Electrochemical Behavior Of Electroactive Ions In Molten Slag Containing FeO

Iron electrowinning in molten slag containing iron oxide by using inert anode is apotential breakthrough steelmaking technology which may reduce the CO2emissions. Inorder to formulate the suitable green electrolytic process parameters, it is necessary tomaster the electrochemical behavior of iron ions and oxygen ions in molten slagelectrolyte. But the systematic research on these aspects has been less reported so far.ZrO2based solid electrolyte has high oxygen ionic conductivity, low electronicconductivity property and strong slag corrosion resistance at high temperature. The cellconstructed by ZrO2based solid electrolyte has been widely used in metallurgicalindustry and scientific research. In recent years, it is further applied to new techniquesin the metallurgy with controlled oxygen flow. In addition,Pt,O2(air)|ZrO2referenceelectrode is also used in many electrochemical measurements with the three electrodesystem. Based on these characteristics of the solid electrolyte cell, an one-end-closedMgO or Y2O3stabilized ZrO2solid electrolyte tube was acted as the isolation membraneof working electrode, counter electrode and the cell container, and an electrolytic cellwith controlled oxygen flow and Pt,O2(air)|ZrO2reference electrode was constructedintegrally. Various of electrochemical techniques such as cyclic voltammetry,chronopotentiometry, square wave voltammetry and constant potential electrolysis wereused to study the electrochemical behavior of electroactive ions in the SiO2-CaO-Al2O3-MgO-FeO molten slag.According to the comparison of some preliminary tests of the electrolytic cell andthe theoretical calculation of Factsage6.1thermodynamic software, a more appropriateelectrolytic cell device with controlled oxygen flow was selected and someelectrochemical test parameters were optimized. The results showed that it was feasibleto study the electrochemical behavior of electroactive ions by using the new tubularelectrolytic cell with controlled oxygen flow. The different stabilizers of ZrO2basedsolid electrolyte had no appreciable effect on the electrochemical test. Test results also indicated that the reduction of Fe2+in the molten slag containing5wt%FeO was an irreversible process in the range of1683to1723K. But when thetemperature was raised to1773K, the reduction of Fe2+turned into a reversible proces.According to the calculation results, the diffusion coefficient value of Fe2+was rangedfrom (3.05±0.05)×10-6cm2s-1to (4.35±0.04)×10-6cm2s-1in1683~1773K and itincreased with a rising of temperature. According to the diffusion coefficients atdifferent temperatures, the activation energy of Fe2+diffusion was about97.27±16.54kJ mol-1. At1723K, the reduction of Fe2+in the molten slag containing3~10wt%FeOwas an irreversible process. The diffusion coefficient value of Fe2+decreased with theincreasing of Fe2+concentration and then remained stable.The oxidation of Ir electrode could be observed at the positive potential, but itsoxide was not stable. When the potential was more positive than the oxidation of Ir,oxygen ion would be oxidated on the working electrode. Oxygen gas was evolution atthe working electrode, which could cause drastic fluctuation of electrochemical curve.However, oxidation peak of oxygen ion was not observed. It showed that the oxygenions moved quickly in the molten slag and teh ZrO2solid electrolyte. The moving ofoxygen ions would not be a controlled step of the reaction and it also would notinterfere with the electrochemical measurement of working electrode.