FLOTATION SYSTEM

Abstract: An apparatus (10) for removing materials from a bath of fluid (14) includes at least one vessel (12) having a feed inlet and outlet. The vessel (12) contains a bath of fluid (14) and froth (20) located above the bath (14). At least one disperser apparatus (40) includes a rotatable shaft (44) and a rotor (48) connected to the shaft (44) and located in the bath (14). At least one froth removing device (22) includes at least one froth-removing surface (68) located at least between the shaft (44) and inwardly of the periphery of the vessel (12).

Description: FLOTATION SYSTEM Field of the Invention: The present invention is directed to the beneficiation of ore and, in particular, to a flotation system for increasing iron recovery from an iron oxide containing material. Background of the Invention; The beneficiation of ore includes numerous steps including crushing, screening, blending, grinding, concentrating, classifying and agglomerating. Flotation is an effective process for increasing the valuable mineral content of ore. Flotation systems can be used in the beneficiation of iron ores and other material such as copper containing ores, for example. The flotation process, as described in the book, The Making, Shaping and Treating of Steel , United States Steel, Ninth Edition, p. 217 (1971) , is based upon the principle that adding certain substances to liquid suspensions of fine particles of minerals and gangue produced by grinding the ore will cause certain minerals to exhibit an affinity for air. The minerals having this affinity cling to bubbles produced by passing air through the suspension and are removed as a froth product. Chemical reagents added to promote the preferential affinity of minerals for bubbles are known as collectors. Other additives may also be added to the feed or suspension to improve the flotation process. In the iron oxide flotation process for increasing the iron content of a material sich as for use in steelmaking, iron oxide-containing feed material is fed into a feed box connected to a first vessel known as a flotation cell. Located in the flotation cell is a rotor and a disperser apparatus which cause movement of the slurry while introducing air bubbles into the slurry. A series of flotation cells are connected to one another and feed liquid passes in series from one cell to the next. In the case of iron oxide-containing slurry, the froth removes silicon dioxide or silica (e.g., SiO-,) from the slurry, thereby increasing iron concentration in the slurry. A chemical collector is typically added to the slurry for generating froth which is effective to remove the silica. Froth is discharged to waste at the end of the flotation process. Therefore, froth that is high in iron content is undesirable in that it reduces the overall iron recovery from the feed material. Each flotation cell includes a lip on a side leading to a froth launder which receives froth overflow and directs it to the end of the line as waste material commonly referred to as "tailings" or "tails". The froth n the launder is sprayed with water. Froth high in iron content is directed by the launders to scavenger flotation cells for further silica removal. The iron content of the froth in the cells is progressively reduced down the line. In conventional flotation processing, a certain amount of froth is required to remove enough silica to produce a final concentrate having a particular composition and physical characteristic or grade. An additional amount of collector is added to increase the rate at which the froth moves toward the lip for removal. Collector consumption is a considerable expense in current iron oxide flotation processes. Summary of the Invention; The present invention is generally directed to an apparatus for removing material from a bath of fluid comprising at least one vessel having a feed inlet and an outlet. A plurality of the vessels are preferably in fluid communication with each other. The vessel contains a bath of fluid and froth located above the bath. At least one disperser apparatus each comprises a rotatable shaft and a rotor connected to the shaft, the rotor being located in the bath. At least one froth-removing device comprises at least one froth moving surface located at least between the shaft and a location inwardly from a periphery of the vessel. The present flotation process advantageously produces final concentrate material with targeted % Si0 2 while maximizing iron unit recovery and minimizing costs. In one preferred embodiment the froth-removing device comprises a rotatable belt supported by at least two shafts and at least one paddle member extending from the belt in the froth and moving at all times. In another embodiment the froth-removing device comprises more than one shaft each having at least one paddle member extending therefrom in the same manner. More specifically, the belt of the froth-removing device extends from adjacent the disperser apparatus (standpipe) to adjacent one of the lips. Each paddle member is pivotably movable to conserve space. A receptacle has a froth inlet for receiving froth from the vessel and a passageway for directing a froth material toward another vessel. The paddle members are spaced upwardly from the bath by a selected height effective to enable the paddle members to contact a predetermined amount of the froth yet not dip into the slurry or fluid. The selected height is effective to enable the paddle members to contact whatever amount of silicon dioxide- containing froth is formed. At least one lip extends around at least a portion of the periphery of the vessel. Also included are apparatuses for preparing iron oxide-containing feed liquid suitable for use in the flotation system. A variable speed drive operates at least one of the froth- removing devices . The greater the amine additions, the higher are the iron oxide losses in the tails. As the amount of amine is increased, it produces a tough, dense, fast moving froth which tends to occlude more iron oxide particles. By using less amine and limiting the chemical mechanism for froth removal, the present invention provides numerous advantages. A coarser grind of ore may be used to make recovery. Using less amine results in decreased iron ("Fe") tails losses and is more economical than current processing in view of the reduced amine consumption. In addition, a lower target silica may be made without a significant recovery penalty (e.g., to produce a direct reduced iron "DRI" quality feed) . Finally, fewer scavenger cells may be needed, since using less amine will result in less iron in the froth. In general, a method of removing material from a fluid according to the invention comprises rotating the rotor on the shaft in the vessel containing the bath of fluid material. The froth is formed above a surface of the bath. The fluid preferably comprises iron oxide and the froth preferably comprises silica removed from the fluid. Froth is removed from the vessel by moving at least one froth moving surface at a location at least between the shaft and a location inwardly from a periphery of the vessel. More specifically, each froth moving surface is formed by a paddle member, the method comprising moving at least one of the paddle members above the bath (e.g., in the froth and not in the bath) . In the embodiment where each paddle member extends from a belt disposed around at least two shafts, the method comprises moving each paddle member with the belt. In particular the rollers are rotated on a shaft and sufficient tension is applied to the belt to cause the belt to rotate with the drive rollers. In another embodiment in which each paddle member extends from a shaft, the method comprises rotating more than one shaft above the bath. A preferred method of the present invention improves upon a method of the type that comprises rotating a rotor connected to a shaft in a bath of fluid material, forming a froth above a surface of the bath, adding an amount of chemical compound effective to remove a portion of a component from the bath, and causing movement of the froth for removing the froth from the vessel by adding additional amounts of the collector reagent. In the improved method the froth-removing step comprises moving at least one froth moving surface in the froth at least between the shaft and a location inwardly from a periphery of the vessel. The speed of rotation of at least one of the shafts may be adjusted to change a rate at which the froth is removed from the vessel. More particular aspects of the preferred method include employing a bath comprising iron minerals or copper minerals. The froth for upgrading iron ores preferably comprises silica removed from the bath. The chemical used to remove silica from the bath preferably comprises an amine. The flotation process results in final concentrate having a reduced amount of silica (and increased iron content). The method may also include the step of agglomerating material made from the final concentrate. The agglomerates may be subjecting to a direct reduced iron process and/or used in the formation of pig iron such as in a blast furnace. Those skilled in the art would appreciate in view of this disclosure that the present invention is applicable to flotation systems which collect valuable minerals in the froth and leave waste in the slurry. Determining which variation of the flotation process to use involves considering whether the flotation process is cost effective with regard to the particular ore that is used. Many additional features, advantages and a fuller understanding of the invention will be had from the accompanying drawings and the detailed description that follows. Brief Description of the Drawings; Fig. 1 is a side elevational view in partial section of a flotation system constructed in accordance with the present invention; Fig. 2 is a top plan view of the system shown in Fig. 1; Fig. 3 is a flow sheet ' of a hematite concentrate process in accordance with the present invention; and Fig. 4 is a flow sheet of a magnetite concentrate process in accordance with the present invention. Detailed Description of Preferred Embodiments: Referring now to the drawings, an apparatus of the present invention for removing oxides from feed material is shown generally at 10. The apparatus comprises vessels or flotation cells 12 each containing a liquid suspension or slurry 14. A rotor disperser apparatus 16 is located centrally in each cell for circulating the slurry and creating gas bubbles 18 therein. A froth 20 is formed on the surface of the bath. A froth-removing device 22 is located in each half of the cell and each includes at least one froth moving surface 24 located at least between a center of the cell and a location inwardly from the periphery of the cell. The flotation system of the present invention is suitable for use in any processes which utilize a vessel containing a bath of fluid material and a froth that comprises at least one component to be removed from the fluid material. For example, an iron oxide-containing feed material (e.g., magnetite, hematite, limonite and goethite) or a heavy metal oxide or sulfide feed material may be treated in accordance with the present invention. Iron oxide flotation slurry comprises water, iron oxides as a first component to be recovered and a second component to be removed such as silica alone or in combination with phosphorus or incidental minerals. A feed or slurry inlet opening 28 is located at the rear portion 30 of each cell and an outlet 32 for slurry is located at the front portion 34 of each cell. A lip 36 extends along one or both peripheral sides of each cell. Froth travels toward and overflows each lip into a receptacle or launder 38. The rear portion of the first flotation cell is connected to a feed box and its front portion is connected to the rear portion of another flotation cell. A first series of flotation cells (e.g., 5 cells) is disposed downstream of the feed box. The first portion of the last cell in this first series communicates with a connection or junction box. The last series of flotation cells (e.g., 5 cells) is disposed downstream of the connection box. The rear portion of the first cell in the last series is in fluid communication with the connection box. The front portion of the first cell in the last series is connected to the rear portion of another flotation cell. The front portion of the last cell of the last series is connected to a discharge box. Both the junction box and the discharge box include pressure sensitive devices called dart valves known to those skilled in the art which control the slurry level upstream of the device. In the first 10 "roughing" cells enough silica is removed to make grade. The rotor-disperser apparatus is any apparatus suitable for circulating and dispersing gas bubbles throughout the slurry. A preferred rotor-disperser apparatus 40 comprises a motor 42 and a shaft 44 (Figure 2)' connected at an upper end via a V-belt drive 46 to the motor and to a rotor 48 spaced from the bottom 49 of the cell. The rotor is disposed in a draft tube 50 on a perforated false bottom support 51. The shaft is supported by bearings (not shown) contained by a housing 52. A disperser 54 and hood 56 are spaced from the bottom of the cell as shown in Figure 1. The disperser and hood are carried by a baseplate 58 which is connected to the cell. A stand pipe 60 having an air intake 61 is supported by the base plate and connected to the disperser 54 and the hood 56. One suitable disperser apparatus is a "1+1 rotor disperser" apparatus manufactured by Wemco. A discussion of the construction and operation of a flotation cell and a preferred rotor disperser apparatus is provided in the brochure, Wemco 1+1 Flotation Cells , copyright 1983, which is incorporated herein by reference in its entirety. In general, air (arrows A) is drawn downwardly into the slurry. As the rotor rotates, slurry (arrows S) is moved axially upwardly relative to the rotor. Air and slurry (arrows A-S) are directed generally outwardly toward the disperser. The disperser has a plurality of small openings and thus, when air contacts the disperser openings the fine air bubbles 18 are created in the slurry. Another suitable rotor disperser apparatus includes a rotor on the end of a shaft disposed at a lower portion of the cell and fixed disperser vanes disposed around the rotor at the bottom of the cell for producing gas bubbles in the slurry. A froth head is characterized by increased speed at which the froth travels and is thus removed from the cell. Instead of adding a collector to increase the head for moving the froth, the present invention advantageously employs the froth- removing device for moving the froth to the lips and removing froth from the vessel as it is formed. Any device located at least between the shaft or standpipe and a location inwardly from the lip which moves froth, is' suitable for use in the present invention. For example, an apparatus that moves the froth by moving paddle members in the froth is preferred. The paddle members preferably move generally parallel to the bath, even more preferably for a distance along a relatively constant generally horizontal plane. This distance preferably extends from adjacent the standpipe to the associated lip. The paddle members preferably contact the froth at a predetermined distance above the bath, for example, about 4 inches above the lip. In a preferred embodiment, the froth removing device comprises at least two shafts 62 each carrying at least one roller 64. Disposed around the rollers is a continuous belt 66 made of a suitable flexible material. The belt is preferably made of a fabric comprised of nylon, polyethylene or the like. Extending from the belt are paddle members 68 which form the froth moving surface 24. The paddle members move the froth toward the lips and overflow the froth into the launder at each side of the cell. The paddle members may be rigid but are preferably comprised of a flexible material such as a fabric, for example, a material having the same composition as the belt. Each paddle member is preferably pivotably movable between an operable position 70 for moving froth and a retracted position 72 for conserving space. Each paddle member formed from a fabric may have a weight secured thereto at a lower portion. Preferred paddle members are attached to or integrally formed with the belt. The paddle members may be in the form of a flap of fabric attached to the belt by sewing and the like. The paddle members may also be removably attached to the belt, for example, by attaching one portion of a VELCRO® brand hook and loop fastener to the belt and the other portion to the paddle member. The number, shape and size of the paddle members may vary so as to be best suited to moving the froth toward the lip, as would be appreciated by those skilled in the art in view of this disclosure. Another preferred embodiment of the froth removing device is shown in Figs. 1 and 2. Instead of one continuous belt on each side of the cell 12, two smaller width belts SB may be used on each side of the cell, each having a V-shaped protrusion VP. Each of the rollers has a correspondingly shaped notch or groove G formed around its periphery to receive the protrusion VP. Instead of one paddle extending up to the entire width of the belt as in the above construction, two paddles 68' are used, each of which spans about half of the length of the shafts and is centered on one of the smaller width belts SB. It is believed that hinges may be fastened to the belts and that the paddles may be fastened to the hinges. Other ways to fasten the paddles to the belts should be apparent to those skilled in the art in view of this disclosure. The paddles may be formed of fabric but are preferably formed of light gauge metal. Each of the paddles is preferably 44 inches in width and about 4 inches high, the space between the paddles on each belt being about 1 to 2 inches. The belts are about 1 foot wide. Although the above sizes and configurations of the belts, paddles, grooves and belt protrusions, are preferable, other suitable such sizes and configurations should be apparent to those skilled in the art in view of this disclosure. The belts ride in the notches in the shafts to avoid slippage. Two belts are employed to avoid the effects of slippage. Otherwise, the operation of the belts SB and paddles 68' is generally the same as was previously discussed in connection with the wider belt and paddles. The belt and rollers in the wider belt design may also be fabricated with the V-shaped protrusion and correspondingly shaped groove. In addition, multiple paddles of different widths may be employed on the wider belt. In an alternative embodiment shown in dotted lines in Fig. 1, in which like parts have the same reference. numerals, the froth removing device comprises more than one shaft 74 located between the shaft of the rotor disperser apparatus and the lip without the continuous belt. Each shaft includes the paddle members 68 extending therefrom. The paddle members extending from the shafts may be flexible or rigid. In this embodiment, moving the froth with "multiple shafts may cause the froth to rise. In addition, the shafts are preferably rotated synchronously with one another, which may complicate adjusting the rotational speed of the rollers. These are not concerns when employing the continuous belt of the first embodiment. A variable speed drive 76 rotates the rollers. In the case of the continuous belt embodiment, the drive rotates one of the rollers, the other being an idler roller, so as to rotate the belt and move each paddle member while in the operable position from the rotor-disperser apparatus to the lip. The paddle members preferably move in a substantially horizontal plane, although belt sag may cause the paddle member movement to vary somewhat. A single drive may be used to drive the rollers of more than one froth remover as shown in Figure 2. In the case of using multiple rollers each having paddle members, the rotation of the paddle members causes the froth to travel toward the lip of the cell. Froth that has been moved toward the lip overflows the lip and travels into the froth launder. Since the drive has a variable speed, the rate of froth removal may be selectively controlled. Froth is present above the bath for a time effective to remove a sufficient amount of silica. If the desired rate of silica removal is being satisfied, the speed of horizontal or rotational movement of the paddles may be kept constant or decreased. Conversely, if the rate of silica removal is too low, the speed of the paddles may be increased to achieve the silica removal set point. The formation and/or removal characteristics of froth are achieved by the addition of suitable chemicals. Chemical reagents or collectors provide the froth with the ability to remove components of the slurry. In the case of the iron oxide slurry, an amine-containing substance (e.g., amine or diamine) is preferably added to create a froth effective to remove silica from the slurry. Any amine which serves to remove silica from the slurry may be used. Other collectors may also be used to form a froth effective to remove intended components from the slurry, as would be known to those skilled in the art in view of this disclosure. Some examples of collectors that may be suitable for use in flotation processing include fatty acids, resin acids, soaps, alkyl sulphates, sulphonates and xanthates. Resin acids are not commonly used for iron oxide flotation. The xanthates are used to remove heavy metal sulfides in copper flotation processing. Although the specification may at times refer specifically to the preferred amine collector, it will be appreciated that other suitable chemical collectors are also intended. Amines are collectors of both silica and iron oxides. However, greater amounts of amine are required to float ("flot") iron oxides than to flot silica. Although not wanting to be bound by theory in this disclosure, iron oxides are believed to be collected into the froth by way of two mechanisms- occlusion in the froth or coflotation with silica. Both mechanisms are highly dependent upon the concentration of amine relative to the amount of iron oxides and silicon dioxide in the bath. Low Fe tails froth is characterized by large glassy bubbles toward the end of the flotation circuit and by slow movement toward the lip. A high Fe tails froth is more dense, matted and flows quickly toward the lip. An objective of the present invention is to reduce tailings losses of Fe (i.e., Fe in the froth waste) since higher amine rates (amounts) result in higher tailings losses of Fe. Therefore, the invention preferably employs the lowest amount of amine necessary for producing a concentrate having a particular grade. By eliminating that portion of the amine added to move the froth and confining use of the amine to forming froth necessary to extract sufficient silica from the slurry to make grade, it is believed that reduced Fe tailings losses and reduced amine consumption will result. Slurry level should be at the highest point in the flotation cell which does not overflow slurry from the lip. Adding more amine than is necessary to reach this level is undesirable as it would create a dέeper froth column resulting in greater Fe tailings losses. Froth forms in the cells downstream even though there is no direct amine addition in these cells. Under any condition, the froth is denser and faster moving in cells where the amine addition is made. Under low amine additions froth columns are high (e.g., 13 inches above the lip) and in this condition froth velocities are as low as 0.1 to 0.2 feet/second (timing bubbles moving from three feet into the cell to the lip) . Under higher amine additions the driving force is greater, thereby creating more of a bulk flot or "mushy" froth which is relatively heavy and does not need as much froth column or head to initiate movement. Froth columns under these high amine conditions are much lower (e.g., 5-6 inches or less above the lip) with froth velocities as high as 2 ft/sec. When using the froth removing device of the present invention the froth preferably extends from the bath to a height of about 4 inches above the lip. A certain tonnage of silica must be removed from the feed to the rougher cells in order to make target silica in the discharge box of the last (e.g., 10th) cell. Because float cell capacity is fixed, froth removal is time dependent. Since both the froth formation area and the overflow lip are fixed and completely utilized, more silica is removed in a fixed capacity by creating a faster moving froth. For froth to flow without mechanical movement from the center of the cells to the lip, which is where the froth becomes a true "tails," a head of froth is conventionally developed to initiate flow. The driving force to create this head is believed to originate in the slurry in the form of mineral- amine laden small air bubbles. The greater the amine addition, the greater the driving force to leave the slurry phase and create a froth. Under low amine conditions, the driving force is less and there is sufficient time for the bubbles to coalesce, form bigger "glassy" bubbles, and gradually migrate to the lip to become tails. The invention advantageously permits low Fe tails froth to be created while removing the froth mechanically at a rapid rate similar to that achieved by adding additional amine to generate a head for moving the froth. The invention will now be described by reference to the following nonlimiting examples. Those skilled in the art will appreciate in view of this disclosure that chemical and operational adjustments may be determined empirically and made to the parameters of the following processes when using the froth removing device in accordance with the present invention. The following hematite and magnetite ore concentrator processing examples focus on features that are important to flotation processing and concentrate usage in the present invention. Concentrator processing may include additional or equivalent steps and materials that would be apparent to those skilled in the art in view of this disclosure. EXAMPLE 1 Referring to Figure 3, hematite ore 80 is fed by feeder 82 to a primary autogenous mill 84. Caustic soda 86 is added to the material to control pH. The pH setpoint is determined empirically by flotation performance and normally is set for a pH ranging from about 10.8 to about 11.2. Reuse water 88 may also be added here and at various other locations of the process such as where indicated. Following the primary mill the material enters a pebble mill 90. Dispersants 92 (e.g., a long chain polyphosphate such as Glass H supplied by FMC Corp.), are added, for example, in an amount of 0.15 to 0.10 pounds per long ton ("lb/LT") of crude to allow adsorption of cornstarch on the iron oxide but not on silica. Water 94 is added for particle separation in a cyclone 96. In the grinding circuit the ore is finely ground to the point at which iron oxide and silica are adequately liberated. For example, 80-90% of the material is less than 25 micrometers (μm) in size in cyclone overflow 98. This cyclone overflow has a 7-10% by weight solids content, for example. Cyclone underflow 100 which is coarser than 25μm is fed back to the pebble mill. Cornstarch 102 supplied by Grain Products Corporation, is added to flocculate the iron minerals in a deslime thickener 104. Deslime thickeners operate in the well known manner using rakes to move the material toward a center of the vessel. Iron oxides sink to the bottom of the deslime thickener and deslime thickener overflow 106 including siliceous material is sent to a tailings thickener 108. Deslime thickener underflow 110 is pumped to a flotation feed distributor 112 leading to several (e.g., 12) flotation lines 114. Cornstarch 116 is also added to the feed distributor in an amount of about 0.07 to 0.30 lbs/LT of crude, for example. Cornstarch is used as a depressent for the iron minerals to decrease flotation and prevent the iron oxides from entering the froth. Feed to the flotation line comes directly from deslime thickener underflow ' ("DTU") and varies with deslime thickener performance. Targeted DTU/flot feed density is 50- 55% solids, for example, which is controlled in desliming. Each flotation line may handle 75-125 long tons per hour ("LTPH") of feed, for example. The feed is passed through an agitator or conditioner 118 to thoroughly mix the feed and starch. Ten "rougher" flotation cells and 15 scavenger cells are used, each cell having 500 cubic feet of volume. Each cell preferably includes two of the froth removing devices 22 of the invention. In both the magnetite and hematite processes the drives used in the flotation process have the ability to move the paddle members at a velocity, for example, ranging from about 0.5 to about 5 feet per second in the case of the continuous belt embodiment or at an equivalent rotational velocity using the froth remover which has shafts carrying the paddle members. The drive preferably moves the paddle members at a velocity up to about 2 feet/second. The froth-remover may advantageously be designed to extend from adjacent the rotor-disperser apparatus to adjacent the lip, whereby approximately 86% of the surface area of the cell may be reached by the paddle members. It is believed that some short time is required to make the silica collecting froth. Therefore, by spacing apart the paddle members and moving the paddle members at variable speeds, froth formation and removal can be optimized. The feed material enters a feed box 120 of rougher cells 121. Amine collector 122 (and optionally phosphorus collector) is added to the feed box. Amine (e.g., PA-1214- 60/40 by To ah Products) is preferably added automatically by a Nola Si0 2 Grade Control Program known to those skilled in the art. The collector reagent is added in the feed box or in the 6th cell air intake for use in the first ten rougher cells in an amount of 0.142 lb/LT of crude, for example. No frother is currently used. Flotation phosphorus collector may be added to the feed box to remove phosphorus-containing minerals from the rougher concentrate. One suitable phosphorus collector is A-trac 880, which is normally added at a rate ranging from about 0.001 to about 0.003 lbs/LT. The collector reagents are controlled automatically by starting reagent feed pumps once the desired lbs/LT feed rate has been set. The launders receive the froth from the rougher cells and water is sprayed on the froth. In the launders the material is then directed by gravity to a feed box 123 of a set of scavenger banks 124 which includes 4 banks, a first bank 126 having 5 cells, a second bank 128 having 4 cells, a third bank 130 having 3 cells and a fourth bank 132 having 3 cells. Froth travels sequentially from the first bank 126 to the fourth bank 132. Scavenger concentrate 134 leaves the end of each scavenger bank and is directed to the rougher line feed box 120. Scavenger tailings 136 from the last scavenger cell bank are directed to the tailings thickener 108. Overflow 138 from the tailings thickener is directed to a reuse water pond 140 and then back to the plant as process water 142. Tailings thickener underflow 144 is directed to a tailings basin 146. Concentrate 148 from the discharge box connected to the last rougher cell is directed to a concentrate thickener 150. A cationic flocculant 152 (e.g., poly-dimethyl dillyl cationic polymer such as WT-35-VHV by CPS Chemical) is fed into the concentrate thickener. Solid overflow 154 from the concentrate thickener is directed to the tailings thickener 108. Concentrate underflow 156 is directed to a slurry tank 158 and then chemicals 160 are added to aid in dewatering including Benewet DOS70 by Glenn Corp. and POL-E-Z 7736 by Calgon Corp. The concentrate material is then optionally subjected to filter cake processing 162. The material is then agglomerated such as by pelletizing 164 or is sent to storage 166. The agglomerates may then be subjected to a direct reduced iron ("DRI") process 168 or are sent to an open hearth furnace 170 to make pig iron. EXAMPLE 2 Referring to Figure 4, magnetite ore 180 is fed by a feeder 182 to a primary autogenous mill 184. Reuse water 186 may also be added here and at various other locations of the process such as where indicated. The material then enters cobble separators 188 which remove nonmagnetic material 190 (e.g., 30-35% by weight removed) which is sent to a tailings thickener 192. The remaining material is then fed into a pebble mill 194. In the grinding circuit the ore is finely ground to the point at which iron oxide and silica are adequately liberated. Reuse water 196 is added for particle separation in a cyclone 198. For example, 80-90% of the material is less than 25 micrometers (μm) in size in cyclone overflow 200. This cyclone overflow has a 7-10% by weight solids content, for example. Cyclone underflow 201 is coarser than 25μm and is fed back to the pebble mill. The material is then fed into a 2 in 1 double deslime thickener 202 and then into a 3 in 1 series deslime thickener 204. Iron sinks to the bottom of the deslime thickeners and deslime thickener overflow 206, 208 from these thickeners is sent to the tailings thickener 192. Deslime thickener underflow 210 is pumped to finisher separators 212 after which highly siliceous overflow material 214 is directed to the tailings thickener 192 and underflow 216 is directed to another deslime thickener 218. Overflow 220 from this deslime thickener is sent to the tailings thickener 192 and underflow 222 is directed to a flotation feed distributor 224 leading to several (e.g., 4) flotation lines 226. Each flotation line may handle 75-125 LTPH of feed, for example. The feed is then sent to a rougher cell line 228. Ten "rougher" flotation cells are subjected to treatment by a collector and one bank 230 of 5 scavenger cells are used, each cell having 500 cubic feet of volume. Each rougher cell preferably includes 2 froth removing devices of the invention. Typical massflows for a flot line range from about 150 to about 350 LTPH as measured by flowmeter and density gauges. Flot feed density is controlled by an automatic dilution water system with an automatic sump level over-ride to prevent sump overflows. Normal flot feed density is targeted at about 25 to about 30% solids. A diamine collector 232 and a frother 234 (and optionally C0 2 ) are added to a feed box 236 of the rougher line. One suitable diamine has two NH 2 sites per molecule (e.g., DA-16-5% acetate diamine by Tomah Products) . Diamine is preferably added automatically by the Nola Si0 2 Grade Control Program. The collector reagent is added in the feed box or junction box in an amount of 0.07 lb/LT of crude, for example. The same type of diamine added to the feed box is added to the 6th rougher cell following a junction box 238. The collector reagents are controlled automatically by adjusting reagent feed pumps once the desired lbs/LT feed rate has been set. One suitable frother is Benefroth 2EH by Glenn Corp. Frother is added to provide a stable froth for removal of the gangue particles. Frother addition is available at the feed box and junction box. Frother is normally added only to the feed box, and may be added at a rate of about 0.005 to 0.020 Ib/LT or crude. The launders receive the froth from the rougher cells and spray water on the froth which material is then directed by gravity to a feed box 240 of the scavenger bank. Scavenger concentrate 242 leaves a discharge box 244 at the end of the scavenger bank and is directed to ihe rougher line feed box. Scavenger tailings 246 from the scavenger cell bank are directed to the tailings thickener 192. Overflow 248 from the tailings thickener is directed to a reuse water pond 250 and then back to the plant as process water 252. Tailings thickener underflow 254 is directed to a tailings basin 256. Concentrate 258 from a discharge box 260 connected to the last rougher cell is directed to a concentrate thickener 262. A cationic flocculant 264 (e.g., polydimethyl dillyl cationic polymer such as WT-35-VHV by CPS Chemical) is fed into the concentrate thickener. Solid overflow 266 from the concentrate thickener is directed to the tailings thickener 192. Concentrate underflow 268 is directed to a slurry tank 270 and then chemicals 272 are added to aid in dewatering including Benewet DOS 70 by Glenn Corp. and POL-E-Z-7736 by Calgon Corp. The concentrate material is then optionally subjected to filter cake processing 274. The material is then agglomerated such as by pelletizing 276 or is sent to storage 278. The agglomerates may then be subjected to a DRI process 280 or are sent to an open hearth furnace 282 to make pig iron. EXAMPLE 3 The following is an example of conventional recovery and amine usage in one month without using the froth-removing device. The iron content of the feed before being subjected to the flotation process was 35.3% by weight. After the flotation process, the concentrate had an iron content of 64.4% by weight and a silica content of 5.05%. In the flotation cells the set point of silica in the slurry was in the range of from about 4.7 to about 5.1% by weight. The amount of amine that was added to hematite in that month was 0.17 lbs/LT of crude or about 279,000 lbs. The iron content in the final tails was 21.9% by weight for that month. Since a portion of the amine was added to create movement of the slurry, a significant amount of this amine addition may be avoided, or the iron content of the final tails may be reduced, using the froth removal device in accordance with the present invention. Many modifications and variations of the invention will be apparent to those of ordinary skill in the art in light of the foregoing disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than has been specifically shown and described.

Claims: What is claimed is: 1. An apparatus for removing material from a bath of fluid comprising: at least one vessel having a feed inlet and an outlet, wherein the vessel contains a bath of fluid and froth located above said bath; at least one disperser apparatus each comprising a rotatable shaft and a rotor connected to said shaft, said rotor being located in said bath; and at least one froth-removing device comprising at least one froth moving surface located at least between said shaft and a location inwardly from' a periphery of the vessel. 2. The apparatus of claim 1 wherein said froth-removing device comprises a rotatable belt supported by at least two shafts and at least one paddle member extending from said belt. 3. The apparatus of claim 1 wherein said froth-removing device comprises more than one shaft each having at least one paddle member extending therefrom. 4. The apparatus of claim 2 wherein said rotatable belt extends from adjacent said disperser apparatus to adjacent the periphery of the vessel. 5. The apparatus of claim 2 wherein said paddle members are pivotably movable. 6. The apparatus of claim 1 comprising at least one lip extending around at least a portion of the periphery of the vessel. 7. The apparatus of claim 1 comprising a plurality of the vessels in fluid communication with each other. 8. The apparatus of claim 1 comprising a variable speed drive for operating at least one said froth-removing device. 9. An apparatus for removing material from a bath of fluid comprising: at least one vessel having a feed inlet and an outlet, wherein the vessel contains a bath of fluid. and froth located above said bath; at least one disperser apparatus each comprising a rotatable shaft and a rotor connected to said shaft, said rotor being located in said bath; and means for removing froth from the vessel by moving at least one surface at least between said shaft and a location inwardly from a periphery of the vessel. 10. An apparatus for removing material from a bath of fluid comprising: at least one vessel having a feed inlet and an outlet, wherein the vessel contains a bath of fluid and froth located above said bath; at least one disperser apparatus each comprising a rotatable shaft and a rotor connected to said shaft, said rotor being located in said bath; and at least one froth-removing device comprising a rotatable belt supported by at least two shafts, and at least one paddle member extending from said belt. 11. The apparatus of claim 10 comprising at least one lip extending around at least a portion of a periphery of the vessel. 12. The apparatus of claim 11 wherein said belt of said froth-removing device extends from adjacent said disperser apparatus to adjacent one said lip. 13. The apparatus of claim 10 wherein each said paddle member is pivotably movable. 14. The apparatus of claim 10 comprising a receptacle having a froth inlet for receiving froth from the vessel and a passageway for directing froth to another vessel. 15. The apparatus of claim 10 comprising a series of the vessels in fluid communication with each other. 16. The apparatus of claim 10 comprising a variable speed drive for rotating at least one of said shafts. 17. The apparatus of claim 10 wherein said paddle members are spaced upwardly from said bath by a selected height effective to enable said pafddle members to contact a predetermined amount of said froth. 18. The apparatus of claim 17 wherein said selected height is effective to enable said paddle members to contact a predetermined amount of froth comprising silicon dioxide. 19. The apparatus of claim 10 comprising means for preparing feed liquid comprising iron oxide for use in said flotation system. 20. A method of removing material from a fluid, comprising: rotating a rotor on a shaft in a vessel containing a bath of fluid material; forming a froth above a surface of the bath; and removing froth from said vessel by moving at least one froth moving surface at a location at least between said shaft and a location inwardly from a periphery of the vessel. 21. The method of claim 20 wherein each said froth moving surface is formed by a paddle member, comprising moving at least one said paddle member above said bath. 22. The method of claim 21 wherein each said paddle member extends from a belt disposed around at least two shafts, comprising moving each said paddle member with said belt. 23. The method of claim 21 wherein each said paddle member extends from a shaft, comprising rotating more than one said shaft above the bath. 24. The method of claim 20 wherein said froth comprises silicon dioxide. 25. The method of claim 20 wherein said fluid comprises iron oxide. 26. In a method of removing oxides from a fluid by a method of the type that comprises rotating a rotor connected to a shaft in a bath of fluid material, forming a froth above a surface of the bath, adding an amount of chemical compound effective to remove a portion of a component from the bath, and causing movement of said froth for removing said froth from the vessel, the improvement wherein said froth moving step comprises moving at least one froth moving surface in said froth at least between said shaft and a location inwardly from a periphery of the vessel. 27. The method of claim 26 wherein each said froth moving surface is formed by a paddle member, comprising moving at least one said paddle member above said bath. 28. The method of claim 27 wherein each said paddle member extends from a belt disposed around at least two shafts, comprising moving each said paddle member with said belt. 29. The method of claim 27 wherein each said paddle member extends from a shaft, comprising rotating more than one said shaft above the bath. 30. The improvement of claim 27 comprising pivoting each said paddle member between an operative position and a retracted position. 31. The improvement of claim 28 comprising adjusting the speed of rotation of at least one of said shafts to change a rate at which said froth is removed from the vessel. 32. The improvement of claim 29 comprising adjusting the speed of rotation of at least one of said shafts to change a rate at which said froth is removed from the vessel. 33. The improvement of claim 26 wherein the bath comprises a major amount of metal. 34. The improvement of claim 33 wherein said metal is iron. 35. The improvement of claim 33 wherein said metal is copper. 36. The improvement of claim 26 wherein said froth comprises silicon dioxide. 37. The improvement of claim 26 wherein said chemical comprises an amine. 38. The improvement of claim 26 comprising forming a final concentrate having a reduced amount of silica. 39. The improvement of claim 38 comprising agglomerating material made from said final concentrate. 40. The improvement of claim 39 comprising subjecting said agglomerates to a direct reduced iron process. 41. The improvement of claim 39 comprising using said agglomerates in the formation of pig iron.

Inventors: PAANANEN ALLAN D, PAANANEN, ALLAN, D.
Applicants: CLEVELAND CLIFFS INC, PAANANEN ALLAN D, CLEVELAND-CLIFFS, INC., PAANANEN, ALLAN, D.
Application year: 1998
Main classification: B03D1
IPC codes: B03B11, B03D1