Transforming granite and marble waste into nano-calcium silicates: an eco-friendly synthesis and comprehensive characterization

Marble and granite industries have expanded significantly over the past few decades, leading to an increase in processing waste. To reduce the environmental impacts of granite and marble processing waste, proper management and potential recycling with sustainable methodologies are crucial. The aim of this study is to synthesize nano-calcium silicates by utilizing a fine fraction of waste derived from the granite (rich in SiO2) and the marble (rich in CaO) processing industries, using a chemical-free solid-state reaction method. The research investigates the effects of three different mix proportions of CaO:SiO2 (1:0.9, 1:1, 1:1.1) on calcium silicate production at a calcination temperature of 1000 ℃. Furthermore, calcium silicate is reduced to nano-size by adopting various milling time intervals (0, 4, 6, 8, 10 h) using a planetary ball mill. The results indicate that the mix proportion of 1:1 yields the highest amount of calcium silicate, and a milling time of 6 h yields the smallest particle size. The confirmation of calcium silicate (in this case, wollastonite) formation is verified using various analysis techniques, such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM). Particle size distribution analysis and transmission electron microscopy (TEM) show that the mean particle size is less than 100 nm, and Brunauer–Emmett–Teller (BET) analysis reveals a surface area of 6 m2/g. The study highlights that the solid-state reaction method might be a promising approach for effectively treating waste materials. Graphical Abstract