US2756878A - Three product wet cyclone - Google Patents

Description

July 31, 1956 E. c. HERKENHOFF THREE PRODUCT WET CYCLONE Filed June 10, 1952 INVENTOR BY Fm 4- l w A ATTORNEYS United States Patent 1 2,756,878 THREE PRODUCT WET CYCLONE Earl C. Herkenholf, Hibbing, Minn., assignor to Erie Mining Company, Hibbing, Minn., a corporation of Minnesota Application June10,-1952, Serial No. 292,643 6 Claims. (Cl. 209--211) This invention relates to an improved wet cyclone, and to improvements in the wet classification or/and thickening of finely divided mineral solids in slurry form and in the wet separation of fragmentary mineral solids by gravity difference or sink-float.

An object of the present invention is to provide a wet cyclone of improved design. Another object of the invention is to provide wet separation procedures, involving use of a wet cyclone as a separating vessel, characterized by rapid and easy control over or modification of the rates and characteristics of the cyclone overflow and underflow products. A further object of the invention is to provide wet separation procedures, involving use of a wet cyclone as a separating vessel, characterized by the ability to remove a middling product which latter, having characteristics intermediate those of the overflow and underflow products, may either be processed as a special product or combined with the overflow or underflow product or recirculated to the cyclone feed. Other inventive objects include the provision of a three-product wet cyclone permitting the rapid and easy modification of a separatory operation, without shut-down or replacement of parts, to meet changes in the type or characteristics of the feed whereby to maintain substantially constant, in the face of such changes, the characteristics of the desired underflow product or overflow product.

It heretofore had been proposed to eflect separation of ore material by gravity dilference or sink-float using therefor a wet cyclone adapted to make two products, viz, an underflow (or spigot) product and an overflow product. The structure of the conventional two-product wet cyclone and the mode of operating same have been described in the literature, e. g., Institute of Fuel Journal, 1945, vol. 19, pages 33-45; Engineering and Mining Journal, 1950, vol. 151, No. 6, pages 71-73; Mining Engineering, August 1951, pages 681690. As is adequately described in the literature, the conventional twoproduct wet cyclone, e. g., the D. S. M. Wet cyclone, comprises a chamber generally circular in cross-section and composed of an upper, relatively short, cylindrical portion and a contiguous lower, relatively long, conical portion; a delivery inlet or feed orifice member generally horizontally disposed adjacent the cylindrical portion and adapted to direct a liquid stream tangentially into the latter; a generally vertically disposed, central, overflow orifice member or vortex finder, the lower, open, end of which extends somewhat beneath the plane of the delivery inlet member and the upper end of which extends through the top of the cylindrical portion of the chamber and to an overflow conduit; and, at the apex of the conical portion, an underflow discharge orifice member which latter member may or may not be adapted for varying the cross-sectional area of the underflow discharge orifice.

In making use of that apparatus in the concentration of ore, e. g., of lean hematitic ore, the particulate ore material, composed of particles varying between onefourth inch diameter and minus 100 mesh, is suspended in a heavy liquid medium, usually an aqueous suspension of finely-ground magnetite, and the resulting pulp is fed under pressure tangentially through the feed orifice member of the wet cyclone. Separation is made in the conical portion of the chamber by the action of centrifugal and centripetal forces, the heavier particles of the ore material and the magnetite particles tending to descend to an exit through the underflow discharge orifice member and the lighter particles tending to exit through the overflow discharge orifice member. It has been found that in this dynamic system the multiplication of gravity greatly increases specific gravity differences among solids particles and distinguishes this operation from simple sink-float separation.

The results obtained through the use of the conventional two-product wet cyclone may be influenced in a number of ways such as by changing the diameter of the underflow discharge orifice or of the overflow orifice (vortex finder). Thus, the effective specific gravity at which separation taken place may be increased by reducing the diameter of the discharge orifice. v Equally important, the quantity and quality of material discharged through the underflow orifice is markedly influenced by the relative size (diameter) of the overflow orifice. However, in an operation involving the use of the conventional device it is possible to take advantage of this latter means of control only by stopping the operation, removing the overflow orifice member and substituting an overflow orifice member having a different diameter. A delay of this nature is highly objectionable and as a result, in production operation, control of the separation by this means must be sacrificed and must be confined to other means such as by varying the specific gravity of the heavy medium or feed pulp or by changing the apex opening, which is more accessible than the overflow opening or vortex finder. There has remained, therefore, a genuine need for a simple, rapid andpositive means for controlling the cyclone separation, in order to obtain optimum separation results with changing types and quantities of ore feeds.

Also it must be borne in mind that the inner surfaces of the cyclone separator are subject to severe abrasion. Any means for mechanically varying the cyclone apertures must take this fact into account, and it is a major advantage of the wet cyclone of the present invention that all parts subject to wear are of simple, rigid construction and easily accessible for replacement when necessary. This is a distinguishing feature over other devices which have been proposed for this purpose.

The wet cyclone of the present invention is adapted to make three products, viz, an underflow product, an overflow product and, in addition, a middling product having properties and characteristics lying between the limits of underflow and overflow. Such middling product may be recirculated to the feed, or kept separate as a special product, or combined either with the overflow or underflow product, as desired. The three-product cyclone is advantageous for use both in (a) wet classification and thickening and in (b) wet separation of fragmentary materials by gravity diiference.

The apparatus is distinguished from the Dutch State Mines cyclone by the provision of a second, annular, overflow opening (hereinafter called the middling opening) concentric with the conventional axially dis posed overflow opening, which middling opening cooperates with a middling chamber and middling take-off conduit separate from and lower than the overflow takeoif conduit, which middling take-01f conduit preferably includes or is operatively associated with means for externally adjusting the size of the exit opening of the middling take-off conduit. With this arrangement, the total overflow of the cyclone may be discharged either through the middling chamber and thence through middling take-off, or through the inner overflow orifice and take-off, or divided between the two, depending upon the selected adjustment of the exit opening of the middling take-off conduit. The quantity of underflow product 3 varies depending upon the manner in which the overflow product leaves the cyclone (i. e., whether by way of the conventional overflow opening or by way of the middling overflow or by both).

It heretofore had been proposed, in U. S. Patent No. 2,098,608 to Berges, to separate solid impurities from a paper pulp suspension by the use of a purifying and classifying apparatus akin to a three-product wet cyclone, which apparatus included an underflow take-01f for discharge of heavy impurities, a centrally disposed overflow take-off for collecting and removing purified pulp suspension, and a conical collecting memberconcentric with the overflow take-off and associated with a conduitfor collecting and discharging liquid charged with light impurities. Said purifying arid classifying apparatus was characterized by employment of relatively long (tall) overflow and middling take-offs, and by being devoid of a middling chamber; it likewise was devoid of means for regulating the flow of light impurity-charged liquid through the conical collecting member.

An important feature of the wet cyclone of the present invention is the relatively large middling chamber, positioned directly over the cylindrical feed inlet section. This chamber, connected to the feed inlet section by a middling overflow member of minimum length and separated from the feed inlet section by a wear disc support ing the middling overflow member, is designed to accommodate ore pulp flows ranging from to 100% of the total cyclone overflow (depending upon the restriction applied to the middling take-off conduit) without interfering with the highly essential rotary motion of the ore pulp or without causing objectionable turbulence and back pressure in the cyclone feed inlet section. Another distinguishing feature over other wet cyclones is the regulation of the flow from the middling take-ofl, the restriction being applied to the middling take-off conduit at an exterior location preferably not too far removed from the middling chamber. Still another feature is the provision for minimizing the lengths of the central vortex finder and the middling overflow member, thus reducing friction losses in the cyclone flow paths. The relative position of the lower ends of said members is important; the central vortex finder should extend below the middling overflow member thereby facilitating accurate splits of the ore pulp stream situated between the two members when the cyclone is making a 3-product separation.

The invention will now be described in greater detail and with reference to the accompanying drawing, in which:

Fig. l is a view in vertical section of. an apparatus embodying the invention, and

Fig. 2 is a top plan view of the apparatus shown in Fig. 1.

In the drawing, the cylindrical feed inlet section of the apparatus is shown at 1. Feed inlet 2 is tangentially disposed with respect to section 1, the orifice 3 of the feed inlet admitting into section 1 at a zone intermediate the top and bottom of the latter. An auxiliary cylindrical section 4, of the same diameter as feed inlet section 1 is shown. Auxiliary section 4 is optional and in some cases may be omitted, the feed inlet section 1 then being directly attached to the conical section 5. Apex end of section 5 extends to underflow conduit 6, the effective opening between them being constituted by apex orifice dimension regulator member 7: this latter may consist of an apertured plate of wear-resistant alloy, or it may be formed of gum rubber backed by an inflatable rubber doughnut.

The vortex finder 8 is a cylindrical pipe coaxially disposed with respect to section 1 and having its lower part extending into the latter: its open lower end terminates intermediate the feed inlet orifice 3 and the bottom of section 1 and nearer the latter than the former. The upper open end of vortex finder 8 is attached to wear disc 19 and extends into cylindrical overflow header 9 which latter may and preferably does have the same diameter as section 1. Overflow conduit 10 communicates with header 9; preferably, conduit 10 is tangentially disposed with respect to the latter, because the discharge from vortex finder 8 takes a whirling path.

Also downwardly extending into section 1, but for a lesser distance than vortex finder 8, is cylindrical middling overflow member 11 attached to wear disc 20 and which is concentric with vortex finder 8 and provides therearound an annular passageway 12 for feed inlet section 1 to middling chamber 13 located intermediate section 1 and overflow header 9. This latter preferably has the same diameter as feed inlet section 1. Header 9 and chamber 13 should be large enough to cause no back pressure on the cyclone when accommodating the maximum volume of flow.

Middling conduit 14 communicates with chamber 13: it may be disposed either tangentially or (as shown) radially with its chamber. At its end remote from chamber 13 middling conduit 14 is provided with a middling flow regulator member 15: this latter includes a flexible tube 16 through which the middling fraction passes and an adjustable constricting device or tube clamp 17 surrounding the same and adjustable by turning adjusting knob 18 for varying the effective discharge opening of the flexible tube 16.

Vortex finder 8 is attached to and depends from wear disc 19, which latter lies between header 9 and chamber 13 and is a plate of wear-resistant metal of somewhat thicker construction than are the side and header portions of the device. Middling overflow member 11 is attached to and depends from a similar thick wear disc 20 lying between chamber 13 and feed inlet section 1 of the cyclone device.

The dimensions of the various parts of the cyclone device preferably are as follows, the values all being given in terms of D, i. e., diameter of the cylindrical part of the cyclone device:

Symbol Dimension Diameter oi:

teed inlet orifice F .172 D. opening in apex orifice dimension U .150 D to .250 D.

regulator member. vortex finder V0 .125 D to .375 D. middling overflow member Va. .516 D to .625 D. opening in middling flow regulator R variable.

member.

P: 187 D P0 187 D Pm 250 1) Cr .644 D C n .544 D conical section H. 1.710 D middling overflow membe M 375 D portion of vortex finder extending O 450 D into teed inlet section. overflow header H0 .544 D middling chamber Hm .544 D apex orifice dimension regulator T .125 D member Length of:

feed inlet P; 1.500 D.

The height of middling chamber 13 may be made less than 0.544 D, e. g., only one-half of the latter value, provided the middling conduit 14 has a cross-sectional area equal to the annular area of middling overflow member 11. It is desirable to minimize-as much as possible the height of the middling chamber in order to insure that the total length of vortex finder 8 is not excessive, thereby avoiding the creation of back pressure.

It should be understood that the dimensions given above are susceptible to some variation without seriously affecting the cyclone performance, and that special adaptations may be required for special problems. Hence it is not intended that the cyclones of the present invention be limited to the precise dimensions shown above, which latter are, however, inherent in the preferred embodiment of the invention.

6 The conical section in Figure 1 has an included angle Relative to the preceding example, it is to be noted of 24 degrees but cones of to degrees, or H=0.70 that Tests Nos. 1 and 4 represent results which could have D to 3.00 D, may be used depending upon the particular been obtained with a D. S. M. two-productcyclone': howapplication. ever, to have changed the point of classification from 5 that which obtained in Test No. l to that'which obtained in Test No. 4, it would have been necessary to shut down the operation, remove the vortex finder, and substitute another vortex finder having a dilIerent orifice diameter. The results of all of the above four tests were securedg the three-product cyclone of the present inventionwithout any shut down and without any change of parts of the device or conditions of pulp feed (such as pulp density).

Table 2 shows that in Test No. 1 the middling (which 15 was the only overflow product) contained 3.83% Weight cumulative of plus mesh material and only 55% weight of minus 325 mesh material. At the other extreme, in Test No. 4 the overflow product was; materially finer. The two intermediate conditions, represented in Tests Nos. 2 and 3, show the degree of control secured with the threeproduct cyclone: In Test No. 2, 96.3 ofthe overflow product was minus 325 mesh material, while in Test N0. 3 the content of the latter was 92.47%. The two fine products (i. e., overflow and middling) could have been i and m 25 combined or kept separate as desired.

The results shown in Tables 1 and 2 are duplicatable in the classification of other ores and similar particulate solid materials, e. g., other base metal ores, gold-silver ores, and non-metallic ores such as feldspar, glass sands,

30 coal and the like.

In Example 11 following are shown the results of three ZA KLA GJLQLLALGM 11111 Table 2 Test 2 Middling 667021 0 1l8029%8 Jan-0 7 5 6 CLASSIFICATION The more im- SCREEN ANALYSES 0F CYCLONE P RODUCTS-EXAMPLE N0. 1

Test 1 Middling EXAMPLE I D=4 inches F= A inch U =15A6 inch Vm=2 /8 inches V0=l inch Table I Feed 81 None- The following are illustrative of the results which have been obtained by use of the three-productwet-cyclone of the present invention in the classification of ore pulps. These particular data were secured from the processing 10 si of a pulp of a Minnesota taconite containing principally magnetite, silica and silicate minerals.

and the feed pressure was maintained, throughout the 20 tests, at between the limits 9 and 11 lbs/sq. in. In Test open, and there was no discharge through overflow conduit 10; in Test No. 2, member 15 was partially restricted; in Test No. 3, member 15 was mostly restricted Test No. 4, member 15 was closed.

The pertinent results of Tests 1-4 are shown in Table 1 following:

DATA ON CYCLONE PRODUCT DISTRIBUTION portant dimensions of the cyclone used were:

No. l, the middling flow regulator member 15 was wide P n d e 5 m w m m w m 1 n PI r. a a n R a .l a e m M 1 n .o m a n s Sun 0 h .10 511 g e r. r. W C, v u m CI M y n t n C s T r a ma h e mqt f f S 1 u h S am o e w m m t d m. c m ma m 6 1 YR I m S m r. t I u a n m m w m m E w u mm. h c .n 0 n0 L r mwcmm m fi .n P vmfl m mm a c m a g d t M .e P a m n s evm .m 2. arm 2. l an Cd 4 H 1 W .0 mm B m t F m I 6 r. n 0 6 WP t m DFUVV Wme a a a l m OCIO oe d a t rm P h 1 a w a 0 mm p: CH d O MW fome e e 6 97K d M cm W dm r n n m t s a3 & 6 6 m W b e e t T am sln M a fl mM miw oR w am 5 0 3 4 m n amma. as a hum m M n m e 0 f SPWD. M m m w mnnmmnno w %m w n 7 2&6 .1.-D.L 5 s he mmmm mwwm hm D m m i mmmmnmwn memt 4 "alum MPPMU 2 ollz nn m w m 0 W0 90 s D m I I n aw mm m iew u w mama n mv m mmmm mmm awmmwwmmm mww e e lfi l F mWbmw l 0 0 m. u I u s e T n n 1 2 3 The screen analyses of the resulting products were as shown in Table 2 following:

Mesh

Total..

in Test No. ,2 the middling take-off flow approximately equalled the top overflow.

Table 3 DATA ON CYCLONE PRODUCT DISTRIBUTION The pertinent results of Tests Nos. 1 and 2 are shown in Table following:

as shown in Table 4 following:

Table 4 SCREEN ANALYSES OF CYCLONE PRODUCTS [Percent weight.]

The screen analyses of the resulting products were as shown in Table 6 following:

683 22657 0 P 010 58606 0 4 ZA OJm m 1 i U m 5 8 5 929 O T 6; 0m0m5fl456 0 mm 17 m d 4 821984 0 W 0 .1%152973 0 d araati u 0 12221 O a 1 2 62738798 0 av g 00035467 0 t mm L5 3 & & s 26 0 B 1 T n n .3460935 0 ew 4! 0 In a u 9 m o n a 5511 8239 0 Mm 0181 4007 O d 0 m m m. U t w 0 T fw M V w m 0 m m o e 0 F 1 u h m w 0 M T The above test results were secured without having to shut down and change parts of the device, and without having to modify the density of the feed.

Table 6 SCREEN ANALYSES OF CYCLONE PRODUCTS [Percent weight.]

212329447277 0 m ouunaam n nm 1 U m n 1161004700 0 a H Kaurraaaar 0 2 .1.m 26 m w M1 m m m n. u "124596941 0 e fluduuonaza 0 v0 8 0 fl 1 d 111213390360 0 F 1 .r 676694677237 0 M 0 nm N U 1 #1. WW M M v 0 8 O 1 T d B 0 m m h n 1 M m m m T 5 O 5 m 5 6 6 L e O C w u .m m t m d r e S a m i m d H w n I 9 0 I m S 3 .m w 1 I e n S .l C e f V Y e r o o P e C 1 h H .l d P t .1 e u t m d t p c r n a e u m m 0 I e h d e C I t O E e O f m m e W 6 O I w 1 m f UH. S I e Z d my D H S I w 9 r v 0 0 e E h h e a C .1 h L t I m d e m m C P w .1 D h a e m r u u t m 0 t h 1 i f .1 t h a w d a m a d t E m .m e d m D H w W n m t W e a a I o w c d g m o h e H t P s s .m s w m a h u .1 m .1 O t C t y m m a m a m .m w r m o d u s m m I m 6 a 0 n W e e n m .m m h I a C T r e eluded.

test, long tons of solids per hour.

that treated in Example I.

1 No middling.

F 1%; inches without changing the feed or without having to shut down f the device. This facility for inification point is extremely adaconite ores inasmuch to adjust the particle for example mesh depending upon the horizon from which -ofi was closed, whereas the taconite ore isrnined.

as it frequently becomes necessary and the feed pressure was maintained between the limits of 24 and 27 lbs./sq. in.

size of the overflow product from, to mesh,

In Test No. 1 the middling take In the conventional separation of particulate ore materials by gravity difference-using a heavy medium and a two-product cyclone-in order to change the separation characteristics it is necessary to substitute for the heavy medium another heavy medium having a different specific gravity, it being most unusual to shut down an operation for overflow orifice changes. The necessity for providing and maintaining equipment suitable to quickly raise the specific gravity of the heavy media is onerous.

Nevertheless, in separation plants which receive, successively and in short periods of time, ores of diilerent types and characteristics-as is the case in many Minnesota mining operations-it is extremely advantageous to be able to vary quickly the separation characteristics in order to meet variations in the ore feed, so as to maintain the production of a uniform underflow product. Through the use of the three-product cyclone of the present invention it is possible to meet such variations, without shut-down and usually without adjusting the specific gravity of the heavy medium.

The following example is illustrative of. the beneficiation of a particulate ore material by gravity diflerence, employing a heavy medium, in accordance with the present invention.

EXAMPLE IV The lean iron ore which was to be beneficiated could not have been marketed because of its low iron content and high silica content. The object, therefore, was to upgrade the ore to a commercially acceptable product and, at the same time, to secure as high a weight recovery of beneficiated material (i. e., concentrate) as possible. It was a washed and classified fraction of lean iron ore containing 49.05% iron, mostly in the form of hematite, and 17.48% silica, the particles varying in size from 4 to 80 mesh. The heavy medium was a finelyground magnetite slurry having a specific gravity of 2.32. The three-product cyclone used was the same as that used in Example II, the more important dimensions bemg:

D=4inches F=1% 6 inch U= V inch Vm=2 /8 inches Vo=1 inch and the feed pressure was maintained at about 20 lbs./ sq. m.

Four tests were run. In the first, the middling take-01f was closed; in the second, the midling take-off was about one-third open; in the third, the middling take-01f was about two-thirds open; and in the fourth, the middling take-ofl was fully open and there was no discharge through overflow conduit 10. The results of these four tests were as shown in Table 7 following:

Table 7 SIN K-FLOA'I CONCENTRATION OF LEAN IRON ORE Percent Percent Assay, Percent Percent Test No. Product Weight Weight Distribu- Pulp Ore tion of Iron Silica Iron Feed 100.00 100.00 49. 05 17. 48 100.00 1 Overflow 65. 28 18. 80 31. 21 43. 20 11.96 Midd1ing Underflow 34. 72 81. 20 53. 18 11. 52 88.04 49. 35 16. 48 100. 00 13. 31. 45 41. 48 8. 29 36. 36 35. 7. 34 77. 03 54. 06 9. 84 84. 37 100. 00 100. 00 49. 22 17. 24 100. O0 3 26. 98 5. 59 28. 48 45. 84 3. 23 Middling- 47.09 17. 60 35. 40 38. 09 12. 66 Underflow 25. 93 76. 81 53. 90 10. 26 84. 11 Feed 100. 00 100. 00 48. 75 17. 60 100. 00 4 Overflow Middling- 79. 26 43. 41 41. 07 28. 16 36. 57 Underflow- 20. 74 56. 59 54. 65 9. 50 63. 43

In Test No. 1 the underflow product (i. e., the desired iron ore concentrate) represented 81.2% of the weight of the total feed, i. e., the weight recovery was 81.2%. The underflow product, viz., 53.18% iron and 11.52% silica, would normally be of an acceptable grade. However, if the criterion had been a silica content of 10% or less, and if a conventional two-product cyclone had been used, it would have been necessaryin order to make a better grade underflowto have substituted for the heavy medium used in Test No. 1 another heavy medium having a higher specific gravity. Using the threeproduct cyclone, the objective was realizedsee Tests Nos. 2, 3 and 4-simply by causing some (as in Tests Nos. 2 and 3) or all (as in Test No. 4) of the overflow to be removed through the middling conduit 14, and without having to shut down or to change the specific gravity of the heavy medium.

The results of Tests Nos. 2 and 3 were superior to those of Test No. 4, particularly as regards weight recovery, although the grade of concentrate in Test No. 4 was somewhat higher than that in the other tests.

It is to be noted, from a consideration of the above data, that through the use of the three-product cyclone a close control of the beneficiation can readily and easily be achieved. It is to be noted, moreover, that a middling product-which can be crushed for further treatment, or recirculated, as desiredis separated, which circumstance, in the cases of many ores, offers a definite advantage.

EXAMPLE V To further illustrate the control of separation which is provided by the three-product cyclone, Example V follows: In this case, the material to be beneficiated was a jig tailing of relatively low iron content and high silica content. However, although much of the iron occurred as middling material and associated with paint rock-a ferruginous shalethere was some free mineral which could be recovered as a marketable concentrate.

The cyclone used in the test was the same as described in Example IV. The jig tailing feed to the cyclone ranged from 4 mesh to mesh in size and the specific gravity of the magnetite medium was 2.43. Feed pressure ranged from 16 to 19 pounds per square inch.

Three tests were run: In the first, all overflow was from the overflow take-off, the middling take-ofi being closed; in the second test, the volume of discharge from the middling and overflow take-ofls was approximately equal; in the third test, all overflow was from the middling takeoff. The results of the test are shown in Table 8 following:

Table 8 CONCENTRATION OF JIG TAILING MATERIAL Per- Per- Percent Test: Product cent cent; Iron Silica Distri- N 0. Weight Weight bution Pulp Ore of Iron Feed I00. 00 100. 00 33. 98 43. 25 1.00.00 1 Overflow 70. 52 49. 46 17.87 26. 05 Middling. Underfiow. 29. 48 50. 54 49. 64 20. 43 73. Feed 32. 75 43. 25 100. 00 2 Overfl0w 18. 40 11. 17 Middlin 24.37 32. 60 Underfiow 18. 94 36. 31 50. 71 16.4 56. 23 Fee 100.00 100.00 33. 18 43. 25 100. 00 3 Overflow M1ddling. 89.98 81.20 28.36 69. 40 Underflow. 10. 02 18.80 54. 01 12. 39 30. 60

It is evident from Table 8 that the concentrate obtained in Test No. 1 contained entirely too much silica (20.43%) to be of any value. An improved concentrate was obtained in Test No. 2, but the silica content remained excessive. A marketable concentrate was produced in Test No. 3, assaying 54.01% iron and 12.39% silica and with a weight recovery of 18.80%.

It is evident from these tests that a slight adjustment in the relative flow rates from the middling and overflow take-offs would yield a concentrate intermediate in grade and weight recovery to those obtained in Tests Nos. 2 and 3.

In conjunction with Example IV, the present example clearly shows that as the separation characteristics of the ores change, the type of product made by the cyclone can be readily changed to meet the required conditions.

This beneficiation process, which has been illustrated with reference to iron ores, is equally applicable to the beneficiation of base metal ores, such as lead-zinc ores, non-metallic ores, such as garnet, coal, magnetite, fluorspar, and other particulate solid materials.

To summarize, the improvements which are realized through use of the three-product cyclone are: (1) the ease of control and adaptability to varying conditions of feed rate, character of feed and structure of feed, (2) the ability to remove a middling which can if desired be separately treated, and (3) simplicity and ruggedness of construction which provide low capital and maintenance costs.

I claim:

1. A wet cyclone separator and classifier, which comprises a cyclone chamber consisting of a cylindrical upper part and a conical lower part, adapted in use to envelop a rotating body of pulp surrounding an air core, the diameter of the base of the conical part being equal to the diameter of the cylindrical upper part, a discharge aperture at the apex of the conical part, an inlet conduit arranged tangentially of said cylindrical upper part of said chamber and adapted to introduce a slurry stream, under pressure, tangentially into the upper part of said chamber, a pair of concentrically arranged cylindrical open-ended vortex finders axially disposed with respect to said chamber and extending downwardly into the top of the upper part of the latter to horizontal planes beneath the inlet conduit the inner of said vortex finders extending farther into said upper part than does the outer and having a length not substantially greater than the diameter of the cylindrical part of said chamber, a middling chamber adjacent the top of said cyclone chamber, a centrally disposed aperture in the bottom of said middling chamber into which aperture the upper end of the outer vortex finder extends, a header adjacent the top of said middling chamber, a centrally disposed aperture in the bottom of said header into which aperture the upper end of the inner vortex finder 'extends,'an open-ended overflow conduit arranged in communication with said header, and a middling conduit arranged in communication with said middling chamber, said middling conduit being provided with means for adjusting the efiective cross-sectional area of that end of said middling conduit remote from said chamber.

2. A wet cyclone as defined in claim 1, in which said middling chamber and said header have the same diameter as does the cylindrical upper part of said cyclone chamber.

3. A wet cyclone as defined in claim 1, in which the diameter of the inner vortex finder is from .125 to .375 the diameter of the cylindrical upper part of said cyclone chamber and in which the diameter of the outer vortex finder is from .516 to .625 the diameter of the cylindrical upper part of said cyclone chamber.

4. A wet cyclone as defined in claim 1, in which the middling conduit has a cross-sectional area at least as great as is the cross-sectional area of the annular space between the inner and outer vortex finders.

5. A wet cyclone as defined in claim 1, in which the length of the inner vortex finder is from .59 to 1.0 the diameter of the cylindrical upper part of said cyclone chamber and in which the length of the outer vortex finder is from .20 to .375 the diameter of the cylindrical upper part of said cyclone chamber.

6. A wet cyclone as defined in claim 5, in which the height of said middling chamber is between one-half and one-quarter of the diameter of the cylindrical upper part of said cyclone chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,265,763 Fender May 14, 1918 2,098,608 Berges Nov. 9, 1937 2,379,411 Berges July 3, 1945 FOREIGN PATENTS 607,785 Great Britain Sept. 6, 1948 661,050 Great Britain Nov. 14, 1951

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