Lignin-graft-poly(acrylic acid) for enhancement of heavy metal ion biosorption

Novel biosorbent, alkaline Lignin-graft-poly(acrylic acid) (AL-g-PAA), was synthesized by radical graft copolymerization. The molecular structure was confirmed by 1H-NMR and thermogravimetric analysis. Taking the Cu(II) ion biosorption as standard, the optimal conditions of the grafting reaction (0.50 g monomer amount/g AL; 0.20 g initiator/g AL; 0.05 g crosslinker/g AL; reaction at 80 °C for 10 min) were selected from the orthogonal tests. Biosorption studies for eliminating Cu(II) and Cd(II) were conducted at different pHs and temperatures to detect kinetic and equilibrium parameters. The biosorption of these two metal ions followed pseudo-second-order rate kinetics and increased with increasing temperature. The biosorption isotherm processes were fitted better to Langmuir model. The maximal biosorption capacities of AL-g-PAA at 25 °C were 0.75 mmol/g (Cu(II)) and 0.68 mmol/g (Cd(II)). Using the biomass waste, lignin, to prepare biosorbent will exert positive effects on environmental and economic sustainability.