Regular Article

Innovative separation model for boron removal from silicon during slag refining based on ion and molecule coexistence theory

¹ National Engineering Research Center for Green Recycling of Strategic Metal Resources, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China
² Ganjiang Innovation Academy, Chinese Academy of Science, Ganzhou 341119, PR China
³ University of Chinese Academy of Sciences, Beijing 100049, PR China

^* e-mail: gyqian@ipe.ac.cn
^** e-mail: wangdong@ipe.ac.cn
^*** e-mail: zwang@ipe.cn.cn

Received: 11 January 2022
Accepted: 2 March 2022

Abstract

How to reduce boron concentration to an extremely low level has become a major obstacle during silicon waste recycling. As a simple and efficient method of removing impurities, slag refining plays an increasingly important role for industrial silicon waste recovery. The deboration ability of slag is usually evaluated by boron distribution ratio L_B. However, the development of a separation prediction model is challenged by the limitations on the recognition of impurity structure in slag and complexity of slag-silicon reactions. Herein, a novel thermodynamic model for predicting boron distribution ratio between CaO-SiO₂ based slags and molten silicon has been developed based on ion and molecule coexistence theory (IMCT), i.e., IMCT-L_B model. The reaction abilities of structural units are represented by the calculated mass action concentration. The predictive boron distribution ratio between CaO-SiO₂, CaO-Al₂O₃-SiO₂, CaF₂-CaO-SiO₂ slags and silicon correspond well with experimental data, reflecting the reasonability of IMCT-L_B model. According to IMCT, deboration reactions between slags and silicon can be represented by ion couples (Ca²⁺ + O^2–), simple molecule Al₂O₃ with SiO₂ to form eight deboration products as B₂O₃, 3CaO · B₂O₃, 2CaO · B₂O₃, CaO · B₂O₃, CaO · 2B₂O₃, 2Al₂O₃· B₂O₃, 9Al₂O₃· B₂O₃, CaO · 2SiO₂· B₂O₃. With the developed IMCT-L_B model, the respective boron distribution ratio L_B,_i of the eight deboration products can be determined quantitatively. Furthermore, the effect of temperature, mass ratio of CaO to SiO₂ (%CaO/%SiO₂), Al₂O₃ and CaF₂ content of CaO-SiO₂ based slags on L_B are fully discussed.