Dissolution windows for hydrometallurgical purification of metallurgical-grade silicon to solar-grade silicon: Eh-pH diagrams for Fe silicides

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Abstract

Potential vs. pH diagrams for the systems Fe-Si-(Cl -)-(F -)-H 2O were generated using the HSC5.0 software and applied to purification of metallurgical-grade silicon (MG-Si) by hydrometallurgical methods. The diagrams for the Fe-Si-H 2O system show that with increasing electrochemical potential (Eh) the order of appearance of Fe silicides is FeSi 2, FeSi, and Fe 3Si. Further, from a thermodynamic standpoint, Si in the Fe silicides (FeSi 2, FeSi, and Fe 3Si) would be easier to oxidize than Fe, due to the lower potentials of the corresponding silicides, compared with Fe. The early formation of SiO 2 during dissolution may prohibit or retard further dissolution of Fe, as verified by previous experimental results. This inhibitive effect is expected to increase with increasing Si content in the silicides. The diagrams for the Fe-Si-Cl --H 2O system indicate that dissolution of Fe silicides with relatively low Si content, such as FeSi and Fe 3Si, is enhanced by adding chloride ions to acidic solutions. In the presence of HF, formation of fluoro-complexes enlarges the stability domains of dissolved iron and silicon, which increase with increasing {F} and/or decreasing temperature. The trends obtained for the Fe-Si-F --H 2O system suggest that the dissolution of Fe silicides would be enhanced by decreasing temperature or removing FeF 2(s) (e.g.; via ultrasonication) during the leaching process.

Original languageEnglish (US)
Pages (from-to)178-186
Number of pages9
JournalHydrometallurgy
Volume127-128
DOIs
StatePublished - Oct 1 2012

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Silicides
Silicon
Purification
Dissolution
Leaching
Chlorides
Iron
Thermodynamics
Ions
Temperature

All Science Journal Classification (ASJC) codes

  • Industrial and Manufacturing Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

@article{ac82255e49dc45eab43a68c8e1897428,
title = "Dissolution windows for hydrometallurgical purification of metallurgical-grade silicon to solar-grade silicon: Eh-pH diagrams for Fe silicides",
abstract = "Potential vs. pH diagrams for the systems Fe-Si-(Cl -)-(F -)-H 2O were generated using the HSC5.0 software and applied to purification of metallurgical-grade silicon (MG-Si) by hydrometallurgical methods. The diagrams for the Fe-Si-H 2O system show that with increasing electrochemical potential (Eh) the order of appearance of Fe silicides is FeSi 2, FeSi, and Fe 3Si. Further, from a thermodynamic standpoint, Si in the Fe silicides (FeSi 2, FeSi, and Fe 3Si) would be easier to oxidize than Fe, due to the lower potentials of the corresponding silicides, compared with Fe. The early formation of SiO 2 during dissolution may prohibit or retard further dissolution of Fe, as verified by previous experimental results. This inhibitive effect is expected to increase with increasing Si content in the silicides. The diagrams for the Fe-Si-Cl --H 2O system indicate that dissolution of Fe silicides with relatively low Si content, such as FeSi and Fe 3Si, is enhanced by adding chloride ions to acidic solutions. In the presence of HF, formation of fluoro-complexes enlarges the stability domains of dissolved iron and silicon, which increase with increasing {F} and/or decreasing temperature. The trends obtained for the Fe-Si-F --H 2O system suggest that the dissolution of Fe silicides would be enhanced by decreasing temperature or removing FeF 2(s) (e.g.; via ultrasonication) during the leaching process.",
author = "Eunyoung Kim and Osseo-Asare, {Kwadwo Asare}",
year = "2012",
month = "10",
day = "1",
doi = "10.1016/j.hydromet.2012.05.013",
language = "English (US)",
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journal = "Hydrometallurgy",
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TY - JOUR

T1 - Dissolution windows for hydrometallurgical purification of metallurgical-grade silicon to solar-grade silicon

T2 - Eh-pH diagrams for Fe silicides

AU - Kim, Eunyoung

AU - Osseo-Asare, Kwadwo Asare

PY - 2012/10/1

Y1 - 2012/10/1

N2 - Potential vs. pH diagrams for the systems Fe-Si-(Cl -)-(F -)-H 2O were generated using the HSC5.0 software and applied to purification of metallurgical-grade silicon (MG-Si) by hydrometallurgical methods. The diagrams for the Fe-Si-H 2O system show that with increasing electrochemical potential (Eh) the order of appearance of Fe silicides is FeSi 2, FeSi, and Fe 3Si. Further, from a thermodynamic standpoint, Si in the Fe silicides (FeSi 2, FeSi, and Fe 3Si) would be easier to oxidize than Fe, due to the lower potentials of the corresponding silicides, compared with Fe. The early formation of SiO 2 during dissolution may prohibit or retard further dissolution of Fe, as verified by previous experimental results. This inhibitive effect is expected to increase with increasing Si content in the silicides. The diagrams for the Fe-Si-Cl --H 2O system indicate that dissolution of Fe silicides with relatively low Si content, such as FeSi and Fe 3Si, is enhanced by adding chloride ions to acidic solutions. In the presence of HF, formation of fluoro-complexes enlarges the stability domains of dissolved iron and silicon, which increase with increasing {F} and/or decreasing temperature. The trends obtained for the Fe-Si-F --H 2O system suggest that the dissolution of Fe silicides would be enhanced by decreasing temperature or removing FeF 2(s) (e.g.; via ultrasonication) during the leaching process.

AB - Potential vs. pH diagrams for the systems Fe-Si-(Cl -)-(F -)-H 2O were generated using the HSC5.0 software and applied to purification of metallurgical-grade silicon (MG-Si) by hydrometallurgical methods. The diagrams for the Fe-Si-H 2O system show that with increasing electrochemical potential (Eh) the order of appearance of Fe silicides is FeSi 2, FeSi, and Fe 3Si. Further, from a thermodynamic standpoint, Si in the Fe silicides (FeSi 2, FeSi, and Fe 3Si) would be easier to oxidize than Fe, due to the lower potentials of the corresponding silicides, compared with Fe. The early formation of SiO 2 during dissolution may prohibit or retard further dissolution of Fe, as verified by previous experimental results. This inhibitive effect is expected to increase with increasing Si content in the silicides. The diagrams for the Fe-Si-Cl --H 2O system indicate that dissolution of Fe silicides with relatively low Si content, such as FeSi and Fe 3Si, is enhanced by adding chloride ions to acidic solutions. In the presence of HF, formation of fluoro-complexes enlarges the stability domains of dissolved iron and silicon, which increase with increasing {F} and/or decreasing temperature. The trends obtained for the Fe-Si-F --H 2O system suggest that the dissolution of Fe silicides would be enhanced by decreasing temperature or removing FeF 2(s) (e.g.; via ultrasonication) during the leaching process.

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