Novel synthesis of ultramarine blue from waste coal fly ash via thiocyanate aluminosilicate sodalite

Abstract

ABSTRACTThis paper for the first time reports the conversion of coal fly ash into intense blue ultramarine via thiocyanate aluminosilicate sodalite Na8[AlSiO4]6(SCN)2. The possibility of stepwise and systemic conversion of thiocyanate aluminosilicate sodalite into intense blue ultramarine had never been previously demonstrated. The ultramarine analogs of various colors have been prepared by structure conversion of thiocyanate aluminosilicate sodalite by calcination (500–950°C). The products obtained are characterized by various investigative techniques including Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), UV-visible spectroscopy, scanning electron microscopy (SEM), electron spin resonance (ESR) spectroscopy. Surface morphology is studied by the SEM technique. Elemental analysis is carried out with the help of EDAX. Results of ESR have been reported and interpreted. Ultraviolet and Raman spectroscopic analysis gave clear evidence of conversion of SCN− to and further on into . These extensive characterizations showed that the ultramarine pigment is good enough and that the sodalite framework is thermally highly stable with its structure undisturbed even at 950°C.