Abstract
Abstract In carbonate-buffer seawater or salt lake brines, three main uranium complexes, U(VI)-CO3 and Ca/Mg-U(VI)-CO3 complexes had been highlighted so far. In this paper, the effects of carbonate and its complexes on U(VI) adsorption onto doped polyaniline (PANI) were investigated using batch adsorption experiments. The adsorption equilibrium of U(VI) on doped PANI was reached within 30 min of contact time when U(VI)-CO3 complexes dominated the aqueous chemistry. Pseudo-second order and Langmuir isotherm models indicated that adsorption occurred on the homogeneous surface via monolayer chemisorption. Moreover, the increase in pHinitial, dissolved carbonate, calcium and magnesium concentrations could suppress the uranium adsorption process. The adsorption mechanisms under the weakly basic conditions were primarily involved in uranium anion species adsorption on nitrogen-containing functional groups instead of the anion exchange reactive sites on the doped PANI surface sites, whereas the U(VI)-CO3 complexes had a greater affinity than the Ca/Mg-U(VI)-CO3 complexes. The findings of this study are significant for the extraction of uranium resources from salt lake brines or seawater and for the prediction of uranium adsorption behaviors in weakly basic solution environments.
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