Kinetics of Roasting Decomposition of the Rare Earth Elements by CaO and Coal

Abstract

The roasting method of magnetic tailing mixed with CaO and coal was used to recycle the rare earth elements (REE) in magnetic tailing. The phase transformation and decomposition process were researched during the roasting processes. The results showed that the decomposition processes of REE in magnetic tailing were divided into two steps. The first step from 380 to 431 °C mainly entailed the decomposition of bastnaesite (REFCO3). The second step from 605 to 716 °C mainly included the decomposition of monazite (REPO4). The decomposition products were primarily RE2O3, Ce0.75Nd0.25O1.875, CeO2, Ca5F(PO4)3, and CaF2. Adding CaO could reduce the decomposition temperature of REFCO3 and REPO4. Meanwhile, the decomposition effect of CaO on bastnaesite and monazite was significant. Besides, the effects of the roasting time, roasting temperature, and CaO addition level on the decomposition rate were studied. The optimum technological conditions were a roasting time of 60 min; roasting temperature of 750 °C; and CaO addition level of 20% (w/w). The maximum decomposition rate of REFCO3 and REPO4 was 99.87%. The roasting time and temperature were the major factors influencing the decomposition rate. The kinetics process of the decomposition of REFCO3 and REPO4 accorded with the interfacial reaction kinetics model. The reaction rate controlling steps were divided into two steps. The first step (at low temperature) was controlled by a chemical reaction with an activation energy of 52.67 kJ/mol. The second step (at high temperature) was controlled by diffusion with an activation energy of 8.5 kJ/mol.

Keywords

• magnetic tailing
• REE
• CaO roasting
• fixing fluorine
• kinetics