INVESTIGATION OF CARBON-BASED REDUCTANT, LOW-TEMPERATURE PROCESS FOR CONVERSION OF HEMATITE IN RED-MUD TO MAGNETITE
Sumedh Gostu1, Dr. Brajendra Mishra1
1Metal Processing Institute, Worcester Polytechnic Institute
CONTACTSumedh GostuWorcester Polytechnic Institute, Email: [email protected]: (540)-449-4920
Red-Mud is a residue generated from the Bayer’s processing of bauxite.
Primary Aluminum production: 50 mT, Bauxite mined: 200 mT(2013).
109 Bayer processing plants around the world, 49 alone in China (700 % increase since 2001).
Annual generation of red mud: 120 mT, 6 % growth rate estimated.
Operating and closed sites: 3 billion tons of red mud accumulated.
STATUS OF RED-MUD
Aluminum1 Ton
Red-Mud1.5 - 4 Tons
Bauxite3.3 - 10.3 Tons
Alumina1.6 - 5 Tons
WHAT IS THE PROBLEM? Variability of Red-Mud composition with variation in
Bauxite composition.
Complex mineralogy associated with mineral phases of Red-Mud: Lack of Liberation.
Complex physical and chemical properties associated with Red-Mud: Basicity, Fine particle size: Problems in Diposal and storage.
Processing strategies developed for Red-Mud utilization are not economical.
Products generated from Red-Mud cannot compete with traditional products.
OBJECTIVE
Investigate the conversion of hematite in Red-Mud to Magnetite and its separation employing a low temperature reduction.
Reduction
• Petroleum coke • Mixture of CO/CO2
Magnetic Separation
• Frantz Dry Magnetic Separator• Davis Tube Wet Magnetic Separation
Microscopy
• Scanning Electron Microscopy• Transmission Electron Microscopy
EXPERIMENTAL
1E-10
1E-08
0.000001
0.0001
0.01
1
100
10000
0 200 400 600 800 1000 1200 1400 1600
PCO
/PC
O2
T (oC)
Stability diagram 1 atm
Fe2O3 to Fe3O4
Fe3O4 to FeO
Fe3O4 to Fe3C
FeO to Fe3C
Carbon solubilization
Fe3O4
FeO
Fe3C
Fe2O3
REDUCTION: EXPERIMENTS & RESULTS3Fe2O3(s) + CO(g) = 2Fe3O4(s) + CO2(g)
ΔGo = -RTlnK
ΔG = -RTln[(aFe3O42
*PCO2)/(aFe2O33
*PCO)]
ΔG = -RTln(PCO2/PCO) (The basis for construction of stability diagram)
The values of ΔG are obtained at various Temperatures are obtained
through the HSC chemistry 5.1, reaction tool box.
Stability Diagram for Fe-C-O system at 1.0 atm
Gases Used CO, CO2, N2
Tube furnace maximum temp= 1000 oC
Copper Coils with compressed air for cooling
CO/CO2 IR analyzer
Objective of work as proposed to CR3
Experimental setup for gaseous reduction experiments
CO/CO2 = 1:1 CO/CO2 = 1:1.5
CO/CO2 = 1.5:1
Optimum conditions forreduction: processingtemperature of 540oC ± 10C ,partial pressures CO(g)andCO2(g) each of 0.070atm (bar) ±0.001atm (8.5 %).(bar)/ inertdiluent-gas: N2(g), for aconversion-time of 30min.
MAGNETIC SEPARATION
Frantz Dry Magnetic Separator
Davis tube Magnetic Separator
MICROSCOPY Agglomerations
SEM micrographs of red-mud -53µm +38µm Agglomeration of fine particles is seen in a larger particle mass.
TEM micrographs of red-mud head
Agglomerates of Nano crystallites. Particle size assigning to red mud is highly ambiguous !!!!
A red-mud particle is composed of agglomerated entities of small Nano-particulates. The Nano-particulates are in the size range of 16-140 nm.
Low temperature (475oC to 600oC) gas-phase reduction of hematite in red-mud to magnetite is viable conversion-process that can be achieved with lowpartial-pressures of CO(g), and CO2(g). N2(g)
Solid-phase reduction-products obtained from the gas-phase reduction of redmud contained Fe3O4 (56.4 – 80.5 m%), Fe2O3 (0 −20 m%), Fe3C (4.8 − 6.8 m %)and paramagnetic 2+ and 3+ phases (14 - 22 m%).
Dry and wet magnetic-separation performed on the reduced samples did notachieve a high grade of separated magnetite.
1) The cation substitution of, primarily, Al3+ and Ti4+/Ti3+ cations in thehydrated-oxide nanoparticles being converted to magnetite or,
2) Nano-size particles of aluminum and titanium “oxides” occluded withinthe predominantly “large-particles/clusters”.
CONCLUSION
FUTURE RECOMMENDATION Structural characterization of nanometer length scale constituents of red-
mud.
Development of a strategy to segregate the Al(lII) and Ti(III/IV) constituents soas to yield a low Al, Ti magnetic fraction and low Fe non magnetic fraction.
• Bauxite Residue Management: Best Practice, World Aluminum, European aluminum association, April 2013. • Power, G, Grafe, M, Klauber, C., “Bauxite residue issue: I. Current managment, disposal and storage practices”,
Hydrometallurgy. 108 (2011), 33-45.• Prasad, P, M., Singh, M., “Problems in the Disposal and Utilization of Red Muds”, The Banaras Metallurgist. 14&15
(1997), 127-140.• Burkin. A.R.,”Production of Aluminum and Alumina”, 1987, Society of Chemical Industry, John Wiley and Sons.• Bruckard, W.J “Smelting of bauxite residue to form a soluble sodium aluminum silicate phase to recover alumina
and soda “ Min. Proc. Ext. Met. Rev., 119 (1) (2010), 18-26.• Li, X. et al., “Recovery of alumina and ferric oxide from Bayer red mud rich in iron by reduction sintering” T.
Nonferr. Metal. Soc., 19 (5) (2009), 1342-1347.• Zhong, L., Zhnag, Y., Zhang, Yi., “Extraction of alumina and sodium oxide from red mud by a mild hydro-chemical
process” Journal of Hazardous Materials. 172 (2009), 1629-1634.
REFERENCES
RED-MUD
Low-Value High-Volume Products
High-Value Low-VolumeProducts
METALS & OXIDES RECOVERY
INDUSTRIAL AGGREGATES
Fe
Ti
Ca
Al
NaREEs
Jamaican Red Mud Composition
0
20
40
60
80
100
0 20 40 60 80 100
GR
ADE
%
(MAG
NET
ITE)
RECOVERY % (MAGNETITE)
0
20
40
60
80
100
0 20 40 60 80 100
GR
ADE
% (M
agne
tite)
RECOVERY % (Magnetite)
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