AU2019290870A1 - Nickel sulfate compound manufacturing method - Google Patents

Abstract

This method for producing a nickel sulfate compound comprises: a conversion step (S1) for converting at least a part of a nickel-containing raw material (10) into a nickel sulfate compound by treating the nickel-containing raw material (10) with concentrated sulfuric acid in the presence of an abrasive material; a solid-liquid separation step (S2) for separating a mixture (11) obtained in the conversion step (S1) into a solid phase (21) and a liquid phase (22); and a dissolution separation step (S3) for adding water to the solid phase (21) obtained in the solid-liquid separation step (S2) and causing the nickel sulfate compound contained in the solid phase (21) to dissolve in water so as to separate impurities (32).

Description

DESCRIPTION METHOD FOR PRODUCING NICKEL SULFATE COMPOUND

Technical Field

[0001]

The present invention relates to a nickel sulfate compound manufacturing

method.

This application claims priority to Japanese Patent Application No. 2018

118046 filed June 21, 2018, and Japanese Patent Application No. 2018-151471 filed

August 10, 2018, the contents of which are hereby incorporated by reference.

Background Art

[0002]

In the related art, a nickel sulfate compound is used as a raw material of

various nickel compounds or metal nickel for use in, for example, electrolysis nickel

plating, electroless nickel plating, and catalyst materials. The recent demand of

secondary batteries including a nickel compound or metal nickel in a positive electrode

material is expected to expand as a power supply of transport machines, such as electric

vehicles, and electronic devices. To produce high-performance secondary batteries,

there is a need to stably supply a high-purity nickel sulfate compound.

[0003]

Examples of impurities that may be contained in low-purity nickel

compounds include other metal compounds, such as iron, copper, cobalt, manganese,

and magnesium compounds. Examples of conventional methods for producing a high

purity nickel compound include a solvent extraction method. The solvent extraction

method involves removing other metal compounds by selective extraction, or taking a nickel compound out by selective extraction. In both cases, a particular chemical is needed to selectively extract particular metal ions, resulting in high costs.

[0004]

Known methods for manufacturing nickel sulfate also include a method in

which the anion of a nickel compound is exchanged with a sulfate ion through ion

exchange, and a method in which a nickel metal powder is dissolved in a sulfuric acid

solution with hydrogen gas generated. Patent Literature 1 describes a method for

producing water-soluble nickel sulfate. The method involves heating, in sulfuric acid,

a green nickel oxide powder having a specific gravity of higher than 6.30 and then

leaching the reaction mass with hot water. In Patent Literature 1, examples of sulfuric

acid used in the heat treatment include a 30% to 60% sulfuric acid solution (Claims 1 to

) and 95% concentrated sulfuric acid (Claims 6 to 7). The use of 95% concentrated

sulfuric acid (Examples 7 to 9) in Patent Literature 1 needs a high temperature of 275°C

or higher.

Citation List

Patent Literature

[0005]

Patent Literature 1: US 3002814

Summary of Invention

Technical Problem

[0006]

In light of the above circumstances, an object of the present invention is to

provide a nickel sulfate compound manufacturing method that enables the manufacture of the nickel sulfate compound at a high conversion rate even under milder conditions than those in the related art.

Solution to Problem

[0007]

A first aspect of the present invention is a nickel sulfate compound

manufacturing method including a conversion step of converting at least part of a

nickel-containing raw material into a nickel sulfate compound by treating the nickel

containing raw material with concentrated sulfuric acid in the presence of an abrasive, a

solid-liquid separation step of separating a mixture obtained in the conversion step into

a solid phase and a liquid phase, and a dissolution-separation step of adding water to the

solid phase obtained in the solid-liquid separation step and dissolving, in the water, the

nickel sulfate compound contained in the solid phase to separate impurities.

[0008]

A second aspect of the present invention is the nickel sulfate compound

manufacturing method according to the first aspect, wherein the nickel-containing raw

material in the conversion step contains at least one selected from the group consisting

of nickel oxide, nickel hydroxide, nickel sulfide, nickel chloride, metal nickel,

ferronickel, and nickel ore.

[0009]

A third aspect of the present invention is the nickel sulfate compound

manufacturing method according to the first aspect, wherein in the conversion step, the

nickel-containing raw material contains nickel sulfide, an oxidizing agent is added, and

the redox potential is 300 mV or higher.

[0010]

A fourth aspect of the present invention is the nickel sulfate compound

manufacturing method according to any one of the first to third aspects, wherein

concentrated sulfuric acid contained in the liquid phase obtained in the solid-liquid

separation step is reused in the conversion step.

[0011]

A fifth aspect of the present invention is the nickel sulfate compound

manufacturing method according to any one of the first to fourth aspects, wherein in the

dissolution-separation step, the water added to the solid phase has a temperature of from

°C to 60°C.

[0012]

A sixth aspect of the present invention is the nickel sulfate compound

manufacturing method according to any one of the first to fifth aspects, wherein in the

dissolution-separation step, a solution obtained by dissolving the nickel sulfate

compound in the water has a pH of 4 to 5 in separating the impurities.

[0013]

A seventh aspect of the present invention is the nickel sulfate compound

manufacturing method according to any one of the first to sixth aspects, further

including a purification step of removing a cobalt compound contained in the solution

obtained in the dissolution-separation step.

[0014]

An eighth aspect of the present invention is the nickel sulfate compound

manufacturing method according to any one of the first to seventh aspects, further

including a crystallization step of precipitating a nickel sulfate compound by adding an

organic solvent into the solution obtained in the dissolution-separation step.

[0015]

A ninth aspect of the present invention is the nickel sulfate compound

manufacturing method according to the eight aspect, wherein the organic solvent in the

crystallization step is at least one selected from the group consisting of methanol,

ethanol, propanol, isopropanol, butyl alcohol, ethylene glycol, and acetone.

[0016]

A tenth aspect of the present invention is the nickel sulfate compound

manufacturing method according to the eighth or ninth aspect, wherein the nickel

sulfate compound obtained in the crystallization step is nickel sulfate hexahydrate.

Advantageous Effects of Invention

[0017]

According to the first aspect, the treatment of the nickel-containing raw

material with concentrated sulfuric acid in the presence of an abrasive can yield a nickel

sulfate compound at a high conversion rate even under milder conditions than those in

the related art. When a mixture containing the yielded nickel sulfate compound and

unreacted concentrated sulfuric acid is subjected to solid-liquid separation, it is easy to

separate the nickel sulfate compound in the solid phase and unreacted concentrated

sulfuric acid in the liquid phase, which enables easy treatment without contact between

unreacted concentrated sulfuric acid and water.

[0018]

According to the second aspect, the use of relatively easily available nickel

containing raw materials can improve productivity.

[0019]

According to the third aspect, the addition of an oxidizing agent can

accelerate the conversion reaction when a nickel-containing raw material containing nickel sulfide, such as nickel matte, is used. In addition, the precipitation of sulfur and the generation of hydrogen sulfide gas are prevented by setting the redox potential in the conversion reaction to an oxidation range of 300 mV or higher, thereby maintaining the conditions under which a sulfur ion, such as HS04- ion, is generated. This can improve the conversion efficiency from nickel sulfide into the nickel sulfate compound.

[0020]

According to the fourth aspect, the effective use of unreacted concentrated

sulfuric acid can reduce costs required for disposal treatment of concentrated sulfuric

acid.

[0021]

According to the fifth aspect, the nickel sulfate compound can be selectively

extracted in the aqueous phase while the dissolution of impurities, such as an iron salt,

is prevented.

[0022]

According to the sixth aspect, the nickel sulfate compound can be selectively

extracted in the aqueous phase while the dissolution of impurities, such as an iron salt,

is prevented.

[0023]

According to the seventh aspect, a high-grade nickel sulfate compound can be

manufactured by removing a cobalt compound which tends to be present together with

the nickel sulfate compound.

[0024]

According to the eighth aspect, the impurities are removed after dissolving, in

water, the nickel sulfate compound contained in the solid phase, and the nickel sulfate

compound is crystallized by using an organic solvent. As a result, the impurities are removed as water-insoluble components or components that remain in the aqueous phase in the crystallization. This allows efficient manufacture of high-purity nickel sulfate compound.

[0025]

According to the ninth aspect, effective purification is possible in

crystallization using a water-miscible organic solvent. In addition, the organic solvent

can be efficiently collected, by distillation, from the liquid phase containing water and

the organic solvent obtained by crystallization.

[0026]

According to the tenth aspect, a high-purity product tends to be formed in

crystallization by the precipitation of nickel sulfate hexahydrate from the solution and is

highly useful as an industrial product.

Brief Description of Drawings

[0027]

Fig. 1 is a schematic flow diagram of a nickel sulfate compound

manufacturing method according to a first embodiment.

Fig. 2 is a schematic flow diagram of a nickel sulfate compound

manufacturing method according to a second embodiment.

Description of Embodiments

[0028]

The present invention will be described below on the basis of preferred

embodiments.

[0029]

As illustrated in Fig. 1, a nickel sulfate compound manufacturing method

according to an embodiment includes a conversion step Si of converting at least part of

a nickel-containing raw material 10 into a nickel sulfate compound by treating the

nickel-containing raw material 10 with concentrated sulfuric acid in the presence of an

abrasive, a solid-liquid separation step S2 of separating a mixture 11 obtained in the

conversion step S Iinto a solid phase 21 and a liquid phase 22, and a dissolution

separation step S3 of adding water to the solid phase 21 obtained in the solid-liquid

separation step S2 and dissolving, in the water, the nickel sulfate compound contained

in the solid phase 21 to separate impurities 32. The dissolution-separation step S3

yields a solution 31 containing the nickel sulfate compound.

[0030]

In the conversion step according to the embodiment, the nickel-containing

raw material is treated with concentrated sulfuric acid in the presence of an abrasive.

[0031]

The nickel-containing raw material may be a nickel compound or metal nickel

as long as it contains element nickel. Examples of the nickel compound include, but

are not limited to, nickel salts, such as nickel oxide, nickel hydroxide, nickel sulfide,

and nickel chloride. The nickel compound may be a hydrate. The metal nickel may

be a nickel alloy, such as ferronickel. When metal nickel (a simple substance or an

alloy) is used as a nickel-containing raw material, metal nickel may be, for example, a

shot formed of a small piece of molten metal. Nickel ore can also be used as the

nickel-containing raw material. Nickel ore is, for example, at least one of oxidized ore

and sulfide ore. For example, nickel matte containing nickel sulfide as a main

component can also be used as the nickel-containing raw material.

[0032]

In the conversion step, the nickel-containing raw material may be used alone

or in combination of two or more. Two or more nickel-containing raw materials may

be supplied in a mixed form or may be supplied separately. Before the nickel

containing raw material is supplied to the conversion step, the particle size of the nickel

containing raw material is preferably reduced by chipping, grinding, abrasion, or other

process. The grinding unit is not limited but may be one or a combination of two or

more selected from a ball mill, a rod mill, a hammer mill, a fluid energy mill, and a

vibrating mill. The particle size after grinding is not limited but may be, for example,

from about 1 to 1000 tm or from about 10 to 100 pm.

[0033]

The abrasive is any material that has a function of abrading the particle

surface of the nickel-containing raw material. The abrasive is preferably, for example,

stainless steel or ceramics which has corrosion resistance to concentrated sulfuric acid,

and particularly preferably ceramic balls. Since concentrated sulfuric acid is separated

as the liquid phase in the solid-liquid separation step after the conversion step in this

embodiment as described below in detail, a substance, such as steel, that is soluble in

dilute sulfuric acid but poorly soluble in concentrated sulfuric acid can be used. Even

when steel or the like is brought into contact with concentrated sulfuric acid so that iron

slightly dissolves in concentrated sulfuric acid, iron can be separated and removed in the

step described below.

[0034]

In a convention dissolution reaction for dissolving a nickel-containing raw

material in a sulfuric acid solution, the sulfuric acid solution permeates the inside of

particles of the nickel-containing raw material so that nickel reacts with sulfuric acid

and dissolves in the sulfuric acid solution. In this case, the diffusion of the sulfuric acid solution in the particle surface corresponds the rate-limiting step of the reaction.

For example, when an insoluble crystal or the like is formed on the particle surface due

to the relationship between the redox range and the pH range, the coverage of the

particle surface with the insoluble matter may cause a problem in which nickel inside

the particles does not dissolve. There is thus a need to, for example, increase the

residence time or increase the reaction temperature in order to improve the conversion

rate into nickel sulfate.

[0035]

In the conversion step, the nickel-containing raw material and the abrasive are

preferably caused to collide with each other by stirring or the like while the nickel

containing raw material, the abrasive, and concentrated sulfuric acid are mixed.

Accordingly, the reaction between the nickel-containing raw material and concentrated

sulfuric acid is the mechanochemical reaction through the abrasive, so that the insoluble

matter is unlikely to deposit on the particle surface of the nickel-containing raw

material, and sulfuric acid easily permeates the inside of the particles. The conversion

rate into the nickel sulfate compound can thus be improved even under mild conditions.

[0036]

Regarding the temperature of the mixture in the conversion step, favorable

conversion proceeds at, for example, 15°C to 200°C, and the time required for

conversion becomes shorter as the temperature increases like 20°C, 90°C, 120°C, and

150°C. The mild reaction condition is preferably 90°C or lower at which sulfuric acid

mist does not spread. In this conversion step, nickel and sulfuric acid are caused to

react with each other to form a nickel sulfate compound. In the case of the conversion

reaction under the heated conditions, the nickel-containing raw material, concentrated

sulfuric acid, and other materials may be heated before being supplied to the system of the conversion reaction and mixed.

[0037]

The solid nickel sulfate compound formed in the conversion step may be in

the form of anhydrous salt, monohydrate, dihydrate, pentahydrate, hexahydrate, or

heptahydrate nickel sulfate. Examples of concentrated sulfuric acid include a liquid

containing 90% or more sulfuric acid. The concentration of concentrated sulfuric acid

is, for example, 95%, 96%, or 98%. At least part of concentrated sulfuric acid used in

the conversion step may be supplied from other source and used. Concentrated

sulfuric acid collected from the liquid phase in the solid-liquid separation step described

below can be reused as at least part of concentrated sulfuric acid used in the conversion

step.

[0038]

The mixing ratio between the nickel-containing raw material and concentrated

sulfuric acid is preferably selected in the range in which the mixture in the form of

slurry has an appropriate viscosity. For example, when the total amount of the nickel

containing raw material and concentrated sulfuric acid is 100 wt%, the proportion of the

nickel-containing raw material is preferably from 5 wt% to 50 wt%. The proportion of

the nickel-containing raw material is more preferably from 5 wt% to 15 wt%, which is a

range in which the mixture has the properties of a Newtonian fluid.

[0039]

When the nickel-containing raw material contains nickel sulfide, the

conversion reaction is preferably accelerated by, for example, injecting oxygen (02) gas

or adding an oxidizing agent, such as hydrogen peroxide (H2 0 2 ) or ozone (03). This

can improve the conversion efficiency from nickel sulfide into the nickel sulfate

compound when a nickel-containing raw material containing nickel sulfide, such as nickel matte, is used. In general, the conversion from a nickel-containing raw material into a nickel sulfate compound uses HS04- in concentrated sulfuric acid. However, when a nickel-containing raw material contains nickel sulfide, sulfur in nickel sulfide exists in the ionic state and does not escape as sulfur gas, so that the sulfur content is unlikely to decrease. Thus, the amount of HS04- in concentrated sulfuric acid is maintained at a predetermined level, and there is no need for additional concentrated sulfuric acid, or the amount of additional concentrated sulfuric acid can be reduced.

To accelerate the reaction with an oxidizing agent, such as oxygen, concentrated sulfuric

acid is preferably heated to, for example, about 95°C to 200°C or about 100°C to

150°C. Hot concentrated sulfuric acid may be used as concentrated sulfuric acid.

[0040]

When nickel matte is used as a nickel-containing raw material, nickel matte is

preferably pulverized into, for example, about 20 pm before being supplied to the

conversion step. The iron content of the nickel matte is preferably reduced beforehand

in a converter or the like. Examples include nickel matte having 1 wt% or less Fe.

The redox potential in the reaction system is preferably 300 mV or higher so that

elemental sulfur (SO) does not precipitate and the HS04- ion is generated. In other

words, sulfur generated from nickel sulfide is used as a sulfur ion at a redox potential of

300 mV or higher in the reaction system. This can improve the conversion efficiency

without the inhibition of the conversion from nickel sulfide into the nickel sulfate

compound due to the precipitation of, for example, elementary sulfur (S) on the surface

of nickel sulfide. In addition, the generation of hydrogen sulfide (H 2 S) is suppressed

at a redox potential of 300 mV or higher in the reaction system.

[0041]

When oxygen gas is injected, a gas mixture containing oxygen, for example, air may be used. The conversion step according to this embodiment can be effectively carried out even under normal pressure, but may be carried out under pressurized conditions in order to increase the solubility of oxygen gas in concentrated sulfuric acid.

The partial pressure of oxygen gas may be about 0.02 MPa, which is the same as that in

the air, or a pressure higher than or equal to about 0.02 MPa, for example, from 1.0 to

2.0 MPa.

[0042]

In the solid-liquid separation step according to this embodiment, the mixture

obtained in the conversion step is separated into the solid phase and the liquid phase.

[0043]

Examples of the solid-liquid separation process include, but are not limited to,

filtration, centrifugation, and sedimentation. Desirably, an apparatus that has a great

ability to separate fine particles contained in the solid phase and in which parts that may

contact concentrated sulfuric acid contained in the liquid phase have high corrosion

resistance to sulfuric acid is preferably used. For example, sulfuric acid resistant

material can be used for a filter material or the like in the filtration process. Examples

of the type of filtration include, but are not limited to, gravity filtration, vacuum

filtration, pressure filtration, centrifugal filtration, filtration with addition of filter aid,

and squeeze filtration.

[0044]

Unreacted concentrated sulfuric acid contained in the liquid phase obtained in

the solid-liquid separation step can be reused as concentrated sulfuric acid to be added

to the nickel-containing raw material in the conversion step. This enables effective use

of unreacted concentrated sulfuric acid and can reduce costs required for disposal

treatment of concentrated sulfuric acid. When metal compounds are dissolved in the collected concentrated sulfuric acid, the metal compounds are preferably removed from concentrated sulfuric acid by treatment in a purification system.

[0045]

In the solid phase obtained in the solid-liquid separation step, a small amount

of concentrated sulfuric acid may remain in order to form a solution in a suitable pH

range in the dissolution-separation step described below. If concentrated sulfuric acid

excessively remains, the amount of concentrated sulfuric acid may be reduced from the

solid phase by subjecting the cake in the solid phase to air blowing or the like. An

economical way to remove concentrated sulfuric acid from the solid phase is to use air

as a fluid that does not react with the sulfate and concentrated sulfuric acid in the solid

phase. However, other fluid or method may be used.

[0046]

In the dissolution-separation step according to this embodiment, impurities

are separated by adding water to the solid phase obtained in the solid-liquid separation

step and dissolving, in water, the nickel sulfate compound contained in the solid phase.

[0047]

Water added to the solid phase in the dissolution-separation step is preferably

pure water treated so as not to contain impurities. The water treatment method is not

limited but may be, for example, one or more selected from filtration, membrane

separation, ion exchange, distillation, sterilization, chemical treatment, and adsorption.

Water used for dissolution may be, for example, clean water obtained from water

sources, or industrial water or may be water obtained by treating wastewater generated

in the crystallization step described below or other process. Two or more types of

water may be used.

[0048]

The solid phase is leached with water so that the components in the solid

phase dissolve in water to provide a solution. To dissolve, in water, the nickel sulfate

compound in the solid phase, the pH of the obtained solution is acidic. To selectively

extract the nickel sulfate compound in the aqueous phase while suppressing dissolution

of impurities, such as iron sulfate, the pH of the solution is about 4 to 5. The pH is

preferably in the oxidation range as the redox potential is measured, that is, for example,

from 3.8 to 5.5.

[0049]

The method for adjusting the pH of the solution is not limited to adjustment of

the amount of concentrated sulfuric acid that remains in the solid-liquid separation step

described above. The pH of the solution can also be adjusted by addition of an acid or

alkali. The acid is not limited to concentrated sulfuric acid and may be dilute sulfuric

acid or the like. The alkali is preferably an alkaline earth metal hydroxide (e.g.,

calcium hydroxide) which is easily removed from the aqueous phase by generating a

precipitate in the presence of sulfate ions. To maintain the solution in the oxidation

range, an oxidizing agent, such as H 2 0 2 , may be added as necessary. When the

oxidizing agent used in the conversion step may still remain in the dissolution

separation step, the amount of remaining oxidizing agent may be adjusted.

[0050]

Examples of impurities that may be present together with the nickel sulfate

compound include iron (Fe), cobalt (Co), and aluminum (Al). In the case where salts

of these metals form sulfates in the conversion step and when the nickel sulfate

compound is dissolved in water, iron sulfate, cobalt sulfate, and the like also dissolve.

Furthermore, when the solution of the nickel sulfate compound in water has a pH of 4 to

, for example, oxides, such as FeOOH, Fe2O3, and Fe304, precipitate in water, and it is easy to remove impurities from the nickel sulfate compound. The solubility of nickel sulfate in water increases as the temperature of water increases. However, the temperature of water is preferably about 15°C to 60°C in order to reduce the solubility of impurities. To adjust the temperature of water, the temperature of water added to the nickel sulfate compound or the surrounding temperature of a container used in dissolution of the nickel sulfate compound may be controlled.

[0051]

Among impurities, metals having lower ionization tendency than hydrogen

(H), such as copper (Cu), gold (Au), silver (Ag), and platinum-group metals (PGM),

remain as solid and thus can be removed by solid-liquid separation, such as filtration.

Examples of the solid-liquid separation process include, but are not limited to, filtration,

centrifugation, and sedimentation. The solid removed by solid-liquid separation may

contain compounds of arsenic (As), lead (Pb), zinc (Zn), and the like, in addition to the

above impurities. The solid containing these impurities can be recycled as a valuable

resource.

[0052]

When the solid phase contains concentrated sulfuric acid, the heat of

dissolution of sulfuric acid in water increases the temperature, but it is preferred to

adjust the temperature in a temperature range suitable for use in the purification step

such as the crystallization step described below. Examples of the temperature

adjustment process include adjustment of the temperature or amount of water added in

the dissolution-separation step, heat exchange, heat dissipation, and cooling. From the

viewpoint of, for example, the solubility of the nickel sulfate compound, the

temperature of the solution is preferably room temperature or higher, for example, 20°C

or higher. When the crystallization step is performed, the temperature of the solution obtained in the dissolution-separation step is preferably lower than the boiling point of the organic solvent used in the crystallization step, and preferably lower than the azeotropic point of a mixture of the organic solvent and water.

[0053]

The solution obtained in the dissolution-separation step contains the nickel

sulfate compound as a main component. The solution of the nickel sulfate compound

can thus be transported and used without any processing or after being, for example,

dried to form a solid of the nickel sulfate compound. Depending on the application,

the amount of, for example, cobalt sulfate and the like, when preferably reduced as

impurities in the solution, can be reduced by a technique, such as solvent extraction,

electrowinning, electrorefining, ion exchange, or crystallization.

[0054]

Solvent extraction preferably uses an extractant capable of extracting cobalt in

a solvent more preferentially or selectively than nickel. The use of such an extractant

allows the nickel sulfate compound to remain in the aqueous solution and enables

efficient purification. Examples of the extractant include organic compounds having a

functional group that may be bonded to a metal ion, such as phosphinic acid group or

thiophosphinic acid group. In solvent extraction, an organic solvent capable of

separating the extractant from water may be used as a diluent. By dissolving the

extractant bonded to a metal ion, such as cobalt ion, in a diluent, it is easy to separate

impurities from the aqueous solution containing the nickel sulfate compound without

using a large amount of the extractant. The diluent is preferably an organic solvent

that is poorly miscible with water.

[0055]

Fig. 2 illustrates an embodiment having a crystallization step S4 of precipitating a nickel sulfate compound 41 by adding an organic solvent to the solution

31 obtained in the dissolution-separation step S3. Since the conversion step Sl, the

solid-liquid separation step S2, and the dissolution-separation step S3 are as described

above, the overlapping description is omitted.

[0056]

In the crystallization step according to this embodiment, an organic solvent is

added to the solution obtained in the dissolution-separation step to precipitate the nickel

sulfate compound. When the dissolution-separation step and the crystallization step

are performed by a batch method (batch method), the container used to form the

solution in the dissolution-separation step can be subsequently used in the

crystallization step. In the continuous method, the solution obtained in the dissolution

separation step may be transferred to a container used in the crystallization step from the

contained used in the dissolution-separation step.

[0057]

The organic solvent used in crystallization is preferably a water-miscible

organic solvent. The organic solvent is, for example, at least one selected from the

group consisting of methanol, ethanol, propanol, isopropanol, butyl alcohol, ethylene

glycol, and acetone. Two or more organic solvents may be used. The concentration

range of the organic solvent to be mixed with water is preferably such that the organic

solvent is added to the extent that the nickel sulfate compound precipitates. The

organic solvent can be mixed with water at any ratio as long as the nickel sulfate

compound precipitates. The organic solvent added in the crystallization step is not

limited to an anhydrous organic solvent and may be a hydrous organic solvent unless

the hydrous organic solvent hinders crystallization. The ratio of water to the organic

solvent is not limited and may be set in the range of, for example, from 1 : 20 to 20 : 1.

The ratio of water to the organic solvent is preferably about 1 : 1, for example, from 1

2to2:1.

[0058]

The nickel sulfate compound that precipitates in the crystallization step may

be in the form of nickel sulfate hexahydrate or other form. The precipitated nickel

sulfate compound can be separated from the solution by solid-liquid separation.

Examples of the solid-liquid separation process include, but are not limited to, filtration,

centrifugation, and sedimentation. The metals dissolved in the solution are preferably

neutralized and removed from the solution through precipitation or other process.

When the cleaned solution is mainly composed of a mixture of water and the organic

solvent, water and the organic solvent can be separated from each other by distillation

or other process.

[0059]

As illustrated in Fig. 2, an organic solvent 45 separated by distillation 43 or

other process from a solution 42 after the crystallization step S4 may be reused in a

stage of adding the organic solvent to the solution 31, which is obtained in the

dissolution-separation step S3, in the crystallization step S4. Water 44 separated from

the solution 42 after the crystallization step S4 may be reused in a stage of adding water

to the solid phase 21, which is obtained in the solid-liquid separation step S2, in the

dissolution-separation step S3.

[0060]

When water or the organic solvent is reused, water or the organic solvent may

be subjected to the purification step as needed before reuse. The step of removing

impurities, such as metals, is not necessarily performed before distillation and may be

performed after distillation. For example, when the amount of impurities is small, the step of removing impurities from the solution that remains after distilling the solution may be provided.

[0061]

The nickel sulfate compound manufacturing method according to this

embodiment provides the following advantageous effects.

1) A nickel sulfate compound with a high added value can be manufactured

from various nickel-containing raw materials. This enables production near sites

where the nickel sulfate compound is in demand and results in low transportation costs.

2) A high-purity nickel sulfate compound can be produced.

3) The operation costs can be reduced by, for example, reusing concentrated

sulfuric acid.

4) The reaction rate can be accelerated in the conversion step. The

generation of oxygen (H 2 ) gas can also be reduced.

5) The productivity can be improved by reducing the residence time in the

conversion step although using a downsized apparatus.

6) The use of concentrated sulfuric acid results in low material costs.

7) It is easy to manage chemicals used since they are small in number.

8) The utilization of evaporation energy is lower than that in conventional

evaporation crystallization since an organic solvent is used for the nickel sulfate

compound in the crystallization step. In addition, the time required for precipitation is

short, which allows facility downsizing.

9) The facility cost is lower than that in conventional methods.

10) In the case where nickel sulfide is caused to react while being oxidized in

the conversion step, sulfuric acid ions are generated from the sulfide. This achieves

high yield for a short time even under normal pressure.

[0062]

The present invention is described above on the basis of preferred

embodiments, but the present invention is not limited to the above embodiments.

Various modifications are possible without departing from the spirit of the present

invention.

[0063]

The conversion step according to the embodiment can be applied to a step of

converting at least part of a raw material containing a metal or metal compound into a

metal sulfate compound by treating the raw material with concentrated sulfuric acid in

the presence of an abrasive. The raw material in this case is not limited to nickel matte

and may be, for example, copper matte or Ni/Cu mixed matte. These mattes may

contain a platinum group metal (PGM). The conversion from the matte preferably

uses an oxidizing agent, such as oxygen, like nickel matte. The solid-liquid separation

step and the dissolution-separation step after the conversion step can efficiently provide

a water-soluble metal sulfate, such as a copper sulfate compound, as well as a nickel

sulfate compound.

Examples

[0064]

The present invention will be described below in detail by way of Examples.

[0065]

<Example 1-1>

In a glass container having a volume of 300 mL, 100 mL of concentrated

sulfuric acid (98% pure H2SO4reagent) and 5 g of nickel oxide (green NiO reagent)

powder were placed and heated with an electric heater while they were stirred with a

stirrer covered with fluorocarbon resin. At the time when the temperature exceeded

100°C, water vapor and white smoke-like sulfuric acid mist were generated on the gas

side. After the mixture was heated to 1200 C, the electric heater was turned off, and the

mixture was continuously stirred for 72 hours. While stirring continues, the mixture in

the glass container was cooled naturally. In the mixture, a very hard crystal different

from the added nickel oxide was partially generated. As a result of X-ray analysis, it

was found that NiSO 4 -H20 was formed.

[0066]

<Example 1-2>

In a glass container having a volume of 300 mL, ceramic ball grinding media

having a diameter of 6 mm were added up to a height of about 15 mm. A stirring

blade made of fluorocarbon resin was inserted thereto, and the glass container was

externally heated in a water bath such that the internal temperature of the glass container

reached 90°C. The rotation speed of the stirring blade was 60 rpm. To the glass

container, 5 g of nickel oxide (green NiO reagent) powder and 100 mL of concentrated

sulfuric acid (98% pure H 2 SO4reagent) were added. The internal temperature of the

glass container reached 90°C after about 30 minutes, and thereafter, the temperature was

maintained at 900 C. In this state, stirring was continued for 6 hours. After 3 hours

and 6 hours during stirring, a sample of the mixture containing the powder and

concentrated sulfuric acid was taken from the inside of the glass container. The

sample was collected in a centrifuge tube and separated into the solid phase and the

liquid phase by centrifugation. The nickel concentration of the liquid phase was 1154

mg/L. As a result of X-ray analysis of the solid phase, it was found that 97.3% of

nickel oxide added to the glass container was converted into nickel sulfate. This result

indicates that the conversion reaction from nickel oxide to nickel sulfate can proceed

directly with concentrated sulfuric acid while nickel oxide is abraded.

[0067]

<Example 1-3>

Ten grams of reagent nickel sulfate hexahydrate (blue NiSO 4 -6H 2 0) was

taken and placed in a glass container having a volume of 300 mL. Amixtureof6.3g

of reagent sulfuric acid and 83.7 g of pure water was added to the glass container,

whereby a solution of nickel sulfate hexahydrate in the sulfuric acid aqueous solution

wasprepared. Aliquots (10 mL) of this solution were dispensed into centrifuge tubes,

and 15 mL of an organic solvent was then added to each centrifuge tube. The organic

solvent was one of four organic solvents including isopropanol, acetone, tributyl

phosphate (TBP), and toluene. Furthermore, a test in which a centrifuge tube was

rapidly cooled externally without adding an organic solvent to the solution was

performed together. The results are shown in Table 1.

[0068]

[Table 1]

Test No. Organic Solvent Water Miscibility Test Temperature Test Result Note

1 isopropanol miscible 250 C precipitation hreiiateo 2 acetone miscible 250 C precipitation

3 tributyl phosphate immiscible 25 0 C no change

4 toluene immiscible 250 C no change

-- 0°C no change rapidly cooled 5 externally with ice

[0069]

As a result, in the case where water-miscible isopropanol or acetone is added

to the solution, the nickel sulfate hydrate crystal was instantly generated at the same

time as addition of the organic solvent. In the case of addition of isopropanol, a

sherbet-like crystal was entirely formed. In the case of addition of acetone, a needle

like fine crystal was formed. It is thus found that water-miscible organic solvents, such as methanol, ethanol, propanol, isopropanol, butyl alcohol, ethylene glycol, and acetone, can be used in crystallization.

[0070]

In the case of addition of isopropanol, a substantially total amount of the

dissolved nickel salt instantly precipitated as a hydrate. The crystallization process

performed by addition of an organic solvent eliminates the need of evaporation energy

and enables crystallization and solid-liquid separation by batch operation (batch

operation) compared with a method in which an aqueous solution is concentrated so as

to exceed the saturation solubility like continuous evaporation crystallization.

[0071]

<Example 2-1>

To a glass container having a volume of 300 mL, a raw material slurry

containing nickel matte (Ni: 78%, Fe: 1%, Co: 1%, S: 20%) and 95% sulfuric acid was

added together with ceramic balls having a diameter of 6 mm. While the raw material

slurry and the ceramic balls were stirred in an oil bath, the bath was heated. The

rotation speed during stirring was 60 rpm. After the temperature reached a

predetermined temperature, a small amount of the sample was taken from the slurry at

predetermined time intervals during stirring. The liquid phase was removed from the

sample slurry by centrifugation. The solid phase was washed with water, and Ni ions

contained in wash water were qualitatively analyzed, whereby the amount of nickel

sulfate compound was determined as NiSO 4-H2 0. In addition, the ratio of S, Al, Ni,

and Fe was qualitatively analyzed by X-ray fluorescence elemental analysis (XRF) of

the residue of the solid phase after washing with water, whereby the amount of nickel

matte and the amount of aluminum oxide derived from the ceramic balls were

determined.

[0072]

The total amount of Ni in the solid phase was determined from the amount of

nickel sulfate compound contained in wash water and the amount of nickel matte

contained in the residue. The conversion rate into the nickel sulfate compound was

determined from the ratio between the total amount of Ni in the solid phase and the

amount of nickel sulfate compound contained in wash water. The conversion reaction

was carried out at three predetermined temperatures of 90°C, 120°C, 150°C, and the

results are shown in Table 2.

[0073]

[Table 2]

Elapsed Time 15 min 30 min 60 min 120 min 240 min 0 90 C 5% 15% 23% 40% 62% Conversion 0 Reaction 120 C 27% 41% 60% 81% Temperature 150°C 70% 82% 93% -

[0074]

The results indicate that, as the temperature increases, the efficiency increases

and the conversion rate into the nickel sulfate compound increases. Since the amount

of Al in the sample increases as the time elapses, it is found that Al generated by

abrasion of the ceramic balls is incorporated into the slurry. Furthermore, the rate k

was obtained from the Arrhenius plot based on the results shown in Table 2, and the

following experimental formula was obtained.

[0075]

y = -6232.727x + 11.693, R2 = 0.998

wherein x = l/T (k), and y = In k.

[0076]

From the Arrhenius plot, the conversion rate at 1800 C and 200°C was

calculated. The conversion rate was 91% at 180°C after 15 minutes and 98% at 200°C

after 15 minutes.

[0077]

<Example 2-2>

An aqueous solution (90 mL) containing 102 g/L of FeSO4 and 33 g/L of

H 2 SO4 was heated to 230°C in an autoclave over 60 minutes, and oxygen gas having a

partial pressure of 1.8 MPa was then blown into the aqueous solution. The pressure

increased as the heat was generated, and the pressure was checked at the time when the

temperature returned to equilibrium. This reveals that, while the amount of blown

oxygen gas was 63 mmol, the consumption of oxygen gas in oxidation of Fe(II) was 15 mmol, the reduction of oxygen gas in the gas phase converted from the reduction in partial pressure was 26 mmol. It is thus found that oxygen dissolved in the sulfuric acid aqueous solution at high temperature to cause reaction. At 60 minutes after the first blowing of oxygen gas, the second blowing was performed with the temperature maintained at 230°C. The pressure did not decrease unlike the first blowing, which indicates that the oxidation reaction completely finished only in the first blowing.

[0078]

This test reveals that the oxidation reaction can be carried out by dissolving

oxygen in the aqueous solution in the presence of acidic sulfuric acid. An example in

which FeSO4 is oxidized in dilute sulfuric acid is mentioned here as reference.

However, the oxidation reaction of NiS in concentrated sulfuric acid as in Example 2-1

can also involve supplying oxygen under pressure.

[0079]

<Example 2-3>

A specified amount of commercially available nickel sulfate reagent (99%

pure) powder was measured and placed in 100 g of pure water. Themixturewas

continuously stirred for 10 minutes after reaching a specified temperature. The

resulting solution was sampled, and the amount of dissolved nickel sulfate was

qualitatively analyzed. As a result, the solubility (the value with respect to 100 g of

the solution) of nickel sulfate was obtained as described below.

[0080]

0°C: 22 g, 15°C: 26.5 g, 35°C: 32 g, 50°C: 35 g, 60°C: 37 g

[0081]

The solid matter produced by the conversion step at 150°C in the same

manner as in Example 2-1 was subjected to solid-liquid separation in a pressure filter to provide a sludge having a temperature of 120°C. Fifty grams of the sludge was taken, and 100 g of pure water at 15°C was added to the sludge such that the sludge concentration was 30 wt%, whereby a solution having a temperature of 22°C was obtained. The concentration of Fe ions in the solution obtained after continuous stirring for 30 minutes was analyzed and found to be several tens ppm. Regarding nickel sulfate, 28 g of nickel sulfate, which was close to the saturation solubility at

22°C, was dissolved in 100 gof the solution. This result indicates that impurities are

effectively removed by dissolving highly soluble nickel sulfate in cold water.

Industrial Applicability

[0082]

The present invention can be used to manufacture a high-purity nickel sulfate

compound useful as a raw material of various nickel compounds and metal nickel used

in, for example, electric components of secondary batteries and like, and chemical

products.

Reference Signs List

[0083]

Si Conversion step

S2 Solid-liquid separation step

S3 Dissolution-separation step

S4 Crystallization step

Nickel-containing raw material

11 Mixture

21 Solid phase

22 Liquid phase

31 Solution

32 Impurities

41 Nickel sulfate compound

42 Solution

43 Distillation

44 Water

Organic solvent

Claims (10)

1. A nickel sulfate compound manufacturing method comprising:

a conversion step of converting at least part of a nickel-containing raw

material into a nickel sulfate compound by treating the nickel-containing raw material

with concentrated sulfuric acid in the presence of an abrasive;

a solid-liquid separation step of separating a mixture obtained in the

conversion step into a solid phase and a liquid phase; and

a dissolution-separation step of adding water to the solid phase obtained in the

solid-liquid separation step and dissolving, in the water, the nickel sulfate compound

contained in the solid phase to separate impurities.

2. The nickel sulfate compound manufacturing method according to claim 1,

wherein the nickel-containing raw material in the conversion step contains at least one

selected from the group consisting of nickel oxide, nickel hydroxide, nickel sulfide,

nickel chloride, metal nickel, ferronickel, and nickel ore.

3. The nickel sulfate compound manufacturing method according to claim 1,

wherein in the conversion step, the nickel-containing raw material contains nickel

sulfide, an oxidizing agent is added, and a redox potential is 300 mV or higher.

4. The nickel sulfate compound manufacturing method according to any one of

claims 1 to 3, wherein concentrated sulfuric acid contained in the liquid phase obtained

in the solid-liquid separation step is reused in the conversion step.

5. The nickel sulfate compound manufacturing method according to any one of

claims 1 to 4, wherein in the dissolution-separation step, the water added to the solid

phase has a temperature of from 15°C to 60°C.

6. The nickel sulfate compound manufacturing method according to any one of

claims 1 to 5, wherein in the dissolution-separation step, a solution obtained by dissolving the nickel sulfate compound in the water has a pH of 4 to 5 in separating the impurities.

7. The nickel sulfate compound manufacturing method according to any one of

claims 1 to 6, further comprising a purification step of removing a cobalt compound

contained in the solution obtained in the dissolution-separation step.

8. The nickel sulfate compound manufacturing method according to any one of

claims 1 to 7, further comprising a crystallization step of precipitating a nickel sulfate

compound by adding an organic solvent into the solution obtained in the dissolution

separation step.

9. The nickel sulfate compound manufacturing method according to claim 8,

wherein the organic solvent in the crystallization step is at least one selected from the

group consisting of methanol, ethanol, propanol, isopropanol, butyl alcohol, ethylene

glycol, and acetone.

10. The nickel sulfate compound manufacturing method according to claim 8 or

9, wherein the nickel sulfate compound obtained in the crystallization step is nickel

sulfate hexahydrate.