A Waste to Wealth Study on Converting Aluminium Dross Schedule

Waste into γ and α Alumina

MEOR YUSOFF M.S., MASLIANA MUSLIM AND WILFRED PAULUS

Materials Technology Group,

Malaysian Nuclear Agency,

Bangi, 43000 Kajang, Selangor,

MALAYSIA.

e-mail: meor@nuclearmalaysia.gov.my http: //www.nuclearmalaysia.gov.my

Abstract:- Aluminium dross waste is classified as a schedule waste and could pose environmental hazards. A

physical and chemical recycling process was developed to turn this harmful waste into high technology alumina

material. Two different types of alumina powders were produced, the first is γ-alumina used mainly in the

catalysis and filtration applications while the second type is α-alumina used for structural, refractory, abrasive,

insulator as well electronic applications. γ-alumina was produced by phase transformation of the aluminium dross

at high temperature involving the dehydroxylation and dissolution-recrystallization reactions. Synthesis of α-

alumina on the other hand involves both chemical and physical processes of leaching, precipitation and also

calcinations. Crystal and morphological tests by x-ray diffraction (XRD), transmission electron microscope

(TEM) and scanning electron microscope (SEM) were also performed to evaluate the properties of these alumina

products. The result shows that the alumina are nano-sized products and comparable with that of the commercial

products.

Keywords:- Aluminium dross, schedule waste, γ-alumina, α-alumina, physical and chemical processes

1 Introduction Aluminium dross is a waste produced during the

aluminium smelting process and it is in the form

of a solid material floating on the aluminium

melt (1). Worldwide aluminium industry

produces nearly five million tonnes of this waste

each year. In Malaysia, aluminium dross is

classified as a schedule waste and its storage,

transportation and disposal activities must be

carried out by licensed contractors. Disposal of

this schedule waste is also a costly process

where a fee of RM2,000 per tonne is charged by

the approved local waste disposal company. The

high disposal fee had also resulted to the

indiscriminate disposal of this aluminium dross

waste in secluded areas such as that happened at

a palm oil plantation in the southern town of

Segamat in January 2006. The incidence was

highlighted by the Malaysian newspapers as a

major environmental disaster and the authorities

were urged to take a more stern action on the

violators. Recycling this schedule waste into a

value-added material will be a welcoming move

to the industrialists as well as safeguarding the

environment.

Hi-tech alumina is one of the common advanced

ceramic with wide range of applications.

Alumina can exist in many crystalline phases

but commercially there are only two types

available in the market. Of the different

crystalline phases or polymorphs, α-alumina is

the only stable crystalline phase (2). Its

properties of high temperature, chemical

resistant, high insulating properties as well as

the second hardest material after diamond make

it suitable for refractory, structural, abrasive and

electrical applications. Another commercial

alumina is γ-alumina that is mainly used for the

catalysis and filtration applications. γ-alumina is

also referred as a meta stable material as it can

be transformed into different phases of alumina

when heated at high temperatures.

RECENT ADVANCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT

ISSN: 1790-5095 17 ISBN: 978-960-474-142-7

2 Methodology

The aluminium dross sample used in this study

was obtained from a Malaysian aluminium

smelting company located in the northern city of

Penang. The waste was characterized for its

crystalline phase using the Panalytical X-pert X-

Ray Diffraction (XRD) spectrometer and also

for its crystal morphology by FEI Scanning

Electron Microscope (SEM). Crystal phase

transformation was done on this sample by

heating it at elevated temperatures range from

500-1300oC in a muffle furnace. The crystalline

phase and morphology was then determined

using the same XRD and SEM methods. A

chemical recycling process was also tried for the

aluminium dross waste. The process involved

washing with water, leaching with dilute

sulphuric acid and precipitation with propanol.

After separating the white precipitate from the

liquid using a vacuum filter, it is dried overnight

in an oven at 70oC. The hydrated alumina

powder produced after the drying stage is then

calcined at 1300oC for 3 hours in a furnace.

Finally XRD, SEM and Joel Transmission

Electron Microscope (TEM) characteristic tests

were performed on the sample and compared it

with the commercial alumina products. The

characteristic equipments are located at the

Malaysian Nuclear Agency complex.

3 Results and Discussion

The initial work was done in characterizing of

the alumina dross waste. This was done by

looking at the crystal morphology by the SEM

and determines the crystalline phase by XRD.

Figure 1 below shows the SEM micrograph and

XRD diffractogram of the starting aluminium

dross waste. The SEM micrograph also shows

that the non-uniformed crystal plate morphology

but of similar crystal type for the aluminium

dross waste.

Figure 1: XRD diffractogram of starting

aluminium dross waste with SEM micrograph

inset (20,000x magnification)

The crystalline phase of this waste was then

determined from the XRD diffractogram (Fig.

1). Using the High Score Plus software with

data base from the International Centre for

Crystal Structure Data (ICSD), the crystalline

phase that best match the analyzed sample is

gibbsite, (Al(OH)3), ICSD reference pattern 98-

001-7326. Results from Fig.1 also show the

occurrence of only a single crystalline phase

with high crystalline as reflected from the sharp

peaks and high count intensities.

When the aluminium dross sample was heated

to 800oC, a phase transformation process

occurred as can be seen from the XRD

diffractogram (Fig. 2). Using the same software

shows that the XRD diffractogram matches with

γ-alumina (γ-Al2O3) and the ICSD reference

pattern is 98-008-0889.

Work done by previous researchers stated that

changes from the gibbsite to γ-alumina may be

attributed to the phase transformation process

(3,4). In the process two major reactions took

place, the dissolution-recrystalization reaction

that happens when gibbsite is converted into

boehmite (AlOH) and the dehydroxylation

reaction when this boehmite is converted to γ-

RECENT ADVANCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT

ISSN: 1790-5095 18 ISBN: 978-960-474-142-7

alumina (3). Peaks shown in Fig.3 are also

broader with low count intensities indicating

that the γ-alumina is in an amorphous state.

Fig. 2: XRD diffractogram of aluminium dross

calcined at 800oC with SEM micrograph inset

(20,000x magnification)

With the available crystal structural data in the

software, a 6.5 nm crystallite size was obtained

for the γ-alumina calculated by using the

Reitveld’s method. This indicates that our γ-

alumina product can be classified as a

nanostructure powder with properties

comparable with other commercial γ-alumina

products (4). Besides the XRD, morphology of

the sample calcined at 800oC was also

determined by using the SEM (Fig. 2). The

morphology shows formation of layers on the

plate single crystal of the alumina product

similar to that of the initial aluminium dross.

These results are also consistent with the crystal

morphology obtained for γ alumina by previous

researchers (5,6,7).

When the aluminium dross was calcined at a

higher temperature of 1300oC, the crystalline

phase and morphology is as that shown in Fig. 3

below. The XRD diffractogram of the

aluminium dross calcined at this temperature

shows that the plate single crystal structure of

the previous calcined aluminium dross had

changed into different shapes. Heating at this

high temperature had also resulted to some of

the crystal grains to fuse with the other. The

XRD diffractogram also reveals the presence of

two different crystal phases, α-alumina (α-

Al2O3) and κ-alumina (κ-Al2O3). This is so as

ICSD reference pattern for α-alumina (98-004-

5328) and κ-alumina (98-006-6714) match the

diffraction peaks. Using Reitveld’s method, we

are then able to obtain the quantity of these

phases as 72.3% α-alumina and 27.3% κ-

alumina. As the commercial requirement of α-

alumina must have a minimum content of 95%

α-alumina crystal phase, our

product cannot meet this requirement (8).

RECENT ADVANCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT

ISSN: 1790-5095 19 ISBN: 978-960-474-142-7

Fig. 2: XRD diffractogram of aluminium dross

calcined at 1300oC with SEM micrograph inset

(20,000x magnification)

An alternative chemical recycling process was

used to produce the α-alumina. White

aluminium hydroxide precipitate formed from

this process was heated at 1300oC to determine

the properties of the calcined product (Fig.3).

The XRD diffractogram shows a single α-

alumina or corundum phase for the sample as

the entire peaks present match with the ICSD

reference pattern for α alumina (98-004-5328).

The sharp peaks with high intensity shows that

this is a highly crystalline material and analysis

of its crystallite by the Reitveld’s method gives

a value of 67 nm. The SEM micrograph of the

sample also shows a different morphology from

the previously aluminium dross sample that was

calcined at 1300oC. Uniformed rounded-edge

crystals are formed by using the chemical

recycling method and this tend to support the

single crystal phase obtained by the XRD. The

α-alumina product seems to fulfill the

commercial requirements of having a minimum

α-alumina crystalline phase of 95%.

Figure 3: XRD diffractogram of alumina sample

calcined at 1300oC with SEM micrograph inset

(50,000x magnification)

TEM analysis was then performed on the

sample to determine the morphology and size of

the crystals (Fig.4). The morphology of the α-

alumina is spherical shape with crystal size of

60-70nm. This result is in agreement with the

XRD result as well as the morphology is similar

to the commercial products (8).

A

A

A

A

A

A

K

K

K

A

A= α-alumina

K= κ-alumina

K

K K

A

A

RECENT ADVANCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT

ISSN: 1790-5095 20 ISBN: 978-960-474-142-7

Fig. 4: TEM micrograph of alumina sample

calcined at 1300oC (10,000x magnification)

4 Conclusion

The study shows that the physical and chemical

aluminium dross recycling process that we used

can produce γ and α-alumina products that meet

the commercial requirements. Analysis of the

crystallite size of these alumina products show

that they can be categorized as nano-sized

materials since their crystal size is much smaller

than the 100 nm. The result also shows that

crystal size measured by XRD is similar to that

of the TEM.

5 Acknowledgement

The authors wish to extend their gratitude to all

parties that had supported the project in

particular to the MTEC staff and manager, BTI

director and Nuclear Malaysia Agency

management.

References

[1] Beelan M.J.M and Van Der K.W., Methods

of processing aluminium dross and aluminium

dross residue into calcium aluminate, US Patent

5716426, 1998.

[2] Joaquin Aquilar-Santillan, Heberto

Balmori-Ramirez and Richard C. Bradt, Sol-gel

formation and kinetic analysis of the in-situ/self-

seeding transformation of bayerite to α-

alumina, Journal of Ceramic Proccessing

Research, 5(3), 2004, pp.196-202.

[3] Inoue M., (2004), Glycothermal synthesis of

metal oxides, J. Phys.: Condens. Matter,

16,2004, pp1291 – 1303

[4] Temuujin J., Jadambaa Ts., Mackenzie

K.J.D., Angerer P., Porte F. and Riley F.,

Thermal formation of corundum from

aluminium hydroxides prepared from various

aluminium salts, Bull. Mater. Sci., 23 (4), 2000,

pp.301-304.

[5] Chiang Chye Yong and John Wang,

Mechanical-activation-triggered gibbsite-to-

boehmite transition and activation-derived

alumina powders, Journal of the American

Ceramic Society, v.84, 6, 2001, pp 1-11

[6] Zarate J., Rosas G. and Perez R., Structural

transformation of the Pseudoboehmite to α

alumina, Journal of Material On-line, vol.1,

2005, pp 1-12.

[7] Chih-Peng Lin, Shaw-Bing Wen and ting-

Tai Lee, Preparation of nanometer-sized α-

alumina powders by calcining an emulsion of

boehmite and oleic acid, Journal of the

American Ceramic Society, 85, 1, 2002, pp.1-7

[8] Nanostructured and Amorphous Material

Inc., 2009, Nano-sized γ and α-alumina

products,

http://www.nanoamor.com/inc/sdetail/, 14th

July, 2009.

RECENT ADVANCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT

ISSN: 1790-5095 21 ISBN: 978-960-474-142-7