Thermodynamic study of the effect of calcium on removal of phosphorus from silicon by acid leaching treatment

Abstract

The interaction between calcium and phosphorus in molten silicon was investigated for predicting the removal of phosphorus from silicon by an acid leaching treatment with calcium addition. In the present study, two immiscible liquids of silicon and lead were equilibrated, and the interaction parameter between calcium and phosphorus and the self-interaction parameter of phosphorus in molten silicon at 1723 K were determined.

$$\varepsilon _{Ca in Si}^P = - 14.6( \pm 1.7) \varepsilon _{Ca in Si}^P = - 13.8( \pm 3.2)$$

In the derivation process, the following activity coefficients and the interaction parameters of metallic impurities in molten silicon and lead at 1723 K were also obtained:

$$\begin{gathered} \ln \gamma _{Pb in Si}^0 = 3.73( \pm 0.010) \ln \gamma _{Si in Pb}^0 = 3.39( \pm 0.040) \hfill \\ \varepsilon _{Pb in Si}^P = - 4.08( \pm 0.80) \varepsilon _{Pb in Si}^P = - 23.8( \pm 18) \hfill \\ \varepsilon _{Pb in Si}^{Ca} = - 8.36( \pm 1.6) \varepsilon _{Si in Pb}^{Ca} = - 14.3( \pm 7.0) \hfill \\ \end{gathered} $$

The effect of the calcium addition to silicon improves the subsequent removal of phosphorus in the acid leaching treatment, and the increase in removal fraction of phosphorus was observed remarkably with the addition of calcium in silicon.