CHLORATE REDUCTION IN EUCALYPTUS PULP BLEACHING, 2008 Engineering, Pulping and Environmental Conference

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An oxygen delignified eucalyptus kraft pulp was bleached with four alternative sequences (D-E_P-D_ND, A/D-E_P-D_ND, D_HT-E_P-D_ND, A-E_P-D_ND) to a target 90 % ISO brightness. Among these sequences, A-E_P-D_ND was characterized by the lowest values for active chlorine consumption (19.5 kg/adt), AOX formation (0.10 kg/adt) and chlorate formation (2.3 kg/adt). The extent of chlorate formation was unaffected by its initial concentration in the bleaching filtrate. Relatively more chlorate was formed in the final bleaching stage which indicated that a reaction between hypochlorous acid and chlorite was the main source of chlorate. In the A-E_P-D_ND sequence chlorate is enriched in a single filtrate which makes its biological or chemical treatment attractive for reducing chlorate to harmless chloride.