Uranium: Radionuclides

Abstract

This article describes the occurrence, chemistry, and bioavailability of uranium (U) in terrestrial and aquatic environments, its analysis in environmental samples, and remedial measures applicable to uranium‐contaminated water and soil. Uranium is widely distributed throughout the world. There are three main isotopes present in natural uranium, which comprises 234 U (0.0055%), 235 U (0.72%), and 238 U (99.27%). Uranium can occur either in its reduced state (U(IV)), which is generally highly immobile, or in its more soluble and mobile (U(VI)) state. Uranium mobility and bioavailability are governed by oxidation state, complexation by organic and inorganic ligands, pH, sorption by minerals including clays and hydroxides, and interactions with organic matter. In uncontaminated surface waters uranium content is generally low (<1 ppb). Most groundwaters are low in uranium but the concentration range is large (<0.001–2600 ppb), resulting from the interaction of groundwater with naturally occurring uranium‐bearing materials or anthropogenic contamination sources. Since groundwater is a major source for drinking water, various methods have been developed to remove uranium from potable water. Similar methods are applied in wastewater treatment. Extraction and processing of uranium ore or minerals containing natural radionuclides has resulted in the generation of waste streams. The major challenge associated with these contaminated waste streams, residues, or sites is typically the larger volumes of material and the relatively low specific activities.