The Ion Exchange and Sorption Properties of Microcrystals of Inorganic Oxides

Detailed studies have been made on the ion exchange and sorptive properties of aqueous dispersions of single crystals of beta-iron oxide hydroxide and monoclinic zirconia. These microcrystals were prepared in the laboratory and characterised by transmission electron micrographs and electron diffraction patterns. The crystals are typically 1000-2000A in size and have amphoteric ion exchange properties. In this work, a multiion selective electrode titration system working with a highly developed computational and graphic system was developed to determine the ion exchange and sorption properties of these crystals. Ion sieving characteristics of betaFeOOH have been proven and extended to include a separation of chloride from solutions containing iodide and bromide and, in alkali, exclusion of sodium ion. Fluoride uptake is determined by ion selective electrode response and alkaline earth uptake is determined by flame emission spectroscopy. Single ion exchange uptake of anions in acid and cations in base is explained by a Donnan model. This predicts anion (cation) capacity to be a single-valued function of the negative logarithm of the corresponding acid (base) activity in the equilibrium solution. Adsorptive properties of fluoride ion on monoclinic zirconia is explained by ligand exchange or incorporation of this adsorbate into the framework of the oxide. Exchange is shown to be reversible for most simple univalent ions and variations in exchange capacity controlled by solution pH and salt concentrations