Removal of Mn (II) from aqueous solution using hematites nanoparticles of different morphologies: Sorption kinetics and equilibrium studies

摘要

This work reports kinetic and equilibrium studies of Mn (II) adsorption by hematite (α- Fe_2O_3) nanoparticles of different morphologies synthesized by acid hydrolysis, transformation of ferrihydrite, sol gel methods in the laboratory. The sizes of the hematite samples were in the range 15.69-85.84nm with morphologies such as hexagonal, plate-like, nano-cubes, sub-rounded and spherical. Kinetic experiments demonstrated rapid uptake of Mn (II) reaching equilibrium at 30-90 minutes. Kinetic data were satisfactorily described by pseudo-second order and the sorption process has been found to be feasible in nature following a chemisorption process. Langmuir, Freundlich, Temkin and Dubinin Radushkevich isotherms were selected to analyze the experimental data. The maximum adsorption capacity of Mn (II) was found to be in the range 2.04-12.3 mgg~(-1) The study revealed that the hematite with sub-rounded morphology gave the highest adsorption capacity. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the adsorption of Mn (II) ion was feasible, spontaneous and exothermic at 300-330K. Equilibrium studies showed that Mn (II) had a high affinity in basic medium and adsorption of Mn (II) ion onto hematite nanoparticles was by inner sphere surface complexation. The FT-IR result of Mn (II) - loaded hematite also showed a strong interaction of the adsorbate on the various hematite samples. This study showed that morphologies play vital role in the adsorption capacities of hematite for the removal of Mn (II) from aqueous solution.