N McEwan, Verref. Chromite A critical raw material for the Refractory Manufacturer

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1 N McEwan, Verref Chromite A critical raw material for the Refractory Manufacturer

2 Agenda: Introduction to Marico Chrome Corporation Marico Chromite deposit Refractory materials Suitability of chromite as a refractory raw material Chromite containing refractories Environmental issues - Chrome containing Refractories Conclusion June 2010

3 Introduction to Marico Chrome Corporation Marico Chrome Corporation 50:50 JV Vereenging Refractories (Verref) Samancor Chrome SA 60 km north of Zeerust Mining commenced from 1956 Estimated 9 million ton of ROM reserves

4 Introduction to Marico Chrome Corporation Current mining rate - estimated life of mine = 45 years Small scale producer ton per annum Metallurgical and refractory grade Consumption in both internal and export markets

6 Marico Chromite deposit Part of the Bushveld Igneous Complex General trends for the Bushveld Complex: Cr2O3 content of the chromite layers decreases upwards. Chromite layer Cr2O3 % LG MG layers UG2 43

7 Marico Chromite deposit Associated upward decrease in Cr:Fe ratio Chromite layer Cr:Fe Ratio LG : 1 MG layers : 1 UG : 1 Alumina content decreases upwards Chromite grain size 2mm to 50 microns from lower to upper layers.

8 Marico Chromite deposit Significant differences to Western Bushveld LG group: Higher Cr2O3 Up to 49% Lower in SiO2 Typically below 1% Higher Cr:Fe ratio Typically 2:1 Lower Magnetite content Highly suitable for refractory applications

9 Refractory materials Refractory Resistant to change Metallurgical industries = Resistance to change at elevated temperatures Branch of ceramics mans oldest art Modern refractory technology Late 18 th century Growth of iron industry

10 Refractory materials Magnesite and chrome brick introduced from 1880 s Only in 1931 Blends of chromite and magnesite for brick Superior hot strength Open hearth and electric steel making furnaces 1960 s Low silica magnesia chrome brick Reconstituted fused grain magnesia chrome Verref commission fusion plant

11 Refractory materials Principle refractory consuming manufacturing processes are: Iron and Steelmaking Non Ferrous Metal production Cement production Glass production Petrochemical production

12 Refractory materials Compounds with melting point > 1500 o C Compound Nr Borides 13 Carbides 19 Nitrides 10 Silicides 7 Oxides 11 Total: 60

13 Refractory materials Reasonable abundance and price Oxide Melting Point (C) Classification Silica SiO Acid Refractory Alumina Al2O Chrome Cr Neutral Refractory Zirconia ZrO Lime CaO 2614 Magnesia MgO 2800 Basic Refractory

14 Suitability of chromite as a refractory raw material High melting point. Marico chromites Higher proportion of Mg than Fe in spinel Spinel Molecular % Melting Point (C) Calculated Melting Point (C) MgO.Al2O MgO.Cr2O FeO.Cr2O FeO.Fe2O Total of melting points of Marico Chromite = 2164

15 Suitability of chromite as a refractory raw material Moderate thermal expansion Brick quality Thermal Expansion Magnesia brick 1.4% Magnesite-Chrome brick 1.1% Chrome-Magnesite brick 1.0% Thermal 1000 C

16 Suitability of chromite as a refractory raw material Neutral chemical behavior

17 Chromite containing refractories Classification of chromite containing refractories Brick quality Cr2O3 % Magnesite-Chrome brick <30 Chrome-Magnesite brick >30 Picrochromite >75

18 Chromite containing refractories Five types of these brick are manufactured Silicate bonded Direct bonded Chemically bonded Co burned Fusion cast

19 Chromite containing refractories Direct bonded: FeO in chromite oxidises to Fe2O3 during firing Diffuses into the MgO at high temperature Magnesio-ferrite (MgO.Fe2O3) a refractory spinel is formed Chromite is stabilised from further oxidation Direct bonding between MgO and Chromite (T>1550 o C)

20 Chromite containing refractories Low Silica and good bonding results in: High hot strength Good spalling resistance High Cr2O3 spinel content results in: Low wet ability by fayalite (2FeO.SiO2) slags Low slag solubility

21 Chromite containing refractories Fusing (melting together) the chromite and magnesia Chromite spinel is completely stabilised Chromite spinel is dispersed as small spinel crystals throughout the Magnesia. Optimum performance is then obtained.

22 Environmental issues - Chrome containing Refractories. Chromium - number of different oxidation states Ability to: Modify other chemical compounds Act as a catalyst in promoting chemical reactions

23 Environmental issues - Chrome containing Refractories. Cr(III) - Trivalent Chrome Most stable oxidation state Low solubility in water Examples: Green chrome oxide (Cr 2 O 3 ) - pigment in paints Chromium in chromite

24 Environmental issues - Chrome containing Refractories. Cr(IV) (CrO 2 ) Black conducting ferromagnetic compound Examples: Used in the production of audio and video tapes

25 Environmental issues - Chrome containing Refractories. Cr(VI) - Hexavalent Chrome Soluble, toxic - increases the risk of respiratory cancer. Examples: Used to surface treat steels to improve corrosion resistance. Sodium and Potassium dichromates and Chromic acid (CrO 3 )

26 Environmental issues - Chrome containing Refractories. Conditions that promote formation of hexavalent chrome Alkali or calcium oxide rich environments Increase in temperatures below 1022 o C Reaction begins along the grain boundaries Chromite grain size important

27 Environmental issues - Chrome containing Refractories. Minimise Cr (VI) formation by: Control level of CaO in brick Use coarse chromite Use fused magnesia chrome or chrome magnesia grains Industries that moved away from Chrome containing materials: Cement Glass

28 Conclusion Chromite as refractory material Cost effective Ideal properties for various metallurgical applications Marico Chrome has specific improved properties No other suitable refractory for non ferrous platinum smelting Under certain conditions hexavalent chrome can form Joint approach by the refractories producer and the user

29 Acknowledgement The input of Ron Parry, Tim Courtney and Phillip Knupfer all of Vereeniging Refractories, is gratefully acknowledged Questions and comments

Chromite A Cost-Effective Refractory Raw Material for Refractories in various Metallurgical Applications

$Chromite A Cost-Effective Refractory Raw Material for Refractories in various Metallurgical Applications$ Southern African Pyrometallurgy 2011, Edited by R.T. Jones & P. den Hoed, Southern African Institute of Mining and Metallurgy, Johannesburg, 6-9 March 2011 Chromite A Cost-Effective Refractory Raw Material