Depressant-free selective flotation separation of bastnaesite and monazite enabled by mineral phase transformation

A method for separating bastnaesite and monazite without inhibitor was proposed. • MPT distinctly modifies the surface properties of bastnaesite and monazite. • Bastnaesite and monazite exhibit significantly different flotation behaviors after MPT treatment. • An optimal MPT condition (700 °C for 10  min) was identified for effective separation. • Ce 4+ /Ce 3+ on Ce 7 O 12 surface is chemically adsorbed with –C NOH group of BHA. This study proposes a selective mineral phase transformation (MPT) pretreatment enhanced micro-flotation method. By optimizing the MPT conditions, the selectivity of benzo hydroxamic acid (BHA) toward the MPT products of bastnaesite is improved, enabling efficient separation of bastnaesite and monazite at the source. This approach enables diversion metallurgy and may reduce the environmental pollution caused by high-temperature concentrated sulfuric acid roasting of mixed rare earth concentrates. The results indicate that during the MPT process, an oxidizing thermal pretreatment conducted in air at the optimized condition of 700 °C for 10  min, bastnaesite (CeCO 3 F) was primarily transformed into Ce 7 O 12 , with cracks and pores appearing on particle surfaces and a significantly increased specific surface area compared with the raw ore, whereas monazite (CePO 4 ) exhibited neither significant phase changes nor structural damage. In subsequent micro-flotation experiments with BHA as the collector, the two minerals exhibited distinct flotation behaviors under identical pH conditions. At pH 5.00, the recovery of Ce 7 O 12 was significantly higher than that of CePO 4 . The artificial mixed ore experiments resulted in a Ce 7 O 12 foam product with a REO grade of 70.74 % and a recovery of 96.39 %, and a monazite tank product with a REO grade of 49.46 % and a recovery of 75.52 %. Remarkably, these separations were achieved without the addition of any depressants. Mechanistic analysis revealed that after MPT treatment, more Ce 4+ was exposed on the Ce 7 O 12 surface, which competed with Ce 3+ for adsorption and preferentially underwent chemical adsorption with the oxime group (–C NOH) of BHA to form Ce-O chelate complexes. In contrast, the interaction between CePO 4 and BHA was weak, thereby enabling efficient flotation separation of Ce 7 O 12 and CePO 4 . Download: Download high-res image (289KB) Download: Download full-size image