In the present invention, a dissolved solution consisting of an aqueous solution of sodium carbonate and sodium sulfide as main components is mixed with calcium oxide in a slaker and reacted in a re-causticizer 10 to prepare an aqueous suspension containing sodium hydroxide and calcium carbonate as main components. Formed, and such an aqueous suspension is filtered on the first filter 19, and subsequently, after dilution with water in the dilution vessels 21, 25, is fed two or three times to the additional filters 22, 26 It is a method of re-causticizing the green solution by a sulfate or Kraft process for wood pulp production, which separates the solids suspended in the suspension by filtration.After the first separation of calcium carbonate as the main component and calcium oxide as a trace component , During dilution in the dilution vessels 18, 21, 25, in particular, in the dilution vessel(s) 21, 25, upstream of at least the second and/or third filter 22, 26, carbon dioxide is added to the aqueous suspension. It discloses a method characterized in that it is added to.
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