Strontium adsorption and penetration in kaolinite at low Sr²⁺concentration

Abstract

Behavior of radioactive strontium (Sr 2+) in contaminated soils is an important issue in relation to nuclear power plant accidents. The Sr 2+ adsorption on kaolinite and its migration in a kaolinite soil were investigated because toxic effects of radioactive Sr 2+ have been found to be very severe for living organisms at low Sr 2+ concentrations. Adsorption isotherms of Sr 2+ on kaolinite at different salt (NaCl) concentration and pH were obtained by the batch method. The calculated distribution coefficients (K D) ranged between 600 and 40,000 L kg −1 , which showed a strong preference for the adsorbed phase. The results were used to evaluate the ratio (r) of penetration length of Sr 2+ relative to that of water in a model kaolinite soil. When the Sr 2+ solution was percolated constantly into the kaolinite soil, the penetration of Sr 2+ was delayed strongly at low Sr 2+ concentration due to adsorption. The Sr 2+ penetration length was only 0.001-0.056 of the water penetration length at pH 6.5 (0.1-10 mmol L −1 NaCl). At pH 4.1 (1 mmol L −1 NaCl) the effect was about 17 times less than at pH 6.5 (1 mmol L −1 NaCl). Under all conditions, the Sr 2+ penetration increased when the Sr 2+ concentration increased due to the K D decrease. The Sr 2+ isotherms could be fitted well to the Langmuir adsorption equation, which indicates that only one site type is involved in the Sr 2+ adsorption.

87 Sr/ 86 Sr isotope ratio as a tool in archaeological investigation: risks and limits

“…Clay minerals, such as smectite, illite, kaolinite, as well as the organic matter may sorb strontium from circulating water solutions because of the cation exchange capacity of these substances. This process is well known in the scientific literature (see, for instance, Wahlberg et al 1965, Wallace et al 2012, Ning et al 2017): generally, strontium sorption increases as strontium concentration and total salinity of the solution decrease.…”

87Sr/86Sr Isotope Ratio as a Tool in Archaeological Investigation: Limits and Risks

“…Clay minerals, such as smectite, illite, and kaolinite, as well as organic matter may sorb strontium from circulating water solutions because of the cation exchange capacity of these substances. This process is well known in the scientific literature (see, for instance, [23][24][25]). Generally, strontium sorption increases as strontium concentration and total salinity of the solution decrease.…”

On the use of a multi-site ion-exchange model to predictively simulate the adsorption behaviour of strontium and caesium onto French agricultural soils

“…Samadfam et al (2000) worked with an unconditioned kaolinite and did not specify its purity. Ning et al (2017) studied the adsorption of Sr 2+ onto an Na-kaolinite and obtained KD between 600 and 40,000 L kg -1 (or mL g -1 ), i.e. log10KD between 2.8 and 4.6 at ionic strength between 10 and 0.1 mmol L -1 NaCl and pH 4.…”

“…Reinoso-Maset and Ly (2014) explored the exchange properties of kaolinite (Na + /H + , K + /H + , Cs + /H + , Ca 2+ /H + , Mg 2+ /H + , Cl -/OH -, and ClO4 -/OH -), but the behaviour of Sr 2+ was not included in the study. Ning et al (2017) evidenced only one type of site for the Sr 2+ adsorption on an Na-kaolinite. Studies are missing in the literature concerning chlorite.…”