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

机译：CaO和煤焙烧分解稀土元素的动力学

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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 (REFCO 3 ). The second step from 605 to 716 °C mainly included the decomposition of monazite (REPO 4 ). The decomposition products were primarily RE 2 O 3 , Ce 0.75 Nd 0.25 O 1.875 , CeO 2 , Ca 5 F(PO 4 ) 3 , and CaF 2 . 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 REFCO 3 and REPO 4 was 99.87%. The roasting time and temperature were the major factors influencing the decomposition rate. The kinetics process of the decomposition of REFCO 3 and REPO 4 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.
机译：用CaO和煤混合的磁尾矿焙烧方法回收了磁尾矿中的稀土元素（REE）。研究了焙烧过程中的相变和分解过程。结果表明，稀土元素在磁尾矿中的分解过程分为两个步骤。从380到431°C的第一步主要是分解贝氏体（REFCO 3）。从605到716°C的第二步主要包括独居石的分解（REPO 4）。分解产物主要是RE 2 O 3，Ce 0.75 Nd 0.25 O 1.875，CeO 2，Ca 5 F（PO 4）3和CaF 2。添加CaO可以降低REFCO3和REPO4的分解温度。同时，CaO分解对镁橄榄石和独居石的影响显着。此外，研究了焙烧时间，焙烧温度和CaO添加量对分解速率的影响。最佳工艺条件是烘烤时间为60分钟;焙烧温度为750°C; CaO添加量为20％（w / w）。 REFCO 3和REPO 4的最大分解率为99.87％。焙烧时间和温度是影响分解速率的主要因素。 REFCO 3和REPO 4分解的动力学过程符合界面反应动力学模型。反应速率控制步骤分为两个步骤。第一步（在低温下）通过化学反应控制，活化能为52.67 kJ / mol。第二步（高温下）通过扩散控制，活化能为8.5 kJ / mol。

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