Phase equilibria in MgO-containing ferro-nickel smelting slags

Shengqi Chen (2005). Phase equilibria in MgO-containing ferro-nickel smelting slags PhD Thesis, School of Engineering, The University of Queensland.

       
Attached Files (Some files may be inaccessible until you login with your UQ eSpace credentials)
Name Description MIMEType Size Downloads
THE18402.pdf Full text application/pdf 87.18MB 2
Author Shengqi Chen
Thesis Title Phase equilibria in MgO-containing ferro-nickel smelting slags
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2005
Thesis type PhD Thesis
Supervisor Prof Peter C. Hayes
A/Prof Evgueni Jak
Total pages 317
Language eng
Subjects 09 Engineering
L
Formatted abstract

Phase equilibria have been experimentally determined in the MgO-"FeO"-SiO2- Al2O3-Cr2O3 system relevant to Cerro Matoso S. A. (CMSA) nickel smelting slags. The research studies are mainly focused on determination of the liquidus in these complex smelting slags. The studies involve the use of advance research techniques involving equilibration, modified rapid quenching techniques and electron probe Xray microanalysis (EPMA) measurements. 

The following phase equilibrium investigations have been carried out:

1.    Microstructural characterization of CMSA slags and determination of liquidus temperature of industrial slags by laboratory testwork. 

2.    Phase equilibria studies on MgO-containing binary systems. 

3.    Solid solution studies in M2SiO4 (M = Ca, Mg, and Fe) systems. 

4.    MgO-"FeO"-SiO2 system in equilibrium with metallic iron.

5.    MgO-"FeO"-SiO2-Al2O3 system with 2, 3 and 5 wt% Al2O3 in equilibrium with metallic iron. 

6.    MgO-"FeO"-SiO2-Al2O3-Cr2O3-CaO-MnO system with 2 wt% Cr2O3, 2 wt% Al2O3 + 2 wt% Cr2O3 and industrial slag composition in equilibrium with metallic iron.

7.   Comparisons of the experimental data with thermodynamic calculations undertaken using the FactSage 2004 program and slag databases. 


The liquidus temperature of "as received" CMSA slag was determined using controlled equilibration quenching and metallography techniques to be between 1535 and 1540°C. The additions of 1 and 3 wt% Al2O3 to this CMSA slag decrease the liquidus temperatures of the slag by approximately 40 and 100°C respectively. 

Experimental studies have been carried out on the binary systems of MgO-SiO2, MgO-Al2O3, MgO-CaO, and MgO-Fe2O3 in air in selected conditions. The results of the present investigation have resolved the inconsistencies in the phase diagrams reported previously for these systems. In the MgO-SiO2 system, it has been shown that there is no solid solution of Mg2SiO4 in MgO. New experimental data were obtained in the SiO2 primary phase field of this system. The experimental results obtained in the systems of MgO-Fe2O3 and MgO-CaO in air confirmed sub-solidus phase equilibria reported in the literature. In the MgO-Al2O3 system, the spinel phase is found to present as stoichiometric compound with no excess solubility of MgO.

Solid solution studies in the systems of Mg2SiO4-Ca2SiO4, Ca2SiO4-Fe2SiO4 and Mg2SiO4-Fe2SiO4 were undertaken. No MgO solid was found in the Mg2SiO4- Ca2SiO4 pseudo-binary system. The liquidus and solidus in the Mg2SiO4-Fe2SiO4 pseudo-binary join in equilibrium with metallic iron are in good agreement with those reported by Bowen and Schairer (1935). The extensive solid solutions of Ca2SiO4 were found in the Ca2SiO4-Fe2SiO4 system. 

In the MgO-"FeO"-SiO2 system in equilibrium with metallic iron, over 200 new data points have been determined to accurately determine the liquidus isotherms and sub-liquidus tie lines in the MgO-"FeO"-SiO2 system. The experiments have been carried out in the silica, pyroxene and olivine primary phase fields at temperatures between 1250-1625°C. The maximum temperature reported in previous investigations of this system is 1500°C. It has been found that present results on the liquidus in the cristobalite (SiO2) primary phase field are in good agreement with those reported by Bowen and Schairer (1935) up to 1500°C. However there are some significant disagreements on the liquidus temperatures and position of the phase boundary between olivine and magnesiowustite between the present work and previous investigation. The new experimental data were obtained in the silica and olivine primary phase fields relevant to CMSA slags region. In the silica primary phase field, at fixed ratio of SiO2/MgO with increase of concentration of 1 wt% FeO, there is a gradual decrease of liquidus temperature by approximately 10-12°C. For a fixed MgO/FeO ratio with increase in 1 wt% Si02 concentration there is an increase in liquidus temperature by approximately 23-35°C. In the olivine primary phase field, at fixed MgO/FeO ratios with increase in 1 wt% SiO2 concentration, there is a gradual non-linear decrease of liquidus temperature by approximately 8-20°C. 

The liquidus surface in the silica primary phase field in the MgO-"FeO"-SiO2-Al2O3 system in equilibrium with metallic iron have been experimentally determined forAl2O3 contains 2, 3 and 5 wt% in the slag. The results are presented in the form of ternary sections MgO-"FeO"-SiO2 at fixed Al2O3 concentrations. It has been found that at fixed SiO2/MgO/FeO in the silica primary phase field an increase in Al2O3 concentration of 2, 3 and 5 wt% decreases the liquidus temperature in the MgO- 'TeO"-SiO2-Al2O3 system by approximately 60, 100 and 200°C respectively. At fixed MgO/FeO ratio, an increase in SiO2 concentration of 1 wt% increases the liquidus temperature in the silica primary phase field by 23-40, 19-36, and 17-46°C, for slags containing 2, 3 and 5 wt% Al2O3 respectively. At fixed SiO2/MgO ratio, an increase in FeO concentration of 1 wt% decreases the liquidus temperature in the silica primary phase field by 10-17, 11-25, and 13-20°C for slags containing 2, 3 and 5 wt% Al2O3 respectively. In olivine primary phase field, the liquidus temperatures are decreased by approximately 25 and 50°C for 2 and 3 wt% Al2O3added respectively. 

The liquidus surface in the MgO-"FeO"-SiO2-Al2O3-Cr2O3 system in equilibrium with metallic iron have been experimentally determined for 2 wt% Cr2O3 and 2 wt% Al2O3 + 2 wt% Cr2O3 respectively. The results are presented in the form of ternary sections MgO-"FeO"-SiO2 at fixed Al2O3 and Cr2O3 concentrations. It has been found that the liquidus temperature of slags are decreased by approximately 35 and 75 °C for 2 wt% Cr2O3, 2 wt% Al2O3 + 2 wt% Cr2O3 added respectively. The liquidus surface in the silica primary phase field of the MgO-"FeO"-SiO2-Al2O3- Cr2O3-CaO-MnO system in equilibrium with metallic iron have been experimentally determined for other elements contain with the same CMSA slag. The results are presented in the form of ternary section MgO-"FeO"-SiO2 at fixed Al2O3, Cr2O3, CaO, and MnO concentrations. The liquidus temperatures were decreased by approximately 100°C due to the presence of those other elements. 

Thermodynamic predictions using FactSage model 2004 were carried out in the slag system (MgO-"FeO"-SiO2-Al2O3), and compared with the new experimental data obtained in the present investigation. The data from present study were included in the new FactSage optimisations as part of a collaborative project. 

Keyword Slag
Smelting
Metallurgy

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
 
Citation counts: Google Scholar Search Google Scholar
Created: Wed, 13 Jun 2012, 16:00:34 EST by Erica Wei on behalf of Scholarly Communication and Digitisation Service