Uranium (VI) biosorption from process solutions

Abstract

Uranium(VI) biosorption from process liquor by Streptomyces levoris, Rhizopus arrhizus, mixed culture (activated sludge), Sacharomyces cerevisiae and Chlorella vulgaris was studied. The process liquor was derived from biological leaching of pyritic uranium ores. The sorption experiments included both dynamic and equilibrium studies. A Langmuir-type isotherm adequately described the sorption equilibrium data. At pH 5 and 20 °C, the maximum equilibrium sorption capacities ranged from 146 mg U VI g −1 (dry weight) biomass (mixed culture) to 240 mg U VI g −1 (dry weight) biomass (Rhizopus arrhizus). At lower pH values, the sorption capacities declined substantially. Thermal inactivation had only a marginal effect on the sorption equilibrium. Increasing the sorption temperature from 4 °C to 35 °C, however, enhanced biosorption by 40% – 90% for both inactivated and viable cells. The sulphate concentration and the metal ion contaminants (Ni, Zn, Cu, Co, Fe, Mn) adversely affected the biosorption of U VI. Of the metal ions tested, the ferric ion competed most effectively with the UO 2 2+ ion for sorption sites. It appeared that the ferric ion was preferentially sorbed by the biomass and increased Fe III concentration at lower pH values was the primary reason for the decline of U VI biosorption from process solutions saturated with respect to ferric hydroxide.