Page:Popular Science Monthly Volume 92.djvu/102

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��Popular Science Monthly

���Froth Flotation Saves Vast Quantities of Base Metals Formerly Wasted

��M>Tiads of glistening, dancing bubbles come surg- ing along the surface of the liciuid, crowding each other in their effort to reach the top with their precious cargo of mineral wealth. When Sulman, Pickard and Ballot discovered the froth process

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 surround- ing 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

��now in use, there was at Broken Hill, Australia, a 12,000,000-ton hill of ore which could not be re- covered by ordinary methods. This ore was saved. When this issue reaches you, approximately 40,000,000 tons will have been treated since January 1917

this way, the bubbles "lay to" and to- gether 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 con- centration.

For years, a story has been told of the accidental discovery of flotation. A Miss Carrie Everson, a sister of an assayer loca- ted 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.

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