Removal of fluoride ions using cuttlefish bones

Abstract

Because of the high toxicity of fluoride to mankind, there is an urgent need to treat fluoride-contaminated drinking water to make it safe for human consumption. This work investigated the possibility of eliminating, by sorption, the excess of fluoride in overloaded water according to World Health Organization WHO recommendations. We tested the cuttlefish bone as an adsorbent material (available in Tunisia) for the defluoridation of water. Initially, we determined the optimal conditions of use (contact time, pH effect, adsorbent dose, initial fluoride concentration) of the cuttlefish bone on synthetic solutions of sodium fluoride. The second step was to verify the effectiveness of the sorption process on the cuttlefish bone by testing it on natural waters loaded with fluoride. The results obtained showed that sorption on the cuttlefish bone could be an effective method for the removal of fluoride. The efficacy of cuttlefish bone to remove fluoride from water was found to be 80% at pH 7.2, 1 h contact time, 15 g L −1 adsorbent dose and 5 mg L −1 initial fluoride concentration. Despite the different anions (Cl − and SO 4 2−) generally present in natural waters, a fluoride concentration in agreement with the norm (<1.5 mg L −1) could be reached whatever the water treated. The regeneration of the cuttlefish bone was performed with a NaOH solution (10 g of cuttlefish bone/1000 mL NaOH 3 M). After 1 h of agitation, 95% of fluorides were desorbed. Following regeneration, the adsorbent can be used for further removal of fluoride.