Abstract
Tests were performed at a pulp mill in northern Finland showed that inorganic chlorine, mainly chloride, constitutes over half of the chlorine load in the pulp liquor continuing from the first D stage to the next bleaching stage. The amount of chlorine depends on the quality of the wash water, the chlorine dioxide dosage in the preceding bleaching stage, and the outlet consistency of the washed pulp. When the kappa number of the incoming pulp and the dosage of chlorine dioxide in the first D stage were higher, the amount of chlorine compounds in the effluent discharge was also higher. The proportion of organic chlorine increased during washing, and the proportion of inorganic chlorine decreased, which suggests that inorganic chlorine is easier to remove than organic chlorine. The removal of sodium, COD, and TOC was not efficient inasmuch as the second wash water to the first D-stage vacuum drum washer contained large amounts of these compounds.