ION EXCHANGE
Ion exchange is the giving and receiving of ions between an ion exchange material
and a process liquid. It takes place as the process liquid flows through the ion
exchange material. Mobile ions on the ion exchange material are exchanged with
ions in the process fluid. For water treatment applications, the ion exchange material
is a resin and the process fluid is water.
Ion exchange resin, is an activated, synthetic, organic,
copolymer matrix comprised of porous beads with a typical diameter of 0.4 – 1.2 mm
(0.01 - 0.04 inch). Ion exchange resin beads (several hundred thousand per cubic
inch) are placed in a pressure vessel to make the ion exchange resin bed. The ion
exchange resin bed and pressure vessel, with associated face piping, valves, and
instruments, comprise an ion exchange unit. As process water passes through the unit, undesirable ions are
exchanged for the mobile (and more desirable) ions in the resin. When the ion
exchange resin bed can no longer remove undesirable ions, it is exhausted. It must
then be regenerated before it is able to remove ions again.
Ion exchange (IX) has been the traditional method for softening and for the removal of
dissolved solids (ions) to low part per million (ppm) concentrations in high purity
water treatment applications. It competes with reverse osmosis for the job of
"working" deionizer (also called demineralizer). A working demineralizer removes
the largest portion, about 95% - 99.9%, of dissolved solids. The remainder is
removed by a "polishing" demineralizer.
Several types of ion exchange resins are available for the treatment of process waters.
The selection of an ion exchange resin for a particular application is based on the
process water analysis and the treatment objective: deionization (demineralization),
softening, dealkalization, or organic scavenging (organic matter removal). There are
also numerous pressure vessel configurations. Ion exchange resins and pressure
vessel configurations are compared to determine the most appropriate ion exchange
units for each treatment application.
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