JP7790157B2 - Method for producing crude zinc oxide and method for treating flue dust - Google Patents

Description

The present invention relates to a method for producing crude zinc oxide and a method for treating flue dust. More specifically, the present invention relates to a method for producing crude zinc oxide from raw materials containing flue dust generated in copper smelting furnaces, and a method for treating flue dust containing zinc and copper generated in copper smelting furnaces.

The flue gas recovered from the exhaust gases generated in copper smelting furnaces contains not only the copper contained in the copper concentrate, but also large amounts of easily volatile elements such as zinc and bismuth. Generally, flue gas generated in the copper smelting process is recycled and returned to the copper smelting furnace, as it contains the metals that are the target of smelting.

However, because the above-mentioned flue dust contains bismuth, if it is repeatedly fed into a copper smelting furnace, the impurity content of bismuth and other substances in the copper anodes obtained in the copper smelting process increases, resulting in the problem of an increased impurity content in the electrolytic copper obtained in the subsequent copper refining process (electrolysis process).

In response to this issue, Patent Document 1 discloses a method for treating flue dust, which contains high concentrations of lead and is generated and recovered during non-ferrous metal smelting, by mixing it with chlorine-containing steel dust to form pellets and then introducing the pellets into a reduction roasting process in a crude zinc oxide production process, in a manner similar to the conventional method for treating steel dust which involves a reduction roasting process.

In the production of crude zinc oxide, steel dust is often used as a raw material. Reduced iron pellets, a by-product of the process of reducing and roasting this steel dust, are recycled by steel manufacturers as a source of iron. However, when the flue gas processed in the reducing and roasting process, as described above, contains copper in particular, a new problem arises: this copper is distributed in the reduced iron pellets. This is because copper is one of the impurities that steel manufacturers that use reduced iron pellets place the strictest restrictions on inclusion in their iron sources.

JP 2013-139618 A

The objective of the present invention is to provide a method for producing crude zinc oxide using steel dust as a raw material, which can effectively utilize flue dust containing zinc and copper generated in copper smelting furnaces as part of the raw material, while avoiding the contamination of reduced iron pellets, which are a by-product and can be used as an iron source, with copper.

The inventors of the present invention came up with the idea that the above-mentioned problems could be solved by changing the process so that flue dust, which was previously fed into the reduction heating process, an upstream step in the crude zinc oxide manufacturing process, together with the primary raw material, steel dust, is fed directly into the drying heating process, a downstream step, as a secondary raw material. Specifically, the present invention provides the following:

(1) A method for producing crude zinc oxide comprising: a reduction roasting process in which steel dust is reduced and roasted to obtain crude zinc oxide dust; a wet process in which the crude zinc oxide dust is subjected to wet treatment to obtain crude zinc oxide cake; and a dry heating process in which the crude zinc oxide cake is calcined to obtain crude zinc oxide cinder; wherein in the dry heating process, flue dust generated in a copper smelting furnace and recovered is calcined together with the crude zinc oxide cake.

According to the crude zinc oxide manufacturing method (1), in the production of crude zinc oxide using steel dust as a raw material, copper-containing flue dust can be effectively used as part of the raw material while avoiding the contamination of reduced iron pellets, which are a by-product and can be used as an iron source. Therefore, when shipping reduced iron pellets to steel manufacturers as an iron source, the possibility of them being rejected due to high copper content can be significantly reduced.

(2) A method for producing crude zinc oxide, comprising: a reduction roasting process in which steel dust is reduced and roasted to obtain crude zinc oxide dust; a wet process in which the crude zinc oxide dust is subjected to wet treatment to obtain crude zinc oxide cake; and a dry heating process in which the crude zinc oxide cake is calcined to obtain crude zinc oxide cinder, wherein in the dry heating process, flue dust containing zinc and copper, with a copper content of 10% or more, is calcined together with the crude zinc oxide cake.

According to the method for producing crude zinc oxide (2), even when flue dust containing zinc and copper, with a particularly high copper content, is used as a raw material at the crude zinc oxide production site, the copper-containing flue dust can be effectively used as part of the raw material while avoiding the contamination of reduced iron pellets, which are a by-product and can be used as an iron source.

(3) The method for producing crude zinc oxide described in (1), wherein the copper smelting furnace is a copper smelting converter.

According to the method for producing crude zinc oxide (3), in the method for producing crude zinc oxide described in (1), lead, zinc, and bismuth can be recovered more efficiently by using flue gas generated in a copper smelting converter, which has a relatively low boiling point and contains large amounts of lead, zinc, bismuth, etc., and which volatilizes and scatters from the molten metal.

(4) A method for producing crude zinc oxide according to any one of (1) to (3), wherein the flue dust has a lead content of 12% or more and a zinc content of 4% or more.

According to the method for producing crude zinc oxide (4), in the method for producing crude zinc oxide described in any one of (1) to (3), by using flue dust containing high concentrations of the target metals, zinc, copper, and lead, it is possible to more efficiently recover zinc, copper, and lead.

(5) A flue ash processing method for processing flue ash generated and recovered from a copper smelting furnace, which flue ash has a lead content of 12% or more, and which uses the flue ash as a secondary raw material to be input into a drying and heating step in a crude zinc oxide production process.

According to the flue dust processing method (5), flue dust generated in copper smelting furnaces and containing high concentrations of lead can be effectively utilized in the production of crude zinc oxide using steel dust as a raw material, while avoiding copper contamination in reduced iron pellets, which are a by-product and can be used as an iron source. This significantly reduces the possibility that reduced iron pellets will be rejected due to their high copper content when shipped as an iron source to steel manufacturers. Furthermore, because the flue dust is processed in a dry heating process, there is no need to go through the upstream processes of the reduction roasting process and the wet process. By reducing the number of processes, the cost of flue dust processing can be reduced.

According to the present invention, in the production of crude zinc oxide using steel dust as a raw material, copper-containing flue dust can be effectively used as part of the raw material while avoiding the contamination of reduced iron pellets, which are by-products and can be used as an iron source.

FIG. 1 is a flow chart showing the flow of a method for producing crude zinc oxide of the present invention using flue dust generated in copper smelting as a secondary raw material.

Preferred embodiments of the present invention will now be described with reference to the drawings as appropriate. Figure 1 is a flow diagram showing the process for producing crude zinc oxide of the present invention, which uses flue dust generated during copper smelting as part of the raw materials.

<Method of producing crude zinc oxide>
The method for producing crude zinc oxide of the present invention is a process that uses zinc-containing steel dust generated from blast furnaces, electric furnaces, etc. in the steel industry as a raw material, and removes impurities from the raw material to produce crude zinc oxide with a zinc content of approximately 65%, which can be used as a raw material for zinc products.

The crude zinc oxide manufacturing method of the present invention is a process for carrying out the conventionally known crude zinc oxide manufacturing process P2, the basic flow of which is shown in Figure 1. In the crude zinc oxide manufacturing method of the present invention, the basic process flow is the same as the conventional method shown in Figure 1.

However, as shown in Figure 1, the crude zinc oxide production method of the present invention is a process with a new feature that differs from conventional processes in that flue dust containing at least zinc and copper (also referred to in this specification as "zinc-copper-containing flue dust"), such as flue dust generated and recovered from the copper smelting furnace in the copper smelting process P1, is directly input as part of the secondary raw material into the drying and heating process ST23, which is a process downstream of the crude zinc oxide production process P2.

The present invention is an excellent method for producing crude zinc oxide in that it recovers zinc at a high recovery rate while avoiding the contamination of reduced iron pellets, which are a by-product and can be used as an iron source, by feeding the "zinc- and copper-containing dust" generated during copper smelting into the drying and heating step ST23 in the crude zinc oxide production process P2, thereby enabling the dust to be effectively used as a secondary raw material.

The present invention is also an excellent method for treating flue dust, in that it can process the "zinc- and copper-containing flue dust" generated during copper smelting at low cost using existing equipment, without the need for new capital investment, such as rotary kilns used in existing crude zinc oxide manufacturing processes.

<Copper smelting process P1>
The copper smelting process P1, which is a supply source of the "zinc- and copper-containing flue dust" used as a secondary raw material in the method for producing crude zinc oxide of the present invention, is a process in which blister copper with a copper content of about 98% is obtained from copper concentrate, and finally electrolytic copper is obtained. In this copper smelting process P1, copper concentrate, which is the raw material for copper smelting, is generally first treated in a flash furnace to be separated into matte with a copper content of about 60% and slag. The matte obtained here is sent to the next converter process, where it is turned into blister copper with a copper content of about 98%. This is then turned into refined blister copper with a copper content of about 99% in the next refining furnace, and cast as anodes for processing in the next refining process. In the refining process, electrolytic copper is obtained from the anodes.

The above-mentioned flash furnace, converter, and refining furnace each generate flue dust with different compositions and properties. The flue dust generated in a flash furnace is a flash smelting process, which includes carryover of concentrates and other materials. Because it has a high copper content, it is preferable to repeatedly process it in a flash furnace. Furthermore, the amount of flue dust generated in a refining furnace is very small. In contrast, the flue dust generated in a converter is a bath smelting process, which contains large amounts of lead, zinc, bismuth, and other elements with relatively low boiling points that volatilize and scatter from the molten metal. Therefore, in the method for producing crude zinc oxide of the present invention, it is particularly preferable that the "zinc- and copper-containing flue dust" used as part of the raw material (or the "zinc- and copper-containing flue dust" to be treated by the flue dust treatment method of the present invention) be flue dust with a high content of lead and zinc obtained from a converter, among the various flue dusts described above. Alternatively, in the method for producing crude zinc oxide of the present invention, flue dust generated in a converter in a copper smelting process (also referred to as a "copper smelting converter" in this specification) can be used, which is obtained by repeatedly treating the flue dust within the copper smelting process and has an increased content of lead and zinc.

Furthermore, the method for producing crude zinc oxide of the present invention exhibits significant advantages over conventional techniques when the "zinc- and copper-containing flue dust" used as part of the raw material (or the "zinc- and copper-containing flue dust" to be treated by the flue dust treatment method of the present invention) contains zinc and copper, with a copper content of 10% or more. Conventionally, when flue dust with such a high copper content was used, there was a risk that the copper component would be mixed into reduced iron pellets, preventing them from being recycled as an iron source. However, this risk can be completely avoided by the present invention, which avoids flue dust treatment in upstream processes and instead concentrates flue dust treatment downstream after the drying and heating process.

Furthermore, in the crude zinc oxide production method or flue dust treatment method of the present invention, the above-mentioned "zinc- and copper-containing flue dust" preferably has a lead content of 12% or more and a zinc content of 4% or more. Even if flue dust containing high concentrations of lead is repeatedly treated at copper smelting sites, it will volatilize again, significantly increasing the amount of material circulating within the process. On the other hand, by feeding such "zinc- and copper-containing flue dust" with a high lead content into the production and treatment methods of the present invention, lead, zinc, and copper can be recovered more efficiently in the crude zinc oxide production process and the subsequent lead and zinc production process.

<Crude zinc oxide production process P2>
The crude zinc oxide production process P2 is a process in which a reduction roasting step ST21, a wet step ST22, and a dry heating step ST23 are sequentially performed, as will be described in detail below.

[Reduction roasting step ST21]
In the reducing roasting step ST21, primary raw materials such as steel dust are roasted in a reducing atmosphere at an appropriate temperature and residence time to reduce and volatilize zinc, lead, and other components, which are then reoxidized to obtain crude zinc oxide dust. Also, in this step, iron is recovered as solid reduced iron pellets. A rotary kiln is preferably used as the reducing roasting furnace for this step.

[Wet process ST22]
The wet process ST22 is a process for obtaining a dehydrated cake of crude zinc oxide (also referred to as "crude zinc oxide cake" in this specification) by further removing remaining impurities such as chlorine and fluorine from the crude zinc oxide dust that has been reoxidized through the reducing roasting process ST21 and contains zinc oxide and lead oxide. The wet process ST22 can be performed using a conventionally known method.

[Drying heating step ST23]
The dry heating step ST23 is a step in which the crude zinc oxide cake that has been subjected to the wet step ST22 is calcined to obtain crude zinc oxide cinder. This step allows for the production of crude zinc oxide cinder (also referred to as "crude zinc oxide cinder" in this specification) with a zinc content of about 65%.

The drying and heating process ST23 uses a rotary kiln, and the raw material, crude zinc oxide cake, and other secondary raw materials are charged into the charging end of the rotary kiln. A burner is installed at the discharge end of the rotary kiln, and this burner dries, heats, and burns the raw materials inside the rotary kiln, producing crude zinc oxide cinder at the discharge end, which has been burned to approximately 800°C to 900°C.

In the crude zinc oxide manufacturing method of the present invention, the copper-containing flue dust used as part of the raw materials is added to this drying and heating step ST23 as part of the secondary raw materials.

When processing the flue dust, the grade of copper, tin, and bismuth, which are contained in large amounts in the flue dust, is predicted from the impurity balance in the resulting crude zinc oxide, and the amount of flue dust to be processed is determined so that it falls within process standards, assuming that it will be recovered in the copper removal process of the lead-zinc smelting process, which is established as a process further downstream in the crude zinc oxide manufacturing process. The crude zinc oxide obtained in the drying and heating process ST23 is also analyzed at regular intervals to confirm that it falls within the above standards.

Furthermore, if the above-mentioned flue dust is introduced into the drying and heating process in its original form, it will be carried over along with dust generated in the conveying equipment and exhaust gas from the rotary kiln, adhering to the perforated plates of the flue and washing tower connected to the rotary kiln and causing blockages. Therefore, to avoid this, it is preferable to granulate the flue dust into pellets in advance, or to mix and process it in advance in a loader with raw materials other than the dehydrated cake to be processed in the drying and heating process, such as sediment (with a moisture content of 20% to 50%).

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[Example]
A trial run for zinc oxide production was conducted according to the flow chart shown in Figure 1. The flue dust used as part of the secondary raw material was flue dust generated in a converter at a copper smelting plant and recovered. The composition of this flue dust was as shown in Table 1 below. In the drying and heating process, 1 ton/day of the flue dust and 170 t/day of crude zinc oxide cake were dried and heated at temperatures of 800 to 900°C to obtain crude zinc oxide cinder. The crude zinc oxide cinder had a copper content of 0.21%, a tin content of 0.09%, and a bismuth content of 0.10%, and was shipped as a raw material for lead-zinc smelting. Copper, tin, and bismuth were separated and recovered in the copper removal process of lead-zinc smelting, which was carried out following the production of crude zinc oxide. In the reduction roasting step, 200 t/day of steel dust was reduced and roasted at a temperature of 1100°C to 1200°C to obtain crude zinc oxide dust containing zinc oxide and reduced iron pellets, which were shipped as iron sources to steel manufacturers.

[Comparative Example]
A test run was carried out under the same conditions as in the example, except that the flue dust was fed to a reduction roasting process together with raw materials such as steel dust, as in the conventional process. In the reduction roasting process, 1 ton/day of the flue dust and 200 t/day of steel dust were reduction roasted at temperatures of 1100°C to 1200°C to obtain crude zinc oxide dust containing zinc oxide and reduced iron pellets. The reduced iron pellets had a copper content of 0.46%, a tin content of 0.053%, and a bismuth content of 0.092%, and were therefore not shipped as an iron source to steel manufacturers.

The crude zinc oxide production method of the present invention can significantly reduce the costs required to process flue dust containing zinc and copper generated during copper smelting by utilizing existing processes and equipment. Furthermore, because the adverse effects of copper on existing processes can be prevented, the quality of reduced iron pellets can be maintained in existing crude zinc oxide production operations, and the zinc, copper, and lead contained in the flue dust can be recovered at a high recovery rate.

P1 Copper smelting process P2 Crude zinc oxide production process ST21 Reduction roasting process ST22 Wet process ST23 Dry heating process

Claims (4)

a reduction roasting step of reducing and roasting the steel dust to obtain crude zinc oxide dust;
a wet process for wet treating the crude zinc oxide dust to obtain a crude zinc oxide cake;
a dry heating step of calcining the crude zinc oxide cake to obtain crude zinc oxide cinder;
A method for producing crude zinc oxide, comprising:
In the drying and heating step, flue dust, which is generated in a copper smelting furnace and recovered, contains zinc, lead, and copper, and has a lead content of 12% or more, a zinc content of 4% or more, and a copper content of 10% or more, is calcined together with the crude zinc oxide cake.
Method for producing crude zinc oxide. In the drying and heating step, flue dust generated in a copper smelting furnace and recovered, containing zinc, lead and copper, with a lead content of 14% or more, a zinc content of 5.6% or more and a copper content of 18% or more, is calcined together with the crude zinc oxide cake.
The method for producing crude zinc oxide according to claim 1. The copper smelting furnace is a copper smelting converter.
The method for producing crude zinc oxide according to claim 1. 1. A flue ash treatment method for subjecting flue ash generated in a copper smelting furnace and recovered, the flue ash having a lead content of 12% or more, a zinc content of 4% or more, and a copper content of 10% or more, to a process for producing crude zinc oxide , comprising:
The process for producing crude zinc oxide comprises a reduction roasting step of reducing and roasting iron and steel dust to obtain crude zinc oxide dust, a wet process of subjecting the crude zinc oxide dust to wet treatment to obtain crude zinc oxide cake, and a dry heating step of calcining the crude zinc oxide cake to obtain crude zinc oxide cinder,
The flue ash treatment method uses the flue ash as a secondary raw material to be input into the drying and heating step in the process for producing crude zinc oxide.