Characterization by nuclear magnetic resonance spectroscopy, ferron assay, and acidification of partially neutralized aluminium solutions

Abstract

Aluminium solutions (0.1 mol dm–3) were hydrolysed at 25 °C by a mild slow procedure involving the addition of NaOH to an aluminium salt. The amount of monomeric and polymeric species deduced from an 27Al n.m.r. analysis of the solutions are in good accordance with results obtained by a spectrophotometric technique using ferron (8-hydroxy-7-iodoquinoline-5-sulphonic acid). It is shown that a minimal number of aluminium species are present, the dominant polymer being of the ‘Al13’ form. A small amount of polymeric species remains unidentified although limited results obtained when solutions are heated above 70 °C seem to indicate that these species contain tetrahedral aluminium. It is also shown that the ‘Al13’ form can be converted into monomeric species by addition of strong acid to the solution. This transformation however follows a complex path.