Gypsum Scale Formation in White Water of a Closed‐Cycled Paper Mill

The accumulation of calcium and sulfate ions in a process stream of a closed papermaking system may cause calcium sulfate scale formation. This study presents measurements of calcium sulfate precipitation conditions and a thermodynamics‐based model for the prediction of such precipitation conditions in the papermaking white water at 50°C. The precipitates were found to have the structure of gypsum (CaSO 4 ·2H 2 O). The model calculations were compared with experimental data and found to be in good agreement.