Kalsine dolomit redüksiyonunda geri dönüşüm ürünü alüminyum kullanımının etkisi
The effect of recycling product aluminum use on calcined dolomite reduction
Yazar: UMUT ALİ SATILMIŞ
Danışman: PROF. DR. ONURALP YÜCEL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Metalurji Mühendisliği = Metallurgical Engineering
Dizin: Alüminyum = Aluminum ; Dolomit = Dolomite ; Geri dönüşüm =   ; Kalsine hammadde = Calcined material ; Redüksiyon =

Özet:
Magnezyum metal üretimi için bugüne kadar birçok yöntem geliştirilmekle birlikte günümüzün hakim teknolojisi, vakumda metalotermik yöntem ile üretimdir. Redükleyici olarak ferrosilisyumun kullanıldığı bu yötem halen tekno-ekonomik olarak geliştirilmeye açıktır. Bu çalışmada redükleyici maddeye alternatif olarak alüminyum seçilmiştir. Alüminyum tüketiminin de hızla artması, üretim artıklarının da (cüruf) çoğalmasına yol açmaktadır. Alüminyum cüruflarının değerlendirilmesi konusu da günümüzün enerji verimliliği ve çevrenin korunması açısından çok öenm kazanmıştır. Alüminyum cüruflarının zenginleştirilmesi ile elde edilen metalik alüminyumca zengin (%53,50 Al) bu malzemeler redükleyici olarak kullanılarak kalsine dolomitten (%38,97 MgO) magnezyum üretimine etki eden parametreler araştırılmıştır.
Termodinamik incelemeler ve stokiometrik hesaplamalar sonrası belirlenmiş karışımlar 1200 - 1300˚C'da 1-6 saat aralığındaki redüksiyon sürelerinde redüklenmiş, redüksiyon ürünü kalıntıdaki magnezyum içeriği ölçülmüş ve bu değerler kullanılarak magnezyum redüksiyon verimleri hesaplanmıştır.
Cüruftan üretilmiş metalik alüminyum değeri %53,50 olan zenginleştirilmiş ürün, kalsine dolomit redüksiyon stokiometrisine uygun olarak redükleyici madde olarak kullanılmış, sıcaklık ve süre gibi parametreler optimize edilmiştir. %100 stokiometri Al ilavesi 1300˚C, 6 saat süreyle 1 mbar vakum ortamında gerçekleştirilen redüksiyon işlemiyle redüksiyon sonrası kalıntıda magnezyum içeriği %9,93'e kadar azalmıştır. Bu şartlarda magnezyum redüksiyon verimi %63,22 olarak gerçekleşmiştir.
Stokiometrik alüminyum ilave miktarının %150 olarak kullanıldığı 1300˚C'de 6 saat süreyle yapılan deneyde kalıntıdaki Mg içeriği %5,31'e azalmış redüksiyon verimi ise %80,81 olarak hesaplanmıştır. Benzer şartlarda CaF2 ilavesi ile 240 dakika süre ile yapılan deneyler sonucunda ise redüksiyon verimi %90,87 ye kadar artırılabilmiştir.
Bu durum alüminyum endüstri atığı cüruftan elde edile metalik alüminyumca zengin ürünün yüksek verimle magnezyum üretiminde kullanılabileceğini göstermiştir.

Abstract:
Magnesium is the lightest of all light metal alloys and therefore is an excellent choice for engineering applications when weight is a critical design element. It is strong, has good heat dissipation, good damping and is readily available. Its properties make it easy to weld, forge, cast or machine. It can be alloyed with other metals, making them more beneficial. The use of pure magnesium is rare due to its volatility at high temperatures and it is extremely corrosive in wet environments. Therefore the use of magnesium alloys when designing aerospace and automotive parts is critical. Today's interest in magnesium alloys for automotive applications is based on the combination of high strength properties and low density. In automotive applications weight reduction will improve the performance of a vehicle by reducing the rolling resistance and energy is used in acceleration, thus reducing fuel consumption and, moreover, a reduction in the greenhouse gas CO2 can be achieved. In the 1920s magnesium began to make an appearance in the automotive industry. The light weight metal began to be used in racing car adding to their competitive edge. Interest in using magnesium in automotive applications has increased over the past decade in response to the increasing environmental and legislative influences. Fuel efficiency, increased performance and sustainability are top-of-mind issues. The use of magnesium in vehicles can, and does, lower overall weight and improves each of these conditions. Many large automotive companies have already replaced steel and aluminum with magnesium in various parts of their products. Magnesium is currently being used in gearboxes, steering columns and driver's air bag housings as well as in steering wheels, seat frames and fuel tank covers. The use of magnesium in automotive applications can provide more than just weight savings. For many years, the desire to identify challenges, solutions, and opportunities regarding the use of magnesium in vehicles has been growing. Magnesium usage on the front end of a vehicle provides not just a lower overall mass for the car, but also allows for the shifting of the center of gravity towards the rear improving the car's handling and turning capabilities. In addition, frequencies that reduce vibration and overall noise can be achieved through the tuning of magnesium parts. Steel components in vehicles can be replaced by a single cast piece of magnesium adding to the strength of the material and allowing for housings to be cast into place. This castability also requires less tooling and fewer gauges, which lowers manufacturing costs.
Cars, vans and trucks are not the only vehicles that have incorporated magnesium in their designs. The aerospace industry has a long history of using the metal in many applications both civil and military. It is critical to lower the weight of air and space craft, as well as projectiles, if we are to achieve decreases in emissions and greater fuel efficiency. These changes will result in lower operational costs as well. Magnesium is an ideal material for use in these applications, due to limited continuing improvements on aluminum weight reduction, the high cost of fiber metal laminates, and the poor impact and damage properties of low density plastics when subjected to extreme temperatures. Spacecraft and missiles also contain magnesium and its alloys. Lift-off weight reduction is of high importance in their design and a material is needed that can withstand the extreme conditions faced during their operation. Magnesium is capable of withstanding the extreme elevated temperatures, exposure to ozone and the impact of high energy particles and matter. It is also used in large quantity in intercontinental ballistic missiles.
In the 1st half of last century, magnesium was first introduced in the medical industry as an orthopedic biomaterial. There are many characteristics and properties that make magnesium a very attractive option for use in implants and similar applications. Other common implant materials have densities that range from 3.1-9.2g/cm3, whereas the density of natural bone is 1.8-2.1g/cm3. Magnesium alloys are much more comparable, at a density of 1.74-2.0g/cm3. Magnesium is also much more akin to natural bone than other materials in regards to fracture toughness, elastic modulus and compressive yield strength. Not only does magnesium provide the mechanical and physical properties desirable in these applications, it also exhibits some special characteristics. Magnesium is found naturally as an ion in the human body equating to about one mole in a 70kg person, half of which is stored within bone tissue. Magnesium within the body assists in metabolic reactions, has good biocompatibility, and is nontoxic. In addition, uncoated magnesium implants can be biodegradable in bodily fluids through corrosion, which eliminates the need for a further surgery to remove implants. Application of protective coatings can prevent corrosion issues in situations where a more permanent solution is needed. Research and testing of different alloys and formulas for protective finishes is currently in progress with the aim of increasing the array of ways in which magnesium can be used in medical applications.
In the current market, small and portable electronics are trending upward. The demand for compact devices that can be easily transported is booming and magnesium is often a key component in meeting this demand. Many magnesium alloys being used to replace plastics are just as light, but they are much stronger and more durable. Magnesium is also better in regards to heat transfer and dissipation as well as its ability to shield electromagnetic and radio frequency interference. Many electronics require parts or casings with complex shapes which are possible with magnesium. Cameras, cell phones, laptops and portable media device housings are all common applications in addition to the arms of hard drives. Similar to its applications in other industries, magnesium is prized for use in sports equipment due to its light weight and impact resistance. Magnesium also has the ability to be formed into intricate shapes, which is ideal for use in golf clubs, tennis rackets and the handles of archery bows. The damping effects of the alloys also make it a good candidate for bicycle frames and the chassis of in-line skates, since the magnesium can absorb shock and vibration. This absorption allows cyclists to exert less energy and enjoy a smoother, more comfortable ride. Magnesium vaulting poles have also come into production as they have minimal twisting due to their high torsional strain resistance.
Magnesium is utilized in optical and hand-held tool design. Wearers of spectacles often desire an aesthetically pleasing frame that is not felt during day-to-day wear but is sturdy enough to handle being removed and replaced throughout the day. Rifle scopes and binoculars must be stable in order to be effective and a light weight is also beneficial in their marketability. Magnesium allows for these design criteria to be met.
Hand-held work tools and devices such chain saws, hand shears, hand drills, pneumatic nail guns and weed whackers are all perfect candidates for magnesium applications. The low density, comparative strength and vibration damping capabilities are all desirable characteristics in creation of handheld tools such as these. Magnesium has also found its way into small household appliances such as vacuums. By utilizing this material for a vacuum head, it will be light enough to easily move around as well as being dent resistant in normal use when coming in contact with furniture and other obstacles. As the inherent benefits of magnesium applications are further realized, the ways in which it can and will be used become numerous. Demand for sustainable, lightweight and recyclable materials is ever increasing with the push towards environmentally-conscious products, which can only be beneficial for the magnesium industry.
Dolomite, one of the minerals in which magnesium is produced, is found in high quantities in our country and new trend is shown in its production.
Many processes have been developed to produce magnesium. In this study, magnesium production was investigated by metalothermic method. However, the important point in the study is that pure aluminum is not used as a reducing agent. Instead, aluminum dross is used which is enriched in reductant, that is to say with increased aluminum content. Because aluminum dross is a side product in aluminum production and its evaluation is very important both in terms of energy and environmental impact. Secondary aluminum replaces primary aluminum with a 95% gain in energy. In addition, a considerably large environmental space is required for the storage of aluminum waste. For these reasons, calcined dolomite was reduced by this dross, which made it possible to use aluminum dross again in production, and magnesium production was investigated.
In experimental studies, as magnesium raw material calcined dolomite (38,97% MgO) and as reducing agent enriched aluminum dross (58,50% Al) have been used. These materials were first ground and mixed to prepare mixtures at appropriate stoichiometric ratios. Each of the mixtures was used for separate experiments. The mixture was pelletized and placed in the alumina boat and it was loaded to a stainless steel retort with water cooling system at the end. The retort is placed so that it is centered in the furnace, closed to ensure vacuum conditions and connected to the vacuum motor. The mixture was kept in the retort during the required test period in the environment where the oven was brought to the proper temperature and the vacuum was about 1 mbar and the weight loss was determined by removing weight at the end of the experiment. Also the chemical analysis of the sample and the X-ray analysis were examined. From these determinations, magnesium production was investigated in the direction of magnesium reduction recovery and the % Mg content of the residue. The effects on the reduction of the different time, temperature, stoichiometry and addition of the scouring agent were investigated as a result of the experiments carried out. As a result of the experiments; In the experiment with 150% Al dross, 5% calcium fluoride, the highest Mg reduction recovery reached 90.87% and the lowest amount of Mg (2.61%) reached during this study. According to this result, in the reduction of calcined dolomite with Al dross; It has been observed that the use of high Al stoichiometry and the addition of scouring agent (CaF2, minimum 5% of mixture) ensure the highest results.