Patent Application
20240149277
The invention relates to dithiocarbamic acids or salts thereof and their use in the recovery of minerals, for example as a depressant in froth flotation separation of minerals, in particular separation of molybdenum sulfides from copper and/or iron sulfides. The invention further relates to a froth flotation mineral recovery process employing said dithiocarbamic acids or salts thereof. The invention further relates to compositions comprising said dithiocarbamic acids or salts thereof and kits of parts comprising said compositions.
Froth flotation is a well-known separation technique employed in the field of mineral processing to separate gangue material from valuable minerals, thereby obtaining a pulp comprising the minerals of interest (often referred to as “mineral concentrate”). Froth flotation relies on hydrophobicity differences between valuable minerals and waste gangue to achieve their separation. While some minerals are naturally hydrophobic and accumulate in the froth, a collector is typically added to increase the affinity of the desired minerals to the froth. Froth flotation separation is often applied in the form of a multi-stage process, the actual number of froth flotation stages depending on factors such as the ore being processed, the desired minerals, the desired yield, the desired purity, etc.
In case complex (mixed) ores (such as chalcopyrite-containing ores) are being processed, froth flotation is also used to further process the mineral concentrate obtained from gangue separation in order to (selectively) separate different minerals, relying on hydrophobicity differences between different minerals to achieve their separation. The technique is used for the separation of a large range of sulfides, carbonates and oxides prior to further refinement. Notable sulfide mineral separations are Copper-Molybdenum, Lead-Zinc, Gold-Silver and Nickel-Copper. In order to steer hydrophobicity differences between minerals and achieve such selective mineral separation, a depressant is typically added. The depressant selectively decreases the affinity of some minerals to the froth such that they remain depressed in the bulk pulp.
Existing froth flotation mineral separation practices generally utilize depressants that lead to concerns with respect to health, safety, and environmental issues. For example, for the separation of molybdenum sulfides from copper sulfides, current practices in the industry consist of a number of different chemical schemes which use Sodium hydrosulfide (NaHS or NaHS), Ferrocyanides, or Nokes reagent (a blend of thiophosphates or dithioarsenates and usually also containing sulfides). These raise many concerns, including transporting materials that contain or readily form hydrogen sulfide, utilizing reagents in the flotation process that are highly toxic and/or that in use form highly toxic hydrogen sulfide off-gassing, environmental impact in case of tailings reservoir failure etc. A more detailed description of background art in the field of Cu—Mo separation can be found in WO2015157498 paragraphs 2-11, incorporated herein by reference.
some alternative reagents have emerged recently for use as a depressant in mineral separation processes, these may also have drawbacks, such as decreased performance compared to NaHS, poor availability, high cost, toxicity, environmental concerns, low efficacy such that many flotation stages are required, non-selective depression such that no separation of different valuable minerals can be achieved, etc.
For example, U.S. Pat. No. 4,595,538 describes the use of Tri-alkali metal di(carboxyalkyl) dithiocarbamates and triammonium-di(carboxyalkyl) dithiocarbamates as depressants.
All in all, any improvements in mineral flotation practice, especially with respect to health and safety, would be of significant importance.
Hence, there remains a need for alternative depressants for use in the froth flotation separation of minerals, in particular for the separation of metal sulfides, for example the depression of copper and iron sulfides in molybdenite flotation circuits.
The present inventors have identified a distinct class of dithiocarbamic acid or salt thereof depressants, useful in the froth flotation separation of minerals, in particular for the depression of copper and iron sulfides in molybdenite flotation circuits.
Hence, in a first aspect the invention concerns a process for recovering a first mineral comprising the steps of:
wherein
SU1614853A1 describes the use of a N-(2-Aminoethyl)carbamodithioic acid salt to depress the sulfide minerals galena (PbS), sphalerite ((Zn,Fe)S) and barite (BaSO4) in order to obtain valuable non-sulfide minerals in the foam.
US2019/0336984A1 describes the use of specific dithiocarbamates to improve the depressant performance of polymers comprising an allyl thiourea functional group and a hydrophilic acrylamide group.
Formula (I) defines a limited group of dithiocarbamic acids or salts thereof wherein at least one of the N substituents comprises a functional group selected from alcohols, amines, ethers, ketones, acetals, ketals, aminoacetals, hemiaminal ethers or combinations thereof. As is illustrated in the appended examples, the present inventors have surprisingly found that dithiocarbamic acids or salts thereof according to formula (I) can be used to achieve highly efficient selective mineral depression and are stable in the operating conditions of a froth flotation cell. In particular, it was found that the compounds of formula (I) can be used to separate different sulfide minerals by selectively depressing one or more sulfide minerals, while allowing one or more other sulfide minerals to be collected in the froth. Furthermore, it was surprisingly found that the compounds of formula (I) can be used effectively without requiring a second depressant.
In another aspect the invention concerns a composition comprising the first depressant as described herein and further comprising one, two, or three of:
In another aspect the invention concerns the use of a dithiocarbamic acid or salt thereof of formula (I) as described herein in the recovery of minerals.
In another aspect the invention concerns a kit of parts comprising a composition (A) comprising the first depressant as described herein and instructions for use of the composition (A) as a depressant in froth flotation recovery of minerals.
In another aspect the invention concerns a kit of parts comprising
In another aspect the invention concerns a dithiocarbamic acid or salt thereof of formula (I) as described herein, preferably 3-amino-1,2-propanediol dithiocarbamic acid or a salt thereof, 2-amino-2-methyl-1,3,-propanediol dithiocarbamic acid or a salt thereof, or N-phenylethylenediamine dithiocarbamic acid or a salt thereof.
In another aspect the invention provides a method of synthesizing a dithiocarbamic acid or salt thereof of formula (I) as described herein, comprising the steps of:
The different aspects of the present invention as set out herein are based on the finding that a distinct class of dithiocarbamic acids or salts thereof, namely dithiocarbamic acids or salts thereof of formula (I), have specific properties rendering them useful as depressants in froth flotation mineral recovery. Hence, the identity of these dithiocarbamic acids or salts thereof of formula (I) and preferred embodiments thereof will first be discussed. The embodiments described herein in relation to the dithiocarbamic acids or salts thereof of formula (I) are applicable to all aspects of the invention, for example to their use in a froth flotation process according to the invention, to the formulations according to the invention comprising a dithiocarbamic acid or salt thereof of formula (I), to the uses according to the invention of the dithiocarbamic acids or salts thereof of formula (I) and to the kit of parts according to the invention comprising a dithiocarbamic acid or salt thereof of formula (I).
It will be understood by the skilled person, in light of the present disclosure, that the expression “a substituent having from 1 to 8 carbon atoms and comprising at least one functional group” or similar expressions as used herein should be construed to specify the total amount of carbon atoms inclusive of any carbon atoms brought by any functional groups comprised in the substituent. For example, even if R1 or R2 comprises an amine (which may be secondary or tertiary) or ether functional group, this implies that the whole of R1 contains 1 to 8 carbon atoms.
It will also be understood by the skilled person that, when defining chemical substituents throughout this specification, such as in the context of R1 and R2 of formula (I), definition of a substituent such as an alkyl chain is intended to encompass linear and branched forms falling within the definition of that substituent, unless indicated otherwise.
It will also be understood by the skilled person that, in accordance with the invention, the definition for R1 and R2 is a closed definition and should be interpreted to mean that R1 and R2 do not comprise any other functional groups than the recited functional groups.
It will also be understood by the skilled person, based on the present teachings, that the compounds of the invention can be provided in free acid form, in the form of a salt, typically a base addition salt, in the form of a mixture of different salts or in the form of a mixture of the free acid and one or more salt forms. In embodiments of the invention R3 represents hydrogen. In embodiments of the invention R3 represents a cation. In principle, the invention is not limited to any specific (group) of salts and R3 can represent any organic or inorganic cation. In certain embodiments, it may be preferable that the cation is selected from the group consisting of alkaline metal ions, alkaline earth metal ions and quaternary ammonium cations represented by the formula NRR′R″R′″ wherein R, R′, R″ and R′″ are independently selected from the group consisting of C1-C6 alkyl and C1-C6 hydroxyalkyl, more preferably the cation is selected from the group consisting of alkaline metal ions and alkaline earth metal ions, more preferably the cation is sodium, calcium, magnesium and/or potassium, most preferably sodium.
In embodiments of the invention, R1 represents a first substituent having from 1 to 6 carbon atoms, preferably from 2 to 5 carbon atoms, and comprising at least one functional group selected from alcohols, amines, ethers, ketones, acetals, ketals, aminoacetals, hemiaminal ethers or combinations thereof, preferably selected from alcohols, amines, ethers or combinations thereof. Preferably R1 comprises one or two functional groups selected from alcohols, amines, ethers, ketones, acetals, ketals, aminoacetals, hemiaminal ethers or combinations thereof, preferably selected from alcohols, amines, ethers or combinations thereof. Hence, in highly preferred embodiments of the invention, R1 represents a first substituent having from 2 to 5 carbon atoms and comprising one or two functional groups selected from alcohols, amines, ethers or combinations thereof, more preferably comprising one or two functional groups selected from amines, ethers or combinations thereof. Examples of such preferred embodiments are compounds of formula (I) wherein:
In some embodiments of the invention, R1 and R2 are identical. Examples of such embodiments are compounds of formula (I) wherein R1 and R2 are identical and wherein:
In some embodiments of the invention, R1 and R2 are not identical. In such embodiments it is preferred that R2 represents H, phenyl or a C1-C5 alkyl, preferably R2 represents H, phenyl or a C1-C2 alkyl, most preferably R2 represents H or a C1-C2 alkyl. Examples of such preferred embodiments are compounds of formula (I) wherein R2 represents H, phenyl or a C1-C5 alkyl, preferably R2 represents H, phenyl or a C1-C2 alkyl, and wherein:
For all embodiments described herein wherein R1 represents a first substituent having from 2 to 5 carbon atoms and comprising one or two alcohols, a particular embodiment of the process described herein is provided wherein the process does not comprise the use of a second depressant selected from polymers comprising an allyl thiourea functional group and a hydrophilic acrylamide group, more preferably wherein the process does not comprise the use of any other depressant than the first depressant.
In all embodiments of R1 it is highly preferred that R1 comprises at most two amine functional groups. As will be understood by the skilled person, this implies that R1 is not a polyamine substituted dithiocarbamate. It is even more preferred that R1 comprises at most two functional groups of the same type, a type being selected from alcohols, amines, ethers, ketones, acetals, ketals, aminoacetals, hemiaminal ethers or combinations thereof.
Furthermore, according to highly preferred embodiments of the invention all carbon atoms comprised in R1 and R2 are saturated. In particularly preferred embodiments of the compounds of formula (I), the examples described in the previous paragraphs are provided wherein R1 and R2 are saturated. The skilled person will understand, in light of the present disclosure, that embodiments of R1 or R2 wherein “all carbon atoms are saturated” or similar expressions as used herein imply that all carbon atoms in R1 or R2 are sp3 hybridized meaning that they are not connected via double or triple bonds. Hence, such embodiments are identical to expressing that R1 or R2 consist of an alkyl chain wherein optionally one or more carbon atoms have been substituted by heteroatoms in order to provide the functional groups as defined herein for R1 and R2, and these expressions may be used interchangeably.
In embodiments of the invention the compound of formula (I) is such that R1 represents —R4—OH, —R5—O—R6, or —R7NR8R9
In some embodiments R1 and R2 are connected to form a heterocyclic 3 to 7 membered ring comprising at least 2 heteroatoms, which is optionally substituted with one, two or three functional groups selected from —OH, C1-C4 alkyl, C2-C4 alkenyl, C1-C4 hydroxyalkyl, —NRaRb and combinations thereof, wherein Ra and Rb are independently selected from H and C1-C4 alkyl. The heteroatoms comprised in the heterocyclic 3 to 7 membered ring are preferably independently selected from S, N, and O, more preferably they are independently selected from N and O. The heterocyclic ring is preferably 5 or 6 membered. The heterocyclic ring preferably comprises 2 hetero atoms.
Hence, in preferred embodiments R1 and R2 are connected to form a heterocyclic 5 or 6 membered ring comprising two heteroatoms which are N and O (e.g. a morpholine ring) or which are two N atoms (e.g. an imidazole ring), the heterocyclic ring being optionally substituted with one, two or three functional groups selected from —OH, C1-C4 alkyl, C2-C4 alkenyl, C1-C4 hydroxyalkyl, —NRaRb and combinations thereof, wherein Ra and Rb are independently selected from H and C1-C4 alkyl. Examples of such preferred embodiments are compounds of formula (I) wherein R1 and R2 are connected to form a heterocyclic 5 or 6 membered ring comprising two heteroatoms which are N and O or which are two N atoms, the heterocyclic ring being optionally substituted with one or two, preferably one functional groups selected from —OH and C1-C4 alkyl, preferably selected from —OH and —CH3, more preferably selected from —CH3.
Highly preferred compounds of formula (I) are the dithiocarbamic acids or salts thereof defined in the following table. Even more preferred compounds of formula (I) are compound 1, 3-6, 8-10, 12-20 acid as defined in the following table, or a salt thereof. Most preferred compounds of formula (I) are compound 1, 3, 8, 9 acid as defined in the following table, or a salt thereof.
In particular embodiments of the invention, the first depressant is as described above, with the provisio that the compound of formula (I) is not N-(2-Aminoethyl)carbamodithioic acid or a salt thereof.
Froth flotation processes in general are known to the skilled person and it is within the routine capabilities of the skilled person, in light of the present disclosure, to adjust operating parameters such that an efficient separation is achieved when operating a process according to the present invention, taking into account factors such as the ore being processed, the desired minerals, the desired yield, the desired purity, the mineral concentration of the pulp, the particle size of the minerals, the water hardness, etc. Reference can be made in this regard to the handbook Fuerstenau, M. C., Jameson, G. J., & Yoon, R. H. (Eds.). (2007). Froth flotation: a century of innovation. SME.
The pulp provided in step (a) of the process according to the invention is also referred to interchangeably as a “slurry”. In preferred embodiments of the invention, the pulp provided in step (a) is a mineral concentrate obtained from the separation of minerals from gangue material in a previous froth flotation stage.
Since transport cost of non-refined ores is not justified by their value, a mining site typically incorporates all stages of ore refinement on-site, starting from mining an ore, followed by comminuting the ore to liberate minerals contained therein and preparing a pulp for froth flotation separation of gangue material. Hence, in some embodiments of the invention step (a) comprises the steps of:
Comminution is typically performed via milling and/or breakage comminution devices, such as autogenous (AG) milling, semiautogenous (SAG) milling, ball milling, rod milling, high pressure grinding rolling (HPGR), vertical roller milling (VRM) etc. Classification devices, such as a rake classifier or cyclones are usually employed in combination with grinding to obtain a comminuted ore having the desired particle size distribution. Flotation recovery is often optimal for particles of an intermediate size, with coarser particles exhibiting slow flotation kinetics, because of their size and poor liberation and fine particles exhibiting slow flotation kinetics because of poor flotation collision efficiency. Thus, the ore is preferably comminuted to a particle size P80 within the range of 1-150 μm, preferably 10-100 μm in step (a2). The optimization of the particle size distribution is within the routine capabilities of the skilled person. The expression “P80” as used herein in the context of particle size is the screen size through which 80% of the particles will pass.
As indicated herein elsewhere, froth flotation separation is often applied in the form of a multi-stage process. Hence, embodiments of the invention are also envisaged wherein the pulp provided in step (a) is a mineral concentrate obtained from the selective separation of minerals in a previous froth flotation stage. This previous froth flotation stage may be a froth flotation process according to the invention (employing the first depressant) or a froth flotation stage employing another depressant.
The pulp provided in step (a) typically has a solids content within the range of 1-70wt. %, such as 2-60 wt. %, preferably 5-35 wt. %. In preferred embodiments the first mineral is present in the pulp provided in step (a) in an amount within the range of 0.01-10 wt. % (based on dry weight), preferably 0.1-5 wt. % (based on dry weight). In case the process according to the invention is used in the context of mineral recovery from tailings the concentration of the first mineral may be lower, for example within the range of 0.001-2 wt. % (based on dry weight), preferably 0.005-0.5 wt. %.
The pulp provided in step (a) typically comprises a collector, for example a collector which was used in a previous froth flotation stage to separate gangue material from valuable minerals. Hence, in some embodiments the process of the invention is provided wherein the pulp provided in step (a) comprises a collector, preferably a collector selected from the group consisting of xanthates, xanthogen formates, thioureas, thionocarbamates, (di)thiophosphates, dithiophosphinates, N-alkoxycarbonyl dithiocarbamates, dialkyldithiocarbamates, mercaptobenzothioazoles, hydrocarbons (such as kerosene), nitriles and combinations thereof.
Suitable xanthate collectors include compounds of general formula Rx—O—(CS2)—H, salts thereof or dimers thereof (also referred to as dixanthogens) wherein Rx is selected from the group consisting of C1-C12 alkyl, preferably Rx is selected from the group consisting of C1-C6 alkyl. The xanthate is preferably provided as an alkaline metal salt and/or an alkaline earth metal salt, more preferably a sodium, calcium, magnesium and/or potassium salt, most preferably a sodium and/or potassium salt. Exemplary xanthate collectors are Sodium isobutyl xanthate, Potassium amyl xanthate, Sodium isopropyl xanthate.
Suitable thionocarbamate collectors include dialkyl thionocarbamates, alkyl alkoxycarbonyl thionocarbamates, and alkyl allyl thionocarbamates having the general formula Ry—O—C(═S)—NHRzor salts thereof wherein Ry is a C1-C8 aliphatic hydrocarbyl, preferably a C1-C4 aliphatic saturated hydrocarbyl, and Rz is selected from the group consisting of hydrogen, a C1-C8 aliphatic hydrocarbyl, a vinyl group, and a group of formula —COORz′ wherein Rz′ is a C1-C8 aliphatic hydrocarbyl, preferably Rz is selected from the group consisting of hydrogen, a C1-C4 aliphatic saturated hydrocarbyl, a vinyl group, and a group of formula —COORz′ wherein Rz′ is a C1-C4 aliphatic hydrocarbyl. The expression an ‘aliphatic saturated hydrocarbyl’ is equivalent to an ‘alkyl group’. In case Rz is hydrogen, the thionocarbamate can be provided as a salt, preferably provided as preferably an alkaline metal salt and/or an alkaline earth metal salt, more preferably a sodium, calcium, magnesium and/or potassium salt, most preferably a sodium and/or potassium salt. An exemplary thionocarbamate collector is isopropyl ethyl thionocarbamate.
Suitable (di)thiophosphate collectors include compounds having the general formula Ru—O—PS2—O—Rv and Ru—O—P(ORv)S—O—Rw or salts thereof wherein Ru, Rv and Rw are independently selected from the group consisting of hydrogen, and C1-C10 aliphatic or aromatic hydrocarbyls and at least one, preferably at least two of Ru, Rv and RRw are not hydrogen. Preferably Ru, Rv and Rw are independently selected from the group consisting of hydrogen and C1-C6 alkyl and at least one, preferably two of Ru, Rv and Rw are not hydrogen. The (di)thiophosphate can be provided as a salt, preferably provided as preferably an alkaline metal salt and/or an alkaline earth metal salt, more preferably a sodium, calcium, magnesium and/or potassium salt, most preferably a sodium and/or potassium salt. Exemplary (di)thiophospate collectors are sodium diisobutyl dithiophosphate abd disecondary butyl dithiophosphate (DBD).
Suitable dithiophosphinate collectors include compounds having the general formula Ru—PS2—Rv or salts thereof wherein Ru and Rv are independently selected from the group consisting of hydrogen, and C1-C10 aliphatic or aromatic hydrocarbyls and at least one, preferably two of Ru and Rv are not hydrogen. Preferably Ru and Rv are independently selected from the group consisting of hydrogen and C1-C6 alkyl and at least one, preferably at least two of Ru and Rv are not hydrogen. The dithiophosphinate can be provided as a salt, preferably provided as preferably an alkaline metal salt and/or an alkaline earth metal salt, more preferably a sodium, calcium, magnesium and/or potassium salt, most preferably a sodium and/or potassium salt. An exemplary dithiophosphinate collector is sodium di(isobutyl)dithiophosphinate.
Suitable N-alkoxycarbonyl dithiocarbamates collectors include compounds of formula RmO—C(═O)—NH—CS2—Rn are described in U.S. Pat. No. 8,376,142B2 and include compounds wherein Rm and Rn are independently chosen from optionally substituted C1-C20 alkyl, optionally substituted C6-C20 aryl, optionally substituted C2-C20 alkenyl, and optionally substituted C2-C20 aralkyl, preferably Rm and Rn are independently chosen from C1-C8 alkyl, phenyl, C2-C8 alkenyl and C7 -C10 aralkyl. Exemplary dithiocarbamate N-alkoxycarbonyl dithiocarbamates are described in U.S. Pat. No. 8,376,142B2 column 3 lines 32-59.
Suitable dialkyldithiocarbamate collectors include compounds having the general formula RfRgN—CH2H or salts thereof wherein Rf and Rg are independently chosen from C1-C12 alkyl, preferably C1-C6 alkyl. The dialkyldithiocarbamate can be provided as a salt, preferably provided as preferably an alkaline metal salt and/or an alkaline earth metal salt, more preferably a sodium, calcium, magnesium and/or potassium salt, most preferably a sodium and/or potassium salt. An exemplary dialkyldithiocarbamate collector is sodium dimethyl dithiocarbamate.
Suitable thiourea collectors include compounds having the general formula RfRgN—CS—NRhRi wherein Rf, Rg, Rh, and Ri are independently chosen from C1-C12 alkyl and C1-C12 alkylethoxycarbonyl, preferably C1-C6 alkyl and C1 -C6 alkylethoxycarbonyl. An exemplary thiourea collector is butyl ethoxycarbonyl thiourea (BECTU).
Suitable xanthogen formate collectors include compounds of general formula Rx—O—(CS2)—C(O)O—Rx′ or salts thereof wherein Rx is selected from the group consisting of C1-C12 alkyl, preferably Rx is selected from the group consisting of C1-C6 alkyl and Rx′ is selected from the group consisting of hydrogen and C1-C12 alkyl, preferably EV is selected from the group consisting of hydrogen and C1-C6 alkyl.
Suitable mercaptobenzothiazole collectors include 2-mercaptobenzothiazole and C1-C14 hydrocarbyl derivatives thereof, preferably C1-C6 alkyl derivatives thereof.
Suitable nitrile collectors include long chain hydrocarbons having from 10 to 50 carbon atoms and comprising one, two or more nitrile functional groups, wherein optionally one or more carbon atoms in the hydrocarbon backbone is substituted by a nitrogen atom. Exemplary nitrile collectors are known under the tradenames Tecflote S10 and Tecflote S11 available from the company Nouryon.
As will be understood by the skilled person in light of the present disclosure, many process variations are possible without deviating from the spirit and scope of the present invention, and it is impossible to list all of these. For example, the pulp provided in step (a) may have been further pretreated by acid digestion, attrition scrubbing, heat treatment, and combinations thereof. Furthermore, the pulp provided in step (a) typically comprises, aside from the ingredients explicitly recited herein elsewhere, 0-10 wt. % (by total weight of the pulp) other additives such as kerosene, diesel oil, organic solvents, polymers, remnants of explosives, pH modifiers, ORP modifiers, etc.
The first depressant may be added to the pulp before and/or during the froth flotation of step (c). As will be understood by the skilled person, many possible addition schemes exist for the first depressant. For example, it is possible to add a portion of first depressant before the froth flotation of step (c), and add the remainder of the first depressant during the froth flotation of step (c). Alternatively it is possible to add the complete amount of first depressant employed in the process of the present invention before the froth flotation of step (c), whereby the addition may take place gradually over a prolonged period of time, or it may take place as a single addition. The first depressant may be added as a pure compound, as a solution (aqueous or otherwise) or as a blend with other compounds. The invention is not particularly limited with regard to the method of addition of the first depressant.
In accordance with preferred embodiments of the invention, the total amount of first depressant added to the pulp is within the range of 0.1-100 lbs/ton (based on dry weight of the pulp), preferably 0.5-50 lbs/ton (based on dry weight of the pulp). The expression “ton” refers to a US ton and equals 2000 lbs. Expressed in ppm this means that in accordance with preferred embodiments of the invention the total amount of first depressant added to the pulp is within the range of 50-50000 ppm (w/w, based on dry weight of the pulp), preferably 250-25000 ppm (w/w, based on dry weight of the pulp).
As is shown in the appended examples, the present inventors have found that the depressants of formula (I) exhibit particular and surprising properties which are desirable in the context of sulfide mineral recovery. For example, several compounds have been shown to achieve >80% sulfide mineral (chalcopyrite) depression while allowing another sulfide mineral (molybdenite) to be recovered in the froth. Hence, in accordance with preferred embodiments of the invention, the first mineral is a sulfide mineral, preferably a molybdenum sulfide mineral. A complete list of sulfide minerals can be found in mindat.org. Preferably the first mineral is a sulfide mineral selected from the group consisting of Acanthite, Chalcocite, Bornite, Galena, Sphalerite, Chalcopyrite, Pyrrhotite, Millerite, Pentlandite, Covellite, Cinnabar, Realgar, Orpiment, Stibnite, Pyrite, Marcasite, Molybdenite, Cobaltite, Arsenopyrite, Gersdorffite, Pyrargyrite, Proustite, Tetrahedrite, Tennantite, Enargite, Bournonite, Jamesonite, Cylindrite, digenite, geerite, Mackinawite, reigite, spionkopite, Troilite, villamaninite, yarrowite, and combinations thereof. In accordance with highly preferred embodiments of the present invention, the first mineral is molybdenite.
In some embodiments, at least part of the first mineral is formed in-situ, for example by chemical conversion of one mineral into another during froth flotation. For example, in case the first mineral is a sulfide mineral, in-situ formation of the first mineral is possible when a sulfidizing agent (such as a polysulfide) is added to the pulp in order to convert any oxidized or hydrolyzed sulfide minerals back into their corresponding sulfides.
The pulp provided in step (a) typically has a pH greater than 7, preferably greater than 8. In preferred embodiments the process is performed such that the pH of the pulp during step (c) is maintained within the range of 8-13, preferably within the range of 8.5-11. The pH adjustment may take place before, during or after step (b). Suitable pH adjusting agents are for example Ca(OH)2, sulfuric acid, CO2, NaOH and/or KOH.
It will be understood by the skilled person that in order to achieve a meaningful recovery of the first mineral, the froth flotation of step (c) is performed such that the first mineral accumulates in the froth, thereby achieving a higher concentration of the first mineral in the froth than in the bulk pulp. Hence, step (d) of the method according to the invention, recovering the froth, will provide a second pulp comprising the first mineral which has an increased concentration of the first mineral (based on dry weight) compared to the pulp provided in step (a). For the sake of clarity it is noted that the froth, once it is recovered and no longer being aerated, will settle into a pulp. In embodiments the process is performed such that the concentration of the first mineral in the second pulp obtained from recovering the froth in step (d) is within the range of 2-40 wt. % (by total weight of pulp), preferably within the range of 5-25 wt. %. In embodiments the process is performed such that the recovery of the first mineral is more than 40%, preferably more than 60%, more preferably more than 85%. In highly preferred embodiments the process is performed such that the ratio of the concentration (based on dry weight) of the first mineral in the second pulp obtained from recovering the froth in step (d) to the concentration (based on dry weight) of the first mineral in the pulp provided in step (a), is more than 1.5, preferably more than 2, more preferably more than 4, most preferably more than 5.
Since achieving a perfectly complete mineral separation by froth flotation is impossible, as indicated herein elsewhere, froth flotation separation is often applied in the form of a multi-stage process. Hence, according to preferred embodiments of the invention the second pulp obtained from recovering the froth in step (d) can be provided as the pulp for a next froth-flotation stage, preferably a next froth-flotation stage according to the invention.
In accordance with highly preferred embodiments of the invention, the solids comprising the first mineral further comprises a second mineral, different from the first mineral. The compounds of formula (I) were found to be highly efficient selective depressants. Hence, the process typically comprises depressing the second mineral into the pulp. According to preferred embodiments, the solids comprising the first mineral further comprises a second mineral and the process comprises depressing the second mineral into the pulp, wherein the second mineral is a sulfide mineral, preferably a copper and/or iron sulfide mineral, which is different from the first mineral. In embodiments the second mineral is a sulfide mineral selected from the group consisting of Acanthite, Chalcocite, Bornite, Galena, Sphalerite, Chalcopyrite, Pyrrhotite, Millerite, Pentlandite, Covellite, Cinnabar, Realgar, Orpiment, Stibnite, Pyrite, Marcasite, Molybdenite, Cobaltite, Arsenopyrite, Gersdorffite, Pyrargyrite, Proustite, Tetrahedrite, Tennantite, Enargite, Bournonite, Jamesonite, Cylindrite, digenite, geerite, Mackinawite, reigite, spionkopite, Troilite, villamaninite, yarrowite, and combinations thereof, preferably selected from the group consisting of chalcocite, villamaninite, covellite, yarrowite, spionkopite, geerite, anilite, digenite, reigite, Pyrrhotite, Troilite, Mackinawite, Marcasite, Pyrite and combinations thereof, and the second mineral is different from the first mineral.
Examples of suitable combinations of first mineral and second mineral in the process of the present invention are as follows:
In accordance with highly preferred embodiments of the present invention, the solids comprising the first mineral further comprises a second mineral and the process comprises depressing the second mineral into the pulp, wherein the first mineral is molybdenite and the second mineral is chalcopyrite. Accordingly, it is preferred that the pulp provided in step (a) is a Cu/Mo concentrate obtained by separation of gangue material from Cu/Mo ore, preferably from an ore comprising molybdenite and chalcopyrite. Such a Cu/Mo concentrate typically has a Cu concentration within the range of 15-40 wt. % (based on dry weight), preferably 25-35 wt. % (based on dry weight) and a Mo concentration within the range of 0.01-10 wt. % (based on dry weight), preferably 0.1-5 wt. % (based on dry weight).
Embodiments of the invention are also envisaged wherein the pulp provided in step (a) is a mineral concentrate obtained from the selective separation of the first and second minerals in a previous froth flotation stage, wherein the previous froth flotation stage also entailed depressing the second mineral. This previous froth flotation stage may be a froth flotation process according to the invention (employing the first depressant) or a froth flotation stage employing another depressant. For example, after gangue separation, a first froth flotation separation stage may be applied employing NaHS as depressant, wherein the second mineral is depressed and the froth comprising the first mineral is collected to obtain a pulp comprising the first mineral, which is provided as the pulp in step (a) of the process of the present invention.
The froth may be produced employing any suitable gas, such as air, oxygen gas, nitrogen gas, CO2 gas or combinations thereof. Preferably the froth is produced employing air, nitrogen gas, CO2 gas of combinations thereof, more preferably air.
The pulp provided in step (a) may comprise a frothing agent and/or the process of the invention may comprise a step of adding a frothing agent. Suitable frothing agents are known to the skilled person, for example
The pulp provided in step (a) may comprise a second depressant and/or the process of the invention may comprise a step of adding a second depressant. Suitable depressants are known to the skilled person, and include but are not limited to:
In particular embodiments, the process of the invention is provided further comprising the step of:
As is shown in the appended examples, the present inventors have found that both alone and in combination with NaHS, the first depressant can achieve excellent performance, such that it can be considered a partial or complete NaHS replacement. Hence, in some embodiments the second depressant is selected from polysulfides, bisulfites, NaHS and combinations thereof, preferably the second depressant is NaHS. This embodiment has the advantage that existing installations do not need to be completely converted to the depressants of the present invention, which may be more economical, while still allowing a significantly reduced NaHS consumption, reducing the negative HSE impact of NaHS. In other embodiments the second depressant is substantially free of, preferably completely free of, NaHS. In some embodiments the complete froth flotation process of the invention does not utilize NaHS. These embodiments have the advantage that the negative HSE impact of NaHS can be completely mitigated.
In some preferred embodiments, the process of the invention is provided further comprising the step of:
In particular embodiments, the process of the present invention is provided with the provisio that when R1 comprises no other functional groups than alcohols, the process does not comprise the use of a second depressant selected from polymers comprising an allyl thiourea functional group and a hydrophilic acrylamide group.
In some embodiments of the present invention the pulp provided in step (a) may be free of depressants other than the first depressant and/or the process of the invention does not comprise the use of any other depressant than the first depressant.
The invention also concerns compositions relating to the use of the dithiocarbamic acids or salts thereof of formula (I) in the field of mining. In another aspect of the invention there is thus provided a composition comprising the first depressant as described herein and further comprising one, two, or three of:
In preferred embodiments of the invention, the composition comprising the first depressant is provided which is a mineral pulp, comprising a sulfide mineral, preferably the first mineral as described herein, in an amount of at least 0.01 wt. % (based on total weight of the mineral pulp), preferably at least 0.1 wt. % and optionally further comprising
In preferred embodiments of the invention, the composition comprising the first depressant is provided which is a mining additive composition comprising a second depressant as described herein in an amount of at least 5 wt. % (based on total weight of the additive composition excluding solvents), preferably at least 10 wt. % (based on total weight of the additive composition excluding solvents); wherein the first depressant is preferably present in an amount of at least 5 wt. % (based on total weight of the additive composition excluding solvents), preferably at least 20 wt. % (based on total weight of the additive composition excluding solvents). The mining additive composition is preferably substantially free of other additives. For example, the combined amount of depressants is preferably more than 90 wt. % (by total weight of the additive composition excluding solvents), preferably more than 95 wt %, more preferably more than 99 wt. %. In some embodiments the mining additive composition essentially consists of (i) the first depressant, (ii) the second depressant, and (iii) solvent, wherein the solvent is preferably selected from water, alcohols, hydrocarbons and combinations thereof, preferably water or alcohol. Examples of suitable alcohol solvents are C1-C6 monoalcohols, and monoglycols, such as monoethylene glycol, 1,3-butanediol and propane-1,2-diol. The mining additive composition may be provided in the form of a concentrate, wherein the first depressant is present in an amount of more than 50 wt. % (by total weight of the concentrate) and wherein the total amount of solvent is less than 40 wt. % (by total weight of the concentrate).
In particular embodiments the compositions described herein are provided with the provisio that the first depressant is not N-(2-Aminoethyl)carbamodithioic acid or a salt thereof or a compound of formula (I) wherein R1 comprises no other functional groups than alcohols.
In another aspect the invention concerns the use of a dithiocarbamic acid or salt thereof of formula (I) as described herein in the recovery of minerals. Preferably the use is in the froth flotation recovery of minerals, preferably of sulfide minerals. More preferably, the use is as a depressant of a second mineral as described herein in the froth flotation recovery of a first mineral as described herein.
In particular embodiments the invention concerns the use of a dithiocarbamic acid or salt thereof of formula (I) as described herein as a depressant of a copper and/or iron sulfide mineral, preferably of chalcopyrite in the froth flotation recovery of another sulfide mineral, preferably of molybdenite.
In particular embodiments the uses described herein are provided with the provisio that the dithiocarbamic acid or salt thereof is not N-(2-Aminoethyl)carbamodithioic acid or a salt thereof or a compound of formula (I) wherein R1 comprises no other functional groups than alcohols.
In another aspect the invention concerns a kit of parts comprising a composition (A) comprising the first depressant as described herein and instructions for use of the composition (A) as a depressant in froth flotation recovery of minerals.
In another aspect the invention concerns a kit of parts comprising
Preferably, the concentration of the first depressant in composition (A) is more than 10 wt. % (by total weight of composition (A), preferably more than 50 wt. %.
Preferably, the concentration of the second depressant in composition (B) is selected from the group consisting of NaHS, Nokes reagent, ferrocyanides, polysulfides, bisulfites, trithiocarbonates and combinations thereof, preferably NaHS.
Preferably the instructions are for use of the composition (A) in the froth flotation recovery of minerals, preferably of sulfide minerals. More preferably, the instructions are for use of the composition (A) as a depressant of a second mineral as described herein in the froth flotation recovery of a first mineral as described herein. In particular embodiments the invention the instructions are for use of the composition (A) as a depressant of a copper and/or iron sulfide mineral, preferably of chalcopyrite in the froth flotation recovery of another sulfide mineral, preferably of molybdenite.
In particular embodiments the kit of parts described herein are provided with the provisio that the first depressant is not N-(2-Aminoethyl)carbamodithioic acid or a salt thereof or a compound of formula (I) wherein R1 comprises no other functional groups than alcohols.
The present inventors believe that some of the dithiocarbamic acids or salts thereof of formula (I) found in the course of this work have not been described before. In another aspect the invention thus concerns a dithiocarbamic acid or salt thereof of formula (I) as described herein before, in particular 3-amino-1,2-propanediol dithiocarbamic acid or a salt thereof, 2-amino-2-methyl-1,3,-propanediol dithiocarbamic acid or a salt thereof, or N-phenylethylenediamine dithiocarbamic acid or a salt thereof, preferably 3-amino-1,2-propanediol dithiocarbamic acid or a salt thereof. These compounds are also referred to herein as compound 3 acid or a salt thereof, compound 7 acid or a salt thereof, or compound 11 acid or a salt thereof. These compounds are also referred to herein by their systematic name as 2,3-dihydroxypropylcarbamodithioic acid or a salt thereof, 2-amino-2-methyl-1,3,-propanediol carbamodithioic acid or a salt thereof, or phenyl(2-aminoethyl)carbamodithioic acid or a salt thereof. As is shown in the below table, all these names concern the same three compounds identified by their structural formula. The present invention claims any one of these three compounds as such, as well as any use thereof.
In another aspect the invention provides a method of synthesizing a dithiocarbamic acid or salt thereof of formula (I) as described herein, comprising the steps of:
The dithiocarbamic acids or salts thereof used in the various examples were synthesized according to a known reaction scheme wherein the R1R2NH is reacted with CS2, R1 and R2 being as described herein before.
To a round-bottom flask fitted with a stirrer, condenser, and thermometer, amine is first placed in solvent. The reaction flask is chilled in an ice bath during the dropwise addition of equimolar carbon disulfide (CS2) so that the reaction temperature does not exceed 38° C. The reaction is then allowed to stir heated (between 32-38° C.) for a minimum of one hour or until the solution has visibly reacted and the CS2 is no longer beaded in the flask. After the reaction is complete, an equimolar amount of base is added dropwise. The solution is again heated between 32-38° C. for one hour and then purged with nitrogen. All syntheses use the same ratio of starting materials, 0.1 mol of the amine, 0.1 mol CS2, 0.1 mol of 50% NaOH in solvent. The final reaction product is a 30-60% salt solution. In some instances a solid is formed which is then isolated. Formation of the dithiocarbamic acid or salt thereof can be confirmed via two distinctive absorption peaks in the UV-Vis region around ˜250 nm and ˜280 nm. Masses of starting materials and final product concentrations are listed in Table 1. It is noted that for some syntheses the order of addition of the different compounds was reversed, first adding amine and base, followed by the addition of carbon disulfide. It is within the routine capabilities of the skilled person to synthesize other compounds of formula (I) based on the guidance provided herein.
Approximately 2.5 g of 95% pure chalcopyrite (CuFeS2, size fraction −105+45 μm, deslimed) is placed in a beaker with 50 mL of 0.001 M KNO3 solution and stirred for two minutes. KNO3 is added to increase the ionic strength of the solution to more closely resemble real-life mining operations. Afterward, a stock solution of collector is added to the slurry for a final concentration of 0.05 mmol/L along with 1.7 μL of methyl isobutyl carbinol (MIBC, a frother) and the mixture is allowed to condition for another five min. Frother and collector are added in order to closely resemble real-life mining operations. Next, a sample of stock solution of dithiocarbamate salt is added to the mixture and the slurry is conditioned for 10 min. The slurry is then transferred to a Hallimond tube along with an additional 70 mL of 0.001 M KNO3 solution and floated for three minutes. The concentrate is obtained from the collection arm. Both concentrate and tail are filtered and weighed.
Table 2 shows the results obtained with potassium amyl xanthate (PAX) as collector.
Table 3 shows the results obtained with potassium amyl xanthate (PAX) as collector for various dithiocarbamate depressant concentrations.
Table 4 shows the results obtained with Isopropyl ethyl thionocarbamate as collector.
It can be observed in Tables 2 and 3 that various compounds according to the present invention, such as sodium 3-amino-1,2-propanediol dithiocarbamate (compound 3), sodium morpholine dithiocarbamate (compound 8), and sodium n-methylpiperazine dithiocarbamate (compound 9) show excellent performance in depressing chalcopyrite both when used as the sole depressant, or when used in combination with sodium hydrosulfide (NaSH). In particular, the compounds consistently outperform sodium hydrosulfide (NaSH) and significantly outperform sodium hydrosulfide (NaSH) when employed at low concentrations. It can be observed in Table 4 that also with other collectors, such as ethyl thionocarbamate, the compounds of the present invention have excellent performance in depressing chalcopyrite.
For molybdenite flotation using a Hallimond Tube, the procedure is nearly identical to the procedure described in example 3. However, no additional desliming is conducted before flotation.
Approximately 2.5 g of 95% pure molybdenite (size fraction −105+45 μm) is placed in a beaker with 50 mL of 0.001 M KNO3 solution and stirred for two minutes. KNO3 is added to increase the ionic strength of the solution to more closely resemble real-life mining conditions. Afterward, a stock solution of kerosene emulsion (collector) is added to the slurry for a final concentration of 20 ppm along with 1.7 μL of methyl isobutyl carbinol (MIBC, a frother) and the mixture is allowed to condition for another five min. Frother and collector are added in order to closely resemble real-life mining operations. Next, a sample of stock solution of dithiocarbamate salt is added to the mixture and the slurry is conditioned for 10 min. The slurry is then transferred to a Hallimond tube along with an additional 70 mL of 0.001 M KNO3 solution and floated for three minutes. The concentrate is obtained from the collection arm. Both concentrate and tail are filtered and weighed.
Table 5 shows the results obtained. It can be observed from Table 5 that next to the excellent chalcopyrite depression shown in Example 2, the depressants according to the present invention also exhibit excellent molybdenite recovery. This effectively shows highly efficient selective depression of different sulfide minerals can be achieved with the depressants according to the present invention.
A slurry (approx. 500 mL of ˜62% solids) containing mineral concentrate is placed into a 1.2 L Denver flotation cell. The concentrate was obtained from a copper mine and is a copper sulfide and molybdenum sulfide containing concentrate obtained after gangue separation from the original ore. The majority of the copper mineral contained in the concentrate is chalcopyrite, and the gangue content was low in view of a previous gangue separation step using a xanthate collector. The remaining volume is filled with water to within 1-2 inches of the top of the cell. Depressant reagent is added to the slurry and conditioned (900 rpm stirring) for 4 minutes, then floated for 10 minutes (nitrogen, 350 mL/min). Two concentrates are collected at 5 and 10 minutes, respectively. The pH was monitored throughout each experiment. The new concentrate and remaining tailings are filtered, weighed, and analyzed.
Table 6 shows the results obtained. It can be observed from table 6 that the depressants according to the present invention exhibit excellent performance in real-world conditions, and can also be used for significantly reducing the amount of sodium hydrosulfide (NaSH) required for achieving good Cu—Mo sulfide separation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21157680.6 | Feb 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/016389 | 2/15/2022 | WO |
