The Effect of iron on montmorillonite stability, 2; Experimental investigation

Wilson, J.*; Cressey, G.*; Cressey, B.*; Cuadros, J.*; Ragnarsdottir, K. V.*; Savage, D.*; Shibata, Masahiro 

This work investigates montmorillonite stability in the presence of metal iron, magnetite under hydrothermal conditions. Two series of experiments were conducted. In the first, mixtures of Na-montmorillonite, native Fe, (magnetite, calcite,) and NaCl solutions were reacted at 250C for about 100 days. In the second, mixtures of Na-montmorillonite, native Fe and FeCl solutions were reacted at 80250C for about 90 days. In the first series, the starting montmorillonite was transformed to Fe(II)-rich smectite only when the Fe metal was predominantly added. The reaction product was oxidised to Fe(III)-rich form on exposure to air. The expansion of this material on ethylene glycol solvation was much reduced compared to the starting montmorillonite. TEM imaging shows that partial loss of tetrahedral sheets, resulting in adjacent layers becoming H-bonded with a 7 angstrom repeat. Solute activities corresponded to the approximate stability field for Fe(II)-saponite. In the second series, significant smectite alteration was only observed at 250C and the product contained a small proportion of a 7 repeat structure, observable by XRD. In these experiments, solute activities coincide with berthierine.