Regular Article

Research on the melt behavior of rare-earth-rich iron minerals by direct reduction

¹ Key Laboratory of Integrated Exploitation of Bayan-Obo Multi-Metal Resources, Inner Mongolia University of Science & Technology, 014010 Baotou, PR China
² Industrial Technology Research Institute, Inner Mongolia University of Science & Technology, 014010 Baotou, PR China
³ College of Energy and Environment, Inner Mongolia University of Science & Technology, 014010 Baotou, PR China
⁴ Inner Mongolia Autonomous Regional Engineering Technology Research Center of Sustainable Exploitation of Rare Earth Secondary Resources, Inner Mongolia University of Science & Technology, 014010 Baotou, PR China

^* e-mail: gwt2016949@imust.edu.cn

Received: 7 November 2019
Accepted: 5 February 2020

Abstract

The evolution of mineral phase structure during the reduction and melting separation of an rare earth (RE)-rich iron mineral (RER-IM) is investigated. The results show the iron oxides are reduced to their metallic iron or FeO at 1373 K. When reduction time is 180 min, the reduction degree is 84%. Both bastnaesite (RE(CO₃)F) and monazite (REPO₄) are transformed into Ca₂RE₈(SiO₄)₆O₂ during carbothermic reduction at 1373 K. The mineral with a reduction degree of 84% is melt-separated in a graphite crucible at 1773 K for 20 min, the resulting slag contains 20.64% RE₂O₃, with RE existing in the form of Ca₂RE₈(SiO₄)₆O₂. Moreover, P from the reduction of Ca₃(PO₄)₂ dissolves in iron with a content ranging from 1.2 to 2.21%. The type of RE phase that occurs in the slag is related to the distribution of P between slag and iron. A low P content in the slag facilitates the formation of Ca₂RE₈(SiO₄)₆O₂, but a high content in the slag favours Ca₃RE₂[(Si, P)O₄]₃F. Thus, it is confirmed that the RE phase structure is controlled by the distribution of P between slag and iron.