Method for producing calcined crude zinc oxide

Abstract

To improve productivity of coarse zinc oxide burnt ore by reducing a carry-over of an input in a dry heating process, in manufacture of the coarse zinc oxide burnt ore where fine powder of the coarse zinc oxide is used as an additional raw material.SOLUTION: A manufacturing method for coarse zinc oxide burnt ore comprises a step S30 for pretreating coarse zinc oxide fine powder where high-quality coarse zinc oxide fine powder is mixed with an exhaust gas dust precipitate obtained by drying an exhaust gas dust slurry to obtain a precipitate containing coarse zinc oxide fine powder; and a step S40 of dry-heating the coarse zinc oxide fine powder in a state where the coarse zinc oxide fine powder is contained in the coarse zinc oxide fine powder-containing precipitate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing crude zinc oxide sinter. More specifically, the present invention relates to a method for producing crude zinc oxide sinter when, in addition to raw materials with relatively low zinc grades such as steel dust, fine powder of crude zinc oxide with a higher zinc grade is used as an additional raw material.

Background Art

[0002] Steel dust generated from blast furnaces and electric furnaces in the steel industry contains a considerable amount of zinc and lead components in addition to iron oxide as its main component. Conventionally, the zinc and lead components in this steel dust have been recovered as crude zinc oxide sinter.

[0003] As a general method for producing this crude zinc oxide sinter, the crude zinc oxide dust obtained by a reduction roasting process (Waelz process) is subjected to removal of halogen components in a wet process, and a dehydrated cake containing zinc oxide obtained in the wet process (hereinafter referred to as "crude zinc oxide cake") is fired in a drying and heating rotary kiln (DRK) that performs a drying and heating process to obtain crude zinc oxide sinter. This method is widely used.

[0004] Here, in the above manufacturing process of crude zinc oxide sinter, in addition to the main raw materials such as steel dust, steel dust generated in a steelworks is further subjected to on-site treatment within the same site using a rotary hearth furnace or the like to obtain a powder raw material in the form of fine powder with a higher zinc grade, and this may be used as an additional raw material. In this specification, hereinafter, such a fine powder raw material containing zinc oxide is referred to as "crude zinc oxide fine powder". Generally, the crude zinc oxide fine powder derived from steel dust has an extremely small particle size with an average particle size (d50) of 2 μm or less on a number basis and a moisture content of generally 3% by weight or less.

[0005] One possible procedure for processing such crude zinc oxide fine powder is to repulp it together with crude zinc oxide dust in a wet process (P1 in Figure 1). However, with this procedure, the cohesiveness in the sedimentation separator after repulping is poor, and the sedimentation rate is extremely slow, so only very small amounts can be processed. Therefore, it was not possible to increase the slurry concentration at the inlet of the solid-liquid separator, i.e., the slurry extracted from the bottom of the sedimentation separator, and thus efficient processing could not be achieved.

[0006] On the other hand, the above-mentioned crude zinc oxide fine powder has a high zinc content and usually contains low levels of impurities such as chlorine and fluorine. Therefore, especially as long as the chlorine concentration is below a predetermined level, it is conceivable to follow a processing procedure (P2 in Figure 1) in which the crude zinc oxide cake that has undergone the wet process is directly added to the DRK (a dry heating and drying process) without going through the wet process. The crude zinc oxide raw materials, such as the crude zinc oxide cake, are usually added to the DRK using a general-purpose quantitative loading device such as a screw feeder (see Patent Document 1).

[0007] However, as mentioned above, the crude zinc oxide fine powder has an extremely small particle size and is dry, so it is difficult to completely mix the crude zinc oxide fine powder and the crude zinc oxide cake using only the general-purpose charging equipment described above. As a result, the crude zinc oxide cake and the dried crude zinc oxide fine powder are introduced into the DRK in a mixed state. Therefore, in conventional processes, the crude zinc oxide fine powder introduced into the DRK was carried away into the exhaust gas with a high carryover rate. In this specification, the "carryover rate" in the drying and heating process refers to the ratio of the weight of dust carried away into the DRK exhaust gas to the weight of all raw materials introduced into the drying and heating furnace such as the DRK, including the crude zinc oxide cake after the reduction roasting process and the crude zinc oxide fine powder.

[0008] When the carryover rate in the drying and heating process increased to 8% by weight or more, problems arose in the DRK exhaust gas treatment equipment, such as the adhesion and accumulation of dust in the exhaust gas flue and equipment due to the increased dust concentration in the DRK exhaust gas, and blockage of the cleaning fluid piping due to the increased slurry concentration of the cleaning fluid. This necessitated frequent shutdowns of the DRK, resulting in a decrease in the operating rate of the crude zinc oxide calcined ore production equipment. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2009-144213 [Overview of the project] [Problems that the invention aims to solve]

[0010] In view of the above circumstances, the present invention aims to improve the productivity of crude zinc oxide calcined ore by reducing the carryover rate of inputs in the drying and heating process when crude zinc oxide fine powder with a high zinc content is used as an additional raw material. [Means for solving the problem]

[0011] The inventors of the present invention have found that the above problem can be solved by adding crude zinc oxide fine powder to the DRK in a mixture with exhaust gas dust sediment separated from the DRK exhaust gas, and have completed the present invention. More specifically, the present invention provides the following.

[0012] (1) A method for producing crude zinc oxide calcined ore using a zinc-containing raw material and a crude zinc oxide fine powder having a higher zinc grade than the zinc-containing raw material, a chlorine concentration of less than 3%, a number-based average particle size (d50) of 2 μm or less, and a moisture content of 3% by mass or less as raw materials, comprising: a reduction roasting step to obtain crude zinc oxide dust by reducing and volatilizing the zinc contained in the zinc-containing raw material by reduction roasting; a wet step to obtain a crude zinc oxide cake by wet processing the crude zinc oxide dust to remove water-soluble impurities contained in the crude zinc oxide dust; and a rotary killer for drying and heating the raw materials comprising the crude zinc oxide cake and the crude zinc oxide fine powder. A method for producing zinc oxide calcined ore, comprising: a drying and heating step of obtaining crude zinc oxide calcined ore by introducing it into a rotary kiln and calcining it; an exhaust gas treatment step of separating zinc-containing exhaust gas dust from the exhaust gas discharged from the rotary kiln for drying and heating in the drying and heating step, and further recovering the exhaust gas dust as an exhaust gas dust slurry; and a crude zinc oxide fine powder pretreatment step of mixing the crude zinc oxide fine powder with exhaust gas dust sediment obtained by drying the exhaust gas dust slurry to obtain a crude zinc oxide fine powder-containing sediment, wherein the crude zinc oxide fine powder is introduced into the drying and heating step while being contained in the crude zinc oxide fine powder-containing sediment.

[0013] (2) The method for producing crude zinc oxide calcined ore according to (1), wherein the crude zinc oxide fine powder-containing precipitate has a moisture content of 14% by mass or more and 40% by mass or less.

[0014] (3) A method for producing crude zinc oxide calcined ore according to (1) or (2), wherein the chlorine content of the exhaust gas dust sediment on a dry weight basis is 2.0% or less.

[0015] (4) A method for producing crude zinc oxide calcined ore according to (1) or (2), wherein the zinc-containing raw material is steel dust. [Effects of the Invention]

[0016] According to the present invention, in the production of crude zinc oxide calcined ore using crude zinc oxide fine powder with a high zinc content as an additional raw material, the productivity of crude zinc oxide calcined ore can be increased by reducing the carryover of input materials in the drying and heating process. [Brief explanation of the drawing]

[0017] [Figure 1] This flowchart shows an example of an embodiment of the method for producing crude zinc oxide calcined ore according to the present invention. [Figure 2] This is a schematic cross-sectional view of a rotary kiln capable of suitably carrying out the method for producing crude zinc oxide calcined ore of the present invention. [Modes for carrying out the invention]

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

[0019] <Overall Process> The present invention provides a method for producing crude zinc oxide calcined ore, which is applicable when a crude zinc oxide calcined ore production plant using the Wertz process uses a process that combines primary raw materials such as steel dust with a crude zinc oxide fine powder with a higher zinc content to produce the crude zinc oxide calcined ore. As shown in Figure 1, the overall process carried out in a plant for producing crude zinc oxide calcined ore by the Wertz process includes: a reduction roasting step S10 in which primary raw materials such as steel dust are reduced and roasted to obtain crude zinc oxide dust; a wet step S20 in which chlorine, cadmium, etc. are separated and removed from the crude zinc oxide dust obtained in the reduction roasting step S10 to obtain crude zinc oxide cake; a drying and heating step S40 in which the raw materials, which include the crude zinc oxide cake and crude zinc oxide fine powder obtained in the wet step S20, are dried and heated to obtain crude zinc oxide calcined ore; an exhaust gas treatment step S50 in which exhaust gas dust is separated from the DRK exhaust gas discharged from the drying and heating step S40, and the separated exhaust gas dust is recovered as an exhaust gas dust slurry; and a wastewater treatment step S60 in which cadmium, etc. are separated from the wastewater discharged from the wet step S20.

[0020] In the method for producing crude zinc oxide sinter of the present invention, in the above overall process of producing crude zinc oxide sinter by the Waelz method, the crude zinc oxide fine powder pretreatment step S30, that is, the crude zinc oxide fine powder to be input into the drying and heating step S40 is preliminarily pretreated to be a mixture (crude zinc oxide fine powder-containing precipitate) with the exhaust gas dust precipitate obtained by drying the above exhaust gas dust slurry recovered in the exhaust gas treatment step S50 as a newly essential step. In the method for producing crude zinc oxide sinter of the present invention, the crude zinc oxide fine powder passes through this crude zinc oxide fine powder pretreatment step S30 and is put into the DRK for performing the drying and heating step S40 in a state of being contained in the crude zinc oxide fine powder-containing precipitate derived from the DRK exhaust gas.

[0021] In addition, the output of crude zinc oxide sinter in a production plant to which the method for producing crude zinc oxide sinter of the present invention can be preferably applied is generally about 6 t / h or more and 10 t / h or less, for example. Also, the general composition of the above steel dust that can be used as a raw material in the production method of the present invention is generally about 18% by weight or more and 45% by weight or less of zinc, 0.2% by weight or more and 3.5% by weight or less of lead, 10% by weight or more and 30% by weight or less of iron, 3% by weight or more and 10% by weight or less of chlorine, and 0.2% by weight or more and 2.0% by weight or less of fluorine (all based on the dry amount). In addition, a zinc content of 18% by weight or more and 45% by weight or less corresponds to a zinc oxide purity of generally 22% by weight or more and 57% by weight or less.

[0022] <Reduction roasting step> The reduction roasting step S10 is a step of reducing and volatilizing zinc contained in the zinc-containing raw material by reduction roasting to obtain crude zinc oxide dust. As a specific method for performing the reduction roasting step S10, it is common to adopt a reduction roasting method using a reduction roasting rotary kiln (RRK). Also, steel dust is widely used as the primary raw material input into the RRK. The steel dust is continuously charged into the RRK together with a carbonaceous reducing agent such as coke and limestone. Inside the RRK body, the maximum temperature of the object to be treated is controlled to be about 1100 °C or higher and 1200 °C or lower by the combustion of heavy oil and the combustion of the charged carbonaceous reducing agent. In this RRK body, the steel dust is reduction roasted, and the volatilized metallic zinc is re-oxidized in the exhaust gas to become powdery zinc oxide. Regarding the small amount of lead contained in the steel dust, it volatilizes as lead oxide. The powdery zinc oxide and lead oxide, etc. are introduced into a dust collector together with the exhaust gas from the RRK, collected, and recovered as crude zinc oxide dust. This crude zinc oxide dust generally contains halogen impurities such as chlorine at about 8% or more and 20% or less.

[0023] <Wet process> The wet process S20 is a wet treatment step of extracting water-soluble impurities such as the above-mentioned halogen impurities contained in the crude zinc oxide dust recovered through the reduction roasting step S10 into a treatment liquid, and further separating the impurities from the crude zinc oxide dust by solid-liquid separation treatment. In the wet process S20, the crude zinc oxide dust is repulped to form a slurry containing crude zinc oxide. By this treatment, mainly halogen impurities such as chlorine and cadmium contained in the crude zinc oxide dust are distributed into the treatment liquid. And in this state, the treatment liquid in which the impurities are distributed is separated by solid-liquid separation to obtain a discharge liquid. Regarding the dehydration treatment for solid-liquid separation, a gravity sedimentation type slurry concentration device such as a thickener or a dehydration device such as a vacuum dehydrator is used. Then, the above-mentioned slurry from which the impurities have been sufficiently removed is dehydrated by a vacuum dehydrator or the like to obtain a crude zinc oxide cake containing zinc oxide. The crude zinc oxide cake is put into the drying and heating step S40 together with the crude zinc oxide fine powder that has been pretreated in the manner to be described in detail below in the crude zinc oxide fine powder pretreatment step S30.

[0024] <Pretreatment process for crude zinc oxide fine powder> The crude zinc oxide fine powder pretreatment step S30 is a step in which the crude zinc oxide fine powder, to be used as an additional raw material, is treated in advance to become a mixture with properties that make it less prone to carryover before being introduced into the drying and heating step S40. Specifically, this treatment is carried out as a step in which crude zinc oxide fine powder is mixed with exhaust gas dust precipitate obtained by drying the exhaust gas dust slurry derived from DRK exhaust gas recovered in the exhaust gas treatment step S50, thereby obtaining a precipitate containing crude zinc oxide fine powder.

[0025] The aforementioned "property of being less prone to carryover" means that, in addition to the crude zinc oxide fine powder containing sediment being within a specific moisture content range, there is also a very small amount of crude zinc oxide fine powder remaining in the sediment in the form of so-called "clumps." In this specification, "clumps" refers to a state in which unconditioned dry fine powder is unevenly present. More specifically, it refers to a state in which dry fine powder is enclosed within the crude zinc oxide fine powder containing sediment. In the manufacturing method of the present invention, the crude zinc oxide fine powder can be mixed in such a way that it is uniformly dispersed in the exhaust gas dust sediment, thereby giving the obtained crude zinc oxide fine powder containing sediment such "property of being less prone to carryover."

[0026] The means by which the crude zinc oxide fine powder is uniformly dispersed in the aforementioned exhaust gas dust sediment is not limited to any particular method, but as an example, it can be done by a betting process, which will be described in detail in the examples.

[0027] Furthermore, the exhaust gas dust sediment described above is obtained by sedimentation separation of dust recovered as slurry from the DRK exhaust gas discharged from the drying and heating process S40 in a washing tower, wet electrostatic precipitator, etc., installed in the exhaust gas treatment process S50, and then drying it to form sediment. The drying method for converting the exhaust gas dust slurry into exhaust gas dust sediment is not particularly limited, but one example is sun drying. The moisture content of the exhaust gas dust sediment after drying is preferably 40% to 60% from the viewpoint of facilitating uniform mixing with the crude zinc oxide fine powder and being a moisture content that can be easily achieved without using a dewatering machine. Alternatively, if it is possible to use dewatering equipment, a belt-type dewatering machine may be used to achieve a moisture content of 20% to 30%.

[0028] The exhaust gas dust sediment obtained in this manner has a chlorine content of at most 2% and usually 1% or less on a dry weight basis, because chlorine is extracted to the water side during each of the wet treatments performed in the exhaust gas treatment process S50. When crude zinc oxide fine powder is introduced into the DRK alone, it tends to carry over in large quantities. By mixing it with exhaust gas dust sediment in this way, which has a sufficiently reduced chlorine content, the carryover due to chlorine volatilization of the zinc component contained in the crude zinc oxide fine powder can be significantly suppressed. In the method for producing crude zinc oxide calcined ore of the present invention, the crude zinc oxide fine powder is introduced into the drying and heating process S40 while contained in the crude zinc oxide fine powder-containing sediment having such "carryover-resistant properties". The composition of the exhaust gas dust sediment is usually 20% to 50% zinc and 0.1% or less cadmium.

[0029] [Coarse zinc oxide fine powder] Here, the crude zinc oxide fine powder that is the target of processing in the manufacturing method of the present invention is a fine powder raw material with a higher zinc content than the zinc-containing raw material, which is the primary raw material introduced into the reduction roasting step S10 in the manufacturing method, and with a chlorine concentration of less than 3%. Preferably, the zinc content of this crude zinc oxide fine powder is 50% by weight or more on a dry weight basis. Furthermore, the number-based average particle size (d50) of this crude zinc oxide fine powder is 2 μm or less, and the moisture content is 3% by weight or less. For example, fine powder crude zinc oxide dust of the type generated by on-site processing of steel dust generated at a steelworks using a rotary hearth furnace or the like broadly falls under this category and is commonly used as a secondary raw material in the production of crude zinc oxide calcined ore. The particle size of the above fine powder is a value that can be measured by laser analysis and scattering method.

[0030] Furthermore, the composition of the crude zinc oxide fine powder derived from the aforementioned steel dust is generally about 52% by weight of zinc, 4% by weight of lead, 12% by weight of iron, 2% by weight of chlorine, and 0.5% by weight of fluorine (all based on dry weight). A zinc content of 52% by weight is roughly equivalent to a zinc oxide purity of 65% by weight.

[0031] [Precipitate containing finely ground crude zinc oxide powder] In the manufacturing method of the present invention, by using the above-mentioned crude zinc oxide fine powder as a crude zinc oxide fine powder-containing precipitate having the "properties of being less prone to carryover" as described above, the carryover rate of the crude zinc oxide fine powder introduced into the drying and heating process can be significantly reduced. The crude zinc oxide fine powder-containing precipitate obtained by the crude zinc oxide fine powder pretreatment step in the manufacturing method of the present invention has a moisture content of 14% by weight or more and 40% by weight or less, preferably 14% by weight or more and 30% by weight or less. If the moisture content of the crude zinc oxide fine powder-containing precipitate is less than 14% by weight, the proportion of pellets containing unconditioned dry fine powder, so-called "clumps," increases. After the crude zinc oxide fine powder-containing precipitate in the "clump" state is charged into the DRK, it cracks as the crude zinc oxide fine powder-containing precipitate dries, and when the "clumps" appear, they scatter, increasing the carryover rate in the DRK. In addition, when the crude zinc oxide fine powder-containing precipitate is transported, "clumps" may appear due to impacts from dropping during transfer between conveyors constituting the transport device, causing dust generation. On the other hand, if the moisture content of the crude zinc oxide fine powder-containing precipitate exceeds 40% by weight, the proportion of cake-like or paste-like material increases due to the excess moisture, leading to increased adhesion to the conveying equipment and causing the hopper to become stiff, making conveying difficult. Furthermore, if the moisture content of the crude zinc oxide fine powder-containing precipitate exceeds 30% by weight, the heavy oil consumption in the drying and heating process increases, so it is preferable that the moisture content be 30% by weight or less.

[0032] In the conventional overall process for manufacturing crude zinc oxide calcined ore, the crude zinc oxide fine powder is either introduced into a wet process (P1), or, in many cases, directly introduced into the DRK where the drying and heating process S40 is performed together with the crude zinc oxide cake obtained in the wet process S20 (P2). As described above, in the former case (P1), the problem of reduced productivity arises mainly due to the low processing efficiency of the wet process, and in the latter case (P2), mainly due to the high carryover rate. In the manufacturing method of the present invention, the problems in both cases can be solved by performing a pretreatment to make the crude zinc oxide fine powder-containing precipitate with "properties that are less prone to carryover" prior to introducing the crude zinc oxide fine powder into the drying and heating process S40.

[0033] <Dry heating process> The drying and heating step S40 is a process in which crude zinc oxide cake and crude zinc oxide fine powder-containing sediment are charged into a rotary kiln (DRK) for drying and heating and calcined to further reduce the cadmium and chlorine concentrations and obtain crude zinc oxide calcined ore.

[0034] In the drying and heating process S40, it is preferable to maintain the heating temperature so that the temperature of the calcined ore discharged from the DRK is between 900°C and 1250°C.

[0035] The moisture content of the crude zinc oxide cake to be processed in this drying and heating process S40 is generally 20% to 30% by mass. The general composition of this crude zinc oxide cake is 60% to 70% by mass of zinc, 3% to 10% by mass of lead, 0.3% to 2.0% by mass of chlorine, and 0.2% to 1.5% by mass of fluorine (all based on dry weight). This crude zinc oxide cake, along with the precipitate containing crude zinc oxide fine powder, is fed into the DRK by a quantitative loading device such as a screw feeder.

[0036] The crude zinc oxide cake and the precipitate containing crude zinc oxide fine powder that are fed into the DRK are dried, heated, and calcined at the discharge end.

[0037] Furthermore, the exhaust gas generated by the DRK is drawn in from the charging end, removed by passing through a wet exhaust gas cleaning system and a wet electrostatic precipitator, and then discharged through an exhaust fan or similar device from the chimney.

[0038] In the drying and heating process S40, the size of the crude zinc oxide calcined ore discharged from DRK is generally between 1 mm and 6 mm, and its typical composition is approximately 60% to 70% by mass of zinc, 3% to 5% by mass of lead, 0.5% to 1.5% by mass of chlorine, and 0.6% by mass or less of fluorine (all based on dry weight).

[0039] [Rotary Kiln] A rotary kiln 1, as shown in Figure 2, can be used as the DRK for the drying and heating process S40. The rotary kiln 1 is a rotary heating furnace comprising a kiln body 10 which is a cylindrical kettle with fire resistance, a conveying device 20 which is a means for conveying crude zinc oxide cake and crude zinc oxide fine powder-containing sediment, a burner section 30 which is a heating device provided near the discharge port 12 side of the kiln body 10 and serves as the heat source for the rotary kiln 1, a drive gear 40 which transmits rotational force in the R direction in the figure to the kiln body 10, a fixed hood 50 which prevents the diffusion of exhaust gas discharged from the kiln body 10, and a kiln support section (not shown) which supports the kiln body 10.

[0040] The rotary kiln 1, having the above configuration, heats the inside of the kiln body 10 to a high temperature of approximately 900°C to 1250°C by the burner section 30, and rotates the kiln body 10 in the R direction by the drive gear 40. The conveying device 20 then continuously feeds the drying and heating process input material 2, which is a mixture of crude zinc oxide cake and crude zinc oxide fine powder-containing sediment, from the input port 11 in the direction a shown in Figure 1. The drying and heating process input material 2, consisting of crude zinc oxide cake and crude zinc oxide fine powder-containing sediment, moves through the inside of the kiln body 10 toward the discharge port 12 while being stirred and fired along the incline of the kiln body 10, and is discharged from the discharge port 12 as a high-temperature fired material in the direction b.

[0041] The conveying device 20 is a device that conveys and loads the crude zinc oxide cake to be fed into the kiln body 10, and is inserted into the kiln from the rear side of the kiln body 10. The conveying device 20 is not particularly limited, but as an example, a twin-screw conveyor with uneven speed that exhibits excellent stirring power, especially during the conveying of the crude zinc oxide cake, can be preferably used. Unlike belt conveyors and conventionally known general screw conveyors, the twin-screw conveyor with uneven speed has two rotating shafts. As a result, subtle phase changes occur, and the conveying material is scraped off by the mixing blades. As a result, the twin-screw conveyor with uneven speed can smoothly convey the raw material 2 for the drying and heating process, which includes the highly adhesive crude zinc oxide cake, without clogging, while self-cleaning.

[0042] The temperature of the calcined zinc oxide discharged from the rotary kiln is continuously measured and monitored using an infrared thermometer. The calcination temperature is maintained within the range of 900°C to 1250°C for the calcined zinc oxide.

[0043] <Exhaust gas treatment process> The exhaust gas treatment process S50 is a process in which zinc-containing exhaust gas dust is separated from the exhaust gas discharged from the DRK in the drying and heating process S40, and the exhaust gas dust is further recovered as an exhaust gas dust slurry.

[0044] In conventional processes for producing crude zinc oxide calcined ore, the DRK exhaust gas dust separated and recovered in the exhaust gas treatment process S50 is repeatedly circulated as a slurry containing zinc oxide to the wet process S20, which is an upstream process of the drying and heating process S40, in order to effectively utilize metal resources. In the production of crude zinc oxide calcined ore of the present invention, as described above, the chlorine concentration (on a dry weight basis) of this exhaust gas dust slurry is at most 2% or less, and in many cases at a low concentration of 1% or less. By mixing this appropriately dried sediment with crude zinc oxide fine powder and introducing it into the DRK, the effective utilization of metal resources within the processing system is promoted while reducing the carryover of crude zinc oxide fine powder in the drying and heating process S40.

[0045] <Wastewater Treatment Process> The wastewater treatment process S60 involves removing cadmium from the wastewater containing high concentrations of chlorine and cadmium, which was separated from the crude zinc oxide dust in the wet process S20. Furthermore, it involves neutralizing trace amounts of heavy metals contained in the wastewater to form precipitates, and finally adjusting the pH to produce harmless wastewater.

[0046] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferred effects arising from the present invention, and the effects of the present invention are not limited to the above embodiments. [Examples]

[0047] In a crude zinc oxide calcined ore production plant capable of carrying out the overall process shown in Figure 1, test operations were conducted to produce crude zinc oxide calcined ore using the manufacturing method of the present invention. The effectiveness of the present invention was verified by measuring the carryover rate of raw materials in the drying and heating process during the test operations of the examples and comparative examples, and by observing the state of dust generation during transport to the DRK. In all operations, steel dust and crude zinc oxide fine powder with the compositions shown in Table 1 below were used as raw materials. The compositions of the crude zinc oxide cake to be processed in the drying and heating process, and the exhaust gas dust sediment mixed with the crude zinc oxide fine powder in the crude zinc oxide fine powder pretreatment process are also shown in Table 1.

[0048] [Table 1]

[0049] [Examples] (Pretreatment process for crude zinc oxide fine powder) Crude zinc oxide fine powder to be introduced into the DRK was mixed with exhaust gas dust sediment obtained by drying the exhaust gas dust slurry recovered in the exhaust gas treatment process to obtain a sediment containing crude zinc oxide fine powder. Specifically, using a shovel loader, 2 tons of exhaust gas dust sediment with a moisture content of 50% was laid in a 100 mm high layer on the field, and then 2 tons of crude zinc oxide fine powder was laid on top of this layer in a 100 mm high layer. After that, these two layers were scooped up with a shovel loader and dropped onto the field to invert them. This process (betting process) was repeated until the crude zinc oxide fine powder was uniformly mixed into the matrix of exhaust gas dust sediment. The moisture content of the crude zinc oxide fine powder-containing sediment obtained in this way was 26%. (dry heating process) The precipitate containing the crude zinc oxide powder obtained in the crude zinc oxide powder pretreatment process described above was added to a DRK (Digital Routing Tank) that produces 7-8 t / h of crude zinc oxide calcined ore at a processing rate of 2-4 t / h, with the crude zinc oxide powder processing rate being 1-2 t / h.

[0050] [Comparative Example] (Pretreatment process for crude zinc oxide fine powder) Without performing a pretreatment step for the crude zinc oxide fine powder, the crude zinc oxide fine powder was added directly to the DRK (procedure P2 in Figure 1). (dry heating process) The drying and heating process was carried out under the same conditions as in the examples.

[0051] [Table 2]

[0052] From the above results, it can be seen that the manufacturing method of the present invention, in the production of crude zinc oxide calcined ore, is a method that significantly reduces the carryover rate when crude zinc oxide fine powder is added to the DRK, which is a secondary raw material with a high zinc content, by performing a pretreatment step of crude zinc oxide fine powder, which is a unique step of the present invention, before adding it to the DRK, which is a drying and heating process. This allows for the effective reuse of intermediates containing zinc in the system, and thus the manufacturing method can significantly contribute to improving the productivity of zinc oxide calcined ore. [Explanation of symbols]

[0053] S10 Reduction Roasting Process S20 Wet process S30 Pretreatment process for crude zinc oxide fine powder S40 Drying and heating process S50 Exhaust gas treatment process S60 Wastewater Treatment Process 1. Rotary Kiln 2 Raw materials input to the drying and heating process 10 Kiln body 11 Inlet 12 Outlet 20 Conveying device 30 burner section 40 Drive gear 50 Fixed Hood

Claims

1. A method for producing crude zinc oxide calcined ore, using a zinc-containing raw material and a crude zinc oxide fine powder having a higher zinc grade than the zinc-containing raw material, a chlorine concentration of less than 3%, a number-based average particle size (d50) of 2 μm or less, and a moisture content of 3% by mass or less, as raw materials, A reduction roasting step is performed to reduce and volatilize the zinc contained in the zinc-containing raw material by reduction roasting the zinc-containing raw material to obtain crude zinc oxide dust. A wet process to obtain a crude zinc oxide cake by wet-treating the crude zinc oxide dust to remove water-soluble impurities contained in the crude zinc oxide dust, A drying and heating step to obtain calcined zinc oxide by placing the raw materials, which include the crude zinc oxide cake and the crude zinc oxide fine powder, into a rotary kiln for drying and heating and firing them, In the drying and heating step, a process is performed to separate zinc-containing exhaust gas dust from the exhaust gas discharged from the rotary kiln for drying and heating, and further to recover the exhaust gas dust as an exhaust gas dust slurry. The system includes a crude zinc oxide powder pretreatment step, in which the crude zinc oxide powder is mixed with exhaust gas dust sediment obtained by drying the exhaust gas dust slurry to obtain a crude zinc oxide powder-containing sediment. The crude zinc oxide fine powder is introduced into the drying and heating step while contained in the crude zinc oxide fine powder-containing sediment having a moisture content of 14% by mass or more and 40% by mass or less. A method for producing calcined crude zinc oxide.

2. The chlorine content of the exhaust gas dust sediment on a dry weight basis is 2.0% or less. A method for producing crude zinc oxide calcined ore according to claim 1.

3. The zinc-containing raw material is steel dust, A method for producing crude zinc oxide calcined ore according to claim 1 or 2.

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