Physicochemical characterization and sorption behavior of Mg-Ca-Al (NO3) hydrotalcite-like compounds toward removal of fluoride from protein solutions

The present study explores the potential of Mg-Ca-Al (NO3) hydrotalcite-like compounds (MgCaAlNO3-HTlcs) for the removal of fluoride from protein solutions. In this study, the Mg3-xCaxAlNO3-HTlcs (x = 0-3, x is the mol.% of Ca) were synthesized and characterized by SEM, XRD, FTIR, BET, ICP-AES and pHzpc analysis. The sorption experiments were conducted in protein systems of bovine serum albumin (BSA) and lysozyme (LSZ). The batch experiment results showed that the NO3-HTlc with Mg/Ca/Al molar ratio of 2.5/0.5/1 had remarkable fluoride sorption ability with maximum sorption capacities of 82.35 mg/g and 72.69 mg/g at pH 5.0 and 40 degrees C in BSA and LSZ system, respectively. Moreover, the loss of BSA of 0.71% was low and there was no loss of LSZ. It was evident that the Mg2.5Ca0.5AlNO3-HTlc could selectively adsorb fluoride from protein solutions. The equilibrium sorption data fitted well to the Langmuir model and the kinetic data conformed to the pseudo-second-order model. Thermodynamic parameters (Delta G degrees, Delta H degrees and Delta S degrees) were evaluated and revealed that the sorption process was spontaneous and endothermic in nature. Furthermore, the results from Antarctic krill processing wastewater study confirmed the feasibility and practicality of the Mg2.5Ca0.5AlNO3-HTlc for fluoride removal in fluoride bearing protein system. (C) 2012 Elsevier B.V. All rights reserved.