The Related Basic Research On Reduction With Controlled Oxygen Flow

The reduction method with controlled oxygen flow is a green metallurgical methods. The reaction produces oxygen at anode and absolutely avoids the emissions of greenhouse gases such as CO₂. The method had not only important meaning in setting up a new metallurgical process, but also provided with a new way to reclaiming valuable metals from waste slags in metallurgy.High added-value products might obtain by this method. This paper studied about several important parameters of reduction with controlled oxygen flow by experiment,and made an attempt on directly extraction of iron from molten oxide slags containing FeO though this technology .The variation plot of the conductivity of 2.18% MgO-stabilized zirconia tube with temperature in air was measured by DC four-electrode technique at the temperature range from 1473K to 1873 K. The results showed the conductivity varied from2.0×10-2～5.0×10-1S?cm-1 at the temperature range from 1473K to 1873K during heating process. The variation plot of the conductivity might divide into three parts. At the temperature range from 1473K to 1673K, and from 1773K to 1873K, it was found that the temperature dependence of the conductivity can be expressed by an Arrhenius equation. Thereinto, the tetragonal to the cubic phase likely occurred above 1673K, which led to the jumps at conductivity. The conductivity could arrive to 0.5 S.cm-1 at the temperature of 1873 K, which could definitely satisfy the process of metallurgy with controlled oxygen flow with the conductivity request.In the present study the diffusivities of oxygen in liquid silver in the temperature range of 1473 to 1773 K were determined by potentiostatic method, in which the cylindrical-like zirconia base solid electrolyte cell arrangement, (+)Pt|air|ZrO₂(MgO)|[O]Ag(l)|Ir(–), was employed. The diffusivity of oxygen (Do) in liquid silver becomes biger with increasing temperature. Least square treatment of the results gave the following relation, (?)In this paper, the diffusivity of oxygen in liquid iron at the temperature from 1823K to 1873K is measured by potentiostatic method, in which the cylindrical-like zirconia base solid electrolyte cell arrangement was employed. The form of the battery using Lanthanum Chromite for the electrode lead wire as follows: Pt | Air| ZrO₂(CaO)| [O]Fe| LaCrO3. Their relationships between conductivity and temperature are given as follows . (?)we can known that the diffusivity of oxygen in liquid iron is gradually larger with increasing temperature. The tentative experiment indicated that using Lanthanum Chromite for the electrode lead wire in liquid iron could gain a steady signal.The method using four-probe electrode with galvanostatic electrochemical impedance spectroscopy(GEIS)by PARSTAT2273 synthetical electrochemistry analysis instrument was applied to measure the conductivity of CaO-SiO₂-Al₂O₃-MgO-FeO slag system.This paper discussed the influences of such factors as the current frequency,inserting depth of probe,solution depth,the best AC value and the two-dimensional eccentricity of the electrode containing four probes on the measuring result as taking KCl as the calibration solution at room temperature. Basing these factors,the experimental results about measuring conductivity of slag suggest that the conductivity of slag is gradually larger with increasing temperature in any composition. The conductivity of slag is also larger,the temperature coefficient decreases and the activation energy decreases as the content of iron oxide in slag increases .Took example for extraction of iron from molten oxide slags containing FeO,this study reduced with controlled oxygen flow under the external voltage by constructing of solid oxygen ion conductor battery:Ir|[O] Ag|ZrO₂(MgO)|FeO(slag)|Fe, with Ag as the anode, pure iron bar as the cathode, and ZrO₂ (MgO) tube as an oxygen ion conductor. Based on experimental study,a new elecrtochemical reaction kinetics model under the external voltage was derived for describing the process of elecrtochemical reduction. The experimental results showed FeO in molten slags might be reduced by reducing with controlled oxygen flow. The study also educed that the higher the applied voltage is and the larger the external circuit current is, the faster the reduction is. So applied voltage could significantly promote the reduction of FeO in slag.In this study Ag liquid as the anode can be recycled and it is possible to build a new and green short metallurgical process. With ZrO₂ (MgO) tube as an oxygen ion conductor,this technology can avoid production being polluted by reducer rather than traditional contact reduction such as traditional melt reduction,and can gain pure metal. This technology is not only used to extract of iron,but only to work out other valuable metals and refrctory metals.