Aug. 22, 1967 J‘ E. LAWVER 3,337,328 IRON ORE BENEFICIATION PROCESS

Filed June 19, 1964 6 Sheets-Sheet l

Heavy Media Tailings Tailing Pond Fines or Semitaconite 25 to 50% Iron FIG. 1 I Crush and/or Grind to Free the Iron Oxide

Partial Concentration to Separate Iron Mineral from Waste Product by one of Following Processes

or or A B C

High Intensity Wet Froth Gravity Magnetic Separation Flotation Separation l l I I Partial Waste Partial Waste Partial Waste Concentrate Product Concentrate Product Concentrate Product L I I . Gravity Gravity Concentrates or Separation of Partial‘ Concentrates Low-grade Hematitic Ore From "An or “all or "ch 40 to 58%‘.Iron

Crush and Grind to Liberate Silica

Coarse Fraction Minus O. 010" plus 0.003" Fine Fraction‘ Less than 0.003" G to 75% Weight @ 25 to 100% Weight Electrodynamic Process to Separate Froth Flotation Process to Separate Iron Oxides and Silica Iron Oxides and Silica Silica Product to Waste Silica Product to Waste

Iron Oxide Concentrate 62 to 65% Iron 5% Silica

' INVENTOR J9me; E. L’ AWl/ER

14 T TORNE Y! Aug. 22, 1967 J. e. LAWVER 3,337,328 IRON ORE BENEFICIATION PROCESS Filed ‘June 19, 1964 6 Sheets-Sheet 2

Crude Ore %Wt. 100. O0 FIG.' 2 %Fe%Insol.4l.l9 39 . 35

4" Screen

-4" Ore +4" Ore %wt.84.45 %Wt. 15.39 %E‘e 4O. 19 %E'e 34. 75 %Inso]l . 48. 57 Crush 8 Screen %Fe Rec.l3.59

_ -___.______+14 Mesh ~~14 Mesh

Heavy Media Sands Slimes Separation '7‘Wt- 9-58 Spirals %E‘e 11.78 Sinks Floats ' Concentrate r(‘ailing %Wt. 11.31 %Wt. 14.12 57 . 00 %Fe I28. 00

Grind to 100% -—48 Mesh Grlnd

—48 +325 Mesh ~325 Mesh (several sizes) Flotation

High Tension ' Flotation Concentrate ‘Failing 7m, 17.48 %wc. 16.70 Concen- Concen- %Fe 50.00 %Fe 5. 0O trate Tailing trate Tailing High Tension Concentrate Tailing Concentrate ‘Failing Wt. 30.04 %Wt. 10.81 %Wt . 10.93 %Wt. 6. 55 Insol.Fe 65.5.0+ 00 %Fe l 34.41 %Insol.%Fe 65.005.0+ %Fe i 25. 0O

if

Combined Concentrate Combined ‘Failing %Wt. 40.97 %Wt. 43. 56 %Fe 65.00 %E‘e 16.81 %Insol_ 5. 0+ %Inso1. 72. 5O Crude %Fe Rec. 67. 68 %§V‘e Rec. 18.73 ~4" Ore %Fe Rec. 78. 32

INVENTOR. JAMES/f. LAWl/ER

‘ 311%WM ‘ A?‘ TORNEK: Aug- 2'2, 1967 J. E. LAWVER I 3,337,328 IRON ORE BENEFICIATION PROCESS Filed June 19, 1964 6 Sheets-Sheet 3

‘Tailings F 3 l.__._.__‘-__.______~—>Grind'through 28 to 48 Mesh Sizing I I Gravity Separations El/Iiddlingv cencet-ltrate 'l‘ai*1 ling I Open Circuit Rod Mill waste I Filter and Dry I I é-xElectrostatiéc Separation I Tailing Conceitrate l To Waste To Briquetting Plant I@—GravityI orSeparation to

Tail‘ings |~-— -— -— —— —-—,—- Grind throughv 35 to 48 Mesh l I . I Float with Fatty Acid, Fatty Acid Soap, I or with Petrolpeum Sulfonate I I Iron Oxide Froth Product ' SilicJCell Product I Open Circuit Rod Mill > Waste I Float with Fatl’q}v Acid or Soap . Y I ‘*Silica Cell Product Iron Oxide Froth Product I Filter Iand. Dry 4 I Electrostatilc Separation I Tailing Final Concentrate I To Waste ' To Briquetting Plant L or to I Gravity Separation

INVENTOR JJ‘IMESE. LA WVER‘ BY mil/Ah 147- TaR/vE Ks‘ Aug- 2.2, 1967' J. E. LAWVER 3,337,328

_ ’ IRON ORE BENVEFICIATION PROCESS Filed June 19, 1964 6 Sheets-Sheet 4

_ F165

Tailings

Grind through 35 to 48 Mesh

Float with Fatty Acid, Fatty Acid Soap, or with Petroleum Sulfonate

Iron Oxide Froth Product Silica Cell ‘Product

Open Circuit Rod Mill Waste

Scrub with 10 lb Sulfuric Acid/Ton Ore

Wash

Float with Calcium Ion and Fatty Acid. l

Iron Oxide Cell Product Silica Froth Product

Filter and Dry Waste Electrostatic Separation Final Concentratq To Briquetting Plant

INVENTOR. JZMEJELAWVER’

ATTORNEY! Aug- 22, 1967 J. E. LAWVER 3,337,328 IRON ORE BENEFICIATION PROCESS

Filed June 19, 1964 ' 6 Sheets-Sheet 5

‘ Crude Ore ' Wt. 100. 00 FIG_ 6 ‘ %Fe 31.31

Crush 5. Grind to Liberation

Wet or Dry Low Intensity Magnetic Separation magnetite Magnetite Free Concentrate Product % Wt. 1.00 % Wt. 99.00 % Fe 60. 0O % Fe 30.01

High Intensity Wet Magnetic Rougher Separator Rouqher 'I‘ailing Rougher Concentrate %‘ Wt. 34. 95 % Wt. 64.05 % Fe 8. 63 % Fe 43.24 --»-~£@¥1Ye __.______j_ High Intensity Wet Magnetic Cleaner Separator

Cleaner Concentrate Cleaner ‘Failing % Wt. 46. 23 ‘7.. Wt . 17. 82 % Fe 52.29 % Fe 19. 76 High Intensity wet Magnetic Recleaner Separator

Recleaner Concentrate Recleaner 'I‘ailing ‘7. Wt, 37. 22 % Wt. 9. 01 % Fe 58. 23 % Fe 27. 76

A or I B

Silica Flotation by Silica Flotation Calcium Activation Using an Amine

Final Conc. Tailing Final Conc. Tailing % Wt. 29.45 % Wt. 7. 77 % Wt. 26.85 ‘ % Wt. 10. 37 % Fe 64. 16 % Fe 35. 75 % Fe 64. 16 % Fe 42.87 % Insol . 5.02 % Insol. ' 5. 01 %Fe Rec. 62 . 34 %Fe Rec. 56.84

INVENTOR. $4ME5E. ZAWVER B Y 1} if

x47- TOR'NE v)" Aug.‘ 22, 1967 J. E. LAWVER 3,337,328 IRON ORE BENEFIGIATION PROCESS

‘ Filed June 19, 1964 e Sheets~$heet e

" 108

.L 5 ‘\ 9%‘<2 ' ‘ m \V) . \, __ aO ‘gIn iL \ g I Q 1 _, 5f I E’ "J wlu / aE: a /- - k / m z (L 9 / E ' k / i1’ § / __ w B‘. / z a; / n ,k / ? / 3: ‘m ./ __ g >& N i

A. : : : : 8 h. we 1r.» ‘t n. w 0 O Q Q Q Q )4 -LN5IJI.=/d§0_) NOLL var/d9!‘ ' \?IMESELAWl/ER’. INVENTOR. BY97/WMM /4 T TOR/YE v5 3,337,328 United States Patent 0 ICC Patented Aug. 22, 1967

1 2 3,337,328 Concentration is also possible by gravity methods, IRON ORE BENEFICIATION PROCESS using such devices as spirals, tables or vanning concen James E. Lawver, Edina, Minn., assignor to The Regents trators. In general, however, gravity concentration of the of the University of Minnesota, Minneapolis, Minn, a ?ner sizes produces a concentrate high in silica unless corporation of Minnesota numerous recleaning stages and large circulating loads Filed June 19, 1964, Ser. No. 376,338 are used. 19 Claims. (Cl. 75-3) It is also known that many of these ores can be concen trated by using high intensity magnetic separators. High This invention relates to a process for the bene?ciation intensity dry magnetic separators have been used com or upgrading of low grade iron-containing minerals and, 10 mercially for years. However, low grade semi-taconite more particularly, to the bene?ciation of semi-taconite cannot be economically concentrated in this manner due ores or altered taconites which have become partially to the high capital costs of such separators and to the leached and oxidized, present plant concentrates produced drying costs implicit in such a process. by gravity separation which are of marginal usefulness Electrodynamic concentration can also be used to bene because of unfavorable physical and chemical properties, 15 ?ciate ores of this type provided that the feed is thor and tailing stock piles from prior gravity separation op oughly deslimed and that the ore is thoroughly dry. In erations. There are huge reserves in the Western Mesabi such a process, however, drying costs are high because a range of Minnesota, and elsewhere, of these relatively low large portion of the original feed would eventually be dis grade iron ores, unsaleable concentrates and tailings carded as a tailing. The problem is to produce a high dumps which are becoming of increasing interest and im 20 grade concentrate at high iron recovery with a minimum portance in our nation’s economy as richer ores and more capital and operating cost. easily concentrated minerals are becoming less readily In view of the known capabilities and the known dis available. Although methods are known by which these advantages of various prior art bene?ciation methods, it low grade minerals may be concentrated and upgraded, is apparent that no single bene?ciation process can be they are unsatisfactory in many instances, either because 25 found which will lend itself to an economically feasible the upgraded or concentrated product is not saleable be ?ow sheet for the production of acceptable saleable con cause it does not meet the minimum and increasingly centrates from semi-taconite ore, from low grade concen' strict requirements of the steel mills, or because it is trates and waste products from previous separations, and prohibitively expensive, or both. other similar services of low grade iron minerals. Accord The principal object of the present invention is to pro ingly, the present invention is based upon the utilization vide an economical iron ore bene?ciation process for the of the advantageous characteristics of a combination of production of saleable concentrates which are acceptable concentrating procedures. By utilizing several types of to the steel mills because they meet the requirements of processing equipment, it is possible to sort the minerals the mills. Such concentrates should contain more than in the ore so that advantage can be taken of the particular about 60% iron and less than about 7% silica. The pres physical and chemical properties of each ore group by out process provides for the highest iron recovery with using a combination of concentrating procedures. minimum capital and operating costs. The process is The invention is illustrated in the accompanying draw‘ adapted to the upgrading of present heavy density and ings in which: spiral concentrates and to the ‘concentration of present FIGURE 1 is an exemplary schematic ?ow sheet of a plant waste products as well as crude semi-taconite ores, process for the bene?ciation of crude semi-taconite ore; and in some cases, even ?ne-grained oxidized taconite. or for the treatment of tailings from previous separation Capital costs are minimized by largely utilizing presently or concentration processes; or upgrading the concentrate existing equipment. product of present concentrating plants; The iron in semi-taconites is present largely in the FIGURE 2 is a ?ow sheet illustrating and showing form of goethite and hematite with minor amounts of 45 typical data of a process for the concentration of crude magnetite. The insoluble material is largely quartz. It semi-taconite ore; is well~known that silica can be ?oated by calcium and FIGURES 3, 4 and 5 are alternative ?ow sheets of magnesium ion activation with an anionic collector. This processes for the treatment of tailings from previous procedure has the advantage of minimum di?‘iculty with crude separation or concentration treatments; slimes, but the cores require rather ?ne grinding and the FIGURE 6 is a ?ow sheet illustrating and showing ?oat seems to be inherently weak and the treatment is typical data for a process of treating crude ore using high very expensive. Thus, a calcium-activated silica ?oat does intensity wet magnetic separation to make an initial crude not lend itself to rejecting a large quantity of coarse silica concentrate and froth ?otation to make a ?nal high grade tailing as a preliminary scalping operation. Although it concentrate; and is possible to ?oat much coarse silica with various amines, 55 FIGURE 7 is a graphic illustration of the separation the reagent cost is high and, in general, amine ?otation coe?icient plotted against maximum ore temperature procedures are extremely slime sensitive. Further, a large showing the effect of heat on separation by electrody percentage of the quartz in semi-taconite ores is stained name means. with iron and thus remains with the iron concentrate in Broadly stated, the present invention is directed to an either an amine ?oat or a calcium-activated silica ?oat. 60 economically feasible process for the production of a It is also well known that iron minerals can be ?oated, ?nal high grade concentrate from low grade iron ore, either by various fatty acids, or by petroleum sulfonates. with high iron recovery, by electrodynamic and/or froth Flotation of the iron minerals has the advantages that a ?otation concentration and, in some cases, in combina scalping operation at a coarse grind is possible, that the tion with high intensity wet magnetic separation. The reagent cost is modest, and that only partial desliming is 65 process is used for concentrating feebly magnetic mate necessary, The production of high grade concentrates is rial. As seen in FIGURE 1, the material is ?rst crushed usually precluded, however, because iron stained quartz and/ or ground to free the iron oxide and a crude concen tends to remain with the iron concentrate. Certain ores trate is produced by gravity methods, high intensity Wet also contain small quantities of calcium and magnesium magnetic separation methods, or by froth ?otation. This so that a fatty acid ?otation concentrate usually contains 70 concentrate will assay from 40 to 58% iron and must an undesirable portion of the quartz grains due to activa then be further treated by electrodynamic concentration tion. and/or by additional grinding and froth ?otation to pro 3,337,323 3 4 duce a ?nal concentrate. The concentrating scheme takes These ground tailings are then subjected to concentration advantage of utilizing differences in the electric, magnetic, by ?otation. The resulting ?otation concentrate is dried surface, and gravity properties between the valuable and by heating to about 125° C. and subjected to further gangue minerals. It is well known that a partial concen concentration by high tension electrodynamic separation. trate can be easily produced by gravity methods, and The two electrodynamic separation concentrates are then under favorable conditions by froth ?otation. Interfering combined with ‘the ?ne ?otation concentrate and agglo gangue materials, however, have in the past precluded merated to produce a satisfactory furnace burden. Waste the production of a high-grade concentrate. The process heat from the agglomerating plant is desirably utilized takes maximum advantage of the differences in the prop in drying the intermediate crude concentrates for the ?nal erties of the mineral species to be sorted in such a manner 10 electrodynamic separation. that it is always possible to eliminate interfering minerals A concentrate of 65% iron and 5% silica was produced and, subsequently, produce a high-grade concentrate. according to this procedure from a crude semi-taconite The details of electrical concentration of minerals are ore containing 39.35% iron and 41.19% silica. After described in “Fundamentals of Electrical Concentration crushing and screening, the —-4 inch ore represented of Minerals” by James E. Lawver, Mines Magazine, 15 84.45% of the original ore and contained 40.19% iron. January 1960. “Electrodynamic” separation refers to use The combined concentrate from the electrodynamic sep of a corona type separator, requiring corona current. aration of the +325 mesh gravity separation concen “Electrostatic” separation refers to use of a separator not trates and the ?otation concentrate of the —325 mesh requiring corona current. It is relatively simple, but ex gravity separation concentrates amounted to 30.04% of pensive, to produce a high grade concentrate by utilizing the total weight and assayed 65% iron and 5% silica. an electrodynamic separator. The present invention is di The ?otation concentrate from the tailings on the heavy rected to preconcentration of the low grade iron ore by media and spiral separations assayed 50% iron. When separation of the initial feed into fractions susceptible to dried and subjected to electrodynamic separation, the economic concentration by electrodynamic means, and resulting concentrate amounted to 10.93% of the initial other fractions susceptible to economic concentration by 25 ore and assayed 65 % iron and 5% silica. The combined froth ?otation, in order to produce a high yield of high ?nal concentrate produced from both the heavy media grade concentrate. High iron recovery renders the entire and spiral separation concentrates and tailings thus process economically feasible. amounted to 40.97% of the initial weight and assayed It has now been discovered that e?‘icient electrodynamic 65 % and 5% silica. Of the iron in the crude ore, 67.68% separation of ores containing goethite is dependent upon 30 was recovered. Of the iron in the —4 inch ore resulting a critical heating step to between about 100 to about 200° from the initial crushing, 78.32% of the iron was re C. and not over about 250° C. The ore is subjected to covered. electrodynamic separation while dry to take maximum According to an alternative process the crude ore is advantage of surface conductivity. It had previously been crushed to less than about 4 inch screen size, the sized thought to be desirable to heat goethite containing min 35 ore is deslimed by scrubbing and the slirnes are discarded. erals to about 400° C. to cause the goethite to lose two The sized and deslimed ore is then crushed to about 14 molecules of water of hydration and become hematite mesh size and screened and subjected to a ?rst gravity which is more conductive. It has now been found, how separation, which may be by available gravity separation ever, that the ore is damaged if heated excessively. As equipment to produce a crude heavy media concentrate, seen in FIGURE 7, the separation coef?cient begins to 40 cyclone concentrate or spiral concentrate. This resulting fall rapidly when the ore is heated substantially above crude gravity separation concentrate is then comminuted about 125° C. and, when the ore has been heated above to less than about 28 to 48 mesh. The mineral of less than 200 to 250° C., electrodynamic separation is not prac about 325 mesh size may be separated and subjected to ticable. In determining the separation coe?icient samples slime ?otation. The remaining material between about 28 of ore were heated to elevated temperature for 12 hours and 325 mesh size is dried to about 125° C. and then or more and then separated at 100° C. FIGURE 7 is a subjected to an electrostatic separation. The gravity sep plot of the electrodynamic separation coefficient K against aration concentrate is desirably dried by utilizing waste the maximum temperature to which the ore was subjected heat from the briquetting plant in which the concentrates prior to separation. The ore samples were heated for more are agglomerated. than 12 hours to the maximum temperature and separated 50 The tailings from the ?rst gravity separation and the at 100° C. electrostatic separation are reduced and sized to less than As one example, as applied to crude semi-taconite ore, about 28 mesh size. These tailings may be subjected to the process as illustrated in ?ow sheet form in FIGURE a further preliminary separation according to one of 2 comprises the steps of ?rst sizing the crude ore to less three separate ?ow sheets as described in detail herein than about 4 inch screen size. The +4 inch material is 55 after. The concentrate resulting from the preliminary ‘treated separately, as described hereinafter. The —-4 inch separation is further reduced by passage through an open material is crushed further and screened to about 14 or closed circuit rod mill, ?ltered and ‘dried and subjected mesh size. The —14 mesh ore is deslimed by scrubbing to an electrostatic separation. The ?nal electrostatic sepa and discarding the slimes. This deslimed material is then ration concentrates are agglomerated to produce a satis subjected to spiral gravity concentration. The +14 mesh 60 factory furnace burden, preferably by briquetting. ore is subjected to heavy media gravity concentration. According to the ?rst alternative ?ow sheet for treat The crude concentrates from the spiral and heavy media ment of the tailings, as shown in FIGURE 3, the pre separations are combined and reduced (as in a rod mill) liminary separation of the reduced and sized tailings is to 100% less than about 48 mesh size. In order to mini by gravity separation methods. The middlings from this mize the iron loss in the extreme ?nes, the —325 mesh 05 gravity separation may be recycled for admixture with material is separated and is subjected to a calcium ac further tailing for further processing and the tailings of tivated silica ?oat. This concentrate is then added to this further gravity separation are discarded to waste. the concentrate produced in the electrodynamic separa The tailings from the further electrostatic separation of tions to furnish part of the ?nes required for balling. The the original tailings may likewise be recycled for admix combined gravity separation concentrate of between 70 ture with original tailings for further processing. about 48 and 325 mesh size is dried by heating to about According .to another of the alternative ?ow sheets for 125 ° C. and then subjected to high tension electrodynamic treatment of tailings, as shown in FIGURE 4, the reduced separation. The ‘tailings from at least the spiral and heavy and sized tailings are subjected to a ?rst ?otation separa media gravity concentrations (and optionally from the tion with fatty acid, fatty acid soap or petroleum sul ?rst electrodynamic separation) are combined and ground. 75 fonate. The silica cell product is discarded as waste and 3,337,323 5 6 the iron oxide froth product is passed through the open the subsequent agglomeration step is such that it is eco~ circuit rod mill and subjected to a second ?otation with nomical to dry rougher magnetic concentrate that is, the fatty acid or soap. The iron oxide froth product of this concentrate from the wet high intensity magnetic separa second ?otation separation is then ?ltered, dried and sub~ tor then the use of costly ?otation agents can be avoided jected to electrostatic separation. The silica cell product and a high grade product is produced by utilizing differ of the second ?otation separation may be recycled along ences in electrical conductivity and in contact potential with the tailings from the ?nal electrostatic separation for charging phenomena, thus sorting the valuable iron miner further processing. als from their gangue in an electrical field. According to the third alternative ?ow sheet, as shown An exemplary ?ow sheet and typical data illustrating in FIGURE 5, the tailings are ?rst ?oated with fatty acid, 10 open circuit tests demonstrating wet magnetic separation fatty acid soap or petroleum sulfonate. The silica cell and two typical silica ?oats on a magnetic concentrate product is discarded as waste and the iron oxide froth are shown in FIGURE 6. Concentrates of about 64% product is passed through a rod or ball mill, scrubbed iron and 5% silica are produced from crude ore con with acid and washed and then subjected to a second taining only about 30% iron. The crude ore is ?rst ?otation with calcium or magnesium ion and fatty acid. 15 crushed and ground to liberate the iron oxides. This The silica froth product of this second ?otation separa crushed and ground ore is then subjected to a low in tion is discarded as waste. The iron oxide cell product is tensity magnetic separation to remove the magnetite pres ?ltered and dried and subjected to electrostatic separa ent. Magnetite concentrate in the amount of 1% of the tion. crude ore and containing 60% iron is separated at this Many of the iron ore deposits throughout the world are 20 stage. The remaining magnetite-free product is then sub easily bene?ciated because the principal iron mineral is jected to high intensity wet magnetic separation in three magnetite. The mineral magnetite, being ferro-magnetic, stages, is easily removed from its gangue material by weak The initial rougher separator divides the magnetite-free magnets, and practically no sophisticated metallurgy is product into two fractions of which the concentrate involved to produce a concentrate. Many of the other 25 amounts to 64.05% of the initial weight in which the iron iron minerals, however, are para-magnetic and can be content is upraded to 43.24%. This rougher concentrate concentrated magnetically only in machines having very is then optionally reground and subjected to an intermedi high magnetic ?elds and high ?eld gradients. For many ate stage cleaner high intensity wet magnetic separation. years dry high intensity magnetic separators have been Again two fractions result, of which the concentrate on the market, and in fact, dry high intensity magnetic 30 amounts to 46.23%, of the initial ore weight and is up separators are used commercially in processing certain graded to 52.29% iron content. This cleaner concentrate ores. The low capacity and concomitant operating costs it subjected to a further high intensity, wet magnetic re of these units, however, preclude their use as a concen cleaner separation stage, from which the concentrate trating device for low grade Minnesota and other domes amounts to 37.22% of the initial ore weight and con tic ores. There are also several high intensity wet mag 35 tains 58.23% iron. netic separators being sold, but until recently, none of the This is below the minimum requirement for an accept available units have had su?icient capacity or su?iciently able concentrate. Accordingly, this material must be ‘fur low operating costs to be usable with low grade iron ther concentrated in order to be suitable for the steel ores. It has now been possible to devise a process for mills. Two alternative silica ?otation systems are shown. bene?ciating the so—called nonmagnetic iron ores. A com 40 In the ?rst a calcium activated silica ?oat is used. The bination process of high intensity wet magnetic separation ?nal concentrate corresponds to 29.45% of the initial followed by either froth ?otation or electrodynamic sepa weight. It has an iron content of 64.16% and a silica con ration permits the production of high grade concentrates tent of 5.02%. Both of these are well within the require with low capital investment and low operating costs. ments of the steel mills. By this method, 62.34% of the A typical process in which a wet high intensity mag iron initially present was recovered. As .an alternative, the netic separation is made is as follows. The ore, in which recleaner concentrate is subjected to a silica ?otation using the iron minerals consist essentially of the so-called non an amine. This produces a ?nal concentrate correspond magnetic iron oxides, hematite and goethite, is ?rst ing to 26.85% of the initial ore weight. This concentrate crushed to liberation. The highly magnetic magnetite, has an iron content of 64.16% along with 5.01% silica which is always present in at least trace quantities, is 50 and corresponds to an iron recovery of 56.84% of that removed by a low intensity magnetic separator. A crude initially present. partial concentrate is then made using a wet high 1n Alternatively, the recleaner concentrates from the last tensity magnetic separator (Carpco) in order to reject the high intensity wet magnetic separation stage may be bulk of the gangue material from the ore and produce processed further according to the ?ow sheet of FIGURE a concentrate appreciably higher in iron content than the 55 1 by being dried to about 125° C. and then subjected feed. If the original comminution step is such that the to further electrodynamic separation to further concentrate gangue materials are completely, liberated in the mag the iron values. As used herein “high intensity” refers to netic concentrate, the concentrate is then further treated a ?eld of the order of about 20,000 to 22,000 gauss and by either ?otation or by electrodynamic separation: If a high ?eld gradient (non-uniform) and “low intensity” complete liberation is not obtained in the initial grind, 60 refers to a ?eld of the order of about 500 to 1500 gauss. the partial concentrate is further ground before subject The mineralogy, liberation characteristics ‘and size dis ing it to the ?nishing steps by ?otation or electrodynamic tribution of the semi-taconite materials are such that any separation. . optimal process must be tailor-?t to the: ore. This is true Flotation is carried out ?oating the silica either with in ?otation as well as in electrostatic or electrodynamic a cationic reagent, such as amine, or by calcium (or other 65 separation. For example, microscopic study of the coarse metal) ion activation and an anionic reagent, such as and ?ne heavy media concentrates from a Western Mesabi tall oil. By making a silica ?oat on the material that ‘has semi-taconite show that there are three stages in the been partially concentrated magnetically, it is possible liberation of the entrapped silica from the concentrates. to produce high grade concentrates that cannot be made The ?rst stage involves the liberation of cherty or ?inty by ?otation alone. This is because, Where the iron ore con 70 rock layers locked with the coarser heavy media con centrate is used as the ?otation feed, it di?ers from the centrate sink fraction that can be substantially liberated crude ore in that it has been freed of ‘many of the ob by grinding through about one-quarter inch. The second jectionable impurities normally causing di??culty in ?ota stage involves liberation of hematite from the cherty tion. The ?nal concentrate whether from ?otation or from layers at about 65 mesh. The third stage involves libera~ electrodynamic separation, is then agglomerated. When 75 tion of silica from the iron rich layer at —325 mesh. While 3,337,323 7 8 study shows that these coarse and ?ne heavy media con 65.2% iron, 5.0% silica and represented recovery of centrates can be slightly upgraded by gravity methods by 66.4% of the original iron content of the concentrate grinding no ?ner than 10 mesh, substantial additional starting material. The -—325 mesh fraction represented improvement in grade requires further grinding below 65 30% of the original weight and this fraction contained mesh with supplementary concentration techniques. 50.5% iron. The ?otation feed after discard of the slimes In the case of cyclone concentrates, mineralogical ob represented 23.0% of the weight and contained 50.1% servations have shown that the dominant mineral is iron. The ?otation concentrate represented 16.4% of the hematite which is substantially liberated in the 60/100 original weight, contained 61.5% iron and 5.7% silica mesh size range. In the case of spiral concentrates, it has and represented recovery of 17.5% of the initial iron content. The concentrates when combined represented been shown that the most effectively concentrated ma 10 terial is in the 28/48 mesh size range Whereas the 48/150 75.3% of the initial weight, contained 64.4% iron and mesh size fraction is the least elfectively concentrated. 5.2% silica and represented 83.9% iron recovery. Microscopic examination of heavy media tailings assay It is apparent that many modi?cations and variations ing 22.75 percent iron showed two liberation points. The of this invention as hereinbefore set forth may be made hematite grains are substantially liberated from the silica 15 without departing from the spirit and scope thereof. The gangue with a 28 to 48 mesh grind. However, concentrates speci?c embodiments described are given by way of ex produced with this coarse grind have ?ne inclusions of ample only and the invention is limited only by the terms silica that require a 65 to 100 mesh grind for liberation. of the appended claims. Grinding costs and slime losses may be minimized by I claim: rejecting a rougher tailings fraction after a coarse grind 20 1. A process for the bene?ciation of low-grade iron and then regrinding the concentrate to effect complete ore material containing principally goethite and hematite liberation. Comminuted and partly deslimed tailings from to produce a concentrate of at least about 60% iron with the heavy media gravity separation is subjected to con no more than about 7% silica, which process comprises: centration by both gravity (tabling) and by froth ?ota (A) crushing the low-grade iron ore material to lib tion. The concentrate from this intermediate step is then 25 eration size to free the iron oxides, dried and upgraded by electrodynamic separation. (B) separating the iron mineral from waste product Studies have shown that the rock rejects, that is, that to form an initial crude concentrate, +4 inch material from initial crushing of crude ore, and (C) crushing and grinding the initial crude concen coarse and ?ne heavy media tailings, are often mineral trate to less than about 0.010 inch particle size ogically and texturally equivalent. Improvement in grade 30 to liberate the silica, occurs about 48 mesh at the size where hematite is (D) separating the iron oxides from the silica and beginning to be liberated from the cherty ground mass. (E) agglomerating the iron oxide concentrate. Cyclone tailings were found to contain nearly the same 2. A process according to claim 1 further characterized hematite to goethite ratio as cyclone concentrate and are in that: amendable to the same type of supplementary concentra 35 (A) the crushed and ground initial crude concentrate tion. Similarly, size or spiral tailings are found to compare is separated into fractions including a ?ne fraction with rock reject and heavy media tailings. The mode of of less than about 0.003 inch particle size and treatment thus depends upon the nature of the initial ore (B) said ?ne fraction is subjected to froth ?otation to starting material. Where the initial feed is crude ore, it is, separate the iron oxides from siliceous gangue. of course, subjected to preliminary crushing and sizing 40 3. A process according to claim 1 further characterized treatments which have already been performed as part of in that the crushed and ground initial concentrate is: ‘another process in the case of plant concentrates and (A) separated into fractions including a coarse frac tailings. tion of more than about 0.003 inch particle size, The percentage of iron in concentrates is raised several (B) said coarse fraction is dried by heating to at least points when a goethetic type concentrate is ?red to make 45 about 100° C. and no more than about 250° C. and a pellet. For example, a 62% iron product is raised to (C) subjected to high tension electrodynamic separa about 65% by ?ring. tion to separate the iron oxides from Waste product. Heavy media concentrates can be easily upgraded by 4. A process according to claim 1 further characterized utilizing differences in surface electrical conductivity be in that: tween the goethite concentrate and the quartz gangue. In 50 (A) said low-grade iron ore material is selected from general, these materials can be sufficiently upgraded by the class consisting of semitaconite ore and tailings making about a 28/48 mesh grind, desliming the com ‘from other iron ore bene?ciation processes contain minuted material and making an electrodynamic separa ing 25 to 50% iron, and tion on the dried deslimed product. However, in order to (B) said initial crude concentrate is produced by high upgrade spiral and cyclone concentrates with high iron 55 intensity wet magnetic separation, and recovery, it is necessary to utilize supplementary concen (C) said initial crude concentrate is upgraded by silica tration techniques. ?otation. One embodiment of a process according to the present 5. A process according to claim 4 further character invention utilized for upgrading present plant spiral and ized in that said high intensity wet magnetic separation cyclone concentrates is as follows. The concentrates are 60 is carried out in a plurality of successive stages in a ?eld ?rst ground to 100% —48 mesh or ?ner. This material of about 14,000 to 22,000 gauss. is then separated and that larger than 325 mesh is dried 6. A process according to claim 1 further character and subjected to high tension electrodynamic separation. ized in that: . The —325 mesh material is treated with a thickener and (A) said low-grade iron ore material is selected from the extreme slimes discarded. The remaining material is 65 the class consisting of semitaconite ore and tailings separated in ?otation cells and the concentrate combined from other iron ore bene?ciation processes contain With the electrodynamic separation concentrate. ing 25 to 50% iron, and By this method spiral and cyclone concentrates con (B) said initial concentrate is produced by froth taining 57.80% iron and 12.35% silica have been up ?otation. graded to produce a concentrate of 64.4% iron and 5.2% 70 7. A process according to claim 1 further characterized silica with 83.9% iron recovery. Upon grinding and in that: screening, 70% of the weight and 60.9% of the iron of (A) said low-grade iron ore material is selected from the original concentrates were in the +325 mesh frac the class consisting of semi-taconite ore, tailings from tion. After electrodynamic separation, the concentrate other iron ore bene?ciation processes containing 25 amounted to 58.9% of the original weight, contained to 50% iron and low-grade hematitic ore and 3,337,323

. . 10 . (B) said initial concentrate is produced by gravity sep (C) scrubbing the —-14 mesh ore and discarding the aration. slimes, 8. A process for the bene?ciation of low-grade iron (D) subjecting the scrubbed -14 mesh ore to gravity ore material containing principally goethite and hematite separation, to produce a concentrate of at least about 60% iron with (E) subjecting the +14 mesh ore to a heavy media no more than about 7% silica, which process comprises: gravity separation, (A) crushing the low-grade iron ore material to lib (F) combining the concentrates from at least the grav eration size to free the iron oxides, ity separations and reducing to less than about 48 (B) separating the iron mineral from waste product mesh size, to form an initial crude concentrate, 10 (G) separating the concentrate into fractions including (C) crushing and grinding the initial crude concen a coarse fraction and a ?ne fraction of gravity separa trate to less than about 0.010 inch particle size to tion concentrate of less than about 325 mesh size and liberate the silica, subjecting that ?ne fraction to metal ion activated (D) separating said concentrate into fractions includ silica ?otation using an anionic collector, ing a coarse fraction and a ?ne fraction of less 15 (H) drying the coarse gravity separation concentrate than about 0.003 inch particle size and subjecting of between about 48 and 325 mesh size by heating to said ?ne fraction to froth ?otation to separate the at least about 100° C. and no more than 250° C. and iron oxides from siliceous gangue. subjecting to a ?rst electrodynamic separation, (E) drying the coarse fraction of crushed and ‘ground (I) combining the tailings from the gravity separations initial concentrate by heating to at least about 100° 20 and grinding, C. and no more than about 250° C. (J) subjecting the ground tailings to concentration by (F) subjecting the dried coarse fraction to electro ?otation, dynamic separation and to separate the iron oxides (K) drying the resulting ?otation concentrate by heat~ from waste product and ing to at least about 100° C. and no more than about (G) combining the iron oxides from the froth ?otation 25 250° C. and subjecting to further concentration by and electrodynamic separations and agglomerating. a second electrodynamic separation, and 9. A process for the bene?ciation of low-grade iron (L) combining and agglomerating the ?rst and second ore material containing principally goethite and hematite electrodynamic concentrates along with the —325 to produce a concentrate of at least about 60% iron with mesh ?otation concentrate. no more than about 7% silica, which process comprises: 17. A process for upgrading gravity separated spiral (A) crushing the low-grade iron ore material to lib and cyclone concentrates of low grade iron ores contain‘ eration size to free the iron oxides, ing principally goethite and hematite to produce an im (B) subjecting the crushed iron ore material to high proved ore concentrate of at least about 60% iron with no intensity Wet magnetic separation to separate the more than about 7% silica, which method comprises: iron mineral from Waste product to form an initial 35 (A) reducing the gravity separation concentrate to less crude concentrate, than about 48 mesh size, (C) separating the iron oxides from the silica in the (B) separating the concentrate into a coarse fraction initial crude concentrate, and and a ?ne fraction and drying the coarse sized gravity I (D) agglomerating the iron ore concentrate. separation concentrate of between about 48 and 325 10. A process according to claim 9 further character mesh size by heating to at least about 100° C. and ized in that said high intensity wet separation is carried no more than about 25 0° C. and subjecting to electro out in a ?eld of about 14,000 to 22,000 gauss. dynamic separation, 11. A process according to claim 9 further charac (C) thickening the ?ne concentrate of less than about terized in that said crushed low—-grade iron ore material 325 mesh size and discarding the slimes, is subjected to an initial low intensity magnetic separa 45 (D) subjecting the thickened ?ne gravity separation tion carried out in a ?eld of about 500 to 1500 gauss to concentrate to further concentration by froth ?ota remove any magnetite present in the ore material. tion, 12. A process according to claim 9 further character (E) combining the electrodynamic and cell ?otation ized in that said high intensity wet magnetic separation concentrates, and is carried out in a plurality of stages, the partial concen 50 (F) agglomerating the combined concentrates. trate from each preceding stage then being further con 18. A process for upgrading tailings containing prin centrated in- a next succeeding stage. cipally goethite and hematite from prior bene?ciation 13. A process according to claim 9 further charac treatments or iron ores to produce from the tailings an terized in that the silica in the initial crude concentrate ore concentrate of at least about 60% iron with no more from the high intensity wet magnetic separation is sep 55 than about 7% silica, which method comprises: arated from the iron oxide by silica froth ?otation. (A) reducing the tailings and sizing to less than about 14. A process according to claim 13 further character 28 mesh size, ized in that said silica ?otation is carried out by use of a (B) subjecting the reduced and sized tailings to a pre ?otation reagent selected from the class consisting of ca liminary separation into a concentrate and a waste tionic ?otation reagents and metal ion activated anionic 60 product, ?otation reagentsf (C) further reducing the concentrate of the preliminary 15. A process according to claim 9 further character tailings separation, ized in that the initial crude concentrate from the high (D) ?ltering and drying the concentrate by heating to intensity wet magnetic separation is ?rst dried and the iron at least about 100° C. and no more than about 250° oxide is separated from the silica by electrodynamic sepa 65 C. ration. (E) subjecting the ?ltered and dried concentrate to 16. A process for the bene?cation of crude semi~taco electrodynamic separation into a further concentrate nite ores to produce an ore concentrate of at least about and further waste product, and 60% iron with no more than about 7% silica, which (F) agglomerating the electrodynamic separation con process comprises: 70 centrate. (A) sizing the crude ore to less than about 4 inch 19. A process according to claim 18? further charac4 screen size, terized in that the electrodynamic separation concentrates (B) crushing the ~—4 inch ore and screening to about are agglomerated by briquetting. 14 mesh size, 75 (References on following page) 3,337,323 11 12 Referencés Cited 2,675,966 4/1954 Kilhlstedt ______241-24 X 11/1960 Weston ______241-24 UNITED STATES PATENTS 2,962,231 3,022,956 2/1962 Haseman ______241-24 2,075,466 3/1937 Queneau ______75-1 3,067,957 12/1962 Erck ______241-24 X 2,175,484 10/1939 Rees ______241-24 X 2,307,064 1/1‘943 Patterson ______241-24 5 WILLIAM W. DYER, IR., Primary Examiner. 2,557,059 6/1951 De Marchi ______241-24 X HARRY F. PEPPER, JR., Examiner. 2,558,635 6/1951 Vedensky ______241-24 X