JP4118240B2 - How to recover lead from waste - Google Patents

Description

The present invention relates to a method of using lead generated when heat-treating waste containing lead as a raw material for smelting.

  The waste is incinerated at the waste intermediate treatment plant and reduced in volume, and the solid matter such as the incineration residue finally discharged is landfilled at the landfill site. Among these solids, fly ash generated during incineration or melting treatment contains heavy metals such as zinc and lead, so fly ash is stabilized by cement solidification, chemical treatment, etc. After being landfilled.

  However, such a disposal method requires a landfill disposal site, and in recent years, it has become very difficult to secure such a disposal site. In addition, even when stabilized, there is a risk that heavy metals such as lead eluted from landfilled fly ash will cause environmental pollution in the ultra-long term. There is also a problem that these useful resources are not utilized even though useful metal resources are included.

Various methods for removing and recovering heavy metals have been proposed for fly ash among incineration ash.
Patent Document 1 discloses a method for treating fly ash containing salts mainly composed of chlorine and sodium generated from an incinerator and heavy metals mainly composed of zinc, copper, and lead. The first step of solid-liquid separation after adjusting the pH of the liquid to 8.0 to 11.0 by adding a compatibilizer; repulping the resulting residue by adding water and adjusting the pH to 3 or less After eluting the heavy metal component mainly composed of zinc / copper, the second step of filtering out the residue containing the heavy metal component mainly composed of lead; and the filtrate obtained in the first step and the second step in the middle A neutralizer is added and neutralized to pH 7 or higher to produce a heavy metal hydroxide mainly composed of zinc. If necessary, a sulfiding agent is added to the filtrate to convert the remaining heavy metal into a sulfide. Included in the fly ash by precipitating and applying a third step of filtering these precipitates Heavy metals are separated and separated into residues (mainly containing lead), hydroxide starch (mainly containing zinc), and sulfurized starch (mainly lead and zinc sulfides). A method that can be used as a raw material is described.
However, according to this method, not only a special agent such as a sulfurizing agent is required, but the heavy metal-containing residue contains a large amount of chlorine, which is used when used as a raw material for non-ferrous smelting. Has a problem that chlorine or a chlorine compound causes various troubles.

  In order to solve the above problem, in Patent Document 2, water is added to fly ash collected when the waste incineration residue is melt-treated, and further, alkali is added as necessary to form a slurry. Liquid separation is performed to separate the solution from which soluble salts are eluted and the residue containing heavy metal, and then the separated residue is subjected to high-temperature heat treatment to remove chlorine and dioxins in the residue. A method of recovering as a raw material for smelting has been proposed. However, this method requires a separate high-temperature heat treatment step.

  Patent Document 3 is obtained by adding acid to fly ash containing heavy metals such as lead discharged from an incinerator to extract heavy metals other than lead, followed by solid-liquid separation, and then solid-liquid separation. After extracting lead by adding a solubilizing agent to the residue containing lead, solid-liquid separation, and further adding an insolubilizing agent to the filtrate obtained by solid-liquid separation to make lead insolubilized, A method for recovering lead in fly ash consisting of solid-liquid separation is described.

  In Patent Document 4, water is added to fly ash, and an alkali is added as necessary to prepare a slurry having a pH of 7 to 11, and the slurry is solid-liquid separated to concentrate the solution from which soluble salts are eluted and heavy metals. The residue containing the heavy metal is added with water, and further added with sulfuric acid to prepare a slurry having a pH of 4 to 6, and the slurry is solid-liquid separated to obtain a solution containing a heavy metal mainly composed of zinc; It is described that it is divided into residues containing heavy metals mainly composed of lead.

All of the above methods are treatments for fly ash containing lead that has already been transformed into a form of lead oxide, and includes a step of re-precipitation and separation after dissolution with an acid, and the operation is complicated. Not only is it economical, it requires acid.
That is, in the conventional method, when the waste containing lead is incinerated, if the atmosphere is an oxidizing atmosphere, the lead contained in the waste becomes lead oxide, the lead remains in the incineration ash, In addition to being difficult to recover, it was necessary to treat lead in the incineration ash.
On the other hand, in recent years, as a waste treatment method that replaces the above-described incineration treatment, heat treatment of waste is performed in a reducing heat treatment furnace. As an example of such a processing method, a gasification melting process by a gasification reforming method has attracted attention. By heat treating the waste in a reducing atmosphere, generation of lead oxide can be suppressed and volatile heavy metals such as lead can be separated.

  In patent document 5, in the waste treatment by the gasification reforming method as described above, from a cleaning liquid containing heavy metals such as lead obtained by cleaning a gas discharged from a high temperature reactor with an acidic aqueous solution, A method for recovering heavy metals has been proposed. This method is obtained by cooling and acid-washing a gas generated by gasification of waste with an acidic aqueous solution adjusted to 2 ≦ pH ≦ 3, and then adding an alkali to the acidic aqueous solution used for the cooling and washing. The treated liquid is separated into solid matter containing heavy metal such as lead and separated water using a solid-liquid separation device such as a membrane separation device.

Patent Document 6 discloses that in waste treatment by a gasification reforming method, an acidic aqueous solution is sprayed on exhaust gas, and quenched and washed to remove impurities such as iron chloride, evaporated zinc, and evaporated lead in the gas. It is described that lead and zinc are recovered as valuable substances.
In Patent Document 7, a gas generated by gasification of waste is cooled and washed with an acidic aqueous solution, and then washed with an aqueous solution having a pH of 6.5 to 7.5, and the aqueous solution used in the washing and the cooling and washing are used. It describes that an alkali agent is added to a mixed aqueous solution with an acidic aqueous solution used in the above, and the obtained mixed aqueous solution is subjected to solid-liquid separation to increase the content of valuable substances in the solid content.
However, the above method has not been a sufficient technique in terms of recovery of valuable substances such as lead and zinc.

  By the way, when the waste is treated in a reducing heat treatment furnace, carbon particles are generated. In order to effectively use this carbon, the carbon particles can be separated into solid and liquid from the cleaning liquid and then returned to the heat treatment furnace for gasification. However, if there is a lot of lead in the waste, lead is insoluble in acid. It remains as a minute and exists as a mixed solid with carbon particles. When this mixed solid is returned to the heat treatment furnace, lead is concentrated in the system and handling becomes difficult. However, the above-mentioned document does not describe countermeasures against this.

JP-A-8-141539 Japanese Patent Laid-Open No. 10-204548 JP-A-10-204552 Japanese Patent Laid-Open No. 10-109077 JP 2003-1041 A JP-A-10-165743 JP 2003-3178 A

  An object of this invention is to isolate | separate and collect | recover lead from the gas which generate | occur | produces when the waste containing lead is heat-processed in reducing environment.

  As a result of intensive studies on the method for achieving the above object, the present inventors have found that lead is dissolved without forming lead sulfide in a solution having a pH of 2 or lower, and zinc is a solution having a pH of 4 or higher. In the present invention, it was found that solid zinc sulfide was produced, and the present invention was completed.

That is, the present invention is as described below.
(1) Waste containing lead, zinc, iron and sulfur is heat-treated in a reducing atmosphere to volatilize lead, the lead-containing gas is acid cleaned with an acid cleaning solution having a pH of 2 or less, and then the acid cleaning solution after cleaning Is separated into a solid residue containing carbon particles and a liquid containing lead, the solid residue containing carbon particles is again heat-treated in a reducing atmosphere, and a lead concentrate is recovered from the liquid containing lead. To collect lead.
(2) Waste containing lead, zinc, iron and sulfur is heat-treated in a reducing atmosphere to volatilize lead, and after the lead-containing gas is acid-washed with an acid cleaning solution having a pH of 2 to 4, the acid after washing The cleaning liquid is separated into a solid residue containing carbon particles and a lead compound and a liquid from which lead has been removed, and then the solid residue is brought to pH 2 or lower, and then separated into a solid residue containing carbon particles and a liquid containing lead. Then, the solid residue containing the carbon particles is again heat-treated in a reducing atmosphere, and a lead concentrate is recovered from the lead-containing liquid.
(3) After oxidizing the liquid from which the lead has been removed with an oxidizing agent, the pH is adjusted to 4 to 7 to produce iron hydroxide, and the iron hydroxide is separated by solid-liquid separation. The method for recovering lead as described in (2) above, wherein zinc hydroxide is produced by adjusting to 11, and the zinc hydroxide is separated and recovered by solid-liquid separation.

(4) A method for recovering a lead concentrate from the lead-containing liquid comprises bringing the lead-containing liquid into contact with hydrogen sulfide gas generated by heat treatment in the reducing atmosphere under acidic conditions of pH 2-4. The method for recovering lead according to any one of (1) to (3) above, wherein solid lead sulfide is produced and then separated into a lead concentrate and a liquid from which lead has been removed by solid-liquid separation.
(5) Waste containing lead, zinc, iron and sulfur is heat-treated in a reducing atmosphere to volatilize lead, and the lead-containing gas is acid-washed with an acid cleaning solution having a pH of 2 to 4, and then the acid after washing The cleaning liquid is separated into a solid residue containing carbon particles and a lead compound and a liquid from which lead has been removed, and then the solid residue is brought to pH 2 or lower, and then separated into a solid residue containing carbon particles and a liquid containing lead. The solid residue containing the carbon particles is again heat-treated in a reducing atmosphere, and an oxidizing agent and an alkali agent are added to the liquid from which the lead has been removed to adjust the pH to 4 to 7 to generate iron hydroxide. The liquid obtained by solid-liquid separation of this iron hydroxide and the liquid containing lead are mixed, adjusted to pH 9-11 to produce lead hydroxide and zinc hydroxide, Lead recovery characterized by recovering zinc hydroxide by solid-liquid separation Law.

  According to the present invention, the carbon content and the lead content generated when the waste is subjected to the reductive heat treatment are efficiently separated, and the carbon content is returned to the reductive heat treatment furnace for effective use. The effect that it can collect | recover efficiently as a raw material for lead smelting is acquired.

The method of the present invention will be described with reference to the drawings by taking the gasification reforming system described above as an example.
First, one example of the gasification reforming system will be described with reference to FIG.
The gasification reforming method shown in FIG. 1 includes the following processes.
1. 1. Press and degas channel (1) Waste compression, (2) Drying and pyrolysis 2. High-temperature reactor / homogenization furnace (3) Gasification and melting, (4) Slag homogenization, (5) Gas reforming Gas purification (6) Rapid cooling (rapid cooling / acid cleaning, acid cleaning), (7) Gas purification (alkali cleaning, desulfurization, dehumidification)
4). Water treatment (8) Water treatment (precipitation, salt production)
5. Use of gas (9) Use of power generation of gas

The basic configuration of this method will be described along the flow as follows.
After the waste accumulated in the bit is compressed by a press, it is heat-distilled by indirect heating in a dry pyrolysis step and sent to a high-temperature reactor. A burner is disposed at the lower part of the high-temperature reactor, and oxygen is introduced by the burner, and the oxygen gas gasifies carbon in the dry distillation product to generate carbon monoxide and carbon dioxide. In addition, since high-temperature steam is present, a water gas reaction occurs between carbon and steam, and the organic compound is decomposed mainly into hydrogen and carbon monoxide.

As a result of the above reaction, the crude synthesis gas is discharged from the top of the high temperature reactor.
On the other hand, the melt produced in the lower part of the high temperature reactor flows from the high temperature reactor to the homogenization furnace. This melt contains carbon, which is gasified and removed in the homogenization furnace. In the homogenization furnace, the metal melt has a large specific gravity, so that it accumulates at the bottom of the slag and is separated. The melt flows down into the granulation system and is cooled and solidified, and the metal / slag mixture is separated into metal and slag by magnetic separation.

  For the combined synthesis gas discharged from the high-temperature reactor, the temperature of the gas is rapidly cooled from about 1200 ° C. to about 70 ° C. by spraying acidic water with a quenching device to prevent resynthesis of dioxins. At this time, the gas is washed with acidic water, and heavy metal components such as lead and chlorine contained in the crude synthesis gas are dissolved in the washing liquid.

  The acid-cleaned synthesis gas is further subjected to acid cleaning as necessary and then alkali-cleaned to neutralize and remove the remaining acidic gas such as hydrogen chloride gas. Next, hydrogen sulfide in the gas is converted to sulfur by a desulfurization washing apparatus and discharged as a sulfur cake. Next, the synthesis gas is used as the generated fuel gas after moisture is removed in the low temperature dehumidification process.

The cleaning liquid contains lead and carbon particles as solid contents.
That is, when organic waste is processed in a reducing heat treatment furnace, a combustible gas mainly composed of hydrogen, carbon monoxide, etc. is generated. When this gas is rapidly cooled, a reaction of 2CO → C + CO ₂ occurs, resulting in fine carbon. Particles are generated. Further, when waste containing lead is treated in a reducing heat treatment furnace, lead is volatilized as lead vapor or lead chloride, and when this is acid cleaned, it is contained in the cleaning liquid as lead chloride. When waste containing sulfur is treated in a reductive heat treatment furnace, sulfide gas is generated. This hydrogen sulfide comes into contact with a cleaning solution containing lead chloride to produce fine insoluble lead sulfide, which is contained in the cleaning solution. It comes to be. Furthermore, ash such as calcium is present in the waste, and most of it becomes slag when melted, but part of it is entrained in the flammable gas and cleaned so that it is contained in the cleaning liquid. Become.

  The present invention is characterized by a configuration for separating and recovering lead and carbon particles from the cleaning liquid containing lead and carbon particles. Below, the processing method of the exhaust gas cleaning liquid will be described in more detail.

  In FIG. 1, the reformed gas generated by gasification reforming of waste discharged from the top of the high temperature reactor is rapidly cooled by injecting an acidic aqueous solution in the middle of a route fed to the gas purification facility. -Acid washed. Chlorine contained in the waste is mainly present in the synthesis gas as hydrogen chloride, and this hydrogen chloride dissolves in the cooling / cleaning liquid. In the present invention, the liquid that has become acidic with hydrochloric acid by dissolving the hydrogen chloride gas generated in the furnace in the cleaning liquid can be used as the cleaning liquid. The crude synthesis gas is washed with the acidic aqueous solution containing hydrogen chloride to remove carbon particles and heavy metals such as lead.

In the present invention, there are mainly the following two methods for separating the lead compound and the carbon particles.
(1) A lead-containing gas is washed with an acidic aqueous solution having a pH of 2 or less to obtain a cleaning solution in which lead is dissolved. The cleaning solution is separated into solid and liquid to recover carbon particles as a solid, and then contains lead. A method to recover lead from an aqueous solution.
(2) After acid-washing the lead-containing gas with an acidic aqueous solution having a pH of 2 to 4, it is subjected to solid-liquid separation, and an acidic aqueous solution having a pH of 2 or less is added to the obtained solid to dissolve lead from the solid, A method of recovering carbon particles as a solid content by liquid separation and then recovering lead from an aqueous solution containing lead.
In this case, the acidic aqueous solution has a pH of 2 to 4 in order to avoid the formation of solid zinc.

Next, the method (1) will be described with reference to FIG.
A crude synthesis gas obtained by gasifying and reforming waste containing lead, zinc, iron and sulfur is subjected to rapid cooling and acid cleaning treatment under conditions of pH 2 or less. A purified synthesis gas can be obtained by further subjecting the gas after washing to alkali washing treatment, desulfurization treatment and dehumidification treatment.

In addition, since the cleaning liquid obtained by quenching and acid cleaning contains carbon particles as a solid content and dissolved lead sulfide, solid carbon particles are obtained by concentrating and separating the solid content. It is done. This carbon solid is returned to the gasifier and converted to fuel gas.
When the cleaning liquid from which the carbon particles have been removed is brought into contact with a reformed gas containing hydrogen sulfide, lead dissolved in the cleaning liquid is deposited as lead sulfide. The lead concentrate can be recovered by separating the solid lead sulfide by solid-liquid separation.

Iron hydroxide is prepared by adjusting the redox potential by adding an oxidizing agent such as hydrogen peroxide to the liquid from which the lead compound has been removed, and adjusting the pH to about 4 to 7 by adding an alkaline agent such as sodium hydroxide. Since aluminum hydroxide and the like are selectively precipitated, the iron and aluminum components can be recovered as slag or metal by separating them and returning them to the gasification reforming furnace.
Furthermore, by adding sodium hydroxide to the liquid from which iron hydroxide and the like are separated to adjust the pH to 9 to 10, metal hydroxide mainly composed of zinc hydroxide can be separated. Collected.
Further, the liquid from which the solid content has been separated is further treated with a salt production apparatus after calcium is removed to obtain reprocessed water and a mixed salt.

Next, the method (2) will be described with reference to FIG.
A crude synthesis gas obtained by gasifying and reforming waste containing lead, zinc, iron and sulfur is subjected to a rapid cooling and acid cleaning treatment under the conditions of pH 2-4. A purified synthesis gas can be obtained by further subjecting the gas after washing to alkali washing treatment, desulfurization treatment and dehumidification treatment.

Further, since the cleaning liquid obtained by quenching and acid cleaning contains carbon particles and lead sulfide as solid contents, the solid contents are separated by solid-liquid separation. By treating the obtained solid content with hydrochloric acid at a pH of 2 or less, lead sulfide is eluted. The carbon solid content obtained by solid-liquid separation is returned to the gasifier and converted into fuel gas.
By adding hydrochloric acid, hydrogen sulfide gas is generated. The hydrogen sulfide gas can be used to generate lead sulfide in the next step.

When the liquid from which the carbon particles have been removed is brought into contact with the previously generated hydrogen sulfide gas, solid lead sulfide is formed, and solid lead sulfide is recovered as a lead concentrate by solid-liquid separation.
Iron hydroxide is prepared by adjusting the redox potential by adding an oxidizing agent such as hydrogen peroxide to the liquid from which the lead compound has been removed, and adjusting the pH to about 4 to 7 by adding an alkaline agent such as sodium hydroxide. Since aluminum hydroxide and the like are selectively precipitated, the iron and aluminum components can be recovered as slag or metal by separating them and returning them to the gasification reforming furnace.

Further, by adding sodium hydroxide to the liquid from which iron hydroxide and the like have been separated and adjusting the pH to 7 to 11, metal hydroxide mainly composed of zinc hydroxide can be separated, which is a zinc concentrate. And recovered as zinc raw material for smelters.
Further, the liquid from which the solid content has been separated is further treated with a salt production apparatus after calcium is removed to obtain reprocessed water and a mixed salt.

4 is a modification of that shown in FIG.
The liquid obtained by separating the solid content containing carbon particles and lead sulfide is adjusted to pH 4-7 to separate the iron content as iron hydroxide, and this separated liquid contains lead after separating the carbon solid content. It is processed by mixing with liquid.

[Comparative Example 1]
After the waste containing lead, zinc, iron, and sulfur was gasified and reformed, after performing quenching and acid cleaning under the conditions of pH 2 to 3, refined synthesis gas was obtained by performing gas purification. In addition, the cleaning liquid that has been rapidly cooled and acid-washed, and the cleaning liquid produced by gas purification are adjusted to pH 5 by adding sodium hydroxide to precipitate iron hydroxide, aluminum hydroxide, etc. separated.
Next, the water to be treated from which the solid content is separated and removed by the second solid-liquid separator is adjusted to a pH of 9 by adding sodium hydroxide to precipitate zinc hydroxide, lead hydroxide, etc., and the solid content is separated. Zinc hydroxide, lead hydroxide, etc. were recovered as solids. Furthermore, after removing calcium, reprocessed water and a mixed salt were obtained with a salt production apparatus.
The solid content obtained by the first solid-liquid separator contained not only carbon particles, iron hydroxide and aluminum hydroxide, but also lead sulfide, and the lead concentration was 10% by mass on a dry basis.

A waste gas containing lead, zinc, iron and sulfur was gasified and reformed, and after quenching and acid cleaning under the conditions of pH 1.6, a purified synthesis gas was obtained by performing gas purification. Further, the solid content of the cleaning liquid that had been quenched and acid-washed was concentrated and separated to obtain solid carbon particles. The separated carbon solid was returned to the gasifier and converted to fuel gas.
Furthermore, when the liquid from which the carbon particles were removed was brought into contact with a reformed gas containing hydrogen sulfide, solid lead sulfide was formed. Solid lead sulfide was subjected to solid-liquid separation to recover a lead concentrate. The resulting lead concentrate was 45% by weight on a dry basis. The resulting lead mixture could be used as a raw material for lead in a smelter.
The liquid from which the lead sulfide has been removed is further adjusted by adding hydrogen peroxide to adjust the redox potential, and by adding sodium hydroxide, the pH is adjusted to 5 to separate iron hydroxide and the like, and the gasification reforming furnace Returned to.
Further, sodium hydroxide was added to the liquid from which iron hydroxide and the like were separated to adjust the pH to 9.5, and metal hydroxide mainly composed of zinc hydroxide was separated and recovered as a solid content. Furthermore, after removing calcium, reprocessed water and a mixed salt were obtained with a salt production apparatus.

A waste gas containing lead, zinc, iron and sulfur was gasified and reformed, then quenched and acid washed under the condition of pH 2.5, and then purified by gas purification to obtain a purified synthesis gas. In addition, the solid content of the cleaning liquid that had been quenched and acid cleaned was separated to obtain carbon particles containing solid lead sulfide. This was adjusted to pH 1.5 by adding hydrochloric acid to dissolve the lead sulfide, and the separated carbon solid was returned to the gasifier and converted to fuel gas. By adding hydrochloric acid, hydrogen sulfide gas is generated. The hydrogen sulfide gas was used for lead sulfide generation in the next step.
Further, when the liquid from which the carbon particles were removed was brought into contact with the previously generated hydrogen sulfide gas, solid lead sulfide was formed. Solid lead sulfide was subjected to solid-liquid separation to recover a lead concentrate. The resulting lead concentrate was 42% by weight on a dry basis. The resulting lead mixture could be used as a raw material for lead in a smelter.
The cleaning liquid from which the solid content has been separated is further added with hydrogen peroxide to adjust the oxidation-reduction potential, and sodium hydroxide is added to adjust the pH to 5 to separate iron hydroxide and the like. Returned to.
Further, sodium hydroxide was added to the liquid from which iron hydroxide and the like were separated to adjust the pH to 9.5, and metal hydroxide mainly composed of zinc hydroxide was separated and recovered as a solid content. Furthermore, after removing calcium, reprocessed water and a mixed salt were obtained with a salt production apparatus.

  Since the present invention can effectively recover lead, which is a valuable material, from waste, its utility is high from the viewpoint of reducing waste discharge and resource recycling.

It is a figure which shows the outline | summary of the waste treatment process by a gasification reforming system. It is a figure which shows the example of the flow sheet of the collection | recovery method of the lead from the waste material of this invention. It is a figure which shows the other example of the flow sheet of the collection | recovery method of the lead from the waste material of this invention. It is a figure which shows the other example of the flow sheet of the collection | recovery method of the lead from the waste material of this invention.

Claims (5)

  Waste containing lead, zinc, iron and sulfur is heat-treated in a reducing atmosphere to volatilize lead, and after the lead-containing gas is acid cleaned with an acid cleaning solution having a pH of 2 or less, the cleaned acid cleaning solution is treated with carbon particles. A solid residue containing lead and a liquid containing lead, the solid residue containing carbon particles is again heat-treated in a reducing atmosphere, and a lead concentrate is recovered from the lead-containing liquid. Collection method.   Waste containing lead, zinc, iron and sulfur is heat-treated in a reducing atmosphere to volatilize lead, and after the lead-containing gas is acid cleaned with an acid cleaning solution having a pH of 2 to 4, the cleaned acid cleaning solution is carbonized. The solid residue containing particles and a lead compound is separated into a liquid from which lead has been removed, and then the solid residue is brought to a pH of 2 or less, and then separated into a solid residue containing carbon particles and a liquid containing lead, A method for recovering lead, comprising heat-treating a solid residue containing carbon particles again in a reducing atmosphere and recovering a lead concentrate from the lead-containing liquid.   After oxidizing the liquid from which the lead has been removed with an oxidizing agent, the pH is adjusted to 4-7 to produce iron hydroxide, the iron hydroxide is separated by solid-liquid separation, and then the separated liquid is adjusted to pH 9-11. Then, zinc hydroxide is produced, and the zinc hydroxide is separated and recovered by solid-liquid separation.   A method for recovering a lead concentrate from a liquid containing lead is obtained by contacting the liquid containing lead with hydrogen sulfide gas generated by heat treatment in the reducing atmosphere under acidic conditions of pH 2-4. The method for recovering lead according to any one of claims 1 to 3, wherein the method is a method of producing lead and then separating the lead concentrate and the liquid from which lead has been removed by solid-liquid separation.   Waste containing lead, zinc, iron and sulfur is heat-treated in a reducing atmosphere to volatilize lead, and after the lead-containing gas is acid cleaned with an acid cleaning solution having a pH of 2 to 4, the cleaned acid cleaning solution is carbonized. The solid residue containing particles and a lead compound is separated into a liquid from which lead has been removed, and then the solid residue is brought to a pH of 2 or less, and then separated into a solid residue containing carbon particles and a liquid containing lead, The solid residue containing carbon particles is again heat-treated in a reducing atmosphere, and an oxidizing agent and an alkaline agent are added to the liquid from which the lead has been removed to adjust the pH to 4 to 7, thereby generating iron hydroxide. A liquid obtained by solid-liquid separation of iron oxide and the liquid containing lead are mixed, adjusted to pH 9 to 11 to generate lead hydroxide and zinc hydroxide, and this lead hydroxide and zinc hydroxide Is recovered by solid-liquid separation.

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