Wencheng Xia

The efficient utilization of lignite is a crucial area of research for the sustainable management of existing coal resources. One potential technique for cost-effective and environmentally friendly coal processing is the application of microbes or their derivatives to modify the surface of lignite for bioflotation. However, the precise process of surface modification between microbes and coal remains largely unknown. In this study, we focused on the use of a white-rot fungus called Hypocrea lixii AH and its various components, including spores, hyphae, extracellular polymer substances (EPSs), and culture solution, as biosurfactants for lignite modification. By employing techniques such as zeta potential analysis, induction time measurement, contact angle measurement, and Fourier infrared spectroscopy, we investigated the changes in the surface properties of raw and modified lignite. Furthermore, we conducted a preliminary bioflotation test using biosurfactants as collectors in order to explore the potential application of fungal modification in this context. Our results revealed that all biosurfactants were effective in improving the surface properties of lignite, with the EPS demonstrating the most prominent effect, followed by the culture solution, hyphae, and spores. The zeta potential and induction time of the modified lignite decreased, indicating enhanced hydrophilicity, while the contact angle exhibited a slight increase, suggesting a minor increase in hydrophobicity. Analysis of the Fourier infrared spectra indicated that EPS treatment resulted in the highest abundance of functional groups, including carboxyl, hydroxyl, and amidogen groups. Although fungal cells were found to improve the hydrophobicity of coal, they did not exhibit a significant effect on the flotation of lignite. Nonetheless, our findings suggest that fungal cells and their derivatives have the potential to remove or transform minerals present in lignite, particularly those containing sulfur. While they may not serve as effective bio-collectors in microflotation, their capability in mineral alteration makes them valuable candidates for lignite processing with a focus on mineral reduction.

The sulfur in coal not only influences the coke quality but also pollutes the environment during the combustion. The desulfurization of high organic sulfur coal is a key issue in coal cleaning science. As the pyrolysis has been used in low-rank coal conversion to obtain gas/liquid products and coal char, the desulfurization effects of pyrolysis on the low-rank coal with high organic sulfur requires further studies. This study investigated the desulfurization performance of high organic sulfur low-rank coal by the pyrolysis and the changes in the coal calorific value and sulfur forms during the pyrolysis. The XPS was applied to analyze the changing regulation of sulfur that forms on coal surface. The results indicated certain amount of FeS was newly created during the pyrolysis and high amounts of sulfate sulfur was transferred to pyrite sulfur and formed more FeS2 when compared to the distribution of raw coal. The total sulfur content of coal was reduced from 2.32% for raw coal to 1.68% for 700 °C pyrolysis coal and then the pyrolysis temperature had little effect on the sulfur content. The net calorific value (at constant volume and air-dry basis) was increased from 17.38 kJ for raw coal to 24.35 kJ for 700 °C pyrolysis coal. The pyrolysis temperature of 700 °C may be the best pyrolysis temperature for both low sulfur content and high calorific value.