A Waste to Wealth Study on Converting Aluminium Dross Schedule Waste into γ and α Alumina

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1 RECENT DVNCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT Waste to Wealth Study on Converting luminium Dross Schedule Waste into γ and α lumina MEOR YUSOFF M.S., MSLIN MUSLIM ND WILFRED PULUS Materials Technology Group, Malaysian Nuclear gency, Bangi, ajang, Selangor, MLYSI. http: // bstract:- luminium dross waste is classified as a schedule waste and could pose environmental hazards. 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. eywords:- luminium dross, schedule waste, γ-alumina, α-alumina, physical and chemical processes 1 Introduction luminium 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 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. lumina 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. nother 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. ISSN: ISBN:

2 RECENT DVNCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT 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 o C in a muffle furnace. The crystalline phase and morphology was then determined using the same XRD and SEM methods. 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. fter separating the white precipitate from the liquid using a vacuum filter, it is dried overnight in an oven at 70 o C. The hydrated alumina powder produced after the drying stage is then calcined at 1300 o C 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 gency 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, (l(oh) 3 ), ICSD reference pattern 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 800 o C, 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-l 2 O 3 ) and the ICSD reference pattern is 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 (loh) and the dehydroxylation reaction when this boehmite is converted to γ- ISSN: ISBN:

3 RECENT DVNCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT 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 800 o C 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 800 o C 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 1300 o C, 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- l 2 O 3 ) and κ-alumina (κ-l 2 O 3 ). This is so as ICSD reference pattern for α-alumina ( ) and κ-alumina ( ) 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. s the commercial requirement of α- alumina must have a minimum content of 95% α-alumina crystal phase, our product cannot meet this requirement (8). ISSN: ISBN:

4 RECENT DVNCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT = α-alumina = κ-alumina Fig. 2: XRD diffractogram of aluminium dross calcined at 1300 o C with SEM micrograph inset (20,000x magnification) n alternative chemical recycling process was used to produce the α-alumina. White aluminium hydroxide precipitate formed from this process was heated at 1300 o C 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 ( ). 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 1300 o C. 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 1300 o C 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). ISSN: ISBN:

5 RECENT DVNCES in ENVIRONMENT, ECOSYSTEMS and DEVELOPMENT Fig. 4: TEM micrograph of alumina sample calcined at 1300 o C (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. nalysis 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 cknowledgement [2] Joaquin quilar-santillan, Heberto Balmori-Ramirez and Richard C. Bradt, Sol-gel formation and kinetic analysis of the in-situ/selfseeding transformation of bayerite to α- alumina, Journal of Ceramic Proccessing Research, 5(3), 2004, pp [3] Inoue M., (2004), Glycothermal synthesis of metal oxides, J. Phys.: Condens. Matter, 16,2004, pp [4] Temuujin J., Jadambaa Ts., Mackenzie.J.D., ngerer 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 [5] Chiang Chye Yong and John Wang, Mechanical-activation-triggered gibbsite-toboehmite transition and activation-derived alumina powders, Journal of the merican 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 [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 merican Ceramic Society, 85, 1, 2002, pp.1-7 [8] Nanostructured and morphous Material Inc., 2009, Nano-sized γ and α-alumina products, 14 th July, 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 gency management. References [1] Beelan M.J.M and Van Der.W., Methods of processing aluminium dross and aluminium dross residue into calcium aluminate, US Patent , ISSN: ISBN: