Units Used for Countercurrent Ion-Exchange Processes

Contactors in which countercurrent motion is used can be classified as follows (1) contactors with continuous motion of an ion-exchanger compact bed (2) contactors with a suspended or fluidized bed of ion- 

Units with vertical columns in which the motion of granulated sorbent as a dense bed is gravity-inspired counter to the upward flow of solution are the simplest countercurrent systems. They are characterized by rather low HETP values. Their efficiency, however, is not high since a sufficiently dense bed of ion exchanger is maintainable only at low rates of solution flow. The solution flow rate is not more than 1-3 m/hr. 

Recovery of substances firom muddy solutions or pulps can be effected in contactors of this group. They are comparatively simple in design and are easy to maintain. Their specific efficiency is considerably higher than with dense-bed columns in continuous motion (10-20 m/hr). But high values of HETP affected in such operation do not allow them to be employed for separating mixtures of components with rather similar properties. 

Units with phases alternately in motion (up to 150 m/hr) are characterized by high specific efficiency and satisfyingly low HETP values. As a consequence, they have found wide application in large-scale production in spite of their more complex design. 

Columns with Gravity Induced Ion-Exchanger Motion 

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