Should we be refining first, then discarding fines, then bleaching?

Abstract

Pulp fibers' bleaching technology has been developing mainly by applying increasingly intensive delignification in the cooking department and implementation of elemental-chlorine-free chemicals in the bleaching department. The resulting effluents load is still considerable, and the environmental consequences largely depend on the effectiveness of wastewater treatment. Now it is well established that pulp fibers' surface layers contain comparatively higher amounts of residual lignin, heteroaromatic compounds, and other lignin-like substances. Based on this knowledge an approach is proposed for consideration. As the pulp fibers' refining process also includes the peeling of fiber wall surface layers, it could be useful to perform such refining first, followed by appropriate screening techniques before the pulp bleaching. The main objection to this approach is related to efficient utilization of the fines, i.e., fractions of the surface layers.