An Evaluation of the Distribution and Behavior of Uranium in Urmia Aquifer

This study examines changes in the concentration of uranium (U) in three different periods, the mechanisms of speciation, distribution, and potential sources of uranium in the groundwater resources of Urmia aquifer. The results show that the U content is generally more than 1 mg/kg in igneous and metamorphic rocks and typically 2–5 mg/kg in sedimentary rocks. Uranium concentration in all groundwater samples are below the maximum levels in drinking water recommended by WHO, USEPA and Iranian standard (30 ppb). The spatial distribution of U indicates that the maximum concentrations of U can be found in the vicinity of igneous rocks. Investigation of Uranium speciation in this aquifer for three consecutive sampling periods shows that uraninite (UO2) is the dominant species in Urmia aquifer in all three periods. The inverse geochemical modeling of groundwater samples demonstrates clearly that all samples are under-saturated respect with all uranium species. Based on the results, the mobility of uranium in groundwater is controlled by some factors such as Eh, pH, and concentrations of coexisting dissolved ions. In general, the three main mechanisms for controlling the mobility or deposition of uranium include the desorption of uranium absorbed onto ferric minerals (e.g. hematite and goethite), desorption of uranium adsorbed onto clay minerals and the release of uranium from the carbonate lattice structure due to replacement with calcium.