Predominance of aqueous Tl(I) species in the river system downstream from the abandoned Carnoulés mine (Southern France)

Abstract

Thallium concentration reached up to 534 μg L-1 in the Reigous acid mine drainage downstream from the abandoned Pb-Zn Carnoulès mine (Southern France). It decreased to 5.44 μg L-1 in the Amous River into which the Reigous creek flows. Tl(I) predominated (>98% of total dissolved Tl) over Tl(III),mainly in the form of Tl+. Small amounts ofTl(III) evidenced in ReigousCreek might be in the form of aqueous TlCl 2+. The range of dissolved to particulate distribution coefficients log Kd = 2.5 L kg-1 to 4.6 L kg-1 indicated low affinity of Tl for particles, mainly ferrihydrite, formed in the AMD-impacted watershed. The low retention of Tl+ on ferrihydrite was demonstrated in sorption experiments, the best fit between experimental and modeled data being achieved for surface complexation constants log K ads = -2.67 for strong sites and log Kads = -3.76 for weak sites. This new set of constants allowed reasonable prediction of the concentrations of aqueous and particulate Tl resulting fromthe mixing of water fromReigousCreek and the Amous River water during laboratory experiments, together with those measured in the Amous River field study. © 2011 American Chemical Society.