A high-resolution TEM-AEM, pH titration, and modeling study of Zn coprecipitation with ferrihydrite

Experiments of Zn²⁺ and Fe³⁺ coprecipitation as a function of pH were conducted in the laboratory at ambient temperature and pressure. X-ray diffraction patterns of the coprecipitates show two broad peaks at 0.149 and 0.258 nm, which is consistent with published patterns for pure 2-line ferrihydrite. Zn²⁺ uptake occurred at pH ≥5 while Fe³⁺ precipitation occurred between pH 3 and 4, although both Zn²⁺ and Fe³⁺ were present in the same solution during the entire range of pH titration. High-resolution transmission electron microscopy shows that the coprecipitates are 2 to 6 nm sized single crystalline particles but aggregated to 50 to 400 nm sized clusters. Analytical electron microscopy indicated that the 5% atomic Zn with respect to Fe was homogeneously distributed. No segregated phases were found in the clusters or at single crystal edges, which is consistent with published extended X-ray absorption fine structure (EXAFS) results at similar Zn/(Zn + Fe) ratios. Hence, occlusion and surface precipitation may be excluded as possible coprecipitation mechanisms. The bulk solution Zn²⁺ sorption edge was fitted to both solid solution and generalized diffuse layer surface complexation models. However, a solid solution model is inconsistent with published EXAFS results that show tetrahedral polydentate Zn²⁺ complexes sharing apices with Fe³⁺octahedra.     

Dielectric constants of apatite,epidote, vesuvianite,and zoisite,and the oxide additivity rule

The dielectric constants and dielectric loss values of 4 Ca-containing minerals were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: vesuvianitel κ′ _a=9.93 tan δ=0.006 κ′ _c=9.79 tan δ=0.005 vesuvianitel κ′ _a=10.02 tan δ=0.002 κ′ _c=9.85 tan δ=0.003 zoisite1 κ′ _a =10.49 tan δ=0.0006 κ′ _b =15.31 tan δ=0.0008 κ′ _c=9.51 tan δ=0.0008 zoisite2 κ′ _a =10.55 tan δ=0.0011 κ′ _b =15.45 tan δ=0.0013 κ′ _c=9.39 tan δ=0.0008 epidote κ′ ₁₁= 9.52 tan δ=0.0008 κ′ ₂₂=17.1 tan δ=0.0009 κ′ ₃₃= 9.37 tan δ=0.0006 fluorapatite1 κ′ _a =10.48 tan δ=0.0008 κ′ _c = 8.72 tan δ=0.0114 fluorapatite2 κ′ _a =10.40 tan δ=0.0010 κ′ _c=8.26 tan δ=0.0178 The deviation (δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α _D (mineral)=∑ α _D (oxides) for vesuvianite is ～ 0.5%. The large deviations of epidote and zoisite from the additivity rule with Δ=+ 10.1 and + 11.7%, respectively, are attributed to “rattling” Ca ions. The combined effects of both a large F thermal parameter and possible F-ion conductivity in fluorapatite are believed to be responsible for Δ=+2–3%. Although variation of oxygen polarizability with oxygen molar volume (V_o) is believed to affect the total polarizabilities, the variation of V_o in these Ca minerals is too small to observe the effect.     

Mercury contribution to an adirondack lake

Elevated copper, lead, and zinc concentrations in the upper 10 to 20 cm of sediment sampled from Cranberry Lake, a large Adirondack lake, are attributed to atmospheric contributions. Pb-210 and pollen core data, however, suggest Cranberry Lake also received mercury discharges during the turn of the century when the area was the center of extensive lumbering and related activities. Elevated mercury concentrations in Cranberry Lake smallmouth bass derived from remobilization from mercury-contaminated bottom sediments which increased the bioavailability to Cranberry Lake organisms. Mercury remobilization and accumulation by fish are promoted by fluctuating pH values resulting from acid precipilation.     

Multiple discriminant analysis of the Drava River alluvial plain sediments

Three discriminant function models are raised and cross-compared in order to distinguish geochemical patterns characteristic for the Drava River floodplain sediments. Based on data representing total element concentrations in samples collected from alluvium (A), terrace (T), and unconsolidated bedrock (B) at the border of a floodplain, four element clusters emerged accounting for discrimination between the referred groups of sediments. The most prominent is contaminant/carbonate cluster characteristic for alluvium. The other two are: silicate cluster typical for unconsolidated geological substrate (Neogene sedimentary rocks); and naturally dispersed heavy metal cluster separating terrace from the former two groups. Models introducing depth intervals and single profiles as grouping criteria reveal identical sediment-heavy metal matrices. The second important issue of this paper is possibility of reclassification of samples originally assigned to one of the a priori defined groups of sediments, based on established geochemical pattern. The mapped geological units can be reconsidered by the post hoc assignments to a different group if geological border between alluvium and terrace or between terrace and bedrock can not be established geologically with absolute certainty.     

梁柱组合节点的拟动力试验研究

本文主要介绍了所开展的梁柱组合节点的拟动力试验,梁柱连接采用高强度螺栓平端板形式。试验采用经过调幅的具有不同地震加速度峰值的Ispara地震动作为激励进行加载,对试件在地震作用下的加速度反应、位移反应、滞回性能、刚度和耗能进行分析,对试验现象和结果进行了比较详细的阐述和分析。     

El Niño and decadal effects on sea‐level variability in northern New Zealand: A wavelet analysis

Sea‐level data from two sites in northern New Zealand, along with the Southern Oscillation Index (SOI), are analysed for interannual and decadal variability using wavelets. The analysis shows, using statistically significant wavelet power, there is a significant relationship between mean sea level (MSL) and SOI. However, the relationship is highly variable, both in magnitude and in the range of time‐scales over which it occurs. This non‐stationarity necessitates the use of techniques such as wavelets for analysis. An interdecadal response in MSL around northern New Zealand has been isolated, with shifts occurring in 1950 and the late 1970s. This behaviour in MSL appears to coincide with shifts in the Pacific Decadal Oscillation, thought previously to be largely centred in the North Pacific. A strong correlation between SOI and sea surface temperature (SST) is also demonstrated. This relationship appears to be stable in magnitude (a large change in SOI produces a large change in SST) and to occur over the same range of time‐scales. More SST and MSL data are required for other parts of New Zealand to determine whether these findings apply elsewhere.     

Cation disorder in garnets along the Mg3Al2Si3O12-Mg4Si4O12 join: an infrared,Raman and NMR study

We have obtained infrared and Raman spectra for garnets synthesized at high (static) pressures and temperatures along the join Mg₃Al₂Si₃O₁₂ (pyrope) — Mg₄Si₄O₁₂ (magnesium majorite). The vibrational spectra of Mg-majorite show a large number of additional weak peaks compared with the spectra of cubic pyrope garnet, consistent with tetragonal symmetry for the MgSiO₃ garnet phase. The Raman bands for this phase show no evidence for line broadening, suggesting that Mg and Si are ordered on octahedral sites in the garnet. The bands for the intermediate garnet compositions are significantly broadened compared with the end-members pyrope and Mg-majorite, indicating cation disorder in the intermediate phases. Solid state ²⁷Al NMR spectroscopy for pyrope and two intermediate compositions show that Al is present only on octahedral sites, so the cation disorder is most likely confined to Mg-Al-Si mixing on the octahedral sites. We have also obtained a Raman spectrum for a natural, shock-produced (Fe,Mg) majorite garnet. The sharp Raman peaks suggest little or no cation disorder in this sample.     

Relationship between Hypoxia and Macrobenthic Production in Chesapeake Bay

Human development has degraded Chesapeake Bay's health, resulting in an increase in the extent and severity of hypoxia (≤2 mg O₂ l^-1). The Bay's hypoxic zones have an adverse effect on both community structure and secondary production of macrobenthos. From 1996 to 2004, the effect of hypoxia on macrobenthic production was assessed in Chesapeake Bay and its three main tributaries (Potomac, Rappahannock, and York Rivers). Each year, in the summer (late July???early September), 25 random samples of the benthic macrofauna were collected from each system, and macrobenthic production in the polyhaline and mesohaline regions was estimated using Edgar's allometric equation. Fluctuations in macrobenthic production were significantly correlated with dissolved oxygen. Macrobenthic production was 90 % lower during hypoxia relative to normoxia. As a result, there was a biomass loss of ~7,320–13,200 metric tons C over an area of 7,720 km², which is estimated to equate to a 20 % to 35 % displacement of the Bay's macrobenthic productivity during the summer. While higher consumers may benefit from easy access to stressed prey in some areas, the large spatial and temporal extent of seasonal hypoxia limits higher trophic level transfer, via the inhibition of macrobenthic production. Such a massive loss of macrobenthic production would be detrimental to the overall health of the Bay, as it comes at a time when epibenthic and demersal predators have high-energy demands.