White liquor

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White liquor is a strongly alkaline solution composed mainly of sodium hydroxide and sodium sulfide. It is used in the first stage of the Kraft process in which lignin and hemicellulose are separated from cellulose fiber for the production of pulp. The white liquor breaks the chemical bonds between lignin and cellulose substructures in wood materials and further degrades the lignin itself. Sulfide is the active component in delignification. White liquor also contains minor amounts of sodium carbonate, sodium sulfate, sodium thiosulfate, sodium chloride, sodium bicarbonate, and calcium carbonate. Since the white liquor is often a regenerated, it can also accumulated in the process recycling. These additional components are considered inert in the Kraft process. When produced by recycling, black liquor is converted to smelt, which is extracted with water to give green liquor. Addition of lime converts green liquor to white liquor, ready for reuse. The chemical characteristics of the white liquor, deriving from its properties, are described by the parameters total alkali, active alkali, effective alkali, sulfidity, causticity, and reduction.