Fig. 9. (a) Variation of distribution coefficient K_d of individual and competitive Cs⁺ and Sr²⁺ with increasing molar concentration of Na⁺ (initial concentrations of the ions were 7.4 (Cs⁺) and 6.9 (Sr²⁺) ppm, V/m ratio was 1000 mL g^–1 and pH ∼ 7), and (b) kinetics of individual Cs⁺, Sr²⁺ and competitive ion-exchange vs. time t (min). The initial concentration was ∼1.2 ppm (for both Cs⁺ and Sr²⁺) and V/m ratio was 1000 mL g^–1 and pH ∼ 7.