Characterisation and surface reactions of iron oxides and fluorapatite in aqueous suspensions

Sammanfattning: The final objective of this study is to produce chemical models of flotation- like systems, including oxidation products of magnetite (maghemite and hematite) together with apatite. This is started by investigating the acid base properties, surface complexation and surface characteristics of the systems hematite-H+ and maghemite-H+ (paper I), fluorapatite-OH- (paper II) and a mixed system of maghemite-fluorapatite-OH- (paper III). Synthetic minerals were prepared and characterised with BET, SEM, XRD, FT-IR and FT- Raman. The acid base properties were investigated using high precision emf potentiometric titrations and z-potential measurements. Titration data were interpreted using models based on the theory of surface complexation, assuming the formation of surface complexes with charge dependent formation constants. The constant capacitance model was applied to interpret titration data for all three systems. The obtained models will contribute to a better understanding of the reactions during the apatite/magnetite separation by flotation. The surface site density Ns (sites/nm2) for maghemite was found to be very low compared to other iron oxides. The mixed system of maghemite and fluorapatite was interpreted with two different models. FT-Raman together with the Ns (sites/nm2) value reveals that interactions occurred between the fluorapatite and maghemite particles in the system. These interactions have to be chemical or sterical, because both surfaces are negatively charged in the actual pH-range.