Investigation of physicochemical form of uranium in sediment of brackish Lake Obuchi using sequential extraction procedure

The physicochemical form of uranium (238U) in the sediment of brackish Lake Obuchi was investigated using the standard procedures of sequential extraction. Approximately 60% to 70% of 238U was composed of the form bound to carbonates and iron (Fe)-manganese (Mn) oxides in silly sediments, whereas more than 50% of 238U existed in the minerals of sandy sediments. The proportions of 238U bound to carbonates in the sediments of brackish Lake Obuchi were larger than those in fresh-water lake sediments. Most of the uranium in the brackish lake sediment was considered to be mainly influenced by UO2(CO3)34- in seawater, judging from the fact that the 234U/ 238U activity ratios (1.13 to 1.16) of silly sediments were very close to that of seawater (1.14). The high correlation found between the 238U concentration in the sediment and the amount of organic matter demonstrated that organic matter acts as a scavenger for 238U accumulation on the lake bottom.