JPH02250928A - Method for recovering zinc - Google Patents

Abstract

PURPOSE:To separate and recover a high purity Zn compd. at a high yield by bringing the dust which is collected from an electric furnace, etc., and contains Zn, Fe and other metals into contact with an acid in the presence of an oxidizing agent to dissolve the Zn, the bringing the same into a contact reaction with an alkaline liquid. CONSTITUTION:The dust discharged from the electric furnace, converter, blast furnace, etc., contains the Zn, Fe and other metals and, therefore, this dust 3 is put into an elution tank 4 and an acid liquid 5 of sulfuric acid, etc., is supplied therein. The oxidizing agent 7, such as O2 or air, is blown thereto under stirring with a stirring device 6 to bring the dust into reaction with the acidic liquid of pH4 to 5.5 to dissolve the Zn in the acid liquid while the dissolution of the Fe in the dust is suppressed. This liquid 9 is separated by a solid- liquid separator 10 and the resulted liquid is supplied to a heat treatment tank 11 where the aq. alkaline liquid 12 such as NaOH is added to adjust the pH to 10 to 12. The dissolved Zn heated to 60 to 100 deg.C by a heater 14 is subjected to a solid-liquid sepn. 17 as recovered cake essentially composed of ZnO. Only the Zn is recovered in the high-purity state.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention provides a method for efficiently separating and recovering zinc from dust containing zinc and iron discharged from electric furnaces, converters, blast furnaces, etc. using a wet method. Regarding.

[Conventional technology]

Dust collected from electric furnaces, etc. contains a large amount of metal zinc as well as iron,
Contains metals such as chromium and nickel. Dust is a powder with a particle diameter of several tens of micrometers and has a large surface area, so the elution rate with acidic liquid is high.

Therefore, in principle, it can be recovered by eluting it with an acid and then neutralizing it with an alkali and separating it as zinc hydroxide.

However, in the acid elution step, since iron is also eluted at the same time as zinc is eluted, the purity of the recovered zinc compound becomes low. Further, when the eluate is neutralized with alkali, gel-like hydroxide is generated, which causes problems such as slow filtration rate and high water content of the recovered cake.

For this reason, wet method recovery of zinc has not been put to practical use due to operability and economical considerations.

Furthermore, as a method for recovering metals such as zinc from dust collected from electric furnaces, etc., a method is known in which the electric furnace layer dust is treated with high-temperature ammonium chloride and each metal is separated and recovered (for example, Japanese Patent Publication No. 57-54450 issue).

However, in such conventional methods, since the dust is treated at high temperatures, there is a strong ammonia odor, and countermeasures are required. In addition, the wastewater contains a high concentration of nitrogen, so
Strict wastewater treatment is required.

Furthermore, there were other problems such as ammonium chloride being expensive.

As described above, in the past, there was no effective treatment method for electric furnace dust, etc., and these were disposed of as industrial waste, resulting in a waste of valuable resources.

[Problem to be solved by the invention]

The purpose of this invention is to solve the above-mentioned problems by proposing a zinc recovery method that can efficiently recover zinc compounds with high purity and low water content from dust while reducing iron elution. That's true.

[Means to solve the problem]

The present invention includes a step of contacting dust containing zinc and iron with an acid in the presence of an oxidizing substance to elute zinc, a step of heat-treating the eluate under alkalinity, and a step of solid-liquid separation. This is a method for recovering zinc.

The dust to be treated in the present invention is dust containing zinc and iron, and may also contain other metals.

Examples include dust collected from smelters such as electric furnaces, converters, and blast furnaces.

In the zinc recovery method of the present invention, first, dust containing zinc and iron is brought into contact with the dust in the presence of an oxidizing agent to elute zinc. As the oxidizing substance, in addition to oxygen and air, an oxidizing agent such as hydrogen peroxide can be used. When using a gas such as oxygen or air, aeration can be performed. As the acid, any acid such as sulfuric acid and hydrochloric acid can be used, but sulfuric acid is preferred.

Elution of zinc is carried out by bringing the dust into contact with acid in the presence of the oxidizing agent, but the pH of the acid solution at this time is 3.
-6, preferably 4-5.5 is suitable.

In the acid elution process, it is necessary to elute as much zinc as possible to be recovered, and this can be done by lowering the PO, but at the same time, more iron is eluted and the amount of acid used increases, resulting in waste. It becomes the economy.

At pH 6, iron elution does not occur, but the amount of zinc elution becomes low. In order to achieve both the elution of zinc and the prevention of elution of iron, it is effective to elute at pH 4 to 5.5 and simultaneously use air stirring or add an oxidizing agent.

When using a gas such as air or oxygen, the oxidizing substance is supplied in an amount sufficient to stir the acid solution.

When using an oxidizing agent, for example, hydrogen peroxide, 250 to 1
About 000mg/jl is used.

These oxidizing substances make it possible to suppress the elution of soluble iron such as iron oxide (Fed). Fe/Z in eluate
When n (weight ratio) is 115 or less, preferably l/10 or less, sludge with good separability can be obtained in the subsequent process. Maintain Zn (weight ratio) within the above range.

The eluate from which zinc has been eluted in this manner is heat treated under alkaline conditions in the next heat treatment step. In this step, an alkali is added to the zinc eluate to adjust the pH to 9 or higher, preferably 10 to 12, and the temperature is 50°C or higher, preferably 60 to 100°C, for 10 minutes to 5 hours, preferably 30 The heat treatment is performed for minutes to 4 hours. As the alkali, sodium hydroxide, magnesium oxide, etc. can be used.

By adding alkali, zinc, iron, etc. in the eluate become hydroxides, and the sludge at this time is gel-like and has poor dewatering properties, but when heated, it becomes a white powder and a sludge with good dewatering properties is obtained. Zinc oxide is produced through dehydration condensation during this heat treatment, but if impurities such as iron coexist, a complex with zinc will form, making it difficult to produce zinc oxide, making it impossible to obtain sludge with good dewatering properties. It is assumed that

By performing solid-liquid separation after heat treatment, a zinc compound mainly composed of zinc oxide can be recovered with high purity. At this time, since the separability of the sludge is good, solid-liquid separation can be efficiently performed by precipitation separation, filtration and dehydration, etc.

Hereinafter, the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a system diagram showing a preferred embodiment of the zinc recovery method.

In the zinc recovery method, first, dust 3 such as electric furnace dust is supplied to an elution tank 4 using a hopper 1 and a conveyor 2. An acid solution is supplied to this elution tank 4 from an acid solution supply path 5. In the elution tank 4, aeration is performed by supplying air with an aeration device M7 while stirring with the stirring device 16, and zinc is eluted from the dust 3 while suppressing the elution of iron. This eluate 8 is supplied to a heat treatment tank 11 after separating insoluble matter by a solid-liquid separator 10 provided in the middle of a flow path 9 . Heat treatment tank 1
1 is supplied with alkaline liquid from an alkaline liquid supply path 12.

While stirring with the stirring device 13 to adjust the pH,
Heat treatment is performed using a heater 14 to precipitate sludge.

This heat-treated liquid 15 is passed through a flow path 16 to a solid-liquid separator 11.
7 (dehydrator) for solid-liquid separation to obtain a recovered cake and a filtrate.

〔Effect of the invention〕

According to this invention, the dust is brought into contact with acid in the presence of an oxidizing substance and then heat-treated under alkaline conditions, so that zinc is eluted with a small amount of iron eluted, and the dehydrating property is Good sludge can be produced, solid-liquid separation can be performed efficiently, and highly pure zinc compounds can be recovered. In this case, the liquid separation rate is high, so
Workability is improved, and since the resulting dehydrated cake has a low water content, transportation costs and heat loss during smelting are low. Zinc recovery also significantly reduces the amount of dust that ends up as waste.

〔Example〕

Examples of the present invention will be described below. In each example, 1% is by weight.

Example 1 Electric furnace dust (Zn 18.4%, Fe 9.87
%, Ni1.03%, CrO,26%, CdO,2
2%) was suspended in water at a ratio of 100 g/l, and while stirring, 20% sulfuric acid was added to maintain a predetermined pH, and zinc was eluted. Figure 2 (A) shows the concentrations of eluted zinc and iron after a predetermined period of time.

Shown in (B).

From the point of zinc elution from Figure 2 (A) and (B), p)
It can be seen that a lower l value is better, and a higher pH value is better for preventing iron elution.

Example 2 In Example 1, when performing elution at pH 4 for 2 hours, there are cases where only stirring is performed, cases where stirring and aeration are used together, and cases where 500 g/n of hydrogen peroxide solution is added as an oxidizing agent during stirring. Table 1 shows the amount of iron eluted.

As is clear from Table 1, it was possible to suppress the elution of iron by aeration or by using an oxidizing agent in combination.

Table 1 Example 3 Reagent Zn5O, 7H, 05,000+g/fl (Zn
) and the reagent FeCQ3.6H,0 was added to the Na25o42,000 mg/Q solution.

The influence of iron concentration was investigated.

Neutralize to pH 11.5 with 20% sodium hydroxide,
The sample was heat-treated at 00°C for 15 minutes, and then left to stand for 1 hour. Figure 3 shows the volume of sludge (zinc hydrate) produced at each concentration of iron.

As is clear from Figure 3, when the eluate with a low iron concentration is not heat-treated, it remains a gel of Zn(OH) and is not separated by precipitation, but when heat-treated, the volume decreases significantly. . However, when the iron concentration is high, the volume decreases little even when heated, and sludge with good dewatering properties cannot be obtained through dehydration condensation.

Example 4 Reagent Zn5O, 7H, 05, OOO g#1 (as Zn), Na25o42.000mg/Q, FeCam
・6H, 0100mg/Q (as Fe), 20%
Adjust to the specified pH with sodium hydroxide, and
Heat treatment was performed for 0 minutes. Thereafter, the sludge volume was measured after being allowed to stand for 1 hour, and the results are shown in Table 2.

As shown in Table 2, the condensation reaction is greatly influenced by pH, and p
This became noticeable at H9 and above.

Table 2 Example 5 Reagent ZnSO4.7H,010,0OOa+g/a (Z
n), NazSO*4+000txg/Q%Fe
CQa・6) 120400mg/ff1 (as Fe)
is adjusted to a specified pH of 11.5 with 20% sodium hydroxide,
Heat treatment was performed at a predetermined temperature for 15 minutes. Table 3 shows the sludge volume after 1 hour of standing.

The influence of liquid temperature on the condensation reaction was large, and the effect became significant at temperatures above 50''C.

Table 3 Table 4 Example 6 As in Example 1, acid elution was carried out at pH 5 for 2 hours while stirring and aeration were performed. The amount of 20% sulfuric acid added is dust 100
It was 150 mQ per n of g/l suspension.

The eluate obtained by solid-liquid separation after elution contains Zn 12,100
■g/12, Fa 105B/n% Ni 15
4mg/L Cd 267B/L Cr1.9+
About 200 mm of 20% sodium hydroxide was added to the ag/Q eluate to adjust the pH to 11.5.

When turbid sludge with a pH of 11.5 is directly dehydrated.

Table 4 shows the filtration rate and water content of the dehydrated cake when dehydrating the sample after heat treatment at 70°C for 30 minutes. The dehydration conditions were a slurry concentration of 2.1%, a filtration pressure of 3.0 kg/dG, a compression cuff, and 0 kg/aJG.

As shown in Table 4, when dehydration condensation was performed by heat treatment, the filtration rate was 1.8 times that of the case without dehydration condensation, and the water content was also significantly improved.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, No. 21M (A
), (B) and FIG. 3 are graphs showing the results of Examples. 3: Dust, 4: Elution tank, 10, 17: Solid-liquid separator,
11: Heat treatment tank. Agent Patent Attorney Sei Yanagihara

Claims (1)

[Claims] (1) Includes a step of contacting dust containing zinc and iron with an acid in the presence of an oxidizing substance to elute zinc, a step of heat-treating the eluate under alkaline conditions, and a step of solid-liquid separation. A method for recovering zinc, characterized by the following.