JP7632040B2 - How zinc oxide ore is produced - Google Patents

Description

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 raw materials such as steel dust that contain zinc as well as lead and trace amounts of mercury as impurities.

Conventionally, zinc oxide ore has been widely used as a raw material for zinc ingots in zinc smelters. Crude zinc oxide, which is the raw material for zinc oxide ore, can also be obtained from steel dust generated from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry. From the perspective of promoting resource recycling, it is desirable to reuse steel dust. However, on the other hand, in addition to its main components of iron oxide and zinc oxide, steel dust also contains trace amounts of mercury as an impurity. It is essential to treat the treated exhaust gas that is ultimately 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 it (see Patent Document 1).

Conventionally, the widely used method for the above-mentioned exhaust gas treatment to sufficiently reduce the mercury concentration has been to control the mercury concentration in the treated exhaust gas that is ultimately 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 raw material, more specifically, by adjusting the input ratio of various raw materials with known mercury concentrations into the treatment system.

However, raw materials such as steel dust vary widely in mercury concentration even when they are the same raw material, and in the zinc oxide ore manufacturing process 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 zinc oxide ore manufacturing process in which raw materials with various mercury concentrations go through complex processes, it has been difficult to accurately manage the "mercury concentration of the treated exhaust gas" that is ultimately discharged outside the processing system using the above 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.

Therefore, when estimating the mercury concentration in treated exhaust gas using the above method, which relies on the mercury concentration at the raw material stage, it is necessary to adjust operating conditions that fully take into account the fluctuation range of the above estimated value of the mercury concentration in treated exhaust gas in order to keep the concentration below the standard value with a sufficient margin. For this reason, in order to ensure safety, it has often been necessary to sacrifice some degree of zinc oxide ore productivity in operating conditions.

In response to this, in recent years, a method has been developed for the above-mentioned exhaust gas treatment to sufficiently reduce the mercury concentration, in which the mercury load is calculated based on the mercury concentration of the intermediate product fed into the drying and heating process that produces the final product, zinc oxide ore, and the amount of product produced, and this is adjusted to maintain it within a specified management 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).

However, in order to accurately measure the concentration of mercury, which is only present in trace amounts in the first place, at the intermediate product stage when 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 using an atomic absorption analyzer (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 to further reduce the costs of controlling the mercury concentration in exhaust gases.

JP 2018-79456 A JP 2020-132970 A

The present invention aims to provide a method for producing zinc oxide ore that can control the mercury concentration of treated exhaust gas that is ultimately discharged outside the treatment system at low cost, quickly, and with high accuracy.

The inventors of the present invention have come up with the idea that it is possible to measure the lead content, which is usually contained in the intermediate product charged to the dry heating process and the auxiliary raw material added directly to the process (collectively referred to in this specification as the "charge for the dry heating process"), in the overall process of manufacturing zinc oxide ore, at a ratio of several percent to about 60%, by fluorescent X-ray analysis, and to calculate with sufficient accuracy the concentration of mercury, which is contained in a very small ratio in the "charge for the dry heating process" from this measurement value. They have then discovered that by utilizing the value of the mercury concentration calculated in this way, it is possible to control the mercury concentration of the treated exhaust gas discharged outside the treatment system at a lower cost, quickly, and with a high degree of accuracy, and have completed the present invention. More specifically, the present invention provides the following.

(1) A method for producing zinc oxide ore, comprising: a dry heating process in which a charge for the dry heating process, 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 process in which mercury is removed from the exhaust gas generated in the dry heating process. The method also includes a mercury concentration calculation process in which the lead content of the charge for the dry heating process is measured by X-ray fluorescence analysis, and the mercury concentration of the charge for the dry heating process is calculated from the measured lead content; and a mercury load adjustment process in which the product of the mercury concentration of the charge for the dry heating process and the charge amount to the dry heating process are regarded as the mercury load, and the mercury concentration of the treated exhaust gas discharged from the exhaust gas treatment process is maintained within a predetermined control standard value range by adjusting the mercury load to increase or decrease as necessary.

According to the zinc oxide ore manufacturing method (1), by making the "mercury concentration calculation process" and the "mercury load adjustment process" performed in a unique manner as essential processes in the production of zinc oxide ore, the mercury concentration of the treated exhaust gas discharged outside the treatment system can be controlled quickly, at low cost, and with high accuracy.

(2) The method for producing zinc oxide ore described in (1), in which the charge for the drying and heating process includes 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 process, adjustment of the amount of charge to the drying and heating process of only the charge for 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.

In the zinc oxide ore manufacturing method (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 sudden fluctuations in the mercury concentration of the treated exhaust gas discharged outside the treatment system, is given priority in adjusting the amount charged to the drying and heating process. This reduces the workload of adjusting the amount of each type of charge, and makes it possible to more efficiently and accurately suppress the mercury concentration of the treated exhaust gas.

(3) The method for producing zinc oxide ore described in (1) or (2), in which the charge in the drying and heating process comprises an exhaust gas dust-containing cake that contains exhaust gas dust discharged from the exhaust gas treatment process, and the mercury load adjustment process prioritizes adjustment of the amount of the exhaust gas dust-containing cake alone charged to the drying and heating process over adjustment of the amount of other charges.

In the manufacturing method of zinc oxide ore (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 "charged material to the drying and heating process" with the relatively highest mercury concentration, the amount of the cake charged to the drying and heating process is adjusted to be given priority over other charges. This makes it possible to suppress the mercury concentration of the treated exhaust gas while keeping the fluctuation range of the production volume in the drying and heating process small.

(4) The method for producing zinc oxide ore according to 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 processing 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 processing system and charging it into the drying and heating furnace, thereby increasing or decreasing the mercury load.

The zinc oxide ore manufacturing method (4) makes it possible to more quickly and flexibly suppress the mercury concentration in treated exhaust gas in response to frequent fluctuations in mercury load during operation.

(5) A method for producing zinc oxide ore according to any one of (1) to (4), comprising: 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, an adjustment is made to decrease the mercury load; and when the mercury concentration of the treated exhaust gas falls below a predetermined lower limit, an adjustment is made to increase the mercury load.

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

The present invention provides a method for producing zinc oxide ore that can control the mercury concentration of treated exhaust gas that is ultimately discharged outside the treatment system at low cost, quickly, and with high accuracy.

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. FIG. 2 is a flow diagram showing an example of a production process path of various "drying and heating process charge materials" in the zinc oxide ore production method of FIG. FIG. 1 is a correlation graph showing the relationship between the lead content (%) in the "drying and heating process charge" and the mercury concentration index. FIG. 1 is a correlation graph showing the relationship between the zinc content (%) in the "drying and heating process charge" and the mercury concentration index.

<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 such as steel dust that contain a very small amount of mercury as an impurity and a certain amount of lead or more. This process is usually carried out as a whole process including the steps shown in Fig. 1, namely, the reducing roasting step S10, the wet process S20, the dry heating step S30, the exhaust gas treatment step S40, and the 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 in the raw materials.

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

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

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

The mercury concentration calculation process ST31 is a process for calculating the mercury concentration of the "drying and heating process charge" charged to the drying and heating process S30 in the overall process for producing zinc oxide ore as illustrated in FIG. 1.

The mercury load adjustment process ST32 is a process for adjusting the "mercury load" calculated from the mercury concentration calculated by the mercury concentration calculation process ST31.

The method for producing zinc oxide ore of the present invention is particularly advantageous in production plants that use steel dust, which has a large variation in mercury concentration, as the main raw material. Below, we will explain in detail an embodiment in which steel dust is used as the main raw material for zinc oxide ore, as a specific example of a preferred embodiment of the method for producing zinc oxide ore of the present invention.

<Reduction roasting process>
The reducing roasting step S10 is a step in which raw materials (primary raw materials) such as steel dust are roasted at high temperature together with a reducing agent using a reducing roasting rotary kiln (RRK), which is usually a large rotary heating furnace. It is preferable to maintain and control the temperature inside the reducing 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.

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, the 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 mercury-containing recovered dust is charged as crude zinc oxide dust into the next process, the wet process S20.

The reduction roasting residue that does not volatilize during the reduction roasting process S10 and remains in the kiln is usually collected from the kiln discharge end as a product called iron-containing clinker, and because it contains a large amount of reduced iron, it is sent to steel manufacturers as raw iron material, etc.

<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.

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, the wet process S20 also includes crude zinc oxide powder, which has the same chemical composition as the crude zinc oxide dust and contains zinc, which is directly charged to the wet process as a secondary raw material without passing through the reduction roasting process S10, and undergoes the same separation process as the crude zinc oxide dust derived from the primary raw materials.

The crude zinc oxide dust that has been separated into a slurry is subjected to pH adjustment, concentration, and dehydration to produce a crude zinc oxide cake. This crude zinc oxide cake is then fed to the next step, the drying and heating step S30, as the "charge for the drying and heating step" (see Figures 1 and 2). For the concentration and dehydration steps, 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.

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 Figure 2). Note that this "exhaust gas dust-containing cake" usually contains a higher concentration of mercury than other zinc-containing materials, which has been concentrated during circulation within the treatment system.

<Drying and 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 produced 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.

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

In this specification, the term "auxiliary crude zinc oxide raw material" refers to raw material that is directly charged into the drying and heating process S30 from outside the processing system of the manufacturing facility that produces zinc oxide ore, without going through the wet process S20. Specifically, like the secondary raw material described above, crude zinc oxide powder containing zinc can be used as the "auxiliary crude zinc oxide raw material".

Then, in the dry heating process S30, almost the entire amount of mercury contained within a certain range in each of the above-mentioned various "dry heating process charges" 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).

<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 is generally a carbon compound such as granular coke having one or more sulfides selected from copper concentrate, zinc concentrate, lead concentrate, etc., attached to its surface.

When the exhaust gas treatment process S40 is performed in an exhaust gas treatment facility configured as described above, the mercury in the exhaust gas is adsorbed and recovered by the mercury adsorbent in the packed tower with a recovery rate of about 90%. However, since the main component of the exhaust gas dust containing mercury is zinc oxide, this is further recycled and charged repeatedly to the wet process S20, thereby making effective use of metal resources.

<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 trace amounts in the wastewater are precipitated and removed by neutralization treatment with slaked lime, and finally a pH adjustment treatment ST51 is performed to turn the treated wastewater into harmless wastewater.

<Method for controlling mercury concentration in treated exhaust gas>
The method for producing zinc oxide ore of the present invention is a partial process applicable to the overall process for producing zinc oxide ore shown in FIG. 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 FIG. 1).

The manufacturing method of zinc oxide ore of 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 exhaust gas." In order to achieve this purpose, the mercury concentration calculation process ST31 is an essential process, in which the concentration of mercury contained in the "drying and heating process charge" in very small amounts is indirectly calculated from the lead content, which is contained at a content rate approximately 10,000 times that of mercury. The mercury load amount that can be obtained based on the mercury concentration calculated in this way is then used as an index for controlling the mercury concentration in the treated exhaust gas in the subsequent mercury load adjustment process ST32.

In the mercury load adjustment process ST32, specifically, 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 charge amount of the "charged material for the dry heating process" is regarded as the "mercury load," and the "mercury load" is appropriately adjusted by increasing or decreasing the charge amount of the "charged material for the dry heating process" so as to maintain the mercury concentration of the treated exhaust gas within the specified control standard value range.

[Mercury concentration calculation process ST31]
The mercury concentration calculation process ST31 is a process for indirectly calculating the mercury concentration of the "drying and heating process charge" 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 the charge is entered into the drying and heating furnace where the drying and heating process S30 is performed.

The mercury concentration calculation process in mercury concentration calculation process ST31 first involves measuring the lead content in the "drying and heating process input material" rather than the mercury concentration in the "drying and heating process input material." This lead content is then measured using X-ray fluorescence analysis.

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 the measurement sample obtained by drying the "drying and heating process charge" sampled at regular intervals, by X-ray fluorescence analysis using an X-ray fluorescence measurement device. The "drying and heating process charge" 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.

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 equation obtained from basic data on the correlation between lead content and mercury concentration that has been previously obtained. Figure 3 shows a specific example of basic data showing the correlation between lead content and the mercury concentration index obtained by dividing the mercury concentration by a specified value.

As mentioned above, the mercury concentration of each type of "cake, etc." may vary greatly, so it is preferable to calculate the mercury concentration of each type of "cake, etc." individually using the above calculation method.

Here, in order to measure the extremely small amount of mercury concentration, which is about 1/10,000 of the lead content in the "drying and heating process charge" using the conventional method, wet analysis using specialized equipment was necessary, and it took about 24 hours from pretreatment of the target material to analysis. Furthermore, the work from pretreatment to analysis had 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, measurement using a fluorescent X-ray device does not require a skilled technician, and can be adequately performed by an operator who is involved in the production of zinc oxide ore. Therefore, according to the mercury concentration calculation process according to the above-mentioned procedure in the mercury concentration calculation process ST31, unlike the conventional method, it is possible to easily and quickly determine the mercury concentration, which is about 1/10,000 of the lead content contained in the "drying and heating process charge," in the manufacturing facility that produces zinc oxide ore, with very little additional cost and very quickly (within a time lag of 3 to 4 hours).

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

[Mercury Load Adjustment Process ST32]
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 charge amount of the "charged material for the dry heating process" is regarded as the "mercury loading," and this "mercury loading" is adjusted 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.

The amount of the "drying and heating process input materials" can be measured, for example, by measuring the amount of the material being conveyed using a conveyor scale provided on the belt conveyor that conveys each of the "drying and heating process input materials (cakes, etc.)" that are fed into the drying and heating process S30.

The mercury load adjustment in the mercury load adjustment process ST32 can be performed by appropriately increasing or decreasing the amount of the "drying and heating process charge" charged to the drying and heating process S30, more specifically, the amount of each of the above-mentioned various "cakes, etc." This charge amount adjustment can be performed, specifically, by adjusting the transport amount of the belt conveyor that transports the "drying and heating process charge ("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.

Alternatively, the amount of the "drying and heating process charge" to the drying and heating process S30 can be increased or decreased by selectively discharging each charge, such as the crude zinc oxide cake or the "exhaust gas dust-containing cake", outside the treatment system and recharging each of the charges once discharged outside the treatment system into the treatment system according to the fluctuation of the "mercury load". When the amount of the "drying and heating process charge" 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 "drying and heating process charge" is discharged outside the treatment system before being charged into the drying and 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. Also, when the mercury concentration of the treated exhaust gas falls below a predetermined lower limit, the "drying and heating process charge" temporarily stored outside the system is returned to the treatment system and charged into the drying and heating furnace in order to increase the "mercury load".

In addition, when increasing or decreasing 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 charge amount adjustment according to the specific mercury concentration of each "cake, etc." and its tendency of variation.

One specific example of the optimization of priority for the above-mentioned adjustment of the charge amount can be an optimization procedure in which adjustment of the charge amount of only the charge materials to the drying and heating process other than the auxiliary crude zinc oxide raw material is given priority over adjustment of the charge amount of the auxiliary crude zinc oxide raw material. The "auxiliary crude zinc oxide raw material" that is 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 charge materials. Therefore, by giving priority to adjusting the charge amount of other charge materials to the drying and heating process, the workload of adjusting the charge amounts of various charge materials can be reduced, and the mercury concentration of the treated exhaust gas can be suppressed more efficiently and with high precision.

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

In this way, the zinc oxide ore manufacturing method of the present invention makes it possible to control the mercury concentration in the treated exhaust gas with high precision using an easy-to-implement method.

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

<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 to 5 t/h, "exhaust gas dust-containing cake": 0 to 2 t/h, "auxiliary crude zinc oxide raw material": 0.5 to 2 t/h, crude zinc oxide cake extracted from the treatment system before being charged into a drying and heating furnace in which a drying and heating step is performed (hereinafter referred to as "extracted crude zinc oxide cake"): 0.5 to 4 t/h, and "exhaust gas dust-containing cake" extracted from the treatment system before being charged into a drying and heating furnace in which a drying and heating step is performed (hereinafter referred to as "extracted exhaust gas dust-containing cake"): 0 to 1 t/h, and the total charging amount of these five types of charges: 7 to 12 t/h.

In the first half of the above test operation (1st to 6th days), the operation was not carried out according to the manufacturing method of the present invention. Specifically, during this period, mercury analysis was carried out once a day by wet analysis, and the "mercury load amount," which is the product of the mercury concentration and the amount charged, was controlled based on the results of the analysis, so that the mercury concentration in the treated exhaust gas was maintained within the specified control standard value range 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." The above wet analysis was carried out by dissolving each cake and measuring it with an atomic absorption spectrometer.

In the latter half of the test operation (7th to 12th days), the production method of the present invention was used. During this period, samples were taken three times per day 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." After three hours of drying, the lead content of each sample was measured using an X-ray fluorescence analyzer. The X-ray fluorescence analyzer used was a "ZSX Primus IV (manufactured by Rigaku Corporation)."

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.

According to the mercury concentration calculated in this way, the amount 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" charged was adjusted, and the "mercury load" was controlled 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 management standard value range.

The results of the accuracy check of mercury concentration management 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).

<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 that the total charging amount of the five types of charges, i.e., "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" obtained from the wet process, was 7 to 11 t/h. Then, during the second seven months, the test operation was carried out under the operating conditions that the total charging amount of the five types of charges was 9 to 12 t/h.

In the first half of the above test operation (1st to 7th months), the operation was not carried out 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 amount charged, was controlled by controlling the amount 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" charged so that the mercury concentration in the treated exhaust gas was maintained within the specified control standard value range. The above wet analysis was carried out by dissolving each cake and measuring it with an atomic absorption spectrometer.

In the latter half of the test operation (8th to 14th months), the production method of the present invention was used. 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." After three hours of drying, the lead content of each sample was measured using an X-ray fluorescence analyzer. The X-ray fluorescence analyzer used in test operation 1 was the same.

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.

Based on the mercury concentration calculated in this way, the "mercury load," which is the product of the mercury concentration and the amount charged, was adjusted by adjusting 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 so that the mercury concentration in the treated exhaust gas was maintained within the specified control standard value range.

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 conducted using the conventional process, it was possible to more than double the processing volume (recharge volume) of the "extracted crude zinc oxide cake" and "extracted exhaust gas dust-containing cake" that were extracted from the processing system. From these results, it was confirmed that by adopting the manufacturing method of the present invention, it is possible to reduce in-process inventory of raw materials and significantly increase the processing volume of raw materials.

The results of the above operation are shown in Figure 5. It can be seen that according to the present invention, the processing volume of the extracted crude zinc oxide cake and the extracted exhaust gas dust-containing cake has more than doubled, from 256 t/D to 538 t/D, improving the process.

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

Claims (3)

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 charged in the dry heating process by fluorescent X-ray analysis and calculating the mercury concentration of the charged material 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. 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 charged to the drying and heating process is given priority over the adjustment of the amount of the raw zinc oxide powder raw material charged.
A method for producing the zinc oxide ore according to claim 1. 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 .

Images