The present invention relates to a method for manufacturing a concentrate enriched in iron min eral content from an ore, which contains an iron mineral and silicate, by a reverse flotation using an amidoamine derivative. A further embodiment is a use of the amidoamine derivative as a flo tation collector.

A typical iron ore benefication process requires a flotation stage to remove silica (S1O2) from the valuable iron mineral, e.g. oxides like hematite or magnetite, and thus to obtain a high-grade iron mineral concentrate. A high-grade iron mineral concentrate allows to make high quality steel. Removal of S1O2 from different ores by froth flotation in combination with hydrophobic amines is a well-known process. Negatively charged silicate particles can be hydrophobized us ing suitable amines. Injection of air in a flotation cell leads to formation of hydrophobic gas bub bles, which can transport the hydrophobized silicate particles to the top of the flotation cell. The formed froth, which can be stabilized by a suitable chemical acting as a froth regulator, contains the hydrophobized silicate particles. Finally, the froth will be removed from the top and the en riched mineral is left at the bottom of the flotation cell.

US 2014-048454 relates to fatty amidoamine collectors for the beneficiation by flotation of aque ous suspensions of ores, the use of said fatty amidoamine collectors in flotation processes for the beneficiation of ores, more particularly in reverse flotation processes for the beneficiation of silicates containing-ore. In its examples, the following amidoamine collectors are employed for an inverse flotation of calcium carbonate at a neutral pH: rapseed oil, N-(3-(dimethylaminopro- pyl)amide (CAS-No. 85408-42-0); tall oil, N-(3-(dimethylaminopropyl)amide (CAS-No. 68650-79- 3) and fish oil, N-(3-(dimethylaminopropyl)amide (CAS-No. 97552-95-9).

US 2014-048453 relates relates to fatty alkoxylated polyamine collectors for the beneficiation by flotation of aqueous suspensions of ores, the use of said fatty alkoxylated polyamine collectors in flotation processes for the beneficiation of ores, more particularly in reverse flotation pro cesses for the beneficiation of silicates containing-ores. In its examples, the following amidoam ine collector is employed for an inverse flotation of calcium carbonate at a neutral pH: rapseed oil, N-(3-(dimethylaminopropyl)amide (CAS-No. 85408-42-0).

US 2014-144290 relates to collector compositions and methods for making and using them. The collector can include one or more etheramines and one or more amidoamines. A liquid suspen sion or slurry comprising one or more particulates can be contacted with the collector to pro duce a treated mixture. A product can be recovered from the treated mixture that includes a pu rified liquid having a reduced concentration of the particulates relative to the treated mixture, a purified particulate product having a reduced concentration of liquid relative to the treated mix ture, or both. In its examples, the inverse flotation of an iron ore at a pH of 10.5 with removal of S1O2 via the froth is shown inter alia with tall oil fatty acid 1 ,3-diamine pentane amide or tall oil fatty acid diethylenetriamine amide.

US 2015-0096925 relates to collector compositions and methods for making and using same to purify one or more crude materials. The collector composition can include one or more ami- doamines having the formula as depicted below

and one or more amines having the formula R ⁶ -NH2, where a weight ratio of the amidoamine to the amine can be about 99:1 to about 1 :99. In its example 1 , a coconut fatty acid diethylenetri amine amidoamine neutralized with glacial acetic acid is used in an inverse flotation of a phos phate ore for removal of silica at a neutral pH. In its example 2, a coconut fatty oil diethylenetri amine amidoamine neutralized with glacial acetic acid is used in an inverse flotation of a phos phate ore for removal of silica at a neutral pH. In its example 3, a tall oil fatty acid diethylenetri amine neutralized with glacial acetic acid is used for an inverse flotation of a phosphate ore for removal of silica at a neutral pH. Other amidoamines similarly employed are lauric acid diethy lenetriamine amidoamine and a rosin acid tetraethylenepentamine amidoamine. Some example provide also a combination of an amidoamine with an amine such as an etheramine composed of 95 wt.% of 3-(8-methylnonoxy)propan-1-amine and 3 wt.% of 8-methylnonan-1-ol, such as cocoamine or such as dodecylamine.

There is still a need for improved methods in inverse flotation of ores containing iron mineral and silicate. Especially the quality of ores has been decreasing. With higher S1O2 content in the ore, a selective removal of silicate is more difficult than in the past with ores of a lower S1O2 con tent. On one side, a loss of iron mineral in the flotation process should be avoided, i.e. a high recovery, and on the other side, S1O2 content should be decreased in a concentrate enriched in iron mineral content to a low level, i.e. selectivity. Especially for direct reduction processes using the concentrate, a low S1O2 content is desirable. Typically, a mine as an ore processing site will set a maximum level of residual S1O2 content that is allowed to remain in the concentrate at the end of the flotation process. This may for instance be 2.5 % by weight, especially 2.0% by weight. The target is generally to at least achieve this maximum silica level without significantly losing any of the iron mineral content. A better recovery in combination with a comparable or a better selectivity reduces iron mineral losses in the tailings and leads to economic benefits.

It is an object of the present invention to provide a method for manufacturing a concentrate en riched in iron mineral content with a high recovery of iron mineral from the applied ore and a low content of S1O2 from the applied ore. Furthermore, it is attractive if an employed collector allows to reduce or even abstain from a necessity for a specific flotation auxiliary. At the same time, it is an advantage if a material applied in the method can economically be manufactured in a chemically relatively pure and thus homogenous form, for example because less side reactions can occur. A chemically relatively pure material offers via combination with other materials, par ticularly other co-collectors, a fine-tuned adjustment to a specific ore.

The object is achieved, according to the invention, by a method for manufacturing a concentrate enriched in iron mineral content from an ore, which contains an iron mineral and silicate, by a reverse flotation, which method comprises the step of

(c) adding a compound of formula I

wherein R ¹ is a linear C ₁₇ alkenyl, a linear C ₁₇ alkyl or a linear C ₁₅ alkyl, or a salt of a protonated compound of formula I and an anion,

to a prepared aqueous pulp of the ore and optionally one or more flotation auxiliaries to obtain an aqueous mixture.

Preferably, the method for manufacturing a concentrate enriched in iron mineral content from an ore, which contains an iron mineral and silicate, comprises the steps of

(a) providing the ore, which contains an iron mineral and silicate,

(b) preparing from the provided ore by addition of water and optionally one or more flota tion auxiliaries an aqueous pulp,

(c) adding a compound of formula I

wherein R ¹ is a linear C ₁₇ alkenyl, a linear C ₁₇ alkyl or a linear C ₁₅ alkyl, or a salt of a protonated compound of formula I and an anion,

to the prepared aqueous pulp of the ore and optionally one or more flotation auxilia ries to obtain an aqueous mixture,

(d) aerating the aqueous mixture in a flotation cell to generate a froth, which is enriched in silicate content, and removing the generated froth from the flotation cell,

(e) obtaining from the flotation cell the concentrate enriched in iron mineral content.

The steps (a), (b), (c), (d) and (e) describe more detailed the reverse flotation.

The ore, which contains an iron mineral and silicate (S1O ₂ ), is for example from a magmatic de posit or from a sedimentary deposit. The step (a) of providing an ore comprises for example also a crushing or a grinding respectively milling of the ore. In case of an ore from a magmatic deposit, the step of providing the ore comprises for example also a crushing of the ore and a grinding respectively milling of the ore. In case of an ore from a sedimentary deposit, the step of providing the ore comprises for example a crushing of the ore, particularly a crushing of the ore and a wet grinding of the ore. Preferably, the step (a) of providing of the ore results in ore particles, which have a particle size allowing 60% to 100% by weight of the particles based on the overall weight of the particles to pass a 100 pm steel mesh sieve as measured by standard dry sieving.

The ore contains for example 20% to 80% by weight of silicate based on the weight of the ore, particularly 25% to 75% by weight, very particularly 30% to 55% by weight and especially 30% to 40% by weight.

Preferably, the iron mineral consists out of 90% to 100% by weight of iron oxide based on all iron mineral in the ore. Very preferably, the iron mineral consists out of at least 97% to 100% by weight of iron oxide, particularly preferably out of 99% to 100%. Typical iron oxides are hematite (Fe2C>3 with 69.9% by weight of iron content), magnetite (FesCU with 72.4% by weight of iron content) or a mixture of both. The weight of iron content is similar to a weight content of Fe atoms.

A typical ore comprises between 40% to 70% by weight of hematite and 30% to 50% by weight of silica, particularly 45% to 65% by weight of hematite and 30% to 45% by weight of silica.

Preferred is an ore, which comprises iron mineral, wherein more than 50% by weight of the comprised iron mineral is an iron oxide, which is hematite. Very preferred, more than 70% to 100% is an iron oxide, which is hematite.

The compound of formula I acts in the method as a collector for froth flotation.

The anion is the deprotonated form of an acid A(-H)p, wherein -H represents an acidic proton and p the number of acidic protons of the acid A(-H)p. Depending on the acid strength of the acid A(-H)p, some acidic protons of the acid A(-H)p might not be deprotonated in a salt with a compound of formula I.

A salt of a protonated compound of formula I and the anion is also expressed by formula l-t1-1 +

wherein A represents the anion, y is an integer, which is at least 1 , and y represents the negative charge of the anion y is not higher than p, which is the number of acidic protons of the acid A(-H)p. Preferred is an anion, which is a deprotonated acid A(-H)p, wherein p is 1 , 2 or 3 and y is 1 for p =1 , y is 1 or 2 for p = 2 and y is 1 , 2, or 3 for p = 3.

The anion is for example C1-C18 carboxylate, fluoride, chloride, bromide, iodide, sulfonate, hy- drogensulfate, sulfate, dihydrogenphosphate, hydrogenphosphate, phosphate, nitrate, hydrofluorosilicate or fluorosilicate. C1-C18 carboxylate is for example an aliphatic or olefinic car- boxylate, preferably an aliphatic C1-C13 carboxylate, very preferably an aliphatic C1-C6 carbox ylate and especially formate, acetate or proprionate. Preferred is C1-C18 carboxylate, fluoride, chloride, sulfonate, hydrogensulfate, sulfate, dihydrogenphosphate, hydrogenphosphate, phos phate or nitrate. Very preferred is aliphatic or olefinic C1-C18 carboxylate, particularly preferred is formate, acetate or proprionate.

Preferred is a method, wherein the anion is C1-C18 carboxylate, fluoride, chloride, bromide, io dide, sulfonate, hydrogensulfate, sulfate, dihydrogenphosphate, hydrogenphosphate, phos phate, nitrate, hydrofluorosilicate or fluorosilicate.

A condensation product of N’,N’-dimethylpropane-1 , 3-diamine with rapeseed-oil is known under CAS-No. 85408-42-0. A condensation product of N’,N’-dimethylpropane-1 , 3-diamine with tall oil is known under CAS-No. 68650-79-3. A condensation product of N’,N’-dimethylpropane-1 ,3-dia- mine with fish oil is known under CAS-No. 97552-95-9. A condensation product of N’,N’-dime- thylpropane-1 , 3-diamine (alternative name: 3-(dimethylamino)propylamine) with soy oil is known under CAS-No. 68188-30-7 and named in CAS registry as amides, soy, N-[3-(dimethylamino) propyl. Soy oil possesses distribution ranges of individual fatty acids, which is described in one literature for example as containing as major components around 8 to 14 mol% palmitic acid, around 1 to 6 mol% stearic acid, around 17 to 30 mol% oleic acid, around 48 to 59 mol% linoleic acid and around 4 to 1 1 mol% linolenic acid - all based on the overall molar amount of fatty ac ids, which is 100 mol%. For example, a specific distribution of major components of soy oil fatty acids is described in the mentioned literature as around 10 mol% palmitic acid, around 5 mol% stearic acid, around 21 mol% oleic acid, around 53 mol% linoleic acid and around 8 mol% lino lenic acid - based on the overall molar amount of fatty acids, which is 100 mol%. The meaning of around in the two previous sentences refers also to the slight differences if one considers wt.% versus mol%. The molecular weight of the major components is not the same but also not too much different, hence in a first approximation, wt.% can be taken as mol% and vice versa. Soy oil fatty acids can be distilled, which might lead to changes versus the fatty acid distribution before distillation. The amidoamine obtained from a condensation of N’,N’-dimethylpropane-1 ,3- diamine with palmitic acid is known under CAS-No. 39669-97-1 , a choride salt of the protonated amidoamine under CAS-No. 151190-60-2, a palmitate salt of the protonated amidoamine under CAS-No. 220820-88-2, an acetate salt of the protonated amidoamine under CAS-No. 83763-68- 2. The amidoamine product obtained from a condensation of N’,N’-dimethylpropane-1 , 3-diamine with stearic acid is known under CAS-No. 7651-02-7, a chloride salt of the protonated amidoam ine under CAS-No. 83607-13-0, a stearate acid salt of the protonated amidoamine under CAS- No. 127358-77-4, an acetate salt of the protonated amidoamine under CAS-No. 13282-70-7.

The amidoamine product obtained from a condensation of N’,N’-dimethylpropane-1 , 3-diamine with oleic acid is known under CAS-No. 109-28-4, a bromide salt of the protonated amidoamine under CAS-No. 76959-11-0, an oleate salt of the protonated amidoamine under CAS-No.

70715-14-9, an acetate salt of the protonated amidoamine under CAS-No. 13282-68-3, a sulfate salt of two with two the protonated amidoamines under CAS-No. 1638206-65-1. The am- idoamine product obtained from a condensation of N’,N’-dimethylpropane-1 , 3-diamine with lino- leic acid is known under CAS-No. 81613-56-1 , a linoleate salt of the protonated amidoamine un der CAS-No. 651294-42-7, a 2-hydroxypropionate salt of the protonated amidoamine under CAS-No. 187939-51-1. The amidoamine product obtained from a condensation of N’,N’-dime- thylpropane-1 , 3-diamine with linolenic acid is known under CAS-No. 122955-03-7.

A compound of formula I, wherein R ¹ is linear C17 alkenyl, which is (8Z)-heptadec-8-enyl, is de picted below

and a chemical name is (Z)-N-[3-(dimethylamino)propyl]octadec-9-enamide.

A compound of formula I, wherein R ¹ is linear C17 alkenyl, which is (8Z, 11Z)-heptadec-8,1 1- dienyl, is depicted below

and a chemical name is (9Z, 12Z)-N-[3-(dimethylamino)propyl]octadeca-9,12-dienamide.

A compound of formula I, wherein R ¹ is linear C17 alkenyl, which is (8Z, 1 1Z, 14Z)-heptadec- 8,1 1 ,14-trienyl, is depicted below

and a chemical name is (9Z,12Z, 15Z)-N-[3-(dimethylamino)propyl]octadeca-9, 12, 15-trienamide.

A compound of formula I, wherein R ¹ is linear C17 alkyl, is depicted below

and a chemical name is N-[3-(dimethylamino)propyl]octadecanamide.

A compound of formula I, wherein R ¹ is linear C15 alkyl, is depicted below and a chemical name is N-[3-(dimethylamino)propyl]hexadecanamide.

Preferred is a method, wherein linear C17 alkenyl is (8Z)-heptadec-8-enyl, (8Z,11Z)-heptadec- 8,11 -dienyl or (8Z, 11 Z, 14Z)-heptadec-8, 11 , 14-trienyl.

Preferred is a method, wherein at step c) a compound of formula I is added, wherein R1 is lin ear Ci7 alkenyl.

Preferred is a method, wherein at step c) a mixture comprising different compounds of formula I or salts of the protonated different compounds of formula I and anions is added.

Preferred is a method, wherein at step c) a mixture comprising different compounds of formula I or salts of the protonated different compounds of formula I and anions are added, and the mix ture comprises

(i) 50 mol% to 100 mol% of a compound of formula I, wherein R ¹ is linear C17 alkenyl, or a salt of the protonated compound of formula I and an an ion,

wherein the amount of (i) is based on all compounds of formula I and salts of the protonated compounds of formula I, which is 100 mol%. Very preferred is an amount of 60 mol% to 100 mol%, particularly preferred is an amount of 70 mol% to 100 mol% and especially preferred is an amount of 72 mol% to 95 mol%.

Preferred is a method, wherein at step c) a mixture comprising different compounds of formula I or salts of the protonated different compounds of formula I and anions are added, and the mix ture comprises

(i) 50 mol% to 98 mol% of a compound of formula I, wherein R ¹ is linear C17 alkenyl, or a salt of the protonated compound of formula I and an an ion,

(ii) 1 mol% to 25 mol% of a compound of formula I, wherein R ¹ is linear C15 alkyl, or a salt of the protonated compound of formula I and an anion, and

(iii) 1 mol% to 25 mol% of a compound of formula I, wherein R ¹ is linear C17 alkyl, or a salt of the protonated compound of formula I and an anion, wherein the overall amount of (i), (ii) and (iii) is 100 mol% based on all compounds of formula I and salts of the protonated compounds of formula I. Preferred is a method, wherein at step c) a mixture comprising different compounds of formula I or salts of the protonated different compounds of formula I and anions are added, and the mix ture comprises

(i) 65 to 91 mol% of a compound of formula I, wherein R ¹ is linear C17 alkenyl, or a salt of the protonated compound of formula I and an anion

(ii) 8 to 22 mol % of a compound of formula I, wherein R ¹ is linear C15 alkyl, or a salt of the protonated compound of formula I and an anion, and

(iii) 1 to 6 mol% of a compound of formula I, wherein R ¹ is linear C17 alkyl or a salt of the protonated compound of formula I and an anion, wherein the overall amount of (i), (ii) and (iii) is 100 mol% based on all compounds of formula I and salts of the protonated compounds of formula I.

Preferred is a method, wherein at step c) a mixture comprising different compounds of formula I or salts of the protonated different compounds of formula I and anions are added, and the mix ture comprises

(i) 67 to 91 mol% of a compound of formula I, wherein R ¹ is linear C17 alkenyl, or a salt of the protonated compound of formula I and an anion

(ii) 8 to 21 mol % of a compound of formula I, wherein R ¹ is linear C15 alkyl, or a salt of the protonated compound of formula I and an anion, and

(iii) 2 to 6 mol% of a compound of formula I, wherein R ¹ is linear C17 alkyl or a salt of the protonated compound of formula I and an anion, wherein the overall amount of (i), (ii) and (iii) is 100 mol% based on all compounds of formula I and salts of the protonated compounds of formula I.

Preferred is a method, wherein at step c) a mixture comprising different compounds of formula I or salts of the protonated different compounds of formula I and anions are added, and for the overall amount of compounds of formula I, wherein R ¹ is linear C17 alkenyl, the molar ratio be tween mono-unsaturated linear C17 alkenyl to poly-unsaturated linear C17 alkenyl is from 0.5 to 0.83.

Preferred is a method, wherein at the step c) a mixture comprising different compounds of for mula I or salts of the protonated different compounds of formula I and anions is added and the mixture is obtained by condensing soy oil fatty acids with N’,N’-dimethylpropane-1 , 3-diamine under removal of water. Very preferred, the mixture is the reaction product obtained at example A-1.

At step c), adding a compound of formula I or adding a salt of the protonated compound of for mula I are two options. In view of the overall added amount of chemicals, the addition of a com pound of formula I without an anion is more attractive for reducing the overall added amount of chemicals. Particularly, if a desired pH value of the inverse flotation is between 8 and 12, very particularly between 9 and 12 and especially between 9 and 11. Preferred is a method, wherein at step c) a compound of formula I is added.

The compound of formula I is added preferably in an amount of 10 g to 500 g per ton of the ore. The calculation is performed on basis of dry ore. The amount is very preferably from 30 g to 300 g per ton of the ore, particularly preferably from 40 g to 280 g per ton of the ore, especially from 70 g to 270 g per ton of the ore and very especially from 170 g to 260 g per ton of the ore.

Preferred is a method, wherein the compound of formula I is added in an amount between 10 g to 500 g per ton of the ore.

Preferred is a method, wherein the compound of formula I is added in an amount between 30 g to 300 g per ton of the ore.

The pH value at the steps (c) and (d) of the method is preferably adjusted with a pH regulator to a specific pH value, typically to a pH value between 8 and 12, particularly between 9 and 11. A pH regulator is typically a strong base, for example sodium hydroxide, potassium hydroxide, so dium carbonate or potassium carbonate. Preferably, the pH value of the aqueous pulp is be tween 8 and 12, particularly between 9 and 11. Preferably, step (c), i.e. adding the compound of formula to the aqueous pulp, takes place at a pH value between 8 and 12, particularly between 9 and 1 1. Preferably, the pH value of the aqueous mixture is between 8 and 12, particularly be tween 9 and 11. Preferably, step (d), i.e. aerating the aqueous mixture, takes place at a pH value between 8 and 12, particularly between 9 and 1 1. Preferably, (e), i.e. obtaining the con centrate enriched in iron mineral content, takes place at a pH value between 8 and 12, particu larly between 9 and 11. A regulation of the pH value supports that the ore, especially the parti cles of the ore, exhibit the correct surface charge.

Preferred is a method, wherein the pH value at step (c) is between 8 and 12.

Preferred is a method, wherein the pH value at step (c) and at step (b) is between 8 and 12.

Preferred is a method, wherein the pH value at step (c) and at step (d) is between 8 and 12.

Preferred is a method, wherein the pH value at step (c), at step (b) and at step (d) is between 8 and 12.

Preferred is a method, wherein the pH value at step (c), at step (b), at step (d) and at step (e) is between 8 and 12.

A flotation auxiliary is for example a depressing agent, a froth regulator, a co-collector or an ex tender oil. A depressing agent helps to prevent flotation of an ingredient of the ore, which is not desired to get part of the froth or supports in general the selectivity of the method of manufacturing the concentrate. A depressing agent is for example a hydrophilic polysaccharide, particularly a starch, or sodium silicate. The starch is for example a native starch or a modified starch. A na tive starch is for example a starch from corn, wheat, oat, barley, rice, millet, potato, pea, tapioca or manioc. The native starch is preferably pregelatinized, i.e. warmed for starch gelatination. A modified starch is either a degraded starch, which possesses a reduced weight-average molec ular weight versus the original starch, a chemically modified starch or a degraded and chemi cally modified starch. A degradation of starch is for example possible by oxidation or treatment by acid, base or enzymes. The degradation leads typically to an increased content on oligosac charides or dextrines. A chemical modification is a functionalization of a starch by covalent link age of a chemical group to the starch. A chemically modified starch is for example obtainable by esterification or etherification of a starch. The esterification of an acid with a starch is for exam ple performed with an anhydride of the acid or a chloride of the acid. The etherification of a starch is for example possible with an organic reagent, which contains a reactive epoxide func tionality. Preferred is a depressing agent, which is a native starch, particularly a pregelatinized starch. A depressing agent is preferably added in an amount of 100 to 3000 g per ton of the ore. The calculation is performed on basis of dry ore. The amount is very preferably from 300 g to 2200 g per ton of the ore, particularly preferably from 400 g to 1900 g per ton of the ore, espe cially from 500 g to 1700 g per ton of the ore and very especially from 600 g to 1400 g per ton of the ore.

A froth regulator helps to improve the efficiency of the method of manufacturing by interfering with the froth generation. A froth property is for example the froth height respectively the volume of the froth or the stability of the froth, i.e. the time to collapse after stop of aerating. A froth reg ulator is for example pine oil, methylisobutyl carbinol, C6-C12 alcohol, particularly 2-ethylhexanol or hexanol, an alcoholic ester, particularly a mixture comprising 2,2,4-trimethyl-1 ,3-pentandiol- monoisobutyrate, terpineol, triethoxybutane, an alkoxylated alcohol, particularly an ethoxylated and/or propoxylated alcohol, polyethylene glycol or polypropylene glycol.

A co-collector is a surface-active compound, which is different to a compound of formula I. A co collector is for example cationic, non-ionic or anionic, preferably cationic or non-ionic and very preferably cationic. A cationic co-collector is for example C9-C18 alkylamine, 2-(Cg-Ci ₈ alkyl- amino)ethyl-1 -amine, N’-(Cg-Ci ₈ alkyl)propane-1 , 3-diamine, 3-(Cg-Ci ₈ alkoxy)propyl-1 -amine, N’-(3-(Cg-Ci ₈ alkoxy)propyl)propane-1 , 3-diamine. A non-ionic co-collector is for example C9-C15 alkyl alcohol, which is branched, or ethoxylated C9-C15 alkyl alcohol, which is branched and eth oxylated with 2 to 4 mole ethylene oxide. In case of a co-collector as a flotation auxiliary, the co collector might be added together with the compound of formula I. In this case, this part of step (b) occurs simultaneously with step (c). It is still attractive, if the method does not require the addition of a co-collector.

Preferred is a method, wherein an amine of formula R ² -N H2, wherein R ² is a C1-C24 alkyl, a phe nyl, a benzyl, a C1-C24 alkenyl, a heterocyclyl, an unsubstituted aryl or an aryl substituted by one or more C Cs alkyl substituents, is contained in a weight ratio below 1 to 100 with 100 being the weight amount of all compounds of formula I. Very preferred, the method is free of adding an amine of formula R ² -N H2. Particularly preferred, the method is free of adding an amine of for mula R ² -NH2 or a salt of a protonated amine of formula R ² -NH2 and an anion.

Preferred is a method, wherein an etheramine is contained in a weight ratio below 20 to 100 with 100 being the weight amount of all compounds of formula I. Very preferred is a method, wherein an etheramine is contained in a weight ratio below 1 to 100 with 100 being the weight amount of all compounds of formula I. Particularly preferred, the method is free of adding an etheramine. Especially preferred, the method is free of adding an etheramine or a salt of a pro tonated etheramine and an anion. An etheramine is herein understood as a molecule, which comprises the structural element alkyl-O-alkylene-NH-... , for example molecules described by alkyl-0-alkylene-NH2 or alkyl-O-alkylene-NH-alkylene-Nhh.

An extender oil is for example kerosene.

Preferred is a method, wherein at step (b) one or more flotation auxiliaries are added and one of the flotation auxiliaries is a depressing agent, a froth regulator, a co-collector or an extender oil.

Preferred is a method, wherein one of the flotation auxiliaries added at step (b) is a depressing agent.

Preferred is a method, wherein one of the flotation auxiliaries added at step (b) is a depressing agent and one of the flotation auxiliaries is a co-collector, which is added at step (b) before step (c) or is added simultaneously with the compound of formula I.

Addition of corn starch, typically foreseen as a depressing agent, is often common practice. It has been found that the addition of a compound of formula I as obtained in example A-1 pro vides improved results in the absence of a pregelatinized corn starch versus the presence of the pregelatinized corn starch. Preferably, the method is free of adding a pregelatinized corn starch, very preferably free of adding a corn starch, particularly free of adding a starch and very particu larly free of adding a hydrophilic polysaccharide.

Preferred is a method, which is fee of adding a corn starch.

In the method of manufacturing a concentrate, conventional inverse flotation plant equipment may be used. Preferably, the compound of formula I and optionally a flotation auxiliary, which is a co-collector, is or are added to the aqueous pulp, which is already in the flotation cell, which is used for aerating the mixture in step (d).

After adding of a compound of formula I to the aqueous pulp, the obtained aqueous mixture is preferably kept, particularly under stirring, for a conditioning period before aerating the aqueous mixture. This allows the compound of formula I and optionally a flotation auxiliary, which is a co collector, to condition the ore, particularly the ore particles, in the aqueous mixture. The condi tioning period lasts for example for one minute or up to 10 or 15 minutes.

At aerating the aqueous mixture, air is typically injected into the base of the flotation cell. Air bubbles are formed and rise to the surface and generate the froth at the surface. The injection of air may be continued until no more froth is formed. This might last for example for one minute or up to 15 or 20 minutes. The froth is removed.

For obtaining the concentrate enriched in iron mineral content, aerating is typically stopped. The concentrate enriched in iron mineral content sinks typically to the bottom of the flotation cell.

In some cases, it may be desirable to treat the concentrate enriched in iron mineral content in a similar manner again. For example, the steps (c) and (d) are repeated as step (d-c) followed by step (d-d) before step (e) is conducted.

The concentrate enriched in iron mineral content contains preferably at least 60% by weight of Fe atoms based on the overall weight of the concentrate enriched in iron mineral content, very preferably at least 65% by weight. The weight of Fe atoms is similar to the weight of iron con tent. The concentrate enriched in iron mineral content contains preferably less than 2.5% by weight of S1O2 based on the overall weight of the concentrate enriched in iron mineral, very pref erably less than 2.1 % by weight and particularly preferably 2.0% or less than 1.9% by weight of S1O2. The concentrate enriched in iron mineral content contains preferably at least 60% by weight of Fe atoms and less than 2.5% by weight of S1O2 based on the overall weight of the concentrate enriched in iron mineral content, very preferably at least 65% by weight of Fe atoms and less than 2.1 % by weight of S1O2.

The above described preferences for the method of manufacturing a concentrate or for the added compound of formula I are described for the method. These preferences apply also to the further embodiment of the invention.

A further embodiment of the invention is a use of a compound of formula I

wherein R ¹ is a linear C ₁₇ alkenyl, a linear C ₁₇ alkyl or a linear C ₁₅ alkyl, or a salt of a protonated compound of formula I and an anion,

as a flotation collector for manufacturing a concentrate enriched in iron mineral content from an ore, which contains an iron mineral and silicate, by a reverse flotation.

Figures 1 to 4 are attached and described below.

Fig. 1 shows an IR spectrum of the material obtained at example A-1. The axis of the abscissas shows the wavelength in cm ^-1 and the axis of ordinates shows the transmission in percent.

Fig. 2 shows a ¹³ C-NMR spectrum of the material obtained at example A-1 in CDCh.

Fig. 3 shows a ¹ H-NMR spectrum of the material obtained at example A-1 in CDCh.

Fig. 4 shows a ¹ H-NMR spectrum between around 0.7 ppm and around 5.6 ppm of the material obtained at example A-2 in CDCh. Fig. 4 is an enlarged extract from Fig. 3.

The following examples illustrate further the invention without limiting it. Percentage values are percentage by weight if not stated differently.

A) employed collector

A-1 : Reaction product of N,N-dimethylpropane-1 , 3-diamine and soy oil fatty acid (101)

A stirred solution of distilled soy oil fatty acid (416 g, 1.5 mol, R ^A1 -C(=0)OH, with a fatty acid composition of C12 0.89%, C14 0.45%, C16 18.20%, C18 4.71 %, monounsaturated C18 29.55%, di-unsaturated C18 43.19%, tri-unsaturated C18 3.01 %) is heated to 40°C and N’,N’- dimethylpropane-1 , 3-diamine (199 g, 1.95 mol; molar ratio of R ^A1 -C(=0)OH to H2N-CH2-CH2- CH ₂ -N(CH ₃ )2 is 1 to 1.3) is added in 5 minutes. The addition causes an exothermic reaction due to a salt formation. After complete addition, the reaction mixture is heated until 80 °C automati cally, and then, slowly heated until 150 °C in 1.5 hours. The mixture is kept at reflux at 150 °C for 1 hour. After this step, water is distilled. Slowly, the reaction temperature is raised until 180 °C and is kept at this temperature for one hour. The acidic index is measured by titration to iden tify the end of the reaction. After all the fatty acid is consumed, the mixture is cooled to 50 °C. The reaction product (101) is obtained as a yellow brownish solid (91 % yield, there are remain ing fatty acids in the reaction product because part of the amine is lost with water distillation). Content of unreacted fatty acids: 13 mg KOH / g of (101) as measured by titration with KOH so lution (0.05%) and phenolphthalein indicator. 13 mg corresponds formally to 65 mg oleic acid per g product.

FT-IR V _max (liquid film, obtained by heating and turning into a liquid for measurement) main bands: 3292.2, 3083.6, 2926.3, 2855.7, 1648.8, 1559, 1462.7 cm-1 ¹³ C-NMR (126 MHz, CDCh): 173.04 (C-6), 130.19 (double bonds), 130.03 (double bonds), 129.97 (double bonds), 129.74 (double bonds), 128.05 (double bonds), 127.92 (double bonds), 58.60 (C-2), 45.39 (C-10, C-11), 39.19 (C-4), 36.95 (C-7), 31.93, 31.91 , 31.53, 29.78, 29.75, 29.70, 29.67, 29.65, 29.53, 29.43, 29.36, 29.33, 29.18, 27.22 (C-21 , C-24), 26.28 (C-3), 25.79 (C-34), 25.64, 22.69, 22.58, 14.11 (C-13). Unassigned carbon signals belong to the fatty acid aliphatic chains.

¹ H-NMR (500 MHz, CDCh): 7.05 (s, 1 H, NH), 5.45 - 5.24 (m, 2H, H-double bonds), 3.39 - 3.27 (m, 2H, H-4), 2.86 - 2.70 (m, 1 H, H-34), 2.37 (t, J(H-3) = 6.4 Hz , 2H, H-2, ), 2.21 (s, 6H, H- 10, H-1 1), 2.14 (t, 2H, H-7), 2.09 - 1.89 (m, 3H, H-21.H-24), 1.63 (q, J(H-2, H-4) = 6.2 Hz, H,

H3), 1.60 (br. s., 2H, H-8) 1.50 - 1.08 (m, 17H, aliphatic protons), 1.01 - 0.79 (m, 3H, H13). The intensity ratio between the CH3-group of the fatty acids (0.9 ppm) and double bond hydrogen signals (5.4 ppm) is around 3 : 2.2. Accordingly, there is more than one double bond in average per fatty acid unit.

The FT-IR spectrum of the reaction product (101) is depicted at Fig 1. The ¹³ C-NMR spectrum of the reaction product (101) is depicted at Fig 2. The ¹ H-NMR spectrum is depicted at Fig. 3 and an enlarged extract is depicted at Fig. 4.

A-2: 3-iso-nonoxypropan-1 -amine (etheramine) (201) [comparative]

B) Flotation

750 g of ore (haematite based, 43.58% Fe, 37.64% SiCh; 0.52% AhCh) is placed in a 1.5 L flota tion cell in a flotation machine. 400 ml_ of distilled water is added at ambient temperature (~21 °C), which results in the formation of a 65% solids pulp. This pulp is conditioned with pregelati nized corn starch (665 g / 1 calculated as dry starch per dry ore) for 5 minutes or without a starch for accordingly, respectively at a stirring of 1000 rpm as stated in table B-1. After 5 minutes, the pH is adjusted to 10.2 with aqueous sodium hydroxide solution (5%). A collector is added as stated in table B-1 (calculated as collector substance per dry ore) in a form of an aqueous solution (1 % of collector substance) prepared in distilled water. The pH is adjusted to 10.2 with the aqueous sodium hydroxide solution (5%). The pulp is further conditioned for 1 mi nute under the same stirring. After conditioning, the vessel volume is filled with distilled water until 2 cm below the lip level under a stirring of 1000 rpm. The pH is corrected to 10.2 again prior to the start of flotation with aqueous sodium hydroxide solution (5%). Flotation is started by opening aeration. The flotation cell is self-aerating and not fitted with an external air supply. The air flow is not measured. The froth is collected with regular manual scraping in a 2 L tray until complete exhaustion. The collected solids-bearing froth in the tray and the remaining cell frac tion are separately dewatered, dried, weighed and Fe-content and SiC>2-content of both are ana lyzed by XRF measurement on a lithium borate based fused bead. The results are listed in table B-1. Table B-1 :

Food notes: a) comparative

b) according to invention

c) Fe cone grade means Fe atom content in cell fraction

d) S1O2 cone grade means S1O2 content in cell fraction

e) recovery is the ratio between the overall amount of Fe atom contained in the cell fraction and the overall amount of Fe atom contained in the ore employed as starting material The results in table B-1 shows that a targeted concentrate grade of lower S1O2 content (2.6%) in example B-1 -3 is achieved in comparison to example B-1 -1 with its S1O2 content (2.8%) and > 65% Fe is met in both examples. Example B-1 -2 shows that the comparative etheramine does not work without pregelatinized starch, whereas example B-1 -4 shows without pregelatinized starch even improved results versus example B-1 -3 in regard to S1O2 content (1.8%) and Fe (67.3%).