Kyanite is usually found with sulfide minerals such as sphalerite and pyrite. In the majority of plants, the ore is first deslimed to remove as much of the clay minerals as possible. The ore is then ground to the desired flotation particle size and the sulfide minerals are removed by flotation using AERO 400 promoter series or other suitable sulfide collectors like AERO XD-702 and AERO XD-700 promoters.
After removing the sulfide minerals, which in most cases are an undesirable commercial mineral, the pulp is placed in a conditioner and the pH depressed to 2.5 to 2.8 with sulfuric acid. AERO 853 promoter, a formulated petroleum sulfonate-based collector, is added at a dosage of 250 to 750 grams per tonne. The pulp is conditioned at 68 to 70 percent solids for five minutes. The conditioned pulp is then diluted with water to 25-30% solids and the kyanite is floated.
The AERO 853 promoter is much more selective than previously-used collectors for kyanite flotation. In one plant, a flotation feed containing 45-48% kyanite is producing a kyanite concentrate grade of 92-95% with a recovery of over 92%.
Iron minerals such as hematite and magnetite will be floated with the kyanite. In most cases, these are removed after flotation by magnetic separation.