Screening of reactive extractants for the lignosulfonate extraction from lignosulfonate model solution and spent sulfite liquor

Crud formation during reactive extraction hinders phase separation and makes the application of conventional extraction equipment more challenging. This study investigates the influence of amines as a reactive extractant, pH value, and temperature on the crud formation and extraction efficiency for the reactive extraction of lignosulfonates from the Ca–lignosulfonate model solution and spent sulfite liquor. The overall extraction efficiency for different amines dissolved in 1-octanol increased in the order quaternary < tertiary < secondary < primary amines for both the model solution and the spent liquor. Phase equilibria for dioctylamine and trioctylamine showed that the temperature increase from 25 to 50 °C had no effect on the extraction efficiency but clearly reduced the crud formation in the extraction step. No crud was observed during back extraction into deionized water, 0.3 M NaOH, or 0.3 M NaHCO3. The pH value highly influences the phase equilibrium; the extraction step has to be performed at low pH values and the back extraction step at high pH values.