Preparation of crystalline rare earth carbonates with large particle size from the lixivium of weathered crust elution-d
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Preparation of crystalline rare earth carbonates with large particle size from the lixivium of weathered crust elution-deposited rare earth ores Jing-qun Yin 1), Zhi-qiang Zou 2), and Jun Tian 1) 1) Institute of Applied Chemistry, Jiangxi Academy of Sciences, Nanchang 330029, China 2) School of Resource and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China (Received: 4 December 2019; revised: 13 April 2020; accepted: 15 April 2020)
Abstract: Crystalline rare-earth (RE) carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the precipitant. Their chemical composition was studied using elemental and thermogravimetric analyses (TGA), and their structure and morphology were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results demonstrate that the crystalline rareearth carbonate is a hydrated basic carbonate or oxycarbonate and not astable intermediate carbonate in the process of thermal decomposition. The particle size of crystalline rare-earth carbonates with large particle size is in the range of 50–200 µm. With an RE2O3 content of up to 95wt%, the quality of crystalline rare-earth carbonates is higher compared to the Chinese National Standard (GB/T 28882–2012). The quality of the product is superior to the Chinese National Standard. Keywords: rare-earth ores; precipitation; crystalline rare-earth carbonate; large particle size
1. Introduction The weathered crust elution-deposited rare-earth ores are reported in China [1] and constitute the primary resources of mid-heavy rare-earth (RE) elements in the world [2–3]. The rare-earth element in the ores is primarily found in the form of ions adsorbed on clay minerals [4], which can be leached using an electrolyte solution such as (NH4)2SO4 and NH4Cl [5–6]. The weathered crust elution-deposited ore is a type of clay mineral that co-exists with other elements and is characterized by complex components and relatively low-grade RE2O3. After leaching, using a solution of ammonium sulfate, the complex components are contained in the lixivium, a result of the electrolyte leaching [7]. Therefore, the composition of rare-earth lixivium is extremely complex and except for a low concentration of RE3+, usually contains certain impurities such as (NH4)2SO4 (~2000 mg/L), Al3+ (~1000 mg/L), Fe3+ (~100 mg/L), and Ca2+ (~1000 mg/L), along with a small amount of Fe2+, Pb2+, and Mn2+, including the remaining lixiviants [8–9]. The extraction of rare-earth elements from this type of lix-
ivium is achieved either by a chemical precipitation process or a non-precipitation process [10]. The process of extracting rare-earth elements from this type of lixivium, a common industry practice, is usually a chemical precipitation process with ammonium bicarbonate used as the precipitant, which includes
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