Towards ambient pressure leaching of boehmite through mechanical activation

• Enhancement of boehmite reactivity through mechanical activation (MA).
• Activation energy for alkali dissolution of boehmite decreases with the extent of MA.
• Shows feasibility of boehmite dissolution in NaOH solution at atmospheric pressure.
• MA has larger influence on dissolution than rise in leaching temperature.
• An attempt to separate the effect of MA and surface area.

This paper explores the possibility of manoeuvring the reactivity of boehmite through mechanical activation (MA) for enhancing the solid/liquid reaction between boehmite and NaOH. Synthetic boehmite, prepared by thermal dehydroxylation of gibbsite, used in this study has been characterised by a large specific surface area (~ 264 m2/g). A planetary mill has been used for MA. Boehmite dissolution during caustic leaching (temperature: 70–90 °C, Na2O concentration: 180 g/l) has been found to increase with the extent of MA. Energy accumulated in the solid (boehmite) structure makes its dissolution in aqueous phase easy. Significantly high dissolution (~ 23 g of boehmite in 210 ml of 180 g/l Na2O solution) has been achieved at atmospheric pressure condition (90 °C) for 240 min milled sample. Kinetic analysis of the leaching data of boehmite milled for different durations (up to 240 min) has shown that the value of apparent activation energy for boehmite dissolution decreases with the extent of MA. Analysis of the results shows that MA has larger influence on dissolution than rise in leaching temperature. An attempt has been made to separate the effect MA from that of surface area.