Journal
MINERALS
Volume 10, Issue 6, Pages -Publisher
MDPI
DOI: 10.3390/min10060532
Keywords
REE; sulfuric acid baking; caustic digestion; acid leaching; water leaching
Funding
- Energy Efficiency and Resources Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) from the Ministry of Trade, Industry and Energy (MOTIE) of the Korean government [20122010300041]
- R&D Center for Valuable Recycling (Global-Top R&BD Program) of the Ministry of Environment of the Korean government [2019002220001/KIGAM 20-9894]
- National Research Foundation of Korea [21A20130012821] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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To improve the recovery of rare earth elements (REEs) from a refractory ore, this study investigated two different chemical decomposition methods, namely sulfuric acid baking and caustic digestion, with their respective leaching processes. The studied lateritic ore contained goethite (FeOOH) as a major constituent with REEs scattered around and forming submicron grains of phosphate minerals, such as apatite and monazite. Therefore, despite the substantially high content of REEs (3.4% total rare earth oxide), the normal acidic leaching efficiency of REEs reached only 60-70%. By introducing sulfuric acid baking and caustic digestion, the REE-leaching efficiency was significantly improved. After sulfuric acid baking at 2.0 acid/solid ratio and 200 degrees C for 2 h, the leaching efficiency reached 97-100% in the subsequent water-leaching. When the ore was digested with a solid/liquid ratio of 100 g/L in a 30 wt% NaOH solution at 115 degrees C and 300 rpm for 3 h, the REE-leaching efficiency of 99-100% was attained at 80 degrees C using a 3.0 M HCl solution. The correlation between the REE and the Fe-leaching was determined. The improvements in REE-leaching in both methods were mostly attributed to the mineral phase and crystallinity changes of Fe-bearing minerals due to the ore pretreatments. Such findings were also supported by X-ray diffraction and scanning electron microscopy analyses.
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