Patent ID: 7029554
Filing Date: 2006-04-18
Classification: D21C

Abstract:
1. A method for brightening pulp at a pH from 4.5 to 9; said method comprising steps of: (a) combining an alkali metal borohydride, an alkali metal hydroxide, an alkali metal bisulfite and phosphoric acid to form a reducing solution which comprises hydrosulfite; and (b) adding the reducing solution to a pulp slurry in an amount from 0.1% to 4% of hydrosulfite based on dry pulp fiber; wherein the alkali metal hydroxide is added in an amount from 1 kg to 10 kg, the alkali metal bisulfite is added in an amount from 10 kg to 30 kg, and phosphoric acid is added in an amount from 1 kg to 30 kg, all on a basis of 1 kg of alkali metal borohydride.