JP2020028858A - Final neutralization method in wet refining process for nickel oxide ore - Google Patents

Abstract

To provide a final neutralization method capable of reducing a cost of a neutralizing agent consumed in a final neutralization step.SOLUTION: In a final neutralization method for removing metals dissolved in a drainage of pH 1.0 to 3.0 discharged in recovering nickel sulfide from a leachate produced in high temperature pressurized acid leaching of nickel oxide ores, a limestone slurry, desirably having an average particle diameter of 5 to 15 μm and a slurry concentration of 20 to 30 mass%, is added to the drainage adjusted to an iron ion concentration of 1.0 to 4.0 g/L to carry out first neutralization treatment at pH 5.0 to 5.4, and then a slaked lime slurry, desirably having an average particle diameter of 15 to 30 μm and a slurry concentration of 20 to 30 mass%, is added to carry out second neutralization treatment at higher pH.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a final neutralization method of a wastewater discharged in a hydrometallurgical process in which nickel is recovered by subjecting nickel oxide ore to high-pressure acid leaching.

  The method of recovering nickel from nickel oxide ore can be roughly classified into a dry method and a wet method. As the latter wet method, a high-temperature pressurized acid leaching (HPAL: High Pressure Acid Leach) process is known. . The HPAL process has advantages in that energy consumption can be reduced as compared with the dry process and nickel can be efficiently recovered from low-grade nickel oxide ore.

  In this HPAL process, for example, a nickel oxide ore is treated in a series of wet processes as shown in Patent Document 1. That is, after adding water to a plurality of types of low-grade nickel oxide ores mixed to have a predetermined Ni grade and impurity grade to form a slurry, the slurry is introduced as a classification means into, for example, a wet sieve, and coarse ore is introduced. By removing ore and contaminants, an ore slurry containing ore having a predetermined particle size is collected below the sieve. This ore slurry is charged together with sulfuric acid into a pressure vessel called an autoclave and subjected to an acid leaching treatment under high temperature and pressure, whereby Ni is leached with sulfuric acid to obtain a leached slurry.

  Since the above leaching slurry contains residual free acid, it is neutralized using limestone in the pre-neutralization step, and then transferred to the solid-liquid separation step to separate the noble liquid consisting of the leaching liquid containing Ni from the leaching residue. I do. The separated leaching residue is sent to a tailing dam after heavy metals are removed in a final neutralization step. On the other hand, in the noble liquid, after impurities are removed in the neutralization step and the purification step, hydrogen sulfide gas is added in the sulfurization step to generate NiCo mixed sulfide. A part of the waste liquid, which is also referred to as a poor liquid discharged when the NiCo mixed sulfide is recovered by solid-liquid separation, is reused in the solid-liquid separation step after the preliminary neutralization step, and the remainder is the final neutralization. Processed in the process.

  As described above, the final neutralization step is performed before discharging the acidic concentrated slurry containing the leaching residue discharged from the solid-liquid separation step and the poor liquid composed of the acidic aqueous solution discharged from the sulfidation step to the outside of the system. It is another object of the present invention to precipitate a metal component dissolved in a liquid and remove it to such an extent that an environmental problem does not occur. Therefore, in the final neutralization step, a two-stage neutralization process is generally performed, in which limestone is added and neutralized by adding limestone and slaked lime is added and neutralized at a higher pH. Neutralization has been performed.

  However, in the above-described two-stage neutralization treatment, depending on the treatment conditions, the consumption of slaked lime having a higher unit price than that of limestone may be too large, resulting in high cost. Therefore, Patent Document 2 proposes a technique for effectively reducing the amount of a neutralizing agent such as slaked lime in a final neutralization step by sorting ore slurries by particle size in a pretreatment stage of the ore slurry. ing.

JP 2010-031302A JP-A-2006-156063

  Although the use amount of the neutralizing agent can be reduced to some extent by employing the technique of Patent Document 2, the consumption cost of the neutralizing agent may still be high. The present invention has been made in view of the above situation, and has as its object to provide a final neutralization method capable of reducing the cost of a neutralizing agent consumed in the final neutralization step.

  In order to achieve the above object, the final neutralization method of the present invention removes a metal dissolved in an effluent discharged when recovering nickel sulfide from a leaching solution generated by high-temperature pressure acid leaching of nickel oxide ore. A final neutralization method in which a limestone slurry is added to a wastewater having an iron ion concentration adjusted to 1.0 to 4.0 g / L and a first neutralization treatment is performed at pH 5.0 to 5.4. After that, the second neutralization treatment is performed at a higher pH by adding slaked lime slurry.

  According to the present invention, since the reaction efficiency of limestone can be increased, the amount of the neutralizing agent consumed in the final final neutralization method as a whole can be reduced.

1 is a process flow diagram of a hydrometallurgical process including a final neutralization method according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram of the neutralization processing equipment which can implement suitably the final neutralization method of embodiment of this invention. It is a graph which shows the relationship between pH of the processing liquid in the neutralization tank which processes by adding limestone, and reaction efficiency of limestone. It is the graph which showed the relationship between the pH of the processing liquid in the neutralization tank which processes by adding limestone, and the cost of the neutralizing agent consumed as the final neutralization method as a whole with the Fe concentration in the poor liquid as a parameter.

  Hereinafter, the hydrometallurgical process of nickel oxide ore including the final neutralization method of the embodiment of the present invention will be described with reference to FIG. In the hydrometallurgical process shown in FIG. 1, a nickel oxide ore as a raw material is subjected to a pretreatment such as pulverization and sieving so as to have a predetermined particle size, and water is added to prepare an ore blending step. S1, a high-pressure sulfuric acid leaching step S2 of adding sulfuric acid to the ore slurry prepared in the ore blending step S1 and subjecting the ore slurry to leaching under high temperature and pressure, and a neutralizing agent added to the leached slurry obtained in the high-pressure sulfuric acid leaching step S2. And a pre-neutralization step S3 for adjusting the pH to a predetermined range, and a leaching slurry containing an impurity element together with nickel and cobalt by washing the leaching slurry whose pH has been adjusted in the pre-neutralization step S3 in multiple stages. A neutralizing precipitate containing impurity elements by adding a pH adjuster to the noble solution, and separating and removing the neutralized precipitate containing zinc together with nickel and cobalt. A neutralization step S5 for obtaining a liquid, and a purification step S6 for generating a zinc sulfide by adding a sulfurizing agent to the neutralized final solution, separating and removing the zinc sulfide to obtain a nickel recovery mother liquor containing nickel and cobalt. And a sulfurization step S7 for adding a sulfurizing agent to the nickel recovery mother liquor to generate a mixed sulfide containing nickel and cobalt, and then recovering the mixed sulfide by solid-liquid separation. And a final neutralization step S8 for removing (also referred to as detoxification) metals dissolved in the poor solution discharged during liquid separation. Hereinafter, each of these steps will be described.

(1) Ore Mixing Step In the ore mixing step S1, nickel oxide ore as a raw material is put into a pulverizer such as a jaw crusher and pulverized, and then sieved with a screen having a predetermined opening to obtain ore having a predetermined particle size. Make it. The sieving may be performed by a wet method.In this case, the ore having a predetermined particle size is sieved in the form of an ore slurry having a desired slurry concentration by introducing the crushed ore into a wet screen together with an appropriate amount of water. Can be collected on the side.

  The nickel oxide ore treated in the ore blending step S1 is mainly a so-called laterite ore such as limonite ore and saprolite ore. The nickel content of laterite ore is generally from 0.8 to 2.5% by mass and is included as hydroxide or formicite (magnesium silicate) mineral. This nickel oxide ore has an iron content of 10 to 50% by mass, which mainly has a form of trivalent hydroxide (goethite), and a part of divalent iron is made of silica Contained in minerals. In addition to the above-mentioned laterite ore, an oxide ore containing valuable metals such as nickel, cobalt, manganese, and copper, such as a manganese nodule existing on the deep sea floor, may be used as a raw material for the ore blending step S1.

(2) High-Pressure Sulfuric Acid Leaching Step In the high-pressure sulfuric acid leaching step S2, the ore slurry prepared in the ore blending step S1 is charged together with sulfuric acid into a pressure vessel called an autoclave, and the ore slurry is stirred for 3 to 4 times. A leaching slurry composed of a leaching solution and a leaching residue is generated by performing high-pressure acid leaching treatment under a high-temperature and high-pressure condition of about 0.5 MPaG and about 220 to 280 ° C.

  In the high-pressure sulfuric acid leaching step S2, a leaching reaction represented by the following formulas 1 to 3 and a high-temperature thermal hydrolysis reaction represented by the following formulas 4 and 5 occur, and leaching as a sulfate such as nickel, cobalt and the like is performed. The immobilized iron sulfate is immobilized as hematite. However, since the immobilization of iron ions does not completely proceed, the liquid portion of the obtained leach slurry usually contains divalent and trivalent iron ions in addition to nickel, cobalt and the like.

[Equation 1]
MO + H ₂ SO ₄ → MSO ₄ + H ₂ O
(In the formula, M is a metal such as Ni, Co, Fe, Zn, Cu, Mg, Cr, and Mn.)
[Equation 2]
2Fe (OH) ₃ + 3H ₂ SO ₄ → Fe ₂ (SO ₄ ) ₃ + 6H ₂ O
[Equation 3]
FeO + H ₂ SO ₄ → FeSO ₄ + H ₂ O
[Equation 4]
2FeSO ₄ + H ₂ SO ₄ + ／ O ₂ → Fe ₂ (SO ₄ ) ₃ + H ₂ O
[Equation 5]
Fe ₂ (SO ₄ ) ₃ + 3H ₂ O → Fe ₂ O ₃ + 3H ₂ SO ₄

  The amount of sulfuric acid to be charged into the autoclave in the high-pressure sulfuric acid leaching step S2 is not particularly limited, but is preferably added in excess so that iron in the ore as the raw material is leached. In the high-pressure sulfuric acid leaching step S2, the pH of the leaching solution was adjusted to 0.1 to 1.0 so that the leaching residue containing the generated hematite did not deteriorate the filterability in the subsequent solid-liquid separation step S4. Is preferred.

(3) Pre-neutralization step In the pre-neutralization step S3, the pH of the leached slurry obtained in the high-pressure sulfuric acid leaching step S2 is adjusted to a predetermined range. That is, in the high-pressure sulfuric acid leaching step S2, since excess sulfuric acid is added from the viewpoint of improving the leaching rate, the leaching slurry extracted from the autoclave contains free sulfuric acid (excess sulfuric acid not involved in the leaching reaction; Free sulfuric acid). Therefore, in the pre-neutralization step S3, the pH of the leached slurry is preferably in the range of about 2.0 to 6.0 so that washing is efficiently performed in the multi-stage washing in the next solid-liquid separation step S4. Adjust to

  If the pH of the leached slurry is lower than 2.0, it is not preferable because a considerable cost is required for countermeasures against corrosion of the liquid contact portion of the apparatus in the subsequent process. Conversely, if the pH of the leaching slurry is higher than 6.0, nickel leached into the leaching slurry is not preferable because it may precipitate during the washing process and precipitate as a residue, thereby lowering the washing efficiency. The method for adjusting the pH is not particularly limited, but can be suitably adjusted by adding a neutralizing agent such as calcium carbonate in the form of a slurry.

(4) Solid-Liquid Separation Step In the solid-liquid separation step S4, the washing liquid is mixed with the leached slurry whose pH has been adjusted in the pre-neutralization step S3, and the coagulant is supplied while being washed by a sedimentation separation facility such as a thickener. Solid-liquid separation is performed using a suitable anionic coagulant supplied from equipment or the like. As a result, the leaching residue is removed, and a noble liquid composed of a crude nickel sulfate aqueous solution containing impurity elements such as zinc in addition to nickel and cobalt is obtained. When the thickener is used as described above, the leaching residue in the leaching slurry is concentrated as sediment, and at this time, depending on the degree of dilution of the leaching slurry with the cleaning liquid, the nickel content attached to the leaching residue may be reduced. it can. The slurry containing the leaching residue extracted from the thickener is subjected to a neutralization treatment in a final neutralization step S8 described below to remove heavy metals, if necessary, and then transferred to a tailing dam.

  In this solid-liquid separation step S4, it is preferable to wash the leached slurry in multiple stages by a continuous countercurrent washing method (CCD method: Counter Current Decantation) using a plurality of thickeners connected in series. In this washing method, the concentrated slurry extracted from the bottom is sequentially transferred to the subsequent thickener by introducing the leached slurry into the first thickener, and the supernatant discharged by overflow is introduced by introducing the washing liquid into the last thickener. The liquid is sequentially transferred to the former thickener, and it is possible to secure a recovery rate of nickel and cobalt of 95% or more while keeping the amount of the cleaning liquid newly introduced into the system small.

  The type of the above-mentioned washing liquid is not particularly limited, but preferably does not contain nickel and does not adversely affect the leached slurry during the solid-liquid separation step. In particular, it is preferable to use an aqueous solution having a pH of about 1.0 to 3.0 as the cleaning liquid. If the pH of the cleaning liquid is higher than 3.0, when aluminum is contained in the leachate, a bulky aluminum hydroxide is generated, and the sedimentation of the leach residue may be deteriorated. As such a washing solution having a pH of about 1.0 to 3.0, a poor solution having a low pH discharged to the liquid phase when the mixed sulfide is recovered by solid-liquid separation in the subsequent sulfurizing step S7 is suitable. Therefore, it is preferable to use this repeatedly.

(5) Neutralization Step In the neutralization step S5, a pH adjusting agent such as calcium carbonate is added to a noble solution composed of a crude nickel sulfate aqueous solution separated from the leaching residue in the solid-liquid separation step S4 to adjust the pH. A neutralized precipitate containing an impurity element is generated while suppressing oxidation of the noble solution. By removing the neutralized precipitate by solid-liquid separation, a neutralized final solution that is a base of a nickel recovery mother liquor containing an impurity element mainly composed of zinc in addition to nickel and cobalt is obtained. In the neutralization step S5, the pH is adjusted so that the pH of the neutralized final solution is 4.0 or less, preferably 3.0 to 3.5, and more preferably 3.1 to 3.2. Preferably, thereby, mainly trivalent iron ions and aluminum ions remaining in the noble solution can be removed as neutralized deposits.

(6) Liquid Purification Step In the liquid purification step S6, for example, the neutralized final solution obtained in the neutralization step S5 is introduced into a pressurized container, and hydrogen sulfide gas is blown into the gas phase of the container. , A sulfurizing treatment is performed by adding a sulfurizing agent, whereby zinc is selectively sulfurized with respect to nickel and cobalt to generate zinc sulfide. By separating and removing the zinc sulfide, a mother liquor for nickel recovery (final dezincing solution) composed of a sulfuric acid solution containing nickel and cobalt is obtained. In addition, the mother liquor for nickel recovery usually contains several g / L of metal ions such as iron, aluminum and manganese as impurity components.

(7) Sulfurization Step In the sulfurization step S7, a sulfide agent such as hydrogen sulfide gas is blown into the mother liquor for nickel recovery, thereby causing a sulfurization reaction to cause sulfide containing nickel and cobalt (nickel-cobalt mixed sulfide). Generate The produced nickel-cobalt mixed sulfide can be recovered by solid-liquid separation such as filtration, and at that time, a poor liquid is discharged to the liquid phase side. Note that the mother liquor for nickel recovery treated in the sulfidation step S7 may contain impurity metal ions such as Fe, Al, and Mn as described above, but these impurity components are higher than those of nickel and cobalt. The stability as a sulfide is low, and thus it is hardly contained in the nickel-cobalt mixed sulfide.

(8) Final Neutralization Step In the final neutralization step S8, a poor solution containing impurity metal ions such as iron, aluminum, and manganese and unreacted Ni ions discharged during the solid-liquid separation in the sulfurization step S7 is performed. Then, by performing a neutralization treatment for adjusting the concentration to a predetermined pH range, these metal ions are removed until the concentration satisfies the emission standard. In the final neutralization step S8, the leaching residue slurry discharged when the noble liquid is separated into solid and liquid in the solid-liquid separation step S4 may be treated as drainage. This makes it possible to reduce the concentration of heavy metals contained in the liquid phase of the leaching residue slurry to the same extent as that of the poor liquid.

  In the final neutralization step S8, as a method for adjusting the pH of the drainage such as the poor liquid, a first neutralization treatment using limestone as a neutralizing agent and a second neutralization treatment using slaked lime as a neutralizing agent are performed. The neutralization process is performed in two stages including the sum process. By performing the stepwise pH adjustment, metal ions such as Fe, Al, Mn, and Ni dissolved in the wastewater can be efficiently and effectively reduced until their respective concentrations become less than 1 mg / L. Can be removed.

  Specifically, first, in the first neutralization treatment, the poor liquid discharged from the sulfurization step S7 and the leach residue slurry separated in the form of a concentrated slurry in the solid-liquid separation step S4, which is optionally processed, are used. Preferably, the most upstream neutralization tank of the first neutralization tank group, in which at least two neutralization tanks are connected in series, was charged with the limestone slurry and stirred, and the pressure was increased by a blower. Air is blown to oxidize metal ions. The processing solution processed in the neutralization tank on the most upstream side in this manner is sequentially transferred to the subsequent neutralization tank by overflow, and the same processing is performed. In the first neutralization treatment, the pH of the treatment liquid in the tank is adjusted to 5.0 to 5.4 by adding limestone slurry. Thereby, trivalent Fe and a part of divalent Fe and Al contained in the treatment liquid can be mainly precipitated.

  Next, in the second neutralization treatment, the slurry extracted from the most downstream neutralization tank of the first neutralization treatment tank group is preferably subjected to solid-liquid separation, and the liquid phase from which the solid content has been removed is preferably used. Is charged and stirred with slaked lime slurry into the most upstream neutralization tank of the second neutralization tank group in which at least two neutralization tanks are connected in series, and air pressurized by a blower is added thereto. Blow to oxidize metal ions. The processing solution processed at the most upstream side of the second neutralization processing tank group in this way is sequentially transferred to the subsequent neutralization tank by overflow and subjected to the same processing. In the second neutralization treatment, the pH of the treatment liquid in the tank is adjusted to 8.0 to 9.5, preferably 8.5 to 9.0 by adding slaked lime slurry. Thereby, the remaining divalent Fe, Mn, and Ni contained in the treatment liquid can be mainly deposited.

  The slurry extracted from the most downstream neutralization tank of the second neutralization tank group is pressurized by a slurry pump, and then subjected to solid-liquid separation by a solid-liquid separation device such as a thickener. The obtained neutralization residue on the solid content side is transferred to a tailing dam together with the solid content removed by the solid-liquid separation after the first neutralization treatment. On the other hand, in the final liquid discharged as the liquid phase, the concentration of metal ions is reduced to less than 1 mg / L as described above, and since this concentration generally satisfies the discharge standard, it is discharged outside the system. can do.

By performing the neutralization treatment in two stages as described above, iron ions contained in the wastewater can be efficiently removed. That is, the precipitate of Fe generated in the final neutralization step S8 is composed of divalent iron (II) hydroxide (Fe (OH) ₂ ) and trivalent iron (III) hydroxide (Fe (OH) ₃ ). There are various types, and iron (III) hydroxide is generally produced in a relatively low pH range of less than pH 6, whereas iron (II) hydroxide is produced in a pH range higher than the above pH range.

  Therefore, when the content of divalent iron in the poor solution is higher than that of trivalent iron, the amount of Fe precipitated in the second neutralization treatment is relatively increased, and thus slaked lime is generally much less than limestone. This is not preferable from the viewpoint of reducing operating costs. Therefore, in the final neutralization method according to the embodiment of the present invention, air is blown into the processing liquid in the first neutralization processing tank group to precipitate as much Fe ions as possible in the first neutralization processing, so that the divalent iron is removed. By oxidizing the ions to trivalent iron ions and increasing the pH as much as possible with limestone, unreacted divalent iron is precipitated as much as possible together with the trivalent iron ions. Thereby, the usage of slaked lime can be reduced.

  However, as shown in FIG. 3, the reaction efficiency of limestone decreases with an increase in pH. Therefore, if the pH is too high in the first neutralization treatment, the amount of limestone used increases, and consequently the amount of limestone increases. Even though the amount of slaked lime can be reduced, the cost of the neutralizing agent as a whole in the final neutralization step may not be much different from the conventional one. On the other hand, in the final neutralization method of the embodiment of the present invention, as described above, the limestone slurry is added to the wastewater in the first neutralization treatment so that the pH falls within the range of 5.0 to 5.4. By appropriately adjusting the above, it is possible to optimize the cost of the neutralizing agent as the whole final neutralizing step S8.

That is, as shown in FIG. 4, for example, when the unit price per ton of limestone is 19.2 $ / ton and the unit price per ton of slaked lime is 108.0 $ / ton, Fe2 ⁺ and Fe3 ^{+ in the} drainage liquid are used. If the total concentration of Fe ions is 1.0 to 4.0 g / L and the pH of the first neutralization tank to which the limestone slurry is added is within the range of 5.0 to 5.4, the medium Since the cost of the wetting agent is the lowest, the pH of the neutralizing agent in the final neutralization step S8 is most controlled by controlling the pH within the range of 5.0 to 5.4, preferably at a pH value showing their minimum value. It is possible to keep it inexpensive. When the Fe concentration in the drainage is out of the range of 1.0 to 4.0 g / L, the amount of the neutralizing agent added in the neutralizing step S5 is adjusted or the above-described continuous countercurrent cleaning method is used. The Fe concentration may be adjusted to fall within the range of 1.0 to 4.0 g / L by adjusting the amount of the cleaning solution introduced into the CCD.

In the first and second neutralization treatment is carried out, the air from the treatment liquid 1m ³ 1.5~3.0Nm ^3, preferably preferably blown at a rate of 1.8~2.0Nm ^3. The limestone slurry to be added has an average particle diameter of 5 to 15 μm, preferably about 10 μm, and preferably has a slurry concentration of 20 to 30% by mass. The slaked lime slurry to be added has an average particle diameter of 15 to 30 μm, Preferably, it is about 20 μm and the slurry concentration is 20 to 30% by mass. Thereby, these neutralizing agents can be made to react more efficiently. The above average particle diameter is a 50% diameter (D50) on a volume basis measured by a laser diffraction particle size distribution analyzer. With the above average particle diameter, the apparent specific gravity of both limestone and slaked lime measured according to JIS K6220 is about 1.2.

<Example>
The poor liquid discharged from the sulfurization step S7 of the hydrometallurgy process of nickel oxide ore as shown in FIG. 1 is subjected to two first neutralization treatments equipped with a stirrer as shown in FIG. Neutralization treatment was performed in a two-stage neutralization treatment facility in which neutralization tanks 11 and 12 and two second neutralization tanks 21 and 22 having a stirrer were connected in series. In this example, the leaching residue slurry from the solid-liquid separation step S4 was not treated.

Specifically, a poor solution having a pH of 1.5 was introduced into the first neutralization tank 11 at a flow rate of 480 m ³ / hr, and was sequentially transferred to the subsequent neutralization tanks 12, 21, and 22 by overflow. At that time, in each tank, air was blown from the blower at a flow rate of 15 Nm ³ / min. The pH of the second neutralization tank 12 was continuously measured with a pH meter, and water was added to limestone having an average particle diameter (D50) of 10 μm in the first neutralization tank 11 so that the value became 5.2. Was added, and a limestone slurry adjusted to a slurry concentration of 22% by mass was added. The pH of the fourth neutralization tank 22 was continuously measured with a pH meter, and the slaked lime having an average particle diameter (D50) of 20 μm was added to the third neutralization tank 21 so that the value became 9.0. Was added to water, and a slaked lime slurry adjusted to a slurry concentration of 22% by mass was added.

The metal ion concentration of the poor solution before the above treatment was measured by ICP emission spectroscopy. As a result, Fe was 2.0 g / L, Al was 1.0 g / L, Mn was 1.5 g / L, and Ni was 0.1 g. / L. The poor solution is treated under the above-described two-stage neutralization conditions, and the concentrations of Fe, Al, Mn, and Ni contained in the wastewater extracted from the fourth neutralization tank 22 are all 1 mg / L. 379 tonnes of limestone and 17.5 tonnes of slaked lime were consumed per day in order to reduce the amount. If the unit price per ton of limestone is 19.2１９ / ton and the unit price per ton of slaked lime is 108.0 ＄ / ton, the cost of these neutralizers is 9.17 × 10 ³ per day. Was.

<Comparative example>
For comparison, a poor solution was treated in the same manner as in the above example except that limestone slurry was added to the first neutralization tank 11 so that the pH of the second neutralization tank 12 became 5.8. . As a result, in order to reduce the concentration of each of Fe, Al, Mn, and Ni contained in the wastewater extracted from the fourth neutralization tank 22 to less than 1 mg / L, 530 tons of limestone and slaked lime per day were used. We consumed 5.8 tons. In this case, the cost of these neutralizing agents was 10.80 × 10 ³ $ per day, which was about 18% higher than the cost in the above example.

S1 Ore preparation process S2 High pressure sulfuric acid leaching process S3 Pre-neutralization process S4 Solid-liquid separation process S5 Neutralization process S6 Purification process S7 Sulfurization process S8 Final neutralization process

Claims (4)

  A final neutralization method for removing metals dissolved in an effluent discharged when recovering nickel sulfide from a leachate produced by high-temperature pressurized acid leaching of a nickel oxide ore, wherein the iron ion concentration is 1.0 to 1.0. Limestone slurry is added to the wastewater adjusted to 4.0 g / L to perform a first neutralization treatment at pH 5.0 to 5.4, and then slaked lime slurry is added to form a first neutralization treatment at a higher pH. 2. A final neutralization method, comprising performing the neutralization treatment of 2.   The drainage is a poor solution having a pH of 1.0 to 3.0 and contains Al at a concentration of 1 to 3 g / L, Mn at a concentration of 1 to 3 g / L, and Ni at a concentration of 0.05 to 0.2 g / L. The final neutralization method according to claim 1, wherein   The limestone slurry has an average particle size of limestone of 5 to 15 μm and a slurry concentration of 20 to 30% by mass, and the slaked lime slurry has an average particle size of slaked lime of 15 to 30 μm and the slurry concentration is The final neutralization method according to claim 1 or 2, wherein the content is 20 to 30% by mass.   4. The solution according to claim 1, wherein each of the solutions after the first and second neutralization treatments has a concentration of Fe, Al, Mn, and Ni less than 1 mg / L. 5. A final neutralization method according to any one of the preceding claims.

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