Efficient preparation of AlV65 alloy through aluminothermic reduction of sodium metavanadate precipitated from shale V-rich solution

Abstract

The use of Al–V alloys as intermediate additives is pivotal for producing high-performance Ti alloys. Traditionally, the synthesis of these alloys relies on high-purity V2O5, with sodium metavanadate as an essential intermediate in V2O5 production. This study explores an alternative approach utilizing sodium metavanadate directly, offering an aluminothermic process to alleviate the environmental impact and reduce the time required for V2O5 preparation. Al–V alloys are synthesized using sodium metavanadate derived from a shale V-rich solution, and the impurity-migration behaviors are comprehensively analyzed, specifically focusing on Fe, Al, and Na. The results reveal that Al interacts with CaO to form a slag phase that is different from the alloy, whereas Na undergoes a sequence of reductions (NaVO3 → Na2V2O5 → NaVO2 → Na) and volatilizes at 25–1200°C, thereby avoiding incorporation into the alloy. Fe, reduced by Al, enriches the alloy phase and induces a phase transition (Al–V → Al–Fe → Fe–V) in the presence of excess Fe. Sodium metavanadate (Fe ≤ 0.05wt%) derived from the shale V-rich solution enables the production of a uniform AlV65 alloy with 66.56wt% V, 33.14wt% Al, 0.08wt% Fe, 0.07wt% C, 0.02wt% N, and 0.12wt% O. These results establish a streamlined, efficient framework for the future preparation of Al–V alloys from shale V-rich solutions.

1. Introduction

V is an essential rare metal, recognized as a critical strategic resource on a global scale, and is extensively utilized across key industries, including iron and steel, nonferrous metals, chemical processing, nuclear energy, and energy storage. Furthermore, V is frequently incorporated into Ti alloys, particularly Al–V alloys, as it enhances the strength, flexibility, and plasticity of these materials [1–4]. Al–V alloys are predominantly employed in the military and aerospace sectors, with TC4 (Ti–6Al–4V) being the most widely used alloy [5–9]. The production of these alloys depends on the aluminothermic reduction process, which is generally classified into four methods: the aluminothermic, electro-aluminothermic, self-propagating, and microwave methods [10–12]. Among these, the aluminothermic method is the most well-established because of its simplicity and high vanadium yield, thereby serving as the primary method for industrial production [13].

Al–V alloys are currently synthesized utilizing 99.9wt% V2O5. Souza et al. [14] explored the process parameters for alloy production using 99.9wt% V2O5 and aluminum powder. Yee et al. [15] utilized aluminum powder with a purity exceeding 99.8wt% alongside V2O5 as raw materials for the preparation of Al–V alloys. Wang et al. [16] specified the use of V2O5 with a purity greater than 99.8wt%, Al exceeding 99.8wt%, and CaO greater than 98.5wt% for the synthesis of Al–V alloys. The production of high-purity V2O5 typically requires the removal of aluminum and iron impurities from the vanadium solution. This is a time-consuming process that requires additional steps to yield 99wt% pure V2O5. This phenomenon can be attributed to the incorporation of excess Al and Fe into the V precipitate, which adversely affects the purity of the resultant V2O5 [17–18]. Önal and Topkaya [19] carried out a re-precipitation process to convert Fe and Al into hematite and alumina respectively at a temperature ranging from 230 to 270°C. Luo et al. [20] employed phosphate ions to convert additional iron and aluminum impurities into complex precipitates, achieving reductions of 82.1wt% and 47.3wt% in the iron and aluminum levels, respectively. Shi et al. [21] used a two-stage method to selectively separate V and Al via crystallization and solvent extraction. The obtained V2O5 exhibited a purity of 98.39wt%. The aforementioned research revealed that eliminating aluminum and iron impurities is a crucial step in the production of high-purity V2O5 products.