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Novel Chemical Treatment Approach and Characterization of Graphite from Industrial Aluminum Waste

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Novel Chemical Treatment Approach and Characterization of Graphite from Industrial Aluminum Waste International Journal of Advances in Science Engineering and Technology, ISSN(p): 2321 –8991, ISSN(e): 2321 –9009 Vol-6, Iss-3, Spl. Issue-2 Sep.-2018, http://iraj.in NOVEL CHEMICAL TREATMENT APPROACH AND CHARACTERIZATION OF GRAPHITE FROM INDUSTRIAL ALUMINUM WASTE 1OMAR ALJAROD, 2ABOUBAKR M. ABDULLAH 1Department of Chemistry, Qatar University, Doha 2713 Qatar 2Center for Advanced Materials, Qatar University, Doha 2713 Qatar E-mail: [email protected], [email protected] Abstract - Thousands of tons of Spent Pot Lining (SPL) are produced annually by the primary aluminum producing industry. SPL is classified into two types, 1st and 2nd cut SPL waste. The 1st cut, which is the material under investigation in this study, is a contaminated graphite/ceramics material (50-60% of it is graphite) that is used in lining the electrolytic cell st where aluminum is produced by the reduction of molten Al2O3. 1 cut SPL is considered as a hazardous material as it contains contaminants such as fluorides, and small traces of cyanides. It also produces flammable gases when it comes in contact with water (i.e. ammonia, hydrogen and methane). This paper fully characterizes Qatalum’s 1st cut SPL that was de- lined from electrolytes cell, chemically treated this 1st cut SPL and extract the graphite component for use in some applications, in heavy metal ions removal from water. The functionalized graphite showed a high efficiency copper ions removal from aqueous solutions at different pH values with the efficiency at pH 7. Keywords - Chemical treatment, Aluminum waste, Graphite extraction, Heavy metal removal, Wastewater treatment I. INTRODUCTION Another composition of the 2nd cut lining is the insulation bricks that are installed under the Nowadays, the number of aluminum production refractory material to protect it from local high factories is growing rapidly to make the aluminum temperature and chemical attacks [16,17]. one of the most products used worldwide. Primary aluminum is mechanically produced by an energy demanding, two separate processes. The Bayer- process is the first-step reaction; where the raw material bauxite is refined having 30-60% alumina (Al2O3) to clear alumina[1, 2]. The second reaction is called the electrochemical reduction. In this process; the alumina is decomposed into its main element by an applied electrical current[3]. The Hall-Heroult process is an example of the aluminum smelting process that is used nowadays. Additionally, liquid aluminum is produced by the dissolving alumina (Al2O3) initially in cryolite (Na3AlF6). The process takes place in an electrolytic cell which is called the pot. A clarification of this pot is shown in Figure 1. The hall that contains the pots is usually located in a long row known as pot lines. The links between pots can be side by side or end by end. The basics of Fig.1Schematic drawing of the main features of an Hall- aluminum electrolysis are well described by Héroultaluminium reduction cell: (1) anode (prebaked); (2) numerous authors elsewhere [1, 4, 5]. electrolyte (bath); (3) Alumina point feeder, (3a) alumina The actual cathode is the reduced Aluminium metal at hopper (3b) air cylinder, (3c) metering chamber, (3d) crust breaker; (4) aluminium pad; (5) anode beam (current supply); the bottom of the cell but the term “cathode” of the (6) anode yoke and stubs (iron); (7) anode rod (aluminium); (8) pot is granted for the carbonaceous pot lining [2,3]. anode clamp; (9) spent anode (butt); (10) alumina crust/ cover; Thepot lining can be classified mainly into 1st cut and (11) crust (side ledge); (12) cathode carbon block; (13) current 2nd cut. The 1st cut is the cathode and is mainly collector bar (steel); (14) ramming paste; (15) refractory; (16) consisting of carbonaceous materials blocks with insulation; (17) steel shell; (18) sidewall block; (19) cast able; st (20) alumina; (21) rock wool and (22) gas collection hood graphitized carbon [4-8]. The role of the 1 cut is (removable).The details in the lining may vary[1]. conducting electricity. The refractory layer that is located below the cathode carbon layer is one of the The life time of the pot is about six years. During this main constituents of the 2nd cut lining [9,10]. Most of present of time, the lining absorbs and collects the refractory materials are composed of alumina- different materials that retard the Al production silicates (Al2O3- SiO2) [11-15]. Its role is distributing process and lower the purity of the produced Al [18- the heat to the cathode and the bath uniformly. 20]. To avoid this, the pot lining has to be removed Novel Chemical Treatment Approach and Characterization of Graphite from Industrial Aluminum Waste 15 International Journal of Advances in Science Engineering and Technology, ISSN(p): 2321 –8991, ISSN(e): 2321 –9009 Vol-6, Iss-3, Spl. Issue-2 Sep.-2018, http://iraj.in and replaced by new ones regularly [13-15]. The were purchased from Sigma Aldrich and used without removed pot lining is also classified accordingly as 1st further purification. and 2nd cut and is nominated as spent pot lining 2.2.Extraction of graphite (SPL). Spent pot lining 1st cut waste was washed with Worldwide, SPL is produced in hundreds of deionized water, where the produced gases were thousands of tons annually as a waste from the collected in gas bags (Supelco analytical, Bellefonte, production process of metallic Aluminum. Qatalum PA, USA) and characterized using gas (Qatar Aluminum Company, Mesaieed Industrial chromatography-mass spectroscopy (GC-MS) to City, Qatar) is an equivalent joint venture between confirm the evolution of hydrogen, methane, oxygen st Qatar Petroleum and Hydro Aluminum of Norway, it and NH3 gas once the 1 Cut SPL come in contact produces 585,000 tons of high efficient aluminum with water. The powder was then treated with cycles items every annum from twin 1.2 kilometer pot lines. of different concentrations of NaOH, HNO3 and Qatalum's has different facility such as carbon plant, deionized water for removal of remaining inorganic port and storage spaces, and in addition a power and organic contaminants. plant. Qatalum has 704 pots (each 12×4 m2) stunted 2.3.Preparation of functionalized Graphene to de-line all of them after 6 years. Each pot is Graphene was produced from the extracted graphite expected to produce 40 tons of 1st Cut SPL. The 1st powder using Hummer’s modified method [25]. Cut SPL is a contaminated graphite/ceramics material Primarily, 2g of graphite powder (200 mesh, 99.99%) that is used in lining the electrolytic cell within which and 1g of Sodium Nitrate were added to 50 ml of the primary aluminum is produced. It consists of 50 – concentrated H2SO4 and stirred vigorously at 0°C for 60% of graphite [20-25]. It is, also, considered as a 3 hr. After that, 6g of potassium permanganate was hazardous material since it contains many other slowly added to the solution and further stirred at contaminants e.g. fluorides, cyanides, lead and RTP for another 3 hr. The solution soon turned pasty chromium in addition to its production of flammable and dark green in color with the evolution of gas gases when it comes in contact with water e.g. bubbles. ammonia, phosphine, hydrogen and methane [19-22]. Subsequently, 100 ml of distilled water was slowly SPL treatment is a great challenge that faces the added to this solution and stirred for 30 min. until a aluminum industry due to the high cost of storage, brown color is visible. Furthermore, 100 ml of transportation and recycling. In this paper, FirstCut Hydrogen peroxide was added which turns the SPL produced by Qatalum is fully characterized with mixture into bright yellow. This suspension is then a focus on the extraction of graphite from the filtered and washed with an excess amount of warm carbonaceous component of SPL to make it deionized water and kept to dry overnight under applicable for use in heavy metal ions removal from vacuum at 60°C. The dried materials is graphene wastewater. oxide (GO). Afterwards, 0.1g of the dried GO was sonicated in 20 ml of deionized water until a II. EXPERIMENTAL homogeneous yellow dispersion was obtained. The GO was dispersed easily in water due to the presence 2.1. Materials of a variety of hydrophilic oxygen groups (i.e. -OH, The 1st cut SPL samples that were used in this work O-2 and COO-) on both the basal planes and edges. were donated by Qatar Aluminum Company The solution was placed inside a conventional (Qatalum) in Mesaieed industrial city (Qatalum microwave after adding 40 µl of the reducing agent Company, Qatar). In 2009, Qatalum started its [hydrazine hydrate (HH)]. The microwave oven was aluminum production. The 1st cut SPL was collected then operated at full power (1000 W), 2.45 GHz, in after five years of operation. The sample was big in 30 s cycles (on for 10 s, off and stirring for 20 s) for a size, rough and very hard. Hence, it was essential to total reaction time of 60 s. The yellow dispersion of have it crushed into small pieces. A cryomill GO gradually changed to a black color indicating the instrument was then used to produce fine SPL chemical reduction to “graphene”. Finally, this powder. Different materials were used, gas bags graphene (reduced graphene oxide) was (Supelco analytical, Bellefonte, PA, USA) to collect functionalized through boiling in 1:1 of gases in it. Also, diluted sodium hydroxide (NaOH) H2SO4:HNO3, washed with deionized water and hot and nitric acid (HNO3) were used (NaOH and HNO3 NaOH to change the carboxylic groups in to ionizable were purchased from Sigma Aldrich and used without carboxylate ones which increases the negative charge any purification).
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