The first successful application of this method in the United States was made by James M. Hyde, in the mill of the Butte & Superior Mining Company, at Butte, Montana, in 1911. This was followed immediately by a suit for infringement of patent brought by the Minerals Separation company, the British core Poration owning the Sulman and Picard patents. The litigation is still in progress, after a number of decisions of an indeterminate character, reflecting the lack of scientific knowl edge concerning the fundamental physical prin ciples involved in the process. It is even doubt ful whether oil is necessary, for experiments have been made indicating that plain sea-water, without an addition-agent, will produce a min eral-bearing froth adequate for the concentra tion of chalcopyrite in the presence of pyrite and pyrrhotite. This calls to mind the fact that flotation can be made preferential as between minerals by creating conditions that affect some and not others. For example, lead sulphide can be separated from zinc sulphide by a super. ficial oxidation of the lead in a roasting-furnace without affecting the zinc, so that the latter is amenable to flotation, whereas the former be comes refractory.
The cost of operation can be given only in general terms; suffice it to say that the proc ess usually requires no new methods of crush ing or of preliminary treatment, but it does demand finer reduction of the ore, say, to 80 mesh. Flotation machines are relatively simple and inexpensive, costing about $8 to $12 per ton for a capacity of 200 tons.daily and $4 to $6 per ton for a capacity of 5,000 tons daily. The cost of operating them, including labor, power, and reagents, is about 10 to 15 cents per ton for a 500-ton plant. The oils used are classified as °frothers° and The selection of them is empirical. Products of distillation from wood and from coal are used; also petroleum products. The creosotes and
kerosene-acid sludge are connnon .agents for f roth-flotation.
The process is applicable to a remarkable variety of ores, including those of copper, lead, and zinc, as well as those of gold and silver. Apparently minerals having a high metallic lustre are particularly amenable. This includes most of the sulphides of the useful metals and excludes most of their oxides; indeed the presence of oxidized material in the copper ores now being treated is the principal reason for a relatively low recovery, say, 70 per cent, as against the high recovery, say, 90 to 95 per cent, on clean copper sulphides. However, methods for treating the oxidized ores of cop per and of lead have been devised, and have been tried on a working scale. The most prom ising of these are based upon the sulphidizing, or coating of the oxides with a film of arti ficial sulphide, so as to present a surface suit able for flotation. Hydrogen sulphide is used for this purpose; or the sulphides of calcium and sodium; also sulphur in various combina tions. As yet, a sodium sulphide, in 1 per cent solution, has given the best results on oxidized lead ore. The process has an application as much wider than that of cyanidation as cyanida tion was more comprehensive than chlorination. About 30,000,000 tons of ore are being treated annually by flotation in the United States, and as soon as the embargo of royalty or of liti gation is lifted from the process there should be an extension of its usefulness in this and in other countries. .
A large body of technical literature has grown around the subject during the last three years. The principal textbooks are Hoover, Theodore J., (Concentrating Ores by Flotation,' (1912) ; Rickard, T. A., The Flotation Process' (1916) ; Rickard, T. A., and Ralston, 0. C., (Flotation) (1917).