This article conducted an investigation on the carbonate formation during kraft pulping (KP) process of eucalyptus under different conditions, from which a kinetic model for predicting the carbonate formation was proposed. It was also found that the time-dependent effective alkali concentration and H factor are the major parameters affecting the carbonate formation. Results showed that the proposed model could describe the carbonate formation during KP at various process conditions, and there is a good correlation (R-2 = 0.923) between the measured and predicted data. According to the model, about 54% of total carbonate formation was contributed from lignin in wood. (C) 2017 American Institute of Chemical Engineers AIChE J