Abstract:
Drinking water containing high amount of fluoride and nitrate can cause serious health hazards
to the people across the globe. Fluoride concentrations between 0.5-1.5 mg/l are beneficial, for
the prevention of dental caries or tooth decay, but concentrations above 1.5 mg/l can cause
fluorosis (dental or skeletal) and neurological disorders in severe cases. For, nitrate
concentrations above 45 mg/l can cause methemoglobinemia, also known as “blue baby
syndrome” especially to infants. Hence it is required to keep the concentrations of fluoride and
nitrate well in the limits prescribed by WHO. Techniques available for fluoride and nitrate
removal include adsorption, chemical treatment, electrochemical methods, dialysis and ion
exchange process. Among them, adsorption is found to be effective, environmental friendly
and economical. Under the above backdrop, the present study has been undertaken to prepare
efficient fluoride and nitrate adsorbent from raw laterite by acid followed by alkali treatment.
Batch experiments were performed to study the adsorption of fluoride and nitrate ions on
Treated Laterite (TL) adsorbent with fixed size. Characterization of TL was carried out using
various techniques such as BET Surface Area Analysis, FTIR, XRD, FE-SEM and EDAX.
Effects of process parameters like pH, Adsorbent dose, contact time and initial ion
concentration on the removal of fluoride and nitrate from synthetic water have been
investigated using TL as adsorbent to determine optimum process conditions for maximum
removal.
The fluoride concentration of 10 mg/l is removed upto 86% by TL effectively. Optimum
adsorbent dose is found to be 12.5 g/l. The optimum time is determined to be 150 min at
optimum pH of 6. Adsorption of fluoride ions on TL has been found to pseudo-second model
among pseudo-first order, pseudo-second order and Webber-Morris model. Among the
conventional isotherms, such as Langmuir, Freundlich and Temkin isotherms, the Temkin
isotherm gave better prediction of specific uptake for fluoride ions at equilibrium.
For nitrate adsorption on TL, optimum adsorbent dose has been found to be 20 g/l for initial
nitrate concentration of 100 mg/l at optimum pH of 5. TL could remove 80% nitrate ions
effectively and the equilibrium was set in 120 min. Langmuir isotherm fitted well to the data
than Freundlich and Temkin isotherm models and adsorption followed pseudo-second order
kinetics.
