The additions of CO₂ gas, SO₂ gas to black liquor were studied for the manufacture of reproduced semichemical pulp cooking liquor from kraft pulp black liquor, by direct sulpliitation and carbonation sulphitation.
The results were found that cooking liquor can be successfully manufactured by selection of the conditions (temp., gas rate etc.) to reduce the Na₂S₂O₃ formation, especially in the carbonation-sulphi tation.