A flotation collector composition and flotation method

Abstract

The invention provides a flotation method comprising: providing a mineral composition comprising comminuted ore particles, the mineral composition comprising at least one target sulfide mineral; producing a pulp comprising the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation; passing gas bubbles through the pulp; and recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in at least one target sulfide mineral, wherein the mineral composition comprises a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 μm, and wherein at least 50% of the at least one target sulfide mineral in the first coarse fraction is recovered in the mineral concentrate.

Description

A flotation collector composition and flotation method

[0001] The present application claims priority from Australian provisional patent application No. 2023904100 filed on 18 December 2023, the contents of which should be considered to be incorporated into this specification by this reference.Technical Field[2] The present invention relates to a flotation method in which a particulate mineral composition is floated in an aqueous phase, thereby producing a mineral concentrate enriched in target sulfide mineral. The aqueous phase comprises a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms and an organic cation. The particulate mineral composition comprises a coarse fraction of comminuted ore particles with large particle sizes, and a high proportion of the target sulfide mineral in the coarse fraction is recovered in the mineral concentrate. The invention further relates to a flotation collector composition comprising a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms and an organic cation.Background of Invention[3] Froth flotation is a well-established mineral separation process used by the mining industry to separate valuable minerals from low value gangue minerals based on differences in their natural or induced hydrophobicity. Flotation provides a cost- effective means of concentrating the valuable components of an ore into a mineral concentrate of a grade suitable for feeding to pyrometallurgical or hydrometallurgical operations to ultimately recover the metals.[4] A flotation process involves comminuting the ore to liberate the valuable mineral and gangue components, pulping the resultant comminuted ore particles with water containing various chemical reagents (e.g. pH modifiers, depressants, activators, collectors, frothers, etc) in a flotation cell, providing sufficient reagent conditioning time, and passing a stream of air bubbles through the pulp to form a froth layer on the pulp surface. Hydrophobic mineral particles in the pulp attach to the air bubbles and arethus transported to and concentrated in the froth, which is then collected from the flotation cell.[5] One of the most important reagents in the flotation process is the collector. Flotation collectors are chemicals used to render the surface of valuable metal-bearing mineral particles hydrophobic, thus facilitating their recovery by flotation. Different types of flotation collector chemistries are available depending on the class or type of minerals to be concentrated, for example sulfide or oxide minerals. Moreover, some flotation collectors selectively separate and recover target minerals over other minerals of the same class (selective collectors) whilst other do not display any significant selectivity and simultaneously float a wide range of minerals from the same class, both valuable and gangue, for maximum recovery (bulk collectors). Stronger, more hydrophobic collectors have increased activity for flotation but conversely tend to have lower selectivity. The solubility, adsorption characteristics, pH application range and physical state (solid or liquid) also vary for different collectors, so that selecting the most appropriate collector to process any given ore is challenging and often made through empirical observations.[6] The most common collectors used for industrial sulfide mineral flotation are anionic thiol collectors, including xanthates (dithiocarbonates), dithiophosphates, dithiophosphinates, mercaptobenzothiazoles and dithiocarbamates. The cationic counterion to the thiol collector anion is an alkali metal ion, typically either Na+or K+. The surface-active collector anions include a thiol functionality with an affinity for sulfide mineral surfaces and a hydrophobic hydrocarbon chain which imparts hydrophobicity (increased water contact angle) to the sulfide mineral particle.[7] The collecting ability of flotation collectors, in terms of rate and overall recovery, increases as the hydrocarbon chain length or branching on the hydrocarbon chain increases due to the greater hydrophobicity imparted to the mineral particles. Studies have also shown that longer chain xanthates are more readily oxidized to dixanthogen (the active hydrophobic flotation agent in some instances) at lower potentials. However, the water solubility of flotation collectors decreases as the hydrocarbon chain length increases. Long-chain xanthates also tend to aggregate as micelles in aqueous solution, with the critical micelle concentration (40°C) of potassium dodecyl xanthate reported as 5.5 x 10’3M (Hamilton and Woods, International Journalof Mineral Processing 1986 17 113). These effects can cause uneven distribution of the collector throughout the flotation pulp and reduced availability of the collector for mineral particle contact and adsorption, leading to unsatisfactory mineral flotation and recovery. Accordingly, anionic thiol collectors used industrially are limited to short hydrocarbon chain lengths. The shortest xanthate sold commercially for industrial application is ethyl xanthate (2 carbon hydrophobic group) and the longest is amyl xanthate (5 carbon hydrophobic group).[8] Recovery of target minerals present in larger ore particles (so-called coarse particles) is particularly challenging, since the required degree of hydrophobicity for bubble attachment increases with increasing particle size, fine particles disproportionately consume collector in the pulp leaving coarser particles with insufficient collector to render them floatable, and larger particles are more likely to be composite particles comprising both target minerals and gangue minerals. These issues can be mitigated to some degree by grinding the ore to finer particle size distributions. However, ore grinding is extremely energy-intensive and costly, and it is desirable to minimise the extent of grinding conducted prior to flotation. Also, a greater proportion of poorly floating fine particles (those <10 pm) are generated with increased grinding.[9] Improvements in flotation technology are therefore needed to increase target mineral recoveries and / or reduce the comminution requirement for ore feedstocks to flotation, particularly feedstocks with a significant coarse fraction. Improvements can in principle be achieved via engineering or chemical approaches, with chemical approaches often being simpler and cheaper to implement. Therefore, effective collectors which can improve sulfide mineral recoveries, in particular the recovery of difficult-to-float coarse and composite particles, would be of great interest to industry. Unfortunately, the commercial collectors available for sulfide mineral flotation are limited in the degree of hydrophobicity they can impart and cannot always meet the higher hydrophobicity demand of coarse and composite particles.

[0010] There is therefore an ongoing need for flotation methods and flotation collector compositions which at least partially address one or more of the above- mentioned short-comings, or provide a useful alternative.

[0011] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.Summary of Invention

[0012] The inventors have now developed flotation collector compositions comprising thiol collector anions which are highly effective for recovering a wide range of target sulfide minerals from particulate ore compositions by froth flotation. Notably, the enhanced overall recovery, compared with common industrially applied collectors, is attributed at least in part to a very substantial improvement in the flotation of coarse and / or composite particles present in the ore composition. The collector compositions can therefore also be used to obtain attractive or at least acceptable target mineral recoveries from ore compositions that are too coarse for satisfactory flotation using conventional collectors.

[0013] The collector compositions disclosed herein include a thiol collector anion having a long-chain hydrophobic group which can impart a high degree of hydrophobicity when the collector is adsorbed to a target mineral surface. Such thiol collector anions were found to be water soluble, and thus practically applicable in froth flotation, when combined with an organic cation, including organic anions lacking surface active properties themselves. Without wishing to be limited by any theory, it is proposed that the bulky and / or asymmetric character of organic cations, in comparison to an alkali metal cation used in common commercial xanthate collectors, achieves the desired effect by reducing the lattice energy of the resultant 1 :1 ion pair, thus encouraging water solubility. An analogy can be recognised here with the field of ionic liquids where a wide range of organic cations, typically including a nitrogen, phosphorous or sulfur moiety, form low melting salts (i.e. ionic liquids) when paired with complementary anions due to the low lattice energy of the salts. Observed flotation results also indicate strong absorption of long-chain xanthates to sulfide particles in the presence of the organic cations, so that adverse effects due to loss of available collector to micelle formation (as previously predicted for long-chain surfactants) are not apparent.

[0014] In accordance with a first aspect, disclosed herein is a flotation method comprising: providing a mineral composition comprising comminuted ore particles, the mineral composition comprising at least one target sulfide mineral; producing a pulp comprising the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation; passing gas bubbles through the pulp; and recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in at least one target sulfide mineral, wherein the mineral composition comprises a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 pm, and wherein at least 50% of the at least one target sulfide mineral in the first coarse fraction is recovered in the mineral concentrate.

[0015] In some embodiments, at least 2 wt.%, or at least 5 wt.%, such as at least 10 wt.%, for example at least 15 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the first coarse fraction.

[0016] In some embodiments, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, for example at least 98%, of the at least one target sulfide mineral in the first coarse fraction is recovered in the mineral concentrate.

[0017] In some embodiments, the mineral composition comprises a second coarse fraction of comminuted ore particles with a particle size between 212 and 425 pm, and at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, for example at least 98%, of the at least one target sulfide mineral in the second coarse fraction is recovered in the mineral concentrate.

[0018] In some embodiments, at least 2 wt.%, or at least 3 wt.%, such as at least 5 wt.%, for example at least 10 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the second coarse fraction.

[0019] In some embodiments, the mineral composition comprises a third coarse fraction of comminuted ore particles with a particle size between 425 and 850 pm, and at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, for example at least 98%, of the at least one target sulfide mineral in the third coarse fraction is recovered in the mineral concentrate.

[0020] In some embodiments, at least 2 wt.%, or at least 3 wt.%, such as at least 5 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the third coarse fraction.

[0021] In some embodiments, the organic cation is a non-surfactant organic cation.

[0022] In some embodiments, producing the pulp comprises (i) providing a flotation collector composition comprising the thiol collector anion and the organic cation; and (ii) dispersing the flotation collector composition in the aqueous phase.

[0023] In some embodiments, the flotation collector composition comprises the thiol collector anion and the organic cation present in a water-soluble salt. The water-soluble salt may comprise: (i) the thiol collector anion in an amount of at least 80 mol% of the total anion component of the water soluble salt and (ii) the organic cation in an amount of at least 80 mol% of the total cation component of the water soluble salt.

[0024] In some embodiments, the water-soluble salt is a solid at room temperature.

[0025] In some embodiments, the flotation collector composition is in the form of water-dispersible pellets or agglomerates.

[0026] In some embodiments, the aqueous phase further comprises a frother.

[0027] In some embodiments, the mineral composition has a Pso particle size of greater than 150 pm, such as greater than 200 pm, for example between 200 pm and 300 pm.

[0028] In some embodiments, at least 50 wt. % of the target sulfide mineral initially present in comminuted ore particles with a particle size greater than the Pso particle size is recovered in the mineral concentrate.

[0029] In some embodiments, the mineral concentrate is enriched in a plurality of target sulfide minerals, and the method further comprises selectively recovering at least one target sulfide mineral from the mineral concentrate by subjecting the mineral concentrate to a subsequent froth flotation stage. The subsequent froth flotation stage may use a flotation collector comprising a thiol collector anion comprising a hydrophobic group with fewer than 8 carbon atoms, or fewer than 6 carbon atoms.

[0030] In some embodiments, the mineral composition comprises a tailings product of a preliminary froth flotation stage, and the method further comprises subjecting a comminuted ore to the preliminary froth flotation stage to produce (i) a concentrate enriched in at least one sulfide mineral and (ii) the tailings product. The preliminary froth flotation stage may use a flotation collector comprising a thiol collector anion comprising a hydrophobic group with fewer than 8 carbon atoms, or fewer than 6 carbon atoms.

[0031] In some embodiments, the at least one target sulfide mineral comprises one or more metals selected from the group consisting of copper, nickel, zinc, cobalt, iron, molybdenum and lead.

[0032] In some embodiments, the at least one target sulfide mineral comprises an iron sulfide mineral, and the mineral composition further comprises a precious metal associated with the iron sulfide mineral.

[0033] In some embodiments, the organic cation comprises a cationic heteroatom selected from nitrogen, phosphorous and sulfur.

[0034] In some embodiments, the organic cation is selected from the group consisting of a pyrrolidinium, imidazolium, benzimidazolium, quaternary ammonium, pyrrolium, indolium, carbazolium, pyridinium, quinolinium, piperidinium, piperazinium, morpholinium, phosphonium, sulfonium and combinations thereof.

[0035] In some embodiments, the organic cation is an N-heterocyclic cation comprising quaternary nitrogen.

[0036] In some embodiments, the organic cation is selected from the group consisting of 1 , 1 -dialkylpyrrolidinium cations, 1 ,3-dialkylimidazolium cations and combinations thereof.

[0037] In some embodiments, the organic cation has a molecular weight in the range of 100 g / mol to 600 g / mol.

[0038] In some embodiments, the thiol collector anion is selected from the group consisting of a xanthate, a dithiophosphate, a dithiocarbamate, a dithiophosphinate, and combinations thereof.

[0039] In some embodiments, the hydrophobic group has between 8 and 18 carbon atoms, such as between 10 and 14 carbon atoms.

[0040] In some embodiments, the hydrophobic group is an alkyl group.

[0041] In accordance with a second aspect, disclosed herein is a flotation method comprising: providing a mineral composition comprising comminuted ore particles, the mineral composition comprising at least one target sulfide mineral; producing a pulp comprising the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation; passing gas bubbles through the pulp; and recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in at least one target sulfide mineral, wherein the mineral composition comprises a second coarse fraction of comminuted ore particles with a particle size between 212 and 425 pm, and wherein at least 50% of the at least one target sulfide mineral in the second coarse fraction is recovered in the mineral concentrate.

[0042] In some embodiments, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, for example at least 98%, of the at least one target sulfide mineral in the second coarse fraction is recovered in the mineral concentrate.

[0043] In some embodiments, at least 2 wt.%, or at least 3. wt.%, such as at least 5 wt.%, for example at least 10 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the second coarse fraction.

[0044] In some embodiments, the mineral composition comprises a third coarse fraction of comminuted ore particles with a particle size between 425 and 850 pm, and at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, for example at least 98%, of the at least one target sulfide mineral in the third coarse fraction is recovered in the mineral concentrate.

[0045] In some embodiments, at least 2 wt.%, or at least 3. wt.%, such as at least 5 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the third coarse fraction.

[0046] Embodiments of the flotation method according to the second aspect may generally have features as disclosed herein in the context of the flotation method according to the first aspect.

[0047] In accordance with a third aspect, disclosed herein is a flotation method comprising: providing a mineral composition comprising comminuted ore particles, the mineral composition comprising at least one target sulfide mineral; producing a pulp comprising the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation; passing gas bubbles through the pulp; and recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in at least one target sulfide mineral, wherein the mineral composition comprises a third coarse fraction of comminuted ore particles with a particle size between 425 and 850 pm, and wherein at least 50% of the at least one target sulfide mineral in the third coarse fraction is recovered in the mineral concentrate.

[0048] In some embodiments, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, for example at least 98%, of the at least one target sulfide mineral in the third coarse fraction is recovered in the mineral concentrate.

[0049] In some embodiments, at least 2 wt.%, or at least 3. wt.%, such as at least5 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the third coarse fraction.

[0050] Embodiments of the flotation method according to the third aspect may generally have features as disclosed herein in the context of the flotation method according to the first aspect.

[0051] In accordance with a fourth aspect, disclosed herein is a flotation collector composition comprising: (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation.

[0052] In some embodiments, the organic cation is a non-surfactant organic cation.

[0053] In some embodiments, the organic cation comprises a cationic heteroatom selected from the group consisting of nitrogen, phosphorous and sulfur.

[0054] In some embodiments, the organic cation is selected from the group consisting of pyrrolidinium, imidazolium, benzimidazolium, quaternary ammonium, pyrrolium, indolium, carbazolium, pyridinium, quinolinium, piperidinium, piperazinium, morpholinium, phosphonium, sulfonium and combinations thereof.

[0055] In some embodiments, the organic cation is an N-heterocyclic cation comprising quaternary nitrogen.

[0056] In some embodiments, the organic cation is selected from the group consisting of 1 , 1 -dialkylpyrrolidinium cations, 1 ,3-dialkylimidazolium cations and combinations thereof.

[0057] In some embodiments, the organic cation has a molecular weight in the range of 100 g / mol to 600 g / mol.

[0058] In some embodiments, the thiol collector anion is selected from the group consisting of a xanthate, a dithiophosphate, a dithiocarbamate, a dithiophosphinate, and combinations thereof.

[0059] In some embodiments, the hydrophobic group has between 8 and 18 carbon atoms, such as between 10 and 14 carbon atoms.

[0060] In some embodiments, the hydrophobic group is an alkyl group.

[0061] In some embodiments, the thiol collector anion and the organic cation are present in a water-soluble salt. The water-soluble salt may comprise: (i) the thiol collector anion in an amount of at least 70 mole%, such as at least 80 mol%, of the total anion component of the water soluble salt and (ii) the organic cation in an amount of at least 70 mol%, such as at least 80 mol%, of the total cation component of the water soluble salt.

[0062] In some embodiments, the water-soluble salt is a solid at room temperature.

[0063] In some embodiments, the flotation collector composition comprises a mineral base.

[0064] In some embodiments, the flotation collector composition is in the form of water-dispersible pellets or agglomerates.

[0065] In accordance with a fifth aspect, disclosed herein is a flotation method comprising: providing a mineral composition comprising comminuted ore particles, the mineral composition comprising at least one target sulfide mineral; producing a pulp comprising the mineral composition and an aqueous phase comprising a flotation collector composition according to any embodiment of the fourth aspect; passing gas bubbles through the pulp; and recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in at least one target sulfide mineral.

[0066] Where the terms “comprise”, “comprises” and “comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0067] As used herein, the terms “first”, “second”, “third” etc in relation to various features of the disclosed devices, methods, systems etc are arbitrarily assigned and are merely intended to differentiate between two or more such features that the device, methods, systems etc may incorporate in various embodiments. The terms do not of themselves indicate any particular orientation or sequence. Moreover, it is to be understood that the presence of a “first” feature does not imply that a “second” feature is present, the presence of a “second” feature does not imply that a “first” feature is present, etc.

[0068] Further aspects of the invention appear below in the detailed description of the invention.Brief Description of Drawings

[0069] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0070] Figure 1 schematically depicts a hydrometallurgical process 100 which utilizes a flotation method according to embodiments of the invention.

[0071] Figure 2 schematically depicts a hydrometallurgical process 200 which utilizes a flotation method according to embodiments of the invention.

[0072] Figure 3 is a graph showing the recovery of sphalerite as a function of time in flotation experiments using salts comprising xanthate collector anions with hydrophobic groups of varying chain length, as investigated in Example 5.

[0073] Figure 4 is a graph showing the recovery of sphalerite in the presence of copper sulphate as a function of sphalerite particle size in flotation experiments using salts comprising xanthate collector anions with a short-chain hydrophobic group (4 carbon atoms) and a long-chain hydrophobic group (12 carbon atoms), as investigated in Example 5.

[0074] Figure 5 is a graph showing the recovery of pyrite as a function of time in flotation experiments using salts comprising xanthate collector anions with a shortchain hydrophobic group (2 carbon atoms) and a long-chain hydrophobic group (12 carbon atoms), and without collector, as investigated in Example 6.

[0075] Figure 6 is a graph showing the recovery of pyrite as a function of pyrite particle size in flotation experiments using salts comprising xanthate collector anions with a short-chain hydrophobic group (2 carbon atoms) and a long-chain hydrophobic group (12 carbon atoms), as investigated in Example 6.

[0076] Figure 7 is a graph showing the recovery of chalcocite as a function of time in flotation experiments using salts comprising xanthate collector anions with hydrophobic groups of varying chain length, and without collector, as investigated in Example 7.

[0077] Figure 8 is a graph showing the recovery of chalcocite as a function of time in flotation experiments using different concentrations of salts comprising xanthate collector anion with a 12 carbon atom hydrophobic group, and without collector, as investigated in Example 8.

[0078] Figure 9 is a graph showing the recovery of chalcocite as a function of chalcocite particle size in flotation experiments using 0.03 mol / t of salt comprising xanthate collector anions with a short-chain hydrophobic group (2 carbon atoms) and a long-chain hydrophobic group (12 carbon atoms), as investigated in Example 8.

[0079] Figure 10 is a graph showing the recovery of chalcocite as a function of chalcocite particle size in flotation experiments using 0.12 mol / t of salt comprisingxanthate collector anions with a short-chain hydrophobic group (2 carbon atoms) and a long-chain hydrophobic group (12 carbon atoms), as investigated in Example 8.

[0080] Figure 1 1 is a graph showing the recovery of chalcocite as a function of time in flotation experiments using a salt comprising different organic cations and xanthate collector anion with a 12 carbon atom hydrophobic group, as investigated in Example 9.

[0081] Figure 12 is a graph showing the recovery of copper as a function of copper particle size in flotation experiments with comminuted copper-bearing ore of different particle size distributions, using salts comprising an organic cation and a xanthate collector anion with a long-chain hydrophobic group (12 carbon atoms), as investigated in Example 10.Detailed DescriptionFlotation collector composition

[0082] Disclosed herein is a flotation collector composition comprising: (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation.Thiol collector anion

[0083] The flotation collector composition comprises a thiol collector anion. Thiol collectors (also known as sulfhydryl collectors) encompass a wide range of surfaceactive species which include (i) a polar, sulfur-based functional group having an affinity for the surface of metal sulfide particles, and (ii) a non-polar aliphatic chain (saturated or unsaturated) to render the surface hydrophobic and thus adherent to air bubbles during flotation. In sulfide mineral flotation, the most commonly used thiol collectors are anionic species, i.e. the thiol functionality is in dissociated form (S’). Such thiol collectors are thus often supplied to the flotation process as a salt comprising the anionic collector anion and a counterion.

[0084] The thiol collector anion comprises a hydrophobic group with at least 8 carbon atoms, for example at least 10, or at least 12 carbon atoms. In some embodiments, the hydrophobic group comprises between 8 and 18 carbon atoms, suchas between 10 and 14 carbon atoms. The thiol collector anions according to the present disclosure include more carbon atoms, and thus typically impart higher hydrophobicity, than common commercially available thiol collectors which have 5 or fewer carbon atoms. Advantageously, thiol collector anions with a hydrophobic group having 8 or more carbon atoms may provide improved activity in sulfide flotation when solubilised according to the principles disclosed herein, with the flotation efficiency positively correlated to the number of carbon atoms.

[0085] In some embodiments, the hydrophobic group with at least 8 carbon atoms is a hydrocarbyl group. In some preferred embodiments, the hydrocarbyl group is an aliphatic hydrocarbyl group, such as a saturated aliphatic hydrocarbyl group, for example a linear or branched alkyl group, suitably a linear alkyl group. However, it is not excluded that the hydrocarbyl hydrophobic group may comprise an aromatic group or an unsaturated aliphatic group.

[0086] In some embodiments, the thiol collector anion is selected from a xanthate (also known as a dithiocarbonate), a dithiophosphate, a dithiocarbamate, a mercaptobenzothiazole, a dithiophosphinate, a mercaptan and combinations thereof. In some embodiments, the thiol collector anion is selected from a xanthate, a dithiophosphate, a dithiocarbamate, a dithiophosphinate, or combinations thereof. Such collectors have in common an anionic sulfur-based functional group of the form -X(=S)S’ where X = C or P, with excellent affinity for sulfide mineral surfaces. Xanthates, dithiophosphates, dithiocarbamates and dithiophosphinates with shortchain alkyl hydrophobic groups are well-known classes of collector used in sulfide mineral flotation processes in the mining industry.

[0087] Suitable xanthate collector anions may have a structure according to Formula (I), in which R1is a hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms. R1may be an aliphatic hydrocarbyl group, such as a saturated aliphatic hydrocarbyl group, for example a linear or branched alkyl group, suitably a linear alkyl group. In some embodiments, R1is a Cs-C linear alkyl group, such as a C10-C14 linear alkyl group.Formula (I)

[0088] Suitable dithiocarbamate collector anions may have a structure according to Formula (II), in which at least R1is a hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms, and R2is an organyl group, preferably a second hydrophobic group with at least two carbon atoms and more preferably a second hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms. R1and R2may each independently be an aliphatic hydrocarbyl group, such as a saturated aliphatic hydrocarbyl group, for example a linear or branched alkyl group, suitably a linear alkyl group. R1and R2may be the same or different; in some embodiments they are the same.Formula (II)

[0089] Suitable dithiophosphate collector anions may have a structure according to Formula (III), in which at least R1is a hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms, and R2is an organyl group, preferably a second hydrophobic group with at least two carbon atoms and more preferably a second hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms. R1and R2may each independently be an aliphatic hydrocarbyl group, such as a saturated aliphatic hydrocarbyl group, for example a linear or branched alkyl group, suitably a linear alkyl group. R1and R2may be the same or different; in some embodiments they are the same.Formula (III)

[0090] Suitable dithiophosphinate collector anions may have a structure according to Formula (IV), in which at least R1is a hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms, and R2is an organyl group, preferably a second hydrophobic group with at least two carbon atoms and more preferably a second hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms. R1and R2may each independently be an aliphatic hydrocarbyl group, such as a saturated aliphatic hydrocarbyl group, for example a linear or branched alkyl group, suitably a linear alkyl group. R1and R2may be the same or different; in some embodiments they are the same.Formula (IV)

[0091] Other suitable thiol collector anions may include, for example, anionic mercaptobenzothiazoles or mercaptans (R-S-). Suitable mercaptobenzothiazole collector anions may have a structure according to Formula (V), in which R3is a hydrocarbyl group. In such collector anions, the Ce aromatic ring and the R3group together form a hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms.

[0092] Suitable mercaptans may have the structure R4-S’, where R4is a hydrophobic group with at least 8 carbon atoms, or at least 10 carbon atoms, or between 8 and 18 carbon atoms, for example between 10 and 14 carbon atoms. R4may be an aliphatic hydrocarbyl group, such as a saturated aliphatic hydrocarbyl group, for example a linear or branched alkyl group, suitably a linear alkyl group. In some embodiments, R4is a Cs-C linear alkyl group, such as a C10-C14 linear alkyl group.Organic cation

[0093] The flotation collector composition further comprises an organic cation.

[0094] In some embodiments, the organic anion is a non-surfactant organic cation. As used herein, a non-surfactant organic cation refers to an organic cation which is not, in itself, sufficiently surface active to act as a flotation collector. For example, quaternary amine cations with long-chain alkyl groups have been applied as cationic flotation collectors for non-sulfide minerals, and the presence of these or similar surfactant cations during flotation of sulfide minerals is considered undesirable due to the potential impact on selectivity. The organic cation is therefore generally not a tetraalkyl ammonium cation having a single alkyl group with 10 or more carbon atoms. In some embodiments, the organic cation is not a tetra-alkyl ammonium cation having a single alkyl group with 8 or more carbon atoms, or 6 or more carbon atoms, or 4 or more carbon atoms. In some embodiments, the organic cation is not a tetra-alkyl ammonium cation having any alkyl groups with 10 or more carbon atoms, or 8 or more carbon atoms, or 6 or more carbon atoms, or 4 or more carbon atoms. As used herein, a tetra-alkyl ammonium cation refers to a cation of the form [NR1R2R3FU where R1, R2, 3 and 4 are alkyl groups. In some embodiments, the organic cation does not comprise a hydrophobic group with 10 or more carbon atoms, or 8 or more carbon atoms, or 6 or more carbon atoms. In some embodiments, the organic cation does not comprise a linear hydrocarbyl group (e.g. linear alkyl group) with 10 or more carbon atoms, or 8 or more carbon atoms, or 6 or more carbon atoms.

[0095] The organic cation may be selected from a wide range of organic cations, typically including a nitrogen, phosphorous or sulfur centre. Such cations are expected to be more sterically bulky, less symmetric and have a more diffuse charge distribution in comparison with alkali metal cations (which can be considered to approximate point charges). Without wishing to be limited by any theory, it is proposed that one or more of these characteristics reduces the lattice energy of crystalline salts formed from the combination of organic cations and thiol collector anions. As a result, the lattice structure can more readily be disrupted by water and the salt thus dissolved. It is also hypothesized that the organic cations may disrupt aggregation of the thiol collector anions in solution, for example in micelles, and thus improve the availability of the thiol collector anion to bind to sulfide mineral surfaces and render them hydrophobic.

[0096] In some embodiments, the organic cation comprises a heteroatom selected from the group consisting of nitrogen, phosphorous and sulfur. For example, the organic cation may be selected from the group consisting of pyrrolidinium, imidazolium, benzimidazolium, quaternary ammonium, pyrrolium, indolium, carbazolium, pyridinium, quinolinium, piperidinium, piperazinium, morpholinium, phosphonium, sulfonium and combinations thereof. Such cations are known in the field of ionic liquids to produce low melting salts with low lattice energies when in a crystalline form. The inventors have found that both imidazolium and pyrrolidinium cations effectively solubilise long- chain thiol collector anions in water. Due to the unsaturated ring structure, imidazolium cations are relatively planar and delocalise the positive charge away from the quaternary nitrogen. In contrast, pyrrolidinium cations are flexible and tend to localise the positive charge on the quaternary nitrogen. Given these divergent properties, it can be expected that a wide range of organic cations will effectively activate long-chain thiol collector ions for sulfide mineral flotation.

[0097] In some embodiments, the organic cation is a heterocyclic cation. In some embodiments, the organic cation is an N-heterocyclic cation comprising quaternary nitrogen. Examples of such cations include pyrrolidinium, imidazolium, benzimidazolium, pyrrolium, indolium, carbazolium, pyridinium, quinolinium, piperidinium, piperazinium and morpholinium. In some embodiments, the organic cation is selected from the group consisting of 1 ,1 -dialkylpyrrolidinium cations, 1 ,3- dialkylimidazolium cations and combinations thereof. Each alkyl group may independently be a Ci-Cs alkyl group, such as a Ci-Ce alkyl group.

[0098] The organic cation is generally bulkier than alkali metal cations conventionally used in combination with thiol collector anions. In some embodiments, the organic cation has a molecular weight of at least 100 g / mol, such as in the range of 100 g / mol to 600 g / mol.Flotation collector composition

[0099] The flotation collector composition may be a solid or a liquid (e.g. viscous oil) at room temperature (20°C) and 1 atmosphere pressure (1 atm). In some embodiments, the flotation collector composition is a solid at 20°C / 1 atm. The solid flotation collector composition may be present in water-dispersible pellets oragglomerates, allowing convenient addition to a flotation cell or reagent mixing tank upstream of the flotation tank.

[0100] In some embodiments, the thiol collector anion and the organic cation together form a water-soluble salt, typically paired in a 1 :1 ratio. The water-soluble salt (whether in solid or liquid form) thus preferably comprises the thiol collector anion and the organic cation as the predominant ionic species. For example, the water-soluble salt may comprise the thiol collector anion in an amount of at least 70 mol%, or at least 80 mol%, such as at least 90 mol%, for example substantially 100 mol%, of the total anion component of the water soluble salt. Similarly, the water-soluble salt may comprise the organic cation in an amount of at least 70 mol%, or at least 80 mol%, such as at least 90 mol%, for example substantially 100 mol%, of the total cation component of the water soluble salt. The water-soluble salt may be a solid or a liquid at 20°C / 1 atm, for example with a melting point of between 0°C and 80°C. Optionally, the water- soluble salt may be a solid at 20°C / 1 atm, for example with a melting point of between 20°C and 80°C, or between 20°C and 50°C. A low melting point may be indicative of a low lattice energy in the water-soluble salt, and the salt may thus be more readily dissolved in aqueous media.

[0101] Exemplary classes of suitable water-soluble salts include: 1 ,1 - dialkylpyrrolidinium Ce-C -alkyl xanthates and 1 ,3-dialkylimidazolium Ce-C -alkyl xanthates. Specific examples may include a liquid salt comprising, and preferably consisting of: (i) one organic cation selected from the group consisting of 1 -ethyl-1 - methylpyrrolidinium, 1 -propyl-1 -methylpyrrolidinium, 1 -butyl-1 -methylpyrrolidinium, 1 - hexyl-1 -methylpyrrolidinium, 1 -octyl-1 -methylpyrrolidinium, 1 ,3-dimethyl-imidazolium, 1 -ethyl-3-methylimidazolium, 1 -propyl-3-methylimidazolium, 1 -butyl-3- methylimidazolium, 1 -hexyl-3-methylimidazolium, 1 -octyl-3-methylimidazolium, 1 - decyl-3-methylimidazolium, 1 ,3-diethyl-imidazolium and (ii) one thiol collector anion selected from the group consisting of n-octyl xanthate, n-nonyl xanthate, n-decyl xanthate, n-undecyl xanthate, n-dodecyl xanthate, n-tridecyl xanthate and n-tetradecyl xanthate.

[0102] It is however not excluded that the flotation collector composition comprises other ionic species together with the thiol collector anion and the organic cation. For example, it is envisaged that the flotation collector composition may comprise a melt orconcentrated solution of (i) a salt of the thiol collector anion and (ii) a salt of the organic cation. The flotation collector composition may thus in principle contain other ionic species such as alkali metal cations, halides and the like which may be accommodated without adverse effects in flotation.

[0103] The thiol collector anion and the organic cation may therefore be present in the flotation collector composition at ratios other than 1 :1 , for example in the range of 5:1 to 1 :5, or 2:1 to 1 :2.

[0104] In some embodiments, the flotation collector composition comprises a single collector, meaning that it comprises a first thiol collector anion in combination with a first organic cation, as disclosed herein, but is substantially free of (i) additional thiol collector anions different from the first thiol collector anions, (ii) neutral collectors, and optionally also (iii) additional organic cations different from the first organic cation. The flotation collector compositions disclosed herein have been found effective as single salt collectors, without the need to combine different flotation collectors.

[0105] The flotation collector composition may comprise a mineral base, such as NaOH or KOH, to stabilise the thiol collector anion. The flotation collector composition may comprise a binder to consolidate the composition in pellet form. The flotation collector composition, optionally in pellet form, may thus in some embodiments comprise a physical mixture of the solid, water-soluble salt as disclosed herein, a mineral base and optionally a binder.Flotation method

[0106] Also disclosed herein is a flotation method. The flotation method comprises providing a mineral composition comprising comminuted ore particles, with the mineral composition comprising at least one target sulfide mineral. A pulp comprising the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms and (ii) an organic cation is produced, and gas bubbles are passed through the pulp. The flotation method further comprises recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in the at least one target sulfide mineral.

[0107] The mineral composition may comprise a coarse fraction of comminuted ore particles, and a high proportion of the at least one target sulfide mineral present in the coarse fraction is recovered in the mineral concentrate. In some embodiments, the mineral composition comprises a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 pm, and a substantial proportion, such as at least 50%, of the at least one target sulfide mineral in the first coarse fraction is recovered in the mineral concentrate. In these or other embodiments, the mineral composition comprises a second coarse fraction of comminuted ore particles with a particle size between 212 and 425 pm, and a substantial proportion, such as at least 50%, of the at least one target sulfide mineral in the second coarse fraction is recovered in the mineral concentrate. In these or other embodiments, the mineral composition comprises a third coarse fraction of comminuted ore particles with a particle size between 425 and 850 pm, and a substantial proportion, such as at least 50%, of the at least one target sulfide mineral in the third coarse fraction is recovered in the mineral concentrateProviding the mineral composition

[0108] The mineral composition comprises comminuted ore particles, which may be produced by grinding an ore to liberate one or more sulfide minerals from gangue minerals and produce comminuted ore particles small enough to be floated. The mineral composition to be processed may be the immediate product of an ore comminution process. In other words, it may contain comminuted ore particles with a composition and particle size distribution as produced by an ore grinding (milling) process. Alternatively, the mineral composition may be a fraction of a comminuted ore which has already been subjected to one or more preliminary separation steps. For example, the mineral composition may be a concentrate or tailings product of a preliminary ore separation process such as froth flotation. Alternatively, the mineral composition may be a size-classified fraction (e.g. a coarse fraction, or fine fraction) of comminuted ore.

[0109] In some embodiments, the mineral composition is a tailings product provided by subjecting a comminuted ore to a preliminary froth flotation stage. The preliminary froth flotation stage need not utilise flotation collector compositions of the type disclosed herein. In some embodiments, a conventional flotation collector suchas a thiol collector anion comprising a short-chain hydrophobic group (fewer than 6 carbon atoms) is used.

[0110] In some embodiments, the preliminary froth flotation stage (also known as a roughing flotation stage), may recover a major but non-quantitative proportion of the target sulfide minerals in the comminuted ore, including most of the smaller-sized sulfide particles. The subsequent froth flotation stage (also known as a scavenger flotation stage) is then conducted, according to the present disclosure, using the rougher tails fraction as feedstock so as to recover residual target sulfide mineral that was not recovered in the roughing stage. A substantial proportion of the residual target sulfide mineral in the tailings product may be present in harder-to-float particles, including larger-sized particles and composite particles. By conducting only the scavenger flotation stage with a long-chain thiol collector anion and organic cation, as disclosed herein, the highly hydrophobic flotation collector composition is thus efficiently directed to the recovery of hard-to-float particles, and not consumed unnecessarily on easy-to-float finer and / or fully liberated target sulfide particles.

[0111] The methods of the present disclosure may thus include a step of subjecting a comminuted ore to a preliminary froth flotation stage to produce a concentrate enriched in at least one sulfide mineral and a tailings product. The tailings product, still comprising at least one target sulfide mineral worth recovering, is then provided as at least a portion of the mineral composition in the methods disclosed herein.

[0112] The methods disclosed herein have been found particularly effective, relative to conventional short-chain thiol collectors, for recovery of larger particles and / or composite particles.

[0113] The mineral composition subjected to flotation may thus comprise one or more coarse fractions of comminuted ore particles. As used herein, a coarse fraction refers to a portion of the mineral composition present in comminuted ore particles with large particle sizes, or within a defined range of large particle sizes, being greater than 106 pm and typically greater than 150 pm.

[0114] It is well known that the efficiency of mineral recovery by flotation drops off sharply with particle sizes above such threshold values, for example as discussed in “Coarse particle flotation: A rev / ew” by Anzoom et al, Minerals Engineering 206 (2024)108499. This is typically addressed in industry by grinding the large particles to smaller sized particles which can be floated: either by grinding the entire mineral composition prior to flotation to a grind sufficiently fine that the problematic coarse fraction is negligible, or by accepting poor recovery of the target mineral in initial flotation and then re-grinding the tails fraction for re-flotation (either by recycling to the initial flotation stage or in a subsequent scavenger flotation stage).

[0115] In some embodiments, the mineral composition comprises a first coarse fraction of comminuted ore particles with a particle size between 150 pm and 212 pm. A significant fraction of the total amount of target sulfide mineral(s) in the mineral composition may be present in the first coarse fraction. In some embodiments, at least 2 wt.%, or at least 5. wt.%, such as at least 10 wt.%, or at least 15 wt.%, for example at least 20 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the first coarse fraction. In some embodiments, less than 80 wt.%, such as less than 50 wt.%, or less than 30 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the first coarse fraction.

[0116] In some embodiments, the mineral composition comprises a second coarse fraction of comminuted ore particles with a particle size between 212 pm and 425 pm. A significant fraction of the total amount of target sulfide mineral(s) in the mineral composition may be present in the second coarse fraction. In some embodiments, at least 2 wt.%, or at least 3. wt.%, such as at least 5 wt.%, for example at least 10 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the second coarse fraction. In some embodiments, less than 50 wt.%, such as less than 30 wt.%, or less than 20 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the second coarse fraction.

[0117] In some embodiments, the mineral composition comprises a third coarse fraction of comminuted ore particles with a particle size between 425 and 850 pm. A significant fraction of the total amount of target sulfide mineral(s) in the mineral composition may be present in the third coarse fraction. In some embodiments, at least 2 wt.%, or at least 3. wt.%, such as at least 5 wt.%, for example at least 10 wt.%, of the at least one target sulfide mineral in the mineral composition is present in the third coarse fraction. In some embodiments, less than 30 wt.%, or less than 20 wt.%, of theat least one target sulfide mineral in the mineral composition is present in the third coarse fraction.

[0118] The presence, and wt.% amount, of large comminuted ore particles, such as within the first, second and / or third coarse fractions, may be determined by sieving methods known to those of skill in the art, in particular with sieves and methods in accordance with ASTM E1 1 -24. Thus, comminuted ore particles with particle size greater than 106 pm may be determined as the wt.% fraction of the mineral composition retained by the 106 pm sieve (ASTM #140 sieve). The first coarse fraction may be determined as the wt.% fraction of the mineral composition passing through the 212 pm sieve (ASTM #70 sieve) and retained by the 150 pm sieve (ASTM #100 sieve). The second coarse fraction may be determined as the wt.% fraction of the mineral composition passing through the 425 pm sieve (ASTM #40 sieve) and retained by the 212 pm sieve (ASTM #70 sieve). The third coarse fraction may be determined as the wt.% fraction of the mineral composition passing through the 850 pm sieve (ASTM #20 sieve) and retained by the 425 pm sieve (ASTM #40 sieve).

[0119] The proportion of the target sulfide mineral(s) within each coarse fraction may be determined based on routine compositional analyses conducted on (i) the mineral composition (i.e. the total feed to flotation) and (ii) each coarse fraction thereof, as separated by sieving. Suitable compositional analyses may include X-ray fluorescence (XRF) or inductively coupled plasma (ICP) techniques routinely available in analytical labs serving the minerals-processing industry.

[0120] The coarseness of the mineral composition may also be characterised by a Pso particle size. In some embodiments, the comminuted ore particles of the mineral composition may have a particle size greater than 150 pm, or greater than 175 pm, or greater than 200 pm, such as between 200 pm and 300 pm as defined by the Pso particle size. As used herein, the Pso particle size is defined as the particle size where 80 wt.% of the comminuted ore particles (all particles, including target mineral sulfides and gangue) are smaller than the Pso particle size. The Pso particle size may be determined for ore or ground ore by standard wet and dry screening methods known to those of skill in the art. In some embodiments, the comminuted ore particles of the mineral composition may comprise composite particles comprising both target sulfide mineral and gangue minerals. For example, at least 2 wt.%, or at least 5 wt.%, or atleast 10 wt.%, of the target sulfide mineral(s) in the mineral composition may be present in such composite particles.

[0121] The flotation method disclosed herein recovers at least one target sulfide mineral initially present in a mineral composition. As used herein, a target sulfide mineral refers to a floatable sulfide mineral which is intended to be concentrated in the mineral concentrate in a flotation step. The at least one target sulfide mineral generally comprises (i) at least one value sulfide mineral, meaning a metal sulfide mineral containing a value metal which is being targeted for recovery in the overall process, or (ii) at least one sulfide mineral associated with a value metal (e.g. a precious metal), with the associated value metal being targeted for recovery in the overall process. However, the at least one target sulfide mineral may, and in many cases will, also comprise additional, low-value metal sulfide minerals. The flotation methods disclosed herein are particularly useful in bulk flotation stages where the goal is to maximise recovery of values, with the acceptable consequence that low-value metal sulfide minerals are also recovered. The low-value metal sulfides can be rejected and separated from the valuable target metal sulfide at a later stage (i.e. the cleaning stages of flotation).

[0122] In principle, the mineral composition may contain only a single target sulfide mineral. More typically, however, the mineral composition comprises a plurality of target sulfide minerals, each of which is enriched in the resultant mineral concentrate due to the exclusion of non-sulfidic and sulfidic gangue.

[0123] The target sulfide mineral(s) in the mineral composition may comprise any of a wide range of known metal sulfide compounds that are susceptible to flotation. In some embodiments, the one or more target sulfide minerals comprise one or more metals selected from the group consisting of copper, nickel, zinc, cobalt, iron, molybdenum and lead. Froth flotation is an important hydrometallurgical separation process used in commercial production of these base metals from sulfidic ores.

[0124] In other embodiments, the at least one target sulfide mineral comprises an iron sulfide mineral, and the mineral concentrate further comprises a precious metal associated with the iron sulfide mineral in the comminuted ore. As used herein, a precious metal refers to gold, silver and the platinum group metals (PGM’s, beingruthenium, rhodium, palladium, osmium, iridium, and platinum). Precious metals may be concentrated from sulfidic ores by flotation of precious metal-bearing iron sulfide minerals, with highly efficient recovery of the iron sulfides thus needed to maximise precious metal yields. For example, gold mining operations may seek to recover auriferous pyrite (gold-bearing FeS2), and PGM-mining operations may seek to recover PGM-bearing pyrrhotite.Flotation

[0125] The flotation method comprises producing a pulp which comprises the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms and (ii) an organic cation. The thiol collector anion and the organic cation may generally be according to any of the embodiments disclosed herein in the context of the flotation collector composition.

[0126] In some embodiments, the pulp is produced by providing a flotation collector composition according to any of the embodiments already disclosed herein, and dispersing this flotation collector composition in the aqueous phase. This may be done directly in the aqueous phase in the flotation cell or in a precursor aqueous phase which may ultimately be further diluted and / or modified with further additives prior to flotation. The thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms and the organic cation are thus present together in a composition, optionally as a water- soluble salt, prior to dispersal of that composition in the aqueous phase. The flotation collector composition may be a liquid or a solid when dispersed in the aqueous phase. In some embodiments, it is a solid, for example in the form of water-dispersible pellets or agglomerates. The thiol collector anion and organic cation may be added, optionally as a pre-formed flotation collector composition, directly to the flotation cell where flotation is to take place or upstream of the flotation cell, for example in a grinder where the comminuted ore particles are produced.

[0127] The thiol collector anion and the organic cation may be present in the flotation collector composition at a ratio of 1 :1 or at a ratio other than 1 :1 , for example in the range of 5:1 to 1 :5, or 2:1 to 1 :2.

[0128] The aqueous phase comprises sufficient thiol collector anion to adsorb to the surfaces of comminuted ore particles containing the target sulfide mineral(s),thereby rendering them hydrophobic and recoverable by flotation. The organic cation may assist to solubilise and / or de-aggregate the thiol collector anion in the aqueous phase according to the principles disclosed herein. It will be appreciated that the amount of thiol collector anion required for effective flotation will depend on factors such as the nature of the target sulfide mineral(s), the amount and particle size distribution of the target sulfide mineral(s) in the mineral composition, the pulp concentration and the required recovery rate and grade. In some embodiments, the aqueous phase comprises the thiol collector anion in an amount of at least 0.01 mol / t, or at least 0.02 mol / t, or at least 0.03 mol / t, such as in the range of 0.03 mol / t and 0.5 mol / t, or in the range of 0.05 mol / ton and 0.4 mol / ton. As used herein, mol / t refers to the moles per ton of mineral composition in the pulp. The thiol collector anion need not be added in a single up-front charge, and may advantageously be added in increments during the flotation process, thereby increasing the availability of the thiol collector anion to hard- to-float particles.

[0129] The aqueous phase may comprise one or more further chemical agents conventionally used in flotation cells, including pH modifiers, depressants, activators and frothers. In some embodiments, the aqueous phase further comprises a frother, such as a polypropylene glycol frother. In some embodiments, an activator is added to the aqueous phase, typically prior to addition of the collector. For example, a copper salt such as copper sulfate may be added to a pulp containing a non-copper target sulfide mineral, e.g. zinc sulfide (sphalerite). This may cause exchange of the Cu ions in solution with the Zn ions in the sphalerite to form pseudo copper sulfide on the particle surface of the non-copper target sulfide mineral prior to collector addition, rendering the surface more susceptible to modification by the thiol collector anion. The pH of the aqueous phase is generally sufficiently high to allow the thiol collector anion to dissociate, or remain dissociated, in solution. The aqueous phase may be weakly alkaline (e.g. in the range of pH 7-1 1 ) during flotation for some easily-dissociated thiol collectors such as xanthates, dithiophosphates and dithiocarbamate, but may be higher (e.g. above 10, or above 1 1 ) for certain harder-to-dissociate thiol collectors such as mercaptans. The pH may be adjusted to the desired operating range as required using a pH modifier (mineral acid or base).

[0130] The pulp may be contained in a wide range of flotation cells known to those of skill in the art. The flotation cell may be operated in batch or continuous mode. Advantageously, the methods disclosed herein can be implemented in conventional and / or pre-existing flotation apparatus, thus providing improved recovery of target sulfide minerals, or a reduced grinding requirement of the ore, without the necessity for new or specialised apparatus.

[0131] The method comprises passing gas bubbles, typically air, through the pulp according to well-known modes of operation in froth flotation technology. Sufficiently hydrophobic comminuted ore particles attach to the rising air bubbles and are thus transported to the froth layer formed above the pulp. The comminuted ore particles captured in the froth are then recovered, for example by overflow from the cell, collection in launders located outside the overflow lip to collect and transport the froth or concentrate product out of the cell tank, and washing the recovered ore particles. A mineral concentrate enriched in the at least one target sulfide mineral is thus produced. The comminuted ore particles remaining in the pulp after a suitable flotation time are taken as a tailings product, which is lean in the at least one target sulfide mineral and enriched in gangue minerals relative to the initial mineral composition.Mineral concentrate

[0132] The mineral concentrate produced by the flotation method is enriched in the at least one target sulfide mineral. In some embodiments, the mineral concentrate is enriched in a plurality of target sulfide minerals. The mineral concentrate is expected to include a high proportion of the easy-to-float comminuted ore particles initially present in the mineral composition. Furthermore, the mineral concentrate may comprise a substantial proportion of hard-to-float comminuted ore particles containing the target sulfide mineral(s), including larger-sized particles which are difficult to float with short-chain thiol collectors. This is particularly useful in the rougher and scavenger cells where recovery is the aim. Larger-sized particles are typically harder to float because they are heavier and / or more likely to be composite particles with non-floatable minerals. These particles are normally dealt with by regrinding and re-flotation in cleaner cells.

[0133] In embodiments where the mineral composition comprises a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 pm, at least 50% of the at least one target sulfide mineral in the first coarse fraction may be recovered in the mineral concentrate. Preferably, at least 60%, or at least 70%, or at least 80%, or at least 90%, for example at least 95%, or at least 98%, of the at least one target sulfide mineral in the first coarse fraction is recovered in the mineral concentrate.

[0134] In embodiments where the mineral composition comprises a second coarse fraction of comminuted ore particles with a particle size between 212 and 425 pm, at least 50% of the at least one target sulfide mineral in the second coarse fraction may be recovered in the mineral concentrate. Preferably, at least 60%, or at least 70%, or at least 80%, or at least 90%, for example at least 95%, or at least 98%, of the at least one target sulfide mineral in the second coarse fraction is recovered in the mineral concentrate.

[0135] In embodiments where the mineral composition comprises a third coarse fraction of comminuted ore particles with a particle size between 425 and 850 pm, at least 50% of the at least one target sulfide mineral in the third coarse fraction may be recovered in the mineral concentrate. Preferably, at least 60%, or at least 70%, or at least 80%, or at least 90%, for example at least 95%, or at least 98%, of the at least one target sulfide mineral in the third coarse fraction is recovered in the mineral concentrate.

[0136] The proportion of the at least one target sulfide mineral in the first, second and / or third coarse fraction recovered in the mineral concentrate may be determined by sieving and compositional analysis methods known to those of skill in the art. The coarse fractions present in the mineral concentrate may be separated with sieves and methods in accordance with ASTM E1 1 -24, and the amount of target sulfide mineral in each fraction may be determined by X-ray fluorescence (XRF) or inductively coupled plasma (ICP) techniques.

[0137] Specifically, the % recovery of the at least one target sulfide mineral in the first coarse fraction in the mineral concentrate may be determined by:• Sieving the mineral composition (as fed to flotation) to determine the wt.% fraction passing through the 212 pm sieve (ASTM #70 sieve) and retained by the 150 pm sieve (ASTM #100 sieve), i.e. in the first coarse fraction of the mineral composition;• Sieving the mineral concentrate (as recovered from flotation) to determine the wt.% fraction passing through the 212 pm sieve (ASTM #70 sieve) and retained by the 150 pm sieve (ASTM #100 sieve), i.e. in a first coarse fraction of the mineral concentrate;• Analysing (i) the first coarse fraction of the mineral composition and (ii) the first coarse fraction of the mineral concentrate to determine the amount of the at least one target sulfide mineral in each fraction; and• Calculating the wt.% fraction of the at least one target sulfide mineral initially present in the first coarse fraction of the mineral concentrate that is present in the first coarse fraction of the mineral concentrate.

[0138] A similar method can be used to determine the % recovery of the at least one target sulfide mineral in the second coarse fraction, or the third coarse fraction, of the mineral concentrate.

[0139] In some embodiments where the comminuted ore particles of the mineral composition have a Pso particle size greater than 150 pm, or greater than 175 pm, or greater than 200 pm, such as between 200 pm and 300 pm, at least 50 wt. %, or at least 60 wt.%, of the target sulfide mineral(s) initially present in comminuted ore particles with a particle size greater than the Pso particle size is recovered in the mineral concentrate.

[0140] The mineral concentrate may be further processed by conventional metallurgical processes, including hydrometallurgical and / or pyrometallurgical processes, to ultimately recover the metal values contained therein. In some embodiments, the mineral concentrate is subjected to a subsequent froth flotation stage, for example a selective flotation stage (also known as a cleaning flotation stage) to selectively recover certain value sulfide minerals while rejecting other low-value sulfide minerals in order to improve the grade. Sometimes this flotation step is precededwith a regrinding step to liberate composite / locked particles and reduce particle size further. The selective flotation stage need not, utilise long-chain flotation collector compositions of the type disclosed herein. Short-chain thiol collectors may be used in the cleaning flotation stage to provide the requisite selectivity. The tailings product of the cleaning flotation stage may be subjected to regrinding to liberate further sulfide mineral values and recycled for reprocessing in the initial flotation stage (performed according to the methods disclosed herein).Embodiments

[0141] A hydrometallurgical process 100 utilizing a flotation method according to embodiments of the invention will now be discussed with reference to Figure 1 . Sulfide- bearing ore 102 is subjected to grinding in milling unit 104 to produce comminuted ore 106. Comminuted ore 106 comprises at least one, and typically a plurality of target sulfide minerals. Milling unit 104 may include one or more mills of any conventional type used to comminute ore for flotation, such as a ball mill. Advantageously, the flotation methods disclosed herein may allow reduced milling intensity in milling unit 104. A coarser grind of comminuted ore 106 can be accommodated due to the efficient flotation of target sulfide minerals, even when present in larger-sized or composite particles that may be difficult to float with conventional collectors. Comminuted ore 106 may comprise a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 pm, for example in an amount of at least 2 wt.%, such as at least 5 wt.%, or at least 10 wt.%. Comminuted ore 106 may have a Pso particle size of greater than 150 pm, or greater than 175 pm, or greater than 200 pm, such as between 200 pm and 300 pm. In many operations now some of the total collector is added to the primary grinding mill and the remainder added to the flotation circuit.

[0142] Comminuted ore 106 is then introduced to flotation cell 108 where it is pulped in an aqueous phase. During flotation, the aqueous phase contains a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms and an organic cation, as disclosed herein. In some embodiments, the thiol collector anion and the organic cation are introduced to flotation cell 108 in flotation collector composition 1 10, which is then dispersed in the aqueous phase. Flotation collector composition 1 10 may be according to any of the embodiments disclosed herein. In some embodiments, it comprises the thiol collector anion and the organic cation as a water-soluble salt. Otheradditives, such as pH modifiers, depressants, activators and frothers, may also be added to flotation cell 108.

[0143] Gas 112, typically air, is introduced to flotation cell 108 so that gas bubbles pass through the pulp contained therein. Sufficiently hydrophobic comminuted ore particles attach to the gas bubbles and are transported to the pulp surface where they are captured in a froth layer above the pulp. Comminuted ore particles with target sulfide mineral(s) at the particle surface are modified by the thiol collector anion, and thus rendered hydrophobic and susceptible to transport into the froth layer. The ore particles captured in the froth layer are recovered, thereby producing mineral concentrate 114 which is enriched in the target sulfide mineral(s). Tailings product 1 16, which is lean in the target sulfide mineral(s), is removed from flotation cell 108 and may be discarded or further processed by conventional means, e.g. in a scavenger flotation stage to recover residual sulfide mineral values.

[0144] At least 50% of the target sulfide mineral(s) in the first coarse fraction of comminuted ore 106 may be recovered in mineral concentrate 114, and preferably significantly higher amounts such as at least 70%, at least 80%, at least 90%, for example at least 95%.

[0145] In some embodiments, comminuted ore 106 comprises target sulfide mineral(s) containing one or more metals selected from the group consisting of copper, nickel, zinc, cobalt, iron, molybdenum and lead. Mineral concentrate 1 14 is thus enriched in these target sulfide mineral(s).

[0146] In some embodiments, comminuted ore 106 comprises target sulfide mineral(s) including at least one iron sulfide mineral, and a precious metal associated with the iron sulfide mineral. Mineral concentrate 114 is thus enriched in the iron sulfide and therefore also the precious metal.

[0147] The flotation performed in flotation cell 108 may be a bulk flotation in which the goal is maximum recovery of the value sulfide minerals. As a consequence, all floatable sulfide minerals, including both value sulfide minerals and gangue sulfide minerals, may be concentrated in mineral concentrate 1 14. In this case, all floatable sulfide minerals in comminuted ore 106 are considered target sulfide minerals for the flotation conducted in flotation cell 108.

[0148] Mineral concentrate 114 may then optionally be introduced to flotation cell 1 18 for a subsequent flotation stage (a cleaning flotation stage) in which one or more value sulfide minerals (including sulfide minerals associated with metal values) are separated with high selectivity from low-value sulfide minerals to produce cleaning stage concentrate 120, which may then be further processed by hydrometallurgical and / or pyrometallurgical techniques to recover the metal values therein. Cleaning stage tailings product 122, comprising the low-value sulfide minerals and unrecovered value sulfide minerals, is removed from flotation cell 1 18 and may be recycled, with optional regrinding in regrinding milling unit 124 to liberate sulfide minerals from gangue, for flotation in flotation cell 108. Since high selectivity is desired in the cleaning flotation stage, where grade rather than recovery is the aim, a selective flotation collector 126 together with other flotation additives is added to flotation cell 118. The collector 126 and additives may be chosen by the skilled person from known options, depending on the nature of the value sulfide minerals and the low-value sulfide minerals to be discriminated. Long-chain thiol collector anions of the type disclosed herein are not expected to provide high selectivity, so that conventional short-chain thiol collectors may be preferred in the cleaning stage. The imperative to recover the value sulfide minerals with high selectivity in flotation cell 1 18 inevitably means a low recovery efficiency of the value sulfide mineral to concentrate 120 (i.e. low percentage recovery), however this can be accommodated in flotation cell 1 18 due to the recycling of of tailings product 122.

[0149] A hydrometallurgical process 200 utilizing a flotation method according to embodiments of the invention will now be discussed with reference to Figure 2. Sulfide- bearing ore 202 is subjected to grinding in milling unit 204 to produce comminuted ore 206. Comminuted ore 206 comprises at least one, and typically a plurality of sulfide minerals. Milling unit 204 may include one or more mills of any conventional type used to comminute ore for flotation, such as a ball mill. Advantageously, the flotation methods disclosed herein may allow reduced milling intensity in milling unit 204. A coarser grind of comminuted ore 206 can be accommodated due to the efficient flotation of target sulfide minerals in the second flotation stage of process 200, even when present in larger-sized or composite particles that may be difficult to float with conventional collectors.

[0150] Comminuted ore 206 is introduced to flotation cell 208 where it is subjected to a preliminary froth flotation stage to produce a preliminary stage mineral concentrate 214 enriched in at least one sulfide mineral, and a preliminary stage tailings product 216 that is lean in the at least one sulfide mineral. The preliminary stage of froth flotation may be a selective flotation, or it may be a bulk flotation (roughing stage) such that preliminary stage mineral concentrate 214 is enriched in a plurality of target sulfide minerals initially present in ore 202, including value sulfide minerals and low-value sulfide minerals. Preliminary stage mineral concentrate 214 may then be further processed by hydrometallurgical and / or pyrometallurgical techniques to recover the metal values therein. Optionally, it may be subjected to at least one further flotation stage (a cleaning flotation stage) to selectively recover value metal sulfide minerals, or sulfide minerals associated with a value metal.

[0151] A flotation collector 210 together with other flotation additives is added to flotation cell 208. Collector 210 may be a conventional flotation collector and not a long-chain flotation collector composition of the type disclosed herein. In some embodiments, collector 210 comprises a thiol collector anion comprising a short-chain hydrophobic group (fewer than 6 carbon atoms).

[0152] Preliminary stage tailings product 216 still contains at least one, and typically a plurality of target sulfide minerals due to non-quantitative recovery of these sulfide minerals in the preliminary flotation stage. The target sulfide mineral(s) remaining in tailings product 216 may be concentrated in hard-to-float particles, including larger- sized particles and composite particles, since the easy-to-float small particles were efficiently floated in flotation cell 208. Tailings product 216 may thus have a coarser particle size distribution than comminuted ore 202. Tailings product 216 may comprise a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 pm, for example in an amount of at least 2 wt.%, such as at least 5 wt.%, or at least 10 wt.%. Tailings product 216 may have a Pso particle size of greater than 150 pm, or greater than 175 pm, or greater than 200 pm, such as between 200 pm and 300 pm.

[0153] Tailings product 216 is thus introduced to flotation cell 218 for a second flotation stage (a scavenger flotation stage) intended to near-quantitatively recover target metal sulfide(s). Tailings product 216 is pulped in an aqueous phase in flotation call 218. During flotation, the aqueous phase contains a thiol collector anion comprisinga hydrophobic group with at least 8 carbon atoms and an organic cation, as disclosed herein. In some embodiments, the thiol collector anion and the organic cation are introduced to flotation cell 218 in flotation collector composition 226, which is then dispersed in the aqueous phase. Flotation collector composition 226 may be according to any of the embodiments disclosed herein. In some embodiments, it comprises the thiol collector anion and the organic cation as a water-soluble salt. Other additives, such as pH modifiers, depressants, activators and frothers, may also be added to flotation cell 218.

[0154] Gas 212, typically air, is introduced to flotation cell 218 so that gas bubbles pass through the pulp contained therein. Sufficiently hydrophobic comminuted ore particles attach to the gas bubbles and are transported to the pulp surface where they are captured in a froth layer above the pulp. Comminuted ore particles with target sulfide mineral(s) at the particle surface are modified by the thiol collector anion, and thus rendered hydrophobic and susceptible to transport into the froth layer. The ore particles captured in the froth layer are recovered, thereby producing mineral concentrate 220 which is enriched in the target sulfide mineral(s). Tailings product 222, which is near-depleted of the target sulfide mineral(s), is removed from flotation cell 218 and may be discarded or further processed by conventional means.

[0155] At least 50% of the target sulfide mineral(s) in the first coarse fraction of tailings product 216 may be recovered in mineral concentrate 220, and preferably significantly higher amounts such as at least 70%, at least 80%, at least 90%, for example at least 95%.

[0156] By conducting only the scavenger flotation stage, in flotation cell 218, with a long-chain thiol collector anion and organic cation, as disclosed herein, the highly hydrophobic flotation collector composition is thus efficiently directed to the recovery of hard-to-float particles, and not consumed unnecessarily on easy-to-float fine and / or fully liberated target sulfide particles in flotation cell 208.

[0157] Mineral concentrate 220 may then be further processed by hydrometallurgical and / or pyrometallurgical techniques to recover the metal values therein. Optionally, it may be combined with preliminary stage mineral concentrate 214 prior to further processing. Optionally, mineral concentrate 220 (or the combination ofmineral concentrates 214 and 220) may be subjected to at least one further flotation stage (a cleaning flotation stage) to selectively recover value metal sulfide minerals, or sulfide minerals associated with a value metal, with or without regrind to liberate value metal sulfide minerals. The cleaning flotation stage may be similar to that previously described in the context of hydrometallurgical process 100, and its tailings product may optionally be reground and partially recycled to either flotation cell 208 or 218.

[0158] In some embodiments, preliminary stage tailings product 216 comprises target sulfide mineral(s) containing one or more metals selected from the group consisting of copper, nickel, zinc, cobalt, iron molybdenum and lead. Mineral concentrate 220 is thus enriched in these target sulfide mineral(s).

[0159] In some embodiments, preliminary stage tailings product 216 comprises target sulfide mineral(s) including at least one iron sulfide mineral, and a precious metal associated with the iron sulfide mineral. Mineral concentrate 220 is thus enriched in the iron sulfide and therefore also the precious metal.EXAMPLES

[0160] The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.Materials and procedures

[0161] General procedure for sulfide mineral-quartz mixture flotation tests. G rou nd pulp comprising sulfide mineral, quartz and distilled water was transferred to a 3 dm3flotation cell and the water level was raised (to fill the cell to the 3 dm3mark) with distilled water. The flotation cell was a modified stainless steel Denver cell (P.J. Guy, Conference Series - Australasian Institute of Mining & Metallurgy, 1992 pp. 75-79) in which the impeller was fitted with a variable speed drive and was driven from below to allow the whole surface of the froth to be scraped with a paddle at a constant depth and rate. The pH was adjusted to the desired test value (with dilute 2.5% solutions of sodium hydroxide or nitric acid) and the pulp aerated for 5 min. The collector was then added and the pulp conditioned for 5 minutes. Frother (commercial quality polypropylene glycol; Cytec Aerofroth 65; prepared as a 0.25% w / v solution) was added continually atthe rate of 5 mg min-1starting 1 minute before turning on the gas flow to commence flotation. Five flotation concentrates were collected over 8 minutes at 0.5, 1 , 2, 4 and 8 minutes by hand scraping at a constant depth and rate. For both conditioning and flotation the impeller speed was 1200 rev / min. Air was delivered to the cell at 8 dm3 / min.

[0162] Particle size analysis was conducted by sieving (wet and dry screening) for +38 micron fractions, according to ASTM E1 1 , and by a cyclosizer for sub-sieve sizing (-38 micron fractions).

[0163] Copper sulphate used in the sphalerite tests was reagent grade. Short hydrocarbon chain xanthate collectors, including potassium ethyl xanthate (KeX), sodium isobutyl xanthate (SiBX) and potassium amyl xanthate (KaX), were obtained from commercial sources. The flotation gas was high purity synthetic air. Distilled water was used in all tests.Example 1. Synthesis of potassium dodecyl xanthate (KdX)

[0164] Finely ground KOH (6.195 g; 0.1 1 mol) was dissolved under a N2 atmosphere in 180 ml pure n-dodecanol at 45°C in a round bottom Schlenk flask equipped with a stirrer bar and septum. Almost all of the KOH was dissolved after stirring for an hour. A weighed amount of CS2 (8.42 g, 0.1 1 mol) was slowly added via a syringe and needle through the septum. Upon addition of CS2 a pale yellow colour developed followed by the precipitation of a more yellow solid. The mixture was stirred overnight resulting in more yellow precipitate formation. The paste-like mixture was diluted with diethyl ether (~100-200 ml) to allow for collection by suction filtration and dissolution of the excess alcohol which is a solid near room temperature. The crude product was transferred back to a flask with diethyl ether and stirred for 30 min, then collected on a sinter frit by vacuum filtration again washing it repeatedly with diethyl ether and drying it under vacuum on the sinter frit. The melting point of KdX is 79°C.Example 2. Synthesis of 1-ethyl-1-methylpyrrolidinium dodecyl xanthate (P12dX)

[0165] Potassium dodecyl xanthate (1 .485 g, 4.94 mmol) was dissolved in a large volume (300 ml) of iso-propanol with gentle heating. The 1 -ethyl- 1 -methyl pyrrolidinium bromide (0.9586 g, 4.94 mmol) was also dissolved in iso-propanol (50 ml) and the twoalcoholic solutions were combined resulting in a cloudy reaction mixture as a result of a white precipitate forming. The mixture was stirred for 2 h and cooled overnight in a fridge to maximise the precipitation of the ion exchange by-product KBr. The mixture was then filtered cold through a 0.45 pm membrane filter to remove the white KBr byproduct. The solvent was removed from the yellow supernatant on a rotary evaporator resulting in a light yellow oil. The crude yellow oil was redissolved in a small volume of acetone and placed in the fridge overnight. The crystalline material which precipitated was collected by vacuum filtration. The melting point of P12dX was found to be 32- 34°C.

[0166] The water solubility of P12dX and KdX was qualitatively compared by addition of the compounds to vials containing water. P12dX dissolved readily in water, in contrast to the mostly insoluble KdX.Example 3. Synthesis of other 1-ethyl-1-methylpyrrolidinium alkyl xanthates

[0167] 1 -Ethyl-1 -methylpyrrolidinium octyl xanthate (P12oX) and 1 -ethyl-1 - methylpyrrolidinium dodecyl xanthate (P12decX) were prepared by the methodology of Examples 1 and 2, using n-octanol and n-decanol as starting materials respectively.Example 4. Synthesis of 1-ethyl-3-methylimidazolium dodecyl xanthate (EMImdX)

[0168] Potassium dodecyl xanthate (1 .025 g, 3.41 mmol) was dissolved in a large volume (300 ml) of iso-propanol with gentle heating. The 1 -ethyl-3-methyl imidazolium chloride (0.500 g, 3.41 mmol) was also dissolved in iso-propanol (50 ml) and the two alcoholic solutions were combined resulting in a cloudy reaction mixture as a result of a white precipitate forming. The mixture was stirred for 2 h and cooled overnight in a fridge to maximise the precipitation of the ion exchange by-product KCL The mixture was then filtered cold through a 0.45 m membrane filter to remove the white KCI byproduct. The solvent was removed from the yellow supernatant on a rotary evaporator resulting in a light yellow oil. The crude yellow oil was redissolved in a small volume of acetone and placed in the fridge overnight. The crystalline material which precipitated was collected by vacuum filtration. The melting point of EMImdX was found to be 39°C.

[0169] The water solubility of EMImdX and KdX was qualitatively compared by addition of the compounds to vials containing water. EMImdX dissolved readily in water, in contrast to the insoluble KdX.Example 5. Zinc flotation

[0170] The flotation of sphalerite (ZnS) from a sphalerite-quartz mixture at pH 8 was investigated with the long hydrocarbon chain collector P12dX and compared to that with several commercial short hydrocarbon chain collectors.

[0171] For each flotation test, 50 g of sphalerite and 450 g of quartz was mixed with distilled water and ground in a stainless steel ball mill with 60 stainless steel balls for 20 minutes at the natural pH and at 67% solids by weight, thereby producing the pulp that was then transferred to the flotation cell. The sphalerite was conditioned with 50 g / t copper sulphate added to the flotation cell immediately before the addition of the collector.

[0172] Figure 3 shows the zinc recovery profiles using xanthates of varying chain length at an equimolar dose of 0.1 1 mol / t. Recovery of copper-activated sphalerite generally increased with increasing hydrocarbon chain length of the xanthate collector. The P12dX collector resulted in the highest (and near-complete) zinc recovery of 97% after 8 minutes of flotation which is 16% higher than the next best zinc recovery achieved with SiBX. There was no significant difference in the zinc recovery obtained with KaX and SiBX. Quartz recovery was low, and in the range expected due to unavoidable entrainment of quartz particles to the froth. This arises due to the mechanical mass transfer of fine quartz particles suspended in the water between bubbles as they make their way to the froth zone and ultimately to the concentrate.

[0173] The particle size dependence of the sphalerite recovery, using SiBX and P12dX, can be seen in Figure 4, which also includes a histogram showing the sphalerite size distribution in the ground feed. The sphalerite in the feed included (i) 9.6 wt.% of a coarse fraction with a particle size between 106 and 150 pm (i.e. -150+106 pm), and (ii) 2.4 wt.% of a coarse fraction with a particle size between 150 and 212 pm (i.e. - 212+150 pm). Almost all the fine and intermediate sphalerite (particularly particles less than 53 pm) is recovered with both collectors but the P12dX recovered significantly more of the coarser sphalerite particles (the -106+75 pm; -150+106 pm; -212+150 pmfractions). The recovery of sphalerite present in the coarse -212+150 pm fraction was 81 % with P12dX.Example 6. Pyrite flotation

[0174] The flotation of the iron sulfide mineral pyrite (FeS2) was investigated from a pyrite-quartz mixture at pH 8 with the collectors P12dX and KeX.

[0175] For each flotation test, 450 g of quartz was ground in a stainless steel ball mill with 60 stainless steel balls for 10 minutes, the mill was opened and 50 g of pyrite was added and the mineral mixture was ground for a further 5 minutes at the natural pH and at 67% solids by weight, thereby producing the pulp which was then transferred to the flotation cell.

[0176] Figure 5 shows that both P12dX and KeX strongly floated pyrite at an equimolar dose of 0.12 mol / t, but that higher recovery yields were obtained with P12dX. After 8 minutes of flotation, the pyrite recovery was 99% and 94% for P12dX and KeX, respectively. Notably P12dX thus effectively recovered all the pyrite. This is encouraging for gold mining operations where maximum pyrite recovery is important because the gold is associated with pyrite in the gold-bearing ore. Quartz recovery was low, and in the range expected due to unavoidable entrainment to the froth zone.

[0177] The particle size dependence of the pyrite recovery with P12dX and KeX is presented in Figure 6, which includes a histogram showing the pyrite size distribution in the ground feed. It is evident that the 5% higher overall pyrite recovery achieved after 8 minutes of flotation with P12dX is due to improved recovery in the three coarsest fractions, specifically the -425+212 pm fraction (32.6% of feed; 99.4% pyrite recovery vs 96.7% pyrite recovery), the -850+425 pm fraction (5.2% of feed 96.3% pyrite recovery vs 89.2% pyrite recovery) and the -1700+850 pm fraction (3.2% of feed; 60.0% pyrite recovery vs 0% pyrite recovery). The apparent recovery differences in in the two finer fractions are insignificant as there were negligible amounts (1 %) of pyrite in these size fractions. Notably, P12dX floated more than half of the pyrite in the coarsest -1700+850 pm fraction, whereas KeX did not float any of this material. This demonstrates the ability of the long-chain collectors to impart the necessary hydrophobicity demanded by the coarser particles to render them floatable. Commercial collectors such as KeX are limited in the degree of hydrophobicity they canimpart and empirically cannot meet the higher hydrophobicity demand of coarse particles to make them floatable.Example 7. Copper flotation

[0178] The flotation of chalcocite (CU2S), an important copper-bearing sulfide mineral, was investigated from a chalcocite-quartz mixture at pH 8 with the collectors 1 -ethyl-1 -methylpyrrolidinium octyl xanthate (P12oX), 1 -ethyl-1 -methylpyrrolidinium dodecyl xanthate (P12decX) and 1 -ethyl-1 -methylpyrrolidinium dodecyl xanthate (P12dX). The hydrocarbon chain of the anionic xanthate increases from 8 carbons in P12oX, to 10 carbons in P12decX and to 12 carbons in P12dX.

[0179] For each flotation test, 450 g of quartz was ground in a stainless steel ball mill with 60 stainless steel balls for 10 minutes, the mill was opened and 50 g of chalcocite was added and the mineral mixture was ground for a further 5 minutes at the natural pH and at 67% solids by weight, thereby producing the pulp which was then transferred to the flotation cell.

[0180] The results in Figure 7 show that chalcocite recovery increased with increasing collector hydrocarbon chain length, although the difference between P12oX and P12decX is small (only 3%). The longest chain xanthate, P12dX, performed best, recovering 86% of chalcocite after 8 minutes of flotation. Each of the 3 long-chain collectors significantly outperformed the well-known short hydrocarbon chain collector potassium ethyl xanthate (KeX) in terms of chalcocite flotation recovery at an equimolar dose of 0.03 mol / t. The flotation recovery of chalcocite in the absence of collector is also presented as a baseline. Quartz recovery was low, and in the range expected due to unavoidable entrainment to the froth zone.Example 8. Variation of collector concentration

[0181] The effect of collector concentration on chalcocite recovery from a chalcocite-quartz mixture at pH 8 was then investigated. Figure 8 shows that recovery increases when increasing P12dX collector concentration (dose) from 0.01 mol / t to 0.03 mol / t to 0.12 mol / t, otherwise using the same procedure as Example 7. At the highest dose, the chalcocite was near-quantitatively recovered (overall recovery of 98%) after 8 minutes of flotation.

[0182] The particle size dependence of chalcocite recovery, after 8 minutes of flotation using P12dX and KeX at the intermediate dose of 0.03 mol / t, is compared in Figure 9. The chalcocite recovery was 86% and 30% for P12dX and KeX, respectively, with the significant difference reflecting the greater degree of hydrophobicity imparted by P12dX. The improvement in overall recovery is caused almost entirely by improved recovery of coarser chalcocite particles (greater than 53 pm) by P12dX compared to KeX. KeX recovered a negligible amount of chalcocite in two coarse fractions, namely -212+106 pm and -425+212 pm, whereas P12dX recovered 97% of the chalcocite in the -212+106 pm fraction (41.0% of feed) and 57% of the chalcocite in the -425+212 pm fraction (19.6% of feed).

[0183] The particle size dependence of chalcocite recovery, after 8 minutes of flotation using P12dX and KeX at the highest dose of 0.12 mol / t, is compared in Figure 10, which also includes a histogram showing the chalcocite size distribution in the ground feed. Chalcocite recovery of 98% and 92% was obtained for P12dX and KeX. The difference is again attributable to the improved recovery of chalcocite present in the coarse fractions, including the -212+106 pm fraction (43.0% of feed; 99.6% chalcocite recovery vs 97.3% chalcocite recovery) and particularly in the -425+212 pm fraction (23.1 % of feed; 99.7% chalcocite recovery vs 69.8% chalcocite recovery) (<2% chalcocite present in the fine fraction).Example 9. Variation of organic cation

[0184] The effect of organic cation variation was investigated by comparing the recovery of chalcocite from a chalcocyite-quartz mixture at pH 8, using the collectors 1 -ethyl-3-methylimidazolium dodecyl xanthate (EMImdX) and the analogous P12dX. Both collectors comprise the same dodecyl xanthate moiety which is responsible for flotation. The two cations have very different structural configurations and ionic properties. Due to its unsaturated ring structure, the imidazolium cation is relatively planar and delocalises the positive charge away from the quaternary nitrogen. In contrast, the pyrrolidinium cation is flexible and localises the positive charge on the quaternary nitrogen. The 1 -ethyl-3-methylimidazolium and 1 -ethyl-1 - methylpyrrolidinium cations can thus be considered representative of a wide range of organic cations.

[0185] The results seen in Figure 1 1 show that both the EMImdX and P12dX collectors floated chalcocite significantly better than the short-chain KeX at an equimolar collector dose of 0.03 mol / t, otherwise using the same procedure as Example 7. The total recovery of chalcocite after 8 minutes of flotation was 10 % lower with EMImdX than with P12dX. However, the flotation kinetics were improved with EMImdX.Example 10. Copper ore flotation

[0186] A copper porphyry ore from the USA containing 0.20 wt% copper, 2.53 wt.% iron and 2.60 wt.% sulphur was used to investigate copper recovery from a real ore. The copper content was present in chalcopyrite and the As-bearing copper sulfide minerals tennantite and enargite. Pyrite was the main sulfide gangue mineral present. Ore samples were prepared for grinding by crushing to -2 mm, then blending and splitting into 1000 g lots.

[0187] For each test, 1000 g of ore was ground in a stainless steel rod mill with 15 stainless steel rods at 67% solids, remainder distilled water. Two grinding conditions were used to produce finer and coarser comminuted ore distributions. For the finer grind, the ore was ground for 14 minutes, yielding a Pso of 165 pm (by weight). For the coarser grind, the ore was ground for 7 minutes, yielding a Pso of 240 pm (by weight).

[0188] The ground pulp was transferred to the 3 dm3flotation cell and the water level raised with distilled water. The pH was adjusted to pH 10 with dilute 2.5% solutions of sodium hydroxide. The collector was then added (freshly prepared before each flotation experiment as a 1 % w / v solution) and the pulp conditioned for 5 minutes. Frother (Cytec Aerofroth 65, a commercial grade polypropylene glycol prepared as a 0.25% w / v solution) was added continuously at the rate of 5 mg min’1starting 1 minute before turning on the gas flow to commence flotation. Concentrates were collected for 8 minutes at 0.5, 1 , 2, 4 and 8 minutes by scraping the surface of the froth with a paddle at a constant depth and rate (once every 5 secs).

[0189] The flotation recovery of copper from the ground copper porphyry ore at two different grind sizes (Pso of 165 pm and 240 pm by weight) at pH 10 was investigated with 100 g / t of the long hydrocarbon chain collector P12dX. Two additions of P12dX were made: 0.14 mol / t at the start of the float, collecting an 8 minute concentrate, and a further 0.14 mol / t added after 8 minutes of flotation, collecting an additional 4 minuteconcentrate. Total copper recovery achieved for the finer and coarser grinds was similar: 84% and 87% respectively.

[0190] Importantly, the copper recovery was maintained even when the feed had a larger proportion of difficult-to-float coarse material, including composite particles where the target copper-bearing minerals were not liberated from gangue. The coarse fractions in the coarser grind contained a significant proportion of unliberated or composite particles. This suggests P12dX can successfully float unliberated or composite coarse particles.

[0191] Figure 12 shows the particle size dependence of copper recovery for the two different grinds after 12 minutes of flotation using 0.28 mol / t P12dX, with histograms showing the copper size distribution in the feed for both grinds (i.e. Cu distribution in various sized fractions of the feed). The coarser grind contained substantially more of the larger sized fractions. Notably, P12dX floats the coarse fractions relatively well (>60% copper recovery even for the -425+300 pm fraction), and the recovery of copper did not substantially decrease as a result of a greater proportion of coarse and / or composite particles.

[0192] The results are shown in Table 1 below, with comparison against an experiment conducted on a similarly coarse grind (Pso of 240 pm by weight) of the same ore using the longest chain commercially available xanthate flotation collector, potassium amyl xanthate (KaX). Significant improvement in the copper recovery from the largest fractions is evident.Table 1.

[0193] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

Claims

Claims1 . A flotation method comprising: providing a mineral composition comprising comminuted ore particles, the mineral composition comprising at least one target sulfide mineral; producing a pulp comprising the mineral composition and an aqueous phase comprising (i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and (ii) an organic cation; passing gas bubbles through the pulp; and recovering comminuted ore particles captured in a froth above the pulp, thereby producing a mineral concentrate enriched in the at least one target sulfide mineral, wherein the mineral composition comprises a first coarse fraction of comminuted ore particles with a particle size between 150 and 212 pm, and wherein at least 50% of the at least one target sulfide mineral in the first coarse fraction is recovered in the mineral concentrate.

2. The flotation method according to claim 1 , wherein at least 2 wt.% of the at least one target sulfide mineral in the mineral composition is present in the first coarse fraction.

3. The flotation method according to claim 1 or claim 2, wherein at least 90% of the at least one target sulfide mineral in the coarse fraction is recovered in the mineral concentrate.

4. The flotation method according to any one of claims 1 to 3, wherein the mineral composition comprises a second coarse fraction of comminuted ore particles with a particle size between 212 and 425 pm, and wherein at least 50% of the at least one target sulfide mineral in the second coarse fraction is recovered in the mineral concentrate.

5. The flotation method according to any one of claims 1 to 4, wherein the organic cation is a non-surfactant organic cation.

6. The flotation method according to any one of claims 1 to 4, wherein producing the pulp comprises (i) providing a flotation collector composition comprising the thiol collector anion and the organic cation; and (ii) dispersing the flotation collector composition in the aqueous phase.

7. The flotation method according to claim 6, wherein the flotation collector composition comprises the thiol collector anion and the organic cation present in a water-soluble salt.

8. The flotation method according to claim 7, wherein the water-soluble salt is a solid at room temperature.

9. The flotation method according to any one of claims 1 to 8, wherein the mineral concentrate is enriched in a plurality of target sulfide minerals, and wherein the method further comprises selectively recovering at least one target sulfide mineral from the mineral concentrate by subjecting the mineral concentrate to a subsequent froth flotation stage.

10. The flotation method according to any one of claims 1 to 9, wherein the mineral composition comprises a tailings product of a preliminary froth flotation stage, and wherein the method further comprises subjecting a comminuted ore to the preliminary froth flotation stage to produce (i) a concentrate enriched in at least one sulfide mineral and (ii) the tailings product.11 .The flotation method according to any one of claims 1 to 10, wherein the at least one target sulfide mineral comprises one or more metals selected from the group consisting of copper, nickel, zinc, cobalt, iron, molybdenum and lead.

12. The flotation method according to any one of claims 1 to 10, wherein the at least one target sulfide mineral comprises an iron sulfide mineral, and wherein the mineral composition further comprises a precious metal associated with the iron sulfide mineral.

13. The flotation method according to any one of claims 1 to 12, wherein the organic cation is selected from the group consisting of a pyrrolidinium, imidazolium, benzimidazolium, quaternary ammonium, pyrrolium, indolium, carbazolium, pyridinium, quinolinium, piperidinium, piperazinium, morpholinium, phosphonium, sulfonium and combinations thereof.

14. The flotation method according to any one of claims 1 to 13, wherein the organic cation is an N-heterocyclic cation comprising quaternary nitrogen.

15. The flotation method according to any one of claims 1 to 14, wherein the organic cation is selected from the group consisting of 1 ,1 -dialkylpyrrolidinium cations, 1 ,3- dialkylimidazolium cations and combinations thereof.

16. The flotation method according to any one of claims 1 to 15, wherein the thiol collector anion is selected from the group consisting of a xanthate, a dithiophosphate, a dithiocarbamate, a dithiophosphinate, and combinations thereof.

17. The flotation method according to any one of claims 1 to 16, wherein the hydrophobic group has between 10 and 14 carbon atoms.

18. A flotation collector composition comprising:(i) a thiol collector anion comprising a hydrophobic group with at least 8 carbon atoms; and(ii) an organic cation.

19. The flotation collector composition according to claim 18, wherein the organic cation is a non-surfactant organic cation.

20. The flotation collector composition according to claim 18 or claim 19, wherein the organic cation is an N-heterocyclic cation comprising quaternary nitrogen.21 .The flotation collector composition according to any one of claims 18 to 20, wherein the organic cation is selected from the group consisting of 1 ,1 -dialkylpyrrolidinium cations, 1 ,3-dialkylimidazolium cations and combinations thereof.

22. The flotation collector composition according to any one of claims 18 to 21 , wherein the thiol collector anion is selected from the group consisting of a xanthate, a dithiophosphate, a dithiocarbamate, a dithiophosphinate, and combinations thereof.

23. The flotation collector composition according to any one of claims 18 to 22, wherein the hydrophobic group has between 10 and 14 carbon atoms.

24. The flotation collector composition according to any one of claims 18 to 23, wherein the thiol collector anion and the organic cation are present in a water- soluble salt, wherein the water-soluble salt comprises: (i) the thiol collector anion in an amount of at least 80 mol% of the total anion component of the water soluble salt and (ii) the organic cation in an amount of at least 80 mol% of the total cation component of the water soluble salt.

25. The flotation collector composition according to any one of claims 18 to 24, in the form of water-dispersible pellets or agglomerates.

Images