Behavior of phosphorus during solidification of the Si-Fe-P ternary alloy melt used in purification of MG-Si

The behavior of phosphorus during the solidification of the Si-Fe-P ternary alloy melt used in purification of MG-Si was investigated using thermodynamic calculations and design of Si-Fe-P alloy materials with specific composition. It was found that when the concentration of Fe in the liquid phase (LFe) is less than 23 wt%, Fe can promote the decomposition of SiP and the solid solution of P in primary Si, basing on positive activity interaction between Fe-P. After LFe exceeds 23 wt%, Fe will attract P to form clusters and enrich in unsolidified liquid phase or Fe3Si7 phase during the primary crystallization of Si and the eutectic of Si and Fe3Si7(A). Then, the eutectic of Fe3Si7(B) and Si4P4Fe ends the solidification of the alloy melt. These characteristic behaviors lead to the distribution coefficient of P between the silicon matrix and A-Fe3Si7 reaching 0.4868, limiting the effectiveness of P removal from MG-Si by Si-Fe alloy refining. Experiments on in-situ etching and acid leaching in different acid agents showed that HCl+HF and Aqua regia were the optimal acid leaching systems for the removal of P enrichment in Fe3Si7 and Si4P4Fe, respectively. (c) 2021 Elsevier B.V. All rights reserved.