H089-0015
DISTRIBUTION OF URANIUM AND ARSENIC BETWEEN SEDIMENTS AND LAKE WATER IN ALKALINE- HYPOSALINE LAKE FROM VALLEY OF GOBI LAKES IN MONGOLIA

Thursday, 10 December 2020
Poster
Baasansuren Gankhurel1, Keisuke Fukushi1, Davaadorj Davaasuren2, Takuma Kitajima3, Noriko Hasebe4 and Eigo Imai1, (1)Kanazawa University, Kanazawa, Japan, (2)National University of Mongolia, Ulaanbaatar, Mongolia, (3)Kanazawa University, Institute of Nature and Environmental Technology, Kanazawa, Japan, (4)Kanazawa Univ, Kanazawa, Japan
Abstract:
Saline lakes represent 23% of the area of all lakes on Earth and located mostly in arid and semiarid climates.

Saline lakes are mainly fed by precipitation and surface flow. But also, water lost by evaporation has significant role in saline lake. Evaporation of the lake water results the formation of contaminated lake water and salt deposits containing high levels of dissolved species including trace elements such as arsenic and uranium. The chemical speciation of trace elements in sediments and distribution between the sediments and lake water are essential for the understanding of formation process and the mobility of trace elements.

This study aims to clarify distribution process of As and U in saline lake water and sediment by using sequential extraction procedure, X-ray diffraction and synchrotron-based X-ray absorption spectroscopy. The water chemistry, the mineralogy of the sediment and suspended material samples of closed-basin alkaline-hyposaline lake (Orog and Olgoy lakes) in semi-arid climates in the Valley of Gobi lakes in Mongolia were studied.

We measured lake water samples in different seasons from 2015 to 2020. Olgoy and Orog lakes exhibited pH exceeded 9 and salinity above 1300 mg/kg. The lake waters major cation and anion are Na, Cl and SO4. The high Na and Cl concentrations are result of evaporation of the lake waters. Also, our results showed that high concentrations of As and U in lake water, respectively. Therefore, the concentration of arsenic and uranium differed in different months which need more clarification to understand the process between lake-sediment interaction. The results of sequential extraction analysis showed that arsenic and uranium in sediments are distributed into calcium carbonates rather than amorphous iron oxide. XRD results shows that sediment sample has authigenic minerals including calcite and Monohydrocalcite.

The present study reveals that high concentration of uranium and arsenic in alkaline saline lake water which might from carbonate minerals of lake sediments. I expect the high concentrations of As and U must be achieved by evaporation of inflow (river water). Part of these elements possibly are removed by the authigenic carbonates. Carbonates are not “source” of these elements but “sink”. However, we need to clarify how much the carbonates play a role of “sink”.

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