Biosorption of nickel using unmodified and modified lignin extracted from agricultural waste

Adsorption capacity for the removal of nickel (II) ions from aqueous solution using unmodified and modified lignin extracted from Tithonia diversifolia was investigated. The lignin was characterized with FT-IR. Parameters like initial pH, initial concentration, and contact time were investigated. The optimum pH for metal removal was found to be 7, while optimum contact time of 360 min was achieved. The modification of the adsorbent by phenol affected the adsorption capacity. The kinetic studies showed that the sorption rates could be described by both pseudo-second-order and intraparticle diffusion models. The pseudo-second-order model showed a better fit with a correlation coefficient of 0.9955 and 0.9958 for both unmodified and modified lignins, respectively. The adsorption isotherm was best fitted using the Freundlich model. The adsorption capacity for Ni(II) on the unmodified and modified lignin was found to be 12.48 and 16.94 mg g−1, respectively.