Reduction of manganese in brownstock--laboratory study and mill trial results.

Application: Adding DTPA to the digester could reduce manganese (Mn) in effluents to receiving waters.

The researchers carried out a laboratory study and two mill trials to find out if reducing the pH or adding chelant could reduce the Mn content of effluents at the Weyerhaeuser pulp mill in Grande Prairie, Alberta, Canada. The laboratory study was promising and showed that the Mn content of the washed pulp decreased with decreasing pH and with the addition of a chelant. The chelants used were EDTA and DTPA.

The first mill trial was inconclusive. In this trial, the researchers focused on acidification. Manganese was freed up from the pulp in the screen room at the lower pH levels. However, the Mn carryover to the bleach plant did not decrease significantly.

The second mill trial was more successful. DTPA was added to the feed of the continuous digester. Manganese content decreased in the unbleached pulp and the bleach plant effluent and increased in the black liquor.

The lab study and the second mill trial showed that adding DTPA was a technically viable solution to the problem. The Mn removed from the unbleached pulp could be sent to recovery in the black liquor and could be discharged to landfill with the green liquor dregs. This approach would reduce the Mn discharged to the receiving waters.

Wohlgemuth is with Weyerhaeuser Company Ltd., P.O. Bag 1020, Grande Prairie, AB, T8V 4M1, CAN. Mannisto is with EKONO Inc., 11061 NE 2nd Street, Suite 107, Bellevue, WA, 98004-5845. Yaraskavitch is employed by Dew Chemical Canada Inc., 75 Mullcraft Crescent, Nepean, ON, K2J 4P7, CAN. Jack works at Weyerhaeuser Technology Center, WTC 2G25, P.O. Box 9777, Federal Way, WA 98063-9777. Email Mannisto at [e-mail].