Observations of the varied reactivity of xenotime and monazite in multiple systems

Abstract

In the present study, a comparison of the amenability of a monazite and xenotime (both rare earth phosphates) sample to treatment via alternative extraction techniques was conducted. Monazite and xenotime concentrates were studied under the effects of organic acids and mechanochemical pre-treatment. Maleic, tartaric, citric and oxalic acids have shown the ability to increase the dissolution of phosphorus in the monazite concentrate. Oxalic acid demonstrated to enhance the release of phosphorus (>30%) at pH < 1.3, room temperature up to 72 h (Lazo et al., 2017) as opposed to xenotime, which underwent very little dissolution under similar conditions (0.2 M, pH 2 for 24 h and 25 °C). Using mechanochemical activation prior to sulphuric acid leaching significantly increased the dissolution of rare earth elements (REEs), P and Fe in monazite (milled 300 RPM for 15 min) whereas in xenotime increased only slightly from a very low starting point. The difference in crystal structure and electronic configuration may play an important role in the more refractory nature of xenotime.