JPH07214029A - Recycling method of heavy metal by making incineration ash or fly ash harmless - Google Patents

Abstract

PURPOSE:To stably fix and separate heavy metals and to make fly ash or the like harmless by heating the fly ash or the like containing the heavy metals to concentrate the heavy metals in the fly ash and executing a means, for example, to collect the heavy metals into a solid precipitate by dissolving the fly ash in an aq. solution and neutralizing. CONSTITUTION:In a 1st process, the heavy metals are concentrated into the fly ash by heating the incineration ash or fly ash containing the heavy metals under a condition that at least 2wt.% chloride expressed in terms of chlorine is present and volatilizing the heavy metals as chloride. And 10 a 2nd process, a slurry is prepared by feeding the fly ash into a dissolving vessel in the preceding process 6 and adjusting the ratio of the solid precipitate in, for example, a sulfuric acid acidic exudation liquid. And an overflow solution from the dissolving vessel is introduced into a neutralizing vessel 1, 2 successively and is neutralized to pH6.0 by, for example, adding NaOH to form a hydroxide precipitate. Furthermore, the hydroxide precipitate containing solution is introduced into a sulfidation reactor 3 to form a sulfide precipitate of the heavy metals.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the detoxification of incineration ash or fly ash containing various heavy metals including harmful substances generated from incinerators and melting furnaces in municipal waste incinerators and industrial waste incinerators. The present invention relates to a method for recycling heavy metals by treatment.

[0002]

2. Description of the Related Art Generally, garbage discharged from business establishments and households (referred to as "urban garbage" or "general waste") is collected at an urban refuse incinerator and incinerated. At that time, cinder and fly ash generated from the incinerator were accumulated at the final disposal site.

However, in recent years, it has been regarded as a problem that it is difficult to secure a deposition site and the harmfulness of heavy metals such as mercury, lead, zinc, cadmium and arsenic contained in the fly ash to be deposited and dioxins.

Therefore, a cement solidification method, a chemical treatment method and the like have been developed and put into practical use in order to stabilize the above-mentioned harmful substances, but the landfill volume cannot be reduced by the cement solidification method and the like, so that the sedimentation site The issue of security remained unresolved. In addition, it is reported that the elution of heavy metals contained in fly ash will be eliminated by the kneading process of fly ash and cement (elution test according to the Environmental Agency Notification No. 13 method), but considering the effect of acid rain, etc. However, heavy metals in fly ash mixed with cement were not always stable (Takeshi Kikuchi, “Detoxification of incineration residue by melting treatment of garbage incineration ash by plasma and generation of slag Recycling "PPM1992 / 5).

On the other hand, there is a report that it is possible to achieve volume reduction and detoxification by thermal decomposition of dioxins by melting and treating the cinders and fly ash from the incinerator (Katsuya Nagata "Urban waste incinerator". Status and Trends of Dioxin Countermeasures in Japan ", Journal of Japan Society of Waste, Vol. 3, No. 3).

However, according to the above-mentioned melting treatment, heavy metals such as lead and cadmium, which have a large vapor pressure, volatilize into the exhaust gas and enter the exhaust gas, and the heavy metal entering the exhaust gas is condensed in the exhaust gas processing equipment and re-flyed. There was a problem that it became ashes.

[0007]

Therefore, the present invention solves the above-mentioned problems of the prior art and positively separates and collects heavy metals contained in fly ash while fixing them in a stable form, and An object of the present invention is to provide a method for treating incineration ash or fly ash from an incinerator and a melting furnace, which enables effective use of valuable metals by recycling without causing pollution problems.

[0008]

Means for Solving the Problems As a result of earnest studies for achieving the above object, the present inventors have found that incineration ash or fly ash containing heavy metals generated from an incinerator or a melting furnace is converted into a chlorine-equivalent amount. Heat treatment is performed in the presence of at least 2 wt% or more, preferably 3 wt% or more chloride to volatilize heavy metal as chloride to concentrate chloride of heavy metal as fly ash, and then recover heavy metal from the concentrate. As a result, it was found that the heavy metal can be recycled as a valuable metal, and the method of the present invention could be developed.

That is, the first invention developed by the present inventors is to heat incineration ash or fly ash containing a heavy metal in the presence of at least 2 wt% or more, preferably 3 wt% or more of chloride in terms of chlorine. The first step of treating and volatilizing heavy metal as chloride and concentrating it as fly ash, and then dissolving the obtained fly ash in the liquid and further neutralizing the heavy metal content to a solid precipitate. After being collected in the solid-liquid separation,
A method for recycling heavy metal by detoxifying incineration ash or fly ash, which comprises a second step of recovering heavy metal content in solid matter; a second invention is incineration ash or fly ash containing heavy metal, The first step of heat-treating in the presence of at least 2 wt% or more, more preferably 3 wt% or more in terms of chlorine of chloride to volatilize heavy metals as chlorides and concentrate as fly ash, the fly ash as it is or in the ore A second step in which a heavy metal other than lead is eluted by being added to an aqueous solution together with an acid and dissolved at a pH of 3 or less, and a lead-containing residue is separated by sedimentation or filtered, or a supernatant produced in the second step or After the filtrate is neutralized to form a hydroxide of a heavy metal mainly containing zinc, the hydroxide is used as a seed crystal and circulated in the neutralization tank for a certain period of time to be circulated for a certain period of time so that a hydroxide having a large particle size can be obtained. 3rd work to be a thing Then, after adding a small amount of a sulfiding agent to the liquid in the third step, the heavy metal on the surface of the hydroxide and a trace amount of heavy metal ions in the liquid are converted into sulfides, and then the solid-liquid separation is performed to recover the heavy metal from the solid precipitate. A fourth step is a method for recycling heavy metals by detoxifying incineration ash or fly ash, which is characterized by comprising the fourth step; and a third invention is at least incineration ash or fly ash containing heavy metals in terms of chlorine. The first step of heat-treating in the presence of 2 wt% or more of chloride, preferably 3 wt% or more, to volatilize heavy metals as chlorides and concentrate as fly ash, the fly ash was dissolved in water containing or not containing mineral acid After that, a neutralizing agent is added to the solution and neutralized to pH 6 or more to generate a hydroxide of a heavy metal mainly containing lead and zinc, and the hydroxide is used as a seed crystal and is kept constant in the neutralization tank. Hydroxylation with large particle diameter by circulating for a long time The second step, and the second step is to add a small amount of a sulfiding agent to the liquid to make a trace amount of heavy metal ions on the surface of the hydroxide and the liquid into sulfide, and then perform solid-liquid separation to obtain a solid substance containing heavy metal. The present invention relates to a method for recycling heavy metals by detoxifying incineration ash or fly ash, which comprises a third step of recovering heavy metals from The chloride used in the first step in the method of the present invention means a compound that can serve as a chlorine source for volatilizing heavy metals as chlorides, and specifically includes NaCl, CaCl ₂ , KCl, MgCl _{2 and the} like.

[0010]

The method of the present invention will be specifically described with an example of a method for treating fly ash generated during melting treatment of incinerated ash in an urban refuse incineration plant.

In the examples of the specification, as the incineration ash, the one produced at the municipal refuse incineration plant was used. However, other substances from the sewage treatment plant and the industrial waste treatment plant, which contain heavy metals, are All can be the target materials of the method of the present invention.

When these incinerated ash or fly ash is used as a processing raw material, electric furnace, arc furnace, burner furnace, plasma furnace, low-frequency furnace or high-frequency furnace is used as means for volatilizing heavy metal components to concentrate as fly ash. The heavy metal in the raw material is volatilized at a temperature of 900 ° C. or higher using a known melting furnace, and the generated fly ash is collected using a collecting device such as an EP, a bag filter or a venturi scrubber.

When collecting the fly ash, it is necessary that at least 2 wt%, preferably 3 wt% or more, of chloride is present in the raw material in terms of chlorine. The reason for this is generally 1200-1400 when melting chloride-free feedstocks.
Although the heavy metal content melts at a temperature of about ℃, it is confirmed by the inventors' tests that the heavy metal content in the raw material volatilizes more at a temperature of about 900 ° C. when chloride is present in an amount of 2 wt% or more. Was completed (first step).

In this case, some starting materials do not have chlorides, but at this time, NaCl or CaCl _{2 is used.}
An appropriate amount of chloride such as the above may be added, or a heavy metal such as fly ash and a raw material containing a large amount of chloride may be melted together.

Next, the fly ash thus obtained is dissolved in a liquid to be neutralized, and then the heavy metal content is collected in a solid substance and solid-liquid separated to collect the heavy metal in the solid substance as a valuable resource. By doing so, the valuable metal is recycled (second step).

As a means for recovering the heavy metal content, first,
Fly ash is dissolved in water or an aqueous liquid to form a slurry, and a mineral acid (inorganic acid) such as hydrochloric acid or sulfuric acid is added to the slurry while stirring to adjust the pH to 3 or less. Since the pH of fly ash varies depending on its composition, the amount of mineral acid added needs to be adjusted according to the pH of fly ash. That is, the lower the pH of the slurry, the higher the lead quality of the lead residue obtained later tends to be, so the optimum pH is set according to the grade of fly ash, etc., and the amount of mineral acid added is adjusted to obtain that pH. All you have to do is do it. Also, if the pH of the slurry is already at the optimum pH, it is not necessary to add mineral acid. Further, the stirring time while maintaining the above pH is at least 10
The temperature at that time may be room temperature.

Next, the slurry is separated by sedimentation or filtered to separate into a residue containing lead and an aqueous solution containing heavy metals other than lead. In addition, in order to remove the leachate adhering to the residue in the above-mentioned filtration, it is necessary to sufficiently wash with water, and this work is particularly important when the obtained residue is utilized as a resource.

The filtrate obtained as described above generally contains cadmium, copper, iron, mercury and the like in addition to zinc. However, when the fly ash contains a large amount of iron, the subsequent step Since the grade of zinc in the heavy metal precipitate mainly containing zinc obtained in (3) is low, it is necessary to selectively separate iron.

In this case, an oxidizing agent (at least one selected from the group consisting of hydrogen peroxide solution, sodium hypochlorite, chlorine gas, etc.) is added to the filtrate and dissolved in the liquid. By oxidizing iron ions to ferric ions and then adding a neutralizing agent such as caustic soda to neutralize them, the ferric ions are precipitated as hydroxides, and the precipitates are filtered to remove iron. Selectively separated.

Next, zinc is mainly contained by adding a neutralizing agent such as sodium hydroxide, sodium carbonate or calcium hydroxide to the filtrate from which lead and iron have been removed to adjust the pH to 6 or more. Produces a heavy metal hydroxide.

In this case, since the particles of the hydroxide compound formed are small, the consumption of the sulfiding agent added in the subsequent step is large. Therefore, in one embodiment of the method of the present invention, the water formed in the neutralization tank is used. The oxidized precipitate was retained and circulated in the tank for a certain period of time as a seed crystal so that a hydroxide compound having large crystal particles was obtained.

Next, the overflow liquid from the neutralization tank, that is, the second step liquid is introduced into the sulfidation reaction tank and a small amount of a sulfidizing agent such as sodium sulfide, sodium hydrosulfide or hydrogen sulfide is added to the surface of the hydroxide precipitate. In addition to sulphidizing only the heavy metal component, a trace amount of heavy metal ions in the liquid are precipitated as sulphide, and this solution is filtered to obtain a zinc precipitate and a neutralized filtrate.

In the conventional sulfide method, very fine crystals are formed and thus the settling rate is slow and the dehydration is poor, and if the sulfiding agent is insufficient, the heavy metal ions in the liquid are not sufficiently low, On the contrary, if the amount was excessive, the heavy metal became polysulfide ion and was dissolved again in the liquid, and the level of heavy metal ion in the waste water did not become low.

On the other hand, the method of the present invention is a method in which only the surface of hydroxide precipitate particles is sulfided. First, large hydroxide precipitate particles are made to form crystals and then sulfided. It is possible to obtain a substance having a high sedimentation rate and a very good dehydration property.

Further, since the sulfurizing agent may be added in an amount sufficient to sufficiently sulfurize only the surfaces of the hydroxide particles, the sulfurizing agent may be about 1/5 to 1/6 of the conventional method or less, Efficiently low wastewater of heavy metal ions can be stably obtained in the liquid without producing polysulfide as in the conventional method, and particularly in heavy metal ions, there is a remarkable effect in reducing the concentration of mercury and cadmium. I understood it.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

[0027]

Example 1 A Incinerator ash from an municipal waste incineration plant was adjusted to a chlorine content of about 12 wt% as a starting material, placed in an electric furnace, and melted for 3 hours at a constant temperature of 1300 ° C. What was volatilized as chloride and concentrated as fly ash was collected by a bag filter (first step).

Then, the obtained fly ash was put into a dissolution tank (not shown) provided in the previous step 6 shown in FIG. 1, and the ratio of the solid precipitate in the sulfuric acid acidic leachate was 50 g / l. It was adjusted so as to form a slurry. The overflow liquid from the dissolution tank is introduced into the neutralization tanks 1 and 2 and NaOH is added as a neutralizing agent.
Neutralized to H6.0. The apparatus used in this example is shown in FIG.
The dimensions of the cylindrical shape as shown in 150mmφ × 210mmH
The two neutralization reaction tanks 1 and 2 and the sulfurization reaction tank 3 that require an overflow port at the upper side. The movement of the liquid between these tanks was carried out using an electromagnetic metering pump. In this case, the flow rate of the leachate was set to 52 to 3.5 ml / min and the addition of the neutralizing agent was set by the electromagnetic metering pump. 22.6 ~
The flow rate was 0.36 ml / min.

The fly ash slurry liquid obtained in the dissolution tank had a liquid temperature of 20 ° C. and a pH of 1.0. This slurry was filtered to obtain a lead-based residue.

Next, the filtrate obtained by the above-mentioned filtration is sent to the neutralization reaction tanks 1 and 2, and a sodium hydroxide aqueous solution whose concentration is adjusted to 200 g / l is added to neutralize it to pH 6 or above to neutralize the hydroxide. The product was produced and the reaction time was adjusted so that the total residence time in the neutralization reaction tanks 1 and 2 was 2 hours, and the liquid was circulated to increase the particle size of the hydroxide precipitate.

Then, the above-mentioned hydroxide-containing solution is introduced into the sulfurization reaction tank 3 and an aqueous solution of sodium hydrosulfide adjusted to a concentration of 10 g / l is added at an oxidation-reduction potential to -100 mV, and water of a heavy metal mainly containing zinc is added. Produced sulfides of oxides and other heavy metals. In this case, the amount of sodium hydrosulfide added was 0.7 g / l in terms of the liquid concentration in the sulfurization reaction tank, and the aggregated particles of the hydroxide hydroxide were sulfides only on the surface of the aggregated particles. It could be confirmed.

Next, the solution in which the above precipitate was formed was filtered and separated into a zinc precipitate and a neutralized filtrate. Cu, Pb, Zn, Fe, Cd, As, Na, K in the residue, precipitate (zinc precipitate), neutralized filtrate and fly ash thus obtained
The contents of Ca, Mg, SiO ₂ , Al ₂ O ₃ , Cl, S, Hg, etc. were examined, and the results are shown in Tables 1 and 2.

[0033]

[Table 1] Raw materials and chemical composition of each product (Unit:% solids, wastewater and Hg is ppm)

[0034]

[Table 2] Raw materials and chemical composition of each product

(Unit:% solids, wastewater and Hg are ppm
) About 10% of the ash treated at this time was recovered as molten fly ash.

As can be seen from Table 1 and Table 2, the heavy metals such as lead and zinc contained in the fly ash were separated almost completely in a stable form. The lead quality in the residue is 35.60.
%, The zinc grade in the precipitate was 38.35%, and these were grades which could be treated as resources in a non-ferrous smelter. Furthermore, the neutralized wastewater was below the discharge standard and could be discharged directly into rivers and the sea.

[0037]

Example 2 The fly ash obtained in the first step of Example 1 was leached in a dissolution tank provided in the previous step 6 of the neutralization reaction tank 1 shown in FIG. 1 to obtain a slurry. After sending to the neutralization reaction tanks 1 and 2, a sodium hydroxide aqueous solution whose concentration is adjusted to 200 g / l is added as a neutralizing agent to neutralize the solution to a pH of 6 or more to form a hydroxide hydroxide, which is then neutralized. The reaction time was adjusted so that the total residence time in the reaction tanks 1 and 2 was 2 hours, and a part of the overflow liquid of the neutralization tank reaction 2 was returned to the neutralization reaction tank 1 to circulate the solution. , The particle size of hydroxide was increased.

Then, the hydroxide-containing solution is introduced into the sulfurization reaction tank 3 and an aqueous solution of sodium hydrosulfide whose concentration is adjusted to 10 g / l is added up to -100 mV at the redox potential, and mainly lead and zinc are added. Heavy metal hydroxides and other heavy metal sulfides were formed. In this case, the amount of sodium hydrosulfide added was 0.8 g / l in the liquid concentration in the sulfurization reaction tank, and it was confirmed that only the surface of the aggregated particles of the hydroxide hydroxide was sulfide. did it.

Next, the solution in which the above precipitate was formed was filtered and separated into a zinc precipitate and a neutralized filtrate. The chemical compositions of the thus obtained precipitate (lead / zinc precipitate), the neutralized filtrate and the fly ash were investigated, and the results are shown in Tables 3 and 4.

[0040]

[Table 3] Raw material and chemical composition of each product (Unit:% solids, wastewater and Hg is ppm)

[0041]

[Table 4] Raw materials and chemical composition of each product

(Unit:% solids, waste water and Hg are ppm
As can be seen from Tables 3 and 4, heavy metals such as lead and zinc contained in the fly ash were separated almost completely in a stable form. At this time, the precipitate contained 12.89% of lead and 24.14% of zinc, which was of a grade that could be processed in a non-ferrous smelter using this precipitate as a resource. Further, the neutralization drainage was below the drainage standard as in Example 1, and could be directly discharged into a river or the sea.

[0043]

Comparative Example 1 Incinerator ash having a chloride content of only 1.3 wt% as a starting material was melted at 1250 ° C. in the electric furnace shown in Example 1 and collected as fly ash with a bag filter. Gathered.

Then, the obtained fly ash was leached in a neutralization reaction tank to form a slurry, and solid-liquid separation was performed to obtain a residue mainly containing lead.

Next, an aqueous solution of sodium hydroxide adjusted to a concentration of 200 g / l was added to the filtrate to neutralize it to a pH of 8 or more to produce a hydroxide hydroxide, and the solution was not circulated to the sulfidation reaction tank of the next step. The sodium hydroxide aqueous solution adjusted to 10 g / l was added up to -100 mV at the redox potential,
Sulfides of zinc and other heavy metals were formed.

Next, the solution in which the above precipitate was formed was filtered and separated into a zinc precipitate and a neutralized filtrate. The chemical compositions of the thus obtained residue, precipitate (zinc precipitate), neutralized filtrate and fly ash were investigated, and the results are shown in Tables 5 and 6.

[0047]

[Table 5] Raw materials and chemical composition of each product (Unit:% solids, wastewater and Hg is ppm)

[0048]

[Table 6] Raw materials and chemical composition of each product

(Unit:% solids, wastewater and Hg are ppm
) At this time, about 3% of the treated ash was recovered as molten fly ash.

As can be seen from Tables 5 and 6, the recovery rate of heavy metals is considerably worse than that of the method of the present invention, and in addition, since the hydroxide precipitate particles produced during the neutralization reaction are small, a large amount of sulfurizing agent is used. Must be added to the
It took twice as much. Furthermore, the dehydration property of the zinc compound was poor, and the water content was 83%. This indicates that the water content of the method of the present invention was 64%, which was extremely inferior to the dehydration property. Further, the heavy metal ion concentrations of zinc, cadmium and mercury in the wastewater were higher than those in the case of the present invention, and the wastewater standards could not be satisfied.

[0051]

As described above, according to the method of the present invention, the heavy metals can be efficiently recovered from the incineration ash as a starting material, and the amount of the neutralizing agent and the sulfurizing agent added in the separation and recovery step can be increased by the conventional method. As compared with the above, since the amount can be reduced considerably, the processing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a processing apparatus used in the method of the present invention.

[Explanation of symbols] 1, 2 Neutralization reaction tank 3 Sulfidation reaction tank 4 Stirring rod 5 Circulating liquid containing seed crystals 6 Previous step 7 Next step

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenta Tabuchi 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (3)

[Claims] 1. An incineration ash or fly ash containing a heavy metal,
The first step of concentrating the heavy metal in fly ash by heat-treating it in the presence of at least 2 wt% chloride in terms of chlorine to evaporate the heavy metal component as chloride, and the obtained fly ash in an aqueous liquid. The second step is to collect the heavy metal content in the solid substance by solidifying the heavy metal content in the solid substance by performing a second step of: A method for recycling heavy metals by detoxifying ash or fly ash. 2. An incineration ash or fly ash containing a heavy metal,
The first step of concentrating heavy metal in fly ash by heat-treating it in the presence of at least 2 wt% chloride in terms of chlorine to volatilize heavy metal components as chloride; A second step in which a heavy metal other than lead is dissolved in the solution by adding it together with an aqueous solution at a pH of 3 or less, and a lead-containing residue is separated from the solution by sedimentation separation or filtration. The obtained supernatant or filtrate is neutralized in a neutralization tank to form a hydroxide of a heavy metal mainly containing zinc, and the hydroxide is used as a seed crystal in the neutralization tank for a certain period of time. Heavy metal on the surface of the hydroxide contained in the liquid and a trace amount in the liquid by adding a small amount of sulfidizing agent to the third step in which the hydroxide is retained and circulated to form a hydroxide having a large particle size, and the third step After converting heavy metal ions to sulfides Fourth step, the method of recycling the heavy metal by detoxification of incineration ash or fly ash, characterized in that it consists in liquid separation to recover heavy metals from the solid builders containing heavy metals. 3. An incineration ash or fly ash containing heavy metals,
The first step of concentrating the heavy metal as fly ash by heat-treating it in the presence of at least 2 wt% of chloride in terms of chlorine to volatilize the heavy metal content in chloride, and the fly ash obtained contains mineral acid. Alternatively, a neutralizing agent is added to a solution dissolved in an aqueous solution not containing it, and neutralized to pH 6 or more to produce a hydroxide of a heavy metal mainly containing lead and zinc. Is used as a seed crystal in the neutralization tank for residence and circulation to form a hydroxide hydroxide having a large particle size, and by adding a sulfidizing agent to the liquid in the second step Recycling heavy metals by detoxifying incineration ash or fly ash, which comprises a third step of recovering heavy metals from solid precipitates containing heavy metals by solid-liquid separation after making trace amounts of heavy metal ions into sulfides. Method.