| Gravity separation and flotation studies have been conducted on Molycorp bastnaesite ore in order to determine if new beneficiation schemes present a more selective and more economical alternative than that which is currently employed at Mountain Pass. Literature on bastnaesite, monazite, barite, and calcite flotation and gravity concentration principles was surveyed. Flotation reagent additions were determined using components that have shown preferential floatability of bastnaesite and monazite over the gangue minerals. Hallimond Tube microflotation tests were performed on crushed and ground ore samples. Heavy liquid separation with sodium polytungstate was used to investigate the effectiveness of gravity separation on the ore. Shaking table and Falcon concentrator tests were performed to gravity concentrate the ore. A gravity-concentrated feed was floated and compared with a non-concentrated ore feed to illustrate the benefit of preconcentration. An economic analysis was generated for flotation plants operating with and without gravity preconcentration that would sell products with two distinct grades and recoveries.;Qualitative microflotation tests produced little selective separation of the rare earth minerals (bastnaesite, parisite, and monazite) from the gangue (calcite, barite, dolomite, and quartz). Heavy liquid tests illustrated the sink/float behavior of the minerals at different specific gravities of separation. Their results suggest that at higher specific gravities the calcite floats while the bastnaesite and barite sink. Shaking table tests showed potential to effect such a separation, but optimum conditions were not determined. A Falcon centrifugal concentrator was used to carry out tests according to a Design of Experiments matrix generated with Stat Ease Design Expert 9. The best conditions from those trials were determined, and the tests were repeated to verify the desirability of those parameters. Bench flotation was then used to compare the standard feed at plant conditions to a feed consisting of the blended gravity concentrates. The flotation results showed that the preconcentrated feed outperformed the typical plant feed. Economic analysis of a plant with and without gravity preconcentration shows that gravity preconcentration, although more capital-intensive, will yield a higher annual profit and a better 10-year net present value. |
