Soluble barium in barite and phosphogypsum amended Mississippi River alluvial sediment

Barite (BaSO4), a density control material used in petroleum drilling fluid s, can enter coastal and wetland environments. Because of its low solubilit y, it has been generally concluded that barium (Ba) will not leach into gro undwater supplies, nor will it be taken up in significant quantities by pla nts and aquatic organisms. Such conclusions were mainly based on experiment s conducted at neutral pH values and under oxidized conditions. The influen ce of pH and redox potential (Eh) on solubility of Be from barite and phosp hogypsum (PG) in Louisiana Mississippi River alluvial sediment was examined . Sediment suspensions containing barite or PG were incubated under oxidize d and reduced conditions at pH 8, 7, 6, 5, and 4. The amount of Ba in solut ion at each combination (Eh-pH) was measured. Results demonstrated that a c ombination 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 e ntering the environment. In this study, approximately 4.4% of the total nat ive Ba present in Louisiana Mississippi River alluvial sediment was convert ed to a soluble form under acidic and anaerobic conditions, compared to app roximately 0.3% under alkaline and either anaerobic or aerobic conditions. Phosphogypsum application to the sediment significantly reduced the level o f soluble Ba compared to control sediments, this was attributed to Be preci pitation as insoluble sulfates or sulfides under oxidized and reduced condi tions.