Applied Geochemistry (v.27, #12)
Comparison of potentially toxic metals leaching from weathered rocks at a closed mine site between laboratory columns and field observation by Omar R. Salinas Villafane; Toshifumi Igarashi; Mitsuru Kurosawa; Toshio Takase (2271-2279).
► Copper, Pb, and Zn leaching from weathered rocks from a former mine were compared. ► Potentially toxic metals leaching from columns and field observations were similar. ► The pH was acidic and did not fluctuate significantly over the experiments. ► Copper and Zn concentrations increased with depth. ► Lead concentrations remained unchanged since Pb-Sulfate restricted its solubility.Potentially toxic metals, such as Cu, Pb and Zn, are leached from weathered rocks at many closed mine sites due to the acidic environments and mineralogical modifications. The mobilized toxic metals may cause contamination of surrounding water bodies. In this study, both laboratory column experiments and field observations at a former mine located in the north of Japan were carried out to compare the leaching behavior of Cu, Pb and Zn. The thickness of the surface weathered rock was varied (10, 20 and 30 cm) for the columns experiments while porous cups for porewater sampling were set up at different depths (GL-15, -45, -70, and -95 cm) for the field observations. Deionized water was added once a week over 75 weeks to the columns to simulate rainfall while porewater was extracted by a vacuum pump in several sampling campaigns (over 18 months). Similar low pH and leaching behavior of potentially toxic metals were observed for column experiments and field observations. A moderate increase in concentration with depth was observed for Cu and Zn. However, no increase in concentration was observed for Pb. This suggests that the leaching of Cu and Zn is enhanced by the length of the flow pathway through the weathered rock layer while Pb concentration is restricted by the precipitation of insoluble Pb sulfate. Thus, the thickness of the weathered rock layer is an important parameter that should be taken into consideration to estimate the loads of some potentially toxic metals, which is important when designing remediation schemes.
Environmental geochemistry of an active Hg mine in Xunyang, Shaanxi Province, China by Guangle Qiu; Xinbin Feng; Bo Meng; Jonas Sommar; Chunhao Gu (2280-2288).
► We investigated mercury distribution in the environment of Xunyang Hg mine in China. ► We found Hg concentrations in air, soil, water, sediment were elevated. ► We showed rice was contaminated with both total Hg and MeHg. ► We showed Hg mining is the source of Hg contamination in the study area.The Xunyang Hg mine (XMM) situated in Shaanxi Province is an active Hg mine in China. Gaseous elemental Hg (GEM) concentrations in ambient air were determined to evaluate its distribution pattern as a consequence of the active mining and retorting in the region. Total Hg (HgT) and methylmercury (MeHg) concentrations in riparian soil, sediment and rice grain samples (polished) as well as Hg speciation in surface water samples were measured to show local dispersion of Hg contamination. As expected, elevated concentrations of GEM were found, ranging from 7.4 to 410 ng m−3. High concentrations of HgT and MeHg were also obtained in riparian soils, ranged from 5.4 to 120 mg kg−1 and 1.2 to 11 μg kg−1, respectively. Concentrations of HgT and MeHg in sediment samples varied widely from 0.048 to 1600 mg kg−1 and 1.0 to 39 μg kg−1, respectively. Surface water samples showed elevated HgT concentrations, ranging from 6.2 to 23,500 ng L−1, but low MeHg concentrations, ranging from 0.022 to 3.7 ng L−1. Rice samples exhibited high concentrations of 50–200 μg kg−1 in HgT and of 8.2–80 μg kg−1 in MeHg. The spatial distribution patterns of Hg speciation in the local environmental compartments suggest that the XMM is the source of Hg contaminations in the study area.
Arsenic attenuation in tailings at a former Cu–W–As mine, SW Finland by Annika Parviainen; Matthew B.J. Lindsay; Rafael Pérez-López; Blair D. Gibson; Carol J. Ptacek; David W. Blowes; Kirsti Loukola-Ruskeeniemi (2289-2299).
► Arsenic attenuation occurred in the vadose zone of tailings at the Ylöjärvi Cu–W–As mine. ► Iron(III) (oxy)hydroxides and Fe(III) arsenates contributed to As attenuation. ► Variations in chemical composition and crystallinity may influence As stability. ► Geochemical conditions favored the stability of Fe(III) (oxy)hydroxides over Fe(III) arsenates.Nearly half a century after mine closure, release of As from the Ylöjärvi Cu–W–As mine tailings in groundwater and surface water run-off was observed. Investigations by scanning electron microscopy (SEM), electron microprobe analysis (EMPA), synchrotron-based micro-X-ray diffraction (μ-XRD), micro-X-ray absorption near edge structure (μ-XANES) and micro-extended X-ray absorption fine structure (μ-EXAFS) spectroscopy, and a sequential extraction procedure were performed to assess As attenuation mechanisms in the vadose zone of this tailings deposit. Results of SEM, EMPA, and sequential extractions indicated that the precipitation of As bearing Fe(III) (oxy)hydroxides (up to 18.4 wt.% As2O5) and Fe(III) arsenates were important secondary controls on As mobility. The μ-XRD, μ-XANES and μ-EXAFS analyses suggested that these phases correspond to poorly crystalline and disordered As-bearing precipitates, including arsenical ferrihydrite, scorodite, kaňkite, and hydrous ferric arsenate (HFA). The pH within 200 cm of the tailings surface averaged 5.7, conditions which favor the precipitation of ferrihydrite. Poorly crystalline Fe(III) arsenates are potentially unstable over time, and their transformation to ferrihydrite, which contributes to As uptake, has potential to increase the As adsorption capacity of the tailings. Arsenic mobility in tailings pore water at the Ylöjärvi mine will depend on continued arsenopyrite oxidation, dissolution or transformation of secondary Fe(III) arsenates, and the As adsorption capacity of Fe(III) (oxy)hydroxides within this tailings deposit.
Mobilization and speciation of arsenic from hydrothermally altered rock containing calcite and pyrite under anoxic conditions by Carlito Baltazar Tabelin; Toshifumi Igarashi; Tetsuro Yoneda (2300-2314).
► As leaching is dependent on the water residence time under anoxic conditions. ► Higher pH and reduced Fe-oxyhydroxide/oxide precipitation enhanced As leaching. ► As[V] predominates close to apparent equilibrium even under anoxic conditions. ► Speciation of As is partly attributed to pH dependent adsorption. ► Anoxic As release mechanisms include dissolution, oxidation and adsorption.The effects of water residence time and anoxic conditions on the mobilization and speciation of As in a calcite- and pyrite-bearing altered rock excavated during a road-tunnel project has been evaluated using batch and column laboratory experiments. Higher infiltration rates (i.e., shorter water residence times) enhanced the leaching of As due to the higher pH values of the effluents and more rapid transport of dissolved As through the columns. The concentration of As in the effluent also increased under anoxic conditions regardless of the water residence time. This enhanced leaching of As under anoxic conditions could be attributed to a significant pH increase and decreased Fe oxyhydroxide/oxide precipitation compared to similar experiments done under ambient conditions. Processes that controlled the evolution of pH and the temporal release mechanisms of As under anoxic conditions were identical to those previously observed under ambient conditions: the dissolution of soluble phases, pyrite oxidation, co-precipitation and/or adsorption/desorption reactions. Speciation of As in the column experiments could partly be attributed to the pH-dependent adsorption of As species onto Fe oxyhydroxide/oxide precipitates. Moreover, apparent equilibrium of the total As and As[III] concentrations was delayed under anoxic conditions in both batch and column experiments.
Comparison of arsenic geochemical evolution in the Datong Basin (Shanxi) and Hetao Basin (Inner Mongolia), China by Ting Luo; Shan Hu; Jinli Cui; Haixia Tian; Chuanyong Jing (2315-2323).
► Comparative studies of As geochemistry in the Datong Basin and Hetao Basin, China. ► Positive correlations between concentrations of As and Fe/Mn in the Datong Basin. ► No correlation of As and Fe/Mn in the Hetao Basin. ► High concentrations of As, Fe, and Mn occurred in the pe range −2 to −4.Insightful knowledge of geochemical processes controlling As mobility is fundamental to understanding the occurrence of elevated As in groundwater. A comparative study of As geochemistry was conducted in the Datong Basin (Shanxi) and Hetao Basin (Inner Mongolia), two strongly As-enriched areas in China. The results show that As concentrations ranged from <1–1160 μg L−1 (n = 37) in the Datong Basin and <1–804 μg L−1 (n = 62) in the Hetao Basin. The groundwater is of the Na-HCO3 type in the Datong Basin and Na-Cl-HCO3 type in the Hetao Basin. Silicate mineral weathering and cation exchange processes dominated the groundwater geochemistry in the two study areas. Principal component analysis of 99 groundwater samples using 12 geochemical parameters indicated positive correlations between concentrations of As and Fe/Mn in the Datong Basin, but no correlation of As and Fe/Mn in the Hetao Basin. Phosphate correlated well with As in the Datong Basin and Hetao Basin, suggesting phosphate competition might be another process affecting As concentrations in groundwater. High concentrations of As, Fe, and Mn occurred in the pe range −2 to −4. The results of this study further understanding of the similarities and differences of As occurrence and mobility at various locations in China.
Organic carbon mobilization in a Bangladesh aquifer explained by seasonal monsoon-driven storativity changes by Britta Planer-Friedrich; Cornelia Härtig; Heidi Lissner; Jörg Steinborn; Elke Süß; M. Qumrul Hassan; Anwar Zahid; Mahmood Alam; Broder Merkel (2324-2334).
► Seasonal storativity changes in clay–peat layers affect groundwater chemistry. ► During dry season, DOC is released and total mineralization increases. ► In rainy season, recharge leads to dilution and decrease of total mineralization. ► Depth-dependent As-distribution confirms DOC-driven reduction of iron hydroxides. ► Seasonal peak arsenic concentration follows peak DOC with an unexplained time lag.Currently, the most widely accepted hypothesis to explain high As concentrations in Bangladesh groundwaters is that dissolved organic C (DOC) reduces solid Fe (hydr)oxides and mobilizes sorbed arsenate. The nature of the DOC and its release mechanism are still controversial. Based on weekly to biweekly sampling over the course of one monsoon cycle at six monitoring wells of different depths, it is proposed that storativity changes drive natural DOC release from clay–peat layers to the adjacent aquifers. With a decrease in hydraulic heads during the dry season, total mineralization and DOC concentrations increased. With the onset of the rainy season and an increase in hydraulic heads, release of clay–peat derived components stopped and vertical water displacement due to groundwater recharge from rainwater occurred, causing aquifer flushing and a decrease in total mineralization and DOC concentrations. Total As and DOC concentrations correlated over depth. However, at the depth of maximum concentrations, the As peak was observed during the rainy season. At present, the reason for this inverse seasonal trend between As and DOC is unclear. Higher mineralization or DOC concentrations could lead to increased As sorption or the increased arsenite release is a time-lag abiotic or microbial response to the DOC peak. The vulnerability of the Pleistocene aquifer towards increased As concentrations was found to be much higher than previously assumed. Though sorption capacities were determined to be higher than in the Holocene aquifer, probably due to intact Fe (hydr)oxides, long-term continuous As input from overlying clay and peat layers by the proposed seasonal storativity changes has led to increased aqueous As concentrations of 85 μg/L, considerably higher than drinking water standards. Until now, aquifer and especially aquitard and aquiclude hydraulics have not been considered sufficiently when attempting to explain As mobilization in Bangladesh.
Evolution of the chemistry of Fe bearing waters during CO2 degassing by J.N. Geroni; C.A. Cravotta; D.J. Sapsford (2335-2347).
► The effect of CO2 stripping on the chemistry of Fe bearing waters was investigated. ► Changes in pH, carbonate speciation and Fe(II) oxidation rates were modelled. ► Both net acid and net alkaline waters were investigated. ► Cascades were shown to degass CO2 more efficiently than mechanical aeration. ► Cascade design did not affect CO2 stripping efficiency at the flow rates measured.The rates of Fe(II) oxidation and precipitation from groundwater are highly pH dependent. Elevated levels of dissolved CO2 can depress pH and cause difficulty in removing dissolved Fe and associated metals during treatment of ferruginous water. This paper demonstrates interdependent changes in pH, dissolved inorganic C species, and Fe(II) oxidation rates that occur as a result of the removal (degassing) of CO2 during aeration of waters discharged from abandoned coal mines. The results of field monitoring of aeration cascades at a treatment facility as well as batchwise aeration experiments conducted using net alkaline and net acidic waters in the UK are combined with geochemical modelling to demonstrate the spatial and temporal evolution of the discharge water chemistry. The aeration cascades removed approximately 67% of the dissolved CO2 initially present but varying the design did not affect the concentration of Fe(II) leaving the treatment ponds. Continued removal of the residual CO2 by mechanical aeration increased pH by as much as 2 units and resulted in large increases in the rates of Fe(II) oxidation and precipitation. Effective exsolution of CO2 led to a reduction in the required lime dose for removal of remaining Fe(II), a very important factor with regard to increasing the sustainability of treatment practices. An important ancillary finding for passive treatment is that varying the design of the cascades had little impact on the rate of CO2 removal at the flow rates measured.
Chemical and isotopic seismic precursory signatures in deep groundwater: Cause and effect by D.V. Reddy; P. Nagabhushanam (2348-2355).
► The first of its kind exploratory research in the Stable Continental Regions. ► The research methodology showed the aquifer response to tectonic stresses. ► Cyclic hydrochemical changes helped in foreseeing the earthquake. ► Real time EC measurement and on-line data transfer may help in short term forecasting. ► The research highlights the recurrence of M > 5 earthquakes every 5 year.Exploratory hydrochemical studies were initiated in Koyna, India, to examine the chemical changes in the deep groundwater due to seismic activity, 2 months before the occurrence of a M 5.1 earthquake on 14th March 2005. A few deep wells (100–250 m), out of a dozen, recorded hydrochemical anomalies induced by this earthquake, and the anomalies continued for the next 3 months. Periodical hydrochemical data of one of the wells indicated a linear increase in Cl−, SO 4 2 - , F− and depleted δ18O from August 2006 to March 2009, though there is no long term change in groundwater level (except short duration seasonal change). The observed linear change is hypothesised as an effect of aquifer response to seismic stress related to an impending earthquake of M ⩾ 5. The observed temporal change in different chemical concentrations projected linearly to the levels of March 2005 and estimated the time of the impending earthquake (the same as that of March 2005 event) as 2011/12. Further, the time projection also made based on exponential increase in hydrochemistry after 3/2009, advanced the possible time window to 2010/11. This hypothesis was realized on 12 December 2009 with an earthquake of M 5.1. Even the simple arithmetic mean of the 45-a earthquake (M > 5) history of Koyna indicates a recurrence time of ∼5.4 a. To account for the observed temporal hydrochemical changes, a model, based on mixing of two aquifer waters caused by seismic stress, was proposed. Hourly monitoring of electrical conductivity (EC) of groundwater also recorded conductivity changes induced by the M 5.1 earthquake on 12th December 2009. A very important observation that emerges from this study is that the cyclic change in subsurface stress leads to earthquakes. Continuous monitoring of EC may be helpful in visualizing the effect of tectonic forces on groundwater chemistry.
The effect of precipitation events on inorganic carbon in soil and shallow groundwater, Konza Prairie LTER Site, NE Kansas, USA by Mikhail Tsypin; G.L. Macpherson (2356-2369).
► Soil CO2 and carbonate minerals are the main sources of groundwater DIC at the Konza Tallgrass Prairie LTER site. ► Carbon is delivered to the aquifer as a gas and as DIC in diffuse-flow recharge. ► There is a 2–3 month lag time between CO2 peaks in soil and groundwater. ► In mid-summer, the soil CO2 gas concentration gradient is both upward and downward.Monthly sampling for 1 year at the Konza Prairie LTER (Long-Term Ecological Research) Site in northeastern Kansas shows a connection between the annual cycles of CO2 in soil air and shallow groundwater DIC (dissolved inorganic C). Soil air CO2 reached 6–7% in July to mid-August, when moisture was not limiting to soil respiration. Following the annual maximum there was a sequential decrease in CO2 in three soil horizons to less than 0.5% because of moisture deficiency in the late summer and temperature decline in the fall and winter. Groundwater pCO2 reached its maximum of 5% in October; the lag-time of 2–3 months may correspond to the travel time of soil-generated CO2 to the water table. The time-variable CO2 caused an annual carbonate-mineral saturation cycle, intensifying limestone dissolution and DIC production when CO2 was high.The C flux depended on respiration and rainfall regimes, and had two main pathways. Transport of soil CO2 in the dissolved form with diffuse flow of recharge water was the most effective during the growing season so long as soil moisture was present. Downward movement of gaseous CO2 and equilibration with groundwater at the water table was favorable in July to August. Storm rainfall events recharged the aquifer within a few hours through preferential flow and stream–groundwater interaction, resulting in dilution of groundwater rather than forcing entrapped CO2 downward. Calculated C flux from the unsaturated zone to the unconfined aquifer in the monitoring period was 0.26 ± 0.03 M/m2/a of C, which is less than 1% of the CO2 that is released by soil to the atmosphere via efflux. However, meteoric precipitation was only 72% of average annual precipitation during the study period, so this study represents dry-condition flux. In addition, increased respiration rates due to warming of the atmosphere have the potential to cause a higher C flux to the saturated zone, intensifying weathering and groundwater acidification, so that further study is suggested.
Solute and geothermal flux monitoring using electrical conductivity in the Madison, Firehole, and Gibbon Rivers, Yellowstone National Park by R. Blaine McCleskey; Laura E. Clor; Jacob B. Lowenstern; William C. Evans; D. Kirk Nordstrom; Henry Heasler; Mark A. Huebner (2370-2381).
► Chloride flux from Yellowstone is determined with constant conductivity monitoring. ► Geyser eruptions are easily identified with conductivity data in receiving rivers. ► Conductivity is used to quantify the mass of salts dissolved during storm events. ► The long-term output of thermal water can be monitored in a cost-effective manner.The thermal output from the Yellowstone magma chamber can be estimated from the Cl flux in the major rivers in Yellowstone National Park; and by utilizing continuous discharge and electrical conductivity measurements the Cl flux can be calculated. The relationship between electrical conductivity and concentrations of Cl and other geothermal solutes (Na, SO4, F, HCO3, SiO2, K, Li, B, and As) was quantified at monitoring sites along the Madison, Gibbon, and Firehole Rivers, which receive discharge from some of the largest and most active geothermal areas in Yellowstone. Except for some trace elements, most solutes behave conservatively and the ratios between geothermal solute concentrations are constant in the Madison, Gibbon, and Firehole Rivers. Hence, dissolved concentrations of Cl, Na, SO4, F, HCO3, SiO2, K, Li, Ca, B and As correlate well with conductivity (R 2 > 0.9 for most solutes) and most exhibit linear trends. The 2011 flux for Cl, SO4, F and HCO3 determined using automated conductivity sensors and discharge data from nearby USGS gaging stations is in good agreement with those of previous years (1983–1994 and 1997–2008) at each of the monitoring sites. Continuous conductivity monitoring provides a cost- and labor-effective alternative to existing protocols whereby flux is estimated through manual collection of numerous water samples and subsequent chemical analysis. Electrical conductivity data also yield insights into a variety of topics of research interest at Yellowstone and elsewhere: (1) Geyser eruptions are easily identified and the solute flux quantified with conductivity data. (2) Short-term heavy rain events can produce conductivity anomalies due to dissolution of efflorescent salts that are temporarily trapped in and around geyser basins during low-flow periods. During a major rain event in October 2010, 180,000 kg of additional solute was measured in the Madison River. (3) The output of thermal water from the Gibbon River appears to have increased by about 0.2%/a in recent years, while the output of thermal water for the Firehole River shows a decrease of about 10% from 1983 to 2011. Confirmation of these trends will require continuing Cl flux monitoring over the coming decades.
The role of deuterium excess in determining the water salinisation mechanism: A case study of the arid Tarim River Basin, NW China by Tianming Huang; Zhonghe Pang (2382-2388).
Display Omitted► We present a stable isotopic method for determining the water salinisation mechanism. ► We show the relation between deuterium excess and the residual fraction during evaporation. ► The mineral dissolution and/or transpiration contributes most salinity in groundwaters in the Tarim River Basin.Understanding the water salinisation mechanism is the basis for regional salt management. Mineral dissolution, evaporation and transpiration are the main factors controlling natural water salinity in arid inland basins; however, the two are difficult to differentiate. Because deuterium excess decreases during evaporation and is unrelated to the isotopic composition of the initial water, it is a potential tool for determining the contribution of the evapoconcentration of a given water body using the relationship between deuterium excess and salinity rather than between δ18O (or δ2H) and salinity. In this paper, the relationship between the residual water fraction and deuterium excess was derived from the Rayleigh distillation equation. The contribution of evapoconcentration and mineral dissolution and/or transpiration for a given water body can be determined by comparing the residual water fraction and salinity between the initial water and the evapoconcentrated water. The extremely arid Tarim River Basin in NW China is taken as an example to demonstrate deuterium excess and salinity evolution from the source stream to river water, lake/reservoir water and groundwater. The results show that mineral dissolution contributes most of the salinity (67–77%) for Boston Lake and the Kongque and Tarim rivers relative to the source stream. Mineral dissolution and/or transpiration contribute greater salinity (73–99.6%) to the groundwater recharged by the river water in the middle and lower reaches of the Tarim River. The study provides a method for determining the salinisation mechanism and is important for salt movement and management.
Comparison of stable isotopes, ratios of 36Cl/Cl and 129I/127I in brine and deep groundwater from the Pacific coastal region and the eastern margin of the Japan Sea by Yasunori Mahara; Tomoko Ohta; Tomochika Tokunaga; Hiroyuki Matsuzaki; Eiji Nakata; Yuki Miyamoto; Yukihiro Mizuochi; Toshiharu Tashiro; Masahiro Ono; Toshifumi Igarashi; Keisuke Nagao (2389-2402).
Fifty-three samples, including brines associated with oil and natural gas reservoirs and groundwater samples from deep boreholes, were collected from the Pacific and Japan Sea coastal regions in Japan. The 129I/127I and 36Cl/Cl ratios, and stable isotopes (δD and δ18O) are compared to investigate differences related to the geotectonic settings of the two regions. The δD and δ18O data indicate that brine and groundwater from the Pacific coastal region reflect mixing of meteoric water with connate seawater in the pores of sedimentary rocks. On the other hand, brine and groundwater from the Japan Sea coastal region have been hydrothermally altered. In particular, brines associated with petroleum accumulations at Niigata and Akita showed the same isotopic characteristics as fluids found in the Kuroko deposits of the Green Tuff region in northeastern Japan. There is little difference in the 36Cl/Cl ratios in brine and groundwater from the Pacific and Japan Sea coasts. Most brine and some deep groundwater, except those from the Pleistocene Kazusa Group, have already reached the average secular equilibrium ratio of 9.9 ± 2.7 × 10−15 for their mudstone and sandstone reservoirs. There was no correlation between the 36Cl/Cl ratios and differences in geotectonic setting between the Pacific and the Japan Sea coast. The molar I/Br ratio suggests that the I in all of water samples was of biogenic origin. The average 129I/127I ratio was 290 ± 130 × 10−15 to 294 ± 105 × 10−15 in both regions, showing no relationship to the different geotectonic settings. The uncontaminated brine and groundwater samples are likely to have retained the original 129I/127I ratios of marine I released from the old organic matter stored in sedimentary rock.
Strontium isotope systematics of mixing groundwater and oil-field brine at Goose Lake in northeastern Montana, USA by Zell E. Peterman; Joanna Thamke; Kiyoto Futa; Todd Preston (2403-2408).
► Wetlands in the Goose Lake oil field have been contaminated by produced water. ► Salinity during the course of evapotranspiration increases during summer months. ► Strontium isotopes are not effected by evaporation and are sensitive indicators of produced water contamination.Groundwater, surface water, and soil in the Goose Lake oil field in northeastern Montana have been affected by Cl−-rich oil-field brines during long-term petroleum production. Ongoing multidisciplinary geochemical and geophysical studies have identified the degree and local extent of interaction between brine and groundwater. Fourteen samples representing groundwater, surface water, and brine were collected for Sr isotope analyses to evaluate the usefulness of 87Sr/86Sr in detecting small amounts of brine. Differences in Sr concentrations and 87Sr/86Sr are optimal at this site for the experiment. Strontium concentrations range from 0.13 to 36.9 mg/L, and corresponding 87Sr/86Sr values range from 0.71097 to 0.70828. The local brine has 168 mg/L Sr and a 87Sr/86Sr value of 0.70802. Mixing relationships are evident in the data set and illustrate the sensitivity of Sr in detecting small amounts of brine in groundwater. The location of data points on a Sr isotope-concentration plot is readily explained by an evaporation-mixing model. The model is supported by the variation in concentrations of most of the other solutes.
Sr evolution in the Upper Permian and Lower Triassic carbonates, northeast Sichuan basin, China: Constraints from chemistry, isotope and fluid inclusions by Kaikai Li; Chunfang Cai; Lei Jiang; Liulu Cai; Lianqi Jia; Bing Zhang; Lei Xiang; Yuyang Yuan (2409-2424).
► Combined effects of various mechanisms resulted in abnormally high Sr concentrations. ► Aragonite neomorphism and closed-system dolomitization led to early Sr enrichment. ► Dissolution of early celestite and calcium sulfate via TSR constantly released Sr2+. ► TSR-water controlled dissolution–precipitation process of Sr-bearing minerals. ► Origin of double-spheroid elemental sulfur-bearing immiscible inclusion was studied.Petrographic features, C, O and Sr isotopes, rare earth and trace elements were determined, and fluid inclusions were analyzed on various stages of interparticle cements and vug-fillings from the Upper Permian and Lower Triassic sour reservoirs in northeastern Sichuan basin. The aim was to assess the origin and evolution of palaeo-waters in the carbonates. The original water was contemporary seawater, from which marine cements precipitated with slightly high Sr contents (mean 1911 ppm), 87Sr/86Sr ratios from 0.7067 to 0.7082 and nonluminescent CL. The palaeo-seawater was diluted by meteoric water, as indicated by bright cathodoluminescence (CL) and Sr-depletion (0–516 ppm) in low-temperature calcite. When buried to temperatures of about 60–90 °C during Middle to Late Triassic, the palaeo-water was enriched in Sr released from the transformation of precursor aragonite and calcite to dolomite, resulting in precipitation of substantial pre-bitumen Sr-rich minerals (SrSO4 and SrCO3). For un-dolomitized limestone sections, aragonite neomorphism may have contributed Sr to the precipitation of small amounts of Sr-bearing minerals and calcite crystals with elevated homogenization temperatures (HTs, mainly from 90 to 130 °C) and wide Sr contents (from 34 to 3825 ppm), as recorded in stage III calcite. Since the Middle Jurassic, almost all of the early stage celestite and significant amounts of solid CaSO4 have been consumed by reactions with hydrocarbons (i.e., TSR), resulting in water enriched in isotopically light CO2 and HCO 3 - , Sr 2 + , Ba 2 + and Eu2+, as recorded in calcite with low δ13C values (down to −18.9‰), 87Sr/86Sr ratios from 0.7072 to 0.7076, high HTs (mainly 110–198 °C), positive Eu anomalies and high Sr and Ba contents. Subsequently, the water was uplifted and cooled down to about 115 °C, celestite and strontianite were precipitated with the occurrence of natural elemental S immiscible inclusions. TSR may have produced significant amounts of freshwater, which brought down Sr concentrations and salinities of the palaeo-waters to not more than about 6.0 wt.% NaCl equivalent.
Tracing industrial sulfur contributions to atmospheric sulfate deposition in the Athabasca oil sands region, Alberta, Canada by Bernadette C. Proemse; Bernhard Mayer; Mark E. Fenn (2425-2434).
► Atmospheric sulfate deposition rates are elevated on industrial sites. ► δ 18O values of sulfate (SO4) at high deposition rates are isotopically distinct. ► δ 18O values are suitable for quantifying industrial sulfur (S) contributions to SO4 deposition. ► δ 34S values of SO4 indicate reduced S emissions from tailing ponds.Anthropogenic S emissions in the Athabasca oil sands region (AOSR) in Alberta, Canada, affect SO4 deposition in close vicinity of industrial emitters. Between May 2008 and May 2009, SO4-S deposition was monitored using open field bulk collectors at 15 sites and throughfall collectors at 14 sites at distances between 3 and 113 km from one of the major emission stacks in the AOSR. At forested plots >90 km from the operations, SO4 deposition was ∼1.4 kg SO4-S ha−1 yr−1 for bulk deposition and ∼3.3 kg SO4-S ha−1 yr−1 for throughfall deposition. Throughfall SO4 deposition rates in the AOSR exceeded bulk deposition rates at all sites by a factor of 2–3, indicating significant inputs of dry deposition especially under forest canopies. Both bulk and throughfall SO4 deposition rates were elevated within 29 km distance of the industrial operations with deposition rates as high as 11.7 kg SO4-S ha−1 yr−1 for bulk deposition and 39.2 kg SO4-S ha−1 yr−1 for throughfall at industrial sites. Sulfur isotope ratio measurements of atmospheric SO4 deposited in the AOSR revealed that at a few selected locations 34S-depleted SO4, likely derived from H2S emissions from tailing ponds contributes to local atmospheric SO4 deposition. In general, however, δ 34S values of SO4 deposition at distant forested plots (>74 km) with low deposition rates were not isotopically different from δ 34S values at sites with high deposition rates in the AOSR and are, therefore, not suitable to determine industrial S contributions. However, O isotope ratios of atmospheric SO4 in bulk and throughfall deposition in the AOSR showed a distinct trend of decreasing δ 18O-SO4 values with increasing SO4 deposition rates allowing quantification of industrial contributions to atmospheric SO4 deposition. Two-end-member mixing calculations revealed that open field bulk SO4 deposition especially at industrial sites in close proximity (<29 km) to the operations is significantly (17–59%) affected by industrial S emissions and that throughfall generally contained 49–100% SO4 of industrial origin. Hence, it is suggested that δ 18O values of SO4 may constitute a suitable tracer for quantifying industrial contributions to atmospheric SO4 deposition in the AOSR.
Hydrogeochemical patterns, processes and mass transfers during aquifer storage and recovery (ASR) in an anoxic sandy aquifer by E.A. Antoniou; B.M. van Breukelen; B. Putters; P.J. Stuyfzand (2435-2452).
► We identify and quantify in time and space the main hydrogeochemical processes. ► We study the effects of subsequent ASR cycles. ► We identify Fe(II) and Mn(II) removal during recovery by particle tracking. ► We quantify and predict the leaching of reactive phases. ► We propose solutions to mitigate the Mn(II) problems in the recovered water.The hydrogeochemical processes that took place during an aquifer storage and recovery (ASR) trial in a confined anoxic sandy aquifer (Herten, the Netherlands) were identified and quantified, using observation wells at 0.1, 8 and 25 m distance from the ASR well. Oxic drinking water was injected in 14 ASR cycles in the period 2000–2009. The main reactions consisted of the oxidation of pyrite, sedimentary organic matter, and (adsorbed) Fe(II) and Mn(II) in all aquifer layers (A–D), whereas the dissolution of carbonates (Mg-calcite and Mn-siderite) occurred mainly in aquifer layer D. Extinction of the mobilization of SO4, Fe(II), Mn(II), As, Co, Ni, Ca and total inorganic C pointed at pyrite and calcite leaching in layer A, whereas reactions with Mn-siderite in layer D did not show a significant extinction over time. Iron(II) and Mn(II) removal during recovery was demonstrated by particle tracking and pointed at sorption to neoformed ferrihydrite. Part of the oxidants was removed by neoformed organic material in the ASR proximal zone (0 – ca. 5 m) where micro-organisms grow during injection and die away when storage exceeds about 1 month. Anoxic conditions during storage led to increased concentrations for a.o. Fe(II), Mn(II) and NH4 as noted for the first 50–200 m3 of abstracted water during the recovery phase. With a mass balance approach the water–sediment reactions and leaching rate of the reactive solid phases were quantified. Leaching of pyrite and calcite reached completion at up to 8 m distance in layer A, but not in layer D. The mass balance approach moreover showed that Mn-siderite in layer D was probably responsible for the Mn(II) exceedances of the drinking water standard (0.9 μmol/L) in the recovered water. Leaching of the Mn-siderite up to 8 m from the ASR well would take 1600 more pore volumes of drinking water injection (on top of the realized 460).
Influence of redox conditions on iodide migration through a deep clay formation (Toarcian argillaceous rock, Tournemire, France) by B. Frasca; S. Savoye; C. Wittebroodt; O.X. Leupin; M. Descostes; B. Grenut; J. Etep-Batanken; J.-L. Michelot (2453-2462).
► Pyrite oxidation appears to greatly enhance iodide retention. ► No clear interaction was observed between iodide and natural organic matter. ► Results show that iodide sorption is controlled by a slow oxidation rate of pyrite.With a half-life of 15.7 Ma, a high mobility and the potential to accumulate in the biosphere, 129I is considered, in safety assessment calculations for radioactive waste repositories, to be one of the main contributors to the radiological dose. Several authors have reported that, at low concentration, I− is weakly retained on argillaceous rocks. This process is not yet well-understood and different hypotheses have been put forward as to whether reactive phases or experimental artifacts (e.g. pyrite oxidation) could be the reason for the retention of I− observed at low concentration. The aim of this study was to investigate the effect on I− mobility of (i) the redox conditions and (ii) the amount of pyrite and natural organic matter (NOM) contents of the rock. These questions were addressed by performing batch sorption, through-diffusion and out-diffusion experiments on rock samples of Toarcian argillaceous rock from Tournemire (Aveyron, France). One of the challenges faced during this study was to distinguish actual transport properties from experimental artifacts. A especially elaborate experimental set-up allowed limiting the (i) oxidation of both argillaceous rock and I−, and (ii) carbonate precipitation. A comparison of the batch sorption results obtained for two Toarcian clay specimens, that differed in their amount of pyrite and NOM, allowed relating I− sorption to pyrite oxidation. However, no evidence was found to associate the I− behavior to the NOM amounts. While the through-diffusion experiments showed a very slight sorption (distribution ratio (Rd ) = 0.016 mL g−1) for the lowest I− concentration under oxic conditions, the out-diffusion tests performed after the through-diffusion experiments on the same cells showed significant sorption under both oxic and anoxic conditions, resulting in Rd ranging from 0.02 mL g−1 to 1.25 mL g−1. The range of Rd values was higher for the upstream reservoir under oxic conditions. The discrepancies observed between the through-diffusion and the out-diffusion experiments suggest a kinetic control of the I− uptake by argillaceous rocks under oxic and anoxic conditions.
Dissolution of sandstone powders in deionised water over the range 50–350 °C by Qingjie Gong; Jun Deng; Meng Han; Liqiang Yang; Wenquan Wang (2463-2475).
► Dissolution of sandstone powders were experimentally determined. ► Dissolution behaviours were measured at higher temperatures and pressures. ► The dissolution rates were quantitatively described with temperatures. ► The release rates of Si increased continuously with temperatures. ► The release rates of Ca increased firstly and then decreased with temperatures.Sandstone dissolution is a common water–rock reaction in the Earth’s crust, but a thorough understanding of this phenomenon is constrained by poorly determined kinetic data. To this end, kinetic data were determined for the dissolution of arkosic sandstone powders in deionised water (pH was about 7.0–7.3 and electrical conductivity was between 0.95 and 1.00 μS/cm). Release rates of dissolved elements were determined over the range 50–350 °C at 20, 15, and 10 MPa using a column flow-through pressure vessel reactor. The conductivity of the outlet solution, measured at room temperature, is dependent on the charge of major cations such as Na+, K+, Ca2+ and Mg2+ at these conditions. The conductivity of the outlet solution was used to determine the steady state of the dissolution of sandstone powders. The pH values of the outlet solutions at the steady state, measured ex situ at room temperature, were about 7.7, 8.3, 8.4, 8.4 and 7.6 at 75, 100, 150, 200 and 250 °C, respectively, at 10 MPa. Silicon, Na, K, Ca, Al and Mg are the major ions found in the solution at low temperatures, but Si is the only major ion retained at higher temperatures (>150 °C). Compared with static experiments, the flowing dissolution experiments occurred at conditions far from equilibrium. The relationship between temperature and dissolution rates of arkosic sandstone powders was described as log R = 0.005469t − 10.50 where R is the dissolution rates of sandstone powders in kg/(m2 s), t is temperature in °C which ranged from 100 to 350 °C at 20 and 15 MPa, and the dissolution rates of sandstone powders were measured only for the major dissolved elements without oxygen in the outlet solutions.The release rates of Si and K increased sharply at temperatures over the 100–350 °C range. The release rates of Mn and Ni increased slowly at low temperatures (<200 °C) but increased sharply over the 200–350 °C range. The release rates of Na, Ca, Mg and U initially increased, then decreased. The release rates of Fe varied slightly from 100 to 250 °C, but increased sharply at 300 °C and 350 °C. A comparison of release rates of Si and Ca with temperature showed that the release rate of Si was lower than that of Ca at temperatures below 150 °C, but clearly higher at temperatures above 150 °C. This phenomenon can explain previous observations for deep layers of oil field drill cores that feldspar showed dissolution pits but no clear dissolution features were found on the surfaces of carbonate minerals. Apparent activation energies of Si release and K release in these sandstone powders dissolution experiments were derived to be 33 kJ/mol and 20 kJ/mol, respectively, over 75–350 °C and 10–20 MPa. The findings thus provide insights into the dissolution behaviours of sandstone powders in deionised water at conditions that are far from equilibrium.
In situ and laboratory investigation of the alteration of Boom Clay (Oligocene) at the air–geological barrier interface within the Mol underground facility (Belgium): Consequences on kerogen and bitumen compositions by P. Blanchart; P. Faure; C. Bruggeman; M. De Craen; R. Michels (2476-2485).
► Comparison of in situ and experimental air oxidation consequences on organic matter. ► The major alteration process of organic matter in the gallery is air oxidation. ► Artificial air oxidation at 80 °C in a ventilated oven simulate the natural oxidation. ► These experiments can be used to assess the long term evolution of the organic matter.The Boom Clay formation (Oligocene) is studied as a reference host rock for methodological studies on deep geological disposal of radioactive waste. During excavation of galleries within the Clay formation (HADES underground research facility, Mol, Belgium), the physico-chemical conditions are significantly modified as an air–clay interface is created. In order to study the long-term impact of the air–clay contact on the organic matter contained in the Boom Clay, two types of samples were studied: (1) a reference series of clay samples having been in contact with the atmosphere of the HADES gallery for increasing times up to several years and (2) unaltered clay samples submitted to artificial oxidation in a ventilated oven at 80 °C. The evolution of geochemical data of the two series was compared using Rock-Eval pyrolysis, GC–MS and size exclusion chromatography. The organic matter of the unaltered clays sampled in the HADES galleries is dominated by type III kerogen (terrestrial) with some contribution of type II (marine) and is thermally immature. The evolution of geochemical parameters during air alteration for the two series are very similar. They show progressive oxidation of kerogen accompanied by the release of bitumen enriched in low molecular weight constituents. Molecular analysis evidences the presence of a complex mixture of aliphatic and aromatic O-bearing compounds, inherited from the degradation of kerogen as well as from the clay catalyzed oxidation of the bitumen. These results show that (1) air oxidation is a major process in the in situ alteration of the organic matter of Boom Clay within the HADES galleries, (2) laboratory oxidation experiments at 80 °C yield similar results as in situ air alteration of Boom Clay and (3) artificial air oxidation may be used to assess the long term exposure of the organic matter to air.
Analysis of long- and short-term temporal variations of the diffuse CO2 emission from Timanfaya volcano, Lanzarote, Canary Islands by Pedro A. Hernández; Germán Padilla; Eleazar Padrón; Nemesio M. Pérez; David Calvo; Dácil Nolasco; Gladys Melián; José Barrancos; Samara Dionis; Fátima Rodríguez; Hirochika Sumino (2486-2499).
► Long- and short-term variations of diffuse CO2 emission were investigated. ► Annual and seasonal discrete CO2 efflux surveys were performed. ► A continuous recording of CO2 efflux was carried out. ► MRA indicates a strong external control on the diffuse CO2 degassing. ► Soil CO2 efflux transport is not structural controlled.Reported herein are the results of eight soil CO2 efflux surveys performed from 2006 to 2011 at Timanfaya Volcanic Field (TVF), Lanzarote Island with the aim of evaluating the long- and short-term temporal variations of the diffuse CO2 emission. Soil CO2 efflux values ranged from non-detectable up to 34.2 g m−2 d−1, with the highest values measured in September 2008. Conditional sequential Gaussian simulations (sGs) were applied to construct soil CO2 efflux distribution maps and to estimate the total CO2 output from the studied area at the TVF. Soil CO2 efflux maps showed a high spatial and temporal variability. Total CO2 emission rates ranged between 41 and 518 t d−1, February 2011 (winter) being the season when maximum diffuse CO2 emission rates were observed. To investigate the influence of external variables on the soil CO2 efflux, a geochemical station (LZT01) was installed at TVF to measure continuously the soil CO2 efflux between July 2010 and March 2012 Since external factors such as barometric pressure, rainfall, soil water content, soil and air temperatures, and wind speed influence strongly the observed soil CO2 effluxes, multiple regression analysis was applied to the time series recorded by the automatic geochemical station LZT01 to remove the contribution of these external factors. The influence of meteorological variables on soil CO2 efflux oscillations accounts for 13% of total variance, with barometric pressure, rainfall and/or soil water content having the most influence in the control of the soil CO2 efflux. These observations along with the results from the eight soil gas surveys performed at TVF indicate that the short and long-term trends in the diffuse CO2 degassing are mainly controlled by environmental factors.
Production of amorphous hydrated impure magnesium carbonate through ex situ carbonation by Andrea Orlando; Matteo Lelli; Luigi Marini (2500-2510).
► We used a serpentinite as Mg source to obtain Mg-rich solutions for CO2 sequestration. ► We adopted three-steps procedure: acid attack, neutralization and carbonation. ► Fe-rich phases formed during neutralization with considerable amounts of Mn and Ni. ► Amorphous Hydrated Magnesium Carbonate phase precipitated in the carbonation step. ► The obtained saturation constant of the Carbonate can be used for geochemical modeling.The evaluation of the feasibility of ex situ carbonation in landfills utilizing raw natural substances (namely serpentinites as Mg-source and the CO2-rich fraction of biogas as C-source) was tested through a laboratory procedure comprising three steps. The first step is the acid attack of a serpentinite at 70 °C, by means of HCl 2 M, to get MgCl2-rich solutions. Attacks of different durations were performed to evaluate the time needed. The second step is the neutralization of the MgCl2-rich solution by addition of concentrated ammonia. The third (carbonation) step is mixing of the neutralized MgCl2-rich solution with a solution of ammonium carbonate. This was produced in a landfill by absorption of CO2 contained in biogas in a solution of ammonia. The neutralization of acid MgCl2-rich solutions caused the precipitation of ferrihydrite with secondary ammonium carnallite and salammoniac, whereas abundant precipitation of Amorphous Hydrated Impure Magnesium Carbonate (AHIMC), sometimes with minor nesquehonite, occurred in the third step. This solid carbonate acts as a stable CO2 sink up to 380 °C. The geochemical behavior of some minor elements was also investigated during the experimental processes revealing that Al, Cr and Ni were removed during neutralization (second step), in contrast to Ca which remained in the circumneutral MgCl2-rich solution and entered into the structure of AHIMC. During the carbonation step, precipitation of artinite, hydromagnesite, lansfordite, magnesite and nesquehonite was thermodynamically impossible as the aqueous phase was undersaturated with respect to these solid phases upon separation of AHIMC.The CO2 sequestered through this multi-step procedure is 0.34 ton for 1 ton of serpentinite utilized. However, despite that the use of Mg-rich silicates is a suitable approach to ex situ carbonation, due to their huge availability worldwide, the CO2 produced in making the chemicals and the overall energy balance of the process must be evaluated to assess its sustainability. Furthermore, this procedure could be of great interest in asbestos inertization and the AHIMC products could possibly be useful in industry.
Evaluating methods for quantifying cation exchange in mildly calcareous sediments in Northern Alberta by A.A. Holden; K.U. Mayer; A.C. Ulrich (2511-2523).
► Compare methods characterizing cation exchange properties in calcareous sediments. ► Assess cation exchange properties of surficial Pleistocene sediments in North Alberta. ► Methylene Blue test was least impacted by the presence of carbonate mineral phases. ► Exchangeable cations, in decreasing abundance, consist of Ca > Mg > K > NH4 > Na. ► Mean CEC was 4.7 ± 2.7 (till), 0.7 ± 0.0 (sand), 4.1 ± 2.3 meq 100 g−1 (till-sand transition).Cation exchange capacity (CEC) and exchangeable cation composition are important properties in defining water–sediment interactions in contaminant transport scenarios, such as the seepage of process-affected water from oil sands tailings impoundments. At present, detailed characterization of these properties has been overlooked in the surficial Pleistocene sediments of the Athabasca Oil Sands region in Canada. Although a great variety of methods for determining CEC exist and continue to be developed, there is a deficiency in detailed comparisons amongst these methods in the literature, and consequently uncertainty still remains as to which extractants/methods are most suitable for use with sediments containing partially soluble carbonate salts. The present study (1) conducts an up-to-date evaluation of several distinct methods for their suitability in characterizing cation exchange properties in mildly calcareous sediments; using them to (2) evaluate the sorptive capacity and easily displaceable cations of mildly calcareous, surficial sediments near Fort McMurray, Alberta. Four conceptually different CEC methods were chosen: (a) a summation method (Lithium Chloride extractant); (b) a method that displaces an index cation after intermediary washes (Sodium Acetate–Ammonium Acetate); (c) a method using a high affinity cation complex (Silver Thiourea); and (d) a titration method using an organic cationic dye (Methylene Blue). Exchangeable cations were characterized using the Lithium Chloride and Silver Thiourea methods. Analysis suggests that the Methylene Blue test is least impacted by the presence of carbonate mineral phases. Results from field sediments suggest that the exchangeable cations, in decreasing abundance, consist of Ca > Mg > K > NH4 > Na; while the CEC was found to be 4.7 ± 2.7 meq 100 g−1 in the clay-rich glacial till, 0.7 ± 0.0 meq 100 g−1 in the underlying sand and 4.1 ± 2.3 meq 100 g−1 in the till-sand transition zone.
Sorption of selenite in a multi-component system using the “dialysis membrane” method by John Muller; Abdesselam Abdelouas; Solange Ribet; Bernd Grambow (2524-2532).
► In the present study we examine 75Se sorption on minerals typically found in soils. ► Dialysis membranes were successfully used to assess the minerals competition for Se sorption. ► We conclude that silica release by bentonite dissolution lowers the Se sorption on goethite. ► The results are successfully modelled using a diffuse double layer model constructed with the geochemical code PhreeqC. 79Se is a potentially mobile long-lived fission product, which may make a dominant contribution to the long-term radiation exposure resulting from deep geological disposal of radioactive waste. Its mobility is affected by sorption on minerals. Selenium sorption processes have been studied mainly by considering interaction with a single mineral surface. In the case of multi-component systems (e.g. soils), it is difficult to predict the radioelement behaviour only from the mineral constituents. This study contributes to the understanding of multi-component controls of Se concentrations towards predicting Se behaviour in soils after migration from a disposal site. This goal was approached by measuring selenite sorption on mono and multi-phase systems physically separated by dialysis membranes. To the best of the authors’ knowledge, very few studies have used dialysis membranes to study the sorption competition of selenite between several mineral phases. Other workers have used this method to study the sorption of pesticides on montmorillonite in the presence of dissolved organic matter. Indeed, this method allows measurement of individual Kd in a system composed of several mineral phases. Dialysis membranes allowed (i) determination of the competition of two mineral phases for selenite sorption (ii) and determination of the role of humic acids (HAs) on selenite sorption in oxidising conditions. Experimental results at pH 7.0 show an average Se(IV) sorption distribution coefficient (Kd ) of approximately 125 and 9410 L kg−1 for bentonite and goethite, respectively. The average Kd for goethite decreases to 613 L kg−1 or 3215 L kg−1 in the presence of bentonite or HA, respectively. For bentonite, the average Kd decreases slightly in the presence of goethite (60 L kg−1) and remains unchanged in the presence of HA. The experimental data were successfully modelled with a surface complexation model using the PHREEQC geochemical code. The drastic decrease in Se(IV) sorption on goethite in a multi-phase system is attributed to competition with dissolved silica released by bentonite. As with Si the HA compete with Se for sorption sites on goethite.
Experimental investigation of main controls to methane adsorption in clay-rich rocks by Liming Ji; Tongwei Zhang; Kitty L. Milliken; Junli Qu; Xiaolong Zhang (2533-2545).
► The difference in clay mineral type is one key element controlling CH4 adsorption in clay-rich rocks. ► BET surface area is a primary proxy for CH4 adsorption capacity in clay-rich rocks. ► Clay type affects gas-sorption capacity and the presence of moisture can greatly reduce gas-sorption capacity. ► Quantitative model prediction is developed to estimate the methane sorption capacity of organic-lean shales.In this study a series of CH4 adsorption experiments on clay-rich rocks were conducted at 35 °C, 50 °C and 65 °C and at CH4 pressure up to 15 MPa under dry conditions. The clay-dominated rock samples used are fresh samples from quarries and mines. Samples are individually dominated by montmorillonite, kaolinite, illite, chlorite, and interstratified illite/smectite. The experimental results show that clay mineral type greatly affects CH4 sorption capacity under the experimental conditions. In terms of relative CH4 sorption capacity: montmorillonite ≫ illite/smectite mixed layer > kaolinite > chlorite > illite. Physisorption is the dominant process for CH4 absorption on clay minerals, as a result, there is a linear correlation between CH4 sorption capacity and BET surface area in these clay-mineral dominated rocks. The abundance of micro-mesopores in the size range of a few to a few 10 s of nanometers in montmorillonite clay and illite–smectite interstratified clay results in large BET surface area values for these mineral species.A good linear relationship between the natural logarithm of Langmuir constant and the reciprocal of temperature exists for clay-mineral dominated rocks, which provides a way to quantify the impact of clay mineral type on gas adsorption capacity. Thermodynamic parameters, the heat of CH4 adsorption and the standard entropy, are calculated based on this linear correlations. The heat of adsorption (q) and the standard entropy (Δso ) range from 9.4 to 16.6 kJ/mol and from −64.8 to −79.5 J/mol/K, respectively, values considerably smaller than those for CH4 adsorption on kerogens. Thus, it is expected that CH4 molecules may preferentially occupy surface sites on organic matter, in addition, the clay minerals are easily blocked by water. As a consequence, organic-rich mudrocks possess a larger CH4 sorption capacity than clay-dominated rocks lacking organic matter.
Holocene lake development and glacial-isostatic uplift at Lake Skallen and Lake Oyako, Lützow-Holm Bay, East Antarctica: Based on biogeochemical facies and molecular signatures by Yoshinori Takano; Jonathan James Tyler; Hisaya Kojima; Yusuke Yokoyama; Yukiko Tanabe; Takaharu Sato; Nanako O. Ogawa; Naohiko Ohkouchi; Manabu Fukui (2546-2559).
Display Omitted► Biogeochemistry and paleo-limnology of lake sediments, East Antarctica. ► Environmental changes during a marine–lacustrine transition. ► Changes in the dominant primary producers during the transition. ► Determination of glacial-isostatic uplift (rate: 3.2 mm yr−1) during late Holocene.The paleolimnology of two lakes which were isolated as a result of the crustal uplift during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica were studied. The focus was on temporal variations in the biogeochemical composition of sediment cores recovered from Lake Skallen at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine settings, as indicated by analyses of C and N contents, nitrogen isotopic compositions (δ15N), and major element concentrations. Changes in the dominant primary producers during the marine–lacustrine transition (marine diatom to cyanobacteria) at L. Skallen was clearly revealed by biogenic opal-A, diatom assemblages, and molecular signature from denaturing gradient gel electrophoresis (DGGE) with 16S ribosomal RNA (rRNA) gene analysis. Radiocarbon dating of acid-insoluble organic C suggested that the environmental transition from marine to fresh water occurred at 2940 ± 100 cal yr BP at L. Skallen and 1060 ± 90 cal yr BP at L. Oyako. Based on these data, a mean crustal uplift rate of 3.2 mm yr−1 is inferred for the history of marine–lacustrine transition via brackish conditions. The geological setting causing glacio-isostatic uplift was the primary factor in controlling the transition event in sedimentary and biological facies.
The occurrence and distribution of phenylphenanthrenes, phenylanthracenes and binaphthyls in Palaeozoic to Cenozoic shales from China by Meijun Li; Shengbao Shi; T.-G. Wang; Ningning Zhong; Guangli Wang; Jingwei Cui (2560-2569).
► We report the occurrence of phenyl PAHs in lacustrine shales for the first time. ► We study the effect of maturity on the distribution of m/z 254 isomers. ► The relative abundance of binaphthyl isomers is an effective maturity indicator. ► The Phenylphenanthrene Ratio shows a reverse change at low maturity stages. ► The absolute concentration of each isomer is obtained by internal standard.The distributions of phenylphenanthrenes, phenylanthracenes and binaphthyls in sediment extracts have been investigated in a set of lacustrine shales from the Eocene Shahejie Formation (well SG 1) in the western Depression of Liaohe Basin, East China. All isomers of these phenyl substituted polycyclic aromatic hydrocarbons (PAHs) have been identified in the m/z 254 mass chromatograms by comparison of the mass spectra and standard retention indices with those published elsewhere. The 2,2′-binaphtyl/1,2′-binaphthyl ratio values show a linear increase with increasing maturity, and have a good correlation with T max (°C). Therefore, they can be used as an effective maturity indictor for source rocks in this study. In the main phase of the oil generation window, the 3-phenylphenanthrene and 2-phenylphenanthrene prevail over other isomers, and some thermodynamically unstable isomers including all phenylanthracenes, 4-phenylphenanthrene and 1,1′-binaphthyl are present at very low concentrations or below the detection limit in the m/z 254 mass chromatograms. The absolute concentrations of individual phenylphenanthrene and binaphthyl isomers were obtained by comparison of the peak areas with that of internal standard phenanthrene-d10. All isomers are present at low concentrations at low maturity stages and then show an abrupt increase at a depth of ≈3100 m, corresponding to the onset of the intensive C15+ hydrocarbon generation. The Phenylphenanthrene Ratio (2- + 3-PhP)/[(2- + 3-PhP) + (4- + 1- + 9-PhP)] shows a reverse change with increasing maturity at the low maturity stage. It displays a drastic increase at a depth of ≈3100 m and then remains at a nearly constant value. This study can expand the understanding of the formation and distribution of phenyl substituted PAHs in sedimentary organic matter deposited in various environments.