Sorption and speciation of radiocesium in the components of soil and soil decontamination (Dissertation submitted for fulfillment of the scientific degree 'Philosophiae doctor' (PhD.))

The determination of radioactive cesium mobility is an important characteristic of environmental geoinformation systems (EGIS). Current methods utilize for cesium speciation sequential leaching or selective replacement from the regular surface (SRIP method). The selective leaching methods do not provide sufficient speciation of univalent ions and SRIP method is not reliable in the presence of humic substances. The method for the determination of cesium mobility in soil was worked out on the basis of partial irreversible sorption model. The method is characterized by the ration of fixed (irreversible sorbed) component Rfix on the frayed edges sites to the distribution coefficient Kd on the regular surface. Montmorillonite K-10 spiked with Cs-137 and humidified with humic acid was used as a reference standard. The portion of fixed cesium in montmorillonite does not depend neither on the concentration of desorption agent nor ionic strength. Repeated desorption was investigated the desorption solutions of salts of 13 cations. The ammonium acetate desorption solution (1 M) was suggested as the most appropriate one for the routine use. The method of the variable ratio of liquid phase volume versus solid state weight (V/m) was elaborated in order to determine the fixed component as well as Kd(Cs). The obtained results correspond with those from repeated leaching. The advantage of the method is simultaneous sample processing resulting in timesaving over the serial EGIS analyses. Sorption and desorption of cesium on the clay minerals result in the decrease of distribution ration values when sorption effect takes place. The effective method designed for decontamination of soil polluted by toxic radionuclides was elaborated. The method utilized magnetic sorbent on the magnetite and blended oxides basis. The magnetic sorbent activated by wet milling with 5% solutions of potassium ferrocyanides removes from soil approximately 60% of mobile cesium and up to 65% of total strontium, respectively within one-staged contact of suspension and sorbent. It was proved that the model of three-phase equilibrium of exchangeable cesium is employed under given conditions. (author)