How zinc oxide ore is produced

Abstract

To provide a method for producing zinc oxide ore that can control a mercury level of treated exhaust to be finally discharged out of the treatment system in the production of zinc oxide ore, at low cost, quickly, and with high accuracy.SOLUTION: A method for producing zinc oxide ore includes: a mercury level calculation ST31 for measuring, by fluorescent X-ray analysis, a lead content of a dry-heating target material and calculating a mercury level of the dry-heating target material from the measured lead content; and a mercury load adjustment ST32 for considering a product of the mercury level of the dry-heating target material and the load to the dry-heating step 30 as a mercury load and, if necessary, make adjustments to increase or decrease the mercury load, thereby keeping the mercury level of the treated exhaust discharged from an exhaust treatment step S40 within a predetermined range of management reference values.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing zinc oxide ore. More specifically, the present invention relates to a method for producing zinc oxide ore that is suitable for producing zinc oxide ore using a raw material such as steel dust that contains zinc as well as lead and a trace amount of mercury as impurities. [Background technology]

[0002] Conventionally, zinc oxide ore has been widely used as a raw material for zinc ingots in zinc smelters. Crude zinc oxide, which is a raw material for zinc oxide ore, can be obtained from, for example, steel dust generated from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry. From the viewpoint of promoting resource recycling, it is desirable to reuse steel dust. However, on the other hand, steel dust contains a small amount of mercury as an impurity in addition to iron oxide and zinc oxide, which are its main components. It is essential to treat the treated exhaust gas that is finally discharged outside the treatment system of the manufacturing plant so that the mercury concentration is strictly below the legal standard value, and various methods are used to treat the exhaust gas generated in the treatment system to remove mercury from the exhaust gas (see Patent Document 1).

[0003] In the past, the widely used method for the above-mentioned flue gas treatment to sufficiently reduce the mercury concentration has been to control the mercury concentration in the treated flue gas that is finally discharged outside the treatment system within a certain concentration range by controlling the mercury concentration mainly at the raw material stage. This control of the mercury concentration at the raw material stage has usually been carried out by adjusting the amount of mercury brought into the treatment system from outside the treatment system as a raw material, more specifically, by adjusting the input ratio of various raw materials with known mercury concentrations into the treatment system.

[0004] However, raw materials such as steel dust vary widely in mercury concentration even when they are the same raw material, and in the manufacturing process of zinc oxide ore in which these are processed, a large amount of material recovered in a downstream process is recycled to an upstream process in order to improve the zinc recovery rate. In this way, in the manufacturing process of zinc oxide ore in which raw materials with various mercury concentrations go through complex processes, it has been difficult to control the "mercury concentration of the treated exhaust gas" that is finally discharged outside the processing system with high accuracy using the above-mentioned method, which estimates the "mercury concentration of the treated exhaust gas" based on the mercury concentration at the raw material mixing stage throughout the entire process of manufacturing zinc oxide ore.

[0005] Therefore, when estimating the mercury concentration in the treated flue gas by the above-mentioned method that relies on the mercury concentration in the raw material stage, in order to keep the mercury concentration below the standard value with a sufficient margin, it is necessary to adjust the operating conditions taking into account the fluctuation range of the above-mentioned estimated value of the mercury concentration in the treated flue gas. For this reason, in order to reliably maintain safety, it has often been necessary to sacrifice the productivity of zinc oxide ore to some extent in the operating conditions.

[0006] In response to this, in recent years, a method has been developed in which the above-mentioned exhaust gas treatment to sufficiently reduce the mercury concentration is carried out by calculating the mercury load based on the mercury concentration of the intermediate product fed to the drying and heating process that produces the final product, zinc oxide ore, and adjusting this to maintain it within a specified control standard value range, thereby controlling with high precision the "mercury concentration of the treated exhaust gas" that is ultimately discharged outside the treatment system (see Patent Document 2).

[0007] However, in order to accurately measure the concentration of mercury, which is only present in a very small amount in the first place, at the intermediate product stage where it is fed into the drying and heating process, analysis using dedicated analytical equipment is essential. Specifically, this analysis can be performed, for example, by dissolving crude zinc oxide cake sampled at regular intervals and measuring the concentration with an atomic absorption spectrometer (see paragraph

[0035] of Patent Document 2), but this requires a lot of time and money. For this reason, there has been a demand at zinc oxide ore manufacturing sites for further reduction in the cost of controlling the mercury concentration in exhaust gas. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-79456 A [Patent Document 2] JP 2020-132970 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method for producing zinc oxide ore, which is capable of controlling the mercury concentration of treated exhaust gas, which is finally discharged outside a treatment system, at low cost, quickly, and with high accuracy in the production of zinc oxide ore. [Means for solving the problem]

[0010] The present inventors have come up with the idea that the lead content, which is usually contained in an intermediate product charged to the drying and heating process and auxiliary raw materials directly added to the process (collectively referred to as "charges for the drying and heating process" in this specification) in the entire process of producing zinc oxide ore, is measured by X-ray fluorescence analysis, and the concentration of mercury, which is contained in a very small amount in the "charges for the drying and heating process", can be calculated with sufficient accuracy from the measured value. The inventors have found that the mercury concentration of the treated exhaust gas discharged outside the treatment system can be controlled at a lower cost, quickly, and with high accuracy by utilizing the value of the mercury concentration calculated in this way, and have completed the present invention. More specifically, the present invention provides the following.

[0011] (1) A method for producing zinc oxide ore, comprising: a dry heating step of calcining a charge for a dry heating step, the charge containing zinc as a main component and further containing lead and mercury, in a dry heating furnace to obtain zinc oxide ore; and an exhaust gas treatment step of removing mercury from the exhaust gas generated in the dry heating step, the method further comprising: a mercury concentration calculation step of measuring the lead content of the charge for the dry heating step by fluorescent X-ray analysis and calculating the mercury concentration of the charge for the dry heating step from the measured lead content; and a mercury load adjustment step of regarding the product of the mercury concentration of the charge for the dry heating step and the charge amount to the dry heating step as the mercury load, and adjusting the mercury load to increase or decrease it as necessary to maintain the mercury concentration of the treated exhaust gas discharged from the exhaust gas treatment step within a predetermined control standard value range.

[0012] According to the zinc oxide ore manufacturing method of (1), by making the "mercury concentration calculation process" and the "mercury load adjustment process", which are performed in a unique manner, essential processes in the production of zinc oxide ore, it is possible to control the mercury concentration of the treated exhaust gas discharged outside the treatment system at low cost, quickly, and with high accuracy.

[0013] (2) A method for producing zinc oxide ore as described in (1), wherein the charge to the drying and heating process comprises an auxiliary crude zinc oxide raw material that is directly charged to the drying and heating process from outside the treatment system, and in the mercury load adjustment treatment, adjustment of the amount of charge to the drying and heating process of only the charge to the drying and heating process other than the auxiliary crude zinc oxide raw material is given priority over adjustment of the amount of charge of the auxiliary crude zinc oxide raw material.

[0014] In the zinc oxide ore manufacturing method in (2), the "auxiliary crude zinc oxide raw material" that is directly charged to the drying and heating process from outside the treatment system has a relatively small variation in mercury concentration compared to other charges, and the amount of other charges that have a relatively large variation in mercury concentration, i.e., charges that are likely to cause abrupt fluctuations in the mercury concentration of the treated flue gas discharged outside the treatment system, is given priority in adjusting the amount to be charged to the drying and heating process. This reduces the workload of adjusting the amount of each type of charge and enables the mercury concentration of the treated flue gas to be controlled more efficiently and accurately.

[0015] (3) A method for producing zinc oxide ore according to (1) or (2), wherein the charge in the drying and heating step comprises an exhaust gas dust-containing cake that contains exhaust gas dust discharged from the exhaust gas treatment step, and the mercury load adjustment treatment gives priority to adjusting the amount of only the exhaust gas dust-containing cake fed to the drying and heating step over adjusting the amounts of other charges fed.

[0016] In the manufacturing method of zinc oxide ore in (3), focusing on the fact that the cake containing exhaust gas dust discharged (referred to as "exhaust gas dust-containing cake" in this specification) is the "charge to the drying and heating process" that has the relatively highest mercury concentration, the amount of the cake to be fed to the drying and heating process is adjusted to be given priority over other charges. This makes it possible to reduce the mercury concentration in the treated exhaust gas while keeping the fluctuation range of the production volume in the drying and heating process small.

[0017] (4) A method for producing zinc oxide ore described in any one of (1) to (3), in which the mercury load adjustment process selectively involves discharging the charge for the drying and heating process outside the treatment system before charging it into the drying and heating furnace, and returning the charge for the drying and heating process discharged by the process back into the treatment system and charging it into the drying and heating furnace, thereby increasing or decreasing the mercury load.

[0018] According to the zinc oxide ore manufacturing method described in (4), the mercury concentration in treated exhaust gas can be controlled more quickly and flexibly in response to frequent fluctuations in mercury load during operation.

[0019] (5) A method for producing zinc oxide ore described in any one of (1) to (4), comprising: conducting a treated exhaust gas mercury concentration measurement process for continuously measuring the mercury concentration of the treated exhaust gas discharged from the exhaust gas treatment process; and in the mercury load adjustment process, when the mercury concentration of the treated exhaust gas exceeds a predetermined upper limit value, adjusting the mercury load to decrease, and when the mercury concentration of the treated exhaust gas falls below a predetermined lower limit value, adjusting the mercury load to increase.

[0020] (5) In the zinc oxide ore manufacturing method, even if the mercury concentration in the treated exhaust gas discharged outside the treatment system suddenly fluctuates due to various factors, it is possible to respond quickly and maintain an extremely high level of safety in the management of the mercury concentration in the treated exhaust gas throughout the entire operating period. Effect of the Invention

[0021] According to the present invention, it is possible to provide a method for producing zinc oxide ore, which can control the mercury concentration of treated exhaust gas that is finally discharged outside a treatment system at low cost, quickly, and with high accuracy in the production of zinc oxide ore. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a flow diagram showing an example of a flow of a method for producing zinc oxide ore according to the present invention. [Diagram 2] FIG. 2 is a flow diagram showing an example of a process path for producing various "charges for the drying and heating process" in the method for producing zinc oxide ore in FIG. 1. [Diagram 3] FIG. 1 is a correlation graph showing the relationship between the lead content (%) in the "charge for the drying and heating process" and the mercury concentration index. [Figure 4] FIG. 1 is a correlation graph showing the relationship between the zinc content (%) in the "charge for the drying and heating process" and the mercury concentration index. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] <Overall process> The method for producing zinc oxide ore to which the present invention is applied is a process for producing zinc oxide ore from raw materials that contain a very small amount of mercury as an impurity, such as steel dust, and also contain a certain amount of lead. This process is usually carried out as a whole process including each step shown in Fig. 1, namely, a reduction roasting step S10, a wet process S20, a dry heating step S30, an exhaust gas treatment step S40, and a wastewater treatment step S50. The above-mentioned "very small amount of mercury concentration in the raw materials" is specifically usually about 1 / 10,000 of the lead content contained in the raw materials.

[0024] The method for producing zinc oxide ore of the present invention is a composite partial process that includes at least the drying and heating step S30 and the exhaust gas treatment step S40 among the above-mentioned steps, and also performs a mercury concentration calculation step ST31 and a mercury load adjustment step ST32 as essential steps linked to these two steps.

[0025] The dry heating process S30 is a process in which the "dry heating process charge" is calcined to produce the product zinc oxide ore. Most of the mercury-containing exhaust gas is generated during this dry heating process S30.

[0026] The exhaust gas treatment step S40 is a step for separating and removing mercury and other harmful substances from the mercury-containing exhaust gas generated in the drying and heating step S30.

[0027] The mercury concentration calculation process ST31 is a process for calculating the mercury concentration of the "drying and heating step charge" charged to the drying and heating step S30 in the overall process for producing zinc oxide ore as exemplified in FIG.

[0028] The mercury loading adjustment process ST32 is a process for adjusting the "mercury loading" calculated from the mercury concentration calculated in the mercury concentration calculation process ST31.

[0029] The method for producing zinc oxide ore of the present invention is particularly advantageous in a production plant that uses iron and steel dust, which has a large variation in mercury concentration, as a main raw material. In the following, an embodiment in which iron and steel dust is used as a main raw material for zinc oxide ore will be described in detail as a specific example of a preferred embodiment of the method for producing zinc oxide ore of the present invention.

[0030] <Reduction roasting process> The reduction roasting step S10 is a step in which raw materials (primary raw materials) such as steel dust are roasted at high temperatures together with a reducing agent using a reduction roasting rotary kiln (RRK), which is usually a large rotary heating furnace. It is preferable to maintain and control the temperature inside the reduction roasting rotary kiln (RRK) so that the maximum temperature of the material to be treated is about 1050°C or higher and 1200°C or lower.

[0031] In the furnace of the rotary kiln (RRK), raw materials such as steel dust are reduced and roasted, and the evaporated metallic zinc is reoxidized in the furnace to become powdered zinc oxide. The powdered zinc oxide is introduced into a dust collector together with the exhaust gas from the rotary kiln (RRK exhaust gas) and captured as recovered dust. At this time, mercury contained in the raw materials is also captured as recovered dust by spraying activated carbon into the RRK exhaust gas and collecting it, and this recovered dust containing mercury is charged as crude zinc oxide dust into the next process, the wet process S20.

[0032] The reduction roasting residue that does not volatilize in the reduction roasting step S10 and remains in the kiln is usually collected from the kiln discharge end as a product called iron-containing clinker. Since it contains a large amount of reduced iron, it is delivered to steel manufacturers as an iron raw material, etc.

[0033] <Wet process> The wet process S20 is a process in which the crude zinc oxide dust recovered in the reduction roasting process S10 is repulped with industrial water or the like, and water-soluble impurities such as fluorine are separated.

[0034] In addition to the crude zinc oxide dust derived from primary raw materials such as steel dust and generated through the upstream reduction roasting process S10, crude zinc oxide powder and the like, which has the same chemical composition as the crude zinc oxide dust and contains zinc, is directly charged into the wet process S20 as a secondary raw material without passing through the reduction roasting process S10, and is subjected to the same separation process as the crude zinc oxide dust derived from the primary raw materials.

[0035] The crude zinc oxide dust that has become a slurry through the above separation process is subjected to pH adjustment, concentration, and dehydration to become a crude zinc oxide cake. This crude zinc oxide cake is then charged as a "drying and heating process charge" to the next process, the drying and heating process S30 (see Figs. 1 and 2). For the above concentration and dehydration processes, a gravity settling type slurry concentration device such as a thickener or a dehydration device such as a vacuum dehydrator can be used as appropriate.

[0036] Here, various zinc-containing materials recovered in downstream processes are also charged into the wet process S20 for repeated processing. The exhaust gas dust obtained from the exhaust gas treatment process S40 also passes through the wet process S30 again to become "exhaust gas dust-containing cake" and is subjected to this repeated processing (see FIG. 2). Note that this "exhaust gas dust-containing cake" usually contains mercury, which has been concentrated during circulation in the treatment system, at a higher concentration than other zinc-containing materials.

[0037] <Dry heating process> The dry heating step S30 is a step of firing the crude zinc oxide cake obtained in the wet step S20 in a dry heating furnace such as a dry heating rotary kiln (DRK). This dry heating step S30 volatilizes residual impurities including mercury to obtain high-quality zinc oxide ore. Regarding the firing temperature in the dry heating treatment, it is preferable to maintain and control the temperature inside the furnace so that the temperature of the fired material when it is discharged from the dry heating rotary kiln (DRK) or the like is in the range of 1000°C to 1200°C, preferably 1100°C to 1150°C.

[0038] As shown in FIG. 2, in the drying and heating step S30, together with the crude zinc oxide cake discharged from the upstream wet step S20, if necessary, an "auxiliary crude zinc oxide raw material" and an "exhaust gas dust-containing cake" containing exhaust gas dust repeatedly discharged from the exhaust gas treatment step S40 are each charged into the drying and heating furnace as part of the "drying and heating step charge".

[0039] Here, in this specification, the term "auxiliary crude zinc oxide raw material" refers to a raw material that is directly charged into the drying and heating step S30 from outside the treatment system of a manufacturing facility that manufactures zinc oxide ore, without going through the wet process S20. Specifically, like the above-mentioned secondary raw material, zinc-containing crude zinc oxide powder or the like can be used as the "auxiliary crude zinc oxide raw material".

[0040] Then, in the drying and heating process S30, almost the entire amount of mercury contained within a certain range in each of the above-mentioned various "drying and heating process input materials" is distributed to the exhaust gas side and sent as mercury-containing exhaust gas to the downstream exhaust gas treatment process S40 (see Figure 1).

[0041] <Exhaust gas treatment process> The exhaust gas treatment step S40 is a step of removing mercury and other impurities from the exhaust gas generated in the drying and heating step S30, dedusting and rendering harmless the exhaust gas, thereby producing a harmless treated exhaust gas. The equipment for carrying out this step is generally a combination of a scrubbing tower, a wet electrostatic precipitator, and a packed tower filled with a mercury adsorbent. The mercury adsorbent that is widely used is one in which one or more sulfides selected from copper concentrate, zinc concentrate, lead concentrate, etc. are attached to the surface of a carbon compound such as granular coke.

[0042] When the flue gas treatment step S40 is performed in the flue gas treatment facility having the above-mentioned configuration, the mercury in the flue gas is adsorbed and recovered by the mercury adsorbent in the packed tower at a recovery rate of about 90%. As for the flue gas dust containing mercury, since the main component is zinc oxide, this is further repeatedly recycled and charged into the wet step S20, thereby making effective use of metal resources.

[0043] <Wastewater treatment process> The wastewater treatment step S50 is a step in which some heavy metals such as cadmium are removed from the wastewater containing high concentrations of water-soluble impurities such as fluorine and cadmium separated from the crude zinc oxide dust in the wet step S20, and then the heavy metals and fluorine remaining in the wastewater are precipitated and removed by neutralization treatment with hydrated lime, and finally a pH adjustment treatment ST51 is performed to turn the treated wastewater into harmless wastewater.

[0044] <Method for controlling mercury concentration in treated exhaust gas> The zinc oxide ore manufacturing method of the present invention is a partial process applicable to the overall zinc oxide ore manufacturing process shown in Figure 1, and is a composite partial process that includes at least a drying and heating step S30 and an exhaust gas treatment step S40, and also performs a mercury concentration calculation process ST31 and a mercury load adjustment process ST32 as essential processes linked to these two steps (see Figure 1).

[0045] The manufacturing method of zinc oxide ore according to the present invention, which is configured as described above, is a technical concept that can be positioned as a "method for controlling the mercury concentration in treated flue gas". In order to achieve this purpose, a mercury concentration calculation process ST31 is required, in which the concentration of mercury contained in the "charged material for the drying and heating process" in a very small amount is indirectly calculated from the lead content, which is contained at a content rate about 10,000 times that of mercury. The mercury load amount obtained based on the mercury concentration thus calculated is then used as an index for controlling the mercury concentration in the treated flue gas in the subsequent mercury load adjustment process ST32.

[0046] Specifically, in the mercury loading adjustment process ST32, the product of the mercury concentration of the "charged material for the dry heating process" obtained in the mercury concentration calculation process ST31 and the amount of the "charged material for the dry heating process" is regarded as the "mercury loading," and the "mercury loading" is appropriately adjusted by increasing or decreasing the amount of the "charged material for the dry heating process" so as to maintain the mercury concentration of the treated exhaust gas within a specified control standard value range.

[0047] [Mercury concentration calculation process ST31] The mercury concentration calculation process ST31 is a process that indirectly calculates the mercury concentration of the "drying and heating process input materials" consisting of "crude zinc oxide cake," "auxiliary crude zinc oxide raw material," "exhaust gas dust-containing cake," etc. (hereinafter, these are collectively referred to as "cake, etc.") at a stage before they are loaded into the drying and heating furnace where the drying and heating process S30 is performed.

[0048] The mercury concentration calculation process ST31 begins with measuring the lead content in the "charge for the dry-heating process", rather than the mercury concentration in the "charge for the dry-heating process". This lead content is measured by X-ray fluorescence analysis.

[0049] The measurement of the lead content, which is a pretreatment for the calculation of the mercury concentration, can be carried out by measuring the lead content in a measurement sample obtained by drying the "charged material for the dry heating process" sampled at regular intervals, by X-ray fluorescence analysis using an X-ray fluorescence measurement device. The "charged material for the dry heating process" to be charged to the dry heating process S30 includes the crude zinc oxide cake discharged from the wet process S20, the "exhaust gas dust-containing cake," and the "auxiliary crude zinc oxide raw material," and these various "cakes, etc." may have significantly different mercury concentrations. Therefore, it is preferable to perform the above sampling for each type of "cake, etc." and measure the lead content of each individually first.

[0050] Next, the mercury concentration of the "charged material for the drying and heating process" is calculated by applying the measured value of the lead content to a relational expression obtained from basic data on the correlation between the lead content and the mercury concentration that has been previously obtained. Figure 3 shows a specific example of basic data showing the correlation between the lead content and the mercury concentration index obtained by dividing the mercury concentration by a predetermined value.

[0051] As described above, since the mercury concentration of each type of "cake, etc." may differ significantly, it is preferable to calculate the mercury concentration of each type of "cake, etc." individually using the above calculation method.

[0052] Here, in order to measure the very small amount of mercury concentration, which is about 1 / 10,000 of the lead content contained in the "charge for the drying and heating process" by the conventional method, wet analysis using dedicated equipment is necessary, and it takes about 24 hours from pretreatment of the target to analysis. Furthermore, the work from pretreatment to analysis needs to be performed by a skilled technician. In contrast, the work time required to calculate the mercury concentration using the above-mentioned calculation method of the present invention is about 3 to 4 hours, most of which is the time required to dry the sample. Moreover, the measurement using the fluorescent X-ray device does not need to be performed by a skilled technician, and can be sufficiently performed by an operator who is involved in the production of zinc oxide ore. Therefore, according to the mercury concentration calculation process ST31 using the above-mentioned procedure, unlike the conventional method, it is possible to easily and quickly determine the mercury concentration, which is approximately 1 / 10,000 of the lead content contained in the ``drying and heating process charge'', within the manufacturing facility that produces zinc oxide ore, at very little additional cost and very quickly (within a time lag of within 3 to 4 hours).

[0053] As an embodiment other than the above, the calculation process of the mercury concentration in the mercury concentration calculation process ST31 can be performed by a method of calculating the mercury concentration from the correlation between the zinc content and the mercury concentration shown in Fig. 4 (Fig. 4 shows the relationship between the zinc content and the mercury concentration index obtained by dividing the mercury concentration by a predetermined value). Calculation of the mercury concentration by such a method can be an effective alternative method, for example, when the zinc content in the "charge for the drying and heating process" is particularly high and the lead content is particularly low.

[0054] [Mercury load adjustment treatment ST32] The mercury loading adjustment process ST32 regards the product of the mercury concentration of the "charge material for the dry heating process" obtained in the mercury concentration calculation process ST31 and the charge amount of the "charge material for the dry heating process" as the "mercury loading," and adjusts this "mercury loading" so as to maintain the mercury concentration of the treated flue gas within a predetermined control standard value range. If the mercury concentration of the treated flue gas exceeds the upper limit of the predetermined control standard value range, an adjustment is made to decrease the mercury loading, and if the mercury concentration of the treated flue gas is below the lower limit of the predetermined control standard value range, an adjustment is made to increase the mercury loading.

[0055] The amount of the above-mentioned "drying heating process input material" can be measured, for example, by measuring the amount transported using a conveyor scale provided on a belt conveyor that transports each "drying heating process input material ("cake, etc.")" that is charged to the drying heating process S30.

[0056] The adjustment of the mercury loading amount in the mercury loading adjustment process ST32 can be performed by appropriately increasing or decreasing the "charged material for the dry heating process" to be charged to the dry heating process S30, more specifically, the amount of each of the above-mentioned various "cakes, etc.". Specifically, this adjustment of the charge amount can be performed by adjusting the transport amount of the belt conveyor that transports the "charged material for the dry heating process ("cakes, etc.")" or by measuring the amount of cut-out, which can be calculated from the relationship between the number of revolutions of the cut-out conveyor from the hopper and the amount of cut-out, and adjusting this amount as necessary.

[0057] Alternatively, the amount of the "charged material for the dry heating process" charged to the dry heating process S30 can be increased or decreased by selectively discharging each charge, such as the crude zinc oxide cake and the "exhaust gas dust-containing cake", from the treatment system and recharging each charge that was once discharged from the treatment system back into the treatment system according to the fluctuation of the "mercury load". When the amount of the "charged material for the dry heating process" charged is increased or decreased by the above procedure, specifically, when the mercury concentration of the treated exhaust gas exceeds a predetermined upper limit, a part of the "charged material for the dry heating process" is discharged from the treatment system before being charged into the dry heating furnace and temporarily stored in a storage location outside the treatment system in order to reduce the "mercury load" obtained based on the mercury concentration calculated in the mercury concentration measurement process ST31. When the mercury concentration of the treated exhaust gas falls below a predetermined lower limit, the "charged material for the dry heating process" temporarily stored outside the system is returned to the treatment system and charged into the dry heating furnace in order to increase the "mercury load".

[0058] Regarding the increase or decrease in the amount of each of the various "cakes, etc." constituting the "drying and heating process charge" by the mercury load adjustment process ST32, it is preferable to appropriately optimize the priority of each "cake, etc." as a target for adjustment of the charge amount, depending on the inherent mercury concentration of each "cake, etc." and its tendency of variation.

[0059] As a specific example of the optimization of the priority of the above-mentioned charging amount adjustment target, there can be mentioned an optimization procedure in which adjustment of the charging amount of only the charging materials to the drying and heating process other than the auxiliary crude zinc oxide raw material is given priority over adjustment of the charging amount of the auxiliary crude zinc oxide raw material. Since the "auxiliary crude zinc oxide raw material" directly charged to the drying and heating process from outside the treatment system usually has a relatively small variation in mercury concentration compared to other charging materials, by preferentially adjusting the charging amount of the other charging materials to the drying and heating process, the workload of adjusting the charging amounts of various charging materials can be reduced and the mercury concentration of the treated flue gas can be suppressed more efficiently and with high accuracy.

[0060] As another specific example of the optimization of the priority of the target of the adjustment of the charging amount, there can be mentioned an optimization procedure in which the adjustment of the charging amount of only the "exhaust gas dust-containing cake" containing the flue gas dust discharged from the flue gas treatment process S40 to the drying and heating process is given priority over the adjustment of the charging amount of other charging materials. Since mercury is mainly distributed to the flue gas in the treatment system, the "exhaust gas dust-containing cake" usually has the highest mercury concentration relatively. Therefore, by preferentially adjusting the charging amount of this "exhaust gas dust-containing cake", it is possible to more efficiently suppress the mercury concentration of the treated flue gas while keeping the fluctuation range of the production volume in the drying and heating process small.

[0061] In this way, according to the method for producing zinc oxide ore of the present invention, the mercury concentration in the treated exhaust gas can be controlled with high accuracy by an easily realized method.

[0062] If the manufacturing facility for producing zinc oxide ore is provided with a means for measuring the mercury concentration in the treated flue gas discharged from the flue gas treatment step S40, it is more preferable to perform a treated flue gas mercury concentration measurement process (not shown) for continuously measuring the mercury concentration in the treated flue gas and to perform control for feeding back information related to fluctuations in the mercury concentration to the mercury load adjustment process ST32. By performing such control, even if the mercury concentration in the treated flue gas suddenly fluctuates due to various factors, it is possible to maintain an extremely high level of safety in the management of the mercury concentration in the treated flue gas throughout the entire operation period. EXAMPLES

[0063] <Test operation 1 (verification of accuracy of mercury concentration management)> A trial operation for zinc oxide production was carried out for 12 days under the operating conditions of "crude zinc oxide cake" obtained from the wet process: 2-5 t / h, "exhaust gas dust-containing cake": 0-2 t / h, "auxiliary crude zinc oxide raw material": 0.5-2 t / h, crude zinc oxide cake extracted from the treatment system before being charged into the drying and heating furnace in the drying and heating process (hereinafter referred to as "extracted crude zinc oxide cake"): 0.5-4 t / h, and "exhaust gas dust-containing cake" extracted from the treatment system before being charged into the drying and heating furnace in the drying and heating process (hereinafter referred to as "extracted flue gas dust-containing cake"): 0-1 t / h, and the total charging amount of these five types of charges: 7-12 t / h.

[0064] In the first half of the above test operation (1st to 6th days), the operation was not performed according to the manufacturing method of the present invention. Specifically, during this period, mercury analysis was performed once a day by wet analysis, and the "mercury load amount", which is the product of the mercury concentration and the charging amount, was controlled according to the results, so that the mercury concentration of the treated exhaust gas was maintained within a predetermined control standard value range by controlling the charging amounts of each of the "crude zinc oxide cake", "exhaust gas dust-containing cake", "auxiliary crude zinc oxide raw material", "extracted crude zinc oxide cake", and "extracted exhaust gas dust-containing cake". The above wet analysis was performed by dissolving each cake and measuring it with an atomic absorption spectrometer.

[0065] In the latter half of the test operation (7th to 12th days), the operation was carried out according to the manufacturing method of the present invention. During this period, the "crude zinc oxide cake", "exhaust gas dust-containing cake", "auxiliary crude zinc oxide raw material", "extracted crude zinc oxide cake" and "extracted exhaust gas dust-containing cake" were sampled three times per day, and then, after three hours of drying treatment, the lead content of each sample was measured using a fluorescent X-ray analyzer. The fluorescent X-ray analyzer used was "ZSX PrimusIV (manufactured by Rigaku Corporation)".

[0066] After measuring the lead content, the mercury concentration of each of the five types of cakes was calculated by applying the measured lead content to a relational equation obtained from basic data on the correlation between lead content and mercury concentration that had been previously obtained. The data on the correlation between lead content and mercury concentration shown in Figure 3 was used as the basic data for calculating the mercury concentration from the lead content.

[0067] According to the mercury concentration calculated in this manner, the charged amounts of "crude zinc oxide cake," "exhaust gas dust-containing cake," "auxiliary crude zinc oxide raw material," "extracted crude zinc oxide cake," and "extracted flue gas dust-containing cake" were adjusted, thereby controlling the "mercury load" in the same way as in the first half of the operation, so that the mercury concentration of the treated exhaust gas was maintained within the specified control standard value range.

[0068] The results of the accuracy check of mercury concentration control in test operation 1 are shown in Table 1 below. In the first half of the test operation period, which was conducted using the conventional process, the average mercury concentration index in the treated flue gas was 181, while the variation (standard deviation) was 112. In contrast, in the second half of the test operation period, the average mercury concentration index in the treated flue gas was 182, while the variation (standard deviation) was 45, confirming a 60% reduction in the variation (standard deviation).

[0069] [Table 1]

[0070] <Test operation 2 (Confirmation of raw material processing volume)> During the first seven months of the operation period, the test operation was carried out under the operating conditions of 7 to 11 t / h of the total charge amount of five types of charges obtained from the wet process, namely, "crude zinc oxide cake", "exhaust gas dust-containing cake", "auxiliary crude zinc oxide raw material", "extracted crude zinc oxide cake", and "extracted exhaust gas dust-containing cake". Then, during the last seven months, the test operation was carried out under the operating conditions of 9 to 12 t / h of the total charge amount of the above five types of charges.

[0071] In the first half of the above test operation (1st month to 7th month), the operation was not performed according to the manufacturing method of the present invention. Specifically, during this period, mercury was analyzed by wet analysis twice a week, and according to the results, the "mercury load amount" which is the product of the mercury concentration and the charged amount was controlled by controlling the charged amounts of each of the "crude zinc oxide cake", "exhaust gas dust-containing cake", "auxiliary crude zinc oxide raw material", "extracted crude zinc oxide cake", and "extracted exhaust gas dust-containing cake" so that the mercury concentration of the treated exhaust gas was maintained within a predetermined control standard value range. The above wet analysis was performed by dissolving each cake and measuring it with an atomic absorption spectrometer.

[0072] In the latter half of the test operation (8th to 14th months), the operation was carried out according to the manufacturing method of the present invention. During this period, samples were taken five times per week for each of the "crude zinc oxide cake", "exhaust gas dust-containing cake", "auxiliary crude zinc oxide raw material", "extracted crude zinc oxide cake" and "extracted exhaust gas dust-containing cake", and then, after a drying process for three hours, the lead content of each sample was measured using a fluorescent X-ray analyzer. The fluorescent X-ray analyzer used was the same as that used in test operation 1.

[0073] After measuring the lead content, the mercury concentration of each of the five types of cakes was calculated by applying the measured lead content to a relational equation obtained from basic data on the correlation between lead content and mercury concentration that had been previously obtained. The data on the correlation between lead content and mercury concentration shown in Figure 3 was used as the basic data for calculating the mercury concentration from the lead content.

[0074] Based on the mercury concentration calculated in this manner, the amounts of "crude zinc oxide cake," "exhaust gas dust-containing cake," "auxiliary crude zinc oxide raw material," "extracted crude zinc oxide cake," and "extracted flue gas dust-containing cake" charged were adjusted to obtain the "mercury load," which is the product of the mercury concentration and the charged amount, so that the mercury concentration in the treated exhaust gas was maintained within the specified control standard value range.

[0075] The results of the raw material processing volume confirmation in test operation 2 are shown in Table 2 below. In the first half of the test operation period, which was carried out using the conventional process, the processing volume (recharge volume) of the "extracted crude zinc oxide cake" and the "extracted exhaust gas dust-containing cake" extracted from the processing system was increased by more than double. From these results, it was confirmed that the adoption of the manufacturing method of the present invention makes it possible to reduce the in-process inventory of raw materials and to significantly increase the processing volume of raw materials.

[0076] [Table 2]

[0077] The results of the above operation are shown in Figure 5. It can be seen that according to the present invention, the processing rates of the extracted crude zinc oxide cake and the extracted exhaust gas dust-containing cake were improved by more than doubling from 256 t / D to 538 t / D. [Explanation of symbols]

[0078] S10 Reduction roasting process S20 Wet process S30 Drying heating process ST31 Mercury concentration calculation process ST32 Mercury load adjustment treatment S40 Exhaust gas treatment process S50 Wastewater treatment process ST51 pH adjustment treatment

Claims

1. A method for producing zinc oxide ore, comprising: a dry heating step in which a charge for the dry heating step, which contains zinc as a main component and further contains lead and mercury, is calcined in a dry heating furnace to obtain zinc oxide ore; and an exhaust gas treatment step in which mercury is removed from exhaust gas generated in the dry heating step, The charge for the dry heating step is A crude zinc oxide cake obtained by a wet process in which crude zinc oxide dust recovered in a reduction roasting process for burning steel dust is separated from water-soluble impurities; A crude zinc oxide powder is directly charged into the drying and heating step from outside the treatment system for obtaining the crude zinc oxide cake; an exhaust gas dust-containing cake containing exhaust gas dust discharged from the exhaust gas treatment step; Contains as an ingredient a mercury concentration calculation process for measuring the lead content of each of the raw materials fed to the dry heating process by fluorescent X-ray analysis and calculating the mercury concentration of the raw materials fed to the dry heating process from the measured lead content; a mercury load adjustment process is performed by increasing or decreasing the amount of each of the raw materials charged in the dry heating process so as to maintain the mercury concentration of the treated flue gas discharged from the flue gas treatment process within a predetermined control standard value range, regarding the product of the mercury concentration of the materials charged in the dry heating process and the amount of the materials charged to the dry heating process as the mercury load. How zinc oxide ore is produced.

2. In the mercury load adjustment process, the adjustment of the amount of only the raw materials other than the crude zinc oxide powder raw material fed to the drying and heating process is given priority over the adjustment of the amount of the raw material zinc oxide powder fed to the drying and heating process. A method for producing the zinc oxide ore according to claim 1.

3. The mercury load adjustment process adjusts the amount of only the exhaust gas dust-containing cake fed to the drying and heating step in preference to adjusting the amount of other feed materials. A method for producing the zinc oxide ore according to claim 1.

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