Method for producing hematite for ironmaking

Abstract

There is provided a method for producing (high purity) hematite for ironmaking, in a process where a mineral acid and an oxidizing agent are added to an ore containing iron and a valuable metal and then the valuable metal is leached under high temperatures and high pressures, comprises the steps of: (1) a high pressure leach step; (2) a preliminary neutralization step; (3) a solid-liquid separation step 1; (4) a neutralization step 1; (5) a neutralization step 2; (6) a solid-liquid separation step 3; (7) seed crystal addition treatment; (8) a solid-liquid separation step 2; and (9) a firing step.

Claims

1. A method for producing hematite for ironmaking by a process where a mineral acid and an oxidizing agent are added to an ore containing iron and a valuable metal and then the valuable metal is leached at high temperatures and high pressures, the method comprising the steps of: (1) a high pressure acid leach step of adding the mineral acid and the oxidizing agent to the ore and leaching the valuable metal contained in the ore under high temperatures and high pressures to obtain a leachate and then adding a neutralizing agent to the leachate for neutralization treatment to form a leach slurry; (2) a preliminary neutralization step of adding a neutralizing agent to the leach slurry to form a slurry including a nickel-enriched component and an iron-enriched component; (3) a first solid-liquid separation step of subjecting the slurry formed by the preliminary neutralization step (2) to solid-liquid separation to separate the slurry into a nickel-enriched slurry and an iron-enriched slurry; (4) a first neutralization step of neutralizing the nickel-enriched slurry using a calcium-based neutralizing agent; (5) a second neutralization step of neutralizing the iron-enriched slurry using a non-calcium-based neutralizing agent; (6) a third solid-liquid separation step of subjecting the iron-enriched slurry after the second neutralization step (5) to solid-liquid separation and washing to produce hematite as a solid component; (7) seed crystal addition treatment of adding, as seed crystals, a part of the iron-enriched slurry obtained in the first solid-liquid separation step (3) to the first neutralization step (4); (8) a second solid-liquid separation step of subjecting a precipitate obtained from the first neutralization step (4) using the nickel-enriched slurry to solid-liquid separation to separate the precipitate into a residue containing a sulfur compound and a liquid component which does not contain sulfur; and (9) a baking step of baking the hematite produced in the third solid-liquid separation step (6) at 1150to 1350C.

2. The method for producing hematite for ironmaking according to claim 1, wherein an amount of the iron-enriched slurry added as seed crystals in the treatment (7) is 50% to 80% by weight with respect to an amount of a precipitate produced by neutralization in the first neutralization step (4).

3. The method for producing hematite for ironmaking according to claim 1, wherein the neutralizing agent added to the leachate in the steps of (1) and (2) is a base rock or magnesium hydroxide.

4. The method for producing hematite for ironmaking according to claim 1, wherein the neutralizing agent used in the second neutralization step (5) is sodium hydroxide or potassium hydroxide.

5. The method for producing hematite for ironmaking according to claim 1, wherein the neutralizing agent used in the first neutralization step (4) is limestone or slaked lime.

6. The method for producing hematite for ironmaking according to claim 1, wherein the ore containing iron and a valuable metal is nickel oxide ore.

7. The method for producing hematite for ironmaking according to claim 1, further comprising a step (10) after the step (6), the step (10) being: (10) a moisture content adjustment step of removing water from the hematite as a solid component obtained in the third solid-liquid separation step (6) to bring the moisture percentage of hematite after water removal to 10% to 17% by weight.

8. The method for producing hematite according to claim 1, wherein a particle size (d50) of the hematite obtained in the third solid-liquid separation step (6) is less than 1m.

9. The method for producing hematite according to claim 1, wherein a particle size (d50) of the baked hematite is 3 to 20 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of production steps of the present invention.

(2) FIG. 2 is a flow chart of conventional production steps.

DETAILED DESCRIPTION

(3) The present invention comprises a method for producing (high purity) hematite for ironmaking in a production process where a mineral acid and an oxidizing agent are added to an ore containing iron and a valuable metal and then the valuable metal is leached under high temperatures and high pressures, the method comprising the following treatments (1) to (9):

(4) (1) a high pressure acid leach step of adding the mineral acid and the oxidizing agent to the ore and leaching the valuable metal contained in the ore under high temperatures and high pressures to obtain a leachate and then adding a neutralizing agent to the leachate for neutralization treatment to form a leach slurry;

(5) (2) a preliminary neutralization step of adding a neutralizing agent to the resulting leach slurry for neutralization treatment to form a slurry after the preliminary neutralization which is separated into a Ni-enriched component and an Fe-enriched component;

(6) (3) a first solid-liquid separation step of subjecting the slurry after preliminary neutralization formed by the (2) preliminary neutralization step to solid-liquid separation to separate the slurry into a Ni-enriched slurry (liquid component) and an Fe-enriched slurry (solid component) with washing;

(7) (4) a first neutralization step of neutralizing the Ni-enriched slurry obtained by the (3) first solid-liquid separation step using a Ca-based neutralizing agent;

(8) (5) a second neutralization step of neutralizing the Fe-enriched slurry obtained by the (3) first solid-liquid separation step using a non-Ca-based neutralizing agent;

(9) (6) a third solid-liquid separation step of subjecting the Fe-enriched slurry after neutralization produced through the (5) second neutralization step to solid-liquid separation and washing to produce hematite as a solid component;

(10) (7) seed crystal addition treatment of adding, as seed crystals, a part of the Fe-enriched slurry obtained in the (3) first solid-liquid separation step to the (4) first neutralization step of neutralizing the Ni-enriched slurry;

(11) (8) a second solid-liquid separation step of subjecting a precipitate obtained from the (4) Ni-enriched slurry first neutralization step to solid-liquid separation to separate the precipitate into a residue (solid component) containing a sulfur compound and a liquid component which does not contain sulfur, with washing: and

(12) (9) a baking step of baking the hematite obtained in the (6) third solid-liquid separation step at 1150 to 1350 C.

(13) Further, hematite may be subjected to a step (10) and then baked in the step (9), the step (10) being: (10) a moisture content adjustment step of removing water from the hematite as a solid component obtained in the (6) third solid-liquid separation step to bring the moisture percentage of hematite after water removal to 10% to 17%.

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

(15) FIG. 1 is a flow chart of production steps of the present invention.

(16) The valuable metal contained in an ore is produced according to the flow shown by solid-line arrows (thin solid-line arrows from the neutralization step) on the leftmost side of FIG. 1.

(17) On the other hand, as shown by thick solid-lines of FIG. 1, hematite which is a by-product of this production process is contained in a leach residue (Fe-enriched slurry) obtained at the head of the thick solid-line arrow branched on the right side from a first solid-liquid separation step (CCD), and then produced according to the flow shown by the thick solid-line arrows on the rightmost side of FIG. 1. Hereinafter, each step will be described in detail.

(18) [Neutralization Treatment]

(19) The neutralization treatment in the present invention is performed in the three steps of 1. Preliminary neutralization step, 2. First neutralization step, and 3. Second neutralization step. The neutralizing agent used in each step is described below.

(20) A base rock, magnesium oxide, or magnesium hydroxide is used as the neutralizing agent in the preliminary neutralization step.

(21) A Ca-based neutralizing agent can be used as the neutralizing agent in the first neutralization step, and inexpensive limestone and slaked lime are used.

(22) A non-Ca-based neutralizing agent is used as the neutralizing agent in the second neutralization step, and sodium hydroxide and potassium hydroxide are used. However, magnesium hydroxide and magnesium oxide may also be used.

(23) Each neutralization step will be described.

(24) 1. Preliminary Neutralization Step

(25) In the preliminary neutralization step of the present invention, neutralization is advanced while suppressing the mixing of calcium by first using, as a neutralizing agent, a base rock, a representative example of the component composition thereof being shown in Table 1 (unit: % by weight). In the case of the refining of nickel oxide ores, the target pH after neutralization is a pH of about 1 to 3 in order to improve the separation efficiency in the next first solid-liquid separation step.

(26) TABLE-US-00001 TABLE 1 Ni Fe Co Si Mg Cr Al Mn Ca S Base rock 0.22 4.92 <0.02 17.4 22.1 0.26 0.13 0.09 0.08 <0.05 Unit: % by weight
2. First Neutralization Step

(27) This step is a first neutralization step of subjecting the liquid component (Ni-enriched slurry) obtained from the first solid-liquid separation step to neutralization treatment, in which an inexpensive Ca-based neutralizing agent such as limestone and slaked lime is used. This allows the operation with stability and low cost. In the case of the refining of nickel oxide ore, the target pH after neutralization is a pH of about 3 to 5 in order to improve the separation efficiency of impurities in a subsequent step.

(28) The solids which are neutralized and separated in this step are sent to the second solid-liquid separation step in the state of slurry from the bottom of a neutralization tank. However, the solids have a disadvantage that they are in the state of a fine precipitate since gypsum is the main component and have a small settling velocity in the neutralization tank, and the solid percentage of the settled precipitate is not sufficiently increased.

(29) Therefore, in order to improve the settling velocity, a part of the Fe-enriched slurry (hematite is the main component) of the leach residue which is the underflow of the first solid-liquid separation step (CCD) is preferably added as seed crystals. The weight of the solids in the addition is preferably in the range of 50% by weight or more and 80% by weight or less of the weight of the precipitate.

(30) If the weight of the solids is less than 50% by weight, the solids cannot play a role of seed crystals, and an increase in settling velocity is insufficient; and if the weight of the solids is more than 80% by weight, the effect of increasing settling velocity will not be much changed, and the production volume of hematite obtained by treating the Fe-enriched slurry will be reduced. Therefore, the weight of the solids in these ranges is disadvantageous.

(31) 3. Second Neutralization Step

(32) In the second neutralization step of neutralizing the leach residue (Fe-enriched slurry), magnesium hydroxide, whose supply is unstable, is not used, but sodium hydroxide and potassium hydroxide are preferably used.

(33) Further, if magnesium hydroxide is used as a neutralizing agent, the amount of Mg in a drain will be increased, and a large amount of neutralizing agent will be required in the final Mg-solidification treatment. Therefore, the use of magnesium hydroxide as a neutralizing agent is not preferred.

(34) The target pH after neutralization is a pH of about 6 to 8 since this is the final neutralization step for hematite.

(35) [Solid-Liquid Separation Treatment]

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

(37) 1. First Solid-Liquid Separation Step

(38) The first solid-liquid separation step is performed using a known method such as CCD (Counter Current Decantation), in which a slurry after preliminary neutralization, which is separated into a Ni-enriched component and an Fe-enriched component, formed by the neutralization in 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) obtained from CCD, and it is called a slurry for convenience since a small amount of solids is mixed into the liquid.

(40) The Ni-enriched slurry is treated by a subsequent step to form an intermediate material, such as a nickel/cobalt mixed sulfide and a nickel sulfate solution, which is further refined to form a valuable metal.

(41) On the other hand, iron oxide for ironmaking (high purity hematite) is recovered from the Fe-enriched slurry as a leach residue through the second neutralization step and the third solid-liquid separation step according to the flow shown by thick solid-line arrows on the rightmost side of FIG. 1.

(42) Note that the solid-liquid separation method used for the first solid-liquid separation step is a solid-liquid separation method, such as the CCD method, in which a material (here, refers to the slurry after preliminary neutralization) is contained in a carrier fluid (here, refers to a washing liquid) and transported. The method is preferred in that a washing liquid created in the production process can be used, which is preferred also in terms of saving resources, and the sulfur impurity in the hematite produced can be reduced. In the first solid-liquid separation step, the CCD method is particularly suitable.

(43) 2. Second Solid-Liquid Separation Step

(44) The second solid-liquid separation step is performed using a known method such as CCD (Counter Current Decantation), in which a liquid component is recovered from a slurry of the precipitate essentially comprising gypsum obtained from the first neutralization step as a washing liquid for the first solid-liquid separation step, and a residue (solid component) is sent to a final treatment step.

(45) The provision of the second solid-liquid separation step allows the washing liquid from which gypsum is removed to be used as a washing liquid for use in the first solid-liquid separation step of producing the Fe-enriched slurry. As a result, gypsum is not mixed into the separated Fe-enriched slurry, and the sulfur impurity of the resulting hematite can be suppressed. Further, the amount of a washing liquid to be newly prepared can also be reduced.

(46) 3. Third Solid-Liquid Separation Step

(47) The third solid-liquid separation step is performed using a known method such as wet classification, thickener, and filter press, in which hematite having a sulfur content of less than 1% is recovered as solids from the Fe-enriched slurry after neutralization obtained from the second neutralization step. Further, the resulting liquid component is recovered as a washing liquid for the first solid-liquid separation step.

(48) Note that when excess acid in a leach slurry is neutralized using a base rock, a leach residue (hereinafter, referred to as a neutralization residue in order to distinguish) after passing through the first solid-liquid separation step is preferably classified using a wet cyclone or the like (wet classification). Thereby, hematite is concentrated on the small particle size side of the neutralization residue (for example, the overflow; O/F side of the wet cyclone), and a material other than hematite is concentrated on the large particle size side (the underflow: U/F side of the wet cyclone), thereby increasing the hematite grade.

(49) As described above, when the Fe-enriched slurry is added to the neutralization step and the precipitate which is a residue produced in the neutralization step is returned to CCD (refer to a flow chart of conventional production steps in FIG. 2) in order to improve the operation efficiency in real operation, only hematite containing about 5 to 8% of sulfur has been able to be obtained. However, hematite having a sulfur content of less than 1% has been able to be obtained by applying the present invention.

(50) On the other hand, a hematite cake (shown as hematite in FIG. 1) obtained in the third solid-liquid separation step in the production method of the present invention has a low sulfur content of less than 1% but a relatively high moisture content of 22%.

(51) Generally, in the transportation of solid matter, if it has a high moisture content, it may cause liquefaction during transportation by ship to cause an overturn of a ship. As a result of investigation by Japan Marine Surveyors and Sworn Measurers' Association, the transportable moisture limit (TML) of the hematite of the present invention has been 17% or less. Therefore, when the hematite is transported by ship, it is necessary to reduce the moisture content of the cake. Further, since the hematite has a very fine particle size of about 1 m, the possibility of raising dust is very high.

(52) The raising dust tends to be reduced by increasing the moisture percentage, but when the moisture percentage is reduced from 17%, fine particles tend to significantly increase at about 10% or less. Therefore, the moisture percentage is preferably 10 to 17%. When the raising dust can be prevented, for example, by using a flexible container during handling, a lower moisture content is preferred.

(53) Therefore, it is preferred to perform a moisture adjustment step of adjusting the moisture content. In the present invention, dehydration of removing water from the hematite cake is performed.

(54) The dehydration method includes a heating method, a filter press method, and a centrifuge separation method, but a method using a filter press (pressure filtration) is widely used in terms of high water removal efficiency and economic efficiency.

(55) However, the resulting hematite is in the form of very fine particles. Therefore, although even the hematite in which the moisture content is adjusted can be used as a raw material for ironmaking, it can be used only in a small amount because the hematite still in the form of very fine particles will easily cause clogging in a blast furnace.

(56) Therefore, the hematite cake obtained from the hematite production step of the present invention which is in the form of very fine particles is baked to form coarse particles.

(57) The hematite obtained by the production method of the present invention has an average particle size of 1 m or less. If the hematite having the above particle size is used as a raw material for ironmaking, it will cause clogging during the charge thereof into a blast furnace. Since this hematite is formed from very fine particles having an average particle size of 1 m or less, it is easily sintered in the baking of hematite, and a sintering aid such as lime, which has been added during baking, is not required.

(58) Therefore, if the average particle size of the resulting hematite is more than 1 such hematite is not preferred since the strength of the baked body obtained after the baking of such hematite is reduced.

(59) The baking of hematite can be easily performed at a temperature of 1150 to 1350 C. without adding a sintering aid such as lime, and the density of the resulting hematite baked body is 4.0 g/cc to 5.0 g/cc.

(60) If the baking temperature of hematite is less than 1150 C., the density of the hematite baked body will be less than 4.0 g/cc. If the density is 4.0 g/cc or less, the number of holes in the baked body will increase to produce cracks in the baked body, causing the baked body to be brittle.

(61) On the other hand, if the baking temperature is higher than 1350 C., the density will exceed 5.0 g/cc. If the density exceeds 5.0 g/cc, it will be difficult for a reducing gas to enter into the baked body, and the reduction efficiency of the reducing gas will be reduced. Therefore, such density is not preferred.

(62) Note that a large portion of sulfur remaining in the above hematite cake is not derived from gypsum but is probably derived from a sulfuric acid component incorporated into the hematite particles in the step of high pressure acid leach, and substantially the total amount of sulfur derived from gypsum can be removed by applying the present invention.

(63) Next, the baking is followed by a crushing step to obtain a particle size (d50) of 3 to 20 mm. If the particle size (d50) is less than 3 mm, the particle size will cause clogging in a blast furnace, reducing the flow of reducing gas. On the other hand, if the particle size exceeds 20 mm, reaction time will be increased to cause the deterioration of productivity.

(64) Further, the particle size of a base rock used for preliminary neutralization treatment is preferably adjusted to the optimum range by crushing or the like.

(65) Specifically, when the particle size of a base rock is in a range that does not exceed 500 m, there will be no difference in neutralization performance, and when a wet cyclone is used for classification, the accuracy of classification can be increased with an increase in the particle size of a material which is intended to be removed by classification. Therefore, when the particle size of a base rock is adjusted to a range of 500 m or less, preferably to an average particle size of around 150 m in consideration of an equipment load, the components other than hematite such as vein stone can be distributed to the U/F side, and the grade of hematite can be improved.

EXAMPLES

(66) Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Conditions common to Examples and Comparative Examples are shown in Table 2 below.

(67) TABLE-US-00002 TABLE 2 Raw material ore: nickel oxide ore having a nickel grade of 1% and an iron grade of 46 to 48%. Ore slurry: pretreated to a 30 to 40% by weight slurry. High pressure acid leach: a slurry mixed with 98% by weight of sulfuric acid was charged into a pressure device and heated to 250 to 290 C. followed by maintaining the temperature for 1 hour to leach nickel in an ore. Neutralizing agent in preliminary neutralization step: a base rock (<about 300 to 400 m) was used. Neutralizing agent in first neutralization step: slaked lime was used. Amount of Fe-enriched slurry added to first neutralization step: set at 70% of the amount of precipitate produced.

(68) Note that the moisture percentage was measured with a heating and drying method moisture meter ML-50 (manufactured by A&D Company, Limited), and the sulfur impurity was measured using a carbon and sulfur analyzer.

(69) The particle size was measured with a size distribution measuring device Model SALD-3100 (manufactured by SHIMADZU CORPORATION).

(70) A hearth rise and fall type high temperature furnace (manufactured by MARUSHO DENKI CO., LTD.) was used as a sintering furnace. The temperature of a sintering material was measured with a thermocouple, and after the temperature reached a predetermined sintering temperature, the sintering temperature was kept for a predetermined period of time.

Example 1

(71) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter press), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed according to the flow of the production steps according to the present invention shown in FIG. 1. Particularly, the operation was performed without returning the precipitate obtained from the first neutralization step to the first solid-liquid separation step.

(72) As a result, hematite having a hematite sulfur impurity of 0.9%, an average particle size of 0.6 m, and a moisture percentage of 22% was able to be obtained.

(73) Since the settling of the precipitate was accelerated by adding the Fe-enriched slurry to the first neutralization step, the operation was achieved at the same efficiency as before.

(74) The resulting hematite cake (10 cm20 cm1 cm) was baked at 1350 C. for 10 minutes. Next, the baked cake was crushed using a jaw crusher.

(75) The resulting baked body had a sulfur impurity of 0.01% and a moisture percentage of 0%. Further, the baked body had a density of 5.0 g/cc and a particle size (d50) of 3 mm.

Example 2

(76) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter press), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed according to the flow of the production steps according to the present invention shown in FIG. 1. Particularly, the operation was performed without returning the precipitate obtained from the first neutralization step to the first solid-liquid separation step.

(77) The resulting hematite cake was subjected to high pressure filter press (high pressure heating filtration apparatus), thereby obtaining hematite having a hematite sulfur impurity of 0.9%, a hematite average particle size of 0.6 m, and a moisture percentage of 13%.

(78) The resulting hematite cake (10 cm20 cm1 cm) was baked at 1350 C. for 10 minutes. Next, the baked cake was crushed using a jaw crusher.

(79) The resulting baked body had a sulfur impurity of 0.01% and a moisture percentage of 0%. Further, the baked body had a density of 5.0 g/cc and a particle size (d50) of 20 mm.

Example 3

(80) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter press), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed according to the flow of the production steps according to the present invention shown in FIG. 1. Particularly, the operation was performed without returning the precipitate obtained from the first neutralization step to the first solid-liquid separation step. The resulting hematite had an average particle of 0.6 m.

(81) The resulting hematite cake was subjected to high pressure filter press (high pressure heating filtration apparatus), thereby obtaining hematite having a hematite sulfur impurity of 0.9% and a moisture percentage of 13%.

(82) The resulting hematite cake (10 cm20 cm1 cm) was baked at 1150 C. for 10 minutes. Next, the baked cake was crushed using a jaw crusher.

(83) The resulting baked body had a sulfur impurity of 0.07% and a moisture percentage of 0%. Further, the baked body had a density of 4.3 g/cc and a particle size (d50) of 20 mm.

Comparative Example 1

(84) The present invention was not applied. The operation was performed by returning the precipitate obtained from the neutralization step to CCD (solid-liquid separation step) as shown in the flow chart of production steps in FIG. 2.

(85) As a result, the sulfur impurity of the resulting hematite was 6.5%, and hematite which is used with difficulty as a raw material for ironmaking was only obtained.

Comparative Example 2

(86) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter press), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed according to the flow of the production steps according to the present invention shown in FIG. 1. Particularly, the operation was performed without returning the precipitate obtained from the first neutralization step to the first solid-liquid separation step.

(87) The resulting hematite had a sulfur impurity of 0.9%, an average particle size of 0.6 m, and a moisture percentage of 22%.

(88) The resulting hematite cake (10 cm20 cm1 cm) was baked at 1400 C. for 10 minutes. Next, the baked cake was crushed using a jaw crusher.

(89) The resulting baked body had a sulfur impurity of 0.01% and a moisture percentage of 0%. Further, the baked body had a density of 5.2 g/cc and a particle size (d50) of 20 mm.

Comparative Example 3

(90) The second solid-liquid separation step (CCD), the third solid-liquid separation step (filter press), and the second neutralization step (neutralizing agent: sodium hydroxide) were performed according to the flow of the production steps according to the present invention shown in FIG. 1. Particularly, the operation was performed without returning the precipitate obtained from the first neutralization step to the first solid-liquid separation step.

(91) The resulting hematite had a sulfur impurity of 0.9%, an average particle size of 0.6 m, and a moisture percentage of 22%.

(92) The resulting hematite cake (10 cm20 cm1 cm) was baked at 1050 C. for 10 minutes. Next, the baked cake was crushed using a jaw crusher.

(93) The resulting baked body had a sulfur impurity of 0.2% and a moisture percentage of 0%. Further, the baked body had a density of 3.8 g/cc and a particle size (d50) of 20 mm.