Molecular weight and chemical reactivity of dissolved trace metals (Cd,Cu, Ni) in surface waters from the Mississippi River to Gulf of Mexico

It is generally assumed that estuarine mixing is continuous for metals from terrestrial sources, gradually decreasing towards the open ocean endmember. Here we show that, chemical reactivity, determined by ion exchange method, and molecular weight distributions, obtained using cross-flow ultrafiltration, of dissolved Cd, Cu, and Ni in the surface waters of the Gulf of Mexico varied systematically across the estuarine mixing zone of the Mississippi River. Most size or chemical affinity fractions of dissolved metals (<0.4 μm) were linearly related to salinity (10.8–36.6), suggesting that the distribution of these elements was mainly controlled by continuous mixing processes. Dissolved concentrations across the salinity gradient ranged for Cd: 87–187 pM; Cu: 1.4–18.3 nM; and Ni: 2.6–18.8 nM, with highest values near the Mississippi river mouth, and lowest concentrations in a warm core ring in the Gulf of Mexico. Dissolved Cd was mostly present as a truly dissolved (<10 kDa, 97 ± 1%) and cationic fraction (Chelex-100 extractable, 94 ± 4%). A novel observation across the estuarine mixing zone was that colloidal metal concentrations were identical to either inert (for Cu, Ni) or AMPG-labile anionic (Cu, Cd) fractions. The difference in behavior between Cu and the other two metals might indicate differences in the biopolymeric nature of the metal–organic chelates. In particular, the anionic-organic Cd fractions accounted for just 3 ± 1%, on average. However, for Cu, it was 24 ± 4%, and for Ni, it was 9 ± 6%. The fractions of the total dissolved metal fractions that were “inert” averaged 31 ± 10% for Cu and 29 ± 12% for Ni. Small but noticeable amounts (6 ± 3%) of dissolved inert Cd fractions were also present. Apparent non-local transport processes, likely associated with cross-shelf sediment resuspension processes, could have been responsible for the relatively high concentrations of ‘inert’ and ‘anionic’ metal fractions in high salinity coastal waters, and accounting for the persistence of metals bound to humic substances in the Gulf of Mexico.     

南极普里兹湾溶解态镉的分布

利用25次南极科考获得的海水样,采用原子分光光度法(AAS)测定了海水中溶解态镉的含量,研究了东南极普里兹湾不同空间与时间尺度下海水中溶解态镉的分布特征.并利用同航次相关的营养盐、叶绿素a等数据,分析了影响海水中溶解态镉分布的主要因素.研究结果显示,普里兹湾表层海水中溶解态镉的分布与叶绿素a具有良好的相关性,生物过程是...     

沈阳细河地区土壤镉污染源地球化学研究

镉是一种毒性很大、在自然界中分布广泛的重金属元素。利用辽河流域生态地球化学调查中取得的土壤、大气干湿沉降、灌溉水及农药化肥等样品,对沈阳细河地区土壤中镉污染源进行了甄别及追踪。结果表明: 沈阳细河地区土壤中镉元素污染是由人为源引起,且镉元素污染源主要为污水灌溉、大气降尘及磷肥三种途径。     

安徽水稻土中镉元素生态安全评价标准探讨

土壤中镉元素稳定的残渣态所占比例在重金属中为最低,其赋存形态以离子态为主,易被植物吸收的活性态较高,生态危害较大。稻米镉元素与土壤镉元素具有显著的正相关性。根据区域土壤镉元素与稻米镉元素含量及稻米镉超标率关系,将水稻种植土壤分为生态安全土壤、具生态安全风险土壤及生态安全高风险土壤,提出了土壤镉元素生态安全定量分级标准。     

根际环境锌镉镍的形态变化与植物有效性

以抚顺西露天采场60平盘5种修复植物根际与非根际土为研究对象，运用顺序提取实验和数理统计分析方法研究了根际与非根际土中Zn、Cd、Ni的形态分布与植物有效性。结果表明，Zn、Ni在根际与非根际土中主要以硫化物态存在；而Cd在非根际土中以硫化物态为主，在根际土中以可交换态和松、紧有机态为主。与Ni相比，非根际土中Zn的紧有机态、氧化物态和Cd的紧有机态、氧化物态、可交换态比例明显偏大；与非根际土相比，根际土中Zn的铁锰氧化物态和硫化物态含量增加，碳酸盐态含量降低，松有机态、紧有机态和可交换态Zn在不同植物根际变化不同。Cd的硫化物态降低，可交换态、松有机态、碳酸盐态、氧化物态和紧有机态含量在不同植物根际变化不同。Ni的紧有机态显著增加，可交换态、碳酸盐态和硫化物态明显降低，松有机态在不同植物根际变化不同；根际Cd的碳酸盐态增加和氧化物态降低有利于植物Cd的吸收；碳酸盐态Zn的减少可促进植物Zn的增高。     

样品处理与保存方法对表层沉积物中金属形态分析的影响

利用改进的Tessier连续萃取法研究了冷藏、冷冻、冻干、烘干和风干等样品处理与保存方法对表层沉积物中金属形态的影响。结果表明：各样品处理与保存过程对沉积物中Fe、Mn、Cu、Zn及Pb的形态均具有不同程度的影响,其中Fe的形态受其影响最小（<3.3%）,Mn的形态受其影响最大（最高可达10.2%）;冻干对各金属形态的影响最小（<4.6%）;烘干和风干对重金属Cu、Zn和Pb的可交换态（Ⅰ+Ⅱ）和非残渣态（Ⅰ-Ⅴ）分布影响较大,而冷藏、冷冻和冻干的影响相对较小。因此,综合考虑重金属的形态分布及其生物可利用性,冻干是较理想的沉积物样品处理与保存方法。     

The role of iron and sulfur in the visual appearance of lake sediment varves

Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H⁺, e^?, Fe³⁺, SO₄ ^2?, H₂CO₃ and included the formation of solid phases such as Fe(OH)₃ (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO₃. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)₃/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves.     

长江宜昌段水系沉积物镉高值带成因

应用贡献因子和富集因子等方法对长江宜昌段水系沉积物Cd的来源进行研究,结果表明：研究区内地层对宜昌段水系沉积物Cd的贡献由大到小依次为：震旦系>二叠系>泥盆系>志留系;前震旦系、寒武系、奥陶系、三叠系、侏罗系和白垩系地层则对长江宜昌段Cd高值带的形成有一定的削弱作用。利用贡献因子、富集因子和MapGIS空间分析综合研究表明,震旦系和二叠系含矿富Cd地层的风化产物是长江宜昌段Cd高值带的主要自然来源。区内锌矿、煤矿和磷矿开采过程中的尾砂、废水的堆积和排放是长江宜昌段Cd高值带的重要人为污染源。     

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log m_Au–m_NaCl–T frame fixed linear dependence between log m_Au and T at any studied iso‐pleth (m_NaCl) in the form of log m_Au = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log m_Au) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied f_O2/f_S2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower f_O2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H₂O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H₂O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 m_HCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log m_Pt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)₂ and Mn₂(OH)₃Cl). These phases are metastable and transfer to Mn₃O₄ with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn₃O₄, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn₂O₃–MnO₂ buffer. So at 400C, dissolved Au (log m_Au) increases from –4. 40 in water to –1. 00 in 0. 1 m_HCl, and ones of Pt (log m_Pt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.     

富镉锌矿成矿流体地球化学研究:以贵州都匀牛角塘富镉锌矿为例

通过对贵州都匀牛角塘富镉锌矿包裹体的研究,发现有一定数量的有机包裹体。该矿床与密西西比河谷型（ＭＶＴ）矿床相似,均属于Ｎａ＾＋－Ｃａ＾２＋－Ｋ＾＋－Ｍｇ＾２＋－Ｃｌ＾－体系,同时,两者在成矿流体温度、盐度和密度方面也有一定差别。该矿床成矿流体组分与油田卤水相似,仅Ｃａ＾２＋和Ｍｇ＾２＋含量偏高,这可能与晚阶段的碳酸盐有关。笔者认为,成矿流体可能与麻江古油藏的油田卤水有关,正是由于油田卤水携带了Ｃｄ