Treatment of Pulp

Abstract

A method of treating a fibre pulp mixture comprises: (a) separating the fibre pulp mixture into at least two fractions to form a coarse fraction and a fine fraction; (b) bleaching the coarse fraction from (a); and (c) precipitating an alkaline earth metal carbonate in the fine fraction from (a). The products from steps (b) and (c) may combined in an integrated paper making process.

1 . A method of treating a fibre pulp mixture comprising:
 (a) separating the fibre pulp mixture into at least two fractions to form a coarse fraction and a fine fraction;   (b) bleaching the coarse fraction from (a);   (c) precipitating an alkaline earth metal carbonate in the fine fraction from (a).   
     
     
         2 . A method according to  claim 1 , wherein prior to bleaching the coarse fraction in (b) the coarse fraction is dewatered. 
     
     
         3 . A method according to  claim 1 , wherein prior to (c) the fine fraction is dewatered. 
     
     
         4 . A method according to  claim 1 , wherein the fine fraction consists predominantly of organic material that will pass through a substantially round hole of 50 μm. 
     
     
         5 . A method according to  claim 1 , wherein the fine fraction obtained in (a) is 15 to 50% by weight, preferably 20 to 30% by weight of the fibre pulp mixture. 
     
     
         6 . A method according to  claim 1 , wherein in (c) the fine solids present in the fine fraction become entrained in the alkaline earth metal carbonate precipitate to form a mixed aggregate material. 
     
     
         7 . A method according to  claim 1 , wherein the alkaline earth metal carbonate precipitate is formed by introducing into the fine fraction a source of alkaline earth metal ions and a source of carbonate ions. 
     
     
         8 . A method according to  claim 7 , wherein the source of alkaline earth metal ions is added to the fine fraction first followed by a source of carbonate ions. 
     
     
         9 . A method according to  claim 7 , wherein the source of carbonate ions is added to the fine fraction first followed by a source of alkaline earth metal ions. 
     
     
         10 . A method according to  claim 7 , wherein the source of alkaline earth metal ions is an alkaline earth metal hydroxide or a water-soluble alkaline earth metal salt. 
     
     
         11 . A method according to  claim 10 , wherein the source of alkaline earth metal ions is the alkaline earth metal hydroxide which is added ready prepared to the fine fraction. 
     
     
         12 . A method according to  claim 10 , wherein the source of alkaline earth metal ions is the alkaline earth metal hydroxide which is prepared in situ. 
     
     
         13 . A method according to  claim 7 , wherein the source of carbonate ions is carbon dioxide gas which is introduced into the fine fraction or the fine fraction containing the source of alkaline earth metal ions. 
     
     
         14 . A method according to  claim 13  wherein the source of the carbon dioxide gas is flue gas. 
     
     
         15 . A method according to  claim 7 , wherein the source of carbonate ions is an alkali metal or ammonium carbonate. 
     
     
         16 . A method according to  claim 1 , wherein the alkaline earth metal is calcium. 
     
     
         17 . A method according to  claim 1 , wherein bleaching is carried out using an oxidising bleaching agent. 
     
     
         18 . A method according to  claim 17 , wherein the bleaching agent is selected from hydrogen peroxide, peracetic acid or ozone. 
     
     
         19 . A method according to  claim 1 , wherein bleaching is carried out using a reducing bleaching agent. 
     
     
         20 . A method according to  claim 19 , wherein the bleaching agent is selected from sulphur dioxide, dithionite, zinc dust, thiourea dioxide. 
     
     
         21 . A method according to  claim 1 , wherein the fibre pulp mixture is selected from SGW pulp, PGW pulp, TMP pulp, TRMP pulp, and DIP. 
     
     
         22 . Use of the mixed aggregate material obtained in step (c) according to  claim 1  in a paper composition. 
     
     
         23 . Use of a mixed aggregate material according to  claim 22 , wherein the aggregated material is incorporated in the form of a suspension. 
     
     
         24 . A paper composition obtained from the method according to  claim 22 . 
     
     
         25 . A method according to  claim 1 , further comprising combining the bleached coarse fraction from (b) with some or all of the product obtained from (c). 
     
     
         26 . A method according to  claim 25 , wherein the bleached coarse fraction and the product obtained from (c) are combined in a paper making process. 
     
     
         27 . A method according to  claim 26 , wherein the bleached coarse fraction and the product obtained from (c) are blended with one or more of kaolin, clay minerals other than kaolin, talc, calcium sulphate, cellulosic fibres, a retention aid, and a sizing agent in a paper making process. 
     
     
         28 . A method of treating a fibre pulp mixture according to  claim 1 , wherein the coarse fraction from (b) is further processed in a paper making process. 
     
     
         29 . Paper obtained according to the method of  claim 26 . 
     
     
         30 . A method according to  claim 22 , further comprising coating the paper with a paper coating composition. 
     
     
         31 . A method according to  claim 22  further comprising calendering or super calendering the paper. 
     
     
         32 . Calendered or super calendered paper obtained according to the method of  claim 31 .