Significance of calcium containing materials for defluoridation of water: a review

Removal of fluoride from groundwater for drinking purpose and from wastewater is a serious global problem. Though several defluoridation methods are available, each of them has certain merits and demerits. Precipitation and adsorption of fluoride are among the low-cost methods that have been used for years. Calcium materials have certain edges over other types of materials applied for precipitation and adsorption of fluoride. Hydroxyapatite (HAP), quick lime, slack lime, calcium chloride, limestone or calcium carbonate, calcium phosphate, calcium nitrate, calcium sulfate, etc. are among the calcium materials used for fluoride removal. In this paper, the significance of use of different calcium containing materials, their fluoride removal mechanism, and the prospects of application for the purpose have been critically reviewed. Considering easy availability, low cost, and high efficiency, HAP and limestone based processes may be potential clean choices for fluoride removal if the capacity and sludge disposal are adequately addressed.