JP2583729B2 - Detoxification and stabilization of waste containing hazardous heavy metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial application] It is mainly used to ultimately reduce harmful cinders, dust, sludge, etc., and liquid waste from nuclear reactor operations to the natural world as defined in the "Law on Waste Cleaning and Disposal". It relates to detoxification and stabilization treatment by embedding in solidified cement.

[0002]

2. Description of the Related Art Stabilization or detoxification methods required for finally reducing harmful heavy metal-containing wastes to the natural world include embedding and solidifying in cement and vitrifying and embedding. However, land reclamation by solidification of cement is most often used as one of the effective means at present.

In general, harmful substances are detoxified and stabilized by cement solidification. Portland cement produces slaked lime by hydration and is highly alkaline (pH = 12 to 1).
The insoluble metal hydroxide is formed by using the above 3), and the hydrate is obtained by mixing tricalcium silicate, dicalcium silicate, and tricalcium aluminate, which are the main components of cement, with water. Forming an adsorption phenomenon due to the interaction between the surface charge of the hydration product and heavy metal ions, and
This is due to the fact that ions or groups in the hydrate are replaced with heavy metal ions in parallel with the adsorption action. In addition, the permeability of cement decreases with the progress of hydration and approaches the value of rock. Therefore, elution tends to decrease with time, and the purpose of physical containment of heavy metals and the like is fulfilled. However, when free lime increases with hydration and becomes highly alkaline (about pH 13), there is an unstable element such that insolubilized hydroxides (such as lead and hexavalent chromium) and cyanide are eluted again.

[0004] Prior to embedding in cement, chemical treatment for detoxifying waste containing harmful heavy metals is sometimes performed. For this purpose, iron salts or sulfurizing agents are used as chemical treatment agents. Is added. Since these additives tend to significantly inhibit the hydration reaction and hardening of cement, it was necessary to carefully consider the selection and application amount of these additives.

On the other hand, during operation of a nuclear reactor used in a power plant or the like, a radioactive liquid containing sodium sulfate and boric acid is discharged. In order to make this harmless and stable, the following processing was performed.

That is, a mixture of ordinary cement and vermiculite is charged into a drum, and a radioactive waste liquid is injected into the drum while reducing the pressure in the drum, and the cement absorbs water and solidifies. For example, in the NU mand seal method, 100 liters of a radioactive waste liquid containing a sodium salt of boric acid (about 20,000 ppm as boron) is charged in an absorption solidifying material 1 previously charged in a drum can.
It was absorbed into 85 kg and solidified.

[0007] Further, many fish and shellfish and algae adhere to cooling water channels of power plants and the like, or their dead bodies decay and accumulate to form sludge, which hinders the normal function of the cooling water channels.
Therefore, it is necessary to remove them regularly. The method of disposing of the removed attached organisms and sludge is buried in the land owned by the company, but there is a limit in securing the land to be disposed within the company, and there is no choice but to rely on an external landfill.
However, sludge emits an unpleasant odor and is difficult to transport to a landfill, and dumping to a landfill is not allowed unless a stabilization treatment such as dehydration is performed. In addition, as an inexpensive stabilization treatment, there is a cement solidification treatment. However, since it contains seawater and a large amount of organic substances, hardening of the cement is inhibited, and the treatment is difficult.

[0008]

Generally, when fine particles are mixed into cement, the formation of crystals of cement minerals is hindered, and the aggregate used in concrete and mortar to prevent solidification of cement is insoluble in water. It is well known that a certain degree of particle size is required, so that fine particles such as clay cannot be used.

Cinders and dusts containing harmful heavy metals and the like often have a particle size of several μm to several tens μm, and are not only those which can be simply solidified by cement. In addition, sludge contains a large amount of water, which inhibits solidification of cement.

[0010] Further, the electric dust collected from a municipal waste cleaning plant and an industrial waste intermediate treatment plant is a deliquescent substance such as calcium chloride or magnesium chloride, sodium chloride, calcium sulfate, potassium chloride, sodium sulfate or the like. Because of the inclusion of hygroscopic salts, it becomes difficult to solidify the cement by mixing it with the cement. Therefore, expensive special cement must be used for embedding the conventional electric dust collection ash containing heavy metals.

In addition, regarding the solidification treatment for injecting radioactive waste liquid discharged from the reactor operation into a drum can, the waste liquid contains a sodium salt of boric acid in a high concentration, so that the setting speed of cement is significantly delayed, Therefore, it cannot be moved for several days after the injection of the waste liquid, and only 15 days at 28 days.
Work efficiency was poor, for example, kgf / cm2 was obtained.

[0012]

SUMMARY OF THE INVENTION The admixtures which are essential parts in the detoxification and stabilization treatment according to the present invention are as follows. That is, the cement mixed with the sand is once hydrated, the sand is removed again, and the resulting cement is immersed and stored in a water tank, and then filtered and dried to lower the pH ( 10) is a cement hydrate containing unhydrated.

[0013] The detoxification and stabilization treatment of the waste is carried out by adding the admixture thus produced to alumina cement.
Waste such as electric dust and sludge is mixed into a solidified material mixed with 200% by weight, and an appropriate amount of water is added to coagulate and solidify. In this way, the amount of special cement such as alumina cement is reduced, and harmful heavy metals are efficiently adsorbed by cement and admixtures, thereby achieving harmlessness and stabilization.

Further, when the waste is a liquid or a substance containing a large amount of liquid, a water retention material is mixed into a mixture of the admixture and the alumina cement to increase water absorption and improve coagulation efficiency. .

[0015]

Embodiment 1 First, the admixture according to the present invention is obtained by the following manufacturing method. That is, sand is mixed with cement 1 at a ratio of 2 to 3 (weight ratio), and further slurried by adding water to cause a hydration reaction. Sand is separated and removed from the slurry by a classifier at a stage where the cement does not solidify. The remaining cement slurry is stored in a water tank while stirring (preventing solidification) while lowering the pH (about 10).
Dry and collect the powder. The hydrated cement powder containing unhydrated material recovered through the partial hydration process is an admixture (hereinafter, this admixture is abbreviated as OC). Such a treatment is characterized in that a dense crystal structure of calcium silicate is precipitated, and thus an admixture having a large specific surface area is obtained. The OC has slightly different chemical components and physical properties depending on the type of cement as a raw material, but examples of standard OC are shown in Tables 1 and 2 in comparison with ordinary cement.

[0016]

[Table 1]

[0017]

[Table 2]

As shown in Tables 1 and 2, OC has a fineness (specific surface area) of at least twice that of ordinary cement.
Therefore, it has a large water absorption, has good adsorbability for heavy metals and the like (FIG. 3), and has a small hydraulic property as a cement material, so that a weak solidified product can be obtained. Chemical components include loss on ignition, acid-insoluble content, SiO2, Al2O3, Mg
O is increasing compared to ordinary cement, CaO, Fe2O
3 has decreased. In these, cement is added by adding sand and moisture, and free lime precipitates at the stage of the hydration reaction, and this calcium hydroxide is washed away during the dehydration treatment, and fine sand remains. That's why.

[0019]

[Table 3]

The second method for producing the admixture is as follows. That is, the aggregate and waste liquid mixed with cement (called cement sludge) discharged when washing the tank of the ready-mixed concrete kneading plant or the tank of the concrete mixer truck are collected, and the above-mentioned OC production process, that is, gravel, sand Aggregates such as are removed, and the remaining cement slurry is stored in water while stirring, and then dewatered and dried. Economically, it is a good idea to use cement sludge discharged from the production and use of such ready-mixed concrete.

The method of using the OC produced in this manner is to add 10 to 300% by weight of the OC to a commercially available cement (and to mix a water retention material depending on the object to be treated).
Further, electric dust ash, cinder, sludge, waste water, etc. and water are added and mixed, and then poured into an appropriate mold to condense and solidify. As shown in Table 2, the amount of condensed water of OC was 9
It is very large at 0% by weight, and the amount of additional water required for treatment of dust ash etc. is considerably larger than that of cement alone, but it is added when mixing and solidifying sludge and other materials having a large amount of water. Of water is small or unnecessary, and the solidification time is reduced.

Conventionally, as a method of solidifying sludge having a higher moisture content, a method of putting cement and sludge into a rotary drier without using a formwork, heating and drying while rotating, and solidifying into sand particles. is there. On the other hand, when the OC according to the present invention is mixed with the cement and mixed with sludge having a high moisture content (or dust), heating the rotary dryer is not required if the amount of added water is adjusted to an appropriate flow value. It can be solidified in the form of sand. This greatly reduces processing costs.

Using OC as an admixture for commercial cement,
Example 1 of embedding electrostatic dust containing harmful heavy metals
Are shown in Tables 4 to 6 in comparison with the commercially available cement alone.
The hazardous heavy metal-containing waste used here is electric dust (hereinafter abbreviated as EP) collected from municipal solid waste incinerators. The chemical components are shown in Table 4 and the contents of heavy metals etc. are shown in Table 5. The results of the dissolution test are shown in Table 6. The particle size of this EP was as very small as about 44 μm or less.

[0024]

[Table 4]

[0025]

[Table 5]

[0026]

[Table 6]

Commercially available cements include ordinary Portland cement (abbreviated as NC, the same applies hereinafter), early-strength Portland cement (VC), jet cement (JC), ultra-high-strength cement (SC), alumina cement (AC), waterproofing The mold for comparing the performance of cement embedding using cement (LC) is 5 based on JIS A 1132.
A compression mold of 0 mm x 100 mm was used. Table 7 shows the embedding strength when 35, 50, and 65% by weight of the commercially available cement was mixed into the EP and solidified, and the ratio of the commercially available cement to the OC was 35:65, 50:50, and 65:
Table 8 shows the embedding strength when 60% by weight of EP was mixed and solidified. In addition, water cement ratio (W
/ P) was adjusted to obtain the same flow value (135-150 mm). As a result, NC, VC, and BC swelled about one hour after molding and did not harden, and are not described.

[0028]

[Table 7]

[0029]

[Table 8]

As shown in Tables 7 and 8, AC-100 (A
(C is 100% by weight) has a high strength in any case of the ratio to EP and is good without disintegrating into water, and then AC-65-60 and AC-5 in which OC is mixed with AC.
0-60 and AC-35-60 were good in both strength and disintegration. Each of SC-100, JC-100, and LC-100, 35, 50, and 65, disintegrates in water, and SC-50-
60, SC-65-60, JC-35, 50, and 65 were improved to a degree that they were slightly disintegrated. There is no provision prohibiting embedding with a solidifying material that disintegrates in water with respect to waste treatment, and therefore the solidified products described above can be used for this purpose. However, at least the solidified cement should have a strength of at least 10 kgf / cm 2 and should not be decomposed into water and be reduced to nature.

Table 9 shows the results of the heavy metal elution test for those satisfying the above criteria. 50% by weight in AC
In the case of mixing OC, although the performance is slightly inferior in the elution of lead, in other cases, the same performance as a cement material of 100% by weight of AC is obtained, and sufficient safety and stability can be obtained even when reduced to nature. I understood. At present, the amount of lead that can be discarded at public landfill sites in Osaka Prefecture is 1.0 mg / l or less, and Table 9 sufficiently satisfies the criteria.

[0032]

[Table 9]

Table 10 shows the relationship between the OC mixing amount, the strength, and the demolding time when EP was embedded and solidified with the cement solidifying material. The demolding time when embedding at 100% by weight of AC is 2 hours, whereas the solidified material mixed with OC is 3 hours.
It has been reduced from 0 minutes to 1 hour.

[0034]

[Table 10]

[0035]

Example 2 As Example 2 of the present invention, Table 11 shows examples of detoxifying and stabilizing harmful sludge discarded from various industries using the solidifying material of the present invention. All the test samples used here are difficult to solidify with cement alone. For example, stabilization processing such as water treatment is not usually performed on dusts. Therefore, it is difficult to detoxify when CN or the like which is re-eluted when it becomes alkaline is contained, and carbon contained in a large amount inhibits hardening of cement and does not provide strength. Pb / Cr-based sludge from the pigment production process has a particularly high Pb content, significantly inhibits the hardening of cement, does not provide sufficient strength, and Pb elutes when it becomes alkaline. As-based duct deposits are the most difficult to detoxify, and are usually diluted 50 times or more and subjected to special solidification. Laboratory sludge is extremely difficult to detoxify because it contains and elutes Hg very much, and is usually diluted 100 times or more and combined with other solidified products.

As described above, harmful sludge which is not hardened by ordinary cement alone or hardly hardened is
The solidification was facilitated by mixing the highly water-absorbing OC with the alumina cement. In this case, it cures in spite of using chemical treatment with additives to make detoxification more reliable.Moreover, the demolding time is shortened, the disintegration resistance to water is good, and sufficient strength is obtained. The subsequent elution of heavy metals and the like was extremely slight, and it was found to be good as a detoxifying and stabilizing treatment method.

[0037]

[Table 11]

[0038]

Example 3 A simulated solution of a radioactive liquid containing sodium salts of boric acid (30,000 ppm as boron) discharged from the operation of a nuclear reactor was mixed with 170 kg of ordinary cement,
Vacuum injection was performed into a drum can charged with 21 kg of vermiculite. This was a conventional method, in which 100 liters of the simulated solution could be injected. It is well known that boron delays the solidification of cement, and in this experiment, it was necessary to allow the cement to stand for one week for solidification.

On the other hand, a calcium silicate heat insulator (JIS A 9510) crushed to 2 mm or less as a water insulator was added to a solidified material obtained by mixing AC at a ratio of 30 and OC at a ratio of 70.
The same amount (weight ratio) is mixed, and 58.1 kg of the mixture is charged into a drum. A solution having a boron concentration of 50,000 ppm (the hardening becomes more difficult as the concentration becomes higher) is simulated as a simulated solution. Injected. In this method, 150 liters of the solution can be injected, and solidified 3 hours after the injection of the solution. After that, the drum can can be moved, and it has been found that the amount of treated water is larger than in the conventional method.

The unconfined compressive strength (one week of material age) of the cement thus solidified is 15 kgf / cm 2 or more, which is in accordance with Article 4.3 of the Technical Standard for Solid Waste No. 2 of the Notification of the Science and Technology Agency. It passed and was good without disintegration against water.

The water retention material in the present invention refers to a porous material containing silicate as a main component (for example, vermiculite, perlite, calcium silicate heat retention material, etc.). This includes waste materials and cutting waste.

[0042]

Embodiment 4 As described above, seawater sludge containing shells and carcasses contains a large amount of seawater and significantly inhibits hardening of cement. The detoxification and stabilization of such seawater sludge is performed as follows. That is, the hardening material is obtained by mixing an equal amount of OC and AC, and further adding the same amount of water retention material as the mixture, and mixing and kneading an equal amount (weight ratio) of seawater sludge into the hardening material. . The solidified product of this treatment can be disposed of for landfill or incinerated.In the case of incineration, the solidification strength may be low, and therefore the mixing ratio of sludge can be increased. In addition, since the incinerated ash can be reused as a water retention material and a solidifying material, the final waste is extremely small.

[0043]

When the above various commercially available cements are used alone, all except AC tend to expand at the time of solidification, and the expansion of NC, BC and VC is not particularly hardened. On the other hand, expansion tends to be prevented by the addition of OC, and in particular, in combination with AC, it can sufficiently withstand use if high strength is not expected.
Can be reduced, and an inexpensive embedding process can be performed.

In addition, the addition of OC shortens the hardening time of the cement, and depending on the object to be treated, can be immediately removed from the mold, thereby shortening the processing time and increasing the efficiency of the processing work area.

OC has a larger specific surface area than ordinary cement, and therefore has a large surface charge and improved adsorption performance due to the interaction of heavy metal ions.

The OC can be obtained by subjecting the mixed concrete to a sand silo or a tank of a mixer truck for transporting ready-mixed concrete, which is produced when the tank is washed with water, by subjecting the mixture to sand and classification to dry the cement. Inexpensive ones are available. Therefore, by mixing and using the alumina cement, it is possible to embed heavy metals at lower cost. As a result, it is possible to prevent the cement sludge from flowing into the natural environment, and two effects can be obtained with respect to environmental conservation.

In the solidification as a detoxifying and stabilizing treatment of a highly concentrated borate solution having radioactivity, high water absorption is achieved by a combination of a porous material mainly composed of OC and silicate, and the throughput is increased. Despite the increase in volume, the volume of the solidified body can be reduced, and the processing time can be reduced.

Since sludge containing a large amount of salt or seawater can be solidified, the scope of detoxification and stabilization by solidification is expanded.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G21F 9/16 521 G21F 9/16 ZAB ZAB B09B 3/00 301S ZAB

Claims (3)

(57) [Claims] The present invention relates to a method for producing a cement mixed with sand, wherein the cement mixed with sand is hydrated, the sand is removed, and the cement is immersed and stored in a water tank. Hydrated cement containing hydrated unhydrated is converted into alumina cement,
A method for detoxifying and stabilizing hazardous waste, characterized in that waste containing harmful heavy metals and the like is mixed into a solidified material whose main component is a mixture of 00% by weight and mixed. 2. A method in which a cement mixed with sand is once hydrated, a cement component obtained by removing the sand is immersed and stored in a water tank, and then filtered and dried to obtain a low pH. Hydrated cement containing hydrated unhydrated is converted into alumina cement,
In addition to the solidified material mainly composed of the mixture, a porous material mainly composed of silicate in the same amount as that of the alumina cement is additionally mixed, and the mixture is added to the solidified material by a reactor operation or the like. A method for detoxifying and stabilizing hazardous waste, characterized by injecting and solidifying discharged liquid waste. 3. The cement mixed with sand is once hydrated, and the cement obtained by removing the sand is immersed and stored in a water tank, and then filtered and dried to obtain a low pH. Hydrated cement containing hydrated unhydrated is converted into alumina cement,
A water-retaining material is filled into a solidified material mainly composed of a mixture of 00% by weight and mixed with seawater-containing sludge, and the mixture is solidified and solidified. Treatment method.