Abstract: Cross-linking of Li-montmorillonite by hydroxy-aluminum oligomers was performed in a specially constructed mixing apparatus. Observations on flocculation and solution composition were carried out during and after the cross-linking reaction; the dry product was studied by scanning electron microscopy.
Flocculation was most pronounced at Al/montmorillonite ratios between 0.98 and 2.45 mM/g; below and above this range, flocculation was much less intensive. These observations can be explained by heterocoagulation and protecting colloid action. A complete neutralization of the montmorillonite charge was estimated at 1.9 mM adsorbed Al per g clay, and in order to account for the electrical charge of the hydroxy-Al, polymers with an average charge of 0.5 per Al atom must be assumed on the montmorillonite surface. Assuming that the hydroxy-aluminum form in the unreacted solution is Al6(OH)3+12, the adsorbed polymer will be Al24(OH)12+60. Alternatively, assuming Al6(OH)3+15 in the unreacted solution, this form will remain unchanged upon adsorption onto the montmorillonite surface.
Differences in the microfabric of dry Al-CLM as a function of Al/montmorillonite ratio can be explained along the lines of the interpretation of the flocculation studies.