THE PHYSICOCHEMICAL INVESTIGATION OF THE ZHURAVLINY LOG KAOLIN. PART 2

Abstract

MAS NMR spectra of concentrated kaolin of the Zhuravliny Log deposit (Chelyabinsky district, Russia) and its heated products were studied. In a raw concentrated kaolin, a sharp absorption of 29Si NMR was observed at –91.2 ppm, which corresponded to the characteristic signal of layered structure in silicates with no Al tetrahedra (Q3(0Al)). In the heated at 800 °C samples, the center of the Si resonance shifted to –102.9 ppm. The peak became broader and partially asymmetric that might ascribe the disordered layered structure of metakaolin (Q3 state). At 900 °C the spectral line center was at –106.8 ppm (Q4 Si) related to the presence of amorphous SiO2 or cristobalite. The 27Al NMR spectrum of a raw kaolinite consisted of only a single sharp resonance centered at 1.3 ppm which was assigned to AlVI. Heat treatment at a temperature above 500 °C led to the partial destruction of the layered structure. Two new lines appeared at 58.1–60.2 and 29.0–32.9 ppm which were attributed to both Al atoms in tetrahedral and penta-coordinated positions, respectively. The signal intensity of AlIV peak increased rapidly. The raw kaolinite had particles with angular edges of pseudo-hexagonal form which suggested a well-ordered mineral. The burning temperature increasing (800–1200 °C), flakes got the more rounded boundaries. At 1000–1200 °C flakes were agglomerated. According to the dilatometry curve for kaolin, in 500–650 °C and 630–880 °C intervals there was a small shrinkage which was related to dehydroxylation of kaolinite and structural reorganization of metakaolinite, respectively, with the subsequent transformation into the Si-Al spinel phase above 900 °C.