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Phase evolution and nature of oxide dissolution in metallurgical slags
Author(s) -
Sun Zhi H. I.,
Guo Xiaoling,
Dyck Joris,
Guo Muxing,
Blanpain Bart
Publication year - 2013
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.14073
Subject(s) - dissolution , lime , diffusion , phase (matter) , oxide , slag (welding) , layer (electronics) , chemistry , particle (ecology) , materials science , calcium oxide , chemical engineering , mineralogy , metallurgy , thermodynamics , analytical chemistry (journal) , chromatography , nanotechnology , physics , oceanography , organic chemistry , geology , engineering
The dissolution of solid lime particles into liquid slags at high temperatures was evaluated by means of confocal scanning laser microscopy. An additional solid layer around the lime particle was observed at the intermediate stage of the dissolution into CaOAl 2 O 3 SiO 2 slags. The dissolution rate was decelerated due to the existence of the additional layer and the dissolution profile could be clearly distinguished into three stages, that is, an early, intermediate, and late stage. By adding 10 wt % MgO, this layer could be effectively eliminated and the slope of the whole dissolution profile kept relatively constant. The dissolution path and mechanisms were subsequently evaluated by incorporating thermodynamic calculations. Both direct and indirect dissolutions could be distinguished. It was realized that the decrease in composition range for solid precipitating after adding MgO could significantly reduce the interfacial reaction (IR) layer formation. Post‐mortem analyses on quenched samples were further carried out to confirm the theoretical calculations. It was found that the solid layer in slags without MgO was (CaO) 2 ·SiO 2 and (CaO) 3 ·SiO 2 which is in line with the thermodynamic calculations. However, only (CaO) 2 ·SiO 2 was noticed in slags with MgO which both (CaO) 2 ·SiO 2 and MgO phases should be present according to the calculations. The nonequilibrium during dissolution may play an important role on phase transformation and MgO particles in much smaller quantity may have dissolved into (CaO) 2 ·SiO 2 phase. The diffusion of CaO in both slags with and without MgO was additionally investigated. The local CaO concentration distributions from the direct dissolution phase to the slag bulk could be well fitted with the theoretical model proposed via Fick's second law. As a result, the local diffusion coefficient in the dissolution region was obtained and the effect of MgO addition on diffusion could be assessed. © 2013 American Institute of Chemical Engineers AIChE J , 59: 2907–2916, 2013