Original Article

Investigation of the effect of P₂O₅ and CaF₂ on the crystallization behavior of La₂O₃-bearing calcium–silicate–aluminum slags using the single hot thermocouple technique

¹ School of Rare Earth Industry (School of Rare Earth Engineering and Technology), Inner Mongolia University of Science and Technology, Baotou 014010, China
² Key Laboratory of Green Extraction & Efficient Utilization of Light Rare-Earth Resources (Inner Mongolia University of Science and Technology), Ministry of Education, Baotou 014010, China
³ Shanxi Jianbang Group Co., Ltd, Houma 043000, China

^* e-mail: xwb2580zxc@163.com

Received: 8 February 2024
Accepted: 2 June 2024

Abstract

The effects of P₂O₅ and CaF₂ components of rare earth (RE)-bearing slags on their crystallization behavior were investigated using single hot-thermocouple technique (SHTT). The time temperature transformation (TTT) diagram exhibited single-nose curves within the examined slag composition range, in agreement with the individual CaLa₄(SiO₄)₃O-type phase detected by an isothermal crystallization experiment in a furnace. Additionally, an increase in the P₂O₅ content shortened the incubation time and increased the nucleation rate of the columnar CaLa₄(SiO₄)₃O-type phase in the 1350–1150 °C temperature range, while an increase in the CaF₂ content had the opposite effects on the incubation time and nucleation rate. The sizes of the CaLa₄(SiO₄)₃O-type phases in the slags with CaF₂ were larger than those in the slags with P₂O₅, as verified by both in situ SHTT images and the crystallization experiment. The continuous cooling transformation (CCT) diagram suggested that an increase in the P₂O₅ content increased the initial crystallization temperature, whereas an increase in the CaF₂ content decreased it. An analysis of the isothermal crystallization kinetics revealed that the columnar CaLa₄(SiO₄)₃O-type phase exhibited phase diffusion-controlled growth. An increase in the P₂O₅ content tended to decrease the crystallization activation energy, while an increase in the CaF₂ content increased the activation energy.