SELECTIVE REMOVAL OF FLUORIDE IONS FROM WATER BY THE ALUMINUM FORM OFTHE AMINOMETHYLPHOSPHONIC ACID-TYPE ION-EXCHANGER

A series of porous matrices were synthesised based on copolymerisation of methyl methacrylate-ethylene glycol dimethacrylate using a suitabl e 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 conve rted into a chelating ion exchanger with aminomethylphosphonic acid gr oups. Each anion exchanger and the chelating ion exchanger derived fro m it were characterised for moisture content and ion-exchange capacity . The aluminium form of each aminomethylphosphonic acid-type ion excha nger was studied for fluoride uptake from tap water. For one selected product, the effect of F- content of water, its pH, the presence of hi gh concentrations of Cl- and SO42- and the duration of equilibration o n the fluoride uptake were exhaustively studied. Its fluoride uptake p erformance was studied under dynamic conditions by varying the F- cont ent of water, the flow-rate and the strength of the regenerant. The pr oduct developed showed good capacity and selectivity for fluoride remo val, and the uptake was found to be reversible and superior as compare d with that of the commercially available strongly acidic cation excha nger Indion 225 and aminomethylphosphonic acid-type chelating ion exch anger Duolite ES 4.67. The chelating ion exchanger developed removed f luoride from a fairly large volume of tap water and gave it out in the form of a concentrated solution of comparatively small volume. The wa ste regenerant could be reused thus bringing down the regenerant consu mption.