One-Step Synthesis of Iron and Titanium-Based Compounds Using Black Mineral Sands and Oxalic Acid under Subcritical Water Conditions

Carla S Valdivieso-Ramírez,Patricia I Pontón,Victor H Guerrero,Bojan A Marinkovic,Anja Dosen

doi:10.3390/min12030306

Carla S Valdivieso-Ramírez, Patricia I Pontón + Show 3 more

Open Access

https://doi.org/10.3390/min12030306

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Abstract

Black mineral sands are widely used to obtain titanium dioxide, titanium, and, more recently, a variety of iron–titanium oxide nanostructures. Highly corrosive mineral acids or alkalis are commonly employed for this purpose. Hence, it is desirable to find eco-friendly ways to process these minerals, deriving high-added value materials. In this study, an Ecuadorian mineral sand precursor (0.6FeTiO3∙0.4Fe2O3 solid solution) was treated with oxalic acid aqueous solutions under subcritical water conditions. The synthesis was conducted in a batch reactor operating at 155 °C, 50 bar, and 700 rpm for 12 h, varying the oxalic acid concentration (0.1, 0.5 to 1.0 M). The as-obtained compounds were physically separated, dried, and analyzed by X-ray powder diffraction, scanning electron microscopy, and Raman spectroscopy. The characterization showed that the precursor was completely converted into two main products, ferrous oxalate, and titanium dioxide polymorphs. Rutile was always found in the as-synthesized products, while anatase only crystallized with high oxalic acid concentrations (0.5 and 1.0 M). These results open the possibility to develop more sustainable routes to synthesize iron and titanium-based materials with promising applications.

Highlights

Ilmenite (FeTiO3 ) black mineral sands have been traditionally used worldwide to generate concentrated titania slag or synthetic rutile as feedstock for further production of titanium dioxide (TiO2 ) and titanium metal (Ti) [1–4]
A dark brown powder (Figure 2a) that resembled that of the precursor was obtained with Subcritical water (sCW) medium whereas yellow, and white powders were obtained with the aqueous oxalic acid medium
Ferrous oxalate and titanium dioxide were synthesized from ferrotitaniferous black sand under sCW conditions at 155 ◦ C and 50 bar using an oxalic acid–H2 O solvent system

Summary

Introduction

Ilmenite (FeTiO3 ) black mineral sands have been traditionally used worldwide to generate concentrated titania slag or synthetic rutile as feedstock for further production of titanium dioxide (TiO2 ) and titanium metal (Ti) [1–4]. The alkaline hydrothermal treatment, for example, is a common route to obtain such nanostructures (i.e., ferrititanate nanosheets, iron-doped titanate nanofibers, ilmenite nanoflowers, iron–titanium oxide flower-like micronic particles, and nanobelts) [8,9,11–13]. It involves the usage of strongly alkaline aqueous solutions, commonly with molarities as high as 10 M. This process is straightforward, it is prone to result in an environmental burden

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