JPH08323321A - Treatment of fly ash - Google Patents

Abstract

PURPOSE: To provide a method for efficiently and easily separating and recovering various heavy metals from a fly ash generated when a waste such as shredder dust is incinerated. CONSTITUTION: A fly ash is cleaned with water while blowing carbon dioxide. The solid residue in the cleaning stage is subjected to flotation using a calcium carbonate reagent to recover calcium carbonate as a floss in the first flotation stage. Sulfuric acid is added to a settled residue in the first flotation stage to convert the heavy metals in the residue to metallic salts. Water is added to a mixture consisting of the metallic salts to dissolve the salts, and the dissolved copper ion is precipitated as metallic copper by metallic Al present in the settled residue. The metallic copper is separated and removed as the cake along with the insolubles in the leaching stage. The cake contg. the insolubles is subjected to flotation using a metal flotation reagent to recover at least copper in the second flotation stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fly ash treatment method capable of recovering heavy metals from incinerated fly ash as a waste resource recycling technique. To be more specific, shredder dust after crushing scrapped automobiles and waste home appliances with a shredder to recover metal is used to recover heavy metals from fly ash generated when incinerated and reduced in volume, or how to effectively use fly ash. It is about.

[0002]

2. Description of the Related Art Increasing amounts of various kinds of waste and this disposal method have become a social problem as an adverse effect on the development of the consumption economy in recent years. At present, large shells such as body shells, electric washing machines, electric refrigerators, etc. after scrapping and collecting valuable parts from scrapped automobiles are crushed by shredders, and iron and non-ferrous metals are collected, but these are collected. The shredder dust, which is mainly made of plastics, is disposed of by landfill.

However, the amount of industrial waste and household waste is increasing, and it is becoming more and more difficult to secure the landfill site due to the problems of saturation of existing landfill sites and environmental pollution. Therefore, recycling of waste and reduction of volume are required. Incineration power generation is being studied as a method for recycling and reducing the volume of the shredder dust. That is, it aims to recover and utilize the thermal energy generated by the combustion of plastics, which occupy the main part of shredder dust, by heat exchange in a power generation boiler or the like, and also to reduce the volume as incinerated ash.
The incineration ash generated when this shredder dust is incinerated includes bottom ash (bottom ash) and fly ash (fly ash) that is contained in the combustion waste gas and is collected by a capturing means such as a filter. is there.

Common fly ash, such as coal ash, is reused and disposed of by aggregates, cement raw materials, landfill disposal, stabilization treatment (pelletization) and the like. Fly ash obtained by incinerating shredder dust, etc. contains many chlorine compounds and metals derived from plastic such as polyvinyl chloride. It cannot be used due to problems such as corrosion and environmental friendliness, and even if it is landfilled, there is a risk of salt damage due to elution of chlorine from the landfill site due to acid rain, etc. There is Furthermore, from the viewpoint of resource reuse, it has been desired to recover metal components from fly ash.

In Japanese Patent Laid-Open No. 49-113703, while maintaining the diluted sulfuric acid eluate of incinerated ash at pH 2.0 to 3.0, sodium sulfide in an amount equal to or higher than the concentration of metal ions contained is added to make it other than iron. Metal is coagulated as sulfide, then polymer flocculant is added to form metal sulfide floc, and amine collector and polypropylene glycol ether foaming agent are added for air supply. It has been proposed that the metal sulfide flocs are levitated as scum and collected. However, the surface of the metal particles present in the incineration ash is oxidized, and since many chlorine compounds are present in the incineration ash, it is not possible to capture a sufficient amount of metal in the form of sulfide, and , It was difficult to collect sulfide efficiently by flotation.

[0006]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for efficiently and easily separating and recovering various heavy metals from fly ash generated when incinerating waste such as shredder dust. And

[0007]

In order to solve the above problems, a method for treating fly ash according to the present invention is a fly ash containing heavy metals and calcium-immobilized chlorine generated when waste is incinerated. A method of treating ash, comprising a cleaning step of cleaning fly ash with water while blowing carbon dioxide gas,
From the solid residue in the washing step, flotation is carried out using a flotation agent for calcium carbonate, a first flotation step of recovering calcium carbonate as floss, and an acid is added to the sedimentation residue of the first flotation step, The heavy metal existing in the precipitation residue is converted to a metal salt state, and water is added to the mixture containing the metal salt to dissolve the metal salt, and at the same time, the dissolved copper ion is added to the metal aluminum (previously present in the precipitation residue). The metal flotation agent was used from the leaching step of precipitating as metallic copper by Al) and separating and removing the metallic copper as a slag together with the insoluble matter, and the slag containing the insoluble matter separated in the leaching step. A second flotation step of recovering at least copper by flotation.

After the washing step, it is preferable to further include a chlorine removing step of concentrating and drying the washing liquid in the washing step to obtain calcium chloride as crystals. After the leaching step, the insoluble matter generated in the leaching step is repulped with water, an activator such as a sulfiding agent is added in a condition tank to activate the surface of the metallic copper, and then the second flotation step is performed. It is preferable to carry out.

[0009] Further, the float produced in the first flotation step or calcium carbonate is added to the filtrate produced in the leaching step to neutralize it to pH 5 to 6, and then air is blown while heating the produced slurry. , A first-stage treatment step of oxidizing Fe (II) into Fe (III) to form iron (III) hydroxide and precipitating with aluminum hydroxide, and adding slaked lime to the solution generated in the first-stage treatment. It is preferable that the pH is adjusted to 6 or higher to precipitate Zn as zinc hydroxide, which is filtered off, and the filtrate further has a second stage treatment step of using the raw fly ash as a cleaning liquid.

The flotation agent for calcium carbonate is not particularly limited, but for example, oleic acid, primary amine acetate, alkyl sulfate, alkyl or allyl phosphate, a collector such as tall oil, pine oil, Foaming agents such as methyl isobutyl carbinol (MIBC), cresylic acid and ethylene glycol are preferably used.

The acid used in the leaching step is hydrochloric acid,
Mineral acids such as sulfuric acid, nitric acid and aqua regia are preferable, and sulfuric acid is particularly preferable. The metal flotation agent is not particularly limited, but includes xanthate, alkyl or allyl diphosphate, dithiocarbanilide or dithiocarbamate, sodium sulfide, hydrogen sulfide, kerosene, alkyl sulfate ester,
Flotation agents such as alkyl or allyl phosphates, pine oil, ethylene glycol, MIBC (methyl isobutyl carbinol) are preferably used.

[0012]

As described above, the present invention is based on the new finding that Al is present as fine metal powder in part, although most of the metals present in fly ash are present as oxides and chlorides. By using this metal Al as a reducing agent, Cu is precipitated and precipitated in leaching with concentrated sulfuric acid or the like, and is separated from other heavy metals that dissolve, thereby efficiently using various chemicals. It collects heavy metals.

The present invention will be described in detail below by taking as an example a series of treatment processes for shredder dust from waste automobiles and waste home electric appliances, which adopts the method for treating incinerated fly ash according to the present invention. First, scrapped automobiles and discarded home appliances are reusable parts, and then shredded by a shredder according to the usual method to recover ferrous and non-ferrous metals.

The shredder dust, which is mainly made of plastic after the recovery, is burned to reduce the volume, but 1000 ° C. or lower, more preferably 800 ° C. to prevent the generation of harmful components such as dioxin due to the burning.
It is carried out using, for example, a fluidized roasting furnace, a grate furnace or the like so that it can be incinerated at a temperature of up to 900 ° C. The heat energy generated at this time is heat-exchanged and recovered in the power generation boiler. In addition, during this combustion, many chlorine compounds are generated due to plastics such as polyvinyl chloride,
At the time of incineration, about 20 to 30 parts by weight of slaked lime or limestone is added to 100 parts by weight of shredder dust to immobilize the chlorine compound as calcium chloride (CaCl ₂ ) to prevent the release of harmful chlorine compounds. Then, the bottom ash, which has been reduced in volume after incineration and remains in the furnace, is subjected to a recovery process of contained metal.

On the other hand, the fly ash contained in the combustion flue gas is captured and collected by a dust collector including a filter or the like provided in the middle of the flue. The fly ash has an average particle size of about 5 to 20 μm, and particles of 10 μm or less account for 60 to 70% of the whole. And in this fly ash, as described above, a large amount of Ca-immobilized chlorine component (CaC
1 ₂ ) and heavy metal components such as Fe, Cu, Zn, Al and Pb are present together with silicic acids. Most of these metals exist as oxides and chlorides, but Al partially exists as fine metal powder. Therefore, in the recovery of heavy metals, it is possible to perform a process of using this metal Al as a reducing agent, as shown below.

In the present invention, in order to remove chlorine components from the fly ash, the fly ash is washed with water as a washing step. Washing with water usually uses 1 to 4 times the volume of fly ash and 1
The leaching time is about 0 to 60 minutes and is performed. CaCl ₂ can be easily dissolved and removed by such a treatment, but in order to leave the metallic form of Al contained in the fly ash as a metal in the solid residue together with the other metals, carbon dioxide is added to this washing water. Add dissolved gas. For example, this treatment is carried out under the condition that the cleaning liquid is added so as to have a pH of 9 or less, preferably 6.5 to 7.0. That is, under high alkaline conditions, aluminum dissolves and aluminum hydroxide precipitates.

Then, for example, after a predetermined leaching time in a sedimentation tank or the like, the overflow fraction of the fly ash slurry and the sedimentation fraction are separated. The sedimentation fraction is obtained as dechlorinated fly ash slime having a water content of about 25 to 40% by weight. The overflow fraction containing a large amount of dissolved calcium chloride obtained in the above washing step is then subjected to a concentration treatment in the chlorine removal step, for example, electrodialysis, and concentration treatment such as evaporative concentration using an evaporator. Finally, it is recovered by spray drying as calcium chloride crystals. For electrodialysis, it is sufficient to use an apparatus having a usual dialysis tank for concentration, which is a combination of a generally known anion exchange membrane and a cation exchange membrane, but an exchange membrane having a higher ion selectivity. It is possible to use For example, calcium chloride having a concentration of about several thousand ppm in the overflow fraction can be concentrated to a concentration of about tens of thousands ppm by electrodialysis, and then can be further concentrated to about 40 to 50% in an evaporator.

The calcium chloride thus recovered typically has a purity of about 60 to 70% and can be used, for example, as a snow melting agent for roads. On the other hand, the dechlorinated fly ash slime in the sludge state is subjected to flotation in the first flotation step and calcium carbonate is recovered as floss. That is, dechlorinated fly ash slime is suspended in 4 to 10 times its volume of water,
Add oleic acid, primary amine acetate, alkyl sulfate, alkyl or allyl phosphate, tall oil as a scavenger, and pine oil, MIBC, cresylic acid, ethylene glycol as a foaming agent, and insufflate. Lather it and make calcium carbonate float up as floss. The amount of the scavenger and the foaming agent used is about 100 to 1,000 mg and 5 to 5 kg of dry weight of dechlorinated fly ash slime, respectively.
It is about 200 mg.

Next, in the leaching step, the sedimentation residue after the first flotation contains an acid, preferably sulfuric acid, and more preferably 90% or more concentrated sulfuric acid in an amount of 1 to 2 kg per 1 kg (dry weight conversion) of the sedimentation residue. Add to the extent and mix well. By this operation, Fe, Cu contained in the sedimentation residue,
Heavy metals such as Zn and Al become sulfates. Here, water is further added to this mixture at a rate of, for example, about 1 to 5. When water is added, sulfates such as Cu, Zn, and Fe are dissolved. At this time, Cu ions are reduced to metallic copper by substituting the metallic aluminum present in the precipitation residue. Then, when this mixture is subjected to filtration or centrifugal separation, the metallic copper becomes PbSO ₄ , SiO ₂ , CaS.
It can be separated and removed as a slag together with the insoluble matter such as O ₄ .2H ₂ O.

Further, in the second flotation step, after resuspending the slag in water, an activator is added to activate the lead sulfate in the slag, and the lead sulfate and the metal are subjected to the flotation. Collect copper. As the activator, hydrogen sulfide water, a sulfidizing agent such as sodium sulfide is used, and as a scavenger, xanthate, alkyl or allyl diphosphate, dithiocarbanilide, dithiocarbamate, alkyl sulfate, Known ones such as alkyl or allyl phosphates and pine oil, ethylene glycol, MIBC and kerosene are also used as a foaming agent.
Of course, it is not limited to these. The amount of the scavenger and the foaming agent used depends on the type thereof, but for example, per 1 kg of the dry weight of the slag,
It is about 50 to 1,000 mg and about 5 to 200 mg. The purity of the metallic copper thus recovered is 20 to
It is about 50%, and can be used as a copper smelting raw material, for example.

In the leaching step, the filtrate separated from the slag contains dissolved sulfates of heavy metals such as Fe, Zn, and Al, and is suspended in the second flotation step. The sedimentation residue after beneficiating contains a sulfate such as Ca as an insoluble matter. Therefore, if necessary, a technique such as a known precipitation separation method or a flotation method may be applied to separate and recover these metals.

The method of the present invention has been described above by taking the case of fly ash generated by incineration of shredder dust from waste automobiles and waste home electric appliances as an example, but it is used in the fly ash treatment method according to the present invention. Fly ash is not limited to fly ash generated by incineration of shredder dust, and is similarly applicable to the treatment of fly ash generated when incinerating other wastes.

[0023]

EXAMPLES The present invention will be specifically described below with reference to examples. The fly ash treatment method will be described step by step according to the order of division. (The process is shown in FIG. 1) The following table 1 shows the main metal component recovery results by process according to this example.

[0024]

[Table 1]

Table 2 below shows the grade of fly ash component analysis in this example.

[0026]

[Table 2]

The first step is a dechlorination step. Fly ash contains water-soluble calcium chloride, and this calcium chloride is removed. Calcium chloride (concentration 2,000 to 5,000 ppm) that has been eluted to become an aqueous solution is concentrated by electrodialysis in the second step. The precipitate from which calcium chloride has been removed is subjected to flotation of calcium carbonate in the third step. 1.5 l of water was added to 100 g of fly ash, and the mixture was impeller-stirred in a 2 l beaker, washed with 1 Hr of water, filtered and dehydrated, and separated into a washing liquid and a residue. 99.4% of Cl component
Was recovered in the wash solution. In addition, when washing with water, in order to prevent aluminization of aluminum, carbon dioxide is injected to adjust the pH.
The pH is adjusted to 6.5 to 7.0 to prevent the dissolution of aluminum and suppress the generation of hydrogen.

In the second step, electrodialysis is carried out for purification and concentration of calcium chloride. The concentration of calcium chloride is increased to 50,000 to 70,000 ppm, and the concentration in the evaporator is reduced to 40 to 50%. It was spray-dried and dihydrate / calcium chloride was recovered as powder or solidified (CaCl ₂ grade 60
(70%) (The electrodialyzer is TS-100-410 type and the dialysis tank is a two-stage system).

In the third step, since calcium carbonate exists in the fly ash from which calcium chloride has been removed, in order to separate it, calcium carbonate was floated by the flotation method and recovered. As the flotation agent, 300 g / t of oleic acid, 50 g / t of tall oil, and 10 g / t of cresylic acid were used. 300 ml of water was added to the water washing residue (water content: 35%, solid dry weight: 99 g), the concentration was adjusted, and the mixture was fed to a Denver Sub A type 300 g floater and adjusted to pH 8.5-9.0 with sodium carbonate. Then, after adding the floating agent, the condition was applied for 10 minutes, the flotation was performed for 15 minutes, and the calcium carbonate concentrate was collected as floss.

In order to suppress SiO _{2 and the} like, by using sodium silicate, tannin, and starch in combination as a flotation auxiliary agent, the concentrate quality can be increased. In this flotation concentrate, in addition to calcium carbonate, gypsum floats. The fourth step is a step of sulfating. When concentrated sulfuric acid is added to the dehydrated cake of the flotation slag that has been treated in the third step, the sulfuric acid heats up violently. It is a method of utilizing this heat to obtain preferable treatment conditions of high temperature and high acid and to perform sulfation in a short time. (In this example, a high temperature condition of 80 ° C. or higher was obtained, and concentrated sulfuric acid was added to the sample for a treatment time of 2 hours.) Sulfation is divided into a solution and an insoluble matter. Sulfated to a solution is the fifth
In the process, the insoluble matter is treated in the sixth process.

In the fifth step, iron and aluminum eluted by sulfation are separated from zinc, so that they are neutralized with calcium carbonate (the calcium carbonate flotation concentrate obtained in the third step can also be used. ). The pH of the solution was adjusted to 6 and air oxidation was performed while heating to separate iron and aluminum as neutralized precipitates.

The pH of the filtrate obtained by filtering the produced neutralized precipitate was further adjusted to 8.5, and zinc was recovered by a conventional technique in which zinc in the solution was precipitated as hydroxide. Use 750 cc of filtrate leached with sulfuric acid and
After the eAl was separated, the filtrate was used to recover Zn by slaked lime.

In this process, the pH was adjusted in two steps to separate the mixed precipitate of iron and aluminum and the precipitate of zinc for recycling. In the sixth step, copper particles reduced by aluminum and lead sulfate formed by sulfation are present in the insoluble matter due to sulfation, and the surface of the particles is sulfided with a sulfidizing agent to obtain a mixture of copper and lead. Since it was revealed that it was possible to recover by a floating concentrate, a mixed concentrate of copper and lead sulfate was recovered as a floating concentrate in the floating concentrate.

A sulphating agent is required for the flotation of metallic copper particles, and hydrogen sulphide, sodium sulphide, sodium hydrosulphide, ammonium sulphide and the like can be used as the sulphating agent. In this embodiment, sodium sulfide 3
00 g / t was added. As the flotation reagent, xanthates, alkyl or allyl diphosphate, dithiocarbanilide or dithiocarbamate, and alkyl sulfate ester are effective. In this example 100 g of ethyl xanthate
/ T, 300 g / t of alkyl sulfate ester were used.

As the foaming agent, those normally used for flotation such as pine oil, MIBC and kerosene can be applied.
Here, 50 g / t of pine oil was used. If sodium silicate is used to control gangue, the quality of the concentrate (floss) can be improved. The flotation recovered by flotation is applied as a raw material for copper smelting or lead smelting by applying a conventional treatment method.

Flotation tailings can be used as part of a cement raw material. Alternatively, landfill disposal is possible. Water for filtration and dehydration residue (water content 35%, solid dry weight 35 g) in the sulfuric acid leaching step 8
Add 5 ml, feed to a Denver Sub A type 100 g flotation machine, adjust the pH to 6.5 with caustic soda (slaked lime is also possible), add 300 g / of sodium sulfide and apply conditions for 5 minutes,
Further, 100 g / t of ethyl xanthate, 300 g / t of alkyl sulfate ester, and 50 g / t of pine oil were added and the conditions were applied for 10 minutes, followed by flotation for 15 minutes, and a copper / lead mixed concentrate was recovered as floss.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope of the present invention.
For example, in the above embodiment, all of the first step to the sixth step shown in FIG. 1 were carried out, but in the present invention, it is not always necessary to carry out all the steps shown in FIG. 1, and at least carbon dioxide gas is blown. While performing a washing step of washing the fly ash with water (corresponding to the first step of FIG. 1) and a flotation using a flotation agent for calcium carbonate from the solid residue in the washing step, calcium carbonate as floss In the first flotation step (corresponding to the third step in FIG. 1) for recovering the water, and an acid is added to the sedimentation residue of the first flotation step to make heavy metals present in the precipitation residue into a metal salt state. Water is added to the mixture containing the metal salt to dissolve the metal salt, and at the same time, the dissolved copper ions are precipitated as metal copper by the metal Al existing in the precipitation residue, and the metal copper is filtered together with the insoluble matter. Separated as The second flotation in which at least copper is recovered from the leaching step (corresponding to the fourth step in FIG. 1) and the filter cake containing the insoluble matter separated in the leaching step by flotation using a metal flotation agent. With a method having a beneficiation step (corresponding to the sixth step in FIG. 1), it becomes possible to recover copper from fly ash, and the initial object of the present invention is achieved.

[0038]

As described above, according to the present invention, heavy metals such as copper can be efficiently converted into a metal form from fly ash by a relatively simple method without using various chemicals.
In addition, it can be separated and recovered as stable salts such as calcium chloride with a relatively high degree of purity, which makes it possible to reuse resources in a high degree of waste and to detoxify fly ash by dechlorination and demetalization. As a result, significant progress is expected in the issue of environmental protection related to disposal. Further, by using only a mineral acid such as sulfuric acid as a main chemical in this way, it is possible to achieve a closed circuit process.

[Brief description of drawings]

FIG. 1 is a diagram showing each step in a fly ash processing method according to an embodiment of the present invention.

Claims (2)

[Claims] 1. A method for treating fly ash containing heavy metals and calcium-immobilized chlorine generated when waste is incinerated, the washing comprising washing the fly ash with water while blowing carbon dioxide gas. A step, a first flotation step of performing flotation from the solid residue in the washing step using a flotation agent for calcium carbonate, and recovering calcium carbonate as floss; and an acid in the sedimentation residue of the first flotation step. Was added to make the heavy metal existing in the precipitation residue into a metal salt state, and water was added to the mixture containing the metal salt to dissolve the metal salt, and at the same time, the dissolved copper ion was present in the precipitation residue. Precipitation as metallic copper with metallic aluminum, a leaching step of separating and removing this metallic copper as a slag together with the insoluble matter, and a slag containing the insoluble matter separated in the leaching step, for metal By flotation using selection agents, processing method of fly ash and having a second flotation step of recovering at least copper. 2. The method for treating fly ash according to claim 1, further comprising a chlorine removal step of concentrating and drying the cleaning liquid in the cleaning step to obtain calcium chloride as crystals after the cleaning step.