Effect of MgO and CaO/SiO sub(2) on the immobilization of chromium in synthetic slags

• Published in: Journal of material cycles and waste management Vol. 14; no. 4; pp. 317 - 324
• Main Authors: Cabrera-Real, Hugo, Romero-Serrano, Antonio, Zeifert, Beatriz, Hernandez-Ramirez, Aurelio, Hallen-Lopez, Manuel, Cruz-Ramirez, Alejandro
• Format: Journal Article
• Language: English
• Published: 01.10.2012
• Subjects: Leaching; Morphology; Spectroscopy
• ISSN: 1438-4957; 1611-8227
• DOI: 10.1007/s10163-012-0072-y

This work investigated the chemical and mineralogical properties of CaO-SiO sub(2)-Cr sub(2)O sub(3)-CaF sub(2)-MgO slags. Synthetic slags were prepared and the effect of the slag basicity (mass ratio CaO/SiO sub(2)) 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/SiO sub(2) = 1, the main Cr-compound was MgCr sub(2)O sub(4) spinel, which forms octahedron crystals. Small amounts of CaCr sub(2)O sub(4) and CaCrO sub(4) were also observed. It was found that with increasing the slag basicity from 1 to 2 the compounds MgCr sub(2)O sub(4) and CaCr sub(2)O sub(4) were formed together with the Cr(V)-containing compound complex Ca sub(5)(CrO sub(4)) sub(3 )F which forms hexagonal crystals. The results showed that the highest Cr concentration levels in the leaching liquors corresponded to slags with CaO/SiO sub(2) = 2, probably owing to the formation of CaCrO sub(4) and Ca sub(5)(CrO sub(4)) sub(3 )F, 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-H sub(2)O and Mg-Cr-H sub(2)O systems at 25 degree C were calculated.