 50% with respect to the contaminated soil.

  As the phosphate fertilizer, the same one as in the first embodiment can be used. Examples of the calcium supply material include lime, slaked lime, limestone, mashed lime, gypsum, and steel slag, and at least one of them can be used. The calcium supply agent may be powder, crushed product, or granular.

  In the above two embodiments, spraying or addition / mixing is adopted as a method for supplying phosphate fertilizer and calcium supply material.

  The method of spraying is not particularly limited, and examples thereof include pressure-feeding spraying with air, rotary spraying spraying, and in the case of powder, mixing with water to form a slurry and spraying with a pump.

  In this case, it is sufficient that the phosphate fertilizer or the calcium supply material is sprayed on the surface of the soil without excavating the soil. In other words, by dispersing phosphate fertilizer and calcium supply material on the surface or surface of contaminated soil, components effective for insolubilizing heavy metals eluted from phosphate fertilizer or calcium supply material penetrate into contaminated soil or sludge. The heavy metals contained are insolubilized by chemical reaction in the process.

  The addition / mixing may be performed either by adding / mixing after spraying the phosphate fertilizer or calcium supply material, or by adding / mixing after excavating the heavy metal-containing contaminated soil. The mixing not only insolubilizes the eluted heavy metals by the chemical reaction associated with the elution of the components effective for insolubilizing the heavy metals from the phosphate fertilizer or calcium feed as described above, but also the phosphate fertilizer or the calcium feed itself. Since heavy metals are insolubilized by adsorption and immobilization of eluted heavy metals from contaminated soil, the contribution to the stabilization of heavy metals is high.

  The mixing method is not particularly limited, and examples thereof include a tiller, a paddle mixer, a bread mixer, a vibrating screen, an impact crusher, a self-propelled soil conditioner, and a mixing method using a bucket.

Hereinafter, the stabilization mechanism of heavy metals will be described in detail.
It is considered that the insolubilization of heavy metals by the phosphate fertilizer calcium supply material is as follows.

  In the process of producing hydroxylapatite by the reaction of the components eluted from phosphoric acid and phosphate from phosphate fertilizer with the calcium released from soil or calcium supply material, and further by chemical reaction with the eluted heavy metals in the soil. , Hardly soluble heavy metal substituted apatite is generated and insolubilized.

  Among these reactions, the chemical reaction formulas related to the production of hydroxyapatite are shown in the formulas (1) to (5), and the chemical reaction formulas for the poorly soluble apatite by heavy metal and hydroxyapatite are shown in the formulas (6) to (8).

  Formulas (6) and (7) are reaction formulas of mercury and cadmium, which are heavy metals that take a cationic state, and form slightly soluble apatite in which a part of calcium is substituted with mercury and cadmium in the process of producing hydroxyapatite.

  On the other hand, in the case of fluorine in an anion state, as shown in formula (8), it is hardly soluble by fluoroapatite generated by substitution of a hydroxyl group and fluorine.

The above reaction formula is the main reaction of the present invention, but the phosphate fertilizer contains phosphoric acid and lime, as well as SiO ₂ , CaSO _{4 and the} like, so CaO—SiO ₂ —H ₂ O—. It is considered that SO ₄ -based compounds are produced and accompanied by a reaction of taking in eluted heavy metals.

  Examples of the present invention will be described below. Needless to say, the present invention is not limited to the following examples.

Example 1
An elution test specified in Ministry of the Environment Notification No. 46 was conducted on fluorine-contaminated soils A, B, and C collected from the factory site. The dissolution test results are shown in Table 1. From Table 1, the fluorine elution amount of any soil exceeded the environmental standard value (0.8 mg / l). A and B were neutral to acidic soil, and C was alkaline soil.

  To 100 parts by mass of the contaminated soils A and B, 5 parts by mass of powdered (-0.25 mm) superphosphate lime and 0.6 parts by mass of powdered (-0.15 mm) quicklime are added, and water is added. Was mixed while shoveling 10 parts by mass. Moreover, 3 mass parts of powdery (-0.25 mm) lime superphosphate was added with respect to 100 mass parts to the contaminated soil C, and shovel mixing was carried out, spraying 10 mass parts of water. The obtained treated soil was hermetically cured in a polyethylene container, and an elution test was conducted by the Notification No. 46 method every time a predetermined period passed. The results are shown in Table 2.

  From Table 2, the effect of any soil was not obtained immediately after mixing, but the environmental standard was cleared when cured on the 5th, and the results of stable suppression of fluorine elution were obtained for a period of 1 year thereafter. The soil pH after one year was neutral with A: 7.5, B: 6.2, and C: 7.8.

(Comparative Example 1)
To 100 parts by mass of the fluorine-contaminated soil of Example 1, 3 parts by mass of polyiron sulfate (13% solution as Fe) and 3 parts by mass of polyaluminum chloride (6% solution as Al) were sprayed and mixed. In order to neutralize this soil, quicklime was added and further mixed to bring the soil pH to about 7. The obtained treated soil was hermetically cured in a polyethylene container, and an elution test was conducted by the Notification No. 46 method every time a predetermined period passed. The results are shown in Table 3.

  Although the elution suppression effect was seen for one month immediately after mixing from Table 3, the elution amount showed the increasing tendency after that, and the long-term stability effect was not acquired.

(Comparative Example 2)
In 100 parts by mass of the A to C fluorine-contaminated soil of Example 1, 5 parts by mass of ordinary Portland cement was dispersed and mixed, and further, shovel was mixed while 10 parts by mass of water was being dispersed. The obtained treated soil was hermetically cured in a polyethylene container, and an elution test was conducted by the Notification No. 46 method every time a predetermined period passed. The results are shown in Table 4.

  From Table 4, the effect of soil with a high elution amount is small, and the elution amount of all soils increased due to long-term curing.

(Example 2)
For the mercury-contaminated soils D and E collected from the factory site, an elution test specified in Ministry of the Environment Notification No. 46 was conducted. The dissolution test results are shown in Table 5. According to Table 5, the mercury elution amount exceeded the environmental standard value (0.0005 mg / l) in all soils. In particular, soil D was highly contaminated soil that exceeded the environmental standard nearly 2000 times.

  To 100 parts by mass of the contaminated soils D and E, 4 parts by mass of powdered (-0.25 mm) superphosphate lime and 0.34 parts by mass of powdered (-0.15 mm) quicklime are added, and water is added. Was mixed while shoveling 10 parts by mass. The obtained treated soil was hermetically cured in a polyethylene container, and an elution test was conducted by the Notification No. 46 method every time a predetermined period passed. The results are shown in Table 6.

  From Table 6, the effect was seen immediately after mixing, and the elution suppression effect was strengthened over time. In addition, the effect did not change even during half-year curing. Moreover, it turned out that the elution suppression of 1/2000 or more is possible with the addition amount of 4% with respect to the amount of soil.

(Comparative Example 3)
0.015 parts by mass of sodium sulfide (Na ₂ S) and polyiron sulfate ((Fe ₂ (OH) _n (SO ₄ ) _{3 -n / 2} ) _m ) 0 with respect to 100 parts by mass of the mercury-contaminated soil D of Example 2 Sprinkling 0.0005 parts by mass of a chelating agent (cysteine) on the treated soil F and 100 parts by mass of the same mercury-contaminated soil D, which are sprinkled and mixed with 10 parts by mass of water and 1 part by mass Then, a treated soil G was obtained by mixing with a shovel while spraying 10 parts by mass of water. The obtained treated soils F and G were hermetically sealed in a polyethylene container, and an elution test according to Notification No. 46 was conducted every time a predetermined period passed. The results are shown in Table 7.

  Although the soil which mixed the insolubilizer from Table 7 had the effect which suppresses elution with respect to untreated, it was not able to clear environmental standard value 0.0005mg / l.

(Example 3)
An elution test specified in Ministry of the Environment Notification No. 46 was conducted on the combined contaminated soil H of mercury and cadmium collected from the factory site. The dissolution test results are shown in Table 8. From Table 8, the lead elution amount and the cadmium elution amount both exceed the environmental standard values (Hg: 0.0005 mg / l, Cd: 0.01 mg / l), which indicates that the soil is contaminated.

  To 100 parts by mass of the contaminated soil H, 4 parts by mass of powdered (-0.25 mm) superphosphate lime and 0.34 parts by mass of powdered (-0.15 mm) quicklime are added, and 10 parts of water is added. The shovel was mixed while mass parts were dispersed. The obtained treated soil was hermetically cured in a polyethylene container, and an elution test was conducted by the Notification No. 46 method every time a predetermined period passed. The results are shown in Table 9.

  From Table 9, it can be seen that the effect is exhibited immediately after mixing, and in the case of cadmium immediately after mixing, in the case of mercury, the environmental standard is cleared after one week, and thereafter, a stable elution suppressing effect is obtained even after 3 months.

  According to the present invention, it is possible to stabilize heavy metals, particularly fluorine, simply by spraying or adding / mixing a relatively inexpensive phosphate fertilizer or a calcium supply agent to a contaminated soil containing heavy metals eluting heavy metals. Since it can be treated, it is extremely simple and low-cost, and is suitable for treating a wide range of contaminated soil such as factory ruins.

Claims (3)

To contaminated soil contaminated with at least one of heavy metals such as fluorine, mercury, and cadmium , superphosphate lime, heavy superphosphate lime, phosphate phosphate fertilizer, molten phosphate fertilizer, calcined phosphate fertilizer, coated phosphate fertilizer, liquid 0.1-20% by mass of only phosphate fertilizer consisting of at least one of phosphate fertilizer, processed phosphate fertilizer, processed mineral phosphate fertilizer, humic phosphate fertilizer, by-product phosphate fertilizer, mixed phosphate fertilizer with respect to the contaminated soil It is sprayed or added / mixed at a ratio to cause the heavy metals contained in the contaminated soil to react with hydroxyapatite to produce hardly soluble apatite or fluoroapatite, thereby insolubilizing the heavy metals in the contaminated soil. A method for treating heavy metal contaminated soil. To contaminated soil contaminated with at least one of heavy metals such as fluorine, mercury, and cadmium , superphosphate lime, heavy superphosphate lime, phosphate phosphate fertilizer, molten phosphate fertilizer, calcined phosphate fertilizer, coated phosphate fertilizer, liquid Phosphate fertilizer, processed phosphate fertilizer, processed mineral phosphate fertilizer, humic acid phosphate fertilizer, by-product phosphate fertilizer, phosphate fertilizer consisting of at least one of mixed phosphate fertilizer and lime, slaked lime, limestone, clay lime, gypsum, steel slag All of the above-mentioned heavy metals and hydroxy contained in the contaminated soil are sprayed or added / mixed with a mass ratio of 0.05 to 10% with respect to the contaminated soil. A method for treating heavy metal-contaminated soil, characterized by reacting apatite to produce sparingly soluble apatite or fluoroapatite to insolubilize the heavy metals in the contaminated soil. The method for treating heavy metal-contaminated soil according to claim 1 or 2 , further comprising spraying or adding water at a mass ratio of 1 to 50% with respect to the contaminated soil.