Decomposition of xenotime concentrate using alkaline fusion method

In this study, Malaysian xenotime concentrate was decomposed using sodium hydroxide (NaOH) via alkaline fusion method for the recovery of rare earth elements (REEs), thorium (Th), uranium (U) and phosphates (PO₄). Overall process consisting of digestion via alkaline fusion followed by washing and filtration was performed to remove the soluble compound with the optimum experimental conditions including alkali to concentrates (A/C) weight ratio (1:2), fusion time (3h) and heating temperature (350℃). The extraction of rare earth elements and thorium was conducted by hydrochloric acid leaching, filtration and selective precipitation using 10% oxalic acid at pH-0.2 while the extraction of uranium was performed by other selective precipitation using 6% ammonium hydroxide solution at pH-8. The phases and elemental compositions of the studied samples were analyzed using X-ray Dispersive (XRD) and Energy Dispersive X-ray Fluorescence (ED-XRF). It was found that the alkaline fusion method allowed for the production of radioactive-free trisodium phosphate (TSP) from xenotime. The final results of the study showed that about 90% of REEs and more than 95% of Th was able to precipitate as rare earths oxalate. Uranium precipitation remained nearly complete (>95%) under rare earths hydroxide. The results indicated that the selective precipitations conducted using oxalic acid and ammonium hydroxide was able to separate Th from U in two separate precipitates. This paper will be highlighting the findings from a research project that is partly supported by IAEA Technical Cooperation Project MAL2007 and Coordinated Research Project T11006. (author)