Sorptive removal of cadmium from aqueous solutions by Delonix regia derived lignin: effect of amination

The relative cadmium sorption ability of unmodified and aminated lignins was examined as a function of solution pH, sorbent—sorbate resident time and ratio, concentration and temperature. Experimental results showed that the surface characteristics of both the unmodified and aminated lignins were favourable to effective cadmium ions sorption from aqueous solutions. Sorption of cadmium was dependent on equilibrium solution pH, as maximum removal was attained at pH 5. The Langmuir and Freundlich isotherm models fitted the experimental data. The biosorption of cadmium onto unmodified and aminated lignins was rapid and equilibrium was attained within 120 min. The sorption kinetic data revealed that the biosorption of cadmium onto these biosorbents followed pseudo-second-order model. This was further supported by Elovich and intraparticle diffusion models. The process was endothermic and ΔG° was positive showing non-spontaneity of the process within the studied temperature range.