Abstract: In order to quantitatively characterize the effects of extraction ratio of black liquor on residual pollution load of pulp, Traditional alkaline cooking was used to cook the pinus koraiensis , and the countercurrent extraction process was used to extract the black liquor.The relationship between the extraction rate of black liquor and the residual lignin content, chemical oxygen demand (CODCr) and biochemical oxygen demand (BOD5) in different pulp concentrations were studied.The results showed that lignin degradation products are the main source of pollution of black liquor organic matter, and high concentration of high black liquor extraction rate can effectively reduce the pollution load.When the extraction rate of high black liquor increased from 71.34% to 98.47%, the content of residual lignin, CODCr and BOD5 in the pulp were significantly reduced.The extraction ratio of black liquor has a linear relationship with remained lignin in pulps, and the remained CODCr and BOD5 in pulps has cubic function of one variable and a uni-variable and hyperbolic relationship respectively.The results showed that high concentration of high extraction was an effective method to reduce the pollution load during pulping and bleaching in papermaking process.

Key words: pulp, extraction ratio of black liquor, pollution load, countercurrent extraction