Phase equilibria and thermodynamic modeling of the Cu-Fe-Sn-O-SiO2 system
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School of Chemical Engineering |
Master's thesis
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en
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98
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Abstract
The rapid growth of electronic waste (e-waste) generation has become a global concern, prompting continuous efforts to improve its treatment and material recovery. One of the key metals of interest for recovery from e-waste is tin. Because primary tin ore deposits are geographically concentrated, tin is classified as a critical raw material in some countries. Furthermore, the high market value of tin makes tin recovery from e-waste economically attractive. Among the available recycling routes, black copper smelting is considered one of the most promising methods, where tin recovery occurs during the slag cleaning stage. In this study, the equilibration-quenching-electron probe microanalysis method was employed to investigate the phase equilibria of the Cu-Fe-Sn-O-SiO₂ system. Thermodynamic simulations were also performed using available databases in FactSage and MTDATA. Two types of slags were used in the experiment, iron-saturated slag and iron-silica-saturated slag. Experiments were conducted at 1200 °C, 1250 °C, and 1300 °C, with tin concentrations in the copper-tin alloy varied from 2.5 wt% to 20 wt%. Comparison of the experimentally determined compositions with the Cu-Fe-Sn ternary diagram generated using the FSstel database in FactSage revealed discrepancies in the liquid alloy phase equilibrium line, indicating the need for further optimization of the liquid phase. Additionally, simulations using the MTOX database in MTDATA provided the estimation of the prevailing oxygen partial pressure, a key factor in many pyrometallurgical processes, that was not possible to be directly measured or controlled in the closed system used in this study. The tin concentration in the studied system did not significantly influence the prevailing oxygen partial pressure. However, the effect of tin on oxygen partial pressure can be calculated with minor approximations from the experimental data. Whereas temperature had a clear effect on the oxygen partial pressure. Evaluation on the metal-slag distribution coefficient revealed that tin recovery improves at lower Sn concentrations in the alloy and at reduced temperatures. This contrasts with the reports suggesting higher temperatures enhance the recovery. The discrepancy might arise because oxygen partial pressure was not independently controlled in this study, but varied with temperature in a closed system, affecting Sn behavior and its distribution between metal and slag.Description
Supervisor
Lindberg, DanielThesis advisor
Jeon, JunmoAvarmaa, Katri