Removal of contaminants from recycled paper fibers

Abstract

The present invention describes a method for removing contaminants from a recycled paper fiber slurry comprising adding a cationized mineral to the paper fiber slurry to form complexes between the cationized mineral and the contaminants and separating the complexes from the paper fibers.

We claim:  
     
         1 . A method of removing contaminants from a recycled paper fiber slurry, comprising: 
 adding a cationized mineral to the paper fiber slurry to form cationized mineral/contaminant complexes;    separating the cationized mineral/contaminant complexes from the paper fiber in the paper fiber slurry.    
     
     
         2 . The method of  claim 1 , wherein the step of separating comprises a process selected from the group consisting of size separation and density separation.  
     
     
         3 . The method of  claim 1 , wherein the step of separating comprises subjecting the paper fiber slurry and cationized mineral/contaminant complexes to a centrifugal separator to produce a first product stream comprising paper fibers and a first reject stream comprising cationized mineral/contaminant complexes.  
     
     
         4 . The method of  claim 3 , further comprising (i) subjecting the first reject stream to a centrifugal separator to produce a second product stream comprising paper fibers and a second reject stream comprising cationized mineral/contaminant complexes; and (ii) combining the first and second product streams.  
     
     
         5 . The method  claim 1 , wherein the cationized mineral is formed by a process comprising adding a cationic compound to the mineral.  
     
     
         6 . The method  claim 5 , wherein the cationic compound is selected from the group consisting of a cationic polymer, cationic wet-end starch, cationic wax-based emulsion, carboxymethylcellulose and mixtures thereof.  
     
     
         7 . The method  claim 6 , wherein the cationic compound is a cationic polymers selected from the group consisting of polyamine, polydadmac, polyacrylamide and mixtures thereof.  
     
     
         8 . The method  claim 1 , further comprising screening the slurry to remove coarse contaminants before the step of adding cationized mineral to the paper fiber slurry.  
     
     
         9 . The method  claim 1 , wherein the mineral is selected from the group consisting of talc, clay, kaolin, montmorillate, bentonite, calcium carbonate, diatomaceous earth, sapponite and wollastonite.  
     
     
         10 . The method  claim 1 , wherein the mineral is talc.  
     
     
         11 . The method  claim 1 , wherein the cationized mineral is added to the paper fiber slurry in an amount between about 5 pounds to about 40 pounds of cationized mineral per pound of paper fiber.  
     
     
         12 . A method of removing contaminants from a recycled paper fiber slurry, comprising: 
 adding a cationized talc to the paper fiber slurry to form cationized talc/contaminant complexes;    separating the cationized talc/contaminant complexes from the paper fiber in the paper fiber slurry based on differences in density between the paper fiber and the cationized talc/contaminant complexes.    
     
     
         13 . The method  claim 12 , wherein the cationic compound is selected from the group consisting of a cationic polymer, cationic wet-end starch, cationic wax-based emulsion, carboxymethylcellulose and mixtures thereof.  
     
     
         14 . The method  claim 13 , wherein the cationic compound is a cationic polymer selected from the group consisting of polyamine, polydadmac, polyacrylamide and mixtures thereof.  
     
     
         15 . The method  claim 12 , wherein the talc has a median particle size of greater than about 2 microns.  
     
     
         16 . The method  claim 12 , wherein the cationized talc is added to the paper fiber slurry in an amount between about 5 pounds to about 40 pounds of cationized talc per pound of paper fiber.  
     
     
         17 . A method of removing contaminants from a recycled paper fiber slurry, comprising: 
 adding a cationized talc to a paper fiber slurry to form cationized talc/contaminant complexes, wherein the talc has a median particle size of greater than about 2 microns, and wherein the cationic compound is a cationic polymer selected from the group consisting of polyamine, polydadmac, polyacrylamide and mixtures thereof,    separating the cationized talc/contaminant complexes from the paper fiber in the paper fiber slurry in a centrifugal separator.    
     
     
         18 . The method  claim 17 , wherein the cationized talc is added to the paper fiber slurry in an amount between about 5 pounds to about 40 pounds of cationized talc per pound of paper fiber.