Thiourea Doped Silica Composite for Lead Removal: Isotherm, Kinetic, and Thermodynamic Studies

In this study, series of experiments were carried out in batch in order to examine the possibility of thiourea doped silica composite for the removal of lead under different experimental conditions. Adsorption of lead (II) ions was investigated with the difference in the parameters of pH, contact time, and lead (II) ions concentration. The adsorption of lead followed pseudo-second-order rate kinetics. Intra-particle diffusion was established not to be the sole rate-controlling step. Thermodynamic studies tell that the adsorption of lead was endothermic and spontaneous, with a good affinity of the adsorbent. Various isotherm models viz, Langmuir, Freundlich, Temkin, Dubinin-Radushkevich and Harkins-Jura isotherms were used to evaluate the equilibrium data. The Freundlich and Temkin models were established to be in actual agreement with the experimental data with high R2, low RMSE, and low χ2 values. The maximum adsorption capacity calculated from Langmuir isotherm was 42.31 mg/g at optimum condition of pH 4 and contact time of 60 min.