MgSO4 vs. Mg(OH)2 as a cellulose protector in oxygen delignification

Abstract

Abstract It has been proposed that magnesium hydroxide can replace magnesium sulfate as a lower cost cellulose protector. This claim has been evaluated based on four commercial unbleached softwood kraft pulps. The selectivity was improved in the presence of soluble MgSO4, but little or no selectivity improvement was obtained when insoluble Mg(OH)2 was applied. It was further observed that in-situ iron concentration in unbleached pulp affects selectivity of oxygen delignification, while in-situ calcium concentration affects efficiency of magnesium protection. The results favor the hypothesis of formation of a Mg-carbohydrate complex as the major mechanism of cellulose protection by magnesium. The application of a soluble magnesium compound is recommended to improve selectivity in oxygen delignification.