WO2024099669A1

WO2024099669A1 - Sulfonated surfactants for the beneficiation of magnetic minerals from low-grade ores

Info

Publication number: WO2024099669A1
Application number: PCT/EP2023/078115
Authority: WO
Inventors: Leandro Seixas Bicalho; Nathalia COSTA; Wagner Claudio Da Silva; Matthias Krull
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 2022-11-11
Filing date: 2023-10-11
Publication date: 2024-05-16
Anticipated expiration: 2025-05-11

Abstract

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 sulfonated surfactant to the low-grade iron ore.

Description

Sulfonated surfactants for the beneficiation of magnetic minerals from low-grade ores

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 about 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.

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 sulfonated surfactant 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 sulfonated compounds 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 sulfonated surfactant 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.

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 sulfonated surfactant; 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 sulfonated surfactant is added to the aqueous slurry prior to subjecting the aqueous slurry to a magnetic separation process, and wherein the addition of the sulfonated surfactant 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.

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 sulfonated surfactant is added to the aqueous slurry prior to subjecting the aqueous slurry to a magnetic separation process, and wherein the addition of the sulfonated surfactant 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.

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 sulfonated surfactant) in comparison to the same process conducted without the features of this invention (i. e. absent a sulfonated surfactant).

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 (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, the sulfonated surfactant comprises a sulfonic acid or its salt according to formula (I),

R¹[(OCH₂CHR²)n-O-CH₂CH(OH)CH2]mSO3- M⁺ (I) wherein

R¹ is an optionally substituted hydrocarbyl group having from 6 to 40 carbon atoms which may be interrupted by at least one ester and/or amide group, R² is hydrogen or an alkyl group having from 1 to 4 carbon atoms; n is 0 or an integer from 1 to 40; m is 0 or 1 ; and

M⁺ is a cation.

In the context of the present disclosure, the term “sulfonated surfactant” refers to all amphiphilic compounds having a sulfonic acid group or a sulfonate group as the polar part bound to a hydrocarbyl group imparting hydrophobic properties to the compound. Preferably, the hydrocarbyl group has at least 6 carbon atoms.

In preferred embodiments, R¹ is selected from optionally substituted alkyl groups, alkenyl, alkylaryl, and arylalkyl groups. In further preferred embodiments, R¹ has from 10 to 28 and more preferred from 12 to 20 carbon atoms, as for example from 6 to 28 carbon atoms, or from 6 to 20 carbon atoms, or from 10 to 40 carbon atoms, or from 10 to 20 carbon atoms, or, or from 12 to 40 carbon atoms, or from 12 to 28 carbon atoms. Preferred substituents of R¹ are hydroxy and ester groups. In a further preferred embodiment, R² is hydrogen or a methyl group and especially preferred R² is hydrogen. In a further preferred embodiment, m is 0.

In a first more preferred embodiment, the sulfonate-based surfactant is an alkane sulfonate, wherein in formula (I) the hydrocarbyl group R¹ is an alkyl group optionally substituted with a hydroxy group and m is 0. Accordingly, preferred alkane sulfonates have the formula R¹-SO3' M⁺. Preferred alkyl groups have from 10 to 28 and more preferred from 12 to 20 carbon atoms, as for example from 6 to 28 carbon atoms, or from 6 to 20 carbon atoms, or from 10 to 40 carbon atoms, or from 10 to 20 carbon atoms, or, or from 12 to 40 carbon atoms, or from 12 to 28 carbon atoms. Preferably, the alkyl group is linear with the sulfonic acid group being attached to a primary alkyl group, and more preferably with the sulfonic acid group being attached to a secondary carbon atom (secondary alkane sulfonate). Alkane sulfonates are also known as paraffin sulfonates. They can be manufactured for example by sulfoxidation or sulfochlorination of paraffins.

In a second more preferred embodiment, the sulfonate-based surfactant is an olefin sulfonate wherein the hydrocarbyl group R¹ is an alkenyl group optionally being substituted with a hydroxy group and m is 0. Accordingly, preferred olefin sulfonates have the formula R¹-SO3' M⁺. Preferred alkenyl groups have from 10 to 28 and more preferred from 12 to 20 carbon atoms, as for example from 6 to 28 carbon atoms, or from 6 to 20 carbon atoms, or from 10to 40 carbon atoms, or from 10 to 20 carbon atoms, or from 12 to 40 carbon atoms, or from 12 to 28 carbon atoms. Olefin sulfonates can be prepared from a-olefins as well as from internal olefins from by sulfonation. a-Olefin sulfonates as well as internal olefin sulfonates are similarly suited for the various aspects of the invention.

Sulfonation of a-olefins results in essentially linear a-olefin sulfonates with the sulfonic acid group being bound either to a primary carbon atom and a C=C double bond between the a- and [3-carbons, or the sulfonic acid group being bound to the secondary carbon atom in the [3-position.

Starting from internal olefins, internal olefin sulfonates are obtained. Due to their manufacturing process, olefin sulfonates are often intermingled with hydroxy alkane sulfonates. Commercial grades of internal olefin sulfonates comprise a range of different molecules, which may differ from one another in terms of carbon number, being branched or unbranched, number of branches, molecular weight and number and distribution of functional groups such as sulfonate and hydroxyl groups. Commercial grades may comprise both hydroxyalkane sulfonate molecules and alkene sulfonate molecules and possibly also di-sulfonate molecules. Di-sulfonate molecules originate from a further sulfonation of for example an alkene sulfonic acid. Such mixtures are also suited for the different aspects of the invention.

In a third more preferred embodiment, the sulfonate-based surfactant is an alkyl aryl sulfonate wherein in formula (I) the hydrocarbyl group R¹ is an aryl group which is substituted with an alkyl group and m is 0. Accordingly, preferred alkane sulfonates have the formula R¹-SO3' M⁺. Preferably, the alkyl group bound to the aryl group has from 1 to 34 carbon atoms, more preferably from 8 to 24 carbon atoms, and especially preferred from 10 to 18 carbon atoms from, such as, for example from 1 to 24 carbon atoms, or from 1 to 18 carbon atoms, or from 8 to 34 carbon atoms, or from 8 to18 carbon atoms, or from 10 to 34 carbon atoms, or from 10 to 24 carbon atoms, with the proviso that the number of carbon atoms in the aryl group and the alkyl group taken together does not exceed 40, preferably not 24 and especially preferred not 18.

Preferred aryl groups in alkyl aryl sulfonates are the naphthylene group as for example in alkyl naphthalene sulfonates, such as diisopropyl naphthalene sulfonate, and the phenylene group as for example in alkyl benzene sulfonates. Especially preferred alkyl aryl sulfonates are the alkyl benzene sulfonates. These correspond to the general formula (II)

R³-C₆H₄-SO₃- M⁺ (II) wherein R³ is an alkyl group having from 1 to 34 carbon atoms, preferably having from 8 to 24 carbon atoms, and especially preferred having from 10 to 18 carbon atoms from, such as, for example from 1 to 24 carbon atoms, or from 1 to 18 carbon atoms, or from 8 to 34 carbon atoms, or from 8 to18 carbon atoms, or from 10 to 34 carbon atoms, or from 10 to 24 carbon atoms.

The alkyl group R³ may be bound to the benzene ring in ortho, meta or para position to the sulfonic acid group. In a preferred embodiment, R³ is in para position to the sulfonic acid group.

In a preferred embodiment, the alkyl group R³ of the alkyl aryl sulfonate is linear or at least essentially linear. Essentially linear means that at least 70 mol-%, more preferred at least 85 mol-%, and especially preferred at least 90 mol-% of the alkyl groups are linear. The aryl group may be bound to a primary carbon atom at the end of the alkyl chain, or it may be bound to any of the secondary carbon atoms along the alkyl chain. In a preferred embodiment, the aryl group is bound to a secondary carbon atom of the alkyl chain. A common route for the preparation of linear alkyl aryl sulfonates is the sulfonation of linear alkyl aromatic compounds, which can themselves be prepared by alkylation of the aromatic compound with a long chain linear a-olefin. Preferably, the a-olefin has from 8 to 34, more preferably from 10 to 24 and especially preferred from 10 to 18 carbon atoms, as for example 10, 12, 13, 14, 16 or 18 carbon atoms. Mixtures of alkyl aryl sulfonates having different chain lengths within the preferred ranges are similarly suited.

In a further preferred embodiment, the alkyl group of the alkyl aryl sulfonate has a branched chain structure. Preferred starting materials for the manufacture of branched chain alkyl aryl sulfonates are oligomers of lower olefins having 3 to 5 carbon atoms and preferably having from 2 to 4 carbon atoms as for example propylene and butylene. Preferably, the degree of oligomerization is from 2 to 10, more preferably from 3 to 8, and especially preferred from 4 to 6, as for example from 2 to 8, or from 2 to 6, or from 3 to 10, or from 3 to 6, or from 4 to 10, or from 4 to 8. Examples for preferred lower olefin oligomers are tripropylene, tetrapropylene, pentapropylene, hexapropylene, heptapropylene, diisobutylene, tributylene, triisobutylene, tetrabutylene, tetraisobutylene, pentabutylene, pentaisobutylene, hexabutylene, hexaisobutylene, heptabutylene, heptaisobutylene and any mixture thereof. In an especially preferred embodiment of the invention, the sulfonated surfactant is dodecyl benzene sulfonic acid based on either tetrapropylene or triisobutylene.

In the context of the present disclosure, the term "branched chain structure" means that the oligo(propenyl) and respectively the oligo(butenyl) and oligo(pentenyl) substituent groups consist of a branched chain propanediyl, butanediyl or pentanediyl repeating radical. For example, the poly(butenyl) substituent group may be regarded as consisting essentially of a relatively long straight acyclic alkyl chain bonded to the aryl group and said alkyl chain is further substituted by two or more methyl and /or ethyl groups along the length of the chain (i. e. the branching is along the relatively long alkyl chain by virtue of pendant methyl and/or ethyl substituent groups). Similarly, the poly(propenyl) substituent group may be regarded as consisting essentially of a relatively long straight acyclic alkyl chain bonded to the benzene ring and said alkyl chain is further substituted by two or more methyl groups along the length of the chain (i. e. the branching is along the relatively long alkyl chain by virtue of pendant methyl substituent groups). In a fourth more preferred embodiment, the sulfonate-based surfactant is a fatty ester sulfonate, wherein in formula (I) the hydrocarbyl group R¹ is an alkyl or alkylene group which is interrupted by an ester group and optionally substituted with a hydroxy group, and m is 0. Depending on the manufacturing process of the fatty ester sulfonate, and/or the starting material, the sulfonate group -SOs' M⁺ may be located at different positions of the alkyl or alkylene chain. For example, by sulfoxidation of a fatty acid ester with SO2, O2, and ultraviolet light of appropriate wavelength it is positioned randomly in the alkyl chain R¹; by sulfonation of the C=C double bond of an unsaturated fatty acid as for example oleic acid using sodium hydrogen sulfite the sulfonate group is located at the position of the acid's double bond; by reaction with sulfur trioxide, fatty acid esters can be converted to a-sulfo fatty acids ester.

In an especially preferred embodiment, the sulfonate group -SO3M is positioned in alpha-position to the carbonyl carbon of the ester group. Preferred a-sulfo fatty esters have the formula (III)

R⁴-CH(SO₃ M⁺)-COOR⁵ (III) wherein

R⁴ represents an alkyl or alkenyl group having from 7 to 25 and preferably having from 9 to 17 carbon atoms;

R⁵ represents an alkyl group having from 1 to 6 and preferably having from 1 to 3 carbon atoms; and

M⁺ represents hydrogen or an alkaline earth metal cation, for example the sodium, potassium, or ammonium cation.

In fatty ester sulfonates, the carbon atoms stemming from the carbonyl group are included in the counting of the carbon atoms of R¹. Accordingly, the number of carbon atoms in R¹ equals the sum of the carbon atoms of R⁴ + R⁵+2. Preferred a- sulfo fatty esters are esters of alcohols having the formula R⁵-OH as for example esters of methanol, ethanol, propanol and/or butanol. An especially preferred embodiment of alkyl ester sulfonates are methyl fatty ester sulfonates and especially a-sulfo fatty methyl esters, wherein in formula (III) R⁴ is an alkyl or alkylene group optionally being substituted with a hydroxy group and having from 7 to 25 and preferably having from 9 to 17 carbon atoms;

R⁵ is methyl; and

M represents hydrogen or an alkaline earth metal cation, for example the sodium, potassium, or ammonium cation.

Preferred fatty ester sulfonates and methyl fatty ester sulfonates are derived from fatty acids or fatty acid esters. The fatty acids as well as their esters may be saturated or unsaturated. They may be linear or branched; preferably they are linear. Being based on fatty acids or fatty acid esters derived from renewable sources, ester sulfonates are alleged to be environmentally friendly anionic surfactants.

Preferred fatty ester sulfonates and preferred methyl fatty ester sulfonates are derived from fatty acids including but not limited to 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. In a preferred embodiment, they are derived from oils and fats of natural origin by hydrolysis. More preferred mixtures of fatty acids and their methyl esters 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. An especially preferred methyl fatty ester sulfonate is sulfo palm stearin fatty acid methyl ester which can be manufactured by sulfonation of a fatty acid methyl ester obtained from palm stearin and comprising mainly C and Cis fatty acid methyl esters.

Fatty ester sulfonates as well as methyl fatty ester sulfonates have proven to be especially advantageous when the pH value of the aqueous slurry is not below 3 and not above 10, more especially when the pH is in the range of from 4.0 to 8.5, and even more especially when the pH is in the range of from 5.0 to 7.5, as for example when the pH of the aqueous slurry is in the range of from 3.0 to 8.5, or from 3.0 to 7.5, or from 4.0 to 10.0, or from 4.0 to 7.5, or from 5.0 to 10.0, or from 5.0 to 8.5.

In a fifth more preferred embodiment, the sulfonate-based surfactant is an alkyl or alkenyl glyceryl ether sulfonate, also known as alk(en)yl alkoxyl glyceryl sulfonate, wherein in formula (I) m is 1 , R¹ is an alkyl or alkenyl group, and n is 0 or an integer between 1 and 40.

In preferred alkyl or alkenyl glyceryl ether sulfonates, R¹ is an alkyl or alkenyl group having from 10 to 28 and more preferably having from 12 to 20 carbon atoms, as for example from 1040 carbon atoms, or from 10 to 20 carbon atoms, or from 6 to 28 carbon atoms, or from 6 to 20 carbon atoms, or from 12 to 40 carbon atoms, or from 12 to 28 carbon atoms. Such alkyl and alkenyl glyceryl ether sulfonates may be derived from fatty alcohols of formula R¹-OH. Preferred fatty alcohols R¹-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. The fatty alcohols may be of synthetic or natural origin.

In a preferred embodiment, the fatty alcohol R¹-OH is 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. The alcohol may be derived from oils and fats by hydrolysis and subsequent reduction of the so obtained fatty acids. More preferred fatty alcohols and fatty alcohol mixtures may be derived for example from coconut oil, soy oil, sunflower oil, palm oil, palm kernel oil, tallow fat, olive oil, rice oil, corn oil, peanut oil, and mixtures thereof. In a further preferred embodiment, the fatty alcohol R¹-OH is a synthetic alcohol. 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/or butylene. Examples for preferred lower olefin oligomers are essentially linear a-olefins having from 6 to 40, more preferably having from 10 to 28 and especially preferred having from 12 to 20 carbon atoms. Further examples for preferred lower olefin oligomers are 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 preferred alkyl or alkenyl glyceryl ether sulfonates, n is an integer from 1 to 40 and more preferably an integer from 2 and to 20, as for example from 1 to 20, or from 2 to 40.

In preferred alkyl or alkenyl glyceryl ether sulfonates, R² is hydrogen or a methyl group, i. e. the alk(en)yl glyceryl ether sulfonate comprises one or more ethoxy and/or propoxy groups. In a specific embodiment the alkyl or alkenyl glyceryl ether sulfonate contains from 0 to 20, preferably from 1 to 10 and more preferably from 2 to 5 ethoxy groups and from 0 to 10 and more preferably from 1 to 5 propoxy groups, with at least one ethoxy or propoxy group being present.

Alkyl or alkenyl glyceryl ether sulfonates can be prepared for example according to US 5,672,740 by sulfonating a terminal glycidate epoxy ether of an optionally alkoxylated fatty alcohol with a mixture of sulfite and bisulfite salt.

In a sixth more preferred embodiment, the sulfonate-based surfactant is a monoalkyl or dialkyl sulfosuccinate or a monoalkyl or dialkyl sulfosuccinamate wherein in formula (I) m is 0 and R¹ is an alkyl or alkenyl group which is interrupted by two ester and/or amide groups. Preferred sulfosuccinates have the general formula (IV) and preferred sulfosuccinamates have the general formula (V)

(IV) (V) wherein

R⁶ and R⁷ are identical or different and, independently of one another, are selected from hydrogen, alkali metals, and alkyl and alkenyl groups having from 6 to 24 carbon atoms, and wherein at least one of R⁶ and R⁷ is an alkyl or alkenyl group; and wherein R⁶ together with R⁷ and the carbon atoms stemming from the succinic acid moiety have from 10 to 40 carbon atoms.

Preferably, R⁶ and/or R⁷ when being an alkyl or alkenyl group, independently of one another have from 8 to 16 carbon atoms. Preferably, R⁶ together with R⁷ and the carbon atoms stemming from the succinic acid moiety have from 10 to 28 and more preferred from 12 to 20 carbon atoms, as for example from 10 to 40 carbon atoms, or from 10 to 20 carbon atoms, or from 12 to 40 carbon atoms, or from 12 to 28 carbon atoms. Preferred alkyl and alkenyl groups R⁶ and R⁷ may be linear, branched or cyclic.

In succinates, R⁶ and/or R⁷ may have the ester group attached to a 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 R⁶-OH and/or R⁷-OH which is part of the ester is a primary or secondary alcohol.

Preferred alcohols R⁶-OH and R⁷-OH may be based on fatty alcohols of synthetic or natural origin. Especially preferred alcohols of synthetic and natural origin are the same as those described for the alkyl and alkenyl glyceryl ether sulfonates according to the fifth more preferred embodiment of the invention.

In succinamates, R⁶ and/or R⁷ may have the amide group attached to a carbon atom which has one, two or three other carbon atoms attached to it. In a preferred embodiment, the amine R⁶-NH2 and/or R⁷-NH2 which is part of the amide is a primary amine.

In a seventh more preferred embodiment, the sulfonated surfactant is a petroleum sulfonate. Natural petroleum sulfonates are defined as those manufactured by sulfonation of crude oil, crude distillates, or any portion of these distillates. Accordingly, natural petroleum sulfonates are much more complex mixtures than synthetic sulfonates as the natural materials used for sulfonation contain, besides aliphatic and simple alkyl aromatic compounds, a wide variety of condensed-ring, as well as single-ring, aromatics that permit multiple sulfonation to occur. The most common synthesis technologies for petroleum sulfonates are the liquid-liquid method with fuming sulfuric acid or with diluted liquid sulfur trioxide as sulfonating agent in stirred tank reactor and the gas-liquid method with diluted gaseous sulfur trioxide as sulfonating agent in falling film reactor.

The cation M⁺ may be any cation, such as hydrogen, an alkali metal or alkaline earth metal cation, ammonium (NH4⁺) or an organic ammonium cation. In a first preferred embodiment, M⁺ is hydrogen. In a further preferred embodiment, M⁺ is selected from metal ions, NH4⁺ and organic ammonium ions derived from amines and/or alkanolamines. Preferred metal ions are alkali metal ions, in particular Na⁺ and K⁺. Preferred organic ammonium cations may be derived from primary, secondary and/or tertiary amines. The organic moieties bound to the nitrogen atom of preferred amines are alkyl groups and/or hydroxyalkyl groups. Preferably, each alkyl and hydroxyalkyl group of preferred amines has from 1 to 10 and more preferably from 2 to 6 carbon atoms, such as, for example, from 1 to 6 or from 2 to 10 carbon atoms. Preferably the total number of carbon atoms of the amine does not exceed 12. Examples for preferred amines are isopropyl amine, cyclohexylamine, monoethanolamine, diethanolamine and triethanolamine. Preferably, M⁺ is hydrogen, ammonium, or an alkali metal cation as for example sodium or potassium.

Preferably, the amount of sulfonated surfactant 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, Na2COs, NaHCOs, KCI, KHCO3, K2CO3, MgCl2, 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, countercurrent 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 sulfonated surfactant. 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 mass recovery obtained in the same process in absence of the sulfonated surfactant.

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 sulfonated surfactant. 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 sulfonated surfactant.

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 sulfonated surfactant according to the invention in the concentrated iron ore fraction does not interfere with the sedimentation process. Often, the presence of a sulfonated surfactant 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 sulfonated surfactant 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 sulfonated surfactant. 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 sulfonated surfactant and a fatty acid. Alternatively, sulfonated surfactant 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, soybean 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, sulfonated surfactant 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 sulfonated surfactant 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 sulfonated surfactant and the water-immiscible organic solvent. In this embodiment the presence of a water-immiscible organic solvent reduces the viscosity of the sulfonated surfactant and facilitates its handling and its spreading in the aqueous slurry of the fine-grained mineral. Alternatively, sulfonated surfactant 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 sulfonated surfactant 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 sulfonated surfactant 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 sulfonated surfactant 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 sulfonated surfactant 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 through which eighty percent of the particles 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 : Sulfonated surfactants 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;

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 sulfonated surfactant 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 a sulfonated surfactant. 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 sulfonated surfactant 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.

2. The use according to claim 1 , wherein the sulfonated surfactant is a sulfonic acid or its salt according to formula (I),

R¹[(OCH₂CHR²)n-O-CH₂CH(OH)CH2]mSO3- M⁺ (I) wherein

R¹ is an optionally substituted hydrocarbyl group having from 6 to 40 carbon atoms which may be interrupted by at least one ester and/or amide group,

R² is hydrogen or an alkyl group having from 1 to 4 carbon atoms; n is 0 or an integer from 1 to 40; m is 0 or 1 ; and

M⁺ is a cation.

3. The use according to claim 2, wherein the sulfonated surfactant is an alkane sulfonate, wherein in formula (I) R¹ is an alkyl group optionally substituted with a hydroxy group and m is 0.

4. The use according to claim 3, wherein the alkane sulfonate corresponds to the general formula R¹-SO3' M⁺ wherein the alkyl group R¹ has from 10 to 28 carbon atoms.

5. The use according to claim 2, wherein the sulfonated surfactant is an olefin sulfonate wherein in formula (I) R¹ is an alkenyl group optionally substituted with a hydroxy group and m is 0.

6. The use according to claim 5 wherein the alkenyl group has from 10 to 28 carbon atoms.

7. The use according to claim 2, wherein the sulfonated surfactant is an alkyl aryl sulfonate wherein in formula (I) R¹ is an aryl group which is substituted with an alkyl group and m is 0.

8. The use according to claim 7, wherein the alkyl aryl sulfonate corresponds to the general formula (II)

R³-C₆H₄-SO₃- M⁺ (II) wherein R³ is an alkyl group having from 1 to 34 carbon atoms,

9. The use according to claim 2, wherein the sulfonated surfactant is a fatty ester sulfonate, wherein in formula (I) R¹ is an alkyl or alkylene group optionally substituted with a hydroxy group which is interrupted by an ester group and m is 0.

10. The use according to claim 9, wherein the fatty ester sulfonate is an a-sulfo fatty ester and corresponds to the general formula (III)

R⁴-CH(SO₃ M⁺)-COOR⁵ (III) wherein

R⁴ is an alkyl or alkenyl group having from 7 to 25 carbon atoms:

R⁵ is an alkyl group having from 1 to 6 carbon atoms; and

11 . The use according to claim 10, wherein the fatty ester sulfonate is a methyl fatty ester sulfonate with R⁵ in general formula (III) being a methyl group.

12. The use according to claim 2, wherein the sulfonated surfactant is an alkyl or alkenyl glyceryl ether sulfonate of formula (I), wherein m is 1 , R¹ is an alkyl or alkenyl group, and n is 0 or an integer between 1 and 40.

13. The use according to claim 1 , wherein the sulfonated surfactant is selected from monoalkyl or dialkyl sulfosuccinates and monoalkyl or dialkyl sulfosuccinamates wherein in formula (I) m is 0 and R¹ is an alkyl or alkenyl group being interrupted by two groups selected from ester and/or amide groups.

14. The use according to claim 13, wherein the monoalkyl and dialkyl sulfosuccinates correspond to the general formula (IV)

wherein

R⁶ and R⁷ are identical or different and, independently of one another, are selected from hydrogen, alkyl and alkenyl groups having from 6 to 24 carbon atoms, and wherein at least one of R⁶ and R⁷ is an alkyl or alkenyl group, and wherein R⁶ and R⁷ together with the carbon atoms stemming from the succinic acid moiety have from 10 to 40 carbon atoms.

15. The use according to claim 13, wherein the monoalkyl and dialkyl sulfosuccinamates correspond to to general formula (V)

wherein

16. The use according to claim 1 , wherein the sulfonated surfactant is a petroleum sulfonate.

17. The use according to one or more of claims 2 to 16, wherein M⁺ is hydrogen, an alkali metal or alkaline earth metal cation, NH4⁺ or an organic ammonium ion.

18. The use according to one or more of claims 1 to 17, wherein the sulfonated surfactant 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.

19. The use according to one or more of claims 1 to 18, wherein the sulfonated surfactant is used in combination with a fatty acid.

20. The use according to one or more of claims 1 to 19, wherein the sulfonated surfactant is used in combination with a water-immiscible organic solvent.

21 . The use according to one or more of claims 1 to 20, wherein the finegrained crude iron ore comprising an iron ore and a gangue mineral has a medium value of the particle size D50 of less than 500 pm, and preferably of less than 200 pm, as determined according to ASTM B822-10.

22. The use according to one or more of claims 1 to 21 , wherein the finegrained crude iron ore comprising an iron ore and a gangue mineral has a medium value of the particle size distribution D50 of less than 106 pm and preferably of less than 20 pm, as determined according to ASTM B822-10.

23. The use according to one or more of claims 1 to 22, wherein the finegrained crude iron ore comprises a ferrimagnetic or paramagnetic iron ore which is attracted by a magnet.

24. The use according to one or more of claims 1 to 23, wherein the finegrained crude iron ore comprises an oxidic iron ore.

25. The use according to one or more of claims 1 to 24, wherein the fine- grained crude iron is a low-grade iron ore having an iron content of from 10 to

53 wt.-%.

26. The use according one or more of claims 23 - 25, wherein the iron ore comprises iron in the form of an oxide and/or oxyhydroxides selected from the group consisting of magnetite, hematite, goethite, limonite, or any mixture thereof.

27. The use according one or more of claims 23 - 26, wherein the iron ore comprises iron in the form of an oxidic mixed metal iron ore.

28. The use according to claim 27, wherein the oxidic mixed metal iron ore comprises, besides iron and oxygen, at least one further metal selected from the transition metals of the 4^th period of the periodic table of elements.

29. The use according to claim 27 or 28, 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.

30. The use according to one or more of claims 27 or 29, wherein the oxidic mixed metal iron ore is selected from the group consisting of chromite, ilmenite, franklinite, and mixtures thereof.

31 . 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 sulfonated surfactant; 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.

32. The method according to claim 31 , wherein the sulfonated surfactant is according to the definition of any of claims 2 to 17.

33. The method according to claim 31 or 32, wherein the sulfonated surfactant 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. The method according to one or more of claims 31 to 33, wherein the sulfonated surfactant is used in combination with a fatty acid.

35. The method according to one or more of claims 31 to 34, wherein sulfonated surfactant is used in combination with a water-immiscible organic solvent.

36. 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 sulfonated surfactant 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.

37. The method according to claim 36, wherein the sulfonated surfactant is according to the definition of any of claims 2 to 17.

38. The method according to claim 36 or 37, wherein the anionic amino acidbased surfactant 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.

39. The method according to one or more of claims 36 to 38, wherein the anionic amino acid-based surfactant is used in combination with a fatty acid.

40. The method according to one or more of claims 36 to 39, wherein the anionic amino acid-based surfactant is used in combination with a water- immiscible organic solvent.

41 . The method according to one or more of claims 36 to 40, wherein the mass recovery rate of iron ore is at least 1 wt.-% higher than in absence of the sulfonated surfactant.

42. 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 sulfonated surfactant 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.

43. The method according to claim 42, wherein the sulfonated surfactant is according to the definition of any of claims 2 to 17.

44. The method according to claim 42 or 43, wherein the sulfonated surfactant 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.

45. The method according to one or more of claims 42 to 44, wherein the sulfonated surfactant is used in combination with a fatty acid.

46. The method according to one or more of claims 42 to 45, wherein the sulfonated surfactant is used in combination with a water-immiscible organic solvent.

47. The method according to one or more of claims 42 to 46, wherein the iron recovery rate is at least 1 wt.-% higher than in absence of the sulfonated surfactant.