Designing For Mill Closure: New Premises in Metals Control, 1997 Pulping Conference Proceedings

Metals control is a key issue in hydrogen peroxide related applications, especially as it relates to the goal of minimum impact manufacturing. The basic understanding of metal chelation in kraft pulps has allowed the development of a new strategy for metals control in the bleach plant. Hexeneuronic acids have been identified as the strong chelating entity in kraft pulps. When these are removed, metals control through a chelation stage becomes more flexible and better suited to the objective of bleach plant effluent reduction. The chelation stage can be operated under alkaline conditions, and with biodegradable chelants. It is even possible to replace the chelation stage with a metal displacement stage to afford optimal hydrogen peroxide bleaching.

This new strategy for metals control can be used to reduce bleach plant effluents as transition metals are removed in alkaline filtrates which can be sent to the recovery boiler. Metal control is as good as in even the most carefully optimized chelation stage and the result in any hydrogen peroxide bleaching stage is optimum performance.