NZ621725B2 - Ore beneficiation - Google Patents

Abstract

The present invention is a method of enriching the iron content of low-grade iron-bearing ore materials has been developed which produces a high iron ore concentrate suitable for processing into pig iron and steel. The process includes reducing the low-grade iron-bearing ore materials to a fine particulate form and treating a water slurry of this material by applying a combination of ultrasonic treatments in a plurality of high and low intensity magnetic separation operations to remove interfering materials and concentrate magnetic and paramagnetic iron-bearing materials into a high-grade ore stock. iculate form and treating a water slurry of this material by applying a combination of ultrasonic treatments in a plurality of high and low intensity magnetic separation operations to remove interfering materials and concentrate magnetic and paramagnetic iron-bearing materials into a high-grade ore stock.

Description

WO 19618 PCT/U52012/048550 ORE BENEFICIATION CROSS-REFERENCED TO RELATED APPLICATIONS This application is a continuation—in—part of application Serial No. 13/195,430, filed August 1, 2011, and that application is deemed incorporated herein by reference in its ty.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates generally to the processing of earing ore als and, particularly, to a s for enriching the usable iron ore content of low—grade, iron~bearing feed materials such as are found in tailings piles and which heretofore have not been commercially usable.

II. Related Art Throughout northeastern Minnesota and other iron mining regions of the world, there exists extensive stockpiles of commercially unusable, low-grade iron ore including large rocks that were rejected as tailings during the active ore l mining phase because they lacked sufficient quantities of key mineral ores having sufficient iron content to justify further commercial sing. These significant volumes of low—grade ores typically contain less than 34% iron and may contain high concentrations of unusable forms of iron and — bearing or clay materials which has rendered these wastes ore deposits as not fit for further processing into taconite pellets or high-grade ore for producing pig iron.

Specifically, the material ned in these large, non—commercial ore stockpiles contains several mineral PCTfU52012/048550 forms of iron ores, including magnetite (Fefih), hematite (Fe203), goethite (FeO'OH), siderite (FeCO3) and limonite (FeO‘OH'ano). All of these forms would be ble as a concentrate, with the ion of limonite, which has a high quantity of attached water of hydration as an undesirable factor. Also present is a large amount of gangue material which includes several silts and clay als, namely, chamosite, stilpnomalanene and kaolin.

These small clay les, also known as slimes, contain silica contaminates that are ult to remove from the mix due to their strong adhesion properties. The clay particles are very small (< 5 microns) and have a propensity to coat particles of iron~bearing materials making the extraction and concentration of those materials very difficult.

It is known to use ultrasonic techniques to dislodge gangue particles from iron ores. Various techniques have been employed and an example of this is found in U.S.

Pat. Pub. 2010/0264241 A1, which uses an ultrasonic crusher pipe system to te gangue from ore in a waterborne slurry. 'Magnetic separators have also been”" employed to enrich magnetic ore concentrations in a feed material, as shown in USPN 5,868,255 to McGaa. Although such ques have been employed with some degree of s, no cal process has heretofore been developed to economically enrich low—grade ores.

It would present a distinct advantage if an overall complete process could be developed whereby non— commercial low-grade iron—bearing materials of various compositions, presently considered waste material, could be processed into a trate containing a much higher percentage of iron that can be cost effectively converted into metallic iron and steel. 6622_1.dOCX SUMMARY OF THE INVENTION In accordance with the present invention, a method of enriching the iron content of low—grade iron—bearing ore materials has been developed which produces an ore concentrate having a high iron content which is in certain embodiments suitable for processing into pig iron and steel. The s includes (a) forming a water slurry of low—grade earing materials having a relatively small particle size; (b) ting the slurry of (a) to a first ultrasonic ent to separate interfering materials, including clays, from iron ore compounds; (c) subjecting the slurry of (b) to at least one stage of low intensity magnetic separation to produce magnetic concentrate and a paramagnetic tail slurry fraction; (d) treating the paramagnetic tail slurry fraction to a thickening operation; (e) ng the thickened paramagnetic tail fraction to a second ultrasonic ent to separate interfering materials; and (f) treating the thickened paramagnetic tail fraction of (e)to at least one stage of high gradient magnetic separation to separate and produce a concentrate of paramagnetic ores.

In one or more embodiments the process includes reducing the low-grade iron—bearing ore materials to a fine particulate form and treating a water slurry of this particulate material to a further process employing a combination of onic treatments and a gflurality of high and low intensity magnetic separation ions to remove interfering materials and concentrate 1000746622a1,docx -3A— magnetic and paramagnetic iron—bearing materials into a high—grade ore stock.

As used herein, the term ”paramagnetic” refers to materials not normally magnetic themselves, but which may react and align when placed in a sufficiently strong ic field. These include hematite (Fefih), goethite (FeOOOH) and te (Fec03) materials, which may be present in the feed material.

In a preferred embodiment, the process includes forming a water slurry of low—grade iron—bearing feedstock materials which have been reduced to a relatively small particle size by subjecting' the lowsgrade iron—bearing‘ material to crushing and ball mill grinding ions. A preferred particle size jiS at least ~325 mesh and preferably —400 to ~500 mesh. The slurry is subjected to a ing step to confirnl particulate size and thereafter is ted to an ultrasonic treatment that is sufficient to dislodge and. separate gangue ing‘ clays and interfering materials from the iron‘ containing particles. The ultrasonically treated material is then subjected to a plurality of relatively low, ity magnetic separation steps to PCT/U82012/048550 concentrate the higher magnetic ore fraction (magnetite) with the slurry containing the separated gangue als and the paramagnetic ore materials being removed for r treatment as a non—magnetic/paramagnetic tail fraction.

In one embodiment, the non—magnetic/paramagnetic tail fraction is subjected to a further ultrasonic step to again separate interfering gangue materials from the ore containing particles. This al is concentrated in a ner and separated from the overflow slurry water, the heavier iron ning materials remaining in the low or bottom fraction. The underflow material is then subjected to a plurality of relatively high field strength magnetic separation stages to separate out other desirable ore fractions.

The first vely high magnetic separation stage following the first ultrasonic treatment and processing ' k . ' +- g. + in a Lulcfiener!l LL QJ S U) 11LA m t field. th to concentrate the h ma (D rt +4 ('1' (D fraction and ensuing stages for separating out paramagnetic materials are operated at a higher field strength to separate out siderite and other desirable ore fractions. The concentrated ore fractions are then subjected to further concentration filtering and drying stages where the magnetic and paramagnetic compound fractions can be combined and made available for use.

An alternative embodiment uses additional pre— treatment grinding and screening in the formation of the initial slurry. In addition, in further processing the non—magnetic/paramagnetic tail fraction, it has been found that it may be advantageous to trate the material in a thickener and separate it from the overflow slurry water prior to further ultrasonic treatment.

Ultrasound is then used to treat the heavier, iron— WO 19618 PCT/U82012/048550 containing underflow or bottom fraction material. After ultrasound treatment, the material is subjected to a plurality of high gradient magnetic separation ents to remove the paramagnetic materials which are combined with the ic materials.

A wide variety of feed material compositions can be successfully processed. The final product is in the form of a loose, processed material having a moisture t of from O—lO% and an iron content of from 40%—62% total iron and 7—9% silica. The concentrate may be further processed into briquettes, pellets or balls, if desired, with various additives using a variety of binders and erating technologies.

The process water can be recycled using cyclone separation and clarifying steps to separate the solid final tailings so that the process actually requires a minimum of makeup water. The solid tailings can be tely stored.

BRIEF DESCRIPTION OF THE DRAWINGS Figure l is a schematic flow m illustrating an embodiment of the process of the invention; Figure 2 is a schematic flow diagram rating tailings treatment and process water recovery; and Figure 3 is a tic flow diagram of an alternate embodiment of the process of the invention.

DETAILED DESCRIPTION The following detailed description illustrates one or more specific embodiments by which the invention may be practiced. The description is intended to present the process by way of example and is not intended to limit the scope of the inventive concepts.

The present invention is directed to a comprehensive process for enriching low-grade iron-bearing ore materials that have heretofore been found to be unusable PCT/U82012/048550 and have generally been disposed of in low—grate or reserve stockpiles, tailing , or the like. The present process makes the use of these materials economically feasible for the production of iron and steel. As indicated, the low—grade iron—bearing materials may stem from a variety of sources and include s fractions of a wide variety of desirable iron compounds and interfering als. The low—grade material may also contain large amounts of undesirable or unusable forms of iron which are not easily processed into metal. Interfering materials or gangue may include fine particulate silica g or other clay materials, which tend to cling to the particulate iron compounds tenaciously.

The present process enriches the low~grade iron— bearing materials by concentrating desirable constituents including magnetite (Fefih), te (Fefih), goethite (FeO II C) H) and possiblv sideritp (£7er 3) : Magm—“ati re an” . . .

(Dm: 1 AL ulu (1' _L te are the main deSired iron ore compounds, The low-grade iron—bearing material is the feed al or feedstock for the t process. In this regard, it will be iated that the relative amounts of the desirable constituents may vary widely among feed materials, particularly, the relative amounts of hematite (Fefih) and magnetite (Fefih) may vary widely. An important aspect of the t process is that it adapts successfully to a wide variety of feed material compositions.

In the s, low—grade iron—bearing materials are obtained, generally from discarded stockpiles, and fed into a conventional ore crushing mill, as shown at 10 in Figure 1. This step is designed to crush the material to a size of % inch (1.9 cm), or less, and preferably the PCT/U82012/048550 material is reduced to a size of % inch (0.64 cm), or less.

The crushed feed material is next fed into a commercially available ball mill at 12, along with an amount of water at 14, where it is further reduced to a size of about —300 to —500 mesh, and able to at least ~4OO mesh. Such ball mills are commercially available in various sizes and capacities, and one such mill is a ill® obtainable from Metso Corporation of Finland. Upon leaving the ball mill, the material may be mixed with additional water at 16 to form a slurry which is subjected to screening at 18 and 20 with the oversize particulates being recycled to the ball mill at 22 and 24. The sizing screens are preferable vibrating screen devices, which are well known. Such screens are available in various capacities from k Corporation of Buffalo, NY, for e.

Material passing the screens proceeds in streams 26 and 28 to undergo ultrasonic ent at 30 as a slurry of approximately —400 mesh or less particulate matter in which the ore compound particles are covered with a layer of fine clay particles, or the like. The surface chemistry interactions of the particles creates a complex environment of electrically charged surfaces that cause fine particles of non—iron-bearing materials to adhere to iron—bearing particles in a manner that makes them difficult to separate using conventional physical separation techniques. The fine non—iron—bearing or gangue materials represent a significant on of the low-grade ore materials and are y small clay particles (slimes) containing silica inates. The clay particles are by nature very small (<5 microns) and need to be separated from the iron—bearing materials in order to allow the material to achieve the desired high PCT/U32012/048550 iron concentration. Due to the plate—like structure of clay, clay particles can form strong adhesion contact with other flat surfaces. This strong adhesion of clay particles to surfaces, such as iron-bearing ore materials, is difficult to break.

It has been found that the ated turbulence produced by the application of a sufficiently strong ultrasonic treatment can cause the adherence tendency to weaken and allow the materials to separate. The ultrasonic ent at 30 causes the slurry to undergo such a highly turbulent phase produced by the ultrasonics, as will be explained.

In ultrasonic treatment, as is well known, ultrasonic waves are produced by applying an AC voltage to a crystal such as lead zirconate titanate which undergoes uous shape s g pulsations that travel through the slurry; and, if generated with §u fiCient amplitude, the pulsations will produce bubbles that grow to a large resonant size and suddenly collapse causing high local pressure changes and a great deal of Violent turbulence in the slurry; 'This type of ultrasonic treatment has been found to be very beneficial in separating si ica and clay als from the iron— bearing compounds in the feed al. The intensity of the ultrasonic turbulence can be controlled as needed to accomplish the desired separation.

In this regard, it has been found that ultrasonic treatment for a selected nce time and using ultrasound having an intensity generally from about 100 watts/gallon of slurry to about 1000 watts/gallon of slurry works well to separate silica and clay fine particles from the earing particles in the slurry.

The residence time and required ultrasound intensity will PCT/U82012/048550 vary ing on the composition of the slurry being sed.

The material g the ultrasonic treatment stage at 32 is a mixture of iron—bearing compound fractions and separated particulates of clay and silica material and other tailing als. This material generally contains both magnetic and paramagnetic iron ore fractions.

The slurry stream 32 is subjected to a first or rough low intensity wet ic separation at 34 using a conventional continuous wet magnetic separator that produces a magnetic field of about 700—1600 gauss. These devices are well known and ble commercially in a range of capacities.

The rough ic separation further concentrates the magnetic fraction in the slurry at 36 and a separate tail fraction containing paramagnetic materials is diverted at 38. Further magnetic separation is carried out in cleaner separators at 40 and 42 and additional makeup water may be added at 44 and 46. In each of the cleaner magnetic operations, the tail or non~magnetic fraction is recirculated in line 48 to undergo further ultrasonic treatment and rough tion where the paramagnetic and interfering materials are ultimately removed at 38.

It will be appreciated that the magnetic separation sequence represented by 34, 40, 42 may be carried out by any desired number of separators which may be operated at any desired intensity level as needed to produce good separation. This may depend on the relative size of the magnetic fraction in a particular feed stock, which may vary widely. The separation generally involves vely low intensity magnetic fields between about PCT/U52012/048550 -10, 700 gauss and 3000 gauss as the magnetic fraction will readily separate under these conditions.

The concentrated magnetic fraction at 50 may have additional water added as at 52. This material is then discharged to a container at 54 and concentrated and thickened and water decanted at 56. Thereafter, it is filtered and the filter cake dried and stored at 58 for shipment separately or in combination with a paramagnetic fraction, as will be ned. The material at 58 is a loose processed material having a solids content of 90~ 95% and may be balled or compressed into pellets or briquettes using well known binders if necessary.

The primary tail stream 38, which includes the gnetic iron ore fraction, along with the interfering materials such as clays, oes further treatment in parallel with the magnetic fraction. As shown in the schematic flow diagram of Figure l, the tail stream 38 is subjected to a further UltIaSLfllC treatment step at 60, sim'lar to that usly described, to again separate the silica and clay fine particulates from the imately 4400 mesh ironlbéaring materialsl The outlet stream 62 ds to a separation step in the form of a thickener 64 which is essentially a clarifier where the heavier iron—bearing materials settle out.

This allows a portion of the lighter on-bearing materials in the slurry including some silica—containing materials and clays to be removed in an overflow stream at 66, which becomes part of the final or total tailing fraction at 88.

The thickened or underflow stream leaving the thickener 64 at 70 is subjected to a r series of magnetic separation operations, as shown at 72 and 74 using a radient magnetic separator such as a SLon vertical ring pulsating high—gradient magnetic separator PCT/U82012/048550 -11, which utilizes the combination of magnetic force, pulsating fluid and gravity to continuously process fine, weakly magnetic or paramagnetic materials. While these separators are generally classified as high intensity magnetic separators, they can be operated over a range of field strengths. The device of 72 is operated at a relatively low field strength of about lOOO—BOOO gauss, which is sufficient to separate out the hematite fraction which is ted at 76 to an intermediate container at 78. The tailing stream 80 is conducted to the second high nt magnetic separator 74. The magnetic separator 74 is operated using a relatively high field strength of about 7500—12,500 gauss which is strong enough to accomplish the tion of the remaining desirable iron ore fraction which is generally chiefly siderite and goethite.

As with the separation of the magnetic constituents, the two stages of high gradient magnetic separators 72 and 74 represent as many stages as may be necessary to accomplish the desired separation. As with the magnetic fraction, the paramagnetic materials are thereafter concentrated and d to settle and the liquid fraction is decanted off at 82. The concentrate is ed and the filter cake is then allowed to dry at 84 and is in the form of a loose material having a solids content of 90%—95%, which can be processed into s or briquettes and/or fter be mixed with the magnetic al for further processing into steel.

The g fractions 66 and 86 are removed in line 88 and 90 as total tailings. The total tailing fraction is thereafter treated to clarify and separate the water for reuse in the process.

The tailings deposit and water ry aspects of the process are illustrated in the schematic diagram of Figure 2 in which the supply and ng operations are represented at 100 and the ng circuit at 102. The ite low intensity magnetic separation circuit, including the several , is represented by 104. The tailings fraction from the magnetic separation operation 104 is seen at 106. The paramagnetic high intensity magnetic separation operation circuit is shown at 108.

The processed ic and paramagnetic concentrate fractions are shown combined for concentration at 110, filtering at 112 and storage at 114. The combined tailings/overflow from the concentration operations is shown at 116, which combines with tail portion 118 to form a total tailings stream at 120. The total tailings fraction is ted to a cyclone separation operation at 122 and the mainly water overflow stream is shown at 124 where it joins feed stream 126 which proceeds to a clarifier 128. The tailings underflow of bottom Lisclar#4.. F ,— m ’D stream from the cyclone sedaraior 122 at 131 and whe .1 “+— 0 .L m H FJ m J_ (31L, 132 are combined at 134 and fed into a tailings pressure filter at 136 where the solid filter cake is collected at 138 for transport to a tailings collection and storage ure and the liquid containing fraction or filtrate material is sent to the clarifier at 140. The clean water from the clarifier proceeds to 142 where it can be recirculated into the process at 144.

A modified or ate embodiment of the process for enriching the usable iron ore content of low—grade iron—bearing feed materials is depicted in the process flow diagram of Figure 3. Feed material is crushed in a conventional ore crushing mill at 200, as in the previous embodiment, and fed to the process, preferably as —3/4 mesh mm) material, and is passed through a screen at 202. Thereafter, the particle size of the material is 2012/048550 further reduced in a Semi—Autogenous Grinding SAG mill at 204 or a ball mill at 206, both of which are well—known and readily ble commercially in any desirable capacity. The SAG mill processes the oversize al in stream 203 and the ball mill, the material passed by the screen 202 in stream 205.

The initially screened and ground processed material is recombined at 208 where it is fed to a further finer screening at 210 using a nes or equivalent fine screen device which is preferably about —400 mesh.

Oversize material is taken off at 212 and subjected to a r grinding process by a second ball mill at 214.

Material passing the fine screen 210 at 216 and material processed by the second ball mill 214 at 218 are subjected to a further screening at 220 as by using a Derrick screen or equivalent which is designed to be ~270 to —500 mesh similar to the embodiment first described above. Oversized material is recycled in line 222 to the second ball mill 214.

It will be appreciated that, as with the first embodiment of the process, plant water may be added to form a slurry of desired consistency to the initially screened material at 224 and 226 and additional plant water may be added to any of slurry streams 208, 212, 216, 218 and 220, if desired.

The slurry of undersized material exiting the screen 220 at 228 undergoes a tion sequence as in the first bed ment including an ultrasonic treatment at 230, which is similar to that described for the first embodiment and is sufficient to separate clay and silica particulates from the iron containing species.

The sequence ues with a rough magnetic separation at 232 which again produces a magnetic fraction 234 and a tailing fraction at 236. Further magnetic separation is carried out at 238 and 240 with the combined tail fractions recycled for further ultrasonic treatment in line 242. Additional plant water can be added at 244 and 246.

As indicated, the ultrasonic treatment induces a turbulence in the slurry generally in the form of a micro turbulence that es a good particulate separation of clay and silica from the ore particles. Residence time and power can be optimized to treat the particular material being processed most efficiently.

Magnetic material exiting the final magnetic separator proceeds in line 248 to a thickener at 250 with the concentrated material being moved to a slurry storage at 252, after which it can be filtered at 254 for further processing as high iron content ore. As with the previously bed embodiment, the magnetic separation sequence may be carried out by any d number of upciateu,1 at J, separ.t0rsii- A..-“ A_A 4-..; any-_ dEblfedi- LUtEHblty-. lEVEl__,i In this embodiment, the primary tail stream 236 which includes paramagnetic and non-magnetic fractions also undergoes further processing?" However, the tail stream 236 is subjected to the thickening operation at 260 prior to further onic separation treatment at 264 of the underflow stream 262, which is similar to those described above. The overflow from the thickener goes into a g fraction in stream 266. After the ultrasonic ent at 264, the al is subjected to a series of high gradient or high field strength magnetic separation ents at 268 and 270 using a field of a strength generally from about 7,500 gauss to about 12,500 gauss with the separated paramagnetic ore ons taken off at 272 and 274 and the tailing in stream 276. The total tailing stream 278 is processed through a thickener at 280 to a slurry storage tank or the like at 282 before 1000664887_1.DOCX being filtered at 284 and further processed as shown in Figure 2.

It is important to note that it is the particular combination of ultrasonic and magnetic treatments that enables the iron content of low—grade, commercially‘ le ore deposits to be converted into commercially Viable feedstocks for iron and steel making processes that contain 40%—62% iron.

Table I shows typical enrichment rates for Roast 'Taconite tite) and hematite tuents and an average 50—50 mixture. 4867_1.DOCX —15A— gag—flan $8.8 38.: $8.5 :8...» flflfl 38.3 used" $8.5 :85 $8.2 “Soda Efia E: «an? Efiafififi: nag—Hung: :86 uses :95 $8.,“ fldfl :8)“ $8.3 $8.2 38.: 38$ .Sofi flag :35 xmmfi wfldflflafl H $8.8 $8.2 $8.2 :83 Ema x83 x86 $8.0 x85 .83 :86 wad 38.0 xooa wflfiflfla mam/NH. gag fig x83 28.3 $8.8 38d... flfifl $3.8 $8.8 x8$ x8.mm x8.mm 28.3 flQfl :33 $3.3 wflfldfiga mumbcmucou 53% . :83 :33 .SSM gsmm flflfi $8.3 :8.mm $8.3.” $8.3 :83 “80.5 £33 x33 amnmm 52m fifldflfifld tam“. g8.5553 2.295 «€83 828$ afifidfim out»: 325»: 9525: annex. 2.2.5: Hausa: wfififl yucca 29355 58.. as: gang“ afl 58¢ 1000746622_1rd0cx —15B— Samples of the enriched. ore material in the form of both nuggets and fine particles have been successfully processed directly into metallic steel (about 1—5% carbon).

This ion has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use ments of the example as :required. However, it is to .be 'understood that the invention can be carried out by specifically different devices and that various modifications can be accomplished t ing from the scope of the invention itself.

As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and. "comprisedfi, are not intended. to exclude other additives, components, integers or steps.

Reference to any prior art in the ication is not, and should not be taken as, an acknowledgment, or any form of suggestion, that this prior art forms part of the common general knowledge in New Zealand or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant Inf a person skilled jII the art. 1000746622_1.d0cx —16-

Claims (36)

1. A method of enriching the iron ore content of low—grade earing materials to provide a concentrate having' a relatively high iron content comprising: 5 (a) forming a water slurry of low—grade iron—bearing materials having a relatively small particle size; (b) subjecting the slurry of (a) to a first ultrasonic treatment to separate interfering materials, including clays, from iron ore nds; 10 (c) subjecting the slurry of (b) to at least one stage of low intensity’ magnetic separation. to produce magnetic concentrate and a paramagnetic tail slurry fraction; (d) treating the paramagnetic tail slurry fraction to a thickening operation; 15 (e) treating the thickened paramagnetic tail fraction to a second ultrasonic treatment to separate interfering materials; and (f) ng the thickened paramagnetic tail fraction of (e) to at least one stage of high nt magnetic 20 separation to te and produce a concentrate of paramagnetic ores.

2. A method as in claim 1 including combining of magnetic and paramagnetic concentrates to form a combined concentrate having a high iron content. 25

3. A method as in claim 1 or 2 wherein (c) includes a plurality of successive stages of low intensity ic separation. 1000746622_1.docx

4. A method as in any one of the preceding claims, wherein (f) includes a plurality of successive stages of high gradient magnetic separation.

5. A method as in claim 4 wherein a concentrated fraction separated by each stage of high gradient magnetic separation is removed separately.

6. A. method as in claim 2 wherein the concentrate is subjected to further thickening and filtering ions.

7. A method as in any one of the preceding , n 10 said high gradient magnetic separation is of a strength from about 7,500 gauss to about 12,500 gauss.

8. A method as in claim 4 or 5 wherein said high gradient magnetic separation. is from about 7,500 gauss to about 12 500 gauss. 15

9. A method as in any one of the preceding , wherein said slurry of low—grade iron—bearing materials of (a) comprises solids of a size S —320 mesh.

10. A method as in any one of the preceding claims, n said low—grade iron—bearing feed material is subjected to crushing 20 and ball mill grinding operations in forming the slurry of (a).

11. A method as in clafln 9 wherein said slurry comprises solids S —400 mesh.

12. A method as in any one of the preceding claims, wherein said ultrasonic treatment includes the generation of micro— 25 turbulence in said slurry.

13. A method as in any one of the preceding , wherein said low—grade earing feed material comprises one or more of the following ore forms: magnetite (Fe3O4), hematite ), geothite (Fe0.0H), siderite (FeCO3). 1000746622_11docx -18—

14. A method as in any one of the ing , further comprising recovering and reusing process water.

15. A method as in any one of the preceding claims, wherein the paramagnetic tail fraction of (c) is separated at the first magnetic separator and successive tail fractions are recycled to (b) .

16. A method as in any one of the preceding claims, wherein said concentrates are further filtered and dried to 90—95wt% solids. 10

17. A method as in any one of the preceding claims, wherein said trates contain at least 52wt% iron.

18. A method as in any one of the preceding claims, wherein said slurry is screened prior to the application of said first ultrasonic treatment. 15

19. A method as in any one of the preceding claims, further comprising adding one or more s of water to said slurry as required.

20. A method of enriching the iron ore content of low-grade iron—bearing materials to provide a concentrate having’ a 20 relatively high iron content comprising: (a) forming a slurry' of low—grade iron-bearing als having a relatively small particle size; (b) subjecting the slurry of (a) to a first ultrasonic treatment to te interfering materials, ing 25 clays, from iron ore compounds; (c) subjecting the slurry of (b) to a plurality of successive stages of low intensity magnetic separation to produce a separate magnetic trate fraction and a paramagnetic tail slurry fraction; 10007466223 .docx (d) treating the paramagnetic tail slurry fraction. to a thickening operation; (e) treating the paramagnetic tail fraction to a second ultrasonic step to separate ering materials; and (f) treating the tail fraction to a plurality of successive stages of high gradient magnetic separation to separate a trate of paramagnetic ores from the tail fraction.

21. A method as in claim 20 wherein (a) involves the use of 10 a plurality of successively smaller mesh screens.

22. A method as in claim 21 wherein material failing to pass first screen is ground in a SAG mill and material passing said first screen is ground in a first ball mill.

23. A method as in claim 22 wherein said material as 15 processed in said SAG mill and said first ball mill is subjected to a further screen of about ~4OO mesh with oversize material being processed in a second or d ball mill.

24. A method as in claim 23 further comprising subjecting the material to a third screen of -270 to —500 mesh and recycling 20 zed material to said second ball mill.

25. A method as in any one of claims 20 to 24 including the combining of magnetic and paramagnetic concentrates.

26. A method as in any one of claims 20 to 25 wherein said ultrasonic treatment es the generation of micro—turbulence 25 in said slurry.

27. A method as in any one of claims 20 to 26 wherein said low-grade iron-bearing feed al comprises one or more of the following ore forms: ite (Fefih), hematite (Fefih), geothite (Fe0.0H), siderite (FeCO3). 1000746822‘1docx

28. A method as in any one of claims 20 to 27 wherein said high gradient magnetic separation. is of a th front about 7,500 gauss to about 12,500 gauss.

29. A method as in any one of claims 20 to 28 wherein the tail fraction is subjected to a thickening step prior to step (d).

30. A method as in any one of claims 20 to 29 wherein the paramagnetic tail fraction of (c) is separated at the first magnetic separator and successive tail fractions are recycled to (b). 10

31. A method as in any one of claims 20 to 30 wherein said trates are further filtered and dried to 90—95wt% solids.

32. A method as in any one of claims 20 to 31 wherein said concentrates contain at least 40wt% iron.

33. A Inethod. as in any' one of claims 20 to 32 r 15 comprising adding one or more amounts of water to said slurry as required.

34. A. method as in any' one of claims 20 to 33 further comprising recovering and reusing process water.

35. A method as in any one of claims 1 to 19 wherein said 20 ultrasonic ents include an. ultrasonic intensity generally from about 100 watts/gallon to about 1000 gallon for a ed sufficient residence time.

36. A method as in any one of claims 20 to 34 wherein said ultrasonic treatments include an. ultrasonic intensity generally 25 from about 100 watts/gallon to about 1000 watts/gallon for a selected sufficient residence time.