Speciation of natural uranium and thorium in surface waters around a uranium mine (Bistrita Mts., Romania)
Résumé
ICP-AES method was used to evaluate the impact of uranium mine dumps on the surface waters from Crucea region (Romania). Speciation modelling indicates that uranyl-carbonate
UO2(CO3)2-2 and hydroxy uranyl-carbonate UO2CO3(OH)3- are the main uranium species and that thorium hydroxyl-carbonate Th(OH)3CO3- represents the main thorium species in these waters. Uranium is the most significant trace element in the surface waters nearby the waste rock dumps, sometimes reaching levels op up to 1 mg L-1, well in excess of the
Romanian standards limits. A remarkably good correlation exists between dissolved U and the sum of anion concentrations (NO3- + CO32- + SO42- + Cl-) whereas no correlation was found between U and silica, indicating that uranium in these stream waters derived mainly from oxidation of uraniferous bitumen and/or dissolution of carbonates.