Adsorption of α-picoline onto rice husk ash and granular activated carbon from aqueous solution: Equilibrium and thermodynamic study

In the present study, the batch adsorption experiments were carried out to calculate the adsorption capacities of rice husk ash (RHA) and commercial grade granular activated carbon (GAC) for the adsorption of α-picoline (Pi) from aqueous solutions. The effect of various parameters like initial pH (pH0), adsorbent dose (m), contact time (t), initial concentration (C0) and temperature (T) on the adsorption of Pi from the aqueous solutions was studied. The maximum uptake of Pi was observed to be 2.34 mg g−1 at lower concentration (50 mg dm−3) and 15.46 mg g−1 at higher concentration (600 mg dm−3) using 20 kg m−3 of RHA and the maximum uptake of Pi by GAC was observed to be 4.55 mg g−1 at lower concentration (50 mg dm−3) and 36 mg g−1 at higher concentration (600 mg dm−3) using 10 kg m−3 of GAC at normal temperature. The equilibrium data can be best represented by Radke–Prausnitz isotherm equation. However, Toth and Redlich–Peterson isotherm equations also represent the equilibrium data adequately. The values of change in Gibb's free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated. Thermodynamic study revealed that the adsorption of Pi onto RHA and GAC is an endothermic process. Isosteric heat of adsorption was found to be decreasing with an increase in surface loading. The acidic water and dilute acids showed higher desorption efficiency for Pi from RHA and GAC. Thus GAC can be regenerated by using acidic water and acids. However, RHA can be disposed off by using it as a fuel in furnaces to recover its energy value.