The general reaction pattern in all bleaching stages is the same with an initial fast phase and a
slower final phase. One example where the brightness is used as a measure of the bleaching result
is shown in Figure 10.3. The figure shows that the bleaching proceeds with decreasing efficiency
to the so called brightness ceiling where no additional brightness increase is obtained.
The figure also shows that the lignin content in the pulp decreases according to a corresponding
relationship with an initial efficient phase and a later less efficient phase where the chemical
consumption increases considerably for an additional decrease in lignin content. Thus, it is beneficial
of economical reasons to concentrate the bleaching to the initial part and to avoid the final
part of the reaction.