Mid Sweden University

In this investigation a new type of recoverable complexing agent (chelating surfactant) has been compared with a conventional complexing agent; diethylenetriamine pentaacetic acid (DTPA), in the metal ion sequestering 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 chelating surfactant-manganese complexes from laboratory made white water by froth flotation was also studied. Two different foaming agents; sodium dodecyl sulphonate (SDS) and dimethyldodecylamine oxide (DDAO), were tested in the froth generation. After an addition of 160 ppm of DDAO, more than 80% of the manganese chelates could be recovered in the foam, containing 3% of the initial water mass.

The influence of a chelating surfactant, different foaming agents, cationic polyelectrolytes, pH value, and temperature on the purification efficiency of process waters from a mechanical pulp mill has been studied by flotation in a 1 L customized unit. Turbidity measurements and gas chromatography (GC) were carried out to determine the removal and characteristics of dissolved and colloidal substances (DisCo). The manganese ion content in the process waters before flotation and the metal chelate removal capacity by flotation were determined by Inductively Coupled Plasma (ICP) and Atomic Absorption Spectrometry (AAS) measurements. It was found that a 99% removal of complex bound manganese ions and a 94% decrease in turbidity of the TMP water produced at the laboratory can be achieved in a single-stage flotation with a chelating surfactant and a foaming agent. Furthermore, a 91% decrease in turbidity, the removal of up to 96% of resin and fatty acids, and 93% of triglycerides from TMP water can be obtained after application of a foaming agent.

The effects of a chelating surfactant and different foaming agents on the efficiency of cleaning process waters from a thermomechanical pulp (TMP) mill were studied in a Voith flotation cell. Turbidity measurements and gas chromatography were used to determine the removal extent and characteristics of dissolved and colloidal substances (DisCo). The metal ion content in the process waters before flotation and the metal chelate removal after flotation were determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). FiberLab (TM) equipment was used to characterize changes in the size of fibers present in the process waters. The results indicate that a decrease in turbidity of up to 91% and the removal of 80% of lipophilic extractives in the TMP water could be obtained using a single-stage flotation unit. Furthermore, the foam fraction was within 5% of the initial volume, and 100% of the Mn2+/chelating surfactant complex added to the TMP water was removed.