WO2024099667A1

WO2024099667A1 - Phosphoric acid esters for the beneficiation of magnetic minerals from low-grade ores

Info

Publication number: WO2024099667A1
Application number: PCT/EP2023/078113
Authority: WO
Inventors: Leandro Seixas Bicalho; Nathalia COSTA; Wagner Silva DA SILVA; Matthias Krull
Original assignee: Clariant International Ltd
Priority date: 2022-11-11
Filing date: 2023-10-11
Publication date: 2024-05-16

Abstract

The use of a phosphoric acid ester to improve the recovery rate of iron from an aqueous slurry of a fine-grained crude iron ore comprising an iron ore and a gangue mineral in a magnetic separation process, the phosphoric acid ester comprises a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II), wherein R1 and R2 are identical or different and, independently of one another, are selected from the group consisting of alkyl groups, alkenyl groups, acyl groups, and optionally substituted phenyl groups, having from 6 to 40 carbon atoms; A is an alkylene group having from 2 to 6 carbon atoms; X is hydrogen or a cation with the valence n; n is 1, 2 or 3; and m is 0 or an integer from 1 to 20.

Description

Phosphoric acid esters for the beneficiation of magnetic minerals from low-grade ores

The present invention is directed to the beneficiation of low-grade iron bearing minerals via wet magnetic separation. More particularly, the invention is directed to the enhancement of the magnetic separation process efficiency by the addition of a phosphoric acid ester to the low-grade iron ore.

Due to the high demand for iron oxides that has existed over many decades, sources of high-grade iron ore have become depleted or, in some areas, exhausted. As a result, a great deal of attention is currently given to the development of technologies to recover iron oxides from iron ore containing materials of lower grades. One approach of the mining industry to satisfy the increasing demand for high-grade iron ores is the beneficiation of slimes and low-grade fines.

Most iron ore operations require beneficiation of run-of-mine ore to produce lump, fine (sinter), and pelletizing concentrate iron ore products. For beneficiation of iron ores different methods have been developed as for example gravity concentration, dense medium separation, electrostatic separation, froth flotation, and magnetic separation. Prior to separation of the valuable ore from the gangue minerals, all these processes require comminution of the ore for liberation of the individual minerals. Accordingly, by crushing and grinding the ore is usually comminuted to particles having sizes between about 200 pm and 40 pm. However, grinding processes produce particles having mesh sizes of -20 pm and often even having mesh sizes of -1 pm as a by-product. However, most of the available beneficiation methods provide insufficient efficiency especially when it comes to the processing of minerals comprising a higher portion of ultrafine sized minerals having a particle size of less than 20 pm. Usually, the fractions having particle sizes between 200 pm and 20 pm, which are referred to as fines, can directly be subjected to a beneficiation process like froth flotation or magnetic separation. The fractions comprising more than 30 wt.-% and especially those comprising more than 50 wt.-% of particles having particle sizes of less than 20 pm, which are referred to as ultrafines, is generally separated as slimes and discarded as part of the tailings - even though it often contains a significant amount of iron ore. In the past, recovery of some additional iron ore from ultrafines was considered not to justify the efforts of further processing steps.

Typically, a significant portion of the mined iron ores, that is, 15 - 20 % of run-of- mine ore, ends up as slimes, i. e. as a slurry of ultrafine particles. Currently there is no commercial utilization for the slimes and consequently the only viable option is to dispose them in tailings ponds or tailings dams for water recovery and potential future use.

Furthermore, beneficiation processes generate - besides the valuable iron ore concentrate - huge amounts of fine tailings having particle sizes between 200 pm and 20 pm. Although being enriched in gangue minerals deleterious to iron ore products such as silica, alumina, phosphorus, sulphur, etc., fine tailings still contain a significant amount of iron ore due to the imperfectness of the beneficiation processes. These fine tailings are usually disposed in similar and sometimes in the same tailings ponds as slimes. Accordingly, plenty of iron ore slimes, low-grade iron ore tailings, and mixtures thereof are stored in tailings ponds which occupy land and pose environmental hazards.

In addition, huge amounts of iron-bearing ores have been mined and ground to particulates, but subsequently deemed unsuitable for further processing due to the finding that they include insufficient quantities of iron oxide and/or too high amounts of deleterious materials to make their beneficiation economically feasible. Many tons of such low-grade iron ores have been placed in lean ore stockpiles.

Accordingly, improved methods for beneficiation of iron ore from slimes and tailings as well as from other fine-grained but low-grade iron ore minerals would improve the economics of mining operations and concomitantly reduce their environmental impact and therefore improve the sustainability of the iron and steel industry. Thus, processing and utilization of iron ore slimes, tailings, and other low-grade fines has become a challenging endeavor. One of the processes established in the mining of iron ores is magnetic separation, wherein magnetic substances are separated from non-magnetic gangue or non-magnetic minerals by attraction to a magnet. Magnetic separation technology enables extraction of large volumes of magnetically susceptible iron oxides from low grade mineral assemblages. In commercial magnetic separation units, a moving stream of dry or wet mineral particles passes through a magnetic field.

The major forces acting upon particles in a magnetic separator are magnetic, hydrodynamic drag, gravity, and friction. Each of these forces varies with design of the magnetic separator. While magnetic forces attract ferrimagnetic and paramagnetic particles, gravity and drag forces work against the attracting magnetic forces. For separation of magnetic particles in a wet magnetic separator, magnetic forces must overcome the hydrodynamic drag forces. However, for ultrafine magnetic particles the liquid drag force is usually greater than the magnetic force and especially particles having a size of less than 10 pm are usually not picked up effectively by magnetic separators. On the other hand, for particles having a size above 200 pm gravity prevails and the separation efficiency diminishes as well.

Furthermore, most of the low-grade iron ores, in addition to some magnetite, typically include substantial amounts of iron oxides in the form of hematite, goethite, limonite or other iron oxides, intermingled with gangue minerals. In contrast to magnetite, which is ferrimagnetic, other iron oxides like hematite, goethite, and limonite are paramagnetic and therefore only weakly influenced by magnetic fields. At least in a low intensity magnetic separator, these nonmagnetite iron oxides most often pass into the tailings fraction together with noniron impurities, resulting in loss of valuable iron ore.

The efficiency of magnetic separation can be improved for example by increasing the magnetic field gradient, the field intensity, and/or the particle size. In a process known as wet high-intensity magnetic separation (WHIMS), high-gradient magnetic separators and superconducting magnetic separators are used. This process has proven to be advantageous for the beneficiation of fine magnetic minerals, and to some extent for paramagnetic minerals. In WHIMS processes, beneficiation of magnetite from -10 pm iron ore is possible. However, the energy consumption of high magnetic field separators is high, and the appliances are expensive.

A further means to improve the efficiency of magnetic separation processes is to increase the mineral particles' size. According to Svoboda et al. (Miner. Eng. 16 (2003) 785-792), with increasing particle size the relative importance of the hydrodynamic drag decreases in comparison to the magnetic force. Increase of particle size can be achieved by agglomeration of small particles for example by selective adsorption of a flocculant on the desired particles of the ore suspension. Aggregation by flocculation can be accomplished by the bridging of many mineral particles by addition of a flocculant. Accordingly, WHIMS applied to ultrafine magnetite particles after size enlargement by polymer flocculation was found to be effective in reducing loss of fine magnetite particles.

US 4,219,408 discloses a process of magnetic ore beneficiation in which a dispersed aqueous slurry of the ore is admixed with a system of ferromagnetic seed particles to enhance the magnetic separation process. The aqueous slurry is dispersed by the addition of dispersants such as sodium silicate, sodium hexametaphosphate and sodium polyacrylate/sodium hexametaphosphate.

US 4,298,169 discloses a method of concentrating low-grade ores wherein a finely ground ore is mixed with a flocculating agent to induce selective flocculation of the desired mineral particles on nuclei of ore particles containing residual magnetite. The flocculated ore particles are then subjected to magnetic separation. Examples of materials used to achieve selective flocculation are carbohydrates, such as com starch, potato starch, other natural and modified starches, tapioca flour, other flours, ammonium alginate, carboxymethyl cellulose, cellulose xanthate, and synthetic polymerized flocculants, such as polyethylene oxide, polyacrylamides and polyacrylonitriles having flocculating properties, PAMG (a polyacrylamide modified with glyoxal tris-2-hydroxyaryl), and the like.

S. Song et al. in Minerals Engineering 15 (2002) 415-422 and S. Roy in Mineral Processing & Extractive Metall. Rev., 33: 170-179, 2012 have shown that the magnetic separation of hematite, goethite and limonite fines from iron ores can be considerably improved by selectively aggregating the fines through the hydrophobic flocculation induced by sodium oleate, kerosene and a sufficient kinetic energy input.

CN1 1396591 A teaches a multi-effect novel iron ore reverse flotation inhibitor, characterized in that the multi-effect novel iron ore reverse flotation inhibitor is a starch-chitosan mixture or/and a modified starch-chitosan mixture, and industrial carboxymethyl cellulose.

US 2021/069729 teaches a concentration process of iron minerals ultrafine tailings (slimes) from iron ore processing through reverse flotation with pH between 8.5 and 10.5 with the addition of amide-amine type collector, or further a mixture thereof with traditional cationic collectors (amines), in the absence of any depressant, alternatively including a step of high field magnetic concentration, which allows to obtain a concentrate with iron content higher than 66% and contents of SiO2+AI2O3 below 4%.

WO-2022/225492 teaches an environmentally-friendly biochemical composition for use as an additive into an aqueous medium in order to increase the process efficiency and resulting grade in all gravimetric and magnetic wet ore concentration and classification methods that essentially require the use of water, in the mining industry. The invention particularly relates to a biochemical liquid concentrate composition for use as an additive into the existing process or feed water, and a method of use thereof, comprising a fermentation supernatant obtained from the culture of Saccharomyces cerevisiae, one or more surfactants selected from the group consisting of non-ionic surfactants and anionic surfactants, preferably hydrogen peroxide or chlorine dioxide, and urea-based or other suitable preservatives, which increases the process efficiency and grade recovery, without requiring an additional facility investment, in said ore beneficiation processes.

As the drive towards resource and energy efficient processes becomes more compellent, improved approaches to the processing of iron ore tailings and especially of iron ore slimes and fines are required. Accordingly, there was the need for an improved beneficiating method for fine iron ores and especially of fine iron ores having particle sizes D50 of e. g 200 pm and below as well as for ultrafine iron ores having particle sizes D50 of e. g. 20 pm and below. Because the mass of high-grade iron ore recovered is of salient economic importance for mining operations, a process for the beneficiation of iron ore which allows for the winning of additional quantities of valuable iron ore from the crude ore and/or for an improved recovery rate of the iron contained in the crude ore would be highly appreciated. In parallel, the silicate content of the recovered iron ore concentrate should be reduced or at least be maintained, i. e. the selectivity between iron ore and contaminants, e. g. silicate, should be improved or at least be maintained. Furthermore, the volume of water required for the process should be minimized and its content of contaminants should be as low as possible for final disposal. As a mining plant in day-to-day operations often processes varying types of iron ore minerals in parallel such beneficiation method should work for a variety of different grades of iron ore minerals. Furthermore, the environmental impact of the process should be minimized, e. g. by using additives based on renewable raw materials and/or additives which are biologically degradable.

Surprisingly it has been found that the recovery rate of iron from fine-grained iron ore minerals in a magnetic separation process can be improved by the addition of a phosphoric acid ester to the aqueous slurry of the fine-grained iron ore mineral prior to subjecting the aqueous slurry to the magnetic separation process. This finding is especially valid for fine-grained iron ore minerals of low grade. Concomitantly, the quartz content of the recovered iron ores is reduced or at least maintained. This allows for the winning of additional valuable iron ore from otherwise worthless slimes, tailings and other low-grade fines, that is it allows for an improved mass recovery of iron ore. Unexpectedly, the presence of the surface-active phosphoric acid esters in the concentrated iron ore slurry obtained from the magnetic separation process does not interfere with the subsequent recovery of the iron ore by conventional flocculation and sedimentation methods.

In a first aspect, the instant invention provides the use of a phosphoric acid ester to improve the recovery rate of iron from an aqueous slurry of a fine-grained crude iron ore comprising an iron ore and a gangue mineral in a magnetic separation process, wherein the phosphoric acid ester comprises a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II),

wherein

R¹ and R² are identical or different and, independently of one another, are selected from the group consisting of alkyl groups, alkenyl groups, acyl groups, and optionally substituted phenyl groups, having from 6 to 40 carbon atoms;

A is an alkylene group having from 2 to 6 carbon atoms;

X is hydrogen or a cation with the valence n; n is 1 , 2 or 3; and m is 0 or an integer from 1 to 20.

In a second aspect, the instant invention provides a method of beneficiating an iron ore from a fine-grained crude iron ore comprising iron ore and a gangue mineral wherein: i) the fine-grained crude iron ore comprising iron ore and a gangue mineral is dispersed in an aqueous phase to give an aqueous slurry; ii) said aqueous slurry is mixed with at least one phosphoric acid ester; iii) the treated aqueous slurry is subjected to magnetic separation means to obtain a fraction of the fine-grained iron ore slurry which is enriched in iron ore and depleted in gangue mineral; and iv) a concentrated iron ore is extracted from the fraction of the iron ore slurry being enriched in iron ore.

In a third aspect, the instant invention provides a method of enhancing the mass recovery of iron ore from an aqueous slurry of a fine-grained crude iron ore comprising iron ore and a gangue mineral in a magnetic separation process, wherein a phosphoric acid ester is added to the aqueous slurry prior to subjecting the aqueous slurry to a magnetic separation process, and wherein the addition of the phosphoric acid ester effects the separation of a concentrated iron ore fraction having a raised iron content from a gangue tailings fraction having a reduced iron content, both in respect to the crude iron ore, wherein the phosphoric acid ester comprises a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II),

wherein

A is an alkylene group having from 2 to 6 carbon atoms;

In a fourth aspect, the instant invention provides a method of enhancing the iron recovery rate from an aqueous slurry of a fine-grained crude iron ore comprising iron ore and a gangue mineral in a magnetic separation process, wherein a phosphoric acid ester is added to the aqueous slurry prior to subjecting the aqueous slurry to a magnetic separation process, and wherein the addition of the phosphoric acid ester effects the separation of a concentrated iron ore fraction having a raised iron content from a gangue tailings fraction having a reduced iron content, both in respect to the crude iron ore, wherein the phosphoric acid ester comprises a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II),

wherein

A is an alkylene group having from 2 to 6 carbon atoms;

In the context of this patent application the term “iron ore” refers to the entirety of ferrimagnetic and paramagnetic iron ores which are attracted by a magnet. Especially it refers to oxidic ferrimagnetic and paramagnetic iron ores which are attracted by a magnet. Accordingly, the term “iron ore” encompasses iron oxides and oxyhydroxides, including magnetite, hematite, martite, specularite, goethite, limonite and any mixture thereof. Such iron ores usually contain minor amounts of contaminants as for example silicates. In addition, the term “iron ore” also encompasses oxidic mixed metal iron ores comprising iron and at least one further metal. Preferably, the at least one further metal is a transition metal of the 4^th period of the Periodic Table of Elements. More preferably the at least one further metal is selected from the group consisting of titanium, vanadium, chromium, manganese, zinc, and any combination thereof. Especially preferred further metals are chromium and titanium. Preferred oxidic mixed metal iron ores include but are not limited to titanomagnetites, which form a line of compositions with the formulae Fe3-_xTi_xO4 with 0 < x <1 , and titanohematites including for example ilmenite (FeTiOs). Further oxidic mixed metal iron ores which can be beneficiated by the various aspects of the invention include but are not limited to chromite, franklinite, jacobsite, and any mixtures thereof. Typical contaminants to be removed from oxidic mixed metal iron ores are silicates like quartz, albite, and talc.

The term “iron ore mineral” refers to mineral assemblages comprising iron ore and one or more gangue minerals. This term includes compositions which resemble the mineralogy of the wanted mineral in a low-grade ore deposit as well as the composition of slimes I tailings to be reworked. Similarly, the terms “crude ore” and “crude iron ore” refer to an iron ore mineral which is used as starting material for the various aspects of the present invention. These terms encompass fine iron ore minerals having a particle size D50 of e. g. less than 500 pm, preferably having a particle size D50 of less than 200 pm (“fines”), and more preferably a particle size D50 of less than 106 pm, and ultrafine iron ore minerals having a particle size D50 of e. g. 20 pm and below (“ultrafines”), including slimes. Similarly, the terms “iron ore mineral”, “crude ore”, and “crude iron ore” encompass mixtures of fines with ultrafines in any ratio. Preferred mixtures comprise fines and ultrafines in a weight ratio of from 1 :99 to 99:1 , and more preferably in weight a ratio of from 5:95 to 95:5, as for example in a weight ratio of from 1 :95 to 99:1 , or from 1 :99 to 95:1 . Accordingly, these terms encompass mixtures of fines and ultrafines resulting from storage of slimes and tailings in the same tailings pond.

In the context of this patent application the term “mass recovery” means the percentage of concentrated iron ore in relation to the total mass of the crude iron ore. The mass recovery Y can be calculated by the formula y = £ * 100 100 , F

wherein

C = dry mass of concentrate from magnetic separation;

F = dry mass of crude ore fed to magnetic separation; f = feed Fe content; c = concentrate Fe content; and r = tailings Fe content. In the context of this patent application the term "iron recovery rate" means the weight ratio of the iron recovered in the concentrated iron ore obtained from the magnetic separation process in relation to the iron content of the crude iron ore. The terms “enhanced recovery rate”, “improved recovery rate” as well as “enhancing the magnetic separation of iron ores from gangue mineral" mean a higher recovery rate of iron obtained in a magnetic separation process including the features of this invention (i. e. in the presence of a phosphoric acid ester) in comparison to the same process conducted without the features of this invention (i. e. absent a phosphoric acid ester).

The iron recovery rate can be calculated by the formula

In the context of this patent application, the term “gangue mineral” refers to a variety of minerals which surround or are closely mixed with the wanted iron ore in the crude iron ore mineral. This includes silica, alumina, phosphorus and sulphur in different forms. While the valuable iron ores are ferrimagnetic or paramagnetic and therefore attracted by a magnet, most of the gangue minerals are diamagnetic and therefore have an inherently low magnetic attractability.

The terms "beneficiate", "beneficiation", and "beneficiated" refer to an ore enrichment process in which the concentration of the desired metal in the ore increases as the process proceeds.

For purposes of the present disclosure, the terms "low-grade iron ore" and “low-grade iron bearing mineral” refer to materials which are composed of a mixture of one or more iron ores and substantial amounts of one or more non-iron mineral impurities, commonly one or more of quartz, chert, alumina, carbonate, or the like.

For iron ores comprising iron essentially in the form of an oxide or oxyhydroxide, low-grade iron ore means an iron content of from 10 to 53 wt.-% and preferably from 15 to 50 wt.-% as for example from 10 to 50 wt.-%, or from 15 to 53 wt.-%. For oxidic mixed metal iron ores comprising iron and a further metal, and specifically comprising iron and a further transition metal of the 4^th period of the Periodic Table of Elements, low grade iron ore means a content of iron and the further metal of from 10 to 53 wt.-% and preferably from 15 to 50 wt.-% as for example from 10 to 50 wt.-%, or from 15 to 53 wt.-%.

"Low-grade iron ores" and “low-grade iron bearing minerals” include tailings and stockpiled lean ores, together with lean ores in their natural state (i.e., unmined and/or unground), whether or not they include some amount of magnetite, and whether they include hematite, goethite, iron oxides other than hematite and goethite, or both. One example of a low-grade iron ore material is the iron ore commonly referred to as taconite, an iron-bearing sedimentary rock, typically having an iron oxide content of from about 15% to about 40% and only part of it being magnetite, with the balance being non-iron impurities.

In the context of this patent application, the term “fine-grained” means a particle size D50 of less than 500 pm, preferably a particle size D50 of less than 200 pm, more preferably a particle size D50 of less than 106 pm and especially a particle size D50 of less than 20 pm. The particle size D50 represents the medium value of the particle size distribution (D50; median diameter), that is the diameter of the particles that 50 wt.-% of a sample's mass is smaller than and 50 wt.-% of a sample's mass is larger than. The particle size distribution can be determined for example by laser diffraction according to ASTM B822-10, a technique based on analysis of the diffraction pattern produced when particles are exposed to a beam of monochromatic light.

In a preferred embodiment, R¹ and R² independently from another are an alkyl, alkenyl or acyl group having from 6 to 24 and especially preferred from 8 to 18 carbon atoms as for example from 6 to 18 carbon atoms, or from 8 to 40 carbon atoms, or from 8 to 24 carbon atoms. R¹ and R² may be the same or different. In a preferred embodiment, both are the same. Preferred phosphoric acid esters of formulae (I) and (II) may be obtained by the reaction of a phosphating agent with an alcohol. Alcohols which are suited for synthesizing the phosphate esters of formulae (I) and/or (II), include fatty alcohols, fatty alcohol alkoxylates, and fatty acid alkoxylates.

Typically, the phosphating agent is an activated phosphorous derivative. The thus obtained phosphoric acid ester products are mixtures of monoalkyl phosphate (monoester), dialkyl phosphate (diester), and trialkyl phosphate (triester) in varying amounts. The reaction products often contain minor amounts of residual alcohol and residual phosphoric acid respectively its activated derivative. The share of the phosphoric acid ester in monoester, diester and triester products can be controlled for example by the molar ratio of the reactants. In a preferred embodiment, the reaction product of an alcohol with an activated phosphorous derivative is used as such, i. e. without further purification.

In a preferred embodiment, the molar ratio of phosphoric acid monoester (I) to phosphoric acid diester (II) is from 1 :10 to 10:1 . More preferably, the molar ratio is from 1 :5 to 5:1 , as for example from 1 :5 to 10:1 , or from 10:1 to 1 :5. In a further preferred embodiment, the share of mono- and diester in a phosphoric acid ester reaction product is at least 50 mol-%, more preferably from 60 to 99 mol-% and especially preferred between 65 and 95 mol-%, as for example from 50 to 95 mol-%, or from 50 to 99 mol-%, or from 60 to 95 mol-%, or from 65 to 99 mol-%, based on all phosphoric acid esters present. In a further preferred embodiment, the share of phosphoric acid triester is preferably below 40 mol-%, more preferably from 0.1 to 25 mol-% and especially preferred from 1 to 10 mol-% as for example from 0.1 to 40 mol-%, or from 0.1 to 25 mol-%, or from 1 to 40 mol-%, or from 1 to 25 mol-%, based on all phosphoric acid esters present.

The most common phosphating agents used for the synthesis of phosphoric acid esters are phosphoric anhydride (P2O5), polyphosphoric acid (H4P2O7), phosphorus oxychloride [P(O)Cl3], orthophosphoric acid (H3PO4) and pyrophosphoric acid. Preferably, the molar ratio between phosphating agent and alcohol is between 1 :0.5 and 1 :4, more preferably between 1 :1 and 1 :2, based on the phosphorous content of the phosphating agent. Means for manufacturing of phosphoric acid esters are known to those skilled in the art.

In a first embodiment, R¹ and R² are alkyl or alkenyl groups, and m is 0. Such esters are derived from fatty alcohols. Preferred fatty alcohols have the general formulae R³-OH and R⁴-OH wherein R³ and R⁴ are identical or different and, independently of one another, are selected from alkyl and alkenyl groups having from 6 to 40 carbon atoms, more preferably having from 6 to 24 carbon atoms and especially preferred having from 8 to 18 carbon atoms as for example from 6 to 18 carbon atoms, or from 8 to 40 carbon atoms, or from 8 to 24 carbon atoms. Preferred fatty alcohols of formulae R³-OH and R⁴-OH may be of synthetic or natural origin.

Preferred fatty alcohols of the general formulae R³-OH and R⁴-OH may be primary, secondary, tertiary alcohols or mixtures thereof, i. e. the alcoholic hydroxy group, -OH, may be attached to a saturated carbon atom which has one (primary alcohol), two (secondary alcohol) or three (tertiary alcohol) other carbon atoms attached to it. In a preferred embodiment, the alcohol is a primary alcohol.

In a preferred embodiment the fatty alcohols R³-OH and R⁴-OH are of natural origin. Preferred alcohols of natural origin are caproic alcohol, caprylic alcohol, capric alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, linolyl alcohol, linolenyl alcohol, elaeostearyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol, brassidyl alcohol, and mixtures thereof. They may be derived from oils and fats by hydrolysis and subsequent reduction of the so obtained fatty acids. More preferred fatty alcohols may be derived for example from coconut oil, soy oil, sunflower oil, palm oil, palm kernel oil, tallow fat, olive oil, rice oil, com oil, peanut oil, and mixtures thereof.

In a further preferred embodiment, the fatty alcohols R³-OH and R⁴-OH are synthetic. Preferred synthetic fatty alcohols may be derived from oligomers of lower olefins having 2 to 5 carbon atoms and preferably having from 2 to 4 carbon atoms as for example from ethylene, propylene, and butylene. Examples for preferred lower olefin oligomers are essentially linear a-olefins having from 4 to 20, more preferably from 6 to 24 and especially preferred from 8 to 18 carbon atoms, tripropylene, tetrapropylene, pentapropylene, diisobutylene, tributylene, triisobutylene, tetrabutylene, tetraisobutylene, pentapropylene and the like. Methods to convert alkenes to alcohols are known to those skilled in the art. Further examples of synthetic alcohols having branched alkyl radicals include hexanol, 2-ethylhexanol, 4-methylpentan-2-ol, octan-2-ol, 6-methylheptan-3-ol, n-nonanol, iso-nonanol, 2,6-dimethyl heptan-4-ol, 2-propylheptanol, iso-decanol, undecanol, 2,6,8-trimethyl-4-nonanol, iso-tridecanol, iso-heptadecanol, and the like.

In a further preferred embodiment, R¹ and R² independently from each other is an acyl group and m is an integer from 1 to 20. In this embodiment, the alcohol used for synthesizing the phosphate esters of formulae (I) and/or (II), is a fatty acid alkoxylate. Preferred acyl groups R¹ and R² have the general formulae R⁵-C(O)- and R⁶-C(O)- wherein R⁵ and R⁶ are identical or different and, independently of each other, are selected from alkyl or alkenyl groups having from 5 to 39, more preferably from 5 to 23 and especially preferred from 7 to 17 carbon atoms, as for example from 5 to 17 carbon atoms, or from 7 to 39 carbon atoms, or from 7 to 23 carbon atoms.

Preferred acyl groups R⁵-C(O)- and R⁶-C(O)- are derived from fatty acids. Preferred fatty acids may be of synthetic or natural origin. Preferred fatty acids of natural origin include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, arachidic acid, elaidic acid, petroselinic acid, linolic acid, linolenic acid, eleostearic acid, arachidonic acid, gadoleic acid, behenic acid, erucic acid, brassidic acid, and mixtures thereof. They may be derived from oils and fats by hydrolysis. More preferred fatty acids may be derived for example from coconut oil, soy oil, sunflower oil, palm oil, palm kernel oil, tallow fat, olive oil, rice oil, com oil, peanut oil. Synthetic fatty acids are similarly suited. Examples for synthetic fatty acids are branched fatty acids like isoundecanoic acid, isotridecanoic acid, versatic acids, and mixtures thereof.

Preferred alkyl and alkenyl groups R³ and R⁴ of fatty alcohols and fatty alcohol alkoxylates as well as alkyl and alkenyl groups R⁵ and R⁶ of fatty acid alkoxylates may be linear, branched, or cyclic. In a first preferred embodiment, the alkyl and alkenyl groups of fatty alcohols and fatty acids of natural origin are predominantly linear. In a second preferred embodiment, the alkyl groups of synthetic fatty alcohols and fatty acids are predominantly branched. Preferred alkenyl groups have one, two or three C=C double bonds. More preferred alkenyl groups have one C=C double bond.

In a further preferred embodiment, the alcohol used for manufacturing of the phosphoric acid esters of formulae (I) and (II) is an alkoxylated fatty alcohol. Preferred alkoxylated fatty alcohols have the general formulae R³-[O-A]_m-OH and R⁴-[O-A]_m-OH wherein R³, R⁴, A and m have the meanings given above. They may be derived from a fatty alcohol of formula R³-OH or R⁴-OH by alkoxylation.

In a further preferred embodiment, R¹ and R² independently from each other is an optionally substituted phenyl group and m is an integer from 1 to 20. In this embodiment, the alcohol used for synthesizing the phosphate esters of formulae (I) and/or (II), is the alkoxylate of an optionally substituted phenol. Preferred optionally substituted aryl groups have the general formulae R⁷-OH and R⁸-OH wherein R⁷ and R⁸ are identical or different and, independently of each other, are selected from phenol and phenol substituted with one or more, as for example 1 , 2 or 3 substituents. R⁷ and R⁸ have from 6 to 40 carbon atoms, more preferably from 6 to 24 carbon atoms and especially preferred from 8 to 18 carbon atoms as for example from 6 to 18 carbon atoms, or from 8 to 40 carbon atoms, or from 8 to 24 carbon atoms. Preferred substituents of the aryl group are alkyl, alkenyl, alkylphenyl and alkenylphenyl groups. In a preferred embodiment, alkyl substituents have from 1 to 36, preferably from 2 to 20 and especially preferred from 4 to 14 carbon atoms, as for example from 1 to 20 carbon atoms, or from 1 to 18 carbon atoms, or from 2 to 36 carbon atoms, or from 2 to 14 carbon atoms, or from 4 to 36 carbon atoms, or from 4 to 20 carbon atoms. The alkyl groups may be linear or if they contain 3 or more carbon atoms, they may be branched. Preferred alkyl phenols of formulae R⁷-OH and R⁸-OH have one alkyl group per phenol. An example for a phenol being substituted by an alkenylphenyl group is tristyrylphenol.

In a further preferred embodiment, the phosphoric acid ester of formulae (I) and/or (II) comprises a mixture of different esters derived from at least two different alcohols selected from the groups of fatty alcohols of formulae R³-OH and/or R⁴-OH; fatty alcohol alkoxylates of formulae R³[-OA]_m-OH and/or R⁴[-OA]_m-OH; fatty acid alkoxylates of general formulae R⁵-C(O)-[-OA]_m-OH and /or R⁶-C(O)-[-OA]_m-OH; and optionally substituted alkoxylated phenols of general formulae R⁷[-OA]_m-OH and/or R⁸[-OA]_m-OH. The portion of each ester in the mixture maybe from 1 to 99 mol-%, preferably from 5 to 95 mol-% and especially preferred from 10 to 90 mol-%, as for example from 1 to 95 mol-%, or from 1 to 90 mol-%, or from 5 to 99 mol-%, or from 5 to 90 mol-%, or from 10 to 99 mol-%, or from 10 to 95 mol-%.

In a preferred embodiment, A is an alkylene group having 2 or 3 carbon atoms and especially preferred having 2 carbon atoms. Accordingly, preferred alkoxylates may be ethoxylates, propoxylates and their mixtures. The degree of alkoxylation is given by the index m.

In a preferred embodiment, m is an integer from 1 to 20, more preferably from 2 to 15 and especially preferred from 3 to 10 as for example from 1 to 15, or from 1 to 10, or from 2 to 20, or from 2 to 10, or from 3 to 20, or from 3 to 15. In this embodiment, the phosphoric acid ester of formulae (I) and/or (II) may be the reaction product of a phosphating agent and an alkoxylated fatty alcohol or an alkoxylated fatty acid.

In a first preferred embodiment, X is hydrogen and n is 1 . This refers to partial esters of phosphoric acid having one or two acid groups. In a further preferred embodiment, the cation Xⁿ⁺ in formulae (I) and (II) is selected from metal ions, NH₄ ⁺ and organic ammonium ions derived from amines and/or alkanolamines. Preferably, n is 1 or 2 and especially preferred n is 1 . Preferred metal ions are alkaline and earth alkaline metal ions, in particular Na⁺, K⁺, Ca²⁺, and Mg²⁺. Preferred organic ammonium salts are derived from primary and secondary alkyl amines having from 1 to 30 carbon atoms and especially preferred having from 4 to 22 carbon atoms. Further preferred amines are alkanolamines as for example monoethanolamine, diethanolamine and triethanolamine. Especially preferred cations are hydrogen, Na⁺, K⁺ and NH₄ ⁺.

Preferably, the amount of phosphoric acid ester added to the aqueous iron ore slurry in the various aspects of the invention is from 1 ppm to 5,000 ppm in respect to the mass of the crude iron ore, more preferably from 10 to 1 ,000 ppm and especially preferred from 20 to 500 ppm, as for example from 1 to 1 ,000 ppm, or from 1 to 500 ppm, or from 10 to 5,000 ppm, or from 10 to 500 ppm, or from 20 to 5,000 ppm, or from 20 to 1 ,000 ppm.

In the context of the present disclosure, the term “aqueous phase” encompasses distilled water, fresh water, tap water, recycled process water, brackish water, and the like. The aqueous phase functions as the continuous phase of the aqueous slurry. Preferably the aqueous phase represents from 20 to 90 percent by weight and more preferably from 30 to 70 percent by weight of the aqueous slurry which is subjected to magnetic separation. Accordingly, in a preferred embodiment the aqueous slurry contains from 80 to 20 wt.-% and more preferably from 70 to 30 wt.-% of solids when being subjected to magnetic separation.

The aqueous phase may contain dissolved inorganic and/or organic salts. Salts may be added intentionally, or they may be dissolved from the minerals. Preferred inorganic salts comprise a cation of one or more alkaline metals, alkaline earth metals, main group metals and transition metals. Preferred anions are halogenides, like chloride, bromide, and iodide, sulfate, carbonate, nitrate, phosphate, and the like. In a preferred embodiment the aqueous phase contains one or more of NaCI, Na2CO3, NaHCOs, KCI, KHCO3, K2CO3, MgCk, CaCl2. In a further preferred embodiment, the aqueous phase contains at least one further additive e. g. for controlling bacterial growth, lowering the freezing point, dispersing fines and/or ultrafines, selectively precipitating ions, and the like.

The pH of the aqueous slurry may vary over a wide range. In preferred embodiments, the pH of the aqueous slurry is from 6 to 11 and more preferred from 6.5 to 10 and especially preferred from 7 to 9 as for example from 6 to 10, or from 6 to 9, or from 6.5 to 11 , or from 6.5 to 9, or from 7 to 11 , or from 7 to 10. If necessary, the pH of the aqueous slurry may be adjusted by the addition of acid or base. The pH may be lowered, if necessary, by addition of an acid as for example HCI, H2SO4, HNO3, H3PO4, and the like. The pH of the aqueous phase may be raised, if necessary, by the addition of a base as for example NaOH, Na2COs, KOH, K2CO3, ammonium hydroxide, sodium silicate, and the like.

The different aspects of the invention are especially advantageous for the beneficiation of fine-grained iron ores like slimes and other fines. However, more coarse-grained ore materials may be treated as well, but they may require further comminution to optimize iron oxide recovery. It is evident that in the separation of any ore by magnetic or other forces, the ore must be crushed and ground sufficiently fine to free the valuable minerals from the gangue, and also that the degree of fineness required in the crushing and grinding process depends upon the physical characteristics of the ore.

The various aspects of the present invention are especially advantageous in wet magnetic separation processes. In wet magnetic separation processes an aqueous slurry of a ground mineral is subjected to a magnetic field. This is accomplished by flowing a stream of the aqueous slurry of the fine-grained mineral over a magnetic surface. The gangue is washed from the magnetic surface and discarded. The retained magnetic minerals are recovered and concentrated by removal from the magnetic surface. Where desired, the magnetically separated concentrate may be further concentrated by conventional beneficiation methods. Commercial magnetic separation units apply continuous separation processes on a moving stream of particles passing through a low or high magnetic field. A variety of different wet magnetic separators are known and commercially available, for example drum, cross-belt, roll, high-gradient magnetic separation (HGMS), high-intensity magnetic separation (HIMS) and low-intensity magnetic separation (LIMS) types. A drum separator consists of a nonmagnetic drum fitted with three to six permanent magnets. It is composed of ceramic or rare earth magnetic alloys in the inner periphery. The drum rotates at uniform motion over a moving stream of wet feed. The magnetic minerals are picked up by the rotating magnets and pinned to the outer surface of the drum. As the drum moves up the concentrate is compressed, dewatered and discharged leaving the gangue in the tailing compartment. More specialized separators used in heavy media plants today are for example, con-current single drum wet magnetic separator, counter-current single drum wet magnetic separators and double drum separators.

For separation by magnetic separation the fine-grained particulate mineral assemblage is suspended in an aqueous phase. The resulting aqueous slurry is passed through a magnetic separator that produces a sufficiently high intensity magnetic field, to separate the mineral assemblage into a concentrate fraction having a higher iron oxide concentration than the mineral assemblage and a tailings fraction having a lower iron oxide concentration than the mineral assemblage. Due to the strong magnetic field that is necessary to influence the trajectories of iron oxides that are only weakly susceptible to magnetic fields, and the need to suspend the low-grade mineral assemblages in water to form a slurry before passage through the magnetic field, devices that are used in this type of process have come to be referred to as wet high-intensity magnetic separation devices, or WHIMS devices.

In a preferred embodiment, the magnetic field intensity used for the magnetic separation process is from 0.5 T to 3.0 T, more preferred from 0.8 T to 2.0 T and especially preferred from 1 .0 T to 1 .8 T.

By the method according to the third aspect of the invention the mass recovery of iron ore is raised preferably by at least 1 wt.-% over the mass recovery obtained in the same process in absence of the phosphoric acid ester. More preferably, the mass recovery of iron ore is raised by at least 2.5 wt.-% and especially preferred by at least 4 wt.-% over the recovery rate obtained in the same process in absence of the phosphoric acid ester.

By the method according to the fourth aspect of the invention the iron recovery rate is raised preferably by at least 1 wt.-% over the iron recovery rate obtained in the same process in absence of the phosphoric acid ester. More preferably, the iron recovery rate is raised by at least 2.5 wt.-% and especially preferred by at least 4 wt.-% over the iron recovery rate obtained in the same process in absence of the phosphoric acid ester.

Usually, the iron ore concentrate fraction obtained from the magnetic separation process is an aqueous or at least wet slurry. To obtain a marketable dry iron ore concentrate, dewatering or solid/liquid separation is required. Dewatering may be accomplished by successive stages of (1 ) sedimentation or thickening, (2) filtration, and (3) thermal drying. In a preferred embodiment, flocculants are added to the aqueous slurry to facilitate the solid/liquid separation and to speed up water clarification. Examples for preferred flocculants are aluminium polychloride and ferric chloride.

Sedimentation or thickening may be made by natural gravity settling of the solid portion of the concentrated slurry. This may take place by continuously feeding the slurry into a cylindrical thickening tank. Upon sedimentation, a clear liquid overflows out of the tank and a thickened pulp that settles at the bottom is taken out as underflow. The effectiveness of the thickening process can be assessed by the solids content of the underflow and/or the turbidity of the overflow. A good separation result is indicated by a high solids content of the underflow and a low turbidity in the overflow. Often, a turbidity of the overflow below 200 NTU (Nephelometric Turbidity Units) and especially below 100 NTU is considered to be a satisfactory separation which allows the overflow to be reused in mining processes like comminution and/or beneficiation. The turbidity can be determined by nephelometry with a turbidimeter according to EPA method 180.1 , or according to ISO 7027. These methods determine the concentration of suspended particles in a sample of water by measuring the intensity of incident light scattered at right angles (90°). The scattered light is captured by a photodiode, which produces an electronic signal that is converted to a turbidity value and converted into NTUs by comparison with the intensity of light scattered by a standard reference slurry or a standard reference suspension. The higher the intensity of scattered light, the higher the turbidity.

In a preferred embodiment, a flocculant is added to the concentrated iron ore fraction obtained from the magnetic separation process to accelerate the sedimentation process. As many flocculants are amphiphilic compounds (surfactants) their presence may interfere with the sedimentation of solids and give rise to a highly turbid overflow. Surprisingly, the presence of a phosphoric acid ester according to the invention in the concentrated iron ore fraction does not interfere with the sedimentation process. Often, the presence of a phosphoric acid ester according to the invention even facilitates the sedimentation process, i. e. it further accelerates sedimentation.

The different aspects of the invention are especially advantageous for the beneficiation of paramagnetic iron oxides like hematite and goethite as well as for the beneficiation of oxidic mixed metal iron ores like ilmenite and chromite from fine-grained iron ore minerals. Likewise, the different aspects of the invention are especially advantageous for the beneficiation of paramagnetic iron ores having a medium value of the particle size distribution D50 of less than 500 pm, preferably having a D50 of less 200 pm, more preferably having a D50 of less than 106 pm and especially for those having a D50 of 20 pm and less. Likewise, they are advantageous for the beneficiation of paramagnetic iron ores comprising more than 25 wt.-%, often also for the beneficiation of paramagnetic iron ores comprising more than 40 wt.-% and sometimes also for paramagnetic iron ores comprising even more than 50 wt.-% of particles having a size smaller than 20 pm.

As will be appreciated by a person of ordinary skill in the art, the term "separated as used herein is not intended to require complete separation of iron oxides from gangue materials. The term rather refers to the separation of a fine-grained low-grade iron ore mineral into a fraction having a higher concentration of iron oxides and a lower concentration of gangue materials (referred to herein as a "concentrate fraction") and a fraction having a lower concentration of iron oxides and a higher concentration of gangue materials (referred to herein as a "tailings fraction"), both in respect to the composition of the initial fine-grained low-grade iron ore mineral. In a preferred embodiment, the recovered concentrate fraction has an iron content at least 1 wt.-%, more preferably at least 7 wt.-% and especially preferred at least 12 wt.-% higher than the initial fine-grained mineral.

In a further preferred embodiment, the phosphoric acid ester according to the invention may be used in combination with a fatty acid or a fatty acid salt. Similarly, the methods according to the second, third and fourth aspect of the invention may be practiced in the presence of a fatty acid in addition to the phosphoric acid ester. Often, this gives rise to a synergistic enhancement of the mass recovery of iron ore and/or the iron recovery rate. This may be accomplished by the use of a concentrate comprising the phosphoric acid ester and a fatty acid. Alternatively, phosphoric acid ester and fatty acid may be added to the mineral slurry separate from each other but prior to the magnetic separation process.

Preferred fatty acids for further enhancement of the mass recovery of iron ore and/or the iron recovery rate have from 6 to 36 and more preferably from 10 to 24 carbon atoms. Examples of fatty acids include caproic acid, caprylic acid, neononanoic acid, capric acid, neodecanoic acid, lauric acid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, arachidic acid, elaidic acid, petroselinic acid, linolic acid, linolenic acid, eleostearic acid, arachidonic acid, gadoleic acid, behenic acid, erucic acid, brassidic acid, and mixtures thereof. More preferred fatty acids and especially fatty acid mixtures may be derived from plant or animal-based triglycerides such as, for example from coconut oil, soy oil, sunflower oil, palm oil, palm kernel oil, tallow fat, olive oil, rice oil, com oil, peanut oil, and mixtures thereof. Preferred fatty acids may be derived from oils and fats by hydrolysis. Synthetic fatty acids are similarly suited. Examples for synthetic fatty acids are the same as listed above but being obtained via a synthetic route as for example by oligomerization of lower olefins like ethylene, propylene and/or butylene and subsequent oxidation of the so obtained oligoolefin. Further examples for preferred fatty acids are neo acids as for example neononanoic acid and neodecanoic acid which are highly branched synthetic trialkyl acetic acids and also known as versatic acids.

In a preferred embodiment, phosphoric acid ester and fatty acid are used in a weight ratio of from 1 : 10 to 10: 1 and more preferred in a weight ratio of from 1 :5 to 5:1.

In a further preferred embodiment, the phosphoric acid ester is used in combination with a water-immiscible organic solvent. Similarly, the methods according to the second, third and fourth aspect of the invention may be practiced in the presence of a water-immiscible organic solvent. Often the presence of a water-immiscible organic solvent has proven to further enhance the mass recovery of iron ore and/or the iron recovery rate. Particularly useful water-immiscible organic solvents are aliphatic, aromatic and alkylaromatic hydrocarbons and mixtures thereof. Preferred solvents do not contain any polar groups in the molecule. Examples of suitable solvents are decane, toluene, ethylbenzene, xylene, diethylbenzene, trimethylbenzene, naphthalene, tetralin, decalin, and commercial solvent mixtures such as Shellsol®, Exxsol®, Isopar®, Solvesso® types, and/or kerosene. In preferred embodiments, the water-immiscible solvent comprises at most 50 % by weight, preferably at most 10 % by weight, and especially preferred at most 5 % by weight, of aromatic components.

The water-immiscible organic solvent may be used as part of a concentrated additive comprising the phosphoric acid ester and the water-immiscible organic solvent. In this embodiment the presence of a water-immiscible organic solvent reduces the viscosity of the phosphoric acid ester and facilitates its handling and its spreading in the aqueous slurry of the fine-grained mineral. Alternatively, phosphoric acid ester and water-immiscible organic solvent may be added separately to the aqueous slurry of the fine-grained mineral prior to the magnetic separation process. Preferably, the phosphoric acid ester and water-immiscible organic solvent are used in a weight ratio of from 1 :20 to 10:1 and more preferred in a weight ratio of from 1 : 10 to 5: 1 . In an especially preferred embodiment the magnetic separation process is conducted in absence of a water-immiscible organic solvent.

Optionally, a dispersant may further be added to the aqueous slurry prior to magnetic separation to support dispersion of the mineral assemblage and to further improve the efficiency of the magnetic separation process. Dispersants such as tannins, lignin sulphonates, and alkaline phosphates may provide a more stable and less-settling slurry. Further preferred dispersants are sodium silicate, sodium hexametaphosphate, sodium polyacrylate and mixtures thereof. A further preferred dispersant is a mixture of caustic soda and sodium silicate. When a dispersant is added, its concentration is preferably from 1 to 5,000 ppm by weight based on the mass of the crude iron ore. In a preferred embodiment, the beneficiation process is conducted in the absence of a further dispersant.

The addition of a phosphate ester to the aqueous slurry of a fine-grained iron ore according to the present invention results in a raised mass recovery of iron ore from an aqueous slurry of a fine-grained mineral comprising iron ore in a magnetic separation process. This is accompanied by a high selectivity in removal of silicate. Accordingly, the presence of the phosphoric acid ester allows for the winning of additional amounts of valuable iron ore with high iron content from previously unexploited minerals and similarly from landfill tailings. In parallel, the mass of tailings to be disposed is reduced. The various advantages of the present invention are applicable over wide variations in the specific types of iron ore encountered in day-to-day mining operations.

The observed iron recovery rates are also superior to those obtained with fatty acids which are used according to the state of the art. In addition, the use of a phosphate ester according to the present invention results in an improved separation of the concentrated fine-grained iron ore from the aqueous slurry obtained upon a magnetic separation process. Accordingly, less solids remain suspended in the aqueous phase and in consequence, the water can easily be treated for disposal or be reused in the beneficiation process.

EXAMPLES:

The additive compositions according to table 1 were tested on laboratory scale in a SLon-100 Cycle Pulsating High Gradient Magnetic Separator. The iron ore samples used for this study were characterized in terms of chemical analysis and particle size analysis with the results given in table 2 (hereinafter also referred to as crude iron ores).

The content of SiO2 in the ores was determined by a gravimetric method. The ore was decomposed by an acid attack (HCI) leading to the dissolution of metal oxides and metal hydroxides and leaving insoluble SiO2 as the residue.

The iron content of the ores was determined by a titration method wherein the sample was decomposed by an acid attack (HCI), trivalent iron was reduced to bivalent iron by addition of stannous chloride (SnCk) and mercury chloride (HgCk) and the iron content was determined by titration with potassium dichromate (K₂Cr₂O₇).

The particle size distribution was determined by laser diffraction according to ASTM B822-10, which is the method to be applied in general for all particle size distributions referenced in this patent document. The results of these analyses are given in table 2 below. P80 represents the diameter of openings of a sieve through which eighty percent of the particles will pass; D50 represents the medium value of the particle size distribution (median diameter), that is the diameter of the particles that 50 wt.-% of the sample's mass is smaller than and 50 wt.-% of the sample's mass is larger than; % -38 pm represents the percentage of particles smaller than 38 pm; % -20 pm represents the percentage of particles smaller than 20 pm; % -10 pm represents the percentage of particles smaller than 10 pm. The mineralogy was determined by X-ray diffraction following Bragg's law. Analysis by X-ray diffraction allows mineral identification through the characterization of its crystalline structure. The results of this analysis are given in the table 2 below.

The turbidity of the overflows was determined by nephelometry with a Hach 2100Q Portable Turbidimeter (EPA) according to EPA method 180.1. The intensity of incident light scattered by the particles present in the sample was measured at right angles (90°) to the path of the incident light. The calibration of the turbidimeter allowed for a measuring range of from 0 to 1000 NTU (FNU).

All percent values refer to percent by weight if not stated otherwise.

Table 1 : Phosphoric esters used

Table 2: Characterization of crude iron ores used for beneficiation by magnetic separation. Iron ores A and B contain a major proportion of slimes; iron ore C contains mainly fine tailings)

n. d. =not determined

For the magnetic separation tests the Slon-100 Cycle Pulsating High Gradient

Magnetic Separator was adjusted to a pulsation of 100 rpm and a magnetic field intensity of 10,000 G (1 T). The pulsation was started and the water flow on the feed of the magnetic separation was adjust to a flow rate to 14 L/min. The crude ore slurry was prepared as follows: 200 grams of the respective crude iron ore were suspended in tap water to give a slurry with 54 wt.-% solids content. As the pH of the pulp was in the range of from 7.0 to 7.5 further adjustment was not required. An additive according to tables 3 to 5 was added to the pulp. The dosage rates given in tables 3 to 5 refer to the mass of additive per mass of the dry crude iron ore. The slurry was conditioned with the additive for 3 minutes and then charged to the magnetic separator feed.

The nonmagnetic mass (tailings) and the magnetic mass (concentrated iron ore) were collected in separate bowls and dried in a lab oven. Both samples (magnetic and nonmagnetic) were then analyzed in respect to weight, SiO2 content and iron content according to the methods described above. The flowchart of the process is represented in figure 1 .

The results are given in terms of the following parameters:

Mass recovery (wt.-%): percentage of concentrated iron ore (magnetic) in relation to the total mass of crude iron ore. The mass recovery Y can be calculated by the formula y = £ * 100 100 , F

wherein

C = dry mass of concentrate from magnetic separation;

F = dry mass of crude ore fed to magnetic separation; f = feed Fe content; c = concentrate Fe content; and r = tailings Fe content.

Iron Recovery Rate (wt.-%): percentage of Fe in the crude ore that is recovered by the concentration process (magnetic mass). The Fe recovery can be calculated by the formula

SiO2 content (wt.-%): content of SiO2 present in the concentrated iron ore (magnetic mass).

Fe content (wt.-%): content of Fe present in the concentrated iron ore (magnetic mass).

Table 3: Results of magnetic separation trials on iron ore A

Table 4: Results of magnetic separation trials on iron ore B

Table 5: Results of magnetic separation trials on iron ore C

For the evaluation of potential side effects of the beneficiation of fine-grained iron ores in the presence of a phosphoric acid ester the magnetic concentrates obtained from the magnetic separation trials were subjected to a sedimentation process. Therefore, 1 ,000 mL of iron ore pulp (magnetic fraction) comprising

10 wt.-% of solids and the residual additive were transferred into a graduated cylinder. It was added 60 g/t of ore of an anionic polyacrylamide as flocculant. The pulp was mixed with the flocculant seven times. Immediately after the last movement a chronometer was started. After 1 hour the turbidity of the overflow was measured. The results are given in Tables 6 to 8.

Table 6: Turbidity of the overflow after 1 hour sedimentation (iron ore A)

Table 7: Turbidity of the overflow after 1 hour sedimentation (iron ore B)

Table 8: Turbidity of the overflow after 1 hour sedimentation (iron ore C)

The experimental results show that the recovery rate of iron from an aqueous slurry of fine-grained mineral comprising iron ore in a magnetic separation process is improved in the presence of phosphoric acid esters. Additional valuable iron ore with high iron content is obtained and besides, the mass of tailings is reduced.

Furthermore, in comparison to fatty acids which have been used according to the state of the art, separation of the concentrated fine-grained iron ore is improved as shown by significantly reduced turbidity of the overflow obtained from the magnetic separation process. Accordingly, less solids remains suspended in the aqueous phase and in consequence, the water can be reused in the process.

Claims

Patent claims

1 . The use of a phosphoric acid ester to improve the recovery rate of iron from an aqueous slurry of a fine-grained crude iron ore comprising an iron ore and a gangue mineral in a magnetic separation process, wherein the phosphoric acid ester is a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II),

wherein

R¹ and R² are identical or different and, independently of one another, are selected from the group consisting of alkyl groups, alkenyl groups, acyl groups and optionally substituted aryl groups having from 6 to 40 carbon atoms;

A is an alkylene group having from 2 to 6 carbon atoms;

2. The use according to claim 1 , wherein R¹ and/or R² is an alkyl or alkenyl group having from 6 to 40 carbon atoms and m is 0.

3. The use according to claim 2, wherein R¹ and/or R² is an alkyl or alkenyl group having from 6 to 40 carbon atoms and m is an integer from 1 to 20.

4. The use according to claim 2, wherein R¹ and/or R² is an acyl group of the general formulae R⁵-C(O)- and R⁶-C(O)-, wherein R⁵ and R⁶ are identical or different and, independently of each other, are selected from alkyl and alkenyl groups having from 5 to 39 carbon atoms and m is an integer from 1 to 20.

5. The use according to claim 2, wherein R¹ and/or R² is an optionally substituted aryl group having from 6 to 40 carbon atoms and m is an integer from 1 to 20.

6. The use according to claim 5 wherein R¹ and/or R² is a phenyl group substituted with an alkyl group having 1 to 36 carbon atoms.

7. The use according to claim 5, wherein R¹ and/or R² is a tristyrylphenyl group.

8. The use according to one or more of claims 1 to 6, wherein R¹ and/or R² have from 6 to 24 carbon atoms.

9. The use according to one or more of claims 1 to 8, wherein X is hydrogen and n is 1 .

10. The use according to one or more of claims 1 to 9, wherein the phosphoric acid ester is added to the aqueous slurry of the fine-grained crude iron ore in a concentration of from 1 ppm by weight to 5,000 ppm by weight in respect to the mass of the crude ore.

11 . The use according to one or more of claims 1 to 10, wherein the phosphoric acid ester is used in combination with a fatty acid.

12. The use according to one or more of claims 1 to 11 , wherein the phosphoric acid ester is used in combination with a water-immiscible organic solvent.

13. The use according to one or more of claims 1 to 13, wherein the finegrained crude iron ore comprising an iron ore and a gangue mineral has a medium value of the particle size of less than 500 pm, and preferably of less than 200 pm, as determined according to ASTM B822-10.

14. The use according to one or more of claims 1 to 14, wherein the finegrained crude iron ore comprising an iron ore and a gangue mineral has a medium value of the particle size distribution (D50; median diameter) of less than 100 pm and even less than 20 pm, as determined according to ASTM B822-10.

15. The use according to one or more of claims 1 to 15, wherein the finegrained crude iron ore comprises a ferrimagnetic or paramagnetic iron ore which is attracted by a magnet.

16. The use according to one or more of claims 1 to 16, wherein the finegrained crude iron ore comprises an oxidic iron ore.

17. The use according to one or more of claims 1 to 17, wherein the finegrained crude iron is a low-grade iron ore having an iron content of from 10 to 53 wt.-%.

18. The use according to one or more of claims 16-18, wherein the iron ore comprises iron in the form of an oxide and/or oxyhydroxide selected from the group consisting of magnetite, hematite, goethite, limonite, or any mixture thereof.

19. The use according one or more of claims 16-19, wherein the iron ore comprises iron in the form of an oxidic mixed metal iron ore.

20. The use according to claim 20, wherein the oxidic mixed metal iron ore comprises, besides iron and oxygen, at least one further metal selected from the 4^th period of the periodic table of elements.

21 . The use according to claim 20 or 21 , wherein the oxidic mixed metal iron ore comprises, besides iron and oxygen, at least one further metal selected from the group consisting of titanium, vanadium, chromium, manganese, and/or zinc and preferably titanium or vanadium.

22. The use according to one or more of claims 20 to 22, wherein the oxidic mixed metal iron ore is selected from the group consisting of chromite, ilmenite, franklinite, and mixtures thereof.

23. A method of beneficiating an iron ore from a fine-grained crude iron ore comprising iron ore and a gangue mineral wherein: i) the fine-grained crude iron ore is dispersed in an aqueous phase to give an aqueous slurry; ii) said aqueous slurry is mixed with at least one phosphoric acid ester; iii) the treated aqueous slurry is subjected to magnetic separation means to obtain a fraction of the fine-grained iron ore slurry which is enriched in iron ore and depleted in gangue mineral; and iv) a concentrated iron ore is extracted from the fraction of the iron ore slurry being enriched in iron ore, and wherein the phosphoric acid ester is a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II),

wherein

A is an alkylene group having from 2 to 6 carbon atoms;

24. A method according to claim 24 or 25, wherein the phosphoric acid ester is added to the aqueous slurry of the fine-grained crude iron ore in a concentration of from 1 ppm by weight to 5,000 ppm by weight in respect to the mass of the crude ore.

25. A method according to one or more of claims 24 to 26, wherein the phosphoric acid ester is used in combination with a fatty acid.

26. A method according to one or more of claims 24 to 27, wherein the phosphoric acid ester is used in combination with a water-immiscible organic solvent.

27. A method of enhancing the mass recovery of iron ore from an aqueous slurry of a fine-grained crude iron ore comprising iron ore and a gangue mineral in a magnetic separation process, wherein a phosphoric acid ester is added to the aqueous slurry prior to subjecting the aqueous slurry to a magnetic separation process which effects the separation of a concentrated iron ore fraction having a raised iron content and a gangue tailings fraction having a reduced iron content, both in respect to the crude iron ore, and wherein the phosphoric acid ester comprises a phosphoric acid monoester according to formula (I), a phosphoric acid diester according to formula (II) or a mixture of phosphoric acid monoester (I) and phosphoric acid diester (II),

wherein

A is an alkylene group having from 2 to 6 carbon atoms;

28. A method according to claim 29 or 30, wherein the phosphoric acid ester is added to the aqueous slurry of the fine-grained crude iron ore in a concentration of from 1 ppm by weight to 5,000 ppm by weight in respect to the mass of the crude ore.

29. A method according to one or more of claims 29 to 31 , wherein the phosphoric acid ester is used in combination with a fatty acid.

30. A method according to one or more of claims 29 to 32, wherein the phosphoric acid ester is used in combination with a water-immiscible organic solvent.

31 . A method according to one or more of claims 29 to 33, wherein the mass recovery rate of iron ore is at least 1 wt.-% higher than in absence of the phosphoric acid ester.

32. A method of enhancing the iron recovery rate from an aqueous slurry of a fine-grained crude iron ore comprising iron ore and a gangue mineral in a magnetic separation process, wherein a phosphoric acid ester is added to the aqueous slurry prior to subjecting the aqueous slurry to a magnetic separation process which effects the separation of a concentrated iron ore fraction having a raised iron content and a gangue tailings fraction having a reduced iron content, both in respect to the crude iron ore.

33. A method according to claim 35 or 36, wherein the phosphoric acid ester is added to the aqueous slurry of the fine-grained crude iron ore in a concentration of from 1 ppm by weight to 5,000 ppm by weight in respect to the mass of the crude ore.

34. A method according to one or more of claims 35 to 37, wherein the phosphoric acid ester is used in combination with a fatty acid.

35. A method according to one or more of claims 35 to 38, wherein the phosphoric acid ester is used in combination with a water-immiscible organic solvent.

36. A method according to one or more of claims 35 to 39, wherein the iron recovery rate is at least 1 wt.-% higher than in absence of the phosphoric acid ester.