US2356648A

US2356648A - Classifying process and apparatus

Info

Publication number: US2356648A
Application number: US413218A
Authority: US
Inventors: Brusset Jean Albert
Original assignee: Individual
Current assignee: Individual
Priority date: 1941-10-01
Filing date: 1941-10-01
Publication date: 1944-08-22
Anticipated expiration: 1961-08-22

Description

Aug. 22, 1944. J. A. BRUssET CLASSIFYING PROCESS AND APPRATUS Filed Oct. l, 1941 3 Sheets-Sheet l Jean/lbert Brusse.

Aug. 22, 1944. J A BRUSSET l2,356,648

CLASSIFYING PROCESS AND APPARATUS Filed Oct. 1, 1941 '5 Sheets-Sheet 2 Aug. 22, 1944. J. A. BRUssE'r CLASSIFYING PROCESS AND APPARATUS Filed Oct. 1, 1941 3 Sheets-Sheet 3 Syvum/vbo@ Jean, .Hilbert Brussel:

Patented Aug. 22, 1944 UNITED STATES PATENT OFFICE 2,356,648 cLAssIFYING PaooEss AND APrARA'rUs Jean Albert Brusset, Blairmore, Alberta, Canada Application October 1, 1941, Serial No. 413,218

8 Claims.

The present invention relates to processes and apparatusfor separating mixed granular materials of difierent specific gravities according to their specific gravities, and particularly into three or more clean-cut products, by means of a novel flotation bath made up 'of a suspension of solid materialin water. i

It has in the past been found relatively easy f to make two-product separations, (one oat," and one sink) in liquids or suspensions. In attempts to split the sink into two further products oi' different specic gravities the prior investigators attempted to effect the further separation by creating rising currents in the bath, it having been the theory that such currents would have more lifting action on the lighter material in the sink, and would be expected to carry this lighter material away to a convenient means of gathering and conveying. However, it

has been found that this theory does not Workout in practice, because these currents select, -among the particles of the sink, not only those particles of lesser specific gravity but also those of smaller size regardless of specific gravities which oier a relatively greater surface to the action of those currents. The result is that the material carried oi by such accessory currents is a mixture of large and small particles of material of intermediate specic gravity, plus small particles of the heavier specific gravity material. Conversely, there remain in the heavier material, separated as tailings ,-or lrefuse, the larger particles of the intermediate material. Thus a clean-cut separation of the sink" into "intermediate and tailing or refuse has not been possible with prior processes using accessory currents. to divide the sink The process of the present invention eliminates the use of any currents in the bath for the selection of refuse and middlings, and thus avoids the danger of impure products, as will be seen below.

A primary object of the invention is to obtain a perfect separation of three very clean-cut products (concentrate, middlings and tailings, or, in the case of coal, clean coal, middlings and refv use) by the use of one unique bath, of appropriate specic gravity, of a suspension of inely divided solid material in water.

An important object of the invention is the provision of an improved novel flotation medium for the separation of a mixture of materials of diierent specic gravities by a sink and oat process.

It is an object of the invention, also, to vprovide novel apparatus for use in eecting this sink and oat process.

The new flotation medium of the. invention consists essentially of an aqueous suspension of finely divided limestone rock, minus 150 mesh, in suiiicient concentration-to provide al medium y,of required'speciiic gravity. The limestoriev rock should be as pure as possible, that is, especially free from shales and clay. Ground limestone rock makes very stable suspensions in water, and all specific gravities of flotation medium, between, 1.30 and 1.70, can readily be provided without undue viscosity oi the medium at the higher values. Y

By grinding the limestone sothat 90% passes a mesh screen there is a small percentage of larger particles which settle more rapidly, thus maintaining a slightly higher specific gravity of medium adjacent the bottom of the bath, which circumstance is an advantage in the present process as it expedites separation of the sink into two final products.

Finely divided limestone rock as the solid ingredient of the suspension medium possesses a number of advantages over previously proposed media: thus, it is readily available almot everywhere; it is easily crushed to the required mesh; it is not abrasive on the machinery; it remains readily in suspension; it does not stick to the finished products `and is easily washed off of them; and it is easily recovered from the wash water by cycloning so that recycling is facilitated.

In' one aspect, the process of the present invention consists essentially `in introducing a mix-` ture of solid particles of lighter and heavier specific gravities into a bath of they aqueous suspension of iinely divided limestone' having a density adjusted to float the lighter but not the heavier particles, and separately removing lighter particles from the top and heavier particles from the bottom of the bath.

I have found that said nely divided limestone suspension may be used as the suspension medium in a modification of the aforesaid process, by which a mixture of lighter, intermediate, and heavier particles can be separated into its components, as follows: The density of the bath of suspension mediumie. g., Iaqueous suspension of finely divided limestone) is so adjusted that the light particles iloat thereon while the intermediate and heavy particles sink therein at varying rates of speed (preferably, s0 adjusted that the intermediate particles sink only very slowly through the bath): after the heavy particles have lsunk through a substantial depth of the `bath there is imparted to thema step-by-step translational movement, to one side or end of the container, by means of a longitudinally reciprocating sloping stepped deck (preferably, a longitudinally reciprocating sloping stepped deck whose forward motion, in the direction of the upper end thereof, is slower than its backward motion), whereby the sunken heavy particles are collected substantially at one line (i. e., the top end of the stepped deck) at which line the socollected heavy particles are separately withdrawn from the container and suspension. The intermediates simultaneously are concentrated at the low end of the stepped deck and are continuously or intermittently withdrawn, admixed with suspension medium, at the latter. The light particles are, of course, separately withdrawn at the top of the bath of suspension medium.

While the aforesaid aqueous suspension of finely divided limestone is admirably suited for use in the 3-way separation just described the latter may be carried out with the use of one or another of the prior art suspension media.

After the removal of the separated components, the latter are washed to remove suspension medium therefrom, and the suspension medium is reformed for reuse in a repetition of the process. From the viewpoint of the suspension medium, the 3-way separation process is a cyclical one, in which the steps constituting one cycle are as follows:

l. Suspension medium, of controlled predetermined density is fed to a separatory vessel to maintain therein a bath of predetermined depth;

2. Suspension medium, plus separated particles of the mixture undergoing treatment, is removed from the bottom of the separatory vessel;

3. Withdrawn suspension medium is removed from said separated particles by washing, thereby producing diluted suspension medium;

4. The so-diluted suspension medium is partially dewatered (the resulting water being use'- ful for the Washing step 3);

5. Fresh suspension medium of predetermined density is reformed from the dewatered suspension obtained 'in step 4 plus additional water, and used as the suspension medium in step 1.

In step 3 of the -cyclical process, the with? drawn material is washed in a plurality of stages,

in the first of which I employ as washing liquid the water obtained by partially dewatering the diluted suspension medium which is the product of that step; in a second stage of which I employ as washing liquid filtrate from the said ,water; and in the final stage of which I employ as washing liquid fresh make-up water. The three wash waters are combined and in step 4, are partially dewatered by treatment in a cyclone separator yielding (a) thickened suspension medium and (b) a water contaminated with a relatively small amount of the solids of the original suspension medium; which latter is divided into two portions one of which is used as initial washing liquid and the other of which is further clarified by filtration for use as intermediate washing liquid. The filter cake, consisting essentially of solids of the original suspension medium, may be and preferably is added to the thickened suspension medium obtained from the cyclone separator.

In carrying out step 5 of the cyclical process, I feed streams of thickened suspension medium and water (specifically, the partially clarified wa# ter from'the cyclone separator) to a mixing vessel, continuously automatically determine the specific gravity of the resulting mixture, and continuously automatically control the rates of feed of thickened suspension medium and water to said mixing tank to maintain the specific gravity of the mixture within narrow predetermined limits, as will be described more fully hereinafter.

The process and apparatus used in practicing the same will be described in greater 'detail with reference to the accompanying drawings which illustrate a preferred embodiment of the invention and in which:

Fig. 1 is a diagrammatic view of a plant embodying the invention;

Fig. 2 is a vertical sectional view of the main separating tank;

Fig. 3 is a sectional view approximately on the line 3-3 of Fig. 2;

Fig. 4 is an enlarged diagrammatic view of the suspension feed controls, and

Fig. 5 is a detail of the mounting of the submerged deck.

The main classifying tank 5, which will vary in size depending on the capacity desired, preferably is a metaltank having at one end a feed bin 6 which discharges onto a slanting feeding shelf 1 and disposed at an angle of about 30 at its lower end within the tank 5. An endless raking conveyor 8, running over sprockets 9 and I0 mounted at opposite ends of the tank, rakes the mixed material oi Aof the feed shelf 'I as the rakes II of the lower flight thereof begin their travel through the tank, and conveys the lighter materials which iioat on the separating medium to the other end and out over a discharge lip I2 at the end opposite the feed bin 6. The rakes II of the conveyor are made of perforated sheet iron and travel at a slow rate of speed through the upper portion of the bath so that they cause no undue agitation which might result in imperfect separation.

The heavy and intermediate materials of the mixture supplied through feed bin E sink through the bath between the lower edge of feed plate l.

' and an inwardly slanting defiecto'r plate I 3' mounted on the inside of tank wall il opposite plate 1 to a reciprocating deck or screen i5. The deck I5 is mounted at an angle of about 5 to 10 to the horizontal with its lower end beneath the plate 1, the amount of the slope being dependent on the characterl of the material being separated, and is supported on arms I6 which y are set perpendicular to the plane of the deck so that the motion of the deck is practically longitudinal in its own plane without any appreciable vertical or jigging component.

The upper .ends of the supporting arms for the reciprocating deck I5 terminate ina spindle I 1 upon which is mounted a heavy block or bushing I8 of rubber clamped between plates I9 by a nut 20. Steel collars 2| carried -on depending brackets 22 secured to the side frames 23 of the deck I5, clamp the rubber bushings I8 to make the connectionbetween the arms and the deck. Similar rubber blocks or bushings 24 mounted on the lower ends of the arms I6 are clamped between collars 25 carried on brackets 26 secured to a stationary member 28 mounted between the side walls of the tank 5. When the deck I5 is reciprocated by the means described hereafter the rubber blocks or bushings I8 and 24 yield sufficiently to allow the motion of the screen to take place and act as bearings not requiring lubrication. This is important because `all of these parts are immersed in the suspension medium.

Reciprocating motion is imparted to the deck I5 by a drive rod 29 which extends through the end wall 30 of the tank, its passage and motion therethrough being sealed by a rubber diaphragm 3I. The inner end of the rod 29 is provided with a rubber bushing 32 which is clamped by a collar 33 carried by a bracket 34 fastened to the deck I5. A roller 35 mounted on the outer end of the rod 29 bears on a rotary cam 36, the

profile of which is formed so as to advance the deck slowly toward its upper end and permit a `l drives. Worm-conveyor 43 also collects and conquick return motion. The quick return motion of the deck is partially caused by the resilience of the rubber block connections at the ends of the supporting arms and in addition is effected by resilient coil springs 31 acting between the upper end of the upper set of arms I6 and a stationary part of the tank 5. The driving cam 36 for imparting reciprocating motion to the deck is driven at the rate of about 120 revolutions a minute.

The supporting surface of the deck I is preferably formed of sheet iron perforated uniformly over its area with A or 1/2 inch holes` 38 and is corrugated or crimped into stepped formation to provide upwardly sloping steps 39 terminating in steep faces or shoulders 40 which face toward the upper end of the deck. The upper end of the deck extendsbeneath the lower end of the deflector plate I3 and terminates over the upper end of a discharge channel 4I. The lower end of the deck I5 extends to a point adiacent the wall 39 under the plate 1 and over the edge of a discharge channel 42.

In the course of operation, the lighter material, or fioat, is evacuated from the box by conveyor 8 over the lip I2. The heavier material sinks between plates 1 and I3 and toward deck I5. The lighter portion of that material, or middlings, which has a specific gravity fairly close to that of the bath, sinks more sluggishly than does the heavier material, which latter tends to reach and rest upon the deck I5. Due to the fact that the deck I5 moves quickly rearwardly, that is, in the direction of the lower end thereof, the heavy material will, because of its inertia, slide forward along the slightly inclined upper faces 39 of the steps, but during the forward and slower motion of the deck, the steep faces 40 of the steps will catch the heavy material and advance it toward the upper end of the deck. The heavy material will thus move step by step towards plate I3 along the deck, and finally will be discharged from the upper end of the de'ck into passage 4I under plate I3.

The intermediate particles or middlings," the gravitational motion of which is too sluggishin the heavy mediumto cause the same to be h eld in contact with the stepped screen, will move in the opposite direction, that is to say, towards veys whatever small heavy particles of material have fallen through the perforations of decl: I5, and the portion of the solid medium which has slowly settled to thebottom of the separating tank 5. v

As may be seen from the above, the separation of the mixture into three products does not make use of any currents whatever. 'I'he only principles involved are those of sink-and-fioat separation in a bath of appropriate specific gravity, plus separation of the sinks into two products by selective fricticnal action of the reciprocating stepped deck on the heavier particles of the sin The clean coal discharged over the lip I2, the middlings discharged into the channel 42 and the refuse discharged into the channel 4I together with the fine heavy material and settled suspension which iinds its way into channel 41 are delivered by suitable conveyors 46--46, 46 and 45, respectively, to washing screens 49, which for convenience are preferably arranged side by side. As the separated materials pass over the screens 49 they are washed successively by water from other stages of the process and finally lby clean make-up water supplied through sprays 50, 5I and 52, respectively.

The spent wash water with the medium washed from the separated materials on screens49 is caught by collectors 53 beneath the screens and flows therefrom to a tank 54. A pump 55 delivers the dilute suspension from tank 54 through pipe 56 tangentially at high speed into a cyclone separator 51 where thebulk of the solids of the sus- .;r, pension medium are separated from the wash medium to tank 54, small quantities of flotation 'n y reagents (oil in the case of coal) and air are by means of injector 58 continuously injected into the right-hand side of the tank 5, under the influence of gravity alone, since the right-end of the deck is lower than the left end. The loosening of the mass of middlings by the motion of the screen will accelerate this displacement under the influence of gravity. The middlings travel past the lower end of the deck I5 and are deposited in a transverse channel 42, the edge of which is overlapped by the end of the deck.

It will be seen that as the specific gravity of the suspension is practically equal to that of the middlings, the latter are subjected to a resultant force which is practically nil; so that if they pipe 56 between pump 55 and the cyclone separa- `tor 51 to produce in the cyclone a flotation reaction which causes the entrained particles of the mixture to' float to the surface and flow to tank 59 in .the flotation foam carried on the water discharged from the cyclone to said tank. A rotary sludge extractor 60 skims the foamy sludge from the surface of the water in tank 59 into a discharge launder 6I mounted thereon. The water overiiowing from the cyclone separator 51 to the tank 59 is relatively free of solids of the suspension medium.

A portion of the water from the cyclone separator is bled olf of the line 62 leading t0 tank 59 and passed to a vacuum filter 63 Where it is claried of all suspension medium. The clarified water from the vacuum filter is fed to the intermediate set of washing sprays 5I over the screens 49.

Under the action of centrifugal force in the cyclone separator 51 the particles of limestone of the suspension medium separate from the water and gather in the bottom of the cyclone which is closed by a, soft rubber pad 64 mounted on the end of a pivoted lever 65 and balanced by a counterT weight 66 adjustable along the other end of the lever. The position of the counterweight 66 is adjusted to balance the pressure of the liquid and solids above the valve pad 64 until a desired minimum concentration of solids which it is desired to extract from the cyclone exists above the valve pad. When the concentration of solids 'in the bottom of the cyclone exceeds the desired minimum value for which the counterweight is set, the pressure above the valve pad overcomes the counterweight to open the valve and the thickened suspension ilows down into the high specic gravity tank 61. When the ilow has continued to the point where the concentration in the cyclone Vdecreases below the desired minimum, the counterweight will close the valve 64 and the flow will be cut oil'` until the concentration again builds up. Thus the tank 61 is kept supplied with concentrated suspension from the cyclone.

Concentrated suspension from the tank 61 flows through pipe 68, equipped with a regulating valve 89, to a mixing tank 18 where it is mixed with water supplied through pipe 1i equipped with a regulating valve 12, from water tank 59. From the mixing tank 18 the reformed suspension medium of desired specic gravity is pumped through pipe 19 by pump 14 to the main separating tank 5 to maintain the level of medium therein and to insure maintenance therein of the proper concentration of the suspension medium.

'I'he delivery of concentrated suspension and water to the mixing tank 18 is regulated so as to maintain at a constant predetermined value the specific gravity of the suspension therein which is fed to the main treatment tank 5. This regulation is eilected by a specific gravity control system generally designated 15. This system includes a container 16 which is constantly supplied with suspension bled oil of the feed pipe 13 at 11. The container is provided with a small drainage opening 18 in the bottom thereof and an overilow 19 at the top so as to maintain a constant level of suspension medium in the container 16 and-prevent building up the concentration therein.

A pipe 88, bent to U-shape, is immersed in the suspension in the tank 16 so that its horizontal portion 8| is about 50 inches below the level of the suspension. A series of small holes 82 are provided in the lower side of the immersed horizontal portion 8| of the U-shaped pipe. One end 83 of the pipe 88 is connected to a diaphragm pressure gauge 84 and the other end 85 is connected to a constant pressure air tank 86 which is supplied with compressed air from` a supply pipe 81 through a reducing valve 88 which is set to maintaina constant pressure of 100" W. G. in the l tank 86. A series of small oriilces 89 in the connection from the tank 86 to the U-shaped pipe 88 provides for low volume feed of air at constant pressure to the Pipe. i

The pressure of air in pipe 88 is always lower than 108" W. G. because air is fed through orices 89 ata very slow rate and as soon as the pressure in pipe 88 reaches the value corresponding to the head of suspension above holes 82, the air escapes through those holes and bubbles up .3 the surface of the bath. As a result, the pressure inside pipe 88 is always equal to that created by the height h (in inches) vof suspension existing above the level of holes 82, or: P=h S where S is the specific gravity oi' the bath. As h is kept constant, pressure P directly measures the speciilc gravity of the suspension in the mixing tank 18. The pressure in the pipe 88 is registered by diaphragm pressure-gauge 84, which may also be made into a recorder if it is desired to keep a close check on the operation of the treatment tank.

The gauge 84 controls the speciilc gravity in mixing tank 18 in an automatic manner. When the specific gravity increases above the desired value, for which the diaphragm is kept at its average position by an adjustable spring 98, the diaphragm is lifted, and through a set of light arms and rods 9| tilts to the left mercury switch 92, thereby starting electric motor 93 which through arm 94, link 95 and lever 96 on valve shaft 91 operates valves 69 and 12 from position #l to position #21. Valve 12, now fully open, admits more water from tank 59 to the mixing tank, while valve 69 which controls the flow of heavy suspension from tank 61 is nearly closed. Thus the specific gravity of the suspension in the mixing tank is quickly reduced. As soon as the speciflc gravity is back to normal, the spring pulls the diaphragm back and so throws open the switch 92, thereby `deenergizing motor 93. Valves 6-9 and 12 then are brought back to position 1 by counterweight 98 on lever 96 and from then on 4deliver a greater proportion oi' heavy suspension than water to the mixing tank, thus tending to increase the specific gravity. By this means, the speciiic gravity of the suspension in tank 18 will continually fluctuate within very narrow limits around the desired value, withoutever exceeding those limits. For instance, for coal-washing, if a gravity of 1.50 is desired, the range 'of variations will be from 1.49 to 1.51, which amounts to keeping an average of 1.50.

All of the

tanks

54, 59, 61 and 18 are provided with agitators 99 to prevent settling out of the solids suspended in the liquids maintained in or passing through the tanks. Make-up limestone dust of the proper nneness is fed to the tank 61 by a feeder |88 to replace the small amount inevitably carried oil' with the separated materials and clean make-up water is supplied to the nal wash spray 52.

While a preferred process and apparatus for use in practicing the same has been described and shown by way of illustration, it will be understood that various modifications in the details thereof may be resorted to without. departing from the spirit oi the invention within the scope of the appended claims.

I claim: I

1. The process of separating a mixture of light, intermediate and heavy solid particles into its components according to their speciiic gravitis, which comprises introducing the mixture into a body of suspension medium comprising finely ground solid particles in water, maintaining the suspension medium at a density to float only the light particles of the mixture whereby the interl mediate and heavy particles tend to fall by gravity in a downward path through the suspension medium, imparting a sidewise propelling movement to the heavy particles across the line of their gravitational path, at a zone in said body of suspension medium intermediate the top and bottom thereof, toward one side of said body, while avoiding creation of vertical currents in the suspension and While simultaneously permitting the intermediate particles to move by gravity below suchl zone of sidewise propelling movement, segregating the so-propelled heavy particles at said side of the body of suspension medium and thereafter removing them -irom said body, and removing the intermediate particles from the body of suspension medium at a location below that at which said heavy particles are segregated.

2. The process of separating light particles, intermediate particles and heavy particles from each other in a mixture thereof in the presence of a medium comprising a suspension of finely divided solid particles in liquid, which comprises maintaining a body of the medium at a density to float the light particles only whereby the intermediate and heavy particles fall by gravity through said suspension medium at varying rates of/speed, feeding the mixture to the upper part of said body of suspension medium, removing floated light particles from the surface of the suspension medium, permitting the intermediate and heavy particles to fall by gravity in a downward path through the suspension meduim, at a zone in said body of suspension meduim intermediate the top and bottom thereof, imparting -to the heavy particles only a sidewise step-bystep translational movement to one side of said body of suspension medium while simultaneously permitting the intermediate particles to progress by gravity past such zone of translational movement, segregating heavy particles at said side thereof, and thereafter removing them from said body of suspension medium, and removing intermediate particles from said body of suspension medium at a location below that at which said heavy particles are withdrawn.

3. The process of separating light particles, intermediate particles and heavy particles from each other in a mixture thereof in the presence of a medium comprising a suspension of nely divided solid particles in liquid, which comprises maintaining a 4body of the medium at a density to float the light particles and nearly to float the intermediate particles, feeding the mixture to the upper part of said body of suspension medium, removing oated light particles from the surface of the suspension medium, permitting the intermediate and heavy particles to fall by gravity in a downward path through the suspension medium, at a zone in said body of suspension medium intermediate the top and bottom thereof, imparting to the heavy particles only a sidewise step-by-step translational movement to one side of said body of suspension medium while simultaneously permitting the intermediate particles to progress by gravity past such zone of translational movement, segregating heavy particles at said side thereof,- and thereafter removing thm from said body of suspension medium, diverting the intermediate particles along a downwardly inclined path toward another side of said body of suspension medium than that to which the heavy particles are moved, and removing intermediate particles from said body of suspension medium at--said other side of the latter and at a location below that at which said heavy particles are withdrawn.

4. In apparatus for separating mixtures of solid materials of different specific gravities by theA oat-and-sink method involving use of a suspension medium essentially consisting of a suspension of finely divided solid material in a liquid and having a density adapted to oat one but not all of the constituents of the mixture to be separated, a tank containing a body of such suspension medium, a sloping deck mounted within the lower portion of said tank and having a stepped surface providing spaced shoulders facing the higher end thereof, means for mounting said deck for a reciprocating motion substantially in the plane thereof, means for reciprocating said deck with a differential motion in which said deck is moved faster toward the lower end than toward the higher end thereof, means for removing heavy material progressing over the` higher end of said deck, means for removing intermediate material gravitating toward the lower end of the said deck, and means for removing light material iioated on the surface of the suspension medium in the tank.

5. In apparatus for separating mixtures of solid materials of different specific gravities by the oat-and-sink method involving use of a suspension medium essentially consisting of a suspension of finely divided solid material in a liquid and having a density adapted to float one but not all of the constituents of the mixture to be separated, a tank containing a body of such suspension medium, a sloping deck mounted within said tank beneath the surface of such body of suspension medium for reciprocation substantially in lts own plane, said deck having a stepped surface providing spaced shoulders facing the higher end thereof, means for imparting reciprocating motion to said deck, and separate means for removing separated materials adjacent the higher and the lower ends of the deck.

6. In apparatus for separating mixtures of solidv materials according to specific gravity wherein the materials are separated by selective action of a suspension medium of iinely divided solid in liquid in a separating tank and wherein separated materials are washed to remove suspension medium therefrom and the wash waters are clarified to produce a supply of thickened suspension medium and water, and thickened suspension medium and water are mixed in regulated quantity to form a suspension medium of desired specific gravity for replenishing the supply in the tank, a mixing tank, means for delivering reformed suspension medium of desired specific gravity from the mixing tank to the separating tank, a control receptacle, means for continuously passing a portion of reformed suspension medium from said mixing tank to said control receptacle to maintain a constantlevel of suspension medium therein, a U-shaped pipe immersed in said control receptacle having perforations below the level of medium therein and connected at one end to a pressure responsive means, means for supplying air under constant pressure to said pipe through the end thereof opposite to that connected to said pressure responsive means, and means under control of said pressure responsive means for controlling the feed of thickened medium and liquid to said mixture tank.

7. The process of separating light particles, intermediate particles and coarse and fine heavy particles from each other in a, mixture thereof in the presence of a medium comprising a suspension of finely divided solid particles in liquid, which comprises maintaining a bath of the medium at a density to float the light particles and nearly to float the intermediate particles, feeding the mixture into said bath of suspension medium, removing floated light particles from the surface of the bath of suspension medium, permitting the intermediate and heavy particles to fall by gravity in a downward path through the suspension medium at varying rates of speed, at a zone in said body of suspension intermediate the top and bottom thereof, imparting to the coarse heavy particles only a sidewise step-bystep translational movement to one side of said body of suspension medium, while permitting the body and thereafter removing them from the latn ter, withdrawing suspension medium and associated fine heavy particles from the bottom of said bath, and separating tine heavy particles from the withdrawn suspension medium.

8. Apparatus for separating a ,mixture of solid materials of different specific gravities according to the fioat-and-sink method involving the use a liquid which suspension medium is maintained at such a density that at least one but not al! of the constituents of the mixture sinks therein. which comprises in combination a separating tank containing a body of such suspension medium, means for delivering the mixture to be separated to the upper part of the body of suspension medium, a-sloping deck mounted within said tank for reci'procation substantially in its own plane. said deck having a stepped upper surface providing spaced shoulders facing the higher of a suspension medium essentially consisting of zo a suspension oi iinely divided solid material in end thereof, means mounted in said tank above said deck for diverting sinking particles onto said deck, means for imparting reciprocating motion to said deck, segregating channels associated with the higher and lower ends of said deck to receive materials discharged over said ends, and separate means for withdrawing segregated materials from said segregating channels.

JEAN ALBERT BRUSSET.