Recovery of iron nanominerals from sacred incense sticks ash waste collected from temples by wet and dry magnetic separation method

Abstract

Indian incense stick ash (ISA) contains about 4%–8% ferrous iron (Fe2＋), the fourth-highest metal oxide mineral in ISA, as confirmed by X-ray fluorescence spectroscopy (XRF). The source of ferrous iron fractions in ISA is coal powder, which facilitates the burning of incense sticks. Ferrous iron is separated by two methods — dry and wet-slurry magnetic separation. Both are eco-friendly and cost-effective and assume a safe and rapid one-step process. The wet-slurry magnetic separation method is found to be more efficient, as its yield is almost twice the separation and purity level of the dry magnetic separation method. Various techniques have been employed to explore the chemical, physical, and morphological properties of recovered ferrous iron fractions. For example, Fourier transform-infrared spectroscopy (FTIR) and X-ray diffraction (XRD) have elucidated the micro-crystalline nature of the separated particles. Two types of microscopy techniques – field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) – have revealed the surface topography and morphology of the recovered ferrous iron particles, which are spherical and sized between 40 and 120 nm. Additionally, energy-dispersive X-ray spectroscopy (EDS) has confirmed that ferrous iron particles were rich in iron content, as the spectra showed prominent peaks for Fe and O, while the presence of Al, Si, Ca, Na, C, Na, Mg, Mn, and K indicates impurities associated with the samples.