Phase Transformation and Thermal Decomposition Kinetics of a Mixed Rare Earth Concentrate

The Bayan Obo rare earth (BORE) concentrate is the largest light rare earth mineral resource in the world. The decomposition of the BORE concentrate is a principal step to develop new technologies to recover useful elements and is therefore of much importance. In this paper, the phase transformation and thermal decomposition kinetics of the BORE concentrate in air were investigated. The results showed that bastnaesite decomposed upon air roasting. The roasted solid was recovered by sulfuric acid leaching. The activation energy and pre-exponential factor of the roasting reaction of the BORE concentrate were calculated through the isoconversional methods of Flynn-Wall-Ozawa and Kissinger, and the probable mechanism function was estimated through the Coats-Redfern method. The kinetic model that best describes the thermal decomposition reaction for the BORE concentrate is the A2 (Avrami-Erofeev 2) model, and the corresponding probable mechanism function is f(α) = 2(1 - α)[-ln(1 - α)]^1/2 and G(α) = [-ln(1 - α)]^1/2.