The electrochemical desulfurization in the molten salt is a promising green route to extract metals directly from sulfide ores. However, less attention has been paid to the process of converting solid sulfides to liquid metals, especially the evolution of the solid sulfide/liquid metal interface. Herein, the electrochemical desulfurization process of converting solid ZnS to liquid Zn in NaCl-KCl was studied through electrochemical measurements, wettability test, and postmortem analysis of the electrolytic product. The continuous solid-to-liquid reaction in the molten salt is ascribed to the poor wettability of liquid Zn on the solid ZnS which prevents the liquid Zn from fully covering the sulfide surface and allows S 2- ions transfer. The desulfurization process consisted of three stages: two-step reduction of zinc sulfide and the reduction of Na + on the liquid Zn to form Na-Zn alloys. The understanding of the solid-to-liquid conversion process is helpful to understand various solid-to-liquid reactions so as to design efficient electrolyzers.
Under the two frequency microwave conditions of 915 and 2450 MHz, orthogonal tests were designed to investigate the effects of organic acid reagent, microwave irradiation time, and mixing time of additives and coal samples on the desulfurization effect of coal. Results show that the effect of irradiation time on the experimental desulfurization efficiency under frequency microwave conditions is large and is the main factor. The desulfurization effect under 915 MHz microwave condition is better than 2450 MHz microwave condition. Two sets of experimental optimal coal samples were used for characterization and analysis. Thermogravimetric analysis revealed that the combustion temperature range of the coal samples is shortened and the integrated combustion index is considerably higher after the microwave irradiation experiment. Fourier-transform infrared spectroscopy analysis showed that the overall chemical structure of the coal samples does not change significantly after the experimental treatment. X-ray photoelectron spectroscopy analysis showed that the intensity of organic sulfur in coal samples is weakened after microwave irradiation, the characteristic peaks of thiols and thioethers are reduced to a great extent, and an increase in the intensity of sulfoxide organic sulfur is observed. On the basis of the results of experimental analysis and quantum chemical simulation calculations, the mechanism of organosulfur structure removal under the action of microwave is revealed.
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