Numerical Physicochemical Modeling of the Geochemical Behavior of Uranium and Thorium in Radon Waters of Southern Siberia

Abstract

The first results obtained by the numerical physicochemical modeling of uranium and thorium behavior in the radon-rich waters of southern Siberia are presented. The studied waters are characterized by a wide variation of geochemical parameters (pH varies from 5.9 to 10.1; Eh from − 500 to + 285 mV), have diverse chemical composition, with dominating HCO₃ Mg–Ca, HCO₃ Na–Ca and Cl–SO₄ –HCO₃ Na, SO₄–HCO₃ Na–Mg–Ca types, with TDS value varying from 0.2 to 2.6 g/dm³ and silicon content 0.52–32.90 mg/dm³. The possibility for uranium minerals to be formed from the radioactive waters of southern Siberia has been established: In particular, uraninite and thorianite can be most actively precipitated within rather broad range of redox conditions, while uranium black is to occur less frequently. The possibility for thorium minerals to occur in trace amounts is also determined, with thorianite ThO₂ as the most probable one. At pH values around 5, the formation of thorium sulfate Th(SO₄)₂ is also possible. In an acidic, strongly reducing environment with Eh < − 300 mV, trace amounts of ThS₂ and Th₂S₃ may be deposited.