Sorption behavior of cesium on silt and clay soil fractions.

The effect of clay mineral composition on Cs adsorption behavior of silt and clay fractions (SC-fractions) of soil was investigated. Surface soil samples were collected within 2 km of Kori and Wolsong nuclear power plants in South Korea, and SC-fractions (<20 µm) were separated. The physicochemical properties of SC-fractions and types of clay minerals contained in the SC-fractions were analyzed. The cesium adsorption capacity of the SC-fractions, and affinity between the SC-fractions and Cs, were investigated by isothermal adsorption analysis using the dual-site Langmuir adsorption model. To understand selective adsorption of Cs, the radiocesium interception potential and distribution coefficient of the SC-fractions were analyzed in the presence or absence of competing ions. The radiocesium distribution coefficient of the SC-fractions showed a trend similar to that of the Langmuir sorption coefficient of high-affinity binding sites for Cs in the SC-fractions. The SC-fractions of Kori soils that contain only non-expandable clay minerals including highly weathered mica had low Cs adsorption capacity. However, the SC-fractions of Kori soils showed higher Cs adsorption selectivity compared to the SC-fractions of Wolsong soils containing expandable clay minerals and micaceous mineral with a low degree of weathering. It is predicted that the highly weathered micas have high affinity to Cs, and such clay minerals contribute the most to the adsorption process in dilute solutions.

A remotely steerable Janus micromotor adsorbent for the active remediation of Cs-contaminated water.

We report the development of magnetically steerable self-propelled micromotors that selectively remove radioactive Cs from contaminated water. Mesoporous silica microspheres were functionalized with the highly Cs-selective copper ferrocyanide, and half of the adsorptive particle surface was then coated with ferromagnetic Ni and catalytic Pt layers to fabricate Janus micromotors. The micromotor adsorbent displayed random propulsion in an H2O2 solution via catalytic bubble evolution from the Pt surface, and the micromotor adsorbent self-propulsion resulted in an 8-fold higher Cs removal compared to the stationary adsorbent within one hour. The ferromagnetism of the Ni layer allowed the micromotor adsorbent to be magnetically and remotely steerable, and the propulsion speed under a magnetic field was ˜11-fold greater than it was in the absence of the magnetophoretic force. The adsorption of Cs by the self-propelling micromotor adsorbent and the subsequent magnetic recovery of the adsorbent enabled the successful removal of radioactive 137Cs from aqueous solutions. More than 98% of the radioactive 137Cs ions were removed from solution, even in the presence of competing ions, such as Na+ (1000 ppm).