Adsorption of lead and cadmium ions in aqueous solutions onto modified lignin from alkali glycerol delignication

Adsorptions of toxic metal ions (Pb(II) and Cd(II)) onto modified lignin from beech and poplar woods by alkali glycerol delignification are presented in this paper. The material exhibits good adsorption capacity and the adsorption data follow the Langmuir model. The maximum adsorption capacities are 8.2-9.0 and 6.7-7.5 mg/g of the modified lignin for Pb(II) and Cd(II), respectively. The maximum adsorption percentage is 95.8 for Pb(II) for 4 h at 330 K and is 95.0 for Cd(II) for 10 h at 290 K. The adsorption of both the metal ions increased with increasing temperature indicating endothermic nature of the adsorption process. The maximum adsorption percentages of Pb(II) and Cd(II) ions decrease with time till 48 and 42 h and then again increase slightly with time. The adsorption of both heavy metal ions increases with pH. The adsorption of Pb(II) ions reached a maximum at a 5.0 value of pH.