Impact of Washing Efficiency After a Metal Removal Stage on the Performance of a Peroxide Stage, 1998 Pulping Conference Proceedings

It has been widely accepted that a metals removal stage prior to a peroxide stage can improve its performance quite significantly. Washing efficiencies on a washer are never 100% and can vary between 50% to 5%. This paper evaluates the impact of washing efficiency after a Q, A and an (AQ) pretreatment on a peroxide bleaching stage. The quality of water used for washing had an effect on the pulp brightness after peroxide bleaching. The highest brightness was achieved when distilled water was used after both the metal removal and the peroxide stage. When tap water was used after both the stages the brightness was 7%ISO lower. A decrease in the washing efficiency from 100% to 80% can decrease the brightness from a peroxide stage by up to 10% ISO. The effect of a decrease in washing efficiency was greater when an acid stage was used for metal removal. The addition of 0.1% DTMPA to the peroxide stage resulted in a higher brightness especially when tap water was used to wash the pulps.