A synthetic method for lanthanum hydroxychloride suitable for industrialization and its thermal decomposition properties

Abstract

A reactive crystallization method for the synthesis of lanthanum hydroxychloride (La(OH)₂Cl) was developed to provide a new low-carbon route for the purification of rare earth elements in hydrometallurgy. The synthetic method reported herein represents a unique low-temperature route, short preparation time and inexpensive materials compared with previous methods, thus making it promising for industrial applications. The key factors controlling the product's phase were determined using single factor tests involving temperature, concentration of NH₄Cl in the base solution and the molar ratio of NH₄OH/La³⁺ added per minute into the base solution. Otherwise, the outcome is lanthanum hydroxide (La(OH)₃). Subsequently, the synthesized products were characterized by employing X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Finally, the thermal decomposition behavior of La(OH)₂Cl was assessed using thermogravimetry (TG) and differential scanning calorimetry (DSC). Lanthanum oxychloride (LaClO) was obtained at about 360 °C. The thermal transformation from LaClO to La₂O₃ started at 400 °C and was a slow oxidation process. Pure La₂O₃ could be obtained when the temperature increased to 1500 °C.