Radon Emanation from Uranium Mill Tailings

Abstract

Alkaline circuit and a mixture of acid and alkaline circuit uranium mill tailings sampled at an inactive millsite near Monticello, Utah, and tailings from an active, acid- leach uranium mill were separated into particle-size fractions ranging from +10 mesh to −325 mesh by dry and wet separation techniques. The radium-226 contents and radon-222 emanation coefficients of these fractions were determined. Dry tailings show a high degree of aggregation that tends to mask the relationship of properties, such as radium content and radon-emanating power, to dispersed-particle size. Coarse-tailings fractions (+ 325 mesh) had emanation coefficients that were from 25 to 45 percent lower than those of their fine-fraction counterparts. Emanation coefficients measured for tailings derived from a salt-roast/carbonate-leach process suggest that such ore roasting does not lead to reductions in radon emanation in the tailings derived therefrom. Three ore samples of differing uranium mineralogies and rock types were leached with either sulfuric acid or sodium carbonate solutions under laboratory conditions to simulate acid or alkaline uranium milling practices. The radon emanation coefficients of the initial ore and of the tailings derived from them were compared. No consistent pattern enabling the prediction of radon emanation coefficients of tailings on the basis of ore type was evident. The similarities in the coefficients of the acid-leach tailings suggest that the lixiviant solution plays an important role in determining the form, and hence, the emanating power of the radium retained therein.