Abstract
In this paper, the separation of phosphorus from metallurgical-grade silicon was investigated based on an Mg alloying and HCl leaching approach. Experimental results show that P concentration was reduced from initial 15.1 ppmw to 0.2 ppmw with also large extent removal of metallic impurities by two times Mg alloying-leaching purification. The mechanism of enhanced P separation is clarified owing to the strong affinity between Mg and P, which is validated by SIMS elemental mapping. A two-parameter analytical model was developed to predict the P removal degree based on the variables of alloying metal concentration and interaction coefficient between alloying metal and P. The model is validated with experimental results and the interaction coefficient εMginSiP was obtained as −10.8. This approach can be applied to model the removal of impurity which follows Gulliver-Scheil solidification from other binary alloying systems. Furthermore, in order to study the effect of applied alloying-leaching operation times, a model was proposed which establishes the mathematical relationships among key processing variables like initial and target P concentrations, the amount of the alloying metal, and the process operation times.
Highlights
The rapid growth of the photovoltaic industry worldwide has given rise to large demands of solar grade silicon (SoG-Si, purity 99.9999%) feedstock production
As one of the crucial steps, the task of acid leaching is aiming at removing large extent metallic impurities, and, more importantly, to reduce the P concentration down to 0.1–0.3 ppmw to meet the restricted high-purity requirement of SoG-Si
The entire acid leaching process of Mg-alloyed Si is a heterogeneous solid-state reaction, the governed reaction is expected to be the decomposition of Mg2Si due to its principal amount
Summary
The rapid growth of the photovoltaic industry worldwide has given rise to large demands of solar grade silicon (SoG-Si, purity 99.9999%) feedstock production. One typical example is the widely known solvent refining [13,14], which mainly relies on a large amount of alloying metal addition like Al [15,16,17,18,19,20,21,22,23,24], Sn [24,25,26,27,28], Cu [29,30,31], and Fe [32] and so on.
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