Pyrite is removed from coal by a 2-stage froth flotation. In the 1st stage, coarse pyrite is removed as underflow in a conventional froth flotation operation. In the 2nd stage, the froth product from the 1st stage is subjected to froth flotation by using a coal flotation depressant and a pyrite flotation collector, thus removing most of the fine pyrite. Thus, 100 lb of coal containing ash 31.8, Total s 2.23 and pyritic s 1.70 pct was ground and floated at ph 6.2 By using potassium amyl xanthate 0.5, Pine oil 0.05, Aero depressant 633 1.0, and hcl 0.9 Lb/ton of coal. The underflow from the 1st flotation weighed 36.3 Lb and contained ash 68.1, Total s 3.4, And pyritic s 3.29 pct. The froth concentrate refuse from the 2nd stage weighed 3.4 Lb and contained ash 17.8, Total s 8.47, and pyritic s 7.71 pct. The clean coal, which is the underflow from the 2nd stage, weighed 60.3 Lb and contained ash 9.7, Total s 1.12, And pyritic s 0.56 pct.
U.S. Pat. 3,807,557; Apr. 30, 1974; Chem. Abstr. 81:39,676X