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: sgostu@wpi.eduPhone: (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

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80

100

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GR

ADE

%

(MAG

NET

ITE)

RECOVERY % (MAGNETITE)

0

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60

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100

0 20 40 60 80 100

GR

ADE

% (M

agne

tite)

RECOVERY % (Magnetite)