BACKGROUND

[0001] Phosphate rocks contain calcium phosphate minerals largely in the form of apatite, usually together with other minerals (e.g., silicate minerals and carbonate minerals, such as calcite). Apatite is a generic name for a group of calcium phosphate minerals also containing other elements or radicals, such as fluorapatite, chlorapatite, hydroxylapatite, carbonate-rich fluorapatite and carbonate-rich hydroxylapatite.

[0002] It is well-known to separate the valuable phosphate minerals from the gangue (commercially unimportant material) by using a froth flotation process where the phosphate minerals are enriched in the float. Good performance in a froth flotation process is achieved by a combination of, on the one hand, a good separation of the valuable mineral from the gangue by using a selective collector composition and, on the other hand, the froth characteristics, if needed by using frothers during the process which are then added in a step after the pulped ore has been conditioned with the collector composition. The froth characteristics include both the volume (height) and the stability of the froth. It is important in the flotation process that the froth collapses as soon as possible after the air supply is stopped, since this is directly connected to the flotation performance. A too stable froth will cause both entrainment of particles and froth product pumping problems. Entrainment, especially on a large scale, will result in decreased selectivity (i.e. grade, recovery). Problems with froth product pumping will make a flotation process technically impossible.

[0003] Collector performance may be improved by using collector combinations of a primary (main) collector and a secondary collector (also called co-collector). In this document the term“collector composition” shall be used to describe compositions containing a primary collector, or both a primary and a secondary collector, as well as a collector aid. For many decades secondary collectors have been used together with primary ionic collectors in salt-type mineral flotation to improve the performance of the primary collector. Nonylphenol ethoxylates have been the dominating nonionic surfactant used as a co-collector in a combination with sarcosine-type primary collectors in selective flotation of apatite from calcite-containing ores. However, due to environmental concerns, an intense search for a replacement of nonylphenol ethoxylates has been ongoing for a long time.

[0004] Thus, there is still a need for collector compositions having a better environmental profile than nonylphenol ethoxylates that perform equally well. Collector compositions aligned with this approach are described herein.

DETAILED DESCRIPTION

[0005] . The Applicant has surprisingly found that employing a primary collector and a collector aid, and optionally a secondary collector, and conditioning a phosphate-containing ore with both these compounds in a froth flotation process will improve froth flotation results such as grade and recovery of the phosphate minerals during such froth flotation process. Further it has been found even more beneficial to pre-mix the primary collector and collector aid, and optionally a secondary collector (to form a collector composition) which will allow the collector composition to be added as a single product to the ore without the need for a separate conditioning step, while at the same time significantly improving the performance of the flotation.

[0006] Accordingly, the present invention relates to a method for froth flotation of an ore to recover phosphate-containing materials from the ore that includes adding a a primary collector and a collector aid to the ore and next performing a conditioning step of the ore in the presence of the primary collector and collector aid, wherein the primary collector is selected from the group consisting of an amphoteric surface-active compound, an anionic surface-active compound and combinations thereof; and the collector aid has the formula R ³ -C0-0-A _n -R ⁴ where R ³ is a linear or branched, alkyl or hydroxyalkyl group having from 3 to 8 carbon atoms, R ⁴ is a linear or branched, alkyl or hydroxyalkyl group having from 3 to 10 carbon atoms, and at least one of R ³ and R ⁴ contains a hydroxyl group; and A is either ethoxy, propoxy or butoxy and n is a number from 0-10

[0007] The primary collector and the collector aid can be added to the ore one after the other or simultaneously in one collector composition. Preferably they are added to the ore pre-blended in one collector composition, which collector composition may optionally contain further compounds, such as for example a secondary collector compound.

[000S] The collector aid was found to boost the overall performance of the collector composition. The primary collector and collector aid in embodiments are contained in a single composition that is used for flotation or are added separately to be both present in the conditioning step. If an ore is conditioned with both the primary collector and the collector aid, the froth flotation results were found to be surprisingly better than when the collector aid component is added to the ore already conditioned with a composition that does not contain the collector aid of the present invention. In the direct flotation of apatite, for example, recovery can be improved by around 4% by weight using the collector composition to which the collector aid was initially pre- blended as neat compared to a process in which conditioning with the primary collector did not include the collector aid. Meanwhile, poor grade of P2O5 was observed when adding the collector aid after the conditioning of the ore as a frother. The collector composition containing both the primary collector and collector aid also yields better frothing characteristics, including improved froth density and stability.

[0009] It may be noted that in US2017/0252753 a process of froth flotating a phosphate-containing ore is disclosed employing a collector composition that contains an anionic or amphoteric primary collector in combination with a non- ionic ethoxy lated alcohol as a secondary collector. In some of the embodiments, a frother is added to the process, that can be 2, 2, 4-trimethyl- l,3-pentanediol monoisobutyrate, but only after the ore was conditioned with the collector composition

[0010] The primary collector disclosed herein is an amphoteric surface-active compound, an anionic surface-active compound or a combination thereof. Surface- active compounds (or surfactants) are compounds that lower the surface tension or interfacial tension between two liquids, between a gas and a liquid, and/or between a solid and a liquid. Anionic surface-active compounds typically contain a negatively charged (anionic) head group. Amphoteric surface-active compounds contain both cationic (positively charged) and anionic moieties within the same molecule. Below some examples of the primary collectors are provided; these examples should only be considered as suitable and are not to be regarded as limiting. [0011] In some embodiments the primary collector is an amphoteric surface- active compound having the formula (II)

where Ri is a hydrocarbyl group with 8-22, preferably 12-18, carbon atoms; A is an alkyleneoxy group having 2-4, preferably 2, carbon atoms; p is the number 0 or 1; q is a number from 0-5, preferably 0; R ₂ is a hydrocarbyl group having 1-4, preferably 1, carbon atoms or R ₂ is the group

where Ri, A, p and q have the same meaning as above; Y is COOH or SO ₃ H, preferably COOH; n is the number 1 or 2, preferably 1; M is a cation, which can be monovalent or divalent and inorganic or organic, and r is the number 1 or 2. The primary collector can also be used in its acid form, where the nitrogen is protonated and no external cation is needed.

[0012] The compounds according to formula (II) can be produced from commercially available starting materials using known procedures. U.S. Patent No.

4,358,368 discloses some ways to produce the compounds where Ri is a hydrocarbyl group with 8-22 carbon atoms (col. 6, line 9 - col. 7, line 52). U.S. Patent No. 4,828,687 (col. 2, line 2 - col. 2, line 31) describes compounds where R ₂ is

attached to the compound of formula (II) via the methylene group.

[0013] In other embodiments the primary collector has the formula (III)

where R ₂ is a hydrocarbyl group with 8-22, preferably 12-18, carbon atoms; D is -CH ₂ - or -CH ₂ CH ₂ - ; k is a number from 0-4, preferably 0-3, and most preferably 0-2, and M is hydrogen or a cation such as sodium or potassium.

[0014] Compounds according to formula (III) are known and produced commercially by methods known in the art. Products where D is -CH ₂ - are prepared by the reaction between a fatty amine and chloroacetic acid or its salts, and products where D is -CH ₂ CH ₂ - are prepared by the reaction between a fatty amine and acrylic acid or esters thereof, in the latter case the reaction is followed by hydrolysis.

[0015] In still other embodiments the primary collector is an anionic surface- active compound, such as fatty acids having an alkyl group with 8-24 carbon atoms, sulfonates, alkyl phosphates, alkyl sulfates and compounds having the formula (IV)

where R is a hydrocarbyl group having from 7-23, preferably 11-21, carbon atoms, optionally substituted; Ri is H or CH ₃ , preferably H; R ₂ is H or an alkyl group having from 1-4 carbon atoms, preferably H; R ₃ is H or CH ₃ , preferably CH ₃ ; n is a number from 0-20; p is a number from 1-3, preferably 1; X is H ⁺ or a cation, organic or inorganic; and m represents the valency of the cation and is the number 1 or 2, preferably 1. The cation is preferably an alkali metal cation, an alkaline earth metal cation, ammonium, or a substituted ammonium group having one or more alkyl and/or hydroxyalkyl groups having from 1-3 carbon atoms.

[0016] For the production of compounds of formula (IV) see the description in

W02015/000931 (corresponding to PCT/EP2014/064014). [0017] Preferably, the primary collector comprises a sodium salt of an alkyl glycinate or sarcosinate having from 12 to 20, more preferably 12 to 16 carbon atoms. In one particular embodiment, the primary collector is N-[2-hydroxy-3-(Cl2-l6- alkyloxy)propyl]-N-methyl glycinate (sodium C14-C15 sarcosinate).

[0018] Suitable fatty acids having an alkyl group with 8-24 carbon atoms include fatty acids based on tall oil and oils of safflower, sunflower, soya, raps, com, lineseed, rapeseed, tallow, coconut, raw coniferous, and raw foliar).

[0019] In other embodiments the primary collector is a phosphate ester. In one embodiment, phosphate esters have the formulas

R ² -(0-CH ₂ -CH ₂ ) _n -0-P(0)(0M)-0-P(0)(0M)-(0-CH ₂ -CH ₂ ) _n -0-R ² , R ² -(0-CH ₂ -CH ₂ ) _n - 0-PO(OM) ₂ or (R ² -(0-CH ₂ -CH ₂ ) _n -0) ₂ -P0-0M or a combination of thereof where R ² is an alkyl group having from 6-22 carbon atoms, preferably 16-18 carbon atoms; n is a number from 0-25 preferably 4; and M is a monovalent cation such as sodium or hydrogen. Alcohol ethoxylate phosphate ester (Phospholan type, Akzo Nobel Surface Chemistry LLC) contains the above phosphate esters where R ² is an alkyl group having 18 carbon atoms, n is 4, and M is sodium or hydrogen.

[0020] Other suitable phosphate esters are monophosphate and diphosphate esters containing from 6-22 carbon atoms (linear or branched, degree of branching 1-3) and from 0-25 ethylene oxide (EO) units, and combination thereof. “Degree of branching” as used herein means the total number of methyl groups present on the main alkyl chain minus one.

[0021] The collector aid of the collector composition is an ester having the formula

R ³ -CO-0-A„-R ⁴

where R ³ is a linear or branched, alkyl or hydroxyalkyl group having from 3 to 8 carbon atoms, R ⁴ is a linear or branched, alkyl or hydroxyalkyl group having from 3 to 10 carbon atoms, and at least one of R ³ and R ⁴ contains a hydroxyl group; and A is either ethoxy, propoxy or butoxy and n is a number from 0-10. Below some examples of the collector aids are provided; these examples should only be considered as suitable and are not to be regarded as limiting.

[0022] Suitable collector aids include 2,2,4-trimethyl-l,3-pentanediol monoisobutyrate (Eastman Chemical Company); pentanoic acid, 3-hydroxy-4,4- dimethyl-2-(l-methylethyl)-, ethyl ester; heptanoic acid, 3-hydroxy-2, 2, 4-trimethyl-, ethyl ester; hexanoic acid, 4-ethyl-3-hydroxy-2, 2-dimethyl-, ethyl ester; 2-ethylhexane- (l,3)-diol mono-n-butyrate; 2-ethylhexane-(l,3)-diol di-n-butyrate, alkoxylated derivatives of same containing from 0-10 alkoxy units (more preferably 0-3 ethoxy units or 0-10 propoxy units), and combinations thereof.

[0023] The weight ratio between the primary collector and the collector aid is from 999:1 to 1 : 1, preferably from 99:1 to 95:5, and more preferably from 99:1 to 96:4. All weight ratios herein refer to the ratio of active materials, unless stated otherwise.

[0024] The collector composition containing the primary collector and the collector aid can optionally include a solvent. The role of the solvent in the collector composition is to improve the flotation froth quality and the liquidity of the final formulation. Suitable solvents include ethoxylated alcohols having from 3 to 10 EO groups, glycols ( e.g ., propylene glycol, diethylene glycol, etc.), non- ionic surfactants, low molecular weight alcohols, such Cl -Cl 5 alcohols, low molecular weight organic acids, such as Cl -Cl 5 organic acids, low molecular weight ethanolamines (e.g., triethanolamine, methyl diethanolamine, diethanolamine, etc.), water, organic solvents (e.g., toluene, hexane, etc.), aliphatic hydrocarbons, such as isoparaffines, paraffines, cycloparaffines, and their combinations. Low molecular weight solvents are in a preferred embodiment defined as solvents that have a molecular weight of up to 120 g/mole. The weight ratio between the primary collector and the optional solvent is preferably from 999:1 to 80:20, preferably from 99:1 to 90:10.

[0025] The collector composition may be prepared by adding the primary collector, the collector aid and the optional solvent to a suitable vessel and mixing to combine. Additional flotation aids described herein can also be added to the collector composition before or after the primary collector and collector aid are combined. No special preparation steps (e.g., high shear mixing, heating, etc.) are necessary to prepare the collector composition.

[0026] This disclosure also describes a method for the froth flotation of non- sulfidic ores, especially phosphate ores, to recover apatite minerals, in which method the collector composition described herein is used. Such froth flotation method for phosphate ores can typically include the following steps: a) conditioning a pulped phosphate-containing ore, wherein the ore includes a phosphate-containing mineral, and gangue minerals, with an effective amount of the collector composition described herein or the primary collector and collector aid separately, and optionally other flotation aids, and b) performing a froth flotation process to recover the phosphate-containing mineral(s).

[0027] The amount of primary collector added to the ore will in general be in the range of from 10 to 1000 g/ton dry ore, preferably in the range of from 20 to 500 g/ton dry ore, more preferably from 100 to 400 g/ton dry ore. The amount of collector aid to added to the ore will in general be in the range of from 0.01-50 g/ton dry ore, preferably in the range of from 0.02-25 g/ton dry ore, more preferably from 0.05-20 g/ton dry ore

[0028] In preferred embodiments a secondary collector can be present during the conditioning step. In more preferred embodiments the secondary collector is selected from the group of anionic collector compounds, non- ionic collector compounds or mixtures of two or more of those, wherein the anionic collector is selected from the group of fatty acids, alkylsulfo succinates, alkylmaleates, alkylamidecarboxylate, esters of alkylamidecarboxylates, alkylbenzenesulphonates, alkylsulfonates, and sulfonated fatty acids, and the non-ionic collector compound is selected from the group of ethoxylates, glycosides, and ethanolamides, most preferably the non-ionic collector compound is selected from the group of branched and unbranched ethoxylated Cl 1-C24 alcohols, ethoxylated C10-C24 alkylamines, sugar surfactants, ethoxylated C10-C24 fatty acids

[0029] Further flotation aids that can be present in the flotation process are depressants such as a polysaccharide, alkalized starch or dextrin; extender oils; frothers/froth regulators such as pine oil, MIBC (methylisobutyl carbinol) and alcohols such as hexanol and alcohol ethoxylates/propoxylates, preferably C6-C10 alcohols and ethoxylates thereof; inorganic dispersants such as silicate of sodium (water glass) and soda ash; and pH-regulators (which can be acidic or alkaline compounds to adjust the pH as desired). These flotation aids can be added to the collector composition or added to the flotation process before or following conditioning of the ore with the primary collector and collector aid, optionally preblended in a collector composition.

[0030] The present invention in a preferred embodiment relates to a method for froth flotation of a phosphate ore, the method comprising: optionally, adding a depressant to the ore; adding the primary collector and collector aid as above to the ore; optionally, adding one or more further components to the ore selected from the group of pH adjusting agents, dispersants and secondary collector; wherein the primary collector, the collector aid and optional secondary collector can be added one after the other or simultaneously, optionally preblended in one collector composition; conditioning the ore in the presence of the primary collector, optional secondary collector, and the collector aid; subsequently, optionally adding one or more further components to the conditioned ore selected from the group of pH adjusting agents, dispersants and frothers; and performing a froth flotation process to recover phosphate-containing materials from the ore.

[0031] In a preferred embodiment of the process of the invention, in a step subsequent to the conditioning of the ore in the presence of the primary collector and collector aid, a frother is added to the conditioned ore.

[0032] The pH during the flotation process will normally be in the range of pH 8-11.

EXAMPLES

[0033] For all Examples, a phosphate ore containing 42% apatite, 38% nepheline, 5% aegirine, 3% feldspar and 2% sphene was crushed and ground to a desirable flotation size (70% -160 pm). In each Example, 500 g of the phosphate ore was placed into a 1.3 L (for rougher), 1.0 L (for cleaner 1) or 0.5 L (for cleaner 2) flotation cell. Tap water (Stenungsund municipal water with hardness 4 °dH) was added to the marked level in the cell (1.4L) and mixing was started. Further, 200 g/t water glass as a 1 wt-% solution was added and conditioned for 1 minute. In each Example flotation was performed at room temperature (20±l °C), and the rougher flotation, the cleaner 1 flotation and the cleaner 2 flotation were performed for 4 minutes, 3 minutes and 2 minutes, respectively. All fractions (tailings, middlings and concentrate) were collected and analysed. For each Example, alcohol ethoxy late phosphate ester (Phospholan type, Akzo Nobel Surface Chemistry LLC, henceforth “Phosphate Ester”) is a phosphate ester having the general formula R ² -(0-CH ₂ -CH ₂ ) _n - 0-PO(OM) ₂ and (R ² -(0-CH ₂ -CH ₂ ) _n -0) ₂ -P0-0M where R ² is an alkyl group having 18 carbon atoms, n is 4, and M is sodium or hydrogen. [0034] Example 1 (Comparative): Collectors added individually- No collector aid

[0035] Separate 1 wt-% solutions were prepared for each of tall oils, alkylbenzene sulfonate and Phosphate Ester.

[0036] The pH of the flotation mixture was adjusted to 9.9 with a 5% aqueous

NaOH solution and quantities of the 1 wt-% solutions of the tall oils, alkylbenzene sulfonate and Phosphate Ester were added to the flotation cell to be equivalent to 150 g/t of a collector composition containing 50 wt-% tall oils, 17 wt-% alkylbenzene sulfonate, and 33 wt-% Phosphate Ester. A conditioning step was carried out at 1000 rpm and room temperature for two minutes. After the conditioning step, the flotation (1000 rpm and 3 L/min rougher; 1500 rpm and 1.3 L/min cleaner 1; and 1500 rpm and 0.6 L/min cleaner 2) was started. The flotation results are shown in Table 1.

[0037] Table 1

[0038] Example 2 (Comparative): Collectors pre-mixed - No collector aid

[0039] A collector composition containing 50 wt-% tall oils, 17 wt-% alkylbenzene sulfonate, and 33 wt-% Phosphate Ester was prepared. The collector composition was diluted in deionized water to a 1 wt-% solution.

[0040] The pH of the flotation mixture was adjusted to 9.9 with a 5% aqueous

NaOH solution and 150 g/t of the collector composition as a 1 wt-% aqueous solution was added to the flotation cell. A conditioning step was carried out at 1000 rpm and room temperature for two minutes. After the conditioning step, the flotation (1000 rpm and 3 L/min rougher; 1500 rpm and 1.3 L/min cleaner 1; and 1500 rpm and 0.6 L/min cleaner 2) was started. The flotation results are shown in Table 2.

[0041] Table 2

[0042] The Example 1 and Example 2 results show, in the absence of the collector aid, a collector composition in which the composition components were separately added to the flotation showed no significant differences with respect to the same collector composition in which the components were pre-mixed and added to the flotation all at once.

[0043] Example 3 (Comparative): Collector aid added as frother after conditioning

[0044] The pH of the flotation mixture was adjusted to 9.9 with a 5% aqueous NaOH solution and quantities of the 1 wt-% solutions of tall oils and Phosphate Ester (the same as in Example 1) were mixed together and added to the flotation cell as a single stock solution to be equivalent to 145.5 g/t of a collector composition containing 61.8 wt-% tall oils and 38.2 wt-% Phosphate Ester. A conditioning step was carried out at 1000 rpm and room temperature for two minutes. After the conditioning step, 4.5 g/t of collector aid (2, 2, 4-trimethyl- l,3-pentanediol monoisobutyrate) was added and the flotation (1000 rpm and 3 L/min rougher; 1500 rpm, 1.3 L/min cleaner 1; and 1500 rpm and 0.6 L/min cleaner 2) was started. The flotation results are shown in Table 3.

[0045] Table 3

[0046] When the collector aid was added as a frother after conditioning the ore with the collectors, the grade of P2O5 dropped below the acceptable level of 39.0%.

[0047] Example 4: Collector aid, pre-mixed with primary collector

[0048] A collector composition containing 60 wt-% tall oils, 37 wt-% Phosphate Ester, and 3 wt-% collector aid (2, 2, 4-trimethyl- l,3-pentanediol monoisobutyrate) was prepared. The collector composition was diluted in deionized water to a 1 wt-% solution.

[0049] The pH of the flotation mixture was adjusted to 9.9 with a 5% aqueous

NaOH solution and 150 g/t of the collector composition as a 1 wt-% aqueous solution was added to the flotation cell. A conditioning step was carried out at 1000 rpm and room temperature for two minutes. After the conditioning step, the flotation (1000 rpm and 3 L/min rougher; 1500 rpm and 1.3 L/min cleaner 1; and 1500 rpm and 0.6 L/min cleaner 2) was started. The flotation results are shown in Table 4. [0050] Table 4

[0051] Grade and recovery were improved over a collector composition having comparable levels of the other collectors but without the collector aid (Example 2).

[0052] As one can see from the results above, collector compositions containing the collector aid described herein ( e.g ., 2, 2, 4-trimethyl- l,3-pentanediol monoisobutyrate) showed improved grade and/or recovery from flotation when compared to collector compositions that did not contain the collector aid and to compositions in which the collector aid was added (as a frother) at a later step in the flotation, namely after the conditioning of the ore. The results clearly show that the presence of the collector aid in the collector composition at the start of the flotation process plays a crucial role in the flotation. [0053] Example 5: Collector aid added to conditioning separately

The pH of the flotation mixture was adjusted to 9.9 with a 5% aqueous NaOH solution and quantities of the 1 wt-% solutions of tall oils and Phosphate Ester (the same as in Example 1) were mixed together and added to the flotation cell to be equivalent to 145.5 g/t of a collector composition containing 61.8 wt-% tall oils and 38.2 wt-%

Phosphate Ester. The collector aid (2, 2, 4-trimethyl- l,3-pentanediol monoisobutyrate) was added to the conditioning step separately from the main collector stock solution to be equivalent to 4.5 g/t. A conditioning step was carried out at 1000 rpm and room temperature for two minutes. The flotation (1000 rpm and 3 L/min rougher; 1500 rpm, 1.3 L/min cleaner 1; and 1500 rpm and 0.6 L/min cleaner 2) was started. The flotation results are shown in Table 5.

Table 5

This Example 5 shows that when the collector was added separately from the main collector solution before the conditioning step of the ore, the grade of P2O5 remained higher than in the Example 3 demonstrating that the collector aid if present during the conditioning step improves the results. Pre-blending the collector aid with the other collector compounds is however preferred as visible from the results obtained in Example 4.