Comparison of strontium retardation for kaolinite, illite, vermiculite and allophane

Adsorption and retardation of Sr²⁺ by four clays were investigated, which were evaluated by using the distribution coefficient (K_D) and average penetration length ratio of Sr²⁺ to water (r). K_D values for Sr²⁺ among the four clay minerals were in the order: kaolinite < illite < vermiculite ≪ allophane, and Sr²⁺ penetration length ratio (r) followed the inverse order. Adsorption was further analyzed by using Langmuir adsorption model for competitive Sr²⁺ and Na⁺ adsorption at constant NaCl concentration. Conditional affinity constants suggested that Sr²⁺ adsorption on the variable charge sites of clay edges contributed to the high conditional Sr²⁺ affinities. (author)