US2174553A - Method of classification - Google Patents

Description

Oct. 3, 1939. A, DAMAN 2,174,553

METHOD OF CLAS S IFI CATION Filed Oct. 14, 1935 3 Sheets-Sheet l INVENTOR. ART/fl/f? C. DANA/V 00 q ATTORNEY.

Oct. 3, 1939. c. DAMAN 2,174,553

METHOD OF CLAS S IFI CATION Filed Oct. 14, 1935 3 Sheets-Sheet 2 I INVENTOR. ARTHUR C. DANA/V Oct. 3, 1939. c, D M 2,174,553

METHOD OF CLASSIFICATION Filed Oct. 14, 1955 3 Sheets-Sheet 5 IIIIIII" go k BY ATTORNEY.

Patented Oct. 3, 1939 UNITED STATES 2,174,553 DIETHOD F CLASSIFICATION Arthur C. Daman, Denver, Colo., assignor, by

mesne assignments, to Mining Process and Patent Company, a corporation of Delaware Application October 14, 1935, Serial No. 44,915

25 Claims.

This invention relates to a method of classifying solids in liquid suspension and relates more particularly to ore-classification in which slimes in liquid suspension are treated in a primary separation zone and removed by overflow while coarse material under treatment is conducted to a settling zone through which it descends by gravity and is thereupon subjected to a dewatering treatment in a second stage of the treatment.

It is an object of the present invention to agitate and aerate the material under treatment,

thereby producing buoyant forces which enhance the separation of fines from coarse material.

Another object resides in combining in a single treatment, the steps of classifying solids in liquid suspension and conditioning the material for subsequent treatment.

A further object of the invention is to control the velocities of the material at difierent stages 20 in the treatment to thereby promote a clean separation between coarse and fine material.

Still another object of the invention is to provide a primary and secondary classification in a treatment in which both the primary and the secondary are subjected to the influence of the same mechanical agitation.

Other objects reside in the provision of novel steps and treatments as will more fully appear in the course of the following description.

30 This invention constitutes a continuation-inpart of my co-pending application, Serial No. 581,-

' 129, filed December 15, 1931, for Classifier. Subjects matter common to both applications have been described and claimed herein in response to a divisional requirement in said co-pending application.

While the method herein described may be effectively incorporated into various types of classification treatments, it has been described and 40 illustrated in connection with-the treatment of ore in a finely divided condition and in liquid suspension, as a typical application of the invention.

The ore is prepared for treatment by any well known method, wet-grinding in a ball mill or rod mill being typical. The discharge from the mill is conducted to the classification stage of the treatment. It will be understood that the classifying element may be operated in either an open-circuit or a closed-circuit arrangement. Where .drygrinding is employed, the ground product must be mixed with a liquid carrier to form a pulp prior to its introduction into the zone of classification.

5,5 The pulp fed to the zone of classification is subjected to both agitation and aeration in said zone. The agitation intimately intermixes the air. and pulp, and the fines in the pulp body are acted upon by the minute bubbles of air rising through the liquid body, which elevate the same 5 to a point of overflow, resulting in a cleaner, more rapid separation than is obtained by present methods.

The direction and velocity of the moving material is subjected to certain control influences 10 through the provision of separate agitation and settling zones. Material is moved upwardly through the zone of agitation at a greater velocity than it descends through the settling zone, and the upward movement is preferably at a progressively decreasing velocity in order to promote the settling of oversize material.

The settled material is thereafter subjected to a second classification in the secondary or dewatering stage of the treatment. Fines passing into this secondary zone with the oversize are separated by a classifying action and returned to the primary zone of classification for further treatment. i

It is advantageous to employ a rotary impeller as the agitating element of the treatment and to maintain the primary and secondary zones of classification in separated and intercommunieating relation. The impeller agitates material in the primary zone, and in cooperation with other elements, controls the velocity of material moving upwardly in said zone and, at the same time, acts as a pump to return the fines from the secondary to the primary zone of classification.

From the foregoing description of the treatment, it is clear that various types of apparatus may be effectively employed in practicing the invention. To promote a better understanding, the invention will be hereinafter described in connection with certain apparatus shown and de- 40 scribed in my co-pending application, Serial No. 581,129, it being understood that such apparatus, while'efi'ective in performing the process, is shown and described merely to constitute an operative arrangement for practicing the invention.

In the drawings in the several views of which like parts have been similarly designated:

Figure 1 represents a sectional elevation of an I arrangement of apparatus, efiective for performing the process;

Figure 2 is a flow sheet, representing the various steps and treatments employed in practicing the process;

Figure 3 is a section taken along the line 3-3,

figure l; Y

modification of the form illustrated in Figure 4;

and

Figure 6, a section taken along the line B-6 in Figure 5.

Referring first to Figure 2, the invention has been described as applied to closed-circuit classification in conditioning an ore pulp for a froth flotation treatment. It is to be understood that the described treatment is merely typical of the use of the invention, and that treatments other than those illustrated and described may be employed within the spirit and scope of the invention.

Ore and water are first fed into a launder 31 which feeds a mill 40, where the ore is ground to a predetermined degree of fineness, and thereafter is discharged into a classifying element 5. This element comprises a primary classification zone A and a secondary classification or dewatering zone B.

Oversize material of the treatment in the primary zone A is delivered into the secondary zone B and moved to an elevated discharge outlet 3| from which it is passed into the launder 31 and returned to the mill for regrinding.

Fines in the secondary zone B are returned to the primary zone A for re-treatment. Reagent is fed into the primary zone A by a suitable feeder 39, which preferably is the type that automatically feeds measured amounts. The pulp and reagent are subjected to the influence of agitation and aeration in the primary zone A and the slimes passing across into an overflow launder 4| at the topof the primary zone constitute a conditioned pulp which is fed into a series of flotation cells 42 where the values are concentrated and discharged in a froth by overflow into a launder 43.

Referring now to Figure 1 of the drawings which illustrates a type of apparatus well adapted for performing the process, the primary classifying element A comprises an inverted cone-shaped vessel 5 having a circular weir 6 for the overflow of slimes, and having at its lower end, an outlet I for the delivery of coarse settling products of the primary classifying operation, to the dewatering and conveying element B.

The weir has a loose rim 8 which may be ad-- justed to raise or lower the line of the overflow which determines the liquid level in the vessel. Two concentrictubes 9 and I in the vessel have their common axis coincident with the vertical axis of the cone-shaped vessel, and conjointly provide an element for conveying material-fed into the space between the tubes through a launder 12, to the lower portion of the vessel.

A rotary movement is imparted to the inner tube by means of a worm wheel l3 supported on a bearing l4 above the vessel and the two tubes are rigidly connected by cross-tubes I5 adjacent their upper ends and by an aperturedflange 16 at their lower ends. The outer tube has at its upper end a bell-shaped enlargement I'I into which the material is fed from the launder l2 and exteriorly of the rim of this enlargement are two opposite shields l8 ordirecting upwardly connections l5 at the material fed into the mouth of the outer tube and air may enter the inner tube, and a sliding valve Zll around the inner tube, normally resting on the cross-connections I5, is adjustable to control the passage of material through the openings l9.

A shaft 2! coaxial with the vessel, extends through the inner tube and carries at its end below the same, an impeller 22 adapted to impart an upward thrust to the material discharged from the tubes. 7

The impeller is rotated through the medium of a sheave 23 supported above the worm-wheel l3. A conical baffle 24, is fastened as by arms 25 to rotate with the concentric tubes, and its lower end houses a part of the impeller in spaced relation thereto.

Another similar baffle-ring 26 laps at its lower end over the upper portion of the baffle 24 in spaced relation thereto and is held stationary by connection with the wall of the vessel.

Scrapers 2'! provided with slanting'blades, are connected with the rotary parts of the classifier, as by means of arms 28, to compel settling material to move along the inner surface of the vessel to the discharge opening 1. The arms 28 of the scrapers may be attached to a vertically adjustable ring 35 around the mouth of the feed tube. By adjustment of this ring the position of the scrapers may be varied, and the edge of the mouth of the feed tube, if necessary, may be elevated to a plane above the liquid level in the vessel.

To permit the use of the device as a conditioner in addition to its function as a classifying element, a conduit 38 from a reagent feeder 39 communicates with the launder 2 for the supply of reagent to the primary classifying element.

The element B comprises a tube 29, preferably rigid, and connected with the outlet 1 of the classifier by a flexible .elbow 30. The tube 29 slants upwardly from the opening with its sanddischarging upper end 3| above the plane of the liquid level in the vessel.

When the classifier is operated in closed-circuit,

the end 3| may be connected with suitable conduits (not shown), and where necessary, a suitof oversize material to the grinding element may be employed.

In Figure 2 another arrangement has been illustrated in which the discharge from tube 29 is fed directly into launder 31.

The foregoing are merely cited as typical, and any arrangement whereby the material discharged from the tube 29 may be returned to the grinding elecent 40 may be employed within the spirit and scope of the invention.

able pump-element, (not shown) for the return A vibratory, longitudinal motion is imparted to the tube 29 by means of electrical vibrators 32, in order to convey the sands upwardly through the tube to its discharge opening. The vibratory movement may be differential to accelerate the upward movement of the sands by alternate slow and rapid strokes imparted to the tube by the vibratory devices. It is apparent that these devices may be of any desired character within the scope of the invention.

The vibratory motion of the tube 29 may be communicated to the vessel 5 in order to expedite the separation of the coarse matter from the fines in the material under treatment. The vessel and the tube are supported for conjoint vibration in such case. Any suitable structure may be employed to support the apparatus and inasmuch as such s ructure must be varied according to the 2,174,558 construction of the mill in which the classifier is erected, detailed illustration of the same has been omitted from the drawings.

In order to maintain the material under treatment at the proper density for the separation of its fine and coarse constituents in a settling action, water may be supplied to the classifier at anydesired point, as for example, at the bend of the elbow below the discharge opening, as shown at 33.

Water may also be supplied to the conveyor as by means of a tube 34, to accelerate the upward.

movement of dewatered sands, in case the density of the material in the tube exceeds a predetermined normal. In addition, the water introduced in this manner facilitates classification in the material passing through the tube by washing down fines which have been trapped in the coarse material.

By extending the conveyor above the plane of the liquid level in the classifier, a hydrostatic balance is established and the coarse matter moved above said plane by the vibratory movement, is delivered through the end of the con.- veyor in a comparatively dry condition andsubstantially free of fines and 'slimes The oversize discharge from the conveyor is conducted to the .The upward thrust imparted to the material causes it to move in an upward current through the conical baiile 24, and thence through the upper stationary baille 26, as indicated by the arrows.

liquid current to move to the lower part of the settling vessel over the upper edges of the baflles.

The finer matter in suspension is divided into fine slimes which rise to the liquid level to be discharged across the overflow, and middlings which enter the space between the shields l8 and the feed tube Ill and pass through the crossconnections I 5 into the inner tube 9 for re-' classification upon its return into the zone above the impeller. 1

By thus moving a part of the material in a closed circuit, it is cleanly divided by repeated separative actions into the slimes which pass across the overflow under the buoyant influence of the aeration, and the coarse sands which pass through the outlet 1 of the vessel into the conveying and dewatering element B, the operation of which has been described hereinbefore.

The scraping action of the rakes 21 moving over the inner surface of the conical vessel, insures a constant movement of all of the gravitating sands to and through the outlet.

During the upward movement of. the material under the influence of the agitation and During the upward movement of the material, coarse particles thereof settle out of the The circulatory movement of the pulp in the classifier aids in maintaining its proper density. Water introduced under pressure through the opening 33 aids in producing the same-result and, moreover, washes the settling sands into the conveyor element B, and thereby replaces slimes that have moved downwardly with the'sands, which are subsequently returned to the primary classification zone by the vibratory motion and by "the suction infiuence of the impeller.

It will be apparent from the foregoing that material is moved upwardly in the primary classification zone at greater velocity than it moves downwardly in the settling zone. The arrangement of the impeller 22, tubes 8 and I0, and

baflles 24 and 28 permits a velocity control which The water supplied to the conveyor through the pipe 34 also functions to force and wash downwardly the slimes carried upwardly with the sands, for their return to the primary zone of classification under the suction'infiuence of the impeller.

Owing to the circulatory movement of the pulp in the classifier, but little water is required to maintain the pulp density. The vibratory movementbf theap'paratus, together with the agitation and aeration keeps theslimes in suspension and thus accelerates their movement to the level of the liquid in the vessel.

The impeller may function as an aerator by creating a vortex which draws in atmospheric air through the tubes 9 and I0, and in that ca- I pacity further aids the separation of material.

In case it is desired to deliver the feed" and/or reagent into the central zone above the impeller, together with the circulating slimes, the openings I9 of the inner tube may be opened by adjustment of the valve 20,112 which case the discharge openings of the outer tube are plugged asindicated '-in broken lines at'sfi'in Figure 1, and by regulatcharged from the primaryclas'sifier A is effected by means of one or more reciprocating rakes 44 moving over the .sloping bottom of a tank 45, in which the primary settling vessel is disposed.

A suitable mechanism for: longitudinal reciprocation of the rakes combined with alternate upward and downward movements, is'shown at 46. This mechanism is old in the art, andfurther detailed description need'not be given.

The construction of the primary classifying element A difiers from that illustrated in Figure 1, mainly'in that the conical vessel-has in the upper portion of its wall, outlets 41 for the return flow of middlings exteriorly of the vessel to the outlet I at the lower ,end of the same.

A second-smaller impeller connected with the other rotates in the lower zone of the vessel to effect or accelerate the upward movement of the middlings through the outlet, together with ny slimes that may have been carried upwardly with the sands by the rakes ,4. r I

The rakes movebelow the outlet of the classifier and the outlet has'been' slotted as at 48, to

- prevent possible clogging of the sands and facilitate their movement to the conveyor.

The outlet 3 la of the tank, is likewise above the liquid level in the vessel, and the tank has below the primary classifying element A. The impeller 22 in this form of the invention projects through the outlet 1 of the primary classifier, and the matter passing downwardly across the baflies, is discharged into the tank 45 of the rakes, to be returned in part to the classifying vessel by the action of the impeller.

By the provision of openings 50 in the lower conical baillle, through which the coarser particles may settle, one or more of the plurality of baffles may be omitted. Otherwise, the primary classifying element is substantially the same as those hereinbefore described.

The impeller is partially below the rakes in the conveying element B. It will be understood that if desired, the impeller may be entirely below the rakes, which is of particular value in re-fitting old classifiers of the rake type now in use.

From the foregoing, it will be apparent that the feed, air and/or reagent is subjected to the action of the impeller in the primary classification zone, and directed in an upwardly direction.

Coarser material is moved outwardly and settles by gravity, while the fines continue to rise and pass across the overflow. The coarser particles pass into the zone of influence of the conveyor and are moved to an elevated point of discharge in ade-watering treatment.

Fines entrapped wlth'the sands are subjected to additional washing and agitation in the secondary zone B, and are returned to the primary zone A by the action of the impeller.

The entire apparatus of the forms illustrated in Figures 4 and 5, like that of Figure 1, may be supported for vibration.

Where the term flotation reagent is used, it is intended to include dispersion agents, which keep the fines dispersed and aid their passage across the over-flow; or which cause certain fineconstituents of the pulp to form in flocks and settle with the oversize; and, also, agents that assist in the attachment of mineral particles to air bubbles in the pulp whereby such particles are elevated to thesurface and pass across the over-flow. 4

Changes and modifications may be availed of within the spirit and scope of the invention, as defined in the hereunto appended claims. 7

What I claim and desire to secure by Letters Patent is:

1. The method of classifying finely divided solids in liquid suspension which comprises agitating a pulp, continuously introducing air into the zone of agitation to form a mineral bearing froth, directing the fines in the material up-- ,the agitation and aeriation, discharging substantially all liquids, fines, and formed froth together at the surface into an overflow, whereby said froth and the uplift of material serve to raise larger particles to said overflow inducing a settling of coarse material by moving the same into a relatively quiescent zone out of the zone of agitation, de-watering the settled material by conducting the same to an elevating discharge and maintaining a hydrostatic balance between the agitation and ole-watering zones.

3. The method of classifying finely divided solids in liquid suspension which comprises agitating a pulp, continuously introducing a controlled flow of air into the same under the influence of the agitation to form a mineral bearing froth, directing the fines in the material upwardly in the pulp body under the influence of the agitation and aeration, discharging substantially all liquids, fines and formed froth together at the surface into an overflow, whereby said froth and the uplift of material serve to raise larger particles to said overflow inducing a settling of coarse material by moving the same into a relatively quiescent zone out of thezone of agitation, and regulating the elevating effect of the aeration by varying the quantity of air admitted to the agitation zone.

4. The method of classifying solids in liquid suspension which comprises agitating a pulp, directing the pulp body in a circulatory movement upwardly through an inner zone, and downwardly through a larger outer zone, under the influence of the agitation, discharging substantially all liquid, lines, and formed froth at the surface into an overflow, progressively increasing the area of the stream of material during its elevation through the inner zone, progressively decreasing the velocity of the rising material, and discharging coarse material adjacent a lower meeting point of said zones.

5. The method of classifying solids in liquid suspension which comprises agitating a pulp, directing the pulp body in a circulatory movement upwardly through an inner zone, and downwardly through a larger outer zone, under the influence of the agitation, discharging substantially all liquid, fines, and formed froth at tht surface, into an overflow, increasing the area of the stream of material during its elevation through the inner zone, and decreasing the velocity of the rising material in ratio to its degree of area increase, and discharging coarse material adjacent a lower meeting point of said zones. I

6. In a method of classifying solids in liquid suspension, the step of imparting to a pulp, a circulatory, elevating movement through an inner zone, and a dire ct downward movement through a larger outer zone, discharging substantially all liquid, fines and formed froth at the surface into an overflow, said downward movement being at a slower velocity than the upward movement through the inner zone, whereby a Settling action takes place, and discharging coarse material adjacent a lower meeting point of said zones.

'7. In a method of classifying solids in liquid suspension, the step of simultaneously increasing the area and decreasing the velocity of a circulatory body of pulp being elevated through an inner zone, and moving downwardly through a larger outer zone, the degree of increase being in inverse ratio to the decrease in velocity, discharging substantially all liquids, fines and formed froth at the surface into an overflow, and discharging coarse material adjacent a lower meeting point of said zones.

8. The method of classifying solids in liquid suspension which comprises agitating a pulp,

introducing air into the zone of agitation, imparting a vibratory movement to the material being treated, directing the fines in the material upwardly under the combined influence of the agitation, the'aeration and the vibratory movement, inducing a settling of coarse material under the influence of the vibratory movement in a quiescent zone out of the agitation zone, and discharging substantially all liquid, fines and formed froth at the surface into an overflow.

9. The method of classifyingsolids in liquid suspension which comprises agitating a pulp, introducing air into the zone of agitation, imparting a vibratory movement to the material being treated, directing the fines in the material upwardly under the combined influence of the agitation, the aeration, and the vibratory movement, inducing a settling of coarse material under the influence of the vibratory movement in a quiescent zone beyond the agitation zone, and subjecting the settled material to a second classification under the influence of the vibrator movement.

10. The method of classifying solids in liquid suspension which comprises agitating a pulp, continuously introducing air into the zone of agitation, imparting a movement to the -material being treated, by the introduction of pressure fluid into the zone of agitation, directing the material upwardly through aninner zone under the combined influence of the agitation, the aeration, and the pressure fluid, and downwardly through a larger outer zone, and inducing a settling of coarse material in said outer zone beyond the zone of agitation.

1 The method of classifying solids in liquid suspension which comprises agitating a pulp, continuously introducing air into the zone of agitation, imparting a movement to the material being treated, by the introduction of pressure fluid into the zone of agitation, directing the material upwardly through an inner zone under the combined influence of the agitation, the aeration and the pressure fluid, and downwardly through a larger outer zone, inducing a settling of coarse material in said outer zone beyond the zone of agitation, de-watering the settled material by conducting the same to an elevated discharge, and subjecting the said material to the action of a pressure fluid during its elevation.

12. The method of classifying solids in liquid suspension which comprises subjecting a pulp to mechanical agitation, directing the material upwardly through an inner zone under the influence of the agitation, inducing a settling of coarse material in a larger outer zone beyond the zone of agitation, subjecting the settled material to a secondary classification in a dewatering zone, and returning fines from the secondary classification to the agitation zone under mixing a pulp, air and a flotation reagent in the pumping influence of the mechanical agitation.

13. The method of classifying finely divided solids in liquid suspension, which comprises agitating a pulp, aerating the pulp in the zone of agitation to form a mineral bearing froth, directing fines in the pulp and the froth together upwardly to an overflow, whereby said uplift of fines and froth serve to raise larger particles .to said overflow inducing a settling of coarse material by moving the same into a quiescent zone beyond the zone of agitation, and controlling the density of the settled material by the introduction of a liquid under pressure into the lower portion of the same,

14. The method of classifying solids in liquid suspension, which comprises intimately intermixing a pulp, air and a flotation reagent in a classification zone, directing the material in a circulatory movement upwardly through said zone and downwardly through another larger zone, thereby elevating fines including mixed fines and reagent through said classification zone, overflowing substantially all the liquid, fines and formed froth together at the surface of the body, and inducing settling of circulating sands and other 'material not acted on by the reagent in the larger zone, beyond the influence of the aeration.

15. The method of treating ore which comprises grinding an ore, suspending the ground product in a liquid carrier to form a pulp, intermixing the pulp with flotation reagents in a zone of classification under the combined influence of agitation and aeration, to condition fines in the pulp, overflowing substantially all the liquid, fines and froth together from the surface of the body, treating fines of the classification in a froth flotation treatment in the presence of added reagent, to reject fine gangue, inducing settling of the remaining solids of the classifi-. cation, and returning same for regrinding.

16. The method of classifying solids in liquid suspension, which comprises intimately intermately intermixing the pulp and a flotation reagent in a zone of classification under the combined influence of agitation and aeration, to condition fines in the pulp, overflowing substantially all the liquid, fines in the pulp, and froth together at the surface of the body, treating fines of the classification in a froth flotation treatment inthe presence of additional flotation reagent to reject fine gangue, inducing settling of ,the' remaining solids of the classification, and

returning same for regrinding.

8. The method of treating ore which comprises wet grinding an ore to form a pulp, intimately intermixing the pulp and a flotation reagent in a zone of classification under the combined influence of agitation and aeration, to 1 condition fines in the pulp, overflowing substantially all the liquid, fines and formed froth together at the surface of thebody, passing the fines of the classification to a froth flotation treatment to reject fine gangue, inducing settling of the remaining solids of the classification, and retuming-same for regrinding.

19. The method of treating ore, which comprises suspending an ore in finely divided condition in a liquid carrier to form a pulp, intimately intermixing the pulp and a flotation reagent in a zone of classification under the combined influence of agitation and aeration to condition fines in the pulp, separating the conditioned constituents from the other constituents of the pulp by a circulatory movement of the various constituents upwardly through one zone and downwardly through a successive zone, overflowing substantially all the liquid, fines in the pulp and mineral bearing froth together at the surface of the body, whereby said froth and the uplift of material serve to raise larger particles to the overflow inducing, settling of the remaining solids of the classification, and returning same for regrinding.

20. The method of classifying solids in liquid suspension, which comprises agitating a pulp, continuously introducing air into the zone of agitation, directing the material in a circulatory movement upwardly through an inner zone and downwardly through a larger outer zone, under the combined influence of agitation and aeration, overflowing substantially all the liquid, fines and froth together at the'surface, and inducing a settling of coarse material in the pulp by movement thereof through said outer zone beyond the zone of agitation.

21. The methodof classifying solids in liquid suspension which comprises agitating a pulp, continuously introducing air in the zone of agitation, directing the material in a circulatorymovement upwardly through an inner zone and downwardly through a larger outer zone, under the combined influence of agitation and aeration, overflowing substantially all the liquid, fines and froth together at the surface, inducing a settling of coarse material in the pulp by movement thereof through said outer zone beyond the zone of agitation, and subjecting the settled material to a de-watering treatment.

22. The method of treating ore which comprises grinding an ore, suspending the ground product in a liquid carrier to form a pulp, feeding the pulp and a flotation reagent having an affinity for one of the pulp constituents, into a. zone of primary classification intimately intermixing the pulp and reagent under the influence of agitation and aeration in said zone to condition the fines, overflowing substantially all the liquid,

fines and froth together from the surface of the body, subjecting the fines separated by the primary classification directly to a froth flotation treatment to reject fine gangue, inducing settling of the remaining solids of the primary classification, through a secondary classification, and re turning same for regrinding.

23. The. method of treating ore which comprises grinding an arc, suspending the ground product in a liquid carrier to form a pulp, feeding pulp and a flotation reagent having an affinity for one of the pulp constituents into a zone of primary classification, intimately intermixing the pulp and reagent under the influence of agitation and aeration in said zones to condition the fines, overflowing substantially all the liquid, fines and froth together fromthe surface of the body, subjecting the fines separated by the primary classification directly to a froth flotation treatment to reject fine gangue, inducing settling of the remaining solids of the primary classification, through a secondary classification, returning same for regrinding, and returning fines from the secondary classification zone to the primary classification zone.

24. The method of classifying finely divided solids in liquid suspension which comprises subjecting a pulp to mechanical agitation, continuouslyintroducing air into the zone of mechanical agitation to form a mineral bearing froth, directing the material upwardly through one zone under the influence of the agitation, and aeration, discharging substantially all liquid, fines, and formed froth together at the surface into an overflow, whereby said froth and the uplift of material serve to raise larger particles to said overflow inducing a settling of coarse material in another zone out of the zone of agitation, subjecting the settled material to a secondary classification in a de-watering zone and returning fines from the secondary classification to the agitation zone under the pumping influence of the mechanical agitation.

25. The method of classifying finely divided solids in liquid suspension which comprises subjecting the pulp to mechanical agitation, continuously introducing air into the zone of mechanical agitation to form a mineral bearing froth, directing the material upwardly through one zone under the influence of the agitation, and aeration, discharging substantially all liquid, fines and formed froth together at the surface into an overflow, whereby said froth and the uplift of material serve to raise larger particles to said overflow inducing a settling of coarse material in another zone beyound the zone of agitation, and regulating the elevating action of the aeration by varying the quantity of air ad mitted to the mechanical agitation zone.

C. DAMAN.

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