Changes In Solution Composition Research Articles

Electrochemical reduction of ethylpicolinate : Competitive aspects of pyridine nucleus hydrogenation and ester reduction

Electrolyses of ethylpicolinate in aqueous sulfuric acid solutions were performed on a lead cathode in galvanostatic mode. The reduction of the ester function was in competition with that of the pyridine nucleus. Study of the change in solution composition with time during electrolysis allowed evaluation of the influence of parameters such as acidity, current density, initial concentration of ethylpicolinate and temperature, on the competing formation of the different electrolysis products. Parameter values were chosen for synthesis of 2-hydroxymethylpyridine.

Studies on the physical and compositional changes in collapsing beer foam

Batches of foam were characterised by analysis of conductivity and quantitative changes in mass and solute composition of material retained both within foam and foam drainage. The conductivity of dispensed beer foam declined exponentially during the initial stages of foam collapse, followed by a secondary or consolidation stage characterised by deviation from exponential decay and increases in the concentration of polypeptide material in both foam and foam drainage. Analysis of the amino acid composition of whole collapsed foams suggested that polypeptides of enhanced hydrophobicity were selectively partitioned to the gas–liquid interface at foam formation and subsequent consolidation. Estimates of the changes in total mass of the liquid phase within dispensed beer foam suggested that foam collapse proceeded by two distinct stages of exponential decay characterised by different rates ( k 1, k 2). The first rate ( k 1) corresponded to the initial stage of foam collapse and accounted for 85–90% loss of foam mass. This was followed by a slower rate of collapse ( k 2) which corresponded to the consolidation stage. The results from physical and compositional analyses suggest that the initial stage of foam collapse is dominated by gravitational drainage from a liquid rich foam followed by a change in emphasis to coalescence and bubble rupture during the consolidation and residual stages of foam collapse. These findings contribute to the understanding and characterisation of foam formation and stability.

An Investigation Into the Mechanism by Which Synthetic Zeolites Reduce Labile Metal Concentrations in Soils

The addition of synthetic zeolites and similar materials to metal contaminated soils has been shown to reduce soil phytotoxicity and to improve the quality of plant growth on such amended soils. To gain an understanding of the mechanism by which the phytotoxicity of contaminated soils is reduced when treated with synthetic zeolites, sequential extraction procedures and soil solution techniques have been used to identify changes associated with metal speciation in amended soils. Sequential extraction data and changes in soil solution composition are presented for three different contaminated soils, amended with three synthetic zeolites (P, 4A and Y) at concentrations of 0.5%, 1% and 5% w/w, or lime at 1%. The soils were collected from the site of a metal refinery, an old lead zinc mine spoil tip and from a field which had been treated with sewage sludge. After incubation of the zeolite treated soils for between one and three months, results showed a reduction in the metal content of the ammonium acetate fraction between 42% and 70%, depending on soil, zeolite and rate of addition, compared with the unamended soils. In addition, soil solution experiments indicated that synthetic zeolite amendments were more efficient at reducing metal content than comparable lime treatment. The mechanism by which synthetic zeolites reduce metal bioavailability in contaminated soils is discussed and compared to other amendments.

Kaolinite and smectite dissolution rate in high molar KOH solutions at 35° and 80°C

Experiments measuring kaolinite and smectite dissolution rates were carried out using batch reactors at 35° and 80°C. No potential catalysts or inhibitors were present in solution. Each reactor was charged with 1 g of clay of the ≤2 μm fraction and 80, 160 or 240 ml of 0.1–4 M KOH solution. An untreated but sized kaolinite from St. Austell and two treated industrial smectites were used in the experiments. One smectite is a nearly pure montmorillonite, while the second has a significant component of beidellitic charge (35%). The change in solution composition and mineralogy was monitored as a function of time. Initially, the 3 clays dissolved congruently. No new formed phases were observed by XRD and SEM during the pure dissolution stage. The kaolinite dissolution is characterized by a linear release of silica and Al as a function of the log of time. This relationship can be explained by a reaction affinity effect which is controlled by the octahedral layer dissolution. Far from equilibrium, dissolution rates are proportional to a 0.56±0.12 OH − at 35°C and to a 0.81±0.12 OH − at 80°C. The activation energy of kaolinite dissolution increases from 33±8 kJ/mol in 0.1 M KOH solutions to 51±8 kJ/mol in 3 M KOH solutions. In contrast to kaolinite, the smectites dissolve at much lower rates and independently of the aqueous silica or Al concentrations. The proportionality of the smectite dissolution rate constant at 35 and 80°C was a 0.15±0.06 OH − . The activation energy of dissolution appears to be independent of pH for smectite and is found to be 52±4 kJ/mol. The differences in behavior between the two kinds of minerals can be explained by structural differences. The hydrolysis of the tetrahedral and the octahedral layer appears as parallel reactions for kaolinite dissolution and as serial reactions for smectite dissolution. The rate limiting step is the dissolution of the octahedral layer in the case of kaolinite, and the tetrahedral layer in the case of smectite.

Ion Exchange Resins as Emerging−Submerging Chemical Sensors

A new concept in chemical sensing has been introduced that uses changes in density of a cross-linked polymer to physically signal changes in solution composition. Prototype systems that have now been developed are based on Amberlite IRA 400 (Cl), where anion exchange provides a driving force for the resin's emergence from, and submergence into, water due to changes in bead density. The potential utility of such sensors is briefly described.

Effect of Supplementary Cementing Materials on the Specific Conductivity of Pore Solution and Its Implications on the Rapid Chloride Permeability Test (AASHTO T277 and ASTM C1202) Results

The American Association of States Highway and Transportation Officials (AASHTO) Test Method T277--Rapid Determination of the Chloride Permeability of Concrete and the American Society of Testing and Materials (ASTM) C1202--Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration have specified a rapid test method to rank the chloride penetration resistance of various concretes by applying a potential of 60 V DC to a concrete specimen and measuring the charge passed through the specimen during 6 hours of testing. The method is essentially a measurement of electrical conductivity of concrete, which depends on both the pore structure and the chemistry of the pore solution. Analyses based on published results have indicated that the replacement of portland cement with supplementary cementing materials, such as silica fume, can reduce the electrical conductivity of concrete more than 90% because of the change in pore solution composition in the concrete. Chemical composition of pore solution has little to do with the transport of chloride ions in the concrete; thus, it is not correct to use passed charge to rank the chloride penetration resistance of concrete made with supplementary cementing materials.

In Situ Study of Salt Film Stability in Simulated Pits of Nickel by Raman and Electrochemical Impedance Spectroscopies

The changes in solution composition and the stability of a salt film in a 10 mm deep, simulated pit electrode made of nickel in a 0.5 M HCl solution were monitored as a function of applied potential using a 532 nm fiber‐optic Raman system. Raman spectroscopy was able to clearly distinguish dissolved Ni(II)Cl species from the salt film of . Furthermore, the gradient of Ni(II)Cl in the pit was measured as a function of potential. At an applied potential of , a salt film was observed at the bottom of the pit after about 5200 s, corresponding to the first big drop in current density. The salt film was not observed below an applied potential of . However, repassivation did not occur above a potential of about . The concentration gradient inside the pit decreased dramatically at and the chloride concentration at the bottom of the pit at repassivation was found to be about 17% of saturation value with respect to . Electrochemical impedance spectroscopy of the simulated pit electrode in the same solution at various applied potentials was used to determine the electronic properties of the salt film and the thickness of the film. EIS suggested that the salt film had a dual structure, with a compact film underneath a thicker porous layer.

Characterization of Colloids Mobilized from Southeastern Coastal Plain Sediments

Two subsurface samples representing highly weathered sediments of the Upper Coastal Plain (Aiken, SC) that differed in Fe-oxide content (7.3 vs 35.9 g Fe kg -1 ) were evaluated in terms of mobile colloid generation in response to changes in solution composition. In repacked columns, the two sediments were leached (∼0.72 m d -1 Darcy velocity) with either 0.001 N NaCI or CaCl 2 solutions for 10 pore volumes followed by 10 pore volumes of deionized water. Bulk clay mineralogy from the two samples and suspensions generated in the column studies was characterized by energy dispersive X-ray analysis (EDXA) using a field-emission scanning electron microscope (SEM). SEM results were confirmed by selected-area electron diffraction (SAED) and EDXA in a transmission electron microscope. In column experiments, the sample lower in Fe oxide displayed increased effluent turbidity that coincided with a decrease in effluent pH during injection of the CaCl 2 solutions. In contrast, no effluentturbiditywas observed during the leaching of NaCl solutions. The sample higher in iron oxide displayed greater effluent turbidity from the onset of leaching that decreased over the duration of injection for both the CaCl 2 and NaCl solutions. Colloids generated from both materials displayed positive electrophoretic mobilities, confirming the importance of iron oxides in controlling dispersion and surface charge properties of the mobile colloids. Minor differences in the clay mineralogy (i.e., iron oxide/kaolinite content) between the samples were reflected in both their sensitivity to pore-solution composition and the relative degree of dispersion observed for each sample. Electron microscopy, EDXA, and thermal gravimetric analysis (TGA) confirmed that the mobile colloids consisted mainly of submicron sized Al-rich goethite, with lesser amounts of kaolinite,the predominate layer silicate of the bulk sediments, and varying amounts of crandallite.

The geochemical effects of benzene, toluene, and xylene (BTX) biodegradation

The geochemical effects of microbially mediated degradation of aromatic hydrocarbons were observed as changes in solution composition of an artificial groundwater in packed-sand laboratory columns. Benzene, toluene, and xylene, both individually and in a combined fashion, were used as substrates in biodegradation experiments conducted under oxygenated and anoxic conditions in columns filled with quartz, calcite, or Fe 3+-coated quartz sand. Typically, column effluent had increased concentrations of dissolved inorganic C, decreased pH, and decreased concentrations of NO 3 and dissolved O 2 relative to column influent. Efficiency of CO 2 generation was similar for the three different substrates, ranging from 22.5 to 26.6% organic C converted to CO 2. When all three substrates were combined, the percentage of CO 2 produced fell within the range observed in the single substrate experiments. Nitrate disappearance was more varied as a function of substrate identity, with greatest amounts lost when toluene was the substrate. Calcite dissolved as a result of CO 2 generated during the biodegradation reactions, and empirically calculated dissolution rates varied between 1.9 and 4.0 x 10 −9 mmol cm −2 s −1. The calcite dissolution rate was slower than the biodegradation rate, as evidenced by excess generation of CO 2 relative to Ca 2+ production. The decrease in pH was less in experiments with calcite present than in those with quartz sand present due to buffering by calcite dissolution. Dissolution of Fe oxyhydroxides was not observed under any experimental conditions.

Linking microscopic and macroscopic data for heterogeneous reactions illustrated by the oxidation of manganese (II) at mineral surfaces

Previously published microscopic observations of the heterogeneous oxidation of Mn(II) at hematite and albite surfaces were used to develop rate expressions that model the changes in solution composition during oxidation experiments. A geometric approach, which approximates the evolution of reactive surface area over the course of an experiment, was used to expand the right side of the following equation: r het = d [ Mn ( II ) ] d t = − d [ β − MnOOH ] d t such that a theoretical link between macroscopic (d[Mn(II)]/dt) and microscopic observations ( d[β − MnOOH]/ dt) was created. Through this analysis, macroscopic rate constants, which are most commonly determined through measurements of the changes in solution composition, are broken down into smaller components that represent a microscopically measured rate constant and the reactive surface area present during an oxidation experiment. These microscopic rate constants can be used to directly compare the reactivities of minerals used in Mn(H) oxidation experiments. The new kinetic models, based on two cases of precipitate development, provide good fits of published solution data ( Davies and Morgan, 1989), suggesting that these models successfully scale the microscopic processes to the macroscopic observations. However, it was also found that very different microscopic mechanisms (e.g., adsorption vs. precipitation) can produce equally good fits of the same macroscopic data. This situation demonstrates the importance of upgrading kinetic models to include more detailed microscopic observations that were not possible to collect just a few years ago.

The Use of Microelectrodes to Study the Precipitation of Calcite upon Algal Biofilms

Calcium and pH ion-selective microelectrodes are used for the first time to measure chemical activity profiles above laboratory-grown algal biofilms (green alga,Chlorococcumsp). The results are used to calculate the solution composition changes above an actively photosynthesizing biofilm. These changes include the total calcium concentration, degree of supersaturation of the solution with respect to calcite, and the partial pressure of carbon dioxide. Measurements are made in a flow-cell, which was designed to hold the templates on which the biofilms are grown. Measurements show pronounced gradients of pH and calcium concentration, within a distance of approximately 500 μm above the biofilm. The high degree of supersaturation caused by the low concentrations of carbon dioxide near the biofilm surface leads to the precipitation of calcite on the biofilm. SEM micrographs illustrate the close association of calcite crystals with the algal cells. Preliminary results are presented of the precipitation rates estimated from the diffusion flux of calcium at the biofilm surface. The results are in broad agreement with the rates expected from calcite seed growth experiments in similar solution conditions.

A possible role of electrode filming in abnormal deposition of alloys

An examination was made of the composition of binary alloys that form deposits whose composition varies relatively little with changes in solution composition or current density. It was found for an appreciable number of these deposits that the atomic ratio of the two metals in the deposits was the ratio of two small whole numbers. This data lends support to the idea that the cause of these abnormal deposition processes is the fact that deposition in these systems occurs by reduction of an insoluble film or a complex ion trapped on the surface of the electrode rather than by reduction of ions that are in thermodynamic equilibrium with the ions in solution. These abnormal plating processes include anomalous codeposition and induced codeposition. In agreement with results from studies of electroreduction of insoluble solids, the simple ratios of the metals in most cases were not the same as the ratios that would be expected by complete reduction of reasonable compounds. This may indicate that the film formation on the cathode involves polymeric anions such as occurs in chromium plating.

Changes in soil solution composition and aluminium speciation under legume based pastures in response to long term phosphate fertiliser applications

This study describes some of the effects of 8 years of annual application of 6 types of phosphatic fertilisers on the chemical composition and aluminium (Al) speciation in soil solution extracted from a soil under pasture. Soil samples at 2 depths, 0-30 and 30-75 mm, were collected at the end of 8 years. Soil solutions were extracted by centrifuging at 12 000 RCF and analysed for Al, Na, K, Ca, Mg, F, NO3, Cl, and SO4, as well as pH and ionic strength. Soil and soil solution pH were significantly increased at both depths by application of North Carolina phosphate rock (NCPR) compared with the control. In contrast, diammonium phosphate (DAP) significantly decreased the soil and solution pH. Single superphosphate (SSP) did not have any significant effect on soil or solution pH compared with the untreated control. The surface soil (0-30 mm) solution pH was on average 0.6 of a unit higher than the subsurface soil (30-75 mm) solution pH. Total monomeric Al concentration [Al], measured by the pyrocatecol violet (PCV; 4 min) method, ranged from 1.5 to 4.8 �M in the surface soil and 2.5 to 12.2 �M in the subsurface soil. The DAP and higher rates of SSP application resulted in a large increase in total and inorganic monomeric [Al] in the soil solution extracted from the subsurface soil. Total soluble [F] ranged from 2.7 to 23.5 �M and 3.2 to 25.6 �M in the surface and subsurface soils, respectively, and was significantly increased by the application of NCPR and by higher rates of SSP. The predominant forms of inorganic monomeric Al present in the soil solution were estimated to be the non-phytotoxic Al-F complexes, AlF2+, and AlF2+. There was a marked decrease in toxic Al species (Al3+, Al(OH)2+, Al(OH)2+) in soil solution following NCPR and SSP application. This was due primarily to complexation of Al with F derived from these fertilisers forming non-toxic AI-F complexes. The results suggest that the long-term application of reactive phosphate rock such as NCPR may contribute to amelioration of soil acidity and Al toxicity under legume-based pastures. In contrast ammonium-containing phosphate fertilisers such as DAP probably decrease soil pH and increase the formation of toxic Al species in the soil solution.

Soil solution composition and aggregate stability changes caused by long-term farming at four contrasting sites in South Australia

The effect of long-term farming on the cation exchange capacity (CEC), organic carbon content, soil solution composition, and aggregate stability was investigated using contrasting soils from 4 sites in the Mid North of South Australia. Undisturbed and farmed profiles were characterised at each site. Farming led to a 10–50% decrease, approximately, in organic matter and CEC in the surface horizon. Scanning electron microscopic study of the surface and selected subsurface soils revealed poor aggregation, compaction, reduced porosity, and a decrease in aggregate particle size in the farmed surface soils. Intra-aggregate binding in the undisturbed soils appeared to be largely due to fungal hypha, with the roots largely contributing to inter-aggregate binding of soil particles. Electrical conductivity (EC) of soil solutions was generally 2–3 times higher in the undisturbed soils than farmed soils, suggesting increased leaching of ions associated with loss of tree cover. This was also supported by a decrease in the concentrations of mobile ions such as Cl-and Na+ in the farmed soils. The concentrations of Na+ and K+ decreased with farming leading to a decrease in the Gapon selectivity constant for Na–Ca and K–Ca exchange. The changes in soil solution composition together with the decline in organic matter concentrations resulted in increased sensitivity of soils to dispersion.

Changes in trace metal species and other components of the rhizosphere during growth of radish

ABSTRACTChanges in the properties of soil solution in the rhizosphere of developing radish plants were investigated. Variations in these properties were expected to affect the distribution and speciation of metals in the soil and soil solution. Applications of essential nutrients were linked to plant transpiration rates and prevented excess addition of nutrient ions, so that subtle changes in soil solution composition would not be obscured. Soil solution pH, the concentration of dissolved organic carbon (DOC) and the concentrations of major and trace elements in solution were found to vary over time. Strict control of fertilizer additions led to the maintenance of a relatively low ionic strength in the soil solution, and under such conditions trace metal solubility appeared to be highy influenced by the concentration of DOC. A chemical speciation analysis was performed which showed that, while dissolved Cd and Zn were largely uncomplexed in unplanted soil, Cd and Zn in the rhizosphere existed mainly as complexed forms. It is hypothesized that this is partly a result of Ca‐metal‐ligand equilibrium in solution, with higher Ca concentrations in unplanted soil leading to more of the Cd and Zn in solution existing in the uncomplexed state. Changes in the concentrations of uncomplexed Cd and Zn with time gave the best correlations with changes in plant uptake of these metals over time, supporting the hypothesis that plants mainly absorb the free metal ion from soil solution.

Formation of porous gel morphology by phase separation in gelling alkoxy-derived silica. Phenomenological study

The mechanisms for forming pore structures and the gel morphology were determined for the system with TMOS:formamide:water = 1:f:r under an acid-catalyzed condition. From SEM micrographs, the pore sizes became larger and the gel morphologies changed from macroscopically homogeneous gels, through interconnected structures and aggregates of particles, to macroscopic two-phase materials with an increase of formamide or with a decrease of water. In particular, it was found from Hg porosimetry and N2 adsorption-desorption measurements that gels with the morphologies of interconnected structures and aggregates of particles had dual pore structures. From 1H NMR measurements and the phase behavior for the oligometric alkoxysilane system, these results were consistently explained that the pore structures and gel morphologies were determined by the competition of structure development by phase separation and structure freezing by gel network formation. It is also found that the phase separation in the present system was not induced by the change of solution composition but by the increase of degree of polymerization.

Corrosion of mild steel in hydrochloric acid solutions containing organophosphonic acids

The effect of some phosphonic acid derivatives on the corrosion behaviour of carbon steel has been investigated in hydrochloric acid solutions by gravimetric and electrochemical methods. Some phosphonic acids were found to have inhibitive effects. These effects depend on the molecular structure: on the number of nitrogen atoms and of phosphono groups, but mainly on their position in the molecules, as shown by the differences in corrosion rate in the presence of various phosphonic acids. The variation of polarisation resistance with time suggests that the inhibitive action of diethylenetriaminepentamethylenephosphonic acid depends mainly on the protective inhibitor film formed on the surface of the steel and is independent of changes in solution composition with time.

Change in Ionic Composition of Soil Solutions from 7 Greenhouse Soils as Affected by Water Content

Change in Ionic Composition of Soil Solutions from 7 Greenhouse Soils as Affected by Water Content

Amelioration of subsurface acidity in sandy soils in low rainfall regions .2. Changes to soil solution composition following the surface application of gypsum and lime

Two field trials were sampled to investigate the changes to soil solution chemical properties of a yellow sandplain soil with an acidic subsoil following the application of gypsum and lime to the soil surface in 1989. The soils were sandy textured and located in a region of low annual rainfall (300-350 mm). Soil was sampled annually to a depth of 1 m and changes in soil solution composition were estimated by extraction of the soil with 0.005 M KCl. Gypsum leaching caused calcium (Ca), sulfate (SO4) and the ionic strength to increase substantially in both topsoil and subsoil by the end of the first year. Continued leaching in the second year caused these properties to decrease by approximately one-half in the topsoil. Gypsum appeared to have minimal effect on pH or total Al (Al-T), although the amount of Al present as toxic monomeric Al decreased and the amount present as non-toxic AlSO+4 ion pairs increased. Magnesium (Mg) was displaced from the topsoil by gypsum and leached to a lower depth in the subsoil. In contrast, lime caused pH to increase and Al to decrease substantially in the topsoil, but relatively little change to any soil solution properties was observed in the subsoil. There was an indication that more lime may have leached in the presence of gypsum in the first year after application at one site. Wheat yields were best related to the soil acidity index Al-T/EC (where EC is electrical conductivity of a 1:5 soil:water extract), although the depth at which the relationship was strongest in the subsoil varied between sites. The ratio Al-T/EC was strongly correlated with the activity of monomeric Al species (i.e. the sum of the activities of Al3+, AlOH2+ and Al(OH)+2 in the soil solution. An increase in the concentration of sulfate in the subsoil solution (which increased the ionic strength, thereby decreasing the activity of Al3+, and also increased the amount of Al present as the AlSO+4 ion pair) was probably the most important factor decreasing Al toxicity to wheat. The results indicated that gypsum could be used to increase wheat growth in aluminium toxic subsoils in sandy soils of low rainfall regions and that a simple soil test could be used to predict responses.

Changes in solid solution composition as a function of artificial ageing time for aluminium alloy 7075

Changes in solid solution composition as a function of artificial ageing time for aluminium alloy 7075