SURFACE CHARGE DEVELOPMENT AT THE BARITE–WATER INTERFACE IN NACL MEDIA, FROM 15 TO 50ºC

Barite is found in a variety of geologic environments; it is deposited in marine environments by evaporation and biogenic processes, and is found in hydrothermally mineralized veins. Barite is used extensively in drilling fluids for oil and gas exploration; conversely, it may be present as scales in industrial pipes. Numerous studies have, therefore, evaluated crystal growth and dissolution of barite. The solubility of barite has been shown to increase, when barite is present in an aqueous system also comprising calcite or gypsum. Similarly, sulfate-reducing bacteria have been shown to increase the solubility of barite in sewage sludge and treatment plants. Collectively, these precipitation/dissolution processes take place at the mineral-water interfaces, and are controlled by proton induced surface charge. Consequently, the surface charging behavior of barite is being investigated by potentiometric titration.

A commercial barite sample is being used in this study. The sample has been characterized extensively by SEM and TEM imaging, XRD, and BET surface area measurements. The particles are euhedral, approximately 50 nm in diameter, and have a surface area of 23 m²/g. The potentiometric titrations are being performed in NaCl media, at ionic strengths from 0.03 to 0.3 m. The titrations are being performed as a function of temperature from 15 to 50 ºC, and a pH range of 3 to 10. The background-corrected titration curves show some common features. At all temperatures the titration curves are shallow between pH 3 and 8, then steepen significantly. The proton induced surface charge of the barite shows strong temperature dependence. The barite surface becomes progressively more positive (deficit of H⁺ in solution) with increasing temperature. At 0.03 m ionic strength, the barite surface is positively charged at all pH suggesting a high pH for the zero net proton charge (pH_znpc) value.