Redox equilibria and kinetics of gas-slag reactions

Self Cite

The distribution of arsenic between calcium ferrite slag and liquid silver (wt pct As in slag/ wt pct As in liquid silver) with 22 wt pct CaO and between iron silicate slag with 24 wt pct SiO 2 and calcium iron silicate slags was measured at 1573 K (1300°C) under a controlled CO-CO 2 -Ar atmosphere. For the calcium ferrite slags, a broad range of oxygen partial pressure (10 -11 to 0.21 atm) was covered, whereas for the silicate slags, the oxygen partial pressure was varied from 10 -9 to 3.1 9 10 -7 atm. The measured relations between the distribution ratio of As and the oxygen partial pressure indicates that the oxidation state of arsenic in these slags is predominantly As 3+ or AsO 1.5 . The measured distribution ratio of arsenic between the calcium ferrite slag and the liquid silver was about an order of magnitude higher than that of the iron silicate slag. In addition, an increasing concentration of SiO 2 in the calcium-ferrite-based melts resulted in decreases in the distribution of arsenic into the slag. Through the use of measured equilibrium data on the arsenic content of the metal and slag in conjunction with the composition dependent on the activity of arsenic in the metal, the activity of AsO 1.5 in the slags was deduced. These activity data on AsO 1.5 show a negative deviation from the ideal behavior in these slags.

Section: Discussionmentioning

confidence: 99%

Thermodynamics of Arsenic in FeOx-CaO-SiO2 Slags

Chen

Jahanshahi

2010

Self Cite

“…[18][19][20][21][22] Therefore, direct measurements of the FeO activity of CaO-SiO 2 -Al 2 O 3 -IN bath smelting, the rate of reduction is proportional to MgO sat -Fe t O slags, equilibrated with liquid iron, are the FeO content of the slag in the smelter. The sulfur content required.…”

Section: Introductionmentioning

confidence: 99%

Measurement of FeO activity and solubility of MgO in smelting slags

Liu

Fruehan

Morales

et al. 2001

In bath smelting, the FeO activity of the slag must be known to predict the equilibrium of slag-metal reactions and for effective control of the rate of reduction in the system. Also, knowledge of the solubility of MgO in these slags is useful for reducing refractory consumption. A series of measurements of the FeO activity in simulated bath smelting slags (CaO-SiO 2 -Al 2 O 3 -MgO sat -FeO) were conducted by the electromotive force (EMF) technique. The influence of the slag composition on the relationship between the FeO activity coefficient and FeO content was studied. It has been found that the measured FeO activity coefficient decreases with increasing FeO content in the slag and increases slightly with increasing slag basicity, which is defined as (CaO ϩ MgO)/(SiO 2 ϩ Al 2 O 3 ) on a mole fraction basis.The measured values of the FeO activity coefficient are in reasonable agreement with previously published data. The solubility of MgO was also measured and found to range from 16 to 30 pct and decrease with increasing basicity.

“…This is thought to be due to relatively low concentrations of Fe 21 in these samples, which contain 5 wt pct FeO x and were pre-equilibrated in air. Based on these data and a review of published data on redox equilibria in basic slags under oxidizing atmosphere, [18] the authors concluded that the predominate oxidation state of iron in these slags is Fe 31 with very low levels of Fe 21 . Mn 31 and Mn 41 are not very stable at high temperatures, and according to the published redox equilibria data, [19] the Mn 31 /Mn 21 should be about 0.2 in the slags studied at about 1500°C in air.…”

Section: Resultsmentioning

confidence: 99%

Effects of additives and temperature on dissolution rate and diffusivity of lime in Al2O3-CaO-SiO2 based slags

Amini

Brungs

Ostrovski

et al. 2006

The dissolution rate of dense lime specimens in calcium aluminosilicate based melts was measured at 1430°C to 1600°C in air, using a rotating disk/cylinder technique. The measured dissolution rates were strongly dependent on the rotation speed with the results indicating mass transfer in the slag phase to be a rate-limiting step. At a given rotation speed, the slag chemistry and temperature had strong effects on the dissolution rate. The diffusivity of CaO in the slag was calculated from the dissolution rate and solubility data, using known mass-transfer correlations. Addition of CaF 2 MnO x , FeO x , and TiO 2 to the slag increased the CaO diffusivity, while SiO 2 had an opposite effect. Addition of CaF 2 had the strongest effect and increased the diffusivity by a factor of 3 to 5 in the temperature range of 1500°C to 1600°C. The deduced activation energy for diffusion of CaO in these slags ranged from about 53 to 246 kJ/mole, depending on the concentration of additives used.