Preconcentration of Radium Isotopes from Natural Waters Using MnO2 Resin

Abstract

We have characterized a new resin, “MnO2 Resin”, developed by the PG Research Foundation, for radium adsorption over wide ranges of pH, reaction times and salt concentrations. We show that the sorption of 133Ba (used as a proxy for Ra) is highly dependent on pH with the most useful range from pH 4 to 8. Apparently, the surface layers of the Mn oxides become more positively charged under acidic conditions (below pH 4), which prevents diffusion of positively charged alkaline earth species (e.g. Ba2+, Ra2+) into the sorption sites. Adsorption at higher pH is thought to be inhibited because of carbonate complexation. We found that the sorption characteristics for radium onto MnO2 Resin are especially favorable for low salinity waters, but the sorption is still very satisfactory (KD=2.8×104) for highly salted solutions but with slower kinetics. For analytical purposes, both column and pump experiments showed high recoveries with no measurable discrimination between Ra and Ba regardless of flow rates in fresh water. Seawater tests showed lower recoveries and higher Ra than Ba adsorption at flow rates above 10 mL/min.