Removal of Fluoride from water using Surfactant Modified Synthetic Zeolites
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Date
MAY, 2016
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Abstract
Although fluoride is beneficial in preventing dental caries, long term consumption of drinking water contaminated with high levels of fluoride (above 1.5 mg/L) could cause teeth mottling. Extreme concentrations may result in severe health conditions such as skeletal fluorosis and even crippling fluorosis. The removal of fluoride from water using synthetic zeolites modified with a cationic surfactant was studied using a batch system. The zeolites employed as adsorbents in the study, zeolite Na-LSX and zeolite Na-LTA, were synthesized from locally available clay materials. A third synthetic zeolite nicknamed zeolite ZR (containing both Na-LSX and Na-LTA phases) was synthesized using only reagent-grade chemicals. Hexadecyltrimethylammonium (HDTMA) bromide surfactant was used to modify the zeolites in order to improve their fluoride removal potential. The X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Fourier Infrared Spectroscopy (FTIR) techniques used to characterize the zeolites confirmed the surface modification by the HDTMA surfactant molecules. Moreover, the characterization confirmed that the structural integrity of the zeolites remained intact after the surface modification. Varying process conditions including surfactant dosage, modification reaction time and pH of the batch processes were investigated to determine the optimal conditions for fluoride uptake. From the batch experiments, fluoride adsorption was found to be highly pH dependent. Zeolite Na-LSX was found to be the best performing adsorbent at a pH of 5.5. Increase in solution pH from 5.5 to 7.5 significantly reduced fluoride removal efficiency (86 % to 15 %). No appreciable removal was observed above pH of 7.5. The best performing HDTMA surfactant dosage was found to be 5 g surfactant/L for all the zeolite types. Fluoride removal performance of modified zeolites increased with increasing modification reaction time from 2 hours until 24 hours, beyond which performance relatively declined.
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A thesis submitted to the Department of Civil Engineering, College of Engineering, in partial fulfillment of the requirements for the degree of Master of Science Water Supply and Environmental Sanitation.