Synthesis, characterization and application of goethite mineral as an adsorbent

In the present work goethite mineral synthesized using chemical precipitation method was evaluated for Cu(II) and Cd(II) uptake. The mineral was characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy for their morphological and structural features. Using this goethite, the adsorption of Cu(II) and Cd(II) was studied in synthetic waste water in a batch system by varying pH in the range 3–5, varying the initial concentration (5–25 mg L−1), varying the adsorbent dose (0.2–1.0 g) and effect of temperature (293–313 K). The adsorption percentage of the Cu(II) and Cd(II) were found to be 98.00% and 87.50% respectively. The adsorption kinetic data were analyzed using pseudo-first-order and pseudo-second-order models. It was found that the pseudo-second-order kinetic model was the most appropriate model, describing the adsorption kinetics. Adsorption isotherms of Cu(II) and Cd(II) onto goethite were determined at 293 K, 303 K and 313 K with 10 mg L−1 as initial concentration of Cu(II) and Cd(II) respectively. The equilibrium isotherm data were analyzed using Freundlich, Langmuir and Temkin isotherm models and isotherm constants were determined. The linear transformed model provided the highest R2 regression coefficient with the Freundlich isotherm than other isotherms. Thermodynamic parameters such as change in the Gibb's free energy of adsorption (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated. The negative values of ΔG° indicate that the adsorption process was spontaneous in nature and the positive value of ΔH° indicates the endothermic nature of Cu(II) and Cd(II) adsorption onto goethite.