Defluoridation of water using calcined magnesia/pullulan composite

In the present study, the performance of a novel adsorbent was investigated for fluoride removal from water. The adsorbent was synthesized by calcining magnesia (MgO) with pullulan, an extracellular water-soluble microbial polysaccharide, and characterized using FTIR, SEM, XRD and BET. The results showed that the surface area and the adsorption micropore of the calcined MgO/pullulan composite were increased from 7.5888 m(2)/g and 13.91507 nm for pure MgO to 32.8992 m(2)/g and 29.11552 nm, respectively. FTIR analysis showed that hydrogen bonds were formed in the adsorption of fluorides onto the calcined MgO/pullulan composite. At 30 degrees C and pH 7.0, the adsorption capacity was determined as 4537 mg/kg using an the initial concentration of 10 mmol/L fluoride solution. The adsorption capacity of calcined MgO/pullulan composite remained stable in the range pH 2-10. The adsorption isotherms fitted well to the Langmuir isotherm model. Thermodynamic parameters viz, Delta G degrees, Delta H degrees and Delta S degrees were measured as Delta G degrees = -22.44 kJ mol(-1), Delta H degrees = 0.58 kJ mol(-1), and Delta S degrees = 0.093 kJ mol(-1) K-1, respectively. The adsorption kinetics of fluoride onto the calcined MgO/pullulan composite closely followed the Lagergren's pseudo-second-order rate mode, which indicates that the chemical adsorption, rather than mass transfer, is the rate-determining step. (C) 2010 Elsevier B.V. All rights reserved.