Question

............... is the waste liquor from the Kraft pulping process after pulping is completed.

• A. White liquor
• B. Black liquor
• C. Brown liquor
• D. Red liquor

Hint:

In the Kraft process: white liquor = input chemical, black liquor = output waste after pulping.

Answer 1

The Correct Option is B

In the Kraft process, which is widely used in the paper industry to produce pulp from wood, several types of liquors are involved at different stages.
- White liquor is the fresh mixture of sodium hydroxide (NaOH) and sodium sulfide (Na$_2$S) used to break down lignin in wood.
- Black liquor is the waste by-product generated after the pulping process is complete. It contains the dissolved lignin, hemicellulose, and the spent chemicals from white liquor.
Once the cellulose fibers are separated out to form pulp, the remaining liquid — which is dark in color and rich in organic compounds and residual chemicals — is called black liquor.
Black liquor is highly alkaline and has significant fuel value due to its organic content. It is commonly burned in recovery boilers to generate energy and recover chemicals for reuse in the process.
Other options like brown liquor and red liquor refer to by-products in different pulping processes (e.g., sulfite or soda processes) but are not specific to Kraft pulping.
Therefore, black liquor is the correct answer.