Regeneration of fluoride-saturated bone char by means of wood ash and heat

Abstract

The regeneration of fluoride ion (F)-saturated bone char with different concentrations of wood ash in distilled water and by heating was investigated. Samples of 100 g of regenerated bone char were added into plastic containers containing 250 mL of natural water with 6.5 mg F/L collected from a borehole. The water was sampled at 30 min intervals for F analysis using an ion selective fluoride meter. The results indicated that the highest F removal efficiencies with the 2, 4, 6, and 8% wood ash concentrations were approximately 83, 84, 86, and 87%, respectively. The F removal efficiencies of the bone char when it was regenerated by heating for 3, 4, and 5 hr were 86, 89, and 89%, respectively. It is suggested that regenerating bone char with wood ash may be a better choice than regeneration with heating because the wood ash is locally available, easy to use in a household, and it does not demand an energy input. In contrast, regeneration by heating might encourage the cutting down of trees. We found that 2% wood ash, with a fluoride removal efficiency of 83%, is the best means for regenerating bone char because it can deliver an effluent with acceptable pH values for human consumption.