Abstract
In chlorine dioxide delignigication or bleaching, chlorate is mainly formed by the reaction between chlorite and hypochlorous acid, thus scavengers of chlorine or hypochlorous acid can be used to reduce the formation of chlorate which is unfavorable to environment. In this study, additives such as sulfamic acid, DMSO, hydrogen peroxide, or sodium chlorite was added to chlorine solution or pure $ClO_2$ solution to check their reactivity with $Cl_2$ and $ClO_2$. These additives were also added directly into general $ClO_2$ solution which contained certain amount of chlorine, then the additive-treated $ClO_2$ solution were used in bleaching stages. The aim of this procedure was to remove the original amount of chlorine that was thought to be possibly the main reason for the formation of chlorate and AOX. The additives were found to be able to eliminate chlorine very fast and selectively, but $H_2$ $O_2$ should be used under pH4, otherwise it also reacts with $ClO_2$. After the additives reacted With $Cl_2$, DMSO turned into an inactive product $(CH_3)_2SO_2$, While Sulfamic acid turned into $HClSO_3H$ that still remained active in oxidation, and $NaClO_2$ produced $ClO_2$. The addition of $HNaClO_2$ showed significant improvement in delignification but the deeper delignification led to higher formation of chlorate. When the additive-treated chlorine dioxide solutions were used in bleaching, both sulfamic acid, DMSO, and hydrogen peroxide showed no significant changes of DE brightness and Kappa number. The formation of chlorate was reduced by addition of sulfamic acid, DMSO and hydrogen peroxide.
