THE ENEXAL BAUXITE RESIDUE TREATMENT PROCESS: INDUSTRIAL

SCALE PILOT PLANT RESULTS

Efthymios Balomenos, Dimitrios Kastritis, Dimitrios Panias, Ioannis Paspaliaris, Dimitrios Boufounos

Aluminion of Greece Laboratory of Metallurgy, NTUA

Bauxite Residues (BR)

Bayer Process: 5 kg of Bauxite ore is split into 3 kg of hydrated alumina and 2 kg of BR (dry basis)

Bauxite Residues (BR)• Produced as a

slurry• 100 -120 Mt / year• Usual handling

practice: Disposed in sealed or unsealed artificial impoundments

Hungary 2010

Bauxite Residues (BR) Dewatering BR in

Filter Presses The filter cake has a

moisture content to 25%, which makes it easier to handle

AoG was one of the first Western European plants to apply this technology

AoG Produces 650,000 t BR per year

Can this BR cake be a potential resource?

Bauxite Residues in AoGChemical Species

%wt (dry basis)

Fe2O3 47.74%Al2O3 16.22%

CaO 10.73%SiO2 6.09%TiO2 5.93%Na2O 2.51%V2O5 0.21%-SO3 0.60%-CO2 1.63%

H2O(cry) 8.35%

Resource for Pig-

Iron Production

• Dried BR are dusty and therefore require agglomeration prior to feeding to conventional reactors (blast furnace/EAF)

• Sodium causes problems with blast furnace refractories

• Un-economic process

Resource for

Mineral Wool

production• High Added

Value product

• Complementary production with Pig Iron reduces energy consumption

• Economic, Zero Waste process

ENEXAL BR Treatment Use of AMRT-

EAF technology allows feeding without agglomeration

No Solid/liquid wastes in the process

Mineral wool produced at 70% less energy cost (no melting req.)

ENEXAL BR TreatmentProcess Design

Define conditions for optimum iron recovery (temperature, carbon addition)

Define physico-chemical properties of the slag through appropriate fluxes (CaO, SiO2) in order to produce a melt suitable for mineral wool production

Thermodynamically Model the Process

Test in Lab, Semi-Industrial and Industrial Pilot Scale

Pig iron standards%C ~ 4%%S <0.02%%P <0.05%%Si 0.4-0.8%

Empirical indexes for mineral wool production(SiO2 +Al2O3 + TiO2)/(CaO+MgO; < 1.8 4.9/[(MgO+CaO+Fe2O3 +Na2O + TiO2)/(SiO2 +Al2O3)] -0.45 < 15

[100 – (SiO2 + Al2O3)]/( SiO2 +Al2O3) 0.8 -1(SiO2 +Al2O3)/(1.4 MgO+ 0.4 Fe2O3 + CaO + TiO2) 1.3 - 1.4 Na2O + MgO + CaO 30 – 40

ENEXAL BR TreatmentAoG Pilot Plant

1 MVA AMRT-EAF (AC, 3-electrode, dust treating, batch capacity 1t)

Melt Fiberizing Line

Static Bed Electric Dryer

One year of operation treating 25 tons of BR

ENEXAL BR TreatmentAMRT-EAF Carbothemic SmeltingOpen bath operationContinuous feeding 6.65 kg/minMelt Temperature app 1600oC Energy Consumption: 1508 kWh/t of BRDust in filters 4% wt of feed

Feed Batch Dry BR (kg) 700Silica (kg) 126 Lime (kg) 105Coke (kg) 140Total Feed (kg) 1071

10

The AMRT Dust Treating EAF technology

• The EAF treats directly dusty material feed• Open bath operation (material reacts upon contact with the bath)• Patented PLC system regulates power supply depending on real time measurement of melt impendence

ENEXAL BR TreatmentPig Iron ProductionProduced metal within specification for use in secondary steel industry, as an up to 20% steel scrap substitute High Cr presence due to initial refractory dissolution (Reft1)More than 5t pig iron produced in total

Pig Iron Refr1 Refr2Fe (%wt) 95.47 93.44C (%wt) 3.36 4.59S (%wt) 0.26 0.07P (%wt) 0.08 0.22Si (%wt) 0.01 1.12Cr (%wt) 0.82 0.50Total 99.99 99.94

White Iron grinding balls produced from BR iron

(21%wt subs)

ENEXAL BR TreatmentMineral Wool ProductionSlag melt within empirical indexesFibre with good quality :

λ = 0,034 W /(mk) [UNI EN 12667] Average fiber diameter 7 micron Bright color (low Mn content) High Mechanical resistance due to high TiO2

Slag Refr1 Refr2Fe2O3 5.0 1.1SiO2 27.6 26.5CaO 25.3 23.4Al2O3 20.9 31.1Cr2O3 3.0 0.1MgO 8.89 8.3TiO2 5.6 6.1Na2O 2.4 1.8 Mineral wool used

inside the plant

ENEXAL BR Treatment

BR Mineral Wool

Commercial Mineral Wool

ENEXAL BR Treatment Smelting energy

14.5% in excess of thermodynamic requirement

Overall plant consumption 2 MWh/t BR

Exergy Utilization efficiency 32%

Increase of alumina refinery exergy utilization by 8 percentile points

ENEXAL BR Treatment Up-scaling will bring higher

energy efficiency, especially in BR drying

Initial studies show the process to be profitable

Break-even point is achieved with a fairly low mineral wool price

but

Pig iron revenues account for only 25% of the operating costs

Treating the AoG annual BR production would produce 0.5 Mt of Mineral Wool products

The ENEXAL BR treatment is successful but it should be a starting point for further BR

and BR-slag product development

Future Research

• The AoG BR also contain app 0.1%wt in REE (mainly as Sc, Ce and Nd)

• In the ENEXAL process these REE concentrate in the slag – can they be recovered?

“EURARE: Development of a sustainable

exploitation scheme for Europe’s REE ore

deposits”

eres2014.conferences.gr

Thank you for attention

The research leading to these results has received

funding from the European Union Seventh

Framework Programme ([FP7/2007-2013]) under

grant agreement n° ENER/FP7EN/249710/ENEXAL