Abstract: STUDIES ON THE ABSORPTION SPECTRA REDOX AND COMPLEXATION REACTION OF NEPTUNIUM IONS IN CARBONATE SOLUTIONLI YADONG；LIGUODING（Department of Environmental Engineering，Tsinghua University, Beijing，100084）ZHANG KUNMIN（National Environmental Proteclion Agency，Beijing，100035）ABSTRACT The behavior of neptunium in concentrated carbonate solutions is studied by controlled-potential electrolysis and spectrophotometry. The absorption spectra of neptunium ions indifferent oxidation states in carbonate solutions are obtained. The redox processes are analyzedand the formal potentials of the related couples are determined．The complex formation of neptu-nium ions in carbonate solutions with different concentrations is also studied.Key words Neptunium Carbonate solution Absorption spectrum RedoxComplexation reaction