Leaching Kinetics of Lanthanide in Sulfuric Acid from Low Grade Bauxite

The utilization of low grade bauxite which was obtained from washing waste in bauxite mining from Madong, Indonesia, was investigated as a resource of the rare earth elements. In this study, the ores of low grade bauxite contained 39.6 ppm lanthanides, such as lanthanum (18.4 ppm), cerium (19.3 ppm), and yttrium (1.9 ppm) was leached by using 3 M sulfuric acid with the ratio of solid to liquid being 1 g/20 mL. The leaching process was measured at different temperatures and reaction time. The leaching kinetics was evaluated by shrinking core model where the leaching undergoes two stages; fast chemical reaction in early stage and slower leaching rate due to diffusion at later stage. The diffusion stage was found to be relatively more temperature-dependent the chemical reaction stage. The leaching results indicated that operating conditions at 60 °C and 3 M sulfuric acid would be efficiently leach and convert the lanthanides into their sulfuric salts with the fractional conversion as high as 0.67. The activation energy of the chemical reaction and diffusion stage was estimated to be 10.37 and 48.15 kJ/mol, respectively. This finding can potentially lead to the development of enhanced leaching processes of lanthanides from low grade bauxite.