Anatase and Rutile Determination in Kaolinite Deposits

Mahmut Sayin and M. L. Jackson*
Department of Soil Science, University of Wisconsin, Madison, WI 53706, U.S.A.
* Research Assistant and Franklin Hiram King Professor of Soil Science, respectively.

Abstract: Hexafluorotitanic acid (H2TiF6) selectively dissolves kaolinite and most other phyllosilicate minerals of soils and sediments, concentrating free crystalline (Ti,Fe)O2 minerals (partially substituted anatase and rutile) in the residue. A series of H2TiF6 reagents was standardized by analysis of the Ti content and by tests with pure anatase and commercial kaolinites. The Ti in the H2TiF6 solution selected (made from 49% HF + reagent TiO2) was 16·5% by weight as analyzed by the Tiron method. Treatment of pure anatase with the reagent H2TiF6 resulted in a 98% by weight recovery of TiO2 in the residue. The fraction of TiO2 recovered in the residue of commercial Georgia kaolinites was 88–101% after treatment with the selected H2TiF6 reagent. Isolates from nine Georgia kaolinite samples with varying amounts of TiO2 and Fe2O3 were examined by X-ray powder diffraction, scanning electron microscopy and elemental analysis. The main constituent of the (Ti,Fe)O2 isolates was anatase for all samples, with minor amounts of coarser rutile and mica from coarser kaolinite. The anatase and rutile isolates contained 74–93% (Ti,Fe)O2 with 0·5–3·1% Fe. The other constituents of the isolates were muscovite of mica (0·3–7%), quartz (0–9%) and amorphous relics of vermiculite and/or kaolinite (6–19%). Rutile, muscovite and quartz appear to be detrital but the anatase and relics are probably authigenic. Fine anatase appears to stick on the muscovite flakes as revealed by scanning electron microscopy and heavy liquid data for separation of these two minerals. The (Ti,Fe)O2 isolates from kaolinites which passed with the first magnetic concentrate of anatase were coarse, on the order of a few microns dia., as revealed by the scanning electron microscopy. Those passed with subsequent extensive magnetic concentrates from the same samples were finer. The anatase isolated from kaolinite purified by removal of as much of the impurities as possible by magnetic means was extremely fine, most of the particles being on the order of 0·1 µm dia. More than one third of the total Fe2O3 in kaolinites magnetically separated in the first pass was extracted by the citrate-bicarbonate-dithionite treatment after hot NaOH dissolution of 52–74% of the kaolinite, showing that the Fe2O3 had been mainly associated within the kaolinite. Only 2–6% of the total Fe2O3 was extracted from magnetically purified kaolinite after 40–50% of this kaolinite had been dissolved, indicating that most of the Fe is in the anatase and rutile fraction.

Clays and Clay Minerals; December 1975 v. 23; no. 6; p. 437-443; DOI: 10.1346/CCMN.1975.0230605
© 1975, The Clay Minerals Society
Clay Minerals Society (www.clays.org)