EFFECT OF THE COMPOSITION ON THE IMMOBILIZATION OF CHROMIUM IN SLAGS

摘要

Chromium containing slags from stainless steelmaking may eventually be leached by acidicenvironments, therefore they should be treated before being stockpiled or land filled. In this work, synthetic slags were prepared and the effect of CaO/SiO_2, Cr_2O_3, MgO and AI_2O_3 contents on the stability of the mineralogical species formed was analyzed. The morphology and composition of the slags were analyzed by XRD and SEM-EDS, whilst their chemical stability was evaluated by leaching with an aqueous acetic acid solution. It was found that CaCr_2O_4 and CaCrO_4 are present in slags prepared with neither MgO nor AI_2O_3. The Al_2O_3-based slags mainly produced Ca2Al2SiC>7 and the Cr(VI)-containing oxide complex Ca_4Al_6CrO_(16), whilst MgO-based slags produced MgCr_2_O_4 as main mineralogical species. Additionally, Eh-pH diagrams for the Ca-Cr-H_2O and Mg-Cr-H_2O systems at 25 °C were constructed. The lowest Cr concentration levels in the leaching liquors corresponded to MgO-based slags owing to the stable binding of Cr in spinel with MgO. It was also observed in the Al_2O_3-based slags that increasing the slag basicity from 1 to 2 the leachability of the slags are notably increased.