Abstract
Demand for Li has risen from 200 metric tons in 1994 to over 40,000 metric tons in 2008, due to the surge in electric cars and other Li-powered battery systems [1]. Sixty-six percent of global Li resources are found in high salinity aqueous solutions (brines) trapped within the Earth’s surface or found as lakes [2]. Therefore, effective Li extraction from this medium is a critical technological goal. One extraction method currently used is the precipitation of Li2CO3. However, at present there is little information about the influence of inorganic ions present in brines on the precipitation and growth of Li2CO3. Therefore, in this study we explore how different inorganic ions in solution compete and interact with Li2CO3 using experiments and computational simulations.
Crystals of Li2CO3 were grown using the method of Taborga et al. [3], with the addition of monovalent (NaCl, KCl) or divalent salts (CaCl2, MgCl2, Na2SO4) at ionic strengths of 1 or 0.1. Experiments were run for 60 minutes in stirred glass batch reactors that were sealed from the atmosphere and heated to at 80 °C using a water bath. After the experiments the precipitate was extracted using gravity filtration and dried in a desiccator for 24 hours. Phase identification was conducted using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction. The morphology of the samples was imaged using a scanning electron microscope (SEM). Changes in morphology were correlated with surface complexation information, gained from attenuated total reflectance (ATR)-FTIR. Finally, the crystal morphology and surface complexation analysis were directly compared with expected crystal equilibrium morphologies derived from surface energies calculated using density function theory (DFT) implemented using the Vienna ab-initio simulations package (VASP).
The analyses showed that Mg2+¬ can effectively outcompete Li+ for the carbonate anion, as only a hydrated MgCO¬3 phase was found after these experiments. Similarly, Ca2+ also competed directly for carbonate, producing calcite (CaCO3) in the most concentrated experiment and a mixture of calcite and Li2CO¬3 in the presence of lower CaCl2 concentrations. Monoclinic Li2CO3 (zabuyelite) was the only precipitate formed in the other experiments. Evidence of growth via a precursor phase was observed in the experiments as hollow cores within crystals in the presence of sulphate, and empty centres of crystal clusters arranged into rosette shapes.
ATR-IR analysis of the Li2CO3 crystals in the sulphate experiments and the computational simulations demonstrated that this anion can interact directly with the growing surfaces of Li2CO3 crystals. In contrast, Na+, K+ and Cl- are only expected for interact with Li2CO3 in a solvent-mediated fashion. This is consistent with solvent-mediated ion pair formation in solution between monovalent monoatomic cations and CO32- 4. Evidence from in situ Raman analysis of Li-carbonate solutions also conducted in this study indicates that Li+ and CO32- can form ion pairs in solution, which are also expected to be solvent mediated due to the strong interactions between Li+ and water molecules5.
References
1. Blomgren J. Electrochem. Soc, 2017 16, A5019.
2. Gruben et al. J. Ind. Ecol. 2011 15, 760.
3. Taborga et al. J. Cryst. Growth 2017 460, 5.
4. Rudolph et al. Dalton Trans. 2008 900-908.
5. Ichieda et al. J. Phys. Chem. A. 2003 107, 7597.
Crystals of Li2CO3 were grown using the method of Taborga et al. [3], with the addition of monovalent (NaCl, KCl) or divalent salts (CaCl2, MgCl2, Na2SO4) at ionic strengths of 1 or 0.1. Experiments were run for 60 minutes in stirred glass batch reactors that were sealed from the atmosphere and heated to at 80 °C using a water bath. After the experiments the precipitate was extracted using gravity filtration and dried in a desiccator for 24 hours. Phase identification was conducted using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction. The morphology of the samples was imaged using a scanning electron microscope (SEM). Changes in morphology were correlated with surface complexation information, gained from attenuated total reflectance (ATR)-FTIR. Finally, the crystal morphology and surface complexation analysis were directly compared with expected crystal equilibrium morphologies derived from surface energies calculated using density function theory (DFT) implemented using the Vienna ab-initio simulations package (VASP).
The analyses showed that Mg2+¬ can effectively outcompete Li+ for the carbonate anion, as only a hydrated MgCO¬3 phase was found after these experiments. Similarly, Ca2+ also competed directly for carbonate, producing calcite (CaCO3) in the most concentrated experiment and a mixture of calcite and Li2CO¬3 in the presence of lower CaCl2 concentrations. Monoclinic Li2CO3 (zabuyelite) was the only precipitate formed in the other experiments. Evidence of growth via a precursor phase was observed in the experiments as hollow cores within crystals in the presence of sulphate, and empty centres of crystal clusters arranged into rosette shapes.
ATR-IR analysis of the Li2CO3 crystals in the sulphate experiments and the computational simulations demonstrated that this anion can interact directly with the growing surfaces of Li2CO3 crystals. In contrast, Na+, K+ and Cl- are only expected for interact with Li2CO3 in a solvent-mediated fashion. This is consistent with solvent-mediated ion pair formation in solution between monovalent monoatomic cations and CO32- 4. Evidence from in situ Raman analysis of Li-carbonate solutions also conducted in this study indicates that Li+ and CO32- can form ion pairs in solution, which are also expected to be solvent mediated due to the strong interactions between Li+ and water molecules5.
References
1. Blomgren J. Electrochem. Soc, 2017 16, A5019.
2. Gruben et al. J. Ind. Ecol. 2011 15, 760.
3. Taborga et al. J. Cryst. Growth 2017 460, 5.
4. Rudolph et al. Dalton Trans. 2008 900-908.
5. Ichieda et al. J. Phys. Chem. A. 2003 107, 7597.
| Original language | English |
|---|---|
| Publication status | Published - 2019 |
| Event | 50th Annual Conference of the British Association for Crystal Growth - London, United Kingdom Duration: 9 Jul 2019 → 11 Jul 2019 |
Conference
| Conference | 50th Annual Conference of the British Association for Crystal Growth |
|---|---|
| Country/Territory | United Kingdom |
| City | London |
| Period | 9/07/19 → 11/07/19 |