US2973096A

US2973096A - Magnetic separation apparatus and treating methods involving magnetic separation

Info

Publication number: US2973096A
Application number: US729411A
Authority: US
Inventors: Melvin J Greaves
Original assignee: ROBERT A CUMMINGS JR
Current assignee: ROBERT A CUMMINGS JR
Priority date: 1958-04-18
Filing date: 1958-04-18
Publication date: 1961-02-28
Anticipated expiration: 1978-02-28

Description

Feb. 28, 1961 M. J. GREAVES 2 7 96 MAGNETIC SEPARATION APPARATUS AND TREATING METHODS INVOLVING MAGNETIC SEPARATION Filed April 18, 1958 3 Sheets-Sheet 1 TOE INVENTOR MELVIN J- GREAVES ATTORNEYS \PN GM 1 +=ltliiiL lll inv-i 1 x I ll Y on a B Feb. 28, 1961 M. J. GREAVES I 2,973,096

MAGNETIC SEPARATION APPARATUS AND TREATING METHODS INVOLVING MAGNETIC SEPARATION Filed April 18, 1958 a Sheets-Sheet 2 FIG. 2

INVENTOR. MELVIN J.G R [AVE 5 ATTORNEYS Feb. 28, 1961 M. J. GREAVES 2,973,

MAGNETIC SEPARATION APPARATUS AND TREATING METHODS mvonvmc MAGNETIC SEPARATION "Filed April 18, 1958 s Sheets-Sheet 3 FIG 6 INVENTOR. MELVIN J. GREAVE AITORNEYS United States Melvin J. Greaves, Parma, Ohio, assignor to Robert A. Cummings, Jr., Pittsburgh, Pa.

Filed Apr. 18, 1958, Ser. No. 729,411

7 Claims. (Cl. 210-65) This application relates to magnetic separation apparatus and treating methods involving magnetic separation. Broadly the invention relates to the separation of materials having different magnetic susceptibilities entrained in a fluid flowing in a moving magnetic field. Specifically the invention has utility in flotation separation, conveying and like processes and apparatus in which magnetic material, generally finely divided, is employed to increase the buoyancy or apparent specific gravity of a liquid medium which is used for the treatment or conveying of bulk material.

In the specification and drawing the invention is illustrated in connection with cleaning of coal by the flotation process, but it will be understood that the invention has other possible and equally important applications.

Coal, as mined, has mixed with it slate and other foreign matters which are referred to generally as gangue which is separated from the coal before marketing. In the flotation process of cleaning coal, the coal, as mined, is discharged into a suitable receptacle containing the flotation treating liquid upon which the coal floats, the heavier materials comprising the gangue sinking to the bottom. The coal, free of gangue, is then removed from the surface of the flotation liquid.

The flotation liquid, for the intended purpose, has a specific gravity greater than that of the coal and a less specific gravity than those portions of the material to be separated from the coal, whereby the coal will float on the liquid and the materials to be separated will sink in the liquid. The flotation liquid is water having entrained therein finely divided solid materials which are insoluble in water and whose specific gravity is high enough so that the resultant mixture has the desired specific gravity for the purpose. Heretofore the procedure was to introduce into the water finely divided magnetic material such as magnetite or ferrosilicon and after use to magnetically separate the magnetic material from the water and return it for re-use. It has been found, however, that during such magnetic separation the material flocculated, thereby rendering it unfit for further re-use, until the material had been deflocculated.

In the present invention, one of the advantages is that the magnetic material is not flocculated during separation and, therefore, may be immediately returned for re-use without further treatment. In the present method of recovering the substantially magnetic material from the liquid comprises flowing the liquid in a stream or through a conduit and impelling toward one side of the stream or conduit the magnetic material by a moving magnetic field and then separately collecting the magnetic material and the substantially magnetic material free liquid. I found it desirable that the magnetic field move parallel to the direction of flow of the liquid and that the speed of movement of the magnetic field approximate the speed of flow of at least that portion of the liquid containing the magnetic material. Preferably, a polyphase alternating magnet located alongside the conduit provides the magnetic field. Such a magnet has the characteristic atent O i 2,973,096 Patented Feb. 28, 1961 that the magnetic field moves along the conduit. The magnet is designed and wound so that the magnetic field advances along the conduit in the same direction as the flow of the liquid within the conduit and at the desired speed. The magnetic material is thus impelled by the magnet, preferably being attracted toward it, which promotes the desired separation.

With such a magnet the magnetic material not becoming permanently magnetized the parties have no attraction one to the other and thus preventing flocculation.

For the purposes of illustration the magnetic material containing liquid is flowed generally horizontal so that the magnetic material within the liquid is drawn downwardly within the liquid by a magnetic field which is moving in the direction of flow. Thus substantially magnetic material free liquid is delivered from above the downwardly drawn magnetic material.

It has been found that all of the material within the conduit, when so treated, will not move at the same velocity. One cause of this is that the magnetic material being drawn toward one side of the direction of flow tends by reason of the increased viscosity of that portion of the liquid to be slower than at the opposite side. The maximum velocity of the stream flowing within the conduit is therefore near the geometric center thereof with the minimum velocity adjacent the side of the conduit nearest the magnet. It is desirable, therefore, that the magnetic field of the magnet moving along the side of the conduit at a speed approximately equal to the speed of flow of the contents of the conduit which contains the magnetic material. Optimum efliciency is obtained by this method.

The intensity of the magnetic field created by any magnet decreases rapidly as the air gap distance from the face of the pole of the magnet increases, There is an economic limit to the magnetic field intensity at the base of the. pole due to the change in the magnetic properties of the iron ore under high magnetic flux densities, to the problem of cooling the magnet and to leakage of flux which does not pass through the face of the poles. These factors make it desirable to restrict the distance from the magnet to the fartherest removed magnetic .material at the zone of entry into the magnetic field.

Once the magnetic material is in sufficiently intense magnetic field to prevent it leavingthe proximity of the magnet, the dimension of the conduit parallel to the direction of the magnetic attraction may be increased without appreciably affecting the operation of the unit.

It is desirable, therefore, to confine the dimension of the stream parallel to the direction of magnetic attraction to a minimum in the zone of entry of the stream into the magnetic field and increase that dimension in a zone advanced in the direction of flow relatively to the first mentioned zone. Preferably the cross-sectional area of the stream is designed so that the velocity of flow of the portion of the stream containing the magnetic material is substantially equal to the speed ofmovement of the magnetic field along the conduit. To this end I may pre-determinedly increase in the direction of flow the dimensionof. the stream which is parallel to thedirection of magnetic attraction and decrease in the direction of flow the dimension of the stream normal to the dimension which is parallel to the direction of magnetic attraction. To reduce energy losses at the point where the stream divides near the end of the magnetic field, it is desirable to employ a relatively large dimension of the stream parallel to the direction of magnetic attraction at that point. Afurther advantage of increasing the dimension of the stream parallel to the direction of magnetic attraction at thedivision point is that a better separation of magnetic material and magnetic materialfree liquid is effected.

For most effective separation the concentration of magnetic material in the liquid may be controlled by recirculating a portion of either the component containing the magnetic material or the magnetic material free component of the liquid. It is desirable that the' magnetic material along the side of the conduit adjacent the magnet form a low resistant circuit for the magnetic flux and the concentration of magnetic material in the liquid is controlled with this end in view. The less magnetic material in the liquid before the greater is the resistance in the magnetic circuit due to the small dimension of the portion of the stream occupied by the magnetic material. The more magnetic material in the liquid the greater is the tendency for the conduit to clog and the more of the magnetic material is admixed with the desirably magnetic material free liquid.

I provide an improvement in the treatment of bulk material in which the bulk material is admixed with liquid and finely divided magnetic material and subsequently separated therefrom, which comprises the steps of magnetically separating a portion of the liquid from the finely divided magnetic material contained therein while maintaining finely divided magnetic material in deflocculated state and returning the deflocculated finely divided magnetic material for re-use. An alternating current magnetic field effects the desired separation without causing flocculation of the magnetic material. The separated liquid may be returned for re-use and may be filtered en route. The separated liquid may be employed for washing the bulk material. In a preferred treatment Fig. 6 is a fragmentary cross-section view to enlarged scale taken in the plane VIVI of Fig. 5.

Referring now more particularly to Figure 1, there is shown a fragment of a reservoir designated generally by reference numeral 2 and which has a sloping bottom as shown. In the portion of the reservoir which appears in Fig. 1 is a flotation liquid 3 on which floats coal 4. The reservoir 2 may be the tank of coal washer or it may be the delivery terminus of a pipe line through which coal has been delivered in the flotation liquid as a carrier. in either event the flotation liquid 3 consists of water and finely divided magnetic material; I prefer to employ magnetite as the finely divided magnetic mapasses about a sprocket 6 which turns in the clockwise I lift the bulk material out the admixed liquid and finely divided magnetic material withdraw a portion of the admixed liquid and finely divided magnetic material, magnetically separate the withdrawn liquid from the finely divided magnetic material contained therein while maintaining the finely divided magnetic material in deflocculated state, return the deflocoulated finely divided magnetic material for re-use, employ the thus separated liquid for washing the bulk material which has been lifted out of the admixed liquid and finely divided magnetic material and conduct the washing liquid back into the admixed liquid and finely divided magnetic material.

{I also provide, in a flotation or like process in which finely divided magnetic material is employed to increase the buoyancy of a liquid treating medium, the steps of separating a portion of the liquid from a finely divided magnetic material contained therein by an alternating current magnetic field and returning the thus separated finely divided magnetic material for re-use. This separation is preferably effected magnetically while maintaining the finely divided magnetic material in deflocculated state as above described.

I further provide apparatus for carrying out in improved manner the novel methods above referred to and which will be more fully described below.

In the accompanying drawings I have shown certain present preferred embodiments of the invention and have illustrated certain present preferred methods of practicing the same, in which:

Fig. 1 is a diagram generally in the form of a vertical cross-section illustrating a coal flotation process and apparatus;

Fig. 2 is a plan view to enlarged scale of the separating conduit of the apparatus illustrated in Fig. 1 with the coil assembly shown in connection therewith;

Fig. 3 is a vertical cross-sectional elevation through the conduit shown in Fig. 2 with the coil assembly shown in section adjacent to the coil supporting core.

Fig. 3a is a view of the circuit diagram illustrating current flow through the magnets of Figs. 2 and 3;

Fig. 4 is a more or less diagrammatic fragmentary view of another form of separator;

Fig. 5 is a similar view of still another form of separator; and

direction viewing Fig. 1 when the apparatus is in use. As the conveyor operates it lifts the coal out of the liquid and delivers it to a transverse belt conveyor shown in cross-section at 7. If the reservoir 2 is a coal washer tank the opposite portions of the tank (i.e., that portion not shown in Fig. 1) has an inclined bottom like the portion shown but inclined in the opposite direction and the endless conveyor 5 extends from the bottom of the tank to a portion above the tank wall at each end. The flights of the flight conveyor may be employed to push the gangue and other matter to be separated from the coal upwardly along the opposite inclined bottom portion of the tank to discharge the same from the tank, one conveyor thus serving to deliver the coal at one side of the tank and the gangue at the opposite side. Such an arrangement is conventional and does not constit-ute my invention.

1 provide a conduit or separator for separating water from magnetite. The conduit is designated 8 and is shown to large scale in Figs. 2 and 3. Beneath the conduit 8 is a polyphase alternating current magnet 9 (Fig. l) which is disposed close to the under surface of the conduit 8 and which operates in known manner to produce by alternating current a magnetic field tending to draw downwardly the particles of magnetite, the magnetic field at the same time moving toward the right, viewing Fig. 1. Those skilled in the electrical art know that by proper Winding and proportioning of the magnet coils provision can be made for creating a magnetic field of desired strength and for movement of that field in the desired direction at a predetermined speed. Accordingly, one representative circuit arrangement is shown in the diagram illustrated in Fig. 3a. Therein, lines x, y and z are connected to a source of three-phase alternating current, not shown. Proper connections for fifteen similar coils a through 0 are illustrated and are such that a traveling magnetic field is produced. The core p consisting of laminated transformer iron has eighteen slots which are filled with coils q except for the top half of the first three slots and the bottom half of the last three slots. This feature is simply one of convenience in order to standardize on one coil design.

The windings, best illustrated in Fig. 3a, are so dis posed that each phase produces the resultant magnetic field which occupies a position electrical degrees apart from each of the other phases, and since these windings are connected to a three-phase circuit, the currents in each of them differ by 120 degrees in phase relation from the current in each of the others. These two conditions result in the production of a magnetic field of uniform strength which moves at a uniform speed.

A duct 10 leads from the reservoir 2 at 11 to the entrance. end 12 of the conduit 8. A pump 13 is positioned in the duct for pumping flotation liquid from the reservoir 2 into the conduit 8. The cross-sectional area of the conduit 8 is preferably designed so that liquid moves through the conduit in such manner that the portion of the liquid containing the magnetic material advances at approximately the speed of advance of the magnetic field.

The dimension of the conduit 8 parallel to the direction of magnetic attraction, i.e., the vertical dimension of the conduit in the embodiment shown in Fig. l, is confined to a minimum in the zone of entry of the stream into the magnetic field. This zone is the zone adjacent the entrance end of the conduit. At the entrance end the conduit is relatively wide in the horizontal direction as shown at 14 in Fig. 2. The purpose of confining the vertical dimension to a minimum in the zone of entry of the stream of liquid into the magnetic field is to cause all of the liquid to pass as near as possible to the magnet 9 for the reason explained above. The vertical dimension of the conduit 8 gradually increases from left to right and the horizontal dimension decreases as shown in Figs. 2 and 3, the cross-sectional area of the conduit being designed so that the portion of the liquid containing the magnetic material advances at approximately the speed of advance of the magnetic field. The magnet 9 creates a magnetic field which advances from left to right at a velocity determined by the design of the magnet. The magnetic field attracts the particles of magnetite, causing them to move to the side of the conduit 8 which is against the magnet, i.e., the lower side, viewing Fig. 1. As the liquid advances through the conduit the magnetite is thus caused to hug the bottom of the conduit while substantially magnetitefree liquid or water moves along the upper part of the conduit. Most effective results are obtained when the velocity of advance of the magnetic field is substantially equal to the velocity of flow of that portion of the contents of the conduit 8 containing the magnetite, i.e., the lower portion thereof, viewing Figs. 1 and 3. The upper portion of the contents of the conduit which is substantially magnetite-free water moves somewhat faster than the relatively viscous lower part.

The magnetite is not permanently magnetized or flocculated by the operation just described. The alternating current field does not permanently magnetize the particles and in addition their orientation is continually being interrupted as they tumble over one another and turn within the liquid as they pass through the conduit 8. There is no flocculation of the magnetite, which is delivered from the conduit 8 in the same unfiocculated condition as upon entry into the conduit 8.

The conduit 8 has at its delivery end two delivery branches, an upper delivery branch 16 for the substantially magnetite free water and a lower delivery branch 17 for the magnetite and enough water to make it flowable (for example, the magnetite and water in the delivery branch 17 may be in approximately equal proportions by weight). The upper delivery branch 16 extends upwardly at an angle of about 45 to the axis of the main portion of the conduit 8 and the lower delivery branch 17 extends downwardly at a like angle. At the junction of the main portion of the conduit 8 with the

delivery portions

16 and 17 is a divider 18 which projects into the main portion of the conduit 8 to separate the contents of that conduit, causing part of the contents to pass upwardly through the delivery portion 16 and part of the contents to pass downwardly through the delivery portion 17. The divider 18 is positioned to roughly divide the magnetite which is disposed at the bottom of the conduit from the magnetite-free liquid or water which is disposed at the top of the conduit. Of course there cannot be a perfect separation between the magnetite and the water but the separation is remarkably efiicient and very little magnetite will pass upwardly through the delivery portion 16. Some water will pass downwardly through the delivery portion 17 along with the magnetite but the amount of such water will not be great.

The water passing through the delivery portion 16 flows through a conduit 19 to a T 20 where it may flow to the right, viewing Fig. 1, past a valve 21 through a filter 22 and by way of pipe 23 back into the reservoir 2. The water may pass from the T past a valve 24 and through a pipe 25 to a spray head 26 where it may be employed for spraying the coal which has been lifted out of the liquid in the reservoir 2 to remove any adhering magnetite. As the coal rises above the surface of the liquid in the reservoir it is covered with magnetite containing liquid which it is desirable to wash off. The liquid sprayed onto the coal through the spray head 26 is substantially clean water virtually free of magnetite and effectively washes the coal, rendering it very clean as it is delivered to the cross conveyor 7.

When the spray head 26 is to be used the valve 21 is closed and the valve 24 is opened so that the water returns 'to the reservoir 2 through the spray head. When it is desired to filter the water instead of spray it onto the coal the valve 21 is opened and the valve 24 is closed and the water passes through the filter 22 and the pipe 23 back to the reservoir 2.

The magnetite delivered through the delivery portion 17 passes through a pipe '27 and past a valve 28 back to the reservoir 2. It is maintained throughout the process in deflocculated condition.

For re-circulating a portion of the separated component containing magnetic material for the purpose of increasing the concentration of magnetic material in the liquid entering the conduit 8 I provide a by-pass 29 extending from the pipe 27 to the duct 10 at the intake side of the pump 13. The by-pass 29 contains a valve 36 which may be opened to a desired extent to control the amount of the component containing magnetic material, which is re-circulated. The greater the amount or" that component which is re-circulated the greater will be the concentration of magnetic material in the liquid entering the conduit 8.

For re-circulating a portion of the separated component consisting of substantially magnetic material free liquid for the purpose of decreasing the concentration of magnetic material in the liquid entering the conduit 8 I provide a by-pass 31 extending from the delivery portion 16 to the duct 10 at the intake side of the pump 13. The by-pass 31 contains a valve 32 which may be opened to a desired extent to control the amount of substantially magnetic material free liquid which is re-circulated. The greater the amount of that component which is recirculated the less will be the concentration of magnetic material in the liquid entering the conduit 8.

Thus by proper setting of the valves 30 and 32 one or the other of the separated components may be re-circulated and through that re-circulation the concentration of magnetic material in the liquid entering the conduit 8 may be controlled for most efficient separation as explained above.

The structure of Figs. 1, 2 and 3 involves a linear arrangement of the magnet and separating conduit. However the separation can be effected otherwise. For example, I may employ a circular magnet similar to the rotor used in a conventional polyphase wound rotor induction motor and a separating conduit extending about a portion of the periphery of the magnet. Such a construction has the advantage of freedom from the undesirable end efiects of a linear magnet and has the further advantage that centrifugal force acts on any particles of relatively nonmagnetic material in the arcuate separation conduit causing the relatively nonmagnetic material to follow the outside of the conduit while the magnetic material follows the inside of the conduit. The relatively nonmagnetic material will pass oif with the substantially magnetic material free fluid. Such a device would be highly useful in the beneficiation of iron ore.

In Fig. 4 there is shown diagrammatically an apparatus which may be employed for the beneficiation of iron ore or in general for the separation of magnetic and nonmagnetic particles contained in a fluid. There is shown at 33 a circular magnet similar tothe rotor used in a conventional polyphase wound rotor induction motor which, as is known to those skilled in the art, creates a magnetic field which advances peripherally about the magnet, the magnet being considered as being stationarily mounted. The magnet is designed and constructed so that the magnetic field advances in a clockwise direction peripherally of the magnet viewing Fig. 4. The speed of advance of the magnetic field is determined by the design of the magnet.

Disposed about a portion of the magnet 33 is a separating conduit 34 through which fluid containing magnetic material and also possibly containing relatively nonmagnetic material is adapted to flow in the clockwise direction as indicated by the arrows in Fig. 4. The conduit is of minimum dimension radially of the magnet at the entering end and the radial dimension gradually increases from the entering end toward the discharge end. The transverse dimension of the conduit at right angles to the radial dimension is designed so that the crosssection of the conduit will be such that the magnetic material will tend to flow through the conduit at about the same speed as the speed of advance of the magnetic field thcrealong. The conduit 34 is at the discharge end divided into two

discharge branches

35 and 36.

To illustrate the use of the apparatus of Fig. 4 for the separation of magnetic and nonmagnetic material carried by a fluid, the fluid containing the admixed magnetic and nonmagnetic material flows through the entering end of theconduit at 37 until the magnetic field created by the magnet 33 causes the magnetic particles to move radially inwardly to lie against the inside of the conduit as indicatedat 38. The nonmagnetic particles are not attracted by the magnet but tend to move toward the outside of the conduit due to centrifugal force as they pass along the curved conduit The nonmagnetic particles are designated 39. Thus through a combination of the magnetic effect upon the magnetic particles and the effect of centrifugal force on the nonmagnetic particles those particles are caused respectively to hug the inner and outer walls of the separating conduit 34. Thus the magnetic particles pass through the discharge branch 36 while the nonmagnetic particles pass through the discharge branch 35. Both the magnetic particles and the nonmagnetic particles are accompanied by a portion of the fluid. If it is desired that less fluid pass through one or the other of the

discharge branches

35 and 36 the crosssectional areas of those branches may be proportioned accordingly or valves may be provided for adjustably reducing the cross-sectional areas of the discharge branches.

In Figs. and 6 there is shown diagrammatically an apparatus for recovering substantially magnetic material free liquid from liquid containing magnetic material and which comprises a hollow cylindrical polyphase alternating current magnet 40 similar to the stator of a conventional induction motor creating a magnetic field which advances in a circular path. A separating conduit 41 is disposed within the magnet 40, the liquid containing magnetic material being introduced through a duct 42 extending parallel to the axis of the core whence it passes through the body of the separating conduit 41, and the separated magnetic material and substantially magnetic material and substantially magnetic material free liquid are delivered through

delivery conduits

43 and 44, respectively, which conduits extend parallel to the axis of the magnet. The proportioning of the separating conduit 41 may be the same as the proportioning of the separating conduits 8 and 34. The magnetic material and the substantially magnetic material free liquid are separated by a divider'45. The magnetic material 46 is drawn outwardly against the outer wall of the separating conduit 41. The centrifugal action as the liquid passes through the curved conduit 41 cooperates with the magnetic action in causing the magnetic particles to move downwardly against the outer wall of the conduit.

The tendency of the portion of the liquid containing magnetic material as the liquid passes through the separating conduit (and this is true Whether the separating conduit be straight or curved) is to move with decreasing velocity'due to its gradually increasing concentration as the separating is effected. To cause the portion of the liquid containing the magnetic material in the separating conduit to move at substantially constant velocity so that'that portion of the contents of the separating conduit may move at a velocity which is substantially equal to the velocity of movement of the magnetic field the cross-section of the separating conduit will normally be reduced from a relatively great cross-section at the. entrance end of the separating conduit to a relatively small cross-section at the discharge end of the separating conduit. For example, in one construction the cross-sectional area of the separating conduit at the entrance end is almost double the cross-sectional area of the separating conduit at the discharge end. The result of this is, of course, to cause increase in the speed of flow through the separating conduit of the liquid as a whole but the effect of the decrease in cross-section simply counteracts the tendency of the portion of the liquid containing the magnetic material to slow up due to its increased concentration, the net result being that the portion of the liquid containing the magnetic material moves at approximately uniform velocity. The exact design of the separating conduit depends upon the particular conditions of operation including the material being treated. Generally speaking, however, when the magnetic field advances at uniform velocity as would normally be the case the separating conduit will have its cross-section gradually decreasing from the entrance end of the discharge end thereof.

It is possible to employ a separating conduit of constant cross-section and a specially wound magnet providing for advance of the magnetic field at a non-uniform velocity, i.e., at a velocity which gradually decreases from the entrance end to the discharge end of the separating conduit consonant with the natural tendency of the portion of the fluid in the separating conduit which contains the magnetic material to slow up as it advances through the separating conduit due to increase in concentration of magnetic material.

While I prefer for most uses to employ a peripherally closed separating conduit the separating conduit may in certain applications be open to the atmosphere.

In any of such cases the'construction is preferably such that the portion of the fluid containing magnetic material is caused to advance as a stream at a speed which at all points along its course is substantially equal to the speed of advance of the magnetic field at those respective points.

- I do not mean to say that the speed of the magnetic particles must be exactly the same as the speed of advance of conduit but the nearer this condition is approached the more efficient will be the separating action. Separation can be effected though at lower efficiency when the speed of advance of the magnetic particles is diiferent from the speed of advance of the magnetic field.

Where I refer to substantially magnetic material free liquid I mean liquid from which the bulk of the magnetic material has been removed, not necessarily liquid ap- "proaching complete freedom from magnetic material. For example, I would consider liquid containing as little as 10 to 15 percent of magnetic material by weight to be substantially magnetic material free for certain purposes although generally I would expect that the percentage by weight of magnetic material in my substantially magnetic ill-r material free liquid would be substantially less than percent, ordinarily of the order of 1 percent or less.

The loss of magnetite and water is very small. By use of the re-circulating system shown in Fig. l the buoyancy of the liquid in the reservoir 2 is maintained substantially constant at the desired point as the quantity of water returned to the reservoir is substantially the same as the quantity of water withdrawn and the quantity of magnetite returned is substantially the same as the quantity of the magnetite withdrawn.

1 thus accomplish in a very simple and efficient way a process which heretofore has been complicated by the flocculation and consequent necessity of deflocculation of the magnetic material. Advantages also accrue by reason of the pumping of the liquid through the separating conduit at a speed such that the contents of the conduit or the portion thereof containing the magnetite moves along the conduit at a speed substantially equal to the speed of movement in the same direction of the magnetic field. The character of the alternating current magnetic field and the agitation of the particles of magnetite as they advance through the separating conduit cooperate to prevent any appreciable permanent magnetization of the particles of magnetite and hence to prevent flocculation of the magnetite.

While I have shown and described certain present preferred embodiments of the invention and certain present preferred methods of practicing the same it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

1. A method of recovering substantially magnetic material free liquid from liquid containing magnetic material comprising flowing in a stream liquid containing magnetic material, impelling toward one side of the stream magnetic material in the liquid by a magnetic field, confining the dimension of the stream parallel to the direction of magnetic impulsion to a minimum in the zone of entry of the stream into the magnetic field, increasing said dimension in a zone advanced in the direction of flow relatively to said first mentioned zone, delivering the magnetic material at said side of the stream and delivering substantially magnetic material free liquid at the opposite side of the stream.

2. A method of recovering substantially magnetic material free liquid from liquid containing magnetic material comprising flowing in a stream liquid containing magnetic material, drawing toward one side of the stream magnetic material in the liquid by a magnetic field, advancing in the direction of flow at approximately equal speeds the magnetic field and that portion of the stream containing the magnetic material, confining the dimension of the stream parallel to the direction of magnetic attraction to a minimum in the zone of entry of the stream into the magnetic field, increasing said dimension in a zone advanced in the direction of flow relatively to said first mentioned zone, delivering the magnetic material at said side of the stream and delivering substantially magnetic material free liquid at the opposite side of the stream.

3. A method of recovering substantially magnetic material free liquid from liquid containing magnetic material comprising flowing in a stream liquid containing magnetic material, irnpelling toward one side of the stream magnetic material in the liquid by a magnetic field, confining the dimension of the stream parallel to the direction of magnetic impulsion to a minimum in the zone of entry of the stream into the magnetic field, increasing said dimension in a zone advanced in the direction of flow relatively to said first mentioned zone, decreasing in the direction of flow the dimension of the stream normal to said first mentioned dimension, delivering the magnetic material at said side of the stream and delivering sub.- stantially magnetic material free liquid at the opposite side of the stream.

4. A method of recovering substantially magnetic material free liquid from liquid containing magnetic material comprising flowing in a generally horizontal stream liquid containing magnetic material, drawing downwardly magnetic material in the liquid by a magnetic field, moving the magnetic field in the direction of flow of the liquid, confining the depth of the stream toa minimum in the zone of entry of the stream into the magnetic field, increasing the depth of the stream in a zone advanced in the direction of flow relatively to said first mentioned zone and delivering substantially magnetic material free liquid from above the downwardly drawn magnetic material.

5. Apparatus for recovering substantially magnetic material free liquid from liquid containing magnetic material comprising means for flowing in a stream liquid containing magnetic material, means creating a magnetic field moving along the stream in the direction of flow drawing toward one side of the stream magnetic material in the liquid, stream defining means confining the dimension of the stream parallel to the direction of magnetic attraction to a minimum in the zone of entry of the stream into the magnetic field and increasing said dimension in a zone advanced in the direction of flow relatively to said first mentioned zone so that the magnetic field and that portion of the stream containing the magnetic material advance in the direction of flow at approximately equal speeds, means for delivering the magnetic material at said side of the stream and means for delivering substantially magnetic material free liquid at the opposite side of the stream.

6. Apparatus for recovering substantially magnetic material free liquid from liquid containing magnetic material comprising means for flowing in a stream liquid containing magnetic material, means creating a magnetic field drawing toward one side of the stream magnetic material in the liquid, stream defining means confining the dimension of the stream parallel to the direction of magnetic attraction to a minimum in the zone of entry of the stream into the magnetic field andv increasing said dimension in a zone advanced in the direction of flow relatively to said first mentioned zone while decreasing in the direction of flow the dimension of the stream normal to said first mentioned dimension, means for delivering the magnetic material at said side of the stream and means for delivering substantially magnetic material free liquid at the opposite side of the stream.

7. Apparatus for recovering substantially magnetic material free liquid from liquid containing magnetic material comprising means for flowing in a generally horizontal stream liquid containing magnetic material, means References Cited in the file of this patent UNITED STATES PATENTS Germany Dec. 17, 1942 I