US3343674A - Froth flotation process and apparatus - Google Patents

Description

P 1967 v. A. ZANDON ETAL 3,343,674

FROTH FLQTATION PROCESS AND APPARATUS Filed Feb. 23, 1965 KW? 13. a,

m A ni United States Patent Ofiflce 3,343,674 Patented Sept. 26, 1967 3,343,674 FROTH FLOTATION PROCESS AND APPARATUS Victor A. Zandon, Carlsbad, N. Mex., J. Stanley Mitchell,

Vicksburg, Miss, and Charles W. Abernethy and Milton H. Klein, Carlsbad, N. Mex., assignors to American Metal Climax, Inc., New York, N.Y., a corporation of New York Filed Feb. 23, 1965, Ser. No. 434,392 7 Claims. (Cl. 209-166) ABSTRACT OF THE DISCLGSURE Froth flotation machine having end walls and side walls. On'fices are located in side walls on a level substantially corresponding to the froth-liquid interface and are advantageously located in upper portion of the side walls intermediate the ends walls. Also disclosed is a process for recovering coarser sylvite particles by longitudinally moving pulped ore through flotation apparatus and transversely removing sylvite from the froth over the lateral edges of the apparatus while transversely withdrawing coarser particles at a lower level which corresponds to the frothliquid interface without disturbing the relative quiescence of the interface.

This invention relates to an improved method and apparatus for effecting the recovery of sylvite values in differential froth flotation procedures.

More particularly, the present invention relates to the recovery of coarse sylvite crystals, and especially those concentrated by froth flotation within the resulting pulp liquid-froth interface, by means of novel froth flotation apparatus.

' Recovery of sylvite values from sylvinite ores by differential flotation processes from a finely ground (eg. all minus 28 mesh) sylvinite ore, moderately well deslimed and conditioned or reagentized by conventional techniques, has been accomplished effectively heretofore. Levitated in these known procedures by air bubbles, individual finely ground sylvite crystals concentrate in a froth column usually of about two inches to four inches in depth above the pulp level of the cell. The froth con taining the fine sylvite values is removed by rotating paddles into the overflow launders and recovered.

Where the sylvinite ore contains a wide range of crystal sizes ranging from coarse through fine, e.g. minus 8 to about 200 mesh, the flotation sequence involves floating and recovery of the sylvite values of minus 28 at the head of the flotation unit as described above. Intermediate sizes of sylvite mineral values within the range of minus 12 to 28 mesh are next floated and removed; the concentration of the intermediate size particles taking place in a much shallower froth column than that for the fine size particles. The particles of minus 8 and +14 mesh, i.e., the coarse particles, are then recovered in varying amounts but with significantly less efliciency in the remainder of the flotation apparatus. During this latter concentration and recovery phase, the depth of the froth column is minimal. Thus, those coarse crystals of sylvite values which are successfully floated are present on the surface of the liquid phase as an agglomerated layer, one particle deep. This agglomerated layer is supported by a multitude of fine air bubbles; the concentration and recovery technique employed being designated as skin flotation. As will be apparent and as is otherwise commonly known, a prerequisite to even relatively successful skin flotation is the relative quiescence of the surface in the flotation unit or machine. That is, the surface must present a substantially unbroken continuum of fine air bubbles with suspended sylvite values therein. Any material disturbance of this surface causes a rupture of the air bubble-mineral agglomerates with the consequent sinking of the coarse particles present therein. Inasmuch as the coarse sylvite crystals are very diflicult to levitate in any event, the losses of such particles in the tailing portion of the flotation pulp are greatly increased by such surface disturbances.

The difficulties in obtaining suitable quiescence for skin flotation result principally from the relative inability known heretofore in effecting proper baflling of the vertical and horizontal circular paths defined by the contents of the flotation cells and resulting from the action of the agitating mechanisms and the introduction of air to effect formation of the desired froth.

Exceptionally coarse textured mineral values, i.e. sylvite, of the flotation feed, arising from the current demand for larger particle sizes thereof for consumer use, thus imposes even more stringent limitations on downward adjustment in speed of the impellers used in accomplishing agitation of the conditioned pulp feed as well as in the volume of compressed air used. Indeed, insufiicient agitation and aeration invariably accelerate the sanding of the flotation cells with consequent cessation of the skin flotation operation.

Accordingly, it has now been discovered that deep agitating flotation cells, such as the deep air cell, for example, the Munro-Pearse deep flotation cell, are ably adapted for use in the concentration of nonmetallic mineral values, such as sylvite, and obviate the aforesaid difficulties relating to undue disturbance of the surface of the liquid suspension present in the flotation unit. Indeed, the use of these so-called deep cells provides the desired quiescence of the surface throughout the length of the flotation unit at the interface between the liquid and froth of the conditioned pulp. However, where, for example, even five or six standard deep cells are used in a flotation unit or machine, the skin flotation condition, very much in evidence in the last three cells of such a unit, is not sufflciently effective as a means for recovery of the coarse particles of the pulp. Attempts to induce transverse motion of the agglomerates provided by skin flotation, as, for example, by use of paddles, to accomplish their passage over the lip of each of the last two or three cells of a six cell flotation machine and into the launders positioned thereunder have evidenced only a limited degree of elficacy.

It has been further discovered, however, that the concentration and recovery. of the coarse particles of desired sylvite values can, surprisingly, be very effectively accomplished by providing a plurality of orifices at the level of the liquid-froth interface of certain of the flotation cells of the flotation machine, defining passage between the cell compartment, in each instance, and the adjacent launder. These orifices disposed in a horizontal plane parallel to the upper lip or edge of theflotation unit provide the machine with the necessary structure to recover substantially all of the coarse par-.

ticles of mineral values since the concentration of coarse sylvite values occurs initially at the aforesaid interface between liquid and froth, particularly in the very shallow froth of the intermediate cells of the flotation unit or bank.

These and other significant objectives and advantages of the present invention will become evident in the course of the detailed description appearing hereinafter considered in concert with the accompanying drawings, showing an illustrative embodiment of the invention.

In the drawings:

FIG. 1 is a cross-sectional semidiagrammatic repre sentation taken on line 1--1 of FIG. 2 of an illustrative 8 3 deep flotation cell for use in the practice of the invention; and

FIG. 2 is a fragmentary isometric view of a series of ,cells forming one flotation machine.

Referring more particularly to the accompanying drawings in which like numbers in the written description and drawings designate like parts, reference is made initially to FIG. 1 where, in a deep agitation flotation cell 5, disposed at the head of a flotation unit 6, including a bottom wall 7 and upstanding side walls 8, air enters the pulp conditioned in standard manner with -a nonmetallic mineral collecting agent and, if desired, a froth flotation oil and slime inhibiting reagent, by means of the hollow impeller shaft 9 with an air connection to the air header 11 which, in turn, receives its high pressure air supply from a compressor (not shown). The air forced into the impeller shaft is disseminated through and below the fin; gers 12 of impeller 13 in the form of minute bubbles. These are mixed vigorously with the pulp and the mixture aerated in this manner travels downward, outward, upward, and through the main body of pulp present in cell 5. As the areated pulp leaves the impeller zone, the mass of bubbles take the shortest path to the surface where the sylvite values collectedby bubbles form a froth column 18 or a layer on the upper surface.

The aerated pulp is thus passed to the surface of the cell wherein a Zone of relative quiet obtains. The aerated pulp, as a result, readily liberates the bubbles present therein which have been mineralized with the desired sylvite values. These bubbles rise, as a result, to form the froth column 18. The liberated and mineralized bubbles from the froth which is limited only by the side walls 8. Thus, the froth is distributed across the width as well as the length of each cell, and is interrupted in each instance only by the impeller shaft 9 in each cell.

The froth containing the desired sylvite values, for example, are recovered in the launders 19 which are conduits disposed exterior to the upper portion of the side walls 8.

At the head cell 5a wherein the pulp is introduced in a standard manner and aeration initially occurs, fine sylvite values are recovered in the froth which passes over the rim or overflow lip 21 of the side wall 8. These values are of about minus 28 mesh, and in the procedure, thus employed, is well-known in the art as described hereinabove.

The head of the unit 6 composed of the cell 5a, and normally a second cell 5b as well, are continuous with each other and with a plurality of further cells, normally three to four in number, which combine to form the flotation unit or machine 6. Each of these cells contains an impeller, e.g., a standard Galligher or Denver impeller, for maintaining agitation of liquid pulp. The froth becomes measurably shallower in succeeding cells and contains intermediate sized sylvite values in the range normally of about 12 to 28 mesh in the intermediate zone encountered along the length of the flotation unit. In the standard unit, the column of froth attains a height of about .25 inch to .5 inch in this intermediate zone, which extends for about the middle one-third to one-half of the length 'of the entire flotation unit.

The ultimate object of flotation procedure is to obtain a quiescent surface conductive to skin flotation and heretofore revolving paddles (not shown) are used on both sides of the cells to push the froth and values therein into the launders. However, the paddles break the desirably continuous quiescent surface which is particularly harmful if the paddle depth extends below the froth into the liquid state. The detailed description to this point is obviously directed to structure and processes well known to the art, it being recognized that deep cells can more easily produce desirable skin flotation.

While the froth layer floats fine particles, the more desirable heavier and coarser particles tend to accumulate as a thin film, one particle thick, just beneath the surface of the liquid stage which is below the froth column. If this film is broken or disturbed, the heavy particles therein rapidly sink and are lost. It has been found that these heavy particles are more effectively recovered by inducing transverse motion at the thin film layer without breaking the film while on the cell.

Accordingly there is shown a preferred method herein of inducing transverse flow. The outer walls 8 of - cells 5c and 5d contain a plurality of orifices 22 at the froth-liquid interface which thus transmit sylvite values of 8 mesh and coarser from cells to the launder 19. The orifices 22 are disposed along a substantially straight horizontal line above the bottom or base of the launder and below the rim or overflow lip 21 of the cell walls 8 and parallel therewith. In intermediate cells 50 and 5d, the orifices occur normally at a depth of 1 to 2 inches below the lip or top of froth.

The orifices are here shown for the middleone-third of the entire unit and it has been found more eflicient to include orifices for the middle one-half to one-third of the unit. However, they can be incorporated along the entire length of the unit with somewhat less effectiveness..

The position or level of the orifices along the entire unit will vary from about /2 to 3 inches below the lip or top of the froth, the greater depths being at the feed end because the froth is thicker at that end.

The diameter of the orifices may be from A to 1 inch, depending somewhat on the number. As shown in cells 5c and 5d there are 21 orifices on each side (10 feet for 2 cells) which are 1% inches below the lip. These orifices may be replaced by intermittent or continuous slots at the appropriate level. In fact, any means of inducing transverse flow without breaking the skin surface on the liquid at the interface is within the scope of this invention. Where the transverse flow is to be induced only on intermediate sections, e.g. cells 50 and 5d, the lips may be lowered in those sections to the point just below the liquid-froth interface to induce the desirable flow.

The launders 19 lead to a common source for subsequent screening of particles to desired size but particle classification could be at least partially accomplished by isolating the flow from the various cells and particularly that from 50 and 5d.

As indicated hereinabove, the removal of the mineral particles present at the foregoing interface in accordance with the preferred practice herein described results from the initial concentration of coarse particles, that is those sylvite values of from about 8 to 14 mesh, at this level in the intermediate zone. At the same time, the intermediate sizes of sylvite in the range of about 12 to 28 mesh are present in the froth above the aforesaid interface, in the intermediate zone of the flotation unit, and are recovered simultaneously with the coarser particles passed through the orifices, in the launders, by passage of froth containing the intermediate size sylvite values over the overflow lip. It will be apparent that a variable quantity of sylvite values having a mesh size of 12 to 14 is transmitted to the launder by either or both means, that is in the overflow of froth or by transmission from the concentratoin of particles at the liquid-froth interface.

Thus, the remainder or terminal end of the flotation bank, comprising about one-third of the unit length normally (and not less than one-fourth) and encompassing cells 5e and 5 of a six cell bank or flotation unit,'is employed to effect recovery of any stray coarse sylvite particles which may have escaped recovery in the foregoing intermediate zone. This scavenging action in the terminal or tail end of the unit is accomplished by skin flotation as described above.

The methods employed in processing a mined sylvinite ore for production of a conditioned pulp to be subjected to flotation in the manner described'he-rein may vary widely, but will include, by way of illustration, the tech niques and methods described and alluded to in application Serial No. 320,388, now Patent No. 3,282,418, and application Ser. No. 363,405, now Patent No. 3,310,170, filed on Oct. 31, 1963, and May 18, 1964, respectively, by Abernethy and Klein, two of the inventors of the subject matter herein described and claimed. 5 While the present invention has been described in terms of deep agitation cells such as the deep air cell, it should be apparent that conventional shallow pneumatic flotation cells, such as the Forrester Cell, can also be employed, but are markedly less preferred due to the disturbance caused not only on the surface of the pulp treated in such cells, but even more significantly, because of the disturbance incited at the liquid-froth interface in the intermediate treatment zone described above. The advantages inherent in the use of the deep air cell are many, as have been made manifest in the foregoing description, and include not only thorough aeration of the pulp, but greater opportunity for froth formation due to enhanced and longer periods of quiescence; a more compact and stable froth; an increased capacity per lineal foot of cell and unit; higher recovery of mineral values and more efiicient operation; and the absence of a tendency of the unit to choke under even adverse conditions.

A preferred deep flotation machine or unit, for purposes of further illustration, for use in the practice of this invention, is one having an approximate length of 30 feet, a width of 9 feet, 6 inches and a depth of 6 feet, as opposed to a 3 foot, 4 inch depth and a width of 7 feet in conventional shallow flotation machines.

Thus, a preferred ratio of length and depth in the flotation machines employed herein is in the range of 4 to 6 (length):1 to 2 (width):l (depth); the most significant relationship being that of length to depth which may be expressed by the range, respectively, of 4 to 6:1.

The significance of the increased efliciency in recovery of nonmetallic mineral values, and particularly sylvite values, employing the induced transverse flow via the orifice-punctuated intermediate treatment zone of the present invention to effect transverse movement of the concentrate of coarse particles, is particularly marked when observed in the standard commercial milieu where cost is extremely critical and the flotation of vast quantitles of nonmetallic mineral values are involved.

Operation of a commercial deep 6-cell unit with the orifices on the middle two cells open as shown in the drawings and subsequently closed gave the following comparative results:

O RIFICES OPEN recovering mineral values of a coarse, intermediate and fine particle size from a liquid pulp containing such values which comprises a bottom wall, end walls and side walls, each of said side walls having an upper portion with a substantially horizontal froth-overflow edge and a liquid pulp fr0th interface level which is below said edge and substantially parallel thereto and at least one of said side walls having a plurality of orifices for receiving and carrying coarse particle size mineral values therethrough to a launder, said orifices being substantially horizontally disposed in the upper portion of said Wall along said interface level.

2. A froth flotation machine as claimed in claim 1 wherein opposed side walls are provided with a plurality of orifices for receiving and carrying coarse particle size mineral values therethrough to launders located on each side wall.

3. A froth flotation machine as claimed in claim 2 wherein said orifices are 4 inch to 3 inches on center below the froth-overflow edge of each opposed side wall.

4. A froth flotation machine as claimed in claim 3 wherein each of the orifices is circular in cross section and has a diameter ranging from A to 1 inch.

5. A froth flotation machine as claimed in claim 4 wherein said machine is formed of a plurality of longitudinally aligned deep air cells and wherein said orifices are disposed along the middle third to middle half of the length of the side Walls of said machine.

6. A process for improving the recovery of coarse particle size sylvite value from sylinite ores in a liquid pulp condition which comprises placing said sylvinite in a flotation enclosure having an open top and sides containing overflow edges, producing a froth column containing sylvite values atop the liquid of the liquid pulp and producing a quiescent interface zone containing coarse sylvite particles between the froth column and the liquid, longitudinally moving said liquid in the enclosure and transversely removing sylvite values from the froth column over the overflow edges of the sides of the enclosure without disturbing the quiescence of the interface zone While transversely removing coarse particles contained in the interface Zone through orifices located at a level below that at which the sylvite values from the froth column are removed.

7. The process as claimed in claim 6 wherein the coarse particles are transversely removed from the enclosure intermediate the ends of the side walls.

Feed Concentrate Tailings Percent K 0 Recovery Percent Percent Percent Percent Percent Percent weight K20 weight K20 weight K20 10 Mesh- 20.1 19. 1 10. 9 61.18 22.2 2.88 89.3 10 Mesh-" 79.9 22.77 89.1 55. 94 77.8 9. 66 9. 83

Total- 100. 0 22. 0a 100. 0 56. 52 100. 0 1.15 96. s

ORIFIOES CLOSED 10 Mesh. 1s. 4 1s. 70 12. 0 61.16 20. 3 4. 77 80.8 10 Mesh. 81.6 22.87 88. 0 56. 57 79. 7 0. 79 97.9

Total. 100. 0 22.10 100. 0 57. 12 100. 0 1.58 95. 5

Thus, there is an absolute increase in KCl recovery References Cited and also in the recovery of the more valuable +10 mesh product. At present prices, a plant having an annual UNITED STATES PATENTS production level of a million tons would have an annual 2,316,770 4/ 1943 Daman t a1 209-169 increased sales value of about $300,000. 2,931,502 4/1960 Schoeld et al 209170 X Various modifications of the invention can be made and to the extent that such modifications and variations incorporate the spirit of this invention, they are intended to be included within the scope of the appended claims.

What is claimed is:

1. A froth flotation machine particularly adapted for HARRY B. THORNTON, Primary Examiner. TIM R. MILES, Examiner.

L. EATHERTON, Assistant Examiner.

Claims (2)

1. A FROTH FLOTATION MACHINE PARTICULARLY ADAPTED FOR RECOVERING MINERAL VALUES OF A COARSE, INTERMEDIATE AND FINE PARTICLE SIZE FROM A LIQUID PULP CONTAINING SUCH VALUES WHICH COMPRISES A BOTTOM WALL, END WALLS AND SIDE WALLS, EACH OF SAID SIDE WALLS HAVING AN UPPER PORTION WITH A SUBSTANTIALLY HORIZONTAL FROTH-OVERFLOW EDGE AND A LIQUID PULP-FROTH INTERFACE LEVEL WHICH IS BELOW SAID EDGE AND SUBSTANTIALLY PARALLEL THERETO AND AT LEAST ONE OF SAID SIDE WALLS HAVING A PLURALITY OF ORIFICES FOR RECEIVING AND CARRYING COARSE PARTICLE SIZE MINERAL VALUES THERETHROUGH TO A LAUNDER, SAID ORIFICES BEING SUBSTANTIALLY HORIZONTALLY DISPOSED IN THE UPPER PORTION OF SAID WALL ALONG SAID INTERFACE LEVEL.

6. A PROCESS FOR IMPROVING THE RECOVERY OF COARSE PARTICLE SIZE SYLVITE VALUE FROM SYLINITE ORES IN A LIQUID PULP CONDITION WHICH COMPRISES PLACING SAID SYLVINITE IN A FLOTATION ENCLOSURE HAVING AN OPEN TOP AND SIDES CONTAINING OVERFLOW EDGES, PRODUCING A FROTH COLUMN CONTAINING SYLVITE VALUES ATOP THE LIQUID OF THE LIQUID PULP AND PRODUCING A QUIESCENT INTERFACE ZONE CONTAINING COARSE SYLVITE PARTICLES BETWEEN THE FROTH COLUMN AND THE LIQUID, LONGI-

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