Abstract
Rare earth elements (REE) are a group of 17 metallic elements in the periodic table, consisting of the fifteen lanthanides plus scandium and yttrium. REE are widely used in many important high technology industrial products, such as catalytic converters in cars [1], magnets used in wind turbines and hybrid cars [2], and missile guidance systems in the defense industry [3]. The current supply of REE is heavily reliant on imports from China, which produces over 80% of the world’s REE [4]. This reliance creates a strategic vulnerability for both the economy and military to adverse actions by foreign governments, natural disasters, and other disruptions in the supply of these critical materials. In response to this vulnerability, Canada has developed a list of 31 minerals considered critical for the sustainable economic success of Canada and its allies, with rare earth elements on this list of critical minerals [5], [6]. Canada has world-class REE deposits, with 40-50% of the world's known REE reserves [7]. The general objective of this research is to investigate the use of indirect bioleaching, i.e., organic acids, to extract REE from low-grade ore and waste, enhance REE selectivity and reduce the amount of highly corrosive reagents (H2SO4). The feasibility of using citric acid leaching to extract light REE (LREE) and heavy REE (HREE) from a Canadian low grade ore and waste sample has been studied. Thermodynamic calculations have been done to assess the feasibility of using different organic acids for REE extraction from different REE-bearing minerals. The extraction of REE has been measured for 2 HREE (Y, Dy) and 2 LREE (Ce, Nd). Different leaching parameters have been studied as follows: effect of type of organic acid (tartaric acid, lactic acid, oxalic acid, and citric acid), effect of temperature (25, 65, 85 °C), effect of particle size (-38, +38-58 and +53-75 µm), and the effect of the organic acid concentration (0.05, 0.2, 0.4 M).
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