Activated carbon produced from Glycyrrhiza glabra residue for the adsorption of nitrate and phosphate: batch and fixed-bed column studies

Abstract

In the present study, Glycyrrhiza glabra residues (GGR) were used for the preparation of activated carbon, with a surface area of 959.22 m2 g−1. Activated carbon was prepared through chemical activation using ZnCl2 at optimum carbonization temperature, and impregnation ratio for nitrate, and phosphate removal. The effect of contact time and adsorbent dosage on the removal efficiency was investigated, and the pseudo-second-order kinetic model correlated well with the adsorption data. The response surface methodology was applied for the determination of the effect of initial concentration, pH, and temperature and their interaction on the removal efficiency in the batch adsorption system. The Langmuir isotherm generated a satisfactory fit with the experimental data, and the maximum adsorption capacity was 142.5 mg g−1 at 308 K and 92.5 mg g−1 at 298 K for nitrate and phosphate removal, respectively. The high adsorption capacity reveals the applicability of the GGR activated carbon for nitrate and phosphate removal. Furthermore, the fixed-bed column adsorption studies were carried out, and the effect of flow rate and influent concentration on the behavior of the breakthrough curve was studied. The breakthrough time decreased by increasing the flow rate and inlet concentration. The Thomas and Yoon–Nelson models were suitable models for the design of GGR activated carbon fixed-bed column. The LUB of 0.44 cm and 4.35 cm was obtained for nitrate and phosphate with the inlet concentration of 20 mg L−1 and a flow rate of 40 mL min−1, respectively. GGR is a new adsorbent that has not been previously utilized for adsorption of phosphate and nitrate.