مطالعه سینتیک استخراج استرانسیوم با کاهش متالوترمیک با استفاده از تزریق پودر های استرونسیم A kinetic study of the strontium extraction by metallothermic reduction using submerged SrO powders injection

۱٫ Introduction Until recently, strontium was one of the less important elements from the production volume point of view. This situation has been changed due the increased application for strontium in the automobile and aerospace industries resulting in growing demand for the metal. This metal is frequently used in master alloy form, such as Al–Sr and Al–Sr–Mg [1]. Strontium is a reactive metal making it difficult and costly to produce except under carefully controlled processes. Nowadays, the most effective method for strontium production is the metallothermic reduction of its oxide. This process, named “Melt Leach Evaporation” (MLE), is under development for the extraction of valuable Group IIA metals of the Periodic Table. The MLE process consists of mixing and contacting the value metal source material, which might be an ore or concentrate, with an excess of molten metal which is acting as a reductant and lixiviant. In the process, the value metal extracted from the source material is dissolved in the excess molten metallic solvent and is subsequently extracted as a vapour by vacuum distillation [2]. For the extraction of strontium from its oxide, different methods have been developed, which work under vacuum conditions and high temperatures. These conditions increase the production cost. In light of the foregoing, the process of strontium extraction from SrO through the use of submerged powders injection of strontium oxide is very attractive alternative from both the technological and the economic points of view. So in this paper, the results obtained about the feasibility to incorporate metallic strontium to Al–Mg liquid alloy from metallothermic reduction of strontium oxide at scale laboratory are presented. ۲٫ Materials and methods The experimental trials were carried out in a high frequency induction furnace 15 kg molten aluminum capacity. The powders injection equipment, whose scheme is presented in Fig. 1, allowed the continuous and controlled feeding of solid material through an inert carrier gas. This equipment is frequently used in the process of Mg and Sb removal from molten aluminum alloy [3,4]. The reactants used in the experiments were as follows: Al (99% purity); Mg (99% purity); SrO (−۷۰ + ۱۴۰ mesh [5]). The selected experimental factors and their levels were temperature (973, 1023, 1073 K), magnesium content in the alloy (1, 2, 3 wt.%) and injection time (15, 30, 45, 60 min). To simplify the process of powder injection, the following parameters were kept constant: amount of liquid alloy: 10± ۰٫۱ kg; powder flow rate to carrier gas flow rate ratio: 17 g SrO/min / 12 L Ar/min. The typical experimental trial was conducted as follows: First, the alloy with the initial chemical composition was melted in the induction furnace. Then, the injection system was attached to the furnace and fixed. The graphite lance was submerged into the melt at the specified depth and position (Fig. 1) [6]. Argon gas (UHP 99.99%) was blown into the melt for 3 min before introducing the particles of the reactive powder to avoid powder clogging. No fluxing or degassing of the melt was performed after melting, so the alloy was only treated for strontium increase. Finally, to obtain kinetic information and metallographic, samples were taken at 15 min intervals and analyzed by using inductively coupled plasma spectrometry (ICP) and Scanning Electron Microscope (SEM) respectively. Dross samples were taken at the end of each experiment and analyzed by X-ray diffraction (XRD) for the qualitative identification of the crystalline compounds.