Effect of MgO and CaO/SiO2 on the immobilization of chromium in synthetic slags |
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Authors: | Hugo Cabrera-Real Antonio Romero-Serrano Beatriz Zeifert Aurelio Hernandez-Ramirez Manuel Hallen-Lopez Alejandro Cruz-Ramirez |
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Institution: | 1. Metallurgy and Materials Department, IPN-ESIQIE, UPALM, Zacatenco, C.P. 07738, Mexico, D.F., Mexico 2. Dios Sol 69, Seccion Parques, C.P. 54720, Cuautitlan Izcalli, Estado de Mexico, Mexico
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Abstract: | This work investigated the chemical and mineralogical properties of CaO–SiO2–Cr2O3–CaF2–MgO slags. Synthetic slags were prepared and the effect of the slag basicity (mass ratio CaO/SiO2) and MgO contents on the stability of the mineralogical species formed was analyzed. The morphology and composition of the slags were analyzed by X-ray powder diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM–EDS), whilst their chemical stability was evaluated by leaching with an aqueous acetic acid solution. It was found that in slags with CaO/SiO2?=?1, the main Cr-compound was MgCr2O4 spinel, which forms octahedron crystals. Small amounts of CaCr2O4 and CaCrO4 were also observed. It was found that with increasing the slag basicity from 1 to 2 the compounds MgCr2O4 and CaCr2O4 were formed together with the Cr(V)-containing compound complex Ca5(CrO4)3F which forms hexagonal crystals. The results showed that the highest Cr concentration levels in the leaching liquors corresponded to slags with CaO/SiO2?=?2, probably owing to the formation of CaCrO4 and Ca5(CrO4)3F, whilst the lowest chromium concentration levels corresponded to MgO-based slags owing to the stable binding of chromium in spinel with MgO. Additionally, potential–pH diagrams for the Ca–Cr–H2O and Mg–Cr–H2O systems at 25?°C were calculated. |
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