Structural and spectroscopic characterization of anorthite synthesized from secondary raw materials

Recycling of secondary raw materials is a priority of waste handling in the countries of the European community. A virtual secondary raw material of great importance is the product of the thermal transformation of cement – asbestos. This work illustrates the study of calcination products obtained starting from the product of the thermal transformation of cement-asbestos at 1200 °C, added to primary raw materials (kaolin, aluminum hydroxide) and boric acid as mineralizing agent. The calcination has been conducted at 1200 °C for 1 hour. The crystallization kinetics has been monitored using in situ high temperature X-ray powder diffraction. The microscopic characterization of the final product of calcination has been conducted with SEM and TEM imaging supported by X-ray microanalysis. The structure refinement was conducted on the powder sample using the Rietveld method. The results are compared with the spectroscopic characterization including Mössbauer and UV-Vis spectroscopies. The final product of the calcination is essentially anorthite (about 89 wt%) with minor spinel (11 wt%). All experimental data converge to support the hypothesis that the anorthite is stoichiometric, and the small amounts of iron detected (1.32 wt%) is Fe3+ hosted in the structure of spinel.