A comprehensive study of the electrochemistry and floatability of pyrite in coal flotation

Pyrite (FeS;To better understand self-induced hydrophobicity of pyrite, chronoamperometry and voltammetry on freshly fractured electrodes were used to explore incipient oxidation and reduction of the mineral. Voltammetry on rotating ring-disc electrodes (RRDE) was carried out to provide information on soluble species and kinetics of oxidation and reduction processes. X-ray photoelectron spectroscopy (XPS) was used for chemical identification of oxidation products. Galvanic coupling with sacrificial anodes was investigated as a practical method to cathodically protect pyrite and prevent its oxidation. Microflotation tests were conducted under controlled potentials at different solution pH's, and the results were correlated with electrochemical studies. The feasibility of improving pyrite rejection by controlling its surface chemistry was tested in flotation experiments conducted with a 2"-diameter microbubble flotation column and a conventional 5-liter Denver flotation cell.;Effects of froth stability on the microbubble flotation of coal were studied with an objective of minimizing hydraulic entrainment of pyrite. The operating parameters were systematically varied to study their effects on water recovery which was used as a measure of froth stability. It has been demonstrated that the upgrading of coal in a flotation column can be significantly improved when froth stability is properly controlled.;In an attempt to enhance the rejection of pyrite in middlings, various column circuits were experimentally examined and theoretically analyzed. The effect of circuit configuration on the overall circuit performance was evaluated by separation efficiency and separation curves. It has been shown that the overall separation efficiency of column flotation is rather insensitive to circuitry due to the unique characteristics of the unit flotation column, i.e., the addition of the wash water into the froth.