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Microspheres of aluminosilicate glass from volcanic sediment, whose surface was modified with functional groups, Shirasu-balloons (SB) were investigated as an adsorbent to remove cadmium ion from the contaminated soil. The introduction of thiol group (-SH) on the surface of SB enabled to adsorb cadmium ion, meanwhile the introduction of an alkyl group (-ODS) made the surface of SB hydrophobic, consequently increased the mechanical strength of SB. Those adsorbents could float up on the water surface after adsorption process. The prepared adsorbent was characterized by FTIR spectrophotometer, elemental analysis and optical microscope for photographic images. The adsorption of cadmium ions on the adsorbent was investigated by comparing the results by a plain SB with those by thiol-functionalized SB. The adsorption maximum for cadmium ion was 3.75 mg/g for SH-SB and 2.62 mg/g for SH-ODS-SB, respectively. The adsorption of cadmium ions on the functionalized SH-SB and SH-ODS-SB was fitted well to the Langmuir isotherm equation. After shaking time for 24 hours, the recovering ratios of the absorbents from soil were 73 wt% for SH-SB and 98 wt% for SH-ODS-SB absorbents. In addition, the kinetic and adsorption-desorption properties of the adsorbent were also discussed.

The interactions between cesium ions and two kinds of 2 : 1 clay minerals (kaolin and vermiculite) were investigated under batch conditions and dynamic equilibrium using the electrokinetic (EK) process. The adsorption capacities of kaolin and vermiculite were 1.2 and 18.8 mg/g, respectively, at pH 6 after 24 h in the batch system. Because the basal spacing of kaolin is 0.93 nm, Cs ions cannot enter the interlayers. On the other hand, the basal spacing of vermiculite is 1.01 nm, and vermiculite can adsorb Cs ions in the interlayers. Four kinds of model soils with di erent ratios of vermiculite to kaolin were prepared by mixing these two types of clay minerals, and the migration behaviors of Cs ions in these soils on the application of the EK process were determined. The Cs ion migration e ciency decreased with an increase in vermiculite content. The content of vermiculite in the soil was an important factor determining the migration behavior of Cs ions under the dynamic equilibrium conditions produced by the EK process. The applications and limitations of the EK process for the removal of cesium from contaminated soil are discussed.

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