Causticizing and Lime reburning - Process info

The spent cooking liquor is evaporated and then incinerated in the recovery boiler. The resulting smelt consisting mainly of sodium carbonate and sodium sulphide is dissolved in water to form green liquor. After clarification burnt lime, calcium oxide, is added to the liquor to recausticize it. This is to convert the sodium carbonate content to sodium hydroxide. Calcium carbonate solids, lime mud, are then separated from the liquor to yield regenerated cooking liquor, white liquor.

The washed and dewatered lime mud it is burnt in the lime kiln to convert the calcium carbonate back into calcium oxide, burnt lime, for reuse.