Cuprospinel

Cuprospinel
General
Category	Oxide mineral - Spinel group
Chemical formula	CuFe2O4 or (Cu,Mg)Fe2O4
Strunz classification	04.BB.05
Identification
Molar mass	239.23
Color	Black, gray in reflected light
Crystal habit	Irregular grains, laminae intergrown with hematite
Crystal system	Isometric (4/m 3 2/m) Space Group: F d3m
Mohs scale hardness	6.5
Luster	Metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	5 - 5.2
Optical properties	Isotropic
Refractive index	n = 1.8
References	[1][2][3]

Cuprospinel, occurs naturally in Baie Verte, Newfoundland, Canada.^[1] The mineral was found in an exposed ore dump, on the property of Consolidated Rambler Mines Limited near Baie Verte, Newfoundland. The mineral was first characterized by Ernest Henry Nickel, a mineralogist with the Department of Energy, Mines and Resources in Australia, in 1973.^[4][5]

Cuprospinel, is an inverse spinel with the formula CuFe₂O₄, where copper substitutes some of the iron cations in the structure.^[6][7] Its structure is similar to that of magnetite, Fe₃O₄, yet with slightly different chemical and physical properties due to the presence of copper.

Structural properties

Cuprospinel, like many other spinels has the general formula AB₂O₄. Yet, cuprospinel is an inverse spinel in that its A element, in this case copper (Cu²⁺), only occupies octahedral sites in the structure and the B element, iron (Fe²⁺ and Fe³⁺), is split between the octahedral and tetrahedral sites in the structure.^[8][9] The Fe²⁺ species will occupy some of the octahedral sites and there will only be Fe³⁺ at the tetrahedral sites.^[8][9] Cuprospinel adopts both cubic and tetragonal phases at room temperature, yet as temperature is elevated the cubic form is most stable.^[6][9]

Uses

Cuprospinel is used in various industrial processes as a catalyst. An example is the water gas shift reaction:^[9]

H₂O_(v) + CO_(g) → CO_2(g) + H_2(g)

This reaction is particularly important for hydrogen production and enrichment.

The interest of cuprospinel arises in that magnetite is a widely used catalyst for many industrial chemical reactions, such as the Fischer-Tropsch process, the Haber-Bosch process and the Water gas shift reaction. It has been shown that doping magnetite with other elements gives it different chemical and physical properties, these different properties sometimes allow the catalyst to work more efficiently. As such, cuprospinel is essentially magnetite doped with copper and this enhances magnetite's water gas shift properties as a heterogeneous catalyst.^[10][11]

References

1. ^ ^{a b} "Cuprospinel". Mineral Data Publishing. http://www.handbookofmineralogy.org/pdfs/cuprospinel.pdf. Retrieved 13 October 2010. 
2. ^ Mindat.org
3. ^ Webmineral data
4. ^ William D. Birch. "Who's Who in Mineral Names". RocksAndMinerals.org. http://www.aspo-australia.org.au/References/Bruce/EHN/EHNickelWhosWhos_JF09.pdf. Retrieved 13 October 2010. 
5. ^ MIchael Fleischer and Joseph A. Mandarino (1974). "New Mineral Names*". American Mineralogist. http://www.minsocam.org/ammin/AM59/AM59_381.pdf. Retrieved 13 October 2010. 
6. ^ ^{a b} Haruyuki Ohnishi; Teruo Teranishi (1961). "Crystal Distortion in Copper Ferrite-Chromite Series". Journal of the Physical Society of Japan 16: 35–43. doi:10.1143/JPSJ.16.35. 
7. ^ J. M. Tranquada; S. M. Heald, and A. R. Moodenbaugh (1987). "X-ray-absorption near-edge-structure study of La2-x(Ba, Sr)xCuO4-y superconductors". Physical Review B 36 (10): 5263–5274. doi:10.1103/PhysRevB.36.5263. 
8. ^ ^{a b} Venkata Krishnan; Ramakrishnan Kalai Selvan, Chanassary Ouso Augustin, Aharon Gedanken, and Helmut Bertagnolli (2007). "EXAFS and XANES Investigations of CuFe2O4 Nanoparticles and CuFe2O4−MO2 (M = Sn, Ce) Nanocomposites". Journal of Physical Chemistry C 111 (45): 16724–16733. doi:10.1021/jp073746t. 
9. ^ ^{a b c d} Michael Estrella; Laura Barrio, Gong Zhou, Xianqin Wang, Qi Wang, Wen Wen, Jonathan C. Hanson, Anatoly I. Frenkel and Jose A. Rodriguez (2009). "In Situ Characterization of CuFe2O4 and Cu/Fe3O4 Water−Gas Shift Catalysts". Journal of Physical Chemistry C 113 (32): 14411–14417. doi:10.1021/jp903818q. 
10. ^ Alexilda Oliveira de Souza and Maria do Carmo Rangel (2006). "Catalytic activity of aluminium and copper-doped magnetite in the high temperature shift reaction". Reaction Kinetics and Catalysis Letters 79 (1): 175–180. doi:10.1023/A:1024132406523. 
11. ^ Emerentino Brazil Quadro; Maria de Lourdes Ribeiro Dias, Adelaide Maria Mendonça Amorim, and Maria do Carmo Rangel (1999). "Chromium and Copper-Doped Magnetite Catalysts for the High Temperature Shift Reaction". Journal of the Brazilian Chemical Society 10 (1). doi:10.1590/S0103-50531999000100009.