Ion effects on the uptake of uranium by Chlorella regularis.

Abstract

The effect of various cations and anions on the uptake of uranium by Chlorella regularis was examined. The uptake of uranium was hindered by phosphate and carbonate ions and was not affected by cations (sodium, potassium, ammonium, magnesium, calcium, manganese, cobalt, nickel, and zinc ions), nitrate, sulfate, and thiosulfate ions. The amounts of uranium taken up by C. regularis rapidly decreased with increasing the concentration of phosphate ion in the uranium solution. The amounts of uranium taken up by C. regularis also rapidly de-creased with increasing the concentration of sodium hydrogencarbonate in the uranium solution. The amounts of uranium taken up by C. regularis in the uranium solution con-taining 1.196×10^-3M/liter of sodium hydrogencarbonate were the largest at pH 5 and rapidly decreased in both low and high pH regions. The compositions of the chemical species of U(VI) in the carbonate solution were calculated, of which results suggested that carbonate ion formed the stable complex ions with uranyl ion, such as UO₂(CO₃)₂^2- or UO₂(CO₃)₃^4-, which were not taken up by C. regularis. From these results, we suggested that the uranium was taken up by C. regularis as the cation form (UO₂²⁺ or UO₂OH⁺), and Chlorella cells took up uranium in exchange for their protons in analogy with some organic chelating agents.