In this investigation, a modified Poisson-Boltzmann approach has been used to estimate the mean ion concentration distributions of ionic species present in black liquors around charged kraft lignin macromolecules at industrially relevant conditions. The distributions were utilized to predict the double layer repulsion and, further, predict the overall pair interaction potentials between two kraft lignin macromolecules or particles immersed in the black liquor electrolyte. The properties of softwood black liquors were used as input data to the model. The numerical results predicted the pair interaction potentials to remain repulsive up to salt concentrations of about 2.5 M at pOH 1. The critical coagulation concentration of salt was predicted to decrease as the pOH of the black liquor was increased. The predictions at 65 °C and moderate levels of pOH (3.5) and salt concentration (1.9 M) were found to be in good agreement with previous observations reported in the literature.