Comparison of sorption behavior of I- and TcO4- on Mg/Al layered double hydroxide

Abstract

The sorption behavior of I- on calcined Mg/Al layered double hydroxide (LDH) was investigated. The batch sorption experiments were carried out in an inert atmosphere and at a constant temperature of 25 degrees C. Sorption is based on stepwise ion-exchange equilibria involving the LDH hydroxide. The determined equilibrium constants of K-1 and K-2 are 7.4+/-1.0 and 0.2+/-0.4, respectively. The dominant reaction is the first ion-exchange equilibrium, which is the replacement of one OH- ion of the LDH hydroxide by an I- ion to form Mg6Al2(OH)(17)(I)(s). The K-1 value for I- sorption is 5 times higher than that for MO4- (M = Tc, Re) sorption. An iodide ion is more selective for sorption on the calcined LDH. The sorption behavior of I- in the presence of TcO4- was investigated. The batch sorption experiments were conducted by using I- and ReO4- as a TcO4- surrogate. The sorbed concentrations of I- and ReO4- in simultaneous sorption are similar to those in single ion sorption. The I- and ReO4- show an independent sorption behavior on calcined LDH when these anions are mixed. It means that Mg6Al2(OH)(17)(ReO4) exists with Mg6Al2(OH)(17)(I) in the LDH unit.