Lepidolite Extraction Solid By-product: Mitigation of Thallium Leaching and Utilization of Radiogenic Strontium Isotopes as a Tracer
Journal: Environmental Advances
Issue: Volume 3, April 2021
Authors: Thai T. Phan a, Leah Fulton a, John Ulkem a, Steve Aiken b, Amber Blackwell b, Joe Walsh c, Peter Walker c, Fereidoun Rezanezhad d
a Department of Earth and Environmental Sciences, University of Waterloo
b Knight Piésold Ltd.
c Lepidico Ltd.
d Ecohydrology Research Group, Department of Earth and Environmental Sciences and Water Institute, University of Waterloo
Abstract
The emerging growth of lithium-ion battery usage necessitates the development of unconventional resources for battery grade lithium carbonate. Extraction of lithium from micas such as lepidolite produces several marketable by-products as well as a silt-sized gypsum rich blended residue containing elevated level of thallium (Tl). The goal of this study was to assess the alternative use of the blended residue as fill material for mine reclamation.
Bulk elemental analysis and shake flask extraction of the blended residue showed that radionuclide and heavy metal levels of the solid blended residue and its leachate were within the guidelines for soil and its leachates. However, Tl concentration (24.7 ± 0.9 mg/kg), possibly in the forms of water-soluble salts in the blended residue, was much higher than the general level of Tl in naturally uncontaminated soil ( < 1 mg/kg). Thus, the efficiency of four easily accessible amendments (peat, clay, biochar, and topsoil) in mitigating the release of Tl was evaluated using a modified SPLP procedure. In addition, the usefulness of radiogenic Sr isotopes ( 87 Sr/ 86 Sr) as a tracer of the leachate plumes derived from the blended residue was assessed. Results from SPLP experiments showed that Tl was released from the blended residue under a wide range of pH values, especially under acidic conditions.
Mixing proportions of the blended residue and amendment (1:9 or 1:1) did not appreciably affect the high Tl removal efficiencies (68 – 89%) of clay, biochar, and topsoil. While mixing time did not affect the Tl removal efficiencies of clay and topsoil, Tl removal efficiency of biochar proportionally increased with mixing time and was at the highest value (~95%) among four amendments, if the mixing time was at least 7 days. Peat was not an effective amendment because its acidity possibly enhanced the release of Tl. The 87 Sr/ 86 Sr ratios in leachates of the blended residue (0.792 – 0.810) and its amendment mixtures were significantly higher than those in surface and groundwaters, soil leachates, and coal mine drainage. Thus, when the blended residue is used as fill material for mine reclamation, 87 Sr/ 86 Sr can be a powerful naturally occurring tracer in distinguishing Tl from the blended residue from other major sources of Tl in the environment. Overall, this study recommends clay and soils as the most promising amendments in mitigating the release of Tl in well-drained systems, and biochar for poor drainage conditions.
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