Study On Electrochemical Behavior Of Ni²⁺ In Molten Slag

Electrolyzing slag containing iron oxide is a potential breakthrough technology forsteelmaking to reduce the emission of CO2. It is possible to refine nickel-containing steelincluding stainless steel to electrolyze molten slag containing nickel and iron oxide withinert electrode. Behavior of nickel oxide in molten slag at high temperature is veryimpotant to establish technique parameters about eletrolyzing molten slag for extractingNi. ZrO2base solid oxide electrolyte has high conductivity of O2-, low electronicconductivity, and strong anti-erosion ability, the electrolytic cell built of which is widelyapplied in metallurgical industry and scientific research. Moreover, there are so manyresearches on electrochemical test with Pt, O2(air)|ZrO2as referece electrode. In thisthesis, on the basis of theory about controlled oxygen flow, a new electrolytic cell wasconstructed integrally with solid electrolyte tube of one-end-closed magnesia partiallystabilized zirconia (MSZ) which was used as container of electrolytic cell and isolatingmembrane between cathodic and anodic zone and Pt, O2(air)|ZrO2was used as referenceelectrode of the cell. The electrolytic cell constructed with solid electrolyte of MSZ wasapplied to investigate electrochemical behavior of Ni2+in SiO2-CaO-MgO-Al2O3moltenslag by means of electrochemical techniques such as cyclic voltammetry (CV), squarewave voltammetry (SWV), chronopotentiometry (CP), chronoamperometry (CA),potentiostatic electrolysis, which can expand application fields of controlled oxygen flowand solid electrolyte of ZrO2.In this thesis, the principle of electrochemical test in electrolytic cell with controlledoxygen flow was analysed, and some parameters of electrochemical test were optimizedby pre-experiment. In the assistance of Factsage software, it was confirmed that Ni2+exists in molten slag instead of Ni3+under the condition of present work. All of theseanalysesdemonstratethatitisfeasibletostudyelectrochemicalbehaviorofNi2+inmoltenslag with the aid of electrolytic cell built on MSZ solid electrolyte with a controlledoxygen flow.Through experimental curves’ analyses of above electrochemical techniques, thereduction of Ni2+on Ir electrode is found to be a reversible reaction with single step inthe molten slag containing3%NiO, and the rate of the process is diffusion controlled.Three diffusion coefficients of Ni2+derived from CV, CP and CA are (3.5±0.2)×10-6, (2.8±0.1)×10-6and (3.6±1.0)10-6cm2/s, respectively.The results of CV test for the molten slag with different concentrations of NiO at1673K show that diffusion coefficients of Ni2+calculated exhibit an increasing tendencywith increase of NiO concentration due to decrease of slag viscosity. All of diffusioncoefficients, derived from electrochemical curves (CV, CP and CA) for the molten slagcontaining3%NiO, increase with increasing temperature. Besides, Two diffusionactivationenergiesofNi2+derivedfromCVandCAare207.0±10.0and157.1±2.5kJ/mol,respectively.