Sorption and desorption of radiocesium on red earth and its solid components: Relative contribution and hysteresis

The relative contributions of organic matter and iron oxides to the Cs⁺ sorption on red earth were investigated by using the batch technique and selective extraction methods. The sorption and desorption isotherms and the distribution coefficients of Cs⁺ on the untreated red earth and the three treated soils to remove organic matter, iron oxides and organic matter plus iron oxides were determined at 20°C, pH 6.3 ± 0.2, in the presence of 0.01 mol/l CaCl₂. It was found that all the isotherms are linear in the Cs⁺ concentration range used here, that the sorption-desorption hysteresis on the red earth actually occurs, and besides the clay minerals, the organic matter present in the red earth is a significant trap of Cs⁺ and is responsible for the hysteresis instead of the iron oxides.