Black liquor in pulp mill and its treatment

Pulping process is an important part of papermaking. At present, the main steps of pulping production include wood handling, cooking, washing, screening, bleaching, drying and finishing. During the pulping process, black liquor is a kind of main spent chemicals, which is full of lignin, resin, starch, low molecular compounds, sodium hydroxide, sodium carbonate, sodium sulfide, sodium sulfate and other sodium salts combined with organic matter. Currently, the ways to treat black are combustion or acidification. However, with the development of membrane separation, this technology has been studied by scholars and there are rich research results. Meanwhile, some research challenges and difficulties still exists, such as membrane manufacture and fouling; thus, it is supposed to be regarded as important research direction to actively explore various reliable and better treatment methods regarding black liquor. This thesis work describes the pulping process, characteristics of white liquor and black liquor; then it depicts two current treatment technologies of black liquor in detail. It introduces new technologies of membrane separation in terms of different principles regarding black liquor, which are membrane filtration and electrodialysis, and some of the research results are listed. Moreover, the comparison of both two membrane treatments and the problems about membrane separation are also mentioned