1. Field of the Invention
The invention relates to an improved method for recovering phosphate rock from ores by froth flotation means. More particularly it relates to more efficiently beneficiating phosphate ores by reducing the pH of the feed slurry after conditioning and before flotation.
2. Summary of Prior Practices
Flotation is a step used in separating mineral values from their gangue or from another valuable component. Ores, such as phosphate ores, are generally separated by froth flotation, in which frothing is achieved by introducing air into finely divided ore and water containing a frothing agent. Those mineral strongly attracted to air bubbles rise to the surface in the froth, thereby allowing convenient separation. For froth flotation to work, the feed particles must be the correct size to be frothed away.
With respect to the preferred phosphate ore, apatite is the name applied to any of a group of calcium phosphate minerals containing other elements or radicals (as fluoride, chlorine, hydroxl, or carbonate), having the approximate general formula Ca.sub.5 (F, Cl, OH, 1/2CO.sub.3) (PO.sub.4).sub.3, and occurring variously as hexagonal crystals, as granular masses, or in fine-grained often impure masses as the chief constituent of phosphate rock and of most or all bones and teeth. Exemplary apatites include fluoroapatite, carbonate apatite, chlorapatite and hydroxyl apatite.
The mineral occurs in the United States mainly in the form of the calcium phosphate ores that are referred to generically as phosphate rock. Phosphate rock is rock that consists of calcium phosphate largely in the form of apatite or carbonate apatite, usually together with calcium carbonate and other minerals, is useful in fertilizers and is a source of phosphorus compounds. It occurs in large beds in the southeastern U.S. and in extensive deposits in Arkansas and the northwestern U.S.