The Sorption Behavior Of Ca/Mg/Al Hydrotalcite-like Compounds Towards Removal Of Fluoride From Protein Solution

The present study explores the potential of Mg-Ca-Al (NO3) hydrotalcite-like compounds 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 by co-precipitation and the structure characteristics of the adsorbents were analyzed by means of SEM, XRD, FTIR, pHzpc, TG-DTA, BET and ICP-AES analysis. The sorption experiments conducted in protein systems of bovine serum albumin (BSA) and lysozyme (LSZ) were mainly studied from aspects of fluoride adsorption properties, mechanism discussions and the losses of protein. The adsorption properties were studied as a function of pH, sorbent dose, contact time, initial fluoride concentration, initial protein concentration, temperature and coexisting ions. The isotherm models and kinetics models were used to fit the experimental data. The removal mechanism was discussed by pHzpc analysis and the comparation between the FTIR patterns of adsorbents and fluoride adsorption capacities at different contact times during adsorption process. Additionally, the performance of Mg3-xCaxAlNO3-HTlcs for fluoride removal from fluoride bearing Antarctic krill processing wastewater with high concentration of proteins was also investigated. The batch experiment results showed that the Mg3-xCaxAlNO3-HTlcs with Mg/Ca/Al molar ratio of2.5/0.5/1had remarkable fluoride sorption ability with maximum sorption capacities of98.7mg/g and83.3mg/g at pH5.0and40℃in BSA and LSZ system, respectively. Moreover, the loss of BSA of0.71%was low and there was no loss of LSZ. It was evident that the Mg2.5Cao5AlNO3-HTlc could selectively adsorb fluoride from protein solutions. The equilibrium sorption data fitted well to the Langmuir-Freundlich and the kinetic data conformed to the pseudo-second-order model. Thermodynamic parameters (AG(?), AH(?) and AS(?)) were evaluated and revealed that the sorption process was spontaneous and endothermic in nature. The analysis of infrared spectra and kinetics models indicated that the fluoride adsorption process of Mg2.5Ca0.5AlNO3-HTlc was mainly the adsorption on external surface of the layers and anion exchange. Furthermore, the results from Antarctic krill processing wastewater study confirmed the feasibility and practicality of the Mg2.5Ca0.5AINO3-HTIc for fluoride removal in fluoride bearing protein system.