Mid Sweden University

In this investigation a new type of recoverable complexing agent (chelating surfactant) has been compared with a conventional complexing agent (DTPA) in the metal ion management of thermomechanical pulps (TMP) to be hydrogen peroxide bleached. After different degrees of washing of the pulps, bleaching experiments at different total alkali charges were performed with and without sodium silicate additions, and the ISO brightness of hand-made sheets was measured. The residual hydrogen peroxide in the bleaching liquor was also determined. No significant difference in either the brightness development or the residual hydrogen peroxide content could be detected between the pulps treated with equivalent molar ratios of the different complexing agents. Furthermore, the recovery of the surfactant-manganese complexes from laboratory made white water by foam flotation was also studied. Two different foaming agents, SDS and DDAO, were tested. After an addition of 160 ppm of the latter surfactant, about 80% of the manganese chelates could be recovered in the foam, containing 3% of the initial water mass.