Calcined and uncalcined carbonate layered double hydroxides for possible water defluoridation in rural communities of the East African Rift Valley

Dore E.;Frau F.

2019-01-01

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Abstract

Health risks linked to the regular consumption of water with high fluoride (F − ) content seriously affect rural areas of the East African Rift Valley. The F − removal capacity has been tested on uncalcined and calcined carbonate layered double hydroxides (LDHs), with different cationic compositions (M 2+ = Mg 2+ , Zn 2+ ; M 3+ = Al 3+ , Fe 3+ ) and M 2+ /M 3+ molar ratio (2, 3, 4), taking into account the necessity of a simple defluoridation method. The 3MgAlFe-cal phase derived from calcination of a hydrotalcite-like compound with composition Mg/(Al + Fe) = 3/(0.5 + 0.5) results to be the best F − remover (43 mg/g) and can uptake up to 92.3 mg/g when the interlayer is fully saturated with F − . At the high pH reached during the experiments (up to pH 12 for calcined LDHs), the presence of carbonate species in solution significantly affects the F − removal capacity. The recyclability of the sorbent was tested by regeneration through calcination of the 3MgAlFe-cal phase: under F − unsaturated interlayer conditions, up to 80% of the starting F − removal capacity is still preserved after four regeneration cycles, indicating that LDHs can be reused after regeneration and have a potential use in water defluoridation.