US1375211A - Apparatus for separating or concentrating ores - Google Patents

Description

D. COLE.

APPARATUS FOR SEPARATING 0R GONCENTRATING OR-ES. v

APPLICATION FILED AUG-3, 1915- 1 ?5,21 1 Patented Apr. 1%,...15921.

5 SHEETS-SHEET l- D. COLE.

APPARATUS FOR SEPARATING' on CONCENTRATING ORES- APPLICATION FILED AUG-3| I915- '1 3?5,]1 1 Patented Apr. 19, 1921..

5 SHED S-SHEET 2.

D. COLE.

APPARATUS FOR SEPARATING' OR CONCENTRATING GRES- APPLICATION FILED AUG-3, I915- 137521 1 v Patented Apr. 19, 1921'.

5 SHEE'! SSHEET 4- Witness D. COLE. APPARATUS ron SEPAR-ATING ancoucammme ORES. APPLICATION ,FILED AUG-3. 1915.

1 375 21 1 a Patented Apr. 19, 1921.

. 5 SHEE'ISSHEET 5.

| I l I I I 1 I l I I I L aeJ-l auto: wag s i To all it may concern:

arren stares raraur oFFice.

DAVID-COLE, or- MORE OI, ARIZONA, ASSIGNOR To MINERALS SEPARATION NORTH AMERICAN conrORATIoN, on NEW YORK, N. Y., A CORPORATION or MARYLAND.

ism-su s FOR SEPARATING on CONCENTRATING onus;

Specification of Letters Patent.

Patented Apr. 19, 1921.

- Application filed August 3, 1915. Serial No. 43,442.

Be ltTikQ QWQ that-a1, DAVID COLE, a citizen of theUnitd States, residing at Morenci,

in the county of Greenlee' and State of Arizona, have invented or discovered certain new and useful Improvements in Apparatus for Separating or Concentrating'Ores, of which the following is a specification, reference being had therein to the accompanying drawings.

This invention relates to the hydraulic classification, separation, and concentration of ore and the like by what is known as the flotation method, and more particularly to that branch of the process known as froth"- ing classification, the latter being an amplification of the flotation method, having for its object the preparation ot'the rejections of the flotation treatment in such a Way that maximum recoveries may be made by the usual gravity methods upon the grains and sizes in the pulp which were not within the range of, and were not susceptible to, recovery by flotation treatment. Grains which will pass a screen having ten thousand openings per square inch will be within the possible range of flotation recovery, but substantially all grains coarser than this size will not be within the range of recovery by flotation.

The mineral grains constituting the prodnot separated and recovered by flotation methods are so fine that substantially ninety- :five per cent. of them will pass through a screen having, f ortyzthousand apertures per square inch. Therefore the range of flotation sizes is substantially limited to the minus one hundred mesh sizes (2. 6., ten thousand holes per square inch above reierred to) and since it is impracticable commereially to reduce all of the ore to be treated to this very fine state of division'it is necessary either to separate the flotation treatment sizes from the gravity treatment sizes and treat them separately, or to so prepare the combined sizes during flotation treatment that the gravity treatment to follow will not be embarrassed in making maximum recoveries upon the sizes of grairrsi-- usually also small amounts of oils and the like to a sizeiwhich will yield the best commerclal recovery, and the resulting pulp 1s 1ntr0duced into a suitable tank provided VYIth means in the lower part of same fbr liberatlng a r in a finely divided state through a suitable porous medium, said air forming very numerous streams ofvery small bubbles which expand in size as they 'rise toward the surface of the pulp in the the particles too large to be lifted by the bubbles, will find their way to the bottom of the tank and be withdrawn therefrom.

The process is usually carried on contin uously, the pulp flowing into the tank at a suitable rate, the froth with its content of fine mineral being continuously discharged in the mineral froth at the top of the tank, and the water and coarser material being continuously discharged at the bottom of the tank Iin order that such apparatus of the pre vious art may operate properly and not become clogged it is necessary that the ore or other material being treated be all of a certain degree of fineness. It is therefore necessary that said material be either carefullypulverized primarily to a very even degree and sufiiciently fine, or else that said material be screened or receive other previous treatment for removing the coarser particles, or oversize, which would embarrass the apparatus and would tend to.

clog it, it is one of the objects ofthe present invention to provide means, associated with a fiotatlon or i'rothing classifier itself,

for automatically I removing the Oversize,

such removal being effected during and in connection with the normal operation of the apparatus, thus preventing embarrassment to the operation and makingit possible to apply the flotation or frothing process primarily in the treatment of ores in a much coarser state of reduction, that is to say, to the ordinary mill run, without subjecting the same to previous screening or other treatment for the pur ose of protecting the frothing machine. n-carrying out this feature of the invention the separating tank is preferably provided with one or more classifying cones each having an outlet and an inlet through which hydraulic water is introduced, said water driving or holding back material of a predetermined fine-I ness (depending upon the form of chamber and pressure or velocity of the water so admitted) and permitting the oversize to passout through the outlet.

In-preparing ore for flotation treatment it is customar to reduce said ore in socalled tube mllls, such mills having been. found in practice to be the most efiiclent and economical for this purpose. In order to operate such mills at their 'maxlmum capacity (that is to say with the greatest efficiency) it is necessary to feed mater1althere to in quantities which result in the discharge of a large amount of oversize, and said oversize must be returned to the mill for regrinding. If the feed to the mill is so regulated in quantity that no oversize is dlscharged, then the work of grinding will be greatly hampered, the amount handled w1ll be greatly reduced, and the cost per ton for grinding will be greatly increased Considering which and as a second ob ect of the invention a combined'apparatus is provided whereby the regular run of a tube mill may be directly discharged into a frothing classifier, the oversize bein automatically separated out in said classifier and re turned to the mill for regrinding, thereby permitting both the, mill and the classlfier to be operated at their maximum efliciency.

and without interruption in closed circuit, eliminating the usual step of mechanical screening or other preliminary classification, and generally simplifying the appa ratus and operation, correspondingly reducing the cost. The separation of the, oversize is preferably effected by means of hydraulic classifying cones as above described, so that, by regulating the amount of hydraulic water admitted, the size andquality of material escaping the closed circuit may be controlled and varied, thus accomplishing, by

the mere regulation of an inlet valve, a result which, in the case of mechanical separation, would require the complete changing of screens or other troublesome operations.

In the usual practice of the frothing process considerable difliculty is encountered by reason of the tendency of the coarser material to lodge upon the porous medium, thereby obstructing the outlet of air, and also by reason of the tendency on the part of the liquid passing to the restricted outlet at the bottom of the tank forma vortex,

the effect of which is to suck down and carry away the bubbles, all of which, in order to secure proper operation, should be allowed to pass freel upward through the liquid m the tank. T e present invention has, therefore for another object to provide, in a frothing classifier, air admission means which will effect a more thorough aeration of the liquid than-any similar means heretofore devised, which is notsubject to clogging by sediment accumulating thereon or nding its way thereinto, and which, at the same time, rovides for the eflicientwithdrawal of t e liquid and coarser material with a minimum tendency to interfere with the free upward passage of-the bubbles.

In the flotation separation of ores and the like it is found to be advantageous to subjectthe material under treatment to more than one passage through the apparatus,

and the'present invention accordingl has for a further object the provision of a frothing classifier which and eflicient manner or the repeated treatment of the material, said apparatus com feature of the invention the transferring means is constructed and arranged to cooperate with the classifying cones in such a manner as to materially assistthe operation.

of the latter and .to reduce materially the amount of hydraulic water required for the proper separation of the oversize and returnable portion. 1

The foregoi and other objects of the .invention,-toget er with means whereby the same may be carried'in'to effect, will best be understood from the following description of certain forms or embodiments thereof illustrated in the accompanying drawings. It will be understood, however, that the particular' constructions described and shown have been-chosen for illustrative purposes rovides in a simple merely, and that the invention, as defined by the claims hereunto appended, ma be otherwise practised without departing rom the spirit and scope thereof.

In said drawings: Figure 1 is a partly sectional diagram matic view. illustrating an apparatus constructed and arranged in accordance with the invention. 7

F ig. 2 is a similar view showing a different form of separator or classifier.

Fig. 3 is an enlarged vertical sectional view of the classifier shown in Fig. 1.

Fig. 4 is an end elevation partly broken lit away of the apparatus shown in Fig. 3, as

viewed from the left in the latter figure.

Fig. 5 is an end elevation part1 broken away of the apparatus shown in ig. 3, as viewed from the right in the latter figure.

Referring first to F ig. 1, 12 denotes a tube mill of any suitable or well known form for reducing the ore or other material to be treated. Said reduced material, containing a certain amount of oversize incidental to the efficient operation of the mill, is discharged from said mill into a chute 13 lead ingjto the'frothing classifier.

he frothin'g classifier shown in Figs. 1, 3, 4 and 5 comprises a series of tanks or compartments 14, 15, 16 supported by' suitable uprights 17 said tanks or compartments being of any desired number (herein shown as three) and being located iminto thin sheets for the purpose of preventing the formation of violent currents in the tank 1%.

At a proper distance above the bottoms of each of the. tanks 14, 15, 16, slots 20 are formed in the ends of said tanks, and. secured to said ends adjacent said slots are manifolds 21 communicating with a suitable source of compressed air. The manifolds 21 of each tank support and communicatewith a series of horizontally disposed tubes 22 which extend throughout the length of the corresponding tank and form a tubular grating substantially coyering; the entire horizontal cross-sectional area of said tank at a point suitably elevated above the bottom thereof. The tubes-22ers so con.-. structed as to have a finely porous air emit ting surface, as by forming said tubes ofa porous material, such as carborundum, or by covering the same when perforated with filtering fabric or the like, whereby the compressed air supplied to the manifolds 21 is discharged through said tubes into the tanks in the form of numerous streams of hue bubbles. The pores of the tubes 22 are too small to allow solids to enter from the outside, under hydraulic pressure when the air pressure is cut offlas would occur in the case of a perforated pipe or the like, thereby preventing the internal clogging of said tubes. The tubes 22 of each grating are spaced from one another a suficient distance to permit easy downward passage between them of the pulp and water under I treatment, while being sufficiently close together to provide for the thorough aeration of the contents of the tanks abdve them. .The outlet from each tank, as will presently be more fully described, is at thebottom thereof, while the tubes 22, as above exlained, are located some distance abovethe ottom. By this arrangement, as also by .reason of the spacing of the tubes 22 as above described, allviolent downward currents or vortices in the vicinity of said tubes, tending'to draw the bubbles downwardly, are avoided, and all possibility of improper discharge of the finer material from the bottom of the tank reduced to a minimum, The construction of the tubes 22 is preferably such as to. permit a discharge of, air throughout their circumference, thereby providing a greatly increased air emitting surface, and, at the same time, free downward passages forthe liquid, as above explained. By virtue of this form and arrangement all possibility of such accumulation of sediment as would clog the exterior of the tubes and interfere with the proper discharge of air therefrom is prevented, it being obvious that, even though the entire upper surfacesof the tubes were covered'by deposits, there'would still be left a total unobstructed air emission surface equal to or greater than the entire transterial, particularly metallic sulfid, and form' r in the upper part of said tanks bubble or froth columns which overflow into a laun der 46 arranged to discharge the froth with its content of fine material at any suitable point.

For the purpose of leading the material from one tank or compartment to the next for successive treatment the transfer tubes 23 are provided. Said transfer tubes are preferably of the S-shaped form shown, pass through the wall separating adjacent tanks or'compartments at points below the tubes 22 of the upper tank, and are preferably flattened laterally, as shown'in Figs. 4 and 5 in order to oppose-theleast possibleresistance to the upward Passage of the hubbles in the lower tank. Each tube is arranged with its inlet adjacent the bottom of its transfer tube 23in each of the tanks and 16 is a valve 24 carrying a deflector similar to the deflector 19. The deflector valves 24 are, adjustablewith ,respect to-the outlets of tank.

the tubes 23 and are carried by stems 25 supported at their upper ends bybeams 26. As shown in Figs. 4 and 5 a plurality of transfer tubes 23 is preferably provided for discharging material from each tank to .the next succeeding, and the deflector valves 24 in each. tank are supported from a single beam 26. Each of the beams 26 is provided at each end with. a threaded stem 27 coiiperating with a hand wheel 28 supported by a bracket 29 suitably secured in stationary position, as to the launder 46. By operating the hand wheels 28 of any pair-the deflector valves of any tank may be simultaneously; adjusted, thereby providing for an even flow through .all of the transfer tubes25 discharging into said Secured to the bottom of the tank 14 adj acent the inlets of the correspond ng transfer tubes 23 are'classifying cones 3( said classifying cones being preferably in the form of separate castings bolted in position to. the bottom of said tank adjacent suitably formed openings in said bottom. Each of the classlfying cones 30 is formed at top with a depression 31 into close proxunlty to which extends the inlet end of the corresponding transfer tube 23, said end being preferably of the flaring or conical form 35 shown and of a diameter at its bottom slightly'.less thanthe diameter of the depression 31. The bottom 'of the depression 31 is provided with an opening in which is located a coarse screen or perforated plate 32, said opening leading to a chamber 33 which communicates through a bushing 34 with a second chamber 35 provided with an outlet 36. Communicating with the chamber 35, prefer'ably at a point above the bottom of the bushing 34, is an inlet pipe 37 for hydraulic water, said pipe'being controlled by a suitable valve 38.

In the operation of the apparatus, considered with respect to' each classifying cone and the corresponding transfer tube, the

water in the tank 14, togetherrwith the material not carried away by the bubbles, reaches the bottom of said tank and is discharged through the transfer tube 23 to water discharged through the outlet 36, a

suflicient quantity of said water passes up-' tated bylthe construction and arrangement as is such that, in addition to' the hydraulict of the transfer tubes 23 with reference to the classifying cones. tank 14 gravitate's' to the points indicated by Ain Fig. 3 where the swift current due to the constricted opening carries the same horizontally toward the center of the funnel-shaped inlet of the transfer'tube and The material in the upwardly into said tube upon reachingthe enlarged chamber in the bell mouth of the transfer tube. The oversize tends to separate out and fall into the chamber 33. This tendency 1s opposed by a gentle upward 3 current composed in part by the hydraulic water flowing upwardlythrough the bushi-ng34 and perforated plate 32, and in part by the lessened speed of upward flow into the transfer tube,,caused byits bell-shaped construction so that said material, minus its oversize particles, after more or less circulation, passes upwardly into the mouth of the transfer tube 23. By this arrangement of parts, enabling the transfer tubes 23 to assist the hydraulic water in carrying away the finer material, very much less hydraulic water is necessary than wouldotherwise be required, this being a very desirable feature inasmuch as the hydraulic water tends to dilute the pulp and 'to interfere with the frothing operation in the next tank. It will of course be understood that the size of material discharged through the outlet 36 will be dependent upon the pressure at which the hydraulic water is admitted through the pipe 37, and this may be regulated at will, and in accordance with requirements, by" means of the valve 38.

The outlets 36 -of the classifying cones 30 discharge into a tank or trough 39 from which aconductor 40 leads to a concentrating table 41 of any suitable or well known form. The material rejected by the concentrating table 41 is delivered to an elevator or conveyer 42 which returns the same to the mill 12. If desired the concentrating table 41 may be omitted and the conductor 40 arranged to" discharge the oversize directly to the elevator or conveyer 42.

It will thus be seen that the classifying cones 30 operate to remove the oversize discharged into the tank 14, which oversize is returned to the mill for regrinding. Ordinarily one set of classifying cones will its accomplish this result satisfactorily, as-

substantially all of the oversize will pass out therethrough, practically none passing through the transfer tubes 23 into the next tank. For this reason, as herein shown, the first tank 14 only is provided with classifying cones, the other tanks 15, 16 etc. being provided at the corresponding points with normally closed cup-shaped castings 43 into which the inlet ends of the corresponding transfer tubes 23 depend. If desirable, however, any or all of the tanks 15, 16, etc. maybe provided with classifying cones in place of the castings 43. In the latter 18. As seen as the water in the firsttank or compartment 14 reaches the level indicated by the dotted line B the second tank or compartment 15' will commence to fill through the first'set of transfer tubes 23, and when this compartment is filled to the level of the outlets to the transfer tubes leading therefrom, the third compartment will fill, and so on until the level ofjthe mouth of the final outlet from the last conipartment is reached in that compartment. Compressed air is then admitted through all of the grates 22. The consequent aeration of the water in all of the compartments causes the level thereof to be raised, and by adjustment of the deflector valves 24 through the wheels 28 as well as by adjustment of the valves 45 ofthe final outlets, the. surface of the liquid is caused to: rise above the deflector valves 24 to or adjacent the tops of the tanks as may be desired. After a proper balance has been established the mill 12 is started and substantially the same volumeof pulp to be treated is substituted for the clear water. On account of the presence of the solids transported by the water, and because of the colloidal and other matter in the pulp which will produce froth, additional adjustments, such as the opening or closing of the deflector valves 24 and discharge valves 45, the admission of a greater or less amount of air through thetubes 22, etc., are usually necessary in order to-establish a new condition of equilibrium after which no other adjustments are necessary under normal and even conditions for use.

The finest particles of metallic sulfids in the pulp are discharged with the froth from the top of the tanks into the launder 46, the coarser particles both silicious and metallic find their way to the bottoms of the tanks,

are transferred through the tubes 23 from one tank to the next for successive treatment, and are finally discharged through the pipes 44, while the oversize is discharged through the classifying cones 30, and, after passing from the concentrating table 41, is returned to the mill 12 for regrinding, all as above described in detail.

The apparatus shown in Fig. 2, as to its general combination and arrangement, is substantially similar to that shown in Fig. 1, a different form of frothing classifier belng, however, employed. This frothing classifier comprises a single tank 50 having an inlet provided with a bafiie plate 51, and with which the chute 13 communicates, and an outlet 52 provided with an adjustable slide,

53 for controlling the level of discharge and consequently the level of the liquid in the tank. The bottom of the tank is provided with a seriesof transversely arranged slots 56 communicating below the tank with hoppers 57 from which lead outlet pipes 58,the several outlets being numbered from 1 to 7, inclusive, in Fig. 2, although the precise number of these outlets may be in accorcance with the requirements. Adjacent each of these slots 56 is a pair of downwardly converging porous plates 59, said plates in-- closing air chambers 60 to which compressed air is admitted through inlets 61 controlled by valves, not shown, which are operated by hand wheels 62.

Compressed air in the chambers 60 is admitted to the tank 50 through the porous plates 59 and passes upwardly through the liquid in the tank in the form of numerous streams offine bubbles, carrying with them the finer material and forming a froth column 54 above the level of the liquid, the froth overflowing the sides of the tank into suitably disposed launders 55 which discharge the same at any desired point, the 0 eration in this respect being substantially similar to that of the frothing classifier first described. Also, asin the apparatus first described, .it will be seen that the outlets 56 are disposed at a lower level than that at which the air is introduced, so that the tendencyfor the bubbles to be drawn down 'wardly into said outlets is very slight.

porous plates 59, collection of sediment plates, there would be a tendency, were these plates of constant thickness throughout, for the air to pass through the portions of the plates in greatest quantities at points of least hydrostatic pressure, namely, at the upper edges of the plates. To compensate for this, and provide for even aeration of the liquid by causing the air to pass through said plates in equal volume from top to bottom, said plates are formed slightly tapering or wed e-shaped in cross-section with their thic est portions at the top, the difference in thickness between the upper and lower edges being just suflicient to compensate for or balance the difference in hydrostatic pressure, so that the air passes through said plates with equal facility and in equal quantities throughout their area.

Of the solid matter not carried upward by the bubbles and assing into ,the launder 55 with the froth, t e coarsest particles and oversize will sink to the bottom of the tank first, and the successively smaller particles at successively later periods. Therefore as the liquid passes through the tank 50 longitudinally from end to end the coarser material and oversize will be discharged through the.

outlet 1 and the successively smaller sizes through the outlets 2, 3 and 4, etc., so that only the solid articles of smallest size will pass out with t e tailing through the outlet 56; The outlets 1 and 2, in accordance with the arrangement shown, are therefore arranged to discharge into the trough or tank 39 from which the material is discharged, through the conductor 40, to the concentrating table 41, and thence returned by the elevator or conveyer 42 to the grinding mill 12 for regrinding, as in the ap aratus above described. The pipes 58 leading from the outlets 3, 4, 5, etc., convey the otherwise classified material to any suitable or desired points.

While, as herein shown, the material discharged from the outlets 1 and 2 is returned to the mill 12 for regrinding, it will be obvious that the, material from outlet 1 only might be so disposed of, or that'additional outlets might be arranged to discharge into the trough or tank 39 in accordance with requirements or conditions of operation.

The trough or tank 39 'is merely shown herein as illustrative of convenient means for receiving the oversize to be returned to themill for regrinding, and it willbe 0bv1ous that other means might readily be employed for conducting the material to the concentrating table 41 or elevator 42, as, for

example,'in the arrangement shown'in Fig. 2, by connecting the conductor 10 directly with the outlet 1.

The particular frothing classifier shown in Fig. 2 is not claimed herein, being covered by the claims of other Patents No. 1,243,814

of October 23. 1917, and N0. 1.351.096 of August-31, 1920. Also certain features of the classifying apparatus shown in Figs. 1, 3, 4 and 5 e? 86, are covered by the claims of Patent 150. 1,319,208 of October 21, 1919, issued upon an application divisional hereof, and are therefore not claimed herein.

Having thus described my invention, I claim 1. The combination with a grinding mill, of a frothing classifier into which the comminuted material from the mill is discharged and means for returning the coarse material separated out by said classifier to said mill for regrinding.

. 2. The combination with a grinding mill, of a frothing classifier into which the comminuted material from the mill is discharged, means associated wlth said frothing classifier for removing oversize material I delivered thereto, and means for returning said oversize material to said mill for regrinding.

3. The combination with agrinding m1ll, of a frothing classifier into which the comminuted material from the mill is discharged, said classifier being provided with a classifying cone for removing oversize material, and means for returning said oversize material to sald mlll for regrlnding.

4. The combination with a grinding mill, of a frothing classifier into which the comminuted material from the mill is discharged, a concentrator to which coarse material separated out by said classifer is delivered, and means for returning the ma terial rejected by said concentrator to sand mill for regrinding.

frothing classifier into which comminuted material from the mill is discharged, means associated with said frothing classifier for removing oversize material delivered thereto, and means for returning said oversize material to said mill for regrinding.

I 8. The combination with a tube mill, ofa frothing classifier into which the comminuted material from the mill is disterial separated out by said classifier is delivered, andmeans for 1 returning the material rejected by said concentrator to said mill for regrindmg.

.7 charged, a concentrator to which coarse ma- Y 9. The combination with a tube mill, of a frothing classifier into which comminuted material from the mill is discharged, a classif in cone associated with said frothing c assifier for removing oversize material delivered thereto, a concentrator to which said oversize material is delivered, and an elevator for supplying material to said mill and to which the material rejected by said concentrator is delivered. 1

10. The combination with a grinding mill, of a frothing classifier into which substantially all of the material discharged from said mill is received, said frothing classifier having provision for removing, during the frothing operation therein, oversize material delivered thereto, and means whereby said oversize material may be returned to said mill for regrinding.

11. A. frothing classifier comprising a plurality of vessels each provided with means for admitting air thereto at the lower part thereof, and means for connecting adjacent vessels consisting of a laterally flattened transfer tube leading from the bottom of one vessel and extending into the next adjacent vessel above the air admitting means thereof.

12. A frothing classifier comprising a plurality of vessels each provided with means for admitting air thereto at the lower part thereof, and means for connecting adjacent vessels consisting of a laterally flattened S shaped transfer tube leading from the bottom of one vessel and extending laterally into. the next adjacent vessel above the air admitting means thereof.

13. A frothing classifier comprising a plurality of vessels each provided with means for admitting air thereto at the lower part thereof, and means for connecting adjacent vessels consisting of a laterally flattened transfer tube leading from one vessel underneath the air admitting means thereof and extending into the next adjacent vessel above the air admitting means thereof.

14:. The combination with a grinding mill, of a frothing classifier comprlsing a vessel into which comminuted material from the mill is discharged, a classifying cone communicating with said vessel and having a water inlet and an outlet, a discharge tube for said vessel'having its inlet arranged adjacent said classifying cone, and means for returnin material discharged by the outlet of said 0 assifying cone to said mill for. regrinding.

15. In a frothing classifier, a vessel, means for admitting air to said vessel at the lower part thereof, a classifying cone at the bottom of said vessel and communicating therewith, said classifying cone having a water inlet and an outlet for oversize, and an upwardly directed tailings discharge tube for said vessel having its inlet arranged adjacent said classifying cone and below said air admitting means.

16. A frothirig classifier comprising, in combination, a plurality of vessels, means for admitting air to all of said vessels, a classifying cone at the bottom of one of said vessels and communicating therewith, said classifying cone having a water. inlet and an outlet for oversize, and a transfer tube leading from said last named vessel, at a point adjacent said classifying cone, to the next adjacent vessel.

17. The combination with a grinding mill, of a frothing classifier comprising a plurality of vessels disposed in stepped arrangement at successively lower levels, means for discharging comminuted material from said mill into the uppermost of said vessels, air tubes supported at their ends in the walls of said vessels at points above the bottom thereof and collectively forming tubular gratings extending over substantially the entire horizontal cross-sectional area of said vessel's, a classifying cone communicating with the bottom of said uppermost vessel and having a water inlet and an outlet, transfer tubes leading from the bottoms of said vessels at points below said tubular gratings to the upper parts of the next ad- 'jacent vessels, the transfer tube leading from said uppermost vessel having its inlet arranged adjacent said classifying cone, and means for returning the material discharged from the outlet of said classifying cone to said mill for regrinding.

18. A frothing separator comprising a vessel, means for admitting air to said vessel to produce froth at the top thereof, a hydraulic classifying cone at the bottom of said vessel for'separating out and removing oversize from said vessel, and means for otherwise discharging from said vessel material smaller than oversize but too coarsefor frothing treatment.-

' In testimon whereof I aflix my signature, 1n presence 0 two witnesses.

DAVID COLE. Witnesses W. L. DU MOULIN, J. P. MONTER.

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