The treatment of papermaking black liquor is the key to the treatment of papermaking waste water. At present, the commonly used black liquor treatment technologies include alkaline recovery, flocculation and sedimentation, membrane separation, acid separation, aerobic activated sludge and biotechnology, etc. Alkaline recovery is the most mature and widely used black liquor treatment method for papermaking.After the black liquor is separated from the slurry, the black liquor extracted from the wood (grass) slurry has a low concentration, so it must be concentrated to 45-80% by removing most of the water in the evaporation system, and then injected into the alkaline recovery boiler furnace for combustion. The heat generated by the black liquor combustion can be used for process or power generation. The organic sodium salt in the black liquor is changed into molten sodium carbonate in the furnace by chemical reaction. Meanwhile, the supplemental glauber salt is reduced to sodium sulfide, and the melt is discharged from the bottom of the alkaline furnace. After dissolution, a green liquid containing a small amount of iron ions is formed. The green solution was reacted with lime and the sodium carbonate was causticized to sodium hydroxide. The causticized clear liquid is called white liquid and can be reused for pulping and cooking. The caustic white clay can be treated with high-temperature calcination to recover lime for the caustic process.