Patent ID: 8900408

Claim:
A process for producing bleached pulp, comprising: subjecting unbleached pulp, which is obtained by cooking a lignocellulose substance, to alkali-oxygen bleaching treatment; and then subjecting the alkali-oxygen bleached pulp to elemental-chlorine-free bleaching treatment including a chlorine dioxide treatment, wherein monopersulfuric acid is added during the chlorine dioxide treatment, and the addition comprises: adding monopersulfuric acid in an initial stage of the chlorine dioxide treatment after the akali-oxygen bleaching treatment with an addition rate of from 0.1 to 1% by mass, at a treatment pH of from 2.5 to 3.5, a treatment time of from 30 to 120 minutes and a treatment temperature of 60° C. to 80° C.; or adding monopersulfuric acid in a final stage of the chlorine dioxide treatment after the alkali-oxygen bleaching treatment with an addition rate of from 0.1 to 1% by mass, at a treatment pH of from 4.0 to 5.5, a treatment time of from 30 to 120 minutes and a treatment temperature of from 60° C. to 80° C., and wherein the monopersulfuric acid is prepared by mixing sulfuric acid and hydrogen peroxide in a mixing ratio by mole of sulfuric acid to hydrogen peroxide of from 2/1 to 4/1.