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 theEuropean community. A virtual secondary raw material of great importance is the product ofthe thermal transformation of cement – asbestos. This work illustrates the study of calcinationproducts obtained starting from the product of the thermal transformation of cement-asbestosat 1200 °C, added to primary raw materials (kaolin, aluminum hydroxide) and boric acid asmineralizing agent. The calcination has been conducted at 1200 °C for 1 hour. Thecrystallization kinetics has been monitored using in situ high temperature X-ray powderdiffraction. The microscopic characterization of the final product of calcination has beenconducted with SEM and TEM imaging supported by X-ray microanalysis. The structurerefinement was conducted on the powder sample using the Rietveld method. The results arecompared with the spectroscopic characterization including Mössbauer and UV-Visspectroscopies. 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 thatthe anorthite is stoichiometric, and the small amounts of iron detected (1.32 wt%) is Fe3+hosted in the structure of spinel