Increasing alkaline pulping yield for softwood with metal ions

Impregnating or spraying softwood chips in a solution containing an appropriate concentration of alkaline earth metal ions selected from the group consisting of calcium ions, barium ions and strontium, preferably calcium ions, at room temperature before a reductive alkaline pulping process, for example kraft pulping, significantly increases pulp yield. Using an agent that complexes with the metal ions, such as hydroxyethylidene diphosphonic acid (HEDP) allows this benefit of metal ions to be achieved during the pulping process rather than in a separate impregnation step.