Production of Ferromolybdenum from Mill Scale via Aluminothermic Process Alüminotermik Yöntem Yoluyla Tufalden Ferromolibden Üretimi

In this study, the production of ferromolybdenum (FeMo), which is an iron-based alloy, was carried out through the metallothermic reaction. This method was chosen due to its low cost, short process time and minimum energy need. Before the experiments, FactSage and HSC software were used for thermochemical modeling. Mill scale was used as a starting material in the experimental studies. Mill scale is waste material and it contains 70% iron by mass. MoO 3 was used as the molybdenum source and aluminum was used as the reducing agent. Produced samples were characterized by Atomic Adsorption Spectrometry (AAS), X-Ray Fluorescence (XRF) and hardness tests (micro-Vickers). Initially, the effect of aluminum stoichiometry, which was used as a reductant, on FeMo efficiency was investigated. The closest result to the target alloy was achieved with the sample having 105% aluminum stoichiometry. Fe and Mo efficiencies were 95.16% and 97.21%, respectively. The effects of weight change on Fe and Mo efficiencies were investigated by using samples having 105% aluminum stoichiometry. It was observed that the closest result to the target alloy was achieved with a 75 g charge. Fe and Mo efficiencies were 99.10% and 97.98%, respectively. These were the highest efficiency values obtained in all experiments. The hardness values of samples were between 678 HV10 and 767 HV10. The highest hardness value was obtained in the alloy containing 100% stoichiometric aluminum. It was concluded that there was no significant difference in the hardness values of the samples due to the similarity in their chemical structures. stokiyometrisine sahip olan numune hedef alaşıma en yakın sonucu vermiştir. Bu numunede elde edilen Fe verimi %95,16, Mo verimi ise %97,21 olmuştur. Ağırlık değişiminin Fe ve Mo verimleri üzerindeki etkisi %105 alüminyum stokiyometrisine sahip olan numuneler kullanılarak araştırılmıştır. Hedef alaşıma en yakın sonucun 75 gram ağırlığındaki şarj ile elde edildiği Bu numunedeki Fe verimi %99,10, Mo verimi ise 97,98 olmuştur. Bu numunede elde edilen Fe ve Mo verimleri bütün deneylerde elde edilen en yüksek verim değerleridir. Numunelere yapılan sertlik testlerinde 678 HV10 ve HV10 arasında değerler elde edilmiştir. En yüksek sertlik değeri %100 stokiyometrik alüminyum içeren numune ile elde edilmiştir. Numunelerin kimyasal yapılarının birbirine yakın olması sebebiyle birbirine yakın sertlik değerlerinin elde edildiği sonucuna varılmıştır.


Introduction
Mill scale is a waste material that occurs during annealing of steel slabs and billets in annealing furnaces, continuous casting plants and rolling mills. Mill scale is an oxide layer that forms on the surface, and it contains 70% iron by mass [1].
Every year, 13.5 million metric tons of mill scale is formed [2].
Recycling of the mill scale is an important issue since it is waste material and is formed in a very high amount. There are many applications where the mill scale is used as an additive. One of the most common use of mill scale as an additive is the Portland cement. It is added to the Portland cement's structure with casting sand and slag [3]. Mill scale is used as an additive in electromagnetic interference shielding [4] and stabilization of expansive soil [5]. Also, it is employed in the adsorbing of lead ions in aqueous solutions [6]. Besides, it is used as an iron oxide source in sintering applications [7].
Furthermore, mill scale is used in hydrogen fuel cells, medical imaging and improving of water quality when it is processed into nano-scale particles [8].

Molybdenum was discovered by
Carl Wilhelm Scheele in 1778. Swedish chemist was working on a mineral which is now known as molybdenite (MoS2). The molybdenite mineral was confused with graphite and lead at that time. However, studies showed that this mineral contains a new element. This element was called as molybdenum by Scheele [9]. MoS2 is the main mineral used in the production of ferroalloys today. centered cubic (a=314 nm), and its external electron shell configuration is 4d 5 5s 1 [10].
Molybdenum is one of the common elements used in the alloying of stainless steels. It is also used in alloyed cast irons and superalloys. Molybdenum provides hardenability in some of the heat-treatable alloys. It is also used in tool steels and hard metals. Besides, molybdenum is used for improving the corrosion resistance of stainless steels [11].
When the ancient artifacts are examined, it is seen that they were made of nearly pure iron. The only alloying element found in the structure of these ancient artifacts is carbon. It has been understood over time that the rate of carbon in iron can be controlled. The amount of carbon in the steel was adjusted to a certain extent by carburization and decarburization throughout the Iron Age. Over time, higher temperatures were reached in the steel production process and as a result, the carbon content of the steels was increased.
Some major alloying elements of modern steels were found as natural impurities in the steels which were produced in ancient times [10]. (up to 20% Si) has been produced [11].
Today, the main method used in the production of ferroalloys is carbothermic reduction. In carbothermic reduction, the metal content of metal oxide is reduced by carbon. The metallothermic reduction is an alternative method for carbothermic reduction. The main principle of metallothermic reduction is to reduce the metal content of metal oxide by using a reductant with a higher oxygen affinity.
Various metals and alloys are produced by using metallothermic processes. In metallothermic reactions, the reaction is started by using external heat, then it self-propagates in the reactant mixture [13]. The exothermic characteristic of metallothermic processes ensures that lower energy is required compared to carbothermic processes. Therefore, the costs of metallothermic processes are lower compared to carbothermic processes.
The completion of the process in a short time and the production of high-purity products without carbon are other important advantages of metallothermic processes. However, metallothermic processes also have some disadvantages. In these processes, the homogeneity problem may arise from time to time and reactants may not react completely. These potential problems can be eliminated by using additives or changing parameters such as particle size, ignition temperature and reaction temperature.
In this study, it was aimed to produce ferromolybdenum by metallothermic reduction using mill scale, which occurs during continuous casting.
Aluminum was used as a reductant and ferromolybdenum meeting ASTM A132-04 standard was chosen as the target alloy.

Theoretical Background
The main principle of metallothermic reduction is to reduce the metal content of metal oxide by using a reductant with a higher oxygen affinity.   Figure 1 and the workflow diagram of the system is given in Figure 2.

Results and Discussion
The main principle of the metallothermic reduction process which is In the studies carried out to produce  Table 2. Efficiencies that were calculated according to this equation are illustrated in Figure 5.
Metal Recovery = 100 × The weight of metal after metallothermic process (g) The weight of aspect metal after metallothermic process (g) (4)     When data obtained from models were evaluated, it was seen that the total reaction will proceed in a controlled