Concentrated KCl Solutions Research Articles

Ultrafast and Highly Selective Sequestration of Radioactive Barium Ions by a Layered Thiostannate.

As a simulant of hazardous 226Ra2+, the simultaneously selective and rapid elimination of radioactive 133Ba2+ ions from geothermal water is necessary but still challenging. In this paper, we demonstrated the usability of a layered thiostannate with facile synthesis and inexpensive cost, namely, K2xSn4-xS8-x (KTS-3, x = 0.65-1), for the remediation of radioactive 133Ba2+ in multiple conditions, including sorption isotherm, kinetics, and the influences of competitive inorganic/organic ions, pH values, and dosages. KTS-3 has a strong barium uptake ability (171.3 mg/g) and an ultrafast adsorption kinetics (about 2 min). Impressively, it can achieve a high preference for barium regardless of the excessive interference ions (Na+, K+, Mg2+, Ca2+, and humic acid) and acidic/alkaline environments, with the largest distribution coefficient Kd value reaching 6.89 × 105 mL/g. Also, the Ba2+-laden products can be easily eluted by a concentrated KCl solution, and its adsorption performances for barium resist well even after five consecutive cycles. In addition, owing to the regular appearance and excellent mechanical strength, the prepared KTS-3/PAN (PAN = polyacrylonitrile) granule displays a good removal efficiency in the flowing ion-exchange column. These advantages mentioned above render it very promising for the effective and efficient cleanup of radioactive 133Ba2+-contaminated wastewater.

Electrical Resistive Tomography to Analyse the Flow Behaviour in Redox Flow Batteries

Redox flow batteries (RFBs) are re-emerging as a safe, scalable, efficient and versatile means of large-scale energy storage. Growing adoption of renewable energy generation has ushered a new optimism regarding future reduction in fossil fuel dependency; limiting further harm dealt to the climate and wider environment. However, this momentum demands more efficient energy storage solutions to reconcile power demand and the intermittent nature of wind, solar and tidal energy generation [1]. Without proper storage, reliable back-up generation – largely provided by fossil fuels – will continue to be an unavoidable reality [2]. RFBs utilise the electrochemical properties of dissolved metal ions to store and release energy. Independent sizing of electrolyte storage tanks and flexible power delivery contributes to the flexibility of RFBs compared to alternative battery technologies [3].RFB reactions occur at the electrode-electrolyte interface, and thus the mass transport at this interface is a critical factor in determining the overall RFB performance. Most RFBs use porous electrodes, with a popular choice of material being carbon felt (CF) due to its low cost, chemical stability and high conductivity [4], although the hydrophobic nature of some CF can cause poor electrode ‘wettability’- decreasing the contact area between the electrode and the electrolyte. Further, electrolyte depletion and asymmetric flow can lead to the presence of ‘dead spots’ where the interface is inactive. Many studies have been conducted on CF to improve the electrochemical performance, using surface treatments, compression and channel flow to improve active area, wettability, and species transport [5-7]. These each have direct impact on current density, pressure drop, overpotentials, and energy efficiency. While the flow of electrolyte in the RFB porous electrodes can be modelled using computational fluid dynamics (CFD) [8], and experimentally assessed using x-ray tomography [9,10] and some optical visualisation methods [11], there are limited experimental methods which can be used on entire RFB stacks.In this study, we explore the use of electrical resistive tomography (ERT) to probe the flow of electrolyte through RFB electrodes. ERT has the advantage that it can provide a non-intrusive means of investigating the hydrodynamics of the otherwise opaque cell stack. Measurements were performed using an array of electrodes place around the perimeter of an RFB electrode chamber which contained conventional carbon felt electrodes. Sensitivity maps were generated using the COMSOL Multiphysics platform and compared with experimental measurements. The flow distribution was evaluated by using injections of concentrated KCl solutions into the background electrolyte. Overall, ERT demonstrated promise as a technique for characterising real-time flow dynamics in RFB stacks and for future research into porous electrode and flow field modifications.

Annular Creep Barrier Evaluation and Qualification Using Ultrasonic Measurements

Summary It is well-known that formations that exhibit active creep behavior under downhole conditions, such as reactive shales and mobile salts, can form annular barriers across uncemented or poorly cemented annular sections behind casing strings. Such creep barriers can simplify well abandonments, particularly in high-cost offshore environments. Evaluation and qualification of creep barriers in the field, however, have proven challenging and labor-intensive when casing is perforated, and annular rock material is pressure-tested to verify its sealing ability. This work seeks to eliminate the need for pressure testing by allowing the barrier to be qualified using only casedhole log measurements. Sophisticated rock mechanical laboratory experiments under realistic downhole conditions were conducted to investigate the formation of creep barriers by North Sea Lark shale. The experiments evaluated barrier formation while varying annular fluid chemistry and temperature. Measurement parameters included creep rate, pressure transmission across newly formed barriers, pressure breakthrough through the newly formed barriers as well as ultrasonic responses by the shale. It was found that the Lark/Horda shale has a distinct anisotropic ultrasonic wave velocity profile that uniquely characterizes it. This can be used to identify its presence in an annular space when contacting the casing. A main conclusion is that a Lark shale barrier can be qualified through casedhole sonic and ultrasonic logging alone without the need for pressure testing if (1) the magnitude of the wave propagation velocity of the shale behind casing can be confirmed (2077 m/s for Lark shale); (2) the characteristic velocity anisotropy profile, unique to the shale (~10.1% for Lark shale), can be verified; (3) good contact with/bonding to the casing is observed; and optionally (4) anisotropy in the time behavior of the shale contacting the pipe is observed when the barrier is stimulated artificially. If these conditions are met, then our experiments show that the barrier will have excellent hydraulic sealing ability, with a permeability of a few microdarcies at most and a breakthrough pressure that approaches the minimum horizontal effective stress value. Additional findings are that shale heating will accelerate barrier formation but may damage the shale formation in the process. Extraordinary fast annular closure and barrier formation with evident shale rehealing was observed by using a concentrated KCl solution as pore fluid, showing the merits of barrier stimulation by chemical means. This result can be explained by considering the effect of solutes on shale hydration forces.

The use of the reference electrode equipped with an ionic liquid salt bridge in electrochemistry of ionic liquids: A convenient way to align the formal potentials of redox reactions in ionic liquids based on the standard hydrogen electrode scale

A hydrophobic ionic liquid composed of a cationic and anionic species having similar magnitudes of hydrophobicity and mobilities can work as a salt bridge separating two electrolyte solutions, that is, the sample solution and the inner solution of the reference electrode. A few examples of superiority of this ionic liquid salt bridge (ILSB) over the traditional salt bridges made of a concentrated aqueous KCl solution have been demonstrated. The present study is a further extension of the use of ILSB to voltammtery of the redox reactions of ferrocene/ferrocenium and cobaltocene/cobaltocenium couples in an ionic liquid, tributyl(2-methoxyethyl) phosphonium bis(pentafluoroethanesulfonyl) amide ([TBMOEP][C2C2N]), which is also used as the ILSB. The obtained mid-point potentials (Ems) are converted straightforwardly to those referred to the standard hydrogen electrode (SHE). A comparison of Em (SHE) values of the two redox couples in [TBMOEP][C2C2N] with the corresponding values in molecular solvents suggests that the environment given by [TBMOEP][C2C2N] to the two redox reactions is macroscopically similar to that of methanol.

Spontaneous accumulation of cesium ions based on the membrane potential using a selectively-permeable-polyvinyl chloride capsule containing concentrated potassium ions and zeolites

Moderate amounts of potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTFPB) and 2-nitrophenyl octyl ether (NPOE) were added in a polyvinyl chloride (PVC) capsule membrane, and a concentrated KCl solution was kept inside the capsule as an inner solution. When the PVC capsule was put into an aqueous solution containing low concentrations of K+, the membrane potential between the capsule outside and inside was generated according to the K+ concentration ratio of the capsule outside to the inside. Since the transport of Cs+ from the aqueous phase to the NPOE phase is much easier than that of K+, Cs+ is always taken from the outside into the membrane phase. Accordingly, it was turned out that Cs+ was spontaneously accumulated from the outside to the inside until the Cs+ concentration ratio of the capsule outside to the inside was equivalent to the K+ concentration ratio. In this case, TFPB− was served as not only a counter anion but also a carrier of K+ and Cs+ within the membrane, and some amounts of K+ was replaced by Cs+. Furthermore, the addition of mordenite to the capsule inside facilitated the accumulation of Cs+ because the activity of Cs+ within the capsule was lowered by the adsorption of Cs+ in mordenite.

Temperature and pH-Dependent Response of Poly(Acrylic Acid) and Poly(Acrylic Acid-co-Methyl Acrylate) in Highly Concentrated Potassium Chloride Aqueous Solutions.

In this study, the phase transition phenomena of linear poly(acrylic acid) (PAA) and linear or star-shaped poly(acrylic acid-co-methyl acrylate) (P(AA-co-MA)) in highly concentrated KCl solutions were investigated. The effects of polymer molecular weight, topology, and composition on their phase transition behavior in solution were investigated. The cloud point temperature (TCP) of polymers drastically increased as the KCl concentration (CKCl) and solution pH increased. CKCl strongly influenced the temperature range at which the phase transition of PAA occurred: CKCl of 1.0–2.2 M allowed the phase transition to occur between 30 and 75 °C. Unfortunately, at CKCl above 2.6 M, the TCP of PAA was too high to theoretically trigger the crystallization of KCl. The addition of hydrophobic methyl acrylate moieties decreased the TCP into a temperature region where KCl crystallization could occur. Additionally, the hydrodynamic diameters (Dh) and zeta potentials of commercial PAA samples were examined at room temperature and at their TCP using dynamic light scattering. The salt concentration (from 1 to 3 M) did not impact the hydrodynamic diameter of the molecules. Dh values were 1500 and 15 nm at room temperature and at TCP, respectively.

Adaptive behavior of clinicians in response to an over-constrained patient safety policy on the administration of concentrated potassium chloride solutions

In response to fatal accidents involving concentrated potassium chloride (KCl) solutions, the Japanese hospital accreditation body released a safety policy in 2004 requiring the use of foolproof diluted KCl solutions throughout hospitals. However, the policy caused difficulties in treating seriously ill patients in critical care settings who require concentrated KCl solutions promptly. Resilient health care (RHC) provides a theoretical perspective for understanding how work is achieved in complex healthcare systems. ‘Work-as-imagined’ (WAI), as it should be done, and ‘work-as-done’ (WAD), as it actually takes place, are core concepts for understanding performance adjustment among individuals. This study aimed to investigate WAD regarding the administration of KCl solutions in the environment changed by WAI according to the authoritative policy.In 2017, we sent questionnaires to 346 critical care physicians. Topics included types of KCl products available in their units, administration methods, need for concentrated KCl solutions, hospital policies, and physician opinions. The response rate was 30.3% (105/346). Thirty-five physicians (33.3%) used conventional products out of compliance with the safety policy. Among 95 physicians using foolproof products, 69 (72.6%) obtained concentrated solutions from the products in an unsafe manner. The gap between WAI and WAD necessitated performance adjustments by physicians that introduced a new risk of adverse events despite the use of safer products.The study demonstrated that RHC theory can be used to inform the development and improvement of patient safety policies. Policy makers need to understand WAD when intervening in complex adaptive systems such as health care.

Effective and Rapid Adsorption of Sr2+ Ions by a Hydrated Pentasodium Cluster Templated Zinc Thiostannate.

Separation of 90Sr from radioactive wastewater not only is essential for human public health and environmental remediation but also bears importance for alternate medical and industrial applications. Here, we report the facile synthesis of an open framework zinc thiostannate, Na5Zn3.5Sn3.5S13·6H2O (ZnSnS-1), templated by hydrated pentasodium clusters. This compound exhibits an effective and rapid ion exchange property for Sr2+ ions. The exchange kinetics conforms to a pseudo-second-order model, implying that the chemical adsorption of Sr2+ may be the rate-determining step. According to the Langmuir-Freundlich isotherm, the maximum exchange capacity of ZnSnS-1 for Sr2+ is 124.2 mg/g and ranks ahead of those of all the reported metal sulfide Sr2+ adsorbents. High exchange performance is observed over the broad pH range 2.5-13, although it could be inhibited to some extent by coexisting ions, especially Na+ and Ca2+. ZnSnS-1 shows a higher affinity for Sr2+ compared to Cs+, and the performance is almost unaffected by the presence of coexisting Cs+ even in excess amounts. Importantly, the Sr2+ in the exchanged product can be conveniently eluted by a concentrated KCl solution, and the recycled exchanger can be further used for Sr2+ exchange. These advantages combined with the robust framework for recycling concerns make ZnSnS-1 a highly promising exchanger for removal of radioactive Sr from the liquid nuclear waste.

Evaluation of interfacial properties of concentrated KCl solutions by molecular dynamics simulation

Understanding the interfacial properties of concentrated salt solutions is critical for various applications in physical, chemical and biological processes. This study aims to evaluate the interfacial properties of potassium chloride (KCl) solutions with concentrations ranging from 1 to 4M using the molecular dynamics simulation technique. We used two different water models, TIP4P/2005 and SPC/E to calculate the local density and angle distribution, viscosity, interfacial tension and surface potential of the salt solutions. The surface tension values predicted by the TIP4P/2005 model showed an incremental trend in agreement with experimental data. For viscosity, the predictions of TIP4P/2005 are close to the experimental data, while the predictions of SPC/E are in poor agreement with the measured viscosities. Our results show that the selection of water models significantly affects the structure properties of concentrated KCl solutions. Also, the TIP4P/2005 model compares very closely with the measured interfacial properties of salt solutions.

Is the Solution Activity Derivative Sufficient to Parametrize Ion-Ion Interactions? Ions for TIP5P Water.

Biomolecular processes involve hydrated ions, and thus molecular simulations of such processes require accurate force-field parameters for these ions. In the best force-fields, both ion-water and anion-cation interactions are explicitly parametrized. First, the ion Lennard-Jones parameters are optimized to reproduce, for example, single ion solvation free energies; then ion-pair interactions are adjusted to match experimental activity or activity derivatives. Here, we apply this approach to derive optimized parameters for concentrated NaCl, KCl, MgCl2, and CaCl2 salt solutions, to be used with the TIP5P water model. These parameters are of interest because of a number of desirable properties of the TIP5P water model, especially for the simulation of carbohydrates. The results show, that this state of the art approach is insufficient, because the activity derivative often reaches a plateau near the target experimental value, for a wide range of parameter values. The plateau emerges from the interconversion between different types of ion pairs, so parameters leading to equally good agreement with the target solution activity or activity derivative yield very different solution structures. To resolve this indetermination, a second target property, such as the experimentally determined ion-ion coordination number, is required to uniquely determine anion-cation interactions. Simulations show that combining activity derivatives and coordination number as experimental target properties to parametrize ion-ion interactions, is a powerful method for reliable ion-water force field parametrization, and gives insight into the concentration of contact or solvent shared ion pairs in a wide range of salt concentrations. For the alkali and halide ions Li+, Rb+, Cs+, F-, Br-, and I-, we present ion-water parameters appropriate at infinite dilution only.

Combining field-amplified sample stacking with moving reaction boundary electrophoresis on a paper chip for the preconcentration and separation of metal ions.

A common drawback of paper-based separation devices is their poor detection limit. In this study, we combined field-amplified sample stacking with moving reaction boundary electrophoresis on a paper chip with six array channels for the parallel separation and concentration of multiple samples. With a new hyphenated technique, the brown I2 from the Fe3+ /I- oxidation-reduction reaction emerged near the boundary between the dilute ethylene diamine tetraacetic acid and potassium iodide and highly concentrated KCl solutions. For the separation and concentration of three components, Cr3+ , Cu2+ , and Fe3+ , the Fe3+ detection limit was improved at least 266-fold by comparing the hyphenated technique with moving reaction boundary electrophoresis. The detection limit of Fe3+ was found to be as low as 0.34 ng (20 μM) on the paper chip. We also demonstrated the analysis of a real sample of four metal ions, with detection limits as follows: 0.16 μg Cr3+ , 1.5 μg Ni2+ , 0.64 μg Cu2+ , and 1.5 μg Co2+ . The synergy of field-amplified sample stacking and moving reaction boundary electrophoresis in the micron paper-based array channels dramatically improved the detection limit and throughput of paper-based electrophoresis.

Chemometric soil analysis on the determination of specific bands for the detection of magnesium and potassium by spectroscopy

The laboratory soil analysis is traditionally used to establish elements, such as those related with fertility. It is costly and time consuming, which insures issues for future of precision agriculture, which is stagnated in some countries. Reflectance spectroscopy has recently emerged as a potential tool to reduce these issues. However, chemical elements are usually only underlined with spectra by a “coincidently” statistics and doesn't provide real detection. This study aims to investigate to interaction of K+ and Mg2+ with electromagnetic energy for decrease the demand of soil analysis and rationalize the use of fertilizers. The experiment was carried out using three major soil classes with different textures from tropical environment in Brazil. To reach K+ and Mg2+ saturation in different levels, the soils were saturated with concentrated solutions of KCl and MgCl2 in vertical columns and then washed with distilled and deionized water to extract the residual elements. A second experiment was made by incubation of these elements in soils during four days in room temperature around 30°C. Laboratory spectral sensing was carried out in the VIS-NIR-SWIR regions (350–2500nm). Spectra were processed by the Continuum Removal, the Principal Components Analysis (PCA) and Partial Least Squares regression. The PCA showed a high degree of association between spectral and chemical variations. There was no alteration on mineralogy, texture, organic matter, moisture and effective cation exchange capacity (CEC) after the experiment occurs. On the other hand, differences on spectral, mainly where occurs CEC around 2200nm, did change. Thus, the incident energy interacts with K+ and Mg2+ which promoted these alterations, mostly for Arenosol and Ferrasol. In Cambisol (2:1 mineralogy) we had a double effect due to effective CEC and cations alteration. Were encountered specific bands which altered features due to K+ and Mg2+ content mainly in 2186, 2189 and 2200nm. Based on the results, the identified bands (related to K+ and Mg2+ contents in the soil) were extracted from the spectral data of soil samples obtained from a Brazilian soil spectral library. Indeed calibrations of K+ and Mg2+ models allowed to quantify these elements with 0.66 R2 for the selected bands and 0.64 for the entire spectrum. Thus, the results indicate that it is possible to detect chemical elements, such K+ and Mg2+ in VIS-NIR-SWIR, looking forward on to assist soil analysis and all inherent approaches.

Efficient Removal and Recovery of Uranium by a Layered Organic–Inorganic Hybrid Thiostannate

Uranium is important in the nuclear fuel cycle both as an energy source and as radioactive waste. It is of vital importance to recover uranium from nuclear waste solutions for further treatment and disposal. Herein we present the first chalcogenide example, (Me2NH2)1.33(Me3NH)0.67Sn3S7·1.25H2O (FJSM-SnS), in which organic amine cations can be used for selective UO2(2+) ion-exchange. The UO2(2+)-exchange kinetics perfectly conforms to pseudo-second-order reaction, which is observed for the first time in a chalcogenide ion-exchanger. This reveals the chemical adsorption process and its ion-exchange mechanism. FJSM-SnS has excellent pH stability in both strongly acidic and basic environments (pH = 2.1-11), with a maximum uranium-exchange capacity of 338.43 mg/g. It can efficiently capture UO2(2+) ions in the presence of high concentrations of Na(+), Ca(2+), or HCO3(-) (the highest distribution coefficient Kd value reached 4.28 × 10(4) mL/g). The material is also very effective in removing of trace levels of U in the presence of excess Na(+) (the relative amounts of U removed are close to 100%). The UO2(2+)···S(2-) interactions are the basis for the high selectivity. Importantly, the uranyl ion in the exchanged products could be easily eluted with an environmentally friendly method, by treating the UO2(2+)-laden materials with a concentrated KCl solution. These advantages coupled with the very high loading capacity, low cost, environmentally friendly nature, and facile synthesis make FJSM-SnS a new promising remediation material for removal of radioactive U from nuclear waste solutions.

Chemisorption and Electrochemical Activity of Thiophenols at Well-Defined Pd(111) Surfaces: Studies by LEED, AES, HREELS, and Electrochemistry

The chemisorption and electrochemical activity of 2 ,5 -dihydroxythiophenol (DHT) and 2-(8mercaptooctyl)-1,4-benzenediol (DHOT) on well-defined Pd(111) surfaces were studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), high resolution electron energyloss spectroscopy (HREELS), and electrochemistry (EC). Results confirm that DHT is chemisorbed in two discrete orientations such that at low concentrations, DHT is oxidatively bound to the surface through the diphenol and mercapto groups as quinonoid and S moieties, respectively, whereas at high concentrations, the molecule is coordinated oxidatively through the –SH group in a vertical S- η 1

Implications of the redissociation phenomenon for mineral-buffered fluids and aqueous species transport at elevated temperatures and pressures

Aqueous species equilibrium constants and activity models form the foundation of the complex speciation codes used to model the geochemistry of geothermal energy production, extremophilic ecosystems, ore deposition, and a variety of other processes. Researchers have shown that a simple three species model (i.e., Na+, Cl−, and NaCl(aq)) can accurately describe conductivity measurements of concentrated NaCl and KCl solutions at elevated temperatures and pressures (Sharygin et al., 2002). In this model, activity coefficients of the charged species (e.g., Na+, K+, Cl−) become sufficiently low that the complexes must redisocciate with increasing salt concentration in order to meet equilibrium constant constraints. Redissociation decreases the proportion of the elements bound up as neutral complexes, and thereby increases the true ionic strength of the solution. In this contribution, we explore the consequences of the redissociation phenomenon in albite–paragonite–quartz (APQ) buffered systems. We focus on the implications of the redissociation phenomenon for mineral solubilities, particularly the observation that, at certain temperatures and pressures, calculated activities of charged ions in solution remain practically constant even as element concentrations increase from <1molal to 4.5molal. Finally, we note that redissociation has a similar effect on pH, and therefore aqueous speciation, in APQ-hosted systems. The calculations and discussion presented here are not limited to APQ-hosted systems, but additionally apply to many others in which the dominant cations and anions can form neutral complexes.

Influence of salt concentration on DCMD performance for treatment of highly concentrated NaCl, KCl, MgCl2 and MgSO4 solutions

Highly concentrated NaCl, KCl, MgCl2 and MgSO4 solutions were treated using DCMD. The effects of salt concentration (1.0–4.0mol/L) and circulation velocity (0.1–0.5m/s), as well as thermodynamic and physical properties of the salt solutions on permeate flux were investigated. Results showed that the permeate fluxes decrease with increasing concentration for the four salts solutions studied, which follows the order of KCl>NaCl>MgSO4>MgCl2 at the salt concentrations higher than 1.0mol/L. The different vapor pressure depression caused by reduction of water activity was identified as the main reason behind this. However, the drastic increase of viscosity of MgSO4 and MgCl2 solutions at higher salt concentrations would also have a notable adverse impact on permeate flux. Under these circumstances, change of hydrodynamics, i.e. increase of circulation velocity would be a great help to improve the heat transfer and then the flux. To prevent salt from crystallizing on membrane surface in saturated conditions, the feed inlet temperature should be controlled within a certain range, and it was 40 to 50°C, 40 to 45°C and 25 to 35°C for NaCl, KCl, and MgSO4, respectively in this study.

Efficient separation of nitrogen-doped carbon nanotube cups

Nitrogen-doped carbon nanotubes synthesized from a mixture of ferrocene, xylenes, and acetonitrile using chemical vapor deposition technique comprise compartmented hollow structures resembling stacked cups. Separating stacked nitrogen-doped carbon nanotube cups (NCNCs) into individual cups is an attractive way to further manipulate their morphology, providing additional opportunities for applications of NCNCs. Here we demonstrate an effective, simple, and low-cost separation method to obtain individual NCNCs around 180nm in length, by sonicating as-synthesized stacked NCNCs in concentrated KCl solution. Another advantage of this technique is that it is highly selective to the separation of adjacent NCNCs and capable of preserving the surface structure and functionalities of stacked NCNCs. Here we demonstrate that the presence of potassium ions is vital for the separation and we hypothesize that the separation mechanism involves a partial intercalation that facilitates the separation of NCNCs.

Measuring velocity of water flow within a gravel layer using an electrolyte tracer method with a Pulse Boundary Model

Summary Water flow within a gravel layer is of great interest in many studies and applications. The electrolyte tracer method, based on the solution to the governing partial differential equation of solute transport in water flow under a pulse boundary condition, the Pulse Boundary Model, was suggested to measure the velocity of water flow within a gravel layer. Laboratory experiments were made to illustrate the measurement method. The dye tracer method was used to make comparative measurements. Gravel of about 2 cm in diameter was placed to a 5 cm thick layer in a flume of 4 m long, 20 cm wide and 50 cm deep. Flow velocities were measured at locations of 0.3, 0.6, 0.9, 1.2 and 1.5 m from the electrolyte tracer injector, which was 1 m from the water inlet, under 3 flow rates of 3, 6 and 12 L/min and for 3 slope gradients of 4°, 8° and 12°. Highly concentrated KCl solution was injected into the water flow within the gravel layer through a funnel. The solute transport processes were registered by the measurement system, as detected by the ion-sensitive sensors, before being used for flow velocity estimations at different locations. The measured flow velocity increased with slope gradient but was similar under the different flow rates used. The velocity values measured by the Pulse Boundary Model were about 20–50% lower than those estimated by the dye tracer method although they were strongly linearly correlated. The measured velocity values were in about the same order of magnitude as those reported in the literature. Therefore, the Pulse Boundary Model electrolyte tracer method was demonstrated to be rational and applicable for measuring the velocity of water flow within a gravel layer.

Effects of concentrated NaCl and KCl solutions on the behaviour of aqueous peptide bond environment: single-particle dynamics and H-bond structural relaxation

The effects of salt concentrations on the structure, dynamics and hydrogen bond structural relaxation properties of ∼1.10 M aqueous N-methylacetamide (NMA) solution at 308 K are studied by classical molecular dynamics simulations. We have considered the concentration range of salts solution from 0.222 to 3.756 M to investigate the behaviour of aqueous environment of peptide bonds in the presence of concentrated NaCl and KCl solution. It is found that the addition of salt solution facilitates the structural breaking of aqueous NMA hydrogen bonds, as a result the number of hydrogen bonds per NMA molecule and their stability decreases. The water and NMA molecule shows slower translational and rotational dynamics with increasing salt concentrations due to additional ion atmospheric friction. Our result shows that the cation–ONMA radial distribution function decreases whereas the Cl−─HNMA radial distribution function increases with ion concentration. On the other hand, the cation–Owater and Cl−─Hwater radial distribution function shows very negligible change with respect to ion concentration. We have also calculated NMA–water and water–water hydrogen bond structural relaxation times. It is observed that the hydrogen bond structural relaxation of ONMA─Hwater is comparatively slower than the HNMA─Owater hydrogen bond, which can be attributed to higher number and greater stability of the former hydrogen bond than the latter. The change of the dynamical quantities observed here is more prominent in addition of NaCl rather than the KCl solution.

Specific effects of background electrolytes on the kinetics of step propagation during calcite growth

The mechanisms by which background electrolytes modify the kinetics of non-equivalent step propagation during calcite growth were investigated using Atomic Force Microscopy (AFM), at constant driving force and solution stoichiometry. Our results suggest that the acute step spreading rate is controlled by kink-site nucleation and, ultimately, by the dehydration of surface sites, while the velocity of obtuse step advancement is mainly determined by hydration of calcium ions in solution. According to our results, kink nucleation at acute steps could be promoted by carbonate-assisted calcium attachment. The different sensitivity of obtuse and acute step propagation kinetics to cation and surface hydration could be the origin of the reversed geometries of calcite growth hillocks (i.e., rate of obtuse step spreading < rate of acute step spreading) observed in concentrated (ionic strength, IS = 0.1) KCl and CsCl solutions. At low IS (0.02), ion-specific effects seem to be mainly associated with changes in the solvation environment of calcium ions in solution. With increasing electrolyte concentration, the stabilization of surface water by weakly paired salts appears to become increasingly important in determining step spreading rate. At high ionic strength (IS = 0.1), overall calcite growth rates increased with increasing hydration of calcium in solution (i.e., decreasing ion pairing of background electrolytes for sodium-bearing salts) and with decreasing hydration of the carbonate surface site (i.e., increasing ion pairing for chloride-bearing salts). Changes in growth hillock morphology were observed in the presence of Li +, F − and SO 4 2 - , and can be interpreted as the result of the stabilization of polar surfaces due to increased ion hydration. These results increase our ability to predict crystal reactivity in natural fluids which contain significant amounts of solutes.