A green synthesis of calcium silicate nanopowders from silica fume and marble sawing dust by a microwave irradiation-assisted route

Abstract

Calcium silicate nanopowders have been successfully synthesized from solution mixtures of silica fume and marble sawing dust via a simple, fast and eco-friendly microwave irradiation method. The formed calcium silicate nanoparticles were characterized via XRD, SEM, EDX, FTIR spectroscopy, Raman spectroscopy, and BET surface area techniques. Wollastonite CaSiO₃ (CS), belite Ca₂SiO₄ (C₂S), alite Ca₃SiO₅ and rankinite Ca₃Si₂O₇ (C₃S) were the main detected phases by XRD analyses. The ratio of calcia CaO (C) to silica SiO₂ (S) and the time of irradiation played a pivotal role in the phase composition of the as-prepared samples. At the C/S molar ratio of 0.53 : 1, the predominant detected phases were alite and rankinite, whereas belite was detected as a minor phase. No other phases or compounds of starting materials could be detected. As the irradiation time increased from 3 to 6 min, the intensity of the XRD main peaks corresponding to alite and rankinite increased. SEM images indicate that the morphology of the as-prepared samples varied from slices on top of each other witha small rod-like shape to rod and plate-like crystals and regular layers on the top of each other by changing the C/S ratio and irradiation time. A sample prepared with a C/S ratio of 0.53 : 1 reveals that the particle size decreased from 680 nm to 345 nm upon irradiation for 40 s for 6 min. The N₂ adsorption–desorption isotherms showed that all samples were of type III with a mesoporous structure (the pores size was in the range of 50–2 nm). The microwave irradiation method might be a promising route to effectively treat other waste materials in a cost–effective and productive way.