High-temperature oxidation behavior of ferrovanadium (FeV 2 O 4 ) and ferrochrome (FeCr 2 O 4 ) spinels is crucial for the application of spinel as an energy material, as well as for the clean usage of high-chromium vanadium slag. Herein, the nonisothermal oxidation behavior of FeV 2 O 4 and FeCr 2 O 4 prepared by high-temperature solid-state reaction was examined by thermogravimetry and X-ray diffraction (XRD) at heating rates of 5, 10, and 15 K/min. The apparent activation energy was determined by the Kissinger–Akahira–Sunose (KAS) method, whereas the mechanism function was elucidated by the Malek method. Moreover, in-situ XRD was conducted to deduce the phase transformation of the oxidation mechanism for FeV 2 O 4 and FeCr 2 O 4 . The results reveal a gradual increase in the overall apparent activation energies for FeV 2 O 4 and FeCr 2 O 4 during oxidation. Four stages of the oxidation process are observed based on the oxidation conversion rate of each compound. The oxidation mechanisms of FeV 2 O 4 and FeCr 2 O 4 are complex and have distinct mechanisms. In particular, the chemical reaction controls the entire oxidation process for FeV 2 O 4 , whereas that for FeCr 2 O 4 transitions from a three-dimensional diffusion model to a chemical reaction model. According to the in-situ XRD results, numerous intermediate products are observed during the oxidation process of both compounds, eventually resulting in the final products FeVO 4 and V 2 O 5 for FeV 2 O 4 and Fe 2 O 3 and Cr 2 O 3 for FeCr 2 O 4 , respectively.
Jianle Wang,Xueming Liu,Zhihua Zhu,Le Yuan,Dongye Zhao,Hong Deng,Zhang Lin
High concentrations of Cr(VI) are often detected in contaminated soil. Yet, cost-effective remediation technologies have been lacking. In this study, we prepared a type of FeS x based on commercial FeSO 4 .7H 2 O and CaS x and tested a microwave-assisted technology based on FeS x for reductive immobilization of high concentrations of Cr(VI) in a field contaminated soil. The as-prepared FeS x particles appeared as a honeycomb-like and highly porous structure. The microwave-assisted FeS x reduction process was able to rapidly reduce the TCLP-based reachability of Cr(VI) from 391.8 to 2.6 mg·L -1 . The dosage of FeS x , S/Fe molar ratio, initial moisture content, microwave power, and irradiation time can all affect the treatment effectiveness. After 500 days curing under atmospheric conditions, the TCLP-leached concentration of Cr remained below the regulatory limit of 5 mg·L -1 , while other treatments failed to meet the goal. S x 2- or S 2- served as the primary electron donors, whereas Fe facilitated the microwave absorption and the formation of the stable final product of FeCr 2 O 4 . S and Fe are mostly precipitated in soil. The microwave-assisted FeS x reduction was shown to be an effective approach to rapidly reduce the leachability of Cr(VI) in contaminated soil, especially in heavily contaminated soil.
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