US2145269A - Apparatus for flotation of minerals - Google Patents

Description

Jan. 31, 1939. A, c. MUNRO ET Al.` 2,145,269

APPARATUS FOR FLOTATION OF MINERALS Filed Oct. 2, 19256 2 Sheets-Sheet l W (nm Jan. 31, 1939. A. c. MUNRO ET Al..

APPARATUS FOR FLOTATION 0F MINERALS Filed Oct. 2, 1956 2 Sheets-Sheet 2 IN V EN TORS Werd/za@ ma, BYHu beni-"H PWS A T l RNEYS.

atented Jan. 3l, 1939 UNITED STATES APPARATUS FOR FLOTATION MNERALS Alexander C. Munro and Hubert A. Pearse, Britannia Beach, British Columbia, Canada Application October 2, 1936, Serial No. 103,703

7 Claims.

This invention relates to the separation of valuable constituents from ores or minerals byA a flotation process, and particularly by a flotation process of a type in which aeration of the pulp is effected by forcing air under pressure through a body of pulp in such manner as to cause the air to be distributed in the pulp under suitable conditions of subdivision andvdistribution for effective notation. In this type of apparatus, sometimes referred to as the air-lift. or pneumatic fiotation apparatus, the air under pressure is generally introduced into a body of pulp at a depth of between two and three feet. Our invention is' based primarily on the discovery that by introducing the air under pressure at a depth considerably greater than ordinarily used, for example, a. depth of about ten feet, a remarkable increase in flotation efficiency is secured, together with a decrease in the power required for a given flotation capacity, and a more than proportional decrease in the horizontal area of the apparatus for a given capacity.

One of the particular objects of the invention is to provide an apparatus which has a higher eapacity per square foot of floor space occupied than has hitherto been obtainable in the air-lift or pneumatic type of flotation apparatus.

A further object of the invention is to provide a flotation apparatus of the air-lift or pneumatic type adapted to operate at a lower horsepower consumption and a. lower volume of air per ton of ore being treated than has hitherto been obtainable.

Our invention is particularly adapted to application to dotation cells of the so-called "matless pneumatic flotation type (such as are described in U. S. Patents No. 1,912,630 to Forrester and No. 1,732,893 to Hunt), wherein air is introduced into a body of pulp through -a plurality thereof, or will be apparent from such descrip` tion. The accompanying drawings illustrate an advantageous embodiment of the present invention, and referring thereto:

Fig. 1 is a plan view of a flotation cell embodying our invention;

Fig. 2 is a section on line 2-2 in Fig. 1; and

Fig. 3 is a section on line 3-3 in Fig. 1.

The flotation cell illustrated in the drawings comprises a tank or trough I having a fluid' supply means or feed inlet 2 at one end and a uid discharge or tails outlet 3 at the other end. The feed inlet 2 may be located at any desired point in one end wall of the tank, preferably below the `ing or varying the overiiow level.

pulp level, and the discharge outlet 3 may be located at any desired point in the opposite end wall of the tank, preferably at a. considerable depth below the normal pulp level, said discharge outlet communicating, for example, through a riser 4 with a tails launder 5, suitable adjustable means indicated at 6 being provided for adjust- The tank I may be of usual or suitable dimensions as regards width and length, but is of a depth considerably greater than the usual practice, being such as to provide a body of pulp not less than four feet and preferably in the neighborhood of about ten feet in depth. Means are provided for forcing air under pressure into the 4pulp contained in said tank, said means comprising, for example, a header or air supply, pipe 1 extending longitudinally over the center line of the tank and a series or plurality of vertical pipes or tubes 8 extending downwardly from the header I and open at their lower ends. Said header communicates with any suitable source of air or equivalent gaseous medium under pressure suiiicient to overcome the submergence of the lower end of the pipes 8 and cause air to be discharged into the body of pulp in the tank in such manner as to distribute the air in the form of bubbles, or a state of iine subdivision, into the pulp.

Any suitable system of bailies may be used in I connection with the tank to control the circulation of pulp and froth, for example, verticalbai'- fles 9 may extend on opposite sides of the series of tubes 8 so as to define an air-lift compartment I0 open at both lower and upper ends and extending to a level adjacent the lower end of the tank I, but spaced therefrom. A defiecting baiiiel I is provided between the upper end of each baffle 9 and the adjacent side wall of the tank I. said bailies I I extending from a point above the froth level to a point slightly below the upper ends of the baiiies 9. Suitable froth overflow lips are preferably provided along the sides of the tank I,

as at I2, and suitable concentrate launders are provided as at I3 to receive froth concentrate discharged over said lips.

The body of pulp within the tank I is maintained at the desired level by means of the tailings overiiow device shown at 6 in this particular form of apparatus, but it will be appreciated that any equivalent level-regulating means may be provided for the. purpose. In general, reference herein to introduction of air at a certain depth sol below the level or surface of the pulp will be understood to refer to the depth below the pulp or tailings overflow means or other equivalent levelregulating means. Furthermore, it will be understood that the level of the froth overow lips, such as I2, is adjacent or somewhat above the normal pulp level, so that the depth of introduction of air, in accordance with this invention,

is in excess of four feet, and preferably in excess of six feet, below the frothv overflow means, and that the preferred value of this depth is ln the neighborhood of ten feet.

In the operation. of the apparatus the pulp, comprising nely divided ore or mineral, together with Water and a suitable froth notation agent, is passed into the tank from the feed inlet 2 and in passing through the tank is subjected to aeration by the action of the air issuing in bubbles or finely divided form from the lower ends of the pipes 8. The resulting mixture of pulp and finely divided air rises in the air-lift compartment Ill (as shown by the ascending arrows in Fig. 2). In this operation, which produces a froth due to the presence of the flotation reagent, certain mineral values of the ore are separated from the remainder of the ore by selective action and become associated with the froth, which passes under the baiiles Il and is discharged into concentrate launders I2. It will be appreciated that not all of the floatable ore particles will be caused to enter the froth in a single path upwardly through the compartment I0, and such particles as have not entered the froth will be carried downwardly through the separating zone of the tank, as defined by the portions of the tank outwardly of said compartment I0 (as indicated by the descending arrows in` Fig. 2), in a repetition of the flotation operation. Such particles as are not subject to flotation are thus gradually worked longitudinally of the tank toward the outlet 3,

thence to the discharge launders 5.

The so-called air-lift or pneumatic type of flotation machine has certain inherent advantages over mechanical flotation machines, such as low maintenance cost due to the absence of moving parts, while having a relatively low power consumption due to the use of low pressure air. In the conventional type of "matless pneumatic flotation machines now in common, use, the depth of pulp maintained in a otation cell is relatively shallow, being generally in the neighborhood of about 30 inches, and the airwhich is introduced under pressure into the body of pulp passes through a relatively shallow layer of pulp in contact therewith for a relatively short time, and consequentlyalargepercentage of the air supplied escapes without doing any useful work. In view of the fact that the bulk of the matless pneumatic machines are of the same general width, the capacity of such machine is conventionally expressed in terms of the length thereof, and it has been found that in the ordinary type of such' pneumatic machine the volume of air required per lineal foot of machine varies from 50 to 80 cubic feet per minute (in terms of free We have found that very material advantages can be obtained by considerably deepening the pneumatic type of machine, so that'the depth of v pulp above the point of admission of the air is established at a height in excess of four feet, and preferably at a height of six feet or more. In our preferred form of machine, the air is introduced at a depth approximating ten feet, depths-much in excess of ten feet having been found to be but little more eectlve than ten foot depths, and not justifying the added cost of compression required to supply the air at the greater depths. Not only does the same volume of air come in contact with a much larger quantity of pulp than in a shallow machine, but also since the air is subjected to greater pressure at the point of admission, it is consequently more widely and uniformly dispersed through the pulp in the form -of smaller bubbles. As a result of this more eiicient utilization of the air, we have found that a machine having air inlets submerged ten feet will treat nearly ve times as much feed as eiiiciently as a machine of similar length and width having air inlets submerged only approximately 30 inches. The volume of air requiredis only one-fifth to one-sixth as much, but even though the air has to be supplied at a considerably higher pressure for the deep machine, the actual consumption of power is less than half of that required for the shallow cell.

We have found that a cell ten feet deep and ten feet long will treat approximately 600 tons of ore per day and make the same metallurgical recovery of copper, iron, and gold as does a standard shallow matless pneumatic type machine of the same width and 100 feet long treating approximately 1200 tons per day. On the particular ore employed in these tests, the most advantageous air consumption of the standard shallow machine was approximately 55 cubic feet per minute of free air per lineal foot of cell, or 5,500 cubic feet of free air per minute for a throughput of 1,200 tons per day. This air was required to be supplied at a pressure of 1.9 pounds per square inch in the standard cell, while in the cell of the present invention only 45 cubic feet of free air per minute were supplied per foot of length of the cell, at a pressure slightly less than 4.5 pounds per square inch.

As above pointed out, quantities of air ranging from 50 to 80 cubic feet per minute per lineal foot of machine are required in the conventional matless pneumatic apparatus, but it has been found that the deep cell of the present invention Will operate satisfactorily with air volumes as low as 30 cubic feet per minute per foot of length and up to 60 cubic feet per minute. Air volumes even lower than 30 cubic feet per minute have been found quite adequate to maintain circulation and frothing within the apparatus, even with coarse feed, whereas the standard shallow pneumatic cell will tend to choke with air voliunes anywhere near comparable to this lower limit. The deep cell of the present invention thus appears to reach a maximum eiliciency with considerably lower air volumes than the shallow cell, and we have found that 45 cubic feet per minute per foot of length is approximately the economic maximum.

The following table sets forth comparative operating data on the above-mentioned standard shallow matless pneumatic cell and a deep cell of the present invention:

Normal economic volume of air or free air rcquired for above pulp (per lineal foot of cell) (cu. ft./min.) 55 45 HP required per li n)cal foot of cell (based on normal volume of a 0. 495 0, Lineal feet of cell required per ton of ore pcr hour 2 0. 4 Cubic feet ot free air required per ton of ore u, GUI) 1,080 HP hours required per ton of orc 0. 378

It may be pointed out that while the operating pressure required in the cell of ten foot depth is greater than that required in the cell of two and one-half foot depth, the proportionate increasein pressure is materially less than the proportionate increase in depth. This difference results primarily from the maintenance of a more thoroughly aerated pulp column in the compartment i0 than is possible in the shallow type of cell, and the improved power eiiiciency and throughput capacity of the present cell is Ia direct result of this more aerated condition of the pulp column, which condition may be maintained at a lower volume of air per lineal foot of cell.

As may be seen from the above data, the pressure at which the gaseous medium was supplied to the pulp, i. e., the -operating pressure of the apparatus, was less than the corresponding hydrostatic pressure of the pulp at the depth of submergence of the air inlet means. It will be appreciated that when a cell is started in operation, the air will have to be introduced at a pressure sumcent to overcome the static hydrostatic pressure of the pulp, which pressure may be gradually reduced to the desired operating pressure as the aerated pulp column is established in the aeration compartment.

The advantages of the deep machine may be summarized as follows:

A saving in power of about 60 per cent or more;

Only about one-fifth of the floor space required;

Somewhat lower initial cost, both for cells and blowing equipment, since the requirement displacement of the latter is so much smaller, even though higher pressure is necessary;

Less liability of the deep machine to choke on coarse feeds 4because circulation is positive and rapid. (The shallow air flotation cell now in considerable use in the copper industry has not been accepted generally in the lead-zinc operations, because o'f choking troubles and sluggish froth conditions with these ores of greater density; in order to prevent chokingswith these ores,

of a moderately coarse grind, the wasteful practice of using abnormally high air pressures for the shallow cell must be resorted to):

The deep machine is not so sensitive to slight changes in reagents, dilution and operating conditions, thus insuring a more positive froth discharge and hence better mineral recovery;

With the more eilicient diffusion of air in the pulp, which results from the injection of higher pressure air, together with the longer contact of air and pulp, excellent otation conditions are obtained immediately at the head of the deep notation machine, whereas to get similarly desirable results in the shallow cell, pulp conditieners ahead of`the cell are essential.

We have had successful results, as stated, with a machine operating with ten feet submergence, but we desire it to be understood that greater depths may be used, if desired. However, we consider that ten feet is about the limit to which the depth can be increased with practical advantages. Nor should it be assumed that it is necessary to reach even ten feet in depth in order to secure some benefit, since a machine only six or seven feet deep, or in any case over four feet, is more eiiicient than one with an effective submergence of air inlets of only two and one-half to three feet. As a specific example of the increasedeiciency of a relatively shallow cell of the present type over, that of. the conventional capacity of a standard cell with a thirty inch effective submergence.

While the form of apparatus herein specifically described shows the use of drop pipes for introduction of the air for otation, it will be appreelated that any of the well-known equivalents for such drop pipes may be substituted therefor without departing from the spirit or scope of this invention. For example, a pervious bottom structure analogous to that shown in U. S. Patent No. 1,547,548 (Allen et al.) may be employed; similarly, upwardly directed air supply openings or nozzles may be provided below the compartment iii, such as are illustrated in U. S. Patent No. 1,441,560 (Connors); and in like manner, a perforated supply pipe may be extended along the lower portion of the compartment ld, after the manner of the'air inlet means shown at 61-62 in U. S. Patent No. 1,912,228 (Shimrnin et al.).

1. A pneumatic or air-lift iiotation apparatus comprising: a tank; means for supplyingl pulp to said tank and for maintaining a body of said pulp therein; baffle means within said tank defining an air-lift compartment and a separating compartment.; means for introducing gaseous medium into said tank below said air-lift compartment at a depth in excess of four feet below the surface of said body of pulp, the depth of submergence being such that the operating pressure required for operation of the apparatus is less than the hydrostatic head of the pulp at such submergence; and means for overow of froth from said separating compartment.

2. A pneumatic or air-lift flotation apparatus comprising: a tank; means for supplying pulp to said tank and for maintaining a body of said pulp therein; baiile means within said tank denn-- ing an air-lift compartment and a separating compartment; 'means for introducing gaseous medium into said tank below said air-lift compartment at a depth in excess of six feet below the surface of said body of pulp, the depth of submergence of said gaseous medium introducing means being such that the operating pressure required for operation of the apparatus is less than the hydrostatic head of the pulp at such submergence; and means yfor overflow of froth from said separating compartment.

3. A pneumatic or air-lift type flotation apparatus, which comprises: a tank provided with lil lili

inlet means for mineral-bearing pulp, and outlet means for tailings: distributing means for delivering a 'gaseous medium into the tank at a submergence of over four -feet in the pulp; means Ai'or supplying a gaseous medium to said distributing means at such pressure as to overcome such submergence and to cause such gaseous medium to issue in nely divided form from the distributing means into the pulp, overflow launder means at the side of the tank for carrying off froth otation concentrates, and baille means in the tank for controlling the flow of froth to the con'- centrates overflow, the depth of submergence being such that the operating pressure required for operation of the apparatus is less than the hydrostatic head of the pulp at such submergence.

4. A pneumatic or "air-lift" type flotation apparatus, which comprises: a tank provided with inlet means for mineral-bearing pulp, and outlet means for tailings; distributing means for delivering a. gaseous medium into the tank at a submergence of over six feet in the pulp; means for supplying a gaseous medium to said distrib uting means at such pressure as to overcome such submergence and to cause such gaseous medium to issue in nely divided form from the distributing means into the pulp, overflow launder means at the side of the tank for carrying off froth otation concentrates, and baille means in the tank for controlling the flow of froth to the concentrates overow, the-depth of submergence being such that the operating pressure required for operation of the apparatus is less than the hydrostatic head of the pulp at such submergence.

5. A pneumatic or air-lift type flotation apparatus, which comprises: a tank provided with inlet means for mineral-bearing pulp, and outlet means for tailings; distributing means for delivering a gaseous medium into the tank at a submergence of approximately ten feet in the pulp, means for supplying 4gaseous medium to said distributing means at such pressure as to overcome such submergence and to cause such gaseous medium to issue in finely divided form from the distributing means into the pulp, overflow launder means at' the side of the tank for carrying oi froth flotation concentrates, and

bale means in the tank for controlling the flow of froth to the concentrates overflow.

6. A pneumatic or air-lift flotation apparatus, which comprises: a tank adapted to hold a body of pulp comprising mineral-bearing solids in fluid suspension; uid supply means for delivery of pulp to said tank; fluid discharge means for withdrawal of pulp from said tank and including means for maintaining a fluid level of pulp within said tank; a source of gaseous medium under pressure; distributing means associated with such source of gaseous medium for delivering the same under pressure into said body of pulp at a depth of approximately ten feet below said fluid level, such pressure being sulficientn to cause such gaseous medium to issue in nely divided form from said distributing means; and overflow launder means for said tank for carrying oi froth flotation concentrates.

7. A pneumatic or air-lift flotation apparatus which comprises: a horizontally elongated tank adapted to hold a body of pulp comprising mineral-bearing solids-in fluid suspension; fluid supply means adjacent one end of said tank for delivery of pulp thereto; fluid discharge means adjacent the other end of said tank for withdrawal o1 pulp therefrom and including overilow means for maintaining a fluid level within said tank; baffle means extending longitudinally of said tank and defining an air-lift compartment therewithin extending vertically downwardly from above said fluid level to a level adjacent but spaced from the bottom of said tank; a source of gaseous medium under pressure; distributing means associated with such supply of gaseous medium for delivering the same under pressure into said body of pulp at a point adjacent the lower end of said air-lift compartment and at a depth of approximately ten feet below said fluid level. such pressure being sufcient to cause such gaseous medium to issue in finely divided form from said distributing means; and overflow launder means at the side of said tank for carrying off froth flotation concentrates.

ALEXANDER C. MUNRO. HUBERT A. PEARSE.

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