Chemical Beneficiation of High-Ash Indian Noncoking Coal by Alkali Leaching under Low-Frequency Ultrasonication

Abstract

Coal mined from the Talcher region of Odisha, India is known to be high-ash, surface-oxidized, and noncoking in nature. It is quite challenging to beneficiate such low-grade coal by physical or physicochemical processes due to its oxidized nature and the presence of complex ash forming mineral matter in its matrix. Chemical beneficiation is one of the alternative process to such problems. However, this chemical process consumes more chemicals, treatment time, and energy, which limits its application further. Therefore, an attempt has been made to chemically beneficiate this coal cost-effectively with optimum chemicals, treatment time, and energy. In the present study, an application of ultrasound at low frequency on alkali-acid leaching is employed to investigate on the demineralization of high-ash Indian noncoking coal. The raw coal properties such as fixed carbon content, CHNS content, Hardgrove grindability index, ash fusion temperature, and gross calorific value (GCV) were investigated before the experiments. The coal samples were leached with three different types of alkali namely, NaOH, KOH, and Na2CO3 followed by H2SO4 and HCl treatment, respectively. The quality of the treated coal was examined by proximate analysis and GCV measurement. The maximum ash removal was achieved on NaOH-leached coal followed by 30% H2SO4 treatment with 73.91% demineralization and 57.21% fixed carbon. The raw and treated coal samples were characterized by Fourier transform infrared, scanning electron microscopy, and X-ray diffraction to confirm the presence of oxygenated functional groups causing surface oxidation, surface modification by ultrasonication, and the formation of alkali aluminosilicates on the coal surface, respectively. The presence of trace elements in the alkali leachates released during ultrasonication was also determined by the inductively coupled plasma atomic emission spectroscopy technique.

Modification of Lakra (Pakistani) Coal by Chemicals Washing and Heat Treatment and Its Application for Removal of Organic Acids (Prop Ionic Acid and Chloroacetic Acid) from Aqueous Solution

“…It has been confirmed by various studies that in static system the ratio of mass, volume and initial concentration of solution affect sorption kinetics parameters (Ho, 2006;Sari et al, 2008;Barma et al, 2018). Constant reaction rate was found to be influenced by the initial solution concentration and ratio of sorbent mass to solution volume.…”

Ultrasound–Promoter Pretreatment for Enhancing the Yield and Combustible Matter Recovery of High-Ash Oxidized Coal Flotation

“…Similar to promoters, studies on intensifying the flotation process by pretreating the coal slurry using ultrasound in removing the oxygenated functional groups from the coal surface were also reported by several researchers. ,− The implementation of ultrasound in coal slurry results in the generation of a cavitation effect at millions of locations. During cavitation, the several cavity bubbles collapse and transmit equivalent microjets, which promote surface pitting on the coal particles.…”

Utilization of low-grade BHQ iron ore by reduction roasting followed by magnetic separation for the production of magnetite-based pellet feed

“…In the batch-wise reduction roasting process, non-coking coal of Indian origin was used as the reducing agent throughout the experiments. Non-coking coals were considered in the present work as a replacement for high-grade coals due to its large availability and low cost in India [14][15][16][17]. Different coal samples were obtained from various locations in India, and their proximate analysis data are presented in Table 2.…”