Aqueous Saline Research Articles

Combining reverse osmosis and pulsed electrical current electrodialysis for improved recovery of dissolved organic matter from seawater

Dissolved organic carbon (DOC) in the oceans is one of the largest dynamic reservoirs of carbon on earth, comparable in size to the atmospheric reservoir of carbon (as CO 2) in the atmosphere, or to the amount of carbon in all terrestrial and aquatic biota. The concerted efforts of earth scientists, atmospheric scientists, and biologists who study global biogeochemical cycles and the earth's climate have yielded a rather detailed understanding of carbon in the atmosphere and in biota. Marine dissolved organic matter (DOM) is far less well characterized, principally because it exists as a highly diluted mixture of perhaps millions of organic compounds in a highly saline aqueous solution. Prior to 2007, only around 1/3 of marine DOM was typically recovered from seawater for research purposes, regardless of the method of isolation. In 2007, reverse osmosis (RO) and electrodialysis (ED) were coupled to achieve recoveries of 64–93% of marine DOM. The level of residual salts in the concentrated samples, however, still precluded the characterization of marine DOM by solid-state NMR, mass spectrometry, or even elemental analysis. This paper describes a major improvement to the RO/ED method, in which pulsed ED is used (at sea) to reach roughly 100-fold greater removal of salts compared to non-pulsed ED while maintaining comparable recoveries of DOM.

A MODEL FOR CALCULATING THE DENSITY OF AQUEOUS MULTICOMPONENT ELECTROLYTE SOLUTIONS

A method is presented for calculating the densities of simple and multicomponent aqueous saline solutions. A total of 38 parameters were obtained for anions and cations which allowed predicting their density in aqueous solution. The proposed method is based on the model of Horsak and Slama1 applicable to simple 1:1 aqueous electrolyte solutions which in the present study was extended to multicomponent systems and for any type of salt. Seventeen aqueous systems containing 2, 3, and 4 salts were studied, obtaining excellent results when compared with the experimental values. The total relative mean standard deviation obtained was 0.08 %. The proposed method used adjustable parameters, which are obtained beginning from experimental data from systems containing a single salt. Two parameters are required for each ion present in the aqueous solution

The zeta potential of surface‐functionalized metallic nanorod particles in aqueous solution

Metallic nanoparticles suspended in aqueous solutions and functionalized with chemical and biological surface coatings are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. We describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11-mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self-assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. For comparison, we present zeta potential data for typical charge-stabilized polystyrene particles. We compare experimental zeta potential data with theoretically predicted values for SAM-coated and bimetallic particles. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.

Interfacial Energetics of Protein Adsorption from Aqueous Buffer to Surfaces with Varying Hydrophilicity

Adsorption isotherms constructed from time-and-concentration-dependent advancing contact angles thetaa show that the profound biochemical diversity among ten different blood proteins with molecular weight spanning 10-1000 kDa has little discernible effect on the amount adsorbed from aqueous phosphate-buffered saline (PBS) solution after 1 h contact with a particular test surface selected from the full range of observable water wettability (as quantified by PBS adhesion tension tauoa=gammaolv cos thetaoa; where gammaolv is the liquid-vapor interfacial tension and thetaoa is the advancing PBS contact angle). The maximum advancing spreading pressure, Pimaxa, determined from adsorption isotherms decreases systematically with tauoa for methyl-terminated self-assembled monolayers (CH3 SAM, tauo=-15 mN/m), polystyrene spun-coated onto electronic-grade SiOx wafers (PS, tauo=7.2 mN/m), aminopropyltriethoxysilane-treated SiOx surfaces (APTES, tauo = 42 mN/m), and fully water wettable SiOx (tauo=72 mN/m). Likewise, the apparent Gibbs' surface excess [Gammasl-Gammasv], which measures the difference in the amount of protein adsorbed Gamma (mol/cm2) at solid-vapor (SV) and solid-liquid (SL) interfaces, decreases with tauo from maximal values measured on the CH3 SAM surface through zero (no protein adsorption in excess of bulk solution concentration) near tauo=30 mN/m (thetaa=65 degrees). These latter results corroborate the conclusion drawn from independent studies that water is too strongly bound to surfaces with tauo>or=30 mN/m to be displaced by adsorbing protein and that, as a consequence, protein does not accumulate within the interfacial region of such surfaces at concentrations exceeding that of bulk solution ([Gammasl-Gammasv]=0 at tauo=30 mN/m). Results are collectively interpreted to mean that water controls protein adsorption to surfaces and that the mechanism of protein adsorption can be understood from this perspective for a diverse set of proteins with very different amino acid compositions.

A fluorescent method based on the competitive displacement of intercalated dyes for the study of DNA polyelectrolyte complexes: Advantages and prospects

The interaction of cationic (bio)polymers with DNA may cause the transfer of the intercalated cationic dye ethidium bromide from the double helix to solution. This effect is accompanied by probe fluorescence quenching. The effective displacement of ethidium from nucleic acid that has been discovered in the study of the cooperative electrostatic binding of DNA to salts of polymeric bases forms the basis of the fluorescent method useful for the investigation of polyelectrolyte complexes of DNA. By the example of a wide range of model polycations, this approach is shown to be fruitful for estimation of the cooperative character of interactions, construction of pH-dependent profiles of complexation reactions and competitive binding, and creation of systems with desired and controlled stability in aqueous-saline solutions. This evidence is of special importance for the design of polyelectrolyte means effective for delivery of genetic materials to the cell.

Absorption spectrum of monomeric pseudoisocyanine: A new perspective and its implications for formation and spectral response of J-aggregates in solution and in thin films

We argued against the current spectral assignment for absorption spectrum of monomeric PIC which is widely accepted since the pioneering works of Scheibe and Jelley [G. Scheibe, Angew. Chem. 49 (1936) 563; E.E. Jelly, Nature 138 (1936) 1009]. A new spectrum is presented along with its conceptual basis. The hypothesized spectrum attributes the previous 0–0 (≈525 nm) and 0–1 (≈490 nm) assignments, respectively, to intermediates acting as the precursor of J-aggregates and to the 0–0 transition of monomeric PIC and brings the spectrum in accord with the seemingly universal spectral fingerprint of cyanines. The hypothesis is used to analyze and interpret the temperature dependence of the UV–vis absorption of PIC aggregates in saline aqueous solution by incorporating the J-band simulations within frenkel exciton formalism. Its implications for aggregate formation kinetics are given on the basis of current spectroscopic evidence. The hypothesis readily answers several long-standing questions: Why compared to many other cyanines at least an order of magnitude higher dye concentration is needed to form J-aggregates of PIC? Why are there no precursors, since aggregation is expected to be a consecutive process? A large number of observations on steady-state and time-resolved spectral properties, and aggregation kinetics in solution/thin films are likely to find reasonable explanations within this hypothesis.

Dielectrophoretic Manipulation and Real‐Time Electrical Detection of Single‐Nanowire Bridges in Aqueous Saline Solutions

Dielectrophoretic manipulation of nanoscale materials is typically performed in nonionic, highly insulating solvents. However, biomolecular recognition processes, such as DNA hybridization and protein binding, typically operate in highly conducting, aqueous saline solutions. Here, we report investigations of the manipulation and real-time detection of individual nanowires bridging microelectrode gaps in saline solutions. Measurements of the electrode impedance versus frequency show a crossover in behavior at a critical frequency that is dependent on the ionic strength. We demonstrate that by operating above this critical frequency, it is possible to use dielectrophoresis to manipulate nanowires across electrode gaps in saline solutions. By using electrical ground planes and nulling schemes to reduce the background currents, we further demonstrate the ability to electrically detect bridging and unbridging events of individual nanowires in saline solutions. The ability to both manipulate and detect bridging events with electrical signals provides a pathway toward automated assembly of nanoscale devices that incorporate biomolecular recognition elements.

Structure of Micelles of Poly(n-butyl acrylate)-block-poly(acrylic acid) Diblock Copolymers in Aqueous Solution

We report the structure and dynamics of micelles of the amphiphilic diblock copolymers poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA−PAA). These self-assembled nanostructures consist of a liquid hydrophobic core and a pH- and ionic strength-sensitive hydrophilic corona. In the first part of this series,1 we reported the synthesis and micellization of these block copolymers in aqueous media without the need of any cosolvent. Here we present a detailed study on the structural and dynamic properties of these micelles in aqueous solutions under various conditions using static and dynamic light scattering (SLS, DLS), small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM). The block copolymers spontaneously dissolve in water, forming rather monodisperse micelles. Although the corona thickness depends on external stimuli, such as pH and salinity, the micelles do not significantly change their shape or aggregation number upon modifications of these parameters, in spite of the liquidlike nature of the hydrophobic block at room temperature. Moreover, the structure of the formed micelles depends on the preparation conditions: aggregates of micelles are initially formed when the polymers are dissolved in saline aqueous solutions even at pH 6.5, which disintegrate within weeks, resulting in isolated micelles with significantly larger size compared to micelles at the same ionic strength but initially prepared in the absence of added salt. The results are explained in terms of a kinetic control of the micellization process, which is dynamic in terms of unimer exchange but slow on the experimental time scale in adapting to external stimuli.

Fault–valve action and vein development during strike–slip faulting: An example from the Ribeira Shear Zone, Southeastern Brazil

Fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of Neoproterozoic–Cambrian age in the Ribeira River Valley area, southeastern Brazil. Geometric and microstructural constraints indicate that foliation–parallel and extensional veins were formed during dextral strike–slip faulting. Both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates, and were crystallized in the presence of CO 2–CH 4 and H 2O–CO 2–CH 4–NaCl immiscible fluids following unmixing from a homogeneous parental fluid. Contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels. Foliation–parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values (319–397 °C and 47–215 MPa), which is compatible with predicted fluid pressure cycle curves derived from fault–valve action. Growth of extensional veins occurred in shallower structural levels, under pressure fluctuating from near hydrostatic to moderately subhydrostatic values (207–218 °C and 18–74 MPa), which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone. Fluid immiscibility and precipitation of quartz in foliation–parallel veins resulted from fluid pressure drop immediately after earthquake rupture. Fluid immiscibility following a local pressure drop during extensional veining occurred in pre-seismic stages in response to the development of fracture porosity in the dilatant zone. Late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity (0.2 to 44 wt.% equivalent NaCl) H 2O–NaCl–CaCl 2 fluid inclusions trapped in healed fractures mainly in foliation–parallel veins, which also exhibit subordinate H 2O–NaCl–CaCl 2, CO 2–(CH 4) and H 2O–CO 2–(CH 4)–NaCl fluid inclusions trapped under subsolvus conditions in single healed microcracks. Recurrent circulation of aqueous–carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post-veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes. A fluid evolution trending toward CH 4 depletion for CO 2–CH 4–bearing fluids and salinity depletion and dilution (approximation of the system H 2O–NaCl) for aqueous–saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history.

Removal of toxic chromium from wastewater using green alga Ulva lactuca and its activated carbon

Biosorption of heavy metals can be an effective process for the removal of toxic chromium ions from wastewater. In this study, the batch removal of toxic hexavalent chromium ions from aqueous solution, saline water and wastewater using marine dried green alga Ulva lactuca was investigated. Activated carbon prepared from U. lactuca by acid decomposition was also used for the removal of chromium from aqueous solution, saline water and wastewater. The chromium uptake was dependent on the initial pH and the initial chromium concentration, with pH ∼1.0, being the optimum pH value. Langmuir, Freundlich, Redlich-Peterson and Koble-Corrigan isotherm models were fitted well the equilibrium data for both sorbents. The maximum efficiencies of chromium removal were 92 and 98% for U. lactuca and its activated carbon, respectively. The maximum adsorption capacity was found to be 10.61 and 112.36 mg g −1 for dried green alga and activated carbon developed from it, respectively. The adsorption capacities of U. lactuca and its activated carbon were independent on the type of solution containing toxic chromium and the efficiency of removal was not affected by the replacing of aqueous solution by saline water or wastewater containing the same chromium concentration. Two hours were necessary to reach the sorption equilibrium. The chromium uptake by U. lactuca and its activated carbon form were best described by pseudo second-order rate model. This study verifies the possibility of using inactivated marine green alga U. lactuca and its activated carbon as valuable material for the removal of chromium from aqueous solutions, saline water or wastewater.

0.15 – 3.72 THz absorption of aqueous salts and saline solutions

It has recently been suggested that near-field terahertz ionic contrast microscopy can be employed to image subtle changes in ionic concentrations arising from neuronal activity. To do so, however, requires that solvated ions exhibit significant absorbance at terahertz frequencies. The authors have investigated this issue and find that, at room temperature, the molar extinctions of both sodium chloride and guanidine hydrochloride are approximately two orders of magnitude below some previous measurements and are, therefore, too low to support the proposed imaging application.

Preservation of microelastic properties of dentin and tooth enamel in vitro—A scanning acoustic microscopy study

Objectives The aim of this study was to examine the influence of storage media on the elastic properties of dentin and tooth enamel with respect to the storage period. Several reports suggest that saline and other aqueous solutions may induce chemical reactions and the dissolution of minerals, which in turn may cause alterations of elastic tissue properties. Methods Three non-erupted human wisdom teeth were extracted and divided in three slices. Sections were stored in three different media for a maximum period of 21 days. During this time all sections were inspected by time-resolved 50-MHz scanning acoustic microscopy. Results Storage in saline solution resulted in a progressive decrease of the acoustic impedance up to 70% in dentin but not in enamel tissue. Hank's balanced salts solution and artificial saliva appeared to maintain the elastic properties of dentin and enamel during the entire time of storage. The measurements of surface wave velocities did not show significant differences. High resolution (900 MHz) inspection of sections cut perpendicular to the surface exposed to the storage media for 21 days revealed a progressive increase of impedance in dentin up to the initial values at a depth of approximately 300 μm. Significance These findings suggest that quantitative SAM is a suitable tool for assessing surface and sub-superficial elastic properties of tooth tissue.

Reciprocity and gyrotropism in magnetic resonance transduction

We give formulas for transduction in magnetic resonance---i.e., the appearance of an emf due to Larmor precession of spins---based upon the modified Lorentz reciprocity principle for gyrotropic (also called ``nonreciprocal'') media, i.e., in which a susceptibility tensor is carried to its transpose by reversal of an external static field [cf., R. F. Harrington and A. T. Villeneuve IRE Trans. Microwave Theory and Technique MTT6, 308 (1958)]. Prior applications of reciprocity to magnetic resonance, despite much success, have ignored the gyrotropism which necessarily arises due to nuclear and/or unpaired electronic spins. For detection with linearly polarized fields, oscillating at the Larmor frequency, the emf is written in terms of a volume integral containing a product of two factors which we define as the antenna patterns, i.e., $({H}_{1x}\ifmmode\pm\else\textpm\fi{}i{H}_{1y})$, where, e.g., for a single transceive antenna, the $H$'s are just the spatially dependent oscillatory magnetic field strengths, per the application of some reference current at the antenna terminals, with the negative sign obtaining for transmission, and the positive for reception. Similar expressions hold for separate transmit and receive antennas; expressions are also given for circular polarization of the fields. We then exhibit a receive-only array antenna of two elements for magnetic resonance imaging of protons, which, due an intensity artifact arising from stray reactive coupling of the elements, produces, despite its own bilateral symmetry, asymmetric proton NMR images of a symmetric cylindrical phantom containing aqueous saline solution [J. Tropp and T. Schirmer, J. Magn. Reson. 151, 146 (2001)]. Modification of this two-port antenna, to function in transmit-receive mode, allows us to demonstrate highly nonreciprocal behavior: that is, to record images (of cylindrical test phantoms containing aqueous saline solution) whose appearance dramatically changes, when the roles of transmission and reception are swapped between the two antenna ports---giving in one instance a signal intensity pattern whose form resembles an umbrella (i.e., with a central column of moderate intensity surmounted by a bright canopy), and in the other, a distorted oval with slight concavities at its horizontal extremes, whose outline suggests that of a cat's eye. The relation between image patterns and drive scheme can be shown to reverse if the static polarizing field is reversed. Electromagnetic and circuit calculations, together with the modified reciprocity principle, allow us to reproduce these pattern changes in numerical simulations, closely and convincingly. Although the imaging experiments are performed at a static field of $3.0\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, and consequently a Larmor frequency of $128\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, the nonreciprocal effects are not related to the shortness of the wavelength in aqueous medium, but appear equally in simulations based in either the quasistatic or full electromagnetic regimes. Finally, we show that although antenna patterns for transmission and reception are swapped with reversal of the polarizing field, meaning that the receive pattern equals the transmit pattern with the field reversed, this in no way invalidates the familiar rotating wave model of spin dynamics in magnetic resonance.

Hygroscopic growth and evaporation in an aerosol with boundary heat and mass transfer

This study demonstrates an experimental method for using temperature measurements as a means for validating computations of particle size distribution in a growing or evaporating high-concentration aerosol flowing in a tube with wall heat and mass transfer. The method is based on the premise that aggregate growth or condensation from an ensemble of aerosol droplets can be inferred by comparing temperature evolution of an aerosol-laden and aerosol-free flow through a heated or cooled tube. The difference in bulk temperature is used as an indicator of latent heat effect which is directly related to condensational and evaporative particle size changes. Dimensional analysis is used to derive the conditions under which such an approach can be used. Two parameters, the “coupling number” and the dimensionless mass concentration are found to govern the sensitivity of continuous phase temperature to aggregate evaporation or condensation of the droplet ensemble, and the sensitivity of temperature to droplet diameter changes, respectively. Experimental data for an aqueous saline aerosol flowing through a heated, constant wall temperature tube are presented and compared to predictions derived using a Lagrangian plug-flow model with a fully moving particle bin structure. Measured and predicted bulk phase temperatures agree to within 3%. Using sensitivity analysis, it is shown that hygroscopic particle diameter changes will be at least as accurate.

In situ micro‐Raman spectroscopy on minerals on‐site in the Grotto Hall of the New Palace, Park Sanssouci, in Potsdam

AbstractQuestions of identity and provenance of minerals that are parts of masterpieces in museums have become increasingly important in mineralogical and historical studies. Detailed investigations of valuable and unique objects require on‐site, nondestructive and noninvasive methods because touching or removing them may cause irreparable damage. A mobile Raman‐microprobe has been used to meet these demands for truly in situ mineralogical studies of the large collection of minerals and rocks of the Prussian kings in the Grotto Hall (Grottensaal) of the New Palace (Neues Palais), Park Sanssouci in Potsdam. Minerals on the walls of the Grotto Hall were analyzed to identify them and thereby to complete the data bank of the collection. Fluid and solid inclusions in the interior of a large quartz crystal have been studied to provide evidence of the provenance of the crystal. The fluid inclusions contain aqueous saline solutions, whereas the solid inclusions are needles of anhydrite with a length of about 1.5 mm. The quartz probably originated from an area in the eastern Alps, from the surroundings of Bad Gastein, Austria. This is the first on‐site and in situ study of inclusions below the surface of a mineral with a mobile Raman‐microprobe outside a laboratory. Copyright © 2006 John Wiley & Sons, Ltd.

Desempenho físico-químico de metais e estruturas de concreto de redes de distribuição de energia: estudo de caso na região de Manaus

The influence of natural aging furthered by atmospheric corrosion of parts of electric transformers and materials, as well as of concrete poles and cross arms containing corrosion inhibitors was evaluated in Manaus. Results for painted materials, it could showed that loss of specular gloss was more intensive in aliphatic polyurethane points than in acrylic polyurethane ones. No corrosion was observed for metal and concrete samples until 400 days of natural aging. Corrosion in steel reinforcement was noticed in some poles, arising from manufacturing faults, such as low cement content, water/cement ratio, thin concrete cover thickness, etc. The performance of corrosion inhibitors was assessed by many techniques after natural and accelerated aging in a 3.5% saline aqueous solution. The results show the need for better chemical component selection and its concentration in the concrete mixture.

Effect of duplex treatments by plasma nitriding and triode sputtering on corrosion behaviour of 32CDV13 low alloy steel

This paper presents corrosion behaviour of duplex treated low alloy steel. Different kinds of samples were tested: non-treated, plasma nitrided, ZrBN-triode sputtered and ZrBN-duplex treated samples. The corrosion behaviour was evaluated by electrochemical techniques (corrosion potential and polarisation resistance evolutions versus immersion time, potentiodynamic curves). The corrosion tests were carried out in neutral aqueous saline solution (NaCl 30 g L − 1 ), naturally aerated. The composition and the structure of layers were determined by EDS and XRD, respectively, while the morphology was observed by SEM. Experimental results showed that the corrosion current density I corr increased with decreasing white layer thickness in plasma nitrided specimens. The nitrides ε-Fe 2 − 3 N and γ′-Fe 4N present in the white layer are nobler than the substrate but may promote, by galvanic effect, a localised corrosion through open porosity. The duplex treated specimens (nitriding + ZrBN coating) present better corrosion protection and enable to overcome the drawbacks of both techniques, mainly the porosity of the deposited films.

Study of the solid–liquid interface of hydroxyl-terminated hyperbranched aromatic polyesters (HBP-OH) in aqueous media: I. Characterisation of the properties and swelling behaviour of HBP-OH thin films

The nature of the solid–liquid interface of hydroxyl-terminated hyperbranched aromatic polyester (HPB-OH) thin films has been studied with respect to further protein adsorption investigations. Contact angle measurements, atomic force microscopy, zeta potential measurements and spectroscopic ellipsometry were used to characterize the physical and chemical structure of the HBP-OH thin films as well as the adsorption-relevant surface properties. It was shown that film properties such as the effective refractive index significantly depends on the thickness of HBP-OH films whereas the water contact angle does not reveal any changes with thickness variations. All surface-sensitive methods used indicate marked swelling behaviour of HBP layers in aqueous phosphate buffer saline. Moreover, the degree of swelling, zeta potential as well as surface free energy (in terms of water contact angle) strongly depend on the time the films had been annealed above their glass transition temperature.

ESTUDO DE INCLUSÕES FLUIDAS EM MINERALIZAÇÃO SULFETADA VULCANOGÊNICA HIDROTERMAL E DE OURO OROGÊNICO NA SERRA DO IPITINGA, AMAZÔNIA, BRASIL

The Ipitinga Group (2.27 Ga) at the Serra do Ipitinga consists of a meta-volcano-sedimentaryunit of mafic and ultramafic metavo1canics, cordierite-antophyllite-and quartzo-chlorite-bearing rocks under1ying chemical (oxide and silicatetype BIFs) and clastic metasedimentary rocks. Part of the mafic and ultramafic lavas was hydrothermally altered, which gave rise to quartz-chlorite-bearing rocks and hydrothermal syndepositional exhalative vo1canogenic sulfide mineralization, formed by pyrrhotite, pyrite, chalcopyrite and sphalerite with Au and Ag and traces of galena , molibdenite and silver telluride. Ali the meta-volcano-sedimentary unit was deformed by ductile-brittle shearing and transformed in present-day NW-SE trending shear belts with a subvertical - NE dip. During this defomational shearing episode, hydrothermal fluids yielded gold-sheared Iodes. Twelve types of fluid inclusions identified in the Ipitinga Group distinguish two fluid systems related to three peculiar hydrothermal events. The quartz of the quartz-chlorite-bearing roeks (hydrothermally - altered basalts), the main host of the volcanogenic sulfide mineralization, eontains eleven types of fluid inclusions. Eight of these oceur only in these rocks, which can be considered to have resulted from fluid-rock reactions related to the first hydrothermal event (1). This event involved an aqueous earbonic fluid consisting mainly of CH 4 and Hp, with traces of N 2 and H 2 S. CO 2 -bearing inclusions are subordinate and contain traces of CH 4 , H 2 S and N 2. The predominance of CH 4 over CO 2 in the aqueous earbonic fluid system is coherent to proposed models for the generation of exhalative volcanogenic sulfide mineralization in mid - oceanic ridge hydrothermal systems. The presence of CH 4 in the first hydrothermal event in the Ipitinga Group is evidence of an ocean-floor metarnorphic-hydrotherrnal process, in an environment similar to present-day ocean spreading eenters. Pressure and temperature values for the sulfide mineralization were considered to be in the range of 0.7 - 2.3 kbar and 250 - 450°C, respectively. Aqueous saline fluid related to the second hidrothermal event (II) oceurs only in the cordierite-anthophyllite rocks. Quartz veins are the products of a third hydrothermal event related to duetile shearing (III) and contain inclusions of an aqueous saline fluid which can also be found in quartz of the quartz-chlorite-bearing roeks. The fluid inelusion study also pointed out the relative chronology for the hydrothermal-metarnorphic events in the Ipitinga Group.

Secondary environment effects on the first step of the protonation of SO 4 2− in saline aqueous solutions

The solubility of strontium sulfate in the mixtures of isomolar LiClO4(NaClO4) and HClO4 aqueous solutions was determined at 25°C and ionic strengths of I = 0.5, 1.0, 2.0, 3.0, and 4.0. At I>-2, the solubility of SrSO4 as a function of the hydrogen ion (HClO4) concentration passes through a maximum, clearly showing a substantial contribution from environment effects (H+ substitution for Li+ or Na+), which counteract complexation (i.e., HSO 4 − formation). A correct method for separating these two effects was proposed, and the parameters of the environment effect and the standard values of pSP° and logβ° were evaluated.