IN VITRO SOLUBILITY OF YELLOWCAKE SAMPLES FROM FOUR URANIUM MILLS AND THE IMPLICATIONS FOR BIOASSAY INTERPRETATION*

Abstract

The rates of dissolution of uranium product (yellowcake) obtained from four uranium ore processing mills were determined. Thirty-day dissolution experiments were conducted in vitro using two solvents: 0.1 M HC1 and a simulant of an ultrafiltrate of blood serum containing diethylenetriaminepentaacetic acid (SUF + DTP A). The samples were characterized using X-ray powder diffraction and infrared spectroscopic techniques as mixtures of ammonium diuranate and U3O8. The combined results show that ammonium diuranate dissolved much more rapidly in either solvent than did U3O8. Dissolution half-times in SUF + DTPA were: ammonium diuranate ≃ 10hr, U3O8 ≃ 10*hr. These values are comparable to those derived from available human exposure data and suggest that ammonium diuranate should be included in the Class D solubility category. The percentage of total material present as the more soluble form was shown to vary from 26 to 86% in agreement with quantitative infrared analyses. The dissolution results indicate that caution must be exercised in the interpretation of bioassay results of workers from different uranium mills.