Fractional deionization process

摘要

A liquid treatment process is described for sequential removal of ionic species of progressively decreasing ionic strength without precipitation or "scaling." An embodiment of the invention includes dual electrodeionization operations. The first electrodeionization operation is performed at a voltage calculated to remove strongly ionized species such as calcium and magnesium from the feed water without scaling. The product of the first electrodeionization operation is then subjected to a second electrodeionization operation. The second electrodeionization operation is performed at a voltage greater than the first electrodeionization operation, and is designed to remove more weakly ionized species such as silica and atmospheric carbon dioxide. The danger of precipitation or "scaling" normally present during electrodeionization of weakly ionized species is not present in this invention, because the strongly ionized species responsible for scaling at higher voltages have already been removed from the feed stream through the first electrodeionization operation. More than two successive electrodeionization operations may be performed if desired. Multiple electrodeionization operations may occur in a single electrodeionization stack or in multiple electrodeionization stacks.