White liquor is a stronglyalkaline solution composed mainly ofsodium hydroxide andsodium sulfide. It is used in the first stage of theKraft process in whichlignin andhemicellulose are separated fromcellulose fiber for the production ofpulp.[1] The white liquor breaks the bonds between lignin and cellulose. It is called white liquor due to its white opaque colour.
White liquor consists mainly ofsodium hydroxide andsodium sulfide in water and is the active component in Kraft pulping.[1] White liquor also contains minor amounts ofsodium carbonate,sodium sulfate,sodium thiosulfate,sodium chloride,calcium carbonate and other accumulated salts and non-process elements. These additional components are considered inert in the Kraft process, except sodium carbonate that contributes to a lesser extent.
The chemical composition and properties of the white liquor are calculated astotal alkali,active alkali,effective alkali,sulfidity,causticity andreduction.
| Total alkali | All Na− compounds | |
| Active alkali (AA) | NaOH + Na2S | g NaOH equivalents, or % on dry wood |
| Effective alkali (EA) | NaOH + ½ Na2S | g NaOH equivalents, or % on dry wood |
| Sulfidity | Na2S / AA | % |
| Causticity | NaOH / (NaOH + Na2CO3) | % |
| Reduction | Na2S / (Na2S + Na2SO4) | % |
The Kraft cooking liquor (white) is used to extract the lignin and break down the cellulose composition of wood chips into usable pulp. The white (cooking) liquor becomes weak black liquor and is sent to the recovery process.
