The Effect of Fulvic Acid on the Leaching of a Weathered Rare-Earth Ore
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ered crust elution-deposited rare-earth ore is composed of a new type of exogenesis rare-earth mineral, which was first found in China.[1] It was mainly located in Jiangxi, Fujian, Guangdong, Yunnan, Hunan, Guangxi, and Zhejiang provinces of China and has the prominent advantages of full range of partitioning, high content of valuable elements, and low specific activity. Moreover, it is the main resource of mid-heavy rare-earth ore in the world.[2] This kind of rare-earth ore occurs in the crust of weathered mineral deposit and the contents of the rare earths are low, which is merely 0.03 to 0.12 pct. The rare
XIAN-PING LUO, Professor, BO FENG and HE-PENG ZHOU, Associate Professors, and XIAO-MING CHEN and PENG-CHENG WANG, Master Students, are with the Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, P.R. China. Contact e-mail: [email protected] Manuscript submitted August 9, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
earths in the ore exist in the following four states: (1) aqueous soluble phase; (2) ion-exchangeable phase; (3) colloid sediment phase; (4) mineral phase. The rareearth content of ion-exchangeable phase is the highest among these four states, which account for 75 to 95 pct, and is the only part that can be extracted economically at present. This type of rare-earth deposits is adsorbed on the surface of clay minerals and cannot be extracted and concentrated by the conventional physical methods such as magnetic separation, electrical separation, gravity concentration, or flotation.[3] But it can be exchanged and desorbed upon contact with cations such as NH4+, K+, Na+, and H+, which exhibit higher chemical activities. Based on these characteristics, scientists and engineers in China have developed a chemical leaching method for recovering this type of rare-earth ores.[4,5] After years of exploitation of weathered crust elutiondeposited rare earth, the amount of rare-earth-rich ores has sharply reduced, only rare-earth lean ores remains, and the rare-earth contents of these ores are usually less than 0.05 pct and have received much attention in the recent years. For these low rare-earth-containing ores, the leaching efficiency worsens. The lixiviant consumption becomes higher and the lixivium exhibits a lower rare-earth concentration, resulting in slow diffusion during the leaching process.[6] To date, finding ways to improve the leaching efficiency and to reduce lixiviant consumption has become an urgent and important task for the industry.[7] In this paper, the effects of fulvic acid on the leaching process of a weathered crust elutiondeposited rare-earth ore, using ammonium sulfate as lixiviant, have been investigated to provide reference for future research. The lean weathered crust elution-deposited rare-earth ore sample was collected from Zudong Rare Earth Mine area located in the Longnan County, Jiangxi Province, China. The chemical composition of the ore is listed in Table I. The lean rare-earth ore contains only 0.066 wt pct rare-earth oxide
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