Preliminary investigations on the defluoridation of water using fired clay chips

Abstract

The adsorption of fluoride ions on ground fired clay pot has been investigated. The maximum efficiency of the adsorbent for defluoridating 1–2 litres of water was found to be 200 mg fluoride kg −1 adsorbent. The investigation showed that 5–20 mg l −1 fluoride, from 1 litre of water, could be reduced to less than 1.5 mg l −1 using 120–240 g of the adsorbing medium. The effects of the dose of the medium, the pH, the contact time and the initial fluoride content were studied in relation to defluoridation efficiency. Comparison of fluoride removal capacity of the adsorbent was also made with those of fired brick, clay soil and red ash. The latter exhibited practically no adsorption. A packed column of the same ground clay pot was saturated with 285 mg fluoride kg −1 of adsorbent when 20 litres of water containing 10 mg l −1 F was allowed to pass through it. This column defluoridated 6 litres of tap water containing 10 ppm F − to below 1.5 mg l −1.