An apparatus to purify a melt is disclosed. A first portion of a melt in a chamber is frozen in a first direction. A fraction of the first portion is melted in the first direction. A second portion of the melt remains frozen. The melt flows from the chamber and the second portion is removed from the chamber. The freezing concentrates solutes in the melt and second portion. The second portion may be a slug with a high solute concentration. This system may be incorporated into a sheet forming apparatus with other components such as, for example, pumps, filters, or particle traps.