Abstract
Cotton pulp black liquor (CPBL) is high alkaline wastewater generated in the production of cotton pulp dreg. The recovery of resource and water is of great practical significance for sustainable development of viscose fiber industry. In this work, precipitation of color biopolymer such as lignin in CPBL was investigated using CaCl2, MgCl2, AlCl3 and FeCl3 as precipitants. The main influencing factors, solid/liquid separation performances, the characteristics of precipitates, and interactions between metal ions and organic compounds were studied. The removal of lignin was found in the order: FeCl3 (89.73%) > AlCl3 (83.96%) > CaCl2 (49.39%) > MgCl2 (42.15%). Removals of organic matter with molecular weight greater than 100 kDa by FeCl3, AlCl3, CaCl2 and MgCl2 precipitation were 94.27%, 93.77%, 74.54% and 76.02%, respectively. The mechanism of biopolymer removal by precipitation was identified as the complexation between high valence metal cations and negatively charged hydroxyl or carboxyl groups. In addition, metal hydroxides or carbonates would form in situ in the native pH condition and may participate in the removal of lignin by adsorption or enmeshment.
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