Kinetics of aluminium leaching from coal fly ash by sulphuric acid

Abstract

The extraction of aluminium from coal fly ash (CFA) is an important industrial process and has produced commercial interest. However, the leaching kinetics of aluminium has received little attention. This work, therefore, addresses the leaching kinetics of aluminium from fly ash in sulphuric acid. A shrinking core model has been used to investigate aluminium extraction kinetics and its results are presented. The effects of leaching time, solid to liquid ratios and reaction temperature on aluminium extraction rate are studied. The process optimization reveals that the extraction rate can reach up to 68.68% when the fly ash reacts with sulphuric acid at a 1:3 solid to liquid ratios of fly ash / H₂SO₄ (100 g / 300 mL) at 220°C for 4 hour reaction time. The sulphuric acid concentration was maintained constant at 18 M. The leaching rate increases with increasing temperature and solid to liquid ratios. The leaching kinetics indicates that chemical reaction at the surface of the particles is the rate-controlling process during the reaction. The shrinking core model enabled the determination of activation energy of about 60.85 kJ/mol, which is likely to be a consequence of the chemical reaction at the surface of the particles.