WO2021155458A1 - Froth flotation process for separation of metal sulfides using hydrophobically modified polyalkyleneimines - Google Patents

Abstract

The present application relates to froth flotation processes for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide. The processes comprise agitating an aqueous suspension comprising particles of the material and a collector that is a hydrophobically modified polyalkyleneimine, while introducing a gas, thereby floating the copper sulfide in a froth fraction and depressing the nickel sulfide in a tails fraction, then separating the froth fraction from the tails fraction.

Description

FROTH FLOTATION PROCESS FOR SEPARATION OF METAL SULFIDES USING HYDROPHOBICALLY MODIFIED POLYALKYLENEIMINES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of priority from co-pending U.S. provisional application no. 62/970,752 filed on February 6, 2020, the contents of which are incorporated herein by reference in their entirety.

FIELD

[0002] The present application relates to froth flotation processes for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide, the processes comprising the use of a collector that is a hydrophobically modified polyalkyleneimine.

BACKGROUND

[0003] Froth flotation is a separation process in which hydrophobic particles can be separated from hydrophilic particles. Hydrophobic particles attach to the surface of air bubbles because air bubbles are naturally hydrophobic. Particles which are naturally hydrophilic can be made hydrophobic by the use of a “collector”. Collectors are compounds that have a hydrophobic “side” and another “side” which can attach to the surface of a hydrophilic particle. Attachment can occur by electrostatic attraction or the formation of chemical bonds. Electrostatic attractions (for example, between a collector having a positively charged amine and a negatively charged particle) are weaker than attachment via a chemical reaction (for example, between a xanthate collector and a metal sulfide particle). The term “xanthate” in reference to a collector typically refers to a salt having the general formula [R^AOCS₂]-M⁺, wherein R^A is alkyl and M⁺ can be Na⁺ or K⁺.

[0004] In an example of a typical froth floatation process, the collector(s), particles and optionally other reagents such as those for pH adjustment and frother(s) are mixed in a slurry wherein the particle surface may be conditioned to “accept” the collector. The slurry then proceeds to a flotation cell or mixing tank where vigorous mixing disperses air introduced to the flotation cell and promotes contact between air bubbles and all particles. The conditions of the froth floatation process are selected so that hydrophobic particles attach to the bubble (a statistical probability) and rise to the surface of the cell in a “froth” which is also called the “concentrate”. Hydrophilic material remains in the flotation cell and then can exit as “tails”. The froth/concentrate will still generally contain some hydrophilic material and the tails will generally be depleted of hydrophobic material.

[0005] Water soluble and environmentally friendly “collectors” are desirable for the flotation of minerals such as sulphide minerals. However, currently used collectors can be toxic in waste water streams, produce toxic by-products by decomposition and/or involve hazardous chemicals during their manufacturing. While a water-soluble collector may be preferred for the purposes of process control and processing, some collectors require preparation in acids or organic solvents or alcohols. Alternative collectors which mitigate one or more of these issues may be advantageous over currently used collectors.

[0006] Collectors reported for separation of sulphide minerals such as those containing heazlewoodite (Ni₃S₂) and chalcocite (CU₂S) by flotation include diphenylguanidine (DPG). The differential flotation of heazlewoodite and chalcocite relies on the conversion of heazlewoodite surfaces into Ni(OH)2 whereas chalcocite converts to CuO. DPG absorption onto CuO peaks at pH 12.4 while absorption onto Ni(OH)2 is lower and constant at any pH.¹ For example, US Patent No. 2,432,456 discloses the use of DPG in a process for recovering copper sulfide and nickel sulfide from Bessemer matte. Nearly half a century later, such a flotation process was reported to still be used by the patentee in almost the original mode.² DPG is effective for separation efficiency, frothing properties and stability throughout the multistage flotation circuit but not significantly water soluble. For the purposes of introduction to processing it may be added, for example, as a dry powder.³ DPG also has non-desirable properties as it contains aromatic moieties, is carcinogenic and there are non-green practices during its manufacture. Repeated exposure may also cause damage to human reproduction.

[0007] Additional collectors such as xanthates and dithiocarbamate (DTC) have been investigated and may be suitable for certain flotation processes but also have safety concerns. For example, the DTC and xanthates both use CS2 in their synthesis. DTC can also produce CS₂ as a decomposition by-product. In addition, xanthates even at 1 ppm can be toxic to aquatic life. [0008] US Patent Application Publication No. 2004/0139559 discloses the use of hydrophobically modified polyethylene imines for use as anti-wrinkle additives in the textile industry. US Patent No. 8,662,311 subsequently disclosed a froth flotation process for the separation of silicates and alkaline earth metal carbonates using a hydrophobically modified polyalkyleneimine collector. US Patent No. 3,425,549 also generally discloses the use of derivatives of polyalkyleneimines in froth flotation processes such as those which separate silica from phosphate rock or iron ores containing magnetite, limonite and quartz.

SUMMARY

[0009] Fatty acid modified polyethyleneimines were prepared and tested for use as collectors in the separation of heazlewoodite (N13S2) and chalcocite (CU2S) from a Bessemer matte material. The polyalkyleneimine that was modified was a branched polyethylenimine (PEI) with a molecular weight of 2,000 Da and the ones tested in froth flotation had C5 and C18 fatty acids. The C18 substituted PEI was not water soluble. The C5 and C3 substituted PEIs were water soluble to at least 10 wt%. The initial flotation performance of the C18 PEI collector was similar to that of diphenylguanidine (DPG) with similar copper recovery and nickel assay. The C5 PEI collector like DPG, has self-frothing properties. The C5 PEI collector was tested at three concentrations. The lowest nickel assay was achieved with 100 g/ton. A combination of C18 and C5 PEI may have advantageous properties as the initial Ni grade was low with C18 PEI and the final Cu recovery was high with C5 PEI.

[0010] Accordingly, the present application includes a froth flotation process for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide, the process comprising: agitating an aqueous suspension comprising particles of the material and a collector while introducing a gas, thereby floating the copper sulfide in a froth fraction and depressing the nickel sulfide in a tails fraction; and separating the froth fraction from the tails fraction, wherein the collector is a hydrophobically modified polyalkyleneimine.

[0011] The present application also includes a use of a hydrophobically modified polyalkyleneimine as a collector in a froth flotation process for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide.

[0012] Other features and advantages of the present application will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating embodiments of the application are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present application will now be described in greater detail with reference to the drawings in which:

[0014] Figure 1 is a plot of copper recovery (wt%) as a function of cumulative nickel assay (wt%) for DPG collectors used in comparative examples to froth flotation processes of the present application.

[0015] Figure 2 shows copper recovery (wt%) plotted against cumulative nickel assay (wt%) for flotation of matte for different fatty acid modified branched polyethyleneimine collectors according to embodiments of the present application.

DETAILED DESCRIPTION

I. Definitions

[0016] Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present application herein described for which they are suitable as would be understood by a person skilled in the art.

[0017] In understanding the scope of the present application, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. The term “consisting” and its derivatives, as used herein, are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The term “consisting essentially of, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of features, elements, components, groups, integers, and/or steps.

[0018] Terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

[0019] The term “and/or” as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that “at least one of” or “one or more” of the listed items is used or present.

[0020] As used in this application, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise.

[0021] The term “suitable” as used herein means that the selection of specific reagents or conditions will depend on the reaction being performed and the desired results, but none-the-less, can generally be made by a person skilled in the art once all relevant information is known.

[0022] The term “P80” as used herein in reference to a material indicates that 80% of the material passes through a stated mesh size. In one embodiment, a P80 of, for example, 100 mesh or 150 μm, (mesh or absolute size) indicates that 80% of the material passes through a screen mesh of 100 μm, or 150 μm.

[0023] The term “grade” as used herein refers to concentration of a component in a fraction. For example, the concentration of copper sulfide in a froth fraction or concentration of nickel sulfide in a tails fraction.

[0024] The term “polyalkyleneimine” as used herein refers to a polymer with a repeating unit made up of an amine group and an alkylene spacer and includes linear polyalkyleneimines and branched polyalkyleneimines. For example, a “polyethyleneimine” is a polyalkyleneimine with a repeating unit made up of an amine group and an ethylene spacer. The amine groups of linear polyalkyleneimines are secondary amines whereas branched polyalkyleneimines contain primary, secondary and tertiary amine groups.

[0025] The term “hydrophobically modified” as used herein in reference to a polyalkyleneimine means that at least a portion of the available amine hydrogen atoms has been replaced with a hydrophobic group.

[0026] The term “available amine hydrogen atoms” as used herein refers to atoms that would be known to a person skilled in the art to be capable of replacement by a hydrophobic group using methods known in the art.

[0027] The term “conditioning” as used herein refers to a step or stage in a froth flotation process wherein there is no gas introduced to produce froth.

[0028] The term “alkyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkyl groups. The number of carbon atoms that are possible in the referenced alkyl group are indicated by the numerical prefix “Cni-n2”. For example, the term C₃-isalkyl means an alkyl group having 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17 or 18 carbon atoms.

[0029] The term “alkylene” as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkylene group, that is, a saturated carbon chain that contains substituents on two of its ends.

[0030] The term “alkenyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, unsaturated alkenyl groups. The number of carbon atoms that are possible in the referenced alkenyl group are indicated by the numerical prefix “Cni-n2”. For example, the term C_3-32alkenyl means an alkenyl group having 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 or 32 carbon atoms and at least one double bond, for example 1 to 3, 1 to 2 or 1 double bond.

[0031] The term “alkynyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, unsaturated alkynyl groups. The number of carbon atoms that are possible in the referenced alkynyl group are indicated by the numerical prefix “Cni-n2”. For example, the term C_3-32alkynyl means an alkynyl group having 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 or 32 carbon atoms and at least one triple bond, for example 1 to 3, 1 to 2 or 1 triple bond. [0032] The term “cycloalkyl” as used herein, whether it is used alone or as part of another group, means a mono- or bicyclic, saturated cycloalkyl group. The number of carbon atoms that are possible in the referenced cycloalkyl group are indicated by the numerical prefix “Cni-n2”. For example, the term C_3-16cycloalkyl means a cycloalkyl group having 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15 or 16 carbon atoms. When a cycloalkyl group contains more than one cyclic structure or rings, the cyclic structures are fused, bridged, spiro connected or linked by a single bond.

[0033] The term “cycloalkenyl” as used herein, whether it is used alone or as part of another group, means a mono- or bicyclic, unsaturated cycloalkenyl group. The number of carbon atoms that are possible in the referenced cycloalkenyl group are indicated by the numerical prefix “Cni-n2”. For example, the term C_5-16cycloalkenyl means a cycloalkenyl group having 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15 or 16 carbon atoms and at least one double bond, for example 1 to 3, 1 to 2 or 1 double bond. When a cycloalkenyl group contains more than one cyclic structure or rings, the cyclic structures are fused, bridged, spiro connected or linked by a single bond.

[0034] The term “cycloalkynyl” as used herein, whether it is used alone or as part of another group, means a mono- or bicyclic, unsaturated cycloalkynyl group. The number of carbon atoms that are possible in the referenced cycloalkynyl group are indicated by the numerical prefix “Cni-n2”. For example, the term C_10-16cycloalkynyl means a cycloalkynyl group having 10, 11 , 12, 13, 14, 15 or 16 carbon atoms and at least one triple bond, for example 1 to 3, 1 to 2 or 1 triple bond. When a cycloalkynyl group contains more than one cyclic structure or rings, the cyclic structures are fused, bridged, spiro connected or linked by a single bond.

[0035] A first cyclic structure being “fused” with a second cyclic structure means the first cyclic structure and the second cyclic structure share at least two adjacent atoms therebetween. A first cyclic structure being “bridged” with a second cyclic structure means the first cyclic structure and the second cyclic structure share at least two non-adjacent atoms therebetween. A first cyclic structure being “spiro connected” with a second cyclic structure means the first cyclic structure and the second cyclic structure share one atom therebetween.

[0036] The term “aryl” as used herein, whether it is used alone or as part of another group, refers to cyclic groups that contain at least one aromatic ring. In an embodiment of the present application, the aryl group contains from 6, 9, 10 or 14 atoms, such as phenyl, naphthyl, indanyl or anthracenyl. In some embodiments, the number of carbon atoms that are possible in the referenced aryl group are indicated by the numerical prefix “Cni-n2”. For example, the term C6-ioaryl means an aryl group having 6, 7, 8, 9 or 10 carbon atoms.

[0037] The term “substituted” as used herein in reference to a cycloalkyl, cycloalkenyl, cycloalkynyl or aryl group means that one of the H atoms in the cycloalkyl, cycloalkenyl, cycloalkynyl or aryl group is replaced by the group with which it is substituted. The term “substituted” as used herein in reference to an alkyl, alkenyl or alkynyl group means that one of the H atoms in the alkyl, alkenyl or alkynyl group is replaced by the group with which it is substituted or that the group with which it is substituted is inserted into the alkyl, alkenyl or alkynyl chain.

[0038] The term “halo” as used herein refers to a halogen atom and includes F, Cl, Br and I.

[0039] The expression “proceed to a sufficient extent” as used herein with reference to a reaction or process step disclosed herein means that the reaction or process step proceeds to an extent that conversion of the starting material or substrate to product is maximized. Conversion may be maximized when greater than about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100% of the starting material or substrate is converted to product.

II. Processes

[0040] Fatty acid modified polyethyleneimines were prepared and tested for use as collectors in the separation of heazlewoodite (N13S2) and chalcocite (CU2S) from a Bessemer matte material. Such hydrophobically modified polyethyleneimines can be water soluble or alcohol soluble or both, depending on the hydrophobic substitution, for example, modifying the degree of substitution and/or the length of an alkyl chain. The polyalkyleneimine that was modified was a branched polyethylenimine (PEI) with a molecular weight of 2,000 Da and the ones tested in froth flotation had C5 and C18 fatty acids which introduced hydrophobicity forfloatability. The C18 substituted PEI was not water soluble. The C5 and C3 substituted PEIs were water soluble to at least 10 wt%. The initial flotation performance of the C18 PEI collector was similar to that of diphenylguanidine (DPG) with similar copper recovery and nickel assay. The C5 PEI collector, like DPG, has self-frothing properties. The C5 PEI collector was tested at three concentrations. The lowest nickel assay was achieved with 100 g/ton. A combination of C18 and C5 PEI may have advantageous properties as the initial Ni grade was low with C18 PEI and the final Cu recovery was high with C5 PEI.

[0041] Accordingly, the present application includes a froth flotation process for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide, the process comprising: agitating an aqueous suspension comprising particles of the material and a collector while introducing a gas, thereby floating the copper sulfide in a froth fraction and depressing the nickel sulfide in a tails fraction; and separating the froth fraction from the tails fraction, wherein the collector is a hydrophobically modified polyalkyleneimine.

[0042] The present application also includes a use of a hydrophobically modified polyalkyleneimine as a collector in a froth flotation process for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide.

[0043] In an embodiment, the copper sulfide is chalcocite, digenite, or a combination thereof. In another embodiment, the nickel sulfide is heazlewoodite. In a further embodiment, the copper sulfide is chalcocite and the nickel sulfide is heazlewoodite.

[0044] In an embodiment, the material is derived from a Bessemer matte. In another embodiment, the material is obtained by a process comprising cooling a Bessemer matte under conditions to obtain the chalcocite and heazlewoodite (i.e. the Bessemer matte is cooled under conditions to obtain growth of separate grains of chalcocite and heazlewoodite). Such conditions can be readily selected by a person skilled in the art and comprise slow-cooling of the Bessemer matte, typically over a period of one or more days.

[0045] In embodiments wherein the material comprises chalcocite and heazlewoodite, for example, where the material is obtained by a process comprising cooling a Bessemer matte under conditions to obtain the chalcocite and heazlewoodite, the aqueous suspension advantageously has a pH in the range of from about 12 to about 12.6. In this range, the surface of heazlewoodite particles in the material will be at least partially oxidized into Ni(OH)2 but chalcocite particles in the material would not have any significant surface oxidation to CuO. Accordingly, in an embodiment, the aqueous suspension has a pH of from about 12 to about 12.6. In an embodiment, the pH is adjusted to and/or maintained at the range of from about 12 to about 12.6 via addition of a base. In an embodiment, the base is lime (Ca(OH)2). In another embodiment, the aqueous suspension has a conductivity of from about 2.5 mS/cm to about 3.5 mS/cm. In a further embodiment, the aqueous suspension has a conductivity of about 3.0 mS/cm. In an embodiment, the conductivity is adjusted to and/or maintained at the range of from about 2.5 mS/cm to about 3.5 mS/cm or at the value of about 3.0 mS/cm via addition of a base. In another embodiment, the base is lime (Ca(OH)₂).

[0046] In an embodiment, the collector is present in an initial dose of from about 100 g/ton to about 400 g/ton of the material.

[0047] The gas introduced during the agitating can be any suitable gas. In an embodiment, the gas is air. In another embodiment, the airflow is from about 0.1 L/min to about 4.0 L/min or about 0.5 L/min to about 2.0 L/min.

[0048] The agitating is carried out by any suitable means, the selection of which can be made by a person skilled in the art. In an embodiment, the means for agitating comprises an agitator (e.g. an impeller) coupled to a rotating shaft.

[0049] In an embodiment, the process further comprises conditioning of the aqueous suspension. Conditioning can optionally be staged throughout a flotation, for example, to adjust pH, allow the collector to interact with particles to be floated in the froth fraction and/or dispersion of frother, if present. In an embodiment, the conditioning is prior to agitating. In another embodiment, the conditioning is during agitating. It will be appreciated by a person skilled in the art that the expression “during agitating” as used herein in reference to conditioning comprises ceasing the introduction of gas for one or more desired periods of time, followed each time by reintroducing the gas to continue the production of froth. In another embodiment, the conditioning is prior to and during agitating.

[0050] In an embodiment, the process further comprises grinding of the material to obtain the particles. It will be appreciated by a person skilled in the art that materials comprising copper sulfide and nickel sulfide often further comprise one or more magnetic materials such as copper-nickel alloy, pyrrhotite and/or nickel metal or optionally other magnetic materials depending, for example, on the source of the material. Accordingly, in some embodiments, the process further comprises separation of magnetic material. In some embodiments, the process further comprises separation of magnetic material from the froth fraction and/or tails fraction. The magnetic material can alternatively or additionally be separated during grinding. Accordingly, in some embodiments, the grinding comprises: primary grinding of a mixture comprising the material and water; magnetic separation of the ground mixture to obtain a magnetic concentrate and a demagnetized tail; and secondary grinding of the demagnetized tail to obtain the particles.

[0051] The grind size of the particles is any suitable grind size and can be readily selected by a person skilled in the art. For example, a suitable grind size may, for example, depend on the composition of the material comprising the copper sulfide and the nickel sulfide and/or the conditions for the preparation thereof. For example, in embodiments wherein the material is obtained by a process comprising cooling a Bessemer matte under conditions to obtain growth of separate grains of chalcocite and heazlewoodite, the person skilled in the art would appreciate that the faster the cooling rate, generally the smaller the grains of heazlewoodite and chalcocite obtained and therefore selecting a lower value for P80 may be useful. In an embodiment, the particles have a P80 of from about 38 μm to about 250 μm. In another embodiment, the particles have a P80 of from about 40 μm to about 60μm. In a further embodiment, the particles have a P80 of about 40 μm.

[0052] In an embodiment, the hydrophobically modified polyalkyleneimine is a hydrophobically modified polyethyleneimine. In another embodiment, the hydrophobically modified polyalkyleneimine is branched. In another embodiment, the hydrophobically modified polyalkyleneimine is linear. [0053] Hydrophobically modified polyalkyleneimines can be prepared by the person skilled in the art using known methods, for example a suitable method disclosed in US 2004/0139559 and/or WO 2011/113866.

[0054] In an embodiment, the hydrophobic groups comprise any suitable alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl and/or aryl groups that are unsubstituted or are optionally substituted with one or more groups selected from any suitable cycloalkyl, cycloalkenyl and aryl groups. In another embodiment, the hydrophobic groups are C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, Cs- 32cycloalkenyl, C_10-32cycloalkynyl or aryl, wherein the C_1-32alkyl, C_3-32alkenyl, C₃- 32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl, C_10-32cycloalkynyl and aryl are unsubstituted or are optionally substituted with one or more groups selected from C₃- i6cycloalkyl, C_5-16cycloalkenyl, C_10-16cycloalkynyl and C6-ioaryl. From an environmental standpoint it can be advantageous if the hydrophobically modified polyalkyleneimine is devoid of aromatic moieties. Accordingly, in an embodiment, the hydrophobic groups are devoid of an aromatic moiety. In another embodiment, the hydrophobic groups are any suitable alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl and/or cycloalkynyl groups that are unsubstituted or are optionally substituted with one or more groups selected from any suitable cycloalkyl, cycloalkenyl and/or cycloalkynyl groups. In another embodiment, the hydrophobic groups are C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl or C_10-32cycloalkynyl, wherein the C₁- 32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl and C10- 32cycloalkynyl are unsubstituted or are optionally substituted with one or more groups selected from C_3-16cycloalkyl, C_5-16cycloalkenyl and C_10-16cycloalkynyl. In a further embodiment, the hydrophobic groups are C_{1 -32}alkyl, C_3-32alkenyl and/or C_3-32alkynyl groups. In another embodiment of the present application, the hydrophobic groups are linear C_1-32alkyl, C_3-32alkenyl and/or C_3-32alkynyl groups. In another embodiment, the hydrophobic group is a linear C_2-17alkyl group. In a further embodiment, the hydrophobic group is n-butyl. In another embodiment, the hydrophobic group is n- heptadecyl. In a further embodiment of the present application, the hydrophobic group is a blend of at least two different hydrophobic groups, for example, the polyalkyleneimine is a blend of at least two different polyalkyleneimines and/or a single polyalkyleneimine has a blend of at least two different hydrophobic groups. [0055] In an embodiment, the hydrophobically modified polyalkyleneimine (e.g. the hydrophobically modified polyethyleneimine) is prepared by reacting a polyalkyleneimine (e.g. a polyethyleneimine) with a suitable source of the hydrophobic group. Suitable sources of hydrophobic groups can be selected by the person skilled in the art and include

wherein each R¹ and R² are independently selected from any suitable alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl and aryl that is unsubstituted or is optionally substituted with one or more groups selected from any suitable cycloalkyl, cycloalkenyl, cycloalkynyl and aryl and X is halo. It will be appreciated by a person skilled in the art that the formula “R¹COOH” refers to a carboxylic acid and that the formula “R¹COCI” refers to an acid chloride. In another embodiment, each R¹ is independently selected from C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, Cs- 32cycloalkenyl, C_10-32cycloalkynyl and aryl, wherein the C_1-32alkyl, C_3-32alkenyl, C₃- 32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl, C_10-32cycloalkynyl and aryl are unsubstituted or are optionally substituted with one or more groups selected from C₃- i6cycloalkyl, C_5-16cycloalkenyl, C_10-16cycloalkynyl and C6-ioaryl, each R² is independently selected from C_1-16alkyl, C_3-16alkenyl, C_3-16alkynyl, C_3-16cycloalkyl, Cs- i6cycloalkenyl, C_10-16cycloalkynyl and aryl, wherein the C_1-16alkyl, C_3-16alkenyl, C₃- i6alkynyl, C_3-16cycloalkyl, C_5-16cycloalkenyl, C_10-16cycloalkynyl and aryl are unsubstituted or are optionally substituted with one or more groups selected from C₃- i6cycloalkyl, C_5-16cycloalkenyl, C_10-16cycloalkynyl and C6-ioaryl and X is halo. In some embodiments, R¹ and R² are devoid of an aromatic moiety. Accordingly, in another embodiment, each R¹ is independently selected from C_1-32alkyl, C_3-32alkenyl, C₃- 32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl and C_10-32cycloalkynyl, wherein the C₁- 32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl and C10- 32cycloalkynyl are unsubstituted or are optionally substituted with one or more groups selected from C_3-16cycloalkyl, C_5-16cycloalkenyl and C_10-16cycloalkynyl, each R² is independently selected from C_1-16alkyl, C_3-16alkenyl, C_3-16alkynyl, C_3-16cycloalkyl, Cs- i6cycloalkenyl and C_10-16cycloalkynyl, wherein the C_1-16alkyl, C_3-16alkenyl, C_3-16alkynyl, C_3-16cycloalkyl, C_5-16cycloalkenyl and C_10-16cycloalkynyl are unsubstituted or are optionally substituted with one or more groups selected from C_3-16cycloalkyl, C_5-16 cycloalkenyl and C_10-16cycloalkynyl and X is halo. In a further embodiment, each R¹ is independently C_1-32alkyl, C_3-32alkenyl or C_3-32alkynyl. In a further embodiment, each R¹ is independently C_2-32alkyl. In another embodiment, each R¹ is independently C_2-17alkyl. In an embodiment, each R¹ is independently a linear C_2-17alkyl. In another embodiment, each R² is independently a linear C_2-8alkyl. In another embodiment, X is Cl. Suitable conditions for reaction of the polyalkyleneimine with the source of hydrophobic group can be readily selected by the person skilled in the art.

[0056] In an embodiment, the hydrophobically modified polyalkyleneimine (e.g. the hydrophobically modified polyethyleneimine) has been prepared by reacting a polyalkyleneimine (e.g. a polyethyleneimine) with R¹COOH, wherein R¹ is C_1-32alkyl, C_{3- 32}alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl, C_10-32cycloalkynyl or aryl, wherein the C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl, C_10-32 cycloalkynyl and aryl are unsubstituted or are optionally substituted with one or more groups selected from C_3-16cycloalkyl, C_5-16cycloalkenyl, C_10-16cycloalkynyl and C_6-10aryl. In some embodiments, R¹ is devoid of an aromatic moiety. Accordingly, in another embodiment, R¹ is C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl or C_10-32cycloalkynyl, wherein the C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl and C_10-32cycloalkynyl are unsubstituted or are optionally substituted with one or more groups selected from C_3-16cycloalkyl, C_5-16cycloalkenyl and C_{10- 16}cycloalkynyl. In a further embodiment, R¹ is C_1-32alkyl, C_3-32alkenyl or C_3-32alkynyl. In a further embodiment, R¹ is C_2-32alkyl. In another embodiment, R¹ is C_2-17alkyl. In another embodiment, R¹ is a linear C_2-17alkyl. In a further embodiment, R¹ is n-butyl. In another embodiment of the present application, R¹ is n-heptadecyl.

[0057] The conditions for reacting the polyalkyleneimine with R¹COOH are any suitable conditions, the selection of which can be made by a person skilled in the art. In an embodiment, the conditions comprise adding a desired amount of the R¹COOH to the polyalkyleneimine at a suitable temperature, for example, a temperature of about 135°C or greater, then stirring at a suitable temperature, for example, at a temperature of about 125°C or greater for a time for the conversion of the polyalkyleneimine and R¹COOH to the hydrophobically modified polyalkyleneimine to proceed to a sufficient extent, for example, a time of about 8 hours to about 24 hours or about 16 hours. Such a method may, for example, have the advantage of being more cost effective than methods involving sources of hydrophobic groups that are more expensive than R¹COOH and/or facile removal of the environmentally harmless water byproduct. For example, methods comprising R¹X as a source of the hydrophobic group may be more costly (as R¹X may be more expensive than R¹COOH), involves halogens, and would produce a strong acid such as HCI during the reaction; and alkylketene dimer sources of hydrophobic groups may be considerably more expensive than R¹COOH. The source of hydrophobic group may also, for example, have an effect on the positive nature of the nitrogens in the polyalkyleneimine and/or solubility of the hydrophobically modified polyalkyleneimines. For example, using a source of hydrophobic group that is devoid of carbonyl moieties may, for example, reduce the water solubility of the resulting hydrophobically modified polyalkyleneimine.

[0058] In some embodiments of the present application, the hydrophobically modified polyalkyleneimine comprises a blend of two or more hydrophobically modified polyalkyleneimines. Accordingly, in an embodiment, the hydrophobically modified polyalkyleneimine is a combination of:

(i) a first hydrophobically modified polyalkyleneimine; and

(ii) a second hydrophobically modified polyalkyleneimine different from the first hydrophobically modified polyalkyleneimine.

[0059] In another embodiment, the hydrophobically modified polyalkyleneimine is a combination of:

(i) a hydrophobically modified polyalkyleneimine prepared by reacting a polyalkyleneimine with R¹COOH, wherein R¹ is n-butyl; and

(ii) a hydrophobically modified polyalkyleneimine prepared by reacting a polyalkyleneimine with R¹COOH, wherein R¹ is n-heptadecyl.

[0060] Branched and linear polyalkyleneimines for use in the reaction with the source of hydrophobic group can be prepared by methods known to the person skilled in the art and/or are available from commercial sources.

[0061] The solubility of the hydrophobically modified polyalkyleneimine (e.g. the hydrophobically modified polyethyleneimine) can be varied, for example, by varying the degree of substitution of available amine hydrogen atoms. In an embodiment, at least about 50% of primary amine sites in the branched polyalkyleneimine are hydrophobically modified. In another embodiment, from about 70% to about 100%, about 85% to about 95% or about 90% of primary amine sites in the branched polyalkyleneimine are hydrophobically modified.

[0062] In an embodiment, the polyalkyleneimine (e.g. the polyethyleneimine) has a weight average molecular weight (M_w) of from about 500 Da to about 50,000 Da. In another embodiment, the M_w is about 2000 Da.

[0063] In the examples described herein below, the n-butyl substituted, branched polyethyleneimine was observed to have self-frothing properties whereas the n-heptadecyl substituted, branched polyethyleneimine did not. Accordingly, in some embodiments of the present application, the process is carried out in the absence of an additional frother. In alternative embodiments of the present application, the process further comprises adding a frother to the aqueous suspension. The frother is any suitable frother and can be selected by a person skilled in the art. For example, the skilled person would readily appreciate that a suitable frother produces and/or increases the lifetime of froth formation. In an embodiment, the frother is selected from methyl isobutyl carbinol, a polypropylene glycol, a polyethylene glycol, pine oil, cresylic acid and blends thereof. In another embodiment, the frother is methyl isobutyl carbinol.

[0064] In an embodiment, the hydrophobically modified polyalkyleneimine (e.g. the hydrophobically modified polyethyleneimine) is water soluble. Accordingly, in such embodiments, the collector may be added to the aqueous suspension comprising particles of the material in the form of an aqueous solution comprising the hydrophobically modified polyalkyleneimine. In other embodiments, the hydrophobically modified polyalkyleneimine is not water soluble. In such embodiments, the collector may be added to the aqueous suspension comprising particles of the material in the form of a solution of a suitable solvent (e.g. ethanol) in which the hydrophobically modified polyalkyleneimine is soluble.

[0065] Hydrophilic nickel sulphide may, for example, “carry over” into the froth fraction even though it is not hydrophobic and/or attached to a bubble. For example, this can occur with smaller nickel particles which are convectively transported up to the froth fraction. Accordingly, in some embodiments of the present application, the process further comprises cleaning the froth fraction. It will be appreciated by the person skilled in the art that the term “cleaning” in reference to a froth flotation process refers to subjecting the fraction to a further stage of flotation. In some embodiments, the process further comprises regrinding the froth fraction prior to cleaning. In another embodiment, the process further comprises repeating the cleaning and optionally the grinding until a froth fraction comprising the copper sulfide of a desired grade is obtained. Similarly, in some embodiments, the process further comprises cleaning the tails fraction. In some embodiments, the process further comprises regrinding the tails fraction prior to cleaning. In another embodiment, the process further comprises repeating the cleaning and optionally the grinding until a tails fraction comprising the nickel sulfide of a desired grade is obtained. In some embodiments, the process further comprises addition of one or more further portions of collector during cleaning and/or regrinding.

[0066] In an embodiment, the process further comprises de-watering the froth fraction and/or the tails fraction. In another embodiment, the process further comprises de-watering the froth fraction. In another embodiment, the process further comprises de-watering the tails fraction. It will be appreciated by a person skilled in the art that in embodiments comprising one or more cleaning steps, the froth fraction orthe tail fraction that is de-watered is the froth fraction or the tail fraction, as the case may be, obtained after all cleaning steps have been carried out.

[0067] The following non-limiting examples are illustrative of the present application:

EXAMPLES

Example 1 : Synthesis of fatty acid polyethylenimine collectors

I. Materials

[0068] Polyethylene imine (PEI): Aldrich 408700-250ml, M_n 1800 by GPC and Mw 2000 by light scattering, 50% in water. It was found by ¹H-NMR spectroscopy that the PEI had a ratio of NH₂ : NH : N of 0.35 : 0.31 : 0.34.

[0069] Fatty acids: stearic (C18; Anachemia), propionic (C3; Aldrich) and valeric (C5; Aldrich) acids were used as received.

II. Methods [0070] PEI was reacted with the fatty acids (FAs) under conditions selected with the objective to convert 90% of all the primary amine (-NH₂) sites in PEI into amides with the desired attached fatty acid (i.e. PEI-NH-CO-FA), wherein FA refers to the alkyl chain moiety of the fatty acid. First, water was evaporated from the 50% PEI water solution by heating to 135°C or more. The fatty acid (solid or liquid, as the case may be) was added slowly to the hot PEI obtained from the previous step. The mixture was left stirring at 125°C or more overnight.

III. Results and Discussion

[0071] Three versions of the modified PEI (RX1 , n=16; RX2, n=1 ; and RX3, n=3) were made and analyzed by NMR to confirm the reaction product and consumption of the reagent (fatty acid). The overall reaction was:

polymer fatty acid modified PEI byproduct

[0072] RX1 (n=16) was not water soluble but dissolved in ethanol (EtOH). RX2 (n=1) and RX3 (n=3) were water soluble to at least 10 wt% . The PEI was a branched form of the polymer with a molecular weight of 1800-2000. However, a range of other polymer molecular weights may be suitable for similar use as a collector (Example 3).

[0073] NMR spectroscopy revealed the fatty acids were attached to the PEI polymer. The polymer modification occurred at the amine sites of the PEI polymer where they reacted with the carboxylic acids and formed amide linkages -NH-C(O)-, followed by the elimination of a water molecule. As a result, the carbon atoms of the newly formed amide groups -NH-C(O)- were different than the fatty acids’ carbon atoms -C(0)-OH therefore the reaction could be monitored by using ¹³C NMR spectroscopy. The -COOH carbon of the fatty acids appeared at 180 ppm while the newly formed amide carbon -C(0)NH- moved to lower frequencies, 174 ppm or lower. The amide carbon atoms always appeared as two peaks, one at 174 ppm and another one at lower frequency around 168 ppm. While not wishing to be limited by theory, there are a few possible explanations: 1) the reaction occurred at both the primary and the secondary amine sites resulting in two different amide carbon atoms, 2) the reaction occurred only at the primary amine sites but the steric hindrance caused by the long alkyl chains resulted in less mobility of the amide bond hence more than one peak for the carbon atom, and 3) it is also possible to have a combination of 1 and 2.

[0074] The ¹H NMR spectra also showed the newly attached alkyl chains onto the PEI backbone. Furthermore, the quantitative aspect of ¹H-NMR allowed for comparison of the areas under the peaks which made it possible to estimate the ratio of attached fatty acid molecules per ethylene repeat unit (-N-CH₂-CH₂-N) of the PEI; the ratio was found to be 1 :3 which was as expected from the reaction’s stoichiometry. In other words, the fatty acid was added quantitatively to yield a degree of substitution of 90% on the primary amines (-NH2-).

Example 2: Testing of modified PEI in high pH conditions

[0075] One of the PEI polymers, PEI-PA (RX2), was tested for stability of the newly formed amide bond under caustic conditions which could potentially cause hydrolysis and detachment of the fatty acid from the polymer.

[0076] A 1 % solution of the polymer in water was prepared and analyzed by ¹ H- NMR as the reference, under neutral conditions. A 1 % solution of the same polymer was then prepared in caustic (pH 12.2) water and analyzed four times by NMR over a 72 hour period at time points of 1 , 4, 7, and 72 hours.

[0077] The fatty acid’s CH₂ group directly attached to the amide moiety is a good candidate for tracking the stability of the amide bond as a function of time because it is in close proximity and would be affected by hydrolysis. The CH₂ signal remained unchanged, in shape and position, even after 72 hours which indicated the PEI-FA amide bonds can withstand caustic (e.g. pH 12.2) conditions.

Example 3: Testing of modified PEIs in froth flotation of sulfides

I. Materials and Methods

[0078] X-Ray Fluorescence (XRF): The XRF was carried out using a 4kW sequential Wavelength Dispersive X-ray Fluorescence Spectrometer (Bruker S4 Pioneer) equipped with a Rh-anode X-ray tube with 75m thin Be end window, four analyzer crystals (LiF200, Ge, PET and XS-55) and two detectors (a scintillation counter detector and a flow counter detector). Beads were prepared by fusion using 0.1 grams of sample pulverized to 35 μm. All assays were based on single beads unless otherwise indicated. The XRF method for quantitative evaluation of flotation performance and reagents was deemed suitable with typical mass balances on copper and nickel within +/- 3 wt %.

[0079] X-ray Powder Diffraction (XRD): The X-ray powder diffractometer (Bruker D8 Advance) was configured with the Bragg Brentano geometry (theta-theta) and with a Cobalt (Co) X-ray tube and a Position Sensitive Detector (VANTEC-1). For samples prepared as random mount, data were collected from 4 to 70°2Q using a step size of 0.02°2Q and a count time 2 seconds per step.

[0080] Collectors: Diphenyl guanidine as pellets (Rokem) was used as a 23% solution in water/acetic acid. The fatty acid modified polyethyleneimines (FA-PEIs) were synthesized as described in Example 1.

[0081] Matte: The matte is made up mainly of nickel sulphide (heazlewoodite, N13S2) and copper sulphide (chalcocite, CU2S). There is also pyrrhotite (FeS(0.8-1.0)), and metallic alloy (nickel alloy with platinum group metals). The elemental composition determined by XRF was 57% Ni, 21 % Cu, 0.8% Fe and 20.8% S (as is before removing magnetic fraction) and 52% Ni, 27% Cu, 0.5% Fe and 23.0% S (flotation feed after removing magnetic fraction). Semi-quantitative XRD of the matte indicated its composition was: 70.81% heazlewoodite, 22.40% metallic nickel, 4.66% chalcocite and 2.13% quartz after a 20 minute grind.

[0082] Mineral Processing: The process water was tap water with lime addition to reach a targeted conductivity of 3 mS/cm. A P80 of 45-60 μm in a rod mill with stainless steel rods and mill body was targeted. In an exemplary test, 1 kg of - 6 mesh matte and 333 mL process water were subjected to a primary grinding step. After 10 minutes, before the magnetics fraction was removed, the P80 was 250 μm. Following the primary grinding, magnetic separation was performed using a magnet tested to have a strength of 730 Gauss for a time of 15 minutes. A weaker magnet of 250 Gauss was also tested and gave similar results for the magnetic fraction that was removed. The magnetic concentrate (MagC) was collected into a first beaker containing water, the MagC was then released, and collected again as the cleaning of MagC. Then the MagC was transferred into a second beaker with water for final collection. The magnetic tail and the first beaker contents were filtered together. After the magnetics fraction was removed from this material, the P80 decreased to 90 μm. Secondary grinding was then performed for 4 minutes with the inclusion of the collector and 180 mL process water. After secondary grinding, the P80 decreased to 40 μm. The rod mill was discharged into a 2.2 L Denver 12 flotation cell and lime was added to adjust electrical conductivity to 3 mS/cm. The flotation was started with a rate of 2 L/min air (unless otherwise specified) and the concentrate collected at intervals of 0.5, 1 , 2, 5, 8 and 12 min (cumulative time) into separate buckets. The tail and concentrates were filtered and dried in an oven overnight. Samples were prepared to obtain representative small quantities for chemical analysis. Table 1 provides the overall test schedule for the collectors used in this Example. The collector dosage indicates an initial dosage as intended in normal operation. Selected tests (as indicated) used additional collector in the later concentrates, see Tables 2-8 for details on the flotation schedule for each test.

II. Results and Discussion

[0083] The chemical structure of an exemplary branched PEI is shown below where the terminating end-groups of NH2 are the primary amines:

[0084] These primary amines are the most reactive and most sterically accessible for reaction. These are the main sites modified by the addition of a fatty acid in the reactions of Example 1 and the resultant structure is an amide.

[0085] Properties of the three FA-PEIs synthesized as described in Example 1 and used in this Example are summarized in Table 9. Tables 10-23 include data for the metallurgical balance and combined products for the froth flotation tests of this Example including mass pulls, Cu and Ni assays and mass balances (Head Call Factors between 97 and 103) validating the results. These head call factors represents an overall balances with an error of +/- 3 wt%.

[0086] In the context of the current separation, the preprocessing at high pH converts nickel sulphides into hydrophilic material. A useful collector then attaches preferentially to the copper sulphide particles. The concentrate is enriched in copper (as sulphide) and the tails is enriched in nickel (as sulphide and metallic nickel) and depleted of copper (sulphide). A plot of copper recovery as a function of the cumulative nickel assay can be used as a means to rank the effectiveness of collectors³. For example, a collector having a position to the “far left” or lowest nickel content for a given copper recovery on such plot may be considered the most effective. However, other factors may also be important, for the selection of a collector such as the ability for a collector to remain active in subsequent flotation tests, in particular, cleaning stages of flotation.

[0087] The first flotation tests with DPG set a benchmark for alternative collectors evaluated and to develop assay methods. A benchmark was used, for example, because of different matte compositions, flotation cell types, impellers, grind times, initial sample particle sizes and pH/conductivity conditions. Benchmarking tests with DPG were performed in triplicate, primarily to address the impact of the different removal rates of magnetic material after the primary grinding step. These benchmarking tests are compared to the DPG results reported by Agar (1993) in Figure 1 of the present application. The copper recovery is in the typical fashion for flotation performance. The abscissa is not the typical mass pull but the cumulative nickel assay. This is a useful method for what is essentially a two component system; the nickel assay in the concentrate is the “impurity”.

[0088] While not wishing to be limited by theory, the lower nickel assay for a given copper recovery in the Agar tests could be attributed to the higher pH and longer grind times used by Agar. For example, a higher pH can result in a more complete oxidation of the nickel sulfide surfaces, acting as a suppression mechanism. Agar (1996) noted that poor flotation occurred when the pH was not controlled properly and dropped below the target pH. While not wishing to be limited by theory, the longer grind times used by Agar 1993 would be expected to generate a lower nickel assay via greater liberation of copper/nickel sulfides. Finally, the matte used in the current work, while having a similar assay to the Agar study in 1993, may be different in terms of mineralogy and grain formation of heazlewoodite and chalcocite. In the current work, good reproducibility was achieved with tests DC-14 and DC-15 where the copper recovery was within 10% over the range of measured nickel assays. The first test, DC- 13 yielded different results: the initial nickel assays were lower than the DC-14/15 tests and lower than the Agar tests under what should have been better suppression of heazlewoodite and better liberation in the Agar tests. The flotation performance in the final part of the rougher-scavenger test in DC-13 decreased. The copper recovery rate decreased rapidly and only reached 75% and the nickel assay increased. The only significant difference between the three tests was the “Mags” value, which represented the mass fraction of matte removed by magnetic separation after 10 minutes of grinding. The magnetics fraction in DC-13 was 39 wt%, compared to 30-31 wt% in the other two DPG benchmarks. While not wishing to be limited by theory, removing a larger fraction of magnetics would have been expected to affect several parts of the overall matte separation. The potential impacts are discussed and rationalized below:

[0089] Particle size distribution: When more material was removed during the de-mag step, a smaller charge was put in the mill for the secondary grind. While not wishing to be limited by theory, the expected result would have been a more efficient grind with a smaller overall particle size. The expected result of this would have been better liberation of heazlewoodite and chalcocite. This could have explained the lower nickel grade at the start of the flotation. Overgrinding could have had a negative impact if the particle sizes were too small and there was non-selective entrainment of both copper and nickel sulfides. However this was not the case at the start of the flotation.

[0090] Nickel suppression: The separation efficiency relies on the deactivation of heazlewoodite to minimize DPG adsorption by creating a nickel hydroxide surface. While not wishing to be limited by theory, if the de-mag removed more material, there would be more hydroxide ions available for a given surface area of heazlewoodite. This effect could have been in opposite trend to an overgrind condition where the surface area would have increased at a greater rate (proportional to the inverse of the square of the particle radius) compared to an overall mass reduction (linear with mass).

[0091] Copper suppression: If more magnetic material was removed, a greater amount of hydroxide ion was available per unit mass of matte. If the oxidation of heazlewoodite was complete, then excess hydroxide would have been available and possibly suppressed chalcocite. However Agar 1993 noted that the separation efficiency increased with increasing conductivity (see Figure 5 of that reference; the conductivity was an indirect measure of hydroxide concentration) and plateaued. This suggested that an excess of hydroxide would not have suppressed chalcocite and resulted in the low recovery of copper. [0092] Slurry concentration: In general, while not wishing to be limited by theory, a reduction of the slurry concentration would have been expected to result in better flotation performance through various mechanisms including lower viscosity, however the opposite effect was observed. A lower slurry concentration would also have resulted in excess DPG based on an overall dosage of 100 g/ton which was based on the raw matte before the de-mag stage. Overdosing DPG was not expected to result in a low copper recovery. In an extreme case, if the higher magnetics fraction resulted in a finer grind in the second stage then there may have been an under dosing of DPG. In the case that it is “stoichiometric” then an overgrind could have resulted in low copper recovery, but still give a high copper grade/low nickel assay in the first concentrates.

[0093] The flotation tests with the fatty acid modified polyethylenimines are summarized in Figure 2 and Table 24. RX1 was not water soluble whereas the RX3 collector was water soluble up to at least 10 wt%. High solubility of a reagent in water may, for example, be advantageous for reasons such as materials handling, dosing, and/or reduced shipping costs. In matte flotation, useful performance of the collector is indicated by high copper recovery (e.g. 90% or more) and lower nickel concentrations. However, tabulated results are not fully indicative of the collector efficacy, and a graphical representation of the flotation results readily indicate differences between the collectors (Figure 2).

[0094] Collector RX1 (DC 18) at 400 g/ton was very effective at the start of the flotation. This test used 20 g/ton of MIBC and yielded initial concentrates with the lowest nickel assays recorded in this work. The nickel assay for the first 45% copper recovery was similar to the best DPG benchmark. Subsequently, the productivity decreased and additional collector (300 g/ton) was added for a 7th concentrate, with no improvement. The flotation in this test, with respect to low copper recovery and high grade, was similar to the DC-13 benchmark with DPG. The DC-13 benchmark and DC-18 test both had higher than normal magnetic fractions removed. While not wishing to be limited by theory, the performance of the RX1 collector may have been similar to the other DPG benchmarks if the magnetic fraction would have been in the range of 30-31 %. [0095] Subsequent tests were performed with the RX3 collector which was modified with the C5 fatty acid. This collector was water soluble and was prepared at 10 wt% in water. This allowed adding less water or ethanol to the mill for secondary grinding. The DC-18 test with RX1 used 40 ml of 1 % FA PEI in ethanol to achieve the dosage rate of 400 g/ton. While not wishing to be limited by theory, the volume of liquid added to introduce the collector could have affected the flotation via two mechanisms: (1) Reduction of the conductivity/pH would have occurred through simple dilution of the hydroxyl ion concentration. 40 ml of water or ethanol could represent a decrease of the conductivity from 3.0 mS/cm to 2.45 mS/cm. This may have reduced the suppression of the heazlewoodite. Ethanol may also have consumed hydroxyl and formed ethoxide ions. (2) Changes in the grinding characteristics may also have occurred because the slurry concentration in the mill decreased in the secondary grind. DPG’s concentration in acetic acid was 26 % and only 0.42 ml was added to achieve a dosage rate of 100 g/ton.

[0096] Subsequent tests with RX3 used 1200 g/ton (DC-20) because the copper recovery in the RX1 test only reached 60%, suggesting underdosing of the collector. The first RX3 (DC-19) test resulted in “excessive frothing” and no separation. The second RX3 test (DC-20) resulted in better separation (lower Ni concentration) and high copper recovery (>90%). Frothing was still excessive. The third RX3 test (DC-21) used 100 g/ton of collector, yielding better separation (lower Ni) at a copper recovery of 60%, the nickel concentration was 24.9 wt% at 100 g/ton compared to 30 wt% at a collector concentration of 400 g/ton. An intermediate concentration (more than 100 and less than 400 g/ton) may give good copper recovery and low nickel in the concentrate. A more detailed discussion follows.

[0097] Flotation tests with the C5 FA-PEI RX3 used dosages of 1200 (DC-19), 400 (DC-20) and 100 g/ton (DC-21 ). Air flows were also adjusted during the tests to account for different frothing behaviour at the different dosages. In the DC-19 flotation test with collector RX3 at 1 ,200 g/ton, the initial air flow was 2 L/min. Frothing was excessive, the test was interrupted, and the concentrates returned to the cell. The air flow was reduced to 1 L/min and then 0.5 L/min and the froth production was reduced. The concentrates were collected with no action by the operator to paddle the concentrate into pans. By contrast, flotation with DPG produced a froth with large bubbles and froth that was not “mobile” but required the operator to manually paddle froth into collection pans.

[0098] The copper recovery-nickel assay results for DC-19 showed that high copper recovery was achieved (80%) but that the nickel grade was very high, approximately 45 to 48 %, or the same as the feed concentration. While not wishing to be limited by theory, this indicated that there was no selectivity for copper over nickel in the concentrate and this was likely the result of the excessive frothing and non- selective entrainment of all materials in the concentrate. The subsequent step used 400 g/ton of RX3 and an air flow of 1 L/min. The copper recovery increased to 91% and the nickel assay decreased to 37 % at 91 % copper recovery. At 80% copper recovery the nickel assay was 32%, indicating the final concentrate was primarily nickel. Frothing was qualitatively aggressive, with a froth depth of 8-11 cm for concentrates 4 and 5.

[0099] The final test used RX3 at a dosage rate of 100 g/ton, the same as DPG. Frothing was not as aggressive and an airflow of 2 L/min was used. The nickel assay in the first concentrate was 19% with 25% copper recovery. Subsequent concentrates increased copper recovery to 60% after which the froth collapsed. The froth height was 2.5, 5 and 8 cm for concentrates 1 , 2 and 3 respectively and was generally dense. These were unusually tall froths and combined with the high density of the froth/fine bubbles, while not wishing to be limited by theory, could have impeded drainage of nickel compounds and decreased copper purity in the concentrate. Despite the tall froth for concentrates 1 , 2 and 3, the froth collapsed during collection of con 4; see the small increase in copper recovery from 60 to 70%. After con 4, 1 ml of MIBC at 1 % was added which generated a deep froth again and raised the copper recovery to 87 %. However, frothing was excessive again and the nickel assay increased.

[00100] The performance of the final test with 100 g/ton may, for example, be further improved with a tall flotation cell, to avoid spontaneous overflow and allow better froth drainage. A lower impeller speed may reduce the froth density to allow for better drainage, or staged addition of collector may be beneficial.

[00101] Comparing the DC-18 and DC-21 tests suggests that an intermediate C number of the fatty acid may reduce the nickel content in the concentrates and reduce frothing to a better degree to avoid entrainment. A strategy combining a blend of RX1 and RX3 may also be advantageous.

III. Summary

[00102] Fatty acid modified PEIs were studied for use as collectors in the separation of heazlewoodite (Ni₃S₂) and chalcocite (CU₂S) from a Bessemer matte material. Two polyalkyleneimines with fatty acid substitutions of Example 1 were tested. The polyalkyleneimine was a branched polyethylenimine (PEI) with a molecular weight of 2,000 Da and the ones tested in this Example had C5 and C18 fatty acids which introduced hydrophobicity forfloatability. The C18 substituted PEI was not water soluble. The C5 and C3 substituted PEI collectors were water soluble to at least 10 wt%. The initial flotation performance of the C18 PEI collector was similar to that of DPG with similar copper recovery and nickel assay. The final copper recovery was lower for both collectors (60-70%) and the nickel assay was 16% using DPG compared to C18 PEI at 21 wt%. The C5 PEI collector was water soluble and tested at three concentrations, with the lowest concentration yielding the best/lowest nickel assay. The C5 PEI collector, like DPG, has self-frothing properties and the first tests, with 1 ,200 g/ton and 400 g/ton doses of C5 PEI frothed aggressively with high nickel entrainment in the froth concentrate. The lowest nickel assay was achieved with 100 g/ton, the same dosage as DPG. Compared to DPG, the nickel assay was higher, however the frothing with C5 PEI at 100 g/ton was still excessive and the high nickel grade was likely due to entrainment rather than poor selectivity. A combination of C18 and C5 PEI may have advantageous properties as the initial Ni grade was low with C18 PEI and the final Cu recovery was high with C5 PEI.

[00103] While the present application has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the application is not limited to the disclosed examples. To the contrary, the present application is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[00104] All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present application is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

FULL CITATIONS FOR DOCUMENTS REFERRED TO IN THE DESCRIPTION

¹ George Asante Nyamekye, “Adsorption Of Dextrin Onto Sulphide Minerals And Its Effect On The Differential Flotation Of The Inco Matte”, PhD Thesis, The University Of British Columbia, Vancouver, February 1993.

² GE Agar et al., “Laboratory flotation separation of Inco bulk matte” Minerals Engineering 1996, 9:12, 1215-1226.

³ GE Agar et al., “Choosing a water soluble collector for matte separation” XVIII International Processing Congress Sydney, 23-28 May 1993, 989-995.

Table 1 : Summary of Matte Flotation Reagent Tests

Table 2: Flotation Schedule for Test DC-13*. DPG 100 g/ton. w

Flotation Cell: Denver, 2.2L; Mag Fraction: 40.5%; Speed: 1320 rpm.

Table 3: Flotation Schedule for Test DC-14*. DPG 100 g/ton. w N

Flotation Cell: Denver, 2.2L; Mag Fraction: 30.6%; Speed: 1320 rpm.

Table 4: Flotation Schedule for Test DC-15*. DPG 100 g/ton and Xanthates. w w

^* Flotation Cell: Denver, 2.2L; Mag Fraction: 30.2%; Speed: 1320 rpm.

^** Rougher 7 was collected after Xanthate and MIBC addition was performed stepwise according to the following schedule:

SIPX = sodium isopropyl xanthate; PAX = potassium amyl xanthate; ^* pH = 11.9; Conductivity = 2.96 mS/cm.

Table 5: Flotation Schedule for Test DC-18*. RX1 400 g/ton. w

Flotation Cell: Denver, 2.2L; Mag Fraction: 35.4%; Speed: 1320 rpm.

Table 6: Flotation Schedule for Test DC-19*. RX3 1200 g/ton. w n

* Flotation Cell: Denver, 2.2L; Mag Fraction: 31.7%; Speed: 1320 rpm.

Table 7: Flotation Schedule for Test DC-20*. RX3400 g/ton. w

CD

Flotation Cell: Denver, 2.2L; Mag Fraction: 31.2%; Speed: 1320 rpm.

Table 8: Flotation Schedule for Test DC-21*. RX3 100 g/ton. w

Flotation Cell: Denver, 2.2L; Mag Fraction: 30.4%; Speed: 1320 rpm.

Table 9: Summary of fatty acid PEI collectors. All PEIs were branched, 2000 Da Mw, degree of substitution was 0.9 on the primary amine.

Table 10: Metallurgical balance for DC-13*. w

CD

Head Direct for Cu, Ni, Ni elemental and Fe are estimates.

Table 11: Combined products for DC-13.

Table 12: Metallurgical balance for DC-14.

Table 13: Combined products for DC-14.

N

Table 14: Metallurgical balance for DC-15. w

Table 15: Combined products for DC-15.

Table 16: Metallurgical balance for DC-18. n

Table 17: Combined products for DC-18.

CD

Table 18: Metallurgical balance for DC-19.

Table 19: Combined products for DC-19.

00

Table 20: Metallurgical balance for DC-20.

CD

Table 21 : Combined products for DC-20.

n o

Table 22: Metallurgical balance for DC-20. n

Table 23: Combined products for DC-20.

n

N

Table 24: Matte separation test conditions, initial Ni concentration, final Cu recovery and final Ni concentration.

Claims

Claims:

1 . A froth flotation process for separating a copper sulfide and a nickel sulfide from a material comprising the copper sulfide and the nickel sulfide, the process comprising: agitating an aqueous suspension comprising particles of the material and a collector while introducing a gas, thereby floating the copper sulfide in a froth fraction and depressing the nickel sulfide in a tails fraction; and separating the froth fraction from the tails fraction, wherein the collector is a hydrophobically modified polyalkyleneimine.

2. The process of claim 1, wherein the copper sulfide is chalcocite, digenite, or a combination thereof, and the nickel sulfide is heazlewoodite.

3. The process of claim 2, wherein the material is obtained by a process comprising cooling a Bessemer matte under conditions to obtain the chalcocite, digenite pr combination thereof, and heazlewoodite.

4. The process of claim 2 or claim 3, wherein the aqueous suspension has a pH of from about 12 to about 12.6.

5. The process of claim 2 or claim 3, wherein the aqueous suspension has a conductivity of from about 2.5 mS/cm to about 3.5 mS/cm.

6. The process of claim 5, wherein the aqueous suspension has a conductivity of about 3.0 mS/cm.

7. The process of any one of claims 1 to 6, wherein the collector is present in an initial dose of from about 100 g/ton to about 400 g/ton of the material.

8. The process of any one of claims 1 to 7, wherein the gas is air.

9. The process of any one of claims 1 to 8, wherein the process further comprises conditioning of the aqueous suspension.

10. The process of any one of claims 1 to 9, wherein the process further comprises grinding of the material to obtain the particles.

11 . The process of claim 10, wherein the grinding comprises: primary grinding of a mixture comprising the material and water; magnetic separation of the ground mixture to obtain a magnetic concentrate and a demagnetized tail; and secondary grinding of the demagnetized tail to obtain the particles.

12. The process of any one of claims 1 to 11 , wherein the hydrophobically modified polyalkyleneimine is a hydrophobically modified polyethyleneimine.

13. The process of any one of claims 1 to 12, wherein the hydrophobically modified polyalkyleneimine is branched.

14. The process of any one of claims 1 to 13, wherein the hydrophobically modified polyalkyleneimine has been prepared by reacting a polyalkyleneimine with R¹COOH, wherein R¹ is C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_3-32cycloalkyl, C_5-32cycloalkenyl, C_10-32cycloalkynyl or aryl, wherein the C_1-32alkyl, C_3-32alkenyl, C_3-32alkynyl, C_{3- 32}cycloalkyl, C_5-32cycloalkenyl, C_10-32cycloalkynyl and aryl are unsubstituted or are optionally substituted with one or more groups selected from C_3-16cycloalkyl, C_{5- 16}cycloalkenyl, C_10-16cycloalkynyl and C6-ioaryl.

15. The process of claim 14, wherein R¹ is a linear C₂-1 zalkyl.

16. The process of claim 14, wherein R¹ is n-butyl.

17. The process of claim 14, wherein R¹ is n-heptadecyl.

18. The process of claim 14, wherein the hydrophobically modified polyalkyleneimine is a combination of:

(i) a hydrophobically modified polyalkyleneimine prepared by reacting a polyalkyleneimine with R¹COOH, wherein R is n-butyl; and

(ii) a hydrophobically modified polyalkyleneimine prepared by reacting a polyalkyleneimine with R¹COOH, wherein R is n-heptadecyl.

19. The process of any one of claims 13 to 18, wherein about 90% of primary amine sites in the branched polyalkyleneimine are hydrophobically modified.

20. The process of any one of claims 13 to 19, wherein the polyalkyleneimine has a weight average molecular weight (M_w) of from about 500 Da to about 50,000 Da, optionally wherein the M_w is about 2000 Da.

21. The process of any one of claims 1 to 16 and 18-20, wherein the process is carried out in the absence of an additional frother.

22. The process of any one of claims 1 to 20, wherein the process further comprises adding a frother to the aqueous suspension.

23. The process of claim 22, wherein the frother is methyl isobutyl carbinol.

24. The process of any one of claims 1 to 23, wherein the process further comprises separation of magnetic material from the froth fraction and/or tails fraction.

25. The process of any one of claims 1 to 24, wherein the process further comprises cleaning the froth fraction, optionally wherein the process further comprises regrinding the froth fraction prior to cleaning.

26. The process of claim 25, wherein the process further comprises repeating the cleaning and optionally the grinding until a froth fraction comprising the copper sulfide of a desired grade is obtained.

27. The process of any one of claims 1 to 26, wherein the process further comprises cleaning the tails fraction, optionally wherein the process further comprises regrinding the tails fraction prior to cleaning.

28. The process of claim 27, wherein the process further comprises repeating the cleaning and optionally the grinding until a tails fraction comprising the nickel sulfide of a desired grade is obtained.

29. The process of any one of claims 25 to 28, wherein the process further comprises addition of one or more further portions of collector during cleaning and optionally regrinding.

30. The process of any one of claims 1 to 29, wherein the process further comprises de-watering the froth fraction and/or the tails fraction.