Dissolution behavior of La₂O₃, Pr₂O₃, Nd₂O₃, CaO and Al₂O₃ in sulfuric acid solutions and study of cerium recovery from rare earth polishing powder waste via two-stage sulfuric acid leaching

Abstract

This study describes a hydrometallurgical process to investigate the cerium recovery from rare earth polishing powder waste (REPPW) containing main elements such as cerium, lanthanum, praseodymium, neodymium, calcium and aluminum. First, dissolution experiments on La₂O₃, Pr₂O₃, Nd₂O₃, CaO and Al₂O₃ with 5 µm particle size in sulfuric acid solutions were carried out using a batch reactor with various acid concentrations (1–15 mol/dm³) at different temperatures (30–180°C). The effects of these two parameters on the dissolution reaction were studied. The obtained results showed that two sequential leaching steps were needed to separate cerium from the mixture of CeO₂, La₂O₃, Pr₂O₃, Nd₂O₃, CaO and Al₂O₃. The total process for cerium recovery from REPPW via two-stage acid leaching was then developed through the collection of experimental results. Moreover, the dissolution rate of Al₂O₃ was expressed by a shrinking core kinetics model. The variation of the dissolution rate constant with temperature obeyed the Arrhenius equation with activation energy of 130 kJ·mol⁻¹ and reaction rate constant as a function of the acid concentration of C⁰.⁴¹. On the basis of the above data, a k-T (reaction rate constant-reaction temperature) diagram for a CeO₂–Al₂O₃–H₂SO4–H₂O system that permits rational extraction of CeO₂ and Al₂O₃ was devised.