Separation Of Mg2 Research Articles

Positively-charged nanofiltration membrane constructed by polyethyleneimine/layered double hydroxide for Mg2+/Li+ separation

As an important resource, lithium is abundant in Salt Lake. The high Mg2+/Li+ ratio is the main obstacle to lithium extraction. Positively-charged nanofiltration membrane has shown great potential in the separation of Mg2+/Li+. Herein, we report a facile method to construct positively-charged nanofiltration membrane by polyethyleneimine (PEI) and layered double hydroxide (LDH) nanosheets on hydrolyzed polyacrylonitrile ultrafiltration membrane. Subsequently, the PEI-LDH composite membrane was crosslinked with glutaraldehyde (GA) to improve its stability. The incorporation of LDH could improve the positive charge of the membrane. Then, the obtained PEI-LDH/GA membrane showed an enhanced separation performance for separating Mg2+/Li+ in an aqueous solution. When the Mg2+/Li+ ratio was 10, the membrane showed a separation factor (SMg2+/Li+) of 18.7. Moreover, the membrane could maintain the separation performance for 100 h, which exhibited a potential application in Mg2+/Li+ separation.

Graphene oxide membranes with a confined mass transfer effect for Li+/Mg2+ separation: a molecular dynamics study.

Membrane separation technology represented by graphene oxide (GO) membranes has been widely used in lithium extraction from salt lakes. It is extraordinary to study the extraction of Li+ by GO membranes from the perspective of the confined mass transfer effect. This study establishes a GO channel model with the confined mass transfer effect to closely fit the actual mass transfer process. Meanwhile, this study investigates the dynamic fluid characteristics in the separation of Li+/Mg2+ by GO membranes using molecular dynamics simulations. The results showed that the Li+/Mg2+ separation ratio is maximum at 1.0 nm layer spacing and 10% oxidation degree of the GO membrane. Water molecules form a bilayer within the channel at the appropriate interlayer channel (1 nm) and oxidation level (10%), which accelerates the ion transport rate. Furthermore, the GO oxidation group has the weakest hydrogen bonding effect on water which promotes the passage of water. Finally, the maximum separation ratio is reached due to the fact that the binding force of Li+ to water molecules in the channel is lower than that of Mg2+. The results of this study will provide theoretical consideration for the design of high-performance Li+/Mg2+ separation membranes.

Unprecedented Mg2+/Li+ separation using layer-by-layer based nanofiltration hollow fiber membranes

The dominant market for lithium-ion batteries (LIBs) in China has driven lithium chemicals with foreseeable growth in demand. Lithium extraction from salt-lake brine in China with high Mg2+/Li+ ratio has become one of the key challenges in the separation of Mg2+ and Li+. In this study, we introduce here an unprecedented, highly permselective nanofiltration hollow fiber membrane prepared by layer-by-layer (LBL) deposition as a novel alternative for Mg2+/Li+ separation. Poly(styrene sulfonate) and poly(allylamine hydrochloride) were deposited alternatively on a tailor-made ultrafiltration hollow fiber support and crosslinking with glutaric dialdehyde. The pure water permeability of LBL NF membrane was 18.4 L m−2 h−1 bar−1. Under the synergistic effect of size sieving and Donnan exclusion effect, it also achieved promising results when tested with simulated brine. The rejection rate of Mg2+ was as high as 99%, and the rejection rate of Li+ was as low as −60%, with a separation factor of 74 was observed, setting a record of permselectivity for Mg2+/Li+ separation for engineerable membranes. This research has paved a new road for the engineering application of LBL nanofiltration membranes for mono and bivalent ion separation.

Effect of coexisting ions on recovering lithium from high Mg2+/Li+ ratio brines by selective-electrodialysis

Abstract Selective-electrodialysis (S-ED) is a booming technology for recovering lithium from salt lake brine and (concentrated) seawater, especially from high Mg2+/Li+ ratio brines. The coexisting ions in the solutions containing lithium can make some impact on the ion fractionation of lithium and magnesium in high Mg2+/Li+ brines. The effect of the concentration of coexisting cations (Na+, K+) and anions (SO42−, HCO3−) on the separation coefficient of magnesium and lithium (FMg-Li), recovery ratio of Li+ (RLi), current efficiency (η) and specific energy consumption (ESEC) was evaluated. The results show that an applied voltage of 6 V is more preferable for lithium ions recovery from high Mg2+/Li+ brines by S-ED. The separation of Mg2+/Li+ tends to unsatisfactory with increasing cation concentration (Na+, K+), and FMg-Li drops from 8.73 to 1.83 with the increase of Na+/Li+ from 1 to 5 and from 8.33 to 2.13 with the rise of K+/Li+ from 1 to 5. The strength of influence on the separation of Mg2+/Li+ is K+ > Na+, correlating with the order of their hydrated ion radiuses. However, FMg-Li rises from 7.99 to 14.66 with the increase of SO42−, reversing with the influence of cations concentration. As for HCO3−, the variation tendency of FMg-Li is opposite to RLi, probably ascribing to the appearance of MgHCO3+. These observations showed that S-ED has a wide adaptability for the ion fractionation of magnesium and lithium from brines.

Chlorine-free alkaline seawater electrolysis for hydrogen production

A new process for chlorine-free seawater electrolysis is proposed in this study. The first step of the process is separation of Mg2+ and Ca2+ ions from seawater by nanofiltration. Next, the NF permeate is dosed into the electrochemical system. There it is completely split into hydrogen and oxygen gases and NaCl precipitate. The electrochemical system comprises an electrochemical cell operated at elevated temperatures (e.g. ≥ 50 °C) and a settling tank filled with aqueous NaOH solution (20–40 %wt) that operates at lower temperatures (e.g. 20–30 °C). High concentration of hydroxide ions in the electrolyzed solution prevents anodic chlorine evolution, while the accumulated NaCl precipitates in the settling tank. Batch electrolysis tests, performed in NaCl-saturated NaOH solutions, showed absolutely no chlorine formation on Ni200 and Ti/IrO2RuO2TiO2 anodes at [NaOH] > 100 g/kgH2O. Three long-term operations (9, 12 and 30 days) of the electrochemical system showed no Cl2 or chlorate (ClO3−) production on both electrodes operated at current densities of 93–467 mA/cm2. The Ni200 anode was corroded in the continuous operation that resulted in formation of nickel oxide on the anode surface. On the other hand, the system was successfully operated at 467 mA/cm2 with Ti/IrO2RuO2TiO2 electrodes in NaCl-saturated solution of NaOH (30 %wt) for 12 days. During this period no formation of Cl2 and ClO3− has been observed and precipitation of NaCl occurred only in the settling tank. The performance of the system was stable during the operation as indicated by the insignificant fluctuations in the applied cell potentials and measured constant concentrations of NaOH(aq) and NaCl(aq) in the electrolyte solution. During 12 days of operation at ≈ 470 mA/cm2 about 1.2 m3 of H2 and ≈150 g of solid NaCl were produced in the system. Electrical energy demand of the electrolysis cell was 5.6–6.7 kWh/m3H2 for the current density range of 187–467 mA/cm2.

Study on Mg2+ removal from ammonium dihydrogen phosphate solution by an emulsion liquid membrane

Mg2+is extracted from ammonium dihydrogen phosphate (NH4H2PO4) solution by an emulsion liquid membrane (ELM) using mono-(2-ethylhexyl) 2-ethylhexyl phosphonate (HEHPEHE)as a carrier, sulfonated liquid polybutadiene (LYF) as a surfactant and kerosene as a solvent. To study the extraction efficiency and advantages of the ELM process in the separation of Mg2+,the effects of various operating conditions on the extraction -HEHPEHE volume fraction, reaction temperature, treat ratio (emulsion phase / external phase), phase ratio (membrane phase / internal phase), agitation speed, extraction time, internal phase concentration, surfactant LYF concentration and initial pH of NH4H2PO4 solution are experimentally investigated and discussed. The results show that Mg2+ in NH4H2PO4 solution can be effectively removed by the ELM process. An extraction efficiency of more than 83.1% is attained at the optimized parameters and superior-grade NH4H2PO4can be obtained by two levels of extraction.

Elution behaviour of anions and cations on a mixed-bed stationary phase of anion and cation exchange resins

The retention mechanism of anions and cations on a mixed-bed column packed with a mixture of strong anion and cation exchange resins has been studied. Organic acids and inorganic anions have showed the same elution behaviour on the mixed-bed column as on a single anion exchange column. In contrast, different elution behaviours for cations have been observed between the mixed-bed column and a single cation exchange column. On the mixed-bed column, cations would be eluted by a mixed retention mechanism. The primary retention mechanism is ion exchange with eluent cation (H+) for all cations. The ion exchange mechanism on the sites occupied by anion exchange groups makes a greater contribution for monovalent cations. A partition mechanism between the stationary phase and mobile phase contributes to the separation of Mg2+ and Ca2+ by forming neutral compounds.

Synthetic Inorganic Ion-Exchange Materials. XIX. Ion-Exchange Behavior and Separation of Alkaline Earth Metals on Crystalline Antimonic(V) Acid as a Cation Exchanger

Abstract A study of the distribution coefficients on crystalline antimonic(V) acid (C-SbA) as a cation exchanger shows an unusual affinity series (Mg < Ba < Ca < Sr) for microamounts of alkaline earth metals in a nitric acid solution. An extremely slow rate of adsorption was observed for calcium and strontium ions on the exchanger. On the basis of the distribution coefficients, the effective separation of Mg2 +-Ba2 +, Mg2 +-Cs+-Ba2 +, and Mg2 +-Cs+-Ca2 +, Sr2 + has been achieved with a small column (1.0 or 2.0 × 0.4 cm i.d.) of C-SbA.