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In this work, the reduction-oxidation two-step method was used for investigating the resource utilization of phosphogypsum. The influences of different decomposition conditions were investigated, including the reducing process and oxidizing process. The reductive organic sulphide in lignite reacted with CaSO 4 and improved the CaSO 4 decomposition rate. High Fe 2 (SO 4 ) 3 content and anhydrous air flow rate promoted the formation of Fe-Ca-Ox, decreasing the CaSO 4 decomposition rate. H 2 O derived from CH 4 reacted with lignite to consume the solid reducing agent. In the reducing process, CaSO 4 reacted with CH 4 and lignite to form CO, CO 2 , H 2 O, and CaS. In the oxidizing process, CaS was mainly oxidized into CaO, SO 2 , and element S. Through a two-step decomposition process (reduction with CH 4 and oxidation with air), the decomposition temperature of phosphogypsum decreases and the decomposition efficiency is improved. Meanwhile, the residual lignite was oxidized into CO and CO 2 . Therefore, it is meaningful and valuable.

Limited by single function, it is difficult for the traditional stirred vessels to meet the requirements of mixing system in biomass wastewater treatment processes. The estimation of biomass wastewater stirring reactor performance by computational fluid dynamics (CFD) during multiphase reactions is important, due to the uncertainty in the numerical results. In this study, a novel double-partition stirred vessel with eccentrically located impellers was developed for the special subject. In addition, many simulations were carried out with the wastewater from biomass ethanol production as the medium to ensure the high reactor performance. The fluid flow was simulated and analyzed using the turbulent RNG k-ε model and multi reference frames. A good agreement is found between the simulation results and the confirmatory experiment. Moreover, the weir crest and interconnected pore were specially designed for the establishment of the circulation of fluid to maintain different technological conditions in the two regions. The distributions of radial velocities and tangential velocities were concentrated near the stirring blade. From the velocity profile, it is deduced that the flow pattern in the stirred vessel is insensitive to Reynolds number. Finally, this simulation study could contribute to the improvement and optimization of the structure, as well as the operation of the novel stirred vessel.