CO–H2 Gas-Based Reduction Behavior of Cr-Rich Electroplating Sludge Mixed with Iron Ore Powder

Abstract

Cr-rich electroplating sludge (CRES) is a complicated solid waste with high contents of chromium and iron. It can be used as a main feed of the FINEX ironmaking process, which requires gas-based reduction before smelting reduction to produce molten iron with the proper addition of iron ore powder. In this study, the CO–H2 gas-based reduction behavior of CRES mixed with iron ore powder was evaluated between 700 °C and 850 °C, with a focus on the variations of key components containing Fe, Cr, and S with reduction temperature and time. It was found that the iron oxides in CRES had stepwise conversions to metallic iron as the reduction reaction proceeded. The iron metallization degree of the mixture of CRES and iron ore powder increased obviously below 750 °C and then grew minorly with the further increase of temperature. Moreover, this index varied similarly with an extension of reduction time up to 80 min. After reduction at 750 °C for 60 min with the volume concentration of H2 of 30% and flow rate of 160 mL/min, the iron metallization degree reached 79.08%. The rate in the process was limited by a chemical reaction with an activation energy of 41.32 kJ/mol. Along with the stepwise reduction of iron oxides to metallic iron, the chromium hydroxide and sulfates in CRES were reduced to Cr2O3 and sulfites and sulfides, respectively.