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

Abstract

The rates of dissolution of U product (yellowcake) obtained from 4 U ore processing mills were determined. Thirty-day dissolution was conducted in vitro using 2 solvents, 0.1 M HCl and a simulant of an ultrafiltrate of blood serum containing diethylenetriaminepentaacetic acid (SUF + DTPA). The samples were chracterized using X-ray powder diffraction and IR spectroscopic techniques as mixtures of ammonium diuranate and U3O8. Ammonium diuranate dissolved much more rapidly in the solvents than U3O8. Dissolution half-times in SUF + DTPA were .simeq. 10 h for ammonium diuranate and 104 h for U3O8. Human exposure values were comparable. Ammonium diuranate should be included in the Class D solubility category. The percentage of total material present as the more soluble form varied from 26-86% in agreement with quantitative IR analyses. The dissolution implies caution must be exercised in the interpretation of bioassays of workers from different U mills.