Study of the anions profile throughout the sulphite pulp line

Abstract

In this study, the sulphur oxide anions profile at all stages of the Mg acid sulphite pulping process was evaluated by Ion Chromatography (IC). The concentration of bisulphite anions decreased almost two-third along the cooking, while the sulphate concentration increased progressively. Of the bisulphite consumed, only a third was converted to sulfates. Unexpectedly, the maximum thiosulphate concentration was found in the pulping acid filling step, being further decreased along the cooking. The chloride ions rise progressively during the cooking being extracted essentially from the wood, although a noticeable part of the phosphate anions belongs to pulping reagents and inlet water. The low molecular weight fraction of lignosulphonates (LS) appeared in the cooking liquor in the residual delignification step and, together with xylonic acid, contributed to an overestimation of the fluoride concentration determined by the IC due to the same retention time in the chromatographic column during the analysis.