Structure and affinity towards Cd2+, Cu2+, Pb2+ of synthetic colloidal amorphous aluminosilicates and their precursors

Amorphous aluminosilicates were synthesised at two different initial reagen t concentrations. Depending on the concentration used, the final reaction p roducts were identified as either imogolite or allophane. In millimolar med ium (millimolar Al initial concentration and Al/Si = 2), imogolite precurso rs are synthesised during hydrolysis and condensed by heating to build up i mogolite tubes. In decimolar medium, precursors with varying local structur es are synthesised and condense upon heating to build up allophanes spheroi ds aggregates. In each medium, silica gel coprecipitated in proportions les s than 10% in mass, which seems to have only a weak influence on aluminosil icate synthesis. The zero point of salt effect of suspensions of imogolite, allophane and their respective precursors were determined, and the affinit y of these four products towards Cd2+, Cu2+ and Pb2+ was studied. For imogo lite and for both precursors, Cu2+ and Pb2+ adsorption can be described as specific, whereas Cd2+ adsorption is only electrostatic. The three metallic cations display specific adsorption towards allophane suspensions. (C) 199 9 Elsevier Science B.V. All rights reserved.