Selective removal of fluoride ions from water by the aluminium form of the aminomethylphosphonic acid-type ion exchanger

A series of porous matrices were synthesised based on copolymerisation of methyl methacrylate-ethylene glycol dimethacrylate using a suitable porosogenic agent. They were characterised for porosity and surface area. Each of them was converted into an anion exchanger by amination with diethylene triamine. Each anion exchanger thus obtained was converted into a chelating ion exchanger with aminomethylphosphonic acid groups. Each anion exchanger and the chelating ion exchanger derived from it were characterised for moisture content and ion-exchange capacity. The aluminium form of each aminomethylphosphonic acid-type ion exchanger was studied for fluoride uptake from tap water. For one selected product, the effect of F − content of water, its pH, the presence of high concentrations of Cl − and SO 2− 4 and the duration of equilibration on the fluoride uptake were exhaustively studied. Its fluoride uptake performance was studied under dynamic conditions by varying the F − content of water, the flow-rate and the strength of the regenerant. The product developed showed good capacity and selectivity for fluoride removal, and the uptake was found to be reversible and superior as compared with that of the commercially available strongly acidic cation exchanger Indion 225 and aminomethylphosphonic acid-type chelating ion exchanger Duolite ES 467. The chelating ion exchanger developed removed fluoride from a fairly large volume of tap water and gave it out in the form of a concentrated solution of comparatively small volume. The waste regenerant could be reused thus bringing down the regenerant consumption.