Generated compounds at the V-slag/CaO diffusion surface and diffusion characteristics of V and Ca in calcium vanadate

• Published in: Journal of hazardous materials Vol. 393; p. 122368
• Main Authors: Yue, Hong-Rui, Xue, Xiang-Xin
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 05.07.2020
• Subjects: Boltzmann-Matano method; Calcium roasting; Diffusion coefficient; Diffusion couple; Vanadium slag; Vanadium slag; Calcium roasting; Diffusion coefficient; Boltzmann-Matano method; Diffusion couple
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2020.122368

•The generated phases at the V-slag surface, the CaO surface are Ca2V2O7, Ca2V2O7 and Ca3V2O8, respectively.•The generated phases at the V-slag surface where the diffused Ca has not reached are mainly consisted of Fe2O3 and Mn2O3.•New method is proposed to determine the Matano surface and calculate the interdiffusion coefficient.•The average interdiffusion coefficient of Ca2+ was greater than that of V5+ in the calcium vanadates. Vanadium slag/CaO diffusion couples were prepared to study the diffusion characteristics of the vanadium slag/CaO interface at 1083 K in the air. The generated phases at different regions were characterized by EPMA, EDS, XRD, and element maps analysis. At the vanadium slag surface that the diffused Ca dose not reached, the main generated phases were Mn2O3 and Fe2O3. V3+ was oxidized to V5+ and reacted with the Ca2+ to form a small amount of Ca2V2O7. Cr was at a disadvantage compared with V in occupying the original Ca2+ of the slag. At the vanadium slag surface that the diffused Ca had reached, the main generated phases were Ca2V2O7. At the CaO surface, the main generated phases were Ca2V2O7 and Ca3V2O8. The interdiffusion coefficients were calculated by a new approach that modified from the Boltzmann-Matano method including the determination of the Matano surface, calculation of the integral and differential using the raw data of the concentration profiles. As the molar fraction of Ca was in the range of 0.15 to 0.86, the average interdiffusion coefficient of Ca2+ was 2.54 × 10−8 cm2·s-1. The average interdiffusion coefficient of V5+ at the V molar fraction of 0.001 to 0.43 was 1.96 × 10−8 cm2·s-1.