Process for producing hematite for ironmaking

Abstract

A process is provided for obtaining a hematite-containing material that can be used for ironmaking. The process includes separating a leach residue from a hydrometallurgical refining plant into an overflow and an underflow using a wet cyclone under a condition that the wet cyclone is adjusted to have a setting between 1 m or less and 2 m or less as a classification particle size for the overflow. The process then includes separating the overflow into a strong magnetic substance and a weak magnetic substance using a strong-magnetic-field magnetic separator under a condition that magnetic field intensity is 5 to 20 [kGauss]. The process then includes using a superheated steam drying system for adjusting a moisture content of the strong magnetic substance after the separation, to be 10 wt % to 17 wt %.

Claims

1. A process for producing hematite for ironmaking that utilizes a leach residue as a raw material, the leach residue being obtained from a hydrometallurgical refining plant where a nickel oxide ore is treated by a high pressure acid leach process, the process for producing hematite comprising at least the following three steps in sequence: a separation step of separating the leach residue into an overflow and an underflow by a wet cyclone so that particles of a selected size or smaller than the selected size are separated into the overflow, and particles greater than the selected size separated into the underflow, the selected size being selected from a range of 1-2 m; a physical separation step of separating the overflow into a strong magnetic substance and a weak magnetic substance with magnetic force using a strong-magnetic-field magnetic separator under a condition such that magnetic field intensity is 5 to 20 kGauss; and a dehydration step of using a superheated steam drying system for adjusting the moisture content of the strong magnetic substance of the overflow after the physical separation step, to be 10% to 17% by weight, thereby producing a hematite cake.

2. The process for producing hematite for ironmaking according to claim 1, wherein the moisture content of the strong magnetic substance of the overflow after the physical separation step is 35% to 45% by weight, and a pressure of superheated steam in the superheated steam drying system is 0.5 MPa to 0.7 MPa and a temperature of the superheated steam is 150 C. to 180 C.

3. The process for producing hematite for ironmaking according to claim 2, wherein the wet cyclone is adjusted in the separation step to have a setting of 1 m or less as a classification particle size for the overflow.

4. The process for producing hematite for ironmaking according to claim 1, wherein the wet cyclone is adjusted in the separation step to have a setting of 1 m or less as a classification particle size for the overflow.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a flowchart of a producing process of producing hematite for ironmaking from a tailings slurry according to the present invention.

(2) FIG. 2 is a flowchart of a conventional producing process of producing hematite for ironmaking from a tailings slurry.

(3) FIG. 3 is a schematic flowchart of a producing process according to an HPAL process.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) A process for producing hematite for ironmaking according to the present invention will be described in detail below with reference to the drawings.

(5) FIG. 1 is a flowchart of a producing process of hematite for ironmaking according to the present invention.

(6) The present invention is to separate a material having a useful component composition from a leach residue (hereinafter, referred to as a final neutralized residue (a tailings slurry) stored in a tailings dam as illustrated in FIG. 3) that is discharged from a hydrometallurgical refining plant where a nickel oxide ore is subjected to a high pressure acid leach (HPAL) process as illustrated in the schematic flowchart of a producing process of the HPAL of FIG. 3.

(7) The process is characterized by sequentially performing at least three steps including in order: a step of separating tailings slurry, which is the leach residue, into an overflow and an underflow using a wet cyclone; a step of separating the separated overflow into a strong magnetic substance (hematite for ironmaking) and a weak magnetic substance using magnetic force; and a dehydration step of a superheated steam drying system of adjusting a moisture content of the strong magnetic substance of the overflow after the physical separation using the magnetic force, to be 10% to 17%, wherein a strong-magnetic-field magnetic separator is used in the step of separating using magnetic force.

(8) Therefore, it is possible to obtain hematite for ironmaking with a high iron grade and a low sulfur grade, which has the iron grade of approximately 53% by weight and the sulfur (S) grade of approximately 1%, from the leach residue containing, for example, iron of 30 to 35% and sulfur (S) of 3 to 10%.

(9) Such hematite having the content of these compositions can be provided for ironmaking by itself, and is easily used with a great adjustment margin even when being used by mixing with other raw materials for iron material.

(10) In solid contents of the leach residue in the HPAL process, the iron and sulfur are contained in the form of hematite and gypsum, respectively.

(11) The particle size of the hematite is, for example, approximately 1 m and the particle size of the gypsum is approximately 30 m; and the hematite has weak magnetism and the others have no magnetism.

(12) In the present invention, such a leach residue is charged into a wet cyclone and the gypsum having the large particle size is mostly removed as an underflow. The hematite having the small particle size is concentrated in the overflow.

(13) Then, the resultant overflow is subjected to a physical separation treatment using a strong-magnetic-field magnetic separator which is magnetizable enough to separate the hematite and chromite from each other.

(14) Magnetic force to be used in typical magnetic separation is at most approximately 2000 [Gauss]. However, for example, for a strong-magnetic-field magnetic separator used in Examples, very strong magnetic force can be applied thereto since a method is employed in which magnetic force is applied when powders pass through a mesh. The mesh is set to have optimum apertures for the powders to be separated.

(15) These configurations makes it possible to separate hematite and chromite, which cannot be substantially separation in the typical magnetic separation. In addition, since the small amount of remaining gypsum has no magnetism, it can be separated from the hematite.

(16) As a result, ultimately, hematite for ironmaking is recovered which contains iron of approximately 53% by weight and sulfur of approximately 1% by weight as discharge substances (magnetized substances) on a magnetic body side of a magnetic separator.

(17) As described above, the process for producing the hematite for ironmaking according to the present invention has a first feature that the separation is performed by the wet cyclone at first and subsequently physical separation is performed by the strong-magnetic-field magnetic separator which can apply a magnetic force capable of separating hematite and chromite from each other. In this process, however, when the separation step by the wet cyclone and the physical separation step by the strong-magnetic-field magnetic separator are merely simply combined with each other, for example, when the steps are performed in a reverse order to the above order, it is difficult to effectively recover the hematite for ironmaking.

(18) More particularly, this is because that when the separation step by the strong-magnetic-field magnetic separator is performed at first, it is difficult to apply the magnetic force enough to separate hematite and chromite having a small particle size because of the presence of gypsum having greatly different particle sizes.

(19) In addition, the separation becomes difficult depending on a process for applying magnetic force of the strong-magnetic-field magnetic separator used. For example, in the strong-magnetic-field magnetic separator which is also used in Examples employing a process for applying the magnetic force when the powders pass through the mesh, the gypsum having a large particle size clogs the mesh immediately after operation and thus the separation treatment does not proceed.

(20) In the process for producing hematite for ironmaking according to the present invention, the separation is first performed by the wet cyclone in such a manner that a classification particle size is set to be in an appropriate range.

(21) Then another separation is performed using the magnetic force of which magnetic field intensity is set to be an appropriate range.

(22) In this regard, as a setting of the classification particle size of the wet cyclone, first, the setting for overflow may be appropriately adjusted according to the particle sizes of hematite and gypsum that are contained therein, but the wet cyclone is preferably adjusted so that the classification particle size for overflow is set to be in a setting range from 1 m or less to 2 m or less.

(23) In particular, since hematite and gypsum contained in the solid content of a leach residue have generally the particle sizes of approximately 1 m and approximately 30 m, respectively, the classification effect by the wet cyclone can be improved in the above range, the leach residue being obtained in such a manner that the nickel oxide ore is subjected to a wet-refining treatment according to the HPAL process and then is treated in a final neutralization process.

(24) Moreover, when the separation is performed using the magnetic force, the magnetic field intensity has preferably a condition of 10 to 15 kGauss, which can be obtained by adjusting a mesh size and load power.

(25) Basically, it is preferable that the magnetic field intensity be strong. The reason is that the hematite is insufficiently separated when the magnetic field intensity is less than 5 kGauss. In addition, when the magnetic field intensity is larger than 20 kGauss, further effects are not expected and it is also not preferable in terms of economy.

(26) On the other hand, in the leach residue that is obtained by a physical separation process in the producing process of the present invention (after the physical separation process, indicating a strong magnetic substance of overflow), the sulfur content in the solid-content leach residue is as low as less than 1%, but the moisture content thereof is as high as approximately 40%.

(27) Typically, it is said that during transportation of a solid material, if the moisture content is high, a liquefaction phenomenon occurs during transportation by ship, and thus there is a possibility that the ship is overturned. From an investigation made by Nippon Kaiji Kentei Kyokai, a transportable moisture limit (TML) of hematite of the present invention is 17% or less. Accordingly, in the case of the transportation by ship, it is necessary to decrease the moisture content of the cake in the case of producing the hematite cake according to the invention.

(28) In addition, a particle size of hematite is as very small as approximately 1 m, and thus the characteristics of dust generation are extremely high under an absolute dry condition. However, when the moisture content becomes 10% or more, the characteristics of the dust generation decreases and dust prevention such as use of a flexible container during handling is not necessary. Therefore, the moisture content of hematite cake is preferably 10% to 17%. In a case where the dust prevention is possible by using the flexible container and the like during the handling, the moisture content of hematite cake may be allowed to be less than 10%.

(29) Therefore, it is understood that the adjustment of the moisture content is preferred, but there are the following problems when dehydration is performed to remove the moisture from the leach residue obtained by physical separation (strong magnetic substance of overflow, moisture content: approximately 40%).

(30) Generally, examples of the dehydration of the leach residue include sun-drying, heating and roasting, filter pressing, and a centrifugal separation, and the filter pressing is preferred in consideration of high moisture removing efficiency and economic efficiency. However, unless the dehydration treatment is performed several times by the high-pressure filter press (high-pressure pressurizing filtration apparatus) especially having high efficiency, it is difficult to achieve a moisture content of 17% or less.

(31) In the case of employing the sun-drying, it is not possible to know the time required for operation due to weather and it is difficult to adjust to the preferred moisture content described above.

(32) Furthermore, in the case of employing the heating and roasting, the dehydration excessively proceeds in many cases, and thus it is difficult to adjust to moisture of 10% or more.

(33) Moreover, in the case of the centrifugal separation process, there is a limit in reducing the moisture content to approximately 20%.

(34) Thus, a second characteristic of the present invention is to include a dehydration step using a superheated steam system as the dehydration.

(35) Specifically, the moisture content of the leach residue obtained by the physical separation and subjected to the dehydration using the superheated steam system is set to be approximately 40%, and the dehydration step is performed under the following dehydration conditions of the superheated steam system: pressure of 0.5 to 0.7 MPa (6 bar); and temperature of 150 to 180 C.

(36) As a result, the moisture content of the leach residue obtained by the physical separation can be set to be 10 to 17% by one operation.

(37) In the dehydration step of the superheated steam system, as is widely known, a dehydrated substance comes in contact with superheated steam to heat the dehydrated substance with the superheated steam and the moisture contained in the dehydrated substance is dehydrated and dried in a state of being taken into the superheated steam at the same time.

(38) In the present invention, the dehydrated substance is the leach residue (strong magnetic substance having the moisture content of approximately 40%) obtained from the physical separation step, and a way of contact of the dehydrated substance with the superheated steam is not particularly limited, but may include a way using a drum-type drier (in which superheated steam blows into a leach residue adhered to a cylindrical drum formed by a filter cloth) or a way using a counterflow heat exchanger (in which a leach residue supplied from the top of the drier body comes in counterflow contact with superheated steam supplied from the bottom and a baffle plate is provided in the middle of falling of the leach residue as necessary to improve contact efficiency).

(39) However, in using the superheated steam for the dehydrated substance, it is important to define pressure and temperature of the superheated steam. That is, since a drying capacity varies depending on the pressure and the temperature of the superheated steam, the pressure and the temperature of the superheated steam are set to be in the range of pressure of 0.5 to 0.7 MPa (6 bar) and in the range of temperature of 150 to 180 C., respectively.

(40) When the drying is performed by the pressure of the superheated steam lower than the above range, insufficient drying proceeds and the moisture content of the obtained hematite cake (hereinafter, referred to a strong magnetic substance of the overflow subjected to adjustment with water) exceeds 17%. On the contrary to this, the drying excessively proceeds at a higher pressure and the moisture content of the obtained hematite cake becomes below 10%. Moreover, it is not preferable because the cost of a pressure-resistant apparatus becomes comparatively higher.

(41) In addition, when the drying is performed by the temperature of the superheated steam lower than the above range, insufficient drying proceeds and the moisture content of the obtained hematite cake exceeds 17%. On the contrary to this, the drying excessively proceeds at high temperature and the moisture content of the obtained hematite cake becomes below 10%. Moreover, it is not economically preferable because energy consumption increases.

(42) On the reason for this, the inventors consider that: a starting raw material is a leach residue at a final neutralization process in a wet-refining process of a nickel oxide ore; a main component of the leach residue obtained by the physical separation to make the content of sulfur contained in the solid content to be approximately 1% or less is a hematite particle of approximately 1 m; and when the moisture content is approximately 40%, a special effect is exhibited in combination of a two-stage process (cyclone and magnetic concentration) as a physical separation step and a dehydration process of the superheated steam system as a dehydration step.

(43) As described above, the final neutralized residue having the moisture content of approximately 70% obtained from the final neutralization process in the wet-refining of the nickel oxide ore is treated, and thus the content of sulfur contained in the solid content is set to be 1% or less from the request of the raw material for ironmaking, the moisture content is set to be 10 to 17% from the request for a transfer, and thus the present invention is suitably used with respect to the request for one dehydration step in terms of operational efficiency.

(44) In addition, it is preferable to granulate the hematite for ironmaking, which is manufactured by the above-described producing process, to obtain a granulated material.

(45) In the hematite cake that is obtained in the producing process of the present invention, the following problems may occur. Specifically, the shape of the hematite cake may be not uniform; dusting may occur; and flowability may deteriorate. Accordingly, the problems may occur as follows: in a case where the hematite cake is mixed with other iron ores by an iron-producing maker, it enters a non-uniform mixed state; charging efficiency deteriorates due to the poor flowability; and dusting tends to occur. Accordingly, when a granulated material having a uniform particle size is obtained by performing the granulation, the above-described problems are solved.

(46) For the granulation, a widely known granulation method such as rolling granulation, compression granulation, and extrusion granulation is preferably used, and thus a granulated material, which is uniform and has favorable flowability, is obtained. In addition, occurrence of dusting can be further suppressed in comparison to the hematite cake.

(47) Furthermore, when the producing process of the present invention is applied, the entirety of sulfur derived from gypsum is removed and it is possible to obtain a hematite cake for ironmaking, in which sulfur considered to be derived from a sulfur component trapped into hematite particles in the high-temperature pressure acid leaching process remains around 1%.

(48) Therefore, when applying the following known processes in combination, there is a possibility that the hematite can be used as a more satisfactory raw material for ironmaking.

(49) Specifically, when applying a process of removing sulfur that remains in hematite by drying and baking a supply material so as to remove sulfur and crystal hydration water which are contained in the supply material as disclosed in JP 2012-517523 W, and a then process of briquetting an iron raw material in a powder type as disclosed in JP 2004-269960 A, or a process of pelleting an iron raw material in a powder type as disclosed in JP 2012-211363 A, or the like in combination, it is possible to expect a more satisfactory raw material for ironmaking.

(50) In addition, it is possible to remove sulfur in hematite particles as SOX by roasting the hematite that is obtained by the present invention at a predetermined temperature and to lower the sulfur content thereof.

(51) Specifically, it is possible to obtain hematite in which a sulfur concentration is 0.5% or less by performing a heat treatment at 600 C. or higher. In a heat treatment at a temperature higher than 1400 C., the sulfur concentration becomes 0.05% or less, and thus the sulfur concentration obtained becomes the same as in a conventional iron ore.

(52) It is possible to obtain hematite with a low sulfur concentration through a heat treatment at a temperature higher than 1400 C. However, when the heat treatment temperature is set to be higher, energy consumption increases, and an operational lifespan of a furnace wall material is shortened, and thus a heat treatment at 1400 C. or lower is economically preferable.

EXAMPLES

(53) Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The common producing conditions and characteristic measuring conditions in Examples and Comparative Examples are summarized in Table 1.

(54) TABLE-US-00001 TABLE 1 Items/Conditions Tailings slurry Solid content: 35 [wt %] Treatment speed: 400 [t/hr] Component in solid content: Fe/35%, S/7% Particle size: hematite(1 m), gypsum (30 m) Wet cyclone Model Number SC224-P manufactured by SOLDER CYCLON CORPORATION Classification setting conditions: Particle Size for Overflow is determined by a setting between 1 m or less and 2 m or less Magnetic High Gradient Magnetic separator; Model Number concentration 120 manufactured by MESSO CORPORATION Aperture of mesh for application of magnetic force: 50 [m] Magnetic field intensity: 12 kGauss Particle-size Laser diffraction-type particle size measurement distribution measuring apparatus SALD-3100 manufactured by SHIMADZU CORPORATION d.sub.50 particle is used as the unit of particle size d.sub.50 particle size: Value measured by laser diffraction method Dehydration Oliver-type rotary drum-drier according to Amount of leach residue adhered to filter cloth: superheated steam 20 g/cm.sup.2 .Math. h drying system Pressure of superheated steam: 0.5 to 0.7 MPa Temperature of superheated steam: 150 to 180 C.

Example 1

(55) The present invention was applied in separating a leach residue. As indicated in Table 1, the leach residue was first separated by the wet cyclone and subsequently the resultant overflow was physically separated using the magnetic separator.

(56) The wet cyclone was adjusted to have a setting of 1 m or less and the magnetic field intensity of the magnetic separator was 5 kGauss.

(57) With respect to an amount of the solid content to be treated, the leach residues of 10 tons were treated to obtain the overflow slurry weight of 9.1 tons.

(58) Moreover, the leach residue (overflow slurry; moisture content of 40% and solid content of 2.2 tons) obtained after being treated by the wet cyclone and the magnetic separator was charged into a superheated steam-type dehydrator (steam pressure: 0.6 MPa, temperature: 165 C.) and is then subjected to dehydration, thereby obtaining hematite cakes of 2.0 tons that indicate characteristics of the iron content of 52%, the sulfur content of 0.8%, and the moisture content of 15%.

Example 2

(59) The present invention was applied in separating a leach residue. First, the leach residue was separated by the wet cyclone indicated in Table 1 and subsequently the resultant overflow was physically separated using the magnetic separator.

(60) The wet cyclone was adjusted to have a setting of 2 m or less and the magnetic field intensity of the magnetic separator was 20 kGauss.

(61) With respect to the amount of the solid content to be treated, the leach residues of 10 tons were treated to obtain the overflow slurry weight of 9.3 tons.

(62) Moreover, the leach residue (overflow slurry; moisture content of 40% and solid content of 2.4 tons) obtained after being treated by the wet cyclone and the magnetic separator was charged into a superheated steam-type dehydrator (steam pressure: 0.6 MPa, temperature: 165 C.) and was then subjected to dehydration, thereby obtaining hematite cakes of 2.3 tons that indicate characteristics of the iron content of 55%, the sulfur content of 0.9%, and the moisture content of 15%.

Comparative Example 1

(63) The treatment was performed in the same operations as in Example 1 except that the present invention was not applied and a normal filter press (compression pressure; 2.0 MPa, temperature; 25 C.) was used in the dehydration process described above.

(64) As a result, it was possible to obtain hematite cakes of 2.0 tons that indicate characteristics of the iron content of 52% and the sulfur content of 0.8%, but the moisture content was as insufficient as 22%.

Comparative Example 2

(65) The treatment was performed in the same operations as in Example 1 except that the present invention was not applied and a high-pressure filter press (high-pressure pressurizing filtration apparatus: compression pressure; 8.0 MPa, temperature; 25 C.) was used in the dehydration process described above.

(66) As a result, it was possible to obtain hematite cakes of 2.0 tons that indicate characteristics of the iron content of 52% and the sulfur content of 0.8%, but the moisture content was as insufficient as 20%.

(67) Then, the moisture content was reduced up to 15% when the dehydration treatment was repeatedly carried out three times. In this case, however, operation efficiency was deteriorated due to the repetitive dehydration treatment, and lifespan of a filter cloth also became a third by a simple calculation, which was insufficient.

Comparative Example 3

(68) The treatment was performed in the same operations as in Example 1 except that the present invention was not applied and a centrifugal dehydrator was used in the dehydration process described above.

(69) As a result, it was possible to obtain hematite cakes of 2.0 tons that indicate characteristics of the iron content of 52% and the sulfur content of 0.8%, but the moisture content was as insufficient as 20%.