Making Millions Out of Bubbles
Huge profits, undreamed of yesterday, are now obtained from the dump pile of low-grade ores
George Merriman Oaks
Managing Editor of the Popular Science Monthly
MILLIONS are at stake in lawsuits brought about by infringement of the froth flotation patents. Clearly, they must be very important patents. In truth, they are the basis of a great industrial achievement. In one mine alone the flotation method increased the daily output of zinc by 200,000 pounds; in another, the daily increase in copper was 120,000 pounds.
The adoption of froth flotation by the five leading porphyry mines of the United States would mean a yearly saving of $17,000,000.
What is froth flotation? Nothing but the industrial utilization of bubbles. Who would believe that bubbles could be turned to money—
Attraction of two bodies not wet by a liquid. In this instance, the pressure is the same at all points indicated by the dotted line, namely, that of the outside atmosphere. Pressure is also that of the atmosphere in the air space between the two bodies; but the water pressure on each side (indicated by the arrows) is greater, pushing the two bodies toward each other. Applies to sulphides in water
Repulsion of two bodies, only one of which is wet by a liquidPressure on left side of wet body is less than that of atmosphere which acts on its right side, pushing it away.from the other body. Pressure on left side of body not wet by liquid is greater (below surface of liquid) than that of atmosphere on right side. Hence the pressure of the liquid pushes the body not wet away from the other body
Attraction of two bodies wet by a liquid. Pressure is the same at all points indicated by dotted line, namely, that of the outside atmosphere. Pressure is less in the liquid between the bodies and above the dotted line. Therefore, the atmospheric pressure outside pushes the bodies toward each other. The liquid rises between the bodies dueto the principle of capillary attraction
yes, millions? And to think of applying such ethereal objects as bubbles, whose greatest achievement has always been to grow a little bigger and
then burst, to an industry like mining!
It seems as though Nature’s most precious gifts are often hedged about with thorns so prickly that ceaseless labor is necessary to obtain them. We find copper combined with sulphur as copper sulphide. Furthermore, the sulphide is shaken up with all sorts of worthless mineral matter, such as sand and limestone, until it seems hopelessly hidden from man’s reach. The same is true of the other base metals, zinc and lead.
The useless matter
found in conjunction with the sulphides of lead, copper and zinc, is referred to as gangue. Concentration is any process of separating the valuable metal from the worthless gangue.
The simplest method of concentration is hand-shaking. We all remember our old American history which contained a picture of a flannelshirted Forty-Niner “panning out” gold from one of California’s rivers. He used an ordinary dish-pan, and by a careful shaking, slopped the water and gangue over the sides, the metal being allowed to settle.
Various Methods of Concentration
Hand-shaking has long since been superseded by mechanical methods, some of which treat the ores wet, and some
dry. Both take advantage of the difference in specific gravity of the gangue and of the metal. In the dry method, a current of air is used to blow away the lighter gangue, leaving the heavier minerals on a flat corrugated surface. In the wet methods, the ore passing through a stream of water separates into two parts, the metals sinking and the gangue being washed away.
But now comes a
process which practically reverses the long-used wet method of concentration. Instead of sinking the sulphides, they are induced to float and the gangue is allowed to sink. Flotation is the term applied to this revolutionary method.
The history of flotation, like that of most great industrial processes, is not centered around any one man. Its development, though rapid, has involved a long list of patents taken out by a large number of American and foreign metallurgists.
The first patent which even suggested the process now known as flotation was obtained in 1860 by William Haynes. He knew that sulphides would stick to oil and in a crude way tried to use this principle in separating the metal from the gangue. He was followed by Bradford, whose method involved surface tension concerning which I shall speak later.
The -Floating Spider
The underlying principles governing flotation are too theoretical to admit of satisfactory explanation.The how is more easily explained than the why. Have.you never observed the trim little water spider go skating across a pool with the greatest ease and agility? And did you make the mistake of believing that he was floating simply because he is so light? Then try floating a needle on the surface of a glass of water. It can easily be accomplished and you will note that the much heavier needle seems to lie in a sort of depression in the surface of the water and does not readily become wet. This is due to surface tension, supposed to play an important role in flotation.
In surface tension we have a tendency on the part of a liquid to act somewhat like an elastic skin, trying always to contract to the minimum area. A drop of water does its best to shape itself into a neat little round sphere instead of spreading out over a large surface. But this is only on surfaces which water does not wet. In contact with paraffined paper, for instance, it maintains the drop form; on the other hand, it quickly sinks
into the meshes of a piece of blotting paper. If a needle is perfectly clean, it will sink; if it is greasy, it can be made to float. The explanation involves two phenomena, surface tension and adhesion.
Surface Tension Is a Force
Surface tension would at first give the impression that an actual film or skin were stretched over the surface of the liquid. In reality, the needle is supported by a force and not by the water itself. This is proved when the needle sinks— the water cannot hold it up.
There exists between the molecules of any body an attraction which holds them together. At the surface of a body of water, the top layer of molecules lacks an attraction from the outside. This lack is compensated by a greater attraction from below and from the sides. Thus a horizontal stretching is produced — called surface tension.
This force can be readily upset by bringing about an attraction from above so that the attraction of the top layer of molecules will be m#re nearly equal in all directions.
Now, water molecules are attracted by iron; consequently a clean needle becomes wet if brought into contact with the water. But water molecules are not attracted by grease; and so a greasy needle does not become wet—which means that a tiny film of air remains around the needle; and the molecules in the top layer of water are still attracted in a horizontal direction (surface tension) so that the needle cannot sink.
Sulphides are not readily wet by water. If crushed into finely divided particles, they tend to float because of surface tension. Gangue, on the other hand, is easily wet by water; consequently it sinks. This may be termed film flotation as distinguished from the newer and far more efficient bubble method known as froth flotation.
A Bubble Bursts by Crushing Itself
Consider the surface tension of a
bubble. Surface tension, as just described, applies to a level water surface. The surface of a quiet body of water is always level since the tendency is to reduce the area to a minimum. The same holds good in the case of rain drops and bubbles. A drop of water falling through the air becomes spherical since the sphere is the figure of least surface for a given volume. A bubble also assumes the spherical form for the same reason. It would at first seem that some interior force causes the bubble to burst or explode. This is not so, if the prevailing theories are correct. It is believed that the surface tension acts like a rubber skin over a bubble, constantly exerting an inward pressure which finally results in the collapse of the bubble. If now we reduce this tension, the bubble will exist much longer. For this purpose, oil is added to the water containing the sulphides and gangue, but in very small quantity.
was an earlier process using as much as three tons of oil to a ton of ore. In 1898, F. E. Elmore invented the so-called bulk-oil
Increasing the Lifting Power of Bubbles with Oil
process. Strictly speaking, it was not a flotative process at all, the object being to recover the sulphides by using a very large quantity of heavy oil. The buoyancy of the oil was the sole agent in floating the metals. Sulphides, being wetted by sufficient oil to overcome the effect of specific gravity, traveled upward into the oil layer, and were consequently floated.
How the Army of Bubbles Work
In the froth flotation process only the faintest trace of oil is used. Briefly, the ore pulp, consisting of finely-ground ore particles suspended in a large quantity of water, is brought into contact with a minute quantity of oil. Through agitation, countless tiny bubbles are formed which carry the mineral particles to the surface with them, forming a dense froth several inches in thickness. The gangue sinks and is allowed to go to waste.
Injecting bubbles into the liq u i d by means of compressed air has been tried generally with less success than when the bubbles are formed within the
liquid itself by violent stirring. The effectiveness of the two methods depends upon the physical characteristics of the ore.
Even when the mineral-laden bubbles reach the surface and burst, the metal particles are not allowed to sink because the bubbles directly underneath continue to buoy them up.
The floating of sulphides is greatly assisted by adsorption, which may be briefly defined as the tendency of gases or dissolved substances to cling to the surfaces of solid bodies. This results in a relatively high concentration of the gas or solution at the place of contact. The tiny particles of gas attach themselves to the solid particles, like barnacles to the hull of a boat. This film of gas surrounding the ore particles does not, of itself, possess sufficient buoyancy to raise the heavy mineral. But when it coalesces, or combines, with a few of the surrounding bubbles, the weight of the mineral is more than offset by the lifting power of the bubbles, and it comes to the surface. In
this way, the bubbles “lay to” and together boost an ore particle to the top.
Carrie Everson’s Contribution
Adsorption was first applied by Carrie Everson, who is regarded as the mother of ore flotation, though she never received any material reward for her discoveries. She added the use of acid to the processes already developed by her predecessors. In her process, the acid, by combining with the metal, was thought to liberate gas which attacked the ore particles and buoyed them up. As a matter of fact, the acid gives the sulphides a clear surface to which the oil will adhere. When left standing, the ores often become oxidized and thus hinder the action of oil in concentration.
For years, a story has been told of the accidental discovery of flotation. A Miss Carrie Everson, a sister of an assayer located in Denver, while washing some dirty sacks, in which concentrate had been sent to her brother, realized that the grease and ore particles floated on the water,
and subsequently patented her discovery. So the story ran. Romantic, indeed— but, like many another tale of the beginning of some great enterprise, it lacked the verification of fact. In reality, Mrs. Everson was the wife of a doctor. She was a good chemist and her discoveries were the result of. laborious experimentation.
Potter and Delprat, though working independently, devised a method also involving the use of gas in adsorption. During the next few years, the names of Froment, Cattermole, Wolf, Elmore, De Bavay, McQuiston and Bradford came into prominence through their efforts in improving upon the earlier methods of ore concentration by flotation.
But not until Sulman, Pickard and Ballot had conjointly rubbed the miner’s lamp which evolved modern froth flotation, did the colossal outlines of this djinn of mining appear in its true significance.
These men were experimenting with the Cattermole process which used oil in the proportion of from forty to one hundred and twenty pounds per ton of ore. The oily metallic particles collected in clusters and then sank from sheer weight.
The gangue was forced upward by streams of water and floated off.
These men decided to see what would happen if the quantity of oil was reduced gradually to the vanishing point.
As the percentage of oil was diminished, the results became less and less satisfactory, until the process failed to work at all. Then to the amazement of the experimenters, upon stopping the agitation, myriads of glistening, dancing bubbles came surging along the surface of the liquid, crowding each other in their effort to reach the top with their precious cargo of mineral wealth. The oil had
entirely disappeared from sight and touch. Investigation revealed the presence of the oil on the metal particles in a very thin film. The bubbles were extremely small and persisted longer.
At Broken Hill, Australia, where the experiments were performed under the supervision of Sulman, Pickard and Ballot, there had accumulated about 12,000,000 tons of ore from which the metals could not be recovered by the ordinary methods. The weight of gangue equalled that of the zinc and lead minerals present. Therefore, separation by gravitation methods was out of the question. While the Cattermole process would recover a reasonably large percentage of these metals, the newly discovered froth method gave unlooked-for success, and has been widely used ever since.
Is the Wind Right for Gas? Look At the Trench Weather Vane
THERE are weather vanes galore in the trenches and throughout the fighting area. Many of them are ornamental in design and plainly testify to the skilful fingers and artistic temperament of some of the boys. The one shown in the accompanying illustration was made by a Canadian soldier out of odds and ends of metal. It represents a cyclist and answers to the slightest breath of wind.
It is vitally important that the soldier know in what direction the wind is blowing or is likely to blow; for if it is coming from over the enemy’s camp there is danger of a gas attack, and when the gas starts over, he has only from twenty to forty seconds in which to adjust his gas mask.
The Stormy Weather Hat—It Protects the Ears and Neck
EAR muffs are clumsy, and for this reason they have always been unpopular, even among those compelled by their outdoor occupation to wear them in bitter weather. So Henry Vaughan, of Montreal, Canada, has invented a hat with a soft woolen flap
attached to the sweatband. This does away with the necessity for the ear muffs. The woolen flap fits up
into the crown of the hat when not in use; but when the wind is blowing a gale or when the snow flies, the wearer of the hat pulls down the flap and tucks it into his upturned coat-collar.
Yesterday, Invincible—To day, Useless
/\R M O R E D automoJi \ biles and motorcycle machine-guns are following closely upon the heels of cavalry in the present war; they are speedily going into disuse. There was a time when much was expected from these swift-darting steel forts, for theory had indicated that no infantry would be capable of stopping their advance. Could not these cars break through the enemy’s lines on the open field and through the enemy’s advance guard while reconnoitering? An interesting question—but the amount of real open field fighting and of land reconnoitering in this war has been practically nil. The important fighting
has taken place not on the smooth ground, but on ground chopped up with networks
of deep trenches. Since ordinary automobiles and motorcycles could hardly charge across these lands, no additional
equipment of this kind will be made for the United States Army. During Pershing's campaign in Mexico, the motorcycle played an important part as a trustworthy vehicle for despatch riders. In addition to this duty, however, there were several motorcycles equipped with machine guns. Plans to organize a company of motorcycle is shaped machine gun operators neck and were never carried out. the ears
One Movement, and Up Goes This Sturdy, Collapsible Ironing Board
A SINGLE action suffices to set up or to fold a new type of ironing board, all parts of which are securely screwed or hinged together so that they cannot become separated. In setting up the board, the hinged central support is swung downward, requiring but one movement of the hand. Although the board is light and folds up compactly, it is firm and rigid when in use. A size smaller than that illustrated is made to fit into the modern housewife’s kitchenette. When not in use the board may be hung up on a hook, the flat end first. This is done so as to prevent the supports from falling down.