Because high-purity silicon is one of the core materials for use in cleaner energy industry, silicon purification techniques have taken on greater importance. An understanding of the thermodynamics of impurity elements in silicon is therefore of great scientific and industrial importance. Experimental and assessment works on the thermodynamics of 23 impurity elements (Ag, Al, Au, B, Ca, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, P, Pb, Sb, Ta, Ti, V, W, Zn, and Zr) in silicon melts are reviewed herein, and their activity coefficients in dilute silicon melts are discussed. The parameters suggested for use in assessing the liquid phase in each of the silicon binary systems are selected based on this discussion. The segregation coefficients of impurity elements calculated using the activity coefficients agree well with reported values and are used to evaluate silicon purification by directional solidification. The purpose of this paper is to provide fundamental and systemic thermodynamics knowledge for the development of silicon purification processes.