EPR Spin-Labeling Techniques For Studying Binding To Mineral Surfaces

The U.S. Bureau of Mines has had an ongoing interest in developing new reagent schemes for floating Stillwater, MT, chromite ore. Previous reagent schemes have been unsuccessful in achieving complete separation, primarily because little is known about the surface chemistry of the minerals in this ore. In order to design a rational reagent scheme, a study of the binding of various functional groups (R = -H, -OH, -CO2H, -NH2) on the two components (chromite and forsterite) of the Stillwater chromite was undertaken. Electron Paramagnetic Resonance (EPR) Spectroscopy was used to determine the adsorption isotherm, from a cyclohexane solution, of spin-probes which contained the functional group of interest. This was complemented by studies of the saturation surface coverage of the spin probe on the two minerals. In each case, more sites existed on chromite than forsterite; however, the forsterite sites were more strongly binding for each functional group. The results are discussed in terms of their implications for flotation.