On the scavenging of gaseous nitrogen compounds by large and small rain drops I. A wind tunnel and theoretical study of the uptake and desorption of NH3 in the presence of CO2

An experimental study has been carried out in the Mainz vertical wind tunnel to determine the rate at which NH₃ in the presence of CO₂ is absorbed by freely suspended water drops. The experimental uptake rates were found to be in good agreement with the rates predicted by the Kronig-Brink convective diffusion model and, for gas concentrations in the ppbv range also by the model in which it is assumed that the absorbed gas is well mixed inside the drop (henceforth called well mixed model). The same conclusion was shown to apply also to the desorption of NH₃ from a drop previously exposed to NH₃. The latter result is in contrast to the desorption of SO₂ which must be described by a model which accounts for the diffusion of the species inside the drop. Comparison of our experimental results with theory show further that the uptake of NH₃ in presence of CO₂ is significantly overestimated if the slow reaction CO_2(aq)+H₂OHCO ₃ ^– +H⁺ is neglected in the theoretical computation.     

On the scavenging of gaseous nitrogen compounds by large and small rain drops: II. Wind tunnel and theoretical studies of the simultaneous uptake of NH3, SO2 and CO2 by water drops

An experimental investigation of the simultaneous absorption of NH₃ and SO₂ from the ambient atmosphere by freely falling water drops has been carried out in the Mainz vertical wind tunnel. The experimental results were found to be in good agreement with the results derived from computations with the Kronig-Brink convective diffusion model and also with a model which assumes a drop to be well mixed at all times. Encouraged by this agreement, these computation schemes for the uptake of gas by single drops where incorporated in a pollution washout model with realistic SO₂, NH₃ and CO₂ gas profiles. This model allows an entire raindrop size distribution to fall through a gas layer. The results of this plume-model show that the SO₂ uptake is strongly dependent on the NH₃ concentration in the atmosphere and on the rainrate. We also find that the small drops contribute more towards the washout of these gases. In the case of simultaneous presence of NH₃ and SO₂, desorption of these gases is negligible.     

Mechanism of Hg(II) immobilization in sediments by sulfate-cement amendment

Reactive amendments such as Portland and super-sulfate cements offer a promising technology for immobilizing metalloid contaminants such as mercury (Hg) in soils and sediments through sequestration in less bioavailable solid forms. Tidal marsh sediments were reacted with dissolved Hg(II) in synthetic seawater and fresh water solutions, treated with Portland cement and FeSO₄ amendment, and aged for up to 90 days. Reacted solids were analyzed with bulk sequential extraction methods and characterized by powder X-ray diffraction (XRD), electron microscopy, and synchrotron X-ray absorption spectroscopy at the Hg L_III- and S K-edge. In amended sediments, XRD, SEM and sulfur K-edge XANES indicated formation of gypsum in seawater experiments or ettringite-type (Ca₆Al₂(SO₄)₃(OH)₁₂^.26H₂O) phases in fresh water experiments, depending on the final solution pH (seawater ∼8.5; freshwater ∼10.5). Analysis of Hg EXAFS spectra showed Cl and Hg ligands in the first- and second-coordination shells at distances characteristic of a polynuclear chloromercury(II) salt, perhaps as a nanoparticulate phase, in both seawater and fresh water experiments. In addition to the chloromercury species, a smaller fraction (∼20–25%) of Hg was bonded to O atoms in fresh water sample spectra, suggesting the presence of a minor sorbed Hg fraction. In the absence of amendment treatment, Hg sorption and resistance to extraction can be accounted for by relatively strong binding by reduced S species present in the marsh sediment detected by S XANES. Thermodynamic calculations predict stable aqueous Hg–Cl species at seawater final pH, but higher final pH in fresh water favors aqueous Hg-hydroxide species. The difference in Hg coordination between aqueous and solid phases suggests that the initial Hg–Cl coordination was stabilized in the cement hydration products and did not re-equilibrate with the bulk solution with aging. Collectively, results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt as the primary immobilization mechanism.     

无色-近无色高温高压合成钻石的谱图特征及其鉴别方法

实验室发现大量小颗粒的无色高温高压(HPHT)合成钻石与天然钻石混杂镶嵌在各种饰品中,前人提出荧光和磷光特征是主要的快速区分特征,然而荧光、磷光特征的差异并不能完全将HPHT合成钻石与天然钻石区分开来。本文将常规的宝石学观察分析与多种高精度谱学测试相结合,对五粒不同的无色-近无色HPHT合成钻石样品进行深入研究。结果表明,五粒钻石在紫外可见吸收光谱无270 nm吸收或是只有极弱的270 nm吸收,随着颜色级别的降低,270 nm吸收越明显。红外光谱测试显示,各粒样品中都含有不等量的硼元素。光致发光光谱测试表明,HPHT合成钻石含有与微量N、Ni、Si等相关的晶格缺陷。超短波紫外光源激发下,所有的HPHT合成钻石都有强磷光,在钻石观察仪下可以观测到清晰的八面体和立方体分区特征。显然,不同的合成钻石的特征略有差异,但综合其荧光及磷光特征以及红外、紫外、光致发光光谱特征,可以准确地将无色HPHT合成钻石与对应的天然钻石区分开来。     

Immobilization of Cu and As in two contaminated soils with zero-valent iron – Long-term performance and mechanisms

Immobilization of trace elements in contaminated soils by zero-valent iron (ZVI) is a promising remediation method, but questions about its long-term performance remain unanswered. To quantify immobilization and predict possible contaminant remobilization on long timescales detailed knowledge about immobilization mechanisms is needed. This study aimed at assessing the long-term effect of ZVI amendments on dissolved copper and arsenic in contaminated soils, at exploring the immobilization mechanism(s), and at setting up a geochemical model able to estimate dissolved copper and arsenic under different scenarios. Samples from untreated and ZVI-treated plots in two field experiments where ZVI had been added 6 and 15 years ago were investigated by a combination of batch experiments, geochemical modeling and extended X-ray absorption fine structure (EXAFS) spectroscopy. Dissolved copper and arsenic concentrations were described by a multisurface geochemical model with surface complexation reactions, verified by EXAFS. The ZVI remained “reactive” after 6–15 years, i.e. the dissolved concentrations of copper and arsenic were lower in the ZVI-treated than in the untreated soils. There was a shift in copper speciation from organic matter complexes in the untreated soil to surface complexes with iron (hydr)oxides in the ZVI-treated soil. The pH value was important for copper immobilization and ZVI did not have a stabilizing effect if pH was lower than about 6. Immobilization of arsenic was slightly pH-dependent and sensitive to the competition with phosphate. If phosphate was ignored in the modeling, the dissolution of arsenate was greatly underestimated.     

Identifying calcium-containing mineral species in the JEB Tailings Management Facility at McClean Lake,Saskatchewan

The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the McClean Lake uranium mill facility that is operated by AREVA Resources Canada. This facility has been designed around the idea that elements of concern (e.g., U, As, Ni, Se, Mo) will be controlled through equilibrium with precipitants. Confirming the presence of calcium-containing carbonates in the JEB TMF is the first step in determining if gypsum (CaSO₄·2H₂O) controls the concentration of HCO₃⁻ (aq), limiting the formation of soluble uranyl bicarbonate complexes. A combination of X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and microprobe X-ray fluorescence (XRF) mapping was used to analyze a series of tailings samples from the JEB TMF. Calcium carbonate in the form of calcite (CaCO₃), aragonite (CaCO₃), and dolomite (CaMg(CO₃)₂) were identified by analysing Ca K-edge μ-XANES spectra coupled with microprobe XRF mapping. This is the first observation of these phases in the JEB TMF. The combination of μ-XANES and XRF mapping provided a greater sensitivity to low concentration calcium species compared to the other techniques used, which were only sensitive to the major species present (e.g., gypsum).     

水合铁离子及铁络合物吸收系数光谱(400-900 nm)测量

测量铁化合物溶解物的吸收光谱曲线是水中铁离子含量遥感反演的关键。采用自主设计的水体透射光测量装置,利用ASD光谱仪测量相同厚度不同浓度铁离子溶液的透射光辐亮度,然后运用比值法计算出水中3种铁化合物(硫酸铁、氯化铁和铁氰化钾)的消光系数和吸收系数,最终得到400—900 nm波长范围内3种铁离子吸收系数光谱。该方法可以较好地消除实验装置和水中悬浮物的影响。结果表明,水中3种铁离子均在紫蓝光波段吸收作用较大,绿光次之,逐渐减少至红光波段后,吸收系数变化很小呈平缓直线。测量结果可作为水体铁离子浓度遥感反演模型所需的基础参数。     

海水中不同价态铬的测定

本文研究了用Aliguat-336萃取,无焰原子吸收分光光度法测定海水中不同价态铬的方法。该方法有较好的精密度,变动系数为6.0%。回收率在80%左右,其特征量为6.3×10~(14)g,较好地应用于海水中不同价态铬的测定。     

海参中微量元素的分析

本文用原子吸收分光光度法研究黑乳参(Holothuria nobilis Seleka)和刺参(StiChops japonicus Selenka)样品的消化方法,并测定样品中11种微量元素(K,Ca,Mg,Fc,Co,Ni,Mn,Cu,Cd,Pb,Zn)的含量。结果表明,这些海参样品,用干法或湿法消化均可得到满意结果。作者还将部分元素的分析结果与阳极溶出伏安法和交流示波极谱滴定法相对照,其结果一致。