Cesium adsorption/desorption behavior of clay minerals considering actual contamination conditions in Fukushima

Cesium adsorption/desorption experiments for various clay minerals, considering actual contamination conditions in Fukushima, were conducted using the Cs-137 radioisotope and an autoradiography using imaging plates (IPs). A 50 mu l solution containing 0.185 similar to 1.85 Bq of Cs-137 (10(-11) similar to 10(-9) molL(-1) of Cs-137) was dropped onto a substrate where various mineral particles were arranged. It was found that partially-vermiculitized biotite, which is termed weathered biotite (WB) in this study, from Fukushima sorbed Cs-137 far more than the other clay minerals (fresh biotite, illite, smectite, kaolinite, halloysite, allophane, imogolite) on the same substrate. When WB was absent on the substrate, the amount of Cs-137 sorbed to the other clay minerals was considerably increased, implying that selective sorption to WB caused depletion of radiocesium in the solution and less sorption to the coexisting minerals. Cs-sorption to WB continued for about one day, whereas that to ferruginous smectite was completed within one hour. The sorbed Cs-137 in WB was hardly leached with hydrochloric acid at pH 1, particularly in samples with a longer sorption time. The presence/absence of WB sorbing radiocesium is a key factor affecting the dynamics and fate of radiocesium in Fukushima.