Utilization of the MgO-Rich Residue Originated from Ludwigite Ore: Hydrothermal Synthesis of MHSH Whiskers

Abstract

Abstract:In this work, from the MgO-enriched residue originated from ludwigite ore, value-added magnesium hydroxide sulfate hydrate (MHSH) whiskers were prepared via sulfuric acid leaching and leachate purification, followed by hydrothermal synthesis. During sulfuric acid leaching, 98.2% magnesium and 99.6% silica were removed under the optimal leaching conditions: sulfuric acid concentration of 40%, leaching temperature of 80 • C, leaching time of 90 min, and liquid to solid ratio of 4 mL/g. After purification of the acidic leachate via oxidation and precipitation to remove impurities including iron and aluminum, the Mg 2+ -rich solution was used to prepare magnesium hydroxide sulfate hydrate whiskers (5Mg(OH) 2 ·MgSO 4 ·2H 2 O, abbreviated as 512MHSH) via hydrothermal synthesis. Finally, 512MHSH whiskers were obtained with 30-100 µm in length, 0.5-1.0 µm in diameter and aspect ratio of approximately 100. The physicochemical characteristics of whiskers were further characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FT-IR) and Thermogravimetry-Differential Scanning Calorimetry (TG-DSC).

Surface treatment of magnesium oxysulfate whiskers through plasma polymerization

“…This process indicates that MOS whiskers possess the essential qualities of an additive‐type fire retardant. Thus, apart from improving the mechanical properties of filled polymers, MOS whiskers can also increase their flame retardancy . However, owing to their strong polarity and high surface energy, MOS whiskers readily combine and are inadequately distributed in the polymer matrix, consequently decreasing the efficiency of target composites .…”