ION EXCHANGE PROPERTIES OF BiO(NO3) 0.5H2O TOWARDS FLUORIDE IONS

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Abstract
We studied the ion exchange behavior of the inorganic anion exchanger BiO(NO3)0.5H2O with regard to fluoride ions. The ion exchange reaction was rapid at pH 1, 6.6, and 12. The mechanisms of ion exchange reactions at pH 1 and pH 2-12 were studied in a solution with fluoride ions excess to BiO(NO3)0.5H2O. A mixture of the β-phase and an unknown phase was produced in the solution at pH 1. BiOF was produced at pH 2-12. Fluoride ions did not react at pH 13, due to the decomposition of BiO(NO3) 0.5H2O at pH 13 to yield Bi2O3 (major) and Bi2O2CO3 (minor). The structure of the reaction products depended on the solution pH, mole ratios of BiO(NO3)0.5H2O to F’, and the reaction time. We observed that BiO(NO3)0.5H2O is capable of removing 99% of the fluoride ions from the solution at pH 1-12 under optimal conditions. The ion exchange reaction of BiO(NO3)0.5H2O with fluoride ions was studied under the co-existence of both Cl and Br−at pH 1, 6.6, 12, and 13. The order of decreasing affinity was found to be (Br−, Cl−)> F−. The reaction product was not a simple mixture of BiOCl, BiOBr, and bismuth oxide fluorides, but an unknown compound.