Leaching of Bauxite Residue with Mineral Acids

Aiming at the industrial scale development of a Scandium (Sc)-selective leaching process 14 of Bauxite Residue (BR), a sufficiently numerous set of process design aspects has been 15 investigated, by appropriate exploitation of available experimental data. The interpretation of 16 experimental data for Sc leaching yield, with sulfuric acid as the leaching solvent, has shown 17 significant impact from acid feed concentration, mixing residence time, liquid to solids ratio, and 18 times of leachate re-usage onto fresh BR. The thin film diffusion model, as the fundamental theory 19 for leaching, either with constant particle size for selective leaching, or with shrinking particle size 20 for less-, or non-, selective leaching, interprets sufficiently well the relevant experimental data. In 21 both cases, a concept for an unyielding core supplements the basic model. Especially for the 22 selective leaching mild conditions, the simplest model version keeps step with the experiments, 23 since both prove 1st order kinetics, while especially for the extreme conditions including very low 24 solvent excess, it is proposed a combined conversion rate model with diffusion and chemical 25 reaction inside particles. The maximization of Sc recovery per unit of consumed solvent (i.e., 26 specific recovery) emerged as highly critical for the process economics. 27