JP2006205020A - Processing method for detoxicating solid waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of volatilizing and separating metal and alkali salt included in solid waste and, at the same time, decomposing harmful organic chlorine compound by adding a chlorination agent to the solid waste, kneading a mixture and, thereafter, performing vacuum operation while heating the mixture. <P>SOLUTION: The processing method for detoxicating solid waste is provided with: a chlorinating process of adding the chlorination agent to the solid waste, kneading the mixture and, thereby, chlorinating the metal included in the solid waste; and a volatilizing and decomposing process of heating the solid waste at a temperature of 550 to 1,000 °C while performing a vacuum operation under an environmental pressure in the range of 1,013 to 1 hPa, volatilizing and separating the alkali salt component included in the solid waste and the chlorinated metal and, at the same time, thermally decomposing the harmful organic chlorine compound included in the solid waste. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides an effective method for volatilizing and separating metal components and alkali salt components from solid waste containing metals, alkali salts and harmful organic chlorine compounds, and thermally decomposing the harmful organic chlorine compounds, thereby harming the solid waste. It relates to the method of making it.

Solid waste such as soot and dust containing metals and alkali salts is designated as specially managed municipal waste, so it is necessary to dispose of it in a managed disposal site after performing a prescribed metal elution prevention treatment. Such solid waste often contains toxic organochlorine compounds such as dioxins, and it is necessary to decompose dioxins separately from the metal elution prevention treatment. In addition, with regard to the existing metal elution prevention treatment, the long-term stability of the metal at the landfill site has been questioned. Further, apart from the problem of metal elution, NaCl, KCl, CaCl ₂ contained in solid waste. There is also a problem that alkali salts such as leached together with rainwater require desalting treatment of drainage. As described above, various unsolved problems remain in the detoxification treatment of solid waste, and since the metal itself is a finite resource, a new detoxification treatment for solid waste to replace elution prevention is required. It was done. On the other hand, solid waste may contain harmful organic chlorine compounds such as dioxins, and a technique for decomposing and removing these harmful organic chlorine compounds is also required.

In response to the above problems, for example, in the method of recovering either one or both of lead and zinc among the valuable metals from the fly ash containing a calcium component, a chlorine component and a valuable metal, the fly ash is acidified with hydrochloric acid. A chlorination step for eluting valuable metal components including zinc by treating with a liquid, a volatile decomposition step for separating lead residues by filtering and removing the treatment liquid of the chlorination step, and the volatile decomposition step From fly ash, comprising a third step in which sulfuric acid is added to the removed liquid for reaction, and a fourth step in which the reaction product solution in the third step is filtered to produce gypsum and hydrochloric acid acidic solution. Has been proposed (Japanese Patent No. 3536901).
In addition, water is added to the fly ash collected when the waste incineration residue is melt-treated, and further, alkali is added if necessary to form a slurry, and the slurry is subjected to solid-liquid separation to dissolve soluble salts and There has been proposed a method for recovering metal from molten fly ash, characterized in that it is divided into residues containing metal, the separated residue is subjected to high-temperature heat treatment, and the processed product is recovered as a metal concentrate (Japanese Patent Laid-Open No. 10-204548).
Furthermore, toxic organochlorine compounds in solid waste usually require heat treatment at 800 ° C. or higher to completely decompose them, but they can be completely decomposed even at temperatures of 300 to 500 ° C. in an oxygen-deficient state. Is shown (Japanese Patent Publication No. 6-38863)

Japanese Patent No. 3536901 Japanese Patent Laid-Open No. 10-204548 Japanese Patent Publication No. 6-38863

However, in the wet process described in Japanese Patent No. 3536901, there is a problem that dioxins in solid waste cannot be decomposed and the recovered metal and alkali salt cannot be separated.

  Further, in the separation and recovery method described in JP-A-10-204548, only two types of metals, mainly lead and zinc, can be recovered, and the remaining metal content is waste. There is a problem that it is said. Furthermore, the obtained metal concentrate is in a state where lead, zinc and the like are still mixed, and there is a problem that a separate metal recovery process using a separate smelting facility is necessary.

  Furthermore, in the method described in Japanese Patent Publication No. 6-38863, in the heating temperature and oxygen-deficient atmosphere, it is possible to decompose only the toxic organic chlorine compound, and the metal in the solid waste cannot be recovered, and another process is required. There is a problem that it is necessary.

  The present invention has been made in view of the above problems, and can separate and volatilize metal and alkali salt components contained in solid waste, and thermally decompose harmful organic chlorine compounds in the solid waste. It is an object to provide a method for detoxifying solid waste that can be detoxified.

To achieve the above object, the solid waste detoxification method according to the present invention includes a chlorination step of adding a chlorinating agent to the solid waste and kneading to chlorinate the metal contained in the solid waste. The solid waste is heated at 550 to 1,000 ° C. while reducing the pressure in the range of atmospheric pressure 1013 to 1 hPa, and the alkali salt component and the chlorinated metal contained in the solid waste are volatilized. And a volatile decomposition step of thermally decomposing a harmful organic chlorine compound contained in the solid waste.
This makes it possible to pyrolyze harmful organic chlorine compounds together with volatile separation of the metal and alkali salt components contained in the solid waste.

Further, the solid waste detoxification method according to the present invention is characterized in that waste hydrochloric acid is used as the chlorinating agent, chlorine gas or hydrogen chloride gas is used, and combustion exhaust gas is used. Thereby, resources can be used effectively.

Further, in the solid waste detoxification method according to the present invention, the depressurization operation in the volatile decomposition step includes a depressurization step for reducing the pressure, and a pressure at which a constant pressure is maintained for a required time before and / or after the depressurization step. And a maintenance step.
Thereby, the contained metal contained in the solid waste can be volatilized and separated separately, and the alkali salt component can also be volatilized and separated.

As is apparent from the above description, the present invention can individually separate the contained metal contained in the solid waste by volatile separation, and can also volatilize the alkali salt component, and is further contained in the solid waste. Since harmful organic chlorine compounds can be thermally decomposed, a solid waste residue containing no chlorine can be obtained.

As a means for solving the above problems, the present inventors have added a chlorinating agent such as hydrochloric acid, hydrogen chloride gas, and chlorine gas to the metal in solid waste, so that the metal can be easily chlorinated at room temperature. It has been found to be a product (Japanese Patent Laid-Open No. 2002-275550). For example, the equilibrium constant of the chlorination reaction between metal and hydrochloric acid at 20 ° C. is 6.3 × 10 ¹⁷ (PbO + HCl (l) = PbCl ₂ + H ₂ O), 1.4 × 10 ⁴ (ZnO + HCl (l) = ZnCl ₂ + H). ₂ O) and 3.6 × 10 ³ (PbO + HCl (l) = PbCl ₂ + H ₂ O) are all directed to the right, and the above reaction occurs even when hydrochloric acid is added to the solid waste. I have confirmed.

As a result of further diligent research based on the above results, the solid waste after adding the chlorinating agent was heat-treated under reduced pressure to separate the contained metals by volatile separation, and the contained alkali salts were also volatilized. We found a method that can be separated. FIG. 1 shows vapor pressure curves of various metals and alkali salts. According to this vapor pressure curve diagram, when solid waste is heated at a temperature of, for example, 850 ° C. for volatile decomposition, and the pressure in the heating furnace is reduced in multiple stages as indicated by arrows, the first stage in ZnCl ₂ is, PbCl ₂ in the second stage, can each volatile separation CuCl ₂ in the third stage, further when we complete the decompression KCl, NaCl, can be volatilized separation also alkali salts such as CaCl ₂ seen.
Further, in the present invention, an oxygen-deficient state is formed in the heating furnace by reducing the pressure, and heating is performed at 550 to 1000 ° C. as a volatile decomposition temperature for volatile separation of the metal. Unlike the invention described in No. 1, it is possible to carry out volatile separation of metals as well as thermal decomposition of harmful organochlorine compounds.

In the present invention, “solid waste” means municipal waste, automobile shredder dust (ASR), medical waste, sewage sludge, construction waste, waste tire, waste plastic, waste solid fuel (RDF) and incineration of these raw materials. Ash and molten fly ash, various types of plating sludge, steelmaking dust, etc. are included. In addition, the “chlorinating agent” in the present invention includes waste hydrochloric acid, hydrogen chloride gas or chlorine gas, combustion exhaust gas containing hydrogen chloride gas or chlorine gas, alkali metal salt and chlorine gas generated during heating of chlorinated waste plastics or It is desirable to use hydrogen chloride gas. As the hydrogen chloride gas or the chlorine gas, synthesized gases can be used, but it is economical to use those contained in the combustion exhaust gas or generated when heating the alkali metal salt and the chlorine-based waste plastic. The addition amount of the “chlorinating agent” is preferably about 1.0 to 3.0 with respect to the equivalent ratio of the molar amount of metal in the solid waste.

The “metal” in the present invention means antimony (Sb), vanadium (V), lithium (Li), niobium (Nb), magnesium (Mg), titanium (Ti), lead (Pb), zinc (Zn). , Copper (Cu), cadmium (Cd), nickel (Ni), chromium (Cr), arsenic (As), selenium (Se), tin (Sn), mercury (Hg), manganese (Mn), and the like.
Furthermore, the “hazardous organic chlorine compound” in the present invention means a polyhalogenated compound such as polychlorinated dibenzodioxin, polychlorinated biphenyl, hexachlorocyclohexane, or a polyhalogenated aromatic compound.

The heating temperature is preferably set to 550 to 1000 ° C. because the harmful organic chlorine compound is decomposed and the metal chloride needs to be in a temperature zone having a vapor pressure. Further, the combination of the heating time and the pressure to be reduced varies depending on the metal to be collected, but it is desirable to adjust the heating time between 10 and 120 minutes and the pressure between 1013 and 1 hPa.

The present invention will be described in more detail by the following embodiments. FIG. 2 is a flowchart showing the steps of the solid waste detoxification method according to the present invention. FIG. 2 shows a chlorination process for reacting a solid waste with a chlorinating agent, a volatile decomposition process for decomposing an organic chlorine compound in the solid waste after the chlorination reaction, separating metals individually, and separating an alkali salt. It is composed of

For example, when the method according to the present invention is applied to detoxification of solid waste containing lead, zinc and copper, it is carried out as follows. First, in the solid waste chlorination step, the metal contained in the solid waste is chlorinated at room temperature by mixing the solid waste and a chlorinating agent using a kneader or the like. Next, in the volatile decomposition step, the solid waste discharged through the chlorination step is subjected to heat treatment for a certain period of time under each pressure determined based on the metal vapor pressure curve diagram of FIG. .

In this volatile decomposition step, as a first step, the inside of the heating furnace is depressurized to AkPa, and the zinc component is volatilized and separated by heating for a certain time while maintaining the pressure. Next, the pressure in the heating furnace is reduced to BkPa, and the lead component is volatilized and separated by heating at that pressure for a certain time. Thereafter, the pressure is reduced to C kPa and the copper component is volatile separated by the same treatment. After volatile separation of the metal content in the solid waste by such depressurization operation, the alkali salt content contained in the solid waste is also reduced by reducing the pressure in the heating furnace to D kPa, which is a lower pressure. Volatilize and discharge as a completely harmless solid residue.

Below, one Example of the detoxification processing method of the solid waste which concerns on this invention is shown. Fig. 3 shows copper, lead, and zinc when heat-treated at 850 ° C by adding 1.0 equivalent of 35 wt% hydrochloric acid to the molten fly ash of automobile shredder dust and the metal content in the molten fly ash. It shows the relationship between the volatilization rate and the furnace pressure.
Note that the pressure in the heating furnace at this time was changed stepwise to 1013,507,253,47,20,13 hPa, and the heat treatment was performed for 120 minutes at each pressure.
From this figure, as an individual separation method of lead, zinc, and copper, in a furnace temperature atmosphere of 850 ° C., lead and zinc are volatilized and separated by performing heat treatment at normal pressure (1013 hPa) as the first stage. After that, it was shown that the copper component can be completely volatile separated by reducing the pressure in the heating furnace stepwise and finally reducing the pressure to 13 hPa.

  Since the present invention relates to a method capable of volatilizing and separating a metal and an alkali salt contained in solid waste and decomposing a harmful organic chlorine compound, the industrial applicability is great.

It is a vapor pressure curve figure of various metal chlorides. It is a figure showing the flow which detoxifies the solid waste which concerns on the method of this invention. It is a figure which shows the relationship between a heavy metal volatilization rate and a heating furnace internal pressure.

Explanation of symbols

1 Kneading machine 2 Heating furnace

Claims (8)

A chlorination step of adding a chlorinating agent to solid waste and kneading to chlorinate the metal contained in the solid waste;
The solid waste is heated at 550 to 1,000 ° C. while reducing the pressure in the range of atmospheric pressure 1013 to 1 hPa, and the alkali salt component and the chlorinated metal contained in the solid waste are volatilized and separated. And a volatile decomposition step of thermally decomposing a harmful organic chlorine compound contained in the solid waste, and a solid waste detoxification treatment method. A method for detoxifying solid waste according to claim 1,
A method for detoxifying solid waste, wherein the chlorinating agent is waste hydrochloric acid. A method for detoxifying solid waste according to claim 1,
A method for detoxifying solid waste, wherein the chlorinating agent is chlorine gas or hydrogen chloride gas. A method for detoxifying solid waste according to claim 3,
A method for detoxifying solid waste, wherein the chlorine gas or hydrogen chloride gas is generated by heating an alkali metal salt and a chlorine-based plastic. A method for detoxifying solid waste according to claim 1,
A solid waste detoxification method, wherein the chlorinating agent is combustion exhaust gas. A method for detoxifying solid waste according to claim 1,
The solid waste characterized in that the depressurization operation in the volatile decomposition step includes a depressurization step for reducing the pressure, and a pressure maintaining step for maintaining a constant pressure for a required time before or / and after the depressurization step. Detoxification treatment method. A method for detoxifying solid waste according to claim 6,
A solid waste detoxification method, wherein the metal contained in the solid waste is individually volatile separated by the depressurization operation. A method for detoxifying solid waste according to claim 7,
After the volatile separation of the contained metals individually, by further reducing the pressure and maintaining the pressure for a required time, the alkali salt component contained in the solid waste is volatile separated and the solid containing no chlorine content A method for detoxifying solid waste, comprising obtaining a residue of waste.