WO2024261343A1

WO2024261343A1 - Process for preparing a nickel oxide

Info

Publication number: WO2024261343A1
Application number: PCT/EP2024/067692
Authority: WO
Inventors: Werner VERDICKT; Joris ROOSEN
Original assignee: Umicore NV SA
Current assignee: Umicore NV SA
Priority date: 2023-06-22
Filing date: 2024-06-24
Publication date: 2024-12-26
Anticipated expiration: 2025-12-22

Abstract

The present invention provides a process for preparing a nickel oxide, said nickel oxide comprising nickel and at least one of cobalt and manganese, said process comprising the steps of: i. extracting nickel and at least one of cobalt and manganese form a feed solution; ii. stripping an obtained organic phase with hydrochloric acid, thereby obtaining an aqueous solution comprising, respectively, nickel chloride, cobalt chloride and/or manganese chloride; iii. mixing nickel chloride and at least one of cobalt chloride and manganese chloride obtained in step ii. in a predetermined ratio; iv. hydropyrolysis of the aqueous solution formed in step iii. to afford a nickel oxide comprising nickel and at least one of cobalt and manganese, and gaseous hydrochloric acid; v. separating the gaseous hydrochloric acid formed in step iv. from said nickel oxide formed in step iv.; and vi. recycling the gaseous hydrochloric acid obtained in step v. upstream of said hydropyrolysis in step iv.

Description

PROCESS FOR PREPARING A NICKEL OXIDE

TECHNICAL FIELD

The present invention relates to a method for the preparation of a nickel oxide via a hydropyrolysis process.

INTRODUCTION

Advanced electronics have become increasingly important, driving the need for efficient utilization and recovery of valuable metals, such as nickel and cobalt. These metals play a crucial role in the performance and lifespan of various devices and systems. As such, the development of effective methods to recover nickel and cobalt from various sources is of paramount importance, both for environmental preservation and the continued growth of technology-dependent industries. Processes for recovering nickel and cobalt include hydrometallurgical and pyrometallurgical processes. Hydrometallurgical processes involve the use of aqueous solutions to extract the metals, while pyrometallurgical processes use heat and chemical reactions to separate the metals. The application of hydrometallurgical and pyrometallurgical processes can be complementary, depending on factors such as volume and purity of the raw feed, and can further depend on factors such as the need for high efficiency and low environmental impact and high purity of the recovered metals.

Amongst many industry tested methods reported in literature, US 5,571,308 A discloses a method for recovering nickel from high magnesium-containing lateritic ores which also contain iron. The ores which are referred to as saprolitic ores are subjected to leaching with a mineral acid from the group consisting of HCI, H2SO4 and HNO3, HCI being preferred. Following leaching with HCI, the pregnant solution obtained is separated from undissolved solids and the nickel preferably recovered by contacting the solution with a resin selective to nickel absorption. The raffinate remaining which contains iron and magnesium chlorides may be subjected to pyrohydrolysis to produce their respective oxides and free HCI for recycle into the leaching system. The nickel is extracted from the resin using a stripping solution of said acid, and the nickel thereafter extracted from the nickel-loaded stripping solution. More recently, AU 2013/211472 Al described a method for recovering base metal values from oxide ore. The ore includes a first metal selected from the group consisting at least one of iron and aluminium and a second metal selected from the group consisting of at least one of nickel, cobalt and copper. The method includes the steps of: contacting the oxide ore with hydrogen chloride gas to obtain chlorides of the first and second metals and subjecting at least the first and second metals to pyro-hydrolysis at a predetermined temperature to decompose the chlorides of the first metal into oxides. The method also includes the step of mixing the oxides of the first metal and the chlorides of the second metal in an aqueous solution to dissolve the chlorides of the second metal and recovering the dissolved ions of the second metal from the aqueous solution.

Whereas the aforementioned processes are focussed on recovering target metal ions from a raw materials feed, there is yet a further need to convert raw materials comprising nickel in an energy and materials efficient manner into metal oxide materials.

In view of the preparation of nickel oxides, current processes for the refining of nickel sulphate often rely on the crystallization of nickel sulphate, which is a tedious and time-consuming process. More process efficient routes are demanded for.

SUMMARY

The current invention provides a solution for at least one of the above mentioned problems by providing a process for preparing a nickel oxide, as described in claim 1.

The inventive process allows for a straightforward method for the preparation of nickel oxides from an aqueous solution comprising multiple metals. Such compositions can be obtained from refining of raw metal materials, including processes such as leaching and purification of the leachate. Tedious process steps such as crystallizing are avoided. Advantageously, the present invention further allows for recycling of valuable resources such as the extractant which is used in the solvent extraction step, and the stripping agent hydrochloric acid which is used in the stripping of the extractant. These agents are recycled in stoichiometric amounts. DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

As used herein, the following terms have the following meanings:

"A", "an", and "the" as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

"About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/- 20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1% or less, and still more preferably +/-0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

"Comprise," "comprising," and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints. All percentages are to be understood as percentage by weight, abbreviated as "wt.%" or as volume per cent, abbreviated as "vol.%", unless otherwise defined or unless a different meaning is obvious to the person skilled in the art from its use and in the context wherein it is used. Regarding the organic phase following terms are used to identify its components or the whole: i. In the context of the present invention, the term "organic phase" is to be understood as synonymous for the term "solvent" or "solvent mixture" and designates a liquid composition comprising one or more extractants, diluents, and optionally one or more modifiers. ii. The "extractant" or extracting agent is the active component in the organic phase that extracts the metal species to the organic phase by chemically binding with it and forming a metal-extractant complex that is better soluble in the organic phase than it is in the aqueous phase. iii. The "diluent" is an organic molecule or usually a mixture of different organic molecules added to the organic phase to dilute the extractant and allow for dissolution of the metal complexes, improve the physical properties of the organic phase (especially phase-separation phenomena) and decrease its cost, given that diluents are usually cheaper than extractants. Diluents are frequently kerosene fractions and can be aliphatic or aromatic hydrocarbons, naphthenes, etc., or mixtures thereof. The diluent is preferably a kerosenebased petroleum fraction such as Escaid, Elixore, Shellsol, Isopar, etc. iv. The organic phase may also contain a "modifier". A modifier is sometimes added to improve solubility of metal complexes into the organic phase, to alter the physical properties of the solvent such to avoid crud formations or third- phase formation as these phenomena are unwanted in solvent extraction. A modifier can also be added to prevent chemical degradation of extractant or diluent. However, modifiers may impair the selectivity of the organic phase as these may participate in the complex formation of the metals with the extractant.

In a preferred embodiment, the extraction process is concluded by separating the organic phase from the aqueous phase, whereby prior to separation, the aqueous phase is acidified to obtain a pH lower than 5, preferably lower than 4. This is advantageous to obtain a better recovery of residual amounts of organic phase from the aqueous phase.

In the context of the present invention, the term "raw material feed" refers to one or more feedstocks that comprise any one or a combination of nickel, cobalt, manganese, or lithium. Said metals may be included as such or may be included as a compound of the aforementioned metals, or as a mixture of compounds. In some embodiments, said raw material feed may comprise any one or combination of raw materials and recycled materials. Examples of raw materials include, but are not limited to, mixed hydroxide precipitates (MHP), mixed sulphide precipitates (MSP), nickel sulphide concentrate, cobalt sulphide concentrate, nickel laterite, nickel matte, or ferronickel. Examples of recycled materials include, but are not limited to, spent cathode material, and material derived from recycled lithium-ion batteries or lithium-ion battery manufacturing scrap, collectively, referred to herein as 'black mass'.

In the context of the present invention, the term "MHP" is to be considered as an abbreviation of the term "mixed hydroxide precipitate." Mixed hydroxide precipitate (MHP) is an intermediate product of nickel metallurgy derived from processing laterite ores which contains primarily nickel and a minor amount of cobalt. MHP is a solid product which is typically prepared by extracting nickel and cobalt from laterite ores. Alternatively, or additionally, MHP may be obtained from nickel and/or cobalt containing materials produced as production waste during preparation of cathode materials or obtained from battery recycling processes.

In the context of the present invention, the term "CHIP" is to be considered as an abbreviation of the term "cobalt hydroxide intermediate precipitate." Cobalt hydroxide intermediate is comprised primarily of cobalt, and typically has a cobalt content of 25 wt.% to 40 wt.%, relative to the total weight of said intermediate product. Typically, said CHIP comprises a significant amount of nickel. CHIP'S are known to have a very low amount of impurities, which render them attractive for processes according to the present invention.

Said "raw material feed" may refer to a solid feed comprising an MHP product, a CHIP product, or a mixture of two or more MHP products, two or more CHIP products, or a mixture of one or more MHP products and one or more CHIP products. Preferably, said raw material feed comprises at least one nickel compound and at least one cobalt compound. Preferably, said nickel compound and said cobalt compound are comprised as a nickel(II) compound and as a cobalt(II) compound, respectively. Yet, said nickel compound and said cobalt compound may also be comprised in higher oxidation states such as 3+ or 4+, or said metal-containing feed may comprise a mixture of nickel and/or cobalt compounds in oxidation state 2+ and in oxidation state 3+ and/or 4+. In addition, said raw material feed may comprise alloys of nickel (0) and cobalt (0), and/or said raw material feed may comprise one or more ores comprising nickel and cobalt.

In the context of the present invention, the term "continuous process" is to be considered as a process in which the produced solution has a substantially constant outflow and composition. Specifically, a continuous process is a process in which the produced solution has a constant composition within the range of what are considered normal process variations. More specifically, the produced solution has a composition wherein the concentration of each ingredient is within the range of +/-20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/- 3% or less of its average concentration. In a preferred embodiment, the present invention provides a continuous process which operates under steady-state conditions.

In the context of the present invention, the term "aqueous medium" is used for a water-based solution. The aqueous medium facilitates the handling of the contents of the reactor, such as mixing or pumping. The aqueous medium may already contain some of the other ingredients taking part in the reaction, or those can be added later. Said aqueous medium may in particular contain the mineral acid.

In a first aspect, the present invention provides a process for preparing a nickel oxide, said nickel oxide comprising nickel and at least one of cobalt and manganese, said process comprising the steps of: i.

(a) extracting nickel from an aqueous feed solution by solvent extraction using an organic phase comprising an extractant, thereby obtaining an aqueous raffinate and a nickel-rich organic phase; and optionally i .(b) and/or i .(c) :

(b) extracting cobalt from an aqueous feed solution by solvent extraction using an organic phase comprising an extractant, thereby obtaining an aqueous raffinate and a cobalt-rich organic phase; and (c) extracting manganese from an aqueous feed solution by solvent extraction using an organic phase comprising an extractant, thereby obtaining an aqueous raffinate and a manganese-rich organic phase; ii. stripping said nickel-rich and optionally said cobalt- and manganese-rich organic phases with hydrochloric acid, thereby obtaining an aqueous solution comprising, respectively, nickel chloride, cobalt chloride and manganese chloride; iii. mixing nickel chloride and at least one of cobalt chloride and manganese chloride in a predetermined ratio; iv. hydropyrolysis of the aqueous solution formed in step iii. to afford a nickel oxide comprising nickel and at least one of cobalt and manganese, and gaseous hydrochloric acid; v. separating the gaseous hydrochloric acid formed in step iv. from said nickel oxide formed in step iv.; and vi. recycling the gaseous hydrochloric acid obtained in step v. upstream of said hydropyrolysis in step iv.

The extraction of nickel and at least one of cobalt and manganese may be selected of the group comprising, but not limited to:

- carboxylic acid extractants, such as versatic acid. These acids form complex ions with nickel ions, which can then be separated from the aqueous phase.

- amine extractants, such as di-2-ethylhexyl amine (DEHA), Alamine 336 and Aliquat 336. These extractants also form complex ions and are specifically suitable for extracting cobalt and manganese ions, which can then be separated from the aqueous phase.

- organophosphorus extractants such as Cyanex 272, PC88A, D2EHPA and alkylphosphine oxides such as tri-n-butylphosphine oxide (TNBP).

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said extractant used in step i. comprises an alkylphosphorus-based acid and/or nickel and/or cobalt and/or manganese salts thereof, preferably nickel salts thereof. Suitable alkylphosphorus-based acids include bis(2-ethylhexyl) phosphoric acid (D2EHPA), (2-ethylhexyl) phosphonic acid mono(2- ethylhexyl) ester (EHEHPA, PC88A), bis-(2,4,4-trimethylpentyl) phosphinic acid (CYAN EX272 or IONQUEST 290) and diisooctylphosphinic acid (DOPA). Alkylphosphorus- based acids act as chelating extractants due to the presence of coordinative phosphorus and oxygen atoms in these molecules. Among the elements in the aqueous solution, an element that forms the corresponding chelate compound with a higher stability facilitates the extraction efficiency more compared to an element that is less likely to form the chelate compound. Alkylphosphorus-based extractants may be chosen from, but are not limited to, the following options:

- alkylphosphoric acids, such as di-(2-ethylhexyl) phosphoric acid (also known as D2EHPA, DEHPA, HDEHP, P204), an organophosphorus compound with the formula (CsH I?O)2PO2H .

- alkylphosphonic acids, such as 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (also known as EHEHPA, HEHEHP, P507, PC88A), an organophosphorus compound with the formula R.1 = (CsHi?) (C8Hi7O)PO2H.

- alkylphosphinic acids, such as bis-(2,4,4-trimethylpentyl) phosphinic acid (also known as Cyanex 272, lonquest 290), an organophosphorus compound with the formula (C16H34) PO2H .

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the metal-rich organic phase, e.g., the nickel-rich, the cobalt-rich and the manganese-rich organic phase, respectively, is stripped in step ii. with hydrochloric acid, preferably with an aqueous hydrochloric acid. This effectively results in the elution of nickel, and if applicable cobalt and manganese, from the respective solvents. As a result, a first aqueous solution comprising nickel chloride is obtained, and one or both of an aqueous solution comprising cobalt chloride and an aqueous solution comprising manganese chloride are obtained, respectively, each in a relatively high concentration. The concentration of nickel in the aqueous nickel chloride solution is between 40 and 180 g/L, preferably between 100 and 180 g/L. The stripping step can be performed in any device suitable and is not specifically limited. Stripping equipment generally includes at least one or more devices consisting of a mixer-settler, a column contactor, a centrifugal contactor or any other type of contactor. Preferably, the stripping is performed in a counter-current configuration. Preferably, said stripping step ii. is performed at a temperature between 40 °C and 60 °C, preferably between 40 °C and 50 °C, and more preferably at a temperature of about 45 °C. In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, further comprising the step of adjusting the composition of said aqueous solution obtained in the stripping step, step ii ., by adding a nickel salt, a cobalt salt and/or a manganese salt.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the obtained nickel chloride solution, and at least one of the obtained cobalt chloride solution and the obtained manganese chloride solution are mixed to form an aqueous metal chloride solution having a predetermined composition, prior to feeding said aqueous solution to said hydropyrolysis in step iv. Preferably, said nickel salt, said cobalt salt and/or said manganese salt are chloride salts. Preferably, said salts are added until a predetermined atom-ratio between nickel, cobalt and manganese is achieved. E.g., nickel chloride and manganese chloride may be added to a solution of nickel chloride and cobalt chloride until an aqueous solution with a desired atom-ratio is achieved. Alternatively, cobalt chloride may be added to a solution comprising nickel chloride to achieve a desired ratio nickel : cobalt.

Furthermore, the present invention provides a process according to the first aspect of the invention, whereby the composition of the aqueous solution which is obtained in step ii. is further adjusted by adding one or more dopants selected from the group consisting of: fluorine, aluminium, tungsten, chromium, zirconium, molybdenum, and vanadium, prior to feeding said aqueous solution in the hydropyrolysis step iv.

Preferably, the stripping step in step ii. further comprises the step of regenerating the organic phase with the organic extractant. The organic phase with the organic extractant is subsequently recycled to step i.

The aqueous solution obtained in step ii., as such or after adjusting the atom ratio between nickel, cobalt and manganese, and/or after doping, is subjected to a hydropyrolysis process in step iv. The solution is introduced in the hydropyrolysis furnace at a temperature of 400 to 800°C, preferably at a temperature between 400 and 650°C and more preferably between 450 and 600°C, with a residence time ranging from 1 minute to 30 minutes, at a pressure between 1 and 10 atm. Next to the hydropyrolysis step iv., the obtained nickel oxide comprising nickel and at least one of cobalt and manganese is collected as a solid precipitate. The solid precipitate is separated from the gaseous atmosphere above. However, not all particulate formed has the same particle size, and particles with smaller size will remain entrained in the gaseous phase comprising further also hydrochloric acid gas. Thus, the atmosphere above the collected solids comprises gaseous hydrochloric acid and a fine particulate comprising nickel oxide, said fine particulate being suspended in the gaseous atmosphere. Accordingly, in a preferred embodiment of the present invention, the fine particulate is separated from the hydrochloric acid. The inventors found that residual amounts of nickel oxide may interact with the extractant present in the organic phase, and may lead to the degradation of the extractant. As such, extraction of nickel, cobalt or manganese, respectively, in a subsequent extraction cycle would be hampered and would lead to product losses.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein fine nickel oxide particles entrained in the gaseous hydrochloric acid are sequestered from said hydrochloric acid using a cyclone separator. The inventors propose a concept whereby the gas stream is tangentially introduced into a cylindrical chamber, generating a centrifugal force that separates the fine oxide particles from the gas stream.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein fine nickel oxide particles entrained in the gaseous hydrochloric acid are sequestered from said hydrochloric acid and are recycled back to the hydropyrolysis reactor to ensure their incorporation into the final nickel oxide product. Removal of fine particulate in the cyclone separator before further processing of the off-gasses in the venturi scrubber is important to limit the amount of metal chlorides that is dissolved in the feed solution used in the venturi scrubber, and thereby limiting the potential for uncontrolled or unwanted crystallization.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the exhaust gases from the cyclone separator having a residual amount of fine nickel oxide particles which were not yet re- moved by the cyclone separator, are contacted with a circulating feed solution comprising nickel chloride and at least one of cobalt chloride and manganese chloride in a venturi scrubber. This has several advantages: (i) entrained metal oxide particles react with hydrochloric acid to form a metal chloride, water and chlorine gas; (ii) gaseous HCI is partially washed out and dissolved in the aqueous phase, thereby reducing the solubility of the metal chloride(s), allowing for crystallization.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the venturi scrubber heats the circulating feed solution, typically having a metal concentration of 160 to 200 g metal per litre, to a temperature of 90 to 99 °C, preferably 90 to 95 °C, facilitating the dissolution of fine metal oxide particles into the feed solution and forming a concentrated metal chloride solution. At these temperatures, crystallization of the metal chlorides is avoided. In one embodiment, the metal chloride solution may be concentrated to a concentration of about 220 to 260 g metal per litre, which is beneficial if crystallization at room temperature is envisaged as a next step. Preferably, the concentrated metal chloride solution from the venturi scrubber is recirculated through the venturi to further enhance particulate removal and feed solution concentration.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the exhaust gases exiting the venturi scrubber are subjected to an off-gas treatment system comprising an HCI column. The HCI column operates as a packed scrubber with counterflow scrubbing preferably using demineralized water to absorb hydrochloric acid vapours and further remove fine metal oxide particles from the gas stream. Preferably, the scrub solution is recycled to the top of the HCI column until HCI is concentrated to a desired concentration, such as e.g. about 200 g HCI per litre, which would form an acidic solution suitable for leaching electrolytically formed nickel or cobalt.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the exhaust gases exiting the venturi scrubber are subjected to an off-gas treatment system comprising an HCI column and at least one scrubber, to remove any remaining hydrochloric acid, chlorine gas, and fine metal oxide particles. Further, a catalyst column may be provided. Advantageously, the process according to the present invention ensures that hydrochloric acid is fully recycled within a closed loop. As such, there is no substantial need for feeding hydrochloric acid to the process. The recycling of gaseous hydrochloric acid and fine nickel oxide particulates enhances the sustainability of the process by reducing the need for fresh reagents and minimizing environmental impact. Also, the heat exchange in the venturi scrubber enhances energy efficiency by utilizing the heat from exhaust gases to preheat the feed solution, reducing overall energy consumption. The combination of cyclone separators and venturi scrubbers ensures thorough removal of fine particulates, improving the quality of the final nickel oxide product. In conclusion, the inventive process provides a comprehensive and efficient method for preparing high-purity nickel oxide comprising nickel and at least one of cobalt and manganese, with an emphasis on sustainability and environmental responsibility.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the gaseous hydrochloric acid obtained in step v. is used as a stripping agent for stripping the metal-rich organic phase in step ii. Preferably, the gaseous hydrochloric acid is dissolved in water to form an aqueous solution comprising hydrochloric acid. Recovering hydrochloric acid from the hydropyrolysis step is advantageous since the total amount of hydrochloric acid necessary for stripping of the metals in the organic phase corresponds to the total amount of hydrochloric acid which is liberated in the hydropyrolysis step i. As such, a fully closed circuit can be realized. Preferred processing units for separating the gaseous hydrochloric acid from said nickel oxide are cyclone separators and fabric filters. Cyclone separators use a centrifugal force to separate particles from a gas stream. Fabric filters use a porous fabric or membrane to capture particles as they pass through. Fabric filters are most preferably used because of their high collection efficiency for fine particulates and low pressure drop.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein a nickel oxide particulate entrained in the gaseous hydrochloric acid phase is sequestered from said hydrochloric acid using a cyclone separator. This allows to remove all nickel oxide from the gaseous phase comprising hydrochloric acid and avoids that the extractant in the organic phase gets oxidized. As such degradation of the extractant and/or the organic phase is avoided. In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the gaseous hydrochloric acid obtained in step v. is absorbed in water and is subsequently used for leaching nickel and cobalt and/or manganese from a raw materials feed prior to solvent extraction in step i. This is advantageous since there is no need for separating any entrained nickel oxide in the gaseous hydrochloric acid phase.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said aqueous feed solution is obtained by leaching a raw materials feed in an aqueous medium using a mineral acid to obtain an aqueous solution comprising a multitude of metal ions, and subsequently reducing the amount of one or more impurities in said aqueous solution comprising said multitude of metal ions, whereby said impurities are selected from the group consisting of aluminium, iron, copper, zinc, cadmium, sodium and lithium. Preferably, said raw materials feed is leached in an aqueous medium using hydrochloric acid. One or more of said impurities may be removed by precipitation after neutralizing and/or basifying the aqueous solution obtained after leaching. One or more of said impurities may be removed by selective solvent extraction.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the hydropyrolysis in step iv. is performed with an aqueous solution comprising nickel, cobalt, and manganese chloride to afford a nickel-manganese-cobalt oxide and hydrochloric acid, according to the general reaction:

wherein MeC = x NiC + y C0CI2 + z MnC , wherein x + y + z = 1, and wherein 0 < x < 1.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the aqueous feed solution comprising nickel and at least one of cobalt and manganese is obtained from metal leaching with hydrochloric acid. In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein the aqueous feed solution comprising nickel and at least one of cobalt and manganese is obtained from metal leaching with sul- phuric acid.

Claims

1. A process for preparing a nickel oxide, said nickel oxide comprising nickel and at least one of cobalt and manganese, said process comprising the steps of: i.

(a) extracting nickel from an aqueous feed solution by solvent extraction using an organic phase comprising an extractant, thereby obtaining an aqueous raffinate and a nickel-rich organic phase; and optionally (b) and/or (c):

(b) extracting cobalt from an aqueous feed solution by solvent extraction using an organic phase comprising an extractant, thereby obtaining an aqueous raffinate and a cobalt-rich organic phase; and

(c) extracting manganese from an aqueous feed solution by solvent extraction using an organic phase comprising an extractant, thereby obtaining an aqueous raffinate and a manganese-rich organic phase; ii. stripping said nickel-rich and optionally said cobalt- and/or manganese- rich organic phases with hydrochloric acid, thereby obtaining an aqueous solution comprising nickel chloride, and one or both of an aqueous solution comprising cobalt chloride and an aqueous solution comprising manganese chloride; iii. mixing the aqueous solution comprising nickel chloride and at least one of an aqueous solution comprising cobalt chloride and an aqueous solution comprising manganese chloride obtained in a predetermined ratio; iv. hydropyrolysis of the aqueous solution formed in step iii. to afford a nickel oxide comprising nickel and at least one of cobalt and manganese, and gaseous hydrochloric acid; v. separating the gaseous hydrochloric acid formed in step iv. from said nickel oxide formed in step iv.; and vi. recycling the gaseous hydrochloric acid obtained in step v. upstream of said hydropyrolysis in step iv. wherein fine nickel oxide particles entrained in the gaseous hydrochloric acid are sequestered from said hydrochloric acid and are recycled back to the hydropyrolysis reactor.

2. Process according to claim 1, wherein fine nickel oxide particles entrained in the gaseous hydrochloric acid are sequestered from said hydrochloric acid using a cyclone separator.

3. Process according to claim 2, wherein the exhaust gases from the cyclone separator, including a residual amount of fine nickel oxide particles, are contacted with a circulating feed solution comprising nickel chloride and at least one of cobalt chloride and manganese chloride in a venturi scrubber.

4. Process according to claim 3, wherein the venturi scrubber heats the circulating feed solution to a temperature between 90 and 99 °C, facilitating the dissolution of fine metal oxide particles into the feed solution and forming a concentrated metal chloride solution.

5. Process according to claim 3 or 4, wherein the exhaust gases exiting the venturi scrubber are subjected to an off-gas treatment system comprising an HCI column and at least one scrubber to remove any remaining hydrochloric acid, chlorine gas, and fine nickel oxide particles.

6. Process according to any of claims 1 to 5, wherein the gaseous hydrochloric acid obtained in step v. is used, optionally after dissolving the gaseous hydrochloric acid in water, as a stripping agent for stripping a metal-rich organic phase in step ii.

7. Process according to any of claims 1 to 6, wherein the extractant used in step i.(a), step i.(b) and/or step i . (c) is selected from the group consisting of carboxylic acids, alkylphosphoric acids, alkylphosphonic acids, alkylphosphinic acids, and salts thereof.

8. Process according to any of claims 1 to 7, wherein the gaseous hydrochloric acid obtained in step v. is used, optionally after dissolving the gaseous hydrochloric acid in water, for leaching nickel and cobalt and/or manganese from a raw materials feed prior to solvent extraction in step i.

9. Process according to any of claims 1 to 8, further comprising the step of adjusting the composition of said aqueous solution obtained in step iii. by adding a nickel salt, a cobalt salt and/or a manganese salt to achieve a predetermined composition, prior to feeding said aqueous solution to said hydropyrolysis in step iv.

10. Process according to any of claims 1 to 9, whereby the composition of the aqueous solution which is fed to the hydropyrolysis step iv. is further adjusted by adding one or more dopants selected from the group consisting of: fluorine, aluminium, tungsten, chromium, zirconium, molybdenum, and vanadium.

11. Process according to any of claims 1 to 10, whereby said aqueous feed solution provided in step i.(a), i .(b) and/or i .(c) is obtained by leaching a raw materials feed in an aqueous medium using a mineral acid to obtain an aqueous solution comprising a multitude of metal ions, and subsequently reducing the amount of one or more impurities in said aqueous solution comprising said multitude of metal ions, whereby said impurities are selected from the group consisting of aluminium, iron, copper, zinc, cadmium, sodium and lithium.

12. Process according to any of claims 1 to 11, wherein the hydropyrolysis process in step iv. is performed at a temperature between 450°C and 650°C.

13. Process according to any of claims 1 to 12, wherein the hydropyrolysis in step iv. is performed with an aqueous solution comprising nickel chloride, cobalt chloride and manganese chloride.

14. Process according to any of claims 1 to 13, wherein the aqueous feed solution comprising nickel and at least one of cobalt and manganese is obtained from metal leaching with hydrochloric acid.

15. Process according to any of claims 1 to 14, wherein the aqueous feed solution comprising nickel and at least one of cobalt and manganese is obtained from metal leaching with sulphuric acid.