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of 17 chemical elements in the periodic table, specifically the 15 lanthanides plus scandium and yttrium. REEs and alloys that contain them are used in devices such as computer memory, rechargeable batteries, cell phones, catalytic converters, magnets, fluorescent lighting, and many more (Krishnamurthy and Gupta, 2004). China supplies about 94% of the REE demand, with the remaining 6% coming from Russia and Estonia, the USA, India, Malaysia, and Brazil (Zhanheng, 2011). Increased industrial development in China has prompted the Chinese government to limit annual export quotas to approximately 35 kt of rare earth oxides (REOs), while non-Chinese annual demand is expected to reach 80 kt by the year 2015. This constriction of supply is being met by the development of many new rare earth mining projects, each of which has its own unique mining and processing challenges (Jordens, Cheng, and Waters, 2013). One of these projects is the Esfordi phosphate project, which is located in Yazd Province in central Iran. The concentrate from the Esfordi flotation plant contains 1.2–1.5% REEs. The REEs occur in over 160 discrete minerals. Most of these minerals are rare but the REE contents, expressed as oxide, can be as high as 60% REOs. Among these, bastnasite ((Ce,La)FCO3) occurs most frequently, monazite ((Ce,La,Nd,Th,U,...)PO4) is second, and xenotime (YPO4) is the distant third. Other rare earth minerals that have been or are now used as REE resources include apatite, brannerite, euxenite, gadolinite, loparite, and uraninite. Allanite, apatite, and other phosphorite sources, eudialyte, fergusonite, floreneite, parisite, perovskite, pyrochlore, zircon, and a few other naturally occurring rare-earth-bearing materials are also considered potential rare earth resources (Krishnamurthy and Gupta, 2004). Ion adsorption clays containing about 0.05–0.2 wt.% REOs are another group of REE deposits (Moldoveanu and Papangelakis, 2012). The general formula for apatite is Ca5(PO4)3X, where X is a fluoride or chloride ion or a hydroxyl group. Apatite, containing an average of 0.1–0.8% REOs, is the main source of phosphate fertilizers and phosphoric acid (Krishnamurthy and Gupta, 2004). The mode of occurrence and distribution of the rare-earth minerals in phosphate concentrates has generally ensured that they could be recovered only as by-products or co-products. Chemical beneficiation or chemical processing of the concentrate obtained after physical beneficiation usually involves hydrometallurgical, and sometimes pyrometallurgical, operations (Krishnamurthy and Gupta, 2004). Selection of an appropriate leaching method for light REEs from Esfordi flotation concentrate based on mineral characterization by F. Soltani*, M. Abdollahy*‡, S.M. Javad Koleini*, and D. Moradkhani†