Hydrolysis of aluminum in synthetic cation exchange resins and dioctahedral vermiculite

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Virginia Polytechnic Institute


The hydrolysis of aluminum in synthetic cation exchange resins differing in charge density was evaluated after treating aluminum and potassium saturated resins with solutions of hydrolyzed aluminum. Fixed aluminum and decrease in exchange capacity were used to calculate the OH/Al ratio of the fixed aluminum. Oowex 50 XI, the resin with lowest charge density, was found to have fixed aluminum with the highest OH/Al ratio. The highest charge density resin tested, Dowex 50 X8, was found to have a limited decrease in exchange capacity. Aluminum was exchanged from potassium saturated resins of low charge density in excess of available negative charge, yielding the conclusion that hydrolyzed forms of aluminum were exchangeable.

Purified dioctahedral vermiculite from a Nason soil was expanded using successive treatments of N BaCl₂, reducing the potassium level In the sample to 0.05 percent. Tota] analysis yielded the average formula (Al1.4Mg.3Fe.3)(Si3.7Al.3O₁₀ (0H)₂-.70 -X+. 70 8H₂0. This structural formula suggested that the lowering of the charge from the theoretical one per half cell to 0.7 was accomplished by oxidation of the iron. This was concluded to be the mechanism initiating the weathering of this type of micaceous material to dloctahedraJ vermiculite.

Structural analyses of both magnesium (13.98 A) and aluminum (14.91 A) saturated dioctahedral vermiculite were carried out using structure factor calculations, one dimensional fourler synthesis, and difference synthesis. Structure factor calculation for the dioctahedral vermiculite studied indicate that the ratio of the intensities of diffraction maxima corresponding to 7 A and 14 A interplanar spacings (7A/14A ratio) should decrease as scattering matter Is added to the interlayer region through hydrolysis of alumininum. Fourier synthesis and difference synthesis indicate that scattering matter was centrally located In the Interlayer in excess of what could be accounted for by exchangeable cations present. It was concluded that a portion of the water was centrally located. A close approach between the remainder of the water and the basal oxygens was the assumption required to explain the observed intensities. The aluminum saturated dloctahedral vermiculite (14.91 A) was observed to collapse in a random interstratified fashion upon hydrolysis treatments with solutions of hydrolyzed aluminum. Upon potassium saturation, the collapse progressed, yielding a 14 A material. Orientation of interlayer water associated with triple charged aluminum ion (Al⁺) was theorized to be the cause of the stable high spacing and the hydrolysis and/or removal of the triple charge ion thought to result in the diminishing spacing.

Both the experiments with synthetic cation exchange resins and the structural analysis of soil-derived vermiculite Indicate that the amount of aluminum that can be added through hydrolysis to the higher charged resins and to dioctahedral vermiculite was limited. It was theorized that hydrolyzed aluminum units could grow in association with a negatively charged surface until the diminishing charge density of the growing hydrolyzed aluminum unit approached that of the associated surface.