Pb (II) adsorption on pumpkin char and modified pumpkin char: optimisation, kinetics, equilibrium and thermodynamics studies

In this research, a low-cost and locally available by-product, pumpkin shell, was used to prepare pumpkin char (PC), and activated carbon using ZnCl₂ (PCZC), H₃PO₄ (PCPA) activation agents and Pb (II) ion removal properties from the aqueous solution were investigated. The adsorption process was studied as a function of solution pH (2–7), initial concentration of Pb (II) (10–50 mg/L), volume of solution (10–200 mL), adsorbent dosage (0.005–0.04 g), contact time (5–120 min) and temperature of solution (308–333 K). The obtained results of experiments show that with the increase in the value of pH, the percentage Pb (II) ion removal increases by 87.59, 88.83 and 94.67% for PC, PCZC and PCPA, respectively. According to these results, the optimised value of pH for PC, PCZC and PCPA adsorbents is 5, 6 and 5, respectively. Moreover, the optimised adsorbent dosages for PC, PCZC and PCPA are 0.015, 0.01 and 0.01 g, respectively. The SEM images of PC, PCZC and PCPA after Pb (II) adsorption show that Pb (II) ions covered the surface of adsorbents in the form of nanoparticles. The experimental data were analysed using two parameter isotherm models namely: Langmuir, Freundlich, Temkin and Dubinin-Radushkevich. The obtained results of the Langmuir model showed that the maximum adsorption capacity of PC, PCZC and PCPA adsorbents was 46.948, 140.845 and 117.647 mg/g at 333 K, respectively. Adsorption of Pb (II) ion onto these adsorbents followed the Langmuir isotherm and PSO kinetic model. In addition, the kinetics data were investigated by the pseudo-first-order (PFO), pseudo-second-order (PSO) and intra-particle diffusion (IPD) models.