The full utilization of solid waste—phosphogypsum (PG)—by reacting it with pyrite can not only produce acid but can also solve the serious issues associated with PG waste. However, this approach is limited because of crusting which blocks the rotary kiln and makes the acid production unsustainable. Hence, it is imperative to design a strategy to increase the eutectic temperature so as to prevent the generation of eutectic compounds, which always lead to crust formation, kiln-ringing, and blockage. In this study, the fusion characteristics of pyrite reduction were investigated via the determination of ash fusion points under various atmospheres as well as using different additives. The structural changes and fusion characteristics, in particular macromorphology, were observed by scanning electron microscopy. Furthermore, the optimal conditions to increase the softening temperatures were determined by means of single-factor and orthogonal experiment methods.

The solubility of ammonium dihydrogen phosphate (MAP) was measured at the temperature range from 283.2 to 343.2 K by using dynamic and static methods in water–ethanol system. The experiment results showed that the solubility of MAP increased with the increase of the investigated temperatures under the constant ethanol concentration and decreased with increasing concentration of ethanol with isothermal operations. The solubility of MAP in water–ethanol system was fitted by the modified Apelblat equation, the correlation coefficient square was greater than 0.990, and the average of the root-mean-square deviation was 4.346 × 10–4, which indicated that the experiment data was well in agreement with the calculation value.

Porous hierarchical LiMn0.5Fe0.5PO4 spheres were synthesized via a novel template-engaged method using pre-synthesized hollow spherical Li3PO4 as template and FeCl2·4H2O/MnCl2·4H2O as Fe2+/Mn2+ source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the porous hierarchical spheres exhibit hollow structure and have a size distribution of 0.4–1 um consisting of aggregated ∼50 nm nanoparticles. A mechanism of the reaction from Li3PO4 to LiMn0.5Fe0.5PO4 was proposed on the basis of the phase and morphology transformation of the intermediates. With the short Li+ diffusion path and porous structure, the carbon coated LiMn0.5Fe0.5PO4 spheres show high specific capacity and superior rate capability with the discharge capacities of 159.3 mA h g−1 at 0.1C and 80.6 mA h g−1 at 20C. The porous hierarchical spheres also exhibit an excellent cycling stability with about 90.7% of the initial value at 1C after 100 cycles.

It is widely accepted that lithium hexafluorophosphate (LiPF6) is the best electrolyte for making lithium ion battery because of its excellent performance. Using acetonitrile (ACN) solvent to pretreat LiPF6 is a green chemical process. However, ACN residue will be introduced into the electrolyte during the preparation process. The effects of ACN on the electrochemical performance of LiFePO4/Li are evaluated in this study. The study results showed that the battery capacity is improved by the addition of 1 wt % ACN to the electrolyte. Surface analyses of the battery cathodes using XPS and FTIR suggested that the cathodes be oxidized in all electrolytes with 0, 1, and 5 wt % ACN, resulting in the formation of Li2CO3, LiF, and ROCO2Li on their surfaces. Li(ACN)4PF6, which reduces the battery capacity, was especially formed on the surface of the cathode in the electrolyte containing 5 wt % ACN.

Lithium hexafluorophosphate (LiPF6) is the best electrolyte for lithium-ion batteries because of its excellent performance. The conversion of KPF6 into LiPF6 is a green chemical process. However, KPF6 residues are introduced into the electrolyte during the preparation process. In this study, we evaluated the effects of KPF6 on the electrochemical performance of natural graphite/Li. The results of a cycling test showed that as the KPF6 content increased in the electrolyte, the specific capacity of the graphite electrode also increased gradually. The impedance of a solid electrolyte interphase (SEI) film was decreased by the addition of KPF6. Cyclic voltammograms showed that the addition of KPF6 had no effects on the insertion and extraction reactions of lithium ions on the graphite electrode. Analyses of the graphite electrodes using scanning electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy suggested that the addition of 0.09 and 0.2 wt% KPF6 did not change the main components of the SEI film, but the ROCO2Li content decreased and the Li2CO3 content increased. Therefore, the electrochemical performance of the graphite electrode was improved by lithium-ion migration on the SEI film, which protected the graphite layer.

Phosphogypsum (PG) is one of the most significant industrial solid wastes from the phosphorus chemical industry. In order to utilize PG more effectively, a new decomposition process of PG by sulfur as a reducer is proposed in this work. Thermodynamic study of the sulfur reduction process including two-step reactions was carried out by both thermodynamic simulation and experimental research. The simulation results indicate that sulfur changes its form in a complex way with rising temperature. The final decomposition temperature of PG by simulation is 993 K in the first-step reaction, and this is in good agreement with that obtained by the experiments. For the second-step reaction, however, the final PG decomposition temperature from the experiments is 250 K lower than the simulation results predict. The reaction heat of the sulfur reduction process is 27.95% less than that of the traditional coke reduction process at T = 1473 K based on enthalpy change calculations. This new process can reduce the emission of CO2 effectively and is more suitable for resource utilization of PG than the coke reduction process, so it may be a promising method for sulfuric acid production from PG.Graphical abstractInnovation of this paper is a new and advanced process of phosphogypsum decomposition by sulfur for sulfuric acid production. Fig. 4 of this manuscript can indicate the innovation appropriately.Highlights► A new and advanced process for sulfuric acid production from phosphogypsum was proposed. ► Thermodynamic simulation of the new process was studied. ► Specific experiments were carried out to verify the thermodynamic simulation. ► Reaction heat of the new process were lower than that of traditional coke reduction process.