Seawater-Washed Activated Bauxite Residue for Fluoride Removal: Waste Utilization Technique Vaibhav R. Chate 1 ; Raviraj M. Kulkarni, Ph.D. 2 ; Vinayak G. Mutalik Desai, Ph.D. 3 ; and Purandara Bekal Kunkangar, Ph.D. 4 Abstract: Adsorption of fluoride on seawater-washed activated bauxite residue (SWABR) was studied by using fluoride ion analyzer (ion-selective electrode meter). Bauxite residue from the Bayer process is a waste of aluminium refinery, which is highly alkaline and generated in large quantities, which make its disposal a growing problem. The characterization of SWABR was done by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy with X-ray microanalysis (SEM/EDS), transmission electron microscope (TEM), and selected-area electron diffraction (SAED) techniques. The adsorption studies indicate the highest fluoride removal efficiency of 95.83% for a SWABR dosage of 50 g=L at pH 5. The effect of pH, SWABR dosage, contact time, and initial fluoride concentration on the fluoride removal efficiency was studied and discussed. Adsorption isotherm experiments showed that fluoride adsorption on SWABR fits Freundlich adsorption isotherm (R 2 ¼ 0.998) better than Langmuir adsorption isotherm (R 2 ¼ 0.983). The field application of SWABR as an adsorbent for defluoridation of groundwater from Gadag District of Karnataka State, India, was also investigated. DOI: 10.1061/(ASCE)EE.1943-7870.0001367. © 2018 American Society of Civil Engineers. Author keywords: Seawater; Activated bauxite residue; Adsorption; Fluoride; Isotherm. Introduction The presence of fluoride ions in water systems is a major concern for environmental scientists (Tripathy et al. 2006). More than 27 developed and developing countries have reported excessive fluoride concentrations in water bodies. A little quantity of fluo- ride in potable water is useful for human beings, but a concen- tration in excess of 1.5 mg=L can have adverse impacts on human health (Singh et al. 2013, 2016; Brindha et al. 2011), such as dental fluorosis or, in case of consuming more than 4–15 mg=L, serious irreversible bone abnormalities. Fluoride ions have been detected both in fresh water (0.01–3.00 mg=L) and groundwater (1.00–35.00 mg=L). Because there is a growing concern of health hazards of fluoride ions to human beings, it is essential to remove fluoride ions during treatment (Deng and Yu 2015; Gago et al. 2014; Du et al. 2017; WHO 2011). Different methods, such as electrodi- alysis, adsorption (Loganathan et al. 2013), reverse osmosis, ultra- filtration, Donnan dialysis, and ion exchange, have been used for defluoridation (Amor et al. 2001; Ndiaye et al. 2005; Guo et al. 2001; Dou et al. 2011; Tor 2007; Sharififard and Soleimani 2015; Fan et al. 2003; Mohapatra et al. 2009; Agarwal et al. 2003). Bauxite residue (BR), a waste generated in alumina plant during the Bayer process is an environmental concern during disposal because of its high alkaline content (Hua et al. 2017; Lopes et al. 2013; Huang et al. 2016; Chauhan and Silori 2010). Bauxite res- idue has been used for the removal of lead, cadmium, nitrate, heavy metals (Lockwood et al. 2014; Cengeloglu et al. 2006), phosphate, and boron (Sutar et al. 2014; Yue et al. 2010; Cengeloglu et al. 2007; Zhao et al. 2009) and in wastewater treatment (Poulin et al. 2008; Zhang et al. 2014; Chen et al. 2016). One of the assets required for keeping the bauxite residue in wet condition is water. The sprinkled water percolates down the heaped bauxite residue and is collected in the lagoon. The pH of the leachate collected is observed to be greater than 10.5, which is well above the permissible limits specified by the Central Pollution Control Board. The coastal tracts of the southwestern parts of India are rich in bauxite deposits; however, water availability is scarce. Thus, an innovative methodology is adopted by washing the bauxite residue with seawater, which is plenty and easily accessible. It appears that little attention has been paid toward the application potential of seawater-washed activated bauxite residue (SWABR) for defluoridation. Hence, the present study was undertaken to recycle the bauxite residue. Adsorption studies were carried out by using fluoride ion-selective electrode. The adsorption behavior of SWABR for fluoride removal was studied by using Freundlich and Langmuir isotherms. Furthermore, the field application of SWABR as an adsorbent was also undertaken for defluoridation of groundwater from Gadag District of Karnataka State, India. Materials and Methods Materials The bauxite residue produced during the Bayer process from Hindalco Industry, Belagavi, Karnataka, India, was used in the 1 Research Scholar, Dept. of Civil Engineering, KLS Gogte Institute of Technology (Autonomous), Visvesvaraya Technological Univ., Udyambag, Belagavi 590008, India. E-mail: chatevaibhav@gmail.com 2 Professor, Dept. of Chemistry, KLS Gogte Institute of Technology (Autonomous), Visvesvaraya Technological Univ., Udyambag, Belagavi 590008, India (corresponding author). ORCID: https://orcid.org/0000- 0001-6894-6888. E-mail: ravirajmk@git.edu 3 Professor, Dept. of Civil Engineering, KLS Gogte Institute of Technology (Autonomous), Visvesvaraya Technological Univ., Udyambag, Belagavi 590008, India. E-mail: vgmdesai@git.edu 4 Scientist-F, Ministry of Water Resources, Government of India, National Institute of Hydrology, Belagavi 591109, India. E-mail: purandarabk@yahoo.com Note. This manuscript was submitted on June 10, 2017; approved on November 1, 2017; published online on March 15, 2018. Discussion period open until August 15, 2018; separate discussions must be submitted for individual papers. This paper is part of the Journal of Environmental Engineering, © ASCE, ISSN 0733-9372. © ASCE 04018031-1 J. Environ. Eng. J. Environ. Eng., 2018, 144(5): 04018031 Downloaded from ascelibrary.org by Gogte Institute Of Technology, Belgaum on 03/15/18. Copyright ASCE. For personal use only; all rights reserved.