Black liquor

Black liquor is an industrial by-product from the kraft process when digesting pulpwood into paper pulp removing lignin, hemicelluloses and other extractives from the wood to free the cellulose fibers.

Overview

The term "black liquor" comes from the characteristic black color of this material, which is a thick, dark liquid. The black liquor comprises a mixture of organic matter and inorganic chemicals. The organic component, which is approximately 40% of the dry solids, consists of lignin fragments, carbohydrates from the wood, and other wood extractives. The inorganic component is primarily sodium sulfate and sodium carbonate, which are the chemicals used in the pulping process.

Production and Use

Black liquor is produced in large quantities in pulp mills as part of the paper production process. The black liquor recovery process not only produces energy (in the form of steam) but also recovers the chemicals that can be reused in the pulping process. This recovery process is critical to the economic viability of pulp mills, as the cost of the chemicals and the energy produced represent significant savings.

Environmental Impact

While black liquor can be a valuable resource for pulp mills, it can also pose environmental challenges. If not properly managed, black liquor can contaminate waterways and harm aquatic life. However, modern pulp mills have systems in place to treat and recycle black liquor, minimizing its environmental impact.

See Also

• Kraft process
• Pulp mill
• Paper production