| Bastnaesite, a rare earth fluocarbonate is the main mineral constituent of the Mountain Pass rare-earth deposits in San Bernardino, California. The present milling process being used at this plant involves froth flotation of bastnaesite from the associated gangue minerals (calcite and barite) with a mixture of tall oil and lignin sulfonate at elevated temperatures. This research work is concerned with an investigation of the related flotation chemistry of bastnaesite ore minerals through Hallimond tube and Denver cell flotation tests together with the adsorption and electrokinetic studies. The synthesis and the surface-chemical characterization of the mineral bastnaesite is also a part of this work.;The preliminary studies and laboratory scale flotation tests on the bastnaesite ore indicate that alkyl hydroxamates are very promising collectors for the beneficiation of ores such as those that occur at Mountain Pass. The adsorption studies of the synthesized potassium hydroxamate collector correlate very well with the observed trends in flotation behavior of these minerals. It is postulated that the primary mechanism of chemisorption in this system is by way of the dissolution of cations, formation of respective hydroxy-complexes and readsorption at the interface, thus providing the sites for the adsorption of hydroxamate. Standard free energies, enthalpies and entropies have been calculated for the adsorption reaction, which confirm the suggested mechanism and is in agreement with other flotation results.;Electrokinetic investigations of bastnaesite, barite and calcite in the presence of added flotation reagents revealed that under flotation conditions in the plant, calcite is positively charged, bastnaesite negatively charged whereas barite surface is being converted into barium carbonate. The addition of soda ash and lignin sulfonate depressant is, though, crucial in controlling flotation, the selective adsorption of chemisorbing fatty acids (tall oil) at high temperatures is the key to successful beneficiation of this ore. The role of these reagents and the effect of temperature on flotation has been investigated in detail. |
