Kinetics of calcination of natural carbonate minerals

Abstract The authors have developed a process for the direct production of the rare earth elements oxides (REO) through the calcination of a raw ore that contains carbonate minerals, such as bastnaesite (a known REE bearing carbonatite) and gangues (e.g., calcite, dolomite, siderite, and ankerite). Due to the complexity of the ore, an elaborated kinetic study was required to gain an insightful understanding of the contribution of each mineral to the overall reaction kinetics. Thus, calcination kinetics of individual carbonates was investigated by thermogravimetric analysis, and subsequently new as well as modified kinetic models were developed. The comparison of kinetic parameters and decomposition conditions of bastnaesite and gangue minerals revealed that the calcination of bastnaesite happens at much lower temperatures than the gangues. Bastnaesite decomposition starts at 400 °C while gangue minerals decompose above 500 °C. So, the selectivity of REO production should be enhanced by adjusting the reactor residence time so that the majority of the gangue remains unreacted, thus reducing the complexity of the downstream hydrometallurgical process.