Autocausticizing of smelt with sodium borates

Copyright Pulp & Paper Canada. Reprinted with permission from Annex Business Media.The autocausticizing technology involving the use of borate to "causticize" sodium carbonate (Na2CO3) in the soda or kraft smelt directly in recovery boilers was reviewed by re-examining the reactions between Na2CO3 and sodium borates (NaBO2 and Na2B4O7) at high temperatures. Both NaBO2 and N~B4O7 were found to react readily with molten N~CO3 at any Na:B molar larger than 3:1 to form trisodium borate (Na3BO3) .The formation of Na3BO3 as a reaction product means that the amount of borate required for the autocausticizing reactions can be substantially lowered than previously suggested.The work at the University of Toronto was supported by U.S. Borax Inc. and the Natural Science and Engineering Research Council of Canada