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

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.

Photocatalytic activity of Fe/Ti-based compounds obtained from ferro-titaniferous mineral sands via a simple soft chemistry route

“…The synthesis of the iron-based catalysts from the ferro-titaniferous sands was carried out in a batch stirred high pressure reactor (Berghof BR-500, Germany) following the methodology described by Valdivieso-Ramírez et al [23], with some modifications. Briefly, 300 g of 1 M oxalic acid solution and 1.75 g of ferro-titaniferous sands were loaded into the reactor.…”