USO DE FeS2 EN LA ESTABILIZACIÓN QUÍMICA DEL CROMO EN ESCORIAS SIDERÚRGICAS

Abstract

Chromium containing slags from stainless steelmaking may eventually be leached by acidic environments, therefore they should be treated before being stockpiled or have contact with the environment. In this work, synthetic chromium-based slags were prepared and the effect of the slag basicity (CaO/SiO2), FeS2 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 slag with CaO/SiO2 = 1 shows the garnet Fe3Cr2Si3O12, while in the slag with basicity CaO/SiO2 = 2 shows CaCr2O4, Cr2O3, and FeS•Cr2S3 FeCr2O4, where chromium is trivalent Cr3+. The other chromium species formed in both kinds of slags were Ca5Cr2SiO12, Cr3S4 and CaCrSi4O10. Pyrite (FeS2) was the chemical agent that minimized the slag leachability since the iron of this compound behaved as a reducing agent. The addition of FeS2 in the slags markedly decreased the amount of chromium leached values, even lower than that required by the Mexican hazardous norm which is 5 ppm Cr This behavior is associated with the formation of the Fe-Cr and Cr-S compounds; Cr3S4 and Fe3Cr2Si3O12 in slags with CaO/SiO2 = 1 and Cr3S4, FeCr2O4 and FeS•Cr2S3 in slags with CaO/SiO2 = 2. Potential-pH diagrams were calculated for different Cr-H2O system at 25 °C. It was observed that the compounds formed in the slags with FeS2 had wider stability in acid regions that those of the Ca-Cr-O compounds which were formed in slags without FeS2.