Black liquor derived lignin adsorbents for removal of organic pollutants from water

We present the preparation of lignin particles from raw black liquor and their chemical modification, so that they can be used as efficient adsorbents to remove organic pollutants from water. For the production of adsorbent powders, pristine black liquor (as obtained from a pulping mill) was emulsified with epichlorohydrin and Span 80 and cured at elevated temperatures. Phospinic esters and organic sulphates were synthetically introduced to the lignin-backbone to modify the adsorbents. The adsorption of organic model compounds, Paraquat, p-nitrophenol, and malachite green were studied. Kinetic and thermodynamic data of the adsorption processes was obtained experimentally and by fitting mathematical models (Langmuir and Freundlich isotherms). Adsorbents showed adsorption capacities of Q_e = 62 mg/g for Paraquat, Q_e = 199 mg/g for p-nitrophenol, and Q_e = 1200 mg/g for malachite green in batch-adsorption experiments. These values are among the highest for any of the model compounds presented in literature. Adsorption occurred reasonably fast for all compounds, reaching plateau-adsorption within minutes to hours.