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Defluoridation of wastewater by natural bentonite clay in batch reactor...

Assaoui J, Kheribech A and Hatim Z

 Adsorption potential of natural bentonite clay (NBC) was investigated for wastewater defluoridation using batch adsorption experiments. Mineralogical and physicochemical characterization of the adsorbent was carried out by X-Ray Diffraction (XRD), XRay Fluorescence (XRF), Energy Dispersive X-Ray attached to Scanning Electron Microscopy (SEM-EDX), BET Specific Surface Area (SSAN2BET) analysis and Fourier-Transform Infrared Spectrometry (FTIR). The effect of various operational parameters such as contact time, initial fluoride concentration, adsorbent dose and initial pH solution were evaluated in batch procedures at room temperature (25 ± 2°C). The results of the batch adsorption experiments proved that 30 min of contact time was sufficient for attaining equilibrium. The maximum wastewater defluoridation (52.2%) was obtained in the acidic conditions (pH=2) and for 5 mg L -1 and 2 g L-1 of initial fluoride concentration and adsorbent dose, respectively. Kinetic studies revealed that fluoride adsorption fitted well to pseudo-second-order. The adsorption isotherm of fluoride sorption on NBC indicated that the maximum adsorption capacity was noted to be 4.4 mg g-1 . Batch adsorption data was better described by Freundlich confirming multilayer adsorption with heterogeneous energetic distribution of active sites and with interaction between adsorbed molecules. The originality of this paper consisted in introducing the mechanisms that might occur in the fluoride adsorption process. SEM-EDX and FTIR characterization techniques were found to be useful for achieving this purpose. The obtained results indicated that the ion exchange was probably the main process involved in the fluoride adsorption, accompanied by interactions of fluoride with metal ions forming Metal–F complexes