Influence of phosphate on the oxidation kinetics of nanomolar Fe(II) in aqueous solution at circumneutral pH     

Yanpeng Mao  A. Ninh Pham  T. David Waite 《Geochimica et cosmochimica acta》2011,75(16):4601-4610

The oxygenation kinetics of nanomolar concentrations of Fe(II) in aqueous solution have been studied in the absence and presence of millimolar concentrations of phosphate over the pH range 6.0-7.8. At each phosphate concentration investigated, the overall oxidation rate constant varied linearly with pH, and increased with increasing phosphate concentration. A model based on equilibrium speciation of Fe(II) was found to satisfactorily explain the results obtained. From this model, the rate constants for oxygenation of the Fe(II)-phosphate species FeH₂PO₄⁺, FeHPO₄ and FePO₄⁻ have been determined for the first time. FePO₄⁻ was found to be the most kinetically reactive species at circumneutral pH with an estimated oxygenation rate constant of (2.2 ± 0.2) × 10 M⁻¹ s⁻¹. FeH₂PO₄⁺ and FeHPO₄ were found to be less reactive with oxygen, with rate constants of (3.2 ± 2) × 10⁻² M⁻¹ s⁻¹ and (1.2 ± 0.8) × 10⁻¹ M⁻¹ s⁻¹, respectively.  相似文献   

Geochemistry of surface waters in the vicinity of open pit mines at the Cay Cham deposit, Thai Nguyen province, northern Vietnam     

Pham Tich Xuan  Nguyen Van Pho  O. L. Gas’kova  S. B. Bortnikova 《Geochemistry International》2013,51(11):931-938

This study provides an assessment of the environmental impact of open pit mining operations at the Cay Cham titanomagnetite-ilmenite deposit (northern Vietnam). The results of surface water sampling indicate the formation of acid mine drainage and contamination of adjacent areas by heavy metals (Cu, Zn, Ni, and Mn). The acid mine drainage is produced by oxidation leaching of sulfide minerals associated with primary mineralization owing to the low neutralization potential of the natural waters in the humid environment of tropical rainforest. The study showed that alternating dry and wet seasons typical of this climatic region promote the generation of stored acidity leading to a sharp decrease in pH of drainage water during the wet season and result in the negative impacts of this mine on both flowing and stagnant surface waters.  相似文献   

Application of multimedia methodology for investigation of karst water in highland regions of Ha Giang Province, Vietnam     

Ngoc Thach Nguyen  Ngoc Hai Pham  Xuan Canh Pham  Thi Thuy Hang Nguyen  Van Lam Nguyen  Thi Thanh Thuy Duong 《Environmental Earth Sciences》2013,70(2):531-542

Ha Giang is one of the largest, northern border provinces of Vietnam, consisting of four districts: Yen Minh, Quan Ba, Dong Van and Meo Vac. This province features varied karst landscape of Carboniferous–Permian limestone. The region has been recognized by UNESCO as one of the 77 geological parks in the world and the second in Southeast Asia on 3 October 2012. In the dry season, little or no rain is recorded; therefore, surface water is very scarce. For this reason, proper delineation and exploitation of the groundwater resource is critical for sustainable water supply. This has been identified as an important challenge under the scientific project KC-08-10 in the national program KC-08. Remote sensing and GIS were used to decipher the signature of karst water in the highland of Ha Giang. Information layers generated were subjected to multi-criteria evaluation using analytic hierarchy process for decision making to identify ideal locations for groundwater prospecting. The study resulted in delineation of ten zones for all regions and 18 ideal drilling sites in Tam Son Town of Quan Ba District. Drilling and resistivity soundings were performed to assess the success of the interpretation. Deep resistivity survey confirmed low resistivity (200–300 Ωm) near the identified potential sites in Tam Son Town of Quan Ba District. Further, successful drilling at site LKTS1 with a discharge of 7–9 l/s is observed, proving the potential of this methodology for rapid exploration of groundwater in water-scare karst terrains of Vietnam.  相似文献   

Coastal and marine ecological changes and fish cage culture development in Phu Quoc,Vietnam (2001 to 2011)     

Diep Thi Hong Nguyen  Wenresti G. Gallardo  Taravudh Tipdecho 《国际地球制图》2013,28(5):486-506

This study employed image enhancement for LANDSAT TM and ALOS imagery to monitor the changing status of coastal resources from 2001 to 2011, object-based classification of high-resolution THEOS imagery to extract fish cage culture sites and interpolation methods to determine marine environmental quality in 2011 in the northern part of Phu Quoc Island. There were five classes in the study site: natural forest, Melaleuca forest, agriculture, peat and built-up areas. Agricultural land and Melaleuca forest changing into built-up areas constituted approximately 51.13% of the total area changing. The benthic seagrass habitat increased dramatically from 2001 to the end of 2010. Besides, marine culture has been concerned to cage culture which is one of the sources directly affecting aquatic life and water quality in coastal environment. Cage culture locations were detected using high-resolution imagery as THEOS data for image fusion and Object-based Image Analysis methods. Water quality criteria including nitrogen, phosphorus and chlorophyll-a concentrations were determined by interpolation method, and the spatial distribution of these parameters showed a concentration in the study area in the range from 0.17 to 0.49?mg/L, 0.012 to 0.073?mg/L and 0.26 to 1.046?μg/L, respectively.  相似文献   

Rotenone treatment has a short-term effect on New Zealand stream macroinvertebrate communities     

Lan Pham  David West  Gerard P. Closs 《新西兰海洋与淡水研究杂志》2018,52(1):42-54

Invasive fish eradication is a key management strategy in aquatic ecosystems, and is often accomplished using piscicides such as rotenone. However, the effects of piscicides on aquatic invertebrate communities are poorly understood, particularly over long time scales. We monitored invertebrate communities in two treatment and two reference streams prior to and for one year following the use of rotenone to eradicate trout in Zealandia wildlife sanctuary, Wellington. Immediately following treatment, invertebrate density and taxonomic richness declined significantly, and community composition diverged markedly relative to reference streams, with pollution sensitive taxa declining greater than more tolerant taxa. Treatment streams recovered to pre-treatment conditions within 4–12 months of rotenone application, indicating minor long-term impacts on invertebrate communities. Speed of recovery of individual taxa appeared to be associated with life history variables, e.g. generation times and dispersal ability. Untreated upstream reaches and nearby water bodies likely facilitated successful invertebrate community recovery. Our results demonstrate that rapid recovery of New Zealand stream invertebrate communities is possible within one year of rotenone application.  相似文献   

豫西地区秦岭造山带武当群Nd-Hf同位素组成及其物源特征   总被引：1，自引：0，他引：1  

祝禧艳  陈福坤  杨力  王伟  HIEU Pham Trung  苗来成  张福勤 《岩石学报》2009,25(11):3017-3028

武当群变质沉积-火山岩组合是南秦岭地体中重要的基底岩石,其形成时代和地球化学特征可以为理解秦岭造山带的构造演化提供重要的证据.本文报道豫西地区武当群上部沉积岩和下部中-酸性火山岩Sm-Nd同位素和锆石Lu-Hf同位素组成,探讨火山岩成因和沉积岩物源的同位素特征.上部沉积岩的碎屑锆石初始ε_(Hf)值变化在-30～+10之间,对应的模式年龄值t_(DM2)在1.0Ga至3.2Ga之间,初始ε_(Nd)值在-4.0至-6.0之间.沉积物源表现为主要与扬子陆块有亲缘关系的地壳物质和近源的下部火山岩混合的特征.火山岩的锆石初始εHf值变化在-35～+15之间,对应的模式年龄值t_(DM2)在0.8Ga至3.5Ga之间,集中于1.5～1.8Ga和2.2～2.4Ga两个峰值.2个变质石英角斑岩样品初始ε_(Nd)值分别为-9.2和-10.7,而报道的湖北武当群的玄武-安山质熔岩的初始ε_(Nd)值以正值为主.因此,武当群不同类型的火山岩可能存在着成因差异.具有低初始ε_(Nd)值和ε_(Hf)值特征的火山岩可能由地壳物质的重熔而形成的;有些火山岩具有初始ε_(Hf)值变化范围较大(-35～+15)或正初始ε_(Nd)值的特点,可能是壳、幔物质混合成因,有显著的幔源或新生地壳物质的贡献.武当群Nd-Hf同位素组成和碎屑锆石年龄分布特征表明,与扬子陆块有亲缘关系的南秦岭地体在元古代期间可能经历多期地壳增生和再造作用.  相似文献   

Effect of alkaline solutions on bentonite properties     

Ha Ngoc Anh  Hyangsig Ahn  Ho Young Jo  Geon-Young Kim 《Environmental Earth Sciences》2017,76(10):374

The influence of alkaline aqueous solutions on the properties of bentonite was investigated to evaluate the performance of bentonitic engineered barriers when contacted with alkaline groundwater. Batch and hydraulic conductivity tests were conducted on Na-bentonite using six different alkaline aqueous solutions. For the batch tests, almost no change in the montmorillonite fraction of the bentonite was observed after reacting with alkaline solutions (pH = 8.4–13.1), regardless of the solution type. On the other hand, aluminosilicate minerals (e.g., albite) were dissolved and secondary minerals (e.g., anorthite) were formed in alkaline NaOH solutions (pH > 13). The cation (Ca or Na) concentration primarily affected the swelling properties of bentonite rather than the pH of the solution, which was comparable to the results of the hydraulic conductivity tests. For the Ca solutions, the hydraulic conductivity of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ solution (6.5 × 10^?9 cm/s) was approximately an order of magnitude lower than that of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (5.0 × 10^?8 cm/s), whereas the hydraulic conductivity to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (pH = 11.3) (5.0 × 10^?8 cm/s) was slightly higher than that to the 1 mol/L CaCl₂ solution (pH_i = 8.4) (4.4 × 10^?8 cm/s). For the NaOH solutions with pH > 13, the hydraulic conductivity of the bentonite specimen decreased with increasing Na concentration, suggesting that the effect of Na concentration was more dominant than that of permeant pH.  相似文献   

Remarkably uniform oxygen isotope systematics for co-existing pairs of gem-spinel and calcite in marble,with special reference to Vietnamese deposits     

Anthony E. Fallick  Gaston Giuliani  Thomas Rigaudier  Adrian J. Boyce  Van Long Pham  Vincent Pardieu 《Comptes Rendus Geoscience》2019,351(1):27-36

Oxygen isotope systematics for co-existing pairs of gem-spinel and calcite in marble from Vietnam and other worldwide deposits have been determined in order to characterize the O-isotope fractionation between calcite and spinel. In Vietnam, the Δ¹⁸O_cc–sp (= 3.7 ± 0.1‰ for six samples from the An Phu and Cong Troi deposits) is remarkably constant. The combination of these data with those obtained on calcite–spinel pairs of Paigutan (Nepal, n = 2), Ipanko (Tanzania, n = 1), and Mogok (Myanmar, = 2) are also consistent with an overall Δ¹⁸O_cc–sp of 3.6 ± 0.3‰ for all the spinel samples (n = 11). The straight line correlation δ¹⁸O_cc = 0.96 δ¹⁸O_sp + 4.4 is excellent despite their worldwide geographic spread. The increment method of calculating oxygen isotope fractionation gave a geologically unreasonable temperature of formation for both minerals at 1374 °C when compared to temperatures obtained by mineral assemblage equilibrium of these marble type deposits, between 610 and 750 °C. The constant Δ¹⁸O_cc–sp reflects a constant temperature for this amphibolite facies assemblage, whose current best estimate is calculated at 620 ± 40 °C, but unquantified uncertainties remain.  相似文献   

Seismic Network,Seismic Activity and Seismological Research of Vietnam     

Nguyen Ngoc Thuy 《中国地震研究》2002,16(3):268-270

In this paper,a historical review of the seismic network of Vietnam and the ability of the network to monitor earthquakes is presented.The seismic activity of Vietnam as a country of high seismictiy in the last century and since the beginning of the new century is described.The current state of seismological research in Vietnam and cooperation with institutions outside of Vietnam is outlined.  相似文献   

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V. N. Pham 《Geophysical Journal International》2005,162(2):337-338

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