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Vanadium pentoxide (V2O5) is one of the fundamental materials applied in the productions of batteries, vanadium-aluminium alloys, biomedicine, catalysis, etc. High purity V2O5 can be prepared from an intermediate product, namely ammonium polyvanadate (APV), using roasting after a drying process. In this paper, microwave heating was used as an alternative drying option for APV, which has advantages including selective heating, high heating efficiency, energy-saving, and environmental protection. The authors investigated the microwave heating characteristics of APV and discussed the effects of microwave power, the mass of APV, and initial water content on the efficiency of microwave drying. The dynamic analysis of the APV microwave drying process was also carried out. Four groups of thin-layer drying dynamic models, namely Modified-Page model, Verma model, Sickmplified-Fick's-diffusion model, and Two-term-exponential model, were fitted with the experimental data. Through comparison, the Modified Page model could better describe the microwave drying process of APV.

Applying microwave heating, in substitution for conventional industrial process heating, renders energy-saving and clean efficient for mineral reduction. In this work, the behavior of low-grade pyrolusite during microwave-assisted heating was systematically investigated, and the phase transformation of pyrolusite during the reduction process was characterized by TG-DTG-DSC and XRD; meanwhile, a model for the reduction mechanism was proposed, with a three-stage reduction process identified. Results indicated that manganese oxide (MnO) powder can be efficiently prepared, and the reduction ratio presented positive relationships with reduction temperature and heating time, obtaining with a high reduction ratio value of 94.4% achieved at 600 °C within a duration time of 40 min. XRD analysis confirmed that the phase transformation during the reduction process followed the conversion sequence as MnO2→Mn2O3→Mn3O4→MnO, and the iron oxides was almost converted to Fe3O4. It was proved that low-grade pyrolusite can be reduced effectively and efficiently to manganese oxide at lower temperature and shorter duration time by microwave heating.

Because of the shortage of natural rutile, synthetic rutile is a widely used substitute welding materials for natural rutile owing to its excellent mechanical and thermal properties. In this work, rutile TiO2 was prepared from oxidation roasting titanium slag, which can be used as special welding materials. The phase microstructure characteristics of the raw materials and the roasted samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) spectroscopic analysis. Results indicated that the contents of sulfur (S) and carbon (C) in titanium slag decreased during oxidation roasting process, and the decreases of sulfur and carbon contents were mainly ascribed to the formation of corresponding oxides. XRD and FT-IR results revealed the formation of rutile TiO2 phase after titanium slag through oxidization roasting; additionally, observed from SEM patterns, the rutile TiO2 phase with a complex short rod-like crystal appeared in the products. Since the contents of sulfur (S), phosphorus (P) and carbon (C) element were all below 0.030% in the prepared rutile TiO2 with the recommended roasting approach (roasted at 1100 °C for 120 min), the present work highlights that Panzhihua titanium slag is a potential resource of titanium for the manufacture of high-quality rutile TiO2 applicable for special welding materials industry.