JPH09299905A - Harmful waste treating agent and its treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste treating agent and the treating method capable of stabilizing so as heavy metals from a waste containing the harmful heavy metals particularly Pb and Cr<+6> , particularly from an incineration ash discharged from am incinerator and containing the harmful heavy metals not to re-eluted. SOLUTION: The waste, from which the harmful heavy metals such as lead, chromium are eluted if not treated, is mixed with a harmful metal stabilizing component composed of one or more kinds selected from cement, a neutralizer, an inorganic absorbent, a cheating agent, sodium silicate a phosphate and other compounds forming a hardly soluble or insoluble compound by allowing to react with the harmful metals such as Pb or harmful metal compounds and a waste treating agent consisting essentially of at least one kind of a ferrous salt a powdery, liquid pr suspended state by 0.5-50wt.% to the waste and if necessary with the addition of water, is kneaded, aged and solidified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste treatment agent and a treatment method effective for stabilizing treatment of wastes containing harmful heavy metals and the like.

[0002]

2. Description of the Related Art At present, about 48 million tons (19
1988) general waste and about 310 million tons (1985)
(Year) industrial waste is discharged. By the year 2000, it is predicted that general waste will reach about 80 million tons and industrial waste will reach about 600 million tons. Of this, about 70% of general waste is incinerated and about 20% is directly disposed of. About 40% of industrial waste is recycled and about 3%
About 30% is directly disposed of at the final disposal site. These incinerated municipal and industrial wastes contain a large amount of harmful heavy metals, and the regulations for disposal are going to be greatly strengthened.

For example, in the case of an urban waste treatment plant, cadmium (Cd), lead (Pb), chromium (Cr), mercury (Hg), arsenic (for arsenic (color-printed paper and cellophane) contained in the waste are included. As) and copper (Cu), and plastics include cadmium, lead, zinc (Zn),
It contains chromium, mercury, arsenic, etc. By incinerating these, heavy metal-rich ash is obtained.
At the incineration site, this ash is often collected by separating it into a main ash made up of waste dust and a fly ash collected from exhaust gas by a bag filter or the like. Heavy metals are contained in both the main ash and the fly ash, but the heavy metals are particularly easily eluted in the fly ash. This is because slaked lime and quick lime are blown in the middle of the exhaust path in order to capture hydrogen chloride gas generated during incineration at the incinerator. That is, since these slaked lime and quick lime are combined with hydrogen chloride gas to form calcium chloride, the hydrogen chloride gas concentration in the exhaust gas can be reduced. However, the fly ash has a pH of 12 because unreacted slaked lime and quick lime remain in the fly ash.
The above is highly alkaline. When lead ash contains a high concentration of lead, it has the property of becoming water-soluble as a lead acid salt in a highly alkaline environment, so as described above, highly alkaline fly ash with unreacted slaked lime and quick lime remaining. If untreated, the lead will be eluted from the waste. Therefore, in the incinerator, fly ash is mixed with cement, mixed with water and kneaded, then cured and solidified and discarded, or mixed with main ash for landfilling in order to prevent elution of harmful metals. However, since cement is alkaline, when a large amount of cement is added to such fly ash, the elution of lead is not suppressed. As described above, the conventional treatment method of simply solidifying with cement has various problems, and secondary pollution may occur unless the use is limited.

Further, a chelating agent has been experimentally used for fly ash treatment, but for fly ash having a particularly high alkali content and a large amount of lead, it may be 6% or more based on the weight of the fly ash. In some cases, if it is not added, it will not be suppressed below the regulation value. Generally, such a chelating agent has a unit price of 50 to 80 times as high as that of cement, and thus is considered to be a heavy burden in terms of running cost.

As described above, it may be difficult to stabilize fly ash generated during incineration of municipal waste by the conventional treatment method using cement or a chelating agent so that heavy metals are not eluted. I understand. Further, in the case of incineration of industrial waste, various kinds of waste are incinerated as compared with the case of the above-mentioned municipal waste, so that the types and amounts of harmful metals contained in the incinerated ash tend to increase. This industrial waste incineration fly ash contains lead (Pb), cadmium (C
d), chromium (Cr), mercury (Hg), arsenic (As) and other metals are generally contained, especially when lead or hexavalent chromium (Cr ⁶⁺ ) is contained, a treatment such as chelate is performed. Even if an agent is used, it is difficult to simultaneously stabilize both lead and hexavalent chromium.

As described above, at present, there is a problem with the treatment agent and the treatment method, and in addition, the shortage of landfill disposal sites in Japan is beginning to become a problem. Addition of a small amount of treatment material causes harmful effects in the waste. A treatment agent and a treatment method capable of strongly stabilizing heavy metals so as not to be re-eluted have been desired.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a waste treatment agent effective for stabilizing treatment of waste containing harmful heavy metals and the like. In particular, the present invention aims to provide a waste treatment agent and a treatment method capable of stabilizing harmful heavy metals and the like contained in incinerator ash discharged from an incinerator so as not to be eluted again as described above. It is what

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found a waste treatment agent which can achieve this object. That is, the treatment agent of the present invention reacts with a cement, a neutralizing agent, an inorganic adsorbent, a chelating agent, water glass, a phosphate, and a harmful metal or a harmful metal compound such as Pb and is hardly soluble or insoluble. It is characterized in that it contains a toxic metal stabilizing component consisting of at least one selected from other compounds forming a compound and a ferrous salt as main components. , At least Pb and Cr,
It is effective for the waste contained in the amount that elutes without treatment.

[0009]

The mechanism of stabilization of harmful heavy metals by the hazardous waste treatment agent of the present invention depends on cements, neutralizing agents, inorganic adsorbents, chelating agents, water glass, phosphates, and other harmful metal stabilizing components. In the case of cements, toxic metals are included and stabilized by solidification and ettringite growth, and in the case of neutralizing agents, amphoteric metals such as Pb and Cd are stabilized due to the pH of the system being around 10. In the case of an inorganic adsorbent, Pb or Cd is stabilized by being chemically or physically adsorbed to the adsorbent, and in the case of a chelating agent, Pb ion or Cd ion forms a chelate bond. It is made insoluble and stabilized by making it, and in the case of water glass, it is stabilized by the adsorption reaction by the adsorbent gelled by the existing polyvalent metal ions and the inclusion by sodium silicate, and In the case of phosphate, stabilized by the inclusion of such Pb ions and Cd ions in generating insoluble compound reacts with calcium ions,
Furthermore, in the case of other harmful metal stabilizing components, Pb
By reacting with harmful metals or harmful metal compounds such as to form insoluble or insoluble compounds to stabilize harmful metals such as Pb and Cd, and by reducing hexavalent chromium by ferrous salts. It is believed that there is. Usually, the reduction of hexavalent chromium is carried out using a ferrous salt under an acidic condition of pH 3 or less, and therefore cannot be applied to highly alkaline fly ash. On the other hand, according to the treating agent of the present invention, elution of hexavalent chromium as well as harmful heavy metals such as Pb can be prevented without adjusting the pH of alkaline incineration ash.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the waste treatment agent of the present invention,
Cement used as a harmful metal stabilizing component, calcined gypsum, Portland cement, early strength cement,
Examples include jet cement, blast furnace cement, and alumina cement.

Similarly, as the neutralizing agent, general-purpose acids such as hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, carbonic acid and boric acid, sulfates such as aluminum sulfate, amorphous aluminum hydroxide,
Examples include iron chloride and phosphoric acid. Of these, sulfate, aluminum hydroxide, and iron chloride are preferable in consideration of price, industrial availability, and ease of practical use, and also react with Pb compound in fly ash. Phosphoric acid capable of forming insoluble compounds is particularly preferred. Further, these neutralizing agents can be used as an aqueous solution, as a powder, or can be used in a state of being dispersed in water, and are within the scope of the present invention.

Examples of the inorganic adsorbents used in the present invention include various types of activated clay, synthetic silicic acid, natural silicic acid processed products, activated carbon, etc., but powdery aluminum silicates having a specific surface area of 200 m ² / g or more, powdery products Silicon dioxide is preferred. Furthermore, due to industrial availability, the specific surface area is 20
0 to 1000 m ² / g is preferable. The specific surface area is 2
Since many inorganic adsorbents having a particle size of 00 m ² / g or more are bulky and are difficult to handle, it is also preferable to perform processing such as granulation in advance.

As the chelating agent used in the present invention,
-OH, -CSH, -SH, = NH, -COOH,-
Examples thereof include compounds having a chelate ligand for a harmful metal such as NH ₂ in the structure, and salts thereof.
Of these, dialkyldithiocarbamate salts such as dimethyldithiocarbamate, diethyldithiocarbamate, and dibutyldithiocarbamate are particularly preferable in terms of Pb elution prevention performance. A chelating agent containing a chelate ligand in the polymer structure is also preferable.

Examples of the water glass used in the present invention include general-purpose water-soluble silicates, that is, sodium silicate, potassium silicate and the like, and the molar ratio (SiO ₂ / M ₂ O composition ratio: M is an alkali metal) is It can be arbitrarily selected within the range of 0.5 to 4.2 which is commercially available. Among such silicates, P
b Considering factors such as elution prevention performance and price, sodium silicate is preferable, and furthermore, JIS standard No. 3 water glass having a molar ratio of about 3 is preferably used. It is also possible to add to water glass an appropriate amount of a compound that reacts with Ca ions such as Na carbonate to form an insoluble or sparingly soluble Ca compound, and further a compound that reacts with water glass and gels, such as sulfuric acid. It is effective for the purpose of improving the Pb elution prevention performance.

Examples of the phosphate used in the present invention include orthophosphate, orthohydrogenphosphate, condensed phosphate, and total hydrogenphosphate. Examples of the salt include sodium salt, potassium salt, magnesium salt, calcium salt, and the like, but a water-soluble salt is preferable, and water-soluble sodium phosphate is preferable.

Other compounds used in the present invention which react with a harmful metal compound such as Pb to form a sparingly soluble or insoluble compound include sulfides such as sodium sulfide,
Examples thereof include carbonates, oxalates, sulfates, chromates and the like.

The ferrous salt used in the present invention is selected from ferrous salts such as ferrous chloride and ferrous sulfate. Ferrous iron salts include anhydrous salts, monohydrates, dihydrates, tetrahydrates, pentahydrates, hexahydrates, heptahydrates, etc., and they can be used without particular limitation. In order to increase the content of ferrous ion per weight, it is desirable to use anhydrous salt or monohydrate.

As described above, the hazardous waste treatment agent according to the present invention includes cements, neutralizing agents, inorganic adsorbents, chelating agents, water glasses, phosphates, and other harmful metals or harmful metal compounds such as Pb. The main component is a toxic metal stabilizing component composed of a compound that reacts with to form a sparingly soluble or insoluble compound, and a ferrous salt, but inevitable impurities may also be contained.

Next, a method of treating waste with the treating agent of the present invention will be described. The treatment method of the present invention is characterized in that the treatment agent as described above is added to the waste, and if necessary, water is added, and the mixture is kneaded to be cured and solidified. In a preferred embodiment of the present invention, wastes such as dust and fly ash collected in a hopper are mixed with the above-mentioned waste treatment agent from another hopper, and water is added to this when necessary. Knead thoroughly in a shaping device and extrude. Generally, in the conventional cement treatment method, 10 to 10
Kneading is performed by adding 30% by weight of cement. On the other hand, when the treating agent of the present invention is used, superior performance is obtained as compared with the case where the same amount of cement is added. The amount of the treatment agent of the present invention to be added is 0.5 to 50% by weight with respect to the waste, but it is usually less than that of cement, and 0.5 to 20% by weight is generally sufficient. . Therefore, it is expected that the volume of the solidified product will be reduced as compared with the case of using cement. The treatment agent of the present invention may be added to the waste in powder form, and water may be added as necessary, or may be added in the form of an aqueous solution or suspension in advance.

[0020]

INDUSTRIAL APPLICABILITY By using the waste treatment agent of the present invention, EP ash or bag ash (particularly EP ash in which slaked lime or quick lime is blown) discharged from an incinerator for industrial waste containing toxic heavy metals and municipal solid waste. Or bug ash), harmful heavy metals,
Particularly, Pb and hexavalent chromium are efficiently stabilized, and the elution amount is reduced. Therefore, by using the waste treatment agent of the present invention, hazardous waste metal-containing industrial waste, or harmful dust collection dust for protecting the working environment at the time of work such as electric furnace melting furnaces in steel mills, and municipal waste. It is possible to stabilize fly ash from the melting furnace or contaminated soil due to landfill disposal, etc. At this time, harmful heavy metals are stabilized and the elution amount is suppressed.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Examples 1 to 9) The treating agent shown in Table 1 was applied to the fly ash A (50 g) discharged from the industrial waste incineration plant, especially for the leaching of lead and hexavalent chromium. , And water (30 g) were added and kneading was performed, followed by curing and solidification at 20 ° C. for 3 days. After that, according to the Environmental Agency Notification No. 13,
An elution test of lead and hexavalent chromium was conducted to quantify the lead and hexavalent chromium concentrations (mg / L) in the eluate. The results are shown in Table 1. The amount of Pb and Cr ⁶⁺ eluted when the dissolution test was carried out in accordance with the Environmental Agency Notification No. 13 method was 11 mg /
L was 2.5 mg / L. As the silicon dioxide, a synthetic silicic acid manufactured by Shionogi (specific surface area 250 m ² / g) is used.
As the aluminum silicate, Wako Pure Chemicals Reagent (specific surface area: 500 m ² / g) is used, sodium dimethyldithiocarbamate and sodium dibutyldithiocarbamate are manufactured by Ouchi Shinko Chemical, and sodium silicate powder is manufactured by Nippon Kagaku Kogyo. Acid soda was used respectively.

Comparative Examples 1 to 8 Table 1 also shows the amounts of Pb and Cr ⁶⁺ eluted when the same fly ash A as in Examples 1 to 9 was treated using Portland cement as a treating agent. .

[0024]

[Table 1]

As is clear from Table 1, when the treating agent of the present invention is used, P
b, Cr ⁶⁺ elution amount was significantly improved.

(Examples 10 to 18) For the fly ash B (50 g) discharged from the industrial waste incineration plant, in which the elution of lead and hexavalent chromium is a problem, the treatment agents shown in Table 2
And water (30 g) were added and kneading was performed.
It was cured and hardened for a day. After that, according to the Environmental Agency Notification No. 13, a dissolution test of lead and hexavalent chromium was conducted.
The hexavalent chromium concentration (mg / L) was quantified. The results are shown in Table 2. In addition, when Pb and Cr ⁶⁺ elution amount is 8 mg / each when the elution test is carried out according to the Environmental Agency Notification No. 13 method, the water is added to fly ash and kneading is similarly performed without adding the treating agent.
L was 0.75 mg / L. The same silicon dioxide, aluminum silicate, sodium dimethyldithiocarbamate, sodium dibutyldithiocarbamate, and sodium powder silicate as in Examples 1 to 9 were used.

(Comparative Examples 9 to 16) Pb and Cr ⁶⁺ in the case of treating fly ash B using cement as a treating agent
The elution amount is also shown in Table 2.

[0028]

[Table 2]

As is clear from Table 2, when the treating agent of the present invention is used, P
b, Cr ⁶⁺ elution amount was significantly improved.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B09B 3/00 301N 301M 304H

Claims (11)

[Claims] 1. A cement, a neutralizing agent, an inorganic adsorbent, a chelating agent, water glass, a phosphate, and Pb, which react with harmful metals or harmful metal compounds to form sparingly soluble or insoluble compounds. Hazardous waste treatment agent comprising as a main component at least one harmful metal stabilizing component selected from the above compounds and at least one ferrous salt. 2. The hazardous waste treatment agent according to claim 1, wherein the ferrous salt is at least one selected from ferrous chloride and ferrous sulfate. 3. The ferrous salt is at least one selected from the group consisting mainly of anhydrous ferrous chloride, monohydrate, and anhydrous ferrous sulfate and monohydrate. The hazardous waste treatment agent according to 1. 4. The neutralizing agent is at least one selected from sulfate, aluminum hydroxide, iron chloride and phosphoric acid.
The hazardous waste treatment agent according to any one of claims 1 to 3, which comprises seeds as a main component. 5. The specific surface area of the inorganic adsorbent is 200 m ²
4. The hazardous waste treatment agent according to any one of claims 1 to 3, which contains at least one selected from the group consisting of aluminum silicate powder / g or more and silicon dioxide powder. 6. The chelating agent contains at least one dialkyldithiocarbamate as a main component.
The hazardous waste treatment agent according to any one of to 3. 7. The hazardous waste treatment agent according to claim 6, wherein the dialkyldithiocarbamate is at least one selected from dimethyldithiocarbamate, diethyldithiocarbamate, and dibutyldithiocarbamate. 8. The hazardous waste treatment agent according to claim 1, wherein the water glass is sodium silicate. 9. The hazardous waste treatment agent according to claim 1, wherein the phosphate is water-soluble sodium phosphate. 10. A hazardous waste containing at least lead and chromium in an amount that elutes the lead and chromium without treatment, and the waste treatment agent according to claim 1;
It is characterized in that it is in the form of powder, solution, or suspension, and is mixed in an amount of 0.5 to 50% by weight with respect to the waste and, if necessary, water is added to knead and cure and solidify. Waste treatment method. 11. The waste treatment method according to claim 10, wherein the hazardous waste is waste incineration fly ash.