Sorption of strontium and fractal scaling of the heterogeneous media in a candidate VLLW disposal site

Because of the deposit and accumulation from the debris flow, the heterogeneous geological characteristics is obvious for a candidate very low level waste (VLLW) disposal site, with the grain size ranging from tens of microns to 75 cm. Therefore, it is challenging to directly measure the sorption capacity of the media and the distribution coefficient of some radionuclides, such as strontium. We have studies the correlation of the particle mass content with different grade size and the sorption capacity, which is important in the modeling of radionuclide migration in the heterogeneous disposal site. A total of three deep pits and five shallow trenches were excavated, and 21 solid samples were collected for laboratory experiments. The grade and percentage of the different-sized particles were obtained, and the fractal dimension (D) of the media was calculated from the results of sieved experiments. Steady state sorption time and sorption isotherm of strontium was determined in the heterogeneous media, and sorption and distribution of strontium in the heterogeneous media were evaluated by the relationship between the mass percentage and distribution coefficient (K _d) of the fine-particle media, which was comprised of selected particles with a diameter less than 1 mm, and the correlation on the K _d and D was regressed fit. The results indicated that fractal dimension bounded from 2.39 to 2.62 in the media, and K _d values of strontium ranged between 119 and 126 in the fine-particle media, and corresponding value was 11 and 43 in the original media. The correlation between K _d and D was approximately linear.     

Transport and retention of strontium in surface-modified quartz sand with different wettability

Instead of radioactive ⁹⁰Sr, common strontium chloride was used to simulate the migration of radioactive strontium chloride in surface hydroxylated, silanized, and common quartz sand. The sorption and retardation characteristics of strontium (Sr²⁺) in these surface modified quartz sands were studied by batch tests and column experiments. The equilibrium sorption data for Sr²⁺ on different wettability sands were described by the Langmuir and Freundlich isotherm models, and the Langmuir model has been found to provide better correlation for hydrophilic sand. The breakthrough curves (BTCs) of Sr²⁺ in these media were analyzed with the equilibrium convection–dispersion equation (CDE) and a non-equilibrium two-region mobile–immobile model (TRM) using a nonlinear least square curve-fitting program CXTFIT. The TRM model showed better fit to the measured BTCs of Sr²⁺, and the parameters of the fraction of mobile water indicated that significant preferential flow effected the non-equilibrium transport of Sr²⁺. Although TRM model could not fit the Sr²⁺ BTCs very well, the parameter estimated by TRM model may be more reliable than those obtained from batch experiments because the transport of Sr²⁺ in these kind of sand is non-equilibrium processes.     

场址地下水特征因子对铀锶吸附的影响研究

为了考察某放射性废物填埋场土壤对待填埋的核素铀锶的阻滞性能,对该填埋场土壤及地下水进行取样分析,根据测量的地下水特性参数,在静态条件下,考察了填埋场地下水主要的阴离子SO42-、CO32和阳离子Ca2、Mg2+、Na+、K+对核素铀锶吸附影响,同时结合填埋场地下水的pH和Eh,考察了溶液pH值对核素的吸附影响;结果表明:当pH在2～3之间时,铀的吸附量突然增大,pH在在4～8之间,铀的吸附量明显变化,在pH＞10,吸附量又出现明显减小;当pH＜6和pH＞8后,锶的迁移分配系数(Kd值)明显的增大,而pH在6～8时,Kd值没有明显的变化;阴离子C032-能明显的增加锶在土壤中的吸附,直接表现为Kd值的明显增大,Kd值增加103数量级;阴离子SO42-、CO32-、C2O42-对铀的吸附的影响表现非常明显,随着离子浓度的增加,几种阴离子明显降低了铀在土壤中的吸附,表现为Kd值大大降低,降低的系数在103数量级;阳离子对锶吸附的影响,Ca2+和Mg2+的影响比Na+要强,Ca2+和Mg2+离子浓度在很小的时候就能明显的降低锶的吸附;阳离子对铀吸附的影响,当Ca2+和Mg2+的浓度较低时对铀的吸附影响不大,当Ca2+达浓度大于1280.0μg·L-1,Kd值出现了较为明显的减小.     

Field study of the migration of Sr, Nd and Ce in a weak loess aquifer

The migration of Sr, Nd and Ce in a weak loess aquifer was investigated with an Underground Research Facility. Quartz mixed with SrCl₂ ·6H₂O, NdCl₃ ·7H₂O, CeCl₃ ·7H₂O and NaBr was introduced into the aquifer with a stainless steel pipe. The local water flow field in the aquifer was monitored using a 3-dimensional sampling system. A block of the aquifer medium was obtained wholly with a special sampling method and cut into 3-dimensional small pieces (samples) and analyzed. Based on the experimental data, the diffusion coefficients of Sr, Nd and Ce in the aquifer were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Migration of strontium and europium in quartz sand column in the presence of humic acid: Effect of ionic strength

Summary We investigated the influence of ionic strength on migration behaviors of Sr and Eu in the presence of humic acid (HA). The breakthrough curve of Sr through a quartz sand column in the presence of HA was identical to that in the absence of HA. Europium migration in quartz sand was enhanced by the presence of HA at low ionic strength. At high ionic strength, Eu migration in the presence of HA was hindered compared to that in the absence of HA. Adsorption of europium on quartz sand in the absence of HA decreases with increased ionic strength.     

Formation of strontium ozonide and strontium hyperoxide in reaction of ozone with strontium peroxide

Conclusions The reaction of a solution of ozone in Freon 12 with a suspension of strontium peroxide in the same medium at a negative temperature gives a mixture of the ozonide Sr(O₃)₂ and the hyperoxide Sr(O₂)2. The ozonide is not formed above –70°, and the hyperoxide is not formed above –20°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2138–2139, September, 1973.     

Modeling the migration behavior of rabbit liver apothioneins in capillary electrophoresis

Metallothioneins (MTs) are a group of low-molecular-mass proteins (6-7 kDa) characterized by their great affinity for heavy metal ions. At acidic pH, the bound metal ions are released from the amino acidic structure and MTs lead to apothioneins. In this study, a general equation is used to model the electrophoretic mobility of rabbit liver apothioneins as a function of the pH of the separation electrolyte. The ability of these relationships to explain the migration behavior of these relatively complex polyprotic proteins in the pH range between 2 and 6 has been investigated. Their relevant ionization constant values in the studied pH range were estimated and employed for molecular charge calculations. The classical semiempirical relationships between electrophoretic mobility and charge-to-mass ratio (me vs. q/Malpha) were tested for prediction of their electrophoretic separations. The accuracy of the separations predicted at acidic pH was confirmed by CE-ESI-MS.     

Field study of the migration of 237Np, 238Pu and 241Am in a weak loess aquifer

Summertime urban PM_2.5 was collected on cellulose filters in downtown Toronto, using a customized air sampler (635 l/min). Mass concentrations for up to 19 trace elements/ions were measured by ICP-AES, INAA and IC. Source apportionment was performed on these results including additional carbon and total mass concentrations using positive matrix factorization (PMF). PMF factors exhibited trends that indicated soil (18%), stationary (19%), secondary (48%), and vehicle (15%) sources. Potential source contribution function (PSCF) analysis identified probable sources of the stationary and secondary PM_2.5 as originating from the south and southwest of Toronto.     

The geometry of the site and its relevance for chain migration and stereospecificity

The structurally well characterized members of the family of the bridged metallocene procatalysts with cyclopentadienyl-fluorenyl ligand framework constitute excellent examples for the investigation of the interrelation between the catalyst geometry and stereospecificity from a dynamic chain perspective. We have thus carefully selected a set of metallocenes, based on the increasing size of their β-substituents and the choice of Zr and Hf as transition metals. By their application as polymerization catalysts we have been able to investigate the impact of the substituent size on the migratory behavior of the chain and stereospecific control of the corresponding catalysts. Through these investigations it has been demonstrated that the degree of freedom for the chain's lateral displacements, and the frequency of its back and forth migrations, varies largely with and is dependent on the steric bulk of the β-positioned substituent and to the degree of the geometrical (stereo-electronic) flexibility of the catalytic site with a given symmetry. It has been inferred from the experimental results that substituents, depending on their voluminosity and spatial expansion, interfer differently with the migratory function of the chain and can bring its migration, temporarily or permanently, to a halt (chain stationary insertion). The ratio of chain migratory insertion to chain stationary insertion and their prevalence in each individual case has the final saying about the degree and the type of the microtacticity of the resulting polymer chains (e.g. syndiotactic, syndiotactic containing isoblock, syndio-isoblock, isotactic, and isotactic with syndioblock.     

Modeling of hydrogen and hydroxyl group migration on graphene

Density functional calculations of optimized geometries for the migration of single hydrogen and hydroxyl groups on graphene are performed. It is shown that the migration energy barrier for the hydroxyl group is three times larger than for hydrogen. The crucial role of supercell size for the values of the migration barriers is discussed. The paired migration of hydrogen and hydroxyl groups has also been examined. It could be concluded that hydroxyl group based magnetism is rather stable in contrast with unstable hydrogen based magnetism of functionalized graphene. The role of water in the migration of hydroxyl groups is also discussed, with the results of the calculations predicting that the presence of water weakens the covalent bonds and makes these groups more fluid. Increasing the number of water molecules associated with hydroxyl groups provides an increase of the migration energy.     

Isotope exchange of strontium and molybdate ions in strontium polymolybdates

The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr²⁺ and MoO₄ ^2- ions in the strontium nitrate and sodium molybdate solutions have been studied using ⁹⁰Sr and ⁹⁹Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (K _ex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr²⁺ cations have a much higher affinity for exchangers than MoO₄ ^2- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (X _m ) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.     

Unravelling the specific site preference in doping of calcium hydroxyapatite with strontium from ab initio investigations and Rietveld analyses

Strontium can be substituted into the calcium sublattice of hydroxyapatite without a solubility limit. However, recent ab initio simulations carried out at 0 K report endothermic nature of this process. There is also striking discrepancy between experimentally observed preference of Sr doping at Ca-II sites and the first principles calculations, which indicate that a Ca-I site is preferred energetically for the Sr substitution. In this paper we combine insights from Density Functional Theory simulations and regular configurational entropy calculations to determine the site preference of Sr doping in the range of 0-100 at% at finite temperatures. In addition, samples of Sr-HA are synthesized and refinement of the relevant structural information provides benchmark information on the experimental unit cell parameters of Sr-HA. We find that the contribution of the entropy of mixing can efficiently overcome the endothermic excess energy at a temperature typical of the calcining step in the synthesis route of hydroxyapatite (700-950 °C). We observe that the most preferential substitution pattern is mixed substitution of Sr regardless of the concentration. For a wet chemical method, carried out at a moderate temperature (90 °C), the mixed doping is still slightly favourable at higher Sr-concentrations, except the range at 20% Sr, where Site II substitution is not restricted energetically and equally possible as the mixed doping. We observe a close correspondence between our theoretical results and available experimental data. Hence it should be possible to apply this theory to other divalent dopants in HA, such as Zn(2+), Mg(2+), Pb(2+), Cu(2+), Ba(2+), Cd(2+) etc.     

Use of chemometrics methods and multicriteria decision-making for site selection for sustainable on-site sewage effluent disposal

This paper presents a study undertaken to evaluate site suitability for sewage effluent renovation based on physico-chemical characteristics of the soil. The results obtained showed that as the soil becomes acidic, the phosphorus concentration in the soil reduces accordingly. The chloride ion concentration was found to be a reliable indicator for evaluating the soil capacity to remove nitrogen. A high cation exchange capacity (CEC) can enhance the renovation of sewage effluent. Soils with high quartz content had a low CEC with high organic matter content (OM) being able to compensate. Therefore, an understanding of the micro-nutrients in the soil, organic matter content and chloride ion concentration are important.To facilitate a multi-variate approach for site selection, multicriteria decision-making (MCDM) methods, PROMETHEE and GAIA, were applied for analysis of a sequence of three matrices consisting of 8, 16, and 48 soil site objects, respectively, and seven soil property parameters. Matrix models and the interpretation of results are discussed in detail. From these analyses, PROMETHEE II net outranking flows, ?, found that two sites were always among the top three ranks of the three matrix models, which suggested that they were the most suitable for sewage effluent renovation. The criteria CEC and OM, were particularly important for the selection of these better sites, but pH and Cl⁻ attributes discriminated the weaker performing sites from the better ones; as well the PO₄³⁻ and the NH₃-N criteria were in general opposition to CEC, OM, pH and Cl⁻ but were much less effective as discriminators. Consideration of net outranking flows suggested an approach method for the selection of other possibly suitable sites for sewage effluent renovation.     

Exchangeable fraction of elements in alluvial sediments under waste disposal site (Zagreb, Croatia)

Concentrations of Ag, Ba, Cd, Ce, Cs, Co, Cr, Eu, Fe, Rb, Sc, Sr, Th, and Zn exchangeable fractions were determined in alluvial sediments at waste disposal site area in the vicinity of water-well field. Samples have been leached with 0.5M NH₄Cl at a sample/solution ratio of 120 during 24 hours without shaking. INAA of dry NH₄Cl residues show that the concentrations of exchangeable elements determined in the most of the sediments below the wastes have natural levels. Ag, Ba and Sr are readily exchangeable; Rb, Cs and Zn have lower exchangeability, while Cd, Ce, Th, Sc, Eu, Cr, Fe and Co are rather immobile. Extremely high total and exchangeable silver concentration was found at 6.5–6.8 meters below waste in the aerated layer occasionally under the water table. Exchangeable concentrations in deeper water-bearing sediment layers are not elevated. Due to this, one can presume that the upper sediment layers act as chemical filter generally preventing the infiltration from overlying wastes into water-bearing layers.     

燃煤过程中碱金属迁移规律的模拟研究与预测分析

基于ASPEN PLUS 平台,对燃煤过程中碱金属迁移规律进行了模拟研究和预测。模拟结果表明,在850K~1650K气态碱金属物质随反应温度的升高而增加;1400K以下,气相中以NaCl、KCl为主,Na2SO4蒸气量明显高于K2SO4;1500K以下,气态碱金属释放量随着煤中氯质量分数的增加而增加;一定温度下,气态碱金属质量分数随压力的升高而降低;常压下煤中氯的质量分数0.1%,温度降到972K时气态碱金属的质量分数可降到2.4×10－8;而当氯的质量分数分别为0.05%和0.01%时,为达到同样的气态碱金属质量分数,温度需分别降到990K和1025K。模拟结果为燃煤联合循环发电系统的设计和优化提供了参考依据。     

Modeling the active site of cytochrome oxidase: synthesis and characterization of a cross-linked histidine-phenol

A cross-linked histidine-phenol compound was synthesized as a chemical analogue of the active site of cytochrome c oxidase. The structure of the cross-linked compound (compound 1) was verified by IR, (1)H and (13)C NMR, mass spectrometry, and single-crystal X-ray analysis. Spectrophotometric titrations indicated that the pK(a) of the phenolic proton on compound 1 (8.34) was lower than the pK(a) of tyrosine (10.1) or of p-cresol (10.2). This decrease in pK(a) is consistent with the hypothesis that a cross-linked histidine-tyrosine may facilitate proton delivery to the binuclear site in cytochrome c oxidase. Time-resolved optical absorption spectra of compound 1 at room temperature, generated by excitation at 266 nm in the presence and absence of dioxygen, indicated a species with absorption maxima at approximately 330 and approximately 500 nm, which we assign to the phenoxyl radical of compound 1. The electron paramagnetic resonance (EPR) spectra of compound 1, obtained after UV photolysis, confirmed the generation of a paramagnetic species at low temperature. Because the cross-linked compound lacks beta-methylene protons, the EPR line shape was dramatically altered when compared to that of the tyrosyl radical. However, simulation of the EPR line shape and measurement of the isotropic g value was consistent with a small coupling to the imidazole nitrogen and with little spin density perturbation in the phenoxyl ring. The ground-state Fourier transform infrared (FT-IR) spectrum of compound 1 showed that addition of the imidazole ring perturbs the frequency of the tyrosine ring stretching vibrations. The difference FT-IR spectrum, associated with the oxidation of the cross-linked compound, detected significant perturbations of the phenoxyl radical vibrational bands. We postulate that phenol oxidation produces a small delocalization of spin density onto the imidazole nitrogen of compound 1, which may explain its unique optical spectral properties.