Method for producing hematite for ironmaking

Abstract

Provided is a method for producing hematite for ironmaking, capable of using a conventional Ca-based neutralizing agent and a base rock-derived neutralizing agent other than the Ca-based neutralizing agent. The method is performed by a process of adding a mineral acid and an oxidizing agent to an ore containing iron and a valuable metal and then leaching the valuable metal under high temperature and pressure, and includes (1) a high-pressure acid leaching step, (2) a preliminary neutralization step, (3) a first solid-liquid separation step, (4) a neutralization step, (5) a second neutralization step, (6) a third solid-liquid separation step, (7) a step of adding part of the Fe-enriched slurry as a seed crystal in the neutralization step (4), and (8) a second solid-liquid separation step.

Claims

1. A method of producing hematite for ironmaking, the method comprising: a high-pressure acid leaching step of mixing an ore slurry with a mineral acid and leaching under a high temperature and pressure to form a leach slurry; a preliminary neutralization step of adding a base rock or magnesium hydroxide to the leach slurry; a first separation step of separating the leach slurry after preliminary neutralization into a Ni-enriched slurry and an Fe-enriched slurry; a first neutralization step of neutralizing the Ni-enriched slurry with limestone or slaked lime, the first neutralization step including adding to the Ni-enriched slurry an amount of the Fe-enriched slurry as a seed crystal; a second separation step of solid liquid separating a precipitate that is obtained from the first neutralization step of neutralizing the Ni-enriched slurry; a second neutralization step of neutralizing the Fe-enriched slurry obtained in the first separation step with sodium hydroxide or potassium hydroxide; and a third separation step of separating the Fe-enriched slurry that is neutralized in the second neutralization step into hematite and a liquid component.

2. The method of producing hematite for ironmaking according to claim 1, wherein the amount of the Fe-enriched slurry added as the seed crystal in the first neutralization step is 50% by weight to 80% by weight with respect to the precipitate that is generated due to the neutralization in terms of a weight ratio.

3. The method of producing hematite for ironmaking according to claim 1, further comprising: adjusting a moisture content of the hematite obtained in the third separation step to provide a hematite with a moisture content of 10% by weight to 17% by weight, the step of adjusting the moisture content being carried out subsequent to the third separation step.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a producing process flow chart according to the present invention.

(2) FIG. 2 is a conventional producing process flow chart.

DETAILED DESCRIPTION

(3) The present invention provides a method of producing (high-purity) hematite for ironmaking by a production process of adding a mineral acid and an oxidizing agent to an ore containing iron and a valuable metal, and of leaching the valuable metal under a high temperature and a high pressure, and the method includes steps (1) to (8) described below.

(4) (1) A high-pressure acid leaching step of adding a neutralizing agent to a leachate that is obtained under a high temperature and a high pressure, for neutralization of the leachate so as to form a leach slurry.

(5) (2) A preliminary neutralization step of converting the leach slurry into a slurry after preliminary neutralization in which a Ni-enriched slurry and an Fe-enriched slurry are separated.

(6) (3) A first solid-liquid separation step of solid-liquid separating, with washing, the slurry after preliminary neutralization that is obtained in the preliminary neutralization step (2) into the Ni-enriched slurry and the Fe-enriched slurry.

(7) (4) A neutralization step of neutralizing the Ni-enriched slurry that is obtained in the first solid-liquid separation step (3), by using a Ca-based neutralizing agent.

(8) (5) A second neutralization step of neutralizing the Fe-enriched slurry that is obtained in the first solid-liquid separation step (3), by using a non-Ca-based neutralizing agent.

(9) (6) A third solid-liquid separation step of solid-liquid separating the Fe-enriched slurry that is neutralized in the second neutralization step (5), and washing the obtained a solid content.

(10) (7) A step of adding part of the Fe-enriched slurry that is obtained in the first solid-liquid separation step (3), as a seed crystal in the neutralization step (4) of neutralizing the Ni-enriched slurry.

(11) (8) A second solid-liquid separation step of solid-liquid separating, with washing, a precipitate that is obtained from the neutralization step (4) of neutralizing the Ni-enriched slurry.

(12) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

(13) FIG. 1 is a producing process flow chart according to the present invention.

(14) A valuable metal, which is contained in an ore, is manufactured according to a flow indicated by a solid-line arrow (fine solid-line arrow after a neutralization process) on a leftmost side in FIG. 1.

(15) On the other hand, as indicated by a thick solid-line arrow in FIG. 1, hematite that is a by-product of the producing process is contained in a leach residue (Fe-enriched slurry) that is obtained at a branch destination indicated by a thick solid-line arrow branched to a right side from a first solid-liquid separation step (CCD), and is manufactured according to a flow indicated by a rightmost thick solid-line arrow in FIG. 1. Hereinafter, respective steps will be described in detail.

(16) [Neutralization]

(17) A neutralization process in the present invention is performed by three steps of “1. Preliminary Neutralization Step”, “2. Neutralization Step”, and “3. Second Neutralization Step”. A neutralizing agent used in respective steps will be described below.

(18) As a neutralizing agent used in the preliminary neutralization step, a base rock, magnesium oxide, or magnesium hydroxide is used.

(19) As a neutralizing agent in the neutralization step, a Ca-based neutralizing agent can be used, and inexpensive limestone or slaked lime is used.

(20) As a neutralizing agent in the second neutralization step, a non-Ca-based neutralizing agent is used, and sodium hydroxide or potassium hydroxide is used. However, magnesium hydroxide or magnesium oxide may be used.

(21) Respective neutralization steps will be described.

(22) 1. Preliminary Neutralization Step

(23) In the preliminary neutralization step of the present invention, first, a base rock (unit: % by weight), of which a representative component composition example is shown in Table 1, is used as a neutralizing agent to allow neutralization to progress while suppressing mixing-in of calcium. In the case of refining a nickel oxide ore, desired pH during the neutralization is approximately pH 1 to pH 3 so as to improve separation efficiency in the first solid-liquid separation step that is a subsequent step.

(24) TABLE-US-00001 TABLE 1 Ni Fe Co Si Mg Cr Al Mn Ca S Base 0.22 4.92 <0.02 17.4 22.1 0.26 0.13 0.09 0.08 <0.05 rock

(25) 2. Neutralization Step

(26) In a neutralization step of neutralizing a liquid component (Ni-enriched slurry) that is obtained in the first solid-liquid separation step, a Ca-based neutralizing agent, such as inexpensive limestone and slaked lime, is used.

(27) This makes it possible to stably perform an operation at the low cost. In the case of refining the nickel oxide ore, desired pH during the neutralization is approximately pH 3 to pH 5 so as to improve efficiency of impurity separation in a subsequent step.

(28) A solid content that is neutralized and separated in this step is transmitted in a slurry state from a lower portion of the bottom of a neutralization bath to the second solid-liquid separation step. Since the solid content includes plaster as a main component, the solid content becomes a fine precipitate, and thus a settling velocity in the neutralization bath is slow. As a result, there is a problem in that a solid ratio of a settled precipitate does not sufficiently increase.

(29) Here, to improve the settling velocity, it is preferable to add an Fe-enriched slurry (including hematite as a main component) of a leach residue, which is an underflow content in the first solid-liquid separation step (CCD), in an amount of 50% by weight to 80% by weight with respect to the weight of the precipitate in terms of solid content weight.

(30) When the solid content weight is less than 50% by weight with respect to the weight of the precipitate, an improvement in the settling velocity is not sufficient. When the solid content weight is greater than 80% by weight, the effect of improving the settling velocity does not vary too much, and besides an amount of hematite that is produced by treating the Fe-enriched slurry decreases, and thus the above-described ranges are disadvantageous.

(31) 3. Second Neutralization Step

(32) In the second neutralization step of neutralizing the leach residue (Fe-enriched slurry), it is preferable to use sodium hydroxide, potassium hydroxide, and the like, instead of magnesium hydroxide and the like whose supply is unstable.

(33) Further, in the case of using the magnesium hydroxide as a neutralizing agent, an amount of Mg in discharged water increases, and thus a large amount of neutralizing agent is necessary for a final Mg solidification treatment. Accordingly, this case is not preferable.

(34) Desired pH during the neutralization is approximately pH 6 to pH 8 in consideration of a final neutralization process of hematite.

(35) [Solid-Liquid Separation]

(36) Next, a solid-liquid separation treatment in the present invention is performed by three steps of “a first solid-liquid separation step”, “a second solid-liquid separation step”, and “a third solid-liquid separation step”.

(37) 1. First Solid-Liquid Separation Step

(38) The first solid-liquid separation step is performed by a known method such as counter current decantation (CCD), and the slurry after the preliminary neutralization that is neutralized by the preliminary neutralization step, is separated into a Ni-enriched slurry (liquid component) and an Fe-enriched slurry (solid component: leach residue).

(39) Here, the Ni-enriched slurry is an overflow liquid (supernatant liquid) that is obtained from CCD, and a slight amount of solid content is mixed therein, and is thus referred to as slurry for convenience.

(40) The Ni-enriched slurry is processed in a subsequent process, and becomes an intermediate raw material such as nickel-cobalt mixed sulfide and nickel sulfate solution, and is further refined to be a valuable metal.

(41) On the other hand, the leach residue of the Fe-enriched slurry is treated by the second neutralization step and the third solid-liquid separation step along a flow indicated by a rightmost solid-line arrow in FIG. 1, and at a result, iron oxide (high-purity hematite) for ironmaking is recovered.

(42) 2. Second Solid-Liquid Separation Step

(43) The second solid-liquid separation step is performed by using a known method such as the counter current decantation (CCD) to recover a liquid component from slurry of a precipitate, which is obtained from the neutralization step and contains plaster as a main component, as a washing liquid used in the first solid-liquid separation step (CCD), and a residue is transmitted to a final processing step.

(44) This second solid-liquid separation step makes it possible to prevent plaster from mixing into the Fe-enriched slurry and to suppress the sulfur content in hematite obtained.

(45) 3. Third Solid-Liquid Separation Step

(46) The third solid-liquid separation step is performed by using a known method, such as wet-classification, a thickener, and filter pressing, to recover hematite having sulfur content of less than 1%, as a solid content from the Fe-enriched slurry after neutralization which is obtained from the second neutralization step. In addition, a liquid component that is obtained is recovered as a washing liquid used in the first solid-liquid separation step (CCD).

(47) In the case of performing neutralization of a surplus acid contained in the leach slurry by using a base rock, it is preferable that after the leach slurry is treated by the first solid-liquid separation step, the resultant leach residue (hereafter, referred to as “neutralized residue” for distinction) be classified (wet-classification) by using a wet cyclone and the like so that hematite be concentrated on a small particle size side of the neutralized residue (O/F side of the wet cyclone) and materials other than hematite be concentrated on a large particle size side (U/F side of the wet cyclone), thereby increasing the grade of hematite.

(48) As described above, in a case where the Fe-enriched slurry is added in the neutralization step, and a precipitate that is a residue generated in the neutralization step is returned to CCD in order to improve operation efficiency during a real operation (refer to a flow chart of a conventional producing process shown in FIG. 2), hematite that contains sulfur in an amount of approximately 5% to 8% is obtained. However, when the present invention is applied, it is possible to obtain hematite in which the sulfur content is less than 1%.

(49) On the other hand, in a hematite cake (described as “hematite” in FIG. 1) that is obtained by the third solid-liquid separation step in the producing method of the present invention, the sulfur content is as low as less than 1%, but the moisture content is as relatively high as 22%.

(50) Typically, 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 Japan Marine Surveyors and Sworn Measurers' Association, it is found that 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 hematite cake. In addition, a particle size of hematite is as very small as approximately 1 μm, and thus a possibility of dust generation is extremely high. As the moisture content increases, the dust generation further decreases.

(51) As the moisture content decreases from 17%, and reaches approximately 10%, fine particles tend to significantly increase, and thus the moisture content is preferably 10% to 17%. In a case where dust prevention is possible by using a flexible container and the like during handling, it is preferable that the moisture content be further lower.

(52) In this regard, a step for adjusting moisture content may be performed to control the moisture content. In the present invention, dehydration is performed to remove the moisture content from the hematite cake.

(53) Examples of the dehydration include a heating, a filter pressing, and a centrifugal separation, and the filter pressing (pressure filtration) has been widely used in consideration of high moisture removing efficiency and economic efficiency.

(54) In addition, it is preferable that a particle size of the base rock to be used in the preliminary neutralization process be adjusted to an optimal size range through pulverization and the like.

(55) Specifically, in a case where the particle size of the base rock is in a range not exceeding 500 μm, there is a little difference in a neutralization performance. In addition, in the case of using a wet cyclone for classification, the greater a particle size of a material to be classified and removed is, the further classification accuracy can increase. Accordingly, when the particle size of the base rock is adjusted to an average particle size in a range of 500 μm or less, and preferably approximately 150 μm in consideration of a facility load, gangue and the like other than hematite is distributed toward the U/F side, and as a result, it is possible to improve the grade of hematite.

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

(57) In the hematite cake that is obtained in the process, the following problems may occur: (1) the shape of the hematite cake may be not uniform; (2) dusting may occur; and (3) since flowability may deteriorate, there is a high possibility that (a) in a case where the hematite cake is mixed with other iron ores by an iron-producing maker, it causes a non-uniform mixed state, (b) charging efficiency deteriorate due to the poor flowability, or (c) dusting tends to occur.

(58) Accordingly, when a granulated material having a uniform particle size is obtained by performing the granulation, the above-described problems are solved. As a granulation method, rolling granulation, compression granulation, and extrusion granulation are widely known. Granulating the hematite by these granulation methods makes it possible to obtain a uniform granulated material having good flowability, is obtained. Besides, occurrence of dusting further decreases in comparison with the hematite cake.

(59) Further, the hematite produced for ironmaking is preferably subjected to a heating treatment at 600° C. to 1400° C. in consideration of a reduction of the sulfur content.

(60) For the majority of sulfur that still remains even though the present invention is applied, it is considered as sulfur in a sulfur component incorporated into hematite particles during the high-temperature pressure acid leaching process, not as sulfur derived from plaster. Accordingly, when applying the present invention, it is possible to substantially remove the entirety of sulfur derived from plaster.

(61) Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The common conditions in Examples and Comparative Examples were set as follows. Raw material ore: a nickel oxide ore having 1% nickel grade and 46% to 48% iron grade. Ore slurry: subjected to a pre-treatment to obtain a slurry of 30% by weight to 40% by weight. High-pressure acid leaching: a slurry mixed with 98% by weight of sulfuric acid was charged into a pressure device, heated to 240° C. to 250° C., and maintained for one hour, and nickel in the ore was then leached. Neutralizing agent used in a preliminary neutralization step: base rock (<approximately 300 μm to 400 μm). Neutralizing agent used in a neutralization step: slaked lime. Amount of Fe-enriched slurry added in the neutralization step: 70% of an amount of a precipitate which occurs.

(62) Moisture content was measured by a heat drying type moisture meter “ML-50” manufactured by A&D Company, Limited, and sulfur grade was measured by using carbon and sulfur analyzer.

Example 1

(63) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter pressing), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed in accordance with a producing process flow of the present invention as shown in FIG. 1. Particularly, the operation was performed without returning a precipitate obtained from the neutralization step to the first solid-liquid separation step.

(64) As a result, the sulfur grade of hematite obtained was 0.9%, and thus hematite capable of being used as a raw material for ironmaking could be obtained.

(65) The Fe-enriched slurry was added to the neutralization step to promote settlement of a precipitate, and thus the operation could be performed at the same efficiency as in the conventional art.

Example 2

(66) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter pressing), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed in accordance with the producing process flow of the present invention as shown in FIG. 1. Particularly, the operation was performed without returning a precipitate obtained from the neutralization step to the first solid-liquid separation step.

(67) The resultant hematite cake was subjected to high-pressure filter pressing (with a high-pressure heating filtration apparatus), thereby obtaining hematite having 0.9% sulfur grade and 13% of moisture content.

Example 3

(68) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter pressing), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed in accordance with the producing process flow of the present invention as shown in FIG. 1. Particularly, the operation was performed without returning a precipitate obtained from the neutralization step to the first solid-liquid separation step.

(69) The resultant hematite cake was subjected to a high-pressure filter pressing (with a high-pressure heating filtration apparatus) and extrusion granulation, thereby obtaining a hematite granulated material having a diameter of 1 mm.

(70) The sulfur grade was 0.9% and the moisture content was 13%.

Example 4

(71) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter pressing), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed in accordance with the producing process flow of the present invention as shown in FIG. 1. Particularly, the operation was performed without returning a precipitate obtained from the neutralization step to the first solid-liquid separation step.

(72) The resultant hematite cake was subjected to high-pressure filter pressing (with a high-pressure heating filtration apparatus), thereby obtaining hematite having 0.9% sulfur grade and 13% of moisture content.

(73) This obtained cake was subjected to a heating treatment at 1400° C., thereby obtaining a hematite granulated material having 0% of moisture content and 0.05% of sulfur concentration.

Comparative Example 1

(74) In accordance with the conventional producing process flow chart as shown in FIG. 2, without applying the present invention, a precipitate obtained in a neutralization step was returned to CCD (a first solid-liquid separation step).

(75) As a result, the sulfur content of hematite obtained was 6.5%, thereby only obtaining hematite not capable of being used as a raw material for ironmaking.

(76) In the hematite in a powder form that is obtained according to the present invention, approximately 1% by weight of sulfur remains. However, when applying the known methods described below in combination, there is a possibility that the hematite can be used as a more satisfactory raw material for ironmaking.

(77) Specifically, when applying a method of removing sulfur that remains in hematite by drying and baking a supply material to remove sulfur and crystal hydration water that are contained in the supply material as described in JP 2012-5175223 T, and then applying a method of briquetting an iron raw material in a powder form, for example, as disclosed in JP 2004-269960 A or a method of pelleting an iron raw material in a powder form as described in JP 2006-233220 A, in combination, it is possible to expect a more favorable raw material for ironmaking.

(78) In addition, it is possible to remove sulfur from hematite particles as SOX by roasting the hematite obtained at a predetermined temperature.

(79) Specifically, it is possible to obtain hematite having a sulfur concentration of 0.5% or less by performing heat treatment at 600° C. or higher. When the heat treatment is performed at a temperature higher than 1400° C., a sulfur concentration becomes 0.05% or less, which concentration is the same as that of a conventional iron ore. Although hematite with a low sulfur concentration can be obtained through a heat treatment at a temperature higher than 1400° C., with such a high heat treatment temperature, an increase of energy consumption and a shortening of operational lifespan of a furnace wall material occur, and thus performing a heat treatment at 1400° C. or lower is economically preferable.