US3037626A - Froth flotation machine - Google Patents

Description

June 5, 1962 SHINYU TAKAHASHI 3,037,626

FROTH FLOTATION MACHINE AND METHOD Filed Feb. 2, 1960 3 Sheets-Sheet 1 LT 2 I? 8 IN VEN TOR.

Shinyu TakahashL June 5, 1962 SHINYU TAKAHASHl 3,037,626

FROTH FLOTATION MACHINE AND METHOD Filed Feb. 2, 1960' 3 Sheets-Sheet 2 IN VEN TOR.

1 W, J NW June 5, 1 2 SHINYU TAKAHASHI 3,037,526

FROTH FLOTATION MACHINE AND METHOD Filed Feb. 2, 1960 3 Sheets-Sheet 3 IN VEN TOR.

Shinyu FL/(cL/ms/M 1 M WM State 1 3,037,626 FRGTH FLOTATION MACHINE Shinyu Takahashi, Tokyo, Japan, assignor to Nippon Mining Company Limited, Tokyo, Japan Filed Feb. 2, 1960, Ser. No. 6,285 Claims priority, application Japan Oct. 5, 1959 4 Claims. (Cl. 209-464) This invention relates to improvements in a froth flotation machine which is applied to concentration of metallic minerals such as gold, silver, copper, lead, zinc and the like metals as well as non-metallic minerals such are barite and gypsum.

The principal object of this invention is to provide a most effective and economical method of producing 3. highest grade of concentrates from the first cell of a series of succeeding cells in a flotation machine without using any additional wash water for the transition of froth.

Another object of this invention is to provide a more simple and eflectively operable flotation machine which can produce a higher grade of concentrates with less power consumption and reagents.

In a conventional type of such flotation machines there is a countercurrent froth flow flotation system as described in the US. Patent No. 2,350,943 in which flotation pulp is fed substantially constantly into one end of a normally static longitudinally extended body of flotation pulp having uniform width, thereby imparting a substantially constant and substantially unidirectional longitudinal displacement to the pulp body and causing pulp to discharge at the opposite end of the pulp body and air is introduced into transient pulp body in graduated quantities from end to end thereof, the greatest quantity being introduced at said pulp discharge end and the resulting pulps are accumulated in the froth on the surface of the pulp body in the proportion of air introduction at corresponding points along the length of the pulp body, thereby forming a hydrostatic head of froth, and causing the froth to flow by gravity along the surface of the pulp body counter to the direction of transition of the pulp, by confining the froth against discharge at said pulp discharge end and laterally along the length of the pulp body. Although this machine incorporates several features of improvements over the then known flotation processes, it also has defects in that in order to induce the counter flow of froth, aeration in the feed end section where it is most preferably needed, is controlled, thereby reducing flotation efliciency by causing poor bubble production with resulting acceleration in the settling of the coarse particles in the cells of highest mineral enrichment. Furthermore, during the phase of operation, the froth near the tailing end, generally and preferably being free of mineral attachment would lack suflicicnt stability to form an adequate froth layer to induce an eflicient automatic flow of froth merely by means of aeration.

There is another type of flotation machine known as the Fahrenwald type which is also based on one of socalled counter froth flow flotation system and incorporating an arrangement to suck in air automatically and to cause agitation mechanically and hydraulically by means of an impeller. In this machine, a series of individual cells are arranged together as a group, each cell having a vertical shaft provided with an open type impeller at its lower end acting as a centrifugal pump by cooperating with a stationary disc on one side, to which is secured a stand pipe surrounding the shaft and a duct is connected to the lower part of the stand pipe to receive the feed or middling return. In the Fahrenwald machine, when the impeller is rotated, air is sucked through the stand pipe together with flotation pulp containing mineral particles which are dispersed by the centrifugal force so that the air suction and agitation are eifected at the same time and bubbles ascend upwards.

In the Fahrenwald machine, the froth in the cells at the feed end section which contains the richest concentratc is generally taken out as a final product, while the low grade froth on the tailing end returned for cleaning to the preceding cell with the addition of spray or wash water in froth launder, which dilutes the concentrate and accordingly the preceding cells receive excessive water thereby necessitating the impeller to perform flotation at greater load with the result the efficiency is considerably reduced.

The Fahrenwald machine is based on the principle such that the pulp containing mineral particles together with frothing reagent is supplied from one cell to another in succession continuously through the partition between adjacent cells so that the pulp flows in one direction up to the tailing cell while the froth is taken out sidewise from some cells and returned to the preceding cell by the addition of spray or water, thus the principle of operation is different from the countercurrent froth flow flotation machine as described in the U.S. Patent No. 2,350,943.

The present invention is somewhat similar to and generally based on the Fahrenwald machine, but is an improvement of the latter and characterized in that it comprises a number of individual cells arranged in series as a group, each of said cells being provided with a feed chamber which is connected to the suction side of the impeller arranged in the succeeding cell while the froth is discharged over the adjustable weirs provided for the partitions between adjacent cells so that froth cascades over in succession from cell to cell in a direction counter to the flow of pulp and the highest grade of concentrate is taken out of the first cell or if desired from any of the successive cells.

The flotation machine of the present invention is provided with cells, each of which is equipped with three overflow weirs on three sides of the cell, and the height of each weir is made adjustable and the weirs provided on the partition between successive cells (called as partition weir) may have successively higher overflow tops so that the level of pulp and froth layer in successive cells may be maintained progressively higher and the froth of the lowest grade floating in the tailing cell flows back to froth layer of the preceding cell over the partition weir by the difference in static head and is subjected to repeated cleaning in froth layer, then returned to the preceding cells over the partition weirs and is taken out as the maximum beneficiated concentrate from the feed end cell. Thus, according to this invention, the height of overflow partition weirs and accordingly the differences in froth levels can be adjusted to regulate the amount and speed of froth as desired.

For a better understanding of this invention, reference is made to the accompanying drawings, in which;

FIG. 1 is a diagrammatic sectional elevation of the flotation machine embodying this invention;

FIG. 2 is a plan view of the machine of FIG. 1;

FIG. 3 is a sectional side elevation of the machine of FIG. 2 taken on the line BB as seen from the left;

FIG. 4 is a sectional side elevation of the machine of FIG. 2 taken on the line A-A, that is, through the center of the first cell as seen from the left side showing that a new feed to the first cell is made through a pipe 19' into the lower part of the stand pipe or into the hood, while the pulp flowing into the rear side box So by passing over the side Weir 5 is delivered through the pipe 10 into the lower part of the stand pipe or hood of the succeeding cell;

FIG. 5 is a diagrammatic plan view of a set of flotation machine embodying this invention, wherein a number of cells are arranged in series as a unit;

FIG. 6 is a diagrammatic sectional elevation of the flotation machine of this invention showing some modification;

FIG. 7 is a plan View of the machine of FIG. 6;

FIGS. 8 and 9 are diagrammatic elevational views respectively illustrating different arrangements of the cell combination.

Referring to the drawings, 1 represents a cell of the flotation machine, 2 represents a partition between successive cells, 3 (see FIG. represents an overflow launder for froth, 4 is an overflow weir for froth which may be provided on the front side of the cell, 5 is a gate for regulating the pulp and froth level, 5a is a rear side box for receiving the pulp which flows over the gate 5, 5b is a regulating handle for the gate 5, "5c is a submerged baffle provided for the gate 5 to prevent the surface flow of froth or pulp to the gate 5 and 6 is an overflow weir for froth provided on each of the partitions 2 between adjacent cells. 7 indicates a driving shaft for the impeller 8 secured to its lower end (driving motor and power transmitting device not shown). 9 represents a stand pipe surrounding the shaft 7 and provided at its lower end with a hood having a flange 8 serving as the suction chamber for the impeller 8 and 10 is a pulp feed pipe for connecting the side tank 5a of one cell to the suction chamber of the impeller 8 in the succeeding cell.

As shown in FIG. 1, the flotation machine of the present invention has an open impeller 8 to be driven by a vertical shaft 7 to operate as a pump cooperating with the stationary disc 8' on one side of the impeller, but a closed type impeller may be used, constituting a main agitator and aerator by sucking in air through the stand pipe 9 and introducing pulp through the pipe 10 for the first cell and through the pipes 10 into the second and succeeding cells causing agitation by the impeller and air bubbles dispersed into the pulp in the cell and the mineral particles are caused to adhere to the air bubbles. The finely divided air bubbles carrying the mineral particles rise to the surface and the accumulated froth layer flows over the partition weir 6 back to the preceding cell. The partition weir 6 is slidably mounted to the partition wall 2 and to be regulated by means of a suitable regulating device 6' so that the heights of overflow lips of successive partition weirs can be made progressively higher and the accumulated froth layer is induced to overflow successive partition weirs, in the direction counter to the flow of pulp, while a surface flow of froth or pulp to the rear side gate 5 is prevented by the submerged baflie 5c, and all pulp in the cell passing beneath the baflle and flowing over the rear side gate to the succeeding cell.

As shown in FIG. 4 the new feed to the first cell is made through a pipe 10' into the lower part of the stand pipe or into the hood, while the pulp flowed into the rear side box 5a by passing over the side weir 5 is delivered through the pipe 10 into the lower part of the stand pipe or hood of the succeeding cell. The new feed through pipe 10' in FIGS. 4 and 5 may be supplied similarly to the second or third section of cells in addition to the first cell (though not shown).

The pulp level in each cell is independent of its adjacent cell and if the level becomes higher than the lip of weir 6 the froth layer floating on the pulp flows over the weir and enters into the preceding cell. The level of pulp in each cell can be regulated by adjusting the height of gate 5 and overflow weirs 4 and 6 and if the pulp levels of successive cells are so adjusted that the pulp level in a cell is progressively higher than the preceding one and the front overflow weir 4 of desired cells are closed, then the froth of the lowest grade in the tailing cell can be transmitted to the preceding cell and then through the successive cells into the feed end cell after being subjected to repeated cleaning in froth layer and the concentrate of the highest grade can be discharged from the feed end cell.

On the other hand, in the conventional type of Fahren- Wald flotation machine the pulp is introduced from the feed end cell through a weir which is provided on the partition to next cell and so on to the tailing cell, while the froth is taken out over the front side weir into the froth launder and thus collected froth is returned to the pulp in preceding cell successively with addition of spray or wash water, where the froth is subjected to the repeated flotation.

Thus, in the Fahrenwald type flotation machine there are many disadvantages in the re-flotation of the froth of lower grade and the efficiency is not satisfactory in view of the fact that when the froth is returned to the preceding cell a large quantity of water should be sprayed on the froth in the launder in order to induce the froth to overflow into the preceding cell, thereby necessitating a considerably large quantity of water to be circulated therein. This is also the case when the pump is used for returning the froth, resulting in the increased volume of fluid passing through each cell per unit volume with resulting decrease in treating time during flotation. Moreover, the density of pulp is unnecessarily lowered which causes a decrease in flotation effect. Furthermore, the minerals of lower flotability which were scarcely floated in the tailing cell are subjected to flotation again in the preceding cells. Therefore it is doubtful that all low flotability minerals will be effectively floated, and evidently a decrease in yield results.

On the contrary, according to this invention the froth while floating on the pulp is transferred to the feed end cell counter to the direction of flow of the pulp and low grade froth is subjected to recleaning in froth layer so that no additional water is necessary, nor the pulp density reduced nor the time of flotation shortened, nor also the yield reduced by the re-flotation as in the case of conventional flotation machines.

In accordance with the present invention the minerals to be recovered are accumulated on the upper layer of the froth layers, while the valueless minerals, rocks and gangue are made to settle in the lower part of the bubble column and the bubbles gradually disappear, and the undesirable materials are returned to the pulp so that the uppermost layer of the froth column contains minerals of the highest grade and the rate of counter flow and amount of the froth are regulated so that a concentrate of higher grade than in the conventional system can be obtained. Generally in the above type of conventional flotation machines the thickness of froth layer is largest in the cell at the feed end section, gradually decreasing in the successive cells. Accordingly by the conventional system it is unfeasible to return the froth in the tailing cell back to the feed end cell in floating condition or to regulate the speed of counter flow at all.

In the flotation machine of this invention as above described the level of pulp in the cell can be maintained progressively higher from the first to the tailing cell and the thickness of froth layer in the tailing cell can be regulated to a desired extent by adjusting the height of overflow weirs 4 and 6 and the period of retention of froth so that the counter flow and amount of the froth can be easily regulated.

In the conventional type of flotation machines, the relation between the surface area and volume of each individual cell is constant, whereas in the machine of this invention the ratio of surface area and the volume of each cell can be made progressively larger from the first to the tailing cell so that the froth layer may be formed not only advantageously but also the amount of minerals to be treated per unit surface area can be increased.

In a device embodying this invention shown in FIG. 6, for facilitating the flow of froth in each cell a conventional means consisting of a rotary wheel or similar device 13 is provided above the overflow weir 6 in the transverse direction of the cell and normally to the direction of the flow of froth, thereby assisting the froth to flow more quickly to the preceding cell from the tailing cell end.

As shown in FIGS. 6 and 7 the first cell is provided with an overflow Weir 611 on the side opposite to the partition of the next cell and the height of the weir is made adjustable as desired and the froth in the first cell can be taken out from the overflow weir 4 on the front of the cell and also over the Weir 6a, that is, the froth can be taken out from two sides.

FIG. 8 shows an arrangement of the flotation machine of this invention wherein the individual flotation cells 1a, 1b, 1c of identical dimensions and construction are arranged in a series of successive steps so as to cause a diiference in the level of pulp in successive cells and to facilitate the counter flow of the froth. FIG. 9 shows an arrangement of two blocks of cells 1a, 1b, 1c, 1d and 12, 1f, 1g, 1h, the cells of each block being on the same level but the cell blocks being on different levels.

Example Conventional Flotation Fahrenwald machine machine, of this On Grade, invention, percent 011 Grade,

percent Feed 10. 22 10. 22 Concentrate 24. 40 25. 8O Tail 2. 83 1.35 Yield 81. 80 91. 60

If the yield and the grade of concentrate are allowable at the same figures as those of the former machine, the present machine of this invention can treat about 160% more ore than the former machine could achieve.

In the flotation system of this invention as above described, the features incorporated therein such as, the adjustability of pulp level in each cell for achieving the desirable return of mineralized froth from cell to cell, the unnecessity of injecting additional water or of installing additional pumps for said purpose, or of subjecting returned pulp to repeated flotation, as required in conventional flotation machines, provide favorable conditions that enable the increase in yield and grade of concentrates treated per unit area, and prevent the dilution of pulp density or the shortening of flotation time. Besides these merits, this invention has advantage over the system patented under US. Patent No. 2,350,943 in overcoming the defect of decrease in efliciency during flotation due to an undesirable control of air at essential point.

What I claim is:

1. A method of operating a counterflow froth flotation machine of the cascade type comprising a plurality of cells connected and arranged in series and separated by partitions between adjacent cells, an adjustable overflow weir provided for each of said partitions to maintain the levels of pulp in successive cells higher successively to the tailing end, a vertical revolving shaft mounted in each cell having an impeller secured to its lower end to act as a centrifugal pump, a stand pipe surrounding said shaft and having a stationary hood at its lower end covering the impeller to induce suction within the hooded chamber of the pump, an auxiliary chamber provided on the rear side of each cell, a regulating gate in the wall between said auxiliary chamber and the cell for regulating the pulp level and the pulp discharge from one cell to the succeeding cell, a submerged baifle spaced from said gate in the cell to prevent a surface flow of pulp and froth over said gate, a feed conduit connected to the suction chamber of the impeller of the first cell, a feed conduit provided between each auxiliary chamber and the stationary hood of the impeller in the succeeding cell, an overflow weir on the front side of the feed end cell to serve as outlet for the final product, said method comprising efl ecting froth flotation by feeding a definite amount of pulp into the first cell through said feed conduit, which pulp, upon operation of said impeller, is sucked into the pump together with air through said stand pipe and the air is dispersed in the cell as fine bubbles, and mineral coated froth floats on the surface of pulp, and the pulp flows to the next cell through said gate, auxiliary chamber and conduit, the pulp body in each individual cell being independent of one another, so that the pulp level can be regulated as desired, and the froth formed and accumulated on the surface of the pulp is induced to flow automatically over the weirs on the successive partition walls, which are regulated to have progressively greater height towards the tailing end, by the difference in hydrostatic heads of pulp in successive cells, in a direction counter to the flow of pulp, and the froth of the highest grade is discharged over the weir of the feed end cell.

2. A froth flotation machine, which comprises a number of cells arranged in series and separated by means of partitions between adjacent cells, an adjustable overflow weir provided on each partition, means for adjusting the height of each of said overflow weirs independently, a vertical shaft rotatably mounted in each cell having an impeller secured to its lower end to operate as a pump, a stand pipe surrounding said shaft and having a stationary hood at its lower end forming a suction chamber of the impeller, an auxiliary chamber provided at the rear side of each cell, a regulating gate in the rear side wall of each cell to control the flow of pulp from said cell to said auxiliary chamber, a submerged baflle spaced from each gate in each cell to prevent a surface flow of pulp and froth over said gate, a conduit connecting each auxiliary chamber with the suction chamber of the impeller in the succeeding cell, means comprising a pipe for feeding raw feed directly to the suction chamber of the impeller in the first cell and overflow weirs provided on the front side of each cell facilitating taking out the froth from a desired cell by adjusting the heights of said overflow weirs.

3. A froth flotation machine according to claim 2, which comprises means for inducing the flow of froth over the partition weir, said means consisting of a mechanically revolving wheel secured above said partition weir, the axle of which is arranged tranverse to the flow of froth so as to assist the counterflow of froth.

4. A froth flotation machine according to claim 2, which comprises a plurality of units of a series of identical cells which are located on different levels to cause the diflerence in the pulp level in the successive cells, thereby inducing the flow of froth back from cell to cell up to the first cell by utilizing the difference in static heads of pulp in successive cells.

References Cited in the file of this patent UNITED STATES PATENTS 2,350,943 Thompson et al June 6, 1944 2,423,456 Logue July 8, 1947 2,494,602 Wright Jan. 17, 1950

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