How zinc oxide ore is produced

Abstract

To provide a method for manufacturing a zinc oxide, including sequentially a reduction roasting step, a wet step and a drying and heating step and capable of reducing a carry-over rate" when directly inserting a powdery raw material in the drying and heating step.SOLUTION: A method for manufacturing a zinc oxide ore comprises: a reduction roasting step S10 of reduction-roasting a primary raw material to obtain crude zinc oxide dust; a wet step S20 of removing water-soluble impurities included in the crude zinc oxide dust to obtain a crude zinc oxide cake; and a drying and heating step S30 of obtaining a zinc oxide ore by sintering the crude zinc oxide cake. The drying and heating step S30 includes inserting a zinc and iron containing secondary raw material with the crude zinc oxide cake into a drying and heating rotary kiln; the secondary raw material is a pellet having a moisture percentage of 14 wt.% or more and 19 wt.% or less; and an iron content is more than 10 wt.%; and a zinc content is less than 50 wt.%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing zinc oxide ore. [Background technology]

[0002] A commonly used method for producing zinc oxide ore is to obtain zinc oxide ore by removing halogen components from crude zinc oxide dust obtained by a reduction roasting process (Weltz process) in a wet process, and then calcining the zinc oxide-containing wet cake obtained in the wet process (hereinafter referred to as "crude zinc oxide cake") in a dry heating rotary kiln (DRK) which performs a dry heating process.

[0003] In the above-mentioned zinc oxide ore manufacturing method, the operation using steel dust, which is generated from blast furnaces and electric furnaces in the steel industry and contains a considerable amount of zinc in addition to iron oxide, which is the main component, as the primary raw material, is widely carried out.

[0004] In addition, in the above-mentioned zinc oxide ore manufacturing method, in addition to the above-mentioned primary raw materials charged in the reduction roasting process, a process is also carried out in which "crude zinc oxide fine powder" refined to have a zinc content of 50% or more and an iron content of about 10% is directly charged as a secondary raw material in the downstream drying and heating process (see Patent Document 1).

[0005] Patent Document 1 also discloses that when the above-mentioned "crude zinc oxide fine powder" is charged into a dry heating rotary kiln (DRK) in which the dry heating process is performed, the powdered material is pelletized with specific properties, thereby making it possible to suppress the "carry-over rate" in the dry heating process. In this specification, the "carry-over rate" in the dry heating process refers to the weight ratio of dust carried away in the DRK exhaust gas to the weight of all raw materials charged into the DRK.

[0006] However, even with the method described in Patent Document 1, the “carry-over rate” of the powdered material fed into the drying and heating process still exceeds 2% (see Example 1 in Table 2, paragraph

[0056] of the specification of Patent Document 1).

[0007] In a method for producing zinc oxide ore, which sequentially involves a reduction roasting process, a wet process, and a dry heating process, there has been a demand for a means for further reducing the "carry-over rate" when a powdered raw material is directly charged into the dry heating process. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-104733 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to reduce the "carry-over rate" in a method for producing zinc oxide ore, which involves sequentially carrying out a reduction roasting step, a wet process, and a dry heating step, when a powdery raw material is directly charged into the dry heating step. [Means for solving the problem]

[0010] The present inventors discovered that when a powdered raw material to be directly charged to a drying and heating process is pelletized and then charged, the quality of iron components, which has conventionally been eliminated as an impurity as much as possible, can be maintained at a certain level or higher, thereby reducing the "carry-over rate," and thus completed the present invention. More specifically, the present invention provides the following.

[0011] (1) A method for producing zinc oxide ore, comprising: a reduction-roasting step of reducing and roasting a primary raw material containing zinc to reduce and volatilize the zinc contained in the primary raw material to obtain crude zinc oxide dust; a wet step of wet-treating the crude zinc oxide dust to remove water-soluble impurities contained in the crude zinc oxide dust to obtain a crude zinc oxide cake; and a dry-heating step of calcining the crude zinc oxide cake to obtain zinc oxide ore, wherein in the dry-heating step, a secondary raw material containing zinc and iron is charged into a dry-heating rotary kiln together with the crude zinc oxide cake, and the secondary raw material is a pellet having a moisture content of 14% by weight or more and 19% by weight or less, an iron content of more than 10% by weight, and a zinc content of less than 50% by weight.

[0012] (2) The method for producing zinc oxide ore according to (1), wherein the secondary raw material is a pellet having a particle size distribution in which the proportion of particles having a particle diameter of 4 mm or more is 30% by weight or more.

[0013] (3) The method for producing zinc oxide ore according to (1) or (2), wherein the secondary raw material is a pellet obtained by granulating powdered iron and steel dust.

[0014] (4) A method for producing zinc oxide ore described in any one of (1) to (3), wherein the secondary raw material has a chlorine content of 3% by weight or more, and the proportion of the secondary raw material in the material to be treated charged into a dry heating rotary kiln in the dry heating step is 30% by weight or less.

[0015] (5) A method for producing zinc oxide ore according to any one of (1) to (4), wherein the secondary raw material has a zinc content of 35% by weight or more. Effect of the Invention

[0016] According to the present invention, in a method for producing zinc oxide ore in which a reduction roasting step, a wet process, and a dry heating step are sequentially performed, the "carry-over rate" can be reduced when a powdery raw material is directly charged into the dry heating step. [Brief description of the drawings]

[0017] [Figure 1] 1 is a flowchart showing an example of an embodiment of a method for producing zinc oxide ore of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A preferred embodiment of the method for producing zinc oxide ore of the present invention will be described below, although the present invention is not limited to the following embodiment.

[0019] <Overall process> The overall process carried out in a zinc oxide ore manufacturing plant using the Weltz process sequentially includes a reduction roasting process S10 in which primary raw materials such as steel dust are reduced and roasted to obtain crude zinc oxide, a wet process S20 in which chlorine, fluorine and cadmium are separated and removed from the crude zinc oxide dust obtained in the reduction roasting process S10 to obtain crude zinc oxide cake, and a dry heating process S30 in which the crude zinc oxide cake obtained in the wet process S20 and the secondary raw materials are dry heated to obtain zinc oxide ore (calcined ore).

[0020] In the above overall process, primary raw materials containing zinc, such as steel dust, are charged into the upstream process of the reduction roasting step S10. Separately, secondary raw materials containing zinc may be directly charged into the downstream process of the drying and heating step S30. The method for producing zinc oxide ore of the present invention is a widely applicable method for cases in which secondary raw materials are directly charged into the drying and heating step S30.

[0021] The main feature of the method for producing zinc oxide ore of the present invention is that it is a process using, as the secondary raw material, a material whose moisture content and iron content are adjusted to fall within specific ranges.

[0022] <Reduction roasting process> The reduction roasting step S10 is a step of obtaining crude zinc oxide dust by reduction roasting a primary raw material containing zinc. The reduction roasting process is carried out by a reduction roasting rotary kiln (RRK).

[0023] In the reduction roasting process S10, steel dust is widely used as the primary raw material charged into the RRK. The steel dust is continuously charged into the RRK together with carbonaceous reducing agents such as coal and coke, and limestone, etc. Inside the RRK, the maximum temperature of the material to be treated is controlled to about 1100°C to 1200°C by the combustion of heavy oil and the charged carbonaceous reducing agents.

[0024] The steel dust is reduced and roasted in the RRK body, and the metallic zinc that is reduced and volatilized is reoxidized in the exhaust gas to become powdered zinc oxide. The small amount of lead contained in the steel dust volatilizes as lead oxide. The powdered zinc oxide and lead oxide are introduced into a dust collector together with the exhaust gas from the RRK, where they are captured and recovered as crude zinc oxide dust. This crude zinc oxide dust generally contains halogen impurities such as chlorine at a concentration of 8% to 20% by weight.

[0025] <Wet process> The wet process S20 is a process for removing water-soluble impurities from the crude zinc oxide dust recovered in the reduction roasting process S10 by wet treatment to obtain a crude zinc oxide cake.

[0026] In the wet process S20, the crude zinc oxide dust is repulped to produce a slurry containing crude zinc oxide. Through this treatment, halogen impurities such as chlorine and cadmium contained in the crude zinc oxide dust are distributed in the treatment liquid. Then, the above slurry from which the impurities have been sufficiently removed is dehydrated by a vacuum suction type dehydrator or the like to produce a wet cake containing zinc oxide (crude zinc oxide cake).

[0027] <Dry heating process> The dry heating step S30 is a step of obtaining zinc oxide ore (calcined ore) by calcining the crude zinc oxide cake obtained in the wet step S20. The calcination process is carried out in a dry heating rotary kiln (DRK).

[0028] In the drying and heating step S30, the crude zinc oxide cake is charged into a DRK and calcined to further reduce the cadmium and fluorine concentrations, producing zinc oxide ore (calcined ore). The main feature of the production method of the present invention is that in the drying and heating step S30, a pellet-shaped "secondary raw material" having unique properties is charged into the DRK together with the crude zinc oxide cake. The properties of the "secondary raw material" unique to the present invention will be described in detail later.

[0029] The pellet-like "secondary raw material" is transported near the DRK using conveyor belts and other transport equipment, and then charged into the DRK together with the crude zinc oxide cake using a fixed-amount charging device such as a screw feeder.

[0030] Regarding the heating temperature in the drying and heating step S30, it is preferable to maintain the temperature of the ore burnt at 1100°C or higher and 1150°C or lower when it is discharged from the DRK. Here, the form of fluorine still remaining in the crude zinc oxide cake charged to the DRK is generally mostly lead chloride fluoride (PbFCl) and a part calcium difluoride (CaF2). Of these, PbFCl is almost entirely decomposed and volatilized by maintaining the temperature of the ore burnt within the above temperature range, and the chlorine and fluorine derived from PbFCl are almost entirely discharged to the exhaust gas treatment facility.

[0031] The moisture content of the crude zinc oxide cake to be treated in the drying and heating step S30 is generally 20% to 30% by weight. The general composition of this crude zinc oxide cake is 61% to 68% by weight of zinc, 7% to 10% by weight of lead, 0.3% to 0.9% by weight of chlorine, and 0.2% to 1.5% by weight of fluorine (all on a dry weight basis).

[0032] In the drying and heating step S30, the size of the zinc oxide ore discharged from the DRK is generally 1 mm or more and 6 mm or less, and its general composition is approximately 60 wt % to 70 wt % zinc, 3 wt % to 5 wt % lead, 0.5 wt % to 1.5 wt % chlorine, and 0.6 wt % or less fluorine (all on a dry weight basis).

[0033] <Secondary raw materials> In the manufacturing method of the present invention, the "secondary raw material" which is charged into the DRK where the drying and heating step S30 is performed together with the crude zinc oxide cake derived from the primary raw material is a "zinc-containing pellet" which is characterized in that it contains a predetermined amount or more of iron in addition to zinc and has a moisture content adjusted to a specific range.

[0034] The particle size distribution of the "zinc-containing pellets" used as the "secondary raw material" may be such that the ratio of particles having a particle diameter of 1 mm or more is 30% by weight or more, and more preferably the ratio of particles having a particle diameter of 4 mm or more is 30% by weight or more. The particle size of the "zinc-containing pellets" after granulation varies depending on the granulation time, and can be adjusted to the above range, for example, by appropriately optimizing the rotation speed of the agitator blades of the granulator. By maintaining the particle size distribution of the "zinc-containing pellets" within the above range, carryover can be suppressed, and dust generation from the conveyor of the conveying device during the conveyance of the fine powder-like crude zinc oxide powder can also be suppressed.

[0035] The moisture content of the "zinc-containing pellets" used as the "secondary raw material" may be 14% by weight or more and 19% by weight or less, and more preferably 16% by weight or more and 19% by weight or less. If the moisture content of the "zinc-containing pellets" is less than 14% by weight, the proportion of powder-like pellets increases, which leads to increased dust generation during transportation and carryover to the DRK. On the other hand, if the moisture content of the "zinc-containing pellets" exceeds 19% by weight, the pellets cannot be granulated due to the excess moisture and become sediment-like, which increases the amount of adhesion to the transport belt and the excavation hopper, making transportation difficult.

[0036] The "zinc-containing pellets" used as the "secondary raw material" are characterized in that, although zinc is the main component, the zinc content is less than 50% by weight and the iron content is more than 10% by weight. The zinc content of the "zinc-containing pellets" is preferably 35% by weight or more, and more preferably 40% by weight or more. The iron content is preferably more than 10% by weight and 30% by weight or less, and more preferably 12% by weight or more and 20% by weight or less.

[0037] As the zinc grade of the "zinc-containing pellets" used as the "secondary raw material" decreases, the zinc grade of the crude zinc oxide cinder obtained from DRK decreases, leading to a deterioration in the zinc recovery efficiency when obtaining zinc from the crude zinc oxide cinder. Therefore, materials with a zinc grade of 50% by weight or more have been widely used as the "secondary raw material" in the past. In contrast, according to the present invention, by maintaining the iron content at a predetermined amount or more, it is possible to suppress the carryover of materials, so that the zinc grade of the crude zinc oxide cinder can be maintained at 60% or more, as in the past, while using "secondary raw material" with a zinc grade of less than 50% by weight. In other words, according to the present invention, it has become possible to select "secondary raw material" with a lower zinc grade than before while maintaining the zinc recovery efficiency at a good level equivalent to that of the past.

[0038] As described above, in the production of zinc oxide ore, high-grade "crude zinc oxide fine powder" with a zinc content of 50% by weight or more has been used as the "secondary raw material" to be charged into the DRK that performs the drying and heating step S30. These "secondary raw materials" have been refined to reduce the content of iron, an impurity, as much as possible in order to increase the zinc content of the final product, zinc oxide ore. Powdered material with increased zinc content and no iron was pelletized to suppress carryover, but despite this, as described above, the production process was still forced to accept a "carryover rate" of more than 2%.

[0039] In contrast, the manufacturing method of the present invention is a novel process that requires intentionally leaving a certain amount of iron in the "secondary raw material" used in the manufacture of zinc oxide ore, which was previously considered to require refining to remove as much iron as possible. The inventors have newly discovered that when a powdered material used as the "secondary raw material" is pelletized, the carryover rate can be reduced if the powder contains a certain amount of iron.

[0040] The "zinc-containing pellets" having the above particle size distribution, moisture content, and iron content, which are essential for the manufacturing method of the present invention, can be obtained by granulating a powdered material whose main component is zinc, with a zinc content of less than 50% by weight and an iron content of more than 10% by weight. Although steel dust is suitable as the powdered material, the powdered material is not limited to steel dust as long as it satisfies the requirements of the present invention.

[0041] In the drying and heating step S30, the ratio of the "zinc-containing pellets" used as the "secondary raw material" to the material to be charged into the DRK is preferably 30% by weight or less. The "zinc-containing pellets" are put into the twin-screw conveyor together with the above-mentioned crude zinc oxide cake, and are extruded from there to be charged into the DRK. If the ratio of the "zinc-containing pellets" in the charged material increases, the pellets are crushed when extruded by the twin-screw conveyor, and some of them are crushed when charged into the DRK. For this reason, by suppressing the ratio of the "zinc-containing pellets" in the amount of processing in the DRK to 30% by weight or less, the crushing of the pellets can be sufficiently avoided, and the effect of reducing the carryover rate can be stably enjoyed.

[0042] In the manufacturing method of the present invention, a powder material having a chlorine content of 3% by weight or more can be used as the raw material of the "zinc-containing pellets" used as the "secondary raw material" in a range of 5% by weight or less. For example, when unrefined steel dust is used as the raw material of the "zinc-containing pellets", the chlorine content is often 4% by weight. If the amount of chlorine brought into the DRK increases, the risk of increase in carry-over due to promotion of chlorination volatilization of lead and the like in the DRK increases. However, by suppressing the ratio of the "zinc-containing pellets" in the processing amount in the DRK to 30% by weight or less, that is, by suppressing the chlorine content of the "zinc-containing pellets" used as the "secondary raw material" and the relative usage amount of the "zinc-containing pellets" in the total processing amount in the drying and heating step S30 within the above range, the merit of the present invention, which reduces the carry-over rate while maintaining the grade of zinc oxide ore, can be fully enjoyed.

[0043] Specifically, the "zinc-containing pellets" can be obtained by adding water to a powder material containing zinc and iron in the above content ratio range, kneading the powder material, and then granulating the material while applying shear force to form pellets. The amount of water added during granulation can be adjusted so that the moisture content after granulation is 14% by weight or more and 19% by weight or less. The above kneading and granulation can be carried out using a granulation facility consisting of, for example, a dow mixer and a dow pelletizer.

[0044] By using the "zinc-containing pellets" obtained in this way as the "secondary raw material", the carry-over rate when the "secondary raw material" consisting of powdered material is charged into the drying and heating process S30 can be reduced more than before. This also makes it possible to suppress clogging of the washing water piping in the washing tower that treats the exhaust gas of the DRK and the progression of adhesion to the exhaust gas duct.

[0045] According to the method for producing zinc oxide ore of the present invention, dust generation during transportation of the "secondary raw material" to the DRK and carryover at the DRK can be suppressed, and unrefined "secondary raw material" derived from steel dust can be directly charged to the DRK without passing through the reduction roasting kiln process or the wet process. This can reduce the consumption of the carbonaceous reducing agent used in the reduction roasting kiln and can also reduce the operating costs of electricity and the like used in each of these upstream processes. In addition, in the production method of the present invention, other "secondary raw materials" than the above-mentioned "zinc-containing pellets" may be added supplementarily within a range that does not impair the above-mentioned effects of the present invention. EXAMPLES

[0046] In a crude zinc oxide production plant capable of carrying out the overall process shown in FIG. 1, a test run of crude zinc oxide ore production by the production method of the present invention was carried out. The carryover rate of the raw material in the drying and heating process in the test run of each Example and Comparative Example was measured, and the state of dust generation during transport to the DRK was observed, thereby verifying the effect of the present invention. In each run, "zinc-containing pellets" obtained by pelletizing any of the powder materials of Powders 1 to 4 having the composition shown in Table 1 below were used as the "secondary raw material". The particle size distribution and moisture content of the "zinc-containing pellets" are shown in Table 2, and the measurement and observation results are shown in Table 3 below.

[0047] [Table 1]

[0048] [Example 1] The powder material (powder 1) was granulated using the granulation equipment consisting of the following variable speed twin-shaft kneader (Dow mixer) and variable speed twin-shaft granulator (Dow pelletizer) to obtain "zinc-containing pellets". The moisture content of the pellets after granulation was adjusted to 19% by weight. The rotation speeds of the above Dow mixer and Dow pelletizer were each 60Hz. The particle size distribution after granulation was 87% by weight for particles 4mm or larger. The above "zinc-containing pellets" were charged into the DRK. In addition, the processing amount of the "zinc-containing pellets" processed as secondary raw materials in the drying heating kiln was 40t / day, compared to the processing amount of 140t / day of crude zinc oxide cake produced from the primary raw material (steel dust) via the reduction roasting kiln. Unequal speed twin-shaft kneader: "Dow Mixer (registered trademark)" manufactured by Shin-Nichinan Co., Ltd. Non-uniform speed twin-shaft granulator: "Dow Pelletizer (registered trademark)" manufactured by Shin-Nichinan Co., Ltd.

[0049] [Comparative Example 1] A test run for producing crude zinc oxide ore was carried out under the same conditions as in Example 1, except that "Powder 3 (iron content: 9.0 wt%)" having a lower iron content than in Example 1 was used as the powder material.

[0050] [Example 2] Except for changing the final moisture content to 14% by weight, the procedure was the same as in Example 1. In the particle size distribution after granulation, the proportion of particles of 4 mm or more was 38% by weight.

[0051] [Comparative Example 2] A test run for producing crude zinc oxide ore was carried out under the same conditions as in Example 2, except that "Powder 3 (iron content: 9.0 wt%)" having a lower iron content than in Example 2 was used as the powder material.

[0052] [Example 3] The same procedure as in Example 1 was carried out except that "Powder 2 (zinc content: 38% by weight)" having a slightly lower zinc content was used as the powder material.

[0053] [Comparative Example 3] The same procedure was followed as in Example 1, except that the final moisture content was 20% by weight. Granulation was not possible due to the excess moisture, and the mixture became sediment-like, and the amount of the mixture adhering to the conveyor belt and the excavation hopper increased, making it difficult to convey the mixture and impossible to charge the mixture into the drying and heating kiln.

[0054] [Example 4] As the powder material, "Powder 4 (zinc content: 48 wt %, iron content: 11 wt %)" having a zinc content of less than 50 wt % and an iron content of more than 10 wt % was pelletized under the same conditions as in Comparative Example 1, and a test operation for producing crude zinc oxide ore was carried out under the same conditions as in Example 1 and Comparative Example 1.

[0055] [Comparative Example 4] The powder materials were charged into the DRK in powder form without granulation.

[0056] [Table 2]

[0057] [Table 3]

[0058] Comparison between Example 1 and Comparative Example 1, and comparison between Example 2 and Comparative Example 2, shows that the carryover of the "zinc-containing pellets" used as the secondary raw material can be reduced when the iron content is more than 10% by weight. Comparison between Example 4 and Comparative Example 1 also shows that the carryover can be reduced when the zinc content is less than 50% by weight, compared to when a material with a high zinc content is used. This is presumably due to an increase in impurities other than zinc, such as Fe, CaO, and SiO2, which increase the strength of the resulting zinc oxide cinder. Therefore, for example, it can be seen that steel dust with an iron content of about 12% by weight and a zinc content of less than 50% by weight can be used as a secondary raw material without refining to reduce the iron content, while maintaining product quality and productivity comparable to that of a powder material that has been refined to reduce the iron content and increase the zinc content.

[0059] From the above results, it can be seen that the manufacturing method of the present invention, in a zinc oxide ore manufacturing method which sequentially performs a reduction roasting process, a wet process, and a dry heating process, is a manufacturing method which can reduce the "carry-over rate" when a powdery raw material is directly charged into the dry heating process, and thus is a manufacturing method which can contribute to improving the productivity of zinc oxide cinder. [Explanation of symbols]

[0060] S10 Reduction roasting process S10 S20 Wet process S30 Drying and heating process

Claims

1. a reduction-roasting step of reducing and roasting a primary raw material containing zinc to reduce and volatilize the zinc contained in the primary raw material to obtain crude zinc oxide dust; a wet process for removing water-soluble impurities contained in the crude zinc oxide dust by wet treating the crude zinc oxide dust to obtain a crude zinc oxide cake; a drying and heating step of calcining the crude zinc oxide cake to obtain zinc oxide ore; A method for producing zinc oxide ore, comprising: In the dry heating step, a secondary raw material containing zinc and iron is charged into a dry heating rotary kiln together with the crude zinc oxide cake; The secondary raw material is a pellet containing moisture, and the moisture content is 14% by weight or more and 19% by weight or less relative to 100% by weight of the pellet. The pellet has an iron content of 12% by weight or more and a zinc content of 38% by weight or more and less than 50% by weight on a dry weight basis. How zinc oxide ore is produced.

2. The secondary raw material has an iron content of 17% by weight or more and 20% by weight or less on a dry weight basis in the pellets. A method for producing the zinc oxide ore according to claim 1.

3. The secondary raw material is a pellet having a particle size distribution in which the proportion of particles having a particle diameter of 4 mm or more is 30% by weight or more. A method for producing zinc oxide ore according to claim 1 or 2.

4. The secondary raw material is a pellet obtained by granulating powdered iron and steel dust. A method for producing zinc oxide ore according to any one of claims 1 to 3.

5. The secondary raw material has a chlorine content of 3% by weight or more, The ratio of the secondary raw material to the material to be treated charged into the dry heating rotary kiln in the dry heating step is 30% by weight or less. A method for producing zinc oxide ore according to any one of claims 1 to 4.

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