Distribution Coefficient of Cesium on Ion Exchangers as a Function of Batch Factor and Cesium Loading

Abstract

A theoretical equation which represents the effects of batch factor, β(=L/W) (cm³/g) and Cs loading, Q(meq/g) on distribution coefficient for Cs⁺, Kd(cm³/g), was derived for the adsorption of Cs⁺ from the outer solution(L cm³) on some ion exchangers of Mⁿ⁺ form(Wg), and compared with experimental results.
Kd was found to be constant with respect to β when the outer solution contains large amounts of Mⁿ⁺ initially, but it is proportional to n√β at constant Q for the adsorption from pure Cs⁺ solutions. It was also found for the adsorption from a solution containing large amounts of coexistent univalent cations except Mⁿ⁺ that Kd, being generally dependent on β, is an increasing function of β in the case of n<<2, although it becomes approximately constant with respect to β for the special case of [A⁺]E=(C_0EC-Q)/β in Eq. (14). These relationships between Kd and p have been expected to hold irrespectively of ideality of ion exchange process and found to be consistent with experimental results by assuming (∂KCS+MN+/∂β)_Q=0 (KCS+MN+: selectivity coefficient).
On the other hand, Kd is a decreasing function of Q for usual ion exhanger (n<<2) of (dKCS+MN+/dQ<<0), and it approaches a constant at infinitely small Q except for Cs⁺ adsorption from pure Cs⁺ solutions. These expectations were in accord with exprimental results except those for Zn₂[Fe(CN)₆] (ZFC). The ion-exchange behavior of Cs⁺ on ZFC was specific in its increasing tendency of Kd with Q and its high Kd value at a relatively large value of Q for the adsorption not only from pure Cs⁺ solutions but also from a 3 mol⋅dm^-3 NaNO₃solution. These findings indicate that ZFC might be preferable as an inorganic ion exchanger for the separation of Cs⁺ by a batch process from a highly concentrated solution of NaNO₃.