Salt Sorption Research Articles

Biochar mitigates negative effects of salt additions on two herbaceous plant species

Addition of pyrolyzed biomass (“biochar”) to soils has commonly been shown to increase crop yields and alleviate plant stresses associated with drought and exposure to toxic materials. Here we investigate the ability of biochar (at two dosages: 5 and 50 t ha−1) to mitigate salt-induced stress, simulating road salt additions in a factorial glasshouse experiment involving the broadleaved herbaceous plants Abutilon theophrasti and Prunella vulgaris. Salt additions of 30 g m−2 NaCl to unamended soils resulted in high mortality rates for both species. Biochar (Fagus grandifolia sawdust pyrolyzed at 378 °C), when applied at 50 t ha−1 as a top dressing, completely alleviated salt-induced mortality in A. theophrasti and prolonged survival of P. vulgaris. Surviving A. theophrasti plants that received both 50 t ha−1 biochar and salt addition treatments showed growth rates and physiological performance similar to plants without salt addition. Biochar treatments alone also substantially increased biomass of P. vulgaris, with a ∼50% increase relative to untreated controls at both biochar dosages. Biochar did not significantly affect photosynthetic carbon gain (Amax), water use efficiency, or chlorophyll fluorescence (Fv/Fm) in either species. Our results indicate that biochar can ameliorate salt stress effects on plants through salt sorption, suggesting novel applications of biochar to mitigate effects of salinization in agricultural, urban, and contaminated soils.

Investigation of Fission Product Transport into Zeolite-A for Pyroprocessing Waste Minimization

Methods to improve fission product salt sorption into zeolite-A have been investigated in an effort to reduce waste associated with the electrochemical treatment of spent nuclear fuel. It was demonstrated that individual fission product chloride salts were absorbed by zeolite-A in a solid-state process. As a result, recycling of LiCl-KCl appears feasible via adding a zone-freezing technique to the current treatment process. Ternary salt molten-state experiments showed the limiting kinetics of CsCl and SrCl2 sorption into the zeolite. CsCl sorption occurred rapidly relative to SrCl2 with no observed dependence on zeolite particle size, while SrCl2 sorption was highly dependent on particle size. The application of experimental data to a developed reaction-diffusion-based sorption model yielded diffusivities of 8.04 × 10-6 and 4.04 × 10-7 cm2/s for CsCl and SrCl2, respectively. Additionally, the chemical reaction term in the developed model was found to be insignificant compared to the diffusion term.

Sodium chloride diffusion in sulfonated polymers for membrane applications

Sodium chloride permeability and sorption measurements were used to calculate average salt diffusion coefficients for charged, sulfonated polymers of interest for membrane applications. A sulfonated polysulfone random copolymer and two phase-separated, sulfonated styrenic pentablock copolymers were considered, and data for these materials were compared with those for an uncharged cross-linked poly(ethylene glycol diacrylate) hydrogel. The average salt diffusion coefficients reported for the block copolymers are apparent salt diffusion coefficients because the values have not been adjusted for the polymer’s phase separated morphology. The sodium chloride permeability of the uncharged hydrogel decreases by about 16% as upstream salt concentration increases from 0.01 to 1molL−1. This salt permeability change results from a decrease in the salt diffusion coefficient with increasing salt concentration because the polymer’s water content decreases as salt concentration increases (i.e., osmotic de-swelling). This decrease in salt diffusion coefficient is consistent with free volume theory, wherein a decrease in water content leads to a decrease in free volume, thereby decreasing the salt diffusion coefficient and, in turn, salt permeability. In contrast, the sodium chloride permeability of the charged polymers increases by more than an order of magnitude as upstream salt concentration increases from 0.01 to 1molL−1. This salt permeability increase is due to increases in both mobile salt sorption and diffusion coefficients with increasing salt concentration, despite the fact that water content (and, therefore, free volume) in the polymer decreases as salt concentration increases. Thus, the increase in salt diffusion coefficient with increasing salt concentration in the charged polymers results from factors (which are currently poorly understood) other than simply water uptake or free volume.

Sodium chloride sorption in sulfonated polymers for membrane applications

Ion sorption measurements were conducted to characterize sodium and chloride sorption in sulfonated polymers of interest for membrane applications. An uncharged polymer, based on cross-linked poly(ethylene glycol diacrylate), was included for comparison. The charged polymers included a sulfonated polysulfone random copolymer and two phase separated sulfonated styrenic pentablock copolymers. The sodium and chloride ion concentrations sorbed in these polymers were measured after polymer films had been equilibrated with 0.01–1.0molL−1 aqueous NaCl solutions at neutral pH. For the sulfonated polymers, cation sorption was measured using a polymer ashing technique and flame atomic absorption spectrophotometry. Anion sorption was measured using a desorption technique and ion chromatography. Polymer charge, i.e., sulfonation, influenced ion sorption. In general, salt sorption increased as water sorption increased in all polymers considered. In the uncharged polymer, the molar concentrations of sorbed sodium and chloride were equal to one another, as expected. However, the sulfonated polymers sorbed much more sodium than chloride ions due to ion exchange. The experimental mobile salt (i.e., anion) sorption data were fit to a model containing contributions from both Donnan exclusion and simple salt partitioning to the overall salt uptake by the polymer. In general, the influence of Donnan exclusion on anion (i.e., mobile salt) sorption in these cation exchange materials is reduced as water uptake increases, presumably due, in part, to dilution of the hydrated polymer’s sulfonate groups.

Desalination of brackish water for household drinking water consumption using typical plant seeds of semi arid regions

The goal of this work was to study the salt sorption capacity of biological materials, such as seeds from several different plant species typical of semi arid regions, and their use in the desalination of brackish water in small quantities, sufficient for household drinking water consumption. The sorption capacity of salt was tested for ten different biological materials. The salinity of the water was determined before and after contact with the biological material. Umbu seeds (Spondias tuberosa Arruda Câmara) were considered the most appropriate material, after treating and drying at different temperatures. The prepared material showed that the process met the Langmuir model. The maximum adsorption capacity of sodium by the material at 30, 40 and 50°C was estimated to be: 52.6, 165 and 250mgg−1 respectively. Thus, 1L of brackish water with salinity between 0.6‰ and 1.2‰, as the samples tested in this work, may have its sodium chloride content removed using only 1g of the seeds treated as described in this study if the water is heated to 50°C. The thermodynamic analysis indicated that the adsorption process is physical and exothermic and that the interactions between the biological material and sodium occurred spontaneously.

Adsorption and retarded transport of nitrate in Andisol subsoils caused by the apparent salt sorption

Adsorption and retarded transport of nitrate in Andisol subsoils caused by the apparent salt sorption

Reactivity of cis and trans isomers of dinitro- and diamino-substituted dibenzo-18-crown-6 in metal salt sorption processes

Reactivity of cis and trans isomers of dinitro- and diamino-substituted dibenzo-18-crown-6 in metal salt sorption processes

Sorption studies on regenerated cellulosic fibers in salt–alkali mixtures

The degrees of salt sorption were determined in lyocell and viscose fibers immersed in aqueous solutions of salt–alkali mixtures with the aim of using salt sorption as an indirect measure of changes to fiber accessibility in presence of alkali. The salt–alkali mixtures used were combinations of NaOH with NaCl or NaBr, and of KOH with KCl or KBr. In general, salt sorption in fibers increased with increase in alkali concentration up to 2 mol/l, and did not change significantly thereafter. The accessibility of Br− salts was greater than the Cl− salts, but that of the Na+ salts was greater than the K+ salts. These trends in salt sorption indicate that salt accessibility in fibers is not influenced by the size of hydrated salt ions, but by the forces of electrostatic attraction and repulsion between the charged fiber surface and salt cations and anions.

Bains Overseas launches fuel additive

Novolac is a low-cost carbon precursor which can be used to derive nanoporous carbon beads in sub-micrometer size. In this study, we introduce this material as a novel electrode material for capacitive deionization (CDI) with high performance stability and superior desalination rate. The polymer beads were synthesized employing a self-emulsifying system in an autoclave, pyrolyzed under argon, and activated with CO2, yielding a specific surface area of 1905 m2 g−1 with a high total pore volume of 1.26 cm3 g−1. After CO2 activation, the material shows a salt sorption capacity of ∼8 mg g−1, but the performance is highly influenced by functional groups, causing an inversion peak and fast performance decay. However, de-functionalization via hydrogen treatment is outlined as an effective strategy to improve the CDI performance. After hydrogen treatment of novolac-derived carbon beads, we obtained a salt sorption capacity of 11.5 mg g−1 with a charge efficiency of more than 80% and a performance stability of around 90% over more than 100 cycles. Particularly attractive for practical application is the very high average salt adsorption rate of 0.104 mg g−1 s−1, outperforming commercial activated carbons, which are commonly used for CDI, by at least a factor of two.

Use of Dilute Oxalate to Recover Exchangeable Aluminum Immobilized by Sulfate Salt Addition to Rhodic Kandiudult Subsoil

While SO4 salts have been shown to be effective in reducing exchangeable aluminum (Al) and solution Al activity in acidic subsoils, few attempts have been made in the laboratory to recover exchangeable Al immobilized by the suggested mechanisms of Al–OH–SO4 mineral precipitation or co-sorption on sesquioxide surfaces with SO4 and cations added in the salt (salt sorption). Some low-molecular-weight aliphatic acids such as oxalate are well-known for their ability to increase the solubility of Al in soils and oxalate has often been identified as the dominant or one of the dominant organic anions in subsoils. Oxalate is also well-known for its ability to form soluble complexes and a precipitate with calcium (Ca). Therefore, the objective of this study was to investigate the effects of dilute oxalate on the apparent recovery of exchangeable Al immobilized in response to the addition of gypsum (CaSO4·2H2O) and langbeinite (K2SO4·2MgSO4). Following a 6-month equilibration in the laboratory, gypsum and langbeinite added at 15 mmol SO4 kg−1 were equally effective in decreasing exchangeable Al in soil collected from the Bt1 horizon of a Paaloa silty clay (clayey, oxidic, isothermic Rhodic Kandiudult). However, an oxalate loading rate of 16 mmol kg−1 appeared to recover 100% of the exchangeable Al immobilized by langbeinite but only 38% of that immobilized by gypsum. This result was likely due to the formation of an oxalate precipitate or complexes with Ca in the gypsum treatment. It is suggested that the longevity of gypsum effects on reduced exchangeable Al under field conditions may be due in part to the role of Ca in oxalate complexation.

Estimation of phosphate adsorption by Acrisols of western Spain from electrical conductivity of potassium dihydrogen phosphate extracts of soil

Summary Estimation of the phosphate adsorption capacity in highly weathered acid soils is crucial for adopting appropriate phosphate fertilization practices. In this work, the salt sorption effect was used to develop a method for estimating phosphate adsorption capacity from the decrease in electrical conductivity of a potassium dihydrogen phosphate solution brought in contact with acidic soil samples from surface and subsurface horizons of Acrisols. The method is fast and simple and requires only the use of a conductimeter.

SIZE EXCLUSION CHROMATOGRAPHY OF HUMIC SUBSTANCES: COMPLEXITIES OF DATA INTERPRETATION ATTRIBUTABLE TO NON-SIZE EXCLUSION EFFECTS

The use of size exclusion chromatography (SEC) to support a theory of conformational changes in humic acids induced by organic acids is reviewed. Particular attention is given to an evaluation of the role of non-size exclusion effects in SEC experiments. In this review, results from SEC studies are interpreted in terms of electrostatic, salt, and specific sorption effects that influence the behavior of the HS on the gel. That interpretation has been proven by experimental results from SEC-fractionation of HS in the absence of organic acids, and this has revealed similar interactions between the HS and the gel. The preference here is for the theory of non-size exclusion effects based on considerations of HS as natural polyelectrolytes.

Estimating sulfate adsorption by measuring electrical conductivity of soil/gypsum solution extracts

The salt sorption effect was used to develop a method for estimating the maximum adsorption of sulfate from the decrease in electrical conductivity of a series of gypsum solutions brought into contact with soil samples. The samples used were from uncultivated Palexerults from western Spain.

Apparent Salt Sorption Reactions in an Unfertilized Acid Subsoil

AbstractThe equivalent retention of Ca2+ and SO2‐4 from gypsum solutions in acid subsoils has recently been reported. The term salt sorption has been coined to describe this process, yet little is known about the nature of the reactions involved. This study was conducted to determine if other cation‐anion combinations would exhibit similar behavior and to examine the extractability of the sorbed ions. An unfertilized acid Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) subsoil was equilibrated using a saturated paste technique, with solutions of six different salts at a loading rate of ≈14.0 mmolc kg‐1. The salt solutions used were CaSO4, MgSO4, Na2SO4, CaCl2, MgCl2, and a deionized water control. This soil exhibited salt sorption with all six electrolyte solutions. The SO4 salts were almost completely sorbed with both cation and anion uptake on the order 13.8 mmolc kg‐1. Calcium and magnesium chloride were sorbed at ≈11.7 mmolc kg‐1, and NaCl was sorbed at 8.2 mmolc kg‐1. The treated soils were air dried and extracted with successive portions of deionized water or 0.5 M NH4NO3. A relatively large proportion of both cations and anions were removed by repeated extraction with water, suggesting that ionic strength played an important role in the salt sorption process. Nearly all of the sorbed cations and Cl‐ were recovered by neutral salt extraction, but <100% of the SO2‐4 could be accounted for by neutral salt extraction. Neutral salt extractable Al was significantly reduced by salt treatment. It appeared that salt sorption in this soil may have resulted from several mechanisms including precipitation, specific adsorption, ionic strength induced charging, and ion pair adsorption operating concurrently.

Effect of Ring-Size Variation within Dibenzocrown Ether Resins upon Ion-Pair Sorption of Alkali-Metal Cations from Aqueous and Aqueous Methanol Solutions

Abstract A batch analysis method has been developed for evaluation of metal salt sorption by crown ether polymers. Selectivity in competitive alkali-metal chloride sorption by a series of formaldehyde condensation polymers of dibenzocrown ethers is influenced by the relationship between the crown ether cavity size and metal ion diameter, as well as the degree of hydration of the metal salt. Effective and selective sorption of KCl from the other alkali-metal chlorides was obtained with a dibenzo-18-crown-6 resin. Excellent sorption selectivity for the monovalent metal chlorides was noted for competitive ion-pair sorption of NaCl, KCl, MgCl2, and CaCl2 by this resin. This resin was examined as a stationary phase for selective column separation of KCl from alkali-metal chlorides and of KCl and NaCl from alkali-metal and alkaline-earth chloride mixtures in 80% methanol—20% water.

Polymer-water interaction and its relation to reverse osmosis desalination efficiency

Water and salt sorption and the homogeneity of water distribution have been determined in various polymers and compared with their reverse osmosis desalination properties. A general relationship between the polymer water sorption, the water distribution in the polymer matrix, and the membrane water- and salt-permeabilities has been determined, which indicates that the uniformity of water distribution in the polymer is an important parameter controlling reverse osmosis desalination efficiency.

Estimation of van der waals dipole-quadrupole interactions

Novolac is a low-cost carbon precursor which can be used to derive nanoporous carbon beads in sub-micrometer size. In this study, we introduce this material as a novel electrode material for capacitive deionization (CDI) with high performance stability and superior desalination rate. The polymer beads were synthesized employing a self-emulsifying system in an autoclave, pyrolyzed under argon, and activated with CO2, yielding a specific surface area of 1905 m2 g−1 with a high total pore volume of 1.26 cm3 g−1. After CO2 activation, the material shows a salt sorption capacity of ∼8 mg g−1, but the performance is highly influenced by functional groups, causing an inversion peak and fast performance decay. However, de-functionalization via hydrogen treatment is outlined as an effective strategy to improve the CDI performance. After hydrogen treatment of novolac-derived carbon beads, we obtained a salt sorption capacity of 11.5 mg g−1 with a charge efficiency of more than 80% and a performance stability of around 90% over more than 100 cycles. Particularly attractive for practical application is the very high average salt adsorption rate of 0.104 mg g−1 s−1, outperforming commercial activated carbons, which are commonly used for CDI, by at least a factor of two.

A Lattice Model for Ion Exchangers. Monte Carlo Computations for Salt Sorption in a Simplified Model.

A Lattice Model for Ion Exchangers. Monte Carlo Computations for Salt Sorption in a Simplified Model.