Presence Of Sulfate Research Articles

Corrosion of a mild steel in agricultural irrigation waters in relation to partially blocked surface

The corrosion behaviour of a mild steel in agricultural irrigation water was investigated in the reference solution constituted of 0.2 g l −1 NaCl solution and the inhibiting effect of sulphate ions was examined by addition of 0.27 g l −1 Na 2SO 4 to the reference solution. The voltammograms obtained with rotating disc electrode showed a cathodic plateau. This limiting current was due mainly to the reduction of dissolved oxygen. In parallel to this reaction, the hydrogen evolution reaction is also taking place for a higher cathodic polarisation potential. At the corrosion potential, however, the diffusion is not the process that determines the corrosion rate. The electrochemical impedance spectroscopy (EIS) at the corrosion potential showed three parallel RC circuits linked hierarchically. The corrosion rate in the presence of sulphate ions was 20 times as fast as in the reference solution. That is, the enhancement of galvanic coupling between local cells prevails on the surface blocking effect of sulphate ions revealed by electrohydrodyanamical (EHD) impedance measurements. In fact by EHD impedance we have shown that sulphate ions actually induce the behaviour identified as partially blocking surface. The active surface areas were roughly estimated to correspond to the crystallographic grain size of mild steel used in this study.

Effects of Anions on Local Structure of Al and Si in Aluminosilicates

Three kinds of amorphous aluminosilicates were synthesized by coprecipitation of silicic acid with aluminum hydroxide in the presence of different inorganic ions: sulfate, chloride, and nitrate. Although the bulk composition of the aluminosilicates obtained was not affected by anion species, their DTA spectra were significantly different, suggesting that their structures also differ. The local structure of Al and Si in the aluminosilicates was studied in detail by 27Al and 29Si MAS NMR. From the 27Al MAS NMR spectra and comparison between 29Si HD- and CP-MAS NMR spectra, it was concluded that the aluminosilicate obtained in the presence of sulfate ions has only a montmorillonite-like structure, whereas in the cases of chloride and nitrate, the solids are composed of three phases: aluminum hydroxide, silica, and the montmorillonite-like aluminosilicate. The difference in the local structure of Al and Si in the aluminosilicates was explained by the difference in interaction between the anions and aluminum ions.

Yttrium and rare earth elements in fluids from various deep-sea hydrothermal systems

Rare earth element (REE) and yttrium (Y) concentrations were measured in fluids collected from deep-sea hydrothermal systems including the Mid-Atlantic Ridge (MAR), i.e., Menez Gwen, Lucky Strike, TAG, and Snakepit; the East Pacific Rise (EPR), i.e., 13°N and 17–19°S; and the Lau (Vai Lili) and Manus (Vienna Woods, PacManus, Desmos) Back-Arc Basins (BAB) in the South-West Pacific. In most fluids, Y is trivalent and behaves like Ho. Chondrite normalized Y-REE (Y-REE N) concentrations of fluids from MAR, EPR, and two BAB sites, i.e., Vai Lili and Vienna Woods, showed common patterns with LREE enrichment and positive Eu anomalies. REE analysis of plagioclase collected at Lucky Strike strengthens the idea that fluid REE contents, are controlled by plagioclase phenocrysts. Other processes, however, such as REE complexation by ligands (Cl −, F − SO 4 2−), secondary phase precipitation, and phase separation modify REE distributions in deep-sea hydrothermal fluids. REE speciation calculations suggest that aqueous REE are mainly complexed by Cl − ions in hot acidic fluids from deep-sea hydrothermal systems. REE concentrations in the fluid phases are, therefore, influenced by temperature, pH, and duration of rock-fluid interaction. Unusual Y-REE N patterns found in the PacManus fluids are characterized by depleted LREE and a positive Eu anomaly. The Demos fluid sample shows a flat Y-REE N pattern, which increases regularly from LREE to HREE with no Eu anomaly. These Manus Basin fluids also have an unusual major element chemistry with relatively high Mg, SO 4, H 2S, and F contents, which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation. REE distribution in PacManus fluids may stem from a subseafloor barite precipitation and the REE in Demos fluids are likely influenced by the presence of sulfate ions.

The effects of anion sorption on sorption and leaching of cadmium

The effect of chloride, sulfate, nitrate, and phosphate anions on the sorption and leaching of cadmium was examined in 2 soils (Manawatu silt loam and Egmont clay loam) which differ in their variable charge components. There was a larger sorption of cadmium in the presence of phosphate than in the presence of sulfate, nitrate, and chloride, and the difference was more pronounced in the Egmont soil. In soils, specific sorption of phosphate increases the negative charge. The increase in negative charge per unit amount of phosphate sorbed decreased with increasing phosphate sorption. The sorption of cadmium increased in response to phosphate sorption. The phosphate-induced cadmium sorption resulted from the increase in negative charge due to phosphate sorption. Column studies indicated that cadmium was less susceptible to leaching in the presence of phosphate than in the presence of nitrate.

Mechanism of the Shape and Structure Control of Monodispersed α-Fe2O3Particles by Sulfate Ions

The characteristics of the adsorption of sulfate ions to hematite (α-Fe2O3) particles have been studied to elucidate the anisotropic growth of hematite particles in the presence of sulfate ions. Sulfate ions were actually found to be most strongly adsorbed to crystal faces parallel to thec-axis of the hexagonal crystal system from the adsorption isotherms of sulfate to hematite particles of different crystal habits, in accord with the retardation of their growth in the direction normal to thec-axis. It was found from FTIR spectroscopy that the adsorbed sulfate ions on the faces parallel to thec-axis, such as the {110} and {100} faces, or on {012} faces took the bidentate structure to Fe ions on the surfaces, while a monodentate structure was suggested for sulfate ions on thec-planes ({001} faces). The adsorbed amount of sulfate ions to the {012} faces of hematite at 100°C decreased with increasing pH and became almost zero at pH ≥5, suggesting that the shape control with sulfate is possible only in the acidic media at pH < 5. EDX and chemical analysis revealed that sulfate ions were almost uniformly incorporated into the ellipsoidal or peanut-type particles during their growth in the presence of sulfate ions. On the other hand, sulfate ions in the solution phase with a high concentration of chloride ions such as 3.0 mol dm−3were likely to be present in the form of free ions without forming a complex with Fe3+, as suggested from UV spectroscopy at 25°C. When the concentration of sulfate ions in the solution phase exceeded the level for shape control of hematite, precipitation of acicular α-FeOOH (goethite) was observed. If hematite particles were present in such a system, α-FeOOH was grown as whiskers on the hematite particles. When [SO2−4] in the solution phase was higher than 0.1 mol dm−3, precipitation of basic ferric sulfate was also observed in addition to the growth of α-FeOOH whiskers on hematite.

Investigation of sulfur release in ETV-ICP-AES and its application for the determination of sulfates

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur species in aqueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample. For understanding this phenomenon the thermal behavior of sulfuric acid, ammonium sulfate and the sulfates of sodium, zinc, magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these sulfates. To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO3)2 and Ge in KOH were successfully applied as modifiers for the stabilization of the sulfates during the thermal pre-treatment step and to establish a uniform thermal behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers is based on the reduction of the sulfates in presence of carbon, resulting in the formation of GeS and PdS, respectively. This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) as modifier the absolute detection limit was 300 pg sulfur (e.g. LOD 30 ng mL–1). The significant influence of phosphates on the determination of sulfur could be essentially reduced by Pd as modifier.

Effect of sulfate and chloride ions on the electrochemical behavior of iron in aqueous phosphate solutions

The electrochemical behavior of iron in aqueous phosphate solutions (0.005–0.1M) of pH∼8 at room temperature was investigated with an emphasis on the effect of chloride and /or sulfate ions on the initiation of the localized attack. Electrochemical techniques were complemented by SEM microscopy, FTIR, X-ray fluorescence analysis and ICP measurements. It has been shown that phosphate ions are very effective inhibitors against localized attack, and in the presence of sulfate ions still show an effect very similar to that of phosphate ions in the active–passive dissolution peak region.

Benzothiophene and dibenzothiophene as the sole sulfur source in Acinetobacter: growth kinetics and oxidation products

Acinetobacter is an aerobic bacterium able to grow on aromatic carbon sources such as phenol and benzoate when given as the only carbon and energy source. In the present research, we have investigated its ability to metabolize benzothiophene (BT) and dibenzothiophene (DBT) given as the sole source of sulfur in presence of lactate as carbon nutrient. The heterocyclic compounds have been used alone and as β-cyclodextrin (β-CD) complexes in order to enhance their solubility and consequently improve their bioavailability. The growth curves obtained in a modified Sokol medium with BT or DBT have been compared to ones obtained in the same medium having inorganic sulfur composition. Our results show that the first two metabolic steps are the same as the pathway known in other micro-organisms, evidentiating the formation of sulphone and sulphoxide products. The bacterial growth curve in DBT displays a trend quite different from the curve obtained with inorganic sulfur. The binding of BT and DBT with cyclodextrins (CD) strongly enhance their water solubility (10 and 15 folds, respectively) thus reducing the replication time of the cells ( T d from 10.2 h to 3.1 h). Growth kinetics with β-CD + DBT display a maximum velocity when the molar concentration of DBT is about 50% of the maximum complex solubility. Over this value, an inhibitory effect is observed.

Gentamicin-Loaded Hydraulic Calcium Phosphate Bone Cement as Antibiotic Delivery System

A hydraulic calcium phosphate cement made of β-tricalcium phosphate [β-Ca3(PO4)2], monocalcium phosphate monohydrate [Ca(H2-PO4)2·H2O], and water was used as a delivery system for the antibiotic gentamicin sulfate (GS). GS, added as powder or as aqueous solution, was very beneficial to the physicochemical properties of the cement. The setting time increased from 2 to 4.5min with 3% (w/w) GS and then slowly decreased to 3.75min with 16% (w/w) GS. The tensile strength increased from 0.4 to 1.6MPa with 16% (w/w) GS. These effects were attributed to the presence of sulfate ions in GS. The release of GS from the cement was measured in a pH 7.4 phosphate-buffered saline solution at 37°C by USP paddle method. Factors such as cement porosity, GS content and presence of sulfate ions or polymeric additives were investigated. The amount of GS released was roughly proportional to the square root of time up to ∼50% release. Afterwards, the release rate markedly slowed down to zero. In all but two cement formulations, the total dose of GS was released within 7days, indicating that no irreversible binding occurred between the cement paste and the antibiotic. When small amounts of hydroxypropylcellulose or poly(acrylic acid) were added to the cement, the maximum fraction released was a few percent lower than the total GS dose, suggesting some binding between the polymer and GS. The GS release rate was strongly influenced by the presence of sulfate ions in the cement paste and by the cement porosity. The higher the sulfate ion content of the cement paste, the lower the GS release rate. This influence was attributed to the finer cement microstructure induced by the presence of sulfate ions. Furthermore, when the initial cement porosity was increased from 38 to 69%, the release rate almost tripled (0.16 to 0.45h−1/2). Finally, the biological activity of GS in the cement was maintained, as measured by assaying the release medium.

Formation of Monodisperse Microcrystals of Basic Aluminum Sulfate by the Gel–Sol Method

A recently developed gel–sol method for the synthesis of monodispersed particles was applied in the preparation of uniform basic aluminum sulfate (Al3(SO4)2(OH)5·2H2O) microcrystals of different shapes including round-cornered cubes, sharp-edged cubes, truncated-corner cubes, hexagonal platelets, and ellipsoids. The process involves aging of a highly condensed aluminum hydroxide gel in the presence of sulfate ions under acidic conditions at 100°C for 3 days or longer. The growth of the basic aluminum sulfate particles was found to proceed through a dissolution–recrystallization mechanism from the aluminum hydroxide gel. The morphological variations were explained in terms of the specific adsorption of anions, such as SO42−, OH−, and Cl−, to different crystal planes during the growth. It has been shown that the technique of the so-called supersaturation quenching enhances the uniformity of the sharp-edged cubic particles and that the systematic control of the mean size is possible by seeding.

Temperature effect on the pore solution chemistry in contaminated cements

The combined effect of chloride and sulphate contamination and temperature on the pore solution chemistry, particularly the OH, Cl and SO42 concentration, in plain and blended cements was evaluated. The cement mortar specimens were contaminated with sodium chloride and sodium chloride plus sodium sulphate and exposed to temperatures in the range 25 to 70°C. Results indicate that the chloride binding capacity of cement is affected by both the temperature and the sulphate contamination. In the chloride contaminated specimens, the chloride binding was influenced by the exposure temperature, while in those contaminated with sodium chloride plus sodium sulphate, it was affected by the presence of sulphate ions. The sulphare concentration in the plain and blended cements was also influenced by the exposure temperature and chloride contamination. The Cl/OH values increased with temperature in both plain and blended cements, indicating the vulnerability to accelerated steel depassivation in concyete exposed to elevated temperature and contaminated with chloride and sulphute ions.

Isolation of the tetrathionate hydrolase from Thiobacillus acidophilus.

An enzyme capable of hydrolysing tetrathionate was purified from cell-free extracts of Thiobacillus acidophilus. The purified enzyme converts tetrathionate into thiosulfate, sulfur and sulfate. In addition, pentathionate could also be converted by the same enzyme. Measurement of the enzyme activity during purification is based on the absorbance of the initial intermediates formed from tetrathionate in the ultraviolet region, which have not been identified. Enzyme activity could also be measured by the scattering of insoluble sulfur in the visible region. The purified enzyme has a pH optimum of 2.5 and a temperature optimum of 65 degrees C. Enzyme activity is strongly stimulated by the presence of sulfate ions. The purified enzyme is a dimer with two identical subunits of 48 kDa. The ultraviolet-visible absorption spectra and denaturation experiments indicate the presence of an organic cofactor.

Polythionate degradation by tetrathionate hydrolase of Thiobacillus ferrooxidans.

Cell-free extracts of Thiobacillus ferrooxidans grown with thiosulfate as energy source and prepared at high ammonium sulfate concentrations and at low pH are capable of polythionate hydrolysis. The enzyme responsible for the hydrolysis of tetrathionate (S4O2- 6) and pentathionate (S4O2- 6) was purified to homogeneity. Enzyme activity during the purification procedure was based on a continuous spectrophotometric method that detects soluble intermediates that absorb in the UV region. The end products of hydrolysis of both polythionates by the pure enzyme were thiosulfate, sulfur and sulfate. The purified enzyme has a pH optimum of around 4 and a temperature optimum of 65 �. The activity is strongly influenced by the presence of sulfate ions. The purified enzyme is a dimer with two identical subunits of molecular mass 52 kDa. During purification of tetrathionate hydrolase, fractions able to hydrolyse trithionate and tetrathionate were separated, indicating that the two substrates are hydrolysed by different enzymes.

On the Kinetics of Solid‐Liquid‐Solid. Phase Transformation

AbstractSolid‐solid phase transformation of different hydrates or polymorphs in suspension proceeds in such a way that the metastable phase dissolves and the stable phase precipitates from the solution. If the starting point lies within the metastable zone of the stable phase, the transformation starts only after elapse of the corresponding induction period. In the case when the starting point is situated outside the metastable zone of the stable solute, the transformation proceeds without any delay. These theoretical considerations are illustrated by an example with recrystallization of calcium sulphate in presence of phosphoric acid; a small concentration change of the acid changes the kinetics significantly.

Studies on Ferric Oxide Hydroxides: II. Structural Properties of Goethite Samples (α-FeOOH) Prepared by Homogeneous Precipitation from Fe(NO3)3Solution in the Presence of Sulfate Ions

A series of goethite samples (α-FeOOH) have been prepared by homogeneous precipitation from Fe(NO3)3solution in the presence of SO−24ions and characterized by various techniques. Although the cell parameters, cell volumes, and crystallite sizes of all the samples prepared under different conditions remain almost same, the surface area, micropore–mesopore ratio, pore volume, pore radius, particle size, and surface acidity are influenced by SO−24/Fe+3ratio, initial pH, and temperature of hydrolysis. The sample prepared at SO−24/Fe+3ratio of 0.5, initial pH of 1.5, and hydrolysis temperature of 90°C has predominantly micropores and possesses high surface area (133.5 m2/g) and acid sites (100 μmol/g).

Effects of sulphate, calcium and aluminum ions upon the hydration of sulphoaluminate belite cement

In the model sulphoaluminate belite cement, the process of hydration is governed by the diffusion and transport phenomena of the main ionic species. The sulphate components and combined sulphate and aluminium ions, exert an accelerating effect upon the kinetics of sulphoaluminate belite cement hydration. Aluminium and calcium ions delay the hydration by creating a retarding layer which can be considered a co-precipitate of aluminium and calcium hydroxides. This is revealed in the calorimetric curves by the duration of induction period and also by the intensities of the main peaks. The appearance of small additional peaks characterizes the formation of 'primary ettringite', due to the presence of sulphate ions in aqueous solution. The intensities of these peaks depend on the ion concentration too.

Effect of anion adsorption on early stages of copper electrocrystallization at Au(111) surface

The monolayer and submonolayer deposition of copper on Au(111) electrode surface in the presence of chloride and sulfate ions was studied by in situ X-ray absorption and electrochemical techniques. The anions coadsorb with the deposited copper adatoms and have a strong influence on the structure of these mixed overlayers. Copper deposited in the presence of chloride forms a bilayer in which copper atoms are sandwiched between the gold substrate and the top layer of chloride ions. The bilayer is well ordered and has a (5×5) long range structure. The copper atoms are packed in registry with the top layer of chloride ions. In contrast, copper adatoms deposited in the presence of sulfate ions are packed in registry with respect to the Au(111) substrate. The coadsorbed copper and sulfate form a highly corrugated overlayer. The copper adatoms assume a honeycomb (√3×√3) structure with the center of the honeycomb occupied by sulfate. The sulfate ion adsorbs with three of its four oxygens directed towards the hexagon of copper adatoms. The bond angle between the copper adatom and the oxygen of the sulfate ion is approximately equal to 45 °. Our data indicate that, in contrary to the literature reports, the (√3×√3) structure observed on STM and AFM images corresponds to the corrugation of adsorbed sulfate ions rather than copper adatoms.

Studies on the passivation behaviour of al-Zn-Mg alloy in chloride solutions containing some anions and cations using electrochemical impedance spectroscopy

Potentiodynamic polarization and impedance measurements were performed on Al-zn-Mg alloy in 0.01M NaCl solution with various concentrations of nitrate, molybdate, sulphate, Cd(II) and Ce(III) ions. At 10 −2M nitrate, molybdate and CE(III) ions, both the open circuit and the pitting potentials were found to shift more in the noble direction as compared to lower concenetrations. In the presence of molybdate and Ce(III) ions a wide passive region was observed, while in the presence of Cd ions, a higher corrision current was noticed. The observed impedance spectra was interpreted in terms of change in characteristics of the already existing oxide film at the surface of the alloy. The low capacitance values measured in the presence of sulphate ions can be related to the morpholigical changes occurring in the film. The effect of the ions in healing and strengthening the existing oxide film of the aluminium alloy was found to increase in the following order: cadmium(II) < sulphate < molybdate < nitrate < Ce(III).

The selective solvent extraction of cadmium by mixtures of carboxylic acids and trialkylphosphine sulphides. Part 2. Practical applications in the separation of cadmium from zinc and nickel

The addition of triisobutylphosphine sulphide (TIBPS) to 3,5-diisopropylsalicylic acid (DIPSA) causes a strong synergistic shift in the extraction of cadmium (1.9 pH units for the addition of 0.50 M TIBPS to 0.50 M DIPSA in xylene). The shifts are considerably smaller (up to 0.6 pH units) for other common divalent base metals; such as zinc, lead, manganese, iron, cobalt, nickel, calcium and magnesium, enabling the selective extraction of cadmium to be carried out in most cases. The influence on the separation between cadmium and zinc of variables such as: extractant concentrations, the identity of diluent, the presence of modifiers and the presence of sulphate ion was studied. In batch counter-current experiments using a synthetic solution containing cadmium (5 gl −1) and nickel (24 gl −1) as sulphates and 0.50 M TIBPS plus 0.50 M DIPSA in xylene at an organic to aqueous phase ratio of 2:3 in three extraction stages, quantitative recoveries of 99.8% pure cadmium and > 99.99% pure nickel were obtained. In a continuous counter-current mini-plant trial, a sulphate leach liquor derived from the cadmium cement cake from an electrolytic zinc plant was treated in four extraction stages, two scrubbing stages, and two stripping stages, using 0.40 M TIBPS plus 0.40 M DIPSA in Shellsol 2325. The feed solution, containing up to 16 gl −1 cadmium and 9 gl −1 zinc, as well as small amounts of lead, thallium and other impurities, was processed through to a strip liquor containing up to 110 gl −1 cadmium with a purity of about 99.95% (Zn 0.01, Pb 0.02, Fe 0.01 and Tl 0.005%).

Crystallization of previously desalted lysozyme in the presence of sulfate ions.

Lysozyme, which is known to crystallize readily in the presence of many salts, has never been crystallized by salting out with ammonium sulfate. In the present study, lysozyme was first completely desalted by treatment with strong cation- (H(+) form) and anion- (OH(-) form) exchange resins. This leads to a protein solution with only H(+) and OH(-) as counterions, corresponding to its isoionic point. Addition of 2.5-3 molar equivalents of H(2)SO(4) to isoionic lysozyme decreases the pH value to 9-8 and allows crystallization to take place. The space group was found to be P4(3)2(1)2, similar to the classical lysozyme crystals grown in the presence of NaCl at pH 4.5, with unit-cell dimensions a = b = 78.9, c = 38.5 A. Tentative explanation of the sulfate/lysozyme interaction was addressed by mass spectrometry, and shows non-covalent binding of the ions on the protein.