JP4478585B2 - How to recover valuable materials from fly ash - Google Patents

Description

The present invention relates to a wet processing method for recovering valuable materials from fly ash generated by incineration and / or melting processing of industrial waste such as shredder dust and electrical component waste.

In general, municipal waste and industrial waste are incinerated, and the generated incineration ash and incineration fly ash are landfilled at the final disposal site, but there is a shortage of landfill disposal sites, heavy metals and dioxins contained in the fly ash The harmfulness of the problem is a problem. For this reason, recently, incineration ash and incineration fly ash are reduced in volume, heavy metals are fixed, dioxins are decomposed at high temperatures, and waste is directly melted, and the generated molten fly ash is disposed of in landfills. Methods are also being implemented.

On the other hand, attempts have been made to collect non-ferrous metals in incineration fly ash and molten fly ash as resources. For example, in JP-A-6-170354 (Patent Document 1), mineral acid is added to fly ash to elute heavy metals other than lead at a pH of 3 or less, and lead residue mainly containing lead is filtered. A method has been proposed in which a neutralizing agent and a sulfurizing agent are added to produce zinc deposits mainly composed of zinc, and these are used as non-ferrous metal resources.
JP-A-6-170354

In the method described in the above patent, when applied to fly ash containing cadmium, arsenic, etc. that have the same behavior associated with copper and copper generated by incineration and melting of industrial waste, copper and accompanying Since non-ferrous metals and zinc co-precipitate, the quality of the recovered zinc deposits becomes high, impeding its use as a non-ferrous metal resource.

The present invention separates and collects copper and non-ferrous metals accompanying copper and zinc when recovering valuable materials contained in fly ash generated by incineration and / or melting treatment of industrial waste using a wet processing method. Thus, the copper content can be utilized as a raw material, and zinc is recovered as zinc hydroxide with a small amount of impurities to obtain a zinc oxide raw material.

Zinc oxide (zinc white) is generally used in rubber vulcanization accelerators, pigments, paints, glazes, pharmaceuticals, and the like. There is a quality standard (JIS K1410) for zinc oxide used for industrial use, and the upper limit value of the component is provided particularly for lead and cadmium which have the same behavior as zinc when vaporizing zinc as a metal component. As a method for producing zinc oxide from industrial waste, there is a method in which electric furnace dust is reduced by electrothermal distillation to oxidize and recover the volatilized zinc (Zinc Handbook (revised edition) pp 56-58). The zinc recovered product of the present invention is suitable as a raw material for this electrothermal distillation method.
JIS K1410 Zinc Handbook (revised version)

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The present invention is shown below.
(1) A method for treating fly ash that is incinerated fly ash generated by incineration and / or melting treatment of industrial waste, and also contains As and Cd ,
Leaching the fly ash while adjusting the pH to 1.0 to 3.0 with sulfuric acid acid solution,
Thereafter, solid-liquid separation, a first step of separating into a leaching residue containing lead (lead residue) and a filtrate containing copper and zinc and accompanying metals and salts,
A sulfide is added to the obtained filtrate to control the oxidation-reduction potential (ORP) based on saturated silver chloride electrode from 0 to -50 mV , and the metals containing As and Cd accompanying the leached copper are used as sulfides. A second step of precipitation and solid-liquid separation;
A third step in which an alkali agent is added to the residual liquid, the pH is adjusted to 10 to 11 and solid-liquid separation is performed, and zinc is precipitated as a hydroxide and separated into a filtrate containing salts;

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A method for recovering valuable materials from fly ash.

In the present invention, non-ferrous metals contained in fly ash generated by incineration and / or melting treatment of industrial waste are separated into lead raw materials, copper raw materials, and zinc oxide raw materials and provided as resources. In the present invention, even with high-impurity fly ash, each metal can be recovered as a raw material by wet processing, and zinc becomes a zinc oxide raw material with higher added value, thus greatly contributing to the construction of a recycling society. Can do.

The fly ash handled in the present invention is fly ash generated by incineration and / or melting treatment of industrial waste, and particularly those containing lead, zinc, and copper.

In general, when industrial waste is incinerated and / or melted, volatile metals such as lead, zinc, cadmium, and arsenic contained in the waste are volatilized by the heating operation and reaction with the contained chlorine. As recovered. A part of copper that is difficult to volatilize is recovered as fly ash.
Industrial waste containing copper has a relatively low content of non-ferrous metals other than lead, zinc, and copper, such as car shredder dust (ASR), and cadmium in addition to lead, zinc, and copper, such as electronic component waste. , Arsenic, etc.
The present invention is characterized in that lead, zinc, and copper can be recovered as resources without being affected by the content of these elements in fly ash.

  When heavy metals other than lead are to be eluted from fly ash, sulfuric acid is added and leaching is performed at a pH of less than 4.5. The reason for using sulfuric acid is to recover lead as lead sulfate (lead residue) that does not dissolve in the leachate. The pH of the leaching solution is usually set to 1 to 3 in order to shorten the leaching time and improve the leaching rate. The lead residue recovered in this way can be processed at a lead smelter as a lead raw material.

  Zinc, copper, cadmium, arsenic, etc. are dissolved in the leachate after the lead is recovered. From this, sulfiding treatment is performed to separate zinc and other metals. This uses the difference in the affinity of each dissolved metal with sulfur. Copper, cadmium, arsenic, and zinc have the highest affinity in this order, and the sulfide produced in the reaction does not dissolve in the liquid and precipitates. It is because it can collect | recover as. Copper, cadmium, and arsenic are sulfided in this order and removed from the solution. In order to stop the treatment before the sulfidation of zinc begins, the oxidation-reduction potential of the solution is continuously measured. Stop. By this operation, only copper, cadmium and arsenic can be selectively removed from the liquid, and only zinc can remain in the liquid. As the sulfiding agent, sodium hydrosulfide or hydrogen sulfide is used. The sulfide mainly composed of copper thus recovered can be processed at a copper smelter as a copper raw material.

  The liquid in which zinc remains is raised to pH 7 or higher at which the solubility of zinc disappears using an alkaline agent, and is precipitated as zinc hydroxide. The upper limit of the pH at this time is 12 at which zinc re-dissolution starts, but the operation is usually carried out in the range of pH 10-11. As the alkali agent, sodium hydroxide, potassium hydroxide, sodium carbonate, etc. can be used. However, an alkali agent containing calcium is not preferable because it produces gypsum and degrades the quality of zinc soot. The recovered zinc hydroxide can be treated as a zinc oxide raw material at a zinc oxide manufacturing plant. A flowchart of the present invention is shown in FIG.

Example 1
Incineration fly ash generated during car shredder dust (ASR) incineration was used for the test. The analysis value of this fly ash is shown in Table 1.

1 liter of ion-exchanged water was added to 100 g of this fly ash and stirred. Concentrated sulfuric acid was added thereto to adjust to pH 1 and stirring was continued for 60 minutes, followed by solid-liquid separation. The leaching conditions and test results are shown in Table 2.

From Table 2, almost no lead was leached out of fly ash, and 98% or more could be recovered as lead sulfate. The lead quality in lead sulfate is low because the calcium content contained in the fly ash is fixed as calcium sulfate. This is because a calcium-based fixing agent is used to fix chlorine in the gas during fly ash collection. If a sodium-based fixing agent is used, the lead quality is increased because it dissolves during leaching.
From the test results, the leaching rates of lead, zinc and copper by sulfuric acid leaching were as shown in Table 3, and it was found that lead and other metals could be separated.

The sulfiding step is carried out in order to deposit and recover only the copper content from the sulfuric acid leachate of fly ash. Here, sodium hydrosulfide (NaSH) was used as a sulfiding agent. As the sulfiding agent, hydrogen sulfide or the like is also put to practical use. As a result of searching for conditions for preferentially depositing only copper without precipitating zinc dissolved in the leachate, the amount of sodium hydrosulfide added was adjusted so that the saturated silver chloride electrode reference redox potential (ORP) of the sulfurization reaction was 0 mV or less. I found out that it should be adjusted. FIG. 2 shows the ORP change, the copper concentration in the liquid, and the zinc concentration change during the sulfurization reaction.
From the data shown in FIG. 2, it was found that when the ORP was 0 mV or less, there was almost no copper in the liquid, and the zinc concentration was hardly lowered. Table 4 shows the change in the liquid composition when sulfiding was performed while controlling the ORP to 0 mV or less.

The copper recovery rate was 97-98% throughout the leaching / sulfiding process. The analysis values of the recovered sulfide are shown in Table 5.

  The copper grade of sulfide is 43 to 58 mass%, which is sufficient as a copper raw material. In addition, it was found that although zinc was partially mixed in the sulfide, most of it remained in the liquid after the sulfidation treatment.

In order to recover zinc from the solution after sulfiding, a sodium hydroxide (NaOH) solution was added and neutralized at pH 10-11. The test results are shown in Table 6.

  The recovered zinc hydroxide had a zinc quality of 42 to 43 mass% and a zinc recovery rate of 97%. The impurity quality of zinc hydroxide was at a level that could be used as a zinc oxide raw material. The heavy metals in the liquid after neutralization were below the wastewater standard.

(Example 2)
Some industrial wastes contain various metals in addition to lead, zinc and copper. As the target fly ash, molten fly ash generated by melting of industrial waste incineration ash was used. The analysis values of fly ash are shown in Table 7.

1 liter of ion-exchanged water was added to 100 g of this fly ash and stirred. Concentrated sulfuric acid was added thereto to adjust to pH 1 and stirring was continued for 60 minutes, followed by solid-liquid separation. The leaching conditions and test results are shown in Table 8.

The lead in the fly ash was hardly leached and 99% could be recovered as lead sulfate. Moreover, the lead quality in lead sulfate was high and could be evaluated as a lead raw material. From the test results, the leaching rates of lead, zinc and copper by sulfuric acid leaching were as shown in Table 9, and it was found that lead and other metals can be separated.

Sodium hydrosulfide (NaSH) was used as a sulfiding agent. The amount of sodium hydrosulfide added was adjusted so that the oxidation-reduction potential (ORP) of the sulfurization reaction was 0 mV or less. FIG. 3 shows ORP changes (saturated silver chloride electrode standard) and copper, cadmium, arsenic and zinc concentration changes during the sulfurization reaction.
From the data in FIG. 3, when the ORP is 0 mV or less, there is almost no copper, cadmium, and arsenic in the solution. On the other hand, although the zinc concentration slightly decreases, zinc and other metals remain in the solution. Can be separated by this method. Table 10 shows the change in the liquid composition when the sulfuration treatment was performed while controlling the ORP to 0 mV or less.

The copper recovery rate was 91-95% throughout the leaching / sulfiding process. Table 11 shows the analytical values of the recovered sulfide.

The recovered sulfide was usable as a copper raw material or a zinc raw material.
In order to recover zinc from the solution after sulfiding, a NaOH solution was added and neutralization was performed at pH 10-11. The test results are shown in Table 12.

  The recovered zinc hydroxide had a zinc quality of 57-60 mass% and a zinc recovery rate of 50-58%. The impurity quality of zinc hydroxide was at a level that could be used as a zinc oxide raw material. The heavy metals in the liquid after neutralization were below the wastewater standard.

It is a flowchart which shows this invention method. It is a graph which shows the amount of addition of sodium hydrosulfide and ORP, zinc concentration, and copper concentration of the liquid in the sulfurization reaction of ASR incineration fly ash sulfuric acid leachate. (The amount of NaSH added is the amount of NaSH added to 1 m3 of sulfuric acid leachate) It is a graph which shows sodium hydrosulfide addition amount and ORP of a liquid, zinc concentration, copper concentration, cadmium concentration, and arsenic concentration change in sulfurization reaction of industrial waste incinerated ash melted fly ash sulfuric acid leachate. (The amount of NaSH added is the amount of NaSH added to 1 m3 of sulfuric acid leachate)

Claims (1)

A method for treating fly ash that is incinerated fly ash generated by incineration and / or melting treatment of industrial waste, and also contains As and Cd ,
Leaching the fly ash while adjusting the pH to 1.0 to 3.0 with sulfuric acid acid solution,
Thereafter, solid-liquid separation, a first step of separating into a leaching residue containing lead (lead residue) and a filtrate containing copper and zinc and accompanying metals and salts,
A sulfide is added to the obtained filtrate to control the oxidation-reduction potential (ORP) based on saturated silver chloride electrode from 0 to -50 mV , and the metals containing As and Cd accompanying the leached copper are used as sulfides. A second step of precipitation and solid-liquid separation;
It is characterized by comprising a third step of adding an alkaline agent to the residual liquid and adjusting the pH to 10 to 11 and solid-liquid separation, and depositing zinc as a hydroxide and separating it into a filtrate containing salts. To recover valuable materials from fly ash.

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