ASSESSMENT OF THE LEVEL AND DISTRIBUTION OF TRACE ELEMENTS IN FLUVIAL SEDIMENTS FROM THE COAL COMBUSTION RESIDUAL IMPACTED AREAS IN ALABAMA

Coal combustion residuals (CCRs) are generated when coal is burned to produce electricity and a long list of toxic trace elements including arsenic, molybdenum, and other carcinogens can be found in CCRs. The contamination of sediments, groundwater, and surface water from CCR is a major problem worldwide since it may pose a risk to the environment and drinking water resources. It is, therefore, crucial to understand the level, fate, and transport of toxic trace elements associated with CCRs under various physicochemical and biogeochemical conditions.

This study focuses on understanding the level, speciation, and distribution of arsenic and molybdenum in riverbed sediments potentially impacted by CCRs. The sediment samples were collected along the Coosa River near two Power Plant sites in Alabama. X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Scanning Electron Microscope and Energy Dispersive Spectroscopy (SEM-EDS) were used to characterize the mineral composition and their arsenic, molybdenum, iron, and sulfur content. Preliminary XRF analysis has confirmed the presence of arsenic and molybdenum in the bulk sediment. To better quantify the concentrations of arsenic and molybdenum in the sediments, high resolution Inductively Coupled Plasma Mass Spectrometer (ICP-MS) is also used. The level and relative abundance of trace elements were evaluated by a comparison of the bulk chemical concentration of sediments collected from adjacent to the power plant sites and those from upstream and downstream locations. Finally, a new thermodynamic database has been created for Geochemist’s Workbench to investigate the speciation and mobility of arsenic and molybdenum under varying pH and redox conditions. Overall, the ongoing mineralogical and geochemical analysis of bulk sediment samples and geochemical modeling will provide new insights and proof of concept for the sequestration of arsenic and molybdenum in CCR-impacted sediments.