Thallium and Radium mobility in the environment

Thallium and Radium are two harmful pollutants with a natural cycle modified by anthropogenic releases. Consequences on these cycles are not completely predictable. Besides, while radium speciation is well known, thallium’s is much less studied. For both Ra and Tl, interactions with natural organic matter are unknown and similar observations are valid for Tl regarding clay minerals. The main purpose of this work was to characterize processes involved in Tl and Ra adsorption/complexation with different phases and their impact on each element cycles. Ra and Tl complexation with a purified humic acid was studied with an experimental device called Donnan Membrane Technique and then described with the NICA-Donnan Model. A similar approach was used while studying Tl sorption on two clay minerals, illite du Puy and Wyoming smectite. Thus, batch experiments were coupled with modelling by ion exchange theory in order to describe Tl interactions with these clay minerals. All these results generated new constants for thallium and radium and allowed new interpretations regarding their speciation in natural waters and soil solutions. Finally, to study the fate of radium at various natural interfaces (e.g. water-sediment), an in-situ passive sensor was tested to measure Ra. Consequently, the second purpose of this study was to address sensor possible limitations at various redox, in changing concentrations over time or regarding competitive effects with major cations in solutions.