Batch and in situ X-ray absorption spectroscopy (XAS) analysis were applied to the identification of selenium in aqueous solution containing selenite (Sed(IV)O-3(2-)) and selenate (Sed(VI)O-4(2-)) ranging from 10 to 1000 mg-Se/L, respectively. Se K-edge XANES spectra were detected by means of a multi-channel silicon drift detector (SDD). Furthermore, the oxidation state of selenium was identified by measuring the energy of X-ray absorption, and the local structure around selenium atom was determined by analyzing the EXAFS. The Se K-edge XANES spectrum of selenite was gradually shifted to that of selenate in the presence of peroxodisulfate ion (S2O82-) which was the dominant oxidizing agent in wet flue gas desulfurization (FGD) liquor and had a subsequent effect on the selenium oxidation in the liquid phase. Concentrations of selenite and selenate calculated by linear fitting analysis of the XANES spectra were in good agreement with the results of quantitative analysis for selenite and selenate by ICP-AES. (C) 2012 Elsevier Ltd. All rights reserved.