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Show The Story of Milling, and Smelting at Midvale : t - ' ft -l )' - k f t f fit f'"' ;-t -b I I v ? , . " -i Flotation is the process of separating the "wheat from the chaff", that Is the valuable minerals from the waste In the Midvale, Utah mill of the United States Smelting Refining and Mining Company batteries' bat-teries' of flotation cells perform this interesting process of lifting the heavier minerals to the surface and leaving the lighter material at the bottom. ly approximately 65 of the ore pulp will pass through a wire mesh screen having 40,000 openings to the square inch. This fine pulp reaches the flotation flota-tion machines where with certain reagents added the lead minerals float while the other minerals sink. The lead float (concentrate) is skimmed off the surface of the flotation cells and the residue, after addition of other chemicals goes to the zinc flotation machines where the zinc mineral floats and is skimmed off as zinc concentrate. Other concentrates of lesser importance im-portance are made as circumstances warrant although it is never pos- N (Editor's Note: This is the third of Berk's of five articles on the story of milling mill-ing and smelting of lead-zinc ore at llidvale.) The previous article of this series mentioned the importance of the discovery and application of the flotation process for the recovery of zinc, previously a penalty element ele-ment In lead-zinc sulphide ores. There is romance in the evolution evolu-tion of flotation. It was common knowledge that substances heavier than water would, under certain suitable conditions, float on the wa ter's surface, for example, a greased or dry needle carefully placed on water. It has been known tor years 1 that some heavy- substances wil float with more certainly thar others. It Is reported that aboul 1SS5- Carrie J. Everson. a westerr ladv school teacher, assisting in hei brother's Denver assay oitice, dis covered the main principles ot which all subsequent flotation worl has been based. She had placet some greasy concentrate sacks ii the wash tub and with the washini (ore bags are rarely, if ever, washet by men) the germ of the idea of oi flotation came under her observa tion. Modern flotation is a concentrat (THE Ft ing process utilizing the buoyancy of air bubbles in water to "float" mineral particles. Certain reagents or "Frothers" are used to strengthen strength-en the bubbles thus forming a strong and persistent froth similiar to soap suds. Other reagents known as "Collectors" and "Modifiers" are ' used to condition the mineral particles par-ticles so that they will or will not . adhere to the air bubbles. This permits selectivity in the flotation . of one or more minerals from the ! mixture of minerals as they occur . in natural ore. I The ore from the company mines i and custom shippers, received at ! Midvale Plant of United States 1 Smelting Refining and Mining com-i com-i pany is weighed in railroad cars t and then goes to the sampling de-l de-l partment where an accurate and r representative small sample is automatically taken. The sample l thus taken is ground to fine powder r. and one part of the sample goes to 1 the shipper. Midvale assay of melal l content determines whether the ore ? goes to the flotation mill or direct 1 to the smelter. 1 After weighing and sampling the ore for the flotation mill it is sent through a scries of crushing, grind-:- ing and recrinding units until linal- 3L-RTH OF THESE ARTICLES WILL APPE sible to recover all the minerals in an ore. As in the case of the floating float-ing needle having a dry or greased surface, particles of ore attach themselves to air bubbles even below be-low the surface of the water as these bubbles are forced through the flotation machine cells along with the chemicals. The flotation concentrates are dewatered in 50-foot thickeners and most of the remaining water is then removed in filters, after which the lead concentrate is transported to the lead smelter and the zinc concentrate con-centrate shipped to a zinc plant. AR SOONJ |