Adsorption of fluoride onto magnesia-Equilibrium and thermodynamic study

摘要

Batch sorption system using magnesium oxide as an adsorbent was investigated to remove fluoride ions from aqueous solutions. The system variables studied include initial concentration of the sorbate, agitation time, adsorbent dose, pH, co-ions and temperature. The experimental data fitted well to the Freundlich isotherm while, poorly to the Langmuir isotherm. Thermodynamic parameters such as DELTA H deg, DELTA S deg and DELTA G deg were calculated indicating that the adsorption was a spontaneous, endothermic and a physical process. Kinetic studies reveal that the adsorption is first order. A mechanism involving three stages (external surface adsorption, intraparticle diffusion and final equilibrium) has been proposed for the adsorption of fluoride ions onto MgO. XRD patterns of the adsorbent were recorded to get a better in sight into the mechanism of the adsorption process.