Change in phase, microstructure, and physical-chemistry properties of high chromium vanadium slag during microwave calcification-roasting process

The effects of microwave roasting and conventional roasting on oxidation behavior of high chromium vanadium slag (HCVS) during calcification -roasted process were compared in terms of the phase transformation, bonding structure change, valence state, microstructure, particle size, and surface properties of HCVS before and after microwave roasting and conventional roasting, which were characterized by XRD,FT-IR, XPS, SEM, BET specific surface area, and contact angle measurement, respectively. The temperature characteristics of HCVS during microwave and conventional roasting process were also investigated. HCVS was heated in a microwave field, and the heating time was shortened to 16 min at a microwave power of 2 kW, and to 58 min for conventional roasting. When compared to conventional roasting, microwave roasting promoted the oxidation degree of HCVS to a greater extent. The relative proportion of V5+ increased to 84.3% after microwave roasting and 76.9% after conventional roasting. The micrographs of HCVS after microwave roasting exhibited a significant change in morphology that involved reduction in particle size and subsequently an increase in roughness and porosity of the solid. BET specific surface area after microwave roasting was significantly increased from 16.3 m(2)/g to 45.1 m(2)/g. Microwave roasting decreaseds the contact angle to liquid and enhanced the wetting properties of HCVS. The leaching ratio of vanadium and chromium after microwave roasting increased from the initial values of 12.7% and 0.4% to 95.9% and 4.2%, respectively, and exceeded 82.5% and 2.1%, respectively, after conventional roasting. (C) 2018 Elsevier B.V. All rights reserved.