Method for producing zinc oxide ore

Abstract

To produce a high-quality zinc oxide ore with sufficiently reduced fluorine concentration, while suppressing a thermal load to a drying furnace due to high temperature operation, in a process of producing a zinc oxide ore from a raw material ore containing fluorine.SOLUTION: A method for producing zinc oxide ore is provided, which includes a raw material ore preparation step S10 for obtaining a raw material ore for a reduction roasting step and regulated to a predetermined ratio of a fluorine content, a reduction roasting step S20, a wet step S30, and a drying and heating step S40. In the raw material ore preparation step S10, more than or equal to 30 mass% of the raw material ore for the reduction roasting process is mixed with a carbonaceous reducing agent and pelletized. In the drying and heating step S40, drying and heating treatment is carried out at a heating temperature of 800°C to 1000°C, and a drying and heating treatment time is adjusted according to a fluoride content ratio of the raw material ore for the reduction roasting process, thereby maintaining a fluoride grade of the zinc oxide ore at 0.050 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, zinc oxide ore obtained by separating and removing impurities from zinc-containing ores such as crude zinc oxide has been widely used as a raw material for zinc ingots in zinc smelters.

[0003] Crude zinc oxide can be obtained, for example, from steel dust generated in steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry through a reducing roasting process. From the viewpoint of promoting resource recycling, it is desirable to reuse the steel dust as a zinc raw material, but on the other hand, the steel dust contains halogens such as fluorine as impurities in addition to iron and zinc.

[0004] There are two types of smelting methods, ISP smelting and electrolytic smelting, in which the final product, zinc oxide ore, is used as a raw material for zinc smelting. Of these, in particular, for zinc oxide ore for electrolytic smelting, which is used as a raw material for the electrolytic smelting method, the fluorine concentration of the zinc oxide ore must be reduced to an extremely low level of 0.050 mass% or less in order to suppress the progression of corrosion of the aluminum permanent cathode used in the electrowinning process (see Patent Document 1).

[0005] In the process of producing zinc oxide ore from iron and steel dust, the zinc in the iron and steel dust volatilizes as metallic zinc in the rotary kiln furnace where the reduction roasting process is carried out, and is then solidified as zinc oxide. This is then collected by a dust collector such as an electrostatic precipitator as particulate crude zinc oxide (crude zinc oxide dust) mixed with halogens, unreacted iron and steel dust carried over from the rotary kiln, and valuable metals that behave in a similar manner to zinc.

[0006] Treatments for separating and removing halogens from crude zinc oxide dust separated and recovered from iron and steel dust by the reducing roasting treatment include an alkali washing method (wet treatment) and a method of decomposing in a dry heating furnace such as a rotary kiln (dry heat treatment). However, because the refining principles of chlorine and fluorine are essentially different and crude zinc oxide dust also contains unreacted iron and steel dust, in the process for producing zinc oxide ore from iron and steel dust, a treatment for separating and removing halogens from crude zinc oxide dust is generally carried out by a combination of both of these methods, i.e., a wet treatment and a dry heat treatment.

[0007] Here, as described above, it is necessary to set the fluorine concentration of zinc oxide ore used as a raw material in the electrolytic smelting process to 0.050 mass% or less. In order to separate and remove fluorine with such high accuracy, the above-mentioned dry heat treatment needs to be carried out at least at 1100°C or more (see Patent Document 1).

[0008] However, if the temperature inside a drying and heating furnace such as a rotary kiln is raised to such a temperature range, energy costs increase. In addition, the increased heat load on the equipment due to high-temperature operation is a factor that shortens the lifespan of equipment such as a rotary kiln.

[0009] To address this problem, a method for producing zinc oxide ore has been developed in which a raw material ore preparation step is carried out in a preparation stage to obtain raw material ore for the reducing roasting step in which the fluorine content ratio is adjusted to a predetermined ratio, and the dry heat treatment time is adjusted according to the fluorine content ratio of the raw material ore for the reducing roasting step thus obtained, thereby making it possible to obtain zinc oxide ore with an extremely low fluoride concentration while performing the dry heat treatment in the dry heat treatment step at a heating temperature of 1000°C or more and 1100°C or less (see Patent Document 2).

[0010] However, even in the production method disclosed in Patent Document 2, when the temperature inside a drying / heating furnace such as a rotary kiln is raised to a temperature range of about 1100°C as described above, the above-mentioned disadvantages associated with high-temperature operation of the drying / heating furnace still remain to be accepted to a certain extent. In particular, at zinc oxide ore production sites where zinc oxide ore for electrolytic smelting is obtained from iron and steel dust, further improvements have been required in the method of removing halogens from crude zinc oxide dust that has been subjected to a reduction treatment. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2014-62304 A [Patent Document 2] JP 2022-103730 A Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to produce high-quality zinc oxide ore in which the fluorine concentration is sufficiently reduced to an extent that it can be used as a raw material for electrolytic smelting, while suppressing the heat load on a drying and heating furnace due to high-temperature operation, in a process for producing zinc oxide ore from fluorine-containing raw material ore such as iron and steel dust. [Means for solving the problem]

[0013] The present inventors have come up with the idea of ​​producing high-quality zinc oxide ore with a sufficiently reduced fluorine concentration while suppressing the heat load on a drying / heating furnace more than in the conventional method, by providing a raw ore preparation step of obtaining a raw ore for a reduction / roasting step in which the fluorine content ratio is optimized to a predetermined ratio as an essential step in a process for producing zinc oxide ore from a raw ore containing fluorine such as steel dust, and further pelletizing a certain proportion of the raw ore for the reduction / roasting step together with a carbonaceous reducing agent before feeding the raw ore into the reduction / roasting step, and have thus completed the present invention. More specifically, the present invention provides the following.

[0014] (1) A method for producing zinc oxide ore from a raw ore containing fluorine, comprising the steps of: preparing a raw ore for a reduction roasting step, the raw ore having a fluorine content ratio adjusted to a predetermined ratio by mixing a plurality of raw ores having different fluorine content ratios, which is the ratio of the fluorine content ratio to the zinc content ratio, or by selecting a raw ore having a fluorine content ratio adjusted to a predetermined ratio; subjecting the raw ore for the reduction roasting step to a reduction roasting treatment to obtain crude zinc oxide dust; and subjecting the crude zinc oxide dust to a wet treatment for removing water-soluble impurities to obtain crude zinc oxide. and a dry heating step of obtaining the zinc oxide ore by subjecting the crude zinc oxide cake to a dry heating treatment, wherein in the raw ore preparation step, 30 mass% or more of the raw ore for the reduction roasting step is mixed with a carbonaceous reducing agent and pelletized, and in the dry heating step, the dry heating treatment is performed at a heating temperature of 800°C or more and 1000°C or less, and the dry heating treatment time is adjusted in accordance with the fluorine content ratio of the raw ore for the reduction roasting step, thereby maintaining the fluorine content of the zinc oxide ore at 0.050 mass% or less.

[0015] (2) The method for producing zinc oxide ore described in (1), wherein in the raw ore preparation step, a plurality of types of raw ores having different fluorine content ratios are mixed to adjust the fluorine content ratio to the predetermined ratio, thereby obtaining a raw ore for the reduction roasting step.

[0016] (3) The method for producing zinc oxide ore according to (1) or (2), wherein the raw material ore is iron ore dust.

[0017] (4) A method for producing zinc oxide ore according to (1) or (2), in which the fluorine content ratio of the raw ore for the reduction roasting process is set to 0.015 or less in the raw ore preparation process, thereby setting the dry heat treatment time in the dry heat process to 100 minutes or more and 130 minutes or less.

[0018] (5) The method for producing zinc oxide ore according to (1) or (2), wherein the crude zinc oxide cake obtained in the wet process has a moisture content of 30% or less. Effect of the Invention

[0019] According to the present invention, in a process for producing zinc oxide ore from a raw material ore containing fluorine, it is possible to produce high-quality zinc oxide ore having a sufficiently reduced fluorine concentration while suppressing the heat load on a drying and heating furnace due to high-temperature operation. The zinc oxide ore obtained by the production method of the present invention can be used as a raw material for electrolytic smelting, and the industrial value of the production method of the present invention is extremely great. [Brief description of the drawings]

[0020] [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

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The present invention is a manufacturing method that can be widely applied when manufacturing zinc oxide ore using a raw material ore containing fluorine as an impurity in addition to zinc. The raw material ore containing fluorine as an impurity is not limited to a specific raw material ore, but a typical example is the above-mentioned iron and steel dust.

[0022] <Overall process> Fig. 1 shows the flow of the entire process of zinc oxide ore production to which the method for producing zinc oxide ore of the present invention can be applied. As shown in Fig. 1, this entire process includes a raw ore preparation step S10 for obtaining a "raw ore for the reduction roasting step" in which a "fluorine content ratio" that is the ratio of the fluorine content to the zinc content in the raw ore is optimized, a reduction roasting step S20 for obtaining crude zinc oxide dust by reduction roasting this "raw ore for the reduction roasting step", a wet process S30 for separating and removing halogen elements such as fluorine and chlorine from the crude zinc oxide dust obtained in the reduction roasting step S20 into a treatment liquid to obtain a crude zinc oxide cake, a dry heating step S40 for drying and heating the crude zinc oxide cake obtained in the wet process S30 to obtain zinc oxide ore, an exhaust gas dust cleaning step S50 for cleaning the exhaust gas dust generated in the dry heating step S40 to obtain a cleaned exhaust gas dust cake, and a wastewater treatment step S60 for detoxifying the discharged liquid discharged from the wet process S30.

[0023] The method for producing zinc oxide ore of the present invention is a method in which the minimum essential steps in the overall process for producing zinc oxide ore are the raw ore preparation step S10, the reduction roasting step S20, the wet step S30, and the dry heating step S40. The exhaust gas dust cleaning step S50 and the wastewater treatment step S60 may be performed according to conventional methods in a required manner as necessary.

[0024] The method for producing zinc oxide ore of the present invention is a method for producing zinc oxide ore using a raw ore containing fluorine, and is mainly characterized by making it possible to maintain the fluorine content of the zinc oxide ore at 0.050 mass% or less, while lowering the dry heating treatment temperature in the dry heating step S40 to a temperature range of 1000°C or less, which is lower than conventional temperatures.

[0025] In addition, the manufacturing method of the present invention is characterized in that the raw ore preparation step S10 is an essential step preceding the reduction roasting step S20 as the most upstream step in the overall process of zinc oxide ore production, in which complex chemical changes occur in stages over multiple stages, and therefore it is possible to control the quality of the final product, zinc oxide ore, with high precision simply by adjusting the operating conditions in the drying and heating step S40, which is the most downstream step.

[0026] The method for producing zinc oxide ore according to the present invention, which has the above-mentioned characteristics, is intended to be carried out in a zinc oxide ore production plant in which a plurality of types of iron and steel dust with different "fluorine content ratios" are sequentially carried in as raw materials. More specifically, the method for producing zinc oxide ore according to the present invention is a method that can be suitably carried out in a zinc oxide ore production plant in which a plurality of types of iron and steel dust to be actually used in each operation period are sequentially selected from the plurality of types of iron and steel dust sequentially carried in and used as raw materials. The above-mentioned condition of iron and steel dust carrying in is not a special condition in the production of zinc oxide ore using iron and steel dust as raw materials, but is also a very common supply mode of raw materials. Therefore, the production method according to the present invention is a process that has sufficient practicality and versatility.

[0027] <Raw ore preparation process> The raw ore preparation step S10 is a step of obtaining raw ore for the reducing roasting step, the fluorine content ratio of which is adjusted to a predetermined ratio, and further mixing 30 mass% or more of the raw ore for the reducing roasting step thus obtained with a carbonaceous reducing agent to form pellets. Note that the "fluorine content ratio" in this specification refers to the ratio of the fluorine grade to the zinc grade in the raw ore.

[0028] In the raw ore preparation step S10, in order to obtain a raw ore for the reducing roasting step in which the "fluorine content ratio" has been adjusted to a predetermined ratio, for example, when multiple types of raw ores having different "fluorine content ratios" are used as described above, the above adjustment can be performed by mixing them in an optimal ratio. Alternatively, by selecting one type of raw ore whose "fluorine content ratio" is the same as or sufficiently close to the predetermined ratio, the selected raw ore can be used as the raw ore for the reducing roasting step.

[0029] The predetermined ratio of the "fluorine content ratio" is determined within a range in which the fluorine content of the zinc oxide ore can be maintained at 0.050 mass% or less by performing the dry heating process in the dry heating step S40 at a heating temperature of 1000°C or less and adjusting the dry heating process time according to the heating temperature and the "fluorine content ratio" of the raw ore for the reduction roasting process. For example, as disclosed later as an example, even when the above heating temperature in the dry heating step S40 is 1000°C, the "fluorine content ratio" is adjusted to a predetermined ratio (e.g., about 0.005), unlike the conventional process, so that the fluorine content of the zinc oxide ore can be reliably maintained at 0.050 mass% or less with the minimum dry heating process time.

[0030] When iron ore dust is used as the raw ore, the "fluorine content ratio" can be adjusted by, for example, investigating in advance the "fluorine content ratios" of multiple brands of steel dust supplied by an electric furnace manufacturer, and mixing these brands of steel dust in a desired ratio. The "fluorine content ratios" of steel dust supplied by an electric furnace manufacturer vary from brand to brand, and there are steel dusts with various fluorine grades, for example, from steel dusts with low fluorine grades having a "fluorine content ratio" of about 0.002 to steel dusts with high fluorine grades having a "fluorine content ratio" of about 0.07. In the production method of the present invention, a mixture of steel dusts with different fluorine grades is used, and therefore, only one specific brand of steel dust is not consumed, and these steel dusts can be consumed in a planned manner.

[0031] Here, Table 1 shows an example of the results of measuring the fluorine content and iron content in the crude zinc oxide dust collected by a gravity settling dust collector and the fluorine content and iron content in the crude zinc oxide dust collected by an electric dust collector downstream of the gravity settling dust collector, in the case where the reduction roasting step S20 is carried out by a conventional zinc oxide ore manufacturing method not carrying out the raw ore preparation step S10. Usually, the crude zinc oxide dust discharged from the reduction roasting rotary kiln is collected in stages as described above. That is, first, the crude zinc oxide dust having a relatively large particle size is collected by the gravity settling dust collector, and the crude zinc oxide dust having a relatively small particle size that was not collected by the gravity settling dust collector is collected by the electric dust collector. As shown in Table 1, the fluorine and iron contents in the crude zinc oxide dust collected by the gravity settling dust collector are higher than those in the crude zinc oxide dust collected by the electrostatic precipitator, suggesting that most of the fluorine and iron are distributed in the crude zinc oxide dust, which has a relatively large particle size. In other words, the results in Table 1 indicate that the iron in the steel dust that did not contribute to the reduction reaction and was carried over unreacted was introduced into the dust collection equipment together with the exhaust gas, and most of it was collected by the gravity settling dust collector. As shown in Table 1, fluorine behaves in a similar manner to iron, so it can be concluded that a portion of the fluorine in the steel dust was also collected by the gravity settling dust collector together with the carried-over iron.

[0032] [Table 1]

[0033] In addition to the fluorine carried over with the iron, the crude zinc oxide dust contains fluorine in the form of a volatile compound such as lead fluoride chloride (PbFCl). Thus, in the conventional manufacturing method, it was extremely difficult to eliminate the distribution of fluorine into the crude zinc oxide dust in the reduction roasting step S20, which was the most upstream step.

[0034] The manufacturing method of the present invention is consistent with the conventional manufacturing method in that crude zinc oxide dust is collected using a gravity settling dust collector and an electric dust collector. Therefore, it is difficult to eliminate the distribution of fluorine in the crude zinc oxide dust, as in the conventional manufacturing method. However, the manufacturing method of the present invention adjusts the "fluorine content ratio" of the iron and steel dust input into the reduction roasting rotary kiln (RRK) to an optimal predetermined ratio in advance when the iron and steel dust is charged into the RRK, and further, in order to sufficiently reduce carryover, at least 30 mass% of the raw material ores charged into the reduction roasting rotary kiln are processed to be molded into carbonaceous reducing agent-containing pellets in a state where they are mixed with a carbonaceous reducing agent. This reduces carryover and increases the efficiency of the zinc reduction and volatilization reaction, thereby relatively reducing the fluorine content. It is therefore possible to maintain high quality of the final product, zinc oxide ore, without making any special adjustments to the operating conditions in the wet process S30, but only by adjusting the operating conditions in the drying and heating process S40, which is the most downstream process and is relatively easy to adjust.

[0035] In the raw ore preparation step S10, the steel dust may be pelletized in advance in the next step S20, in order to reduce carryover, even in conventional manufacturing methods. However, since a considerable amount of time has passed since pelletization, the steel dust is often dried, and many pellets with insufficient strength are often mixed in. If such weak pellets are charged into a rotary kiln for reduction roasting, the pellets break in the furnace, and some of the broken pellets are powdered, causing excessive carryover due to the gas flow in the furnace. As mentioned above, the carried-over steel dust is mainly collected by a gravity settling type dust collector, and the fluorine contained in the collected steel dust increases the F content of the crude zinc oxide dust. In order to suppress the carryover of iron and steel dust, which is a factor in increasing the F content, in the method for producing zinc oxide ore of the present invention, at least 30 mass% of the raw ore for the reduction roasting process to be charged into the reduction roasting rotary kiln is mixed with a carbonaceous reducing agent to form carbonaceous reducing agent-containing pellets, which are then charged into the reduction roasting rotary kiln.

[0036] As the carbonaceous reducing agent to be mixed with the raw ore such as steel dust in pelletizing the raw ore for the reduction roasting process, carbon, recycled carbon, etc., which can be pelletized in powder or slurry form, can be appropriately selected and used. Among them, recycled carbon can be preferably used from the viewpoint of promoting resource recycling and reducing costs. In the carbonaceous reducing agent-containing pellets, the mixing ratio of the raw ore such as steel dust to the carbonaceous reducing agent is preferably about 90:10 to 80:20, more preferably about 90:10 to 85:15.

[0037] In addition, the pelletizing process for obtaining the carbonaceous reducing agent-containing pellets can be carried out using a commonly used pelletizing device. For example, a rotary pan-type pelletizer or a two-shaft pin-type pelletizer equipped with two-shaft rotor pins is used to continuously supply steel dust and the carbonaceous reducing agent, and pelletize the pellets while adding mist-like moisture. The particle size of the carbonaceous reducing agent-containing pellets is preferably about 5 mm or more and 10 mm or less. In addition, the moisture content of the carbonaceous reducing agent-containing pellets is preferably about 10 mass % or more and 20 mass % or less.

[0038] <Reduction roasting process> As a specific method for carrying out the reduction roasting step S20 for recovering crude zinc oxide from steel dust and the like, a reduction roasting method using a reduction roasting rotary kiln (RRK) is widely adopted. The reduction roasting step S20 will be described in detail below for the case where steel dust is used as the raw material for crude zinc oxide and reduced and roasted in an RRK. In this case, it is preferable that the steel dust, including the portion other than the above-mentioned carbonaceous reducing agent-containing pellets, is previously formed into pellets having a size of about 5 mm to 10 mm as necessary, and the steel dust is continuously charged into the RRK together with coal, a carbonaceous reducing agent such as coke, limestone (CaCO3), and the like.

[0039] During the reduction roasting step S20, the maximum temperature of the material to be treated inside the RRK furnace is controlled to about 1000°C to 1400°C by the combustion of heavy oil and the charged carbonaceous reducing agent. The steel dust is reduction roasted in this furnace, and the volatilized metallic zinc is reoxidized in the RRK furnace to become particulate crude zinc oxide (crude zinc oxide dust).

[0040] Small amounts of lead contained in steel dust are also roasted under reduced conditions, and the evaporated metallic lead is reoxidized in the furnace to form powdered lead oxide. If a large amount of halogen is present in the steel dust, some of the metallic zinc and lead are evaporated as halogen compounds.

[0041] In this reduction roasting step S20, the reduction roasting residue that does not volatilize and remains in the furnace of the reduction roasting rotary kiln contains a large amount of reduced iron, so it is recovered from the kiln discharge end as a product called reduced iron pellets and delivered to steel manufacturers as iron raw material.

[0042] As described above, the powdered zinc oxide and lead oxide are introduced into a dust collection facility consisting of multiple dust collectors connected together with the exhaust gas from the RRK, and are recovered in stages as crude zinc oxide dust. The dust collection facility is composed of a gravity settling dust collector arranged at the most upstream of the exhaust gas treatment path, an electric dust collector connected downstream of the gravity settling dust collector, and a bag filter connected further downstream of the electric dust collector. First, crude zinc oxide dust with a relatively large particle size is collected by the gravity settling dust collector, and crude zinc oxide dust with a relatively small particle size that was not collected by the gravity settling dust collector is collected by the electric dust collector and bag filter. The gravity settling dust collector is a dust collector that settles and collects crude zinc oxide dust contained in the exhaust gas by a sudden decrease in the flow rate of the exhaust gas and the impact effect on the inner wall, and the electric dust collector is a dust collector that introduces crude zinc oxide dust charged by corona discharge into an electric field and collects it on a dust collection electrode. A bag filter is a dust collector that collects particles by filtering them using a filter cloth.

[0043] <Wet process> The wet process S30 is a wet process in which water-soluble impurities contained in the crude zinc oxide dust are separated and extracted into a treatment liquid, and then the impurities are removed from the crude zinc oxide by a water washing method through a solid-liquid separation process to obtain a crude zinc oxide cake. The wet process can be performed by a conventionally known method in which the treatment liquid in which the impurities are distributed is removed from the slurry by solid-liquid separation in a state in which impurities such as fluorine have been removed from the treatment liquid. As a result, the crude zinc oxide slurry becomes a crude zinc oxide cake with a high concentration. For the dehydration process for solid-liquid separation, a gravity settling type slurry concentrator such as a thickener or a forced moisture dehydrator such as a vacuum dehydrator can be used.

[0044] The crude zinc oxide cake obtained in the wet process preferably has a moisture content of 30% by mass or less, more preferably 25% or less. Since impurities such as fluorine are removed in the treatment liquid, the amount of impurities such as fluorine that are mixed in with the moisture can be reduced by lowering the moisture content of the crude zinc oxide cake. For this reason, in the dehydration treatment for solid-liquid separation, the moisture content can be set to the above range by combining, for example, a gravity settling type slurry concentrator such as a thickener with a belt filter.

[0045] In the wet process S30, the crude zinc oxide dust obtained in the reduction roasting process S20 is repulped with industrial water or the like. It is not essential to use an alkaline solution for this repulping. The crude zinc oxide slurry is subjected to pH adjustment and coagulation treatment, and then to primary dehydration. In this case, the pH is adjusted to a weak acid solution of about 6 to 7 to elute cadmium, and a coagulant or the like is used for coagulation to increase sedimentation. After this primary dehydration, the crude zinc oxide cake is diluted with industrial water and further subjected to secondary dehydration. It is preferable that the halogen concentration of the crude zinc oxide cake is reduced to less than 0.3 mass% for the fluorine concentration and less than 1.0 mass% for the chlorine concentration by these two washing and dehydration processes.

[0046] Alternatively, the wet treatment can be divided into a first wet treatment in which the crude zinc oxide slurry obtained by repulping using fresh water or suitable circulating water in the production line and dissolving sodium carbonate or sodium hydroxide is adjusted to a low pH treatment solution of about pH 6.5 to remove mainly cadmium from the crude zinc oxide, and a second wet treatment in which a pH adjuster is added to the crude zinc oxide slurry obtained by the first wet treatment to adjust the pH to a high pH treatment solution of about pH 8.5 to remove mainly fluorine compounds from the crude zinc oxide. In this case, the pH adjuster used in the second wet treatment can be the neutralization treatment solution generated in the wastewater treatment step S60 described later.

[0047] <Dry heating process> The dry heating step S40 is a step in which the crude zinc oxide cake obtained in the wet step S30 is loaded into a heating furnace such as a dry heating rotary kiln (DRK) for calcination and granulation. By passing through this step, the fluorine concentration can be further reduced and high-quality zinc oxide ore can be granulated. In the production method of the present invention, the heating temperature of the dry heating treatment in the dry heating step S40 is maintained in a temperature range of 800°C to 1000°C, preferably 800°C to 900°C. Note that the heating temperature in the above-mentioned DRK can usually be adjusted in units of about 100°C, and is adjusted so that the fluctuation in the heating temperature in the furnace falls within a temperature range of about 100°C.

[0048] Here, the fluorine remaining in the crude zinc oxide cake can be in the form of volatile (e.g., lead trifluoride (PbFCl)) or non-volatile (e.g., calcium difluoride (CaF2)). Of these, the volatile substance (PbFCl) is almost entirely volatilized by maintaining the temperature of the ore calcination within the above-mentioned temperature range, and the volatile chlorine and fluorine are almost entirely discharged to the exhaust gas treatment equipment in the exhaust gas dust cleaning process S50. On the other hand, the non-volatile substance (CaF2) is an extremely stable compound and is fixed in the zinc oxide ore without decomposing and volatilizing in the DRK.

[0049] As described above, the manufacturing method of the present invention requires that the heating temperature of the dry heat treatment is maintained in a temperature range of 800°C or more and 1000°C or less. As such, on the premise that the heating temperature is maintained in a range lower than the conventional range, the drying heat treatment time of the crude zinc oxide cake charged into the DRK is adjusted within a range that makes it possible to obtain, under such temperature conditions, high-quality zinc oxide ore equivalent to that obtained during conventional high-temperature operation, specifically, high-quality zinc oxide ore having a fluorine content of 0.050 mass% or less. According to the present invention, the fluorine content of the zinc oxide ore, which is the final product, is maintained at 0.050 mass% or less. The average fluorine content of this zinc oxide ore exceeds 0.03 mass%.

[0050] In the method for producing zinc oxide ore of the present invention, in the raw ore preparation step S10, which is the most upstream step, the "fluorine content ratio" (F / Zn ratio) of the raw ore such as steel dust is adjusted to a predetermined ratio, and further, the carryover of the raw ore in the RRK is effectively suppressed by an appropriate pelletizing process, so that the non-volatile form of fluorine input into the DRK can be effectively suppressed. In addition, by pelletizing the raw ore such as steel dust together with a carbonaceous reducing agent, it is possible to enjoy the effect of increasing the efficiency of the reduction and volatilization reaction of zinc and relatively reducing the fluorine content. Furthermore, by optimally adjusting the drying and heating treatment time of the crude zinc oxide cake based on the above-mentioned "fluorine content ratio" (F / Zn ratio), the volatile form of fluorine input into the DRK can be effectively volatilized and removed.

[0051] For example, when the "fluorine content ratio" (F / Zn ratio) of the steel dust charged into the RRK is adjusted to 0.015 in order to obtain high-quality zinc oxide ore, even if the heating temperature in the drying and heating step S40 is lowered to a temperature range of 800° C. or higher and 1000° C. or lower, high-quality zinc oxide ore with a fluorine content of 0.050 mass% or less can be obtained by adjusting the drying and heating treatment time of the crude zinc oxide cake charged into the DRK to 100 minutes. It is preferable to determine in advance by testing or the like an appropriate combination of the "fluorine content ratio" (F / Zn ratio) of the steel dust and the drying and heating treatment time of the crude zinc oxide cake.

[0052] When a rotary kiln is used as the drying / heating furnace, the drying / heating treatment time is equal to the residence time in the furnace, and can be calculated by the known calculation formula shown below. Formula: Residence time [min]=0.19L / (NDtanθs) L: Furnace length [m] N: Rotation speed [rpm] D: Furnace inner diameter [m] θs: Inclination angle of furnace [deg]

[0053] Incidentally, the lower the fluorine content in zinc oxide ore, the higher the quality. In other words, zinc oxide ore with a fluorine content of 0 is the highest quality. However, in order to obtain such high-quality zinc oxide ore, it is necessary to adjust the "fluorine content ratio" (F / Zn ratio) of the steel dust to be lower and the drying heat treatment time of the crude zinc oxide cake to be longer, and such adjustment is often difficult to make in actual operation. For this reason, in the production method of the present invention, it is preferable to adjust the "fluorine content ratio" (F / Zn ratio) of the steel dust to an optimal combination within a range that satisfies the conditions that the lower limit of the "fluorine content ratio" (F / Zn ratio) is 0.002 and the upper limit of the drying heat treatment time is 130 minutes or less, preferably 120 minutes or less, and more preferably 110 minutes or less. The above lower limit of the "fluorine content ratio" (F / Zn ratio) is the fluorine content of the brand of steel dust that has the lowest fluorine content among the brands of steel dust actually supplied. In addition, the shorter the drying heat treatment time is adjusted to within a range where the fluorine content of the zinc oxide ore can be maintained at 0.050 mass% or less, the more advantageous it is because the heat load on the DRK is reduced and the energy used in the drying heat treatment can be reduced. If the drying heat treatment time exceeds 130 minutes, there is a concern that the heat load on the heating furnace will increase, and operation will become inefficient.

[0054] More specifically, the above-mentioned optimum combination of the "fluorine content ratio" (F / Zn ratio) and the dry heat treatment time can be, for example, a combination in which the "fluorine content ratio" (F / Zn ratio) of the raw ore for the reduction roasting process in the raw ore preparation process S10 is set to 0.015 or less, and the dry heat treatment time in the dry heat process S40 is adjusted to within a range of 100 minutes to 130 minutes. By operating under these conditions, the fluorine content of the zinc oxide ore can be reduced to 0.045 mass% or less.

[0055] In order to reduce the "fluorine content ratio" (F / Zn ratio) of the raw ore for the reduction roasting process, the Zn content of the raw ore for the reduction roasting process is preferably 30 mass% or more. In the raw ore preparation step S10, it is preferable to appropriately select the steel dust to be used so that the Zn content of the raw ore for the reduction roasting process can be maintained at the above level or more.

[0056] <Exhaust gas dust cleaning process> The exhaust gas dust cleaning step S50 is a step in which the exhaust gas dust generated in the drying and heating step S40 is cleaned to obtain a cleaned exhaust gas dust cake. The cleaning equipment for carrying out the exhaust gas dust cleaning step S50 generally comprises a combination of a cleaning tower and a wet-type electric dust collector. The cleaned exhaust gas dust cake recovered in these facilities is repeatedly recycled and fed into an upstream process such as a drying and heating rotary kiln in the drying and heating step S40, thereby making effective use of metal resources.

[0057] <Wastewater treatment process> The wastewater treatment process S60 is a process in which fluorine and cadmium are removed from the wastewater separated from the crude zinc oxide in the wet process S30 and containing high concentrations of these metals, and further, heavy metals contained in trace amounts in the wastewater are extracted by neutralization treatment, and finally, the pH is adjusted to make the wastewater harmless.

[0058] The waste liquid separated in the wet process S30 also contains trace amounts of zinc and / or lead components eluted from the crude zinc oxide. To recover these heavy metal components, a neutralization process is carried out as described above. This neutralization process is generally carried out by adding slaked lime. The slaked lime can be added by directly adding solid slaked lime to the wet processing liquid, or by adding a solution of slaked lime dissolved in a liquid form to the wet processing liquid. The amount of slaked lime added can also be adjusted by measuring the pH of the neutralization process liquid after the addition.

[0059] In addition, the neutralization residue containing zinc compounds or lead compounds recovered by this neutralization treatment is repeatedly used in the wet treatment step, where it is wet treated together with the zinc oxide slurry obtained from the reduction roasting step, and is generally calcined and granulated in a dry heating rotary kiln to fix it into zinc oxide ore.

[0060] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments. Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the examples of the present invention. EXAMPLES

[0061] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0062] [Example 1] Zinc oxide ore was experimentally produced by the production method of the present invention. Specifically, the following steps were carried out in order under the conditions shown below, and the fluorine grade of the obtained zinc oxide ore was measured. The results are shown in Table 2. In Table 2, the "fluorine content ratio" and "Zn grade" shown in the column for the raw ore preparation step indicate the grades of the "raw ore for the reduction roasting step", and the "proportion of carbonaceous reducing agent-containing pellets" indicates the proportion of the "raw ore for the reduction roasting step" that was pelletized in the following manner. In addition, the "F grade" shown in the column for the wet process indicates the fluorine grade of the crude zinc oxide cake. (Raw ore preparation process) As the raw material ore of crude zinc oxide, steel dust of several brands with different fluorine grades was mixed and adjusted to have a "fluorine content ratio" (F / Zn ratio) of 0.005 to obtain "raw material ore for reduction roasting process" with a fluorine content ratio adjusted to a predetermined ratio. Then, 40 mass% of this "raw material ore for reduction roasting process" was mixed with powdered carbon to obtain carbonaceous reducing agent-containing pellets. The mixture ratio of the "raw material ore for reduction roasting process" to carbon was 86:14, and the mixture was pelletized using a two-axis pin-type granulator. The pellets had a particle size of about 5 mm to 10 mm, and a moisture content of about 15 mass%. (Reduction roasting process) This "raw ore for the reduction roasting process" was charged into a reduction roasting rotary kiln (RRK) together with coal, coke and other carbonaceous reducing agents, limestone, etc., and reduction roasting was carried out while controlling the temperature of the reduction roasting rotary kiln so that the maximum temperature of the treated material was 1000°C to 1400°C. The crude zinc oxide dust generated during this process was collected using a gravity settling type dust collector and an electric dust collector and a bag filter connected downstream of the gravity settling type dust collector, to obtain crude zinc oxide dust. (Wet process) The entire amount of crude zinc oxide dust collected by the gravity settling dust collector was removed from the system, and the remaining crude zinc oxide dust was repulped with water to obtain a low pH treatment liquid with a pH adjusted to 6.5. About 5 to 10 mass ppm of a polymeric flocculant was added to the low pH treatment liquid, and solid-liquid separation was performed in a thickener to obtain a crude zinc oxide slurry with reduced chlorine and fluorine. The crude zinc oxide slurry obtained by the above treatment was dehydrated using a press roll to obtain a crude zinc oxide cake with a moisture content of about 20 mass% to 25 mass%. (dry heating process) This crude zinc oxide cake was loaded into a dry-heat rotary kiln (DRK) and subjected to dry-heat treatment while controlling the temperature and residence time of the dry-heat rotary kiln (DRK) so that the maximum temperature of the treated material was 800°C or higher and 900°C or lower, and the dry-heat treatment time was 100 minutes.

[0063] [Other Examples and Comparative Examples] In Examples 2 to 6 and Comparative Examples 1 to 7, in the raw ore preparation step, either or both of the "fluorine content ratio" (F / Zn ratio) of the "raw ore for reduction roasting step" and the proportion (mass%) of the carbonaceous reducing agent-containing pellets in the dry heating step were controlled under different conditions as shown in Table 2 below for each Example and Comparative Example. Except for this, zinc oxide ore was produced under the same conditions as in Example 1, and the fluorine grade of the obtained zinc oxide ore was measured in the same manner. The results are shown in Table 2.

[0064] [evaluation] Table 2 shows the embodiment of each test operation of the Examples and Comparative Examples, and the fluorine grade (F grade) of the zinc oxide ore obtained under each condition. Each Example and Comparative Example was evaluated from the viewpoints of Evaluation 1 and Evaluation 2 below, and if an evaluation of "○ (good)" was obtained in both evaluations, the overall evaluation was determined to be "○ (good)".

[0065] (Rating 1) In the drying and heating process, we evaluated whether the heat load on the drying and heating furnace due to high temperature operation was suppressed. The evaluation criteria are as follows. Heating temperature below 900℃: 〇 (good) Heating temperature is over 900℃ and below 1000℃: △ (OK) Heating temperature exceeds 1000℃: × (bad)

[0066] (Rating 2) In the drying and heating process, an evaluation was performed to see whether the fluorine content of zinc oxide ore required for high-quality zinc oxide ore could be maintained. The evaluation criteria were as follows: F content in zinc oxide ore [mass%] is 0.050 mass% or less: ○ (good) F content in zinc oxide ore [mass%] exceeds 0.050 mass%: × (bad) [Table 2]

[0067] As shown in Table 2, under the conditions of Example 1, the fluorine content of the zinc oxide ore was the lowest, and an extremely high-quality zinc oxide ore was obtained. Under the conditions of Examples 2 to 7, the fluorine content of the zinc oxide ore was slightly higher than that of Example 1, but zinc oxide ore of the second highest quality after Example 1 was obtained. On the other hand, under the conditions of Comparative Examples 1 and 2, the fluorine content of the zinc oxide ore further increased to exceed 0.050 mass%. Moreover, under the conditions of Comparative Examples 3 to 5, the fluorine content of the zinc oxide ore was 0.050 mass% or less, but the heat load on the dry heating rotary kiln (DRK) increased.

[0068] From the above test and evaluation results, it has been confirmed that the zinc oxide ore manufacturing method of the present invention makes it possible to produce high-quality zinc oxide ore with a sufficiently reduced fluorine concentration while suppressing the heat load on the drying and heating furnace due to high-temperature operation in the process of manufacturing zinc oxide ore from raw ore containing fluorine. [Explanation of symbols]

[0069] S10 Raw ore preparation process S20 Reduction roasting process S30 Wet process S40 Drying and heating process S50 Exhaust gas dust cleaning process S60 Wastewater treatment process

Claims

1. A method for producing zinc oxide ore, comprising the steps of: producing zinc oxide ore from a raw material ore containing fluorine, the method comprising the steps of: a raw material ore preparation step of obtaining a raw material ore for a reduction roasting step, the raw material ore having a fluorine content ratio adjusted to a predetermined ratio by mixing a plurality of raw material ores having different fluorine content ratios, which is the ratio of the fluorine content ratio to the zinc content ratio, or by selecting a raw material ore having a fluorine content ratio adjusted to a predetermined ratio; a reduction roasting step for obtaining crude zinc oxide dust by subjecting the raw material ore for the reduction roasting step to a reduction roasting treatment; a wet process for removing water-soluble impurities from the crude zinc oxide dust to obtain a crude zinc oxide cake; a drying and heating step of subjecting the crude zinc oxide cake to a dry and heat treatment to obtain the zinc oxide ore; comprising In the raw ore preparation step, 30 mass% or more of the raw ore for the reduction roasting step is mixed with a carbonaceous reducing agent and pelletized, In the dry heating step, the dry heating treatment is performed at a heating temperature of 800° C. or more and 1000° C. or less, and the dry heating treatment time is adjusted according to the fluorine content ratio of the raw material ore for the reduction roasting step. A method for producing zinc oxide ore, wherein the fluorine content of the zinc oxide ore is maintained at 0.050 mass% or less.

2. In the raw ore preparation step, a plurality of types of raw ores having different fluorine content ratios are mixed to adjust the fluorine content ratio to the predetermined ratio, thereby obtaining a raw ore for the reduction roasting step; A method for producing the zinc oxide ore according to claim 1.

3. The raw material ore is iron and steel dust. A method for producing zinc oxide ore according to claim 1 or 2.

4. In the raw ore preparation step, the fluorine content ratio of the raw ore for the reduction roasting step is set to 0.015 or less, and the dry heat treatment time in the dry heat step is set to 100 minutes or more and 130 minutes or less. A method for producing zinc oxide ore according to claim 1 or 2.

5. The crude zinc oxide cake obtained in the wet process has a moisture content of 30% or less. A method for producing zinc oxide ore according to claim 1 or 2.

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