Pulping black liquor-based polymer hydrogel as water retention material and slow-release fertilizer

Black liquor produced by pulping industry is generally difficult to utilize considering its complex constitutions including lignin with undefined primary structure, various polysaccharides and mineral salts, thus generally being regarded as industrial waste. In this work, we report the preparation of black liquor-based hydrogel (BLH) by a redox free radical induced polymerization process and its applications as both water retention material and slow-release fertilizer. Comparing with the hydrogel prepared without black liquor, the maximum water swelling ratio of the BLH can be enhanced from 69 g/g to 359 g/g, and the water retention ratio was increased from 24.42% to 45.25 %. The hydrogel's potential application as both water retention material and slow-release fertilizer was verified by performing a cultivating plant test in the hydrogel-mixed sand. Applying this polymer hydrogel as water retention material and slow-release fertilizer achieves the utilization of the whole components of black liquor that were treated as industrial waste before, which not only solve the pollution problem of paper-making process, but also expand its promising application prospect to the afforestation of desertification control projects.