Leaching behaviour of high surface area synthetic boehmite in NaOH solution

Abstract

This study pertains to alkali leaching of a high surface area synthetic boehmite prepared by thermal decomposition of gibbsite. Synthesised boehmite particles are found to be agglomerates of platelets. These particles are characterised by a monomodal size distribution with a median size of 110μm and high specific surface area (~264m2/g). Leaching studies, in the temperature range 70 to 90°C, have been carried out in NaOH solutions of Na2O concentration, CNa2O=100 and 180g/l. Significant dissolution of this boehmite is seen to occur in NaOH solutions, unlike in many other studies, owing to the high surface area. Both alkali concentration and temperature have influenced the dissolution. Reduced time plot analysis indicates that the shrinking core with surface reaction model (R3) describes the initial stages of the dissolution process reasonably well. Particle size analysis data complemented the results of the reduced time analysis. The value of apparent activation energy for the initial stages of dissolution is evaluated to be around 65kJ/mol.Deviation from shrinking core model R3 is observed in the later stages. Besides the shrinking of size due to dissolution, particle size reduction is also identified due to the detachment of platelets from the agglomerates of particles. Detailed characterisation of the leach residues involving morphological and particle size analyses has established such detachment of platelets and ensuing particle size reduction. Deviation from shrinking core model in the later stages of leaching has been attributed to particle fragmentation arising from platelet separation.