Softwood kraft pulp bleaching in the presence of sodium nitrate/nitrite mixtures. I. Factors affecting the process

Pretreatment of spruce kraft pulp with NaNO3/NaNO2 mixtures in acidic mediu m is investigated. The main factors affecting the delignification degree ar e chemical charge, NaNO3/NaNO2 ratio and pH. In the presence of 4% NaNO3, 2 % NaNO2, at pH 2.5-3 (sulfuric acid), followed by alkaline extraction, the lignin content is decreased by 50-60%, without extensive loss of viscosity. As a result of treatment with NaNO3/NaNO2, the reactivity of residual lign in is increased prior to final bleaching. This new pulp pretreatment method can be a realistic alternative to oxygen/alkali delignification.