<p>A method of refining low-purity silicon with a slug especially by removing boron. By the method, high-purity silicon usable as a raw material for solar cells or the like is produced at low cost while inhibiting the reaction vessel from being damaged/worn by the slug. SiO<SUB>2</SUB> and an alkali oxide or alkali carbonate are added as materials for a slug to molten silicon to thereby form a slug. In this operation, either the same substance as the material of the reaction vessel used or one or more of the substances constituting the material of the reaction vessel are added to the slug. Thus, impurities contained in the molten silicon are removed.</p>
