Separation methods for isolation, determination and speciation of radionuclides

The thesis is an overview of author's research activity in separation processes for radionuclides isolation, determination and speciation. Extraction method was used for separation of technetium and palladium from nuclear waste acid solutions left from Purex separation process. Solutions of trioctylamine (TOA) in tetrachloromethane are suitable for extraction of pertechnate anions from nitrate solutions without used of solubilizers. The radiation and chemical instability of the extractants is practically manifested only by the formation of limited quantity of hydrochloride acid. The possibility of simultaneous extraction of palladium and technetium from nitrate solutions with TOA was proved. Extraction of pertechnetate after reduction with thiourea from nitric solutions was achieved by bis(1,2-dicarbollyl)cobalt (III) anion in organic mixture of nitrobenzene-chloroform or bromoform. Theoretical comparison of the equilibria and kinetics of solvent extraction (SX) and emulsion liquid membrane extraction (MX) was performed using the distribution ratios at the outer inner boundaries of liquid membrane. Enhancement factors, per-traction factor (p) and multiplication factor (N), were proposed to express efficiency of the MX technique. The extraction of cesium, strontium, uranium, cobalt, cerium and technetium was investigated from this point of view. The most perspective systems are those with chelating reagents, especially at low concentration or reagent. A continuous liquid membrane extraction device for preconcentration of metals with light phase internal recycle was developed. The system was used for preconcentration of cobalt and uranium. Transport strontium using bulk liquid membrane with 18-crown-6 ether and picric acid was studied. Per-traction parameters as well as influence of surfactants SPAN 80 and ECA 4360 were established. Supported liquid membrane with 18-crown-6 ether and picric acid and dichlorobenzene were used for alkali and alkaline earth metals. The system proved that transport rate of metals trough organic membrane depends on the stability constant of metal with 18-crown-6 for the same condition. An on column radiometric detector for capillary isotachophoresis was developed. The detector from plastic scintillator with counting efficiency 13-15 % for low beta emitters proved its application for the study of radiolabelled compounds. Organised structure systems containing micelles and aphrons were used for separation of strontium. Membrane or sorption technique was used to separate formed heterogeneous system and pre-concentrate strontium from aqueous phase. Coprecipitation of radium and lead with strontium or calcium complexes with 18-crown-6 or 15-crown-5 and tungstosilicic acid was studied. The sorption of cesium, strontium, plutonium and heavy metals from aqueous solutions by natural zeolitic materials, bentonite, illite and synthetic materials were studied. The metal uptake and the distribution coefficient (Kd) values determined for the of different origin were correlated with their mineralogical composition and their gross cation exchange capacity (CEC). The sorption on materials was correlated with their Gross Annual Stopping Power (GASP). The comparison of the obtained data indicated, that Slovak synthetic zeolite NaY shows the best sorption characteristics among the studied materials. Different Illite particles showed that selectivity for cesium depends on the total surface of frayed site. A composite synthetic material on the base of ferrocyanide and silica gel materials for selective cesium sorption was developed. This material is suitable for cesium sorption from liquid radioactive wastes from nuclear power plant (NPP). Modified silica gel material with imidazole, dibenzo-18-crown-6 (DB18C6) and diaza-18-crown-6 (DA18C6) were prepared. It was proved that meso-porous silica materials with uniform pore diameter have a positive influence on access of cobalt ion to sorption center to increase of sorption capacity of sorbent. Extraction method was used for separation strontium-90 and plutonium-239, 240 prior to its determination in environmental samples or radioactive wastes. The method was used for monitoring of the environment of NPP. Speciation of radionuclides in milk and aqueous solutions containing humic acids was studied by high performance size exclusion chromatography and ultrafiltration technique. (author)