INTRODUCTION AND THEORY OF ION EXCHANGE

Contaminant cations such as calcium, magnesium, barium, strontium, and radium, and anions such as fluoride, nitrate, fulvates, humates, arsenate, selenate, chromate, and anionic complexes of uranium can be removed from water by using ion exchange with resins or by adsorption onto hydrous metal oxides such as activated alumina (AAl) granules or coagulated Fe(II), Fe(III), Al(III), and Mn(IV) surfaces. This chapter deals only with the theory and practice of ion exchange with resins and adsorption with activated alumina (AAl). The reader interested in cation and anion adsorption onto hydrous metal oxides in general is referred to Schindler s and Stumm s publications on the solid-water interface (Schindler, 1981; Stumm, 1992) as a starting point.

Ion exchange with synthetic resins and adsorption onto activated alumina are water treatment processes in which a presaturant ion on the solid phase, the adsor bent, is exchanged for an unwanted ion in the water. In order to accomplish the exchange reaction, a packed bed of ion-exchange resin beads or alumina granules is used. Source water is continually passed through the bed in a downflow or upflow mode until the adsorbent is exhausted, as evidenced by the appearance (break through) of the unwanted contaminant at an unacceptable concentration in the effluent.

The most useful ion-exchange reactions are reversible. In the simplest cases, the exhausted bed is regenerated using an excess of the...