ABSTRACT
Vanadium is a transition metal primarily used in the production of steels, as well as a chemical catalyst and alloying element. The Philippines, which is rich in iron resources, has a potential to use its iron ores for vanadium production. The demand for vanadium is expected to increase in the upcoming years due to its commercialization for large-scale energy storage applications. The study examines the feasibility of vanadium extraction from titanomagnetite ores in the country. Iron ores from Camarines Norte, Leyte, and Zamboanga were extracted via direct leaching method. Calcium fluoride addition (3-5 wt.%), solid-liquid (S/L) ratio (2.5-3.5 ml/g), and sulfuric acid concentration (4-5 M) were optimized using Response Surface Methodology (RSM) based on a three-factor, three-level Box Behnken design. Results of the statistical analyses suggest that the optimum leaching parameters are 4.02 wt.%, 2.74, and 4.73 M calcium fluoride addition, S/L ratio, and sulfuric acid concentration, respectively. Under these conditions, vanadium recovery of 88.67% is achieved. The results of the direct leaching test validates the efficiency of the direct leaching method on vanadium extraction employed to the iron ores of the country.
1. Introduction
Vanadium (V) is a transition metal widely used in the production of high-quality ferrous and non-ferrous alloys, and chemical catalysts [1] . Eighty-five percent (85%) of vanadium globally is used in the steel industry, where 0.05-0.2% V is utilized in the production of High-Strength Low-Alloy (HSLA) steels [1,2]. Vanadium is primarily known to improve the strength of titanium and vanadium-titanium alloys, which are used in the production of aircraft. Heat exchangers in nuclear reactors also utilize V-Cr-Ti alloys which are durable at high temperatures, and corrosion resistant. Vanadium compounds are also used as catalysts in the chemical industry. Oxides of vanadium are known to speed up the chemical reaction in the formation of sulfuric acid.
Vanadium occurs in nature as part of the following minerals: carnotite, mica, vanadinite, mottramite, and patronite [3]. The common oxidation states for vanadium are +2, +3. +4, and +5. In particular, the trivalent ion V3+, has an octahedral radius of 0.061 nm, which is nearly identical to the radius of a Fe3+ ion (0.063 nm). As a result, vanadium is mostly associated with iron-rich minerals, such as magnetite, pyroxene, amphibole, and biotite. It also replaces aluminum (0.056 nm) in case of ferric minerals containing magnesium. It is also abundant in mafic igneous rocks, while rocks of ultramafic and intermediate composition contain vanadium and lesser amounts [3]. Vanadium is also present in organic shales, with average concentrations of 130-205 ppm.
The extraction of vanadium from titano-magnetite ores are divided into two major categories: direct extraction (from ores), and indirect extraction from slag after ironmaking and steelmaking [4]. The former involves roasting the ore with
NaCl or Na2CO3 at above 1000 ̊C followed by water leaching. Indirect extraction, on the other hand, is the main method in vanadium pentoxide production, which is comprised by the following steps: roasting with Na2CO3, water leaching, precipitation and purification [4].
However, an increase in the demand for vanadium is expected to happen in the upcoming years, primarily due to the prospect of vanadium as a main material for energy storage applications. Vanadium has been widely used in the production of redox flow batteries – a new technology that allows the charge and discharge of energy simultaneously [1]. In particular, the use of vanadium redox flow batteries (VRB’s) is a novel method in the stabilization of high amounts of energy. This is used in applications such as energy storage in wind generation facilities.
The Philippines is rich in iron ore, particularly in the form of magnetite. In estimate, around 1.56 billion MT of ore containing 5.7-64,4% magnetite are part of the country's resources [5]. However, majority of the iron ores are subjected to minimal value adding and are directly exported to other countries. Hence, there is still no current production of vanadium in the country. With this in consideration, the study aims to introduce a viable method of vanadium extraction that is both technically and environmentally acceptable – one that will aid in the development of a value-adding activity in the mineral sector. This will enhance the value of iron ores in the country with the generation of new products in the market. In addition, this will also benefit the steel industry as it can be a source of raw concentrates to improve the quality of steel products.
In this work, the feasibility of vanadium extraction using iron ores in the country is investigated. In addition, Direct leaching, a promising method of vanadium extraction, was employed. Optimization of leaching conditions (calcium fluoride addition, solid-to-liquid ratio, and sulfuric acid concentration), were carried out through response surface methodology (RSM) based on the Box-Behnken Design (BBD). In addition, the effects of these induvial parameters to vanadium recovery were investigated. Vanadium recovery in these conditions were assessed in order to evaluate the feasibility of vanadium extraction from Philippine iron ores via direct leaching method.