water as pure as does ion exchange. In the production
Ammonia, caustic, or lime can be used to regenerate
the weak base anion resin and sulfuric, hydrochloric,
of steam, it is sometimes necessary to use water with a
lower level of total dissolved solids. Ion exchange
nitric, or sulfurous acid can be used to regenerate the
weak acid cation resin. The two unit variation of the
should be considered if water with less than
approximately 300 milligrams per liter of total dissolved
Desal Process is shown in figure 8-4.
solids must be purified further.
Demineralization. No other demineralization or
desalination technique can, in a single pass, produce
Figure 8-3. Three-unit variation Desal Process.