Ion exchange - Principles of Chemical Separations with Environmental Applications - page 226

D A

I K

G

G

E

Resin

H

G Sand

J

F B

C

Figure 8.6 Typical fixed bed. A, feed; B, effluent; C, backwash supply;
D, backwash overflow to resin trap; E, eluant supply; F, spent eluant; G, dis-
tributor manifolds; H, resin removal line; I, access hole; J, drain; K, pressure
gage and vent [1]. Copyright 1987 John Wiley & Sons, Inc. This material is used
by permission of John Wiley & Sons, Inc.

Mixed beds contain a thoroughly mixed bed of strong-acid and strong-base resins. These
beds are used for deionization of water and typically provide better water quality than two
beds in series. A key issue is regeneration. The two resins need to be separated after the
ion-exchange cycle and prior to regeneration. Strong-base resins are typically lighter than
strong-acid resins. Backwashing can be used to segregate the resins. The regeneration is
then done simultaneously with the appropriate regenerant introduced at the top and bottom
of the column and withdrawn at the region between the two segregated resins. Obviously,
the resins will need to be remixed prior to the next ion-exchange cycle.

8.7.2 Design procedures

Many of the design principles that apply to adsorption columns may also be applied
to ion-exchange columns. For example, breakthrough curves from a pilot column along