The Adsorption of Pb(II) Using Silica Gel Synthesized from Chemical Bottle Waste: Optimization Using Box-Behnken Design

The adsorption of Pb(II) on silica gel synthesized from chemical glass bottle waste has been studied. The effect of independent variables (adsorbent dose, initial concentration of Pb(II), contact time, and pH) on the Pb(II) removal from water was evaluated and optimized using the Response Surface Methodology (RSM). Under optimized conditions (adsorbent dose: 20 mg; contact time: 30 min; initial Pb(II) concentration: 120 mg.L⁻¹; and pH: 8), the removal of Pb(II) was 99.77%. The adsorption equilibrium data obtained from the batch experiment were investigated using different isotherm models. The Langmuir isotherm model fits the experimental data. This shows that the surface of the silica gel synthesized from chemical bottles waste was covered by a Pb(II) monolayer. XRF analysis showed that the synthesized silica gel had a SiO₂ content of 75.63%. Amorphous silica was observed from XRD analysis. SEM-EDX characterization showed that Pb was adsorbed on the silica gel surface. SEM analysis showed that silica gel has irregular particles with a surface area of 297.08 m².g⁻¹ with a pore radius of 15.74 nm calculated from BET analysis.