Reduction of boron-bearing iron ore concentrate/coal composite pellet and kinetics analysis

Abstract

Ludwigite is a complex iron ore containing boron and it is the most abundant boron resource in China. Boron-bearing iron ore concentrate is an intermediate product of the ore dressing process of crude low-grade ludwigite and extracting boron from it has great influence on the total boron yield. Pre-reduction of the boron-bearing iron ore concentrate is one of the important steps of the pyrometallurgical boron and iron separation process. In the present work, non-isothermal and isothermal reduction of boron-bearing iron ore concentrate/coal composite pellet was performed. The evolution of reaction fraction, carbon consumption, off-gas evolution, phase composition and microstructure were systematically revealed based on reduction experimental results in conjunction with X-ray diffraction, scanning electron microscope-energy dispersive spectrometer and electron probe micro analyzer analysis. The kinetics of the reduction of the composite pellet was also analysed. The reduction mechanism changed at a temperature around 1150°C. The rate of carbon gasification in the composite pellet during the reduction decreased mainly due to the chemical inhibition by B₂O₃ on the electron transfer.

Keywords:

• Ludwigite
• Boron-bearing iron ore concentrate
• Carbon composite pellet
• Direct reduction
• Mechanism

Acknowledgements

The authors would like to express their gratitude for the financial support of the National Natural Science Foundation of China (Grant No.51274033) as well as the research grant from the State Key Laboratory of Advanced Metallurgy, University of Science and Technology, Beijing.