US20160076121A1 - Hydrometallurgical process for nickel oxide ore - Google Patents

Hydrometallurgical process for nickel oxide ore Download PDF

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US20160076121A1
US20160076121A1 US14/785,695 US201414785695A US2016076121A1 US 20160076121 A1 US20160076121 A1 US 20160076121A1 US 201414785695 A US201414785695 A US 201414785695A US 2016076121 A1 US2016076121 A1 US 2016076121A1
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slurry
ore
nickel
nickel oxide
leaching
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Go Ohara
Hideki Sasaki
Yasumasa Kan
Masaki Imamura
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Sumitomo Metal Mining Co Ltd
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Assigned to SUMITOMO METAL MINING CO., LTD. reassignment SUMITOMO METAL MINING CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SASAKI, HIDEKI, IMAMURA, MASAKI, OHARA, GO
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B23/00—Obtaining nickel or cobalt
    • C22B23/04—Obtaining nickel or cobalt by wet processes
    • C22B23/0407—Leaching processes
    • C22B23/0415—Leaching processes with acids or salt solutions except ammonium salts solutions
    • C22B23/043—Sulfurated acids or salts thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B23/00—Obtaining nickel or cobalt
    • C22B23/04—Obtaining nickel or cobalt by wet processes
    • C22B23/0407—Leaching processes
    • C22B23/0415—Leaching processes with acids or salt solutions except ammonium salts solutions
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B23/00—Obtaining nickel or cobalt
    • C22B23/04—Obtaining nickel or cobalt by wet processes
    • C22B23/0453—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B23/0461—Treatment or purification of solutions, e.g. obtained by leaching by chemical methods
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
    • C22B3/08—Sulfuric acid, other sulfurated acids or salts thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/22—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B34/00—Obtaining refractory metals
    • C22B34/30—Obtaining chromium, molybdenum or tungsten
    • C22B34/32—Obtaining chromium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to a hydrometallurgical process for nickel oxide ore, and relates to a hydrometallurgical process for nickel oxide ore of recovering nickel and cobalt from nickel oxide ore by a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step and a final neutralization step.
  • the hydrometallurgical process can achieve the tasks of suppressing the abrasion of facilities such as piping and pumps caused by the ore slurry produced from the ore processing step, increasing durability, reducing the amount of a final neutralized residue produced from the final neutralization step, and suppressing the cost and environmental risks by compressing the volume of the tailings dam that stores the leaching residue that will be disposed, neutralized precipitate, and the like, and also enables separation and recovery of impurity components that can be effectively utilized by recycling.
  • the high pressure acid leaching does not include dry processes such as a reduction process and a drying process, unlike a pyrometallurgical method which is a conventional common smelting method for nickel oxide ore, and is advantageous in terms of energy and cost. Therefore, the high pressure acid leaching will be continuously considered as a promising technology as a smelting method for low grade nickel oxide ore.
  • the leach rate of nickel from ore is increased by performing two-stage leaching of subjecting an ore slurry to normal-pressure leaching (step (a)), and then subjecting the normal-pressure leach residue to acid leaching under pressure (step (b)).
  • step (a) normal-pressure leaching
  • step (b) acid leaching under pressure
  • step (c) burden of the neutralization step
  • Nickel oxide ore is prepared into a slurry, sulfuric acid is added thereto, the mixture is stirred at a temperature of 220° C. to 280° C., and thus a leached slurry is formed.
  • Neutralization step The pH of the leachate obtained in the solid-liquid separation step is adjusted to 4 or less using calcium carbonate while suppressing oxidation of the leachate, a neutralized precipitate containing trivalent iron is produced, and the neutralized precipitate is separated into a neutralized precipitate slurry and a mother liquor for nickel recovery.
  • FIG. 2 is a smelting process diagram illustrating an exemplary practical plant based on the hydrometallurgical process for nickel oxide ore (JP 2005-350766 A).
  • nickel oxide ore 8 is first mixed with water to form a mixed liquid, subsequently the removal of foreign material from the mixed liquid and the adjustment of ore particle size are carried out, and an ore slurry 9 is formed, in ore processing step (1).
  • the obtained ore slurry 9 is subjected to high-temperature pressure leaching using sulfuric acid, thereby a leached slurry 10 is formed, in leaching step (2).
  • the leached slurry 10 obtained is subjected to solid-liquid separation step (3) to be washed in multiple stages, and then the leached slurry is separated into a leachate 11 containing nickel and cobalt, and a leach residue slurry 12 .
  • the separated leachate 11 is subjected to neutralization step (4), and is separated into a neutralized precipitate slurry 13 containing trivalent iron hydroxide and a mother liquor (1) 14 for nickel recovery.
  • the mother liquor (1) 14 is subjected to zinc removal step (5) of adding a sulfurizing agent, and the mother liquor is separated into a zinc sulfide precipitate 15 containing zinc sulfide, and a mother liquor (2) 16 for nickel recovery.
  • the mother liquor (2) 16 is subjected to sulfurization step (6), and is separated into a mixed sulfide containing nickel and cobalt, and a barren liquor 18 having nickel and the like removed therefrom.
  • the barren liquor 18 is used as washing water for the leach residue in solid-liquid separation step (3).
  • the leach residue slurry 12 is subjected to final neutralization step (7) together with an excess amount of the barren liquor 18 , and the leach residue slurry is neutralized.
  • a final neutralized residue 19 is stored in a tailings dam 20 .
  • a feature of this method lies in that by washing the leached slurry in multiple stages in the solid-liquid separation step, the amount of neutralizing agent consumption and the amount of precipitate in the neutralization step can be reduced; since the true density of the leach residue can be increased, the solid-liquid separation characteristics can be improved; and the process is simplified by performing the leaching step simply by high-temperature pressure leaching.
  • this method is considered to be advantageous against the method suggested in JP 6-116660 A.
  • the loss of nickel can be reduced, and therefore, it is believed to be more advantageous.
  • the leach residue obtained in the solid-liquid separation step is combined with excess barren liquor produced from the sulfurization step, and the mixture is made harmless by a neutralization treatment of adding limestone slurry or a slaked lime slurry thereto.
  • the final neutralized residue produced from this final neutralization treatment step (hereinafter, may be referred to as final neutralization step) is stored in the tailings dam.
  • the final neutralized residue contains, in addition to impurity components such as hematite and chromite in the leach residue, gypsum that is formed by the neutralization treatment so that the final neutralized residue cannot be recycled, and there is a heavy burden of expenses for the construction and maintenance management of the tailings dam.
  • JP 2005-350766 A a hydrometallurgical process for nickel oxide ore, which includes a step of physically separating and recovering particles containing at least one selected from silica mineral, chromite or silica-magnesia mineral from ore slurry, and a step of physically separating and recovering hematite particles in the leach residue slurry, in a hydrometallurgical process based on a high pressure acid leaching.
  • improvements have been further needed for efficient separation and recovery of impurity components contained in ore or leach residue.
  • the invention was achieved in view of the problems of the conventional technologies, and it is an object of the invention to provide a hydrometallurgical process for nickel oxide ore of recovering nickel and cobalt using a high-pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step.
  • the hydrometallurgical process can achieve the tasks of suppressing the abrasion of facilities such as piping and pumps caused by the ore slurry produced from the ore processing step, increasing durability, increasing the solid content ratio of the ore slurry, simplifying the facilities of the ore processing step, reducing the amount of a final neutralized residue produced from the final neutralization step, and suppressing the cost and environmental risks by compressing the volume of the tailings dam that stores the leaching residue that will be disposed, neutralized precipitate, and the like, and also enables separation and recovery of impurity components, such as chromite and hematite, that can be effectively utilized by recycling.
  • impurity components such as chromite and hematite
  • the inventors of the invention conducted extensive investigations on the solution for the problems described above, in connection with a hydrometallurgical process for recovering nickel and cobalt from nickel oxide ore by a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step.
  • a hydrometallurgical process for nickel oxide ore of recovering nickel and cobalt using a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, the hydrometallurgical process including at least one step selected from the following step (A), step (B-1), and step (B-2):
  • Step (B-1) a step of neutralizing a leachate with a magnesium-based neutralizing agent, the leachate being produced by subjecting the ore slurry that has a chromium grade lowered after the step (A), to the leaching step and the solid-liquid separation step; and
  • Step (B-2) a step of neutralizing a leach residue slurry with a magnesium-based neutralizing agent to recover hematite particles, the leach residue slurry being produced by subjecting the ore slurry that has a chromium grade lowered after the step (A), to the leaching step and the solid-liquid separation step.
  • a second aspect of the invention is a hydrometallurgical process for nickel oxide ore of recovering nickel and cobalt from nickel oxide ore using a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, the method including the following step (A), step (B-1), and step (B-2).
  • Step (B-1) a step of neutralizing a leachate with a magnesium-based neutralizing agent, the leachate being produced by subjecting the ore slurry that has a chromium grade lowered after the step (A), to the leaching step and the solid-liquid separation step; and
  • Step (B-2) a step of neutralizing a leach residue slurry with a magnesium-based neutralizing agent to recover hematite particles, the leach residue slurry being produced by subjecting the ore slurry that has a chromium grade lowered after the step (A), to the leaching step and the solid-liquid separation step.
  • a third aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first and second aspects, wherein the recovery process of the step (A) includes subjecting the ore slurry to cyclone classification, reducing fine iron hydroxide particles, and then recovering chromite particles in the ore slurry from the ore slurry as a concentrate of chromite using the specific gravity separation.
  • a fourth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the third aspect, wherein the recovery process of the step (A) includes performing cyclone classification without diluting the slurry concentration of the ore slurry.
  • a fifth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to fourth aspects, wherein the recovery process of the step (A) includes collecting chromite into an underflow in cyclone classification in the entire amount except for unavoidable losses.
  • a sixth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to fifth aspects, wherein the specific gravity separation includes at least one step of selected from a step of using a density separator and a step of using a spiral concentrator.
  • a seventh aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the sixth aspect, wherein the step of using the density separator is performed two times or more on concentrated slurry using the density separator.
  • An eighth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the sixth aspect, wherein the step of using the spiral concentrator is performed two times or more on concentrated slurry using the spiral concentrator.
  • a ninth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the sixth aspect, wherein a pulp content of a slurry that is supplied to the spiral concentrator is 15 wt % solids to 35 wt % solids, preferably 20 wt % solids to 30 wt % solids.
  • a tenth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the sixth aspect, wherein an amount of teeter water supplied to the density separator is 0.5 to 7.0 [m3 ⁇ h ⁇ 1/m2].
  • An eleventh aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to tenth aspects, wherein after the specific gravity separation, the slurry is subjected to a magnetic separation, which is a physical separation, to remove hematite, and non-magnetized material is then recovered as a chromite concentrate.
  • a twelfth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first and second aspects, wherein in the step (B-2), a pH of the leach residue slurry neutralized is adjusted to be in a range of 4 to 7, and thereafter, final neutralization is carried out using an alkali other than a magnesium-based neutralizing agent.
  • a thirteenth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to third aspects, wherein in the step (B-2), the leach residue slurry or a neutralized residue slurry including the leach residue slurry is subjected to cyclone classification, and a fine particle portion thus classified is recovered as a concentrate of hematite.
  • a fourteenth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to thirteenth aspects, wherein the ore processing step is a step of performing removal of foreign material in mined raw material ore and adjustment of the ore particle size to form an ore slurry; the leaching step is a step of adding sulfuric acid to the ore slurry and stirring the mixture at a high temperature and a high pressure to form a leached slurry that is composed of a leach residue and the leachate; the solid-liquid separation step is a step of washing the leached slurry in multiple stages to obtain the leachate containing nickel and cobalt, and the leach residue slurry; the neutralization step is a step of adding an alkali to the leachate, to form a neutralized precipitate slurry containing trivalent iron, and a mother liquor for nickel recovery; the zinc removal step is a step of blowing in hydrogen sulfide gas into the mother liquor for nickel recovery to form a zinc sulf
  • a fifteenth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to fourteenth aspects, wherein the adjustment of a particle size of the ore in the ore processing step is carried out by screening to a particle size of 2 mm or less.
  • a sixteenth aspect of the invention is the hydrometallurgical process for nickel oxide ore according to the first to fifteenth aspects, wherein a grade of chromium(III) oxide in the concentrated chromite is 41 wt % or more.
  • step (A) and step (B) are adopted in a hydrometallurgical process of recovering nickel and cobalt from nickel oxide ore by a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step
  • a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step
  • the conventional problems described above can be solved as below. Therefore, the industrial value of the hydrometallurgical process is enormous.
  • step (A) of the invention particles containing chromite in the ore slurry that is produced in the ore processing step are separated and recovered, so that abrasion of facilities such as piping and pumps at the time of transportation of the ore slurry can be suppressed.
  • chromite is separated before wet smelting, reduction of the amount of leach residue can be expected, and the amount of a final neutralized residue can be reduced. Furthermore, when the chromite thus separated can be concentrated, the concentrated chromite can also be effectively utilized as a resource.
  • step (B) of the invention since hematite in the leach residue that is produced in the solid-liquid separation step is separated and recovered, reduction of the amount of a final neutralized residue that is produced from the final neutralization step can be promoted, the cost and environmental risks caused by compression of the volume of the tailings dam that stores the leach residue that will be disposed, a neutralized precipitate, and the like, can be suppressed, and also, the hematite that has been separated and recovered can be effectively utilized as a resource for iron.
  • FIG. 1 is a flowchart of an embodiment of a hydrometallurgical process for nickel oxide ore according to the invention.
  • FIG. 2 is a flowchart of a practical plant based on a conventional hydrometallurgical process for nickel oxide ore (JP 2005-350766 A).
  • FIG. 3 is an exemplary flow diagram of Example 1 of the invention.
  • FIG. 4 is an exemplary flow diagram of Example 2 of the invention.
  • FIG. 5 is an exemplary flow diagram of Comparative Example 1 of the invention.
  • FIG. 6 is an exemplary flow diagram of Comparative Example 4 of the invention.
  • the hydrometallurgical process for nickel oxide ore of the invention is a hydrometallurgical process of recovering nickel and cobalt from nickel oxide ore by a high pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, the hydrometallurgical process including at least one step selected from the following step (A), step (B-1), and step (B-2).
  • This is a step of separating and recovering chromite particles in the ore slurry produced from the ore processing step, by a recovery process including a specific gravity separation.
  • This is a step of performing neutralization of a leachate that is obtained by subjecting the ore slurry having a lowered Cr grade through the step (A) to a leaching step and a solid-liquid separation step, using an Mg-based neutralizing agent such as Mg(OH) 2 or MgO.
  • an Mg-based neutralizing agent such as Mg(OH) 2 or MgO.
  • This is a step of performing neutralization of a leach residue slurry that is obtained by subjecting the ore slurry having a lowered Cr grade through the step (A) to a leaching step and a solid-liquid separation step, using an Mg-based neutralizing agent such as Mg(OH) 2 or MgO, thereby recovering hematite particles.
  • an Mg-based neutralizing agent such as Mg(OH) 2 or MgO
  • Adoption of the step (A) is intended to suppress the abrasion of facilities, such as piping and pumps, at the time of transportation of the ore slurry, by separating and recovering particles containing chromite in the ore slurry produced from the previous ore processing step.
  • abrasion is suppressed by separating chromite that is generally contained in nickel oxide ore and has a very high hardness value. Furthermore, by eliminating in advance chromite from the ore slurry before wet smelting, reduction of the amount of leach residue is expected, and the amount of a final neutralized residue may be reduced.
  • the chromite when the separated and recovered chromite can be sufficiently concentrated, the chromite can also be effectively utilized as a resource.
  • step (B) since adoption of step (B) enables separation and recovery of hematite in the leach residue produced from the solid-liquid separation step, the amount of the final neutralized residue produced from the final neutralization step is reduced, and the expenses and environmental risks caused by compression of the volume of the tailings dam for storing the leach residue to be disposed, a neutralized precipitate and the like, can be suppressed. At the same time, the hematite thus separated and recovered can also be effectively utilized as a resource for iron.
  • iron in the nickel oxide ore is hydrolyzed at a high temperature in the leaching step, and therefore, iron is contained in the form of hematite in the final neutralized residue.
  • the final neutralized residue contains gypsum that is formed by a neutralization treatment using a neutralizing agent containing Ca, in addition to chromite in the leach residue, the iron grade is as low as 30% to 40% by weight, and it is not feasible to effectively utilize the final neutralized residue directly as a raw material for iron making or the like.
  • sulfur gypsum; calcium sulfate
  • chromium chromite
  • FIG. 1 is a smelting flowchart of an exemplary embodiment according to the hydrometallurgical process for nickel oxide ore related to the invention.
  • nickel oxide ore 8 is mixed with water to form a mixed liquid in ore processing step [1], and then the removal of foreign material from the mixed liquid and the adjustment of the ore particle size are carried out to form an ore slurry 9 .
  • step (A) Thereafter, the ore slurry 9 is subjected to step (A), which is newly provided, to separate and recover chromite 23 .
  • An autoclave-supplied slurry 22 on one side is supplied to leaching step [2].
  • the autoclave-supplied slurry 22 is converted to a leached slurry 10 by leaching valuable components such as nickel and cobalt with sulfuric acid using an autoclave or the like.
  • the leached slurry 10 thus formed is supplied to solid-liquid separation step [3] that uses multi-stage thickeners or the like, and is separated into a leachate 11 containing nickel and cobalt, and a leach residue slurry 12 .
  • the separated leachate 11 is supplied to the step (B-1), and is separated into a residue 26 after the step (B-1) containing trivalent iron hydroxide as a main component, and a mother liquor (1) 14 containing nickel.
  • the mother liquor (1) 14 is subjected to zinc removal step [5] in which a sulfurizing agent is added, and is then separated into a zinc sulfide precipitate 15 containing zinc sulfide, and a mother liquor (2) 16 for nickel recovery.
  • the mother liquor (2) 16 is subjected to sulfurization step [6] in which a sulfurizing agent is added, and is separated into a mixed sulfide 17 containing nickel and cobalt, and a barren liquor 18 .
  • the barren liquor 18 may be used as washing water for the leach residue in the solid-liquid separation step [3], and the barren liquor 18 may also be supplied to the final neutralization step.
  • a treatment solution 27 after the step (B-2), and the other portion of the leach residue slurry 12 that was not supplied to the step (B-2) are supplied to [7] final neutralization step, and the leach residue slurry is neutralized to about pH 8 to 9.
  • the final neutralized residue 19 thus obtained is stored in the tailings dam 20 .
  • the ore processing step is a step of forming ore slurry by performing removal of foreign material and adjustment of the ore particle size.
  • nickel oxide ore is classified using a wet sieve or the like to separate any foreign material that cannot be leached in a leaching step, ore particles having a particle size that is difficult to be transported by a pump, and the like.
  • the screened particle size is about 2 mm, and ore particles having particle sizes greater than that are subjected to a pulverization treatment.
  • a slurry is formed by the ore that has undergone pulverization-screening treatment, and then the slurry is settled and concentrated, so that an autoclave-supplied slurry having an adjusted solid concentration in the slurry (hereinafter, referred to as slurry concentration) is prepared.
  • slurry concentration an autoclave-supplied slurry having an adjusted solid concentration in the slurry.
  • the nickel oxide ore that serves as the raw material to be treated by the hydrometallurgical process of the invention is composed mainly of so-called lateritic ore, such as limonite and saprolite.
  • the nickel content of this lateritic ore is usually 0.8% to 2.5% by weight, and nickel is contained in the form of hydroxide or hydrous silica-magnesia (magnesium silicate) mineral.
  • iron is 10% to 50% by weight, and iron is mainly in the form of trivalent hydroxide (goethite); however, some divalent iron is contained in hydrous silica-magnesia mineral or the like.
  • Silicic acid components are contained in silica mineral such as cristobalite (amorphous silica), and hydrous silica-magnesia mineral.
  • chromium components are contained 1 to 5 wt % as chromite mineral containing iron or magnesium.
  • magnesia components are contained in silica-magnesia mineral that almost do not contain nickel, which is unweathered and has a high hardness value, in addition to the hydrous silica-magnesia mineral.
  • silica mineral, chromite mineral, and silica-magnesia mineral are so-called gangue components that almost do not contain nickel, in regard to lateritic ore.
  • chromium content has a high proportion of chromium existing as a single phase independent of a major portion of the iron content, and there are many particles having a particle size of 20 ⁇ m to 1000 ⁇ m.
  • minerals including chromium are contained in large amounts in particles having a particle size of about 20 ⁇ m or more, and minerals including nickel and iron are contained in large amounts in particles having a particle size of about 20 ⁇ m or less.
  • the crushed particle size at this time can be determined in consideration of the original purpose of forming the ore slurry; however, the crushed particle size is preferably about 2 mm or less.
  • Table 1 shows an example of the ore particle size distribution of the ore slurry obtained by crushing the ore to a particle size of about 2 mm or less, and the grades of various components at various particle size scales.
  • step (A) is a step of separating and recovering chromite in the ore slurry produced from the ore processing step. It is also possible to separate and remove mineral particles of silica mineral, silica-magnesia, or the like as process intermediates.
  • step (A) may be carried out as a process included in the ore processing step, or may be carried out subsequently to the ore processing step.
  • the method for step (A) is not particularly limited, and methods using various physical separation means that separate chromite from the ore slurry can be applied.
  • methods using various physical separation means that separate chromite from the ore slurry can be applied.
  • wet physical separation methods including a specific gravity separation is essential.
  • the classification particle size in this classification may be any particle size as long as the goethite containing nickel of the fine particle portion can be efficiently separated, and it is preferable that the classification particle size be selected preferably in the range of 20 ⁇ m to 150 ⁇ m, and more preferably in the range of 45 ⁇ m to 75 ⁇ m.
  • the lower limit of the classification point that can be industrially implemented is 20 ⁇ m in most cases, and when this classification particle size is less than 20 ⁇ m concentration of chromite in the coarse particle portion is insufficiently achieved, and also, nickel in the ore slurry used in the leaching step is lost.
  • the classification particle size is more than 150 ⁇ m, removal of silica mineral, chromite, and silica-magnesia in the fine particle portion is insufficiently achieved.
  • the technique for this classification is not particularly limited, but it is desirable to select cyclone classification that is capable of processing of large quantities with high performance.
  • the specific gravity of chromite is known to be larger than that of iron hydroxide such as goethite, and thus, coarse chromite having a large specific gravity and fine goethite having a small specific gravity can be separated efficiently by a cyclone.
  • the operation pressure of the cyclone is desirably 0.1 MPa to 0.3 MPa when the separation performance and the processing speed are taken into consideration.
  • the shape of the cyclone it is desirable to adjust the shape such that the pulp content of the underflow would be 50 wt % or more.
  • the pulp content of the ore slurry supplied to the cyclone is preferably 10 wt % to 30 wt %, and more preferably 15 wt % to 20 wt %.
  • Separation using a cyclone can be achieved even at a pulp content of 10 wt % or less; however, a large amount of water is needed, and it is also disadvantageous in precipitate concentration in the subsequent steps. Also, when the pulp content is more than 30 wt %, the viscosity of the slurry increases, and separation may become difficult.
  • the pulp content after the ore processing step is set to 10 wt % to 30 wt % of the range described above, it is not necessary to supply water afresh, and a tank for dilution is also not necessary, which is preferable.
  • the specific gravity separation apparatus used is not particularly limited; however, it is preferable to select at least one of a shaking table, a density separator, and a spiral concentrator, and it is more preferable to select at least one of a density separator and a spiral concentrator, which are adequate for processing of large quantities.
  • the pulp content of the slurry supplied to this is preferably more than 15 wt % but less than 35 wt %, and more preferably more than 20 wt % but less than 30 wt %.
  • the separation performance may be deteriorated, and when the pulp content is 35 wt % or more, the flow of particles on the chromite concentration side (inner side) is retained during the separation with a spiral concentrator, and build-up occurs, so that separation may not be achieved sufficiently.
  • a spiral treatment is performed several times on chromite (outer side) which is concentrated to 15 wt % or more and 40 wt % or less and thus the recovery rate of chromite is increased.
  • the density separator it is desirable to set the amount of teeter water to 0.5 to 7.0 [m3 ⁇ h ⁇ 1/m2].
  • concentration can be achieved to obtain a Cr2O3-grade in chromite of 41 wt % to 50 wt % or more; however, in order to achieve further concentration, it is desirable to separate and remove hematite that is contained in a trace amount.
  • the magnetic field strength is not particularly limited, and may vary depending on the belt speed, belt thickness, or other apparatuses; however, the magnetic field strength is preferably in the range of 200 [Oe] to 2000 [Oe].
  • the magnetic field strength is less than 200 [Oe]
  • the magnetic field is so weak that separation and elimination of hematite may be achieved insufficiently.
  • the magnetic field strength is more than 2000 [Oe]
  • there is no problem with the removal of hematite but there are occasions in which even chromite is magnetized, and thus the magnetic separation does not work.
  • the leaching step is a step of forming a leached slurry composed of a leach residue and a leachate, by adding sulfuric acid to the ore slurry obtained through the ore processing step and step (A), and then stirring the mixture at a temperature of 220° C. to 280° C.
  • a preheater, an autoclave, and a flash tank are used as main facilities.
  • leaching of nickel, cobalt and the like as sulfates, and fixation of the leached iron sulfate as hematite are achieved by a leaching reaction represented by the following reaction formulae (1) to (3), and a high temperature thermal hydrolysis reaction represented by reaction formulae (4) and (5).
  • the liquid portion of the leached slurry thus obtainable usually contains divalent and trivalent iron ions in addition to nickel, cobalt and the like.
  • M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn or the like
  • the reaction temperature for the leaching step is 220° C. to 280° C., and preferably 240° C. to 270° C.
  • the amount of use of sulfuric acid used in the leaching step is not particularly limited, and an amount slightly excessive compared to the stoichiometric amount required for the iron in the ore to be leached and converted to hematite, for example, 300 kg to 400 kg per ton of the ore, is used. Particularly, when the amount of addition of sulfuric acid per ton of the ore is more than 400 kg, the cost for sulfuric acid and the cost for the neutralizing agent in the subsequent steps are increased, which is not preferable.
  • the concentration of free sulfuric acid at the time of completion of leaching is aimed to be 25 g/L to 50 g/L, and preferably, an amount of use of sulfuric acid of 35 g/L to 45 g/L is used.
  • the solid-liquid separation step is a step of washing in multiple stages the leached slurry formed in the previous leaching step, and obtaining a leachate containing nickel and cobalt, and a leach residue. Thereby, nickel and the like that adhere to the leach residue and are disposed are recovered into the leachate.
  • This step (B-1) is a step in which a neutralizing agent (pH adjusting agent) is added to adjust the pH to 4 or less, and preferably to be in the range of 3.2 to 3.8, while oxidation of a leachate 11 obtained in the leaching step is suppressed by neutralizing the leachate 11 that has been separated in the previous solid-liquid separation step, and a residue 26 after the step (B-1) as a neutralized precipitate slurry containing trivalent iron, and a mother liquor (1) 14 for nickel recovery are formed.
  • a neutralizing agent pH adjusting agent
  • an Mg-based alkali such as Mg(OH)2, which does not contain Ca, or an Mg-based neutralizing agent such as MgO, which dissolves in the leachate and thereby exhibits alkalinity, is used as the neutralizing agent.
  • This zinc removal step is a step in which, prior to the step of separating nickel and cobalt as sulfides, hydrogen sulfide gas is blown into the mother liquor obtained in the previous step, sulfides containing zinc are produced, and zinc sulfide precipitate slurry and a mother liquor for nickel and cobalt recovery are formed.
  • This zinc sulfide precipitate slurry thus obtained can be sent to the final neutralization step (7) and treated, similarly to the neutralized precipitate slurry obtainable in the neutralization step.
  • This sulfurization step is a step of blowing hydrogen sulfide into the mother liquor (2) for nickel and cobalt recovery obtained in the zinc removal step, and producing a mixed sulfide (zinc sulfide precipitate) 17 containing nickel and cobalt, and a barren liquor 18 .
  • the barren liquor 18 thus obtained is at a pH of about 1 to 3, and contains impurities such as iron, magnesium and manganese that are contained without being sulfurized, as well as slight amounts of nickel and cobalt as a recovery loss. Therefore, the barren liquor 18 is used as washing water for the leach residue in the solid-liquid separation step, and as the washing water for the neutralized residue produced in the neutralization step.
  • This step (B-2) is a step of neutralizing part of the leach residue (leach residue slurry 12 ) produced in the solid-liquid separation step, using an Mg-based alkali such as Mg(OH) 2 or an Mg-based neutralizing agent such as MgO, and recovering hematite particles.
  • an Mg-based alkali such as Mg(OH) 2 or an Mg-based neutralizing agent such as MgO
  • the method for step (B-2) is not particularly limited, but a Ca-based alkali is not used as the neutralizing agent.
  • a Ca-based alkali is not used as the neutralizing agent.
  • CaCO 3 is used as the neutralizing agent, this compound reacts with adhering sulfuric acid, and gypsum is produced. Since this gypsum has low solubility, gypsum is precipitated as a solid and increases the sulfur grade in the residue.
  • MgSO 4 has high solubility, this compound is not easily precipitated as a solid, and is effective for the decrease of sulfur.
  • the neutralizing agent is preferably Mg(OH) 2 , which is an Mg-based alkali; however, an Mg-based neutralizing agent such as MgO 2 may be used.
  • Table 2 shows an example of the ore particle size distribution of the leach residue obtained by leaching the ore slurry obtained by crushing the ore to a particle size of about 2 mm or less, and the grades of various components at various particle size scales.
  • the particles containing iron at a high content are fine particles than those particles containing chromium, silicon and the like at high contents
  • the particles containing iron can be separated from the coarse particle portion containing chromium, silicon and the like at high contents, by means of screening means such as a classification method, and driven away out of the system, and hematite can be recovered as a resource.
  • the classification method is preferably a treatment using a cyclone or the like, which is capable of processing of large quantities.
  • This final neutralization step is a step of precipitating metal ions in the liquid as neutralized precipitate and obtaining a final neutralized residue 19 , by adding a treatment solution 27 after the step (B-2), which is obtained in the step (B-2), the portion of the slurry that has not been treated in the step (B-2) in the leach residue slurry 12 obtained after the solid-liquid separation step, and the residue 26 after the step (B-1), or optionally, a product obtained by slurrifying the zinc sulfide precipitate obtainable in the zinc removal step; further adding a limestone slurry and a slaked lime slurry; and adjusting the pH to about 8 or 9. Meanwhile, the final neutralized residue 19 thus obtained is stored in the tailings dam 20 .
  • analyses are carried out using a fluorescent X-ray analysis method or an ICP emission analysis method for the analysis of metals.
  • the step (A) for the ore slurry 9 was performed according to the exemplary flow diagram illustrated in FIG. 3 , the ore slurry 9 was subjected to the classification treatment with the hydrocyclone, goethite was separated from the ore slurry 9 , and then the specific gravity separation 1 was performed by combination in the order of a density separator and a spiral concentrator.
  • Classification of an ore slurry having a composition as indicated in Table 3 was carried out using a hydrocyclone (manufactured by Daiki Ataka Engineering Co., Ltd., Model MD-9) as the classification apparatus used in the step (A).
  • Example 1 classification was carried out under the conditions of a slurry concentration of 15 wt %, a slurry temperature set to normal temperature, and an operation pressure of 0.2 MPa.
  • silica mineral and chromite are concentrated and separated in the coarse particle portion by classification of the ore slurry.
  • the hydrocyclone U/F (slurry concentration: 33 wt %) was supplied to a density separator (manufactured by Outotec, Inc., “TANKSIZER TS-Lab”, and having an inner diameter of tank: 228.6 mm).
  • the supply rate was set to 56 [kg/Hr], and the slurry temperature was set to normal temperature.
  • the process was carried out by setting the amount of teeter water at this time to 6.9 [m3 ⁇ h ⁇ 1/m2], and the set point (set value of the densitometer) to 20.
  • compositions of the feed of the density separator (hydrocyclone U/F) and the underflow (density separator U/F) are presented in Table 4.
  • the level of Cr 2 O 3 was increased to 16.9 wt % relative to 13.5 wt % at the time of the classification with the hydrocyclone (hydrocyclone U/F).
  • the level of SiO 2 was reduced to 1.9 wt % relative to 6.0 wt % and the level of iron was reduced to 35.2 wt % relative to 45.2 wt %.
  • silica mineral and chromite are concentrated and separated in the coarse particle portion by the density separator treatment.
  • the level of Cr2O3 was increased to 24.4 wt % in the Middling. On the other hand, the level of Cr2O3 was 5.3 wt % in the Tailing.
  • the density separator U/F (1) (slurry concentration: 75 wt %) obtained by the density separator was diluted with water to obtain a slurry concentration of 25 wt % in accordance with the flow in FIG. 3 , and was subjected to a separation test using a spiral concentrator (manufactured by Outotec, Inc., “MC7000”).
  • the level of Cr 2 O 3 was increased to 24.3 wt % in the Middling. On the other hand, the level of Cr 2 O 3 was 5.0 wt % in the Tailing.
  • the “Concentrate” obtained by the spiral test was diluted to a slurry concentration of 20 wt %, and the dilution was supplied to a low-magnetic field magnetic concentrator (manufactured by Outotec, Inc., “Inprosys benchtop LIMS”) at a supply rate of 45.4 [kg/Hr].
  • a low-magnetic field magnetic concentrator manufactured by Outotec, Inc., “Inprosys benchtop LIMS”
  • magnetized material (Mag) and non-magnetized material (Non-mag) were obtained.
  • the Cr 2 O 3 obtained by the low-magnetic field magnetic concentration was increased to 45.3 wt % relative to 41.2 wt % in the supplied ore.
  • the Fe was reduced to 23.1 wt % from 28.5 wt %.
  • the Fe-grade of the Cr 2 O 3 (magnetized material/Mag) was 43.7 wt %, which indicates that the Fe-grade was high, it can be seen that magnetite was separated and removed by magnetic concentration, and the Cr 2 O 3 -grade of chromite was increased.
  • the recovery rate of the chromite obtained in Example 1 was 42.5 wt %.
  • the specific gravity separation was repeatedly performed two times using the density separator as illustrated in the exemplary flow diagram illustrated in FIG. 4 , and then the specific gravity separation was performed using the spiral concentrator.
  • Example 2 the classification was carried out under the conditions of a slurry concentration of 15% by weight, a slurry temperature set to normal temperature, and an operation pressure of 0.2 MPa.
  • the level of Cr 2 O 3 was increased to 13.5 wt % relative to 2.5 wt % in the supplied ore, and the level of SiO 2 was increased to 6.0 wt % relative to 4.4 wt % in the supplied ore; however, the level of Fe was reduced to 45.2 wt % relative to the iron grade 51.5 wt % in the supplied ore.
  • silica mineral and chromite are concentrated and separated in the coarse particle portion by classification of the ore slurry.
  • the hydrocyclone U/F (slurry concentration: 33 wt %) was supplied to a density separator (manufactured by Outotec, Inc., “Tanksizer TS-Lab”, and having an inner diameter of tank: 228.6 mm).
  • the supply rate was set to 56 [kg/Hr], and the slurry temperature was set to normal temperature.
  • the process was carried out by setting the amount of teeter water at this time to 6.9 [m3 ⁇ h ⁇ 1/m2], and the set point (set value of the densitometer) to 20.
  • compositions of the feed of the density separator (1) (hydrocyclone U/F) and the underflow (density separator U/F (1)) are presented in Table 9.
  • the level of Cr 2 O 3 was increased to 16.9 wt % relative to 13.5 wt % at the time of the classification with the cyclone (HC-U/F).
  • the level of SiO 2 was reduced to 1.9 wt % relative to 6.0 wt % and the level of iron was reduced to 35.2 wt % relative to 45.2 wt %.
  • silica mineral and chromite are concentrated and separated in the coarse particle portion by the density separator treatment.
  • the density separator U/F (1) (slurry concentration: 75 wt %) was diluted with water to obtain a slurry concentration of 40 wt %, and was again subjected to the density separator treatment.
  • the compositions of the feed of the density separator (2) (density separator U/F (1) obtained by the first density separator treatment) and the underflow (density separator U/F (2) obtained by the second density separator treatment) are presented in Table 10.
  • the Cr 2 O 3 was increased to 44.5 wt % relative to 21.1 wt % in the supplied ore.
  • the Cr 2 O 3 was increased to 30.3 wt % in the “Middling”.
  • the Cr 2 O 3 was 6.3 wt % in the “Tailing”.
  • the Cr 2 O 3 was increased to 42.5 wt % relative to 30.3 wt % in the supplied ore.
  • the Cr 2 O 3 was reduced to 19.4 wt % in a Middling (2) and was reduced to 19.5 wt % in a Tailing.
  • these Middling (2) and Tailing are again subjected to the spiral treatment as necessary.
  • the “Concentrate” obtained by two spiral tests was mixed and diluted to a slurry concentration of 20 wt %, and the dilution was supplied to a low-magnetic field magnetic concentrator (manufactured by Outotec, Inc., “Inprosys benchtop LIMS”) at a supply rate of 45.4 [kg/Hr].
  • a low-magnetic field magnetic concentrator manufactured by Outotec, Inc., “Inprosys benchtop LIMS”
  • magnetized material (Mag) and non-magnetized material (Non-mag) were obtained.
  • the results are presented in Table 13.
  • the Cr 2 O 3 obtained by the low-magnetic field magnetic concentration was increased to 48.5 wt % relative to 44.1 wt % in the supplied ore.
  • the Fe was reduced to 20.0 wt % from 24.7 wt %.
  • the Fe-grade of the Cr 2 O 3 (magnetized material/Mag) was 36.6 wt %, which indicates that the Fe-grade was high, it can be seen that magnetite was separated and removed by magnetic concentration, and the Cr 2 O 3 -grade of chromite was increased.
  • the recovery rate of the chromite obtained in Example 2 was 44%.
  • Example 1 After a classification treatment was performed using a hydrocyclone according to an exemplary flow diagram according to Comparative Example 1 illustrated in FIG. 5 , the separation was performed using a high-mesh separator according to the size of solids contained in the ore slurry 9 , instead of the specific gravity separation treatment in Example 1.
  • classification was carried out under the conditions of a slurry concentration of 9.8% by weight, a slurry temperature set to normal temperature, and an operation pressure of 0.22 MPa.
  • hydrocyclone underflow (hydrocyclone U/F) having a slurry concentration of 33 wt % was diluted to a slurry concentration of 4.9 wt %, and the dilution was charged into a high-mesh separator (manufactured by Kikosha Co., Ltd., “KUC-612S”).
  • the supply rate to the high-mesh separator was 0.98 [m3/hour], the speed of rotation of the bucket was 0.8 rpm, the bucket length was 75 mm, and the bucket had holes having a diameter of 4 mm opened at a pitch of 6 mm, while the ratio of hole area was 40%.
  • the amount of washing water was set to 6 m3/hour.
  • compositions of the ore slurry and the hydrocyclone underflow (hydrocyclone U/F) and the composition of the underflow of the high-mesh separator (high-mesh separator U/F) are presented in Table 14.
  • concentration was achieved from the Cr 2 O 3 -grade of the ore slurry of 4.1 wt % to 13.0 wt % in the coarse particle portion of the hydrocyclone (hydrocyclone U/F), and to 19.1 wt % in the coarse particle portion of the high-mesh separator (high-mesh separator U/F); however, the intended composition level of commercially available products was not achieved.
  • the high-mesh separator performed only the operation of slime removal, and did not perform the operation of specific gravity separation.
  • the leached slurry thus produced was separated into a leachate 11 and a leach residue slurry 12 by a solid-liquid separation step.
  • Leaching temperature 245° C.
  • Mg(OH) 2 slurry as a neutralizing agent at a concentration of 20 wt % was added to the leach residue slurry 12 , and the leach residue slurry was neutralized at 70° C. to obtain a pH of 2.5.
  • this slurry was subjected to solid-liquid separation using a 5 C filter paper.
  • the Mg(OH) 2 slurry was further added thereto until the slurry reached pH 6, and then the slurry was further subjected to solid-liquid separation using the 5 C filter paper.
  • the Cr 2 O 3 -grade of the final neutralized residue thus obtained was 0.9 wt %. Since the solubility of MgSO 4 to be produced was high, the sulfur-grade of the residue was 0.53 wt %.
  • Example 1 The ore slurry of Example 1 was treated in the same manner as in Example 3, except that the ore slurry was introduced into an autoclave without treating the slurry with a hydrocyclone and a density separator.
  • the Cr 2 O 3 -grade of the final neutralized residue thus obtained was 2.1 wt %.
  • Example 3 As is obvious from a comparison between Example 3 and Comparative Example 2, when the ore slurry was first classified with the hydrocyclone and then treated with the density separator, which is one of specific gravity separation apparatuses, chromite in the ore slurry could be separated and removed, and the Cr 2 O 3 -grade in the residue could be halved.
  • the density separator which is one of specific gravity separation apparatuses
  • a leach residue slurry 12 was produced in the same manner as in Example 3, slaked lime slurry at a concentration of 25 wt % was added as a neutralizing agent to the entire amount of the leach residue slurry, and the slurry was neutralized to pH 8.5 at 60° C. Metal ions were precipitated as precipitate, and a neutralized residue and a treatment solution after neutralization were obtained by solid-liquid separation.
  • This neutralized residue was subjected to cyclone classification, and thus hematite 28 was separated.
  • a mixed liquid was prepared by mixing the remaining neutralized residue from which hematite 28 had been separated with the treatment solution after neutralization, and a slaked lime slurry at a concentration of 25 wt % was added thereto. Thereafter, solid-liquid separation was repeated using a 5 C filter paper, and thus a final neutralized residue was obtained.
  • the Cr2O3-grade of the final neutralized residue thus obtained was 0.8 wt %. Since the solubility of CaSO 4 to be produced was small, the sulfur-grade of the residue was 5.72 wt %, and the Ca-grade was 8.49 wt %.
  • Example 6 As illustrated in an exemplary flow diagram according to Comparative Example 4 illustrated in FIG. 6 , a separation test was performed under the same condition as that of Example 1, except that the ore slurry 9 was subjected to the specific gravity separation in the same manner as in Example 1 without the classification treatment by the hydrocyclone and the classification treatment was finally performed by the hydrocyclone.
  • Table 16 indicates results obtained in such a manner that the ore which was not subjected to the classification treatment by the hydrocyclone was subjected to a specific gravity separation treatment using a density separator.
  • the viscosity of a feed (ore slurry) was high, but the concentration of Cr 2 O 3 subjected to the classification treatment by the density separator was not as high as the underflow (see a density separator U/F in Table 6) subjected to feeding.
  • the concentration of Cr 2 O 3 was 35.3 wt %, but did not meet 41 wt % or more.
  • the concentration could be achieved up to a concentration above the Cr 2 O 3 grade of the chromite which was commercially available in the market. From this fact, it can be found that it is important that the cyclone classification is performed first to remove microparticles.
  • the hydrometallurgical process for nickel oxide ore of the present invention is suitable as a smelting method based on high pressure leaching that is used in the hydrometallurgical field of nickel oxide ore.

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