Effects of nitrate and water on the oxygen isotopic analysis of barium sulfate precipitated from water samples

BaSO₄ precipitated from mixed salt solutions by common techniques for SO isotopic analysis may contain quantities of H₂O and NO that introduce errors in O isotope measurements. Experiments with synthetic solutions indicate that δ¹⁸O values of CO produced by decomposition of precipitated BaSO₄ in a carbon reactor may be either too low or too high, depending on the relative concentrations of SO and NO and the δ¹⁸O values of the H₂O, NO, and SO. Typical δ¹⁸O errors are of the order of 0.5 to 1‰ in many sample types, and can be larger in samples containing atmospheric NO, which can cause similar errors in δ¹⁷O and Δ¹⁷O. These errors can be reduced by (1) ion chromatographic separation of SO from NO, (2) increasing the salinity of the solutions before precipitating BaSO₄ to minimize incorporation of H₂O, (3) heating BaSO₄ under vacuum to remove H₂O, (4) preparing isotopic reference materials as aqueous samples to mimic the conditions of the samples, and (5) adjusting measured δ¹⁸O values based on amounts and isotopic compositions of coexisting H₂O and NO. These procedures are demonstrated for SO isotopic reference materials, synthetic solutions with isotopically known reagents, atmospheric deposition from Shenandoah National Park, Virginia, USA, and sulfate salt deposits from the Atacama Desert, Chile, and Mojave Desert, California, USA. These results have implications for the calibration and use of O isotope data in studies of SO sources and reaction mechanisms. Published in 2008 by John Wiley & Sons, Ltd.     

Preconcentration and spectrophotometric determination of chromium(vi) in natural waters by coprecipitation with barium sulfate

A selective preconcentration of chromium(VI) is proposed for analysis of natural waters. Chromium(VI) is quantitatively separated from chromium(III) by coprecipitation with barium sulfate; salicylic acid is used as a masking agent for iron(III), aluminum(III) and chromium(III). The precipitate is fused with alkali carbonate, and the chromium(VI) in the melt is isolated with hot water and determined spectrophotometrically with diphenylcarbazide. The detection limit is 0.02 μg l^-1 the relative standard deviation for chromium(VI) in river water is less than 5%.     

Note on the coprecipitation of barium and lead selenates

Analytical and Bioanalytical Chemistry -     

The role of the cation in the oxygen isotopic exchange in crystalline sulfate salt hydrates

The oxygen isotopic exchange during dehydration and decomposition of five sulfate salt hydrates (CoSO₄·6H₂O, NiSO₄·7H₂O, ZnSO₄·7H₂O, CaSO₄·2H₂O, Li₂SO₄·H₂O) was studied in detail by temperature programmed desorption mass spectrometry (TPD-MS) in a supersonic molecular beam (SMB) inlet mode. Crystals of the ¹⁸O-enriched salts were grown and the detailed desorption steps of the various gaseous products released during dehydration and decomposition of these compounds were recorded. The desorption patterns confirmed the known characteristic stepwise dehydration of these salts, where regardless of the crystalline structure and composition, in all the salts (excluding the Li and Ca sulfates) a major group of n ? 1 loosely bounded water of crystallization molecules (out of total of n molecules in the fully hydrated form) are released at adjacent temperatures in a typical low temperature range (<200 °C), while the last, most strongly bounded water molecule, consistently desorbs at relatively higher temperatures (240 < T < 440 °C). Interestingly, it is established that the oxygen isotopic exchange occurs exclusively between that latter, most strongly bound water molecule, and the salt anion. Remarkably, the results point out that the exchange process is mostly of solid-solid nature. Finally, the results point out that the probability of the isotopic exchange increases with the increment in the desorption temperature of the last dehydration step, i.e. with the bond strength in the monohydrate, between the last water molecule of crystallization and the cation.     

Separation of dissolved alkyllead and inorganic lead species by coprecipitation with barium sulphate

Coprecipitation with barium sulphate is shown to be an efficient and convenient method of preventing the interference of relatively large amounts of inorganic lead in the determination of alkyllead species by differential-pulse anodic stripping voltammetry. The coprecipitation method has several advantages over complexation of lead with EDTA; ionic alkyllead can be measured in solutions of low pH (pH < 2), or at deposition potentials more negative than ?1.0 V.     

酸碱滴定法间接测定重晶石中的硫酸钡

利用偏磷酸与重晶石在400℃时的复分解反应，将硫酸钡转化为聚偏磷酸钡，同时生成的H2SO4在高温下可挥发除去。在强碱性溶液和过氧化氢的作用下，聚偏磷酸钡转化为有确定磷钡比的磷酸钡。将磷酸钡用盐酸溶解后，在CaCl2存在下，以甲基红和酚酞为指示剂，用氢氧化钠标准溶液滴定磷酸，以间接测定重晶石中硫酸钡的含量。本法所需时间6h，分析结果与标准方法（SN／T0480．5－95）吻合，RSD为0．33％－0．68％。     

Measurements in the ultraviolet region of apparent absorption by barium sulfate sols

Absorbance measurements in the ultraviolet have been shown to be useful for following changes with time in the average particle size of barium sulfate sols. The effects of the method of adding the barium chloride, a change in the temperature, the presence of 1.00M calcium chloride and the percentage of ethanol in the solution have been examined as a function of time. By measuring the apparent absorbance of barium sulfate sols in 10 cm cells, sulfate can be determined in the range of 2.5–10.0 μg per ml. This is a range which, in the past, has had to be handled by nephelometry.     

Phase composition of aluminum-zirconium oxide nanocrystals prepared by electrochemical coprecipitation

Phase transitions in aluminum-zirconium oxide nanocrystals prepared by coprecipitation in the anode compartment of a membrane electrolyzer are investigated by X-ray diffraction, differential thermogravimetry, and differential scanning calorimetry. The influence of the coprecipitation conditions (pH and temperature) on the chemical and phase composition of the synthesized systems is studied.     

Purification of potassium nitrate solutions by coprecipitation of impurities on hydrated aluminum oxide

Coprecipitation of 3d-element impurities from potassium nitrate solutions on hydrated aluminum oxide was studied. The efficiency of the process was examined in relation to the weight of the collector, the solution-collector contact time, pH of medium, concentration of microimpurities, and presence of oxidant. The parameters for efficient purification of potassium nitrate solutions were determined.     

磷酸铈共沉淀分离富集硫酸钴中痕量铅及铅的原子吸收光谱测定

提出了用磷酸铈(CePO4)作为共沉淀捕集剂分离富集CoSO4溶液中的痕量Pb2+,用火焰原子吸收光谱(FAAS)测定的方法。共沉淀效率受pH、Ce(NO3)3和H3PO4溶液用量的影响。结果显示,在溶液pH3.0～4.0时,CePO4能够定量共沉淀CoSO4溶液中的Pb2+,对于20mL的样品溶液,方法的检出限为5.59×10-2mg/L,铅的标准加入回收率为98.32%,排除了基体干扰,取得了较为满意的结果。     

Coagulation of silver halide sols by thorium nitrate in the presence of potassium nitrate and potassium sulfate

Summary When silver iodide, silver bromide and silver chloride solsin statu nascendi are coagulated by thorium nitrate in the presence of potassium nitrate, three coagulation maxima appear. Two of them are identical with maxima that are found in absence of KNO₃, denoted with (II) and (IV) in fig. 1. The new maximum appears in the stability region of recharged sols (III). It is believed that this maximum is also—as maximum (IV)—caused by the coagulation of recharged silver halide sols by nitrate ions. Appearance of two nitrate coagulation maxima is explained by different charge densities on sol particles at various concentrations of Th(NO₃)₄ where they are formed. The new maximum indicates a lower charge density of sol particles. The possibility that the new maximum could have been caused by ionic complex species between thorium and nitrate ions has been rejected for data are available that the equilibrium constant for such complexes is small. In the presence of K₂SO₄ the coagulation effects of thorium nitrate on silver halide sols are markedly different. In acidified solutions only one coagulation maximum appears at rather high thorium nitrate concentrations [∼ 10⁻³ N Th (NO₃)₄] and the sol remains negatively charged [up to ∼ 10⁻² N Th (NO₃)₄] This is explained by complex formation of Th-ions and sulfate ions whereby ionic species of lower charge are formed, which exert a weaker coagulation effect. In neutral solutions another maximum at lower concentration of Th (NO₃)₄ is formed which appears to be the usual coagulation maximum produced by hydrolyzed thorium ions. The antagonistic effects of the salt pair Th (NO₃)₄-K₂SO₄ upon the coagulation of silver halides has been discussed and we have concluded that the large effects repeatedly reported can be explained not by simple electrostatic effects of ions in solution but rather by the formation of complexes between Th- and SO₄-ions.

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Zusammenfassung Die Koagulationseffekte des Thoriumnitrats in Anwesenheit von Kaliumnitrat und Kaliumsulfat an Silberhalogenid-Solenin statu nascendi wurden ausführlich untersucht. Wenn Silberhalogenid-Sole durch Thoriumnitrat-L?sungen koaguliert werden, bilden sich zwei Koagulationsmaxima (II und IV, Abb. 1). Bei sehr niedrigen Konzentrationen des Thoriumnitrats koaguliert das Thorium-Ion (oder Komplex) die negativen Silberhalogenid-Sole, w?hrend bei h?heren Thoriumnitrat-Konzentrationen die ungeladenen Sole durch die NitratIonen koaguliert werden. Zwischen den zwei Maxima besteht ein weites Gebiet der stabilen umgeladenen Sole (III). Unter dem Zusatz von konstanten Mengen des Kaliumnitrats wird in diesem Gebiet ein neues (drittes) Maximum gebildet (Abb. 2–5), das auch als Koagulationsmaximum identifiziert wurde. Es wird angenommen, da? dieses Maximum wieder eine Koagulation der umgeladenen Silberhalogenid-Sole durch Nitrat-Ionen darstellt. Das Auftreten von zwei Koagulationsmaxima, verursacht durch Nitrat-Ionen, wird durch die verschiedenen Ladungsdichten an Solteilchen in Gebieten der Thoriumnitrat-Konzentrationen, in denen Maxima erscheinen, erkl?rt. Die M?glichkeit eines Koagulationseffektes der komplexen Ionen zwischen Thorium und Nitrat wurde ausgeschlossen, da die Gleichgewichtskonstante solcher Komplexe ziemlich niedrig ist. In Anwesenheit von Kaliumsulfat sieht die Koagulationskurve für Silberhalogenid Sole sehr unterschiedlich aus (Abb. 6–8). In den mit Salpeters?ure (0,001N) versetzten Solen erscheint nur ein Maximum bei ziemlich hohen Thoriumnitrat-Konzentrationen [∼ 10⁻³ N Th (NO₃)₄], wobei die Solteilchen noch immer negativ sind. Da Thorium- und Sulfat-Ionen sehr stabile Ionen-Komplexe bilden, die eine niedrigere Valenz aufweisen, kann das Maximum als Folge der Koagulationseffekte solcher Komplexe an die Silberhalogenid-Sole angesehen werden. In neutralen L?sungen zeigt sich neben dem beschriebenen Maximum noch ein anderes Maximum bei niedrigerer Thoriumnitrat-Konzentration. Dieses Maximum, hervorgerufen durch die hydrolysierten Thorium-Ionen, scheint das „normale“ Koagulationsmaximum zu sein. Dieantagonistischen Effekte des Salzpaares Th (NO₃)₄-K₂SO₄ bei der Koagulation der Silberhalogenide wurden diskutiert, und es wurde geschlossen, da? die gro?en Effekte, die wiederholt ver?ffentlicht worden waren, sehr schwer nur durch die elektrostatischen Anziehungen zwischen den Ionen erkl?rt werden k?nnen. Die Komplexbildung zwischen Thorium- und Sulfat-Ionen wird für den sogenannten antagonistischen Effekt in diesem Falle als verantwortlich angesehen.

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Supported in part by U.S. Atomic Energy Commission Contract No. AT (30-1)-1801.     

Indirect determination of thionic compounds by nephelometric determination of barium sulfate

The indirect determination of thionic compounds by nephelometric determination of barium sulfate, formed after treatment of the compounds containing the group CS with potassium permanganate in neutral aqueous solutions, has been studied. Allylthiourea, thiourea, thioacetamide and thiosemicarbazide have been tested. The determination limit was 0.05 g/ml and the RSD less than 10%.     

Catalytic effect of zinc oxide on the reduction of barium sulfate by methane

Reduction of barium sulfate by methane was investigated in this work. The thermogravimetric method was used to obtain kinetic parameters of the reaction in the temperature range of 900–975 °C at atmospheric pressure. The kinetics of the reaction has been studied both in the absence and presence of zinc oxide as a catalyst. The conversion–time data have been interpreted by using the grain model, and the effect of catalyst on the kinetic parameters has been elucidated. It was found that zinc oxide acted as fairly strong catalyst for the reaction, especially at higher temperatures. At about 975 °C the reaction rate constant was increased more than 7 times by using 2% of zinc oxide. This enhancement in the rate constant is valuable for industries.     

Recrystallization of 223Ra with barium sulfate

In this work, the kinetics of barium sulfate recrystallization has been studied in acidic 0.01 mol dm^?3 sodium sulfate solution using ²²³Ra and ¹³³Ba tracers at very low total radium concentration, i.e. less than 10^?13 mol dm^?3. It was found that the system follows the homogeneous recrystallization model and that recrystallization rates, inferred by the decrease of ²²³Ra and ¹³³Ba in the aqueous solution, are fast. Therefore, even at very low concentrations, below the solubility limit, radium will be retained by barium sulfate—a mineral present in the deep underground repository.     

The interaction of EDTA with barium sulfate

Ethylenediaminetetraacetic acid (EDTA) is a known complexing agent that interacts with a host of cations. In this paper, various techniques are used to elucidate the mechanism of interaction between EDTA and barium sulfate surfaces. It is shown that complexation with metal ions is not sufficient to explain the inhibition of barite crystallization but that other processes such as chemisorption must also occur. EDTA is shown to always adsorb as the mono-protonated species - suggesting that the molecule is able to lose a proton when it adsorbs at lower pH. Molecular modelling shows that the interaction of the surface barium ions with the carboxylate group is an important one. Finally, in situ turbidity measurements provide information about the mechanism of nucleation/growth modification. It is found that the EDTA molecule inhibits barium sulfate nucleation and that this could be its primary means of inhibiting precipitation of barium sulfate.     

Investigation of the oxygen isotopic composition in oxidic uranium compounds as a new property in nuclear forensic science

The analysis of seized nuclear material aims at identifying the origin of the material. Determination of the n(18O)/n(16O) ratio for the uranium oxide adds another characteristic property to the pattern which enables location of the production area of the material. A method has been developed for n(18O)/n(16O) ratio measurement which uses thermal ionization mass spectrometric (TIMS) analysis of the 238UO+ species. It has been shown that uranium oxides of different geographic origin have significantly different n(18O)/n(16O) ratios, whereas different samples of the same origin have constant oxygen isotopes ratios.