WO2024231491A1

WO2024231491A1 - Copper-catalyzed leaching of a raw material containing nickel and iron

Info

Publication number: WO2024231491A1
Application number: PCT/EP2024/062825
Authority: WO
Inventors: Bart KLAASEN; Werner VERDICKT
Original assignee: Umicore
Priority date: 2023-05-11
Filing date: 2024-05-08
Publication date: 2024-11-14

Abstract

The present invention provides a process for the selective separation of iron from a raw material containing nickel and iron, comprising the steps of:  contacting the raw material containing nickel and iron with an acid solution thereby obtaining a leach solution containing iron and nickel, and a residue containing a major part of the iron;  adding a copper containing material to the leach solution and/or to the raw material containing nickel and iron, thereby precipitating the iron in the leach solution; and  separating the leach solution from the residue.

Description

COPPER-CATALYZED LEACHING OF A RAW MATERIAL CONTAINING NICKEL AND IRON

TECHNICAL FIELD

The present invention relates to a process for the selective copper-catalysed leaching of a raw material containing nickel and iron.

INTRODUCTION

In traditional schemes for processing raw materials containing iron and nickel, iron is first dissolved in a leaching operation and subsequently removed from solution in a downstream iron removal. For example, when leaching alloyed powder using sulphuric acid in the presence of oxygen, iron is first dissolved as ferrous sulphate during leaching according to the reaction:

Fe + H2SO4 + % O2 FeSO4 + H2O.

Subsequently the iron can be removed from solution by further oxidation and precipitation , for example as ferric oxyhydroxide according to:

Acid released during the precipitation of iron is typically neutralized, for example using Ca(OH)2 or NaOH and transformed into CaSO4 or Na2SO4 salts:

H₂SO₄ + Ca(OH)₂ CaSO₄ + 2 H₂O or

In such a traditional scheme, iron first consumes a stoichiometric amount of acid during leaching. In the subsequent iron removal operation, this acid is neutralized with caustic compounds such as carbonates or hydroxides of Na, K, Mg, Ca, Li, or ammonia. The reaction products are often ammonium salts, alkali salt or earth-alkali salt. These reaction products can end up in the product solution, introducing additional impurities like Na, K, Mg, Ca, Li, NH4. Alternatively, these reaction products end up in the iron residue, introducing additional impurities and increase the mass of this residue, which is often considered as a waste product. Ferronickel is a widely available raw material containing primarily iron in an amount of about 75 wt.% and nickel in an amount of about 25 wt.%. Due to its high iron content, hydrometallurgical processing into high purity nickel products remains challenging. Leaching and precipitation by hydrolysis requires a large consumption of neutralizing agents. A further disadvantage is the introduction of Ca/Na into the solution. Finally, large volumes of iron residues are generated.

These drawbacks can however be eliminated when applying a selective leaching process in which only nickel is dissolved, while iron stays in the residue. Therefore, there is still a need for selective iron removal from raw materials containing nickel and high amounts of iron, such as 50 wt.% or more as compared to the total weight of the raw material. WO 2022/140863 Al presents processes and methods for refining ferronickel alloy, and producing nickel sulfate or other nickel product, are provided, where the ferronickel alloy is treated with an oxidizing leach. The oxidizing leach may be, for example, a pressure oxidation (POX) leach or a leach with peroxide or copper (II) ions. The treatment may be in the presence of added copper, such as by providing a copper sulfate solution. Producing nickel sulfate may comprise removing copper and iron after the leach, removing impurities, and either crystallizing the nickel sulfate or precipitating/winning another nickel product. Yet, such processes and methods require harsh conditions such as pressure oxidation, which proceeds usually at a pressure of 15 to 50 bar and at a temperature between 160°C and 230°C, and/or proceed in presence of harsh reagents such as hydrogen peroxide. There is thus a need for new processes and methods that allow for selectively removing iron from iron-nickel alloys under mild conditions, while maintaining a high selectivity.

Moreover, there is a need for the production of battery-grade nickel sulphate solutions from raw-materials that only contain low amounts of nickel and high amounts of iron, such as ferronickel.

SUMMARY

The inventors have surprisingly found that the addition of a copper containing material to a raw material containing nickel and iron or to a leach slurry of a raw material containing nickel and iron and an acid solution enables the selective separation of the iron, particularly if the raw material contains high amounts of iron such as ferronickel. Thus, the inventors further found that through the addition of copper ferronickel can be effectively used as a source for high quality nickel sulphate solutions such as required in battery production.

The inventors found that the iron precipitation is accelerated by the copper under relatively mild reaction conditions. The released acid can be consumed by additional nickel dissolution. Accordingly, a first aspect of the invention is a process for the selective separation of iron from a raw material containing nickel and iron, wherein said raw material containing nickel and iron contains at least 5 wt.% nickel and at most 95 wt.% iron, relative to the total weight of said raw material, said process comprising the steps of: i. contacting the raw material containing nickel and iron with an acid solution, thereby obtaining a leach solution containing iron and nickel, and a residue containing at least 50 wt.% of iron, relative to the total amount of iron in said raw material, whereby at least 50 wt.%, at least 75 wt.% or even at least 90 wt.%, of said iron in said residue is comprised as an iron hydroxide; ii. adding a copper containing material, preferably in an amount of 0.25 to 50 g copper per litre of the leach solution, preferably a water-soluble copper salt, such as copper chloride or copper sulphate to the leach solution and/or to the raw material containing nickel and iron, thereby precipitating the iron in the leach solution; and iii. separating the leach solution from the residue.

Iron hydroxide precipitate is formed under mild leaching conditions in step i. in the same reactor, which is easily separated from the liquid phase by filtration or decantation or the like. Copper can be added upfront or during the leaching reaction to accelerate the formation of iron precipitate in the reactor. There is no need to transfer the contents of the reactor in step i. to a second reactor to proceed with step ii. Under harsh leaching conditions such as at higher temperatures, i.e. temperatures above 125°C, and/or at higher pressures, i.e. pressures above 15 bar or even above 20 bar or even above 30 bar, and/or in presence of peroxides such as hydrogen peroxide, iron in the leaching solution forms an iron oxide precipitate, also known as hematite. In a preferred embodiment, said raw material containing nickel and iron is contacted with an acid solution under oxidizing conditions. Preferably, said raw material con- taining nickel and iron is contacted with an acid solution in presence of a mild oxidizing agent, such as but not limited to air, oxygen. Preferably, said raw material containing nickel and iron is contacted with an acid solution in absence of a harsh oxidizing agent, such as peroxides, e.g. hydrogen peroxide. Alternatively, said raw material containing nickel and iron is contacted with an acid solution in presence of an oxidizing agent, such as but not limited to air, oxygen and hydrogen peroxide.

In another aspect, the acid, preferably sulphuric acid or hydrochloric acid, is dosed in a stoichiometric amount to the amount of nickel.

In another aspect, the acid is hydrochloric acid and the copper containing material is preferably copper chloride.

In another aspect, the acid is sulphuric acid and the copper containing material is preferably copper sulphate.

In a preferred embodiment, steps i., ii. and iii. are performed at a pressure below 10 bar, or below 5 bar, or at about atmospheric pressure, i.e., about 1 bar, or at an under-pressure of less than 0.2 bar, or less than 0.1 bar, or even less than 0.05 bar or even less than 0.02 bar. Since none of the steps of the process need to proceed at high temperatures, the present invention provides advantages over the prior art in that the reactor, or column reactor, may be equipped also equipped with an overflow conduct preferably provided with means for a solid-liquid separation. The primary object of this solid-liquid separation is removal the solid residue containing iron hydroxide from solution. This solid-liquid separation can be done by filtration, centrifugation, decantation or a combination thereof.

In another aspect, the raw material containing nickel and iron contains nickel in an amount of at least 0.5 wt.%, preferably at least 1 wt.%, more preferably 2 wt.% and even more preferably at least 5 wt.% or even at least 10 wt.%, relative to the total weight of said raw material. Preferably, the raw material containing nickel and iron contains at most 99.5 wt.% iron, relative to the total weight of said raw material, more preferably at most 99 wt.%, or at most 98 wt.%, or at most 95 wt.% or even at most 90 wt.%. Preferably, the raw material containing nickel and iron may contain copper. Preferably, said raw material contains copper in an amount of not more than 10 wt.%, preferably not more than 5 wt.%, more preferably not more than 2 wt.% and even more preferably not more than 1 wt.%. Most preferably, the amount of copper in said raw material is less than 0.5 wt.% or even less than 0.2 wt.%.

In another aspect, the raw material containing nickel and iron further contains metals, preferably cobalt in an amount from 0.1 wt.% to 10 wt.%, even more preferably from 0.5 wt.% to 5 wt.%, even more preferably from 1 wt.% to 3 wt.%.

In another aspect, the copper containing material is added in an amount of copper from 0.5 g /I to 25 g/L, preferably from 1 g/L to 22.5 g/L, even more preferably from 2 g/L to 20 g/L relative to the amount of the leach solution.

In another aspect, the copper containing material is added at the start or after an initial reaction time, preferably after 1 hour to 10 hours, more preferably after 2 hours to 8 hours from the start of the reaction.

In another aspect, the raw material containing iron and nickel is

■ in the form of chunks, plates or spheric particles, preferably pellets, shots or granules; or

■ size-reduced by milling, preferably by high-shear milling.

■ size-reduced by atomization, either gas or water based atomization. This can be done either during the production of the raw material or after re-melting.

In another aspect, the raw material containing nickel and iron, especially when obtained by atomization or milling, has a particle size distribution with a D50 of 10 pm to 1500 pm, preferably from 50 pm to 800 pm even more preferably 100 to 500 pm, as determined by sieving. Such a particle size distribution facilitates processing of the raw material in a stirred reactor.

In another aspect, the raw material containing nickel and iron is contacted with the acid solution in oxidizing conditions, preferably by the addition of an O2-bearing gas such as air or oxygen-enriched air and/or an CI2 bearing gas. In another aspect, the reaction temperature is from 50 °C to 95 °C, more preferably from 70 °C to 90 °C, even more preferably from 75 °C to 85 °C.

In another aspect, the raw material containing nickel and iron, especially when in the form of shots or granules, is reacted with the acid solution in a tower or column reactor.

In another aspect, the pH of the leach solution prior to separation from the residue is adjusted to allow for a solubility of iron of at most 10 g/L.

In another aspect, the process comprises the subsequent steps of treating the leach solution comprising nickel and residual soluble iron in a further reactor by acidification and oxidation.

Another aspect is the use of the residue obtained according to the process of the invention as a starting material for steel-making.

DESCRIPTION OF THE FIGURES

By means of further guidance, figures are included to better appreciate the teaching of the present invention. Said figures are intended to assist the description of the invention and are nowhere intended as a limitation of the presently disclosed invention.

The figures and symbols contained therein have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Figure 1 shows the oxidation reduction potential (ORP, measured in mV vs Ag/AgCI), the temperature (in °C) and the amount of a 500 g/L sulphuric acid solution (in mL) added to the system on the left vertical axis and the pH on the right vertical axis in function of the time of example 1.1 - Leaching ferronickel in H2SO4 with CuSCU addition. Figure 2 shows the concentrations of metals in solution of example 1.1 - Leaching ferronickel in H2SO4 with CuSO4 addition.

Figure 3 shows the oxidation reduction potential (ORP, measured in mV vs Ag/AgCI), temperature (in °C) and the amount of a 37 wt.% hydrochloric acid solution (in mL) on the left vertical axis and the pH on the right vertical axis in function of the time of example 1.2 - Leaching ferronickel in HCI with CuCh addition.

Figure 4 shows the concentrations of metals in solution of example 1.2 - Leaching ferronickel in HCI with CuCh addition.

Figure shows the oxidation reduction potential (ORP, measured in mV vs Ag/AgCI), temperature (in °C) and the amount of a 37 wt. % hydrochloric acid solution (in mL) on the left vertical axis and the pH on the right vertical axis in function of the time of example 1.5-HL-ARC0235: selective leaching of size-reduced ferronickel in HCI.

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.

Raw material containing nickel and iron

The present invention concerns a process for the selective separation of iron from a raw material containing nickel and iron. The composition of the raw material containing nickel and iron may vary widely. The present inventors surprisingly found that through the addition of copper, iron can be selectively separated from raw materials that contain high amounts of iron and nickel.

Preferably, the raw material containing nickel and iron contains nickel in an amount of at least 0.5 wt.%, preferably at least 1 wt.%, more preferably 2 wt.% and even more preferably at least 5 wt.% or even at least 10 wt.%, relative to the total weight of said raw material. Preferably, the raw material containing nickel and iron contains at most 99.5 wt.% iron, relative to the total weight of said raw material, more preferably at most 99 wt.%, or at most 98 wt.%, or at most 95 wt.% or even at most 90 wt.%. Preferably, the raw material containing nickel and iron may contain copper. Preferably, said raw material contains copper in an amount of not more than 10 wt.%, preferably not more than 5 wt.%, more preferably not more than 2 wt.% and even more preferably not more than 1 wt.%. Most preferably, the amount of copper in said raw material is less than 0.5 wt.% or even less than 0.25 wt.%.

In one embodiment, the raw material containing nickel and iron contains at least 50 wt.% iron.

In one embodiment, the raw material containing nickel and iron contains iron in an amount from 60 wt.% to 90 wt.%, preferably from 70 wt.% to 80 wt.%.

In one embodiment, the raw material containing nickel and iron contains nickel in an amount from 10 wt.% to 40 wt.%, preferably from 20 wt.% to 30 wt.%.

In a preferred embodiment, the raw material containing nickel and iron does not contain any copper or only contains a very low amount of copper, such as from 0.001 wt.% to 1 wt.%, preferably from 0.01 wt.% to 0.5 wt.%, even more preferably from 0.05 to 0.25 wt.% before the addition of the copper containing material.

In one embodiment, the raw material containing nickel and iron contains further metals other than copper in an amount from 0.1 wt.% to 10 wt.%, even more preferably from 0.5 wt.% to 5 wt.%, even more preferably from 1 wt.% to 3 wt.%.

In one embodiment, the raw material containing nickel and iron contains cobalt in an amount from 0.1 wt.% to 10 wt.%, even more preferably from 0.5 wt.% to 5 wt.%, even more preferably from 1 wt.% to 3 wt.%.

In one embodiment, the raw material containing nickel and iron is ferronickel or nickel pig iron.

Preferably, the raw material containing nickel and iron contains nickel and iron in a metallic state characterized by an oxidation state of zero, more preferably at least 80 wt.% of nickel and iron are contained in the metallic state, or even at least 90 wt.%, or even at least 95 wt.%, or at least 98 wt.% or at least 99 wt.%. In one embodiment, the raw material containing iron and nickel is in the form of chunks, plates or spherical particles, preferably pellets. In one embodiment, raw material is contained as particles or pellets, and the spherical particles have a diameter of from 0.1 to 5 cm, preferably from 0.1 to 1 cm, and even more preferably from 0.25 to 0.75 cm.

Size-reduction

The inventors found that upfront size-reduction improves the reactivity and the efficiency of the selective iron removal through the addition of copper.

Accordingly, in one embodiment, the raw material containing iron and nickel is size- reduced, preferably by milling. The inventors found that milling enables the use of stirred reactors.

In a preferred embodiment, the raw material containing iron and nickel is size-reduced by high-shear milling techniques. High shear mills are preferred in case of ductile properties of raw materials containing nickel and copper such as ferronickel.

In another embodiment, the raw material containing iron and nickel is size-reduced by atomization, either gas or water based atomization. This can be done either during the production of the raw material or after re-melting.

In one embodiment, the raw material containing nickel and iron is size-reduced to 10 pm to 1500 pm, preferably from 50 pm to 800 pm even more preferably 100 pm to 500 pm, as determined by sieving.

Addition of a copper containing material

The inventors have found that the addition of a copper containing material to the raw material containing nickel and iron or to the leach solution enables a selective separation of the iron of any raw material that contains high amounts of iron, such as for example 75 wt.% iron and nickel in low amounts such as 25 wt.%.

The copper containing material comprises elemental copper, Cu⁺ and/or Cu²⁺. In a preferred embodiment, copper containing material comprises copper in an amount of at least 1 wt.%, preferably at least 2 wt.% or even at least 5 wt.% and more preferably at least 10 wt.%, at least 20 wt.%, at least 50 wt.%, at least 80 wt.% or at least 90 wt.%. Said copper containing material may further comprise nickel. In one embodiment, the copper containing material is copper chloride (CuCh). This is advantage if the acid is hydrochloric acid.

In one embodiment, the copper containing material is copper sulphate (CuSCU). This is advantageous if the acid is sulphuric acid.

In one embodiment, the copper containing material is added in an amount of copper from 0.25 g/L to 25 g/L, preferably from 0.5 g/L to 20 g/L, even more preferably from 1 g/L to 15 g/L.

In one embodiment, the copper containing material is added at the start of the leach reaction.

In one embodiment, the copper containing material is added after an initial reaction time, preferably after 1 hours to 10 hours, more preferably after 2 hours to 8 hours from the start of the reaction.

Leach solution

The leach solution containing iron and nickel is obtained by contacting the raw material containing nickel and iron with an acid solution.

In a preferred embodiment, the pH at the outlet is adjusted, i.e. increased, to ensure a reduced solubility of iron, specifically to allow for a solubility of iron of at most 10 g/L.

Separation

The leach solution is separated from the residue, for example by filtration.

In a preferred embodiment, a further purification step reduces the concentration of impurities selected from the list comprising Cu, Zn, Co, Mn, Al, F, C, Ca, Si, P, As, Cd, Sb and Mg for example by the addition of a base. Preferably, said base is added until the pH of the leach solution is between 2 and 5, preferably between 2.5 and 4.8, and more preferably between 3.0 and 4.5.

Reaction temperature

In one embodiment, the reaction temperature is from 50 °C to 95 °C, more preferably from 70 °C to 90 °C, even more preferably from 75 °C to 85 °C. Oxygen-sources, agitation or circulation

In a preferred embodiment, the raw material containing nickel and iron is contacted with the acid solution in oxidizing conditions, preferably by the addition of O2 and/or an 02-bearing gas such as air or enriched air, and/or a CI2 bearing gas.

In one embodiment, the leach solution is agitated. Agitation is advantageous when the raw-material has been size-reduced by milling or by atomization.

In one embodiment, the leach solution is circulated. Circulation is advantageous when the raw material containing nickel and iron is coarse, such as pellets.

Acid solution

The acid in the acid solution preferably is sulphuric acid or hydrochloric acid.

In a preferred embodiment, the acid is dosed in a stoichiometric amount relative to the total amount of nickel, cobalt and copper.

The inventors found that residual iron in the leach solution is caused by too much acid allowing for more iron in the leach solution.

The inventors found that the use of a stoichiometric amount of acid relative to the total amount of nickel, cobalt and copper decreases the residual iron in the leach solution.

Pressure

In a preferred embodiment, the leach reaction is carried out at atmospheric pressure, i.e. 1 bar, or at an under-pressure of less than 0.2 bar, preferably less than 0.1 bar, and more preferably less than 0.05 bar or even less than 0.02 bar.

Preferably, the leach solution is contacted with the raw material containing nickel and iron under an atmosphere of oxygen, air, oxygen-enriched air or chlorine gas. Tower reactor

Unless the raw material is milled or atomised, the raw material containing nickel and iron is reacted with the acid solution in a tower or column reactor.

In the context of the present invention, the term "column" is to be considered equivalent to the term "column reactor", "packed bed" or "packed bed reactor", "tower" or "tower reactor" and refers to a column reactor having a substantially cylindrical form having an internal diameter D and a height H.

In one embodiment, the tower or column reactor consists of a vertically arranged cylindrical column and is arranged to operate preferably without mechanical agitation, preferably in the up-flow mode, i.e. fluid flow from bottom to top of the column.

In one embodiment, the tower reactor is further characterized by

■ a feed section at the bottom of the cylindrical reactor for feeding liquid reagents;

■ a top section or an overflow zone at the upper part or top end of the column reactor, at the opposite side of the feed section, characterized by an effluent for collecting the overflowing leach solution; and

■ a middle section or a reaction section in the middle of said cylindrical reactor, where the leaching reaction proceeds.

Further, the column reactor is preferably also equipped with means for radially and uniformly distributing the leach solution in the feed section of the column reactor.

In a preferred embodiment, the overflow conduct comprises a solid-liquid separation. The primary object of this solid-liquid separation is removal the solid residue containing iron from solution. This solid-liquid separation can be done by filtration, centrifugation, decantation or a combination.

In a preferred embodiment, the column reactor is cylindrically shaped and has an internal diameter D and a height H, whereby the ratio of the height H to the diameter D is significantly higher than 1, such as between 1.0 and 10.0, preferably between 1.5 and 8.0, more preferably between 2.0 and 5.0 and most preferably about 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, or any value in between. High nickel dissolution

The selective removal of iron through the addition of copper enables a high dissolution of nickel.

Accordingly, in one embodiment at least 90 wt.%, preferably at least 95 wt.%, even more preferably 99 wt.% of nickel in the raw material containing nickel and iron is dissolved in the leach solution.

Residue containing a major part of the iron

In one embodiment, the residue contains a major part of the iron.

By "major part" of the iron is meant at least 50 wt.%, preferably at least 60 wt.%, even more preferably at least 70 wt.%, even more preferably at least 80 wt.%, even more preferably at least 90 wt.%, and even more preferably at least 95 wt.% by weight of iron as compared to the iron contained in the raw material containing nickel and iron.

In one embodiment, the iron in the residue is iron hydroxide. Said iron hydroxide may be an iron (III) hydroxide, such as Fe(OH)3 and/or FeOOH.

System

In one embodiment, the process comprises the subsequent steps of treating the leach solution comprising nickel and residual soluble iron in a further reactor by acidification and oxidation. An exemplary process and system for the selective removal of iron from a raw material containing nickel and iron is shown in Figure 6.

Multiple principles are combined in the exemplary process and system shown in Figure 6. A tower reactor is filled with a coarse raw material containing nickel and iron, preferably ferronickel granules. The raw material containing nickel and iron is dissolved using an incoming acid solution.

In Figure 6, the ferric ions serve as an oxidation source. The tower at the outlet preferably operates in a pH range that allows only a limited solubility of iron, preferably at most 10 g/L. Additional iron that is oxidized usually is present as fines and is entrained with the solution to a decanter and removed from the system. In Figure 6, the residual soluble iron, together with the dissolved nickel, is then treated in a separate reactor. Said separate reactor may be configured to accelerate the oxidation reaction of ferrous iron to ferric iron, e.g. by operating at elevated temperatures and/or elevated pressure to ensure an enhance partial oxygen pressure in the aqueous reaction medium. By acidifying and oxidizing the solution the tower can be regenerated. Alternatively, oxidation can be done directly in the tower. A portion of the leach solution is removed to harvest the nickel.

In one embodiment, the residual iron and copper can be removed by a subsequent hydrolysis step.

The inventors found that the system of Figure 6 enables the production of a pure nickel solution. Copper and iron, together with an excess of reagent for the hydrolysis, can be recycled back to the system.

Use of residue

In one embodiment, the residue obtained according to the process of the invention is used as a starting material for steel-making.

In one embodiment, the content of copper in the residue is at most 1 wt.%, preferably at most 0.1 wt.% and even more preferably at most 0.05 wt.%.

EXAMPLES

The following examples are intended to further clarify the present invention. The examples are nowhere intended to limit the scope of the present invention.

Example 1 - Ferronickel leaching with copper addition

A closed beaker of 3 litre equipped with a condenser was used: The beaker was filled with a certain amount of water and coarse ferronickel particles as raw material containing nickel and iron. A turbine agitator was used to mix the solution while preventing the coarse raw material to be suspended. The solution was heated to 85°C and oxygen was continuously dispersed in the solution at a flow rate of 75 l/h. The amount of acid was adjusted to the nickel and cobalt content in the feed. The acid was dosed over a time period of 4 to 5 hours.

Both H2SO4 was used in example 1.1-HL-HRF0015 and HCI was used in example 1.2- HL-HRF0016 and reacted overnight. Cu (20 g/L) was added to the solution. The experiment was continued again over a time of at least 12 hours.

In example 1.3-HL-HRF0047 and example 1.4: HL-HRF0048 Cu is already added to the start solution.

Example 1.5-HL-ARC0235 was performed on ferronickel that has undergone a pretreatment. The material was finely ground by means of a cross-beater mill. The crossbeater mill was equipped with a sieve with pore size of 750 pm. Size-reduction by cross-beater mills proved to be advantageous for the ductile properties of the ferronickel particles.

Overview of the examples 1.1 to 1.5:

■ Example 1.1-HL-HRF0015: leaching ferronickel in H2SO4 with CuSCU addition after 24h in the amount of Cu 20 g/L;

■ Example 1.2-HL-HRF0016: leaching ferronickel in HCI with CuCh addition after 24h;

■ Example 1.3-HL-HRF0047: leaching ferronickel in H2SO4 with 2 g/L Cu;

■ Example 1.4-HL-HRF0048: leaching ferronickel in HCI with 2 g/L Cu;

■ Example 1.5-HL-ARC0235: selective leaching of size-reduced ferronickel in HCI with 2 g/L Cu.

Example 1.1 - Leaching ferronickel in H2SO4 with C11SO4 addition

Figure 1 shows the results of example 1.1 - Leaching ferronickel in H2SO4 with CuSCU addition after 24 h.

Once all acid was dosed, the pH dropped but increased again with time. After 13.5 h, the pH and ORP changed likely because of fouling of the electrode. The other fluctuations at around 23 hours, 28 hours and near the end of the test are explained by a replacement of the electrode. Based on the trends the system has reached a relatively steady stage just before addition of Cu, after 22 h. At this point, 20 g/L of Cu²⁺ is added. This led to foaming and exothermic behaviour. Again, the pH stabilized toward the end of the test.

Figure 2 plots the concentrations of the metals in the leach solution. Figure 2 shows that Fe, Ni and Co are dissolved gradually during the first part of the leach. Ni leaches preferentially over Fe. Before addition of the Cu, the inventors expected that the Ni and Fe concentrations reached an equilibrium. Only very limited free acid was present at this point (pH of 2 measured with new electrode). Additional dissolution was likely limited. After the addition of Cu, the Fe concentration decreased sharply. The inventors found that the Fe precipitation was accelerated by the Cu. The released acid was used to dissolve further Ni.

Table 1 shows the yields after leaching in H2SO4 of example 1.1-HL-HR.F0015: Leaching ferronickel in H2SO4 with CuSO4 addition after 24h.

Table 1: leach yields of example 1.1 (wt.%)

Very high Ni yields were obtained in example 1.1-HL-HR.F0015: leaching ferronickel in H2SO4 with CuSO4 addition after 24h. 33 g/L Fe was still present in the end solution and can be removed in downstream iron removal steps.

The inventors found that the residual iron is caused by too much acid allowing for more Fe in the leach solution. The inventors further found that the use of a stoichiometric amount of acid relative to the amount of nickel decreases the residual iron in the leach solution. Example 1.2 - Leaching ferronickel in HCI with CuCh addition

Figure 3 shows the OPR., temperature and HCI, pH in function of the reaction time.

After acid addition, the pH stabilized at around 1.4. About 2 hours after acid addition, the pH of the solution stabilized. In this case, less fluctuations in the measurements were observed. The electrode was replaced only once, at around 21.5 hours, with limited impact on the measurement. The inventors found that after 6 hours an equilibrium was installed. The addition of Cu (as CuCh) after ca. 22 h increased the pH to 2.7 in a relatively short timeframe, suggesting fast kinetics. It resulted in a solution without Fe (0.01 g/L) after 30 hours of leaching. After the leaching, a Fe-hydroxide residue remains.

Figure 4 shows the concentrations of the metals in solution. The same trends were observed as with H2SO4- example 1.1. However, the reaction kinetics of example 1.2 were much faster. The selectivity for Fe was very good. The amount of iron in the filtrate was less than 10 m g/L.

Table 2 shows the total leach yields of example 1.2-HL-HRF0016: Leaching ferronickel in HCI with CuCh addition after 24 h. Cu was considered in the composition of the feed.

Table 2: leach yields of example 1.2 (wt.%)

A total of 95 wt.% of the initial amount of cobalt went into solution. A total of 97 wt.% of the nickel went into solution. Only 16 wt.% of the added Cu was found in the filtrate. The residue did not contain a significant amount of Cu. This indicates that the copper was cemented. The filtrate did not contain Fe (< 10 m g/L). This indicates that iron was separated into the residue and provided a very good selective leaching. The residue was a Fe-hydroxide with traces of Ni and Cu. The inventors found that the limited Ni and Cu yields were caused by an acid deficit and could be increased by an acid increase.

Examples 1.3 and 1.4: Leaching ferronickel with 2 g/L Cu A concentration of 2 g/L Cu²⁺ was added in the initial solution. After 24 h, the experiment was stopped. The filtrate and residue compositions were analysed. The experiments were not continued until all metal was dissolved but focused on a comparison of kinetics. Table 3: leach yields of examples 1.3 and 1.4 (wt.%)

A very pure Fe residue was obtained in both examples 1.3- H2SO4 and example 1.4- HCI. Respectively 40% and 33% of the metal remains after 24 h in H2SO4 and HCI. This is shown in table 4 below, expressing the leach kinetics.

Table 4: Leach kinetics of examples 1.3 and 1.4:

Typically, these numbers are too low to justify leaching in stirred reactors. The inventors found that tower leaching is advantageous if the raw material is coarse as in example 1.1 to 1.4.

Example 1.5: milled ferronickel leached with HCI

Milled ferronickel particles were placed in a beaker and mixed until full suspension. O2 was injected at 75 l/h. The pulp was heated to 80°C before starting acid supply (HCI). The target was 60 g/L metal in solution (Co/Ni). The amount of acid corresponded to 110% with respect to Ni and Co. CuCh was added in an amount of (2 g/L Cu²⁺ after the acid addition.

The pH stabilized at around 2 after acid addition. When CuCh was added, there was a momentary peak in OR.P and a slight drop in pH. A sample was taken every hour to analyse the composition of the filtrate with semi-quantitative EDXR.F to detect the trends. After 7h the experiment was stopped, and the entire contents were filtered. Both the filtrate and the residue were analysed quantitatively.

Table 5: Filtrate composition of example 1.5:

Table 6: leach yields of examples 1.5 after leaching with HCI (wt.%):

Fe and Ni concentrations in the final solution are around 45 g/L and 20 g/L, respectively. No copper was found in the filtrate but only in the residue. The inventors found that upon addition of Cu, Cu was precipitated nearly instantaneously by cementation on the feed material.

Milling of the feed strongly increased its reactivity. This resulted in a much faster dissolution. However, the increased reactivity hindered the Fe oxidation by cementing Cu from the solution.

Example 2 - Leaching of ferronickel chunks with sulphuric and hydrochloric acid

Ferronickel chunks containing about 75 wt.% iron and 25 wt.% nickel were leached in a tower reactor with both sulphuric acid (example 2.1) and hydrochloric acid (example 2.2).

Table 7: Leach kinetics of examples 2.1 and 2.2:

Reactivity of the ferronickel chunks can be increased by size reduction, such as milling.

Claims

1. A process for the selective separation of iron from a raw material comprising a nickel-iron alloy, wherein said raw material containing nickel and iron contains at least 5 wt.% nickel and at most 95 wt.% iron, relative to the total weight of said raw material, said process comprising the steps of: i. contacting the raw material containing a nickel-iron alloy with an acid solution, thereby obtaining a leach solution containing iron and nickel, and a residue containing at least 50 wt.% of iron, relative to the total amount of iron in said raw material, whereby at least 50 wt.% of said iron in said residue is comprised as an iron hydroxide; ii. adding a copper containing material, in an amount of 0.25 to 50 g copper per litre of the leach solution, to the leach solution and/or to the raw material containing a nickel-iron alloy to facilitate precipitation of iron in the leach solution; and iii. separating the leach solution from the residue.

2. The process according to claim 1, wherein the acid is dosed in a stoichiometric amount relative to the total amount of nickel, cobalt and copper.

3. The process according to any one of the preceding claims, whereby steps i., ii. and iii. are performed at a pressure below 10 bar, preferably at atmospheric pressure.

4. The process according to any one of the preceding claims, wherein the reaction temperature is from 50 °C to 95 °C, more preferably from 70 °C to 90 °C, even more preferably from 75 °C to 85 °C.

5. The process according any one of the preceding claims, wherein the raw material containing nickel and iron is contacted with the acid solution in oxidizing conditions in absence of hydrogen peroxide, preferably by the addition of an O2-bearing gas and/or CI2.

6. The process according to any one of the preceding claims, wherein: ■ the acid is hydrochloric acid and wherein the copper containing material is preferably copper chloride; or

■ the acid is sulphuric acid and the copper containing material is preferably copper sulphate.

7. The process according to any one of the preceding claims, wherein the raw material containing nickel and iron contains 10 wt.% to 40 wt.% nickel and at most 60 wt.% to 90 wt.% iron, relative to the total weight of said raw material.

8. The process according to any one of the preceding claims, wherein the raw material containing nickel and iron further contains metals, preferably cobalt in an amount from 0.1 wt.% to 10 wt.%, even more preferably from 0.5 wt.% to 5 wt.%, even more preferably from 1 wt.% to 3 wt.%.

9. The process according to any one of the preceding claims, wherein the copper containing material is added in an amount of copper from 0.25 g/L to 25 g/L, preferably from 0.5 g/L to 20 g/L, even more preferably from 1 g/L to 15 g/L relative to the amount of the leach solution.

10. The process according to any one of the preceding claims, wherein the copper containing material is added at the start or after an initial reaction time, preferably after 1 hours to 10 hours, more preferably after 2 hours to 8 hours from the start of the reaction.

11. The process according to any one of the preceding claims, wherein the raw material containing a nickel-iron alloy is:

■ in the form of chunks, plates or spheric particles, preferably pellets; or

■ size-reduced, preferably by high-shear milling.

12. The process according to any one of the preceding claims, wherein the raw material containing nickel has a particle size of 10 pm to 1500 pm, preferably from 50 pm to 800 pm even more preferably 100 to 500 pm, as determined by sieving.

13. The process according to any one of the preceding claims, wherein the raw material containing nickel and iron are reacted with the acid solution in a tower or column reactor.

14. The process according to any one of the preceding claims, wherein the pH of the leach solution prior to separation from the residue is adjusted to allow for a solubility of iron of at most 10 g/L.

15. The process according to any one of the preceding claims, wherein the process comprises the subsequent steps of treating the leach solution comprising nickel and residual soluble iron in a further reactor by acidification and oxidation.