Adsorptive removal of lead (Pb), copper (Cu), nickel (Ni) and mercury (Hg) ions from water using chitosan silica gel composite

Silica gel chitosan composite was prepared to perform adsorptive experiment of different heavy metal ion solutions. The characterization of chitosan + silica gel (Ch + Sg) composite was done by FTIR and SEM-EDS to understand the presence of active sites and to have an insight on the surface morphology. The adsorption study of heavy metal ions by Ch + Sg composite gives maximum removal percent for Cu, Pb and Ni which were obtained at pH 5 and for Hg at pH 6.The trend of removal by Ch + Sg signifies that maximum removal percent was attained at 120 min. The surface of Ch + Sg is heterogeneous for the adsorption of Hg, Ni and Cu and homogeneous for Pb adsorption. The values obtained for Pb signify that its adsorption best fitted to pseudo first order with the R-2 value of 0.986, whereas pseudo second order best fitted to the experimental data of Cu, Ni and Hg as R-2 values which are 0.983, 0.819 and 0.957 respectively. The values of change in entropy (angle S) obtained for Pb, Cu, Ni and Hg are - 69.33, - 118, - 63.33 and - 98.52 J/mol K respectively. Negative values of change in enthalpy, angle H in (kJ/mol) are in the range of - 18.2 to - 37.66 which indicates both physical and chemical adsorption involves in the process of adsorption.