Kinetic and thermodynamic studies on adsorption of sulphate from aqueous solution by magnetite, activated carbon and magnetite-activated carbon composites

Abstract

Magnetite nanoparticles, activated Carbon and their composites were synthesized in the laboratory. The adsorbents were characterized by bulk density, pH, pzc, surface area, iodine value, moisture contents, volatile components, Brunauer Emmett and Teller (BET) surface area, Scanning electron microscopy (SEM) coupled with Energy dispersive X-ray (EDX), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The adsorbents were employed for the batch adsorption of sulphate ion from aqueous solution. Some variable effects such as pH, initial concentration, contact time, adsorbent dosage and temperature on adsorption were also investigated. The data obtained were fitted into isotherms, kinetic model and thermodynamic process. The adsorption studies results revealed R² value ranging from 0.961 - 0.996 for Freundlich and Langmuir isotherm ranges from 0.954 – 0.979 for all types of adsorbents studied. Pseudo-first-order kinetic models correlation coefficient factor ranges between 0.818 – 0.947 while Pseudo-second-order kinetic models R² values ranges from 0.999 - 1. The equilibrium time for all adsorbent types range from 45-120 minutes and the maximum monolayer capacity (q_max) was observed to be between 83.0 - 142.86 mg/g for all the adsorbents at optimum pH 5. Thermodynamic studies revealed ΔH value to be in the range 1.484-4.573kJ/mol and ΔG value in the range -7.054- (-5.314) kJ/mol for all adsorbent types. Thermodynamic result revealed that the adsorption system was feasible, spontaneous and endothermic in nature.

Keywords: Sulphate, Adsorption, Magnetite, Composites, Isotherm, Thermodynamic