Document Type

Journal Article

Publication Title

Process Safety and Environmental Protection



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School of Engineering


National Key R&D Program of China / Beijing Zhong Dian Hua Yuan Environment Protection Technology Co., Ltd. / Ningbo Science and Technology Innovation Key Projects / Ningbo Municipal Commonweal Key Program / S&T Program of Hebei / Mineral Resources Analytical and Testing Center, Institute of Process Engineering, Chinese Academy of Science


Chao, L., Xuebin, A., Hu, J., Wang, Y., Wang, S., Wang, Y., . . . Sun, Y. (2024). Enhanced phosphogypsum thermal reduction by carbon in presence of sodium chloride at high temperature. Process Safety and Environmental Protection, 185, 64-75.


This paper reports an enhanced approach of thermal reduction of phosphogypsum (PG) in the presence of sodium chloride (NaCl) in its molten phase. The thermodynamic together with in-situ thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR) result indicates the yield of CaS (solid) at the investigated temperature range (800–850 °C). Addition of NaCl not only appreciably reduces the activation energy of this reaction (800–850 °C) on average from 315 to 175 (kJ·mol−1) materially, but also significantly improve the conversion from CaSO4 to CaS. Additionally, the NaCl based waste salt (NaCl-WS) containing organic compounds (0.21 wt%) was found to produce similar results when compared with the pure NaCl addition at investigated temperature range. The optimal conditions via parametric optimization: i.e., 800–850 °C, 15 wt% (NaCl-WS), and 6 (ratio of PG/C (carbon) wt/wt), were determined. The mechanistic study together with using density functional theories (DFT) shows that the synergistic effect by NaCl addition was caused by the coupled-vacancy diffusion mechanism when NaCl melts at high temperature and C atom shows proximity to oxygen (O) atom from the SO42- cluster in the CaSO4 crystallite structure. The evaluation of the process shows appealing advantages over the conventional PG thermal reduction. By carefully manipulating temperature range together with the NaCl-WS addition, the proposed new process simultaneously realizes PG thermal reduction and environmental utilization of NaCl-WS.



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This work is licensed under a Creative Commons Attribution 4.0 License.