Alüminyum beyaz droslarının pirometalurjik değerlendirilmesi
Pyrometallurgical evaluation of aluminum white dross
Yazar: HASAN GÜNEY
Danışman: PROF. DR. ONURALP YÜCEL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Dünyada artan alüminyum üretimiyle birlikte ergitme işleminde ortaya çıkan alüminyum dros miktarı da artmaktadır. Ortaya çıkan droslar içerdiği metalik alüminyum miktarına göre siyah ve beyaz dros olarak ayrılmaktadır. Hem içerdiği yüksek alüminyum metal oranı hem de üretim miktarı daha yüksek olan beyaz drosun geri dönüşüme kazandırılması yüksek önem arz etmektedir. Normal şartlarda mekanik yöntemlerle iki farklı kısıma ayrılan beyaz dros, metalik alüminyumca zengin kısmı geri dönüşüm ile değerlendirilirken, metalik olmayan kalıntı ise atık depolama sahalarında gömülerek bertaraf edilmektedir. Metalik olmayan kalıntı içerdiği bileşiklerden dolayı depolandığı alanda çevreye olumsuz etkilere sebep olmaktadır. Bu çalışmada ise beyaz drosun tamamıyla geri dönüşüme katılması için deneysel çalışmalar gerçekleştirilmiştir. İlk deney grubunda iki farklı flaks kullanımı ile indüksiyon fırınında farklı sıcaklık ve sürelerde ergitme yöntemi ile alüminyum alaşım külçesi üretimi yapılmıştır. Üretilen alüminyum külçelere yapılan kimyasal analizler yardımı ile kütle denklik hesabı yapılarak alüminyum geri kazanım verimi hesaplanmıştır. Belirlenen optimum şartlar ile %98,36 safiyette alüminyum külçe üretimi, %85,81 oranında alüminyum kazanım verimi ile gerçekleştirilmiştir. İkinci deney setinde ise beyaz drosun metalik olmayan kalıntı kısmı, atık gömme alanlarında bertaraf edilmek yerine içerdiği yüksek alüminyum oksit içeriği sebebiyle bir hammadde olarak kullanılmış ve tekno-ekonomik değeri olan ergimiş alümina dönüştürülmüştür. Elektrik ark fırınında ergimiş alümina üretimi sırasında hammadde olarak kullanılan boksite alternatif olarak metalik olmayan kalıntı kısmı kullanılmıştır. Deneylerde 270 kVA DC gücündeki laboratuvar tipi elektrik ark fırınında hammadde olarak ilk elektroliz kalite alümina kullanılarak, ergimiş alümina eldesi için  bilgi ve tecrübe biriktirilmiş, fırın konfigürasyonları yapılmıştır. Daha sonra metalik olmayan kalıntı kısmı hammadde olarak kullanılmış ve farklı parametreler ile ergimiş alümina üretimi gerçekleştirilmiştir. Elde edilen ürünlere kimyasal analiz, XRD analizi, yoğunluk ve sertlik testleri gerçekleştirilmiştir. Sonuçta standartlara uygun ergimiş alümina üretimi yapılabildiği belirlenmiştir.
İlk deney grubunda hali hazırda küçük geri döünüşüm işletmelerinde ilkel yöntemler ile işlenen metalik alüminyumca zengin kısım, yüksek safiyette ve yüksek kazanım verimleri ile ergitilerek ingot halinde döküm için çalışmalar yapılmıştır.

Abstract:
With the increasing production of aluminum worldwide, the amount of aluminum dross generated during the production process is also significantly increasing. Aluminum dross is categorized into black and white dross based on the metallic aluminum content. White dross (or wet dross) occurs in primary aluminium production. White dross has a high concentration of metals and lesser amounts of salts and oxides. The metallic aluminium content can range from 20% to 80%. It occurs as compact material in large pieces or blocks. White dross is ground and sieved to separate the metallic aluminium from the oxides and iron impurities. White dross is considered a valuable material because the metallic aluminium can be recovered and the oxides can be used to make other refractory materials. Black dross (or dry dross) derives its name from its dark characteristic colour. It has a granular structure with a low metal content and a high salt and oxide concentration. Black dross is generated during aluminium recycling and, depending on the recycled scrap and processing conditions, the recoverable aluminium content is typically between 5% and 25%. Black dross mainly consists of metallic aluminium, aluminium nitride, alumina, sodium chloride, potassium chloride and silica.
White dross is particularly important for recycling due to its high metallic aluminum content and larger production quantities. Typically, white dross is mechanically separated into two parts: the part rich in metallic aluminum is recycled, while the non-metallic residue is disposed of in landfills. However, the non-metallic residue contains compounds that can have negative environmental impacts. This situation can lead to serious environmental and economic issues, such as soil and water contamination, which can harm local ecosystems and human health.
In this study, two different experimental sets were prepared to fully recycle white dross. The first experimental set focused on the evaluation of the part rich in metallic aluminum, which is also used in the industry. In the first experimental set, aluminum alloy ingots were produced by melting with different parameters in an induction furnace using two different salt methods. The salts and melting parameters used in this process are crucial for the quality and efficiency of the produced product. For instance, the type of salt and the temperature at which melting occurs can significantly influence the purity and yield of the aluminum ingots. Chemical analysis was performed on the produced ingots, and the aluminum recovery efficiency was calculated using mass balance calculations. These chemical analyses play a critical role in determining the purity of the obtained aluminum alloys and the proportions of other elements present. High-purity aluminum ingots are essential for various industrial applications, including the manufacturing of electronics, automotive parts, and aerospace components. As a result, an ingot containing 98.36% aluminum was produced, and an aluminum recovery rate of 85.81% was achieved from the waste raw material. This high recovery rate demonstrates the efficiency and economic viability of the process, indicating that a significant portion of the aluminum contained in the dross can be successfully recovered and reused.
In the second experimental set, the non-metallic residue of white dross was evaluated. Due to its high aluminum oxide content, this residue was used as a raw material to produce fused alumina. During this process, which was carried out in an electric arc furnace, the non-metallic residue was used as an alternative to bauxite. This method contributes to environmental sustainability by reducing the use of natural resources like bauxite, which is a primary ore of aluminum. Bauxite mining can have severe environmental impacts, including deforestation, habitat destruction, and water pollution. By using the non-metallic residue of white dross as a substitute, these negative effects can be mitigated. In the experiments conducted in a 270 kVA DC laboratory-type electric arc furnace, initially, electrolysis-grade alumina was used to gain knowledge and experience, and furnace configurations were made. Proper furnace configurations are essential for optimizing the melting process, ensuring uniform heating, and achieving the desired chemical composition in the final product. Subsequently, the non-metallic residue was used as a raw material, and fused alumina was produced with different parameters. The obtained products were subjected to chemical analysis, XRD analysis, density, and hardness tests. These analyses are important for evaluating the quality and industrial potential of the produced alumina. High-quality fused alumina is used in various applications, including refractory materials, abrasives, and ceramics, highlighting the industrial value of recycling non-metallic residues.
As a result, the experimental studies showed that both the part of white dross rich in metallic aluminum and the non-metallic residue can be recycled. This process offers significant economic and environmental benefits. Recycling white dross not only recovers valuable aluminum metal but also prevents the disposal of environmentally harmful waste. This is crucial for sustainable industrial practice and helps make aluminum production processes more environmentally friendly and efficient. Additionally, these recycling methods provide innovative solutions in industrial waste management, contributing to waste minimization and resource efficiency goals. Effective waste management is essential for industries to reduce their environmental footprint and comply with increasingly stringent environmental regulations.
Studies on the recycling of white dross can be integrated into industrial applications and applied on a large scale. These applications can be standardized in aluminum production facilities, creating a model for large-scale recycling projects. Furthermore, such recycling projects can improve waste management strategies, contribute to the conservation of natural resources, and ensure environmental sustainability. These processes not only provide economic benefits but also play an important role in fulfilling social and environmental responsibilities. Industries that adopt sustainable practices can enhance their reputation, meet the expectations of environmentally conscious consumers, and gain a competitive advantage in the market.
In summary, the recycling of white dross presents a significant opportunity for the aluminum industry both economically and environmentally. This process not only conserves valuable resources but also reduces the environmental impact of industrial waste, taking an important step towards a more sustainable future. Effective recycling of white dross contributes to the proliferation of innovative and environmentally friendly practices in aluminum production, enhancing the overall performance and sustainability of the industry. The findings of this study form an important basis for the development and application of recycling technologies. By demonstrating the feasibility and benefits of recycling aluminum dross, this research encourages further investment and innovation in recycling technologies, ultimately leading to more sustainable industrial practices and a reduction in the environmental impact of aluminum production. The advancement of recycling technologies will ensure the efficient use of resources and the spread of environmentally friendly production processes. This will be a critical step for the future growth and development strategies of the aluminum industry, contributing to both economic and environmental sustainability in the long term.