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Soluble Barium in Barite and Phosphogypsum Amended Mississippi River Alluvial Sediment

Carbonell, A. A., Pulido, R., DeLaune, R. D., Patrick, W. H.
Journal of environmental quality 1999 v.28 no.1 pp. 316-321
aerobic conditions, anaerobic conditions, aquatic plants, barite, barium, barium sulfate, chemical precipitation, drilling, groundwater, pH, petroleum, phosphogypsum, redox potential, sediment contamination, sediments, solubility, sulfides, wetlands, Louisiana, Mississippi River
Barite (BaSO), a density control material used in petroleum drilling fluids, can enter coastal and wetland environments. Because of its low solubility, it has been generally concluded that barium (Ba) will not leach into groundwater supplies, nor will it be taken up in significant quantities by plants and aquatic organisms. Such conclusions were mainly based on experiments conducted at neutral pH values and under oxidized conditions. The influence of pH and redox potential (Eh) on solubility of Ba from barite and phosphogypsum (PG) in Louisiana Mississippi River alluvial sediment was examined. Sediment suspensions containing barite or PG were incubated under oxidized and reduced conditions at pH 8, 7, 6, 5, and 4. The amount of Ba in solution at each combination (Eh-pH) was measured. Results demonstrated that a combination of low pH and highly anaerobic conditions resulted in a release of Ba to the sediment solution. If low pH and anaerobic environment happen simultaneously, barite can account for significant levels of dissolved Ba entering the environment. In this study, approximately 4.4% of the total native Ba present in Louisiana Mississippi River alluvial sediment was converted to a soluble form under acidic and anaerobic conditions, compared to approximately 0.3% under alkaline and either anaerobic or aerobic conditions. Phosphogypsum application to the sediment significantly reduced the level of soluble Ba compared to control sediments, this was attributed to Ba precipitation as insoluble sulfates or sulfides under oxidized and reduced conditions.