Mineral dissolution and groundwater arsenic (As) and uranium (U) contamination in Newfoundland

Abstract

The studies presented in this thesis provide critical insights in understanding: (i) arsenic and uranium hosting minerals in natural sediments, and (ii) mechanisms that control arsenic and uranium release from natural sediments to groundwater. Two distinct sediment samples were collected, characterized, and examined with batch leaching experiments. Scanning electronic microscopy equipped with energy dispersive spectroscopy (SEM-EDX) and sequential extraction results showed that silicate minerals are the main arsenic hosting mineral, containing 75% of the total arsenic. Carbonate, Fe-Mn oxyhydroxides and silicate minerals are the major uranium hosting mineral. Batch leaching experiments showed that, besides desorption, dissolution of Fe oxyhydroxides and silicate minerals is an important mechanism controlling arsenic release. Uranium release increased with increasing pH, Eh, citrate, bicarbonate and natural organic matter (NOM) concentrations. Uranium desorption is the dominant uranium release mechanism under most of the water chemistry conditions tested in our leaching experiments.