Experimental study and mathematical modelling of red mud leaching: application of Bayesian techniques

This study presents the mathematical modelling and estimates the kinetic parameters of red mud leaching using the Markov chain Monte Carlo method with the Metropolis-Hastings algorithm. The red mud used in this study comes from the Amazon region in Brazil and was characterised and leached with 20 and 30% (v/v) sulphuric acid at 60, 80 and 90 oC through calcined and uncalcined hydrometallurgical routes. During leaching, samples were collected every 30 min and centrifuged to separate the leachate from the concentrate. The mathematical model for the leaching kinetics of red mud is a system of coupled differential equations and was based on the shrinking core model. The maximum iron and aluminium oxides leached averaged 96 and 91%, respectively, while the maximum recovery of titanium in the sulphuric acid solution has not exceeded 26%. The leaching kinetics of iron, titanium and aluminium oxides had average reaction order values of 1.52, 2.96 and 2.05, respectively. The activation energy values ranged from 64 to 176 kJ/mol. The proposed mathematical model was properly validated, enabling its application in other leaching processes and in the estimation of the kinetic parameters of other chemical elements present in the red mud.