Salt Sorption Research Articles

Cucurbit[6]uril builds a water channel for improving the water/salt selectivity of polybenzimidazole

Polybenzimidazole (PBI) has garnered significant interest in desalination due to its exceptional chemical stability and mechanical strength, but suffers from poor water permeability. In this work, different contents of hydroxylated Cucurbit [6]uril (CB [6] were added to PBI to build a “water transport channel”. The effects of CB [6] addition on the chemical structure and surface morphology were analyzed by FTIR, SEM, and Zeta potential, respectively. Based on the solution-diffusion model, the effect of CB [6] on the water/salt transport properties of PBI membranes was thoroughly investigated. The results show that appropriate CB [6] doping can enhance water sorption of PBI through the special “outer hydrophilic and inner hydrophobic cavity” structure, and boost water diffusion with the channeling effect of the hydrophobic CB [6] cavity. While the complexation between the carbonyl group in CB [6] and Na+ ions slightly increased salt sorption, the specific cavity structure of CB [6] can significantly decrease salt diffusion by blocking salt ions and increasing transport path tortuosity. The cavity effect of CB [6] was further confirmed by hybridizing CB [6] with biphenylsulfonyl-substituted PBI when the cavity can be occupied. Therefore, the introduction of CB [6] improves the water/salt diffusion selectivity and then the permeability selectivity of PBI. Notably, the PBI@CB [6] membrane with a 0.25 wt% CB [6] loading exhibited a 40-fold increase in water permeability coefficient compared to pure PBI, while experiencing only a slight decrease in salt permeability coefficient, water/salt selectivity almost exceeding the empirical upper bound line of polymers. This work provides a theoretical foundation for the development of high-performance desalination membranes based on macrocyclic molecules such as CB [6].

Describing the permeability of permanganate co-ions in a CEM with varying supporting electrolyte concentrations

Redox flow batteries (RFBs), a promising technology for large-scale power grid energy storage, utilize a membrane separator to facilitate an ionic current while preventing mixing of the anolyte and catholyte solutions. The anolyte and catholyte of an RFB each contain an electroactive species, and usually an additional supporting electrolyte to charge balance the anode and cathode redox reactions and reduce overall ohmic losses. This study investigates the impact of the supporting electrolyte concentration and composition on Nafion’s transport properties using permanganate as the permeant. The permanganate concentration was kept constant at 0.1m, while sodium chloride and sodium hydroxide were both studied as supporting electrolytes. The sodium chloride concentration was varied from 0.1m to 4.0m, while the sodium hydroxide concentration was varied from 0.1m to 10m. The permanganate permeability, water sorption coefficient, and salt sorption coefficients were measured for Nafion, with a peak permeability being observed at a supporting electrolyte concentration of 1m for both electrolytes. A framework to describe the observed behavior was derived using first principles to determine the transport coefficients under these conditions. It was found that at low concentrations, the permanganate permeability is controlled by Donnan exclusion and salt sorption, while at high concentrations it is controlled by salt diffusion and osmotic deswelling.

Fluorination as a powerful tool for improving water/salt selectivity of hydrophilic polyethersulfone

Fluorination is an important tool for tuning polymer free volume properties, but the effect of fluorination on the water/salt transport properties of desalting polymers remains uncertain. In this work, a series of novel cysteine-based polyethersulfones (PES-Cys and PES-Cys-2F, PES-Cys-6H and PES-Cys-6F, PES-Cys-8H, and PES-Cys-8F) were designed in pair (4,4'-difluorodiphenyl sulfone versus 3,3',4,4'-tetrafluorodiphenyl sulfone, bisphenol A versus hexafluorobisphenol A, and 4,4'-dihydroxybiphenyl versus decafluorobiphenyl). Upon casting into membranes via the solvent evaporation method, the membranes/polymers were characterized by 1H NMR, FTIR, XRD, DSC, Zeta potential, and the water/salt transport properties of the membranes was investigated systematically. It has been demonstrated that fluorination brings out greater spatial site resistance, stronger hydrophobicity, and higher electronegativity to polyethersulfone chains, leading to decreased water sorption but increased salt sorption. Fluorinated polyethersulfone displayed higher water diffusion coefficient because the C–F group can shatter water clusters into water molecules, which can diffuse more rapidly. Fluorinated polyethersulfone exhibit superior water/salt selectivity, with the most rigid PES-Cys-8F of the highest fluorine content showing water/salt selectivity over the empirical upper bound line. The enhanced water/salt selectivity is mostly because that fluorination improves water permeability by significantly increasing the water diffusion coefficient, while the electrostatic barrier provided by the electronegative fluorine atoms inhibits salt diffusion. This study provides valuable theoretical guidance for future molecular design of antioxidant desalting polymers.

Questions of mathematical modelling in the study of acid retardation on ion–exchange resins

In this paper, the chemical equilibrium of a multicomponent solution is considered in detail as part of a dynamic model of the acid retardation method. A detailed study of the chemical equilibrium, represented as a system of nonlinear equations, is a key step for building an effective dynamic model in the case of a multicomponent solution. This paper presents an algorithm for efficient calculation of chemical equilibrium using extractive phosphoric acid as an example. This algorithm can be used in a dynamic model to calculate chemical equilibrium at each point of the spatial grid and at each integration step. Moreover, for the concentrations of substances in the experiment on the purification of extractive phosphoric acid, it is shown that the nonlinear system of equations of chemical equilibrium allows one to obtain simple algebraic relations for the connection of the concentration of molecules of the substance with the total concentration of substances of all elements in solution with good accuracy. In addition, it was shown that for each metal, only one type of salt sorption can be considered due to the low concentration of other types, which makes it possible to reduce the number of differential equations in the dynamic model of the acid retardation method.

Accounting for Ion Pairing Effects on Sulfate Salt Sorption in Cation Exchange Membranes.

Ion exchange membranes (IEMs) are frequently used in water treatment and electrochemical applications, with their ion separation properties largely governed by equilibrium ion partitioning between a membrane and contiguous solution. Despite an expansive literature on IEMs, the influence of electrolyte association (i.e., ion pairing) on ion sorption remains relatively unexplored. In this study, salt sorption in two commercial cation exchange membranes equilibrated with 0.01-1.0 M MgSO4 and Na2SO4 is investigated experimentally and theoretically. Association measurements of salt solutions using conductometric experiments and the Stokes-Einstein approximation show significant concentrations of ion pairs in MgSO4 and Na2SO4 relative to those in simple electrolytes (i.e., NaCl), which is consistent with prior studies of sulfate salts. The Manning/Donnan model, developed and validated for halide salts in previous studies, substantially underpredicts sulfate sorption measurements, presumably due to ion pairing effects not accounted for in this established theory. These findings suggest that ion pairing can enhance salt sorption in IEMs due to partitioning of reduced valence species. By reformulating the Donnan and Manning models, a theoretical framework for predicting salt sorption in IEMs that explicitly considers electrolyte association is developed. Remarkably, theoretical predictions of sulfate sorption are improved by over an order of magnitude by accounting for ion speciation. In some cases, good quantitative agreement is observed between theoretical and experimental values for external salt concentrations between 0.1 and 1.0 M using no adjustable parameters.

Poly-condensation of N-(2-acetamido)-2-aminoethanesulfonic acid with formaldehyde for the synthesis of a highly efficient sorbent for Cs(I)

A new sorbent (ACES-F micro-particles) is readily synthesized by the one-pot reaction of N-(2-acetamido)-2-aminoethanesulfonic acid with formaldehyde (poly-condensation reaction). The mesoporous sorbent is characterized by BET analysis (SBET: ≈6 m2 g−1), SEM-EDX (N: ≈7–8 % and S: 5 %), FTIR spectroscopy (identification of amine, sulfonic groups and their interactions with metal ions), TGA, elemental analysis, and titration (pHPZC: ≈5.7). The study of pH effect on Cs(I) shows an optimum close to 8 (with intermediary optimum at pH 4, associated with different reactive groups). The micron-size sorbent shows fast sorption (equilibrium in 60 min) and the pseudo-first order rate equation fits the kinetic profile. The sorption isotherm reaches up to 1.99 mmol Cs g−1; the Langmuir equation models isotherm profiles. The sorption decreases with increasing temperature; sorption is exothermic. Cesium uptake is affected by the presence of NaCl; however, even in large excess of salt (i.e., 4 M) sorption remains relatively high (loss <60 %). Selectivity is confirmed by the remarkable preference of the sorbent for Cs against alkali and other competitor metal ions, especially at pHeq ≈7. Metal desorption is highly effective using 0.3 M HNO3 solutions: complete desorption occurs in 30 min. The sorbent can be recycled for at least five cycles (losses <3 %). The interest of ACES-F for cesium recovery from seawater is confirmed by the study of Cs(I) sorption (and other major elements) from Vietnam and Egypt samples. The safety of the sorbent for aqueous bodies is evaluated by the cytotoxicity of the sorbent (limited against normal cells but highly reactive for cancerous cells); while the sorbent shows interesting antimicrobial properties for Gram+, Gram- and pathogenic yeast.

Elevating the water/salt selectivity of polybenzimidazole to the empirical upper bound of desalting polymers by marrying N-substitution with chlorination

Polybenzimidazole (PBI) was modified by marrying N-substitution with chlorination in order to improve its desalination properties. Based on the solution-diffusion theory, the effect of N-substitution and then chlorination on the water/salt transport properties of PBI was systematically analyzed. Although the introduction of hydrophobic p-toluenesulfonyl groups decreases water sorption, significantly increases water diffusion by weakening the hydrogen bonding between polymer chains. As a result, the water permeability of substituted PBI (SPBI) was 20 times higher than that of PBI. In terms of salt transport, the increase in salt diffusion of SPBI caused by the weaker inter-chain interactions was offset by a substantial decrease in salt sorption due to the combined effect of electrostatic repulsion and increased accessibility of hydrophilic groups to bind water, leading to equivalent salt permeability of PBI to SPBI. Controlled chlorination of SPBI under acidic conditions can further improve polymer water diffusion and thus water/salt diffusivity selectivity. The permeation of both SPBI and chlorinated SPBI is diffusion dependent. Therefore, combining N-substitution and chlorination is an effective strategy to simultaneously improve PBI permeability and water/salt selectivity for desalination applications.

Multi-form heat storage performance of expanded graphite based CaCl2 composites for low-grade heat source

Hydrated salt CaCl2 is a promising material for low-grade thermochemical heat storage. To improve cyclic stability of the material, porous matrixes are usually employed to synthesize​ CaCl2/matrix composites. However, the multi-step reaction of the salt and multi-form sorption of the composites increase the complexity during the practical application. This study proposed a novel method to study the multi-form heat storage performance. By combining TG/DSC measurement with Peak-fitting analysis, the multi-form mechanism of hydration/dehydration is revealed quantitatively. A series of EG/CaCl2 composites are synthesized with different salt content in the range of 23.8 wt% ∼57.8 wt%. All of the composites show well endothermic dehydration performance below 130 °C. A highest heat storage density of 1637.6 kJ/kg was obtained with a salt content of 48.1 wt% and a water uptake of 0.79 g/g. Water uptake of EG/CaCl2 composites is composed of chemisorption water loaded through reversible hydration reactions and solution absorption water introduced from salt deliquescence. The solution absorption plays nearly the equitant important role as chemical sorption, both in water adsorption ability and thermal storage capacity. The EG/CaCl2 composite show great support capacity for both salt and solution, making it an interesting material for low-grade heat storage.

Salt and ion transport in a series of crosslinked AMPS/PEGDA hydrogel membranes

Salt permeability and ionic conductivity are critical properties for membranes in water purification and energy applications. Both properties depend on individual ion sorption and diffusion coefficients, which are significantly influenced by polymer chemical and physical parameters such as fixed charge concentration and membrane water content. However, systematic studies connecting polymer structure to ion transport properties are still lacking. In this study, a series of uncharged and charged membranes were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as a cross-linker and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a charged monomer. Membrane fixed charge concentration and water uptake were systematically varied by adjusting AMPS content in the pre-polymerization mixture. Salt sorption and permeability coefficients and ionic conductivity of these membranes were measured as a function of NaCl solution concentration (0.01–1 M). Combining the solution-diffusion model and Nernst-Planck equation, individual ion diffusion coefficients were calculated. Experimental Na+ diffusion coefficients for all materials were well described by the Mackie and Meares tortuosity model, highlighting the strong influence of water content on ion diffusivity in both uncharged and charged polymers. Model predictions for Cl− diffusion coefficients agree reasonably well with experimental values, with some deviations occurring in more highly charged membranes. This discrepancy might result from interactions not captured by the Mackie and Meares model (e.g., fixed charge-ion interactions).

Efficient desalination system for brackish water incorporating biomass-derived porous material

BackgroundCapacitive deionization (CDI) is a recent advancement to monitor massive reverse osmosis (RO) reject concentrate. With the conventional material activated carbon developed from biomass, surface modifications and composite materials have improved surface properties. MethodTherefore, with the green motive to re-use agro-waste, the walnut shell powder was calcined (WSAC), which was modified with potassium hydroxide (K-WSAC), incorporated with iron nanoparticles (Fe@Nanoparticle) and iron-copper nanoparticles (FeCu@Nanoparticle) for fabricating CDI electrodes. FindingsDeveloped electrodes were electrochemically characterized, revealing the specific capacitance of 97.5 F/g and implemented for deionizing the RO concentrate. The FeCu@Nanoparticles electrodes showed the best desalination performance of 89.8% removal with an initial concentration of 1000 ppm at an electro-sorption time of 20 min exhibiting a salt sorption rate of 1.21 mg/g min. The economics of the system was evaluated, revealing the least energy consumed system of 0.5 kWh m−3. FeCu@Nanoparticles electrodes were implemented to treat real samples from commercial and domestic drinking water systems and groundwater samples, resulting in positive outcomes. Therefore, the investigation revealed that WSAC based electrodes resulted in the development of an excellent desalination system.

Influence of fixed charge concentration and water uptake on ion sorption in AMPS/PEGDA membranes

Water content and charge density strongly influence ion sorption in charged membranes. However, isolating the individual effect of each parameter on ion sorption can be difficult due to experimental challenges associated with independently controlling these two variables during membrane synthesis. This frustrates development and validation of fundamental models and structure/property relationships. In this study, three series of uncharged and negatively charged hydrogel membranes were prepared using poly(ethylene glycol) diacrylate (PEGDA) as a cross-linker and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as an ionic monomer. Water content and charge density were controlled by varying AMPS content and PEGDA chain length. Ion sorption in these materials was measured using aqueous NaCl solutions at concentrations ranging from 0.01 to 1.0 M. At constant charge density, salt sorption increased as water content increased. At fixed water content, salt sorption decreased as charge density increased. Salt sorption in membranes with the highest water content and charge density was predicted using the Donnan/Manning model, which accounts for solution and membrane phase thermodynamic non-idealities. However, this approach could not predict sorption in weakly charged and uncharged membranes, presumably due to additional membrane phase thermodynamic non-idealities associated with ion solvation and uncharged polymer segments. • High ion activity coefficients in uncharged membranes suggest ions have a much greater affinity for aqueous solution than swollen, uncharged membranes. • The Donnan/Manning model predicts experimental sorption well for highly hydrated and/or highly charged membranes. • Model predictions agree poorly with experimental data for membranes that are less hydrated, weakly charged, or uncharged due to phenomena not accounted for in Manning's theory (e.g., dielectric exclusion and non-idealities introduced by polymer segment-water-ion interactions).

Influence of speciation distribution and particle size on heavy metal leaching from MSWI fly ash.

Fly ash from municipal solid waste incineration (MSWI-FA) contains leachable heavy metals. In the present study the correlations between heavy metal content, particle size, speciation distribution with respect to water leaching are investigated, using a combination of solid-state bulk analytical techniques, leaching treatments, sequential extractions and thermodynamic geochemical modelling. Among the analyzed heavy metals, Zn and Pb are the most abundant in any grain size class, followed by Cu, Cr, Cd and Ni, with concentration that tends to increase with a decrease of the grain size. The phase composition is constituted of salt (halite, sylvite, anhydrite and syngenite), which provide the main minerals regardless of the particle size class; calcite, quartz and gehlenite occur in comparatively lower amounts, while 50% wt is composed of amorphous fraction. Heavy metal leaching is strongly correlated to speciation distribution, and in particular to the fraction (F1) associated with salt, carbonate and weak surface sorption. Leaching from speciation due to surface complexation on Al/Fe (hydr)oxide becomes relevant at acidic regime. Particle size and heavy metal content, in turn, moderately correlate with leaching. The F1-speciation as a function of particle size does not exhibit a definite trend shared by all heavy metals under investigation. This suggests that i) differences in speciation distribution, rather than bare heavy metal content or particle size, govern leaching from MSWI-FA; ii) F1 can be regarded as a marker of the potential heavy metal leaching; iii) a comparatively modest efficiency in managing MSWI-FA is expected from grain size separation strategies.

Chloride salt sorption flux of cohesive sediment beds with different degrees of fluidization in quiescent water

Cohesive sediments with different degrees of fluidization exhibit different rheological properties that affect chloride salt sorption in sediment and water columns. Recent studies have revealed that yield stress may be a more relevant parameter to describe the chloride salt sorption capacity of cohesive sediments at various degrees of sediment fluidization or consolidation. In this study, 365 experiments were performed to investigate the effects of sediment concentration and yield stress on chloride salt sorption flux in cohesive sediments. The results showed a negative power relationship between chloride salt sorption flux and yield stress. The chloride salt sorption flux increases with temperature, surface coefficient of fine particles, and the salinity difference between the sediment and water column. This study found that the sediment yield stress significantly affected the chloride salt sorption flux of the fluidized sediments. An empirical formula for the chloride salt sorption flux of cohesive sediment at various degrees of fluidization in quiescent water was proposed.

Methoxy groups increase water and decrease salt permeability properties of sulfonated polysulfone desalination membranes

A promising desalination membrane material, sulfonated polysulfone, was structurally modified to increase its water/salt transport selectivity. The structural modification was achieved by adding methoxy groups to the polymer backbone. This modification simultaneously increased water permeability and decreased salt permeability. These changes in properties are both favorable for desalination applications, and they may result from changes in polymer density and the free volume element size distribution. Relative permittivity and salt sorption data for these charged polysulfones suggest that Donnan exclusion may influence salt sorption properties to a greater extent than electrostatic or dielectric exclusion forces, which is reasonable for charged polymers. The Donnan-Manning model did not quantitatively describe the salt sorption properties of the sulfonated polysulfone materials perhaps due to a combination of low water content and a heterogeneous distribution of fixed charge groups throughout the polymer. Interestingly, addition of methoxy groups to the charged polysulfone backbone more strongly influenced the diffusion properties than the sorption properties, and this observation may be important to guide the engineering of highly selective polymeric materials for desalination applications.

Thermophysical properties of frozen parsley: A state diagram representation

AbstractSorption behavior and glass transition of frozen parsley were investigated in order to study the physical modifications, represented as state diagram to figure out information about product behavior for storage and supply chain handling. Frozen products may be located in the state diagram in all the possible freezing temperatures to understand the structure state and study feasible corrective actions mainly focused on temperature and solid content. Parsley was totally dehydrated and equilibrated at selected relative humidity. Sorption behavior was evaluated by saturated salt slurry method and sorption isotherm fitting, while solid components in terms of mass fraction were investigated by using differential scanning calorimetry. Brunauer–Emmet–Teller (BET) model well fitted with moisture and water activity data (R2 = 0.995, p‐level &lt; 0.05). The characteristic ranges of stability, in terms of system mobility and physical modification, are the monolayer values (0.240 water activity; 0.052 kg/kg dry basis) and the critical water activity range (0.424 water activity; 0.078 kg/kg dry basis). Glass transition and melting temperature were used to define parsley state diagram. Different zones figure out a specific physical behavior: depending on solid content and temperature. Unfrozen water was estimated as monolayer BET value 0.84 kg/kg wet basis and extrapolated from state diagram 0.984 kg/kg wet basis.Practical applicationsFrozen high‐quality product and energy efficiency can be obtained by a correct temperature management. Thermophysical properties of parsley represented in a state diagram are reported in the typical solute and temperature range of freezing process and storage. These data can relate physical structure and temperature, allowing different possible conditions management.

Adsorption of Sodium Cholate on Cationic Dextran Gels: Comparison of Isotherm Binding Models

Cationic dextran hydrogels having pendent 51-59 mol% N-alkyl-N,N-dimethylammonium chloride groups were synthesized and tested as adsorbents for sodium cholate. The bile acid salt sorption by these gels was evaluated by equilibrium analysis in water and 10 mM NaCl solution. The best adsorption results were obtained with amphiphilic dextran-based gels having two types of pendant ammonium chloride groups with different polarities. Experimental adsorption data for all polymers fitted good with Langmuir, Dubinin-Raduskevich and Temkin models over the entire range of ligand concentrations. The maximum experimental adsorption capacity of dextran sorbents for sodium cholate was in the range 850-1075 mg/g.

Water and salt transport properties of the cellulose triacetate/reduced graphene oxide nanocomposite membranes

The relationship between desalting membrane and its water/salt transport properties remain largely unknown. This is especially true for polyamide thin film nanocomposite (TFN) membranes which have shown excellent desalination performance and attracted booming attention in recent years. Considering cellulose triacetate (CTA) can be made into dense membranes whose transport properties can be measured based on the solution-diffusion theory, we systematically study the water/salt transport property of the CTA nanocomposite membranes blended with reduced graphene oxide (rGO) of varying reduction degrees, with multilayer graphene oxide (MGO) and single layer graphene oxide (SGO) as control samples. The nanocomposite membranes show enhanced membrane density and glass transition temperature (Tg) due to the interaction of the polar group in GO/rGO with CTA chains. The GO (rGO) frustrates the polymer chain packing and decreases crystallinity of CTA membrane. The adding of rGO increases the water permeability by increasing its diffusivity due to the decreased crystallinity and additional channel from (r)GO, but decreases the salt permeability by decreasing its diffusivity due to membrane densification and the interactions of ions with GO/rGO. The water permeability and diffusivity of the nanocomposites increase when its water sorption decreases, which is against the trend of pure polymers, presumably due to the fact that water sorption is not a good reflection of the free volume in this heterogeneous membrane. Meanwhile, the GO/rGO blending slightly increases water sorption without changing the salt sorption because the newly-introduced polar groups in GO/rGO traps water and suppress its solvation capacity for salt. Both the water permeability and the water/salt selectivity increase with the reduction degree due to the decreased water transport resistance.

Salt inclusion and deliquescence in salt/zeolite X composites for thermochemical heat storage

Abstract Composites of commercially available zeolite Na-X beads and the salts NaCl, CaCl2, MgCl2, and MgSO4 (loadings up to 24 mol mol−1 or 18 wt.-%) were prepared by ion-exchange followed by incipient wetness impregnation and characterized by elemental analysis (XRF), XRD, N2 sorption, mercury porosimetry, and SEM. During loading of the zeolite with salt, the Donnan effect leads to an inclusion of salt ions into the zeolitic micropores. Salt is included up to a threshold loading of ~20 mol mol−1 depending on the nature of salt. Thermochemical properties are determined at 30 °C and a humidity of 3–21 g kg−1. Both water loading lift and heat storage density decrease with increasing salt loading below the deliquescence humidity of the salt. Above the deliquescence humidity, absorption into a salt solution within the secondary pores of the zeolite beads contributes to the water uptake. Heat storage densities up to 275 kWh m−3 (153% of the salt-free zeolite) are reached at high salt loadings and sorption humidity.

Influence of water content on alkali metal chloride transport in cross-linked Poly(ethylene glycol) diacrylate.2. Ion diffusion

In this study, the influence of polymer water content on ion diffusion coefficients of alkali metal chlorides (LiCl, NaCl, and KCl) in cross-linked poly(ethylene glycol) diacrylate (XLPEGDA) hydrogels was investigated. This research is part of a broader effort to understand the fundamentals of water and ion transport in hydrated polymers. Salt diffusion coefficients were calculated from salt permeability and sorption measurements. XLPEGDA hydrogels were synthesized with three different water contents (50, 67, and 93 g water/g dry polymer). The diffusion coefficients of alkali metal chlorides in XLPEGDA polymers increased as water content increased. The Mackie and Meares model, which accounts for polymer chain obstruction (i.e., tortuosity) effects on salt diffusion in hydrated polymers, was used to interpret salt diffusion coefficients. The general trend of the experimentally determined salt diffusion coefficients in these polymers is consistent with the model. Individual ion diffusion coefficients in the samples were obtained by combining salt permeability/sorption data with ionic conductivity results. The chloride ion diffusion coefficients were similar for all salts. The relative order of alkali metal ion diffusion coefficients in these polymers was different from that in aqueous solution (i.e., DK+s>DNa+s>DLi+s). Moreover, this order changes as polymer water content varies, suggesting that alkali metal chloride diffusion behavior in XLPEGDA polymers is influenced by both ion hydration and polymer-ion specific interactions.

Features of Sorption and Proton-Desorption of Heavy Metals (M2+) from Aqueous Solutions by Biopolymers

Several features of the sorption and proton-desorption mechanisms of heavy metals (M2+) from aqueous solutions of acids and native salts (cellulose, chitosan, keratin) by modified biopolymers with acidic (Cell–COOH), salt (–OOC–W–NH3+), amine (CS–NH2), and other sorption sites were examined. Sorption isotherms of metal cations from their aqueous salt solutions (pH < 7) by biopolymers were described well in terms of the Langmuir model. The distributions of Cu2+, Fe2+, Ni2+, Zn2+, and Cd2+ in the heterophasic system H2O–H2SO4–MSO4–biopolymer were linear functions of the solution acidity in logarithmic coordinates log $$ \left({K}_{D{\mathrm{M}}^{2+}}\right) $$ vs. pH with tan α ≈ 0.5.