Study of sorption of selenium dominant species on goethite as a model system for the long-lived radioisotope of selenium

Long-lived radionuclides may be considered in the future as a biosphere contaminants. The potential of releasing radionuclides from geological repositories, in future climate scenarios, is currently topic of the research. Selenium has a radioactive long-lived isotope ⁷⁹Se. As suitable sorption material for the removal of selenium from water are iron oxohydroxides, which have a large sorption capacity for many elements. In our work we investigated the sorption properties of goethite against the dominant oxidation states selenite and selenate, which showed different sorption behaviour. The sorption of selenite is optimal in range of pH 1.5 - 5,0. On the other hand the sorption of selenate is optimal in range of pH 1.5 - 2.0. Sorption kinetics have been fitted by pseudo-first and pseudo-second order models and thermodynamic has been fitted by Langmuir and Freundlich isotherms. Study on competitive sorption behaviour showed significant influence of phosphate on selenite sorption. There was relatively small influence with equimolar concentrations and no influence with excessive concentrations of sulphate and chloride ions. (authors)