How much do you know about black liquor

The wastewater produced by the alkaline process (soda caustic process and sulphate process) of the paper industry. It contains a large amount of lignin, which is dark brown, so it is called black liquor. 

Black liquor from paper industry

Black liquor contains a large amount of suspended solids, organic pollutants and toxic substances, which are directly discharged into the water body and cause serious pollution. The main hazards are: papermaking wastewater containing a large amount of fiber, pigment and inorganic salt will make the water body black and have a special foul odor; the black liquor of papermaking black liquor containing high concentration of organic pollutants can have a high biochemical oxygen demand (BOD) 5000~40000g/L, it will consume a lot of dissolved oxygen in the water, affecting the water quality; the alkaline substance in the black liquor will increase the pH value of the water body sharply and destroy the balance of the water environment.

In the pulping process, the extruded black liquor contains a large amount of lignin. The lignin sulfonate product can be comprehensively utilized by making black liquor for papermaking. The comprehensive utilization of papermaking black liquor resources is based on black liquor as raw material, which is concentrated, sulfonated and dusted to produce lignosulfonate products. Widely used in concrete water reducer, coal water slurry dispersant, asphalt emulsifier, ceramics, oil well mining additives. The papermaking black liquor is made into lignin products for comprehensive utilization, which can eliminate the damage to the ecological environment and create an environmentally friendly and natural harmonious development road. Realize the unity of economic, environmental and social benefits.

black liquor

Cause of papermaking black liquor

The paper mill discharges three waters according to the process, one is the pulping and cooking waste liquid, which is generally called the papermaking black liquor; the other is the washing, selecting and rinsing of the pulp after separating the black liquor, also called the middle water; the third is the white water on the paper machine, the white water It can be processed and reused. The middle water is less than 10% of the total amount of the remaining black liquor extraction. The pollutants contained in the black liquor account for more than 90% of the total pollution discharge of the whole plant. Therefore, black liquor emissions are the main source of pollution in paper mills.

Black liquor composition editing Raw materials such as straw used in papermaking raw materials contain cellulose, lignin and hemicellulose (glycans). The paper is only used for cellulose (about 40%), and about 25% of the wood. About 18% of hemicellulose and xylose, potassium, nitrogen, phosphorus, etc., are discarded with black liquor. The lignin and hemicellulose contained in the black liquor and the substances such as xylose, potassium, nitrogen and phosphorus are highly valuable in industrial and agricultural production.

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