Influence of shaking or stirring dynamic methods in the defluoridation behavior of activated tamarind fruit shell carbon

Fluoride is essential when it is present less than 0.5 mg L−1 in water but its excess presence causes dental and skeletal fluorosis. In the present work, Tamarindus indica Fruit Shells (TIFSs) were activated by ammonium carbonate and then carbonized leading to carbon abbreviated as ACA–TIFSC. This material with a BET surface area of 473 m2 g−1 was used for the defluoridation studies by shaking and stirring dynamic experiments. For the two dynamic studies, the fluoride removal efficiency of ACA–TIFSC as a function of pH, initial fluoride concentration, sorbent dose and co-ionic interference was investigated. The kinetic and isotherm models were used to interpret the nature of the fluoride sorption onto ACA–TIFSC. From the experimental results, it may be evaluated that the fluoride removal efficiency of ACA–TIFSC during stirring was greater than with the shaking dynamics. The results suggest that the active sites of the adsorbent are more easily reached by fluoride anions under stirring agitation. Characterization of ACA–TIFSC through SEM and XRD studies was done before and after the fluoride loading process. The prominent feature of ACA–TIFSC is the presence of CaCO3 compounds in the carbon matrix which is evident from the results of defluoridation studies. Groundwater samples with fluoride more than 1.5 mg L−1 were efficiently treated by ACA–TIFSC. The fluoride scavenging capacity of ACA–TIFSC was improved to a maximum of 8% and 11% in the bicarbonate-free groundwater during shaking and stirring sorption methods, respectively.

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► The carbonization of tamarind fruit shell improved its defluoridation efficiency.
► Calcium carbonate particles in the carbonized tamarind fruit shell were involved in the defluoridation process.
► The defluoridation efficiency of stirring dynamics was greater than shaking dynamics.
► Maximum fluoride removal was achieved at pH 7–8.
► Fluoride removal was greater in bicarbonate-free groundwater.