Preparation of porous alumina adsorbent from kaolin using acid leach method: studies on removal of fluoride toxic ions f

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Preparation of porous alumina adsorbent from kaolin using acid leach method: studies on removal of fluoride toxic ions from an aqueous system Amit Kumar Yadav1   · Sunipa Bhattacharyya1 Received: 31 July 2019 / Revised: 10 October 2019 / Accepted: 10 December 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019

Abstract In the present study, feasibility of the porous alpha alumina beads for the removal of fluoride has been investigated. The porous alumina beads were fabricated by choosing the low-cost method i.e., oil drop method through extraction of alumina from kaolin. Extraction of alumina from kaolinite is a well-defined process from long decade. After preparation, alumina beads were characterized using powder X-ray diffractometer (XRD) which shows major phase as alpha alumina (α-Al2O3) with minor phase of theta alumina (θ-Al2O3) at 1050 °C. Further these beads were examined through scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) using N ­ 2 adsorption–desorption isotherm. The specific surface area of 54.54 m2/g was estimated through BET experiment. Alumina beads were then used to eliminate the fluoride toxic ions from the aqueous system using adsorption process. Further, the adsorbent dose and kinetics parameters were thoroughly studied to achieve the maximum removal in the aqueous system. The microstructural analysis was carried out before and after the adsorption process using SEM with EDX to compare the surface morphology of the alumina beads. Batch adsorption study show the mechanism and adsorption capacity of the porous alpha alumina beads which suggests the Freundlich adsorption i.e., heterogeneous behavior of fluoride ions towards alumina surface. Through batch adsorption study it was clearly observed that adsorption belongs to pseudo second order kinetic with inter particle diffusion. At initial fluoride concentration of 10 mg/L (adsorbent dose = 3 g/L; pH 6.7 ± 0.3; time = 48 h) the defluoridation efficiency was 26% with Freundlich adsorption capacity ­kf = 0.91795 (mg/g) (L/mg)1/n. Keywords  α-Alumina · Kaolinite · Adsorption · Fluoride ions · Acid-leach method

1 Introduction Fluoride is desired for the growth of bones in human. However, excessive fluoride intake (> 1.5 mg/L) creates chronic diseases like fluorosis. The consumption of this excessive fluoride is through groundwater which is the primary source of drinking water in India (Barbier et al. 2010; Singh et al. 2018; Zuo et al. 2018). Many methods, namely coagulation-precipitation, ion exchange, adsorption and membrane process, are used to control fluoride ion concentration in drinking water (Hu and Dickson 2006; Meenakshi and Viswanathan 2007; Reardon and Wang 2000; Ben Sik Ali * Amit Kumar Yadav [email protected] 1



Department of Ceramic Engineering, National Institute of Technology, Rourkela, Odisha 769008, India

et al. 2013; Singh et al. 1999). Among these methods, the adsorption process is the easiest and inexpensive one(Yadav et al. 2018). In the adsorption process, ceramic materials e