Behavior of radium, thorium and uranium in groundwater near the Buena Lagoon in the Coastal Zone of the State of Rio de Janeiro, Brazil

Abstract

Groundwater found near the head of the Buena Lagoon in the State of Rio de Janeiro, Brazil, has high salinity and low pH values. There is a strong correlation between concentrations of radium and light rare earth elements (LREEs) that suggests the leaching of monazite as a common source. Radium is present predominantly as 228Ra. The factors responsible for high radium mobility in groundwater seem to be high levels of salinity resulting in the competition for adsorption sites, and low pH values resulting in the limited adsorption of Ra2+ on the positively-charged surface of adsorbents. The behavior of uranium and thorium is also influenced by their speciation and low pH conditions. Uranium is present as a positively charged uranyl ion UO22+ in low pH samples and is very mobile. Similarly, the presence of positively charged Th4+ and thorium complexes with sulfate result in relatively high thorium concentrations at a low pH range. On the other hand, the mobility of phosphate released by dissolving monazite is probably reduced due to its adsorption and precipitation close to its source.