Impact of laterite characteristics on fluoride removal from water

BACKGROUNDThe presence of high concentrations of fluoride in groundwater is a threat to the provision of potable water especially to rural communities. Various substances have been suggested for the removal of fluoride from water. This work investigates the characteristics of laterite, which makes it an adsorbent applicable to fluoride removal. RESULTSChemical and mineralogical analyses of the laterite using X-ray fluorescence (XRF) and X-ray diffraction (XRD) techniques showed varying amounts of iron oxide/hydroxide (goethite/hematite), silica (quartz) and kaolinite. Scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) analysis revealed intimate association of all minerals. Isoelectronic point (IEP) value was largely influenced by the mineralogical composition with higher values for higher iron oxide/hydroxide content. CONCLUSIONWhile variation in the initial pH of fluoride solution had an effect on fluoride adsorption, the impact of IEP (and hence indirectly pH(pzc)) was not significant in adsorption. Samples heat treated at 400 degrees C performed better in fluoride adsorption. The mechanism for fluoride adsorption in this study was attributed to two processes: (i) ion exchange between hydroxide ion of the laterite surface and fluoride ion in solution; and (ii) fluoride uptake by specific surface reactions involving H3O+F- which leads to the release of hydroxonium (H3O+) ions in solution. (c) 2015 Society of Chemical Industry