Search Results (24)

Many Greek islands host geothermal springs whose waters can be desalinated to produce drinking water. Some of these waters contain meaningful concentrations of the valuable Rb⁺ and Cs⁺ ions, which, when extracted from the desalination brine as RbCl and CsCl salts, can yield revenues exceeding the freshwater production costs. We demonstrate the use of reverse osmosis (RO) to produce freshwater and apply theoretical simulations to assess a proven extraction method applied to the RO retentate of geothermal water from Samothrace, characterized by [Rb⁺] = 2.72, [Cs⁺] = 0.55, [K⁺] = 514, [Na⁺] = 3759 (all in mg/L) and pH 6. The extraction method, developed by the authors, relies on ion exchange using a PES-coated Zn-hexacyanoferrate sorbent with high affinity for monovalent cations (no affinity for multi-valent cations), followed by a unique ion-chromatography separation. We show that the production cost remains <25% of the salts’ market price, with ROI of ~4.5 years. Full article

In this paper, results of studying the properties of armbrusterite, a natural heterophyllosilicate, are presented. Due to its crystal structure consisting of parallel HOH-type sheets separated by a network of large-diameter (4–6 Å) channels, this mineral is of interest as a prototype for producing novel compounds to be used as sorbents. The studies were conducted by X-ray powder diffraction and X-ray single crystal diffraction analyses, electron microscopy, and IR spectroscopy. The natural sample is shown to be able to selectively extract monovalent cations from the solution of complex composition consisting of mono- and divalent salts. Furthermore, the preliminary results of hydrothermal synthesis of an analog of this mineral are reported. It is demonstrated that the mineral can be produced under milder conditions than the known methods for synthesizing heterophyllosilicates using platinum capsules (Tuttle bombs) at 380–450 °C. Full article

This study investigates electrodialysis (ED) performance for desalination and concentration of monovalent salts (NaCl, NH₄Cl, KCl, and NaNO₃) at varying mass concentrations. Systematic comparisons of current efficiency (η), energy consumption, water loss, desalination rate η_salt, and other key parameters reveal salt-specific behaviors and process determinants. Experimental results show distinct performance hierarchies across operational phases. In the 1% desalination phase, KCl achieved optimal performance with 95.3% salt removal, a dilute η of 99.96%, a production capacity (Q) of 54.95 L/(h·m²), and a unit energy consumption (E_u) of 3.24 kWh/t. This performance outshone that of NaCl (η_salt = 95.2%) and NaNO₃ (η_salt = 89.5%), with NH₄Cl showing the lowest value (80.6%) in this phase. This trend inversely correlated with cation hydration energies. On the other hand, in the 3% concentration phase, NH₄Cl demonstrated superior performance with a concentrate η of 83.49%, a flux of 35.71 L/(h·m²), and the lowest E_u (5.30 kWh/t), despite a lower concentration factor (5.33) than NaNO₃ (6.48). These findings highlight that KCl is ideal for energy-efficient brine treatment (<3% salinity), while NH₄Cl is better suited to high-purity recovery. Although NaNO₃ has a high E_u during concentration, it is favorable for applications where minimizing energy usage is critical. Full article

The mean force between two highly like-charged macroions in the presence of monovalent counterions and added multivalent salt within solvents of varying dielectric constants was studied using Monte Carlo simulations. Without additional salt, the mean force is strongly repulsive at all macroion separations in solvents with a dielectric constant ${ϵ}_r$ ≥ 30. However, in solvents with ${ϵ}_r$≤ 30, macroions experience effective attraction, indicating that attractive interactions between highly charged macroions can occur even without multivalent salt in nonpolar solvents with low dielectric constants. The total multivalent counterion charge-to-total macroion charge ratio is defined as β which determines the amount of salt that is added to the system. At β = 0.075, the mean force becomes attractive at short separations in solvents with ${ϵ}_r$= 54 containing 1:3 salt, as well as in all solvents with 1:5 salt, while still exhibiting significant repulsion at longer separations. In contrast, for solvents with 1:3 salt and dielectric constants ${ϵ}_r$= 68 and ${ϵ}_r$= 78.4, the mean force turns attractive at a higher salt concentration, around β = 0.225. The shift in the mean force to an attractive state at short separations signifies charge inversion on the macroion surface when a sufficient amount of salt is present. At a stoichiometric ratio of multivalent counterions, long-range repulsion vanishes, and attraction becomes significant. However, with excess salt, the strength of the attractive mean force diminishes. Additionally, the attractive force at a given salt concentration increases as the dielectric constant decreases and is stronger in systems with 1:5 salt than in those with 1:3 salt. Full article

The rapid development of the global energy industry has driven an escalating worldwide demand for lithium resources. As a major lithium source, salt lake brines contain abundant divalent ions that hinder efficient lithium extraction. Compared with conventional lithium recovery technologies, nanofiltration membranes emerge as an energy-efficient and environmentally friendly alternative. Over the past decade, interfacial polymerization has been widely adopted to fabricate nanofiltration membranes for lithium–magnesium separation, with studies confirming the superior performance of positively charged membranes in distinguishing monovalent and divalent cations. This review systematically summarizes recent advancements in positively charged nanofiltration membranes synthesized via interfacial polymerization for lithium–magnesium separation, categorizing the design strategies into five distinct approaches. The correlations between intrinsic membrane structural characteristics and separation performance are critically analyzed. Furthermore, current challenges and future research directions are discussed to provide new perspectives for developing high-performance positively charged composite nanofiltration membranes. This work aims to inspire innovative designs and accelerate the practical implementation of nanofiltration technology in lithium extraction from salt lake brines. Full article

End-stage renal disease occurs when there is permanent loss of the kidney’s ability to filter toxins from the blood. Due to the limited number of transplants, dialysis is currently the most common treatment, but it significantly limits a patient’s lifestyle and has significant side effects. One solution is an artificial kidney, but significant challenges remain in its development. One challenge is the separation of glucose from urea. Nanofiltration is ideal for this separation; however, there is little understanding of the important parameters for this separation under physiological conditions. In this study, operating parameters (pressure and temperature) as well as feed conditions (increased glucose/salt) were explored for their effects on the separation of glucose from urea in six commercial membranes. The rejection of monovalent and divalent ions was also characterized. While increasing pressure increased flux, it had little effect on metabolite rejection, except for glucose, which increased above 20 psi. Increasing temperature led to a slight increase in flux and a slight decrease in the rejection of divalent ions. Glucose rejection was sensitive to feed conditions, while urea rejection was less affected. Divalent ions were rejected more strongly than monovalent ions and were also more affected by feed conditions. Full article

This study examines the effects of natural organic matter (NOM) and dissolved solids on fluoride (F⁻) retention in polyelectrolyte multilayer-based hollow-fiber nanofiltration membranes (dNF40). Lab-scale filtration experiments were conducted under varying operating conditions (initial salt concentration, NOM concentration, permeate flux, crossflow velocity, and recovery rate). dNF40 membranes exhibited F⁻ retention above 70% ± 1.2 in the absence of NOM and competing ions. However, when filtering synthetic model water (SMW) designed to simulate groundwater contaminated with high total dissolved solids (TDSs) and NOM, F⁻ retention decreased to approximately 60% ± 0.7, which was generally attributed to ion competition. Furthermore, despite limited declines in normalized permeability, the addition of NOM to SMW notably deceased F⁻ retention in the steady state to~20% due to fouling effects. The facilitated transport of the divalent cations Ca²⁺ and Mg²⁺ could be observed, as they accumulated in the organic fouling layer. While SO₄²⁻ retention remained relatively stable, the retention of monovalent anions (NO₃⁻, Cl⁻, and F⁻) decreased substantially due to drag effects. Na⁺ retention improved slightly to maintain electroneutrality. Feed salinity was shown to significantly affect separation efficiency, with PEC layers undergoing swelling and certain structural changes as the ionic strength increased. During batch filtration experiments at varying recovery rates, the retention of monovalent anions further decreased, with F⁻ retention reducing to just ~10% at a 90% recovery rate. This study provides valuable insights into better understanding and optimizing the performance of PEC-based NF membranes across diverse water treatment scenarios. Full article

To fulfil the goals of the circular economy, the treatment of textile wastewater should be focused on the recovery of valuable components. Monovalent anion-selective electrodialysis (MASED) was applied for the separation of reactive dyes from mineral salts. Standard cation-exchange membranes (CM membranes) and monovalent selective anion-exchange membranes (MVA membranes) were used in the electrodialysis (ED) stack. The separation efficiency was evaluated for model solutions of various reactive dyes (varying in molecular weight and chemical reactivity) containing NaCl. In the course of MASED, the mineral salt was successfully removed from the dye solutions with an efficacy of 97.4–99.4%, irrespectively of the composition of the treated solution. The transport of dye molecules through the ion-exchange membranes (IEMs) from diluate to concentrate compartments was irrelevant. Nonetheless, a significant adsorption of dye particles on the membranes was observed. Around 11–40% of the initial dye mass was deposited in the ED stack. Dye adsorption intensity was significantly affected by dye reactivity. This study showed the potential of the MASED process for the separation of the reactive dye from the mineral salt on condition that antifouling membrane properties are improved. The obtained streams (the concentrate rich in mineral salt and the diluate containing the reactive dye) can be reused in the dye-house textile operations; however, some loss of dye mass should be included. Full article

Efficient dye/salt separation poses a great challenge to nanofiltration (NF) membrane technology in the desalting sector of the dye synthesis industry. In this study, we fabricated a novel loose polyester NF membrane via an interfacial polymerization method using “hydroxyl-ammonium” biquaternary diethanolamine (MDET) and trimesoyl chloride. The molecular design of MDET provides a loose crosslinking network, showing high rejection of dyes and the passage of monovalent salt/divalent salt ions in the dye solution, exhibiting exceptional filtration efficiency with high selectivity. Furthermore, the membrane exhibits excellent operational stability for over 100 h, demonstrating superior antifouling properties and high resistance to chlorine. This study provides new insights into the role of dyes and mono- and divalent ions in desalination processes related to the dye synthesis industry. Full article

Different oils can be homogeneously dispersed in the network junctions of the separated bicontinuous micellar phases. Upon dilution, these dispersions spontaneously form nanoemulsions. The possibility of a micellar sponge phase formation in the case of mixtures with three anionic and two zwitterionic surfactants in the presence of divalent and monovalent salts is studied. The best results are obtained using sodium lauryl ether sulfate with 1 ethylene oxide group (SLES-1EO) and both cocamidopropyl betaine (CAPB) or N,N-dimethyldodecylamine N-oxide (DDAO) in the presence of an appropriate small amount of MgCl₂ and CaCl₂. Bicontinuous micellar phases can be produced also in high-salinity NaCl solutions. The bulk properties of these phases are independent of the concentration of the initial solutions from which they are separated, and their Newtonian viscosities are in the range from 0.3 Pa·s to 0.8 Pa·s. Both 8 wt% CAPB- and DDAO-containing sponge phases engulf up to 10 wt% limonene and spontaneously form nanoemulsion upon dilution with droplet sizes of 110–120 nm. Vitamin E can be homogeneously dispersed only in CAPB-containing saturated micellar network, and upon dilution, these dispersions spontaneously form nanoemulsions with smaller droplet sizes of 66 nm for both 8 diastereomers and 2 diastereomers mixtures of vitamin E. Full article

Competition for the migration of interfering cations limits the scale-up and implementation of the Donnan dialysis process for the recovery of ammonia nitrogen (NH₄⁺-N) from wastewater in practice. Highly efficient selective permeation of NH₄⁺ through a cation exchange membrane (CEM) is expected to be modulated via tuning the surface charge and structure of CEM. In this work, a novel CEM was designed to form a graphene oxide (GO)-polyethyleneimine (PEI) cross-linked layer by introducing self-assembling layers of GO and PEI on the surface of a commercial CEM, which rationally regulates the surface charge and structure of the membrane. The resulting positively charged membrane surface exhibits stronger repulsion for divalent cations compared to monovalent cations according to Coulomb’s law, while, simultaneously, GO forms π–metal cation conjugates between metal cations (e.g., Mg²⁺ and Ca²⁺), thus limiting metal cation transport across the membrane. During the DD process, higher NH₄⁺ concentrations resulted in a longer time to reach Donnan equilibrium and higher NH₄⁺ flux, while increased Mg²⁺ concentrations resulted in lower NH₄⁺ flux (from 0.414 to 0.213 mol·m⁻²·h⁻¹). Using the synergistic effect of electrostatic interaction and non-covalent cross-linking, the designed membrane, referred to as GO-PEI (20) and prepared by a 20 min impregnation in the GO-PEI mixture, exhibited an NH₄⁺ transport rate of 0.429 mol·m⁻²·h⁻¹ and a Mg²⁺ transport rate of 0.003 mol·m⁻²·h⁻¹ in single-salt solution tests and an NH₄⁺/Mg²⁺ selectivity of 15.46, outperforming those of the unmodified and PEI membranes (1.30 and 5.74, respectively). In mixed salt solution tests, the GO-PEI (20) membrane showed a selectivity of 15.46 (~1.36, the unmodified membrane) for NH₄⁺/Mg²⁺ and a good structural stability after 72 h of continuous operation. Therefore, this facile surface charge modulation approach provides a promising avenue for achieving efficient NH₄⁺-selective separation by modified CEMs. Full article

The present work reports the preparation of gardenia yellow pigment containing paraffin oil nanoemulsions stabilized by Span80 and Tween80. The preparation of the required nanoemulsions was optimized by testing different conditions, such as varying the hydrophilic–lipophilic balance (HLB), the emulsifier concentration (EC), the oil–water ratio (OWR), and the temperature (T), as determined by the average droplet diameter (ADD) and polydispersity index (PDI). Our results indicated that a minimum ADD of 65.9 nm and PDI of 0.116 were obtained at an optimum HLB value of 6.0, EC of 10% (w/w), OWR of 2:1, and T of 40 °C. Both the steady-state and dynamic rheological parameters were further investigated, revealing that the emulsions exhibited pseudoplastic behaviors. The long-term stabilities of the nanoemulsions after the addition of inorganic salts were monitored by observing their visual appearances. It was found that the emulsions containing pure water or 0.1 M CaCl₂ and AlCl₃ became slightly separated, while the emulsions containing 0.1 M KCl and NaCl showed no separation after 30 days of storage at room T. This difference among different salts could be related to the number of valence electrons of their cations. The spatial electrostatic effects of the monovalent cationic (KCl and NaCl) and the nonionic surfactants were greater than the delamination/sedimentation forces of the system, which was better than the salt based on the cations with valences greater than one (CaCl₂ and AlCl₃). In conclusion, the present work illustrated the formation, rheological properties, and stability of water containing gardenia yellow pigment in paraffin oil nanoemulsions, which can be of great significance for the application of gardenia-yellow-pigment-based formulations. Full article

Non-ionic surfactants are one of the most useful surfactants as they are the second largest group, produced by volume at about 35%. Due to their low toxicity, the demand for them is escalating due to an extensive use of these amphiphilic materials for an efficient, non-energy-requiring recovery of volatile organic acids (VOAs) from aqueous mixtures. This separation process is mainly due to the cloud point property of surfactants, which is referred to as the temperature of the system at which two phases are formed. One of the phases is micellar-rich and the other is micellar-poor. In these micelles, the surfactant molecules are oriented in such a way that the hydrophilic heads shield the hydrophobic tails from the other water molecules in the system. This assembly partitions the organic compounds within the interior of the micelles, which act as the pseudo-organic phase. This work elucidates how salting-out affects the cloud point of ethoxylated non-ionic surfactants, resulting in VOA separation. Studies suggest the sensitivity of the cloud point to the presence of electrolytes and its dependence on the parameters’ hydrophile–lipophile balance (HLB) and on the number of ethylene oxide (EON) units in the surfactant molecule. Electrolyte addition, in the form of salt, causes the dehydration of micelles as salt is a water-structure maker. The salt changes the solvent structure through aggregation and formation of larger micelles. This translates into a lipophilic shift, which reduces the cloud point and the surfactant’s HLB. As the HLB decreases, the more hydrophobic the surfactant becomes, resulting in better separation. The type of salt influences the characteristics of the interphase that separates the phases formed. Typically, polyvalent cations such as Al³⁺ and Ca²⁺ are more effective in decreasing the HLB than the monovalent cations (e.g., Na⁺ and K⁺) because of their higher surface charge densities. Since the surfactant’s HLB is dictated by its ethylene oxide component (i.e., HLB decreases with EON), it follows that non-ionic surfactants with a lower EON could achieve better separation in the presence of salt. Although the actual separation of VOAs could possibly be affected by other parameters (e.g., amount of added surfactant and salts and mass transfer rates), the response of surfactant’s properties (i.e., cloud point, HLB, and EON) to salt addition could be utilized to establish an enhanced VOAs extraction from aqueous systems. Full article

Membrane chromatography is a modern, high-throughput separation method that finds important applications in therapeutic protein purification. Multimodal, salt-tolerant membranes are the most recent innovation in chromatographic membrane adsorbents. Due to the complex structure of their ligands and the bimodal texture of their carriers, their adsorption properties have not been sufficiently investigated. This work deals with the equilibrium and kinetic properties of a multimodal anion-exchange chromatography membrane, Sartobind STIC. Single- and two-component adsorption experiments were carried out with bovine serum albumin (BSA) and salmon DNA as model target and impurity components. The effect of the Hofmeister series ions and ionic strength on the BSA/DNA adsorption was investigated in micromembrane flow experiments. A significant difference was observed between the effects of monovalent and polyvalent ions when strong kosmotropic salts with polyvalent anions acted as strong displacers of BSA. On the contrary, DNA binding was rather high at elevated ionic strength, independent of the salt type. Two-component micromembrane experiments confirmed very high selectivity of DNA binding at a rather low sodium sulfate feed content and at pH 8. The strength of binding was examined in more than a dozen different desorption experiments. While BSA was desorbed relatively easily using high salt concentrations independent of buffer type and pH, while DNA was desorbed only in a very limited measure under any conditions. Separation experiments in a laboratory membrane module were carried out for the feed containing 1 g/L of BSA, 0.3 g/L of DNA, and 0.15 M of sodium sulfate. The negative flow-through mode was found to be more advantageous than the bind-elute mode, as BSA was obtained with 99% purity and a 97% yield. Membrane reuse was investigated in three adsorption-desorption-regeneration cycles. Full article

The separation of chloride and sulphate is important for the treatment of high salt wastewater, and monovalent selective electrodialysis (MSED) has advantages in terms of energy consumption and pre-treatment costs compared to nanofiltration salt separation. Most of the research on monovalent anion-selective membranes (MASM) is still on a laboratory scale due to the preparation process, cost, and other reasons. In this study, a low-cost, easy-to-operate modification scheme was used to prepare MASM, which was applied to assemble a pilot-scale electrodialysis device to treat reverse osmosis concentrated water with a salt content of 4% to 5%. The results indicate that the optimum operating conditions for the device are: 250 L/h influent flow rate for the concentration and dilute compartments, 350 L/h influent flow rate for the electrode compartment and a constant voltage of 20 V. The separation effect of the pilot electrodialysis plant at optimal operating conditions was: the $C{l}^{-}$ and $S{O}_4^{2-}$ transmission rates of 80% and 2.54% respectively, the separation efficiency ($S$) of 93.85% and the Energy consumption per unit of NaCl ($E_{NaCl}$) of 0.344 kWh/kg. The analysis of the variation of the three parameters of selective separation performance during electrodialysis indicates that the separation efficiency ($S$) is a suitable parameter for measuring the selective separation performance of the device compared to the monovalent selectivity coefficient ($P_{S{O}_4^{2-}}^{C{l}^{-}}$). Full article