JP7585921B2 - Hydrometallurgical process for nickel oxide ore - Google Patents

Description

The present invention relates to a method for hydrometallurgy of nickel oxide ore, and to a method that can effectively reduce nickel recovery losses.

Nickel is widely used as a raw material for stainless steel, and as the sulfide ore from which it is made is becoming scarce, technology to refine low-grade oxide ore has been developed and put into practical use.

Specifically, a manufacturing process known as "High Pressure Acid Leach (HPAL)" has been put into practical use, in which nickel oxide ores such as limonite or saprolite are placed in a pressurized device such as an autoclave together with a sulfuric acid solution, and nickel is leached under high temperatures and pressures of around 240°C to 260°C.

Specifically, in the hydrometallurgical process of nickel oxide ore using the HPAL method, first, several kinds of low-grade nickel oxide ores are mixed to have a predetermined nickel grade and impurity grade, and then mixed with water to form a slurry, which is then sieved, and only the ore of a predetermined undersize (undersize) is used (ore slurry preparation step S11). Next, the ore slurry is charged into a pressurized reaction device such as an autoclave, and sulfuric acid is added under high temperature and pressure to leach nickel (leaching step S12). Next, the residual free acid contained in the leaching slurry is removed by neutralization (pre-neutralization step S13). The slurry after the pre-neutralization is transferred to a solid-liquid separation device such as a thickener, and separated into a leachate and a leach residue while being washed in multiple stages (solid-liquid separation step S14). The leach residue after solid-liquid separation is transferred to a tailings dam (residue dam) after heavy metals are removed to a predetermined concentration in the final neutralization step S17.

Next, a neutralizing agent is added to the leachate (pregnant liquor) obtained by solid-liquid separation to perform a neutralization process to remove impurities (neutralization process S15), and then a sulfurizing agent such as hydrogen sulfide gas is supplied to the neutralized final liquor, which is the mother liquor for nickel recovery, to generate and recover a mixed sulfide of nickel and cobalt (hereinafter also referred to as "nickel sulfide") (sulfurization process S16). The barren liquor after the nickel sulfide is separated and recovered in the sulfurization process is transferred to the final neutralization process S17 and made harmless. Note that a portion of the barren liquor is reused in the process in the solid-liquid separation process S14 after the preliminary neutralization process S13.

Here, for example, in the treatment in the neutralization step S15, a slurry of limestone, hydrated lime, or the like is added as a neutralizing agent to the leachate to perform neutralization treatment, which produces a precipitate (neutralized precipitate) mainly composed of hydroxides and gypsum as impurity metal elements. The slurry containing the neutralized precipitate is transferred to a solid-liquid separation device such as a thickener for solid-liquid separation. In addition, a portion of the neutralized precipitate slurry is repeatedly sent to the solid-liquid separation step S14 for solid-liquid separation together with the leachate slurry in order to reduce the recovery loss of nickel in the precipitate (see, for example, Patent Document 1).

In slurries containing such precipitates, the liquid contains a high concentration of nickel, which causes deterioration of cleaning during the solid-liquid separation process. For this reason, it is desirable to keep the amount of liquid in the slurry containing precipitates as small as possible.

Previously, for example, improvements have been made to solid-liquid separation during the neutralization process (see, for example, Patent Documents 2 to 4). However, these conventional techniques are primarily aimed at improving the clarity of the supernatant liquid, and are not very effective at reducing the amount of liquid in the slurry that is repeated in the process. In addition, there is a limit to how much liquid can be reduced in the slurry that is repeated, i.e., how much the solid concentration of the slurry can be increased, so there is a need to develop a method for further reducing nickel loss.

For example, Patent Document 5 discloses that in order to reduce nickel recovery losses, a portion of the neutralized sediment slurry after the neutralization step is repeatedly sent to the solid-liquid separation step S14. In this case, it is preferable to transfer the neutralized sediment slurry to a thickener in the latter stage of the multi-stage washing in order to suppress an increase in the sediment load in the thickener.

However, this method is not sufficient to reduce nickel recovery losses while reducing the sediment load in solid-liquid separation processing, and there is a need to develop a more effective method for reducing nickel losses.

JP 2005-350766 A JP 2004-225120 A JP 2017-145454 A JP 2017-201056 A JP 2019-049020 A

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide a method for hydrometallurgical smelting of nickel oxide ore that can reduce the sediment load in the solid-liquid separation process and effectively reduce nickel recovery losses.

After extensive research, the inventors discovered that the above-mentioned problems could be solved by adding the slurry of leaching residue separated in the solid-liquid separation process to the leachate to be used for neutralization in the neutralization process, and repeating the process of the solid-liquid separation process to produce a neutralized precipitate slurry. When repeating the neutralized precipitate slurry, the slurry is transferred to the first thickener located at the most upstream of the multiple thickener stages in the solid-liquid separation device. This led to the completion of the present invention.

(1) The first invention of the present invention is a method for hydrometallurgy of nickel oxide ore, which comprises adding an acid to nickel oxide ore to perform a leaching treatment, and obtaining nickel and cobalt sulfides from the obtained leachate, the method comprising a solid-liquid separation process for the leach slurry obtained by the leaching treatment, while performing multi-stage washing using a solid-liquid separation device having multiple thickeners, to obtain a leachate and a leachate residue, and a neutralizing process for adding a neutralizing agent to the leachate to obtain a neutralized precipitate containing impurities and a neutralized final liquid containing nickel and cobalt. and a neutralization step of obtaining a nickel oxide ore, in which the neutralization step includes a step of adding the slurry of the leaching residue separated in the solid-liquid separation step to the leachate to be subjected to neutralization treatment to perform neutralization treatment, and a step of repeating the neutralization precipitate slurry generated by the neutralization treatment to the solid-liquid separation step, in which the slurry is transferred to a first-stage thickener located at the most upstream of the thickeners provided in multiple stages in the solid-liquid separation device.

(2) The second invention of the present invention is a method for hydrometallurgical smelting of nickel oxide ore according to the first invention, in which the solid-liquid separation step is carried out using a solid-liquid separation device having 4 to 7 thickener stages.

(3) The third invention of the present invention is a method for hydrometallurgy of nickel oxide ore according to the first or second invention, in which the turbidity and viscosity of the supernatant liquid in the first-stage thickener are periodically measured and monitored in the solid-liquid separation process, and the amount of flocculant added in the solid-liquid separation process is adjusted.

(4) The fourth invention of the present invention is a method for hydrometallurgy of nickel oxide ore according to the third invention, in which the turbidity of the supernatant liquid in the first-stage thickener is adjusted to 200 NTU or less in the solid-liquid separation process.

The present invention provides a method for hydrometallurgical smelting of nickel oxide ore that can reduce the sediment load in the solid-liquid separation process and effectively reduce nickel recovery losses.

FIG. 1 is a process diagram showing an example of a flow of a hydrometallurgical process for nickel oxide ore. FIG. 1 is a diagram showing an example of the configuration of a solid-liquid separation device in which thickeners are connected in multiple stages to perform a CCD method. FIG. 2 is a diagram showing an example of the configuration of a thickener (only one stage) constituting each stage of a solid-liquid separation device.

A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the gist of the present invention. In this specification, when it is expressed as "X to Y" (X and Y are arbitrary numerical values), it means "X or more and Y or less" unless otherwise specified.

≪1. Overview≫
The hydrometallurgical method for nickel oxide ore according to the present embodiment is a method for adding an acid to nickel oxide ore to perform a leaching treatment, and obtaining a nickel-containing sulfide from the obtained leachate. Note that in the hydrometallurgical process for nickel oxide ore, a nickel-cobalt mixed sulfide containing nickel and cobalt leached into the leachate is obtained by performing a sulfidation treatment based on the leachate, and the term "nickel-containing sulfide (nickel sulfide)" includes the meaning of the nickel-cobalt mixed sulfide.

Specifically, this method includes a solid-liquid separation process in which the leaching slurry obtained by the leaching process is subjected to a solid-liquid separation process while being washed in multiple stages using a solid-liquid separation device equipped with multiple thickeners to obtain a leaching solution and a leaching residue, and a neutralization process in which a neutralizing agent is added to the leaching solution to obtain a neutralized precipitate containing impurities and a neutralized final solution containing nickel and cobalt. In the neutralization process, the slurry of the leaching residue separated in the solid-liquid separation process is added to the leaching solution to be subjected to the neutralization process, and the neutralization process is performed.

In addition, in this method, the neutralization process includes repeating the neutralized precipitate slurry generated by the neutralization process to the solid-liquid separation process, and when repeating the neutralized precipitate slurry, the slurry is transferred to the first-stage thickener located at the most upstream of the multiple thickener stages provided in the solid-liquid separation device.

This method effectively reduces nickel recovery losses without increasing the sediment load during the solid-liquid separation process.

≪2. Hydrometallurgical process of nickel oxide ore≫
First, each step of the hydrometallurgical process for nickel oxide ore will be described in detail.

Figure 1 is a process diagram showing an example of the flow of a hydrometallurgical process for nickel oxide ore. As shown in Figure 1, the hydrometallurgical process for nickel oxide ore includes a leaching process S1 in which sulfuric acid is added to a slurry of raw nickel oxide ore and leaching is performed under high temperature and pressure, a solid-liquid separation process S2 in which the leaching residue is separated from the leaching slurry to obtain a leachate containing nickel, a neutralization process S3 in which the pH of the leachate is adjusted to separate impurities in the leachate as a neutralization precipitate to obtain a neutralization end liquid, and a sulfurization process S4 in which a sulfurizing agent is added to the neutralization end liquid to generate nickel sulfides.

(1) Leaching Step In the leaching step S1, a high-temperature pressurized reaction tank such as an autoclave is used to add sulfuric acid to a slurry of nickel oxide ore (hereinafter also referred to as "ore slurry") and perform leaching treatment by stirring under conditions of, for example, a temperature of about 230° C. to 270° C. and a pressure of about 3 MPa to 5 MPa. This produces a leaching slurry consisting of a leachate and a leach residue.

The raw nickel oxide ore mainly includes so-called laterite ores such as limonite ore and saprolite ore. The nickel content of laterite ore is usually 0.8% to 2.5% by weight, and is contained as hydroxide or magnesium silicate mineral. The iron content is 10% to 50% by weight, and is mainly in the form of trivalent hydroxide, although some divalent iron is contained in magnesium silicate mineral. In addition to such laterite ore, oxide ores containing valuable metals such as nickel, cobalt, manganese, and copper, such as manganese nodules present on the deep seabed, can be used in the leaching step S1.

In the leaching process, for example, the leaching reactions represented by the following formulas [1] to [5] and high-temperature hydrolysis reactions occur, resulting in the leaching of nickel, cobalt, etc. as sulfates and the fixation of the leached iron sulfate as hematite. However, since the fixation of iron ions does not proceed completely, the liquid portion of the resulting leaching slurry usually contains divalent and trivalent iron ions in addition to nickel, cobalt, etc. In addition, in the leaching process, it is preferable to adjust the pH of the resulting leaching solution to 0.1 to 1.0 from the viewpoint of the filterability of the leaching residue containing hematite separated in the next solid-liquid separation step S2.

Leaching reaction MO + _H2SO4 → _{MSO4 + H2O} ... [1]
(In the formula, M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn, etc.)
2Fe(OH) ₃ +3H ₂ SO ₄ →Fe ₂ (SO ₄ ) ₃ +6H ₂ O...[2]
FeO+H ₂ SO ₄ →FeSO ₄ +H ₂ O...[3]
High-temperature hydrolysis reaction _2FeSO4 + _H2SO4 + 1/ _{2O2 → Fe2(SO4)3 + H2O ... [} 4]
Fe ₂ (SO ₄ ) ₃ +3H ₂ O→Fe ₂ O ₃ +3H ₂ SO ₄ ...[5]

The amount of sulfuric acid added to the autoclave containing the ore slurry is not particularly limited, but an excess amount is used so that the iron in the ore is leached. For example, the ratio is 300 kg to 400 kg per ton of ore.

(2) Solid-liquid separation step In the solid-liquid separation step S2, a solid-liquid separation treatment is carried out to separate the leaching solution containing valuable metals such as nickel from the leaching residue while washing the leaching slurry produced in the leaching step S1 in multiple stages.

In the solid-liquid separation step S2, a solid-liquid separation device with thickeners connected in multiple stages is used to mix the leaching slurry with the washing liquid, and then a process is performed to separate the leaching liquid and leaching residue into solid-liquid separation. Specifically, the leaching slurry is first diluted with the washing liquid, and then the leaching residue in the leaching slurry is concentrated as a sediment in the thickener. This makes it possible to reduce the amount of nickel adhering to the leaching residue according to the degree of dilution. In addition, by using thickeners connected in multiple stages in this way to perform solid-liquid separation while performing multi-stage washing, it is possible to improve the nickel recovery rate in the washing liquid, i.e., the leaching liquid.

Here, in the solid-liquid separation step S2, at least a portion of the neutralized precipitate slurry obtained in the next neutralization step S3 is transferred and separated into solid and liquid together with the leaching slurry. This reduces nickel recovery losses.

As a multi-stage washing method in the solid-liquid separation process, for example, a continuous countercurrent washing method (CCD method) is used, in which a washing solution that does not contain nickel is used in a countercurrent. The washing solution is not particularly limited, but any solution that does not contain nickel and does not affect the process can be used. Among them, it is preferable to use an aqueous solution with a pH of 1 to 3. If the pH of the washing solution is high, bulky aluminum hydroxide is generated when aluminum is contained in the leaching solution, which causes poor settling of the leaching residue in the thickener. In addition, as the washing solution, it is preferable to repeatedly use a low pH (pH of about 1 to 3) barren solution obtained in the subsequent sulfurization step S4. This makes it possible to reduce the amount of washing solution newly introduced into the system and to increase the recovery rate of nickel and cobalt.

As a solid-liquid separation device, for example, one having a thickener equipped with a settling separation tank having an overflow section at the periphery for discharging supernatant liquid and a cylindrical feed well arranged vertically in the center, and a stirring tank can be used. In the solid-liquid separation device, the thickeners are connected in multiple stages, and the leaching slurry to be treated is washed in multiple stages while separating and removing the leaching residue, which is the solid content.

The leachate separated by this solid-liquid separation process is subjected to neutralization in the next neutralization step S3. Meanwhile, a portion of the separated leachate slurry is added to the leachate that is subjected to neutralization in the subsequent neutralization step S3, and the remainder is appropriately treated as wastewater.

The specific operation of the solid-liquid separation device and the multi-stage cleaning process using the device will be described in detail later.

(3) Neutralization step In the neutralization step S3, a neutralizing agent is added to the obtained leachate while suppressing oxidation of the leachate to adjust the pH to a predetermined range, thereby producing a neutralized precipitate containing impurity elements and a neutralization end liquid that serves as a mother liquor for nickel recovery. By carrying out such neutralization treatment, the impurity content in the obtained neutralization end liquid can be reduced, and the quality of the nickel sulfide (product) obtained by carrying out a sulfurization treatment (sulfurization step S4) on the neutralization end liquid can be improved.

Specifically, in the neutralization step S3, a neutralizing agent is added to the leachate to adjust the pH, thereby producing a neutralized end liquid and a neutralized precipitate slurry containing, for example, trivalent iron as an impurity element. By neutralizing the leachate in this way, the excess acid used in the leaching process in the leaching step S1 is neutralized to produce a neutralized end liquid, and impurity elements such as iron ions and aluminum ions remaining in the solution are removed as neutralized precipitate.

In the method according to the present embodiment, in the neutralization process, a slurry of the leaching residue obtained by subjecting the leaching slurry to solid-liquid separation in the solid-liquid separation step S2 is added in a predetermined ratio to the leaching solution to be subjected to the neutralization process. In this way, by adding the leaching residue slurry to the leaching solution, the turbidity of the resulting neutralization end solution can be effectively reduced, and nickel recovery loss can be reduced.

At least a portion of the neutralized precipitate slurry obtained by the neutralization process is sent back to the solid-liquid separation step S2, where it is subjected to solid-liquid separation together with the leaching slurry. In this case, in the method according to the present embodiment, a leaching residue slurry is added to the leachate used in the neutralization process at a predetermined ratio, which prevents an excessive increase in the neutralized precipitate slurry and reduces nickel recovery loss while reducing the precipitate load in the solid-liquid separation step S2.

(4) Sulfurization Step In the sulfurization step (nickel recovery step) S4, the neutralization end liquid, which is the mother liquor for nickel recovery, is used as a sulfurization reaction starting liquid, and a sulfurization reaction is caused by adding a sulfurizing agent such as hydrogen sulfide gas to the sulfurization reaction starting liquid, thereby producing a sulfide containing nickel with a small amount of impurity components (nickel sulfide) and a sulfurization reaction ending liquid, which is a barren liquid in which the nickel concentration is stabilized at a low level.

If the neutralization end solution contains zinc, the zinc can be selectively separated as a sulfide prior to separating the nickel as a sulfide.

The sulfurization treatment in the sulfurization step S4 can be carried out using a sulfurization reaction tank or the like. For example, hydrogen sulfide gas can be blown into the gas phase of the sulfurization reaction starting liquid introduced into the sulfurization reaction tank, and the hydrogen sulfide gas that moves into the solution can cause a gentle sulfurization reaction. This sulfurization treatment fixes the nickel as a sulfide.

After the sulfurization reaction is completed, the resulting slurry containing nickel sulfide is placed in a filtration device such as a filter press and filtered to collect the sulfide on the filter cloth. The aqueous solution components that pass through the filter cloth are collected as poor liquid. In order to reduce the amount of liquid passing through the filtration device, it is advisable to first place the slurry in a sedimentation concentration device such as a thickener and remove the supernatant liquid as poor liquid.

≪3. Solid-liquid separation treatment in the solid-liquid separation process≫
Here, the solid-liquid separation apparatus used in the treatment in the solid-liquid separation step S2 in the above-mentioned hydrometallurgical process and the specific treatment operation using the apparatus will be described in more detail.

As described above, in the solid-liquid separation step S2, a solid-liquid separation device consisting of thickeners connected in multiple stages is used to perform multi-stage washing using a continuous countercurrent washing method (CCD method) in which the leaching slurry obtained by the leaching treatment in the leaching step S1 is contacted with a nickel-free washing solution in a countercurrent manner, while separating the solids (leaching residue) contained in the leaching slurry, and obtaining a crude nickel sulfate aqueous solution (leachate) from which the solids have been removed.

<3-1. Structure of solid-liquid separator (thickener) and multi-stage cleaning>
Fig. 2 is a diagram showing an example of a solid-liquid separation apparatus in which thickeners are connected in multiple stages to perform the CCD method. The solid-liquid separation apparatus 1 shown in Fig. 2 shows an example of a configuration in which thickeners are connected in five stages, and although the number of connected stages is not limited to this, a solid-liquid separation apparatus having 4 to 7 thickener stages is preferable.

In the CCD method, a solid-liquid separator 1 is used in which a thickener consisting of a settling tank where solid-liquid separation is performed and a stirring tank is connected in series in multiple stages, for example, 4 to 7 stages. In the solid-liquid separator 1, the leaching slurry obtained in the leaching process S1 is charged into the first stage thickener located at the most upstream side (side A in Figure 2), and the final stage (fifth stage) thickener located at the most downstream side (side B in Figure 2) is charged with, for example, wash water such as industrial water or smelting waste liquid (bare liquid).

In the solid-liquid separation device 1, the leaching slurry and the cleaning liquid that are charged come into contact with each other in a countercurrent flow within the device, and at the same time, a flocculant is added to the leaching slurry that is charged from the most upstream side (side A), flocculating the solids in the slurry and promoting solid-liquid separation.

(About each thickener and mixing tank)
Fig. 3 shows a configuration diagram of a thickener (only one stage) constituting each stage of the solid-liquid separation apparatus 1 shown in Fig. 2. As described above, the solid-liquid separation apparatus 1 has a plurality of thickeners connected in multiple stages, and the thickener 10 is composed of an agitation tank 11 and a sedimentation tank 12.

The stirring tank 11 is a tank equipped with stirring members such as a stirring shaft and stirring blades inside. In the stirring tank 11, the leaching slurry and the overflow liquid sent from the thickener in the subsequent stage are charged and stirred and mixed. Note that the stirring tank 11 of the thickener in the final stage (the fifth stage in the example of Figure 2) is charged with smelting waste liquid (poor liquid) or new washing water, rather than overflow liquid. In such a stirring tank 11, the leaching slurry and the overflow liquid are stirred and mixed, and the leaching slurry is washed, and the adhering liquid adhering to the solids is washed away.

The settling tank 12 is, for example, a cylindrical treatment tank into which the leaching slurry is charged and the solids in the leaching slurry are allowed to settle and separate. The settling tank 12 is provided with a vertically disposed cylindrical feedwell 13 inside. For example, when the settling tank 12 is cylindrical, the feedwell 13 is provided approximately concentrically with the settling tank 12. The feedwell 13 serves as a passage for sending (feeding) the leaching slurry supplied from the stirring tank 11 into the settling tank 12.

The settling tank 12 is provided with an overflow section 14 at the periphery of the upper part of the tank for overflowing (OF) the leachate, which is the supernatant liquid obtained by settling and separating the solids in the leaching slurry. The overflow section 14 is shaped, for example, like a gutter, and is connected to a flow path for sending the overflow liquid from the thickener in the downstream stage to the mixing tank 11.

In addition, in the settling tank 12, the overflowed solution (hereinafter also referred to as "overflow liquid") is sent to the upstream stirring tank 11 as described above, while the slurry including the remaining solids is taken out from the bottom of the settling tank 12 and sent to the downstream stirring tank 11 by the pump 15.

(Basic flow of multi-stage cleaning)
Next, a basic flow of the leaching slurry during multi-stage washing using the solid-liquid separator 1 (FIG. 2) will be described. The arrows in FIG. 2 indicate the flow of the leaching slurry and the overflow liquid.

First, in the first-stage thickener, the leaching slurry obtained by the leaching process in the leaching step S1 and the overflow liquid from the settling tank 12 of the subsequent second-stage thickener are charged into the stirring tank 11, and they are stirred and mixed. In the stirring tank 11 of the first-stage thickener, the adhering liquid adhering to the solids in the leaching slurry is washed away by the overflow liquid, and then the washed leaching slurry is charged from the stirring tank into the settling tank 12 via the feedwell 13.

At this time, in the first-stage thickener, a flocculant for flocculating the solids in the slurry is added via the feedwell 13 together with the leaching slurry. The leaching slurry and the flocculant are then mixed in the settling tank 12, and the solids in the slurry are flocculated and precipitated to separate them.

In addition, as will be described in more detail later, in the method according to the present embodiment, the neutralized precipitate slurry generated by the neutralization process in the neutralization step S3 is transferred and added to the first-stage thickener via the feedwell 13. In this way, in the method according to the present embodiment, the neutralized precipitate slurry is repeatedly subjected to the solid-liquid separation step S2, and is particularly characterized in that it is added to the first-stage thickener in the solid-liquid separation device 1, which is composed of multiple connected thickener stages.

The slurry containing the separated solids is extracted from the bottom of the settling tank 12 and transferred via a pump to the stirring tank 11 of the second-stage thickener. Meanwhile, the supernatant liquid that overflows from the settling tank 12 via the overflow section 14 is supplied to the next neutralization step S3 in the hydrometallurgical process.

Next, in the second-stage thickener, the solids extracted from the lower part of the settling tank 12 of the first-stage thickener in the previous stage are charged into the stirring tank 11, and the overflow liquid from the settling tank 12 of the third-stage thickener in the subsequent stage is charged, and the moisture adhering to the solids is washed away by the overflow liquid. Then, the slurry obtained by washing in the stirring tank 11 is charged into the settling tank 12 via the feed well 13, and the solids in the slurry are separated by coagulation and precipitation. The slurry containing the separated solids is discharged from the lower part of the settling tank 12 and transferred to the stirring tank 11 of the third-stage thickener in the subsequent stage via a pump. On the other hand, the overflow liquid that overflows from the settling tank 12 via the overflow section 14 is charged into the stirring tank 11 via piping or the like connected to the stirring tank 11 of the first-stage thickener in the previous stage.

Then, in the third and fourth thickeners, the same procedure is followed to wash the slurry containing solids in multiple stages by coming into countercurrent contact with the overflow liquid.

Then, in the fifth thickener, which is the final stage located at the most downstream side, the solids extracted from the lower part of the settling tank 12 of the preceding fourth thickener are charged into its stirring tank 11, and new washing water (e.g., a process liquid with a low nickel concentration in a hydrometallurgical process) is charged, and the water adhering to the solids is washed away with the washing water. The slurry obtained by washing in the stirring tank 11 is charged into the settling tank 12 via the feedwell 13, and the solids in the slurry are separated by coagulation and settling.

The slurry containing the separated solids is pumped out from the bottom of the settling tank 12 and treated as leaching residue (CCD residue). Meanwhile, the overflow liquid that overflows from the settling tank 12 via the overflow section 14 is charged into the agitation tank 11 of the fourth-stage thickener in the previous stage via piping or the like connected to that tank.

In addition, by carrying out solid-liquid separation processing while performing multiple washing steps on the leaching slurry in this way, new washing water only needs to be charged to the thickener in the final stage, and new washing water is not required for each thickener stage other than the final stage. This makes it possible to significantly save washing water.

<3-2. Specific operations of solid-liquid separation treatment>
As for the overflow liquid from each thickener stage, the overflow liquid from the thickener in the final stage (the fifth stage in FIG. 2) has the smallest content of valuable metals such as nickel and cobalt. One reason for this is that the valuable metals have already been washed in the stirring tank 11 of the thickener in the stage before (the third stage in FIG. 2). Another reason is that the slurry separated from the solid-liquid in the previous stage (the fourth stage in FIG. 2) and new washing water overflow, and the slurry is further charged into the stirring tank 11 in the previous stage (the fourth stage in FIG. 2), stirred and washed, and then charged into the thickener in the final stage.

On the other hand, the overflow from the stage before the final stage (the fourth stage in Figure 2) has a higher content of valuable metals adhering to the solids than the final stage, and the more distant it is from the final stage, the more valuable metals there are, with the overflow from the first thickener having the highest valuable metal content. In general, the plant is operated to recover a crude nickel sulfate aqueous solution (leachate), which is an overflow liquid with a nickel and cobalt recovery rate of 90% or more.

In addition, the overflow liquid from the first thickener is subjected to solid-liquid separation in each thickener stage, and the settling of fine particles is also progressing. Therefore, the overflow liquid from the first thickener has the lowest turbidity (highest transparency). Specifically, it is operated so that the turbidity is 200 NTU or less.

In the method according to the present embodiment, the slurry of the leaching residue separated in the solid-liquid separation step S2 is added to the leachate to be subjected to the neutralization treatment in the next neutralization step S3, and the neutralized precipitate slurry produced by the neutralization treatment is repeated in the solid-liquid separation step. When the neutralized precipitate slurry is repeated in the solid-liquid separation step S2, the slurry is transferred to the first-stage thickener located at the most upstream position. This method makes it possible to reduce the load of precipitate in the solid-liquid separation process while suppressing nickel recovery loss.

Here, in the solid-liquid separation process, an appropriate amount of flocculant is added to the thickener containing the leaching slurry. In this case, in the method according to the present embodiment, it is preferable to periodically measure and monitor the turbidity and viscosity of the supernatant liquid (overflow liquid, leaching liquid) in the first-stage thickener located at the most upstream position, and adjust the amount of flocculant added in the solid-liquid separation process based on the monitoring results.

It is known that the recovery rate of nickel and cobalt recovered from the leachate (crude nickel sulfate aqueous solution) is correlated with the turbidity of the leachate. For this reason, the recovery rate of nickel and cobalt in actual operation can be controlled by the turbidity of the obtained leachate. Specifically, the value is 200 NTU or less as measured by a turbidity meter (for example, HACH's 2100P scattered light turbidity meter). This means that the higher the transparency of the leachate (the lower the turbidity), the more the solids have coagulated and the more thoroughly the adhering liquid has been washed off, and a good correlation is established.

Therefore, by periodically measuring and monitoring the turbidity of the supernatant (overflow liquid) and adjusting the amount of flocculant added based on the change over time, the flocculant can be efficiently added to the solids in the leaching slurry, and solid-liquid separation can proceed more effectively. This effectively reduces the turbidity of the supernatant from the first-stage thickener, and increases its clarity.

Specifically, if the turbidity of the supernatant is higher than a specified value (e.g., 200 NTU), the amount of flocculant added is increased to restore clarity. On the other hand, if the turbidity of the supernatant is lower than the specified value, the amount of flocculant added is decreased. This makes it possible to prevent excessive use of flocculant and perform efficient processing.

However, if the turbidity becomes low, the clarity may suddenly deteriorate after the amount of flocculant added is reduced. Therefore, it is preferable to control the amount of flocculant added by periodically measuring and monitoring the turbidity.

In order to prevent a sudden deterioration in clarity, it is also preferable to periodically measure and monitor the viscosity of the supernatant (overflow liquid). The viscosity of the supernatant can be measured using the filtration time of a certain amount of the supernatant as a parameter. Specifically, the filtration time can be measured as the time required to aspirate and filter a predetermined amount of the supernatant from the first-stage thickener through a membrane filter with a mesh size of 0.45 μm.

For example, when the concentration of the flocculant is reduced, the filtration time of the supernatant from the first-stage thickener decreases accordingly. This is presumably because the reduced concentration of the flocculant solution inhibits aggregation of the flocculant components, lowering the viscosity of the supernatant. For this reason, the clarity of the supernatant can be maintained by setting a lower limit for the viscosity of the supernatant and periodically monitoring the results of viscosity measurements to maintain the amount of flocculant added so that the viscosity of the supernatant does not fall below the set lower limit.

In this way, preferably, the turbidity and viscosity of the supernatant liquid (overflow liquid, leachate) in the first-stage thickener are periodically measured and monitored, and the amount of flocculant added in the solid-liquid separation process is adjusted, so that the sediment load can be more effectively reduced even when the neutralized sediment slurry is repeatedly charged from the neutralization step S3 (in other words, when the processing load due to the sediment fluctuates). And, by repeatedly charging the neutralized sediment and subjecting it to solid-liquid separation process together with the leach slurry, the effect of reducing nickel recovery loss can be more effectively achieved.

It is also possible to prevent the addition of excess flocculant, effectively reducing the amount of flocculant used and enabling more efficient processing.

≪4. Neutralization process in the neutralization process≫
In the hydrometallurgical smelting method for nickel oxide ore according to the present embodiment, in the neutralization treatment in the neutralization step S3, a neutralizing agent is added to the leachate to be treated to adjust the pH to a predetermined value. At this time, a slurry of the leachate residue obtained by solid-liquid separation of the leachate slurry is added at a predetermined ratio to the leachate to be subjected to the neutralization treatment.

(pH adjustment)
In the neutralization process, it is preferable to adjust the pH of the resulting neutralized final solution to a range of 2.5 to 3.5 by adding a neutralizing agent to the leachate. If the pH of the neutralized final solution is adjusted to less than 2.5, impurity elements contained in the leachate may not be sufficiently converted into precipitates such as hydroxides. This increases the impurity content of the resulting neutralized final solution, and the amount of impurities in the nickel-containing sulfide produced in the sulfurization step S4 increases. On the other hand, if the pH of the neutralized final solution is adjusted to more than 3.5, fine particles with poor sedimentation properties are generated, making the turbidity likely to increase. In addition, when zinc is removed as sulfide in a subsequent step, some of the nickel and cobalt are also precipitated.

The neutralizing agent is not particularly limited, and for example, an aqueous solution or slurry of an alkali metal hydroxide or an alkali metal carbonate, such as magnesium hydroxide or calcium carbonate, can be used. From an industrial perspective, it is preferable to use a slurry of inexpensive calcium carbonate.

(Addition of leach residue slurry)
In the neutralization treatment, a neutralizing agent is added, and a slurry of the leaching residue obtained by solid-liquid separation of the leaching slurry is added. This effectively reduces the turbidity of the resulting neutralization end solution. This effectively reduces the impurity content in the nickel sulfide obtained by subjecting the neutralization end solution to a sulfurization treatment, thereby improving the quality of the nickel sulfide.

Here, the leaching residue slurry is a slurry of the leaching residue obtained by subjecting the leaching slurry generated in the leaching step S1 of the hydrometallurgical process to solid-liquid separation in the solid-liquid separation step S2. The leaching residue contains hematite (Fe ₂ O ₃ ) as a main component (usually 50 mass% to 70 mass%) and has a large specific gravity. In addition, the leaching residue contains a trace amount of nickel that did not migrate into the leachate and became a precipitate due to the leaching treatment in the leaching step S1.

In the neutralization treatment of the leachate, a slurry of the leach residue is added and neutralization treatment is performed, so that the neutralization precipitate is formed by agglomerating the leach residue with a high specific gravity as a nucleus, and as a result, the settling property of the neutralization precipitate can be increased and the turbidity of the resulting neutralization end liquid can be reduced. Then, by using the neutralization end liquid (nickel recovery mother liquor) with effectively reduced turbidity as the starting liquid for the sulfurization reaction in the sulfurization step S4, nickel sulfide with an extremely low impurity content can be produced.

In addition, as mentioned above, the leaching residue contains trace amounts of nickel, so nickel recovery losses can be reduced by adding a slurry of the leaching residue to the leaching solution and returning it to the process system.

The amount of leaching residue slurry added to the leachate is not particularly limited, but is preferably added at a flow rate that is 5.0 volume % or more, more preferably 6.0 volume % or more, relative to the flow rate of the leachate used in the neutralization treatment. The leach residue slurry is also added at a flow rate that is preferably 8.0 volume % or less, more preferably 7.5 volume % or less, relative to the flow rate of the leachate. In this way, by adding the leach residue slurry to the leachate at a flow rate in the above-mentioned range, the turbidity of the resulting neutralized end solution can be reduced, for example, to less than 100 NTU, preferably less than 70 NTU. On the other hand, it is possible to prevent an excessive increase in the neutralized precipitate slurry, and while suppressing the precipitate load, it is possible to effectively suppress a decrease in the recovery rate of nickel obtained through the hydrometallurgical process.

Regarding the amount of leaching residue slurry added, if it is less than 5% by volume relative to the flow rate of the leaching solution, there will be a shortage of nuclei on which the neutralized precipitate can precipitate, which will lead to high turbidity and an increase in the impurity content in the subsequent process. On the other hand, if it exceeds 8% by volume relative to the flow rate of the leaching solution, the amount of neutralized precipitate generated will be excessive, resulting in a decrease in the nickel recovery rate. That is, as will be described in detail later, the generated neutralized precipitate is transferred to a treatment tank that performs the solid-liquid separation process S2 and is subjected to solid-liquid separation treatment together with the leaching slurry. However, if there is an excess of neutralized precipitate slurry, the nickel in the neutralized precipitate will transfer to the leaching residue separated by solid-liquid separation, which will increase the load of the precipitate in the solid-liquid separation process S2 and decrease the nickel recovery rate obtained through the hydrometallurgical process of nickel oxide ore.

The leaching residue slurry is preferably obtained by solid-liquid separation through multi-stage washing in the solid-liquid separation step S2. The leaching residue obtained by such multi-stage washing has little adhesion of acid or alkali. This prevents the leaching residue from interfering with the pH control of the entire leaching solution during the neutralization process. In addition, the local pH in the vicinity of the added leaching residue also follows the change in the bulk pH, making it easy to control the precipitation rate and particle size of the neutralized precipitate. Furthermore, the leaching residue obtained by solid-liquid separation through multi-stage washing has excellent specific gravity separation properties and filtration separation properties with water. By selecting and using leaching residue with particularly strong such properties (for example, the bottom of the thickener or initial precipitate), the neutralized precipitate can be separated even more easily, and the turbidity of the final neutralization solution can be reduced more effectively.

The leaching residue slurry preferably has a slurry concentration in the range of 1.5 t/m ³ to 1.7 t/m ^3. By using the leaching residue slurry with such a slurry concentration, the turbidity of the final neutralization solution can be more effectively reduced.

When adding the leaching residue slurry to the leachate to be subjected to neutralization treatment, it is preferable to add a coagulant as well. Generally, neutralized precipitates such as hydroxide precipitates are known to have poor settling properties. By adding the leaching residue slurry, which serves as the base for aggregation, and a coagulant, the leaching residue slurry, which has a high specific gravity, and the neutralized precipitates such as hydroxide precipitates can be coagulated, further promoting settling properties. Examples of coagulants that can be used include polyamines, polydadomacs, polyethyleneimines, and polyacrylamides.

When the flow rate of the leachate used in the neutralization treatment is increased or decreased, it is preferable to increase or decrease the amount of leach residue slurry added accordingly. However, when increasing the flow rate of the leach residue slurry added, it is desirable to do so gradually. Since the leach residue only becomes effective when it coagulates with the neutralized precipitate, depending on the composition of the neutralized precipitate and the amount of coagulant added, increasing the amount added may not promote the settling of the neutralized precipitate, which may be disadvantageous in terms of retention time.

<5. Repetition of the neutralization precipitate slurry from the neutralization process to the solid-liquid separation process>
As described above, the method according to the present embodiment includes a process in which at least a part of the neutralized precipitate slurry obtained in the neutralization step S3 is repeatedly subjected to the solid-liquid separation step S2. In this manner, the neutralized precipitate slurry is repeatedly subjected to the solid-liquid separation step S2, and the neutralized precipitate slurry is subjected to a solid-liquid separation treatment together with the leaching slurry in the solid-liquid separation step S2, whereby nickel can be recovered from the neutralized precipitate slurry and nickel recovery loss can be effectively reduced.

Nickel loss to the neutralized precipitate is due to the adhesion of nickel hydroxide due to the adhesion liquid of the neutralized precipitate and the local reaction on the surface of the neutralized precipitate, and neither can be completely prevented. In contrast, by repeatedly processing the neutralized precipitate slurry in the solid-liquid separation step S2, which is operated at a low pH, it is possible to promote the dissolution of the locally reacted nickel hydroxide while at the same time washing the leaching residue in the solid-liquid separation process by multi-stage washing.

When the neutralized precipitate slurry from the neutralization step S3 is transferred to the solid-liquid separation step S2, it is subjected to solid-liquid separation treatment together with the leaching slurry in the solid-liquid separation step S2. When transferring the neutralized precipitate slurry to the solid-liquid separation treatment, the slurry is transferred to the first-stage thickener located at the most upstream of the multiple thickener stages in the solid-liquid separation equipment 1 (see Figure 2). This makes it possible to more effectively reduce nickel recovery losses.

As described above, it is preferable to periodically measure and monitor the turbidity and viscosity of the supernatant in the first-stage thickener and adjust the amount of flocculant added in the solid-liquid separation process, thereby more effectively reducing the sediment load even when the neutralized sediment slurry is transferred to the first-stage thickener in the solid-liquid separation process.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Example 1]
In the hydrometallurgical smelting method of nickel oxide ore (see FIG. 1), the neutralization step includes adding a slurry of the leachate separated in the solid-liquid separation step to the leachate to be subjected to the neutralization treatment. In the neutralization step, the slurry of the neutralized precipitate generated by the neutralization treatment is repeatedly subjected to the solid-liquid separation step.

In the solid-liquid separation process, a solid-liquid separation device (see overview in Figure 2) consisting of seven connected thickeners is used, and multi-stage washing is performed using the continuous countercurrent washing method (CCD method) in which nickel-free washing solution is brought into countercurrent contact with the leaching slurry to be treated, while separating the leaching residue (solid content), and the leachate from which the solid content has been removed is collected as the supernatant liquid (overflow liquid).

When the slurry of the neutralized precipitate produced by the neutralization treatment was transferred to the solid-liquid separation treatment in the solid-liquid separation step, the slurry was transferred to the first-stage thickener located at the most upstream position in the solid-liquid separation device. In addition, in the solid-liquid separation treatment, the turbidity and viscosity of the supernatant liquid (overflow liquid) from the first-stage thickener were periodically measured and monitored to control the amount of flocculant added, thereby controlling the clarity of the supernatant liquid during treatment.

As a result of this treatment, the nickel loss rate in the solid-liquid separation process was 2.92%.

The nickel loss rate is expressed as a percentage of the amount of nickel contained in the slurry liquid discharged to the final neutralization process after solid-liquid separation treatment, relative to the amount of nickel contained in the ore slurry used in the hydrometallurgical process.

[Comparative Example 1]
In Comparative Example 1, when the slurry of the neutralized precipitate generated by the neutralization treatment was transferred to the solid-liquid separation treatment in the solid-liquid separation step, the slurry was transferred to a second-stage thickener connected subsequent to the first stage in the solid-liquid separation device. In addition, the clarity of the supernatant from the first-stage thickener located at the most upstream side was not controlled during the treatment. The other conditions were the same as those in Example 1.

As a result of this treatment, the nickel loss rate in the solid-liquid separation process was 3.10%. Compared to Example 1, the nickel loss has increased.

Claims (4)

A method for hydrometallurgy of nickel oxide ore, comprising adding an acid to nickel oxide ore to subject the nickel oxide ore to a leaching treatment, and obtaining nickel and cobalt sulfides from the resulting leachate, the method comprising the steps of:
a solid-liquid separation step in which the leaching slurry obtained by the leaching treatment is subjected to a solid-liquid separation treatment while being washed in multiple stages using a solid-liquid separation device provided with multiple thickeners, thereby obtaining a leachate and a leaching residue;
A neutralization step of adding a neutralizing agent to the leachate to perform a neutralization treatment, thereby obtaining a neutralized precipitate containing impurities and a neutralized final solution containing nickel and cobalt,
In the neutralization step,
neutralizing the leachate by adding the slurry of the leachate separated in the solid-liquid separation step to the leachate to be subjected to the neutralization treatment in an amount of 5.0 vol. % or more and 8.0 vol. % or less with respect to the flow rate of the leachate to be subjected to the neutralization treatment ;
The neutralization treatment includes repeating the neutralization precipitate slurry produced by the neutralization treatment to the solid-liquid separation step,
When the neutralized precipitate slurry is subjected to the solid-liquid separation step again, the slurry is transferred to a first-stage thickener located at the most upstream of the thickeners provided in multiple stages in the solid-liquid separation device.
A hydrometallurgical process for nickel oxide ores. In the solid-liquid separation step,
The treatment is carried out using a solid-liquid separation device having 4 to 7 thickeners in multiple stages.
2. The method for hydrometallurgy of nickel oxide ore according to claim 1. In the solid-liquid separation step,
The turbidity and viscosity of the supernatant in the first-stage thickener are periodically measured and monitored, and the amount of flocculant added in the solid-liquid separation treatment is adjusted.
3. The method for hydrometallurgy of nickel oxide ore according to claim 1 or 2. In the solid-liquid separation step,
The turbidity of the supernatant in the first-stage thickener is adjusted to be less than 100 NTU.
The method for hydrometallurgy of nickel oxide ore according to claim 3.

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