Circular 106—Selective flotation of molybdenite from chalcopyrite concentrates by potassium permanganate

By S. J. Escalera and R. B. Bhappu, 1970, 15 pp., 6 figs.

The effectiveness of potassium permanganate, compared to conventional oxidants used in flotation of molybdenite from copper concentrates, is affected by reagent concentration, pH, temperature, and conditioning time. Each has advantages and disadvantages. It is well known that potassium permanganate has excellent oxidizing characteristics in flotation systems. The exact mechanism by which the permanganate performs its useful functions in the process has been the subject of recent studies at the New Mexico Bureau of Mines and Mineral Resources.

Treatment of collector-coated flotation concentrates with KMnO₄ oxidizes the organic constituents of the adsorbed layer on the mineral surface and renders the floated particles nonfloatable. In addition to its tendency to oxidize selectively, permanganate, when chemically reduced, also forms a hydrous manganese oxide that may precipitate on the surfaces of certain components of the concentrate, thereby serving further to depress the floatability of these components.

The theoretical aspects of sulfide depression by permanganate oxidation have been discussed and this study investigated the oxidizing characteristics of permanganate on actual flotation-plant concentrates by comparing it with two other oxidizers used in the selective flotation of molybdenite. The oxidizing characteristics of potassium permanganate as compared to those of the conventional oxidants H₂O₂ and NaClO in the selective flotation of molybdenite from flotation-plant bulk copper concentrates have been investigated. The study shows that the effectiveness of these reagents in the depression of copper sulfide minerals is affected by reagent concentration, pH, temperature, and conditioning time.

Xanthate-coated copper sulfide minerals are depressed through the oxidation of xanthate ions into dixanthogen. All three oxidants require high concentrations to obtain even moderate depression initially. Potassium permanganate shows improved depression at higher concentrations, whereas the others do not, possibly because of the formation of a mineral surface coating by colloidal MnO2 that inhibits any further xanthate action.

All reagents are most effective at pH 6.5 and appear to decompose at higher and lower pH values, with the exception of permanganate which is stable at high pH values. Optimum temperature for depression is different for each oxidant. Conditioning time is critical for the action of permanganate; its depression effectiveness decreasing rapidly after 10 minutes of conditioning, but H₂O₂ and NaClO show increasing depression with increasing conditioning time.