Oxidative precipitation of cerium in acidic chloride solutions: Part II-oxidation in a mixed REE system

Cerium is the most prevalent and lowest cost rare earth element (REE) in hard rock bastnaesite type ores. Cerium separation is facilitated by oxidation of cerium from trivalent to tetravalent state, where its solubility is greatly reduced. In the initial study, the thermodynamics and kinetics of cerium oxidation were investigated in acidic chloride solutions. The leach solutions in REE processes contain a large mixture of rare earths in trivalent form. Part two of this study investigates the ability of this process to separate cerium from mixed REE leach solutions of more industrially important REE. The cerium oxidation process developed in Part I of this study was implemented on mixed REE solutions under similar conditions. Cerium was oxidized using sodium hypochlorite, hydrogen peroxide, potassium permanganate, and Caro's Acid. Reactions were tested at pH 3.0 and 25 degrees C. The greatest cerium removal, 98.4%, was achieved using permanganate as an oxidant in multi REE solutions leaving a product with a cerium to total REE (Ce/TREE) ratio of 0.62. Varying levels of cerium removal were achieved with lower selectivity using the other oxidants. To investigate the adsorption of other REE to cerium, adsorption isotherms of neodymium and terbium were created using eerie hydroxide and fitted to the Langmuir and Freundlich isotherms.