MgSO₄ Application

in

O₂ Delign, Eo & Eop Stage

Canadian Mill Survey

Oct 16, 2000 PAPTAC Bleaching Committee Meeting,

Prince George, BC

Production

(x 1000 tonne/d)

Bleached Kraft Mills in Canada: 40

Bleach Lines*: 54 36.9 - 37.8

SW**: 45 27.0 - 31.5

HW**: 13 4.7 - 10.1

* Note 1: Some bleach lines swing between SW & HW (SW & HW campaign).

**Note 2: Max number of bleach line.

Results:

Bleach Prod’n Bleach Prod’n

line (x 1000 tonne/d) Line w/ (x 1000 tonne/d)

MgSO₄

O₂ Delign Stage:

18 13.8 - 14.6 17 12.0

SW: 17 10.9 - 13.2 16 12.2

HW: 3 0.6 - 3.8 1 0.55

MgSO₄ Dosage: 0.05% - 0.30%

Eo Stage:

10 7.0 - 8.4 1 1.0

SW: 7 4.6 - 5.4 1 1.0

HW: 5 2.3 – 4.4 0 0

MgSO₄ Dosage: 0.05%

Eop Stage:

37 25.4 - 26.2 8 4.35

SW: 35 20.7 - 24.4 8 4.35

HW: 5 1.2 - 4.4 0 0

MgSO₄ Dosage: 0.05% - 0.40%

Summary:

1) O2 delign Stage:

- 1/3 (18 out of 54 lines) of all the bleach lines has O2 delign.

- Almost every SW bleach line, 94% (16 out of 17), except one uses MgSO4. This particular line thinks there may be sufficient Mg⁺⁺ ions carried-over from the talc used in the process.

- Only 1 out of 3 HW lines uses MgSO4. This might be due to the furnish.

2) Eo Stage:

- About 19% (10 out of 54) of all bleach lines has Eo stage.

- Only 1 of 7 SW line (14%) uses MgSO4.

- No HW line(4 total) uses MgSO4.

3) Eop Stage:

- About 69% (37 out of 54) of all bleach lines has Eop stage.

- Only 23% SW lines (8 out 35 lines) uses MgSO4.

- No HW line (5 total) uses MgSO4.

Comments:

- It is believed that the magnesium hydroxide absorbs the metal ions or forms complexes with them, making them unavailable to catalyze peroxide decomposition.

- In hydrogen peroxide bleaching, Mg/Mn molar ratio of 20 or wt ratio of 30 and higher have been mentioned in various literatures.

Acknowledgement:

- All Mills,

- Ted Tam, Cariboo

- Russell Girard, Praxair

- Kris Kanter. PCI