THE SURFACE-CHEMISTRY OF BASTNAESITE, BARITE AND CALCITE IN AQUEOUS CARBONATE SOLUTIONS

The surface chemistry of bastnaesite, barite and calcite in aqueous carbonate solutions was investigated to delineate the performance of a flotation scheme used for separating barite and calcite from bastnaesite. Sodium carbonate additions to suspensions of these minerals affect both the pH of the system and the zeta potential of the mineral. Significant pH and zeta potential changes, however, are mineral dependent and occur at different levels of added carbonate. They appear to be controlled by the solubility of the mineral in the case of bastnaesite and calcite, and by the formation of a new surface compound, namely barium carbonate, in the case of barite. The conditions for the onset of barium carbonate precipitation in barite suspensions containing fixed concentrations of added carbonate were determined from computations of barite-aqueous carbonate equilibria, and they closely correlate with the experimental results. Using soda ash as a pH modifier in the flotation beneficiation of a rare-earth ore containing barite can lead to carbonation of the barium sulfate surface, thereby causing this mineral to exhibit the flotation behavior of barium carbonate.