Mechanical Activation of Gibbsite and Boehmite: New Findings and their Implications

Almost the entire metallurgical grade alumina is produced from bauxite using the Bayer process. The leaching conditions in Bayer process depend on various Al-oxyhydroxide minerals/phases present in the bauxite. Among the various bauxite types, gibbsitic (trihydrate) bauxite is easiest to digest. Monohydrate (boehmitic and diasporic) bauxites need more stringent digestion conditions in terms of temperature, pressure and alkali concentration. Mechanical activation during milling, especially high energy milling, results in enhanced reactivity of solids due to physicochemical changes induced by milling. This paper is an overview of our recent research on mechanical activation of bauxite and its constituent phases, gibbsite and boehmite. This paper focuses on the leaching of mechanically activated bauxite ores. Complementary results on mechanical activation of gibbsite and boehmite phases are included for a deeper understanding of mechanical activation of bauxite. Implications of these results are highlighted in the context of the Bayer process.