Terpolymer compositions, methods for their preparation, and their use for separating minerals

Abstract

A terpolymer composition, and method of preparing the same, said terpolymer composition comprising 5 to 90 mol% of recurring units having an uncharged functional group, 5 to 40 mol% of recurring units having a sulfur-containing functional group, and 5 to 90 mol% of recurring units having a charged functional group, based on total mols of the terpolymer composition, wherein the terpolymer composition comprises a weight averaged molecular weight (Mw) in a range of 1000 Da to 15000 Da. The present invention also relates to a method of selectively recovering sulfide minerals comprising conditioning a process ore slurry with the terpolymer composition, and conducting a froth flotation process to separate the process ore slurry into a non-value mineral stream and a value mineral stream.

Description

[0001] TERPOLYMER COMPOSITIONS AND THEIR USE FOR SEPARATING MINERALS

[0002] FIELD OF INVENTION

[0003] The technological concept disclosed herein generally relates to formulations of terpolymer compositions for the recovery of value sulfides minerals from an ore slurry.

[0004] BACKGROUND

[0005] Flotation processes rely on differential water wettability of solids to achieve a separation between them. In these processes, ores which are naturally occurring sources of value and non-value metals / minerals are ground using mills to “liberate” the value minerals from the non-values. Water is then added to the ground rock, and the resulting slurry is treated with certain reagents. One family of reagents are surfactants, also known as collectors, which selectively render target minerals hydrophobic. These collectors are amphiphilic molecules that have both a mineral specific functional group (which forms a complex with the mineral surface), and a hydrocarbon chain, which alters its wettability (makes it more hydrophobic or water repelling). Air is then passed through the tank containing the agitating slurry. The turbulence allows for repeated contact between the hydrophobic particles and air bubbles, resulting in the attachment of hydrophobic particles to bubbles, which are levitated to the surface.

[0006] Certain other reagents called frothers are also added which adsorb onto the liquid air-interface to help reduce the size of bubbles and also facilitate the creation of a transient froth, which traps the value hydrophobized particles. This froth is removed from the surface of the tank resulting in a separation of these hydrophobized particles from the rest of the slurry. Achieving the necessary selectivity in the separation necessitates the use of a third family or reagents known as modifiers. Modifiers comprise a wide array of reagents ranging from small inorganic molecules such as lime (Ca(OH)2), sodium cyanide (NaCN) and sodium hydrosulfide (NaSH), to small organic molecules such as carboxymethyl trithiocarb onate, to polymeric reagents. The function of these modifiers is to sharpen the separation of the value metals / minerals from non-value metals / minerals by further modifying their surfaces. One function of such modifiers is to adsorb onto certain non- value minerals that are hydrophobic and render them hydrophilic so that they do not attach to air bubbles, a phenomenon referred to as “depression” by practitioners in the field, with the chemical being called a depressant. Another possible function of these modifiers is to “depress” the value minerals and float the non-value minerals thus effecting a “reverse flotation” process, as it is described by practitioners in the field.

[0007] Often times, in hardrock mining (for base and precious metals) minerals present in the ore are generally classified into sulfide minerals and non-sulfide minerals because of certain common responses / behaviors of these minerals in the flotation process. Sulfide minerals refer to those minerals that contain sulfur directly bonded to a metal atom. Some sulfides are typically value minerals (e.g. chalcopyrite, chalcocite, molybdenite etc), and tend to be more hydrophobic (e.g. molybdenite) or rendered fully hydrophobic fairly easily using small quantities of collector reagent (e.g. chalcopyrite). Non-sulfide minerals are those in which sulfur is not present or if present not directly bonded to a metal atom. There, however, exists a class of non-sulfide minerals that are naturally hydrophobic, namely talc, pyrophyllite, organic carbon (identified as TOC or total organic carbon by practitioners), and certain types of shales and are thus, oftentimes undesirably found with the hydrophobic value sulfides. Separating sulfide minerals like chalcopyrite, chalcocite and pyrite from the non-sulfide non-value minerals via direct flotation involves the use of talc depressants, which can be expensive because large quantities can be needed, and these can depress some amount of sulfide value minerals. Reverse flotation, whereby the sulfide minerals are depressed, and values floated, is rarely practiced because: a) once the sulfides are depressed, they are difficult to reactivate, b) large doses of reagents with poor HSE (Health, Safety, and Environmental) profiles may be required to achieve the separation.

[0008] On the other hand, a bigger issue that has thus far been deemed impractical if not impossible to achieve is the separation of the naturally hydrophobic value sulfide mineral molybdenite from talc, carbon and other such hydrophobic non-sulfide (and non-value) minerals by the flotation process. Collectors like hydrocarbon oils that further boost hydrophobicity of molybdenite show similar affinities for talc, pyrophyllite, carbon and certain types of shales.

[0009] One approach to address this problem adopts the use of a depressant for these non- sulfide, naturally hydrophobic minerals like talc, pyrophyllite, thus floating the value molybdenite. Unfortunately, these depressants tend to depress both molybdenite and talc / carbon minerals. In primary molybdenum (Mo) plants, use of these talc depressants results in the loss of molybdenite to the tailings. In plants that produce molybdenite as a byproduct of copper production, molybdenum (Mo) is also depressed and reports to the copper (Cu) product stream.

[0010] Another strategy involves the use of “depressants” that target the sulfide minerals like molybdenite and allowing for the flotation of talc. In this regard, the use of polymeric depressants has been proposed in Braga et al (2014) where dextrin is used to depress molybdenite and float off talc in the beneficiation of emeralds; this work was done using single mineral systems, and there are studies which show that the separation is far from perfect in real ores. Kelebek et al. (2006) have also used lignosulfonates (with MIBC as frother) to depress molybdenite and floating off talc although there seems to be too narrow of a selectivity window as just a bit extra lignosulfonate will result in depression of the talc. Reports of the use of ligninsulfonates for talc-Mo separation in the industry (e.g. Twin Buttes in Arizona) have also been reported (Hiscox et al. 1976). Humic acids have also been reported as molybdenite depressants, being effective in a wide range of pH values (Yuan, D. et al. 2018) but they admit to a narrow window of selectivity. This can be said in general for most of these polymeric depressants.

[0011] Lipp et al (1988) teaches the use of acrylamide and allyl thiourea copolymers as depressants for all sulfide minerals. Furthermore, Wang et al (1988) describes the use of a copolymers containing acrylic acid and allyl thiourea to depress sulfide minerals in general. These patents do not discuss the role of terpolymers, nor the selectivity of these polymers against non-sulfide hydrophobic gangue like talc, carbon and certain types of shales.

[0012] The use of inorganic salts has also been discussed for the separation of talc from molybdenite (as proposed in US patent 3,921,810 by Huch et al. 1975), where it is believed that metal hydroxide species formed from salt cations are responsible for talc depression. The disadvantage of this approach is the requirement for very high salt dosages (up to 20 kg / t) and the use of toxic heavy metal ions. The industrial use of a combination of aluminum sulfate with sodium silicate to depress talc has also been reported (Parkinson, G. 1976) suffering from similar disadvantages as the inorganic salts.

[0013] Some other strategies, both chemical and physical, have been tried in the past and some were even practiced at the industrial scale, however, currently these have been discontinued. For example, roasting of concentrates was used by the Pima Mining Company in Arizona (US patent 3,921,810 by Huch et al. 1975) to render molybdenite less floatable and allowing talc (which remained unaffected) to float off. The disadvantages of this process are the requirement of expensive and elaborate systems: multiple hearth roasters or spray dryers with adequate dust collecting systems, control of temperature, retention time and degree of oxidation of the minerals; all parameters that are critical for effective separation; and high expenditure of energy for heat and transportation of the ore concentrate which proves to be costly.

[0014] Most importantly, this process is only viable if talc is consistently present in most of the ore body which makes it unsuitable for plants with inconsistent ore quality or those that rely on scheduled campaigns which use existing equipment for different processes. Thus, investing in these expensive and elaborate systems that may take multiple days to start up and run efficiently is not economic, and all such plants have been decommissioned.

[0015] The talc-molybdenite separation has also been tried electrostatically or by hydroseparation (G.I. Mathieu and R.W. Bruce 1974) which, despite working in low-talc- containing concentrate (62% M0S2, 28% talc), were shown to be ineffective for high-talccontaining concentrate (30% M0S2, 60% talc) by not being able to achieve a M0S2 concentrate with a grade higher than 40% (saleable M0S2 concentrate contains > 80% M0S2).

[0016] Thus, when talc, carbon, pyrophyllite or other such minerals are present with molybdenite in ores, the inability to further upgrade / purify molybdenite concentrates to salable grade (typically ~>80% M0S2) results in the wasting of these concentrates, resulting in a large loss of revenue. There is thus a need to identify a process to enable the separation of very hydrophobic sulfide minerals such as molybdenite, as well as easily hydrophobized sulfide minerals such as chalcopyrite, chalcocite, bornite, covellite, galena, sphalerite etc., from talc, carbon and certain types of shales which are broadly classified as hydrophobic non-sulfide minerals.

[0017] There has previously been some discussion of acrylamide-allylthiourea copolymers and acrylic acid-allylthiourea polymers as depressants for various sulfide minerals (Lipp et al 1988, Wang et al, 1988). However, the dosages required to achieve sufficient depression of sulfide minerals are quite substantial. Furthermore, removing the depressants from the surfaces they had adsorbed onto for subsequent re-flotation has proven to be challenging. SUMMARY

[0018] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0019] In one aspect, embodiments disclosed herein relate to a terpolymer composition including 5 to 90 mol% of recurring units having an uncharged functional group, 5 to 40 mol% of recurring units having a sulfur-containing functional group, and 5 to 90 mol% of recurring units having a charged functional group, based on total mols of the terpolymer composition, wherein the terpolymer composition comprises a weight averaged molecular weight (Mw) in a range of 1000 Da to 15000 Da.

[0020] Another embodiment disclosed herein relates to a method of preparing the terpolymer composition including contacting monomer units of allyl thiourea with a chain transfer agent thereby forming a pre-reaction mixture, dosing the pre-reaction mixture with a solution of a polymerization initiator, and a solution of acrylamide or a combined solution of acrylamide and acrylic acid, thereby forming a reaction mixture, and isolating the terpolymer composition from the reaction mixture.

[0021] Embodiments disclosed herein also relate to a method of selectively recovering sulfides minerals via the froth flotation process, the method including conditioning a process ore slurry with the terpolymer composition at a dose of 20-20000 g / ton, passing air bubbles through the tank and thus, separating the process ore slurry into a non-value mineral stream and a value mineral stream (attached to bubbles and float) and a value mineral stream (these minerals will sink due to the action of the depressant)., and removing the non-value mineral stream to recover the value mineral stream.

[0022] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

[0023] DETAILED DESCRIPTION

[0024] Embodiments disclosed herein are directed to methods of improving the separation via the flotation process of sulfide minerals using a sulfide mineral depressant comprising a terpolymer composition. To overcome the technical barriers discussed above, the present disclosure provides a terpolymer composition for use as a sulfide mineral depressant that selectively depresses sulfide minerals. The terpolymer composition being of a defined molar ratio and molecular weight range includes the following functional groups: charged, uncharged, and sulfur-containing. In the method described herein, the terpolymer may be used when sulfide minerals are the value minerals and when the non-sulfide minerals are the non-value minerals. The terpolymer compositions may be used in direct flotation as well as reverse flotation processes for the separation of sulfide minerals from other non- sulfide minerals. Furthermore, the present terpolymer compositions may be used to selectively depress metal sulfide minerals while not depressing talc, pyrophyllite and other hydrophobic non-sulfide mineral species. These polymers achieve selective depression of metal sulfide minerals in a more dose efficient manner and allow these minerals to be subsequently refloated.

[0025] Terpolymer Composition

[0026] The terpolymer composition comprises recurring units of an uncharged functional group, recurring units of a sulfur-containing functional group and recurring units of a charged functional group.

[0027] In one or more embodiments, the terpolymer composition may have a weight averaged molecular weight (Mw) of less than 15000 Da, such as in the range of 1000 Da to 15000 Da, such as from a lower limit of 1000, 2000, 3000, or 4000 Da to an upper limit of 8000, 10000, 12000 or 15000 Da, where any lower limit may be paired with any upper limit. For example, the weight averaged molecular weight (Mw) is in the range of 2000 Da to 10000 Da, preferably in the range of 3000 Da to 8000 Da.

[0028] It has been unexpectedly and advantageously found that certain terpolymer compositions including a non-charged group, a charged group, and a sulfur-functionalized group in a defined molecular weight range can function effectively as depressants for sulfide minerals like molybdenite, chalcopyrite and pyrite while not depressing naturally hydrophobic minerals like talc, pyrophyllite, organic carbon, and certain types of shales, at much lower dosages than those disclosed in the prior art. Furthermore, removal of these polymers from the sulfide mineral surfaces for reactivation (for flotation) is now possible with certain “activating” reagents. However, all three components are needed to make an effective separation, or the efficacy suffers. Recurring Units (X)

[0029] In one or more embodiments, the recurring units of the uncharged functional group may be derived or formed (obtained) from an acrylamide monomer, resulting in a recurring unit of formula (X): where R, R1and R2are each independently selected from -H, C1-C12 alkyl, allyl, benzyl, phenyl, and R1and R2are each independently also selected from cyclic C4-C6 alkyl groups or cyclic imides.

[0030] Thus, the recurring units of the uncharged functional group that may be derived or obtained from an acrylamide monomer are represented by formula (X) as defined above.

[0031] In one or more embodiments, cyclic C4-C6 alkyl groups include but are not limited to cyclopentyl or succinic (-C(O)-CH2CH2-C(O)-) groups, and cyclic imides include that of phthalic imides and the like.

[0032] The recurring units derived or formed from an acrylamide of formula (X) include but are not limited to alkyl acrylamides such as methacrylamide, etc. and N-substituted acrylamides and methacrylamides such as N-N’ -dimethylacrylamide, etc.

[0033] The recurring units derived or formed from an acrylamide of formula (X) may be present in the terpolymer composition in an amount in the range of 5 mol% to 90 mol% based on total mols of the terpolymer composition, such as from a lower limit of 5, 10, 20, 30, 40 or 50 mol % to an upper limit of 60, 70, 80, or 90 mol%, where any lower limit may be paired with any upper limit.

[0034] Recurring Units (Y)

[0035] In one or more embodiments, recurring units of the sulfur-containing functional group may be derived or formed (obtained) from a thiourea or a thiosemicarbazide. These recurring units include but are not limited to thiourea derivatives or thiosemicarbazides derivatives, such as allylthiourea, N-allyl-N'-methylthiourea, N-allyl-N’,N’- dimethylthiourea, N-(2-thioureidoethyl)acrylamide, N-(2-(3- methylthioureido)ethyl)acrylamide, N-(2-(3-acetylthioureido)ethyl)acrylamide, N-(3- thioureidopropyl)acrylamide, 2-acryloylhydrazine-l -carbothioamide.

[0036] According to one or more embodiments, the recurring of the sulfur-containing functional group may be derived or formed from an allyl thiourea monomer, resulting in a recurring unit of formula (Y): where R3, R4, R5and R6are each independently selected from -H, C1-C12 alkyl, allyl, benzyl, phenyl, R5and R6are each independently also selected from cyclic C4-C6 alkyl groups or cyclic imides and W is -(CH2)n- where n is 1 to 6 or -C(0)NH(CH2)m- where m is 2 to 6. As will be readily understood by those skilled in the art, n and m are integers.

[0037] Thus, the recurring units of the sulfur-containing functional group that may be derived or obtained from an allyl thiourea monomer are represented by formula (Y) as defined above.

[0038] In one or more embodiments, cyclic C4-C6 alkyl groups include but are not limited to cyclopentyl or succinic (-C(O)-CH2CH2-C(O)-) groups, and cyclic imides include that of phthalic imides and the like.

[0039] The recurring units derived or formed from a thiourea or a thiosemicarbazide may be present in the terpolymer composition in an amount in the range of 5 mol% to 40 mol% based on total mols of the terpolymer composition, such as from a lower limit of 5, 10, or 15 mol % to an upper limit of 20, 30 or 40 mol%, where any lower limit may be paired with any upper limit.

[0040] Recurring Units (Z)

[0041] In one or more embodiments, recurring units of the charged functional group may be derived or formed (obtained) from an acrylic acid-type monomer, according to formula (Z). Acrylic acid derivatives include but are not limited to acrylic, methacrylic or maleic acids, their alkali metal salts (e.g. sodium, potassium or ammonium salts), and alkyl esters thereof.

[0042] The recurring units derived or formed from an acrylic acid may be present in the terpolymer composition in an amount in the range of 5 mol% to 90 mol% based on total mols of the terpolymer composition, such as from a lower limit of 5, 10, 25, 20, 30, or 40 mol% to an upper limit of 50, 60, 70, 80, or 90 mol%, where any lower limit may be paired with any upper limit. According to one or more embodiments, the recurring unit may be present in an amount ranging from 5 to 50 mol% or 10 to 25 mol% based on total mols of the terpolymer composition.

[0043] Method of Forming the Terpolymer

[0044] The terpolymers of a specific molecular weight range, composition and homogeneity, as described above, may be made according to two methods. The first method includes a two-step reaction of copolymerizing the uncharged functional group with the sulfur containing functional group, followed by the partial hydrolysis of the uncharged functional group resulting in a third charged functional group. The second method involves the copolymerization / terpolymerization of the three types of individual functional group monomers. Both methods incorporate the use of a chain transfer agent and controlled variable dosing of the monomers and polymerization initiators.

[0045] According to one or more embodiments, the method of forming the terpolymer composition described above comprises the steps of contacting monomers forming units of the sulfur containing functional group with a chain transfer agent thereby forming a prereaction mixture, dosing the pre-reaction mixture with a solution of a polymerization initiator and a solution of monomers forming units of the uncharged functional group or a solution of monomers forming units of the uncharged functional group and units of the charged functional group thereby forming a reaction mixture, and isolating the terpolymer composition from the reaction mixture following polymerization. The above-described solutions may be formed in water and formed at any mol% solute of the solvent. The dosing step may be performed in increments using pumps or any other introduction method that allows for the introduction of the separate solutions of monomer at different amounts and / or times during the method. Furthermore, in embodiments where the terpolymerization includes acrylamide, the acrylamide units in the polymer may be partially hydrolyzed to acrylic acid. Thus, a method of forming a terpolymer of acrylamide, allyl thiourea and acrylic acid may include steps of contacting allyl thiourea with a chain transfer agent thereby forming a pre-reaction mixture; dosing the pre-reaction mixture with a solution of a polymerization initiator, and a solution of acrylamide or a combined solution of acrylamide and acrylic acid, thereby forming a reaction mixture, and isolating the terpolymer composition from the reaction mixture following polymerization.

[0046] According to one or more embodiments, the chain transfer agent may include but is not limited to 3-(methylthio)propanoic acid, (methylthio)acetic acid, dithiodiglycolic acid, 3, 3 '-dithiodi propionic acid, sodium hypophosphite, ammonium formate, isopropyl alcohol, peroxides or other agents that do not react with the monomers of the recurring units such as Rhodixan® Al, or combinations thereof. The chain transfer agent may be present in an amount of in a range of 0.5 to 10 mol%, based on the total moles of the reaction mixture, such as from a lower limit of 0.5, 1, 2 or 3 mol% to an upper limit of 5, 7 or 10 mol%, where any lower limit may be paired with any upper limit.

[0047] According to one or more embodiments, the polymerization initiator may include but is not limited to azo initiators such as VA-044, V-50 and APS / Na-MBS type redox pairs. The polymerization initiator may be present in an amount in a range of 0.1 to 5 mol%, based on the total moles of the reaction mixture, such as from a lower limit of 0.1, 0.2, 0.5 or 1 mol% to an upper limit of 2, 3, 4 or 5 mol%, where any lower limit may be paired with any upper limit.

[0048] The terpolymer composition may be prepared at a temperature in a range of 50 to about 100°C (reflux). The terpolymer composition may be isolated by any method known in the art, notably applying vacuum distillation, pH adjustments (acidification and / or neutralization), precipitation, rotary evaporation and combinations thereof.

[0049] Sulfide Mineral Depressant

[0050] According to one or more embodiments, the above terpolymer composition may be used as a sulfide mineral depressant. It is also envisioned that the terpolymer composition may be combined with other depressants to further improve selectivity for certain separations. For example, the terpolymer composition may be combined with another sulfide depressant to improve the overall recovery of value sulfides from an ore slurry. Thus, the terpolymer composition may be combined with other depressants that include but are not limited to carboxymethyl dithiocarbamate, carboxymethyl trithiocarb onate, sodium hydrosulfide, sodium thioglycolate or mixtures thereof.

[0051] Use of Sulfide Mineral Depressant

[0052] The terpolymer composition, alone or in combination with the other sulfide depressants, may be used as a sulfide mineral depressant to selectively recover sulfide minerals by rejecting non-sulfide gangue minerals. Therefore, according to one or more embodiments, the terpolymer composition may be used in a method comprising mixing the terpolymer composition with other depressants to form a mixture. The resulting mixture may then be used in a method of selectively recovering sulfide minerals. Alternatively, the terpolymer composition may be used in a method of selectively recovering sulfide minerals that includes conditioning a process ore slurry and the terpolymer composition described above, and separating the process ore slurry into a floated non-value mineral stream and a depressed value mineral stream by conducting a froth flotation process.

[0053] The process ore from a mining site may grind or size ore down to a particular mesh size to liberate minerals. This process aids in the separation of value and non-value minerals in subsequent process steps. The ground ore, such as having a size of 1-400 microns, is then slurried in water or with another process stream, thereby forming a process ore slurry, to be used in the flotation process. According to one or more embodiments, the process ore slurry includes sulfide and non-sulfide minerals. The sulfide minerals, as value mineral, include but are not limited to chalcopyrite, chalcocite, covellite, bornite, digenite, pyrite, and molybdenite. The non-sulfide minerals, as non-value minerals, include but are not limited to talc, organic carbon, shales and pyrophyllite, and may also include or generally be referred to as gangue. According to another embodiment, the process ore slurry may comprise other silicate and carbonate minerals present in hardrock ores, including non-hydrophobic non-sulfide gangue mineral that are generally recovered via entrainment.

[0054] The process ore slurry may be conditioned with the above-described terpolymer or with a sulfide mineral depressant that comprises the terpolymer. According to one or more embodiments, the amount of the terpolymer used to condition the process ore slurry is in the range of 20 to 20000 grams / ton (g / ton) of the dry ore or dry feed stream, such as from a lower limit of 20, 50, 100, 200 ,400, 500 and 1000 g / ton to an upper limit of 2,000, 2,500, 3,000, 4,000, 5,000, 10,000, or even 20,000 g / ton, where any lower limit may be paired with any upper limit. One of ordinary skill in the art would appreciate that the dose of the polymer may be selected as a function of the amount of sulfide minerals present, but the depressant should work for any amount of sulfide mineral content. However, those skilled in the art would appreciate that when sulfide content is too low, depressant efficacy may suffer. Further, in rare situations, over 20 kg / ton of dry ore or dry feed stream may be used.

[0055] As described above, the method includes a conditioning step. The conditioning step may include mixing the terpolymer with the other depressants outlined above to form a mixture of depressants. The terpolymer and other depressants may be combined to enhance the separation of value and non-value minerals.

[0056] The selection of a frothing agent is not particularly limited. Therefore, any frothing agent known in the art to affect a reduction in the size of bubbles and also facilitate the creation of a transient froth, which traps the hydrophobized particles, may be used. Examples of frothing agents include but are not limited to alcohols such as methyl isobutyl carbinol and esters thereof, polyglycols and their ethers, pine oil, ketones, and cresols.

[0057] In one or more embodiments, the method comprises a step of separating the process ore slurry into a non-value mineral stream and a value mineral stream via the flotation process. In a direct flotation process, the process ore slurry can be separated into a floated value mineral stream and a depressed non-value mineral stream.

[0058] More typically, the method described herein can also be used in a reverse float process, where the process ore slurry can be separated to form a depressed value mineral stream and a floated non-value mineral stream.

[0059] In one or more embodiments, the method includes the step of removing the non- value mineral stream to recover the value mineral stream. Depending on the makeup of the ore, the methods described herein may rely on additional steps to remove the non-value mineral stream and to recover the value mineral stream. Further, the process may be repeated to further purify the non-value or value minerals streams to achieve target specifications as demanded by the process and product quality requirements.

[0060] It is also noted that it is possible to selectively reactivate various depressed sulfide mineral species when this terpolymer or mixtures thereof are used. For example, if the depressed species include molybdenite, chalcopyrite and pyrite, the molybdenite could be selectively reactivated by adding certain reactivators. Another example is that if the depressed species include chalcopyrite and pyrite, the chalcopyrite could be selectively reactivated by adding activators.

[0061] According to one or more embodiments, the method may also include adding a reactivator to selectively activate at least one component of the value mineral stream. The reactivator may be a mineral specific collector, or a modifier. The modifier may be a sulfur containing modifier including but not limited to sodium sulfide (Na2S) and sodium hydrosulfide (NaHS), ammonium sulfide (NHT^S. Examples of non-sulfur containing modifiers include but are not limited to polyglycols such as polyethylene glycol, polypropylene glycol, ethers of polypropylene glycol and polypropylene glycol, and similar compounds can also be used as reactivators. The molecular weight of these polyglycols may range from 100 to 2000 Da. When Cu, Ni, Pb, or Zn need to be reactivated, collectors may be used and include but are not limited to xanthates, dithiophosphates, dithiocarbamates, thionocarbamates, xanthate esters, xanthogen formates, thioureas etc, as well as modified versions of these may be used, as well as mixtures thereof. The non-sulfur containing modifiers can also activate, with limited success, Cu, Ni, Pb, Zn, Ag, and Au containing minerals.

[0062] According to one or more embodiments, the method described above may be used to selectively recovervalue sulfide minerals from non-value non-sulfide minerals of sulfide ores. The depressant for sulfide minerals may be used to depress a value sulfide minerals stream comprising chalcopyrite, chalconite, and pyrite, while not depressing certain hydrophobic non-sulfide gangue minerals like talc, organic carbon and pyrophyllite as a non-value mineral stream.

[0063] Furthermore, the method described herein may be used to separate molybdenite and chalcopyrite (or other Cu containing minerals) from talc or pyrophyllite. In this process, the terpolymer described above may be used to separate the process ore slurry into a value sulfide mineral stream and a non-value non-sulfide mineral stream where the value sulfide mineral stream comprises molybdenite and chalcopyrite. Following the separation of the streams, the non-value stream of talc is removed, and reactivators are added to the value sulfide stream to selectively reactivate (for flotation) the molybdenite as the at least one component from the value sulfide stream. According to one or more embodiments, the reactivator may be NaHS or Na?S or (NHFkS, which reactivates molybdenite for flotation. This process may be repeated as needed to reach the target grade / quality of molybdenite desired. The chalcopyrite or other copper mineral stream is thus one value mineral stream, and the molybdenite rich product is the other. In one embodiment, the tailings from one stage of the process may be transferred to the head of the previous stage to improve separation efficiency.

[0064] In a similar vein, the terpolymers above can be used in the removal of hydrophobic gangue from sulfides in preflotation cleaning stages. In these scenarios, the hydrophobic gangue is more concentrated in the bulk and present alongside a small amount of value minerals (minerals containing Pb, Zn, Au, Ag, Cu, and Ni values). In these cases, it is also possible to depress the value metal containing minerals such as chalcopyrite (which contains Cu as value) and then reactivate it for subsequent recovery.

[0065] A similar approach can be used to treat historical or existing tailings which can be reprocessed by flotation. Mines that contain both Cu and Mo values alongside hydrophobic gangue (talc) typically have to discard the Mo and talc-containing product to tailings. With the inventive terpolymers described above here, it is possible to treat these tailings rich in talc and Mo to produce a higher or salable grade Mo product.

[0066] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0067] The following examples are given for a better understanding of the present invention and should not be construed as limiting to the scope and objects of same.

[0068] Example 1

[0069] Step 1: N-allylthiourea (0.124 moles) and a chain transfer agent at a desired molar amount are dissolved in water (7 moles) in a suitable reaction vessel equipped with a nitrogen gas inlet and an agitator. The solution is agitated for 30 minutes and heated to 80°C. An acrylamide solution is prepared separately by combining acrylamide (0.7 moles) with water (2.765 moles). An initiator solution is prepared separately by combining polymerization initiator 2,2'-Azobis(2-methylpropionamidine)dihydrochloride (0.009 moles) with water (1.190 moles). 10 weight percent of the acrylamide solution and 10 weight percent of the initiator solution are then injected into the reaction vessel. Using 2 syringe pumps, acrylamide solution and initiator solutions are then dosed into the reaction vessel at the following rates: 80 weight percent of both acrylamide solution and initiator solution are added to the reaction vessel in linear fashion for 60 minutes, then the remaining 10 weight percent of acrylamide solution and remaining 10 weight percent of initiator solution were added for 30 minutes. The reaction mixture is stirred for 150 additional minutes at 80°C.

[0070] Step 2: 21.95 grams of water were removed from the reaction mixture via vacuumdistillation. The reaction mixture was cooled to 60°C and NaOH solution (0.100 moles NaOH in 0.666 moles water) was added. After 60 minutes, the reaction mixture was further cooled in an ice bath to approximately 15°C. A concentrated HC1 solution was added to adjust pH to 6.7.

[0071] The resultant terpolymer was a homogeneous mixture of the terpolymer in water with a composition of 70 mol% acrylamide, 15 mol% N-allylthiourea and 15 mol % acrylic acid (determined via a combination of13C NMR spectroscopy and infrared spectroscopy) and a molecular weight (Mw) of 6800 Daltons. The terpolymer was further characterized using HP-SEC with the following conditions: Instrumentation: Agilent 1260 Infinity Isocratic Pump and Autosampler. Detectors: Viscotek Triple Detector Array (TDA-305) Refractive index, Viscometer, and Light scattering (RALS and LALS); Temp: 40°C. Column (2): PL Aquagel OH-20 column, 8 pm particle size; Temp: 40oC. Mobile Phase: 0. IM Na2HPO4 / NaH2PO4in 80 % H2O + 20% ACN, pH ~ 7. Flow Rate: 0.6 mL / min. Concentration: Approximately 3 mg / mL. Injection Volume: 80 pL. Run Time: 55 min.

[0072] The acquisition and data analysis were performed using Malvern’s OmniSEC software version 4.7. The samples were dissolved in the mobile phase and were left to tumble for 2 hours to facilitate dissolution. All sample solutions were filtered with 0.45 pm PES syringe filter. Absolute molecular weight was calculated using accurate polymer concentration and a nominal dn / dc. The refractive index increment (dn / dc) of the polymer was taken to be 0.156 mL / g. The molecular weight determination was performed using differential refractive index and light scattering (right angle). The properties of the formed terpolymer are shown in Table 1

[0073] Example 2

[0074] N-allylthiourea (0.196 moles) and a chain transfer agent in a desired molar amount are dissolved in water (6.4 moles) in a suitable reaction vessel equipped with a nitrogen gas inlet and an agitator. The solution is agitated for 30 minutes and heated to 80 °C. Monomer solution is prepared separately by combining acrylamide (0.85 moles) and acrylic acid (0.26 moles) with water (4.76 moles). The initiator solution is prepared separately by combining the polymerization initiator 2,2'-Azobis(2- methylpropionamidine) dihydrochloride (0.013 moles) with water (1.44 moles). 10 weight percent of the monomer solution and 10 weight percent of the initiator solution are then injected into the reaction vessel. Using 2 pumps, the monomer solution and initiator solutions are then dosed separately into the reaction vessel at the following rates: 80 weight percent of both monomer solution and initiator solution are added in linear fashion for 60 minutes, then the remaining 10 weight percent of monomer solution and 10 weight percent of initiator solution are added for 30 minutes. The reaction mixture is stirred for 150 additional minutes at 80 °C. The properties of the formed terpolymer are shown in Table 1.

[0075] Table 1

[0076] Example 3

[0077] Acrylamide monomer (19.5601 g, 0.2752 mol) and N-((2-acrylamidoethyl) carbamothioyl)benzamide (TEABz) monomer (25.4399 g, 0.0917 mol) was added into a IL 4 necked flask. 204 ml of water and 251 ml of t-butanol were subsequently added into the flask (Solid content = 10 wt%). The flask is heated to 60 °C along with nitrogen purging to dissolve the monomers completely. Subsequently, a chain transfer agent was added in a desired molar amount. The reaction mixture was purged with nitrogen gas for 30 minutes and then, the polymerization initiator VA-044 (0.2698 g, 0.001 mol) was added. The reaction was performed at 65 °C for 20 h (NMR done to check complete conversion of the monomers). After completion of polymerization, 2 eqv. (with respect to moles of TEABz) of 1(N) NaOH soln, was added to perform benzoyl deprotection at 60 °C for 2-3h. Complete benzoyl deprotection was evaluated using NMR. The reaction mixture was neutralized with trifluoroacetic acid to pH 7 and then concentrated in a rotary evaporator. Afterwards, the solution was dried in open air for 2-3 days and then in oven at 85 °C (12- 14h) to dryness. The MW and PDI data for the formed terpolymer were similar to results obtained in Example 1. Examples 4C-11 : Copper-Talc Separation

[0078] A mine treats an ore where the value metals are copper (present in the form of chalcopyrite). Talc is the non-value hydrophobic gangue mineral, which carries the penalty element Fluorine. Other non-value gangue minerals are also present. The plant produced a concentrate containing mostly chalcopyrite, pyrite and talc, along with other minerals. The feed sample was 0.3% Cu, the F content in the feed was 1400 ppm, and the Mg content of the feed was 2%. The bulk concentrate was evenly split into 500g charges to conduct flotation tests. The purpose of these examples was to depress the chalcopyrite (Cu containing mineral) while floating the talc, and then subsequently reactivating the chalcopyrite for recovery.

[0079] Each charge was added to a flotation cell (total capacity 1.25L). Makeup water was added to fill the cell to 1 inch below the lip. The solids density (% solids) was about 33%. The depressant / terpolymer compositions (shown below in table 2) were added to the individual flotation cells, conditioned for 3 minutes, and flotation was carried out for 6 minutes. After this step, a collector (potassium amyl xanthate) was added to the flotation cell at a dose of lOOg / t with the goal of reactivating the Cu for flotation. Results are shown in Table 2. For the following examples, AMD: acrylamide. ATU: allyl thiourea. AA: acrylic acid.

[0080]

[0081] Using existing processes without the terpolymer composition, as shown in 4C, results in both Cu and talc being recovered in the product stream, and the product stream is thus contaminated. Upon addition of the conventional treatment sodium hydrosulfide (NaHS) 5C, depression of Cu and the flotation of talc was observed. However, in the subsequent stages, when Cu needs to be reactivated for flotation, the Cu recovery was insufficient, suggesting that the Cu depression is hard to reverse.

[0082] Upon addition of copolymers of AMD / ATU, as prepared according to Lipp et al. (US4866150) and dosed at 400g / t (6C), poor depression of Cu was observed. When the dose of this polymer was increased to 750g / t (7C), it was observed that the Cu is depressed, but the talc is also depressed. Therefore, copolymers of AMD / ATU are not suitable for separations of Cu and talc. Test 8C showed that if the MW of the copolymer of AMD / ATU is lowered to 8K, Cu depression was still poor.

[0083] Test 9C demonstrates a terpolymer sample prepared to achieve a MW of 40KDa. The results show that, at the same dose of 400g / t and a molecular weight as the copolymer of 6C, the terpolymer performs better than the copolymers prepared according to Lipp et al. by showing better Cu depression, but still insufficient. On increasing the dose of the terpolymer to 750g / t (IOC), sufficient Cu depression is observed, but Cu reactivation is poor. The talc is also depressed in test IOC. When terpolymers with a molecular weight within the preferred MW range are used, as shown in test 11, excellent Cu depression at low dosage (400g / t) is observed and results in only 5% of the Cu recovered (this is considered acceptable). Excellent flotation of talc is also observed. In the subsequent reactivation step, Cu recovery is increased to 80%. While a terpolymer of AMD / ATU / AA (60 / 30 / 10) at a molecular weight of 8K was made, the terpolymer composition was found to be insoluble.

[0084] Example 12C-14: Copper-Molybdenum-Talc Separation

[0085] A mine treats an ore where the value metals are copper (present in the form of chalcopyrite) and molybdenum (present in the form of molybdenite. Talc is the non-value hydrophobic gangue mineral, and other non-value gangue are hydrophilic minerals. The plant produced a bulk concentrate containing mostly chalcopyrite, pyrite, molybdenite and talc, along with other minerals. The bulk concentrate was evenly split into 500g charges to conduct flotation tests. Each charge was added to the flotation cell (total capacity 1.25L). Makeup water was added to fill the cell to 1 inch below the lip. The solids density (% solids) was about 33%. The sample contained 30% Cu, 0.8% Mo, and 2% talc.

[0086] 12C - comparative test

[0087] The results from this study are illustrated in Table 3 and show the distribution of each element (Cu, Mo) as well as the mineral talc to each product stream. The data shows that when the standard process (addition of NaHS) is used for the separation of molybdenite from chalcopyrite, very poor results are obtained. Instead of 95% Mo recovery to Mo concentrate that is considered typical, the recovery is 55%. This is because talc, which is hydrophobic, floats preferentially to the molybdenite crowding it out of the froth, resulting in its loss to the Cu product stream. Because the molybdenite is not recovered to the molybdenite product stream and instead ends up in the Cu product stream, the Cu product stream is thus lower quality product that may be unsaleable. For this reason, Mo production is typically shut down when too much talc is present.

[0088] This example demonstrates how the inventive terpolymers enable both Cu and Mo products that are saleable and high quality. This is achieved by depressing both Cu and Mo containing minerals, while floating away the non-value hydrophobic mineral talc. Then, Mo is selectively reactivated for flotation to generate a product stream. The results are shown in Table 4.

[0089] The terpolymer of the present invention was first added to the bulk Cu-Mo concentrate at a dose of 780 grams per ton of bulk concentrate, to achieve depression of Cu and Mo, while floating the talc (this stage is the “talc rougher”). To the resulting “rougher” concentrate stream, an additional dose (250g per ton of bulk concentrate) of the terpolymer was added. Flotation was conducted again to “clean” the talc-containing (to be discarded) stream further. As shown in Table 4, the resultant stream contained 88% of the talc that was contained in the bulk concentrate and was very concentrated (26% talc). Only 1% Cu and 1% Mo was lost to the talc (discard) stream. The tailings from the cleaner talc flotation are sent to the Cu-Mo separation stage, along with the tails from the talc rougher. Activator (NaHS) is added to activate the Mo, and molybdenite is floated. We see that the resultant Mo concentrate contains 92.2% of the Mo in the bulk concentrate (feed) at 5% Mo grade. Upon further cleaning, we can upgrade the Mo to 20% in the Mo product stream, reduce the Cu from 20 to 6%, and reduce the talc from 4% to 3%. With further upgrading cycles, a higher grade Mo concentrate can easily be produced. In a full-scale implementation of this process, with the Mo cleaner tail being sent back to the Mo rougher stage, it is possible to achieve significantly higher Mo grade in the Mo rougher stream. The tailings from this step constitute the Cu product (90% of the Cu is recovered).

[0090] Example 14

[0091] The tests for Example 13 were repeated with a copolymer of AMD / ATU (90 / 10) with a molecular weight of 8K in Example 14. As shown in Table 5, the use of the copolymer results in poor Mo recovery.

[0092]

[0093] Examples 15C-17 - Preflotation Cleaning

[0094] This example demonstrates how organic carbon (Corg) can be managed in a preflotation cleaning stage. A mine treats a Cu-Au ore with a significant amount of Corg present. The Cu is very active and floats readily in the preflotation stage with a recovery of 90%. 50% of the Au also floats in the preflotation stage. The preflotation rougher concentrate was prepared. A 500g sample of preflotation rougher concentrate was added to the flotation cell and conditioned with the depressant / terpolymer of choice for 4 minutes. A Corg pre-flotation cleaning stage was conducted for 5 minutes. After this, the preflotation tails were treated with a collector (potassium amyl xanthate) at 50g / ton of ore to reactivate and float the Cu and Au. Flotation was then conducted for 5 minutes to recover the “reactivated” Cu. All samples were assayed for Cu, Au and Corg. The sample contained 1% Cu, 0.05ppm Au, and 2% talc. Results are shown in Table 6.

[0095] Example 15C represents a typical plant situation where no reagents are added in the preflotation cleaning. As a result, significant Cu losses to the preflotation cleaner concentrate (80%) were seen. Example 16C explored the use of NaHS in preflotation cleaning. While the copper was depressed, it was not well reactivated. Example 17 used the inventive terpolymer and displayed improved copper depression (only 5% lost to preflotation) and the copper reactivation was far improved at 90%, when greater than 80% is desired.

[0096] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMS1. A terpolymer composition comprising:- 5 to 90 mol% of recurring units having an uncharged functional group;- 5 to 40 mol% of recurring units having a sulfur-containing functional group; and- 5 to 90 mol%, preferably from 5 to 50 mol%, more preferably from 10 to 25 mol%, of recurring units having a charged functional group, based on total mols of the terpolymer composition, wherein the terpolymer composition comprises a weight averaged molecular weight (Mw) in a range of 1000 Da to 15000 Da, preferably in the range of 2000 Da to 10000 Da, more preferably in the range of 3000 Da to 8000 Da.

2. The terpolymer composition according to claim 1, wherein the recurring units having the uncharged functional group are derived from an acrylamide monomer, resulting in a recurring unit of formula (X);whereinR, R1and R2are each independently selected from -H, C1-C12 alkyl, allyl, benzyl, and phenyl; andR1and R2are each independently also selected from cyclic C4-Ce alkyl groups, preferably cyclopentyl or succinic (-C(O)-CH2CH2-C(O)-) groups, and cyclic imides, preferably phthalic imides.

3. The terpolymer composition according to claim 1 or claim 2, wherein the recurring units having the sulfur-containing functional group are derived from a thiourea or a thi osemi carb azi de .

4. The terpolymer composition according to any of claims 1 to 3, wherein the recurring units having the sulfur-containing functional group are derived from an allyl thiourea monomer, resulting in a recurring unit of formula (Y):whereinR3, R4, R5, and R6are each independently selected from -H, C1-C12 alkyl, allyl, benzyl, and phenyl; andR5and R6are each independently also selected from cyclic C4-Ce alkyl groups, preferably cyclopentyl or succinic (-C(O)-CH2CH2-C(O)-) groups, and cyclic imides, preferably phthalic imides andW is -(CH2)n, wherein n is from 1 to 6- or C(0)NH(CH2)m, wherein m is from 2 to 6.

5. The terpolymer composition according to any one of claims 1 to 4, wherein the recurring units having the charged functional group are derived from an acrylic acidtype monomer, according to formula (Z);-W -6. The terpolymer composition according to claim 2, wherein the recurring units of formula (X) comprise alkyl acrylamides, N-substituted acrylamides and methacrylamides, preferably chosen from methacrylamide and N-N’- dimethylacrylamide.

7. The terpolymer composition according to claim 4, wherein the recurring units of formula (Y) comprise N-allyl-N'-methylthiourea, N-allyl-N’,N’ -dimethylthiourea, N-(2-thioureidoethyl)acrylamide, N-(2-(3-methylthioureido)ethyl)acrylamide, N-(2- (3-acetylthioureido)ethyl)acrylamide, N-(3-thioureidopropyl)acrylamide, 2- acryloylhydrazine- 1 -carbothioamide.

8. The terpolymer composition according to claim 5, wherein the recurring units of formula (Z) include acrylic, methacrylic or maleic acids, their alkali metal salts, and alkyl esters thereof.

9. A sulfide mineral depressant comprising the terpolymer composition according to any one of claims 1 to 8 and at least one other depressant, preferably chosen from carboxymethyl dithiocarbamate, carboxymethyl trithiocarbonate, sodium hydrosulfide, sodium thioglycolate or mixtures thereof.

10. A method of preparing the terpolymer composition according to any one of claims 1 to 8, comprising: contacting monomer units of the sulfur containing functional group, preferably of the allyl thiourea, with a chain transfer agent thereby forming a pre-reaction mixture; dosing the pre-reaction mixture with a solution of a polymerization initiator, preferably an azo initiator, and a solution of monomers forming units of the uncharged functional group or a combined solution of monomers forming units of the uncharged functional group and units of the charged functional group, preferably a solution of acrylamide or a combined solution of acrylamide and acrylic acid, thereby forming a reaction mixture, and isolating the terpolymer composition from the reaction mixture.

11. The method according to claim 10, wherein the chain transfer agent comprise 3- (methylthio)propanoic acid, (methylthio)acetic acid, dithiodiglycolic acid, 3,3'- dithiodipropionic acid, sodium hypophosphite, ammonium formate, isopropyl alcohol, peroxides or combinations thereof.

12. The method according to claim 10 or claim 11, wherein dosing the pre-reaction mixture with the solution of acrylamide comprises partially hydrolyzing acrylamide groups of the terpolymer composition to acrylic acid.

13. The method according to any one of claims 10 to 12, wherein isolating the terpolymer composition from the reaction mixture comprises applying vacuum distillation to the reaction mixture and / or neutralizing the reaction mixture.

14. Use of the terpolymer composition as defined in any one of claims 1 to 8, as a sulfide mineral depressant for selectively recovering value sulfide minerals from an ore slurry by rejecting non-sulfide gangue minerals.

15. The use according to claim 14, wherein the terpolymer composition is in combination with another sulfide mineral depressant chosen from carboxymethyl dithiocarbamate, carboxymethyl trithiocarb onate, sodium hydrosulfide, sodium thioglycolate or mixtures thereof, as a sulfide mineral depressant to selectively recover sulfide minerals by rejecting non-sulfide gangue minerals.

16. A method of selectively recovering sulfide minerals, the method comprising: conditioning a process ore slurry with the terpolymer composition as defined in any one of claims 1 to 8, preferably at a dose of 20-20000 g / ton of ore, and conducting a froth flotation process to separate the process ore slurry into a non-value mineral stream and a value mineral stream.

17. The method according to claim 16, wherein removing the non-value mineral stream to recover the value mineral stream comprises: adding a reactivator to selectively reactivate at least one component of the value mineral stream for removal.

18. The method according to claim 16 or 17, wherein the process ore slurry comprises pyrophyllite, organic carbon, shales, talc, chalcopyrite, covellite, bornite, chalcocite, digenite, pyrite and molybdenite.

19. The method according to any one of claims 16 to 18, wherein the non-value mineral stream comprises pyrophyllite, organic carbon, shales, and talc.

20. The method according to any one of claims 16 to 19, wherein the value mineral stream comprises at least one of chalcopyrite, covellite, bornite, chalcocite, digenite, pyrite and molybdenite.

21. The method according to any one of claims 16 to 20, wherein the conditioning step further comprises mixing the terpolymer composition with at least one other depressant to form a mixture of depressants, preferably the other depressantscomprise carboxymethyl trithiocarb onate, carboxymethyl dithiocarbamate, sodium hydrosulfide, sodium thioglycolate or mixtures thereof.

22. The method according to any one of claims 17 to 21, wherein the reactivator is a mineral specific collector or a modifier.

23. The method according to claim 22, wherein the mineral specific collectors comprise xanthates, dithiophosphates, dithiocarbamates, thionocarbamates, xanthate esters, xanthogen formates, thioureas, modified versions of these, and mixtures thereof.

24. The method according to claim 22, wherein the modifiers comprise sulfur containing modifiers comprising sodium sulfide (Na2S), sodium hydrosulfide (NaHS), ammonium sulfide (NHT^S, or non-sulfur containing modifiers comprising polyglycols, preferably with a molecular weight in a range of 100 to 2000 Da.

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