Reaction of Montmorillonite with Iron(III)

The reaction between montmorillonite and Fe(III) was studied at two different degrees of neutralization of the FeCl 3 solutions. The adsorption of iron was found to reach a definite saturation value which depended on the initial degree of neutralization of the FeCl 3 . The maximum amount of Fe(III) adsorbed from FeCl 3 solution, having molar OH/Fe ratio = 2, corresponded to the calculated amount of Fe(III) required to form a complete monolayer of octahedrally coordinated Fe(III) on both planar surfaces of the moutmorillonite. The Fe(III)‐montmorillonite complex had a net positive charge at pH 5, which decreased with increase in pH; its cation exchange capacity, however, remained constant at about 45 meq/100 g within the pH range from5 to 7.