As an alternative to the chemical approach reducing the pH of black liquor to precipitate lignin using carbon dioxide and sulfuric acid, we have developed an electrochemical avenue for lowering pH while recovering caustic. It includes electrolytic treatment of black liquor that reduces its alkalinity to the critical point of lignin precipitation without using chemicals of external source. In this study, we modeled the mass transfer phenomena of most important ions through the membrane during electrolysis. We report on the investigation of sodium, protons hydroxyls ions and pH profiles across the membrane under typical operating conditions along with sodium transfer performance.