PHYSICAL AND CHEMICAL MECHANISMS OF URANIUM AND ARSENIC SORPTION IN LIMESTONE

This study investigates the physical and chemical mechanisms affecting the removal of uranium (U) and arsenic (As) using natural limestone in batch and column experiments. We will use spectroscopy, microscopy, diffraction, and aqueous chemical analysis in order to understand chemical speciation of U and As and their interactions with limestone. This study is relevant due to the extensive number of abandoned uranium mine sites located in Native American communities in which metal mixtures occur and negatively affect water quality. There are existing concerns about potential health hazards for communities located near these abandoned mine sites. Limestone has proven to be a useful material to remove heavy metals from water. Nonetheless, limited research has been conducted to identify the specific mechanisms affecting uranium reactivity with other metals onto limestone for potential affordable remediation applications. Our initial results from limestone column experiments indicate removal efficiencies up to 90% for As and 80% for U. These results suggest a high affinity of limestone to sorb these metals (e.g., via adsorption/precipitation) which could be a promising remediation strategy in abandoned mine sites. Current and future studies include additional batch and flow through experiments in order to investigate the influence of dissolved species, optimal mass to volume ratio and contact time, and sorption kinetic mechanisms. These experiments will be integrated with synchrotron-based techniques to identify adsorption and precipitation reactions. These data will provide insights to better understand the mechanisms facilitating U and As immobilization using natural limestone.