An optimization study for defluoridation from synthetic fluoride solution using scale of Indian major carp Catla (Catla catla): An Unconventional Biosorbent Ria Bhaumik, Naba Kumar Mondal*, Soumya Chattoraj Environmental Chemistry Laboratory, Department of Environmental Science, The University of Burdwan, West Bengal, India A R T I C L E I N F O Article history: Received 13 October 2016 Received in revised form 3 January 2017 Accepted 13 January 2017 Available online 19 January 2017 Keywords: Adsorption Fluoride Box-Behnken design Fish scale powder Response surface methodology A B S T R A C T Higher level of fluoride (F) in underground water has become a tremendous problem worldwide. The present study explores the feasibility of fish scale dust for removal of F from aqueous solution. The adsorbent was characterized by SEM, FTIR and pH ZPC . Various operating variables (pH, adsorbent dose, initial fluoride concentration, agitation speed, contact time and temperature) and their combined effect on removal of fluoride was assessed by using computerise software model known as Response Surface Methodology (RSM) based on Box-Behnken design (BBD). The optimized values of initial concentration, pH, adsorbent dose, and contact time for fluoride adsorption were found as 8.49 mg/L; 9.93; 2.26 g/ 100 mL and 179.72 min, respectively. Among the equilibrium isotherms, Langumir model was found to be the best fitted one suggesting homogeneous mode of F biosorption on fish scale. Kinetic studies showed better applicability of pseudo-second-order model. The results also suggest the thermodynamic feasibility of fluoride adsorption. Therefore, fish scale powder could be used as a potential adsorbent for F containing aqueous solution. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Literature highlighted that fluoride bearing rocks are abundant in India, therefore, it can leaches out and contaminates the underground water [1]. Fluorine is a strong electronegative as well as toxic element. Moreover, its toxicity can cause adverse health effect of both human beings and animals. World Health Organization (WHO) has already set limit between 0.5 and 1.0 mg/L [2]. The physiological effects of fluoride ingestion on public health have been studied extensively [3]. Higher fluoride concentration effects on the metabolism of human body and leads to dental and skeletal fluorosis. Fluoride naturally occurs in soil and rock as fluorapatite, fluorspar and amphiboles etc. [4]. Beside this, fluoride can also be found in various industrial work, chiefly semiconductor, electroplating, glass, steel, ceramic and fertilizers industries [5]. Then fluoride is contaminated with groundwater through leaching by earth crust and geochemical deposits and enters into natural water systems. Higher concentration of fluoride (>1.5 mg/L) [6] in drinking water causes serious health problems like skeletal and dental fluorosis, brain damage, osteoporosis, thyroid disorder and cancer etc. [7]. There are many technologies available for removal of pollutants from aqueous solution such as ultrafiltration, precipitation, reverse osmosis, electrode deposition etc., but all these technologies have some technical drawbacks including low adsorption capacity [8]. Among these methods, adsorption is the most widely used because it is universal, low cost and viable. Previous researchers used various low-cost adsorbents such as activated silica gel, rice husk [9], tea ash [10], activated carbon [11], calcite [12], calcareous soil [13], zeolite [14] activated charcoal [15], bleaching earth [16], red mud [17], brick powder [18], restructuring of lignite [19], etc. But most of the adsorbents works under very low pH which practically very difficult to neutralize. Now-a-days scientists are rushing towards the use of bio- materials as an adsorbent which binds the pollutants to the cell wall of biomass [20]. Previous literature highlighted that several nonliving biomass like aquatic plants, algae, fungi, bacteria, yeast etc. were extensively used for the removal of pollutant from aqueous medium [21–23]. In this work, scales of Catla catla (fish) are used as an effective adsorbent. Huge amounts of these scales are being generated from the fish market and are dumped as a waste. It is composed of a surface layer containing hydroxyl apatite [Ca 10 (PO 4 ) 6 (OH) 2 ] or [Ca 5 (PO 4 ) 3 OH] 6 and calcium carbonate and a deeper layer * Corresponding author. E-mail address: nkmenvbu@gmail.com (N.K. Mondal). http://dx.doi.org/10.1016/j.jfluchem.2017.01.015 0022-1139/© 2017 Elsevier B.V. All rights reserved. Journal of Fluorine Chemistry 195 (2017) 57–69 Contents lists available at ScienceDirect Journal of Fluorine Chemistry journal homepage: www.else vie r.com/locate /fluor