Uranium and thorium in sediments of the Ishim plain lakes (Northern Kazakhstan)

Abstract

The Ishim plain lakes adjoin to the Northern Kazakhstan uranium province suggesting leaching of uranium and trace metals by surface and underground water and their subsequent deposition in the lake sediments. The relevance of the study is caused by the need for ecological assessment of the lakes and their suitability for agricultural use. The main aim of the study is to determine chemical and mineral composition of sediments in the Ishim plain lakes as well as uranium content and deportment in bottom sediments to estimate their ecological safety for agricultural use. The methods used in this study: subsequent leaching of the sediments, X-ray fluorescence, X-ray diffraction analysis, IR-spectrophotometry, inductively coupled plasma mass spectrometry. The results of the study showed that concentrations of radioactive elements in the upper layer of the sediments are on background levels (U=0,78-3,3 ppm, Th=1,2-8,1 ppm, Th/U=1,5-4,7). This is representative for the undrained lakes of Western Siberia. The sediments have low uranium, thorium and trace elements concentrations; therefore the Ishim plain is ecologically safe region for agricultural use and use of mud for balneology. The following conclusion is drawn on the basis of the received data: the main factor of accumulation and redistribution of uranium in the Ishim plain lakes is the intensive salt deflation resulting in loss of uranium from the upper layer of the sediments.

Keywords

• geoecology
• hydrogeochemistry
• "water-sediments" system
• saline lakes
• sediments
• uranium