Patent ID: 7727502

Claim:
A batch casting process for purifying low-purity metallurgical grade silicon, containing at least one of the following contaminants Al, As, Ba, Bi, Ca, Cd, Fe, Co, Cr, Cu, Fe, La, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Sc, Sn, Sr, Ti, V, Zn, Zr, and B, and obtaining a higher-purity solid polycrystalline silicon, said process comprising the steps of: a. containing a melt of low-purity metallurgical grade silicon in a mould, said mould having an insulated bottom wall, insulated side walls, and an open top; b. solidifying the melt by unidirectional solidification from said open top towards said insulated bottom wall of said mould while electromagnetically stirring the melt so as to wash a solidification interface and prevent impurity rich liquid to be trapped by dendrite formation; c. controlling a rate of said unidirectional solidification; d. stopping said unidirectional solidification when the melt has partially solidified to produce an ingot having an exterior shell comprising said higher-purity solid polycrystalline silicon and a center comprising an impurity-enriched liquid silicon; and e. creating an opening in said exterior shell of said ingot to outflow said impurity-enriched liquid silicon and leave the exterior shell comprising said higher-purity solid polycrystalline silicon thereby obtaining said higher-purity solid polycrystalline silicon.