Abstract
Rare earth elements (REE) are considered to be a critical resource, because of their importance in green energy applications and the overdependence on Chinese imports. REE rich ion-adsorption deposits (IAD) result from tropical weathering of REE enriched igneous rocks. Commercial REE leaching from IAD, using salt solutions occurs via an ion-exchange mechanism. Bioleaching of IAD by Aspergillus or Bacillus, was compared to Uninoculated Control and Salt leaching (0.5 M ammonium sulfate) over 60 days. Salt leaching was most effective, followed by Aspergillus, Bacillus then Uninoculated Control. Most of the REE and major elements released by Salt leaching occurred before day 3. With bioleaching, REE and major elements release increased with time and had a greater heavy to light REE ratio. Similar total heavy REE release was observed in Salt leaching and Aspergillus (73.1% and 70.7% Lu respectively). In bioleaching experiments, pH was inversely correlated with REE release (R2 = 0.947 for Lu) indicating leaching by microbially produced acids. These experiments show the potential for bioleaching of REE from IAD, but dissolution of undesirable elements could cause problems in downstream processing. Further understanding of the bioleaching mechanisms could lead to optimization of REE recovery.
Highlights
The rare earth elements (REE) are a group of metals that include the lanthanides and sometimes yttrium and/or scandium
Of the 40 isolates chosen for further screening, 31 distinct isolates were identified and 16 of these were selected for identification by DNA sequencing (Table 3)
The results demonstrated that the Salt leaching yielded the greatest amount of REE released, followed by Aspergillus, Bacillus and Uninoculated Control experiments
Summary
The rare earth elements (REE) are a group of metals that include the lanthanides and sometimes yttrium and/or scandium. The heavy REE (HREE) and light REE (LREE) are among 20 raw materials, or groups of materials, that are considered a critical resource [1]. The HREE are considered more critical than LREE. REE are not rare in terms of global abundance, but do not concentrate into metal-rich ores as do iron or aluminum. They are found in a variety of different geological settings and, with up to 8.2% rare earth oxides (REO), carbonatites are the most common geological resource. Alkaline igneous rocks are mined for REE and have typical concentration of 1.5% REO [3]
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