Fluoride contamination of groundwater in parts of eastern India and a preliminary experimental study of fluoride adsorption by natural haematite iron ore and synthetic magnetite

Incidence of high fluoride (F-) in groundwater (> 1.5 mg/L) in two tribal belts of eastern India, one around Chukru in the Palamau district of Jharkhand and the other around Karlakot in the Nuapada district of Odisha, has been studied. The maximum concentration of F- in groundwater from dug wells and tube wells is 10.30 mg/L in Chukru and 4.62 mg/L in Karlakot. The groundwaters are mildly alkaline with pH ranges of 7.52-8.22 and 7.33-8.20 in Chukru and Karlakot, respectively. The F- concentration is positively correlated with pH, electrical conductivity and SO4 (2-) in both areas. The high F- in groundwater resulted mainly from dissolution of biotite and fluorapatite in quartzofeldspathic gneiss. The ionic dominance pattern (in meq/L) is mostly in the order Ca2+ > Na+ > Mg2+ > K+ among cations and HCO3 (-) > SO4 (2-) > < Cl- > F- among anions in the Karlakot groundwater. Preliminary adsorption experiments were conducted on natural haematite iron ore and synthetic magnetite to evaluate their potential for F- removal from water. Effects of different parameters such as contact time, pH, adsorbent dose and initial F- concentration on the adsorption capacity of these materials were investigated. Strong dependence of F- removal on pH was observed for both the adsorbents. With natural haematite iron ore, the maximum F- removal of 66 % occurred at an initial pH of 3.2 for a solution with F- concentration of 3 mg/L, adsorbent dose of 7 g/L and overnight contact time. The haematite iron ore was observed to increase the pH of the F- solution. Adsorption equilibrium was not achieved with this adsorbent even after a contact time of 45.2 h. In the case of synthetic magnetite, 84 % F- removal was achieved after 2 min of contact time for a solution with F- concentration of 6 mg/L, adsorbent dose of 10 g/L and initial pH of 7. The results indicate high potential of both natural haematite iron ore and synthetic magnetite as adsorbents of F- in water.