The dephosphorization behaviour of malaysian monazite concentrates

Abstract

High temperature dephosphorization was performed to remove the phosphorous content in the Malaysian Monazite Concentrates (MMC) to enhance Thorium Dioxide (ThO2) recovery. Thermodynamic evaluation of dephosphorization of the rare earth element (REE) phosphates in the monazite was conducted in terms of Gibbs free energy and minimization study. The influence of temperature and MMC to carbon reductant molar ratio on the dephosphorization behavior was investigated between 1350-1450°C with 0.3 - 0.7 molar ratio. Standard central composite design with 32full factorial was used to develop the experimental design. The study was based on design of experiments (DOE) to examine the role of the process variables on the extent of phosphorous removal. The phases and morphology of the dephosphorized samples were analyzed by XRD and SEM/EDX. Results confirm the formation of REE namely CeO2 and phases of combined Ce, La and Th sub-oxides. DOE analysis based on weight loss validated by quantitative elemental analysis tests, indicated a high rate of dephosphorization at 1450°C at monazite to graphite molar ratio of 0.7.