Purified Precipitated Calcium Carbonate and Purified Calcium Silicate Compounds, a Method for Their Production, and Their Use as Paper Fillers

Abstract

Methods for the production of high purity calcium carbonate and high purity calcium silicate. Products are washed before introduction into a paper machine furnish, to avoid filler loss and brightness reversion. In one embodiment, multiple superatmospheric reactors may be provided, for switching production between reactors, and advantageously utilizing process waste heat. On site production of both precipitated calcium carbonate and calcium silicate hydrates is thus achieved in a paper mill.

1 . A method for the production of calcium carbonate, said method comprising: 
 (a) providing an aqueous lime slurry, said aqueous lime slurry comprising (i) Ca(OH) 2  solids and (ii) dissolved Ca(OH) 2  in the form of Ca ++  ions;    (b) screening grit from said aqueous lime slurry;    (c) conditioning said aqueous lime slurry to a predetermined temperature;    (d) feeding a first portion of said aqueous lime slurry into a first reactor;    (e) agitating the contents of said first reactor at super-atmospheric pressure;    (f) introducing a stream of CO 2  into said aqueous lime slurry in said first reactor, to form CO 3   −2 ;    (g) reacting said CO 3   −2 ; and said Ca ++  in a carbonation reaction to produce insoluble precipitated calcium carbonate (CaCO 3 ) in said first reactor;    (h) removing said insoluble precipitated calcium carbonate and associated water from said first reactor;    (i) dewatering said insoluble precipitated calcium carbonate;    (j) washing said insoluble precipitated calcium carbonate with a selected wash water;    
   
   
       2 . The method as set forth in  claim 1 , wherein said selected wash water comprises high purity water.  
   
   
       3 . The method as set forth in  claim 2 , wherein said high purity water comprises deionized water.  
   
   
       4 . The method as set forth in  claim 1 , further comprising adding a sodium silicate solution to said reactor, so that said sodium silicate is present during the production of insoluble precipitated calcium carbonate.  
   
   
       5 . The method as set forth in  claim 4 , wherein said sodium silicate is added in the form of an aqueous sodium silicate stream at about 5% sodium silicate.  
   
   
       6 . The method as set forth in  claim 1 , further comprising adding (a) magnesium oxide, (b) a selected hexamataphosphate, and (c) phosphoric acid to said reactor, so that said additives are present during the production of insoluble precipitated calcium carbonate.  
   
   
       7 . The method as set forth in  claim 6 , wherein said phosphoric acid comprises about a 2% phosphoric acid aqueous mixture.  
   
   
       8 . The method as set forth in  claim 1 , wherein said insoluble precipitated calcium carbonate comprises aragonite.  
   
   
       9 . A method for the production of calcium silicate hydrate, said method comprising: 
 (a) charging a reactor with a first aqueous silica slurry comprising silica at a concentration of from about 1 to about 1.5 pounds of silica per gallon of said first aqueous silica slurry;    (b) charging said reactor with an aqueous lime slurry;    (c) heating the contents of the reactor under hydrothermal conditions to produce a calcium silicate.    (d) removing the calcium silicate from the reactor;    (e) dewatering said calcium silicate;    (f) washing said calcium silicate with a selected wash water;    
   
   
       10 . The method as set forth in  claim 9 , wherein said selected wash water comprises high purity water.  
   
   
       11 . The method as set forth in  claim 10 , wherein said high purity water comprises deionized water.  
   
   
       12 . The method as set forth in  claim 9 , wherein the properties of the calcium silicate hydrate product are controlled by adjusting one or more of the process variables selected from a group consisting of: 
 (1) calcium to silica mole ratio,    (2) lime plus silica slurry concentration,    (3) reaction temperature, and    (4) reaction pressure.    
   
   
       13 . The method as set forth in  claim 12 , wherein the calcium to silica mole ratio is in the range of 1.2 to 1.6.  
   
   
       14 . The method as set forth in  claim 13 , wherein said calcium silicate hydrate comprises foshagite consisting of fibrous crystals ranging in size from 0.1 to 0.3 microns and in length up to about 5 microns.  
   
   
       15 . The method as set forth in  claim 12 , wherein said calcium silicate hydrate comprises primary fibrous particles interlocked into a secondary particle structure, and wherein said secondary particle structure has a size varying from about 10 microns to about 40 microns.  
   
   
       16 . The method as set forth in claim  40  wherein the x-ray diffraction pattern of said calcium silicate hydrate, when dried, comprises: 
 Foshagite: dMajor=2.97 Å    dMinor=5.05 Å   Xenotlite: dMajor=3.107 Å    dMinor=3.66 Å   
   
   
       17 . A paper composition, said composition comprising: an effective amount of a filler, said filler comprising a multiple phase calcium silicate hydrate comprising foshagite and xonotlite, and having peaks in the XRD patterns from the foshagite and xenotlite components in the complex having the characteristic XDR, which comprises: 
 Foshagite: dMajor=2.97 Å    dMinor=5.05 Å   Xenotlite: dMajor=3.107 Å    dMinor=3.66 Å   
   
   
       18 . A paper composition according to  claim 17 , wherein said multiple phase calcium silicate hydrate has a water absorption range of at least about 500 percent.  
   
   
       19 . A paper composition according to  claim 17 , wherein said multiple phase calcium silicate hydrate has a water adsorption range of up to approximately 1000 percent.  
   
   
       20 . A paper composition according to  claim 17 , wherein said paper is a wood containing paper.  
   
   
       21 . A paper composition according to  claim 17 , wherein said filler comprises at least 30% of said paper by weight.  
   
   
       22 . A paper composition according to  claim 21 , wherein brightness of said paper is at least 74 GE.  
   
   
       23 . A paper composition according to  claim 21 , wherein opacity of said paper is at least 94.  
   
   
       24 . A paper composition according to  claim 21 , wherein opacity of said paper is at least 95.  
   
   
       25 . A paper composition according to  claim 21 , wherein opacity of said paper is at least 96.  
   
   
       26 . A method for the hydrothermal production of calcium silicate hydrate and calcium carbonate in a set of common reactors, said method comprising: 
 (a) providing an aqueous lime slurry, said aqueous lime slurry comprising (i) Ca(OH) 2  solids and (ii) dissolved Ca(OH) 2  in the form of Ca ++  ions;    (b) screening grit from said aqueous lime slurry;    (c) conditioning said aqueous lime slurry to a predetermined temperature;    (d) feeding a first portion of said aqueous lime slurry into a first reactor of said set of common reactors;    (e) agitating the contents of said first reactor at super-atmospheric pressure;    (f) introducing a stream of CO 2  into said aqueous lime slurry in said first reactor, to form CO 3   −2 ;    (g) reacting said CO 3   −2 ; and said Ca ++  in a carbonation reaction to produce insoluble precipitated calcium carbonate (CaCO 3 ) in said first reactor;    (h) removing said insoluble precipitated calcium carbonate and associated water from said first reactor;    (i) dewatering said insoluble precipitated calcium carbonate;    (j) washing said insoluble precipitated calcium carbonate with a selected wash water;    (k) charging a second reactor of said set of common reactors with a first aqueous silica slurry comprising silica at a concentration of from about 1 to about 1.5 pounds of silica per gallon of said first aqueous silica slurry;    (l) charging said second reactor of said set of common reactors with a second portion of said aqueous lime slurry;    (m) heating the contents of said second reactor under hydrothermal conditions to produce a calcium silicate.    (n) removing said calcium silicate from said second reactor;    (o) dewatering said calcium silicate;    (p) washing said calcium silicate with a selected wash water;    (q) switching feed of said first portion of said aqueous lime slurry and said CO 2  to said second reactor from said first reactor, and switching feed of said first aqueous silica slurry and said second portion of aqueous lime slurry to said first reactor, so that precipitated calcium carbonate is produced in said second reactor, and calcium silicate is produced in said first reactor.    
   
   
       27 . The method as set forth in  claim 26 , wherein said silica comprises fluxed calcined diatomaceous earth (FCDE).  
   
   
       28 . The method as set forth in  claim 26 , wherein said selected wash water comprises high purity water.  
   
   
       29 . The method as set forth in  claim 28 , wherein said high purity water comprises deionized water.  
   
   
       30 . The method as set forth in  claim 26 , further comprising adding, during production of said precipitated calcium carbonate, (a) magnesium oxide, (b) a selected hexamataphosphate, and (c) phosphoric acid to said reactor, so that said additives are present during the production of insoluble precipitated calcium carbonate.