Improving peroxide bleaching of mechanical pulps by an enhanced chelation process

The addition of a small amount of sodium hydrosulphite to a DTPA chelation, the so-called reducing agent assisted chelation (Q(y)) enhances the remova l of transition metal ions from mechanical pulp fibres. In this paper we re port the results from lab trials, mill trials and the mill experience of im plementing the Q(y) process at the TMP bleach plant of Irving Paper Inc. Th e lah trials showed that the Q(y) chelated pulps contained less residual ma nganese than the DTPA chelated (Q) pulps under otherwise the same condition s and that more brightness gain was achieved during the subsequent peroxide bleaching for the Q(y) pulps than for the Q pulps. These results were furt her confirmed during the mill trials. It was shown that a significant savin g in bleaching cost can be achieved, while the capital cost of implementing the Q(y) process is low.