Barium Concentrations Research Articles

Assessing the Contributions of Atmospheric/Meteoric Water and Sea Ice Meltwater and Their Influences on Geochemical Properties in Estuaries of the Canadian Arctic Archipelago

Salinity and stable oxygen isotope (δ18O) data collected from eight estuaries distributed throughout the Canadian Arctic Archipelago were used to apportion contributions from local meteoric water (MW) and sea ice meltwater (SIM) sources during July and August of 2015 and 2016. The size of the rivers flowing into the estuaries varied by an order of magnitude (in terms of mean annual discharge); however, the inventories of MW were always greater or equal to SIM inventories, indicating that MW was the dominant freshwater source. Residence times of MW generally ranged between 1 and 8 days, with longer times (> 20 days) computed for estuaries in the Somerset Island and Baffin Island regions. Shorter residence times indicate, but do not confirm, that river waters move through the estuaries and proceed offshore relatively quickly. Despite this swift transport, nonconservative behaviors were observed for barium and dissolved organic carbon (DOC). These behaviors were identified via examination of total alkalinity, barium, and DOC concentrations that remained after accounting for contributions from MW and seawater . Remaining concentrations/anomalies that deviated significantly from a linear correlation with SIM were attributed to nonconservative behaviors (e.g., desorption of barium from river-borne particles, remineralization of DOC) or inaccurate assignments of endmember values in the water type analyses. Thus, these anomalies offer a means to better inform water type analyses in the correct assignment of endmember properties that best represent the environment studied.

Surface chemistry of BSCF material after Ar+ ion treatment and at elevated temperatures

The microstructure and electronic structure of barium strontium iron cobalt oxide of nominal composition Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) was studied using Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Chemical states of the iron, cobalt, barium and strontium core levels were identified both from the surface and bulk material. The influence of low energy Ar+ ion bombardment on the electronic structure of the sample was studied. The SEM and XPS studies were executed at room temperature and after annealing in situ at temperatures up to 700 °C. The changes of the atomic concentration were found and were attributed to ion and thermal treatment. The clear differences of morphology were found for polished and in situ annealed surfaces. The loss of oxygen during cleaning by Ar+ ion sputtering was determined. The valencity of Co2+ was detected on the surface. The changes of atomic concentration of barium in relation to strontium indicated higher mobility of barium at elevated temperatures. The changes in conductivity of the surface layer upon Ar+ ion treatment and annealing at 700 °C was deduced from the valence band spectra.

Barium concentration, phytoavailability, and risk assessment in soil-rice systems from an active barium mining region

Barium (Ba) is a non-essential and toxic element. In China, intensive Ba mining and Ba salt manufacturing have led to sharp increases in Ba in the environment, but little information is available regarding Ba concentrations in paddy soil and rice. The total concentrations and phytoavailability of Ba in paddy soils and paired rice samples collected from the world's largest Ba mine in Dahebian, Tianzhu, Guizhou Province, southwestern China, were investigated. Risk assessments of Ba exposure via rice consumption were also evaluated. The results indicated that extremely high Ba concentrations existed in paddy soils, ranging between 518 mg/kg and 65,760 mg/kg, which demonstrated severe Ba contamination, as expected. The concentrations of rice Ba varied from 0.10 to 3.5 mg/kg, and a significantly positive correlation (r = 0.51, p < 0.05) between rice Ba and water-extractable Ba was observed, suggesting that water, rather than weak acid (0.43 M CH3COOH), chelating agents (DTPA) or neutral salts (0.1 M NaNO3, 0.01 M CaCl2 or 1 M NH4OAc), is a suitable extractant for predicting the phytoavailable Ba in the studied soils. Risk assessments showed that residents experienced low Ba exposure via rice consumption when considered in isolation of other sources in this study area.

Urinary and hair concentrations of trace metals in pregnant women from Northeastern British Columbia, Canada: a pilot study.

Northeastern British Columbia (Canada) is an area of intense natural gas exploitation by hydraulic fracturing. Hydraulic fracturing can release contaminants, including trace metals, many of which are known developmental toxicants. To date, there is limited data on human exposure to contaminants in this region. We aimed to examine trace metals in urine and hair samples from 29 Indigenous and non-Indigenous pregnant women from two communities (Chetwynd and Dawson Creek) in Northeastern British Columbia. We recruited 29 pregnant women who provided spot urine samples over five consecutive days and one hair sample. We measured 19 trace metals in pooled urine samples from each participant and in the first 2 cm of hair closest to the scalp. We compared urinary and hair concentrations to those measured in women from the general population using data from the Canadian Health Measure Survey (CHMS), or reference values found in the literature for trace metals not measured in the CHMS. Median urinary (0.49 μg/L) and hair (0.16 μg/g) concentrations of manganese were higher in our participants than in the CHMS (<0.05 µg/L in urine) or reference population (0.067 μg/g in hair). In hair, median values for barium (4.48 μg/g), aluminum (4.37 μg/g) and strontium (4.47 μg/g) were respectively 16, 3, and 6 times higher compared with median values in a reference population. Concentrations of barium and strontium in hair were higher in self-identified Indigenous participants (5.9 and 5.46 μg/g, respectively) compared to non-Indigenous participants (3.88 and 2.60 μg/g) (p-values = 0.02 and 0.03). Our results suggest higher gestational exposure to certain trace metals in our study population compared to reference populations.

Effect of barium doping on electrical and electromechanical properties of (1-x)(Na0.5Bi0.5)TiO3-xBaTiO3

&lt;p&gt;The effect of Barium doping is studied on ferroelectric properties of (1-x)(Na&lt;sub&gt;0.5&lt;/sub&gt;Bi&lt;sub&gt;0&lt;/sub&gt;.&lt;sub&gt;5&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt;-xBaTiO&lt;sub&gt;3&lt;/sub&gt; with( x = 0.00; 0.0 3; 0.05; 0.06; 0.07; 0.08 and 0.10) prepared through solid state sintering route. X-ray diffraction along with Rietveld refinement revealed a gradual change in crystal structure from rhombohedral to tetragonal with increasing BaTiO3 doping in the compound. SEM images have shown a uniform distribution of grains and change in grain size with BaTiO&lt;sub&gt;3&lt;/sub&gt; concentration. Dielectric and dispersive studies have been carried out. The rhombohedral distortion of the unit cell slightly increased and ferroelectric transition temperature, T&lt;sub&gt;m&lt;/sub&gt; decreased with the increase of Barium content and all compositions of (1-x)(Na&lt;sub&gt;0.5&lt;/sub&gt;Bi&lt;sub&gt;0&lt;/sub&gt;.&lt;sub&gt;5&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt;-xBaTiO&lt;sub&gt;3&lt;/sub&gt;ceramic materials reveal diffuse phase transition that is marked by a strong frequency dispersion of the permittivity which would be related with the cation disorder in the A site of the unit cell. Combined impedance and electrical propriety were used to analyze impedance data. The electromechanical parameters were calculated from the resonant and anti-resonant frequencies from the evolution of the permittivity according to the frequency plots. The electromechanical coefficients for (1-x)(Na&lt;sub&gt;0.5&lt;/sub&gt;Bi&lt;sub&gt;0&lt;/sub&gt;.&lt;sub&gt;5&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt;-xBaTiO&lt;sub&gt;3&lt;/sub&gt;with all compositions were found to be much larger than that of pure Na&lt;sub&gt;0.5&lt;/sub&gt;Bi&lt;sub&gt;0.5&lt;/sub&gt;TiO&lt;sub&gt;3.&lt;/sub&gt;&lt;/p&gt;

Room-temperature synthesis and optical properties of nanostructured Ba-Doped ZnO thin films

Abstract Zinc oxide films with and without barium-doping have been prepared by the SILAR technique at different concentrations (1 mol%, 3 mol%, 5 mol% and 7 mol%) of Ba content on glass slides. The effects of the concentration of barium doped zinc oxide (BaZnO) were characterized using x-ray difffractometry (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED) techniques, ultraviolet–visible spectroscopy and photoluminescence (PL) studies. The structural studies using XRD plots confirmed the polycrystalline nature of ZnO films. The Ba doped ZnO films deposited were found to have strong orientation at (002) lattice plane which exhibited polycrystalline hexagonal wurtzite structure. TEM and SAED results confirmed the morphological and structural properties of the films. The SEM showed that the grain size of the films increased as a result of increase in the concentration of barium doping. EDX results confirmed the elemental presence of the films. An increase in the Ba concentration showed a decrease in the optical band gap values between 3.41 eV and 3.19 eV. PL studies confirmed the presence of defects in the ZnO films.

Reference Values for Healthy Swallowing Across the Range From Thin to Extremely Thick Liquids.

PurposeThickened liquids are frequently used as an intervention for dysphagia, but gaps persist in our understanding of variations in swallowing behavior based on incremental thickening of liquids. The goal of this study was to establish reference values for measures of bolus flow and swallowing physiology in healthy adults across the continuum from thin to extremely thick liquids.MethodA sex-balanced sample of 38 healthy adults underwent videofluoroscopy and swallowed 20% weight-to-volume concentration barium prepared in thin and slightly, mildly, moderately, and extremely thick consistencies using a xanthan gum thickener. Participants took comfortable sips and swallowed without a cue; sip volume was measured based on presip and postsip cup weights. A standard operating procedure (the ASPEKT method: Analysis of Swallowing Physiology: Events, Kinematics and Timing) was used to analyze videofluoroscopy recordings.ResultsThe results clarify that, for thin liquid sips (10–14 ml), a single swallow without clearing swallows is typical and is characterized by complete laryngeal vestibule closure, complete pharyngeal constriction, and minimal postswallow residue. Aspiration was not seen, and penetration was extremely rare. Bolus position at swallow onset was variable, extending as low as the pyriform sinuses in 37% of cases. With thicker liquids, no changes in event sequencing, laryngeal vestibule closure, pharyngeal constriction, or postswallow residue were seen. The odds of penetration were significantly reduced. A longer timing interval until onset of the hyoid burst movement was seen, with an associated higher bolus position at swallow onset. Other timing measures remained unaffected by changes in bolus consistency.ConclusionThe results include new reference data for swallowing in healthy adults across the range from thin to extremely thick liquids.

Development of an In-Field Method for the Detection of Barium in Various Water Samples Using Differential Pulse Anodic Stripping Voltammetry

This work presents a reliable, cost-effective, rapid and in-field voltammetric method for the detection of barium. The optimized method consists of an ultrathin mercury film deposited in situ on a glassy carbon electrode in dilute potassium chloride without deoxygenation, using differential pulse anodic stripping voltammetry (DP-ASV). Application of the method allowed for the quantitative determination of barium concentration in a variety of waters and brake pad dust samples. Comparative analysis of sample results from DP-ASV with inductively coupled plasma mass spectroscopy (ICP-MS) showed a mean percent difference of 1.8%.

What caused Earth's largest mass extinction event? New evidence from the Permian-Triassic boundary in northeastern Utah

Abstract The discovery of a Permian-Triassic boundary section in northeastern Utah provided an opportunity to study the chemistry and geology associated with this event that led to one of the greatest mass extinctions on the planet. From 83% to 97% of the species living on the planet went extinct during this relatively short interval of geological time that defines the major geological boundary between the Paleozoic and Mesozoic Eras. The cause and resulting sequence of events that led to this extinction have puzzled geologists for years. The new stratigraphic section in Utah provided a framework for reconstruction of the chemistry that was in the ocean during the mass extinction. Geochemical analysis of the section demonstrates, moving across the boundary from the Paleozoic to the Mesozoic, a significant drop in carbonate and total organic carbon, and a delayed occurrence of pyrite. Carbon isotope ratios (δ13C) show a negative excursion in carbonate with ratios dropping from 2.59‰ to −3.63‰. Elevated mercury is present at the boundary with a 4-fold increase from background levels. The boundary layer also has elevated zinc, lead, strontium, and nickel, but not at high enough levels to indicate a volcanic ash source. There is no evidence in concentrations of siderophile and chalcophile elements for an extraterrestrial impact. The stratigraphic section in Utah supports the theory of a massive release of carbon dioxide, resulting in the acidification of the oceans. High levels of mercury, as well as elevated levels of zinc and lead, implicate a coal source triggered by the contemporary Siberian Traps sill complex. The delay of enriched sulfur and barium content in the stratigraphic record indicates an anoxic ocean and upwelling of methane hydrates from depth. Further study of this stratigraphic section will aid our understanding of the global impact these catastrophic events had on life.

A comparative study of the co-precipitate synthesis of barium-calcium-aluminates impregnants for dispenser cathodes by using different precipitants

Abstract In order to optimize the synthesis process of barium-calcium-aluminate (BCA) for the application of impregnated dispenser cathodes, the influence of two precipitants, ammonium carbonate (AC) and ammonium hydrogen carbonate (AHC), on the chemical composition, phase transformation, thermal behaviors and morphology of the precursors was systematically investigated by means of XRD, TG-DSC, FESEM, and EDS mapping analysis. The results revealed that AC precipitant facilities to form NH4Al (OH)2CO3 (AACH) phase and barium calcium carbonate in the precursor, while the product precipitated by AHC comprises amorphous γ-AlOOH phase and the carbonate. Both precursors precipitated by the AC and AHC undergo various stages of phase transformations and finally converted to an emission-active material Ba3CaAl2O7 phase after sintering at 1200 °C. DC emission current values have been measured and the maximum space charge limited current densities are 8.0 ± 0.3 and 6.5 ± 0.4 A/cm2 at 1130 °Cb for the testing cathodes impregnated with the AC and AHC precursor aluminates, respectively. The difference in the emission capacity originates from the barium content in the aluminates prepared with different precipitants.

Toxicological Evaluation of Thermal Treatment of Drilling Waste from Shale Gas Exploration in Poland

Abstract The oil containing drilling waste is a worldwide environmental problem associated with oil and gas exploration. In Poland, the problem of the drilling waste has become important since starting of shale gas exploration. The results of thermal treatment of drilling waste from shale gas exploration are presented. It has been shown that organic content vaporized completely at temperature up to 500 °C. The main problem is high content of chloride, sulfate, sodium, potassium, magnesium in the waste and its water leachate. Toxicity tests confirmed that high salinity of the samples pose important risk for environment. Due to the high content of barium, the drilling waste may be utilized in production of cement with high chemical and heat resistance and opaque to X-ray. Thermal treatment process is a viable option for remediation of the drilling waste; however, the product of the process needs further treatment in order to remove its high salinity.

Electrodialysis of concentrated brines: Effects of multivalent cations

Electrodialysis is an electrochemically driven membrane technology usually used for treating feed water containing several thousand mg/l total dissolved solids (TDS). This research investigated the use of conventional ED for the treatment of flowback water from shale gas hydraulic fracturing that contains up to tens of thousands of mg/l TDS and contain a mixture of multivalent cations. This paper discusses efforts to treat concentrated brines with electrodialysis and focuses on the mitigation of the detrimental effects of multivalent cations such as calcium, magnesium, barium, iron, and in the feedstock. A previous paper detailed the effects of calcium under defined lab conditions. The apparent calcium fouling (in and around) the electrode cells was mitigated by changing the single cathode chamber boundary membrane to a (CMX-S) that was more selective for monovalent cations. This paper covers efforts undertaken to mitigate problems associated with high concentrations of calcium, barium, iron, and magnesium. Four field samples of produced water from oil and gas operations in from the Marcellus shale formation (generally Pennsylvania, USA) and the Barnett shale formation (generally north central Texas, USA) were also tested. These results from field samples were similar to the results from lab defined tests. Mechanisms of process interference by the different multivalent cations appear different for each species. Calcium, magnesium, barium, and iron were preferentially transported from the diluate to the concentrate compared to sodium by a factor of about 1.4:1 on a charge basis resulting in a suppression of the flux of sodium to the concentrate. A single CMX-S membrane selective for monovalent cations was placed at the cathode barrier resulting in a reduced flux of calcium, magnesium and barium into the electrode rinse. However total ion flux was inhibited caused by apparent blockage of the cation transfer sites on the CMX-S membrane by the stagnant multivalent cations. A series of tests with periodic pulse polarity-reversal (anode and cathode reversed for a brief time) indicted the blockage by calcium and barium was immediately reversable, however, iron was more problematic and may have precipitated on membrane surfaces other than the cathode barrier.

Health risk assessment of potentially toxic elements in soils along the Central Elbe River, Germany

Floodplain soils across Central Elbe River (CER), Germany, vary considerably in potentially toxic element (PTE) content. However, there has never been a comprehensive study that links PTE levels with human health risk for children and adults. Our objective was to determine the contamination of 13 PTEs in 94 soil profiles along CER and assess the associated health risk via diverse indices for adults and children. Of 94 soil profiles, we measured soil properties and total content of arsenic, barium, chromium, copper, nickel, lead, rubidium, tin, strontium, vanadium, zinc, and zirconium using x-ray fluorescence spectrometer (XRF). We calculated the Contamination Factor and the Pollution Load Index (PLI), and assessed the health risk for male and female adults as well as for children. Topsoil median contents of Cr (84 mg kg−1), Cu (42), Ni (33), and Zn (195) exceeded the Precautionary Values for sandy soils according to the German Federal Soil Protection and Contaminated Sites Ordinance, while As, Pb, and V were 32, 73, and 77 mg kg−1, respectively. Median topsoil PLI was 1.73, indicating elevated multi-element contamination, with 90th percentile and maximum values being 3.20 and 4.31, respectively. All PTE concentrations were higher in top- compared to subsoils. Also at the 50th percentile the most enriched elements were Sn and As, followed by Zr and Rb, while in the 90th percentile Sn and As were followed by Zn, Pb and Cu. Median children's hazard index (HI) was higher than unity (HI = 2.27) and the 90th percentile was 5.53, indicating elevated health risk. Adult median HIs were 0.18 for male and 0.21 for female persons. Arsenic was found to be the primary contributor to total risk, accounting of 57.4% of HI in all three-person groupings, with Cr (17.3%) being the second, and V (10.2%) the third. Children's health is at dramatically higher risk than that of adults; also As, Cr, Pb, and V have a predominant role in contamination-related health risks. The presence of V, a less-expected element, among those of major risk contribution, reveals the necessity of monitoring areas at large scale. Our results demonstrate that our study may serve as a model for similar works studying multi-element-contaminated areas in future.

The effect of barium content on the crystallization and microhardness of barium fluormica glass-ceramics

Mica glass-ceramics are easily machined due to their “House-of-Cards” microstructure. Barium fluormica glass-ceramics were developed and indicated good mechanical properties. This work studies the effect of varying barium content on the crystallization and microhardness of mica glass-ceramics. Four glasses were produced with different baria contents, then converted to mica glass-ceramics using a two-step heat treatment. They were characterized using Differential Scanning Calorimetry [DSC], X-ray Diffraction [XRD], Scanning electron microscopy [SEM] and Vickers microhardness. DSC showed some formulations indicated bulk crystallisation as the dominant mechanism. XRD showed the crystallization of Barium fluorphlogopite in all the compositions with minor secondary phases. SEM showed the formation of “House-of-Cards” microstructures and with an increase in BaO content, a decrease in contrast was observed in back scattered mode. Exceptionally low hardness values (<2 GPa) were obtained for longer heat treatments/holding times and are related to the well-developed house-of-cards microstructures formed.

The analysis of the possibility of using biological tests for assessment of toxicity of leachate from an active municipal landfill

One of the consequence of municipal waste deposition is the production of landfill leachate. Its volume and composition is determined by numerous factors, including waste composition, landfill age and the volume of precipitation. Leachate may contain a number of mineral and organic compounds, the volume of which must be controlled regularly. One of the methods of determining the toxicity of substances contained in landfill leachate is the use of biological tests, based − among others − on aquatic organisms sensitive to environmental contamination. The purpose of this study was to analyse the possibility of using ecotoxicological tests (supplementing the physical and chemical tests) for the purpose of assessment of landfill leachate toxicity. The tests were conducted at an operating municipal landfill in Stary Sącz (southern Małopolska Region, Poland N: 49°55’33”76, E: 20°65’68’70) from December 2015 to October 2016. The scope of the tests included the analysis of physical and chemical indicators as part of the landfill monitoring process, and also the analysis of additional selected indicators: namely the boron, barium and vanadium content. The selected ecotoxicological tests included tests using Daphnia magna Straus (Cladocera, Crustacea).Leachate tests conducted with the use of physical and chemical indicators have, for nearly twenty years, mainly demonstrated changes related to the age of the used landfill; besides increased boron and barium values, no evident contamination has been found, excluding the case of boron. However, a statistically significant correlation between the B and Ba contents and the amount of precipitation was determined. In two cases, the used biological tests have confirmed the toxicity of the leachate: in January and June 2016. In the same months, the highest and abnormal boron contents were measured, which could cause a toxic effect of leachates.

Elevated Barium concentrations in rain water from east-coast of India: role of regional lithology

Alkaline earth metals act as dominating acid-neutralizing species in atmosphere and hence, regulate the rain water chemistry significantly. In this contribution, concentrations of these metals (Mg, Ca, Sr and Ba) and other major ions in rain water samples, collected during south-west monsoon of year 2017, from a coastal location (Berhampur) in eastern part of India have been analyzed to trace their provenances and controlling factors. The chemical compositions of rain water reveal oceanic and continental supply of Mg and Sr to the site, whereas Ca and Ba are pre-dominantly supplied through continental sources. The dominancy of continental fluxes at this coastal site is mainly due to particulate fluxes from regional lithologies and favorable wind pattern for long-range transport from south-western/western directions. An inverse model involving chemical mass balance between rain water composition and its possible sources have been adopted in this study to quantify the source(s) contributions. These model results show that the continental Mg is mainly derived from long-range transport of mafic minerals from Deccan Traps (40 ± 21%) with sub-ordinate contribution (15 ± 6%) from regional lithologies. On average, about 70% of rain water Ca at Berhampur is derived from carbonates, whereas most of the Ba (~95%) is supplied from regional silicates (charnockites and khondalites). Owing to faster dissolution kinetics of these silicates with higher Ba content, the silicates contribute most of the rain water Ba concentration over this region. The median Ba content (29 nM) at this location is systematically higher than available literature Ba data for rain water worldwide (1-22 nM). The observed higher concentrations of Ba, a micronutrient, in rain water emphasize important role of regional lithology in the biogeochemical cycling of nutrients over the region via wet deposition.

Is the Cooking Salt Safe in China? Assessment of Chemical Contaminants in Cooking Salt.

Global environmental pollution is becoming more serious, and most dietary salts come from nature. We postulated that chemical pollutants could affect the quality of salt. Forty-five different types of salt were collected from supermarkets, convenience stores, and online retailers in Shanghai, 2015. These comprised more than 90% of all cooking salts consumed in Shanghai, China. We measured and analyzed heavy metal elements, fluoride, potassium ferrocyanide, and 16 phthalate plasticizers. Lead was detected in only two types of salt at concentrations recorded of 0.047mg/kg and 0.077mg/kg. The concentrations of total arsenic, total mercury, cadmium, and barium were under limit of detection (LOD) in all samples. The maximum fluoride concentration of salts was 2.50mg/kg. The median fluoride concentration of domestic salts was significantly lower than foreign-produced salts, and it was significantly higher in sea salt than in other types of salt (P < 0.05). The maximum potassium ferrocyanide concentration in 12 types of salts was 9.20mg/kg, which was under the Chinese national standard. Just three salt types had low levels of diethylhexyl phthalate concentrations that were above the LOD, at 0.208mg/kg, 0.375mg/kg, and 0.380mg/kg, respectively. All other phthalate indicators were below the LOD in all samples. The level of chemical pollutants in salt is either very low or under LOD. We believe that dietary salt products are safe at retail, and the long-term dietary exposure of cooking salts will not pose any significant health risk.

Solid-state transformation of (NH4, Ba)-clinoptilolite to monocelsian, mullite, and cristobalite

Abstract Three clinoptilolite-based materials, with Ba2+/NH4+ ratios of 2.27, 0.60 and 0.11, were prepared starting from a powder containing about 90% of NH4-clinoptilolite. The samples were submitted to thermal treatments of 2 h up to 1200 °C. Further treatments were carried out at 1100 and 1200 °C for 4, 8, 16 and 32 h. The sequence of reactions observed in heating (NH4, Ba)-clinoptilolite is: dehydration; de-ammoniation (along with residual dehydration); dehydroxylation; amorphization; crystallization of new phases. Amorphization temperature varied from 700 to 900 °C, and increased with barium content. Monocelsian, mullite and cristobalite/tridymite were obtained from all samples heated 32 h at 1100 °C, along with residual glass that never exceeded 9%. The Ba2+/NH4+ ratio resulted the main factor in determining type and quantity of the phases formed in the fired products, as well as their order of crystallization, but also temperature and duration of treatment affected the result. At 1100 °C mullite crystallized as last phase in the Ba-rich sample, and it did not form at 1200 °C. Similarly, celsian was never obtained at 1200 °C from the ammonium-rich material, and was the last phase to crystallize at 1100 °C. Transformations were faster at 1200 °C, but the amounts of residual glass were higher. Hexacelsian, the metastable polymorph of Ba-feldspar which is always formed during the heating of Ba-exchanged zeolites A and X, was never recorded among crystallization products obtained from (NH4, Ba)-clinoptilolite.

APPLICATION OF ZSM-5 AND ZSM-12 ZEOLITES (IN SODIUM AND AMMONICAL FORMS) IN THE BARIUM ADSORPTION

Heavy metals are often released into aquatic environments through various sources of industrial processes. However, conventional treatment technologies demand high cost and/or are inefficient for the recovery of these resources. In this context, the technical application of adsorption has been highlighted by its simplicity and practicality, especially when zeolites are used as adsorbents due to their excellent physicalchemical and textural properties, among them: their high availability, high selectivity and low cost. The present work characterized and evaluated the performance of Na-ZSM-5, Na-ZSM-12, NH4-ZSM-5 and NH4-ZSM-12 zeolites on barium adsorption as an alternative for the treatment of produced water. The Na-ZSM-5 and Na-ZSM-12 zeolites were synthesized by the hydrothermal method and subjected to ion exchange to obtain the ammoniacal form (NH4-ZSM-5 and NH4-ZSM-12). The characterization was done by: DRX, SEM, FRX and Adsorption / Desorption of Nitrogen, and barium concentration was measured by Atomic Absorption Spectroscopy (AAS). The adsorption studies were conducted under agitation at the times of 1, 6, 12 and 24 h. The results were promising for this application, because the Na-ZSM-5 zeolite presented the highest adsorption capacity, a fact related to its textural properties (volume and area of micropores).

The impact of Ba substitution in lanthanum‑strontium ferrite on the mobility of charge carriers

The effect of barium content on the mobility of oxygen ions and that of electronic charge carriers in La0.49Sr0.5–xBaxFeO3–δ (x = 0, 0.25, 0.50) was studied by means of electrical conductivity modeling with the use of the results of the conductivity and oxygen content measurements depending on the partial pressure of oxygen in the gas phase. In accordance with the simulation results, an increase of oxygen content in oxides leads to increased mobility of p-type charge carriers, while it does not affect the mobility of n-type charge carriers. An increase in barium content has been shown to result in decreasing the mobility of all charge carriers. The mobility of electrons, holes, and oxygen ions has been found to be decreased at 950 °C by factors of 1.9, 2.4, and 2.7, respectively, as a result of half of the strontium substitution with barium. A negative effect of barium on the mobility of electronic charge carriers is believed to be conditioned by a FeO bond elongation. A decrease in the mobility of oxygen ions occurs mainly due to local distortions of the crystal lattice near large barium ions. The average mobility of holes in oxides has been found to be about twenty times higher than that of electrons. Such a strong difference is explained by a difference in the electronic configuration of iron ions responsible for the transfer of holes and electrons.