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Magnesium Doping for the Stabilization of a Spinel lithium Manganese Oxide for Lithium Recovery from Flowback and Produced Water

  • Author / Creator
    Wu, Fangshuai
  • Flowback and produced water (FPW), a potentially hazardous byproduct of oil and gas production, is a complex mixture of dissolved salts and organic compounds. FPW often contains modest concentrations of lithium, from tens to hundreds of parts-per-million. For this reason, and in response to the rising global demand for lithium driven by the recent surge in the battery industry, FPW is being regarded as a potential source for lithium production. Among the various direct lithium extraction (DLE) approaches, spinel lithium manganese oxide (LMO) ion-sieves stand out as one of the most promising materials for lithium recovery from FPW due to their high lithium selectivity as well as high uptake. However, LMO (Li1.6Mn1.6O4) experiences mass loss due to the reductive dissolution of manganese, which is a result of high concentrations of free electrons in FPW. Consequently, mass loss leads to structural degradation of the ion sieve, affecting its regeneration. To solve the problem of ion-sieve mass loss, we doped pristine LMO with different concentrations of magnesium by a solid-state method to synthesize magnesium-doped lithium manganese oxides, Li1.6MgxMn1.6-xO4 or LMMO-x (where x = 0.1, 0.2, 0.3, 0.4). The lithium uptake in FPW decreases from 25.7 mg∙g-1 for acid-treated LMO to 11.3 mg∙g-1 for LMMO-0.4. Subsequent studies reveal that the kinetics of lithium adsorption of these ion-sieves follow a pseudo-second-order kinetic model, and LMMOs exhibit relatively slower lithium uptake rates. However, LMMOs retain 95% of their initial lithium uptake after the 5th cycle of use, whereas LMO only maintains 90%, indicating that LMMOs are more stable and exhibit better reusability as a result of the magnesium doping. More importantly, during the acid desorption step to recover lithium, the average manganese loss decreases significantly from 3.19% for LMO to 0.73% for LMMO-0.4 because substitution of manganese by magnesium reduces the content of structural trivalent manganese. The mean oxidation states (ZMn) of manganese determined by a standard oxalic acid method in conjunction with X-ray absorption near edge structure (XANES) spectra support the conjecture that doping magnesium into LMO leads to an increase of ZMn, resulting in improved structural stability. Combined transmission electron microscopy – electron energy loss spectroscopy (TEM-EELS) shows that homogeneous doping of magnesium in LMO makes it less susceptible to manganese reduction when exposed to FPW. Furthermore, extended X-ray absorption fine structure (EXAFS) spectra reveal that pristine LMO undergoes an irreversible structural contraction during regeneration, while such an effect is not observed in LMMOs. Our results show that LMMOs are promising candidates for scale-up to an economic DLE technology.

  • Subjects / Keywords
  • Graduation date
    Spring 2024
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-5mj5-g722
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.