Equilibrium and Kinetics of Glass Beads and Activated Carbon for Removal of Pb (II), Hg (II), and Cd (II) from Wastewater by Adsorption

The effect of partially replacing granular activated carbon (GAC) by glass beads (GB) in fixed bed for adsorption of Pb(II), Hg(II), and Cd(II) ions onto activated carbon were investigated. Experiments were carried out to study the effect of various GAC-GB weight ratio, adsorbate concentration, flow rate and bed depth on the performance of fixed bed. Isotherm experiments show that the results of Langmuir isotherm model is the best fit, the adsorption data R2 , 0.9816, 0.822, and 0.810 for Pb (II), Hg (II), and Cd (II) respectively. Optimum pH was found to be 4 for Pb(II), Hg(II) and 6 for Cd(II). While contact time was 360 min for each pollutant. Results suggest that replacing 5% by weight GAC by GB increasing the breakthrough time by 80% while, replacing 10% of GAC makes the adsorption inefficient compared with 0% GB. A general rate model (GRM) was formulated to describe the mass transfer kinetics in the fixed bed adsorber. The GRM includes external mass transfer and pore diffusion coefficient using nonlinear isotherms, provides a good description of the adsorption process.