Peroxide bleaching of wood pulp using stabilizers and sodium hydrosulfide reducing agent

A process for peroxide bleaching of mechanical or high yield pulp, said process consisting of:

• adding to a pulp slurry DTPA as a stabilizer for chelating transition metal ions and sodium hydrosulfite as a reducing agent;
• subsequently removing from said slurry the resulting chelated transition metal ions;
• adding to said slurry, after removing said chelated transition metal ions,
• (a) sodium silicate and 0 to 0.1% MgSO4 by weight on dry pulp as stabilizers, and
• (b) optionally at least one chelating agent selected from DTPA and EDTA;
• subsequently adding hydrogen peroxide to said slurry at a preselected point in said process;
• adding caustic soda to said slurry simultaneously with or subsequent to adding said stabilizers and said optionally at least one chelating agent, such that the pH of the resulting slurry does not at any point exceed 11.5;
• and
• subjecting said slurry to preselected conditions to complete said process for peroxide bleaching.