Primary charging behavior and the interaction of Calcium at the barite-water Interface from 15 to 50C



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Barite (BaSO4), a relatively insoluble mineral, is found in a variety of geologic environments, including marine deposits from evaporation and biogenic processes, and hydrothermally mineralized veins. Barite is also of industrial importance. It is found as scale in pipes and is used as an additive to drilling fluids for oil and gas exploration. In order to better understand barite scale prevention and removal, previous studies have investigated the precipitation and dissolution of barite. Additionally, an understanding of the surface charging and adsorption behavior of barite is needed if scaling reactions are to be evaluated fully; however, these studies are limited. This study evaluated the primary charging behavior of barite in NaCl media by potentiometric titrations. Additionally, the interaction of Ca2+ ions with barite was studied. The commercial barite sample used in this study was washed to remove impurities and characterized extensively by SEM and TEM, XRD and BET surface area measurements. Characterization revealed that the particles were euhedral, approximately 40 nm in diameter, and had a surface area of 22.1m2/g. Potentiometric titrations were performed in NaCl media as a function of ionic strength (0.03, 0.1 and 0.3 m), pH (3 to 10), and temperature (15, 25, 35 and 50˚C). A second series of titrations were performed with Ca2+ added to the solution. The Ca2+ titrations were performed at 0.03 and 0.3 m ionic strength, with 0.001 or 0.002 m Ca2+. The Ca2+ concentration at the end of each titration was sampled and analyzed by ICP. Primary charging effects (NaCl media alone) of barite were small; consequently, all titration results were background corrected. Titration curves show strong temperature dependence, becoming progressively more positive with increasing temperature. Additionally, surface charging increases with increased ionic strength. Titrations curves also suggest a pH of approximately 9.4 for the zero net proton charge (pHznpc) value. The presence of Ca2+ in solution appears to decrease the apparent pHznpc value to roughly 8.6 and steepen the charging curves. From ICP analysis it is apparent that there is not substantial specific adsorption of Ca2+, suggesting that calcium ions are weakly attracted outer-sphere complexes. There was slight dissolution of the barite with increasing temperature and decreasing pH, suggesting small concentrations of Ba2+ and SO42- available to interact with ions in solution.



Barite, surface charge, Charging behavior, Adsorption, Potentiometric titration, Titrations, Zero net proton charge, Ionic strength, Temperature, pH, Calcium adsorption, Sodium chloride media