Extraction of rare earth elements from coal fly ash by alkali fusion–acid leaching: Mechanism analysis

Coal fly ash (CFA) in some areas contains higher levels of rare earth elements (REEs), which can be seen as a potential substitute for rare earth resources. As an effective method of hydrometallurgy, alkali fusion has been widely used in the recovery of precious metals from secondary resources. In this study, taking a CFA sample and five REEs named Y, La, Ce, Pr, and Nd in the sample as objects, the mechanism of alkali fusion processes of CFA with different alkali fluxes (Na2CO3, NaCl, Na2O2, NaOH, KOH, and Ca(OH)(2)) was studied. The results showed that Na2CO3, Na2O2, NaOH, and KOH can destroy the structure of CFA to effectively improve the leaching efficiency of REEs from CFA. The total leaching efficiency of the five REEs can reach to 57.45%, 49.25%, 74.23%, and 64.93%, respectively, when these four alkalis were used as fluxs. In addition, with DSC analysis, the non-model fitting dynamics Kissinger method was used to calculate the kinetic parameters of alkali fusion reaction between CFA and Na2CO3. The calculated alkali fusion activation energy E was 895.52 kJ center dot mol(-1), the pre-exponential factor A was 3.47 x 10(41) min(-1), and the reaction rate constant K was 1.68 min(-1).