Highly mineralized closed lakes on the territory of ore regions of Mongolia are of special interest in relation to the search for nonconventional sources of metals. Water of soda Shaazgai-Nuur Lake contains ~1 mg/L U, and the content of the undesirable admixture of As is up to 300 g/L. Uranium and Arsenic speciation in solution and in the bottom sediments of the lake was estimated using thermodynamic modeling, and a method of their separation was suggested. Calculation of the models of sorption of these elements by goethite and calcite showed that at pH 9.4 typical of natural water it could be effective only at a high concentration of FeOOH sorbent. In this case, at pH < 5 and > 8 (the area of U sorption), As may be removed by simple filtering of solutions from the suspension upon additional coagulation
