JP7279546B2 - Nickel oxide ore leaching method and hydrometallurgical method including the same - Google Patents

Description

The present invention relates to a method for leaching nickel oxide ore by adding sulfuric acid under high temperature and high pressure and a hydrometallurgical method including the same, and in particular, it is performed while controlling the aluminum leaching rate by adjusting the concentration of free sulfuric acid. The present invention relates to a nickel oxide ore leaching method and a hydrometallurgical method including the same.

As a method for recovering valuable metals such as nickel and cobalt from low-grade nickel oxide ores with low nickel grade, for example, hydrometallurgical refining by a high pressure acid leaching (HPAL) method as disclosed in Patent Document 1 process is known. In this hydrometallurgical process, an ore slurry prepared by adding water to low-grade nickel oxide ore as a raw material is subjected to a leaching treatment with sulfuric acid under high temperature and high pressure, followed by a wet treatment to convert the valuable metal into sulfide. and it is possible to efficiently recover valuable metals from low-grade raw material ores.

The above high pressure acid leaching hydrometallurgical process generally consists of the following series of wet treatment steps. That is, an ore blending step of adjusting the nickel grade and particle size of a low-grade nickel oxide ore as a raw material, adding water to prepare an ore slurry, and a reaction vessel for high-pressure reaction called an autoclave with the ore slurry together with sulfuric acid. a leaching step in which nickel is leached with sulfuric acid under high temperature and pressure, a preliminary neutralization step in which free sulfuric acid remaining in the leaching slurry produced in the leaching step is neutralized using limestone, and the preliminary A solid-liquid separation step of solid-liquid separation of the leaching slurry neutralized in the neutralization step to obtain a pregnant solution (leaching solution) from which the leaching residue has been removed, and a neutralization treatment of the pregnant solution mainly composed of iron. A neutralization step of removing impurities to obtain a neutralization final solution, a solution purification step of removing impurities mainly composed of zinc contained in the neutralization final solution to obtain a nickel recovery mother liquor, and the nickel recovery. A sulfurization step of adding hydrogen sulfide gas to the mother liquor to recover nickel and cobalt in the form of a mixed sulfide, a poor liquid discharged during recovery of the mixed sulfide, and discharged from the solid-liquid separation step It is mainly composed of a final neutralization step in which heavy metals are removed to a predetermined concentration by neutralizing the leach residue before it is sent to the tailing dam.

In the above HPAL method, various techniques have been introduced to increase throughput. For example, Patent Document 1 above discloses a technique for adjusting the concentration of free sulfuric acid to 35 to 45 g/L at the end of the leaching process. It is described that the solid-liquid separation property of the slurry containing the leaching residue can be improved as a result of the stable production. Further, Patent Document 2 discloses a technique of sedimentation and separation of the leaching residue in the solid-liquid separation process by using a plurality of series-connected thickeners for multi-stage washing. Incidentally, in Patent Document 2, the poor liquid discharged from the sulfurization process is used as the washing liquid for the multi-stage washing.

Furthermore, Patent Document 3 discloses a technique of blending the grade of Mg+Al in the ore slurry to about 1.5 to 4.5% in order to control the oxygen consumption in the high-pressure sulfuric acid leaching process. In addition, in Patent Document 4, in order to reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate, A technique for adjusting the amount of sulfuric acid to be added is disclosed.

JP 2005-350766 A JP 2019-000834 A JP 2014-037632 A JP 2019-035113 A

By the way, the raw material nickel oxide ore contains aluminum (Al) and magnesium (Mg) as impurities. In the neutralization step, the amount of sediment produced from aluminum hydroxide increases, and the load of solid-liquid separation in the subsequent step becomes overloaded, or the clarity of the liquid phase after the solid-liquid separation deteriorates. There were problems. In addition, since the sediment made of aluminum hydroxide has a small particle size and a low specific gravity, solid-liquid separation is difficult, and the above-mentioned clarity is further deteriorated.

In this way, when the aluminum grade and magnesium grade of the raw material ore fluctuate, the operation after the leaching step becomes unstable, and the processing capacity of the hydrometallurgical process as a whole may decrease. The present invention has been made in view of the above situation, and even if the Al and Mg grades of nickel oxide ore used as a raw material for sulfuric acid leaching under high temperature and high pressure fluctuate, the sulfuric acid leaching process can be performed. It is an object of the present invention to provide a method for keeping the rate of aluminum leaching low during production.

The present inventors have made intensive studies to achieve the above object, and as a result, adjusted the amount of sulfuric acid to be added according to the Al / Mg ratio of the nickel oxide ore used as the raw material for the sulfuric acid leaching treatment under high temperature and high pressure conditions. As a result, the inventors have found that the aluminum leaching rate can be kept low, and have completed the present invention.

That is, the method for leaching a nickel oxide ore according to the present invention includes adding sulfuric acid to an ore slurry prepared by adding water to a nickel oxide ore containing aluminum and magnesium, and performing a sulfuric acid leaching treatment under high temperature and high pressure conditions. A leaching method for producing a leaching slurry consisting of a leaching solution containing nickel and a leaching residue, wherein the free sulfuric acid concentration of the leaching solution is a predetermined amount according to the ratio of the aluminum content to the magnesium content of the nickel oxide ore It is characterized by adjusting the addition amount of the sulfuric acid so as to fall within the range.

According to the present invention, since the aluminum leaching rate can be kept low, it is possible to keep the processing capacity of the hydrometallurgical process as a whole from deteriorating.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block flow diagram of a hydrometallurgical method that preferably includes a nickel oxide ore leaching treatment method according to the present invention; FIG. 2 is a schematic process flow diagram of a continuous countercurrent washing method preferably performed in the solid-liquid separation step of the hydrometallurgical process of FIG. 1; 1 is a graph showing the relationship between the Al/Mg ratio of ore raw materials used in the leaching method of the example of the present invention and the aluminum leaching rate during the leaching treatment thereof.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a nickel oxide ore leaching method according to the present invention will be described below with reference to the drawings. First, a hydrometallurgical process comprising a series of hydrometallurgical processes including a nickel oxide ore leaching process according to an embodiment of the present invention will be described, and then an embodiment of the present invention included in this hydrometallurgical process The leaching treatment method according to is explained.

1. Nickel oxide ore hydrometallurgical method In the nickel oxide ore hydrometallurgical method including the leaching treatment method according to the embodiment of the present invention, an ore slurry containing nickel oxide ore as a raw material is subjected to high pressure acid leaching (HPAL). After nickel and cobalt are leached according to the method), impurities such as iron and zinc contained in the resulting leaching solution are removed, and the nickel and cobalt are recovered in the form of mixed sulfides.

Specifically, as shown in FIG. 1, this nickel oxide ore hydrometallurgical method involves mixing a plurality of types of nickel oxide ore in order to adjust the nickel grade and the like, and adding water to wet classify the ore. a high-pressure sulfuric acid leaching step S2 in which sulfuric acid is added to the obtained ore slurry and subjected to leaching treatment under high temperature and high pressure; and a neutralizing agent is added to the leaching slurry obtained by the leaching treatment. a preliminary neutralization step S3 in which the pH is adjusted by adding the above, a solid-liquid separation step S4 in which the leaching residue is separated and removed by solid-liquid separation while washing the pH-adjusted leaching slurry in multiple stages, and the leaching residue A neutralizing agent is added to the leachate containing impurity elements together with nickel and cobalt obtained by the separation and removal of (1) to produce a neutralized sediment containing the impurity elements, which is separated and removed to contain zinc together with nickel and cobalt. A neutralization step S5 for obtaining a final neutralization solution, and a sulfiding agent such as hydrogen sulfide gas is added to the final neutralization solution to generate zinc sulfide, which is separated and removed to recover nickel containing nickel and cobalt. a sulfiding step S6 of adding a sulfiding agent to the mother liquor for recovering nickel to produce a mixed sulfide containing nickel and cobalt and recovering the mixed sulfide by solid-liquid separation; Neutralization treatment of the leaching residue containing free sulfuric acid separated and removed in the liquid separation step S4, and neutralization of the poor liquid containing impurities such as magnesium, aluminum, iron, etc. discharged during the solid-liquid separation in the sulfurization step S7. It is mainly composed of a final neutralization step S8 for processing. Each of these series of wet processing steps is described in detail below.

(1) Ore blending step S1
In the ore blending step S1, nickel oxide ores typified by so-called laterite ores such as limonite ore and saprolite ore are used as raw material ores, and a plurality of types of nickel oxide ores with different lots etc. are mixed so as to obtain desired nickel grades and impurity grades. Nickel oxide ore is mixed and introduced into a grinder or screen to make the particle size uniform to some extent, and then introduced into a wet classifier together with water to remove oversized ore particles. As a result, ore slurry containing nickel oxide ore having a predetermined particle size is recovered from the under-sieve side of the wet classifier.

With regard to the above wet classifier, the raw material nickel oxide ore is classified at a predetermined classification point to remove oversized ore particles and impurities, and the undersized ore particles are efficiently removed together with water on the underside of the sieve. There is no particular limitation as long as it can be recovered, and for example, a general wet vibrating sieve or a rotating wet sieve such as a trommel can be preferably used. In addition, although there is no particular limitation on the classification point to be adopted in this wet classifier, in order to ensure that the nickel oxide ore collected on the underside of the sieve is efficiently leached in the high-pressure sulfuric acid leaching process in the subsequent process, it is appropriate A sieve with a large opening is selected.

(2) High pressure sulfuric acid leaching step S2
In the high-pressure sulfuric acid leaching step S2, the ore slurry containing the nickel oxide ore prepared in the ore preparation step S1 is introduced into the reaction vessel together with sulfuric acid, and the pressure is about 3.0 to 5.0 MPaG and the temperature is about 220 to 260°C. Leaching is performed under high temperature and high pressure conditions. As a result, a leaching reaction and a high-temperature thermal hydrolysis reaction occur, leaching nickel, cobalt, etc. as sulfate salts, and fixing the leached iron sulfate as hematite, resulting in a leaching solution and a leaching residue. A leach slurry is produced. As the reaction vessel, a pressure vessel for high-temperature, high-pressure reaction, called an autoclave, which has a horizontal cylindrical shape and whose interior is partitioned into a plurality of compartments by weirs is preferably used.

The amount of sulfuric acid added to the ore slurry is excessive so that the iron in the nickel oxide ore is leached. At that time, in the high-pressure sulfuric acid leaching step S2, from the viewpoint of improving the solid-liquid separation property of the leaching residue containing hematite in the subsequent solid-liquid separation step S4, the pH of the leaching solution is adjusted to 0.1 to 1.0. It is preferable to adjust the amount of sulfuric acid added. In this leaching treatment, iron ions are not completely immobilized, so the leaching solution contains divalent and trivalent iron ions in addition to valuable metals such as nickel and cobalt.

(3) Preliminary neutralization step S3
In the preliminary neutralization step S3, a neutralizing agent is added to the leaching slurry obtained in the high-pressure sulfuric acid leaching step S2 to adjust the pH of the leaching slurry within a predetermined range. As described above, in the high-pressure sulfuric acid leaching step S2, in order to improve the leaching rate of the valuable metals, sulfuric acid in excess of the stoichiometric amount required for leaching the valuable metals is supplied to the autoclave. Therefore, the leaching slurry withdrawn from the autoclave after the leaching process contains surplus sulfuric acid that did not participate in the leaching reaction, and its pH is very low. In order to neutralize the surplus sulfuric acid and efficiently perform multi-stage washing in the subsequent solid-liquid separation step S4, the pH of the leached slurry is adjusted to a predetermined range in the preliminary neutralization step S3.

Specifically, it is preferable to adjust the pH of the leached slurry supplied to the solid-liquid separation step S4 so that the pH is about 2 to 6. If the pH is lower than 2, considerable cost is required to make the post-process equipment acid-resistant. Conversely, if the pH is higher than 6, the nickel leached into the leaching solution precipitates during the multi-stage cleaning process and is removed together with the leaching residue. There is a risk.

In the preliminary neutralization step S3, the leaching slurry supplied to the solid-liquid separation step S4 is used to suppress the pH fluctuation range in the subsequent neutralization step S5 and to improve the reaction efficiency in the liquid purification step S6 and the sulfurization step S7. It is preferable to set the pH value of . However, when the pH value of the leaching slurry increases, the amount of SS (suspended solids) due to fine particle components contained in the leaching slurry increases. There have been problems such as insufficient liquid separation and easy clogging of the filter in the liquid purification step S6. In order to suppress this problem, in the preliminary neutralization step S3, it is more preferable to adjust the pH of the liquid phase portion of the leaching slurry supplied to the solid-liquid separation step S4 to 2.5 to 3.4. . The method for adjusting the pH is not particularly limited, but the pH can be preferably adjusted within the above range by adjusting the amount of a neutralizing agent such as calcium carbonate slurry to be added.

(4) Solid-liquid separation step S4
In the solid-liquid separation step S4, the leaching slurry pH-adjusted in the preliminary neutralization step S3 is washed in multiple stages, and the leaching residue is separated and removed by gravitational sedimentation. A leachate can be obtained. In this solid-liquid separation step S4, the leaching slurry is mixed with the cleaning liquid and then solid-liquid separated using a sedimentation device such as a thickener, so that the leaching slurry is first diluted with the cleaning liquid, and then the leaching slurry is separated by sedimentation. The leaching residue settles to the bottom of the thickener and is discharged in the form of a thickened slurry. As a result, the amount of nickel adhering to the leaching residue can be reduced according to the degree of dilution.

In the solid-liquid separation by the thickener, as shown in FIG. 2, the leaching slurry and the washing liquid are introduced into a plurality of thickeners T ₁ to T _n connected in series so as to flow in countercurrent to each other, and washing is performed in multiple stages. A continuous countercurrent washing method (CCD method: Counter Current Decantation method) is preferably used. That is, among a plurality of continuous thickeners T ₁ to T _n , the leaching slurry pH-adjusted in the preliminary neutralization step S3 is introduced into the most upstream thickener T ₁ , and the washing liquid is introduced into the most downstream thickener T _n . .

In each of the plurality of thickeners T ₁ to T _n , the concentrated slurry withdrawn from the bottom is transferred to the downstream thickener via the slurry pump P (the concentrated slurry in the most downstream thickener T _n is the final neutralization step). S8), on the other hand, the clarified liquid overflowing from the upper end is immediately transferred to the upstream thickener (the clarified liquid in the uppermost thickener _T1 is transferred to the neutralization step S5). As a result, the amount of soluble nickel and cobalt adhering to the residue contained in the leaching slurry can be reduced, so that the cleaning liquid newly introduced into the system can be reduced and the recovery rate of nickel and cobalt can be improved. can be done. In addition, it is preferable to add a flocculating agent to each thickener to flocculate the leaching residue, thereby further enhancing the sedimentation separation property.

The clarified liquid overflowing from the upper end portion of the most upstream thickener _T1 is sent to the subsequent neutralization step S5 as a pregnant liquid. In the solid-liquid separation step S4, it is preferable to maintain the clarity of the pregnant liquid at a high level. is improved, and as a result, the productivity of the hydrometallurgical process as a whole is improved. In other words, if the clarity of the pregnant liquid is low and it contains many suspended particles, for example, the pressure loss in the filter will increase immediately and the flow rate of the liquid will decrease at an early stage. It may become a bottleneck and reduce the throughput of the entire process.

As the cleaning liquid, it is preferable to use a low pH aqueous solution that contains almost no nickel and has almost no adverse effect on the reaction after the solid-liquid separation step S4, and in particular, it is more preferable to use an aqueous solution with a pH of about 1 to 3. . If the pH of the cleaning solution is higher than 3, and aluminum is contained in the leaching solution, aluminum hydroxide having a high bulk is produced, which may cause the sedimentation failure of the leaching residue in the thickener. The cleaning liquid that satisfies the above conditions is not limited, but since the poor liquid discharged from the subsequent sulfurization step S7 has a pH of about 1 to 3, it is preferable to use this repeatedly.

(5) Neutralization step S5
In the neutralization step S5, a neutralizing agent such as calcium carbonate is added to the pregnant liquid (leaching liquid) obtained by separating and removing the leaching residue in the solid-liquid separation step S4 to adjust the pH of the pregnant liquid. Neutralized sediment is produced from the impurity elements contained in the This neutralized sediment is separated and removed using a thickener or the like to recover a final neutralization solution containing zinc together with nickel and cobalt. In the above pH adjustment, the pH of the neutralization final solution is preferably 4 or less, more preferably 3.0 to 3.5, most preferably 3.1 to 3, while suppressing oxidation of the pregnant solution. Adjust the amount of the neutralizing agent to be added to obtain .2. As a result, the sulfuric acid excessively added in the high-pressure sulfuric acid leaching step S2 is neutralized to produce a neutralization final solution that is the source of the mother liquor for recovering nickel, and the trivalent iron ions and aluminum remaining in the leaching solution Impurities such as ions can be removed as neutralized sediments. This neutralized precipitate may be returned to the preceding solid-liquid separation step S4.

(6) Liquid purification step S6
In the liquid purification step S6, a sulfiding agent such as hydrogen sulfide gas is added to the final neutralization liquid produced in the previous neutralization step S5 to carry out a sulfidation treatment. and cobalt-containing mother liquor for recovering nickel (final dezincing liquor). The sulfurization treatment is preferably carried out by blowing hydrogen sulfide gas into the gas phase portion of the low-pressure reaction vessel while introducing the final neutralization solution into the low-pressure reaction vessel which is slightly pressurized. As a result, zinc can be selectively sulfided with respect to nickel and cobalt and removed as zinc sulfide, and a dezincing final solution can be efficiently produced as a mother liquor for recovering nickel.

(7) Sulfurization step S7
In the sulfurization step S7, the final dezincing solution produced in the liquid purification step S6 is subjected to a sulfurization treatment as the starting solution for the sulfurization reaction, thereby producing a mixed sulfide of nickel and cobalt containing few impurity components. Specifically, the sulfurization reaction initial liquid is charged into a pressurized sulfurization reaction tank, and hydrogen sulfide gas is blown into the gas phase portion in the sulfurization reaction tank, and the hydrogen sulfide gas is introduced into the sulfurization reaction initial liquid. Dissolve. This causes a sulfurization reaction to fix nickel and cobalt contained in the starting solution of the sulfurization reaction as a mixed sulfide. The mixed sulfide can be recovered by withdrawing the slurry containing the mixed sulfide of nickel and cobalt from the sulfurization reaction tank and subjecting it to solid-liquid separation using a solid-liquid separator such as a thickener.

When the solid-liquid separator is a thickener, the mixed sulfide separated by gravity settling is recovered from the bottom of the thickener in the form of a concentrated slurry. On the other hand, the supernatant liquid from which the mixed sulfide has been separated is discharged as a poor liquid by overflow from the upper end of the thickener. This poor solution is an aqueous solution in which the concentration of valuable metals such as nickel is stabilized at an extremely low level, but it contains impurity elements such as iron, magnesium and manganese that remain without being sulfided. Therefore, this poor liquid is usually transferred to the final neutralization step S8 and detoxified, but if necessary, at least part of it is returned to the solid-liquid separation step S4 and reused for nickel recovery. be.

(8) Final neutralization step S8
In the final neutralization step S8, when the leaching residue containing free sulfuric acid separated and removed in the solid-liquid separation step S4 and the mixed sulfide produced in the sulfurization step S7 are collected by sedimentation separation, filtration, etc., the liquid A neutralizing agent is added to the poor liquid containing impurities such as magnesium, aluminum and iron discharged to the phase side for neutralization. As a result, it is possible to prevent the environmentally problematic slurry from being discharged out of the system from the present hydrometallurgical process. Specifically, a neutralizing agent is added to the leaching residue or poor liquid to adjust the pH to a predetermined range. As a result, free sulfuric acid contained in the leaching residue is almost completely neutralized, and impurities contained in the poor liquor are fixed as hydroxides. The slurry containing hydroxides of impurities thus produced is transferred as a waste slurry (tailing) to a tailing dam (waste reservoir).

2. Method for Leaching Slurry of Nickel Oxide Ore The method for leaching nickel oxide ore according to the embodiment of the present invention is carried out in the high-pressure sulfuric acid leaching step S2 of the above hydrometallurgical method. In this leaching treatment method, nickel oxide ore containing aluminum and magnesium prepared in the preceding ore preparation step S1 is subjected to leaching treatment. In addition, as described above, in this leaching method, the ore slurry containing the nickel oxide ore charged into a reaction vessel called an autoclave under high temperature and high pressure is subjected to leaching treatment with sulfuric acid. It is possible to very efficiently produce a leaching slurry composed of a leaching solution containing and a leaching residue.

That is, in this leaching treatment, sulfuric acid is added to the ore slurry under high temperature and pressure to cause leaching reactions represented by the following formulas i to iii and high-temperature hot hydration represented by the following formulas iv to v. A decomposition reaction is caused, whereby nickel, cobalt, etc. are leached out as sulfate salts and the leached out iron sulfate is fixed as hematite. Since the fixation of iron ions does not proceed completely, the liquid phase portion of the resulting leach slurry normally contains divalent and trivalent iron ions in addition to nickel, cobalt, and the like.

(leaching reaction)
[Formula i]
MO+ _{H2SO4 → MSO4} + _H2O
(In the formula, M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn, etc.)
[Formula ii]
2Fe(OH) _{3 + 3H2SO4} → _Fe2 ( _SO4 ) ₃ + _6H2O
[Formula iii]
FeO _{+ H2SO4} → _FeSO4 + _H2O

(High temperature thermal hydrolysis reaction)
[Formula iv]
_2FeSO4 + _{H2SO4 +} 1/ _2O2 → _Fe2 ( _SO4 ) ₃ + _H2O
[Formula v]
_{Fe2 ( SO4} ) ₃ + _3H2O → _{Fe2O3 + 3H2SO4}

In order to efficiently carry out the leaching reaction and to fix most of the iron in the raw material ore as hematite, the reaction temperature in the autoclave is preferably maintained at about 220 to 260°C, more preferably about 240 to 255°C. leaching treatment. If the reaction temperature is lower than 220°C, the high-temperature thermohydrolysis reaction rate slows down, iron remains dissolved in the reaction solution, and removal of this iron increases the load of the liquid purification step S6 in the subsequent process. Separation from nickel becomes difficult. Conversely, if the reaction temperature exceeds 260°C, although the high-temperature hydrolysis reaction itself is promoted, it becomes difficult to select the material for the autoclave that performs high-temperature and high-pressure leaching, and the thermal energy cost required to raise the temperature increases. do.

The amount of sulfuric acid added to the ore slurry during the leaching process is generally an excess amount compared to the stoichiometric amount calculated from the above formulas iv, for example, 150 to 150 to 1 ton of ore. About 250 kg of sulfuric acid are added. However, the amount of sulfuric acid added is preferably as small as possible from the viewpoint of the consumption cost of sulfuric acid. If the amount of sulfuric acid added per ton of ore exceeds 250 kg, the cost of sulfuric acid becomes too high, which is not preferable. Conversely, if the amount of sulfuric acid added per ton of ore is less than 150 kg, the leaching of nickel may be insufficient.

The raw nickel oxide ore to be subjected to the above leaching treatment is so-called laterite ore represented by limonite ore and saprolite ore. This laterite ore usually contains nickel at a content of about 0.8 to 2.5% by mass as a hydroxide or magnesium silicate (magnesium silicate) mineral. In addition, this nickel oxide ore has an iron content of about 10 to 50% by mass, which is mainly in the form of trivalent hydroxide (goethite), but partly contains divalent iron. It is contained in siliceous minerals. In addition to the above-mentioned laterite ore, the nickel oxide ore used as a raw material is an oxide ore containing valuable metals such as nickel, cobalt, manganese, and copper, such as manganese nodules existing in the deep seabed. There is

In the leaching treatment, sulfuric acid is added to the ore slurry containing the nickel oxide ore prepared in the previous step to cause a leaching reaction. The ore slurry in the form of slurry preferably has a solid content concentration (also referred to as slurry concentration) of about 15 to 45% by mass. If the slurry concentration is less than 15% by mass, an excessively large autoclave is required to ensure the desired residence time, and the amount of sulfuric acid added increases accordingly, which is not preferable. Conversely, if the slurry concentration exceeds 45% by mass, although the scale of the facility can be reduced, it becomes difficult to transfer the high-concentration slurry, frequent clogging occurs in the transfer pipe, and excessive energy is required for transfer. It is not preferable because it becomes

By the way, the above-mentioned nickel oxide ore contains aluminum and magnesium as impurities, and if the grades of these impurities fluctuate due to reasons such as switching raw material lots, the operation after the solid-liquid separation step S4 will become unstable. was there. Therefore, in the leaching method of the embodiment of the present invention, the amount of sulfuric acid added to the ore slurry containing the nickel oxide ore is defined by the ratio of the aluminum content to the magnesium content of the nickel oxide ore. The concentration of free sulfuric acid in the leachate contained in the leach slurry is adjusted within a predetermined range by increasing or decreasing according to the standard Al/Mg ratio (hereinafter also referred to as the Al/Mg ratio).

As a result, the aluminum leaching rate can be controlled, so even if the Al/Mg ratio in the nickel oxide ore becomes higher than usual, the load of the solid-liquid separation in the subsequent solid-liquid separation step S4 may become too high or Problems such as deterioration of solid-liquid separability can be suppressed. The aluminum content and magnesium content can be determined, for example, by analyzing the raw nickel oxide ore by ICP emission spectrometry. In addition, the aluminum content and magnesium content are sometimes referred to as the aluminum content (or grade) and the magnesium content (grade), respectively. Furthermore, since the ore slurry is produced by adding water to the raw nickel oxide ore, the value of the Al/Mg ratio of the nickel oxide ore is the same as the value of the Al/Mg ratio of the ore slurry containing the nickel oxide ore. are essentially the same.

Specifically, the aluminum content of nickel oxide ore such as laterite ore, which is the solid content in the ore slurry, is usually in the range of about 2.0 to 3.5% by mass, and the magnesium content is usually 0.5% by mass. It is within the range of about 8 to 1.8% by mass. Therefore, the Al/Mg ratio of the nickel oxide ore is in the range of approximately 1.1 to 4.4. When the ore slurry of nickel oxide ore containing aluminum and magnesium within this range of Al/Mg ratio is leached in the high-pressure sulfuric acid leaching step S2, nickel, magnesium, and aluminum are leached according to formulas 1 to 3 below. A part of the leached aluminum is leached by the reaction and is immobilized by the hydrolysis reaction of the following formula 4.

[Formula 1]
NiO _{+ H2SO4} = _NiSO4 + _H2O
[Formula 2]
MgO _{+ H2SO4} = _MgSO4 + _H2O
[Formula 3]
2Al ₍ OH) ₃ + _3H2SO4 → _Al2 ( _SO4 ) ₃ + _6H2O
[Formula 4]
_3Al2 ( _SO4 ) ₃ + _14H2O →
2 _{( H3O} ) _Al3 ( _SO4 ) ₂ (OH) ₆ + _5H2SO4

In the above leaching treatment, it is preferable that the aluminum leaching rate is suppressed to 25.0% or less. If the aluminum leaching rate exceeds 25.0%, the concentration of aluminum in the leaching solution becomes excessive, resulting in an excessive amount of sediment formed of aluminum hydroxide in the subsequent preliminary neutralization step S3, resulting in an excessive amount of precipitation in the solid-liquid separation step. Sometimes the S4 load became too high and the clarity of the pregnant liquor deteriorated. In addition, since the sediment made of aluminum hydroxide has a small particle size and a low specific gravity, it is difficult to settle in the sedimentation device of the thickener, and the above-mentioned clarity is further deteriorated. As a result, the throughput of the hydrometallurgical process as a whole has sometimes decreased. Note that the aluminum leaching rate (Al leaching rate) can be defined by Equation 5 below.

[Formula 5]
Al leaching rate = (Amount of leachate produced per unit time x Al mass concentration in leachate) ÷ (Amount of nickel oxide ore processed per unit time x Al grade of nickel oxide ore) x 100

Therefore, in the leaching treatment method of the embodiment of the present invention, the amount of sulfuric acid added to the autoclave is adjusted so that the concentration of free sulfuric acid in the leaching solution falls within a predetermined range according to the Al/Mg ratio of the ore slurry charged into the autoclave. Adjusting the amount added. For example, when the Al/Mg ratio of the ore slurry charged into the autoclave tends to increase, the amount of sulfuric acid added is decreased so that the concentration of free sulfuric acid in the leachate contained in the leach slurry discharged from the autoclave decreases. When the Al/Mg ratio of the ore slurry charged into the autoclave tends to decrease, the opposite operation is performed.

More specifically, it is determined whether the Al/Mg ratio of the ore slurry charged into the autoclave is higher or lower than the threshold value of 2.0, and if the Al/Mg ratio is 2.0 or more, The amount of sulfuric acid added to the autoclave is adjusted so that the concentration of free sulfuric acid in the leachate contained in the leach slurry extracted from the autoclave is within the range of 32 g/L or more and 38 g/L or less.

By adjusting the free sulfuric acid concentration of the leaching solution within the above range, the aluminum leaching rate can be kept low when nickel oxide ore containing aluminum and magnesium is leached in the autoclave. That is, if the free sulfuric acid concentration exceeds 38 g/L, the aluminum leaching rate during the leaching treatment may become too high. Conversely, if the free sulfuric acid concentration is less than 32 g/L, the nickel leaching rate when the nickel oxide ore is leached in the autoclave may not satisfy the desired conditions.

On the other hand, when the Al/Mg ratio in the ore slurry charged into the autoclave is less than 2.0, the concentration of free sulfuric acid in the leachate contained in the leach slurry extracted from the autoclave after the leach treatment in the autoclave is The amount of sulfuric acid to be added to the autoclave is adjusted so as to be more than 38 g/L and 50 g/L or less, more preferably 40 g/L or more and 50 g/L or less.

Thus, when the Al/Mg ratio of the ore slurry is less than 2.0, the free sulfuric acid concentration is made higher than when the Al/Mg ratio is 2.0 or more. If the Al/Mg ratio is reduced compared to the case where the Al/Mg ratio is 2.0 or more, the aluminum leaching rate is slightly lowered, but the magnesium grade in the ore slurry is higher than that when the Al/Mg ratio is 2.0 or more. This is because the added sulfuric acid is preferentially used for magnesium, making it difficult to obtain the effect of reducing the aluminum leaching rate by lowering the concentration of free sulfuric acid, and conversely, the nickel leaching rate decreases.

That is, when the Al/Mg ratio of the nickel oxide ore processed in the high-pressure sulfuric acid leaching step S2 described above is low (this corresponds to the case where the magnesium grade is relatively high), the reaction of the above formula 2 is preferentially performed. Since the reaction progresses, the reaction of the above formula 3 is inhibited or the reaction of the above formula 4 is promoted, so that the aluminum leaching rate tends to be at a low level. On the other hand, when the Al/Mg ratio of the nickel oxide ore processed in the high-pressure sulfuric acid leaching step S2 is high (this corresponds to the case where the magnesium grade is relatively low), the leachate is Since a sufficient concentration of free sulfuric acid is maintained and the concentration of metal ions in the leachate is low, the reaction of formula 3 above is promoted and the reaction of formula 4 above is inhibited, so that the aluminum leaching rate is at a high level. Prone.

As in the latter case, when the raw material nickel oxide ore has a high Al/Mg ratio, the aluminum leaching rate tends to be high. actively reduce it. As a result, it is possible to suppress the progress of the reaction of the above formula 3 or to advance the reaction of the above formula 4, so that it is possible to effectively prevent the aluminum leaching rate from becoming excessively large.

Although the nickel oxide ore leaching method of the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various alternative examples and It may contain modifications. That is, the scope of rights of the present invention covers the claims and their equivalents. Next, the leaching method of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

<Example>
Raw material ores of samples 1 to 6 consisting of laterite ores with different Al contents and Mg contents were prepared, and water was added to each of them to prepare an ore slurry having a solid content concentration of about 40% by mass. . Each of the ore slurries of Samples 1 to 6 was continuously charged into an autoclave, and 98% sulfuric acid was continuously added with a standard of 200 kg per ton of ore, and the leaching temperature was about 253 ° C. and the leaching pressure was about A sulfuric acid leaching treatment was performed under high temperature and high pressure conditions of 4500 kPaG to produce a leaching slurry.

At that time, the charging flow rate of the ore slurry was adjusted so that the residence time in the autoclave was 60 minutes. On the other hand, when the Al/Mg ratio of the raw ore is less than 2.0, the concentration of free sulfuric acid in the leachate contained in the leach slurry continuously discharged from the autoclave is 38 g/L or more and 50 g/L. If the Al/Mg ratio of the raw material ore is 2.0 or more, adjust so that the free sulfuric acid concentration of the leachate is within the range of 32 g/L or more and 38 g/L or less. bottom.

In this way, the leaching slurry obtained by leaching the raw material ore of each sample with sulfuric acid is sampled, and this is introduced into a Nutsche lined with filter paper to separate and remove the leaching residue. The concentration of aluminum was measured by ICP emission spectroscopy. The aluminum leaching rate was obtained by substituting the obtained aluminum concentration (mass %) into the above-described formula 5. The results are shown in Table 1 below together with the Al content, Mg content, Al/Mg ratio of the raw ore, and the concentration of free sulfuric acid in the leachate. Also, the relationship between the Al/Mg ratio of the ore raw material and the aluminum leaching rate was plotted on the graph of FIG. The Al content and Mg content of the raw material ore were measured by ICP emission spectrometry, and the concentration of free sulfuric acid in the leachate was measured by neutralization titration.

As can be seen from Table 1 and FIG. 3 above, by adjusting the amount of sulfuric acid added so that the concentration of free sulfuric acid in the leachate falls within a predetermined range according to the Al/Mg ratio of the raw ore, the Al leaching rate was reduced to 25. We were able to keep it below 0%. Even in the region where the Al/Mg ratio is less than 2.0, if the free sulfuric acid concentration is lowered, the aluminum leaching rate is thought to decrease slightly. Lowering the free sulfuric acid concentration to lower the rate is generally unacceptable from an economic standpoint.

<Comparative example>
Raw material ores of samples 7 to 12 consisting of laterite ores with different Al contents and Mg contents were prepared, and water was added to each of them in the same manner as in the example to obtain a solid content concentration of about 40% by mass. An ore slurry was prepared. For each of the ore slurries of Samples 7 to 12, regardless of the value of the Al/Mg ratio of the raw material ore, the free sulfuric acid concentration of the leachate was always within the range of 40 g / L or more and 50 g / L or less. The leaching treatment was carried out in the same manner as in the above examples, except that the addition flow rate of sulfuric acid was adjusted. The results are shown in Table 2 below together with the Al content, Mg content, Al/Mg ratio of the raw ore, and the concentration of free sulfuric acid in the leachate. Also, the relationship between the Al/Mg ratio of the ore raw material and the aluminum leaching rate was plotted on the graph of FIG.

As can be seen from Table 2 and FIG. 3, even when the Al/Mg ratio of the raw material ore is 2.0 or more, the concentration of free sulfuric acid in the leachate is always within the range of 40 g/L or more and 50 g/L or less. Since the addition flow rate of sulfuric acid was adjusted so that the Al leaching rate could not be suppressed to 25.0% or less.

From the results of the above examples and comparative examples, it can be seen that a desired aluminum leaching rate can be obtained by adjusting the concentration of free sulfuric acid according to the value of the Al/Mg ratio of the raw material ore. That is, it was found that the suitable concentration of free sulfuric acid varies depending on the Al/Mg ratio of the raw ore. For example, when the Al/Mg ratio of the raw material ore is 2.0 or more, it was found that the aluminum leaching rate can be reduced by reducing the amount of sulfuric acid added so that the free sulfuric acid concentration in the leachate is lowered. This is believed to be due to either the inhibition of the aluminum leaching reaction or the acceleration of the hydrolysis reaction of aluminum sulfate, or both, due to the lower concentration of free sulfuric acid.

S1 Ore blending process S2 High-pressure sulfuric acid leaching process S3 Preliminary neutralization process S4 Solid-liquid separation process S5 Neutralization process S6 Liquid purification process S7 Sulfurization process S8 Final neutralization process T ₁ to T _n thickener P Slurry pump

Claims (4)

Sulfuric acid is added to an ore slurry prepared by adding water to a nickel oxide ore containing aluminum and magnesium, and sulfuric acid leaching is performed under high temperature and high pressure conditions to produce a leaching slurry consisting of a leaching solution containing nickel and a leaching residue. A leaching method for
The amount of sulfuric acid added is adjusted so that the concentration of free sulfuric acid in the leachate falls within a predetermined range according to the ratio of the aluminum content to the magnesium content of the nickel oxide ore. Leaching treatment method. When the ratio is 2.0 or more, the amount of sulfuric acid added is adjusted so that the free sulfuric acid concentration of the leachate is in the range of 32 g/L or more and 38 g/L or less, and the ratio is less than 2.0. 2. The nickel oxide ore according to claim 1 , wherein the amount of sulfuric acid added is adjusted so that the concentration of free sulfuric acid in the leachate is in the range of more than 38 g / L and 50 g / L or less. Leaching treatment method. The nickel oxide ore leaching method according to claim 1 or 2 , wherein the sulfuric acid leaching treatment is carried out at a reaction temperature of 220 to 260°C in an autoclave comprising a reaction vessel for high temperature and high pressure reaction. a high-pressure sulfuric acid leaching step of leaching an ore slurry prepared by adding water to the raw material nickel oxide ore using the nickel oxide ore leaching method according to any one of claims 1 to 3 ; A solid-liquid separation step of separating the leach solution containing nickel generated by the leaching treatment from the leach residue, and a neutralization step of adding a neutralizing agent to the leach solution obtained in the solid-liquid separation step to remove impurities; A hydrometallurgical method for nickel oxide ore, comprising a sulfurization step of adding a sulfiding agent to the leachate from which impurities have been removed in the neutralization step to recover the nickel in the form of sulfide.

Images