Evaluation of the Effect of Nepheline Sinter Structure on Hydration Activity During Alumina Production

Abstract

Under conditions for maintaining a stable demand for aluminum in the world, the problem of providing basic high-quality raw material for its preparation, i.e., alumina, remains unresolved. In this connection, work is important aimed at finding ways of improved efficiency for preparing alumina, in particular, by an alkaline sintering method. Experimental data are presented for the defective nature of the structure of different modifications of (α′-, β-) dicalcium silicate 2CaО·SiO₂ (С₂S), comprising the basis of nepheline sinters. A thermoluminescence method (TSL) is used for C₂S specimens prepared with different heat treatment regimes in the range from 1270 to 25°C, and different spectra are established that point to correlation of crystal lattice defect concentration and the degree of test C₂S specimen cooling. A correlation is established between the degree of decomposition of different forms of C₂S in aluminate-alkaline solution and structural defectiveness evaluated by TSL. It is shown that C₂S crystal lattice defectiveness decreases with a reduction in the cooling rate. It is established that β-C₂S formed with slow cooling exhibits less defectiveness compared with α′-C₂S. Introduction of measures based on results of these studies makes it possible to increase alumina yield and quality used in primary aluminum production.