Method for producing defluorinated residue and method for producing zinc oxide

Abstract

To provide a technique for efficiently removing fluorine from a residue obtained after subjecting crude zinc oxide to acid leaching.SOLUTION: The present invention provides a method for producing a defluorinated residue and related techniques, the method comprising heating, under humid conditions, an acid leaching residue obtained after acid-leaching of zinc from crude zinc oxide containing fluorine, at a temperature of 500°C or more and 1300°C or less, thereby lowering the mass ratio of fluorine in the acid leaching residue.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Steel dust (steel dust) generated during the steel manufacturing process contains a relatively large amount of zinc in addition to iron. Therefore, steel dust is used as zinc-containing ore, and the zinc contained in it is widely recovered as crude zinc oxide dust to produce zinc oxide ore.

[0003] Patent Document 1 describes (abstract) a method for producing zinc oxide ore that can increase the chlorine removal rate while suppressing the use of sodium carbonate in a wet process, thereby maintaining the chlorine content in the crude zinc oxide cake at a low level. Patent Document 1 states: a reduction roasting step of reducing and roasting a primary raw material, which is an iron-containing crude zinc oxide raw material containing chlorine and iron, to obtain crude zinc oxide dust; a wet process for obtaining a crude zinc oxide cake by repulping the crude zinc oxide cake raw material, which is composed of the crude zinc oxide dust and a secondary raw material that is a non-iron-containing crude zinc oxide raw material that contains chlorine and does not contain iron, with an aqueous sodium carbonate solution and then dehydrating the raw material; A process for producing zinc oxide ore is described, which comprises a dry heating step of calcining the crude zinc oxide cake to obtain zinc oxide ore (claim 1). It is also described that the firing temperature in the drying and heating step is preferably 1000° C. or higher and 1200° C. or lower (

[0046] ).

[0004] Patent Document 2 describes (abstract) an improvement in the efficiency of removing fluorine and chlorine in a method for recovering valuable metals and removing fluorine and chlorine from steelmaking dust containing zinc, iron, fluorine, chlorine, etc. Patent Document 2 describes a method for recovering valuable metals such as zinc from steelmaking dust, which comprises kneading the steelmaking dust with sulfuric acid and then performing sulfation roasting at a temperature of 350 to 550°C, thereby transferring chlorine and fluorine to the roasting exhaust gas (Claim 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-123778 [Patent Document 2] Japanese Patent Application Publication No. 07-316677 Summary of the Invention [Problem to be solved by the invention]

[0006] In both Patent Document 1 and Patent Document 2, steelmaking dust is treated. As a method for recovering zinc from crude zinc oxide obtained by roasting steelmaking dust, there is a method of acid leaching the crude zinc oxide and recovering the leached zinc. The residue of the acid leaching contains zinc, and from the viewpoint of effective utilization of resources, the residue is input as a zinc raw material to a roasting process of zinc refining to recover zinc. In this case, if the fluorine content of the residue is high, problems such as poor quality of neutralization by-products in the treatment of exhaust gas from a roasting furnace may occur. For this reason, there is a demand for removing fluorine from the residue after acid leaching of crude zinc oxide obtained by roasting steelmaking dust.

[0007] An object of the present invention is to provide a technique for efficiently removing fluorine from the residue after acid leaching of crude zinc oxide. [Means for solving the problem]

[0008] The inventors of the present invention have made it clear through extensive research that by introducing water from outside the heating container into the heating container in which the residue exists to humidify the container and setting the temperature inside the heating container to 500° C. or more and 1,300° C. or less, a significantly higher fluorine volatilization rate can be achieved as compared to the case in which water is not introduced, as will be shown in the Examples section below.

[0009] The first invention based on the above findings is: This is a method for producing a defluorination residue, which comprises heating an acid leaching residue remaining after subjecting fluorine-containing crude zinc oxide to acid leaching to remove zinc in an acid leaching residue in a humidified atmosphere at 500°C or higher and 1,300°C or lower, thereby reducing the mass proportion of fluorine in the acid leaching residue.

[0010] The second invention is a humidifying step of placing the acid leaching residue in a heating vessel and introducing water into the heating vessel to create a humid atmosphere in the heating vessel; a heating step of lowering the mass ratio of fluorine in the acid leaching residue by adjusting the temperature inside the heating vessel humidified in the humidifying step to 500° C. or more and 1,300° C. or less; The method for producing a defluorination residue according to claim 1, comprising the steps of:

[0011] The third invention is In the humidification step, the temperature inside the humidified heating container is set to 500° C. or more and 1000° C. or less, and the water pressure inside the heating container is set to 0.2 atm or more and 0.8 atm or less, thereby reducing the mass ratio of fluorine in the acid leaching residue to 100 ppm or less.

[0012] The fourth invention is In the method for producing a defluorination residue, the acid leaching residue before the humidification step has a fluorine mass percentage of 0.3 mass % or more and a chlorine mass percentage of 0.5 mass % or more.

[0013] The fifth invention is A method for producing zinc oxide, comprising the steps of: obtaining zinc oxide by using the defluorination residue produced by the method for producing the defluorination residue as a zinc smelting raw material. Effect of the Invention

[0014] According to the present invention, fluorine can be efficiently removed from the residue remaining after acid leaching of crude zinc oxide. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional side view of an apparatus for carrying out the humidifying step and the heating step in this embodiment. [Diagram 2] FIG. 2 is a graph showing the results when the fluorine volatilization rate (%) from the acid leaching residue is plotted on the vertical axis and the water supply amount (mL / h) (water pressure (atm)) is plotted on the horizontal axis. [Diagram 3] FIG. 3 is a graph showing the results when the fluorine volatilization rate (%) from the acid leaching residue is plotted on the vertical axis and the temperature (°C) inside the heating vessel is plotted on the horizontal axis, in which ◯ indicates a humidification rate of 0 mL / h (comparative example) and ■ indicates a humidification rate of 16 mL / h (embodiment). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] This embodiment will be described below. The symbol "to" indicates a value greater than or equal to a given value and less than or equal to a given value.

[0017] The present embodiment relates to a method for producing a defluorination residue, which reduces the mass ratio of fluorine from a residue remaining after acid leaching of zinc from fluorine-containing crude zinc oxide. The present embodiment also has an aspect of being an invention of a method for removing fluorine from the fluorine-containing residue. Here, the residue remaining after acid leaching of zinc from fluorine-containing crude zinc oxide is also referred to as an "acid leaching residue." Moreover, the residue remaining after the defluorination treatment is also referred to as a "defluorination residue."

[0018] In this embodiment, the residue obtained after subjecting fluorine-containing crude zinc oxide to acid leaching is heated to 500° C. or higher and 1300° C. or lower in a humidified atmosphere to reduce the mass ratio of fluorine in the acid leaching residue. This treatment is also called "defluorination treatment."

[0019] The contents of the defluorination treatment may be expressed by dividing it into steps as follows. A humidification step of placing the acid leaching residue in a heating vessel and introducing water into the heating vessel to create a humid atmosphere in the heating vessel. a heating step of lowering the mass ratio of fluorine in the acid leaching residue by adjusting the temperature in the heating vessel humidified in the humidifying step to 500° C. or more and 1,300° C. or less;

[0020] The "residue (acid leaching residue) remaining after subjecting crude zinc oxide to acid leaching of zinc" is the residue remaining after leaching of zinc from crude zinc oxide obtained from, for example, steelmaking dust. The acid leaching residue is mainly composed of a composite oxide of zinc and iron (highest mass%). On the other hand, the acid leaching residue contains fluorine. Therefore, the residue may be referred to as a "fluorine-containing metal oxide."

[0021] The acid leaching may be zinc leaching by mixing an acid with crude zinc oxide. The acid may be, for example, a sulfuric acid solution. As shown in the examples below, in a test example using a residue after acid leaching of crude zinc oxide with a sulfuric acid solution, a higher fluorine volatilization rate can be achieved compared to a case where water is not introduced in the heating step when the heating temperature is the same as that when water is not introduced. On the other hand, the acid may be other acid solutions (mineral acids, organic acids). The mineral acid solution may or may not contain sulfuric acid in addition to other mineral acids (nitric acid, hydrochloric acid).

[0022] In this specification, the term "humidified atmosphere" is not limited as long as water in the form of liquid, droplets (e.g., mist), or water vapor is introduced into a heating vessel containing the acid leaching residue.

[0023] For example, mist-like water may be introduced from outside the heating container while the inside of the heating container is heated to 100°C or higher (e.g., 200°C) to humidify the inside of the heating container containing the residue, and then the inside of the heating container may be heated to 500°C or higher and 1300°C or lower. Alternatively, water vapor may be introduced directly into the heating container. Also, after water is introduced into the heating container, the inside of the heating container may be heated from room temperature to the above-mentioned temperature range. All of the examples in this paragraph are encompassed by the "humidified atmosphere." The main gas in the heating vessel may be the atmosphere, and the pressure inside the heating vessel may be approximately atmospheric pressure.

[0024] The lower limit of the temperature may be 700° C. or 800° C. While a lower temperature reduces the cost of operation, a higher temperature results in a higher fluorine volatilization rate, as shown in the Examples section below. Setting the lower limit at 700° C. or 800° C. is one example of a lower limit determined in consideration of the balance between the cost and the fluorine volatilization rate.

[0025] The upper limit of the temperature may be 1100°C, which has been tested as shown in the Examples section below, or may be 1000°C or lower, or may be less than 1000°C.

[0026] An example of a combination of the upper and lower limits is 500°C or higher and 1300°C or lower, or 700°C or higher and 1000°C or lower, or 800°C or higher and less than 1000°C. The temperature may be constant, but may also be varied up or down during processing. The heating device to be installed in the heating vessel may be a commercially available furnace, for example a tubular furnace which is resistant to halogens and the atmosphere therein is easily controlled.

[0027] By going through the above-mentioned steps, fluorine can be efficiently removed from the residue (acid leaching residue) remaining after the crude zinc oxide is leached with acid.

[0028] As an example of a specific result, as shown in the Examples section below, the mass ratio of fluorine in the residue after the defluorination treatment (defluorination residue) can be reduced to 100 ppm or less, and even 70 ppm or less. Moreover, as shown in the Examples section below, these results can be achieved by setting the temperature in the heating container to a relatively low temperature of 1000°C or less. The heating temperature, heating time, and amount of water introduced into the heating container in the heating step can be appropriately set according to the fluorine content in the residue to be subjected to the heating step and the upper limit of the fluorine content required for the residue after the defluorination treatment. In this case, the lower the heating temperature and the shorter the heating time in the heating step, the more advantageous it is in terms of cost.

[0029] As shown in the Examples section below, not only the mass ratio of fluorine in the defluorination residue but also the mass ratio of halogens other than fluorine (e.g., chlorine) is low (e.g., less than 50 ppm). In other words, the mass ratio of halogens other than fluorine (e.g., chlorine) in the defluorination residue can be made less than 50 ppm, or 100 ppm or less. According to this embodiment, such a state of low mass ratio can be quickly achieved (within 1 hour of heating time in the Examples section below).

[0030] The lower limit of the mass ratio of fluorine in the residue before the defluorination treatment is, for example, more than 0.01 mass%, and may be 0.3 mass% or more. There is no upper limit, but it may be, for example, 0.5 mass% or less. The lower limit of the mass ratio of halogens other than fluorine (e.g., chlorine) in the residue before the defluorination treatment is, for example, more than 0.01 mass%, and may be 0.5 mass% or more. There is no upper limit, but it may be, for example, 12 mass% or less, and preferably 10 mass% or less.

[0031] In addition, as the name suggests, the humidification process requires only introducing water from outside the heating vessel to humidify the inside of the vessel. Water is sufficient for humidification, and this also contributes to low-cost fluorine removal. If the goal is to reduce costs, water other than pure water (for example, tap water or industrial water) may be used.

[0032] In the humidification step, the temperature in the humidified heating vessel can be set to 500° C. or more and 1300° C. or less, and at this time, the water pressure (defined in the Examples section below) in the heating vessel is preferably set to 0.2 atm. or more and 0.8 atm. The lower limit may be 0.3 atm or 0.4 atm. This allows the mass proportion of fluorine in the acid leaching residue to be reduced to 100 ppm or less.

[0033] In the heating step, the time for keeping the temperature in the heating vessel at 500°C or more and 1300°C or less may be 30 minutes or more and 24 hours or less. According to this embodiment, the acid leaching residue can be quickly (30 minutes or more and 24 hours or less) transferred to a state in which the mass proportion of fluorine is low. Keeping the temperature in the heating vessel at 900°C or more is preferable in terms of the volatilization rate of fluorine, as shown in the Examples section below.

[0034] The defluorination residue obtained by each of the above steps may be used as a raw material for zinc smelting, for example, without any limitation. The present embodiment also has an aspect of an invention of a method for producing zinc oxide, which obtains zinc oxide from the raw material for zinc smelting. A known zinc smelting method may be adopted as a method for producing zinc oxide. As an example, for example, the defluorination residue (composite oxide of zinc and iron) may be roasted to extract zinc, and zinc may be obtained from the leachate by electrolytic deposition. The zinc in the defluorination residue (composite oxide of zinc and iron) may be leached under high pressure and strong acid. Alternatively, the zinc may be leached using an autoclave while adopting a method called the hematite method (for example, the specification of Japanese Patent No. 5114764).

[0035] According to this embodiment, fluorine can be efficiently removed from the residue after acid leaching of crude zinc oxide. In addition, it becomes possible to select a treatment at a lower temperature than the high temperature (1000°C or higher and 1200°C or lower) described in Patent Document 1. In addition, the sulfation roasting described in Patent Document 2 becomes unnecessary, which leads to cost reduction.

[0036] The technical scope of the present invention is not limited to the above-described embodiment, but includes various modifications and improvements within the scope of the specific effects obtained by the constituent elements of the invention and their combinations. EXAMPLES

[0037] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples. Furthermore, the comparative examples described below are not necessarily publicly known examples.

[0038] Example 1 Crude zinc oxide obtained by roasting steel dust was subjected to an acid leaching treatment to extract zinc. A sulfuric acid solution was used as the leaching solution, and after the leaching treatment, the residue was recovered by solid-liquid separation. The composition of the acid leaching residue was as follows. The composition described in the Examples section was measured using an ICP analyzer (iCAP6000 manufactured by Thermo Scientific). F (fluorine): 0.38% by mass Cl (chlorine): 0.51% by mass Fe (iron): 19.8% by mass Pb (lead): 9.2% by mass Zn (zinc): 20.9% by mass (The remainder is mainly oxygen and sulfur)

[0039] FIG. 1 is a schematic cross-sectional side view of an apparatus for carrying out the humidifying step and the heating step in this embodiment.

[0040] 3.5 g of the acid leaching residue (S) is placed in a heating vessel 1 shown in the center of FIG.

[0041] A water supply unit 2 is shown on the lower right side of the heating vessel 1 in Fig. 1. The water supply amount (flow rate) using a peristaltic pump was set to 0 mL / h (treated as a comparative example), 16 mL / h, 37 mL / h, and 100 mL / h for each test example. Distilled water was supplied.

[0042] An air supply unit 3 is shown above the right side of the heating vessel 1 in Fig. 1. Air is introduced into the heating vessel 1 at a rate of 500 mL / min.

[0043] On the left side of the heating vessel 1 in Fig. 1, there is an exhaust section that absorbs gas generated in the heating vessel 1. Three absorption tubes (41-43) are connected in series in the exhaust section, and an aqueous sodium hydroxide solution (0.1 M) is contained in the absorption tube 42. The absorption tube 41 is provided as a measure against backflow of the aqueous sodium hydroxide solution in the absorption tube 42. The water in the heating vessel 1 condenses and creates negative pressure, which can cause the backflow. With the absorption tube 41, even if the aqueous sodium hydroxide solution backflows, it will remain inside the absorption tube 41.

[0044] The specific steps are as follows: After placing the acid leaching residue (S) in the heating vessel 1, the inflow of air is started to heat the inside of the heating vessel 1. This heating is also called roasting. When the temperature inside the heating vessel 1 reaches about 150 to 200°C, the supply of water is started. Then, the vessel is heated at about 50°C / min to the temperature shown in each test example (700°C, 800°C, 900°C, 1000°C, 1100°C), and the temperature is maintained for 1 hour. Thereafter, the water supply is stopped, and the temperature is lowered while the air supply is maintained. After the temperature is lowered, the residue is taken out.

[0045] As an example, after roasting to 900°C and supplying water at 100 mL / h for 1 hour, the composition of the residue was as follows: F(fluorine): 51ppm Cl (chlorine): Less than 50 ppm Fe (iron): 23.6 mass% Pb (lead): 9.34% by mass Zn (zinc): 23.6% by mass

[0046] FIG. 2 is a graph showing the results when the fluorine volatilization rate (%) from the residue is plotted on the vertical axis and the water supply amount (mL / h) (and the water pressure (atm) at that time) is plotted on the horizontal axis.

[0047] In this specification, the "moisture pressure" is defined as the ratio of the amount of air inflow when the temperature is raised to a predetermined heating temperature (roasting temperature) with an air inflow rate of 500 mL / min, to the amount of air inflow when the supplied water turns to water vapor. In Fig. 2, the value of the moisture pressure at an added water rate of 37 mL / h is 0.6 atm. The value of the moisture pressure at an added water rate of 0 mL / h is the value assumed to be the amount of water vapor at 25°C, atmospheric pressure, and humidity of 70%.

[0048] In this specification, the "volatility rate of fluorine" is a value obtained by the formula (1-A / B), where A and B are as follows: A = F (fluorine) content after heating process / Fe (iron) content after heating process B = F (fluorine) content before heating process / Fe (iron) content after heating process The reason for setting the above A and B is to avoid the effect on the volatilization rate due to partial loss of the residue after the heating process, and to set it as the Fe (iron) content standard.

[0049] As shown in Figure 2, when the amount of added water was 0 mL / h, the volatilization rate was about 65% at 700°C, about 90% at 800°C, and about 97% at 900°C. On the other hand, when the amount of added water was 16 mL / h, the volatilization rate was 85% at 700°C, 95% at 800°C, and 98% at 900°C. Humidification significantly increased the fluorine volatilization rate. The tendency for the fluorine volatilization rate to increase significantly was also observed when the amount of added water was 37 mL / h and 100 mL / h.

[0050] As shown in Fig. 2, if a humidification step is performed, a good fluorine volatilization rate can be achieved even at 1000°C or lower. Looking at it from another perspective, the results are not very different whether the temperature is 1100°C, 1000°C, or 900°C. In that case, when considering the operating costs, it is preferable to adopt the relatively low temperature of 900°C among these temperature options. With the present invention, it is possible to adopt heating at such a relatively low temperature when removing fluorine. However, this is merely a possible temperature, and the present invention is not limited to this temperature.

[0051] FIG. 3 is a graph showing the results when the fluorine volatilization rate (%) from the residue is plotted on the vertical axis and the temperature (°C) inside the heating container is plotted on the horizontal axis, in which a circle indicates a humidification rate of 0 mL / h (comparative example) and a square indicates a humidification rate of 16 mL / h (embodiment).

[0052] As shown in Figure 3, by performing the humidification process, a better fluorine volatilization rate can be achieved compared to when the humidification process is not performed. In the relatively low temperature range below 1000°C (especially in the range of 700-800°C), the difference in the fluorine volatilization rate is significant, and the effect of performing the humidification process is remarkable. [Explanation of symbols]

[0053] 1 heating container 2 Water supply section 3 Air supply section M. Distilled water S Acid leaching residue 41 Absorber tube 42 Absorber tube 43 Absorber tube

Claims

1. A method for producing a defluorination residue, comprising heating an acid leaching residue remaining after subjecting fluorine-containing crude zinc oxide to acid leaching to 500° C. or more and 1,300° C. or less in a humidified atmosphere to reduce a mass ratio of fluorine in the acid leaching residue.

2. a humidifying step of placing the acid leaching residue in a heating vessel and introducing water into the heating vessel to create a humid atmosphere in the heating vessel; a heating step of lowering the mass ratio of fluorine in the acid leaching residue by adjusting the temperature inside the heating vessel humidified in the humidifying step to 500° C. or more and 1,300° C. or less; The method for producing a defluorinated residue according to claim 1 , comprising the steps of:

3. 3. The method for producing a defluorinated residue according to claim 2, wherein in the humidifying step, a temperature in the humidified heating container is set to 500° C. or more and 1000° C. or less, and a water pressure in the heating container is set to 0.2 atm or more and 0.8 atm or less, thereby reducing a mass ratio of fluorine in the acid leaching residue to 100 ppm or less.

4. 3. The method for producing a defluorinated residue according to claim 2, wherein the acid leaching residue before the humidification step has a fluorine mass percentage of 0.3 mass% or more and a chlorine mass percentage of 0.5 mass% or more.

5. A method for producing zinc oxide, comprising the steps of: obtaining zinc oxide by using a defluorination residue produced by the method for producing a defluorination residue according to claim 1 or 2 as a raw material for zinc smelting.

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