Regular Article

Solid-state reaction mechanism of columbite-to-pyrochlore conversion at different temperature

¹ Changsha Research Institute of Mining and Metallurgy, Co, Ltd, Changsha 410012, China
² School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China

^* e-mail: lakers198787@126.com

Received: 31 August 2022
Accepted: 29 September 2022

Abstract

Columbite-to-pyrochlore conversion is proposed to enhance the difference of physicochemical properties between niobium minerals and gangue minerals with the aim of improving the niobium minerals processing of Bayan Obo deposit. Columbite mixed NaF and CaCO₃ could be converted into pyrochlore. Gibbs free energies of the conversions were calculated by two-parameter model. The reaction mechanism was clarified through X-ray diffraction and scanning electron microscopy equipped with an energy dispersion spectrometer. Oxygen benefited the conversion because FeO, by-product of the reaction is oxidized into Fe₂O₃, releasing a large amount of heat. Experimental results indicated that NaF reacted with CaCO₃ before columbite conversion. Columbite-to-NaNbO₃ conversion was dominant as sintering temperature was from 873 K to 973 K. Columbite-to-pyrochlore conversion dominated with the temperature increasing to 1073 K although the reaction occurred at 973 K. Therefore, Columbite-to-pyrochlore conversion preferred to occur when columbite mixtures were placed into the tubular furnace with a temperature of 1073 K directly.