Presence Of Sulfate Research Articles

Evidences of the Electrochemical Production of Sulfate Radicals at Cathodically Polarized TiO2 Nanotubes Electrodes

This work presents a novel approach for cathodically polarized TiO2 nanotube electrodes in electrochemical advanced oxidation processes generating sulfate radicals. Although TiO2 do not offer electrochemical response at the anodic region in the dark, its simple self-doping can enable oxidation capacity. Cathodically polarized TiO2 electrode (CP-TNT) was applied in the electrolysis of p-nitrosodimethylaniline dye in sulfate and nitrate aqueous electrolytes, showing much better decolorization efficiency in the presence of sulfate ions. Another evidence of SO4•− generation was the detection of persulfate ions (SO4•− + SO4•− → S2O82−) formed during bulk electrolysis of a sulfate aqueous solution (38 μmol L−1 S2O82− after 30 min). These results open the way for application of CP-TNT electrodes in EAOPs as an alternative for highly cost anodes for electrochemical generation of active sulfate species for degradation of organic contaminants.

Formation of Large Native Sulfur Deposits Does Not Require Molecular Oxygen.

Large native (i.e., elemental) sulfur deposits can be part of caprock assemblages found on top of or in lateral position to salt diapirs and as stratabound mineralization in gypsum and anhydrite lithologies. Native sulfur is formed when hydrocarbons come in contact with sulfate minerals in presence of liquid water. The prevailing model for native sulfur formation in such settings is that sulfide produced by sulfate-reducing bacteria is oxidized to zero-valent sulfur in presence of molecular oxygen (O2). Although possible, such a scenario is problematic because: (1) exposure to oxygen would drastically decrease growth of microbial sulfate-reducing organisms, thereby slowing down sulfide production; (2) on geologic timescales, excess supply with oxygen would convert sulfide into sulfate rather than native sulfur; and (3) to produce large native sulfur deposits, enormous amounts of oxygenated water would need to be brought in close proximity to environments in which ample hydrocarbon supply sustains sulfate reduction. However, sulfur stable isotope data from native sulfur deposits emplaced at a stage after the formation of the host rocks indicate that the sulfur was formed in a setting with little solute exchange with the ambient environment and little supply of dissolved oxygen. We deduce that there must be a process for the formation of native sulfur in absence of an external oxidant for sulfide. We hypothesize that in systems with little solute exchange, sulfate-reducing organisms, possibly in cooperation with other anaerobic microbial partners, drive the formation of native sulfur deposits. In order to cope with sulfide stress, microbes may shift from harmful sulfide production to non-hazardous native sulfur production. We propose four possible mechanisms as a means to form native sulfur: (1) a modified sulfate reduction process that produces sulfur compounds with an intermediate oxidation state, (2) coupling of sulfide oxidation to methanogenesis that utilizes methylated compounds, acetate or carbon dioxide, (3) ammonium oxidation coupled to sulfate reduction, and (4) sulfur comproportionation of sulfate and sulfide. We show these reactions are thermodynamically favorable and especially useful in environments with multiple stressors, such as salt and dissolved sulfide, and provide evidence that microbial species functioning in such environments produce native sulfur. Integrating these insights, we argue that microbes may form large native sulfur deposits in absence of light and external oxidants such as O2, nitrate, and metal oxides. The existence of such a process would not only explain enigmatic occurrences of native sulfur in the geologic record, but also provide an explanation for cryptic sulfur and carbon cycling beneath the seabed.

Density and partial molar volume of Sodium Dodecyl Sulfate in presence and absence of Sodium Sulfate and Zinc Sulfate in distilled water

The precise measurements of density of sodium dodecyl sulfate (SDS) in distilled water and in presence of 0.01M Na2SO4 and 0.01M ZnSO4 atroom temperature were measured by Ostwald-Sprengel type pycnometer. The density of SDS in distilled water was found lower than the density of SDS in Na2SO4 and ZnSO4 solutions whereas the density of SDS in the presence of ZnSO4 is higher than the density of SDS in the presence of Na2SO4. The partial molar volume of SDS in distilled water was obtained higher than in presence of Na2SO4 and ZnSO4 solutions.BIBECHANA 16 (2019) 131-136

Slag hydration and chloride binding in slag cements exposed to a combined chloride-sulphate solution

The effects of curing temperature (20 °C or 38 °C), slag composition and slag content on the hydration and chloride binding characteristics of ground granulated blast-furnace slag (ggbs) – blended cements have been studied. Two slags (CaO/SiO2 = 1.05 or 0.94) were each blended with CEM I 52.5R at 30% and 70% replacement. Paste samples of constant 0.5 w/b ratio were hydrated for 56 days, dried and exposed to either sodium chloride or combined sodium chloride – sodium sulphate solutions. Sodium sulphate concentration was 3 g/L, while chloride concentrations varied from 0.1 to 3.0 M. Post-exposure reaction products were characterised by XRD and thermal analysis. Chloride binding was followed via Friedel’s salt formation, with thermal analysis showing a decrease in Friedel’s salt formation in the presence of sulphate ions. Increasing slag content changed the nature of the chloride binding mechanism significantly. Hydration of slag studied by SEM-BSE image analysis showed that the higher basicity slag was more reactive, with the degree of slag hydration increasing with temperature. An increase in the slag load reduced the degree of slag hydration. Apart from the increase in slag load, the other changes in hydration corresponded well with the chloride binding characteristics of the blends.

Assessment of the Photocatalytic Efficiency of TiO<sub>2</sub> in the Presence of Sulphate

The use of salts on the degradation of toxic substances may cause the acceleration or delay of radicals production originating from the degradation process. This work had as its objective to investigate the presence and absence of potassium sulphate salt on the photocatalysis of Bentazone using TiO2 as a catalyzer. The effect of the sulphate ion on the photodegradation of the Bentazone herbicide was studied using concentrations of 0,05; 0,10 and 0,20 g L-1 with 0,5 g L-1 of TiO2, in suspension of 180 mL from bentazone solution (3,0x10-5 mol L-1). The samples were analyzed through UV-Vis spectroscopy. The presence of sulphate ions presented a difference of 3,3% on the degradation of bentazone in comparison to TiO2 alone.

On the kinetics of phase transformations of dried porous vaterite particles immersed in deionized and tap water

Calcium carbonate exists in three allotropic forms: vaterite, aragonite and calcite. Metastable vaterite can be easily transformed into calcite and/or aragonite via different routes. We report how dry vaterite particles transform into aragonite and calcite when they are immersed into DeIonized water (DI) or tap water without additives at different temperature (22, 40 and 60 °C) with and without stirring. We show that the transformation rate of vaterite into more stable crystallographic forms is influenced not only by temperature but also by stirring and water purity. Low temperature, absence of stirring and absence of ions in water significantly slow down the kinetics of transformation of vaterite. Additionally, water purity influences the nature of the allotropic phase obtained after transformation. High temperatures and DI water favor the transformation of vaterite into single crystalline nanowires of aragonite, while tap water yields the transformation of vaterite into calcite. The absence of aragonite in tap water at high temperature can be explained by the presence of sulfate ions, which inhibit the formation of this phase. On the contrary, Mg2+ ions tend to stabilize vaterite.

Durability of cement concrete under chemical erosion

This paper launches the study on how the sulfate particle and chloride ions interact to impact the concrete durability. It is analyzed that there is a diffusion law of two particles in concrete, whether the concrete presents corrosion resistance and permeability as contacts with them. The findings reveal that the content of chloride ions decreases with the deepening of the concrete profile. The presence of sulfate ions does not break up the diffusion trend of chloride ions in concrete, but in the case when Cl- and SO42- act together, the content of chloride ions at a constant profile depth is less than that under the action of a single Cl-. When sulfate ions permeate the cement, they will react with hydrate product of cement to generate new chemical substances that fill the inner pores of the cement, thereby suppressing the diffusion of chloride ions. The higher the concrete water-binder ratio, the lower the compression strength; the more inner pores, the weaker its resistance to chemical attack. When mineral admixtures are added to the concrete, the sulfate ions can react with the hydrate products of the cement and mineral admixtures to generate new crystals that largely fill the original pores in the concrete and make it more compact. In this way, the concrete corrosion resistance is built up. Concrete gets most vulnerable to sulfate attack at an ambient temperature of 21-24°C, and relieved at 30- 35°C. Lower relative humidity, high temperature environment are the decisive factors that accelerate the concrete erosion.

Express Al/Fe oxide–oxyhydroxide sorbent systems for Cr(VI) removal from aqueous solutions

Today, one of the most important global tasks is the treatment of waste water from various pollutants, including heavy metal. Adsorption is a promising method of wastewater treatment in terms of efficiency and cost. In this paper, the Al/Fe oxide-oxyhydroxide composite powders, prepared by hydrothermal method using metal sulfate solutions and urea as precursors, are investigated as adsorbents for chromium. The influence of the [Al3+]:[Fe3+] ratio on the phase composition, textural properties, morphology, and thermal effects of composites was also investigated. It is shown that the maximum specific surface area (190 m2/g) is reached for samples synthesized from solutions with [Al3+]:[Fe3+] = 1:0 and 1:1. Cr(VI) adsorption from solutions was performed under static (batch adsorption) and dynamic (column adsorption) conditions. It is shown that the presence of sulfate ions on the surface of Al-containing samples suppresses the Cr(VI) adsorption. The maximum adsorption capacity in batch adsorption (3.66 mg/g) has a sample synthesized from solutions with [Al3+]:[Fe3+] = 1:6, which is characterized by a high (but not maximal) surface area (102 m2/g), a low content of sulfates and maximum zeta potential. Sorption experiments showed that the mean free adsorption energy is below 8 kJ/mol for all samples, indicating the adsorption process as the physical in nature and suggesting the possibility of Cr(VI) desorption and adsorbent regeneration. Based on the results of fixed-bed adsorption experiments, an atypical form of breakthrough curves is noted, as well as an increase in sorption capacity of about 4–5 times as compared with batch adsorption.

Sorption of Hg(II) and Pb(II) Ions on Chitosan-Iron(III) from Aqueous Solutions: Single and Binary Systems.

The present work describes the study of mercury Hg(II) and lead Pb(II) removal in single and binary component systems into easily prepared chitosan-iron(III) bio-composite beads. Scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and point of zero charge (pHpzc) analysis were carried out. The experimental set covered pH study, single and competitive equilibrium, kinetics, chloride and sulfate effects as well as sorption–desorption cycles. In single systems, the Langmuir nonlinear model fitted the experimental data better than the Freundlich and Sips equations. The sorbent material has more affinity to Hg(II) rather than Pb(II) ions, the maximum sorption capacities were 1.8 mmol·g−1 and 0.56 mmol·g−1 for Hg(II) and Pb(II), respectively. The binary systems data were adjusted with competitive Langmuir isotherm model. The presence of sulfate ions in the multicomponent system [Hg(II)-Pb(II)] had a lesser impact on the sorption efficiency than did chloride ions, however, the presence of chloride ions improves the selectivity towards Hg(II) ions. The bio-based material showed good recovery performance of metal ions along three sorption–desorption cycles.

The Influence of Salt Anions on Heavy Metal Ion Adsorption on the Example of Nickel.

The biodegradable polysaccharide chitosan possesses protonated and natural amino groups at medium pH values and has therefore been used as an adsorbing material for nickel salts in water treatment. Nickel is a problematic heavy metal ion which can cause various diseases and disorders in living organisms. Here, we show the influence of oxyanions (e.g., nitrate and sulfate) to the adsorption of nickel ions. Hence, simultaneously we are addressing the increasing global problem of nitrate and sulfate ion pollution in groundwater and surface water. A series of adsorption experiments was carried out in order to determine (i) the adsorption equilibrium, (ii) the adsorption capacity in dependence on the initial nickel ion concentration, and (iii) the influence of the anion presented in solution for the adsorption capacity. Surface morphology of chitosan flakes before and after the adsorption process has been studied with SEM-EDX analysis. The chitosan flakes exhibited promising adsorption capacities of 81.9 mg·g−1 and 21.2 mg·g−1 for nickel (sulfate) and nickel (nitrate), respectively. The calculated values of Gibbs free energy change ΔG0 confirm the higher adsorption of nickel ions in presence of sulfate ions. Hence, higher anion valence leads to a higher adsorption capacity.

Development of nanoscale zirconium molybdate embedded anion exchange resin for selective removal of phosphate

Development of a selective adsorbent with an enhanced removal efficiency for phosphate from wastewater is urgently needed. Here, a hybrid adsorbent of nanoscale zirconium molybdate embedded in a macroporous anion exchange resin (ZMAE) is proposed for the selective removal of phosphate. The ZMAE consists of a low agglomeration of zirconium molybdate nanoparticles (ZM NPs) dispersed within the structure of the anion exchange (AE) resin. As major results, the phosphate adsorption capacity of the ZMAE (26.1 mg-P/g) in the presence of excess sulfate (5 mM) is superior to that of the pristine AE resin (1.8 mg-P/g) although their phosphate uptake capacity was similar in the absence of sulfate and these results were supported by the high selectivity coefficient of the ZMAE toward phosphate over sulfate (SPO4/SO4) more than 100 times compared to the pristine AE resin. This superior selective performance of the ZMAE for phosphate in the presence of sulfate ions is well explained by the role of the ZM NPs that contributed to 69% of the phosphate capacity which is based on an observation that the phosphate adsorption capacity of the ZM NPs is not affected by the presence of sulfate. In addition, the behavior of the selective phosphate removal by the ZMAE was well demonstrated by not only in the batch mode experiment with simulated Mekong river water and representative wastewater effluent but also in a column test.

Micellization of sodium dodecyl sulphate in presence and absence of alkali metal halides at different temperatures in water and methanol-water mixtures

The micellization of sodium dodecyl sulphate (SDS) in presence and absence of KCl, KBr, NaBr and NaCl in water and methanol-water mixtures containing 8, 16, 25 and 34wt% of methanol at 298.15 to 323.15K have been assessed from conductometric measurements. The concentrations of SDS were varied from ~0.001 to ~0.05molL−1 and salts concentration was 0.01molL−1. The critical micelle concentration (CMC) of SDS in presence and absence of salts in water as well as in methanol-water mixtures are found to increase with the increase in temperature and found to decrease with the addition of salts. The CMC of SDS in water and methanol-water mixtures in presence of studied salts is found in the order NaCl>NaBr>KCl>KBr.Thermodynamic properties of micellization such as the standard free energy of micellization, standard enthalpy of micellization, the standard entropy of micellization, the standard free energy of transfer and heat capacity of micellization of SDS in presence and absence of salts have been examined. The micellization of SDS with presence and absence of salts has been assessed in terms of different solvent parameters. The solvophobic parameters have been presented.

Optimization of Smart Water Chemical Composition for Carbonate Rocks Through Comparison of Active Cations Performance

Designing smart water (SW) by optimizing the chemical composition of injected brine is a promising low-cost technique that has been developed for both sandstone and carbonate reservoirs for several decades. In this study, the impact of SW flooding during tertiary oil recovery phase was investigated by core flooding analysis of pure limestone carbonate rocks. Increasing the sulfate ion concentration by using CaSO4 and MgSO4 of NaCl concentration and finally reducing the total salinity were the main manipulations performed to optimize SW. The main objective of this research is to compare active cations including Ca2+ and Mg2+ in the presence of sulfate ions (SO42−) with regard to their efficiency in the enhancement of oil production during SW flooding of carbonate cores. The results revealed a 14.5% increase in the recovery factor by CaSO4 proving its greater effectiveness compared to MgSO4, which led to an 11.5% production enhancement. It was also realized that low-salinity water flooding (LSWF) did not lead to a significant positive effect as it contributed less than 2% in the tertiary stage.

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Current efficiency in the sodium chlorate process is a key issue in the evaluation of the power consumption. A pilot cell unit for executing the sodium chlorate process was constructed to study the current efficiency of the anode and cathode separately. The effects of sodium dichromate and sodium sulphate concentrations and the electrolyte temperature on the anode and cathode current efficiencies were studied. Corrosion products formed on the mild steel cathodes after their removal from the cell were characterised using X-ray diffraction and infrared spectroscopy. The results show that the cathodic current efficiency increases with increasing dichromate concentrations in the electrolyte until approximately 5 g dm−3 is reached. At this optimum concentration of dichromate, the presence of sulphate ions decreases the cathodic current efficiency. For moderate increases in temperature, the cathodic current efficiency increases, but oxygen evolution is promoted, and the power consumption also increases. Surface characterisation of the electrodes after their exposure to air shows two primary types of behaviour, depending on the process parameters. At low dichromate concentrations, amorphous corrosion layers are formed, while at higher concentrations, reduced forms of iron hydroxides, i.e., “green rust”, are identified. Although the electrodes were positioned at the open circuit potential for 40 min before their removal from the cell, chromium remains on the cathode surface. This result might explain the corrosion-inhibiting effect of the addition of chromate to the electrolyte. The results from this study can be used to optimise operating procedures in real plants, decrease the energy consumption and minimise the environmental impact of these processes.Graphical

Synthesis of ordered porous zirconia containing sulfate ions and evaluation of its surface acidic properties

The synthesis and characterization of sulfated ZrO2 with ordered pores as a solid acid catalyst were investigated. Ordered porous ZrO2 containing sulfate ions was synthesized by hydrolysis of zirconium n-propoxide in the presence of HCl, surfactant and (NH4)2SO4 dissolved in distilled water, when the SO4/Zr molar ratio was changed in the range of 0.8–1.4. BET surface area of sulfated ZrO2 thus synthesized was found to be 150–160 m2 g−1. The presence of sulfate ions in ZrO2 was confirmed by an appearance of IR band at ca. 1398 cm−1 in the IR spectra of sulfated ZrO2. Since two IR bands due to surface hydroxyl groups were still observed for sulfated ZrO2, the possibility that sulfate ions are highly dispersed on the surface of ordered porous ZrO2 was suggested. From the evaluation of surface acidity by NH3-TPD measurements, not only the amount of NH3 desorption but also the strength of acid sites related to NH3 desorption temperature were found to be increased with increasing the SO4/Zr ratio up to 1.2. On the other hand, FTIR spectroscopy following pyridine adsorption revealed that the maximum surface density of Bronsted acid sites was attained for sulfated ZrO2 with SO4/Zr ratio of 1.0. Sulfate species interacting strongly with nano-sized tetragonal ZrO2 was considered to be responsible for the creation of Bronsted acid sites. In accordance with the surface density of Bronsted acid sites, sulfated ZrO2 with SO4/Zr ratio of 1.0 showed the highest activity for the skeletal isomerization of 3,3-dimethylbut-1-ene, which predominantly occurs on Bronsted acid sites.

Study of behaviour of Ni(III) macrocyclic complexes in acidic aqueous medium through kinetic measurement involving hydrogen peroxide oxidation and DFT calculations

The Cu(II) ion-catalysed kinetics of oxidation of H2O2 by [Ni IIIL] [where L = L1 (cyclam) and L2 (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)] was studied in the pH range of 3.6–5.6 in acetic acid-acetate buffer medium at 25°C in the presence of sulphate ion. The ionic strength (I) was maintained at 0.5 M (NaClO4). The rate constants showed an inverse acid dependence and [Ni III L 2] was observed to be more stable than [Ni III L 1]. The rate of the reaction of both complexes with hydrogen peroxide shows contrasting behaviour at pH > 2.5 when compared to the same reaction in perchloric acid medium. DFT calculations performed on the complexes [Ni III L 1(SO4)(OAc)] and [Ni III L 2(SO4)(OAc)] reveal that both the acetate and sulphate ligands are axially coordinated to the metal centre. In addition, there is strong hydrogen bonding between the axial ligand and NH hydrogen of the macrocyclic ligand. The computed covalent bond orders in the aqueous medium predict that the acetate forms stronger coordinate bond with Ni ion than the sulphate ligand. The hydroxyl group present in one of the pendant groups of L2 forms a strong hydrogen bond with the sulphate ligand which leads to additional stability in [Ni III L 2(SO4)(OAc)]. The Cu(II) ion-catalysed kinetics of oxidation of H2O2 by [NiIIIL] [where L = L1 (cyclam) and L2 (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)] was studied in the pH range of 3.6-5.6. The structure and bonding patterns of the [NiIIIL1(SO4)(OAc)] and [NiIIIL2(SO4)(OAc)] were studied using DFT calculations.

Study of the evolution of properties of mortar under sulfate attack at different concentrations

In this study, the samples of ordinary Portland cement mortar were fully immersed in sodium sulfate solutions of different concentrations (0%, 5% and 15%) for up to 270 d. The evolution of the properties of the samples (compressive strength, static modulus of elasticity, stress–strain behaviour, hardened density, water permeability coefficient and length change) was monitored. The surface deterioration of the samples was also observed and the morphological features of the products were investigated using scanning electron microscopy. Water immersion was found to improve for the properties of the samples and reduce the water permeability coefficient. Moreover, at the initial stage of sodium sulfate attack, the presence of sulfate ions had a positive effect on the evolution of the properties due to the formation of ettringite and gypsum. Afterwards, the samples immersed in sodium sulfate solution showed a degradation in the properties, induced by the expansion of expansive products and the generation of micro-cracks. Furthermore, the mortar immersed in sodium sulfate solution showed higher expansion and a larger hardened density than the mortar immersed in water. An increase in the concentration of the sodium sulfate solution was found to reduce the time needed to reach peak properties and to accelerate deterioration of the properties at the late stage.

Synthesis and structure modeling of ZnS based quantum dots

Quantum dots (QDs) based on zinc sulfide are synthesized by a microwave method in an aqueous medium using dioctyl sodium sulfosuccinate (DS) or 4,4′-bipyridine (BP). Based on the analysis of X-ray diffraction profiles the conclusion is drawn that QDs obtained have a structure of cubic zinc blende with an average particle size of 5.6 nm for the ZnSDS sample and 4.8 nm for ZnSBP. Transmission electron microscopy images show the presence of spherical aggregates of particles only for ZnSDS. FTIR data indicate the presence of sulfate ions in both samples; DS remains in the sample, facilitating the QD agglomeration, while BP is effectively washed out. From the optical diffuse reflectance spectra the band gap is estimated, which turns out to be larger than the expected one due to the presence of elemental sulfur in the samples and partial oxidation of the QD surface. The QD structure based on ZnS particles is also modeled in the work. The possibility to employ X-ray absorption near-edge spectroscopy for the verification of atomic structural parameters around zinc sites in QDs based on zinc sulfide is demonstrated.

Conserved methionine dictates substrate preference in Nramp-family divalent metal transporters

Natural resistance-associated macrophage protein (Nramp) family transporters catalyze uptake of essential divalent transition metals like iron and manganese. To discriminate against abundant competitors, the Nramp metal-binding site should favor softer transition metals, which interact either covalently or ionically with coordinating molecules, over hard calcium and magnesium, which interact mainly ionically. The metal-binding site contains an unusual, but conserved, methionine, and its sulfur coordinates transition metal substrates, suggesting a vital role in their transport. Using a bacterial Nramp model system, we show that, surprisingly, this conserved methionine is dispensable for transport of the physiological manganese substrate and similar divalents iron and cobalt, with several small amino acid replacements still enabling robust uptake. Moreover, the methionine sulfur's presence makes the toxic metal cadmium a preferred substrate. However, a methionine-to-alanine substitution enables transport of calcium and magnesium. Thus, the putative evolutionary pressure to maintain the Nramp metal-binding methionine likely exists because it-more effectively than any other amino acid-increases selectivity for low-abundance transition metal transport in the presence of high-abundance divalents like calcium and magnesium.

Microstructural Analysis of Corroded Carbon Steel Used in Process Equipment Handling Caustic Soda

Heat exchanger tubes and pipes made of carbon steel to handle aqueous solutions of spent caustic and crude caustic soda, respectively, at a petrochemical plant have prematurely sustained corrosion damage. Microstructural analysis of representative samples has been conducted using scanning electron microscopy combined with energy- and wavelength-dispersive spectroscopy and X-ray diffraction. It is shown that the tubes were corroded due to the presence of sulfate ions in the spent caustic solution. The corrosion damage sustained by the pipes has been related to the presence of carry over chloride ions in the caustic solution. It is concluded that for better performance, both media require the use of Ni or some Ni alloys rather than carbon steels.