Initial Solution Composition Research Articles

Calcium carbonate precipitation by anoxygenic phototrophic bacteria

Carbonate biomineralization is considered as one of the main natural processes controlling CO 2 levels in the atmosphere both in the past and at present time. In contrast to extensive studies of cyanobacterial calcification, biomineralization of anoxygenic phototrophic bacteria (APB) remained largely underestimated, despite their potentially important role on CaCO 3 precipitation in the biomats, notably in the past. Haloalcaliphilic Rhodovulum steppense A-20s and halophilic neutrophilic Rhodovulum sp. S-17-65 were examined with respect to their ability to precipitate CaCO 3 under controlled laboratory conditions. To characterize the link between the rate of bacterial growth (biomass production) and the rate of CaCO 3 precipitation, batch kinetic experiments with live, dead and inactivated bacteria both in nutrient solution and in inert electrolyte were performed and produced precipitates were examined by SEM, TEM and XRD techniques. Active strains A-20s and S-17-65 precipitated calcite from initially supersaturated solutions ( Ω calcite = 10 to 40) via increasing Ω calcite to 80–120 before the precipitation. The amount of precipitated CaCO 3 (mole) was directly correlated with the amount of organic C in bacterial biomass produced with a slope of dependence ranging from 0.3 to 0.6 and from 0.1 to 0.3 for A-20s and S-17-65, respectively, depending on the initial solution composition. For both bacterial strains, only live actively photosynthetizing bacteria were capable of effectively decreasing Ca concentration and form CaCO 3 with apparent bulk precipitation rates ranging from 0.001 to 0.0150 mmol/h at 10–20 g wet/L of biomass, similar to rates reported for other bacteria. SEM and XRD analyses of precipitates reveal the dominance of calcite with some amount of vaterite and monohydrocalcite forming spheres up to 100 μm diameter. The TEM analysis of bacterial suspension at the end of precipitation experiments did not demonstrate the presence of CaCO 3 at the surface or in the vicinity of live cells. This suggests the existence of certain cell protection mechanism against carbonate precipitation at the cell surface. Given the lower efficiency of photoheterotrophic APB, compared to photoautotrophic cyanobacteria, to precipitate CaCO 3 in natural conditions, it is possible that the overall potential of phototrophic community to form massive carbonate deposits was strongly limited before the appearance of oxygenic phototrophs.

The influence of the blast furnace slag replacement on chloride penetration in concrete

Corrosion of steel reinforcement due to chloride penetration is the greatest cause of durability problems in concrete; intense international research has been carried out to understand and avoid this. This paper summarises the results of a theoretical and experimental research programme investigating the influence of blast furnace slag on chloride-related transport properties. The relationship between the apparent chloride diffusion coefficient, electrical resistivity and compressive strength was measured. Chloride, hydroxide, sodium and potassium's intrinsic diffusion coefficients were obtained by using a computational model and an electrical migration test. The initial hydroxide composition of the pore solution, porosity and chloride binding capacity were also determined from the model. The results showed that blast furnace slag improved chloride penetration resistance, resulting in concrete which was less vulnerable to corrosion.

Liquid−Liquid Biphasic Synthesis of Layered Zinc Hydroxides Intercalated with Long-Chain Carboxylate Ions and Their Conversion into ZnO Nanostructures

A method for synthesizing layered zinc hydroxide compounds in high yields is developed using an immiscible liquid-liquid system in one pot. Long-chain carboxylate ions such as heptanoate, decanoate, and dodecanoate were successfully intercalated between zinc hydroxide layers in one process starting from a xylene-water system. Typically, a xylene phase dissolving the respective carboxylic acids was allowed to stand in contact with an aqueous phase dissolving zinc nitrate hexahydrate and urea. During keeping the resultant biphasic system at 80 °C, urea was thermo-hydrolyzed to supply OH(-) in the aqueous phase while the carboxylic acids were continuously transferred from the xylene phase under the distribution law. The aqueous phase was then supersaturated, and a solid phase of layered basic zinc carboxylate was precipitated as films on glass substrates through heterogeneous nucleation and subsequent two-dimensional crystal growth. Crystal structures and morphology of the films were modulated by the kind of the carboxylic acids employed. The layered basic zinc carboxylate films could be converted to nanostructured, mesoporous ZnO films by heating at 450 °C in air. The relationship between the initial solution compositions and the final solid products was systematically examined to discuss reaction mechanisms in the biphasic systems.

Production of pH-Responsive Microparticles by Spray Drying: Investigation of Experimental Parameter Effects on Morphological and Release Properties

During spray drying, emphasis is placed on process optimisation to generate favourable particle morphological and flow properties. The effect of the initial feed solution composition on the drug release from the prepared microparticles (MPs) is rarely considered. We investigated the effects of solvent composition, feed solution concentration and drug-loading on sodium salicylate, hydrocortisone and triamcinolone release from spray-dried Eudragit L100 MPs. Eudragit L100 is a pH-responsive polymer whose dissolution threshold is pH 6 so dissolution testing of the prepared MPs at pH 5 and 1.2 illustrated non-polymer controlled burst release. Increasing the water content of the initial ethanolic feed solution significantly reduced hydrocortisone burst release at pH 5, as did reducing the feed solution concentration. These findings caution that changes in feed solution concentration or solvent composition not only affect particles' morphological characteristics but can also negatively alter their drug release properties. This work also illustrate that drug-free MPs can have different morphological properties to drug-loaded MPs. Therefore, process optimisation needs to be carried out using drug-loaded systems. Depending on the physicochemical properties of the encapsulated active pharmaceutical ingredient (API), drug-loading can affect the polymer solubility in the initial feed solution with consequent impact on MPs morphological and release properties.

Synthesis of Inorganic−Organic Layered Compounds Using Immiscible Liquid−Liquid Systems under the Distribution Law

A method for synthesizing inorganic-organic layered compounds is proposed using a biphasic liquid-liquid system in one pot. Layered basic zinc benzoate (LBZB) compounds were chosen, and their formation was investigated starting from a xylene-water system. In a typical synthesis, a xylene phase dissolving benzoic acid was allowed to stand in contact with an equal amount of an aqueous phase dissolving zinc nitrate hexahydrate and urea. A role of urea is to supply OH(-) gradually by hydrolysis at an elevated temperature. The biphasically separated solutions were maintained at 80 °C, and then LBZB was obtained in the aqueous phase. Two kinds of layered structures with a basal spacing of 27.14 and 14.77 Å were formed by changing a C(6)H(5)COOH/Zn molar ratio. Chemical compositions of the 27.14 and the 14.77 Å layered phases were estimated to be Zn(OH)(1.74)(C(6)H(5)COO)(0.26)·0.29H(2)O and Zn(OH)(1.12)(C(6)H(5)COO)(0.88)·0.21H(2)O, respectively. The 27.14 Å phase could also be deposited as a film on substrates by heterogeneous nucleation. The film consisted of standing platelike particles and exhibited a two-dimensional structure, which could be converted to ZnO by heating. The relationship between the initial solution compositions and the final solid products was systematically examined on the basis of distribution law for benzoic acid in the xylene-water system.

Effect of complexation of poly(acrylic acid) with Cu2+ ions on the size of copper nanoparticles prepared via reduction in aqueous solutions

Sols of zero-valence copper are prepared via the chemical reduction of Cu(II) ions by hydrazine borane in aqueous solutions of high-molecular-mass poly(acrylic acid), which forms stable complexes with copper ions at 20°C in a wide pH range. The study of the composition of coordination centers, the ligand surrounding of metal ions, and the character of distribution of copper ions over poly(acrylic acid) coils in a wide range of solution compositions and pH values shows that the size of copper nanoparticles in the sols can be controlled by varying the ratio between ligand groups (carboxylate anions in poly(acrylic acid)) and copper ions in the reaction system during the synthesis of sols. This effect can be accomplished either by variation in the initial composition of solution or change in pH (the degree of ionization of the initial poly(acrylic acid) in the presence of copper ions).

Determination of the transport properties of a blended concrete from its electrical properties measured during a migration test

The Nernst–Planck equation describes ionic movements in saturated porous materials subject to chemical concentration gradients in the pore fluid and applied electric fields. When applied to a macroscopic system the equation supposes that the flux of each ion is independent of every other one. However, owing to the ionic exchange among different or similar species, there are ionic potentials that affect the final flux. These will distort the applied electric field and thus keep the electroneutrality of the sum of all the ionic species involved. The applied potential will fall linearly across the sample but an additional ‘membrane' potential will change with position and time. This paper summarises a theoretical and experimental investigation into the application of the non-linear electric membrane potential to the simulation of the migration of chlorides in concrete. A new electrochemical test has been developed and carried out with different samples of concrete blended with pulverised fuel ash (PFA) and ground granulated blastfurnace slag (GGBS). During the tests the transient current and the electrical membrane potential were measured. A numerical model developed previously using the classical equations, but including changes in the concrete membrane potential, was optimised using an artificial neural network (ANN). Based on the experimental results and the simulations, the intrinsic diffusion coefficients of chloride, hydroxide, sodium and potassium were obtained. Also, the initial hydroxide composition of the pore solution, the porosity, and the chloride binding capacity were determined. The results showed good agreement with the theory and can help to explain the complex phenomena that occur during a concrete migration test.

Behaviour of 4-(−2-Hydroxyethyl)-1-Piperazineethanesulphonic Acid under Electrospray Ionisation Mass Spectrometry Conditions

Our previous experiments on ESI-MS analysis of reaction mixture solutions containing HEPES (4-(-2- hydroxyethyl)-1-piperazineethanesulfonic acid), a commonly used buffer, indicated that HEPES species did not significantly suppress analyte species, even in reaction mixture solutions with significant amounts of HEPES. With the purpose of investigating the behaviour of HEPES under ESI-MS conditions, HEPES aqueous solutions and HEPES aqueous solutions containing analyte with high and low polarity and with different acid/base chemistry, were therefore investigated. For electrosprayed aqueous solutions of HEPES with concentrations above 10(-5) M, an enhanced formation of HEPES multimer ions, regarding HEPES monomer ions formation, was observed. This enhanced formation of HEPES multimer ions is much higher than the one observed for other polar compounds, such as acetyl-arginine, acetyl-lysine and histidine. Information from solution behaviour such as, HEPES concentration, solution pH, and instrumental factors, namely the capillary temperature, was related with information from mass spectra. The results obtained led us to conclude that the formation of HEPES ions is related with the initial solution composition. The influence of analyte species on HEPES species formation, for electrosprayed HEPES solutions with analyte, was also investigated. The variations observed for HEPES monomer and multimer ions abundances, which were found to be consistent with those observed for analyte monomer ions abundances, were related with type of analyte, i.e. to their acid/base nature. Strikingly, the variations observed between HEPES monomer and multimer ions abundances, enable to discriminate among the different influence of analyte species on HEPES species formation. The results obtained also enabled to provide an explanation for the observation that HEPES species do not suppress significantly analyte species ion signals, when high concentrated HEPES solutions with analyte are electrosprayed. According to our results, the association behaviour between HEPES species seems to be preserved in the gas phase during electrospray ionization. This observation may provide some information that may be useful regarding the behaviours involved in the gas phase ion formation process from charged droplets during electrospray ionization or, at least, to differentiate among behaviours.

Formation of periodic polymer structures on the surface of optical fibers

The self-organization of solutions of organic and inorganic polymers on the surface of round fibers during the evaporation of a solvent leads to the formation of longitudinal and transverse periodic structures. The structure period ranges from several tens to several hundreds of microns and depends on the type of polymer, the initial solution composition, and the fiber diameter. Nanoporous periodic structures made of inorganic materials can be formed from a suspension of inorganic nanoparticles in a polymer solution upon thermal decomposition of the polymer. These processes are shown to be used to create long-period fiber gratings for fiber sensor systems and fiber optical filters.

Hierarchical inorganic nanopatterning (INP) through direct easy block-copolymer templating

We introduce a simple route towards hierarchical TiO2 nanopatterns using a block-copolymer template approach combined with a dip-coating process and soft inorganic chemistry. The bimodal characteristic is associated to the preparation of solutions that contain two distinct populations of micelles PB-b-PEO (with the same chemical nature but different sizes) that do not mix or aggregate. The relative quantity of each population can be precisely adjusted in the initial solution composition by mixing the corresponding proportion of parent solutions, and is recovered in the final TiO2 nanopattern. The latter hierarchical nanopatterning exhibits homogeneous distribution of 2 distinct sizes of nanoperforations in relation to the presence of both micelles. We show that the bimodal micellar solution is stable for more than four weeks at RT, revealing an unexpected dynamic stability. We believe that the resulting nanopatterns could be useful for investigating the behaviour of block copolymer micelles in solutions. The present study is mainly supported by DLS and AFM analyses.

Solidification of binary alloy in a finned enclosure from the bottom

This paper presents experimental findings on the phenomenon of solidification of a binary alloy in a finned enclosure using aqueous ammonium chloride solution. Solidification experiments are carried out over a wide range of initial composition of binary alloy solution from hypoeutectic to hypereutectic concentration ranging from 8, 16 and 24% of ammonium chloride are discussed. An interesting “snowing” phenomenon is observed for the hypereutectic concentration in a finned enclosure.

Hydrolysis of titanium sulphate compounds

AbstractThe influence of TiOSO4 and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis markedly depends on the studied parameters. The lower was the content of TiOSO4 in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between 81 % (420 g TiOSO4 dm−3, 216 g H2SO4 dm−3) and 92 % (300 g TiOSO4 dm−3, 216 g H2SO4 dm−3). The same relation was obtained when changing the concentration of free H2SO4 in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H2SO4 dm−3, 340 g TiOSO4 dm−3) and 96 % (136 g H2SO4 dm−3, 340 g TiOSO4 dm−3). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition.

Coprecipitation of radium with barium sulfate from salt solutions

Coprecipitation of radium with barium sulfate from highly concentrated NaCl solutions is studied, including the effects of the initial solution composition, alkaline reagent (CaO, NaOH), supporting electrolyte (NaCl) concentration, and pH. The process is promoted by high NaCl concentration in the initial solution, which is due to structural transformation and change in the sorption activity of the BaSO4 precipitate in salt solutions. The results obtained were applied to recovery of radium from process solutions in chlorination of loparite concentrates.

Prediction of chloride ingress into saturated concrete on the basis of a multi-species model by numerical calculations

A multi-species model based on the Nernst-Planck equation has been developed by using a finite volume method. The model makes it possible to simulate transport due to an electrical field or by diffusion and to predict chloride penetration through water saturated concrete. The model is used in this paper to assess and analyse chloride diffusion coefficients and chloride binding isotherms. The experimental assessment of the effective chloride diffusion coefficient consists in measuring the chloride penetration depth by using a colorimetric method. The effective diffusion coefficient determined numerically allows to correctly reproduce the chloride penetration depth measured experimentally. Then, a new approach for the determination of chloride binding, based on non-steady state diffusion tests, is proposed. The binding isotherm is identified by a numerical inverse method from a single experimental total chloride concentration profile obtained at a given exposure time and from Freundlich's formula. In order to determine the initial pore solution composition (required as initial conditions for the model), the method of Taylor that describes the release of alkalis from cement and alkali sorption by the hydration products is used here. Finally, with these input data, prediction of total and water-soluble chloride concentration profiles has been performed. The method is validated by comparing the results of numerical simulations to experimental results obtained on various types of concretes and under different exposure conditions.

Combustion Synthesis of α-Al<sub>2</sub>O<sub>3</sub> Powders

Among ceramic materials, the alumina has high importance because of its characteristics of resistance and refractory. The possibility to improve the final characteristics of this material, open possibilities for new applications. The aim of this work is to synthesize (α-Al2O3) alumina powders by combustion reaction and to evaluate the effect of the urea content in the final characteristics of the α-Al2O3 powders. Three compositions were studied : a) stoichiometric, b) with 10% of urea reduction and c) with 20% of urea reduction. The initial solution composition was based on the total valence of the reagents by using chemical concepts of the propellant. This powders were characterized by X-ray diffraction (XRD), granulometric determination by laser diffraction, nitrogen adsorption by BET, scanning electron microscopy (SEM), infrared spectroscopy (IR) and helium picnometer. The results showed that the urea reduction change the temperature of the reaction from 525 to 463oC , the characteristics of the powders, and principally the reduction of the particles size.

Forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide

The products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers. Although forsterite is not a common mineral in deep saline aquifers, the experiments offer insights into the effects of relevant temperatures and P CO 2 levels on silicate mineral dissolution and subsequent carbonate precipitation. Mineral suspensions and aqueous solutions were reacted at 30 °C and 95 °C in batch reactors, and at each temperature experiments were conducted with headspaces containing fixed P CO 2 values of 1 and 100 bar. Reaction products and progress were determined by elemental analysis of the dissolved phase, geochemical modeling, and analysis of the solid phase using scanning electron microscopy, infrared spectroscopy, and X-ray diffraction. The extent of forsterite dissolution increased with both increasing temperature and P CO 2 . The release of Mg and Si from forsterite was stoichiometric, but the Si concentration was ultimately controlled by the solubility of amorphous silica. During forsterite dissolution initiated in deionized water, the aqueous solution reached supersaturated conditions with respect to magnesite; however, magnesite precipitation was not observed for reaction times of nearly four weeks. Magnesite precipitation was observed in a series of experiments with initial solution compositions that simulated extensive forsterite dissolution. The precipitation of magnesite appears to be limited by the process of nucleation, and nucleation requires a critical saturation index between 0.25 and 1.14 at 95 °C and 100 bar P CO 2 . Magnesite precipitation is fastest in the presence of an initial magnesite seed. Although magnesite precipitates do form on the surfaces of forsterite particles, the presence of the forsterite surface does not significantly accelerate magnesite precipitation relative to solid-free systems.

Release dynamic process identification for a cement based material in various leaching conditions. Part I. Influence of leaching conditions on the release amount

In this paper we investigate at laboratory scale the influence of the liquid/solid leaching conditions on the release of different chemical species from a reference porous material obtained by solidification of PbO and CdO with Portland cement. The pH influence on the dissolution of pollutants and the initial pore solution composition (target elements: Na +, K +, Ca 2+, Pb 2+, Cd 2+, SO 4 2 − ) were assessed by applying a methodology consisting of two equilibrium leaching tests, the Acid Neutralization Capacity (ANC) and the Pore Water (PW) tests and geochemical modelling. Samples of the same material were submitted in parallel to four different dynamic leaching tests in order to determine the influence of the sample shape (monolithic or granular) and eluate hydrodynamics (instantaneous L/S ratio, eluate renewal) on the leaching of the target elements. The comparison criteria were the eluate saturation state, the cumulative release and the released flux. Generally, the eluates obtained in the tests applied on granular material were more concentrated, even saturated for the eluate pH value with respect to Ca 2+, Pb 2+ and SO 4 2 − . The consequence of the eluate saturation is the slowing down effect on the dynamic release. The highest released flux was observed for the Monolith Leaching Test (MLT) involving the highest instantaneous L/S ratio and the lowest solid/liquid exchange surface and for which no saturation was observed, except Pb 2+ and SO 4 2 − in some eluates. The maximum cumulative released-mass was obtained for the Column Leaching Test (CLT) applied on granular material having the highest exchange surface, the lowest instantaneous L/S and a continuous input flow of the leachant. The experimental results demonstrate the significance of the liquid/solid contact type which is also a scenario specific parameter.

Laboratory experiments to predict changes in radiocaesium root uptake after flooding events

Changes in soil solution composition after a flooding event were hypothesised to be one of the key factors in explaining changes in radiocaesium incorporation in the food chain in the areas affected by the Chernobyl accident. A laboratory methodology was set up to monitor changes in the soil solution composition after a sequence of flooding cycles. Experiments were performed using column and batch approaches on test soils with contrasting initial soil solution composition (high and low initial concentrations of K +). Results from column experiments indicated a potential increase in NH 4 + concentrations, a parameter which could lead to an increase in the radiocaesium root uptake. Batch results in the soil with high initial K + concentration showed that after a number of flooding cycles, especially for high ratios of flooding solution/mass of soil, K + concentration decreased sometimes below a threshold value (around 0.5–1 mmol l −1), a fact that could lead to an increase in radiocaesium transfer. For the soils with a low initial K + concentration, the flooding solution increased K + and NH 4 + values in the soil solution. The comparison of test soils with soils from Ukraine areas affected by flooding showed that the final stage in soil solution composition was similar in both cases, regardless of the initial composition of the soil solution. Moreover, the comparison with unflooded soils from the same area showed that potential changes in other soil parameters, such as 137Cs activity concentration, clay content, and radiocaesium interception potential, RIP (a parameter that estimates the radiocaesium specific sorption capacity of a soil), should also be monitored for additional effects due to the flooding event. Therefore, the changes in the root uptake would depend on the resulting situation from changes in RIP, K + and NH 4 + values in the soil solution.

Preparation of Agglomerate-Free and Highly Crystalline (Ba0.5, Sr0.5)TiO3 Nanoparticles by Salt-Assisted Spray Pyrolysis

Optimum conditions for the synthesis of non-agglomerated barium strontium titanate (BST) nanoparticles were examined. The effects of salt concentration, operating temperature, and droplet/particle residence time in the hot zone as a function of carrier gas flow rate and heating zones on particle size, crystallinity, and chemical composition of BST nanoparticles were investigated. Highly crystalline, dense BST nanoparticles in a size range of 17-60 nm with a narrow size distribution (σ g =1.2) were prepared using a salt-assisted spray pyrolysis (SASP) method without the need for post-annealing or for controlling of initial excess of barium and strontium in the solution, relative to titanium. The particle size decreased with decreasing salt concentration, operating temperature and droplet/particle residence time in the hot zones. The chemical homogeneity of the resulting particles was analyzed using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The chemical composition of the resulting powder completely reflected the initial solution composition. SASP can be used to produce highly crystalline (Ba 1-x , Sr x )TiO 3 (x=0.5) nanoparticles in sizes as small as 30 nm in a single step.

Prediction of the effects of soil-based countermeasures on soil solution chemistry of soils contaminated with radiocesium using the hydrogeochemical code PHREEQC

For agriculturally used areas, which are contaminated by the debris from a nuclear accident, the use of chemical amendmends (e.g. potassium chloride and lime) is among the most common soil-based countermeasures. These countermeasures are intended to reduce the plant uptake of radionuclides (mainly 137Cs and 90Sr) by competitive inhibition by chemically similar ions. So far, the impacts of countermeasures on soil solution composition — and thus, their effectiveness — have almost exclusively been established experimentally, since they depend on mineral composition and chemical characteristics of the soil affected. In this study, which focuses on caesium contamination, the well-established code PHREEQC was used as a geochemical model to calculate the changes in the ionic compositions of soil solutions, which result from the application of potassium or ammonium in batch equilibrium experiments. The simple ion exchange model used by PHREEQC was improved by taking into account selective sorption of Cs +, NH 4+ and K + by clay minerals. Calculations were performed with three different initial soil solution compositions, corresponding to particular soil types (loam, sand, peat). For loamy and sandy soils, our calculational results agree well with experimental data reported by Nisbet (Effectiveness of soil-based countermeasures six months and one year after contamination of five diverse soil types with caesium-134 and strontium-90. Contract Report NRPB-M546, National Radiation Protection Board, Chilton, 1995.). For peat, discrepancies were found indicating that for organic soils a reliable set of exchange constants of the relevant cations still has to be determined experimentally. For cesium, however, these discrepancies almost disappeared if selective sites were assumed to be inaccessible. Additionally, results of sensitivity analyses are presented by which the influence of the main soil parameters on Cs + concentrations in solution after soil treatment has been systematically studied. It is shown that calculating the impacts of soil-based chemical countermeasures on soil solution chemistry using geochemical codes such as PHREEQC offers an attractive alternative to establishing these impacts by often time-consuming and site-specific experiments.