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Environmental Engineering Research 2002;7(3): 149-157. DOI: https://doi.org/10.4491/eer.2002.7.3.149
Mun Ja Kang, Bo Eun Han, and Pil Soo Hahn
Radioactive Waste Disposal Team, Korea Atomic Energy Research Institute, P.O. Box 105, Yuseong, Daejeon 305-600, Korea
Corresponding Author: Mun Ja Kang ,Tel: +82-42-868-2078, Fax: +82-42-868-8850, Email: munkang@kaeri.re.kr
Received: May 19, 2002;  Accepted: July 19, 2002.
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The uranium speciation at underground aqueous conditions was investigated by an equilibrium model calculation as well as precipitation experiments. Complexation reactions involving the aqueous and solid-phases of uranium hydroxide, uranium hydroxyl carbonate, uranium carbonate, and uranium oxide were considered in the model calculation using MINTEQA2 geochemical code. The batch-type precipitation or adsorption experiments were carried out at pHs 4-10 under 0% C02, air, and, 10% CO2 conditions. The dominant uranium species is VO22' at pHs 5 or below. Uranium is precipitated as species of /? -U02(OH)2(s) at a neutral pH. The precipitated uranium increases rapidly and then decreases with the increment of pH. The aqueous phases having a negative charge such as UOafOHK, (UChhCCyOHV and UChfCCh^4" are dominant species at a high pH. Adsorption characteristics of uranium on kaolinite are explained by complexation reaction on mineral surface and precipitation of uranium. The adsorbed fraction and precipitated fraction have the same tendencies as a function of pH. However, the absolute amount of adsorbed uranium is higher than that of precipitated uranium. This difference is mainly caused by the surface complexation of UCh2* and other uranium species. The rapid decrease in the adsorbed amount at a high pH can also be caused by the uranium species having a negative charge.
Keywords: adsorption | precipitation | speciation | uranium
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