Metal Management in ECF Bleaching and the Effect on Peroxide Efficiency in the EPO Stage, 1994 Pulping Conference Proceedings

N. G. Johansson, S. E. Johnson, B. W. Biggers, F. M. Clark, M. P. Bergeron, P. Jean

A mill study was conducted to evaluate the effect of D0 stage pH and chelation on metal management and the corresponding effect on efficiency of an extraction stage reinforced with peroxide and oxygen. Complementary lab studies were first performed to help establish mill operating parameters.

Levels of manganese and iron remaining after an acidic D0 stage with a terminal pH ranging from 2.3 to 3.6 did not affect the EPO stage delignification or brightness in the mill study. EPO stage delignification and brightness were sensitive to levels of magnesium and calcium remaining after the D0 stage. Viscosity drop through the EPO stage showed a strong correlation with the level of magnesium entering the EPO stage. These mill investigations indicate a D0 stage terminal pH range of 2.8 – 3.2 is optimum for EPO stage delignification, brightness development, and viscosity preservation.

Addition of 2 kg/t of EDTA prior to the D0 stage did not adversely affect the D0 stage delignification but caused a reduction in brightness development across the D0 stage. The EDTA improved the delignification and brightness gain across the EPO stage.