Ion Activity In Solution Research Articles

Electrolytic Seawater Mineralization and the Mass Balances That Demonstrate Carbon Dioxide Removal.

We present the mass balances associated with carbon dioxide (CO2) removal (CDR) using seawater as both the source of reactants and as the reaction medium via electrolysis following the "Equatic" (formerly known as "SeaChange") process. This process, extensively detailed in La Plante E.C.; ACS Sustain. Chem. Eng.2021, 9, ( (3), ), 1073-1089, involves the application of an electric overpotential that splits water to form H+ and OH- ions, producing acidity and alkalinity, i.e., in addition to gaseous coproducts, at the anode and cathode, respectively. The alkalinity that results, i.e., via the "continuous electrolytic pH pump" results in the instantaneous precipitation of calcium carbonate (CaCO3), hydrated magnesium carbonates (e.g., nesquehonite: MgCO3·3H2O, hydromagnesite: Mg5(CO3)4(OH)2·4H2O, etc.), and/or magnesium hydroxide (Mg(OH)2) depending on the CO32- ion-activity in solution. This results in the trapping and, hence, durable and permanent (at least ∼10 000-100 000 years) immobilization of CO2 that was originally dissolved in water, and that is additionally drawn down from the atmosphere within: (a) mineral carbonates, and/or (b) as solvated bicarbonate (HCO3-) and carbonate (CO32-) ions (i.e., due to the absorption of atmospheric CO2 into seawater having enhanced alkalinity). Taken together, these actions result in the net removal of ∼4.6 kg of CO2 per m3 of seawater catholyte processed. Geochemical simulations quantify the extents of net CO2 removal including the dependencies on the process configuration. It is furthermore indicated that the efficiency of realkalinization of the acidic anolyte using alkaline solids depends on their acid neutralization capacity and dissolution reactivity. We also assess changes in seawater chemistry resulting from Mg(OH)2 dissolution with emphasis on the change in seawater alkalinity and saturation state. Overall, this analysis provides direct quantifications of the ability of the Equatic process to serve as a means for technological CDR to mitigate the worst effects of accelerating climate change.

Rare earth element behavior during groundwater–seawater mixing along the Kona Coast of Hawaii

Groundwater and seawater samples were collected from nearshore wells and offshore along the Kona Coast of the Big Island of Hawaii to investigate rare earth element (REE) behavior in local subterranean estuaries. Previous investigations showed that submarine groundwater discharge (SGD) is the predominant flux of terrestrial waters to the coastal ocean along the arid Kona Coast of Hawaii. Groundwater and seawater samples were filtered through 0.45μm and 0.02μm pore-size filters to evaluate the importance of colloidal and soluble (i.e., truly dissolved ionic species and/or low molecular weight [LMW] colloids) fractions of the REEs in the local subterranean estuaries. Mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility (WWTF) proximal to the Kaloko-Hanokohau National Historic Park, and more “pristine” groundwater from a well constructed in a lava tube at Kiholo Bay, were conducted with local seawater to study the effect of solution composition (i.e., pH, salinity) on the concentrations and fractionation behavior of the REEs as groundwater mixes with seawater in Kona Coast subterranean estuaries. The mixed waters were also filtered through 0.45 or 0.02μm filters to ascertain the behavior of colloidal and soluble fractions of the REEs across the salinity gradient in each mixing experiment. Concentrations of the REEs were statistically identical (two-tailed Student t-test, 95% confidence) between the sequentially filtered sample aliquots, indicating that the REEs occur as dissolved ionic species and/or LMW colloids in Kona Coast groundwaters. The mixing experiments revealed that the REEs are released to solution from suspended particles or colloids when Kona Coast groundwater waters mix with local seawater. The order of release that accompanies increasing pH and salinity follows light REE (LREE)>middle REE (MREE)>heavy REE (HREE). Release of REEs in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each REE that occurs in solution as dicarbonato complexes [i.e., Ln(CO3)2−] as pH increases across the salinity gradient. Input-normalized REE patterns of Kona Coast groundwater and coastal seawater are nearly identical and relatively flat compared to North Pacific seawater, indicating that SGD is the chief source of these trace elements to the ocean along the Kona Coast. Additionally, REE concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open-ocean seawater values from the North Pacific, further demonstrating the importance of SGD fluxes of REEs to these coastal waters. Taken together, these observations indicate that large-scale removal of REEs, which characterizes the behavior of REEs in the low salinity reaches of many surface estuaries, is not a feature of the subterranean estuary along the Kona Coast. A large positive gadolinium (Gd) anomaly characterizes groundwater from the vicinity of the WWTF. The positive Gd anomaly can be traced to the coastal ocean, providing further evidence of the impact of SGD on the coastal waters. Estimates of the SGD fluxes of the REEs to the coastal ocean along the Kona Coast (i.e., 1.3–2.6mmolNdday−1) are similar to recent estimates of SGD fluxes of REEs along Florida’s east coast and to Rhode Island Sound, all of which points to the importance of SGD as significant flux of REEs to the coastal ocean.

Influence of pH and temperature on alunite dissolution: Rates, products and insights on mechanisms from atomistic simulation

The processes, rates, controlling factors and products of alunite (KAl3(SO4)2(OH)6) dissolution were assessed using batch dissolution experiments at pHs of c. 3, 4, 4.6, 7 and 8, and temperatures of c. 280, 293 and 313K. Alunite dissolution is roughly congruent at pH3, while at pH≥3.9 the process is incongruent, giving a lower Al/K ratio in solution than in the pristine alunite sample. The decrease in the Al/K ratio appears to be caused by precipitation of secondary aluminium sulfate/hydroxysulfate minerals coating the surface of the dissolving alunite, as inferred from SEM images and XPS determinations, but these minerals do not passivate the alunite surface for the time frame of the experiments (up to 400h). The lowest dissolution rates are obtained for pH4.6 and 280K. Both the temperature increase and any pH variation from that point lead to faster dissolution rates.Based on the potassium release to solution, the influence of pH and temperature on the alunite dissolution rate for pH of 4.8 and below can be expressed as;rateK=10-4.4±0.5aH+0.10±0.02e-32±3/RTwhere rateK is the alunite dissolution rate (in mol·m−2·s−1); aH+ is the activity of hydrogen ions in solution; R is the Universal gas constant (in kJ·mol−1·K−1) and T is temperature (in K).For pH of 4.6 and above, the alunite dissolution rate can instead be expressed as;rateK=10-2.5±0.8aOH-0.14±0.02e-39±4/RTwhere aOH- is the activity of hydroxyl ions in solution.In light of the calculated values for the activation energy under the two sets of pH conditions (32±3 and 39±4kJ·mol−1), alunite dissolution appears to be surface-controlled. Examination of the most stable solvated alunite surfaces obtained by atomistic computer simulations suggests that the least energetically favourable steps during alunite dissolution are the detachment of either Al atoms or SO4 tetrahedra from exposed surfaces. Thus, these processes are most probably the rate-determining steps in alunite dissolution.

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.

Tailoring of antibacterial Ag nanostructures on TiO2 nanotube layers by magnetron sputtering

AbstractTo reduce the incidence of postsurgical bacterial infection that may cause implantation failure at the implant–bone interface, surface treatment of titanium implants with antibiotic materials such as silver (Ag) has been proposed. The purpose of this work was to create TiO2 nanotubes using plasma electrolytic oxidation (PEO), followed by formation of an antibacterial Ag nanostructure coating on the TiO2 nanotube layer using a magnetron sputtering system. PEO was performed on commercially pure Ti sheets. The Ag nanostructure was added onto the resulting TiO2 nanotube using magnetron sputtering at varying deposition rates. Field emission scanning electron microscopy and transmission electron microscopy were used to characterize the surface, and Ag content on the TiO2 nanotube layer was analyzed by X‐ray diffraction and X‐ray photoelectron spectroscopy. Scanning probe microscopy for surface roughness and contact angle measurement were used to indirectly confirm enhanced TiO2 nanotube hydrophilicity. Antibacterial activity of Ag ions in solution was determined by inductively coupled plasma mass spectrometry and antibacterial testing against Staphylococcus aureus (S. aureus). In vitro, TiO2 nanotubes coated with sputtered Ag resulted in significantly reduced S. aureus. Cell viability assays showed no toxicity for the lowest sputtering time group in the osteoblastic cell line MC3T3‐E1. These results suggest that a multinanostructured layer with a biocompatible TiO2 nanotube and antimicrobial Ag coating is a promising biomaterial that can be tailored with magnetron sputtering for optimal performance. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 592–603, 2014.

Thermodynamic assessment of chemical and electrochemical stability of nickel–silicon system alloys

Phase and chemical equilibria in Ni–Si system at 298K are considered. The possible maximum solid solubility of Si in fcc-Ni at 298K is estimated.The Ni–Si–O state diagram at 298K is plotted. The Ni–Si–O system invariant conditions are calculated. The potential–pH diagram of the Ni–Si–H2O system at 298K, air pressure of 1bar and activities of ions in solution, equal to 1mol/l is plotted. Basic chemical and electrochemical equilibria in Ni–Si–H2O system are considered.

The use of a bromide ion selective electrode for the measurement of counter-ion activity in cationic surfactant solutions.

Abstract A bromide ion selective electrode has been used in conjunction with a saturated calomel reference electrode to measure bromide ion activity in solutions of n-decyl, n-dodecyl, n-tetradecyl and n-hexadecyl 1-trimethylammonium bromides at 30°; the critical micelle concentrations of the surfactants were measured by electrical conductance. Calibration of the electrode pair in potassium bromide solutions produced a linear response over the range 0·5 to 5·0p Bra− with a slope of 59·1 mV for a 10-fold change in activity. Results for the surfactants were treated to give values for the degree of micellar dissociation; literature values for this quantity reveal wide variation depending on the technique used.

Copper Toxicity to Bioluminescent Nitrosomonas europaea in Soil Is Explained by the Free Metal Ion Activity in Pore Water

The terrestrial biotic ligand model (BLM) for metal toxicity in soil postulates that metal toxicity depends on the free metal ion activity in solution and on ions competing for metal sorption to the biotic ligand. Unequivocal evidence for the BLM assumptions is most difficult to obtain for native soil microorganisms because the abiotic and biotic compartments cannot be experimentally separated. Here, we report copper (Cu) toxicity to a bioluminescent Nitrosomonas europaea reporter strain that was used in a solid phase-contact assay and in corresponding soil extracts and artificial soil solutions. The Cu(2+) ion activities that halve bioluminescence (EC50) in artificial solutions ranged 10(-5) to 10(-7) M and increased with increasing activities of H(+), Ca(2+) and Mg(2+) according to the BLM concept. The solution based Cu(2+) EC50 values of N. europaea in six contaminated soils ranged 2 × 10(-6) to 2 × 10(-9) M and these thresholds for both solid phase or soil extract based assays were well predicted by the ion competition model fitted to artificial solution data. In addition, solution based Cu(2+) EC50 of the solid phase-contact assay were never smaller than corresponding values in soil extracts suggesting no additional solid phase toxic route. By restricting the analysis to the same added species, we show that the Cu(2+) in solution represents the toxic species to this bacterium.

Ageing and structural effects on the sorption characteristics of Cd2+ by clinoptilolite and Y-type zeolite studied using isotope exchange technique

This research investigates the long-term kinetics of Cd2+ sorption and desorption by calcium-exchanged clinoptilolite (CaCpt) and Y-type (CaY) zeolite using isotopic exchange with 109Cd while maintaining pH at circumneutral values. The effects of Si/Al ratio and crystal structure of these zeolitic materials on intracrystalline transport of Cd are discussed. A first-order kinetic model was developed to describe the progressive transfer of Cd2+ to a less reactive form within the zeolite structure, following initial sorption and subsequent desorption of Cd subject to different initial contact times. The kinetic model differentiates between two forms of sorbed Cd2+ designated ‘labile’ and ‘non-labile’ in which the labile form is in immediate equilibrium with the free Cd2+ ion activity in solution. A model combining diffusion and first-order kinetics for cation exchange was also employed to determine Cd2+ diffusivity and intracrystalline exchange rates in CaY and CaCpt. The efficiency of Permeable Reactive Barriers (PRBs) containing zeolitic materials in protecting water systems against lateral flow of metal-contaminated leachate was simulated for three contrasting zeolites. The slow transfer of Cd between labile and non-labile forms was particularly important in moderating high concentration pulses of Cd traversing the PRB. In addition, the reversibility of Cd fixation effectively restored the sorption capability of the zeolite through slow leakage to drainage water.

Evidence for Bioavailable Copper−Dissolved Organic Matter Complexes and Transiently Increased Copper Bioavailability in Manure-Amended Soils as Determined by Bioluminescent Bacterial Biosensors

The short-term (3 months) dynamics of bioavailable copper (Cu) species was determined in soils amended with various amounts of manure and Cu. Bioavailable Cu species were operationally defined as those species that were able to induce gene expression in a Cu-specific Pseudomonas fluorescens biosensor. Biosensor measurements were backed by analysis of total Cu in soil and of total Cu and free Cu2+ ion activity in solution. Cu bioavailability relative to the total Cu concentration increased dramatically with increasing Cu loading of manure and with increasing manure amendment to soil. In both cases, the immediate increase in bioavailability could be explained in part by increased Cu concentration in solution and in part by an increased bioavailability of dissolved Cu species. In contrast to Cu bioavailability, Cu2+ ion activity decreased progressively with increasing manure loading. Cu bioavailability declined rapidly during the weeks after manure amendment concomitant with a marked slow-down of C mineralization indicating a shift from initially bioavailable Cu-dissolved organic matter (Cu-DOM) complexes to nonavailable Cu-DOM complexes over time. Our data do not support the conventional view of metal bioavailability being primarily related to the free metal ion activity and strongly suggest differential bioavailability of Cu-DOM complexes in manure-amended soils.

Kinetics of Cd sorption, desorption and fixation by calcite: A long-term radiotracer study

Time-dependent sorption and desorption of Cd on calcite was studied over 210 days utilizing 109Cd as a tracer to distinguish between ‘labile’ and ‘non-labile’ forms of sorbed Cd. Stabilizing the calcite suspensions for 12 months under atmospheric P CO2 and controlled temperature was necessary to reliably follow Cd dynamics following initial sorption. Results revealed time-dependant Cd sorption and marked desorption hysteresis by calcite under environmentally relevant conditions. Data obtained were fitted to a first-order kinetic model and a concentric shell diffusion model. Both models described the progressive transfer of Cd 2+ to a less reactive form within calcite and subsequent desorption of Cd subject to different initial contact times. The kinetic model provided a better fit to the combined sorption and desorption data ( R 2 = 0.992). It differentiates between two ‘pools’ of sorbed Cd 2+ on calcite, ‘labile’ and ‘non-labile’, in which labile sorbed Cd is in immediate equilibrium with the free Cd 2+ ion activity in solution whereas non-labile Cd is kinetically restricted. For the diffusion model ( R 2 = 0.959), the rate constants describing Cd dynamics in calcite produced a half-life for Cd desorption of ∼175 d, for release to a ‘zero-sink’ solution. Results from this study allow comment on the likely mechanisms occurring at the calcite surface following long-term Cd sorption.

Time-dependent sorption of Cd 2+ on CaX zeolite: Experimental observations and model predictions

Sorption, fixation and desorption kinetics of Cd 2+ on calcium-exchanged zeolite-X were studied using an isotopic dilution technique utilizing 109Cd. The technique provided reliable measurements of time-dependent fixation of Cd and was validated using chabazite, which demonstrated wholly reversible Cd 2+ ion exchange. A first-order kinetic model was developed to describe the progressive transfer of Cd 2+ to a less reactive form in X-zeolite, following initial sorption, and subsequent desorption of Cd subject to different initial contact times. The kinetic model differentiates between two ‘pools’ of sorbed Cd 2+ on zeolite-X, designated labile and non-labile sorbed Cd in which the labile sorbed Cd is in immediate equilibrium with the free Cd 2+ ion activity in solution. Additionally, an intra-particle diffusion model was developed and compared with the kinetic model to determine whether time-dependent Cd sorption is controlled by reaction kinetics or diffusion within zeolite particles. The kinetic model provided a much better fit to the experimental data ( R 2 = 0.987) than the diffusion model. The rate constants describing Cd dynamics in CaX zeolite gave a half-time for Cd desorption of ∼77 d, for release to a ‘zero-sink’.

Roles of Metal Ion Complexation and Membrane Permeability in the Metal Flux through Lipophilic Membranes. Labile Complexes at Permeation Liquid Membranes

The various physicochemical factors that influence the flux of carrier-transported metal ions through permeation liquid membranes (PLM) are studied systematically. Understanding PLM behavior is important (i) to optimize the application of PLM as metal speciation sensors in environmental media and (ii) because PLM may serve as bioanalogical devices that help to elucidate the environmental physicochemical processes occurring at the surface of biological membranes. Diffusion of free and complexed metal ions in solution, as well as diffusion of the metal carrier complex in the membrane, is considered. The respective roles of diffusion layer thickness, ligand concentration, complex stability, carrier concentration, and membrane thickness are studied experimentally in detail and compared with theory, using various labile complexes, namely, Pb(II)-diglycolate, Cu(II)-diglycolate, and Cu(II)-N-(2-carboxyphenyl)glycine. Conditions where either membrane diffusion or solution diffusion is rate limiting are clearly discriminated. It is shown in particular, that, by tuning the carrier concentration or membrane thickness, either the free metal ion concentration or the total labile metal species are measured. PLM can thus be used to determine whether models based on the free ion activity in solution (such as BLM or FIAM models) are applicable to metal uptake by microorganisms in a real natural medium.

Rhizotoxicity of cadmium and copper in soil extracts

Dissolved organic matter (DOM) influences metal speciation in soil solutions and, hence, metal toxicity. Root-elongation experiments were conducted to examine the effect of soil solution components, such as Ca, H, and DOM, on metal rhizotoxicity. A biotic ligand model (BLM) was tested for its ability to predict the rhizotoxicity of Cd and Cu in soil extracts. It was hypothesized that the concentration of Cd and Cu bound to functional groups at the root surface estimated using a BLM would be a better predictor of rhizotoxicity than the free-metal ion activity in solution. Both metals became less toxic at higher DOM, Ca, and H concentrations. Solution speciation and the effect on root growth explained most of the variability observed in the DOM experiments, but not in the cation experiments. It was concluded that Ca and H inhibited the rhizotoxicity of both metals tested. Rhizotoxicity data correlated better with estimates of metal-root complexes that have been estimated with a BLM than with free-metal ion activity or with total metal concentrations. The BLM seems to be a promising approach for predicting metal availability in soils and for assessing the associated risk.

Lead (II) Ion Inhibition of Respiration and Replication in a Toluene-Enriched Microbial Population

ABSTRACT Bioremediation is inhibited in mine leachate water because of high concentrations of heavy metals and low pH. Inhibition of cellular respiration (A N ) and replication (U N ) by lead ions were measured at pH values near 5 for a mixed microbial culture from a wastewater treatment plant, grown aerobically using toluene as the primary carbon source. Gram-negative microorganisms dominated the toluene-selected microbial population. Microorganisms sequestered lead at binding sites having two different strengths. The stronger binding sites were saturated at about 0.5 mg/L Pb(II) concentration; no evidence of saturation of weaker binding sites was observed up to 15 mg/L of Pb(II). Most of the weak-binding capacity for lead was extracellular, which increased with lead ion concentration without saturating; the intracellular portion of the weak-binding capacity saturated at about 1.0 mg of lead per milligram of dry cells. Lead toxicity, measured by inhibition of respiration and replication, increased as lead accumulated at weak binding sites. However, toxicity to respiration and replication exhibited significantly different dose dependences with lead ion exposure. Replication decreased linearly with the amount of lead sequestered by the cells, consistent with nonspecific inhibition of reproductive catalysis. Respiration was correlated with lead ion activity in solution. Dependence of acute respiration toxicity on Pb(II) concentration and pH were consistent with a modified free ion activity model involving bis binding of lead at inhibition sites. Using a few easily determined parameters, inhibition of respiration and inhibition of reproduction for a natural microbial populations by Pb(II)-contaminated water at low pH are described by the modified free-ion activity model coupled with an appropriate dose-response function.

Characteristics of anionic metal species biosorption with waste crab shells

Anionic metal complexes are very effectively bound by biomass types containing an abundance of amine groups. Readily available chitinous materials such as acid-washed Ucides shells (AWUS) sorbed well anionic gold-cyanide (Au(CN) 2 −), selenate (SeO 4 2−), chromate (CrO 4 2−) and vanadate (VO 4 3−) at low pH. Equilibrium biosorption uptakes by AWUS were up to 0.17 mmol Au/g AWUS (pH 3.4), 0.15 mmol Se/g (pH 3.0), 0.54 mmol Cr/g (pH 2.0) and 0.79 mmol V/g (pH 2.5). An increased ionic strength (IS) suppressed the primary anion uptake as chloride ions competed for biosorbent protonated sites and higher IS reduced the activity of ions in solution. The biosorption mechanism was suspected to involve electrostatic attraction.

Ion exchange equilibria between clinoptilolite and aqueous solutions of Na +/Cu 2+, Na +/Cd 2+ and Na +/Pb 2+

Binary ion exchange equilibrium has been studied by the batch technique using the clinoptilolite as cation exchanger. The equilibrium zeolite loading data were generated for Na + ↔ Cu 2+, Na + ↔ Cd 2+ and Na + ↔ Pb 2+ systems. Three different types of equations were used to predict experimental data: Freundlich, Langmuir and the thermodynamic equilibrium models. The last one was applied taking into account the following factors: (i) concentration of ions in solution and zeolite phase, (ii) activity of ions in solution and concentration in zeolite phase, (iii) activity of ions in solution and in zeolite phase. The Pitzer and Bromley models were used to calculate the activity coefficients of the solution phase. Wilson’s approach was used to predict activity coefficient in zeolite phase. The results show that the agreement between calculated and real values was increasingly better as the concentrations were replaced by activities. To achieve good prediction of experimental data for binary systems, we may assume ideal behaviour of the zeolite phase, which allows us to reduce the complexity of mathematical calculations. On the other hand, the Wilson binary interaction parameters obtained from the model which considers activity coefficients in both phases can be applied for modeling multi-component systems equilibria.

Modelling cation exchange in columns of disturbed and undisturbed subsoil

SummaryCation exchange is often studied with disturbed and dried soils, but the applicability of the results to undisturbed soils is not straightforward. We investigated the value of exchange coefficients obtained from standard procedures for predicting cation exchange in soil. Columns of undisturbed and disturbed subsoil of a Luvisol (SBt horizon) were leached under saturated conditions with 0.4, 4, 20, 41, 102 and 205 mm BaCl2 at a Darcy velocity of 1400 mm day−1. The model PHREEQC was used to calculate one‐dimensional transport, inorganic complexation and multiple cation exchange. Two model variants were tested: m1 (exchangeable cations obtained by percolation with NH4Cl) and m2 (exchangeable cations obtained by shaking the soil with BaCl2). The exchange coefficients (Gaines–Thomas formalism) were calculated from the ion activities in solution and exchangeable cations obtained by NH4Cl percolation (m1) or shaking with BaCl2 (m2). Variant m1 predicted cation exchange of the disturbed (homogenized) soil for the entire BaCl2 concentration range, whereas variant m2 resulted in a two‐fold overestimation of desorbed K for all experiments, which was related to large amounts of K released from the soil by shaking with BaCl2. In experiments with undisturbed soil, variant m1 predicted the concentrations of Mg, Ca, K, and Na in the solution phase and the sum of cations released from exchange sites. However, variant m2 predicted changes in ion concentrations and exchangeable cations somewhat less well. This study suggests that the amounts of exchangeable cations and exchange coefficients obtained from experiments with homogenized soil by percolation are useful to predict cation concentrations in column experiments with undisturbed soils.

Lipophilic derivative of rhodamine 19: characterization and spectroscopic properties

A new octadecylamide derivative of rhodamine 19 was synthesized by reaction of rhodamine 19 ethyl ester (rhodamine 6 G) with octadecylamine. This lipophilic dye exists in two forms: as a cationic species containing a secondary amide group and as an electrically neutral molecule containing an additional ring closed between the oxygen of the amide group and the central carbon of the xanthene part. Both forms were isolated and characterized in detail by means of elemental analysis, mass spectrometry, IR, NMR and UV–VIS spectroscopy. Depending on the hydrogen ion activity in solution and the availability of solvent hydrogen for hydrogen bond formation, the cationic form easily converted into a neutral one and vice versa. On the basis of absorption and emission UV–VIS spectroscopic data, the equilibrium of the two forms was studied in various solvents. An increase in dye concentration in acidified methanol/water mixture (volume fraction of water, ϕ=80%) led to aggregation of the cationic molecules. Using the UV–VIS absorption data, a corresponding dimerization constant was evaluated.

Surface Chemistry and Surface Charge Formation for an Alumina Powder in Ethanol with the Addition of HCl and KOH

Surface charge and surface adsorption on an alpha-alumina powder were investigated in a 99.5/0.5 wt% ethanol/water suspension. A model is proposed in which ethanol molecules are dissociatively adsorbed as ethoxide ions and protons to Lewis acid and base sites on the surface. These ions can then desorb separately from the surface. The surface, therefore, acts as a catalyst for the autoprotolysis of the solvent and creates its own ionic atmosphere which cannot be predicted directly from chemistry in the bulk of the solvent. 3.5μmol/m2 of HCl is reversibly adsorbed to the surface by replacement of ethoxide ions adsorbed to surface acid sites by chloride ions. 2.4μmol/m2 of KOH is adsorbed to the surface by replacement of surface adsorbed protons with potassium ions. More rapid desorption of negative ions from the surface leaves the particles with a net positive surface charge except when the concentration of negative ions in solution is sufficient to supress this desorption and net surface charge goes to zero. Surface charge is found to be a function only of the activity of the negative ions in solution at the surface. No significant negative surface charge was measured under any conditions here. Equilibrium constants for surface adsorption and charge density as a function of surface activity of ethoxide and chloride ions are calculated. No effect of adsorbed potassium ions on the surface potential was found.