RMC5, Budapest, 19-22 September 2012

Atomic order and cluster energetics

in amorphous aluminosilicate systems

G.S.E. Antipas1, L. Temleitner2,3, K. Karalis1,

S. Kohara3, L. Pusztai2 and A. Xenidis1

1School of Mining Engineering and MetallurgyNational Technical University of Athens

Zografou Campus, Athens 15780Greece

Tel. +30 210 7722388Email: gantipas@metal.ntua.gr

2Research Institute for Solid State Physics and OpticsHungarian Academy of Sciences,

H-1121 Budapest,Konkoly-Thege M. ut 29-33

Hungary

3Japan Synchrotron Radiation Research Institute (SPring-8/JASRI)1-1-1 Kouto, Sayo

Hyogo 679-5198, CREST-JSTJapan

RMC5, Budapest, 19-22 September 2012

The pyrometallurgical processThe pyrometallurgical process

Rotary Kiln

Electric Arc Furnace (EAF)

Converter

90m

18m

4m5cycle/min

6m

1700 ◦C, oxidation of part of Fe from Fe-Ni to produce slag which is disposed of, increasing the concentration of Ni in the final product, typically up to 18%w.t.

Calcine @ 800 ◦C,

(mixed oxides) %w.t.:

28.6 Fe, 17.6 Si, 3.7 Mg,

2.3 Ca, 1.6 Cr, 3 Al, 1 Ni

Laterite oreFe2O3, SiO2

(Mg,Ni,Al,Fe)6(Si,Al)4O10

CaCO3, Cr2O3

+Solid fuel, e.g. lignite

3 carbon electrodes

1.5 m diameter each

DC or AC 70-75kA,

consumption 0.5m/day

2000 ◦C electrodes

Reduction of calcine to

produce slag (density 3.5

gr/cm3) & metallic Fe-Ni at

15%w.t. Ni (Fe-Ni density

5.5-7 gr/cm3)

RMC5, Budapest, 19-22 September 2012

FerronickelFerronickel

• 4 active mines / annual ore usage ~ 2.5 million tons

annual nickel production of ~ 10,000 tons

covers 6-7% of the European demand for Nickel

• 4 active mines / annual ore usage ~ 2.5 million tons

annual nickel production of ~ 10,000 tons

covers 6-7% of the European demand for Nickel

RMC5, Budapest, 19-22 September 2012

The pyrometallurgical processThe pyrometallurgical process

Rotary Kiln

Electric Arc Furnace (EAF)

Converter

90m

18m

4m5cycle/min

6m

1700 ◦C, oxidation of part of Fe from Fe-Ni to produce slag which is disposed of, increasing the concentration of Ni in the final product, typically up to 18%w.t.

Calcine @ 800 ◦C,

(mixed oxides) %w.t.:

28.6 Fe, 17.6 Si, 3.7 Mg,

2.3 Ca, 1.6 Cr, 3 Al, 1 Ni

Laterite oreFe2O3, SiO2

(Mg,Ni,Al,Fe)6(Si,Al)4O10

CaCO3, Cr2O3

+Solid fuel, e.g. lignite

Reduction of calcine to produce

slag (density 3.5 gr/cm3) &

metallic Fe-Ni at 15%w.t. Ni (Fe-Ni

density 5.5-7 gr/cm3)

RMC5, Budapest, 19-22 September 2012

• Electrode/energy consumption is proportional to slag electrical resistivity

• Slag conductivity is correlated to the concentration of (ferric) Fe3+

• Fe3+, can be either a network modifier (octahedral) or former (tetrahedral)

• Tetrahedral coordination is achieved for all ferric iron when Fe3+ : Fe2+ exceeds 1:1

• Octahedral Fe2+, acts as a network modifier / what about tetrahedral Fe2+ ?

• Diffusion of network-modifying cations dominate the kinetics of redox Fe2+/Fe3+

equilibrium in transition metal-bearing amorphous silicates

• Could oxygen coordination of the Fe2+/Fe3+ ions also affect the redox equilibrium?

Slag – the role of Fe2+/Fe3+Slag – the role of Fe2+/Fe3+

3 carbon electrodes

1.5 m diameter each

DC or AC 70-75kA,

consumption 0.5m/day

2000 ◦C electrodes

1700 ◦C slag

RMC5, Budapest, 19-22 September 2012

main mineralogical phases

• fayalite (Fe2SiO4)

• forsterite (Mg2SiO4)

• magnetite (Fe3O4)

• christobalite (SiO2)• chromite (FeCr2O4)• ferrosilite (Ca0.5Fe1.5Si2O6)

• magnesioferrite (Al0.47Fe1.52MgO4)

main mineralogical phases

• fayalite (Fe2SiO4)

• forsterite (Mg2SiO4)

• magnetite (Fe3O4)

• christobalite (SiO2)• chromite (FeCr2O4)• ferrosilite (Ca0.5Fe1.5Si2O6)

• magnesioferrite (Al0.47Fe1.52MgO4)

Slag elemental concentration (%w.t.) and XRD spectrumSlag elemental concentration (%w.t.) and XRD spectrum

RMC5, Budapest, 19-22 September 2012

Levitation (liquid) and post-levitation (glass)

XRD characterisation - BL04B2 beamline

Levitation (liquid) and post-levitation (glass)

XRD characterisation - BL04B2 beamline

• photon wavelength of 0.20194 Å (60 keV)

• Q range of up to 21 Å-1 , 2θ up to 40◦

• aerodynamic levitation by a compressed air flow

• melting by a CO2 laser with max power of 100W

• Sample temperature reached 1400°C

• photon wavelength of 0.20194 Å (60 keV)

• Q range of up to 21 Å-1 , 2θ up to 40◦

• aerodynamic levitation by a compressed air flow

• melting by a CO2 laser with max power of 100W

• Sample temperature reached 1400°C

* G.S.E. Antipas, L. Temleitner, K. Karalis, S. Kohara, L. Pusztai and A. Xenidis,, J. Mol. Struct (2012)

*

*

RMC5, Budapest, 19-22 September 2012

Reverse Monte Carlo – RMC_POTReverse Monte Carlo – RMC_POT

Liquid

Glass

Si-OFe-O/Mg-O

Fe

-Si/

Ca

-O

Si-Si/O-O

Fe-Fe

RMC5, Budapest, 19-22 September 2012

RMC-generated environmentsRMC-generated environments

RMC5, Budapest, 19-22 September 2012

RMC-generated environments (cntd)RMC-generated environments (cntd)

Marked reduction of Si NBO

Oxygen (% of total O atoms in supercell)

Increase of Fe-Si BO

Single (XRD) dataset-based RMC not to be over-interpreted

Increase of Fe-2Si BO

Marked reduction of “uncoordinated” O

Marked increase of Fe-Fe BO

Increase of Fe-Si-Mg BO

Increase of Fe-Mg BO

Increase of Si-2Fe BO

Marked reduction of Al NBO

increase of Si-Mg-Al BO

2nd neighbour coordinationGlass Liquid

Fe-Fe 3 3Fe-Si 3 2Fe-Mg ~1 ~1Si-Si 2 2

No Fe CN > 5No Fe CN > 5

RMC5, Budapest, 19-22 September 2012

Gas phase, spin un. (open shell) BLYP/TZ2P level of theory, frozen cores: Fe(3p), Si(2p), Mg(2p), O(1s)

DFT cluster energetics - clusters based on O environmentDFT cluster energetics - clusters based on O environment

Tetrahedral Fe2+

Mg mostly mediates stability of Fe3+

Single bridging O – all clusters are linked via corner sharing

Increasing Si polyhedra coordination stabilizes Fe2+ (in the absence of network modifiers?)

Fe diclusters show a preference to at least one Fe3+ moiety

RMC5, Budapest, 19-22 September 2012

• Fe2+ is most preferred in the liquid state (most likely as a network modifier)

• In the liquid state, at CN=3 Fe2+ appears to be readily oxidized to Fe3+

• In the glassy state, CN=4, Fe2+ is energetically more favoured; increasing Mg content lowers

the Fe2+/Fe3+ ratio but at a slower rate compared to the liquid phase

DFT cluster energetics - clusters based on Fe environmentDFT cluster energetics - clusters based on Fe environment

RMC5, Budapest, 19-22 September 2012

The EAF slag was studied in the liquid/glass state by a/d levitation and RMC modeling

• Stereochemical features of both states were similar and in par with literature

- both states may consist of the same fundamental clusters, the rel. number of which may

define the state (?)

• Transition from liquid to glass involves:

- a 3-fold decrease in uncoordinated O (to within the 1st RDF min)

- a marked increase of Fe-Si-Mg polyhedra bridging O

• Spin unrestricted DFT BLYP/TZ2P calculations for Si-Fe-Mg-O suggested that

- the oxidation state of Fe depends on its polyhedra coordination

I) Fe polyhedra always favour Fe2+ in the absence of Mg; the latter promotes Fe3+

II) At CN=3 (liquid) the ratio of Fe2+/Fe3+ is reduced at a lower rate than at CN=4 for

increasing Mg concentration

III) Fe2+/Fe3+ - O bond sterngth in the liquid state ??? – correlation to viscosity

SummarySummary

RMC5, Budapest, 19-22 September 2012

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RMC5, Budapest, 19-22 September 2012

References

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