PRIMARY CHARGING BEHAVIOR AND THE INTERACTION OF CALCIUM AT THE BARITE–WATER INTERFACE FROM 15 TO 50ºC

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 presentation will describe the application of potentiometric titrations to evaluate the primary charging behavior of barite in NaCl media. Additionally, the interaction of Ca²⁺ ions with barite has been 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 are euhedral, approximately 40 nm in diameter, and have 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 high pH for the zero net proton charge (pH_znpc) value. The presence of Ca²⁺ in solution appears to decrease the apparent pH_znpc value and steepen the charging curves. From the ICP analyses it is apparent that there is not substantial specific adsorption of Ca²⁺; however, there was slight dissolution of the barite with increasing temperature.