Abstract-Titanium in TiO2 minerals was differentiated from that isomorphously substituted into minerals by the use of dihydrogen hexafluorotitanate (hydrofluotitanic acid, H2TiF6), which selectively dissolved minerals containing substituted Ti 4+, leaving free crystalline TiO2 minerals in the residue. Titanium analyses on the original samples and the residues remaining after H2TiF6 treatment, by both wet chemical (Tiron) and neutron activation methods, indicated that an average of 86 per cent of the titanium in seven kaolinite samples was present in the residual TiOz form (largely anatase), whereas only 28 per cent in two bentonites was present in the TiO2 form. Residual Ti accounted for 100 per cent of the Ti in synthetic anatase and for 92 per cent of the Ti in coarse clay sized futile, the latter value suggesting that about 8 per cent amorphous TiO2 was removed from the mechanically dry ground rutile by the H2TiF6 reagent. The Ti present as residual TiO2 in a variety of other samples ranged from 0 to 100 per cent.
Cation exchange selectivity (CES) values for montmorillonite, vermiculite, biotite, muscovite, and micaceous vermiculitic clays from Triangle and Harpster soils were determined by equilibration of each exchanger with a mixed, equinormal solution containing two competing cations. The cation affinity of Na‐saturated materials increased in the order K < Mg < Ca < Sr < Ba for montmorillonite and the soil clays, Mg < K < Ca < Sr < Ba for biotite, Mg < Ca < Sr < K < Ba for muscovite, and K < Ba < Sr < Ca < Mg for vermiculite. Sodium‐saturated micaceous vermiculite gave a K/Ca CES value of 0.2, whereas K‐saturated, dried vermiculite gave a K/Ca CES value of 0.4, indicating that the large number of interlayer wedge sites produced by the structural collapse in K‐saturated and dried vermiculite increased the selectivity for K ions. Potassium‐saturated and dried muscovite having a CEC equal to the similarly treated vermiculite gave a K/Ca CES value of 4.0 compared to 0.4 for the vermiculite, suggesting that layer charge density has a large influence upon K selectivity. The higher CES values for muscovite relative to those for biotite are explained by the smaller ditrigonal holes and the oblique orientation of hydroxyl groups in the muscovite structure.
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