Heavy-media separation for the concentration of Minerals

Abstract

Processes for the concentration of minerals including coals by separating the raw products into fractions of different specific gravity, have been operating for many years. The first heavy-medium process was patented in 1858 by Henry Bessemer who covered the use of dense solutions of chlorides of iron, calcium, magnesium, and barium as separating liquids in a cone-shaped separator. Incidentally, a saturated solution of calcium chloride is still used as the parting liquid in the Lessing and the Belknap processes, while in the Du Pont process, water insoluble chlorinated hydrocarbons of varying specific gravities and low viscosity, are used. Such processes, using dense liquids, did not, however, make much process owing to the difficulties and expense of maintaining the separation medium. In 1916, Chance took out the first patent covering the use of a suspension of solids in water for heavy-medium separation, but confined the practical application of his patent to the cleaning of coal, using a suspension of sand in water. His process is akin to hindered settling and the separation is not made truly by gravity difference. In 1928, De Vooys brought out a process using a suspension of barytes and clay as the medium for coal cleaning. Subsequently Tromp, Ridley, Dutch State Mines and others introduced similar types of process, all of which are being used for coal cleaning. Many attempts have been made to simulate a heavy liquid by using a suspension of finely divided solid in water, but the first attempt to produce a suspension with a high enough density for ore treatment was made by Weunsch in 1930. The work of Weunsch was further developed by Rakowsky and the American Zinc, Lead & Smelting Co. If the solid phase of such a suspension is ground fine enough, the suspension can be made stable or so slow setting that a substantially uniform specific-gravity can be maintained from top to bottom of the medium.