Form and Stability of Aluminum Hydroxide Complexes in Dilute Solution

_ _ _____________________________________________________ Al Purpose and scope._______________________________________________ 2 Acknowledgments. ________________________________________________ 2 Previous studies.___________________________________________________ 2 Dissolved and suspended species___.______ _______________________ 3 Nature of precipitated solids, _-----__-__-________-_---___-______ 7 Structures of aqueous aluminum species_____________________________ 8 Hydrolysis experiments.--..--_____________-_____._____--_____--_-__ 11 Behavior of anionic aluminum species.___________________________ 15 Behavior of cationic aluminum species.___________________________ 20 Potentiometric measurements._-___-_-_-_-___-__-___________ 20 Measurement and significance of aluminum concentrations______ 23 Filtration experiments.____----_____--___-_____--__-_-______ 24 Characteristics of filterable material--_____-_____--_.__-______ 26 Structure of aluminum hydroxide polymers. __________________ 26 Mechanisms of polymerization.____-___________--__---______ 32 Verification of polymeric structure.__________________________ 33 Electron microscopy. ___--____--____--____-___._--__-__ 33 Reaction-rate studies___________________________________ 33 Interpretation of results of rate studies.____----____--____ 41 Direct determination of unpolymerized aluminum. ______ _.__ 43 Replacement of hydroxide by fluoride ions__-_____-___-_-_____ 45 Calculation of aluminum hydroxide solubility.________________ 46 Calculation of *Ki____---__--_____--____-____--_____---___48 Factors controlling pH_____________________________________ 50 Summary and conclusions. _________________________________________ 51 Application to natural conditions._______________________________ 52 Literature cited._______ _____________-________----_____._-----___53