Radium geochemistry of ground waters in Paleozoic carbonate aquifers,midcontinent, USA |
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| Institution: | 1. Southern California Coastal Water Research Project, Costa Mesa, CA, United States;2. ADH Environmental, Arcata, CA, United States;3. Applied Marine Sciences, Santa Cruz, CA, United States;1. Departamento de Petrologia e Metalogenia, Universidade Estadual Paulista (UNESP), Câmpus de Rio Claro, Av. 24-ANo.1515, C.P. 178, CEP 13506-900 Rio Claro, São Paulo, Brazil;2. College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518060, China;3. Science and Engineering Faculty, Queensland University of Technology (QUT), GPO Box 2434, Brisbane, Qld 4001, Australia;1. U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 95819, United States;2. U.S. Geological Survey, 10 Bearfoot Road, Northborough, MA 01532, United States |
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| Abstract: | The purpose of this study was to elucidate the processes controlling the distribution and behavior of the longer-lived Ra isotopes in continuous Paleozoic carbonate aquifers of parts of Missouri, Kansas, and Oklahoma. Activities of (228Ra) and (226Ra) were analyzed in fresh and saline ground waters, brines, and rocks. The fluids have a wide salinity range (200–250,000 mg l?1 total dissolved solids). The (226Ra) activity ranges from 0.66–7660 dpm kg?1 and correlates with salinity and other alkaline earth element (Ca, Sr, and Ba) concentrations. The range of (228Ra:226Ra) ratios in the fluids (0.06–1.48) is similar to that in the aquifer rocks (0.21–1.53). The relatively low mean fluid (228Ra:226Ra) ratio (0.30) reflects the low Th:U ratio of the predominant carbonate aquifer rock. Radium occurs mostly (≥77%) as Ra2+ species in the fluids. Salinity-dependent sorption–desorption processes (with log K values from 100–104 and negatively correlated with salinity), involving Th-enriched surface coatings on aquifer flow channels, can explain the rapid solid–fluid transfer of Ra isotopes in the system and the correlation of Ra with salinity. |
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