A liquid treatment process is described for sequential removal of ionic species
of progressively decreasing ionic strength without precipitation or "scaling."
An aspect 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 carbon dioxide, preventing
scaling. 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.
