Investigation of Sensor-Based sorting and selective comminution for pre-concentration of an unusual parisite-rich REE ore, South Namxe, Vietnam

Abstract

The South Namxe deposit in Vietnam contains unusually high quantities of parisite, in addition to minor quantities of other fluorocarbonates, such as synchysite and bastnaesite. Together these minerals constitute the main REE-bearing minerals. This carbonatite-related deposit presents tabular (dykes) or lens-form ore bodies, up to several tens of meters wide and tens to hundreds of meters in length, that are hosted in Permian limestone and Triassic basalts. The main gangue minerals in the ore bodies are from the barite-celestine solid solution series, ankerite and calcite. It was considered necessary to assess the different grain characteristics presented by the presence of parisite intergrowths and its association with minerals of the barite-celestine solid solution series to structure a probable initial beneficiation strategy. Mineral liberation analysis revealed that an optimal liberation particle size between 45 µm and 90 µm could be achieved without overgrinding the material. Additionally, it showed a strong mineral association between fluorocarbonates, baryto-celestine, and calcite. Grinding below 100 µm is necessary. One substantial energy saving potential is removing the host rock prior to grinding. The potential for pre-concentration with sensor-based sorting and selective comminution is investigated in a pre-study. Sensor-based sorting using X-ray transmission resulted in an enrichment of REE by a factor of 4, a reduction of the mass stream down to approximately 30%, and a loss of rare earths below 2%. Selective comminution using a pin mill, at a circumferential speed of 20 m/s, yielded a recovery of 96.5% of REE minerals and allowed rejection of 27% of barren material. This shows that both selective comminution and sensor-based sorting can be considered as complementary beneficiation steps when processing these REE ores.