|
Flotation concentration of non-sulfide or nonmetallic minerals is generally more complicated and less efficient than that of sulfide minerals. Difficulties may be partially due to the fact that flotation of non-metallics is a relatively new field. However, the primary problem lies in the minerals themselves. The sulfide minerals are generally dense, well-defined crystals of definite chemical composition and they differ considerably from the gangue minerals.
The non-sulfides are often porous, poorly defined crystals of varying chemical composition and they are physically very nearly the same as the gangue. The last factor is important because it makes severance difficult in the grinding stage. “Over-grinding “ of a large part of the non-sulfide ore is therefore often necessary to obtain satisfactory mineral liberation.
The porosity of many non-sulfide minerals means large surface areas and therefore larger reagent consumption. Perhaps the greatest difficulty is caused by the wide variation in chemical composition. For example, one manganese plant treats an ore containing manganese carbonate (rhodo-chrosite) which when pure should contain 47.8% Mn and as such should make a high-grade concentrate. However, analysis of various crystals in this deposit revealed compositions ranging from manganous calcite to the pure rhodochrosite. Under these conditions, high recovery with good concentrate grade is, of course, not possible.
On the other hand, excellent metallurgical results may be obtainable if the separation to be made is between acidic (silicate) and basic (oxide or carbonate) minerals. These two types of minerals are floated with different collectors. The silicates are floated with the cationic collectors such as the long-chained amines; the oxides and carbonates are floated with the fatty acid (anionic-type) collectors. |
