Background: Fluorosis is a chronic environmental health problem caused by intake of excess fluoride, mainly in the drinking groundwater. Therefore, adsorptive removal of fluoride by locally available low-cost materials is very important for the provision of safe drinking water in the fluorosis endemic regions where there are no water treatment facilities.
Aim: The purpose of the study was to investigate fluoride sorption capacity of gypsiferous limestone (GLS) using natural groundwater samples containing different fluoride concentrations.
Methods: Sets of batch adsorption setup along with blank and control experiments were conducted at room temperature to examine the pattern of fluoride removal with varying contact time, solution pH, adsorbent dose and initial concentration using contaminated natural groundwater.
Results: Equilibrium was achieved within 24 h of agitation time. Kinetics data of fluoride adsorption followed well the non-linear pseudo-first order rate equation (R2 ~ 0.99). Fluoride adsorption was greatly dependent on the pH of the groundwater. High fluoride removal efficiency (~ 89%) was observed over acidic medium at pH 3 and 5. The Langmuir isotherm model well described the equilibrium fluoride adsorption, giving an adsorption capacity of 1.07 mg/g. The removal of fluoride enhanced when the adsorbent was calcined at 200 °C for 4 h. The fluoride loaded adsorbent was successfully regenerated using NaOH solution.
Conclusion: The results of the study have provided fundamental information for further investigation of GLS in the defluoridation of drinking water.
Key words: Adsorption isotherm, groundwater, gypsiferous limestone, thermal activation, sorption kinetics
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