Microscopic Study of Carbon Surfaces Interacting with High Carbon Ferromanganese Slag

Abstract

The interaction of carbon materials with molten slags occurs in many pyro-metallurgical processes. In the production of high carbon ferromanganese in submerged arc furnace, the carbothermic reduction of MnO-containing silicate slags yields the metal product. In order to study the interaction of carbon with MnO containing slags, sessile drop wettability technique is employed in this study to reduce MnO from a molten slag drop by carbon substrates. The interfacial area on the carbon substrate before and after reaction with slag is studied by scanning electron microscope. It is indicated that no Mn metal particles are found at the interface through the reduction of the MnO slag. Moreover, the reduction of MnO occurs through the contribution of Boudouard reaction and it causes carbon consumption in particular active sites at the interface, which generate carbon degradation and open pore growth at the interface. It is shown that the slag is fragmented to many micro-droplets at the reaction interface, potentially due to the effect on the interfacial energies of a provisional liquid Mn thin film. The rapid reduction of these slag micro-droplets affects the carbon surface with making deep micro-pores. A mechanism for the formation of slag micro-droplets is proposed, which is based on the formation of provisional micro thin films of liquid Mn at the interface.2

Reduction and Dissolution Behaviour of Manganese Slag in the Ferromanganese Process

“…The activation energy for Assmang charges is calculated to be 230 kJ/mol, significantly lower than that of Comilog charges (470 kJ/mol). This may explain why Comilog charges have significantly higher reduction rates at high temperature, as the activation energy is the factor showing the temperature dependency [20,21]. Table 5 illustrates the reported calculated activation energies for MnO reduction by carbon (solid or dissolved) from different studies.…”

Smelting separation behaviors and mechanisms of high-alumina rich-manganese ore obtained from metallic reduction and magnetic separation

“…researchers [10][11][12][13][14][15][16][17][18] studied and calculated equilibrium phase chemistry in the Al 2 O 3 -MgO-SiO 2 -CaO-MnO slag system. The slag basicity was optimized by flux addition to obtain the higher manganese recovery and qualified metal with slag containing Al 2 O 3 content at a range of 7.5 to 16.0 wt %, and an Al 2 O 3 /SiO 2 weight ratio of 0.2-0.5.…”

The Influence of Sulfur Content on the Carbothermal Reduction of SiMn Slag

“…The reported activation energy for the carbothermal reduction of MnO ranges from 332 to kJ/mol [7,8,28,29], and for the carbothermal reduction of SiO2, the range is 796-870 kJ/mol [22,25,30]. Therefore, the reduction of MnO and SiO2 is highly sensitive to temperature.…”

“…In recent decades, the kinetics of MnO reduction in the field of ferromanganese (FeMn) production processes, where solid MnO still exists, have been studied extensively [5][6][7][8]. In this process, the activity of MnO is hence much higher than in SiMn slag [5][6][7][8]. It has been observed that stirring has no effect on the kinetics of MnO reduction, while the reduction rate is highly sensitive to temperature.…”

“…The rate and extent of MnO reduction are affected by the slag chemistry, including concentrations of different oxides and trace elements. In a homogenous liquid slag, higher basicity was found to produce a higher reduction rate of MnO [6][7][8]. This finding could be due to the higher driving force given by the effect of CaO and MgO on the activity of MnO or by the effect these oxides have on the viscosity of the slag.…”