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Industrial Production of Magnesium

CHEMRAWN-XVII and ICCDU-IX Conference on Greenhouse Gases Kingston, Ontario, July 8-12, 2007 The Pidgeon Process for Magnesium Production: Dolomite Calcination and MgO Silicothermic Reduction: Fuel Savings and CO 2 Emission Avoidance.

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Industrial Production of Magnesium

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  1. CHEMRAWN-XVII and ICCDU-IX Conference on Greenhouse GasesKingston, Ontario, July 8-12, 2007The Pidgeon Process for Magnesium Production: Dolomite Calcination and MgO Silicothermic Reduction: Fuel Savings and CO2 Emission Avoidance M. Halmann1 and A. Steinfeld 21Weizmann Institute of Science, Department of Environmental Sciences and Energy Research, Rehovot, Israel 2ETH, Department of Mechanical and Process Engineering, Zurich, and Paul Scherrer Institute, Villigen, Switzerland

  2. Industrial Production of Magnesium • Silicothermic Reduction of Calcined Dolomite, CaMg(CO3)2, Pioneered by Loyd M. Pidgeon in Canada during World War II. Afterwards replaced by the 2. Electrochemical Reduction of Fused Magnesium Chloride, derived from Brine Lakes, such as the Dead Sea, or from Seawater – mainly in the U.S.A., Russia, Canada, and Israel.

  3. Strong Revival of the Pidgeon Process since about 20 Years. About 73% of World Primary Magnesium Production now in China Advantages of Pidgeon Process- • Abundant Occurrence of Raw Materials: Dolomite, Coal, Silica (sand), Iron Oxide (hematite). • Formation of High Purity Magnesium (99.97%). • Relative Simplicity of the Process. Drawbacks of Pidgeon Process – • Severe Environmental Pollution (dust, toxic gases). • High Fuel Consumption. • Heavy CO2 Emissions.

  4. World Primary Magnesium Production –about 726,000 Ton/year (in 2006) Of these produced in: China: 526,000 Ton Canada: 50,000 Ton Russia: 50,000 Ton U.S.A. 43,000 Ton Israel: 28,000 Ton Kazakhstan: 20,000 Ton U.S.Geological Survey, 2007 www.intlmag.org

  5. The Three Steps of the Pidgeon Process • Calcination of Dolomite, CaMg(CO3)2 = CaO + MgO + 2CO2 • Ferrosilicon Alloy Production , Fe2O3 + 4SiO2 + 11C = 2(Fe)Si2 + 11CO • Silicothermic Reduction of MgO by Ferrosilicon, 2MgO + 2CaO + (Fe)Si = 2Mg(g) + Ca2SiO4(s) + Fe Toguri and Pidgeon, Can. J. Chem., 40, 1769 (1962)

  6. Energy Consumption and Greenhouse Gas Emissions in the Industrial Pidgeon ProcessFrom Ramakrishnan and Koltun, Resources, Conservation & Recycling, 42, 49 (2004)

  7. Purpose of Present Study To identify Potential Fuel Savings and CO2 Emission Avoidance in the three Steps of the Pidgeon Process by 1. Applying Concentrated Solar Energy. 2. Co-production of Syngas Converted to Methanol.

  8. THERMOCHEMICAL CALCULATIONS

  9. The 1st Step of the Pidgeon Process Calcination of Dolomite, at ~1300o C, CaMg(CO3)2 = CaO + MgO + 2CO2 Highly Endothermic Reaction. CO2 Released both from the Reaction, and from Fuel Burned for Process Heat.

  10. CO2 Dolomite MgO CaO

  11. H2 H2O CO CO2 CH4 MgO

  12. H2 CO C(gr) MgO

  13. The 2nd Step of the Pidgeon Process Ferrosilicon Alloy Production by Electric Arc through Mixture of Hematite, Quartz Sand, and Coal. Extremely Endothermic Reaction; Emits Toxic CO. Literature Reported Reaction: Fe2O3 + 4SiO2 + 11C = 2(Fe)Si2 + 11CO

  14. CO C(gr) SiO2 FeSi SiC SiO

  15. H2 CO C(gr) FeSi

  16. Equilibrium Composition vs. Temperature for the System Fe2O3 + 4SiO2 + 11CH4 at 1 bar At 19000 K the Calculated Equilibrium Reaction is Fe2O3 + 4SiO2 + 11CH4 = 2FeSi + 22H2 + 10CO + SiC + SiO

  17. CO H2 C(gr) FeSi SiO2

  18. Thermogravimetric Experiment Purpose of experiment: To test if for Ferrosilicon Production, the Customary Internal Heating by an Electric Arc could be Replaced by External Heating, potentially with Concentrated Solar Energy. Expected Reaction from Literature: Fe2O3 + 4SiO2 + 11C = 2(Fe)Si2 + 11CO A mixture of hematite, quartz sand and active carbon was heated under constant Ar flow in a high-temperature thermogravimeter. Evolved gases measured by gas chromatography. Solid products analyzed by X-ray diffraction. Frei, Halmann and Steinfeld, unpublished

  19. From Calculated Equilibrium:Fe2O3 + 4SiO2 + 11C = 2FeSi(s) + SiC(s) + 10CO(g) + SiO(g) Calculated weight loss by release of gaseous CO and SiO: 61% Observed weight loss: 59%

  20. XRD of the Solid Product of the Reaction Fe2O3 + 4SiO2 + 11C = 2FeSi + SiC + 10CO + SiOIdentified FeSi and SiC

  21. The Products of Ferrosilicon Production According to the Literature: Fe2O3 + 4SiO2 + 11C = 2(Fe)Si2 + 11CO At 20000 K, the Equilibrium Products are: Fe2O3 + 4SiO2 + 11C = 2FeSi + 10CO + SiC + SiO Confirmed by above Experiments

  22. The 3rd Step of the Pidgeon Process Silicothermic Reduction of MgO by Ferrosilicon, at ~1200-1500oC under Vacuum. Highly Endothermic Reaction, 2MgO + 2CaO + (Fe)Si = 2Mg(g) + Ca2SiO4(s) + Fe Products: Gaseous Mg and Slag of Dicalcium Silicate.

  23. Mg(g) Ca2SiO4(s) MgO(s)

  24. Potential Fuel Savings and CO2 Emission Avoidance in a Solar Pidgeon Process Combined with Conversion of Syngas (if formed) to Methanol – vs. Conventional Processes.

  25. Conclusions • Considerable Fuel Savings and CO2 Emission Avoidance Predicted by using Concentrated Solar Energy for Process Heat in all Three Steps of the Pidgeon Process for Mg Production. • For Dolomite Calcination, and for Ferrosilicon Production, Additional Fuel Saving and CO2 Emission Avoidance Possible by using CH4 or C + H2O as Reductant, resulting in Co-Production of Magnesium and Syngas.

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