JPH083655A - Method for recovering heavy metals from flying ash - Google Patents

Abstract

PURPOSE:To separate and recover metals included in flying ashes generated at the time of incineration and volume reduction of shredder dust from waste automobiles, waste household appliances, etc. CONSTITUTION:The flying ashes contg. the heavy metals and Ca imobilized chlorine generated at the time of incineration of wastes are washed with water while carbon dioxide is blown thereto. The washing liquid thereof concentrated and dried to obtain calcium chloride as a crystal. The solid residues in the washing stage are subjected to flotation using an oleic acid, etc., as a capturing agent and pine oil, etc., as a foaming agent. Calcium carbonate is recovered as froth. A sulfuric acid is sufficiently mixed into the residues of settling of the flotation state to convert the heavy metals to sulfate. Water is added to such mixture to dissolve the sulfate of the metals exclusive of Al and the dissolved Cu ions are precipitated as metal Cu by the metal Al existing thus far in the residues of settling. The metal Cu is separated away as filter cake together with the non-dissolved matter. The filter cake is resuspended in water and an activator is added thereto to execute the activation treatment of the metal copper and lead sulfate in the filter slag. The metal copper and the lead sulfate are recovered by flotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering heavy metals from incinerated fly ash as a technique for recycling waste.
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]

The present invention for solving the above problems is a method for recovering heavy metals from fly ash containing heavy metals and Ca-immobilized chlorine generated when waste is incinerated. A) a step of washing fly ash with water while blowing carbon dioxide gas, b) a step of concentrating and drying the washing liquid in the above a) washing step to obtain calcium chloride as crystals, and c) the a. ) Oleic acid is added to the solid residue in the washing step,
Using primary amine acetate, alkyl sulfate, alkyl or allyl phosphate, tall oil, cresylic acid as a scavenger, and pine oil, MIBC, ethylene glycol as a foaming agent to perform flotation. A step of recovering calcium carbonate as floss; and d) sulfuric acid is sufficiently mixed with the sedimentation residue of the above-mentioned c) flotation step to make the heavy metal remaining in the sedimentation residue a sulfate, and water is added to this mixture to remove the metal At the same time as dissolving the sulfate
Dissolved copper ions were present in the precipitation residue as metal Al
The step of precipitating as metallic copper by means of the above, and separating and removing it as a slag together with the insoluble matter; And the flotation agent is xanthate, alkyl or allyl diphosphate, dithiocarbanilide or dithiocarbamate,
Sodium sulfide, hydrogen sulfide, kerosene, alkyl sulfates, alkyl or allyl phosphates, pine oil, ethylene
The present invention is characterized by having a step of performing flotation using a flotation agent such as glycol, methyl isobutyl carbinol, etc., and recovering copper and lead sulfate as a mixed concentrate of flotation.

The above-mentioned e) of the present invention is preferably
After adding the flotation or calcium carbonate of the above c) to the filtrate of the above d) and neutralizing it to pH 5-6, air is blown in while heating the resulting slurry to oxidize Fe (II) to Fe (III). To elute iron (III) hydroxide with aluminum hydroxide and separate by filtration. E) Slaked lime is added to the solution generated in the first treatment and the first treatment to adjust the pH to 6 or more to precipitate Zn as zinc hydroxide. It is characterized in that it is filtered and the filtrate has the above-mentioned e) second stage treatment which is used as a cleaning liquid for the raw material fly ash.

[0009]

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 utilizing this metallic Al as a reducing agent, Cu is precipitated and precipitated in concentrated sulfuric acid leaching and separated from other heavy metals which are dissolved, so that heavy metals can be efficiently recovered without using various chemicals. It is a thing.

The present invention will be described in detail below by taking as an example a series of treatment processes of shredder dust from waste automobiles and waste home electric appliances which incorporate the method for recovering metals from incinerated fly ash according to the present invention. First, for abandoned cars and home appliances,
After recovering reusable parts, they are crushed 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 in order to prevent the generation of harmful components such as dioxin due to the burning, the temperature is 1000 ° C. or less, more preferably 800.
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, which is provided in the middle of the flue and is composed of a filter or the like. 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, first, in order to remove chlorine components from the fly ash, the fly ash is washed with water in step a). 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. Although CaCl2 can be easily dissolved and removed by such a treatment, carbon dioxide gas is added to this washing water in order to leave the metallic form of Al contained in the fly ash as a metal in the solid residue together with other metals. Is dissolved and added, for example, under the condition that the cleaning liquid is added so that the pH is 9 or less, preferably 6.5 to 7.0. That is, under high alkaline conditions, aluminum dissolves and aluminum hydroxide precipitates.

The addition of this carbon dioxide gas also facilitates the leaching of calcium chloride, but it may be shortened by further stirring if necessary. Then, after elapse of a predetermined leaching time in, for example, a sedimentation tank, 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 step b), for example, electrodialysis, concentration such as evaporation concentration using an evaporator. After processing, it is finally spray-dried and recovered 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 that has been separated and sludge is then subjected to flotation in step c) to recover calcium carbonate as floss. That is, dechlorinated fly ash slime is suspended in 4 to 10 times its volume of water to collect oleic acid, primary amine acetate, alkyl sulfate, alkyl or allyl phosphate, tall oil, and cresylic acid. As a foaming agent, pine oil, MIBC, and ethylene glycol are added, and air is bubbled to make calcium carbonate float up as froth. The amount of scavenger and foaming agent used is 1 kg of dry weight of dechlorinated fly ash slime,
About 100 to 1,000 mg and 5 to 20 respectively
It is about 0 mg.

Next, in step d), sulfuric acid, preferably 90% or more concentrated sulfuric acid, is added to the sedimentation residue after flotation in an amount of about 1 to 2 kg per 1 kg of sedimentation residue (dry weight conversion). Mixed. By this operation, heavy metals such as Fe, Cu, Zn, and Al contained in the sedimentation residue become sulfates. Here, water is further added to this mixture at a rate of, for example, about 1 to 5. With the addition of water, C
Sulfates such as u, Zn, and Fe dissolve, but 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 centrifugation, the metallic copper can be separated and removed together with the insoluble matter such as PbSO4, SiO2 and CaSO4 together with the insoluble matter as a residue.

Further, in the step e), after resuspending the filtered slag in water, an activator is added to activate the metallic copper in the filtered slag, and metallic copper and lead sulfate are removed by flotation. to recover. As the activator, hydrogen sulfide water, sodium sulfide, etc. are used, and as the scavenger, xanthate, alkyl or allyl diphosphate, dithiocarbanilide, dithiocarbamate, alkyl sulfate ester, alkyl or allyl. Known compounds such as phosphates and pine oil, ethylene glycol, MIBC, kerosene, etc. are used as the foaming agent, but the foaming agent is not limited thereto. The amounts of the scavenger and the foaming agent used depend on the types thereof, but for example, 50 to 1,000 m per 1 kg of the dry weight of the slag, respectively.
It is about g and about 5 to 200 mg. The purity of the metallic copper thus recovered is about 20 to 50%,
For example, it can be used as a copper scouring raw material.

It should be noted that, in the filtrate separated from the residue in the step d), sulfates of heavy metals such as Fe, Zn and Al are dissolved and contained, and after the flotation in the step e). The sulfate residue such as Ca is contained as an insoluble substance in the sedimentation residue. 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 as an example the case of fly ash produced by the incineration of shredder dust from waste automobiles and waste home electric appliances. The method for recovering metal from fly ash of the present invention is as follows. The same applies to the treatment of fly ash generated when other wastes are incinerated.

[0021]

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.

[0022]

[Table 1]

Table 2 shows the fly ash component analysis grades in this example.

[0024]

[Table 2]

The first step is a dechlorination step. Fly ash contains water-soluble calcium chloride and removes this calcium chloride. 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 liters of water was added to 100 g of fly ash, and the mixture was impeller-stirred in a 2 liter beaker, washed with 1 Hr water, filtered and dehydrated, and separated into a washing liquid and a residue. 99.4% of Cl component
Was recovered in the wash solution. When washing with water, in order to prevent aluminization of aluminum, carbon dioxide gas is injected to
The pH is adjusted to 6.5 to 7.0 to prevent the dissolution of aluminum and suppress the generation of hydrogen.

The second step is electrodialysis for purification and concentration of calcium chloride.
The content was raised to 10,000 to 70,000 ppm, concentrated in an evaporator to a concentration of 40 to 50%, and then spray dried to powder or solidify the dihydrate / calcium chloride and collect it. (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, calcium carbonate is present in the fly ash excluding calcium chloride. The calcium carbonate was collected by flotation by the flotation method. The flotation agent is 300 g / t oleic acid, 50 g / t tall oil,
Cresic acid 10 g / t was used. Water washing residue (water content 3
300 ml of water was added to 5% solid dry weight (99 g), and after adjusting the concentration, it was fed to a Denver Sub A type 300 g floating machine, the pH was adjusted to 8.5-9.0 with sodium carbonate, and a floating agent was added. After that, conditions were applied for 10 minutes, and flotation was performed for 15 minutes to recover calcium carbonate concentrate as floss.

By using a combination of sodium silicate, tannin, and starch as a flotation auxiliary agent for suppressing SiO ₂ etc., 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. Third
When concentrated sulfuric acid is added to the dehydrated cake of the flotation slag that has been treated in the process, the sulfuric acid vigorously generates heat. 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. The solution that is sulphated into a solution is treated in the fifth step, and the insoluble matter is treated in the sixth step.

In the fifth step, neutralization is carried out with calcium carbonate in order to separate iron, aluminum and zinc eluted by sulfation (the calcium carbonate flotation concentrate obtained in the third step can also be used). The pH of the solution was adjusted to 6 and oxidation was performed with air while heating to separate iron and aluminum as neutralized precipitates. The resulting neutralized precipitate was filtered and the filtrate was
The H was adjusted to 8.5, and the zinc was recovered by a conventional technique in which the zinc in the solution was precipitated as a hydroxide.

After separating FeAl with calcium carbonate using a filtrate 750 cc of sulfuric acid leaching, the filtrate is Zu with slaked lime.
Was recovered. In this process, the pH was adjusted in two steps to separate the 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 were present in the insoluble matter by sulfation, and the surface of the particles was sulfurized with a sulfiding agent to mix copper and lead. Since it was revealed that it was possible to recover by a floating concentrate in the state, a mixed concentrate of copper and lead sulfate was recovered as a floating concentrate in the floating concentrate.

A sulphating agent is required for flotation of the 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. Floating ore collected 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.

Filtration and dehydration residue in the sulfuric acid leaching step (water content: 35
%, Solid dry weight (35 g) and water (85 ml) were added to a Denver Sub-A type 100 g flotation machine, and the pH was adjusted to 6.5 with caustic soda (slaked lime was acceptable).
Was added for 5 minutes, and ethyl xanthate 10 was added.
0 g / t, 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 collected as floss.

[0034]

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. Also, by using only sulfuric acid as the main chemical,
The process can be closed circuit.

[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 recovering heavy metals from fly ash containing heavy metals and Ca-immobilized chlorine generated when waste is incinerated, comprising: a) blowing fly ash with carbon dioxide gas to remove water. And b) a step of concentrating and drying the washing liquid in the a) washing step to obtain calcium chloride as crystals, and c) the solid residue in the a) washing step and oleic acid,
Using primary amine acetate, alkyl sulfate, alkyl or allyl phosphate, tall oil, cresylic acid as a scavenger, and pine oil, MIBC, ethylene glycol as a foaming agent to perform flotation. A step of recovering calcium carbonate as floss; and d) sulfuric acid is sufficiently mixed with the sedimentation residue of the above-mentioned c) flotation step to make the heavy metal remaining in the sedimentation residue a sulfate, and water is added to this mixture to remove the metal At the same time as dissolving the sulfate
Dissolved copper ions were present in the precipitation residue as metal Al
The step of precipitating as metallic copper by means of the above, and separating and removing as a slag together with the insoluble matter, e) repulping the insoluble matter separated in step d) with water and adding a sulfiding agent in a condition tank to the surface of the metallic copper And the flotation agent is xanthate, alkyl or allyl diphosphate, dithiocarbanilide or dithiocarbamate,
Sodium sulfide, hydrogen sulfide, kerosene, alkyl sulfates, alkyl or allyl phosphates, pine oil, ethylene
Heavy metal from fly ash, characterized by having a step of performing flotation using a flotation agent such as glycol, methyl isobutyl carbinol, etc., and recovering copper and lead sulfate as a mixed concentrate of the flotation. Method of collecting items. 2. In the e), the flotation or calcium carbonate of the above c) is added to the filtrate of the above d) to neutralize it to a pH of 5 to 6, and then the produced slurry is heated and air is blown into the filtrate.
The e) first treatment in which e (II) is oxidized to Fe (III) to form iron (III) hydroxide and aluminum hydroxide is precipitated and filtered, and slaked lime is added to the solution generated in the first stage treatment. 2. Recovery of heavy metals from fly ash according to claim 1, wherein the pH is adjusted to 6 or higher and Zn is precipitated as zinc hydroxide and filtered off, and the filtrate has e) the second stage treatment which is used as a cleaning solution for the raw fly ash. Method.