Utilization of Fly Ashes from the Coal Burning Processes to Produce Effective Low-Cost Sorbents

摘要

The paper presents a novel method to produce sorbents from fly ash (FAI) based on modification by chitosan for zinc(II) removal from aqueous solutions. It also describes a study of the effectiveness of Zn(II) sorption onto the sorbents prepared from FA by thermal activation (from FAI-373 to FAI-1173) as well as by thermal activation and chemical modification using chitosan (from FAICS-373 to FAICS-1173). Serial batch kinetics and static tests were conducted in order to investigate the effects of some important parameters such as the initial concentration, the phase contact time, the pH value of the solution, the obtained sorbent amount, as well as the temperature. The kinetic process was described using the pseudo first order (PFO), pseudo second order (PSO), and intraparticle diffusion (IPD) models. The experimental data were analyzed using the Langmuir, Freundlich, and Temkin isotherm models in order to study adsorption mechanisms. The correlation coefficient values show that for the FAICS the sorption process can be well-defined by the Langmuir isotherm model, while for the FAI sorbent it can be defined by the Freundlich isotherm one. The maximum adsorption capacities were equal to 21.41 mg/g for FAI and 29.59 mg/g for FAICS-773. The results showed higher efficiency of Zn(II) removal onto FAI modified by temperature and CS compared with FAI. In addition, the determined thermodynamic parameters (such as entropy, enthalpy, and free energy of the process) indicate that the process was spontaneous, favorable; and endothermic in nature. The kinetic data were well fitted by the pseudo second kinetic model. On the basis of the present study, it can be concluded that production of sorbents by modification of fly ash using chitosan (CS) could become an effective and low-cost technology for Zn(II) ions removal from aqueous solution.