Peroxide bleaching of wood pulp

Abstract

There is provided a new and useful process for peroxide bleaching of mechanical or high yield pulp, the process comprising adding to a pulp slurry at least one stabilizer for stabilizing low valency states of transition metal ions in the slurry; subsequently adding caustic soda to said slurry simultaneously with or subsequent to adding said at least one stabilizer; adding hydrogen peroxide to the slurry at a preselected point; and subjecting the slurry to preselected conditions to complete the bleaching process.

1 - 16 . (canceled)  
   
   
       17 . A process for peroxide bleaching of mechanical or high yield pulp, said process consisting of: 
 adding to a pulp slurry 
 (a) 0 to 0.1% MgSO 4  by weight on dry pulp as a stabilizer, and  
 (b) a stabilizer selected from silicate, at least one chelating agent and mixtures thereof;  
   subsequently adding hydrogen peroxide to said slurry at a preselected point;    adding an alkali source to said slurry simultaneously with or subsequent to adding said stabilizer(s) 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,    wherein the alkali source is selected from caustic soda, soda ash, magnesium hydroxide and magnesium oxide, such that when the alkali source is caustic soda or soda ash, silicate must be present as one of said stabilizers.    
   
   
       18 . The process of  claim 17 , wherein the pH of said slurry at the completion of said process is less than 9.5.  
   
   
       19 . The process of  claim 17 , wherein said at least one chelating agent is selected from DTPA, EDTA, their salts and mixtures thereof.  
   
   
       20 . The process of  claim 17 , wherein said stabilizers are a combination of MgSO 4 , sodium silicate and DTPA.  
   
   
       21 . The process of  claim 17 , wherein said alkali source is caustic soda.  
   
   
       22 . The process of  claim 17 , wherein said alkali source is magnesium hydroxide.  
   
   
       23 . The process of  claim 17 , further consisting of the pretreatment steps of adding at least one chelating agent to said pulp slurry for chelating transition metal ions and subsequently removing the resulting chelated transition metal ions from said slurry.  
   
   
       24 . The process of  claim 23 , wherein said at least one chelating agent is selected from DTPA, EDTA, their salts and mixtures thereof.  
   
   
       25 . The process of  claim 24 , wherein said at least one chelating agent is DTPA.  
   
   
       26 . The process of  claim 17 , further consisting of the pretreatment steps of adding at least one chelating agent for chelating transition metal ions and a reducing agent to said pulp slurry and subsequently removing the resulting chelated transition metal ions from said slurry.  
   
   
       27 . The process of  claim 26 , wherein said at least one chelating agent is DTPA and said reducing agent is sodium hydrosulfite.  
   
   
       28 . The process of  claim 17 , further consisting of the step of mixing said stabilizer(s) with said pulp slurry prior to adding said hydrogen peroxide.  
   
   
       29 . The process of  claim 17 , further consisting of the step of providing a predetermined time delay between the addition of said stabilizer(s) and the addition of said hydrogen peroxide.