Corresponding Author

Xu Wu(Profxuwu@hust.edu.cn)


It is preferred to simultaneously recover resource and energy from waster. Sulfur dioxide, SO2, a common air pollutant, a potential energy resource, is a key link to sulfur nature circulation. SO2 can be conversed to NH4HSO3 and (NH4)2SO3 during the ammonia desulfurization process, which can be used to produce (NH4)2SO4 fertilizer. For high quality (NH4)2SO4 fertilizer and high heat transfer efficiency of the evaporative crystallization, HSO3- or SO32- needs to be oxidized to form SO42- before evaporative crystallization. Anodic oxidation of HSO3- or SO32- coupled with hydrogen evolution can significantly reduce cost of hydrogen evolution due to a low reaction potential. This work uses a filter-press membrane electrode assembly electrochemical reactor to recover commercially valuable (NH4)2SO4 fertilizer and produce hydrogen. It can simultaneously achieve waster recycle and energy storage, which is conformed to the domestic circulation and dual carbon goals. The electrooxidation mechanisms and dynamic parameters of (NH4)2SO3 and NH4HSO3 on homemade PtPd2.75/C catalyst were investigated, particularly by cyclic voltammetry and rotating disk electrode system. According to Randles-Sevĉik equation and Levich equation, the number of the electron transfer during the electro-oxidation of SO32- or HSO3- is 1.86. The diffusion coefficients of SO32- and HSO3- are 2.29 × 10-6 cm2·s-1 and 1.18 × 10-5 cm2·s-1, respectively. A 1 cm × 1 cm electrolyser was homemade by graphite. The desulfurization wastewater was used as the anolyte, while water as the catholyte. The anolyte and catholyte were separated by a proton exchange membrane. The homemade PtPd2.75/C catalyst was used as both sulfite oxidation catalyst and hydrogen evolution catalyst. The catalyst was loaded to carbon clothes firstly, and then hot-pressed to the proton exchange membrane to fabricate the membrane electrode assembly. The influences of operation conditions on the electrolyser performances have been studied by potentiodynamic scans and electrochemical impedance spectroscopy. The optimal conditions were chosen as follow: pH = 7.5 of the ammonium sulfite wastewater as the anolyte, pure water as the catholyte, 50 oC. The electrolyser exhibited excellent SO32- electro-oxidation performance and stability. Under the optimal experimental conditions, the electrolyser could achieve 294.63 mA·cm-2 at 1.5 V. At a current density of 200 mA·cm-2, the SO32- conversion rate could reach 94% without exceeding the applied cell voltage of 2 V. It could produce 0.70 t ammonium sulfate and 2.98 kg hydrogen when 1 m3 ammonium sulfite wastewater was electrolyzed for 20 h. The electricity consumption was 137.24 kWh per m3 wastewater, which can create a profit of 1302.70 yuans. Such a strategy has shed a light on further development towards industrial application.

Graphical Abstract


desulfurization wastewater, electro-oxidation, hydrogen evolution, ammonium sulfate, recycling

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