A lignin-based composite hydrogel for the removal of heavy metal ions from aqueous solution

In order to remove Pb(II), Ni(II) and Mn(II) from aqueous solution, a lignin-based composite hydrogel (LS-g-P(AA-co-AM)/OMMT) was synthesized by free radical polymerization using sodium lignosulfonate (LS) and organic montmorillonite (OMMT) as raw materials. The obtained hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the LS-g-P(AA-co-AM)/OMMT contains abundant C and O containing surface groups, which were favorable for the adsorption of Pb(II), Ni(II), Mn(II). The effects of adsorbent dosage, solution pH, temperature, initial concentration and time on hydrogel adsorption of Pb(II), Ni(II) and Mn(II) were investigated. The maximum adsorption amounts were 575.5, 326.67 and 282.82 mg/g, respectively. The adsorption process of heavy metal ions conforms to the pseudo-second-order kinetics and Langmuir model, which indicates that the adsorption of Pb(II), Ni(II) and Mn(II) by LS-g-P(AA-co-AM)/OMMT is a monolayer adsorption process dominated by chemical adsorption. The main adsorption mechanisms are ion exchange and coordination complexation. Conclusively, the prepared biomass adsorbent was proved as promising adsorbents for the removal of heavy metals.