Analytical methodology for the study of decontamination factors in mixer-settlers

Due to the complexity of the samples, the choice of the analytical methodology to be applied at a radiochemical laboratory, for the evaluation of different separation steps if of a great importance. It is necessary to know the performance of mixer-settlers in two extreme situations: efficiency limit determined by fluid dynamic factors and separation factor determined by physicochemical variables. The element used to determine the efficiency limit was magnesium, due to its low distribution coefficient in tri-n-butyl phosphate (TBP). Zirconium, being one of the principal fission product, is partially extracted and was used to study the influence of chemical conditions. Atomic absorption spectrometry was selected for the determination of micro quantities of magnesium, and complexometry for macro quantities of this element. It was necessary to separate uranium using extraction chromatography with Kel F-TBP columns. Concentration range was 0.1 - 1 mg/L and 7 - 70 g/L respectively. Zirconium was determined by spectrophotometry with xylenol orange. For organic samples, it was necessary to reextract the analyte with fluoride, to evaporate with sulfuric acid and to complex the excess of fluoride with aluminum. Uranium determinations, required for mass balance, were carried out by spectrophotometry and potentiometry depending upon concentration. Because of the presence of zirconium, two methods were developed for uranium determination using liquid-liquid extraction in the presence of complexing agents. In one case, TBP was used as extractant, dibenzoylmethane as chromogenic reagent and EDTA as complexing agent. For very low quantities of uranium, tri-octyl phosphine oxide (TOPO) was the extractant, 2-(2-thiazolylazo)-5-diethylaminophenol (TAAP) the chromogenic reagent, and (1-2-cyclohexylenedinitrilo) tetraacetic acid (CDTA) the complexing agent. (Author)