Some Aspects of Fixation of Uranium from Natural Waters

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Uranium in natural waters can be fixed either by precipitation of uranium minerals or by adsorption on some adsorbents such as clay minerals and carbonaceous materials. The precipitation is controlled by factors contributing to the conditions of a system from which a uranium mineral is precipitated, such as temperature, pressure, pH, Eh. and concentration of the elements constituting it. Each factor was examined thermochemically along with some experiments. Decrease in Eh is most effective for the formation of primary uranium minerals, while pH and concentration of such anions as phosphorus, vanadium and arsenic play the most important role in the precipitation of secondary uranium minerals. Adsorption and desorption experiments of hexavalent uranium to montmorillonite, kaolin, and limonite reveal that they have more or less an order of 10, 000ml/g of enrichment factor (Kd) at about pH6. The adsorbed uranium was found to alter to a uranium mineral most favourable for the surrounding condition when aged experimentally. It suggests that the adsorbents perform a kind of catalytic action for the formation of uranium minerals from very dilute solution such as surface waters.
資源地質学会の論文