A simple correlation for predicting gypsum deposition from brine solutions

Calcium sulfate scale occurrence is one of the major problems encountered on heat exchanger surfaces, membrane surfaces of reverse osmosis (RO) plants, and oilfield facilities. Scale prevention and treatment are extensively applied for confronting this problem. A successful scaling prevention and treatment need to be able to identify whether sulfate scale is likely to occur under certain operating conditions. This paper is aimed at assessing the solubility product of calcium sulfate (gypsum) in brine solutions, through which the gypsum scaling tendency can be easily obtained. The simple solubility product prediction correlation, described by a simple equation, is established from experimental sodium sulfate solubilities available in the literature. The predicted gypsum solubilities show excellent agreement with the experimental data for the temperature range of 25 to 80 °C and pressures up to 1,000 bar with NaCl concentration up to 5 M. The method is simple, compact, and reliable and can be applied to any environment where gypsum is expected to precipitate.