Green liquor is the dissolved smelt of sodium carbonate

Sodium carbonate

Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 and sodium sulfide

Sodium sulfide

Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...

 from the recovery boiler

Recovery boiler

Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor, which contains lignin from previously processed wood. The black liquor is burned, generating heat, which is usually used in the process or in making electricity,...

 in the kraft process

Kraft process

The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...

. Although the color of such a solution is indeed green, no literature sources were found to explain what specific compounds are responsible for this color.

The green liquor is usually reacted with lime

Calcium oxide

Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

 (CaO) in the causticizing stage to regenerate white liquor

White liquor

White liquor is a strongly alkaline solution used in the first stage of the Kraft process in which lignin and hemicellulose are separated from the cellulose fiber in Kraft process for the production of pulp...

. Alternatively, green liquor can be used prior to white liquor to extract some hemicellulose.