Method for filtering wastewater, filter, method for producing ferronickel, and equipment for producing ferronickel

Abstract

To reduce concentration of suspended substances in waste water discharged in a process of a wet process, and prevent a recovery rate of nickel from lowering by preventing loss of nickel contained in the suspended substances, in a dry-type smelting method for manufacturing ferronickel.SOLUTION: In a dry-type smelting method for manufacturing ferronickel by sequentially performing a drying step S1, a firing step S2 and a melting reduction step S3, a filtration method of waste water includes using ferronickel slag as a filter medium 44, separated and removed from ferronickel metal in the melting reduction step S3, in the filtration method of waste water containing suspended substances separated and recovered by wet process from an exhaust gas generated in the drying step S1 and / or the firing step S2 and containing dust derived from raw material ore 11.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for filtering drainage, a method for manufacturing ferronickel using the filtering method, a filter that can be suitably used for the filtering method, and a ferronickel manufacturing facility equipped with the filter.

Background Art

[0002] In the manufacturing process of ferronickel, which is an alloy of iron and nickel, nickel oxide ores such as saprolite ore containing nickel (hereinafter also simply referred to as "ore") are used as raw materials, and a series of processes including a drying process, a firing process, and a smelting reduction process are performed on this ore to manufacture ferronickel. A dry smelting method is generally adopted (see Patent Document 1).

[0003] The above drying process is performed using a rotary dryer. In this process, dust derived from ores and the like is generated during the drying treatment. This dust is discharged together with the exhaust gas from the rotary dryer and recovered by the exhaust gas treatment equipment installed alongside the rotary dryer. Then, the dust recovered by the above exhaust gas treatment equipment is adjusted to a moisture content of about 25% to 35% by mass by adding water or the like for dust prevention, and then re-introduced into the rotary dryer that performs the drying process together with the raw material ore. The moist dust is subjected to a drying treatment together with the raw material ore, and the ore dried by reducing the attached moisture to about 15% to 25% by mass (hereinafter referred to as "dried ore") is charged into a rotary kiln that performs the firing process (see FIGS. 1 and 4).

[0004] Incidentally, the moisture content of the mixture of dried ore and dust discharged from the rotary dryer outlet is approximately 15% to 25% by mass, making it more prone to generating dust compared to the raw ore. Therefore, a wet dust collector (see Figure 2) is used as a dust collection system at the rotary dryer outlet to recover the dust. In this wet dust collector, the airflow introduced into the machine comes into contact with the washing water supplied to the machine, thereby capturing solid matter (dust) in the airflow into the liquid. As a result, the airflow is discharged outside the machine with the dust removed. On the other hand, dust captured in the liquid that is large enough to settle is discharged outside the machine via a bottom-discharge valve located at the bottom. Other dust that is not large enough to settle is discharged outside the machine via an overflow. However, at this time, it disperses as suspended matter in the washing water (wastewater), causing the wastewater to suspend. Therefore, before discharging the wastewater from the system, a coagulant is added to separate the suspended matter by settling.

[0005] In the operation using the wet dust collector described above, fluctuations in operations and raw materials could cause a sudden increase in the amount of dust in the airflow. In this case, the concentration of suspended solids in the wastewater discharged from the wet dust collector would also suddenly increase, resulting in insufficient sedimentation and separation, and the suspended solids could be discharged outside the system. Since the discharged suspended solids also contain nickel, a decrease in the nickel recovery rate was also a problem. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-206344 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to reduce the concentration of suspended solids in wastewater discharged during the wet treatment process in a dry smelting method for producing ferronickel, and to prevent the loss of nickel contained in the suspended solids, thereby preventing a decrease in the nickel recovery rate. [Means for solving the problem]

[0008] The inventors of the present invention have come to the realization that the above problem can be solved by using ferronickel slag, obtained by smelting nickel oxide ore, as a filter material for filtering wastewater containing suspended solids discharged during the wet treatment process in a dry smelting method for producing ferronickel, and have completed the present invention.

[0009] (1) In a dry smelting method for producing ferronickel by sequentially carrying out a drying process, a calcination process and a melt-reduction process, a method for filtering wastewater containing suspended solids separated and recovered by wet treatment from exhaust gas generated in the drying process and / or calcination process and containing dust derived from the raw ore, wherein the filter material for filtering the wastewater is ferronickel slag separated and removed from ferronickel metal in the melt-reduction process. Methods for filtering wastewater.

[0010] According to the wastewater filtration method of (1), in the dry smelting method for producing ferronickel, the concentration of suspended solids in the wastewater discharged during the wet treatment process can be reduced, and the loss of nickel contained in the suspended solids can be prevented, thereby preventing a decrease in the nickel recovery rate.

[0011] (2) The wastewater filtration method according to (1), wherein the exhaust gas is an exhaust gas containing dust derived from raw ore that is generated when the dried ore that has been dried through the drying process is discharged.

[0012] The wastewater filtration method in (2), similar to the wastewater filtration method in (1), reduces the concentration of suspended solids in the wastewater discharged during the wet treatment process, prevents the loss of nickel contained in the suspended solids, and prevents a decrease in the nickel recovery rate in the dry smelting method for producing ferronickel. Here, the exhaust gas containing dust discharged from the outlet of the rotary dryer, etc., which performs the drying process in the dry smelting method for producing ferronickel, has a relatively low discharge temperature and contains water vapor. For this reason, if a dry dust collector is used as the dust collection equipment, there is a concern that problems may arise, such as a decrease in dust removal capacity due to clogging caused by the filter cloth getting wet. Therefore, it is preferable to use a wet dust collector to recover the dust discharged from the outlet of such a rotary dryer, etc., thereby reliably avoiding the above-mentioned problems. Furthermore, by applying the wastewater filtration method in (2) to a manufacturing process that requires dust collection by wet treatment in this way, the nickel recovery rate in the process can be maintained at a higher level than before.

[0013] (3) The wastewater filtration method according to (1) or (2), wherein the coarseness ratio of the ferronickel slag is 2.6 or more and 3.2 or less.

[0014] According to the wastewater filtration method of (3), the recovery rate of suspended solids and nickel from the wastewater discharged during the wet treatment process can be further improved in the wastewater filtration method of (1).

[0015] (4) The wastewater filtration method according to (1) or (2), wherein the wastewater is subjected to a sedimentation treatment before the filtration is performed.

[0016] According to the wastewater filtration method of (4), the lifespan of the filter material can be extended when implementing the wastewater filtration method of (1) or (2), and furthermore, the concentration of suspended solids in the wastewater discharged during the wet treatment process can be reduced.

[0017] (5) The wastewater filtration method according to (3), wherein the wastewater is subjected to a sedimentation treatment before the filtration is performed.

[0018] According to the wastewater filtration method of (5), the lifespan of the filter material can be extended when implementing the wastewater filtration method of (3), and the concentration of suspended solids in the wastewater discharged during the wet treatment process can be reduced more significantly.

[0019] (6) A dry smelting method for producing ferronickel by sequentially carrying out the drying step, the calcination step and the melting reduction step, wherein the filter material after being filtered by the wastewater filtration method described in (1) or (2) is put back into the drying step.

[0020] According to the ferronickel manufacturing method of (6), in the dry smelting method for producing ferronickel, the nickel-containing suspended solids recovered by the wastewater filtration method described in (1) or (2) can be easily recovered into the system together with a filter material made of ferronickel slag. This prevents the loss of nickel contained in the suspended solids in the wastewater and prevents a decrease in the nickel recovery rate by only performing an easily carried out recovery operation.

[0021] (7) A filter for a dry smelting method for producing ferronickel by sequentially performing a drying process, a calcination process and a melt-reduction process, wherein the filter filters wastewater containing suspended solids separated and recovered by wet treatment from exhaust gas generated in the drying process and / or calcination process and containing dust derived from the raw ore, the filter comprising a casing filled with a filter material, wherein the filter material used is ferronickel slag separated and removed from ferronickel metal in the melt-reduction process.

[0022] According to the filter in (7), in the dry smelting method for producing ferronickel, using it reduces the concentration of suspended solids in the wastewater discharged during the wet treatment process, prevents the loss of nickel contained in the suspended solids, and prevents a decrease in the nickel recovery rate.

[0023] (8) A rotary dryer for performing the drying process, a rotary kiln for performing the firing process, a reduction furnace for performing the smelting reduction process, and a wet dust collector for performing an exhaust gas treatment process of recovering dust derived from raw ore by wet treatment from the exhaust gas discharged from the drying process, and the filter according to (7). The manufacturing equipment of ferronickel.

[0024] According to the manufacturing equipment of ferronickel in (8), in the production of ferronickel by the dry smelting method, the concentration of suspended substances in the wastewater discharged during the wet treatment process is reduced, and the loss of nickel contained in the suspended substances is prevented. It is possible to prevent a decrease in the nickel recovery rate. [Advantages of the Invention]

[0025] According to the present invention, in the dry smelting method for producing ferronickel, the concentration of suspended substances in the wastewater discharged during the wet treatment process is reduced, and the loss of nickel contained in the suspended substances is prevented, thereby preventing a decrease in the nickel recovery rate. [Brief Description of the Drawings]

[0026] [Figure 1] It is a diagram schematically showing an example of the configuration and arrangement of a rotary dryer and a rotary kiln that perform a drying process and a firing process in a dry smelting method for producing ferronickel. [Figure 2] It is a diagram showing an example of the internal structure of a wet dust collector that performs an exhaust gas treatment process in a dry smelting method for producing ferronickel. [Figure 3] It is a diagram schematically showing an example of the configuration of a filter that can be used in the wastewater filtration method of the present invention. [Figure 4] It is a process diagram showing an example of the flow of the ferronickel production method of the present invention. [Embodiments for Carrying Out the Invention]

[0027] Embodiments of the present invention will be described below. However, the present invention is not limited to the embodiments described below.

[0028] <Method for producing ferronickel> Ferronickel is an alloy of iron and nickel and is used as a raw material for stainless steel and specialty steels. A common method for producing ferronickel is dry smelting using nickel oxide ore as a raw material. The "method for producing ferronickel" of the present invention is a suitable method for producing ferronickel using this dry smelting method.

[0029] As shown in Figure 4, the dry smelting method for producing ferronickel involves introducing nickel oxide ore or the like as raw material ore 11, and then sequentially carrying out a drying process S1, a calcination process S2, and a melting and reduction process S3 to obtain ferronickel. In the dry smelting method for producing ferronickel, the crude ferronickel (hereinafter also simply referred to as "metal") obtained in the melting and reduction process S3 is purified to remove impurities such as sulfur and becomes the ferronickel product. On the other hand, the ferronickel slag (hereinafter also simply referred to as "slag") separated and removed in this process is subjected to high-pressure water granulation treatment and then used as a slag material for steelmaking, fine aggregate for concrete, and materials for civil engineering works (see Figure 4).

[0030] In a broad sense, the "method for producing ferronickel" of the present invention is a manufacturing method characterized in that, in the dry smelting method described above, in the exhaust gas treatment step S5 in which dust derived from the raw ore 11 is recovered from the exhaust gas generated in the drying step S1 and / or calcination step S2, the filtration treatment of the wastewater containing the dust as suspended matter is carried out using the unique "wastewater filtration method" of the present invention.

[0031] Furthermore, as a more preferred embodiment, the "method for producing ferronickel" of the present invention can be implemented as a manufacturing method characterized in that, in the exhaust gas treatment step S5 in the dry smelting method described above, dust derived from the raw ore 11 is recovered from the exhaust gas generated when the dried ore dried through the drying step S1 is discharged, and the filtration treatment of the wastewater containing the dust as suspended matter is performed using the unique "wastewater filtration method" of the present invention.

[0032] The "wastewater filtration method," which is a characteristic partial process in the "method for producing ferronickel" of the present invention, is a process for filtering wastewater discharged during the wet treatment process and containing dust derived from the raw ore 11 as suspended matter, in all of the above embodiments. This "wastewater filtration method" is characterized by using the ferronickel slag separated and removed in the melting and reduction process S3 as a "filter material" for the above wastewater filtration treatment. Below, the details of each step in the "method for producing ferronickel" of the present invention will be explained first, and the details of the unique "wastewater filtration method" of the present invention will be described separately.

[0033] [Drying process] Drying step S1 is a process of drying the raw ore (nickel oxide ore) 11 to obtain dried ore 12, which is dried so that the amount of adhering moisture contained in the ore is reduced to approximately 15% by mass or more and 25% by mass or less. Drying step S1 is carried out using a rotary dryer 1, which is a rotary kiln for pre-drying the raw ore 11, as shown in Figure 1. In this specification, the rotary kiln used for drying in drying step S1 is referred to as a "rotary dryer," and the rotary kiln used for firing and reduction in the subsequent firing step S2 is simply referred to as a "rotary kiln," and each method and each piece of equipment according to the present invention will be described accordingly.

[0034] In the drying process S1, it is preferable to adjust the blending ratio of multiple types of nickel oxide ore used as raw material ore so that the composition of the slag obtained in the melting and reduction process S3 is CaO: 1.0% or less, MgO: 40.0% or less, SiO2: 55.0% or less, S: 0.5% or less, and Fe: 10.0% or less. Slag having such a composition contains most of the iron oxide in the raw material ore, as well as silicon dioxide and magnesium oxide, and is a chemically stable glassy slag with excellent environmental properties, such as no leaching of contained elements. Furthermore, because the above slag contains a large amount of magnesium oxide, it has a high specific gravity and is hard. For this reason, it is also preferable as it is easy to use as a magnesia flux for adjusting the composition in the sintering process of steel, as fine aggregate for concrete, as a material for civil engineering works, and as a fluidized bed material for boilers.

[0035] In the rotary dryer 1 that performs the drying process S1 of the present invention, dust derived from the raw ore 11, which has been separated and recovered from the exhaust gas generated in the drying process S1, is reintroduced along with the raw ore 11. This reduces the loss of nickel that would otherwise be discharged from the system along with suspended solids, thereby preventing a decrease in the nickel recovery rate.

[0036] [Firing process] The calcination process S2 involves heating the dried ore 12 obtained in the drying process S1 to a temperature of approximately 800°C to 1000°C with a carbonaceous reducing agent (coal) and a flux added as needed. This process completely removes (dries) any adhering water and crystal water remaining in the dried ore 12, and also reduces a portion of the dried ore 12, thereby obtaining dried and partially reduced calcined ore 13. As shown in Figure 1, the calcination process S2 is carried out using a rotary kiln 2 for calcination and reduction, which performs calcination and partial reduction of the dried ore 12.

[0037] Furthermore, as described above, in the firing process S2, the exhaust gas generated from the rotary kiln 2 can also be separated and recovered to remove dust derived from the raw ore 11, and then reintroduced into the drying process S1. This helps to reduce nickel loss and prevent a decrease in the nickel recovery rate. It is preferable to add moisture to the dust recovered in this process to make it wet, similar to the above, before charging it into the rotary dryer 1.

[0038] [Melting reduction process] The melting and reduction process S3 is a process in which the calcined ore 13, which has undergone decomposition of crystalline water (calcination) and partial reduction treatment in the calcination process S2, is fed into a reduction furnace (not shown), such as an electric furnace or blast furnace, which functions as a reduction melting means, and is reduced and melted to form crude ferronickel (metal) and ferronickel slag (slag). The crude ferronickel produced in the reduction furnace is mainly composed of iron and contains nickel of a grade of 16% to 25% by weight depending on the set amount of carbonaceous reducing agent, as well as many impurities such as sulfur derived from the raw materials, reducing agent, and fuel. If desulfurization treatment is required depending on the product specifications, this crude ferronickel is moved to the desulfurization process, where desulfurization treatment is performed using a mechanical stirring device with a ladle or the like, or an electric induction stirring device, to remove impurities such as sulfur and produce a ferronickel product.

[0039] Furthermore, in the melting and reduction process S3, it is preferable to adjust the heating temperature of the reduction furnace so that the slag temperature is between 1500°C and 1650°C. This makes it possible to obtain slag with low viscosity, i.e., a viscosity ratio of 50 poise or less, in the melting and reduction process S3.

[0040] [Water granulation process] The water granulation process S4 is a process in which molten slag at approximately 1500°C discharged from the reduction furnace performing the molten reduction process S3 is put into a water granulation trough of the water granulation mechanism and rapidly cooled to below 100°C by contacting it with a large amount of water flowing through the trough, thereby obtaining water-granulated slag that has been crushed into fine particles. The water-granulated slag obtained in this way has conventionally been reused as a slag material for steelmaking, fine aggregate for concrete, and material for civil engineering works. In the "method for producing ferronickel" of the present invention, a portion of this water-granulated slag is used as a filter material to filter wastewater containing dust derived from the raw ore 11 as suspended matter, thereby preventing the loss of nickel, and the nickel contained in the suspended matter, which was conventionally difficult to recover, is recovered into the system by reintroducing the recovered nickel-containing suspended matter together with the filter material.

[0041] [Exhaust gas treatment process] The exhaust gas treatment process S5 is a process of recovering dust derived from the raw ore 11 contained in the exhaust gas generated from the rotary dryer 1 that performs the drying process S1 and / or the rotary kiln 2 that performs the calcination process S2.

[0042] Furthermore, in a more preferred embodiment, the exhaust gas treatment process S5 can be carried out as a process of recovering dust derived from the raw ore 11 contained in the exhaust gas, which contains dust derived from the raw ore generated when the dried ore is discharged from the rotary dryer 1 that performs the drying process S1.

[0043] (Method of filtering wastewater) Here, the moisture content of the mixture of dried ore 12 and dust discharged from the outlet of the rotary dryer 1 is approximately 15% by mass to 25% by mass, and it is more prone to generating dust compared to the raw ore 11. Therefore, the exhaust gas treatment process S5, which treats the exhaust gas containing dust derived from the raw ore 11, is performed by wet treatment using a wet dust collector 3 (see Figure 2). The wastewater, which is the post-wash liquid containing dust separated from the exhaust gas by this wet treatment, is then filtered using the "wastewater filtration method" of the present invention. Furthermore, this "wastewater filtration method" is performed using the "filter" of the present invention.

[0044] (Wet type dust collector) As shown in Figure 2, the wet dust collector 3 used in the exhaust gas treatment process S5 includes a body section 31 that stores cleaning water supplied from a water inlet 34 at the bottom and discharges exhaust gas introduced from a gas inlet 32 ​​from the top after separating dust, a gas-liquid introduction section 33 that introduces exhaust gas into the interior together with cleaning water, a throat section 35 for accelerating the flow velocity of the introduced exhaust gas airflow, a scrubbing section 36 that uses the accelerated airflow to lift the cleaning water from below and separates the mixture into the cleaning water by gas-liquid mixing of the mixture and cleaning water, a gas outlet 37 for discharging the exhaust gas from which dust has been separated and removed, an underflow outlet 38 located at the bottom of the body section 31 for draining the mixture such as dust in the cleaning water that has settled due to specific gravity separation, and an overflow outlet 39 located on the side of the body section 31 for discharging the overflow liquid of the cleaning water containing dust, etc.

[0045] In this wet dust collector 3, dust particles dispersed in the washing water with a particle size of approximately 2 mm or larger are discharged from the underflow outlet 38. On the other hand, dust particles dispersed in the washing water with a particle size of approximately 1 μm to 2 mm are discharged from the overflow outlet 39 as suspended solids dispersed in the washing water (wastewater). A filter 4, which has a unique configuration of the present invention, is installed downstream of the wet dust collector 3, and dust originating from nickel-containing raw ore 11 dispersed in the washing water as suspended solids is recovered by this filter 4.

[0046] (filter) In the exhaust gas treatment step S5 of the "method for producing ferronickel" of the present invention, the filtration of wastewater containing dust derived from the raw ore 11 as suspended solids can be performed using the filter 4 of the present invention, which is characterized in that it uses ferronickel slag separated and removed from the ferronickel metal in the melting and reduction step S3 as the filter material. The filter 4 is installed downstream of the wet dust collector 3 and performs the above-mentioned wastewater filtration treatment, discharging wastewater in a state in which the content of suspended solids has been reduced.

[0047] This filter 4 consists of a housing 41 filled with a filter material 44. It is a device that captures suspended solids by the filter material 44 during the process of introducing wastewater containing dust as suspended solids through an inlet 42 at one end of the housing 41 and circulating it through the housing 41 to an outlet 43 at the other end. The main feature of this filter 4 is that the filter material 44 is ferronickel slag separated and removed from ferronickel metal in the melting and reduction process S3. Regarding the components other than the material of the filter material 44, filters with configurations similar to those of various conventionally known filters can be used as appropriate. As an example of such a filter, a filter in which the cylindrical housing is formed of carbon steel can be cited.

[0048] By using slag obtained in the melting and reduction process S3 (for example, granulated slag) as the filter material 44 that constitutes the filter machine 4, the filter material 44 after capturing suspended solids (i.e., used slag) can be reused while still containing suspended solids that contain nickel, thereby enabling the nickel in the suspended solids to be recovered into the system through an easy operation.

[0049] Furthermore, while the coarseness ratio of the granulated slag described above is usually in the range of 3.6 to 4.5, in the present invention, as shown in the examples described later, it is preferable to make the coarseness ratio 3.2 or less. By further crushing the granulated slag of normal size, the recovery rate of suspended solids and nickel can be further improved. In this case as well, it is preferable to set the lower limit of the coarseness ratio of the granulated slag to 2.6 or higher, thereby maintaining a high recovery rate of suspended solids and nickel without significantly reducing the filtration rate. Here, the coarseness ratio is the mass fraction that remains between each of the consecutive sieves (80 mm, 40 mm, 20 mm, 10 mm, 5 mm, 2.5 mm, 1.2 mm, 0.6 mm, 0.3 mm, 0.15 mm) specified in JIS A1102 (Test method for sieving aggregates), and is an indicator of the coarseness of the aggregate. The larger the value, the coarser the aggregate.

[0050] Furthermore, the optimal size of the housing 41 that constitutes the filter 4 and the optimal amount of filter material 44 to be filled can be specifically determined by investigating the relationship between the discharge volume and properties of the wastewater discharged from the wet dust collector 3 and the properties of the wastewater after the filter material 44 has been passed through it.

[0051] Furthermore, since the wastewater discharged from the filter 4 has had its suspended solids sufficiently reduced, even if a coagulant is added to this wastewater to further treat it and allow any remaining suspended solids to settle, this treatment can be carried out without any problems.

[0052] (Other embodiments of wastewater filtration methods) In addition, although the above describes an embodiment in which the wastewater discharged from the wet dust collector 3 is directly introduced into the filter 4, the "wastewater filtration method" of the present invention can also be an embodiment in which, for example, the wastewater is subjected to a sedimentation treatment before filtration by the filter 4, rather than directly introducing the wastewater discharged from the wet dust collector 3 into the filter 4 as described above.

[0053] To perform wastewater filtration according to the above embodiment, a sedimentation device is installed before the filter 4 to receive wastewater from the wet dust collector 3 and separate the solids and liquids by settling the suspended solids in the wastewater. The procedure is to introduce only the liquid phase (supernatant) separated by this sedimentation device into the filter 4. This reduces the load on the filter material 44 of the filter 4, effectively avoiding problems such as poor liquid flow due to a shortened lifespan of the filter material 44. Furthermore, it is possible to further reduce the amount of suspended solids in the wastewater, which already has a reduced content of suspended solids discharged from the filter 4.

[0054] Furthermore, in the above embodiment, it is preferable to set the residence time of the wastewater containing dust in the sedimentation device to 3 hours or more. By setting the residence time to 3 hours or more, it is possible to reliably separate the wastewater, which is entirely in a suspended state, into a solid phase and a liquid phase, thereby further reducing the load on the filter material 44 of the filter 4.

[0055] For example, Table 1 shows the change in the total amount of suspended solids in the liquid (daily amount) at each stage when suspended solids are recovered in two stages, using a system consisting of a sedimentation device that receives the wastewater and a filter 4 located downstream of the sedimentation device that introduces the liquid phase (supernatant) separated by the sedimentation device. Specifically, Table 1 shows how the total amount of suspended solids in the wastewater with reduced suspended solid content decreases compared to the total amount of suspended solids in the wastewater discharged from the wet dust collector 3, the total amount of suspended solids in the liquid phase (supernatant) separated by the sedimentation device, and the total amount of suspended solids in the wastewater discharged from the filter 4.

[0056] [Table 1]

[0057] Table 1 shows that by configuring the suspended solids recovery equipment as described above, first, 265.7 kg / day (= 437.1 kg / day - 166.0 kg / day) of suspended solids contained in the wastewater discharged from the wet dust collector 3 can be recovered by the sedimentation device, and then another 68.4 kg / day (= 166.0 kg / day - 97.6 kg / day) of suspended solids can be recovered by the filter 4. In other words, by configuring the suspended solids recovery equipment in a manner that incorporates the sedimentation device before the filter 4, it is possible to recover 334.1 kg / day (= 265.7 kg / day + 68.4 kg / day) of suspended solids from the wastewater discharged from the wet dust collector 3. This recovered amount is equivalent to 77% of the total amount of suspended solids (daily amount) contained in the wastewater discharged from the wet dust collector 3.

[0058] Furthermore, Table 1 shows that the sedimentation device can recover 3 to 4 times the amount of suspended solids that can be recovered in the filter 4. Therefore, it can be seen that the load on the filter material 44 of the filter 4 can be reduced in proportion to the amount of suspended solids recovered in the sedimentation device. Alternatively, it can be seen that the amount of filter material 44 used in the filter 4 can be reduced compared to the case where suspended solids are recovered using only the filter 4 without using the sedimentation device.

[0059] <Ferronickel manufacturing equipment (dry smelting equipment)> The ferronickel manufacturing method of the present invention can be suitably implemented in the "ferronickel manufacturing facility" of the present invention, which comprises a rotary dryer 1 for performing a drying step S1, a rotary kiln 2 for performing a calcination step S2, a reduction furnace for performing a melting and reduction step S3, a wet dust collector 3 for performing an exhaust gas treatment step S5 to recover dust from exhaust gas discharged from the rotary dryer 1 and / or rotary kiln 2 by wet treatment, and a filter 4 for filtering the wastewater containing the recovered dust. This facility can be configured by installing a filter with a unique configuration of the present invention, namely a filter 4 using ferronickel slag as the filter material 44, in addition to existing manufacturing equipment. This makes it possible to significantly improve the nickel recovery rate in the facility with extremely low introduction costs. [Examples]

[0060] Using the filter 4 shown in Figure 2 and a "test filter" (see Figure 3) that differs in size and material but has substantially the same shape and structure, tests were conducted to investigate the filtration capacity of the filter material used in the filter of the present invention. The above-mentioned "test filter" has an open upper end and a shape that converges toward the central axis midway towards the lower end, and the horizontal cross-sectional area S other than the converged part is 9.5 × 10 -3 m 3 The enclosure was formed using a transparent PET container with a height of 200 mm, and the beaker was placed below this PET container for each test.

[0061] A filter material was packed into a PET container to a thickness D of 0.15 m. Water containing suspended solids with known properties (undiluted solution) was poured in through an opening at the top of the container, causing the suspended solids to be captured by the filter material. The water with reduced suspended solids (filtrate) discharged from the bottom of the container was collected in a beaker.

[0062] Table 2 shows the properties of the stock solution poured into the opening at the top of the housing of the "test filter." In this example, in both "Example 1" and "Example 2," wastewater containing suspended solids discharged as overflow from a wet dust collector in an operating ferronickel manufacturing facility was used as the stock solution.

[0063] [Table 2]

[0064] [Example 1] As a filter material, granulated slag (hereinafter also referred to as "in-state product") with a coarseness ratio in the range of 3.5 to 4.7, as shown in Table 3, was used, and the slag was filled to a height of 3 / 4 of the total height from the bottom end (150 mm from the bottom end) of the PET container that constitutes the housing of the "test filter." Next, 500 mL of the stock solution with the properties shown in Table 2 was poured in through the opening at the top end of the PET container, and the filtrate discharged from the bottom end of the PET container was collected in a beaker and its properties were investigated.

[0065] [Table 3]

[0066] [Example 2] The test was conducted under the same conditions as in Example 1, except that the granulated slag (in its original form) used in Example 1 was prepared separately and crushed to obtain granulated slag with a coarseness ratio in the range of 3.2 (+0.2, -0.2).

[0067] Table 4 shows the results of investigating the properties of the filtrates obtained in Example 1 and Example 2. Furthermore, the nickel recovery rate in Table 4 is defined as follows. Nickel recovery rate [%] = (Nickel concentration in stock solution [mg / L] - Nickel concentration in filtrate [mg / L]) ÷ Nickel concentration in the original solution [mg / L] × 100

[0068] [Table 4]

[0069] The results shown in Table 4 demonstrate that the "wastewater filtration method" of the present invention can effectively reduce suspended solids in wastewater and effectively remove nickel from the wastewater. Therefore, the "ferronickel production method" of the present invention is a production method that can recover nickel more efficiently by feeding used slag back into the reduction furnace, and its industrial value is extremely high. [Explanation of symbols]

[0070] 1 Rotary Dryer 2 Rotary Kiln 11. Raw material ore (nickel oxide ore) 12 Dry Ore 13. Burned Ore 3 Wet type dust collector 31 Torso 32 Gas Inlet 33. Gas-liquid introduction section 34 Water inlet 35 Throat section 36 Scrubbing section 37 Gas outlet 38 Underflow outlet 39 Overflow outlet 4 Filter machine 41 cabinets 42 Inlet 43 Outlet 44 Filter media S1 Drying process S2 firing process S3 Melting reduction process S4 Water Granulation Process S5 Exhaust gas treatment process

Claims

1. In a dry smelting method for producing ferronickel by sequentially performing a drying step, a calcination step, and a melt-reduction step, a method for filtering wastewater containing suspended solids separated and recovered by wet treatment from exhaust gas generated in the drying step and / or calcination step and containing dust derived from the raw ore, As a filter material for filtering the wastewater, ferronickel slag separated and removed from ferronickel metal in the melting and reduction process is used. Methods for filtering wastewater.

2. The exhaust gas is exhaust gas containing dust derived from the raw ore that is generated when the dried ore that has been dried through the drying process is discharged. The wastewater filtration method according to claim 1.

3. The coarseness ratio of the ferronickel slag is 2.6 or more and 3.2 or less. A method for filtering wastewater according to claim 1 or 2.

4. Before performing the aforementioned filtration, the wastewater is subjected to a sedimentation treatment. A method for filtering wastewater according to claim 1 or 2.

5. Before performing the aforementioned filtration, the wastewater is subjected to a sedimentation treatment. The wastewater filtration method according to claim 3.

6. A dry smelting method for producing ferronickel by sequentially performing the drying step, the calcination step, and the melting reduction step, The filter material, after being filtered by the wastewater filtration method described in claim 1 or 2, is reintroduced into the drying step. A method for manufacturing ferronickel.

7. In a dry smelting method for producing ferronickel by sequentially performing a drying process, a calcination process, and a melt-reduction process, a filter is provided for filtering wastewater containing suspended solids separated and recovered by wet treatment from exhaust gas generated in the drying process and / or calcination process and containing dust derived from the raw ore, It consists of a housing filled with a filter material, and the filter material used is ferronickel slag separated and removed from ferronickel metal in the melting and reduction process. filtration machine.

8. A ferronickel manufacturing apparatus comprising: a rotary dryer for performing the drying process; a rotary kiln for performing the firing process; a reduction furnace for performing the melting and reduction process; a wet dust collector for performing an exhaust gas treatment process to recover dust derived from raw ore from exhaust gas discharged from the drying process by wet treatment; and the filter according to claim 7.

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