Adsorption of an emerging contaminant (primidone) onto activated carbon: kinetic, equilibrium, thermodynamic, and...

The current study addresses the removal of an emerging environmental contaminant (primidone) in batch adsorption experiments using commercial-grade powdered activated charcoal (PAC). The experiments for the removal of primidone were performed to identify the effect of various adsorption parameters. The second-order rate expression best represented the adsorption kinetics data. The Freundlich isotherm equation was best fitted to the experimental adsorption data at equilibrium for removal of primidone using PAC. The values for change in entropy (ΔS^o) were positive, which indicates that the degree of freedom of the process increases. The negative values of change in enthalpy (ΔH^o) and change in Gibb's free energy (ΔG^o) indicate that the physical adsorption is a dominant phenomenon, and the process is feasible and spontaneous. The negative value of ΔH^o also represented the exothermicity of the adsorption process. The Taguchi optimization technique calculated the influence of variation of different process parameters, viz., initial pH (pH₀), PAC dosage (m), initial adsorbate concentration (C₀), solution temperature (T), and process contact time (t), on the removal of primidone by adsorption from aqueous solution. Each of the above parameters was examined at three levels to study their effects on the adsorptive uptake of primidone using PAC (q_e, mg g^-1), and the optimum value necessary to maximize q_e was determined. The findings from the ANOVA indicate that the PAC dose (m) is the most notable parameter contributing 62.16% to q_e and a 71.96% to the signal to noise (S/N) ratio data, respectively. The confirmation experiments performed at the optimum parameter condition validated the applicability of the Taguchi design of experiments. The percent removal and adsorptive uptake at the optimal condition were 86.11% and 0.258 mg g^-1, respectively.