Iron conversion and ammonium salt calcination whitening process and mechanism of pre-calcined coal gangue

Abstract

The resource utilization of coal gangue is of great significance for the reduction of bulk solid waste and the decrease of environmental risk. In this study, we changed the existence of iron-bearing substances (mainly hematite, Fe2O3) contained in the pre-calcinated coal gangue into iron sulfate (Fe2(SO4)3) by ammonium sulfate calcination. The results suggested that after being calcined with 40 % of (NH4)2SO4 at 500 °C and removing soluble iron salts (Fe2(SO4)3) by rinsing, the whiteness and specific surface area of raw coal gangue was upgraded from 38.5 % and 12.85 m2/g to 85.3 % and 34.79 m2/g, respectively, and the total amount of iron-bearing substances was reduced to 0.08 %. Moreover, the gas products obtained from the ammonium sulfate calcined coal gangue process were analyzed by simultaneous Thermogravimetry-Fourier transform infrared spectroscopy-Mass spectrometer (TG-FTIR-MS), and the main compounds released from CG860 + 40 % (NH4)2SO4 in the whole calcination process were NH3, H2O, SO, SO2, and NO.