Applied Geochemistry (v.78, #C)
High-resolution reconstruction of the 20th century history of trace metals, major elements, and organic matter in sediments in a contaminated area of Lake Geneva, Switzerland by Elena Gascón Díez; Juan Pablo Corella; Thierry Adatte; Florian Thevenon; Jean-Luc Loizeau (1-11).
Toxic trace metals in lacustrine sediments are of major concern since they can be hazardous to biota and human health. A high-resolution multiproxy study, including trace metals and major elements (measured by ICP-MS and XRF), total organic carbon, mineral carbon, Hydrogen Index, Oxygen Index, and C/N ratios, was performed on a sediment core from Vidy Bay in Lake Geneva. This bay has been affected by hazardous compounds released via the sewage effluent of a major wastewater treatment plant (WWTP). Anthropogenic trace metals, such as Pb, Cd, Cu, Zn, and Hg, increased following the industrial revolution in Europe. The highest amounts of these toxic metals, together with Ni, Cr, Co, Ag, Bi, and Fe, were recorded in sediments from 1964, the date of the WWTP implementation. During this period, all trace elements exceeded the sediment quality guideline “probable effect concentration” (PEC), with the following maximum concentrations (in mg kg−1): Pb 4000, Cd 23, Cu 1200, Zn 8600, Hg 11, Ni 140, Cr 270, Ag 130, and Bi 310. The geochemistry of detrital elements (Al, Si, Ca, Ti, K, Zr, Rb, and Sr), as well as S, Fe, P, and the nature and quality of organic matter were clearly also affected by the effluent. The sedimentary record revealed that, after some improvements in the wastewater treatment processes and the relocation of the outlet pipe, the sediments tended to return to concentrations similar to those prevailing before the WWTP implementation. However, despite the reduction in the contamination load from the WWTP, which could be reinforced with the construction of a new plant in the near future, the sediments deposited in Vidy Bay represent a major contaminant legacy that constitutes a potential threat to the lake biota in the case of sediment remobilization.
Keywords: Heavy metals; Trace metals; Wastewater; Sediment contamination; Organic matter;
Changes in the geochemical parameters of karst lakes over the past three decades – The case of Plitvice Lakes, Croatia by Andreja Sironić; Jadranka Barešić; Nada Horvatinčić; Andrijana Brozinčević; Maja Vurnek; Sanja Kapelj (12-22).
One of the major reasons for the increase in global air temperature since the early 20th century is considered to be the increase in the atmospheric CO2 concentration. Karst relief is considered an important carbon sink, but it can also be a natural source of carbon and CO2 emission. Aquatic systems in karst areas facilitate carbon exchange between the karst and the atmosphere, often through groundwater geochemical carbonate rock dissolution (carbon sink) and in the form of secondary calcium carbonate precipitation (possible carbon source).The protected area of Plitvice Lakes National Park, located in the karst region of Croatia, was chosen as a case study on karst geochemical processes. The lakes are also specific for their authigenic calcite precipitation in the form of tufa barriers and lake sediment. Physical and chemical data (temperature, pH, Ca2+, HCO3 −, Mg2+ and CO2 concentrations, calcite saturation index (SI calc ), calcite dissolution ionic ratio (IR calc ), and Mg/Ca ratio) from water samples collected at 8 locations (2 springs, 2 rivers, and 4 lakes) from 1981 to 2014 were studied.The data were not collected systematically, so long-term changes have been mostly assessed through comparison between parameters from two selected periods (1981–1986 and 2010–2014) and through temporal correlations for each observed parameter in each calendar month.For the 33 years studied, an increase in air and water temperature, Ca2+ and HCO3 − concentrations, calcite saturation index (SI calc ), calcite dissolution ionic ratio (IR calc ), and a decrease in the Mg/Ca ratio were observed. No statistically significant change was observed for pH or CO2 and Mg2+ concentrations. Average discharge rates did not display any significant change over the past three decades, however there was a change in their seasonal distribution.The significant increase in Ca2+ and HCO3 − concentrations at lake locations were primarily caused by an increase in Ca2+ and HCO3 − values in the water of the springs. Simultaneously, Mg2+ concentrations remained constant, which indicates higher levels of limestone (calcite) dissolution than dolomite dissolution. One of the reasons for this could be higher air/soil temperatures, resulting in higher soil CO2 production, which appears to result in the higher dissolution of calcite exclusively. An increase in HCO3 − concentrations at the springs implies that karst groundwater is a carbon sink. Furthermore, the fact that the spatial decrease in HCO3 − concentration in downstream waters was the same during the 1981–1986 and 2010–2014 periods implies that the entire observed karst lake system itself is a carbon sink.Temporal and spatial changes in SI calc and IR calc values in surface waters were mainly attributed to an increase in the intensity of bioactivity, which is in turn connected with an increase in water temperature.
Keywords: Karst geochemistry; Karst lakes; Hydrogeochemical parameters; Global temperature change;
Circulation path of thermal waters within the Laga foredeep basin inferred from chemical and isotopic (δ18O, δD, 3H, 87Sr/86Sr) data by Alessandro Fusari; Michael R. Carroll; Stefano Ferraro; Rita Giovannetti; Geoffrey Giudetti; Chiara Invernizzi; Mario Mussi; Maddalena Pennisi (23-34).
The geochemistry of thermal spring waters in the Acquasanta Terme area, located on the Adriatic side of central Italy, has been investigated in order to characterize the geothermal feeding system. The springs discharge more than 100 L/s at temperature ranging between 20 and 30 °C. They occur in a tectonic window of Mesozoic limestones in the central sector of the Acquasanta anticline within the Laga foredeep Basin. Chemical and isotopic compositions of thermal and cold fluids were investigated, most of them monitored for one year, in order to understand the thermal fluid circulation paths. The chemistry of the major elements defines the existence of Na–Cl and Ca–Cl–SO4 2- hot discharging waters and permits the characterization of the thermal end-member hosted in carbonate-dominated reservoir (Burano Anhydrites Fm–Calcare Massiccio Fm). This deep fluid is well represented by the sample T1 and shows high temperature and electrical conductivity (EC), very stable over time, and not affected by mixing phenomena. This is also confirmed by tritium results (0 T.U.). Close to the surface at different depth, such water undergoes mixing or dilution processes with HCO3 − rich freshwaters, driven by the complex structural setting of the area and by diffuse karst caves. This is identified as the main reason for observed compositional variations of sampled springs, and three areas affected by different mixing phenomena have been defined at the surface. The concentrations of SO4 2− and H2S suggest redox processes affecting sulfur after interaction with evaporitic formations, identified with the Burano Anhydrites, at the base of the Umbria–Marche sedimentary sequence (∼3500-m-deep). Contribution from this reservoir is also supported by characteristic Sr isotope signature. δ18O and δD values indicate a meteoric origin of the thermal waters and allow estimation of an average infiltration altitude ranging between 1500 and 1700 m a.s.l. This datum, supported by structural data, suggests the Laga Mountains as the recharge area of the system. Reservoir temperature inferred by SO4 2−–HCO3 −–F, Ca/Mg and SO4 2−/F geothermometers is about 80 °C, consistent with the geothermal gradient of the foredeep basin, and deserving further investigations for potential economic implications about this low-enthalpy geothermal area.
Keywords: Thermal waters; Geochemistry; Isotopes; Fluid circulation; Laga basin;
Holocene climate change influences on trace metal and organic matter geochemistry in the sediments of an Arctic lake over 7,000 years by P.M. Outridge; H. Sanei; C.J. Courtney Mustaphi; K. Gajewski (35-48).
This study employed a 6.48 m long dated sediment core to characterize the amount of variation in background trace metal concentrations, and develop an understanding of the role of climatic influences on sediment inorganic and organic geochemistry in a High Arctic lake over ∼7000 years of the Holocene. Element geochemistry reflected varying detrital contributions from two geological sources within the catchment: carbonates (dolomites and limestones) which provided the dominant major element by weight (i.e., Ca), and carbonaceous mudrocks (primarily shales) which may have contributed most of the other trace and minor elements. The presence of eroded shale-hosted organic matter (OM) in sediments was confirmed by reflectance measurements on reworked vitrinitic macerals which had similar values to Palaeozoic carbonaceous rocks in the watershed. Bimodal distribution of the reflectance data suggested that two sources of vitrinitic macerals were present, from different formations. Variable dilution of shale-sourced elements by carbonates, related to climate (temperature)-influenced rates of dissolution and erosion, was the dominant process controlling inorganic geochemical composition. RockEval pyrolysis of bulk sediment OM revealed the unusual finding of two distinct sources of sediment kerogen which alternated in importance during the Holocene: a “baseline” state of eroded shale-hosted OM which was probably always present but which dominated sediment OM when autochthonous (algal) production was minimal, and an “enhanced algal state” which dominated when limnological conditions favored higher autochthonous productivity. Periods with more frequent examples of the enhanced algal state occurred during the mid- and late-Holocene, coincident with periods of relatively high summer air temperatures in the region. This study provides evidence that climate, particularly air temperature, influenced sediment inorganic and organic geochemical compositions in this lake through its effect on catchment geology erosion rates and aquatic primary productivity. It shows the value of studying very long periods of sediment accumulation as a background context for recent sediment metal concentrations.
Keywords: Arctic; Sediments; Trace metals; Climate; Holocene; Organic matter; Shale; Carbonates;
Stable isotope (δ13C and δ15N) based interpretation of organic matter source and paleoenvironmental conditions in Al-Azraq basin, Jordan by Khaldoun Ahmad; Caroline Davies (49-60).
This study examines the stable isotopes of carbon and nitrogen from cored lacustrine sediments of the Al-Azraq, an arid lake basin on the Jordan Plateau. Lacustrine sediments contain valuable records of paleoenvironmental conditions, recording local and regional responses to environmental change. Previous paleo-reconstructions on the Jordan Plateau are based on archaeology, pollen, mineralogy, and stratigraphy. The application of organic geochemistry analyses to these lake sediments identifies multiple sources of organic matter, biological production, and contributes to understanding the paleoenvironments of the Al-Azraq basin during the mid-Pleistocene period. Organic carbon concentration (Corg) provides an overview of the organic matter distribution. Carbon isotopic composition (δ13Corg) and nitrogen isotopic composition (δ15N) are indicators of organic matter sources and paleoproductivity. Magnetic susceptibility (MGSUS) measured the concentration of ferromagnetic minerals and indicated aeolian inputs. Organic geochemistry differentiated five paleoenvironmental zones with specific sources of organic matter, both aquatic and terrestrial. It identified a long period of climate wetter than the present, punctuated by a short intense period of aridity. Diagenesis plays an important role in the decomposition of organic matter and studies indicate this degradation can alter the isotopic signals of organic matter. Analyses of the isotopic signals and statistical analyses demonstrate diagenesis is not a factor in the Al-Azraq sediments in all but Zone 4 of the paleoenvironmental zones. This Zone is defined by less negative carbon isotopic composition and the presence of thick primary gypsum layers, in addition to the influx of high peaks of aeolian sediment as reflected in the magnetic susceptibility data. Stable isotope geochemistry provides detailed information on the paleoenvironments of lake sediments, and is applicable to typically challenging arid basin sediments.
Keywords: Stable isotope; Organic matter; Paleoenvironments; Arid lake; Al-Azraq; Jordan;
Experimental assessment of well integrity for CO2 geological storage: A numerical study of the geochemical interactions between a CO2-brine mixture and a sandstone-cement-steel sample by Joachim Tremosa; Saeko Mito; Pascal Audigane; Ziqiu Xue (61-73).
Geologic storage of CO2 is one option for avoiding CO2 emissions from a large-scale point source such as a thermal power plant and a gas refinery. The alteration of well materials by CO2 under reservoir conditions requires characterization because the wells are the main possible leakage pathways for CO2 from a geological reservoir. This paper presents a numerical modeling of interaction experiments involving a composite well sample formed from steel casing surrounded by Portland cement, itself surrounded by sandstone and CO2-saturated brine at 10 MPa and 50 °C during a period of up to 8 weeks, as reported by Mito et al. (2015). A reactive-transport model was developed to simulate diffusion of the CO2-saturated brine in the well sample and the resulting successive dissolution/precipitation reactions in the sandstone, cement and steel. The observed changes in mineralogy (which primarily consist of dissolution of portlandite and Ca-rich CSH phases and precipitation of calcite, amorphous silica and zeolite) and the associated evolution in brine composition were reproduced by the model. A buffering role of sandstone on the cement degradation was evidenced, thus avoiding the re-dissolution of calcite usually observed in experiments with direct interaction between cement and CO2-saturated brine. Interestingly, the model results also noted a possible perturbation in the measured pH and Ca content due to CO2 outgassing during solution sampling. The Si behavior control linked with the uncertainty in zeolite stability is also discussed.
Keywords: Well integrity; CO2 storage; Cement carbonation; Reactive transport modeling; Phreeqc;
Np(V) uptake by bentonite clay: Effect of accessory Fe oxides/hydroxides on sorption and speciation by Parveen K. Verma; Anna Yu. Romanchuk; Irina E. Vlasova; Victoria V. Krupskaya; Sergey V. Zakusin; Alexey V. Sobolev; Alexander V. Egorov; Prasanta K. Mohapatra; Stepan N. Kalmykov (74-82).
Batch sorption experiments on thoroughly characterized bentonites and thermodynamic modeling studies were conducted to reveal the role of iron-containing accessory phases on the interfacial behavior of Np(V). Bentonite clays from different industrial deposits with varying total iron contents were selected for the studies. The samples were characterized by XRD, Mossbauer spectroscopy, XRF, HRTEM, SEM-EDX and other techniques, and wherever possible, the accessory iron phases were identified and quantified. Thermodynamic modeling using available surface complexation data revealed the dominant role of the goethite accessory phase, which was present as nanoparticles, in Np(V) sorption at trace level concentrations (10−14 M). This fact is independently supported by the combination of SEM-EDX and α-track radiography. These studies illustrate the important role that accessory minerals can play in radionuclides sorption data. This is important to the understanding and modeling of the molecular-level speciation of radionuclides.Display Omitted
Keywords: Neptunium; Interfacial behavior; Sorption; Speciation; Bentonite clays; Iron oxides; Goethite nanoparticles; Accessory minerals; Thermodynamic modeling; Surface complexation modeling;
Uptake of arsenate by aluminum (hydr)oxide coated red scoria and pumice by Tsegaye Girma Asere; Jeriffa De Clercq; Kim Verbeken; Dejene A. Tessema; Fekadu Fufa; Christian V. Stevens; Gijs Du Laing (83-95).
The development of cost effective and environmentally benign adsorbents for arsenic removal is absolutely required due to arsenic contamination of water sources in many regions around the globe. The use of materials which are locally available in the affected regions is important for successful implementation of the developed technologies in rural areas. In this regard, we treated volcanic rocks (red scoria and pumice) locally available in Ethiopia with an aluminum sulphate solution and evaluated these materials for their capacity to remove As(V) from aqueous systems. The adsorbents were characterized using ICP-OES, EDX, SEM and BET. The experimental sorption data fitted well a Freundlich isotherm and the pseudo-second-order model was found to be more suitable than the pseudo-first-order model to describe the adsorption kinetics. The Langmuir maximum adsorption capacity was 0.18 mg/g for aluminum-treated red scoria (Al-Rs) and 2.68 mg/g for aluminum-treated pumice (Al-Pu). The effect of pH, adsorbent dose, initial As(V) concentration and interfering ions on arsenic adsorption were studied. The leaching of aluminum from the adsorbent during the adsorption process was also investigated. Results of column experiments indicated that Al-Pu is suitable to treat low concentration of As(V) contaminated water. The Al-Pu adsorbent is recyclable with only about 9% loss of its original efficiency after the 3rd adsorption cycle (99.5%–90.2%). The data obtained from both batch and column studies indicate that Al-Rs and Al-Pu remove As(V) effectively from aqueous systems, with the latter being more efficient.
Keywords: Red scoria; Pumice; Aluminum; Arsenic; Adsorption;
“Old” carbon entering the South China Sea from the carbonate-rich Pearl River Basin: Coupled action of carbonate weathering and aquatic photosynthesis by Zaihua Liu; Min Zhao; Hailong Sun; Rui Yang; Bo Chen; Mingxing Yang; Qingrui Zeng; Haitao Zeng (96-104).
Generally, negative Δ14C values of riverine particulate organic carbon (POC) are interpreted as old carbon derived from the erosion of deep soils and sedimentary rocks. Here we present natural 14C and 13C data from the carbonate-rich Pearl River Basin that discharges into the South China Sea. We found that the Δ14C values of POC and DIC (dissolved inorganic carbon) transported by the carbonate-rich river are all negative. This, however, does not mean the POC is necessarily old but indicates control of carbonate weathering (producing “old” DIC with negative Δ14C values) coupled with contemporary aquatic photosynthesis (producing new autochthonous POC but with negative Δ14C values) through the “dead carbon” effect of carbonate rocks, which was further evidenced by particular seasonal change in Δ14C values of DIC and POC (both higher in the rainy season and lower in dry season), spatial variation (both getting higher downstream), and negative correlation between δ13C and “age” of POC. This finding indicates that previous studies suggesting that riverine POC depleted in 14C is old may be problematic in carbonate-dominated river basins. The finding that river basins rich in carbonates can release “old” POC may have important implications for the interpretation of organic carbon age in rivers and coastal oceans affected by the runoff from this basin type. It also indicates that it is necessary to examine the concentrations of both DIC and autochthonous organic carbon in rivers to correctly assess the carbon sink produced by rock weathering.
Keywords: Carbon age; DIC; POC; Carbon source; Carbonate weathering; Aquatic photosynthesis; Pearl River;
Evidence of trace element emission during the combustion of sulfide-bearing metallurgical slags by Svetlana Borisovna Bortnikova; Vladimir Vladimirovich Olenchenko; Olga Lukinichna Gaskova; Konstantin Ivanovich Chernii; Anna Yurevna Devyatova; Dmitrii Olegovich Kucher (105-115).
The present study shows the results of field and laboratory studies of trace element transfer from waste heaps of metallurgical slags (Kemerovo region, town of Belovo). Temperature anomalies were observed, with high temperatures up to 81.2 °C on the top of the heap. A visual geophysical model of the inner parts of the heap with contrasting resistivity zones was obtained using the electrical resistivity tomography (ERT) method, and quantitative characteristics were derived. Dry and frozen slag zones were characterized by resistivity of 50–500 Ohm·m. The resistivity of wet slag varied from 5 to 10 Ohm·m for slag with low humidity of 1–2 Ohm·m for slag saturated with highly mineralized solutions. The local anomaly of extremely low resistivity (0.3–0.5 Ohm·m) might be associated with a combustion centre or high pore solutions TDS. Basic major elements (Ca, Mg, K, Na, Si, and Al), metals (Cu, Zn, Pb, and Cd) and anionic elements (As, Sb, and V) were determined in gas condensates in situ. The most volatile elements were basic elements: Ca > Cu > Mg > Na > Mn > Fe, Zn. Lower concentration in the condensates was determined for Si > K > As > Sr > Al > V and Pb, Ba, La were also found. The observed mineral paragenetic sequences were primary minerals of barite-polymetallic ores and sphalerite concentrate, high-temperature minerals formed during pyrometallurgical processing and/or permanent combustion of the heap surface, efflorescence minerals formed by atmospheric oxidation accelerated by acid steam condensation. An experimental investigations using stepwise and 500 °C heating of the same samples were performed to compare the elements that were released into the gas phase in situ and off-site.Display Omitted
Keywords: Metallurgical slags; Combustion; Condensates; Experimental study; Geophysical and chemical modeling;
Tracking the interaction between injected CO2 and reservoir fluids using noble gas isotopes in an analogue of large-scale carbon capture and storage by Domokos Györe; Stuart M.V. Gilfillan; Finlay M. Stuart (116-128).
Industrial scale carbon capture and storage technology relies on the secure long term storage of CO2 in the subsurface. The engineering and safety of a geological storage site is critically dependent on how and where CO2 will be stored over the lifetime of the site. Hence, there is a need to determine how injected CO2 is stored and identify how injected CO2 interacts with sub-surface fluids. Since July 2008 ∼1 Mt of CO2 has been injected into the Cranfield enhanced oil recovery (EOR) field (MS, USA), sourced from a portion of the natural CO2 produced from the nearby Jackson Dome CO2 reservoir. Monitoring and tracking of the amount of recycled CO2 shows that a portion of the injected CO2 has been retained in the reservoir. Here, we show that the noble gases (20Ne, 36Ar, 84Kr, 132Xe) that are intrinsic to the injected CO2 can be combined with CO2/3He and δ13CCO2 measurements to trace both the dissolution of the CO2 into the formation water, and the interaction of CO2 with the residual oil. Samples collected 18 months after CO2 injection commenced show that the CO2 has stripped the noble gases from the formation water. The isotopic composition of He suggests that ∼0.2%, some 7 kt, of the injected CO2 has dissolved into formation water. The CO2/3He and δ13CCO2 values imply that dissolution is occurring at pH = 5.8, consistent with the previous determinations. δ13CCO2 measurements and geochemical modelling rule out significant carbonate precipitation and we determine that the undissolved CO2 after 18 months of injection (1.5 Mt) is stored by stratigraphic or residual trapping. After 45 months of CO2 injection, the noble gas concentrations appear to be affected by CO2-oil interaction, overprinting the signature of the formation water.
Keywords: Carbon capture and storage; Geological storage; Geochemical tracing; Carbon isotope; Noble gas isotope; Mass spectrometry;
Examining nitrogen dynamics in the unsaturated zone under an inactive cesspit using chemical tracers and environmental isotopes by Claudia Varnier; Ricardo Hirata; Ramon Aravena (129-138).
This study evaluates the dynamics of nitrogen compounds generated by infiltration of wastewater from an inactive cesspit in the unconfined and sedimentary Adamantina Aquifer in Urânia, Brazil. A monitoring station, consisting of an 11.2 m well (1.8 m in diameter) with an array of 12 tensiometers and 12 suction lysimeters, was installed to monitor the shallow unsaturated zone from 0.5 to 9 m depth. A monitoring well was also installed below the water level to monitor the shallow aquifer. High amounts of ammonium (up to 96 mg/L NH4 +-N) and nitrate (up to 458 mg/L NO3 −-N) were observed in the unsaturated zone porewater which is comparable to active septic systems effluents. The distribution of NO3 −, Cl− and Na+, typical constituents of sewage effluents, varied seasonally and spatially, which is correlated with changes in infiltration rates between the wet and dry seasons and with hydraulic conductivity variations in interlayered sandy and clayey sediments. A detailed monitoring of porewater geochemistry demonstrated the occurrence of several important reactions affecting nitrogen dynamics in the unsaturated zone: i) oxidation of organic matter, ii) ammonification, iii) nitrification, iv) methanogenesis, v) denitrification and likely, vi) sulfate reduction. The changes in nitrogen compound distribution and δ15NNO3 and δ18ONO3 values in porewater, in association with the N2O concentration and δ15NN2O and δ18ON2O signatures in gas samples, indicate the occurrence of nitrification and denitrification, suggesting the coexistence of reducing and oxidizing microsites in the unsaturated zone. This study indicated that cesspits can generate a significant amount of nitrate even a few years after being inactivated which can represent a potential long-term source of nitrate to groundwater in highly populated areas.
Keywords: Cesspits; Unsaturated zone; Nitrate; Stable isotopes; Gases;
Hydromagnesite precipitation in the Alkaline Lake Dujiali, central Qinghai-Tibetan Plateau: Constraints on hydromagnesite precipitation from hydrochemistry and stable isotopes by Yongjie Lin; Mianping Zheng; Chuanyong Ye (139-148).
The mineral hydromagnesite, Mg5(CO3)4(OH)2·4H2O, is a common form of hydrated Mg-carbonate in alkaline lakes, yet the processes involved in its formation are not well understood. This study focuses on Dujiali Lake, in the central Qinghai-Tibetan Plateau (QTP), which is one of the few environments on the earth's surface with extensive Holocene precipitation of hydromagnesite. The hydrogeochemistry of surface waters, and the mineralogical, stable isotope (δ13C and δ18O), and radiogenic isotope content of hydromagnesite deposits were analyzed to investigate formation mechanisms. The chemical composition of surface water around Dujiali Lake evolved from the rock-weathering-type waters of T1 (Ca―Mg―HCO3 water type) to more concentrated sodic waters of T2 (Na―SO4 ―Cl water type) due to evaporation. XRD results show that the mineralogical composition of samples is pure hydromagnesite. Analysis of oxygen isotopes in the hydromagnesite indicates that supergene formation with authigenic carbonate crystallization from evaporation water is the dominant precipitation process. Combined carbon-oxygen isotope analysis suggests atmospheric CO2 provided a carbon source for the precipitation of hydromagnesite. These findings suggest that hydromagnesite precipitation at Lake Dujiali is mainly inorganic in nature, and the greenhouse gas, CO2, is trapped and stored in the hydromagnesite directly from the atmosphere. AMS radiocarbon dating of samples indicates CO2 was sequestered between 5845 ± 30 to 6090 ± 25 cal a BP in the Dujiali Lake hydromagnesite deposit. The study contributes to improved understanding of hydromagnesite formation in modern and ancient playas.
Keywords: Hydromagnesite; Hydrochemistry; Stable isotopes; Evaporative sedimentation; Alkaline lake; Qinghai-Tibetan Plateau;
Effects of warming and increased nitrogen and sulfur deposition on boreal mire geochemistry by Carolina Olid; Richard Bindler; Mats B. Nilsson; Tobias Eriksson; Jonatan Klaminder (149-157).
Boreal mire ecosystems are predicted to experience warmer air temperatures as well as changed deposition loads of nitrogen and sulfur during the coming century. In this study, we hypothesized that vegetation changes that accompany these new environmental conditions alter the chemical composition of peat. To test this hypothesis, we quantified changes in peat geochemistry (Al, Ca, Fe, Mg, Na, P, Pb, and Zn) that have occurred in field manipulation plots exposed to 12 years of warming and nitrogen and sulfur additions in a nutrient-poor boreal mire. In contrast to non-nutrients with a mainly atmospheric origin (i.e. Pb), Al-normalized inventories of micronutrients (Zn and Fe) and macronutrients (P and Ca) were significantly (P < 0.05) higher as a result of warming. For P and Ca, enrichments were also induced by nitrogen additions alone. These results suggest that mires evolving under increasing temperatures and availability of nitrogen are around two times more effective in storing nutrients in the accumulating peat. Our study provides the first empirical evidence that predicted changes in climate and nitrogen deposition scenarios will increase the retention of Ca, Fe, P, and Zn in surface peat of boreal mires in the near future, which may cause a depletion of nutrients released to inland waters dependent on mire inputs.
Keywords: Peat geochemistry; Nutrients; Mire; Climate change; Temperature; Nitrogen;
Rare earth element enriched birnessite in water-bearing fractures, the Ytterby mine, Sweden by Susanne Sjöberg; Bert Allard; Jayne E. Rattray; Nolwenn Callac; Anja Grawunder; Magnus Ivarsson; Viktor Sjöberg; Stefan Karlsson; Alasdair Skelton; Christophe Dupraz (158-171).
Characterization of a black substance exuding from fractured bedrock in a subterranean tunnel revealed a secondary manganese oxide mineralisation exceptionally enriched in rare earth elements (REE). Concentrations are among the highest observed in secondary ferromanganese precipitates in nature. The tunnel is located in the unsaturated zone at shallow depth in the former Ytterby mine, known for the discovery of yttrium, scandium, tantalum and five rare earth elements.Elemental analysis and X-ray diffraction of the black substance establish that the main component is a manganese oxide of the birnessite type. Minor fractions of calcite, other manganese oxides, feldspars, quartz and about 1% organic matter were also found, but no iron oxides were identified. The Ytterby birnessite contains REE, as well as calcium, magnesium and traces of other metals. The REE, which constitute 1% of the dry mass and 2% of the metal content, are firmly included in the mineral structure and are not released by leaching at pH 1.5 or higher. A strong preference for the trivalent REE over divalent and monovalent metals is indicated by concentration ratios of the substance to fracture water. The REE-enriched birnessite has the general formula Mx(Mn3+,Mn4+)2O4·(H2O)n with M = (0.37–0.41) Ca + 0.02 (REE + Y), 0.04 Mg and (0.02–0.03) other metals, and with [Mn3+]/[Mn4+] = 0.86–1.00.The influence of microorganisms on the accumulation of this REE enriched substance is demonstrated by electron paramagnetic resonance spectroscopy. Results show that it is composed of two or more manganese phases, one of which has a biogenic signature. In addition, the occurrence of C31 to C35 extended side chain hopanoids among the identified lipid biomarkers combined with the absence of ergosterol, a fungal lipid biomarker, indicate that the in-situ microbial community is bacterial rather than fungal.
Keywords: Ytterby mine; Manganese oxides; Birnessite; Rare earth elements; Microbial mediation;
Efficacy of acetate-amended biostimulation for uranium sequestration: Combined analysis of sediment/groundwater geochemistry and bacterial community structure by Jie Xu; Harish Veeramani; Nikolla P. Qafoku; Gargi Singh; Maria V. Riquelme; Amy Pruden; Ravi K. Kukkadapu; Brandy N. Gartman; Michael F. Hochella (172-185).
Systematic flow-through column experiments were conducted using sediments and ground water collected from different subsurface localities at the U.S. Department of Energy's Integrated Field Research Challenge site in Rifle, Colorado. The principal purpose of this study is to gain a better understanding of the interactive effects of groundwater geochemistry, sediment mineralogy, and indigenous bacterial community structures on the efficacy of uranium removal from the groundwater with/without acetate amendment. Overall, we find that the subtle variations in the sediments' mineralogy, redox conditions, as well as contents of metal(loid) co-contaminants showed a pronounced effect on the associated bacterial population and composition, which mainly determines the system's performance with respect to uranium removal. Positive relationship was identified between the abundance of dissimilatory sulfate-reduction genes (i.e., drsA), markers of sulfate-reducing bacteria, and the sediments' propensity to sequester aqueous uranium. In contrast, no obvious connections were observed between the abundance of common iron-reducing bacteria, e.g., Geobacter spp., and the sediments' ability to sequester uranium. In the sediments with low bacterial biomass and the absence of sulfate-reducing conditions, abiotic adsorption onto mineral surfaces such as phyllosilicates likely played a relatively major role in the attenuation of aqueous uranium; however, in these scenarios, acetate amendment induced detectable rebounds in the effluent uranium concentrations. The results of this study suggest that immobilization of uranium can be achieved under predominantly sulfate-reducing conditions, and provide insight into the integrated roles of various biogeochemical components in long-term uranium sequestration.
Keywords: Uranium bioremediation; Sulfate reducing bacteria; Bacterial communities;
Heavy metal content in urban residential and park soils: A case study in Spokane, Washington, USA by Carmen A. Nezat; Shyla A. Hatch; Ted Uecker (186-193).
Urban soils may be contaminated with heavy metals due to historical and current use of fertilizers, pesticides, wood preservatives, and construction materials. To examine the amount of trace metals from natural and anthropogenic sources, we focused on a middle-to-upper income, residential area in Spokane, Washington which was developed in the late 1800s but has not experienced heavy industrial activity. Surface soil was collected from thirty sites (including residential lawns, gardens, and city parks), and digested using EPA Method 3050B. The average As, Pb, and Zn concentrations in residential soils (11 mg kg−1, 59 mg kg−1, and 107 mg kg−1, respectively) exceeded those in below surface rural soils (9 mg kg−1, 15 mg kg−1, and 66 mg kg−1) indicating sources of contamination in this urban environment. Four sites had As or Pb concentrations above Washington State Department of Ecology levels for unrestricted land use (20 mg kg−1 and 250 mg kg−1, respectively). At one of these sites, Pb exceeded 1200 mg kg−1, the USEPA threshold for residential soil with unrestricted use, and an additional site had Pb concentrations above the 400 mg kg−1, the limit for children's play areas. The Pb:As ratio in soils with elevated As concentrations suggest that the likely source is arsenical pesticide or an As-bearing fertilizer. In soils with elevated Pb concentrations, Ba, Pb, and Zn were correlated which suggests ─ along with the soils' proximity to structures ─ that lead-based paint is likely the source. Although vehicle emissions also add these metals to soils near roadways, traffic density near our study sites was low.
Keywords: Urban; Soil; Metals; Arsenic; Lead; Paint;
Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH by Jill E. Burrows; Charles A. Cravotta; Stephen C. Peters (194-210).
Net-alkaline, anoxic coal-mine drainage containing ∼20 mg/L FeII and ∼0.05 mg/L Al and Zn was subjected to parallel batch experiments: control, aeration (Aer 1 12.6 mL/s; Aer 2 16.8 mL/s; Aer 3 25.0 mL/s), and hydrogen peroxide (H2O2) to test the hypothesis that aeration increases pH, FeII oxidation, hydrous FeIII oxide (HFO) formation, and trace-metal removal through adsorption and coprecipitation with HFO. During 5.5-hr field experiments, pH increased from 6.4 to 6.7, 7.1, 7.6, and 8.1 for the control, Aer 1, Aer 2, and Aer 3, respectively, but decreased to 6.3 for the H2O2 treatment. Aeration accelerated removal of dissolved CO2, Fe, Al, and Zn. In Aer 3, dissolved Al was completely removed within 1 h, but increased to ∼20% of the initial concentration after 2.5 h when pH exceeded 7.5. H2O2 promoted rapid removal of all dissolved Fe and Al, and 13% of dissolved Zn.Kinetic modeling with PHREEQC simulated effects of aeration on pH, CO2, Fe, Zn, and Al. Aeration enhanced Zn adsorption by increasing pH and HFO formation while decreasing aqueous CO2 available to form ZnCO3 0 and Zn(CO3)2 2− at high pH. Al concentrations were inconsistent with solubility control by Al minerals or Al-containing HFO, but could be simulated by adsorption on HFO at pH < 7.5 and desorption at higher pH where Al(OH)4 − was predominant. Thus, aeration or chemical oxidation with pH adjustment to ∼7.5 could be effective for treating high-Fe and moderate-Zn concentrations, whereas chemical oxidation without pH adjustment may be effective for treating high-Fe and moderate-Al concentrations.
Keywords: PHREEQC modeling; Fe oxidation kinetics; CO2 outgassing; Metals adsorption; Coprecipitation; Carbonate complexing;
Hg(II) reduction by siderite (FeCO3) by Juyoung Ha; Xiuhong Zhao; Riqing Yu; Tamar Barkay; Nathan Yee (211-218).
In groundwater, chemical reactions of Hg(II) with mineral surfaces play an important role in determining the concentration of mercury that is mobile and bioavailable. In this study, we investigated Hg(II) reduction by the ferrous carbonate mineral, siderite (FeCO3), to better understand reductive transformation of mercury in anoxic carbonate-bearing waters. Kinetic experiments and X-ray adsorption spectroscopy (XAS) were conducted to examine the rate and mechanism of Hg(II) reaction with siderite. Hg(II) was reacted with synthesized siderite mineral at various concentrations and the subsequently formed Hg(0) was measured to assess the extent of mercury reduction by siderite. Our experimental data showed that Hg(II) reduction by siderite resulted in the loss of Hg when reacted with siderite mineral suspensions concurrent to formation of gaseous Hg(0). Hg(II) reduction occurred within minutes and reaction rates increased with increasing siderite surface area. XAS analysis confirmed that Hg(II) was reduced to Hg(0) and revealed that reduced mercury was sorbed to siderite surfaces suggesting that electron transfer reactions occur at siderite/water interface. The results of our study suggest that Hg(II) reduction by siderite is a kinetically favorable pathway for the mercury mobilization in ferruginous carbonate-bearing waters.
Reactive transport modelling of the hydro-geochemical behaviour of partially oxidized acid-generating mine tailings with a monolayer cover by Thomas Pabst; John Molson; Michel Aubertin; Bruno Bussière (219-233).
The efficiency of a monolayer cover to prevent acid mine drainage (AMD) generation from two pre-oxidized tailings impoundments was assessed using the MIN3P code, a finite volume model for coupled groundwater flow, oxygen diffusion and multi-component reactive transport. Numerical simulations were validated using large column tests set up in the laboratory and monitored during 19 wetting and drying cycles, over approximately two years. Results indicate that a monolayer cover made of either non acid-generating tailings or a till was not able to prevent sulfide oxidation in the underlying reactive tailings, both for the conditions applied in the laboratory and under conditions more representative of field observations. The efficiency of the simulated monolayer cover was highly dependent on the position of the water table. Despite improved water quality, the reactive tailings nonetheless continued to oxidize and generate AMD, even when the water table was close to the surface of the tailings (1 m depth). The results from this study indicate that the efficiency criteria for cover systems on fresh unoxidized tailings may not be directly applicable for pre-oxidized tailings. The paper also presents a few modifications to the MIN3P code that were successfully applied to simulate the hydrogeological and geochemical response of pre-oxidized, already acidic and highly contaminated tailings.
Keywords: Acid mine drainage (AMD); Monolayer cover; Elevated water table (EWT); Reactive transport modelling;
Arsenic oxyanion binding to NOM from dung and aquaculture pond sediments in Bangladesh: Importance of site-specific binding constants by Tiffany Y. Lin; Saeedreza Hafeznezami; Lynn Rice; Janna Lee; Amanda Maki; Tiffany Sevilla; Mason Stahl; Rebecca Neumann; Charles Harvey; I.H.(Mel) Suffet; A. Borhan M. Badruzzaman; Jennifer A. Jay (234-240).
Groundwater contamination by arsenic (As) is a serious public health concern in many different areas worldwide, particularly in the Bengal region. Mobilization and fate of As in natural waters is controlled by a variety of factors including the presence of natural organic matter (NOM). This study experimentally determined conditional distribution coefficients (with KD defined as the ratio between As bound to NOM and truly dissolved As) and apparent stability constants between AsIII oxyanions and NOM from cow dung, chicken dung, and Bangladeshi aquaculture pond sediment prior to and after one year of operation. As-sorption experiments with cow dung as the source of NOM resulted in the highest range for log KD, from 4.7 to 6.3. Pond sediment from Bangladesh after a year of operation for fish production showed greater affinity for binding As oxyanions than fresh sediment prior to fish production. PHREEQCI modeling using constants derived from the experiments along with water chemistry parameters typical for the site supports the dominance of AsIII oxyanion-NOM complexation in this system. Models employing constants from previous studies using purified NOM considerably underestimate observed complexation by environmental NOM; thus, applying site-specific constants to geochemical models will better predict As speciation for the field site.
Keywords: Arsenic; Organic matter; Modeling; Complexation; Binding; Groundwater; Manure; Sediment;
Complexation of europium and uranium with natural organic matter (NOM) in highly saline water matrices analysed by ultrafiltration and inductively coupled plasma mass spectrometry (ICP-MS) by Ramona Hahn; Christina Hein; Jonas M. Sander; Ralf Kautenburger (241-249).
Along with general scientific developments for the safe long-term storage as well as for disposal of high level radioactive waste (HLW) an onward improvement in the geochemical process understanding is crucial. Natural organic matter (NOM) can play an important role in the immobilisation or mobilisation of these metal ions due to their complexation and colloid formation tendency. In this study, the complexation behavior of humic acids (HA) and other NOM from different sources and its influence on the mobilisation of europium as homologues of the trivalent actinides like americium and uranium as main component of HLW have been analysed in highly saline solutions of CaCl2 and NaCl solutions up to 1 moL L−1 ion strength. Ultrafiltration (UF) in combination with inductively coupled plasma mass spectrometry (ICP-MS) has been used for the evaluation of complex stability constants log β. In selected cases capillary electrophoresis (CE) coupled to ICP-MS is used as complementary speciation technique to verify the UF results. To determine the complex stability constants a simple single site model is used. Depending on the source of the analysed NOM log β values in the range of 6.8–4.5 for Eu(III) and 6.3–4.5 for U(VI) (UO2 2+) can be estimated by UF and CE-ICP-MS experiments. Increasing ionic strength (1 moL L−1 NaCl) reduces the available complexation sites of NOM resulting in lower amounts of NOM-complexed Eu(III) and U(VI) (UO2 2+), respectively. The additional presence of calcium (0.5–5 mmoL L−1 CaCl2 added to 0.1 moL L−1 NaCl) as a bivalent competing cation leads to lower levels of binding to NOM particularly for europium and Aldrich HA as well as for Eu and HA extracted from Gorleben site. In the case of uranyl, the results are different in comparison to europium. Higher amounts of Ca (5 mmoL L−1) in solution increase the levels of NOM complexation for uranyl. In contrast to the results for HA the used Suwannee river NOM reveals log β values in the range of nearly two orders of magnitude lower (4.5–4.1 for Eu3+ and 4.8–4.6 for UO2 2+). Moreover, the three examined HA from different sources (soil and river HA extracts) show significant differences in their complexation behavior under the geochemical conditions applied in this study.Display Omitted
Keywords: Ultrafiltration; ICP-MS; Europium; Uranium; NOM; Complex stability constants; Salinity;
Impact of elevated CO2 concentrations on carbonate mineral precipitation ability of sulfate-reducing bacteria and implications for CO2 sequestration by Varun G. Paul; David J. Wronkiewicz; Melanie R. Mormile (250-271).
Interest in anthropogenic CO2 release and associated global climatic change has prompted numerous laboratory-scale and commercial efforts focused on capturing, sequestering or utilizing CO2 in the subsurface. Known carbonate mineral precipitating microorganisms, such as the anaerobic sulfate-reducing bacteria (SRB), could enhance the rate of conversion of CO2 into solid minerals and thereby improve long-term storage of captured gasses. The ability of SRB to induce carbonate mineral precipitation, when exposed to atmospheric and elevated pCO2, was investigated in laboratory scale tests with bacteria from organic-rich sediments collected from hypersaline Lake Estancia, New Mexico. The enriched SRB culture was inoculated in continuous gas flow and batch reactors under variable headspace pCO2 (0.0059 psi to 20 psi). Solution pH, redox conditions, sulfide, calcium and magnesium concentrations were monitored in the reactors. Those reactors containing SRB that were exposed to pCO2 of 14.7 psi or less showed Mg-calcite precipitation. Reactors exposed to 20 psi pCO2 did not exhibit any carbonate mineralization, likely due to the inhibition of bacterial metabolism caused by the high levels of CO2. Hydrogen, lactate and formate served as suitable electron donors for the SRB metabolism and related carbonate mineralization. Carbon isotopic studies confirmed that ∼53% of carbon in the precipitated carbonate minerals was derived from the CO2 headspace, with the remaining carbon being derived from the organic electron donors, and the bicarbonate ions available in the liquid medium. The ability of halotolerant SRB to induce the precipitation of carbonate minerals can potentially be applied to the long-term storage of anthropogenic CO2 in saline aquifers and other ideal subsurface rock units by converting the gas into solid immobile phases.
Adsorption of inorganic pollutants on bauxite residues: An example of methodology to simulate adsorption in complex solids mixtures by Mehwish Taneez; Charlotte Hurel; Nicolas Marmier; Grégory Lefèvre (272-278).
Bauxite residue rich in iron and aluminum oxide is good adsorbing material for inorganic pollutants. Composition and physic-chemical parameters of 2 bauxite residues (Bauxaline® and Bauxsol) were determined. Adsorption of arsenic and cadmium from aqueous solutions on Bauxaline® and Bauxsol was studied as a function of solid to liquid ratios, pH and initial adsorbate concentrations. Both solids showed optimum removal of As and Cd at near to neutral pH. Adsorption data were modeled using2-pK/Double Layer Model. In the model, the complex composition of bauxite residues was simplified by considering that Bauxaline® and Bauxsol were made of a binary mixture of iron and aluminum oxides. Considering acid-base and surface complexation (for As and Cd) equilibriums and constants from the literature, the model proposed in this work has shown to be predictive. Adsorption mechanism was found consistent with the formation of a surface complex along with surface precipitation for cadmium.Display Omitted
Keywords: Surface complexation model; Red mud; Iron oxide; Aluminum oxide;
Effect of flavin compounds on uranium(VI) reduction- kinetic study using electrochemical methods with UV-vis spectroscopy by Shinya Yamasaki; Kazuya Tanaka; Naofumi Kozai; Toshihiko Ohnuki (279-286).
The reduction of uranium hexavalent (U(VI)) to tetravalent (U(IV)) is an important reaction because of the change in its mobility in the natural environment. Although the flavin mononucleotide (FMN) has acted as an electron shuttle for the U(VI) reduction in vivo system, which is called an electron mediator, only the rate constant for the electron transfer from FMN to U(VI) has been determined. This study examined the rate constant for the U(VI) reduction process by three flavin analogues (riboflavin, flavin mononucleotide, flavin adenine dinucleotide) to elucidate their substituent group effect on the U(VI) reduction rate by electrochemical methods. The formation of the U(IV) was monitored by UV-vis spectrometry at 660 nm during the constant potential electrolysis of the U(VI) solution in the presence of the mediator. The cyclic voltammograms indicated that the three flavin analogues behaved as electron mediator to reduce U(VI). The logarithmic rate constant for the U(VI) reduction was related to the standard redox potential of the mediators. This linear relationship indicated that the redox-active group of the mediator and the substituent group of the mediator dominate capability of the U(VI) reduction and its rate, respectively. The apparent reduction potential of U(VI) increased about 0.2 V in the presence of the mediators, which strongly suggests that the biological electron mediator makes the U(VI) reduction possible even under more oxidative conditions.
Keywords: Cyclic voltammetry; Electron shuttles; Flavin; Electron mediator; Catalytic reduction;
Vertical distributions of Pu and radiocesium isotopes in sediments from Lake Inba after the Fukushima Daiichi Nuclear Power Plant accident: Source identification and accumulation by Liguo Cao; Nobuyoshi Ishii; Jian Zheng; Maiko Kagami; Shaoming Pan; Keiko Tagami; Shigeo Uchida (287-294).
Radiocesium isotopes were released into the environment in the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, which resulted from the massive Tohoku earthquake in March 2011. Lake Inba is located in Chiba Prefecture about 200 km from the FDNPP site and the lake was contaminated by radioactivity from the accident. The present work was carried out in order to investigate the vertical distributions and accumulations of radiocesium and Pu in sediment cores collected during 2011–2015, and to study the migration behaviors of radiocesium and Pu isotopes in the sediments. The observed 134Cs/137Cs activity ratios in the core samples were approximately 1 (decay-corrected to 15 March, 2011), suggesting that sediment samples were contaminated by the FDNPP-released radiocesium. Compared with radiocesium inventories in soil in the area surrounding the Lake Inba, the calculated higher radiocesium inventories of the collected sediment cores indicated that most of the radiocesium was subsequently accumulated in the lake, and that the radiocesium input by atmospheric deposition and input from surrounding soil were greater than the output of the radiocesium. The 239+240Pu activities in the sediments were all within the background level seen before the accident. The atom ratios of 240Pu/239Pu ranged from 0.175 to 0.210, suggesting that Pu originated from global stratospheric fallout rather than from the FDNPP accident.
Organic matter maturity and hydrocarbon potential of the Lower Oligocene Menilite facies in the Eastern Flysch Carpathians (Tarcău and Vrancea Nappes), Romania by Małgorzata Wendorff; Mariusz J. Rospondek; Bartosz Kluska; Leszek Marynowski (295-310).
Bulk organic geochemical and molecular composition data have been used to analyse the hydrocarbon potential and organic matter maturity of the Lower Oligocene Menilite facies from two adjacent tectonic units of the Eastern Flysch Carpathians (Tarcău and Vrancea Nappes), Romania due to the importance of these source rocks in hydrocarbon exploration in entire Paratethys realm. The data show strong variability in organic matter quantity and quality. Organic carbon content reaches peak values in the siliceous facies of the Lower Menilite Member (up to 8.6 wt% TOC), which contains type II kerogen. With increasing contribution of flysch sedimentation mixed type II/III kerogen gains importance. The biomarker distribution reveals strong variation in the supplied organic matter common for flysch-influenced sedimentary environments. Terrigenous input is marked by epicuticular wax imprint in n-alkane distribution and occurrence of conifer biomarkers, while marine organic matter origin is expressed by the occurrence of short-chain n-alkanes and hopanes especially in the siliceous facies. Thus, these source rocks can be classified as oil-prone and subordinately mixed oil/gas-prone. The maturity in the outer tectonic unit (Vrancea) is low (T max ∼425 °C, Ro ∼0.4%) but increases towards the inner Tarcău Nappe (T max ∼430 °C, Ro ∼0.5%) reaching onset of hydrocarbon generation. The studied rocks have good petroleum potential, but hydrocarbons were generated only in more mature Tarcău Nappe, where solid bitumen veins were observed. Bitumen impregnation of numerous vitrinite grains possibly suppressed vitrinite reflectance, thus leading to more accurate maturity assessment based on molecular proxies (biomarker maturity indices). The observed difference in maturity levels between the nappes results from the more inner position of the sampled Tarcău Nappe succession within the orogen relative to the Vrancea unit. This is related to different burial histories, as well as variation in subsequent erosion and exhumation levels. The actual hydrocarbon potential in the studied area varies due to local interplay of these critical factors.
Keywords: Eastern Flysch Carpathians; Lower Oligocene; Menilite facies; Thermal maturity; Hydrocarbon potential; Biomarker ratios;
Darapskite solubility in basic solutions at 25 °C: A Pitzer model for the Na―NO3 ―SO4 ―OH―H2O system by Adeline Lach; Laurent André; Arnault Lassin (311-320).
We propose a set of Pitzer interaction parameters to describe the chemical behavior of the Na2SO4 ―NaNO3 ―NaOH―H2O quaternary system at 25 °C. With these parameters we have been able to adequately predict the properties of Na2SO4 ―NaNO3 ―H2O, Na2SO4 ―NaOH―H2O and NaNO3 ―NaOH―H2O ternary and Na2SO4 ―NaNO3 ―NaOH―H2O quaternary systems, including the solubility of different single salts and the double salt darapskite (Na2SO4·NaNO3·H2O), a mineral that is expected to form in the matrix of some radioactive waste containers. We also successfully reproduced the osmotic coefficient, the water activity and the mean activity coefficients for the Na2SO4 ―H2O, NaNO3 ―H2O and NaOH―H2O binary systems. We obtained the set of Pitzer parameters using a step-by-step modeling approach. First, we investigated the binary systems: the NaOH―H2O and Na2SO4 ―H2O binary system interaction parameters were established in previous studies from heat capacity and osmotic coefficient data. Among the various chemical models proposed in the literature that describe the properties of the NaNO3 ―H2O binary system, we chose the full dissociation hypothesis, since it allowed complete description of the system with the minimal number of interaction parameters. Next, from the mineral solubility data, we determined the specific interaction parameters for ternary systems. Without further parameterization, the solubility of the various salts in the quaternary system could be reproduced accurately.
Keywords: Pitzer model; Darapskite; Solubility; NaOH; Alkaline systems;
Biotic arsenic release from spent adsorbents under anaerobic landfill conditions by Mengling Y. Stuckman; Lauren N. Corrigan; John J. Lenhart (321-333).
The influence of biotic processes that occur in anaerobic conditions in landfills on arsenic (As) release from As-laden waste and the dependence of these processes on leachate composition was evaluated using incubations of an As-bearing water treatment residual comprised of the iron-oxide E33 adsorbent. This adsorbent, which is mainly goethite, was incubated with an As(V) and sulfate reducing bacterium, Bacillus benzoevorans HT1, and an Fe(III) and As(V) reducing bacterium, Shewanella putrefaciens CN32, in synthetic leachate with composition similar to landfill leachate. The influence of leachate composition on biotic As release was evaluated by studying systems prepared with a leachate solution that incorporated elevated concentrations of phosphate, bicarbonate, sulfate or silicate. The total As released under biotic conditions was two orders of magnitude higher than that in the abiotic control and during the initial stages of the incubations we observed most of the arsenic as As(III), consistent with the dissimilatory reduction of As(V). At later times, however, trends differed based upon whether the system was equilibrated with CN32 or HT1. Under the baseline leachate conditions, CN32-mediated As release was further promoted by reductive dissolution of goethite, while HT1-mediated As release was limited via indirect reductive goethite dissolution controlled by dissimilatory sulfate reduction. Biotic incubations with elevated anions identified As release behavior that reflected the influence of the different anions. Elevating phosphate not only promoted rapid As release via enhanced As(V) bioreduction in the first 2 days of incubation, but also incurred secondary As release from iron sulfide phases, which were secondary mineral phases generated from Fe(III) reduction. Increasing bicarbonate stimulated As release as it exchanged with sorbed As at the goethite surface thereby increasing the availability of As(V) for bioreduction. Elevating sulfate and silicate both decreased biotic As release as they appeared to inhibit Fe(III) bioreduction. Overall, our results identified that biotic As release mechanisms were related to bacteria metabolic diversity and leachate composition. Such information can assist in evaluating As risk assessment and As-laden waste management in biologically active environments, such as landfills.
Use of nitrogen isotopes and other geochemical tools to evaluate the source of ammonium in a confined glacial drift aquifer, Ottawa County, Michigan, USA by Derrick A. Lingle; Alan E. Kehew; R.V. Krishnamurthy (334-342).
This study utilized several isotopic tracers and geochemical parameters to characterize the source and hydrogeochemical setting of elevated ammonium (NH4 +) concentrations (>2 mg/L) in a confined glacial drift aquifer in Ottawa County, Michigan. Results from this investigation indicate that NH4 + is attributed to degrading in situ organic matter and not from surficial anthropogenic sources. Tritium, δ18O, and δ2H values suggest that primary recharge in the confined aquifer occurred during the middle to late Holocene and before the mid-1900's. Geochemical constituents, including redox parameters and a suite of common ions, demonstrate a compositional difference between the confined and unconfined aquifers in the study area and therefore further support the isolation of the confined aquifer from a significant amount of recent recharge (post 1950's). Insignificant δ15N- NH4 + fractionation (+0.81‰ to +1.38‰) implies that NH4 + in the confined aquifer originated from degrading in situ organic matter. A complete Rotosonic glacial sediment core, collected to characterize the physical setting of the NH4 +-rich aquifer, confirmed the presence of in situ organic matter in the confined aquifer. A limited set of δ15N-NO3 and δ18O-NO3 values suggest that the application of manure to row crops may be contributing nitrate (up to 10 mg/L) to nearby shallow residential wells. As implemented in this study, the use of multiple geochemical and isotopic parameters, including δ15N-NH4, can be applied to evaluate the potential source of NH4 + in an aquifer.
Keywords: Ammonium; Nitrogen isotopes; Buried organic matter; Glacial drift aquifer; Deuterium excess;
Lithium recovery from shale gas produced water using solvent extraction by Eunyoung Jang; Yunjai Jang; Eunhyea Chung (343-350).
Shale gas produced water is hypersaline wastewater generated after hydraulic fracturing. Since the produced water is a mixture of shale formation water and fracturing fluid, it contains various organic and inorganic components, including lithium, a useful resource for such industries as automobile and electronics. The produced water in the Marcellus shale area contains about 95 mg/L lithium on average. This study suggests a two-stage solvent extraction technique for lithium recovery from shale gas produced water, and determines the extraction mechanism of ions in each stage. All experiments were conducted using synthetic shale gas produced water. In the first-stage, which was designed for the removal of divalent cations, more than 94.4% of Ca2+, Mg2+, Sr2+, and Ba2+ ions were removed by using 1.0 M di-(2-ethylhexyl) phosphoric acid (D2EHPA) as an extractant. In the second-stage, for lithium recovery, we could obtain a lithium extraction efficiency of 41.2% by using 1.5 M D2EHPA and 0.3 M tributyl phosphate (TBP). Lithium loss in the first-stage was 25.1%, and therefore, the total amount of lithium recovered at the end of the two-step extraction procedure was 30.8%. Through this study, lithium, one of the useful mineral resources, could be selectively recovered from the shale gas produced water and it would also reduce the wastewater treatment cost during the development of shale gas.Display Omitted
Carbon isotope fractionation between amorphous calcium carbonate and calcite in earthworm-produced calcium carbonate by E.A.A. Versteegh; S. Black; M.E. Hodson (351-356).
In this study we investigate carbon isotope fractionation during the crystallization of biogenic calcium carbonate. Several species of earthworm including Lumbricus terrestris secrete CaCO3. Initially a milky fluid comprising micro-spherules of amorphous CaCO3 (ACC) is secreted into pouches of the earthworm calciferous gland. The micro-spherules coalesce and crystalize to form millimetre scale granules, largely comprising calcite. These are secreted into the earthworm intestine and from there into the soil. L. terrestris were cultured for 28 days in two different soils, moistened with three different mineral waters at 10, 16 and 20 °C. The milky fluid in the calciferous glands, granules in the pouches of the calciferous glands and granules excreted into the soil were collected and analysed by FTIR spectroscopy to determine the form of CaCO3 present and by IRMS to determine δ13C values. The milky fluid was ACC. Granules removed from the pouches and soil were largely calcite; the granules removed from the pouches contained more residual ACC than those recovered from the soil. The δ13C values of milky fluid and pouch granules became significantly more negative with increasing temperature (p ≤ 0.001). For samples from each temperature treatment, δ13C values became significantly (p ≤ 0.001) more negative from the milky fluid to the pouch granules to the soil granules (−13.77, −14.69 and −15.00 respectively at 10 °C; −14.37, −15.07 and −15.18 respectively at 16 °C and −14.89, −15.41 and −15.65 respectively at 20 °C). Fractionation of C isotopes occurred as the ACC recrystallized to form calcite with the fractionation factor εcalcite-ACC = −1.20 ± 0.52‰. This is consistent with the crystallization involving dissolution and reprecipitation rather than a solid state rearrangement. Although C isotopic fractionation has previously been described between different species of dissolved inorganic carbon and various CaCO3 polymorphs, this is the first documented evidence for C isotope fractionation between ACC and the calcite it recrystallizes to. This phenomenon may prove important for the interpretation of CaCO3-based C isotope environmental proxies.
Keywords: Earthworms; Calcium carbonate; Calcite; Carbon isotopes; Fractionation; Crystallization;
Comparison of three persulfate digestion methods for total phosphorus analysis and estimation of suspended sediments by Elizabeth Ann Dayton; Shane Whitacre; Christopher Holloman (357-362).
As a result of impairments to fresh surface water quality due to phosphorus enrichment, substantial research effort has been put forth to quantify agricultural runoff phosphorus as related to on-field practices. While the analysis of runoff dissolved phosphorus is well prescribed and leaves little room for variability in methodology, there are several methods and variations of sample preparation reagents as well as analysis procedures for determining runoff total phosphorus. Due to the variation in methodology for determination of total phosphorus and an additional laboratory procedure required to measure suspended solids, the objectives of the current study are to i. compare the performance of three persulfate digestion methods (Acid Persulfate, USGS, and Alkaline Persulfate) for total phosphorus percent recovery across a wide range of suspended sediments (SS), and ii. evaluate the ability of using Al and/or Fe in digestion solution to predict SS as a surrogate to the traditional gravimetric method. Percent recovery of total phosphorus was determined using suspensions prepared from soils collected from 21 agricultural fields in Ohio. The Acid Persulfate method was most effective, with an average total phosphorus percent recovery of 96.6%. The second most effective method was the USGS with an average total phosphorus recovery of 76.1%. However, the Alkaline Persulfate method performed poorly with an average 24.5% total phosphorus recovery. As a result application of Alkaline Persulfate digestion to edge of field monitoring may drastically underestimated runoff total phosphorus. In addition to excellent recovery of total phosphorus, the Acid Persulfate method combined with analysis of Al and Fe by inductively coupled plasma atomic emission spectrometry provides a robust estimate of total SS. Due to the large quantity of samples that can result from water quality monitoring, an indirect measure of total SS could be very valuable when time and budget constraints limit the number of procedures that can be run on a single water sample.
Keywords: Agricultural runoff; Phosphorus; Persulfate digestion;
Uranium delivery and uptake in a montane wetland, north-central Colorado, USA by R. Randall Schumann; Robert A. Zielinski; James K. Otton; Michael P. Pantea; William H. Orem (363-379).
Comprehensive sampling of peat, underlying lakebed sediments, and coexisting waters of a naturally uraniferous montane wetland are combined with hydrologic measurements to define the important controls on uranium (U) supply and uptake. The major source of U to the wetland is groundwater flowing through locally fractured and faulted granite gneiss of Proterozoic age. Dissolved U concentrations in four springs and one seep ranged from 20 to 83 ppb (μg/l). Maximum U concentrations are ∼300 ppm (mg/kg) in lakebed sediments and >3000 ppm in peat. Uranium in lakebed sediments is primarily stratabound in the more organic-rich layers, but samples of similar organic content display variable U concentrations. Post-depositional modifications include variable additions of U delivered by groundwater. Uranium distribution in peat is heterogeneous and primarily controlled by proximity to groundwater-fed springs and seeps that act as local point sources of U, and by proximity to groundwater directed along the peat/lakebeds contact. Uranium is initially sorbed on various organic components of peat as oxidized U(VI) present in groundwater. Selective extractions indicate that the majority of sorbed U remains as the oxidized species despite reducing conditions that should favor formation of U(IV). Possible explanations are kinetic hindrances related to strong complex formation between uranyl and humic substances, inhibition of anaerobic bacterial activity by low supply of dissolved iron and sulfate, and by cold temperatures.
Keywords: Uranium; Wetland; Peat; Groundwater;