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Projeto de investigação
Sustainable recovery of lithium from saline streams by flow capacitive deionization
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Deep eutectic solvent flow electrodes for high-voltage desalination via flow electrode capacitive deionisation
Publication . Gabirondo, Elena; Saif, Hafiz M.; Alves, Vitor D.; Crespo, João G.; Tomé, Liliana C.; Pawlowski, Sylwin; LAQV@REQUIMTE; DQ - Departamento de Química; Instituto de Tecnologia Química e Biológica António Xavier (ITQB); Elsevier
This study pioneers the application of deep eutectic solvents (DES) as electrolytes in flow electrode capacitive deionisation (FCDI) desalination systems, providing a novel and improved alternative to aqueous flow electrodes. The deep eutectic solvent, choline chloride-urea (ChCl-U), was selected for its wide electrochemical stability window, allowing voltages exceeding 1.23 V, which is the limit for aqueous flow electrodes. The effect of water doping on the viscosity and performance of the DES flow electrodes was also investigated. Cyclic voltammetry confirmed the electrochemical stability, while rheological and electrochemical impedance spectroscopy revealed that the addition of water reduced the viscosity and enhanced the conductivity of ChCl-U, making it suitable for use as an electrolyte in FCDI. Desalination experiments were performed within a potential range of up to 2.2 V. The ChCl-U flow electrode, containing 20 wt% water and 10 wt% activated carbon, achieved the best balance between desalination efficiency (83 %), desalination rate (0.17 mg/cm2.min), and effluent quality. Furthermore, 1H NMR analysis confirmed the absence of traces of the deep eutectic solvent in the dilute stream. The results highlight the potential of DES flow electrodes to enhance desalination processes by enabling higher operational voltages and improved performance, thereby paving the way for more efficient FCDI desalination systems.
How should flow electrode capacitive deionization (FCDI) be operated to achieve efficient desalination and scalability?
Publication . Saif, H. M.; Crespo, J. G.; Pawlowski, S.; DQ - Departamento de Química; LAQV@REQUIMTE; Instituto de Tecnologia Química e Biológica António Xavier (ITQB); Elsevier
Flow electrode capacitive deionization (FCDI) is an emerging desalination technology that utilises flowable electrodes and can be operated in diverse configuration modes. This study provides a systematic assessment of the three main configuration arrangements under a voltage range between 0.8 and 2.0 V: isolated closed-cycle (ICC), short-circuited closed-cycle (SCC), and single-cycle with separate concentrate chamber (SCSC). The ICC mode shows the highest specific energy consumption (up to 72.02 Wh/mol of NaCl at 2.0 V) and low operational stability manifested by extreme alteration of pH in the electrode compartments (anode compartment pH down to 2.17; cathode compartment pH up to 12.08), which leads to the need for frequent electrode regeneration or replacement. In comparison to the ICC mode, the SCC mode exhibited superior performance, with a 44.3 % increase in salt removal and up to 3.95 % higher current efficiency at 2.0 V, due to the regeneration of electrodes through short-circuiting, as it reduces the electrical resistance and minimises the side reactions. The SCSC mode emerged as the most stable and reliable among the three, with uniform current and conductivity profiles, as well as minimal pH fluctuations, which is critical to produce treated water within desired quality standards. These findings highlight the promising potential of SCSC mode as an optimal configuration for scalable, continuous and energy-efficient FCDI systems, providing a balanced solution for long-term desalination with reduced operational complexity and costs.
Lithium recovery from brines by lithium membrane flow capacitive deionization (Li-MFCDI)
Publication . Saif, H. M.; Crespo, J. G.; Pawlowski, S.; DQ - Departamento de Química; LAQV@REQUIMTE; Elsevier
The demand of lithium for electric vehicles and energy storage devices is increasing rapidly, thus new sources of lithium (such as seawater and natural or industrial brines), as well as sustainable methods for its recovery, will need to be explored/developed soon. This work presents a novel electromembrane process, called Lithium Membrane Flow Capacitive Deionization (Li-MFCDI), which was tested to recover lithium from a synthetic geothermal brine containing a much higher mass concentration of sodium than lithium (more than 650 times). Specifically, a ceramic lithium-selective membrane was integrated into a flow capacitive deionization (FCDI) cell, which was specifically designed, and 3D printed, to allow simultaneous charging and regeneration of the employed flow electrodes. Despite the extremely high Na+/Li+ mass ratio in the feed stream, 99.98% of the sodium was rejected and the process selectivity for lithium over other monovalent cations was 141 ± 5.85 for Li+/Na+ and 46 ± 1.46 for Li+/K+. The Li-MFCDI process exhibited a stable behaviour over a 7-day test period, and the estimated energy consumption was 16.70 ± 1.63 kWh/kg of Li+ recovered in the draw solution. These results demonstrate promising potential of the Li-MFCDI for the sustainable lithium recovery from saline streams.
The influence of flow electrode channel design on flow capacitive deionization performance
Publication . Saif, H. M.; Gebregeorgis, T. H.; Crespo, J. G.; Pawlowski, S.; DQ - Departamento de Química; LAQV@REQUIMTE; Instituto de Tecnologia Química e Biológica António Xavier (ITQB); Elsevier
Flow capacitive deionization (FCDI) is an emerging desalination technology at which flow electrodes (shear-thinning flowable carbon slurries) are used to remove ions from saline water. The geometry of flow electrode channels, which provide the path and ensure the distribution and mixing of the flow electrodes, is one of the most important aspects to be optimized. This work presents experimental and computational fluid dynamics (CFD) modelling analysis of the influence of the geometry of flow electrode channels on FCDI performance. Flow electrode gaskets (with open, serpentine (short) horizontal and serpentine (long) vertical channels) were 3D printed using a polyethylene terephthalate glycol (PET-G) filament. The FCDI cell with a vertical serpentine flow electrode channel exhibited the poorest performance due to channel blockage by carbon particles, while the best results were achieved with a horizontal serpentine flow electrode channel. CFD simulations aided in understanding this behaviour by showing that the channel geometry strongly affects the local shear rate, and thus the local viscosity of flow electrodes. Thus, it is recommended to design channels that induce flow disturbance aiming for increasing the shear rate and hence reducing flow electrode viscosity, therefore promoting their flowability and reducing clogging chances.
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2020.09828.BD