Technical processes for separating minerals by flotation

1 Until about 1919 the practice of flotation was conducted with much secrecy, and was on a semi-empirical basis. Since then the literature has become voluminous and in recent years the scientific principles underlying it have been fairly well elucidated. A long paper by Sulman (Trans. Inst. Min. and Met., 29,44-204 (1919)) gave the first comprehensive description of the froth-flotation process and showed the fundamental importance of the contact angle. The reader will find excellent text-books in Gaudin s Flotation (1932), Luyken and Bierbrauer s Flotation (1931), 

R being a hydrocarbon group and M a metal or other base, usually an alkali metal. They are used in exceedingly small amounts under the best conditions it may be unnecessary to use more than the amount needed 

Quite frequently the natural surface of a mineral requires preliminary chemical treatment before it will form the surface film required for collection One of the commonest instances of this is with sphalerite (zinc sulphide), which does not float properly when treated with xanthates. If, however, it is given a preliminary treatment with dilute copper sulphate solution, a very small amount of copper sulphide is deposited on the surface and the ore becomes floatable, the surface being now capable of reaction with xanthates. Such treatment is usually termed activation in general, an activating solution for a sulphide mineral should contain a metallic ion whose sulphide is less soluble than that contained in the mineral for zinc sulphides, silver, copper, mercury, cadmium, and lead salts are all effective activators. 

By the use of other reagents certain oxidized ores may be floated. For the oxides and carbonates of basic metals, fatty acids such as oleic, and soaps, are frequently useful. These no doubt form an oriented thin film of the soap of the heavy metal present in the mineral, by double decomposition with the surface layer the long hydrocarbon chain is probably oriented outwards. By special activation it is said that even quartz may be floated by the judicious use of soaps, if its surface is contaminated naturally or artificially with small amounts of heavy metals. There would appear to be a vast range of possibilities in the separation of complex minerals, by proper selection of reagents capable of modifying their surfaces. A detailed study of the flotation of various silicate minerals, with oleic acid, has been given by Patek.4 

In addition to collectors, frothers usually have to be added. The best 

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