Removal of heavy metal ions from aqueous solutions via adsorption onto modified lignin from pulping wastes

The aim for this research is to study inexpensive and effective metal ion adsorbents from biomass sources of modified lignin to offer these adsorbents as replacements for existing commercial materials. The initial concentrations were increased up to 12.7 ppm for Pb2+, Cd2+, and Zn2+ in order to reach the plateau values which represent saturation of the active points which are available for interaction with metal ions on the lignin samples. The maximum adsorption capacities are 11.3, 17.5, and 7.7 mg per g of the lignin for Zn2+, Pb2+, and Cd2+, respectively. The maximum adsorption capacity is higher than 20 mg per g of the lignin for Cu2+ ion. The maximum adsorption percentage is 96.7 for Pb2+ for 4 h at 330 K and is 95.0 for Zn2+ for 10 h at 290 K. The adsorption of all heavy metal ions first increases with pH and almost reaches a plateau value around 4.0 for Cu2+, 4.5 for Zn2+, 5.0 for Pb2+. High adsorption at higher pH values implies that metal ions interact with lignin by ion exchange.