US1912630A - Flotation process and apparatus - Google Patents

Description

June 6, 1933. FQRRESTER 1,912,630

FLOA'IATION PROCESS AND APPARATUS Filed June 8, 1928 2 Sheets-Sheet l June 6, 1933. D. FORRESTER I FLOATATION PROCESS AND APPARATUS Patented June 6, 1933 UNITED STATES PATENT OFFICE DAVID LAWTON FORRESTER, OF GLOBE, ARIZONA, ASSIGNOR 1'0 MATLESS CELL LATENT HOLDING CORPORATION, A CORPORATION OF ARIZONA 4 r'nom'rron rnocrss AND urmarus Application filed June a, 1928. Serial No. 283,781.

rocky constituents thereof. By this inven-' tion the pulp is aerated so as to produce bubbles of efiective flotation size in sufliclent quantity to persist efl'ectively throughout the operation of separation and concentration of the particles to be floated; the aerated pulp may be introduced from the agitation chamber into the separation chamber substantlally throughout its entire depth; and current-s and eddies are set up in the separation chamber by which the entire volume of pulp in the separation chamber is impre ated with a plenum of flotation bubbles, a ording opportunity for repeated contact between flotation bubbles and particles to be, floated. At the same time the intercommunicating agitation chamber and separation chamberare so arranged that there are maintained simultaneously a pulp in violent agitation in the agitation chamber, and in the separation chamber currents and eddies of pulp positive and\d'istinct enoughto assure required dissemination of flotation bubbles and particles to be float- 5 ed throughout the entire volume of pulp in the separation chamber, but at the same time mild and gentle enongh to permit the formation of the desired froth.

By the resent invention certain improvements in otation method and ap aratus are provided which by simplicity 0 operation and construction afford better metallurgical results and reduce the cost of production, in: stallation and operation.

The prior-art indicates that the requirements of the effective bubble column apparatus and method have been supplied in the past by introducing air through a porous medium, e. g. canvas, blanket, or a porous 50 solid, perforated pipe, etc., or by introducing bubbles, of efi'ecti've flotation size from the air by a mechanically operated impeller which beat air into the pulp in an agitation chamber, either from the open atmosphere in the agitation chamber or from air supplied. under pressure through the bottom of the agitation chamber, or by cascading or splashing streams or bodies of pulp into a mass of pulp in the fashion of a waterfall. These three methods of air introduction and dispersion are known respectively as pneumatic, centrifugal, and cascade or plunging stream methods.

In the early commercial pneumatic flotation machine andmethod, the aeration, agitation, and circulation were produced by passing the air at arelatively high pressure through a porous medium. In this manner the air is introduced in a finely divided state into the pulp from below. The minute air moment of introduction into the pulp, produce some agitation of the pulp efi'ective aeration of the pulp, and a circulation by displacement of the pulp within the cell, resultmg in the formation of a mineral bearing froth on the surface of the pulp. This method has certain apparent disadvantages in practice, the more important of which are the high power costs, high repair and operation costs in keeping the porous medium clean, loss of efficiency in the entire or partial blinding of the porous medium, loss of efliciency in performing the functions of agitation and separation in the same chamber, loss of efliciency in necessary restriction of volume of air admitted so as to maintain agitation sulficiently mild to permit froth formation. There are not present the currents and eddies of pulp essential to the most eificient operation. 4 In the centrifugal method, aeration, agitation and circulation are produced by a mechanically rotated impeller which beats air into the pulp in an agitation chamber, either from the open atmosphere in the agitation chamber or from air supplied under pressure through the bottom of the agitation chamber and causes the pulp to circulate from top of the agitation chamber into the separation chamber down through the separation chamber and back into the agitation chamber at the bottom thereof. The main disadvantages of this method are, original cost of installation, cost of power and repair, and want of thorough consistent impregnation of the entire volume of pulp in the separation chamber so that the'pulp falls back upon itself and on to the mass of pulp in the separation.

chamber. The theory is, that the cascading of the pulp entrains air for the purpose of providing the requisite bubbles of efiective flotation size. The main disadvantages of the cascade method are that suflicient air is not entrained in the pulp for most eflective flotation, nor are the proper currents produced and maintained in the separation chambers for the thorough and proper impregnation of the pulp in the separation chambers with bubbles of effective flotation sizes permitting the formation of an etficient mineral bearing froth.

The invention may be understood from the description in connection with the accompanying drawings in which Fig. 1 is a longitudinal section through an illustrative embodiment of the invention; Fig. 2 is a secdicates the bottom of a flotation cell that tion along the line 2-2 of Fig. 1; Figs. 3, 4 and 5 are sections similar to Fig. 2 showing modifications; Fig. 6 is a plan view of another modification; and Fig. 7 is a section along-the line 77 of Fig. 6.

In the drawings reference character 1 inmay be horizontal or may be made to slope from the inlet to the outlet at the end of the cell. The cell is provided with side walls 2 which slope upwardly and outwardly .from the bottom. The vertical side walls 3 extend from the upper edges of the sloping walls 2 and are of such a height that the froth that is formed flows over the upper edges of the walls 3 into the launders 4 for the concentrate. The end walls 5 of the cell proper extend entirely across the same.

Vertically disposed partitions 6 extend from one end of the cell to the other, and are so located that their upper edges extend some distance above the normal liquid level in the cell, and high enough to prevent splash over the top from the agitation chamber into the separation chamber. The lower edges of the partition 6 may terminate either near the liquid level or may extend a considerable distance below the normal liquid level. The lower portions of the partition 6 in the froth and liquid zones may be provided with holes or openings 6 through which the liquid may flow. The greater distance the partition 6 extends below the pulp essentialwhich also extend from the front end wall 5 to the rear end wall 5 of the cell. These lpO)(.':.rtitions are shown in Figs. 1 and 2 as ing inclined outwardly and downwardly with their upper edges extending some distance above the lower edges of the partitions 6. Deflecting strips 7 may be provided along the outer sides of the partitions 7 to aid in directing the flow of the liquid.

A rowof open-ended pipes 8 extends into the lower portion of the cell and these pipes are connected to the air manifold 9 through which air under pressure can be forced into the liquid to agitate the same.

An inlet compartment 10 is located at one end of the cell and an opening 11 is provided 'in the end wall 5 through which the pulp that is introduced into the compartment 10 can enter the cell proper. An opening 12 is provided in the lower portion of the rear end wall 5 through which the tailings pass into the outlet compartment 13. An adjustable weir discharge14 is provided for the outlet compartment 13 over which the tailings flow and by which the pulp level in the cell can be regulated. The tailings after flowing over the weir 14, then finally pass out through the opening 15. v

The operation is as follows: Air is introduced through the pipes 8 at a sufficient distance below the level of the pulp to cause violent agitation of the same, the formation of sufiicient bubbles of effective flotation size, and inducement of the required currents and eddies of pulp in the separation chambers. The pipes may be about three-quarters of an inch in diameter so that large bubbles of air escape from the pipe and rise upwardly through the liquid. These bubbles and downward cross and counter currents of the pulp are created with the result that the large bubbles of air are rapidly and thoroughly broken up and dispersed into numerous small bubbles of efl'ective flotation size. These small bubbles of efi'ective flotation size are suflicient in quantity and persist for a suflicient length of time to permit the same to be efliciently disseminated throughout the pulp and cause flotation of the mineral particles to take place as desired.

The continuous entrance of the large bubbles and the consequent agitation of the pulp and its thorough impregnation with air cause the pulp to assume a higher hydrostatic head over a considerable area above the points of entry of the air, than in the remainder of @the walls 3- and 2 and again upwardly between the partitions 7. The aerated pulp flows into the compartments outside of the L partitions 6 from the compartment between those partitions not only through the holes 6' and under the edges of the partitions 6, but also for substantially the entire depth below the partitions 6. In this way currents and eddies required for eflicient dissemination of the bubbles and pulp in the separation chambers between the partitions 6 and the walls 3 are set up, thus throwing out into the body of pulp in the separation chambers a very large number of bubbles of effective flotation size which rise through the pulp in the'separation chambers to the surface, thus forming the mineral bearing froth which flows over the upper edges of the walls 3 into the launders 4. In this way the currents and eddies of pulp in the separation chambers so impregnate and saturate the pulp with the bubbles of effective flotation size that repeated contact between these bubbles and particles of mineral to be floated takes place throughout the volume of pulp in the separation chambers before the pulp carried in the downward current near the walls 3 and. 2 re-enters the current passing upwardly between the partitions 7 The rapidity of flow of the aerated pulp fromthe chamber between the partitions 6 to the chambers outside of these partitions'may be controlled by the difference in hydrostatic head between the chambers, by the adjustments of the partitions 6 and 7 and also by adjusting the normal pulp level in the cell by means of the overflow weir 14. The difference in hydrostatic head may be regulated by the amount of air introduced through the pipe 8 in large bubbles or by the pulp level in the cell.

- By the arrangement above described, there is procured a violent agitation in the space above the ends of the pipe and to each side thereof, and at the same time the induced currents and eddies which enter the separation chambers are mild and gentle enough to permit the formation of the mineral bearin froth and are positive and distinct enough to bring about the required dissemination of bubbles and mineral particles in the entire volume of pulp in the separation chambers.

It has been found that with this invention there isconcentration progress throughout'the depth of the separation chambers, the percentage of content of the mineral to be floated increasing from the bottom to the top of the pulp in the separation chamber. Air at low pressure and in suflicient volume is introduced in large bubbles so that the disadvantages that occur when porous media and mechanical aerators and agitators are used are eliminated.

By providing the'large number of bubbles of effective flotation size and transferring them to the separation chambers, as above described, it is possible to o erate the process with varying levels of pu pin the cell and with practically any level of pulp, which may be varied to suit the particular ore that is being treated.

By this invention primary flotation may be carried out in which the more easily floated minerals are treated and a clean concentrate is desired in one operation, or secondary flotation may be carried out following a primary flotation so as to separate the more refractory mineral particles which escape the primary. treatment, thus producing a low grade concentrate, or a cleaning flotation can be carried out for the purpose of cleaning low grade concentrates from the secondary flotation or for recleaning all concentrates. In any of these flotation operations, the aeration is effectively produced by the entering air bubbles and the pulp is saturated with bubbles of effective flotation size. When primary flotation is being carried on the currents and eddies may be. less pronounced and vigorous; when the cleaning flotation is being carried on the currents and eddies may be least pronounced and vigorous; and when the secondary flotation is being carried on the currents and eddies should be most pronounced and vigorous.

The process can be used for carrying on different sorts of flotation merely by regulating the quantity of air that is introduced .or by raising or lowering the pulp level in the cell so as to produce the desired intensity of currents and eddies for the best results.

In the modification shown in Fig. 3, the strips'7 are left off of the partitions 7 and the upper edges of the partitions 7 are shown as being located approximately at the same level as the lower edges of the partitions 6.

The operation is similar to that already describe 1 In the modification shown in Fig. 4, the partitions 7 are omitted entirely and the lower edges of the partitions 6 terminate near the pulp level and have no openings therethrough. The partitions 6 in all the modifications may be made sufliciently high to prevent the pulp from splashing over the u er edges thereof or a hood 16, as shown 4, may be provided for thispurpose.

In the partitions 7 are located some distance apart modification shown in Fig. 5, the.

on opposite sides of pipes 8 and are shown as being installed parallel to each other. In this modification the upper edges of the partitions 7 extend some considerable distance above the normal pulp level so that the pulp agitated and aerated by the incoming air flows over the upper edges of the partitions 7. After the aerated pulp drops over the edges of the partition 7, it then passes under the lower edges of the partitions 6, or through the holes 6' in a manner similar to that already described. The arrangement of the partitions 7 as shown in Fig. 5 is advantageous in certain operations, particularly where a primary flotation or roughing operation is desired. The dropping of the pulp over the upper edges of the partitions 7 is not for the purpose of entrapping or entraining air in the pulp for flotation purposes, since the pulp has already'been saturated with bubbles of effective flotation size prior to its drop over the partitions 7. This action seems in certain instances to aid in disseminating the bubbles of effective flotation size that have already been produced by the agitation of the rising air from the pipes 8. a

In the modification shown in Figs. 6 and 7 the cell is shown as a circular one with a circular bottom 21, conical wall 22 and a cylindrical wall 23. An annular launder 24 is provided around the circular wall 23 and an lar partition 26 that performs a function similar to the partitions 6 already described, is located within the circular wall 23 and may be provided with openings 26' along the lower portion thereof in the froth and liquid zones. An air pipe 28 extends down inside the partition 26 and its lower open end terminates at a sufiicient distance below the pulp level to provide eflicient agitation and formation of suflicient bubbles of effective flotation size and to induce the required currents and edof pipes 28 may be used for the same purpose.

The mineral' pulp may be introduced into the cell and the tailings discharged therefrom as is ordinarily done in cells of this type The operation of the modification s own in Figs. 6 and 7 is similar to that al- Ieady described in connection with the other res. 'l he location of the partitions 6 or the partition 26 should be approximately at the line of demarcation between the portion. of the liquid that is raised by'the air bubbles and the remainder of the surface area of the cell. This area is convex, and is, ina cell of a commercial size, about 20 or 22 inches wide and extends from one end of the cell to the other with a row of air inlet pipes 8, as indicated in Figs. 1 to 5. This area is, of course, circular-in the modification shown'in Figs. 6 and 7 and is approximately 20 inches in dierate satisfactorily without the partitions 7,

but in certain instances the partitions 7 have some advantages.

The following is given as a specific example of a cell operated and made in accordance with this invention, but it is to be understood that dimensions may be altered and variations and modifications can be made without departing from the invention: A cell similar to those described-in connection with Figs. 1 to 5 may be made 4 feet wide and 50 feet long with the air pipes 8 extending about 2 feet below the level of the pulp. The'partitions 6 may be placed about 22 inches apart and havetheir lower edges terminating near the pulp level "or the lower edges may extend downwardly several inches into the pulp. The usual flotation agents-may be used with mineral pulp and the air may be introduced at about 1 lbs. pressure through pipes of about three-quarters inch in diameter placed approximately 5 inches apart.

I claim:

1. The process of concentrating ore or other substances by flotation which comprises introduc'ing air in large bubbles into a pulp in an unobstructed space near the middle of a cell at a suflicient distance below the surface thereof to aerate the pulp and provide enough bubbles of effective flotation size for flotation, segregating the surface area of the pulp above the point where the air is introduced from the area outside of it, and passing the aerated pulp into the space below said lastnamed area throughout substantially the entire depth of said space and also substantially vertically below the outer edges of said space. v

2. The process of concentratingore or other substances by flotation which comprises introducing air in large bubbles into a pulp in an unobstructed space near the middle of a cell along a row of points at a suflicientdistance below the surface thereof to aerate the pulp and provide enough bubbles of effective flotation size for flotation, segregating the surface area of the pulp above the point where the air in introduced from the area outside of it, and passing the aerated pulp into the space below said last-named area throughout substantially the entire depth of said space and also substantially vertically below the outer edges of saidspace.

3. In a flotation apparatus for ore concentration, a cell, means for introducing air in-large bubbles into an unobstructed space in said cell below the normal liquid level therein in suificient quantity to cause violent agitation, partitions to separate the surface area of the liquid in said cell that is violently agitated by introducing the air from the re- Inainder of the surface area, said partitions extending only a short distance below the normal liquid level, and partitions converging upwardly below and between said first named partitions.

4. In a flotation apparatus for ore concentration, a cell, means for introducing air in large bubbles into an unobstructed space in said cell below the normal liquid level therein in suflicient quantity to cause violent agitation, means comprising partitions to separate the surface area of the liquid in said cell that is violently agitated by introducing the air from the remainder of the surface area, and

- separate partitions located at a lower level than said first-named partitions with .unobstructed spaces between the lower edges of said first named partitions and the upper edges of said last named partitions.

DAVID LAWTON FORRESTER.

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