We investigated the effect of flux (lime) addition on the reduction behavior of iron oxide in copper slag by solid carbon at 1773 K (1500 °C). In particular, we quantified the recovery of iron by performing typical kinetic analysis and considering slag foaming, which is strongly affected by the thermophysical properties of slags. The iron oxide in the copper slag was consistently reduced by solid carbon over time. In the kinetic analysis, we determined mass transfer coefficients with and without considering slag foaming using a gas holdup factor. The mass transfer of FeO was not significantly changed by CaO addition when slag foaming was ignored, whereas the mass transfer of FeO when slag foaming was considered was at a minimum in the 20 mass pct CaO system. Iron recovery, defined as the ratio of the amount of iron clearly transferred to the base metal ingot to the initial amount of iron in the slag phase before reduction, was maximal (about 90 pct) in the 20 mass pct CaO system. Various types of solid compounds, including Mg2SiO4 and Ca2SiO4, were precipitated in slags during the FeO reduction process, and these compounds strongly affected the reduction kinetics of FeO as well as iron recovery. Iron recovery was the greatest in the 20 mass pct CaO system because no solid compounds formed in this system, resulting in a highly fluid slag. This fluid slag allowed iron droplets to fall rapidly with high terminal velocity to the bottom of the crucible. A linear relationship between the mass transfer coefficient of FeO considering slag foaming and foam stability was obtained, from which we concluded that the mass transfer of FeO in slag was effectively promoted not only by gas evolution due to reduction reactions but also by foamy slag containing solid compounds. However, the reduced iron droplets were finely dispersed in foamy and viscous slags, making actual iron recovery a challenge.

Effect of CaO Addition on Iron Recovery from Copper Smelting Slags by Solid Carbon

The thermodynamic descriptions for all the stable phases in the Fe-Sn system are obtained by a least-square optimisation of the thermochemical and the phase diagram data from literature. The latest recommended of expressions for Gibbs energies of pure elements are used. The calculated phase diagram and thermochemical properties are compared with the experimental data.

Thermodynamic evaluation of Fe-Sn phase diagram

The isothermal experiment of carbothermic reduction of chromium oxide was carried out. The reduction rate increased by increasing temperature, using a moderate carrier gas flow rate and the fine graphite particles. XRD analysis revealed that Cr 3 C 2 , Cr 7 C 3 , Cr 23 C 6 and Cr were formed in turn as the reaction products at 1 673 K. The relation among the products, reduction temperature and time was summarized from the XRD results at the temperature range from 1373 to 1 673 K. It is confirmed that the reduction contains various kinds of reactions, such as direct reduction, indirect reduction of chromium oxide, the carbon solution loss reaction and the reaction of chromium carbide with carbon dioxide. At the initial stage of reduction, the direct reduction dominates the reduction rate. At the later stage of reduction, because of the chromium carbide layer formed on the surface of graphite particles and rather slow reduction rate, the rate-controlling step is deduced to be CO and CO 2 gas diffusion through the layer of reduction products.

Mechanism of Carbothermic Reduction of Chromium Oxide

Sn–Bi–Fe thermodynamic modeling and Sn–Bi/Fe interfacial reactions

The present study experimentally investigates the effect of Cr2O3 on the viscosity of molten slags. The viscosities of CaO-SiO2-10 pct Al2O3-Cr2O3 quaternary slags with two different binary basicities (R, basic slag with R = 1.2 and acidic slag with R = 0.8) were measured by the rotating cylindrical method from 1813 K to 1953 K (1540 °C to 1680 °C). The results showed that the viscosity of both types of slag decreased as the Cr2O3 content increased, but the viscosity of acidic slags exhibited a greater decrease. The slags showed good Newtonian behavior at such high temperatures. Cr2O3 could act as a network modifier to simplify the Si-O-Si tetrahedral structure, as verified by the Raman spectral analysis, which was consistent with the decreasing trend of viscosity. The activation energy of viscous flow decreased slightly with increasing Cr2O3, but increasing the basicity seemed to be more effective in decreasing the viscosity than adding Cr2O3.

Effects of the Cr 2 O 3 Content on the Viscosity of CaO-SiO 2 -10 Pct Al 2 O 3 -Cr 2 O 3 Quaternary Slag

https://www.jstage.jst.go.jp/article/tetsutohagane1955/88/12/88_12_838/_pdf

Effect of Slag Properties on Reduction Rate of Chromium Oxide in Cr2O3 Containing Slag by Carbon in Steel

Equilibrium Distribution of Sn between Solid and Liquid Phases in Fe-Sn and Fe-C-Sn Alloys

PROBLEM TO BE SOLVED: To provide an elution testing method that allows measurement of an elution amount of a component having elution property from an inorganic substance such as steel making slag with higher accuracy in shorter time.SOLUTION: In an elution testing method that measures an elution amount of a component eluted from a specimen immersed in water, a solid inorganic substance that is the specimen is pulverized using a pulverizer capable of free pulverizing and continuous pulverizing so as to achieve a grain size in a range of 2 mm or smaller. The pulverized inorganic substance is immersed in immersion water of room temperature to max. 90°C so that components having elution property is eluted. Among the eluted components having elution property, the elution amount is measured with respect to at least one component selected from a group constituted of lead, chromium hexavalent, cadmium, arsenic, selenium, fluorine and boron.

Elution testing method

PROBLEM TO BE SOLVED: To provide a method capable of stably reducing the dust producing quantity in a high carbon concentration region at the first half period of the refining, and also stably suppressing the chromium oxidizing quantity at the ending period of the refining when producing a chromium-based stainless steel by a decarbonization refining process. SOLUTION: When smelting the chromium-based stainless steel having 10 mass% to 3 /hr to 3 /hr per one ton of molten steel, and at the time when the decarbonization proceeds in the range of ≤2% to ≥0.5% carbon concentration, the top-blowing oxygen flowing quantity is reduced so as to become in the range of 75 Nm 3 /hr to 3 /hr per one ton of molten steel, and the distance LG between the top end of the lance and the standstill surface of the molten iron is adjusted so that the L/L 0 of molten iron recessed depth L to the top blowing oxygen jet and the molten iron depth L 0 is in the range of 0.2-0.5 through the refining. COPYRIGHT: (C)2009,JPO&INPIT

Decarbonization refine method for chromium-based stainless steel

PURPOSE:To produce molten steel having low N content by efficiently executing reduction- refining of molten steel with stirred small grain Al with inert gas under the reduced atmospheric pressure after executing decarburize-refining by oxygen-blowing refining of the molten steel in the low vacuum range and finish refining under the reduced atmospheric pressure. CONSTITUTION:At the time of producing a low carbon stainless steel by executing the decarburize-refining to a raw high Cr steel with a VOD method, at first C in the molten steel is oxidized by the oxygen-blowing in the low vacuum atmosphere to execute the decarburization, and in order to lower further C content, the oxygen-blowing is executed in the low CO partial pressure at =400W/ton of molten steel to stir the molten steel. On the stirred molten steel surface, the small grain Al having <=30mm grain diameter is added to reduce the oxide of Cr, etc., produced by oxygen-blowing. As this operation is executed in the high vacuumn atmosphere, absorbing action of nitrogen from the air is not executed and the extra low N stainless steel can be produced.

Toshitaka Yuki

Papers

Effect of Slag Properties on Reduction Rate of Chromium Oxide in Cr2O3 Containing Slag by Carbon in Steel

Equilibrium Distribution of Sn between Solid and Liquid Phases in Fe-Sn and Fe-C-Sn Alloys

Elution testing method

Decarbonization refine method for chromium-based stainless steel

Method for melting low n steel in vacuum refining furnace