The nature of the complex that had been formed by precipitating aluminum hydroxide between interlayer spaces of montmorillonite in the presence of anions Cl and SO4 was examined by chemical, X-ray, thermal, and infrared absorption methods. Results indicated that the complex was a hydroxy aluminum sulfate–montmorillonite with the structural formula: Al0.02(H2O)3[Al(OH)2.53(SO4)0.18] + silicate layer of montmorillonite [O10(OH)2 basis]. The atomic ratio, Al:OH:SO4, of the interlayer material was 1:2.53:0.18, which was similar to the ratio 1:2.5:0.25 of "basaluminite." X-ray data showed that the complex had spacings of 19.7, 21.9, and 24.4 A, under an extremely dry condition, moist condition, and on solvation with glycerol, respectively. During the heat treatments between 100 and 200 C, the d001 spacing was sharply reduced to 16 A and the newly developed phase persisted over a wide range of temperature from 200 to 600 C. This phase was considered as an interstratified structure consisting of a 14.3-A unit (chloritelike structure) and a 17.7-A unit (dehydrated basaluminite + silicate layer of montmorillonite). Although the d001 spacing observed for the unheated material was larger than that expected for the amount of aluminum precipitated in the montmorillonite, it was interpreted in terms of voluminous Al13O40 polyhedra that were described previously as basic structural units of a basic aluminum sulfate.
Extraction of Ta and Nb from a Coltan Bearing Ore by Means of Ammonium Bifluoride Fluorination and Sulfuric Acid Leaching