BLEACH FILTRATE RECYCLE IN BLEACHING FOR EUCALYPTUS CHEMIMECHANICAL PULPS

摘要

The eucalyptus wood chips are already used on a large scale to produce chemimechanical pulps (CMPs) by many Chinese pulp mills. The bleach filtrate recycling in bleaching for eucalyptus CMPs was investigated. The CMPs used in the experiments have good bleaching responses to hydrogen peroxide with a brightness of more than 80% ISO at a H2O2 charge of 2%. A positive effect to the pulps brightness, a brightness increase of 0.3 points, is observed of recycling the bleach filtrate once. No obvious negative effect is observed by using multi-time recycling of the filtrate. Compared with that of control bleaching，pulp brightness suffers only a brightness loss of 0.3 points after recycling seven times. The filtrate characters of COD, electrical conductivity, etc, increase gradually with the recycling times at the beginning and level off after five times. The bleach filtrate recycling in bleaching of eucalyptus CMPs can be expected to save 50% of processing fresh water，and 50% of Na2SiO3 and 50% of DTPA without observed negative effects on bleaching efficiency and pulp strength properties.