Flotation recovery of monazite from kaolinite using sodium oleate collector: Understanding mineral–collector interaction

Recently, the flotation of major rare earth elements (REE) minerals including bastnasite, monazite, and xenotime has been attracting high level of attention. However, there are numerous challenges associated with achieving selective recovery of REE minerals from different gangue minerals. Paramount among the challenges is the abundance of fine clay and silicate gangue minerals in complex low grade REE bearing ores. These gangue minerals are usually recovered along with REE minerals, which can result in concentrate grade dilution. In this study, laboratory microflotation tests, coupled with physicochemical characterization techniques including zeta potential and X-ray photoelectron spectroscopy (XPS) analyses were conducted on monazite and kaolinite using sodium oleate as a collector. Microflotation experiments established that the floatability of monazite is high at pH 5–9, where kaolinite had lower flotation response. Complementary zeta potential and XPS measurements revealed that at pH 9, sodium oleate adsorbs onto monazite surfaces via hydroxylated REE ions and the adsorbed oleate contributes oxygen atoms to the metaphosphate components on monazite surfaces, leading to the chemical bonding between oleate and monazite surfaces, whiles there was marginal/negligible interaction between oleate and kaolinite. The findings from this study demonstrate distinct differences in the flotation characteristics of monazite and kaolinite. The selective adsorption of oleate ions onto monazite surface was responsible for the distinct flotation response identified at alkaline pulp pH conditions. The learnings from this work indicate that kaolinite is not likely to be recovered via true flotation, at the conditions applied in this study, thus monazite can be separated from kaolinite when using sodium oleate as a collector.