Applied Geochemistry (v.25, #6)

Mechanisms of Nd(III) uptake by 11 Å tobermorite and xonotlite by P. Mandaliev; E. Wieland; R. Dähn; J. Tits; S.V. Churakov; O. Zaharko (763-777).
The uptake of Nd(III) by the crystalline C–S–H phases 11 Å tobermorite and xonotlite has been investigated by the combined use of wet chemistry techniques, extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray diffraction (XRD) in combination with Rietveld refinement. The results from XRD and EXAFS allowed the different modes of Nd–Ca substitution in tobermorite and xonotlite to be distinguished from each other. Wet chemistry and EXAFS data showed that the formation of any Nd solid phase with fixed stoichiometry could be ruled out. XRD studies on the samples with high Nd loading (350 μmol Nd/g solid phase) further showed that Nd was bound in the structure of C–S–H phases. The EXAFS data suggested that Nd could form several species on xonotlite and tobermorite at low loadings (7–35 μmol Nd/g solid phase). Neodymium was predominantly bound on the external surface of both crystalline C–S–H phases after 1 day of reaction time and predominantly incorporated in the Ca layers of the crystalline C–S–H phases in the long run (⩾60 days reaction time). The latter process was faster at low Nd loadings and was apparently controlled by re-crystallization of the C–S–H phases. Neodymium incorporation was accompanied by the release of “zeolitic” water (water molecules in the interlayer of C–S–H) and bridging Si tetrahedra, reflected by the formation of more disordered structures in both C–S–H phases. The Nd retention model proposed in this study helps to improve understanding of the immobilization of trivalent lanthanides and actinides in cementitious materials. This knowledge is essential for long-term predictions of radionuclide retention in conjunction with a more detailed assessment of the safe disposal of actinides in the cementitious near field of a repository for radioactive waste.

Post-depositional redistribution of trace metals in reservoir sediments of a mining/smelting-impacted watershed (the Lot River, SW France) by Stéphane Audry; Cécile Grosbois; Hubert Bril; Jörg Schäfer; Jakub Kierczak; Gérard Blanc (778-794).
Mining/smelting wastes and reservoir sediment cores from the Lot River watershed were studied using mineralogical (XRD, SEM–EDS, EMPA) and geochemical (redox dynamics, selective extractions) approaches to characterize the main carrier phases of trace metals. These two approaches permitted determining the role of post-depositional redistribution processes in sediments and their effects on the fate and mobility of trace metals. The mining/smelting wastes showed heterogeneous mineral compositions with highly variable contents of trace metals. The main trace metal-bearing phases include spinels affected by secondary processes, silicates and sulfates. The results indicate a clear change in the chemical partitioning of trace metals between the reservoir sediments upstream and downstream of the mining/smelting activities, with the downstream sediments showing a 2-fold to 5-fold greater contribution of the oxidizable fraction. This increase was ascribed to stronger post-depositional redistribution of trace metals related to intense early diagenetic processes, including dissolution of trace metal-bearing phases and precipitation of authigenic sulfide phases through organic matter (OM) mineralization. This redistribution is due to high inputs (derived from mining/smelting waste weathering) at the water–sediment interface of (i) dissolved SO4 promoting more efficient OM mineralization, and (ii) highly reactive trace metal-bearing particles. As a result, the main trace metal-bearing phases in the downstream sediments are represented by Zn- and Fe-sulfides, with minor occurrence of detrital zincian spinels, sulfates and Fe-oxyhydroxides. Sequestration of trace metals in sulfides at depth in reservoir sediments does not represent long term sequestration owing to possible resuspension of anoxic sediments by natural (floods) and/or anthropogenic (dredging, dam flush) events that might promote trace metal mobilization through sulfide oxidation. It is estimated that, during a major flood event, about 870 t of Zn, 18 t of Cd, 25 t of Pb and 17 t of Cu could be mobilized from the downstream reservoir sediments along the Lot River by resuspension-induced oxidation of sulfide phases. These amounts are equivalent to 13-fold (Cd), ∼6-fold (Zn), 4-fold (Pb) the mean annual inputs of the respective dissolved trace metals into the Gironde estuary.

This study reports changes in coal-mine drainage constituent concentrations through a passive treatment wetland and over diel cycles. The purpose of the study was to determine what physiochemical mechanisms control attenuation of metals and if they varied by location and through time. The source water was slightly acidic (average pH 5.43); downstream degassing of CO2 contributed to an increase in pH prior to discharge from the site (average pH 7.05). Aluminum, Fe, rare earth elements (REE) and Y were removed to a greater extent than were Mn, Co and Ni. At acidic pH, the REE and Y were generally complexed by SO4. At higher pH, carbonate complexes became more important. The REE and Y concentrations were normalized to the North American Shale Composite standard; the normalized patterns were coherent near the source but anomalies of Ce and Y were present further downstream indicating oxidation and sorption processes. Four sets of diel-based samples were collected, one from a shallow, surface-flow wetland and three from a deeper, newly constructed wetland. Well-defined diel cycles were observed for concentrations of Si, Mn, Fe, Co, Ni, As, REE and Y in the shallow wetland. In all cases, the concentrations increased (up to 863%) during night and decreased during the day. These cycles had an inverse relationship with the temperature cycle (pH had no discernable cycle). The consistency of concentration cycles suggests a common mechanism, most likely associated with the formation of Fe oxyhydroxides. The increased rate of Fe2+ oxidation in warm water can account for the cycles in Fe; scavenging of the other elements by the Fe precipitate can account for the consistency of the cycles even though the elements include cations, anions ( H 2 AsO 4 - or HAsO 4 - 2 ), and neutral species ( H 4 SiO 4 0 ). While REE and Y had clear cycles in the constructed wetland, the other elements did not. This is partially due to the lower elemental concentrations (including Fe) but the cycles may also be damped by the deeper, slower-moving water. This study illustrates the dynamic nature of metal removal in passive treatment systems. Furthermore, it suggests that grab samples collected during daytime hours may underestimate the concentrations and flux of metals in these systems.

The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal were simulated in a series of tests. Cylindrical cells with an inner length of 60 cm and a diameter of 7 cm were constructed. Inside the cells, 6 blocks of FEBEX bentonite compacted to a dry density of 1.65 g/cm3 were stacked, resulting in a total length similar to the thickness of the clay barrier in a repository, as per the Spanish Reference Concept. The material was heated at 100 °C on the bottom surface and hydrated through the top surface with granitic water. Tests were performed for durations of 6, 12, 24 and 92 months. At the end of the heating and hydration (HH) treatment, exhaustive post-mortem analyses were performed to check the mineralogical, geochemical and pore water chemistry variations in the bentonite, the objective being to identify the bentonite–water interaction hydrogeochemical processes that occur over time. DRX, SEM and FTIR analyses did not show any evidence of smectite alteration. However, the chemical composition of the pore water evolved with time as a function of hydration of the bentonite, which was affected in turn by the temperature and by the geochemical processes in the bentonite–water system. The pore waters were initially of the Na―Mg―Cl type with an ionic strength of 0.2 M, and evolved to 0.03 M Na―Cl―SO4 type water close to the hydration source, and to Na―(Mg)―Cl type water further away, with ionic strengths ranging from 0.3 to 0.9 M, depending on the particular location and the experiment run time.Dilution and evaporation of the pore water due to hydration and heating at the top and bottom of the bentonite, respectively, were the main processes controlling the conservative species (such as Cl), which moved through the bentonite by advective–diffusive transport. The non-conservative species, such as carbonates, sulfates and cations, were involved in dissolution-precipitation processes and exchange reactions. The pH of the pore water was controlled by surface complexation reactions at edge sites and by carbonates. In the hydrated zones, there was dissolution of sulfates and carbonates, affecting the distribution of the exchangeable cations and the pH of the pore water. The CaX2 content increased at interlayer sites, and CEC values tended to increase, probably due to pH changes towards more alkaline values. In the heating zones, water evaporation resulted in a concentration of the pore water and in the precipitation of anhydrite, mainly in the stages before the hydration of the warmest zones. Evaporation and CO2 degassing due to temperature led to the precipitation of calcite, decreasing the pH of the pore water, which probably caused the CEC values to decrease. There was also an increase in the content of MgX2 and KX at the interlayer sites close to the heater zone, decreasing the NaX and the CaX2 content with time.

The effect of high pH alkaline solutions on the mineral stability of the Boom Clay – Batch experiments at 60 °C by M. Honty; M. De Craen; L. Wang; J. Madejová; A. Czímerová; M. Pentrák; I. Stríček; M. Van Geet (825-840).
Boom Clay is currently viewed as a reference host formation for studies on deep geological disposal of radioactive waste in Belgium. The interactions between bulk rock Boom Clay and 0.1 M KOH, 0.1 M NaOH, 0.1 M Ca(OH)2, young cement water and evolved cement water solutions, ranging in pH from 12.5 to 13.2, were examined as static batch experiments at 60 °C to simulate alkaline plume perturbations, which are expected to occur in the repository due to the presence of concrete. Both liquids and solids were investigated at specific times between 90 and 510 days in order to control the elemental budget and to search for potential mineralogical alterations. Also, the clay fraction was separated from the whole-rock Boom Clay at the end of each run and characterized for its mineralogical composition. Thereby, the importance of the mineral matrix to buffer the alkaline attack and the role of organic matter to protect clay minerals were also addressed. The results indicate that the degree of geochemical perturbation in Boom Clay is dependent on the initial pH of the applied solution together with the nature of the major cation in the reactant fluids. The higher the initial pH of the media, the stronger its interaction with Boom Clay. No major non-clay mineralogical alteration of the Boom Clay was detected, but dissolution of kaolinite, smectite and illite occurred within the studied experimental conditions. The dissolution of clays is accompanied by the decrease in the layer charge, followed by a decrease in the cation-exchange capacity. The highest TOC values coincide with the highest total elemental concentrations in the leachates, and correspondingly, the highest dissolution degree. However, no quantitative link could be established between the degree of organic matter decomposition and clay dissolution.

Soil Cd, Cu, Pb and Zn contaminants around Mount Isa city, Queensland, Australia: Potential sources and risks to human health by Mark P. Taylor; Alana K. Mackay; Karen A. Hudson-Edwards; Elmar Holz (841-855).
This article investigates the relationship between soil Cd, Cu, Pb and Zn contaminants and the location and activities of the Pb–Zn–Ag and Cu mines at Mount Isa, Queensland, Australia. Analysis of the data focuses primarily on soil Pb distributions and concentrations because of their potential impact on children’s health. The Xstrata Mount Isa Mines lease (XMIM) is Australia’s leading emitter of numerous contaminants to the environment, including Cu and Pb, and the mining-related activities have been linked causally to the findings of a 2008 study that showed 11.3% of local children (12–60 months) have blood Pb levels >10 μg/dL. Queensland government authorities and Xstrata Mount Isa Mines Pty Ltd maintain that contaminants within environmental systems around Mount Isa are largely the result of near-surface mineralization. The evidence for whether the contamination is derived from XMIM or other possible sources, such as the natural weathering of ore-rich bedrock, is investigated using data from surface and subsurface soil chemistry, atmospheric modelling of metal contaminants from mining and smelting operations and local geological and associated geochemical studies. Sixty surface soil samples collected from sites adjacent to houses, parks and schools throughout Mount Isa city were analyzed for their total extractable Cd, Cu, Pb and Zn concentrations in the <2 mm to >180 μm (coarser) and <180 μm (finer) grain size fractions. Concentrations in the finer size fraction reveal a range of values: Cd – 0.7–12.5 ppm; Cu – 31–12,100 ppm; Pb – 8–5770 ppm; Zn – 26–11,100 ppm, with several samples exceeding Australian residential health investigation guidelines. Spatial analysis shows that surface soil metal concentrations are significantly higher within 2 km of XMIM compared to more distant samples, and that more than 1000 property lots are at risk of having detrimentally high soil Pb levels. Determination of metal concentrations in 49 samples from eight soil pits shows that surface samples (0–2 cm) are enriched significantly relative to those at depth (10–20 cm), suggesting an atmospheric depositional origin. AUSPLUME air dispersal modelling of Pb originating from the Cu and Pb smelter stacks and mine site fugitive sources confirms that Pb is deposited across the urban area, during periods of the year (∼20%/a) when the wind blows from the direction of XMIM towards the urban area and disperses dusts from the uncovered spoil and road surfaces, as well as from stack emission sources. Although there are some spatially restricted outcrops of Pb close to the surface in parts of the urban area, the Cu-ore body is ∼244 m below the surface. However, enriched and significantly correlated surface soil concentrations of Cu and Pb (Pearson correlation 0.879, p  = 0.000) in and around the urban area of Mount Isa can only be explained by atmospheric transport and deposition of metals from the adjoining mining and smelting operations. The results from this study provide unequivocal evidence that both historic and ongoing emissions from XMIM are contaminating the urban environment. Given the ongoing Pb poisoning issues in Mount Isa children, it is clear that remediation, reductions in mine emissions and more stringent regulatory actions are warranted.

K–Ar dating and δ 18O–δD tracing of illitization within and outside the Shea Creek uranium prospect, Athabasca Basin, Canada by Emmanuel Laverret; Norbert Clauer; Anthony Fallick; Julien Mercadier; Patricia Patrier; Daniel Beaufort; Patrice Bruneton (856-871).
Isotope analyses (K–Ar, δ 18O and δD) were performed on illite from both the sandstone cover and the underlying basement, close to and distant from Shea Creek, an unconformity-type U deposit (Athabasca Basin, Canada); the illite had previously been characterized crystallographically. In the barren areas away from deposit, illite is mainly of the cis-vacant 1M polytype occurring as relatively coarse-grained lath-shaped particles, while it occurs as fine-grained particles of the trans-vacant 1M type next to and in the U mineralized strata. The tectonic-induced hydrothermal system that favored illite crystallization was multi-episodic 1453 ± 2, 1330 ± 20 and probably about 1235 Ma ago. These illite-forming episodes appear to have occurred contemporaneously to those favoring the concentration of the associated U oxides, which were dated independently by the U–Pb method in the Shea Creek deposits and elsewhere in the Athabasca Basin.No relationship was found between the illite polytypes and their crystallization ages, meaning that precipitation of each, either as the cis-vacant or the trans-vacant type, did not relate to a specific event, but to variable physical and chemical crystallization conditions during the same event. The change in the contemporaneous illite polytypes appears to relate to an increase in the δ 18O with distance to the U deposit. Such a change could result from a progressively lower formation temperature with increasing distance to the U deposit, probably combined to a changing δ 18O of the interstitial fluids due to variable water–rock interactions in the rocks. Variable water–rock ratios could have resulted from variable tectonic adjustments of the basement. The authors are inclined to believe that the cis-vacant 1M type crystallized from chemically different fluids, at slightly lower temperatures and away from U concentrations than the equivalent trans-vacant 1M type detected next to the U ores, both precipitating contemporaneously within analytical uncertainty. In addition, comparison of the δD of the hydroxyls from cis-vacant and trans-vacant types suggests that the illite mineral structure was not affected by radiation related to radioactive decay within the deposit or by further natural alteration, as advocated for other occurrences.

Dissolved organic matter (DOM) in groundwater and surface water samples from the Florida coastal Everglades were studied using excitation–emission matrix fluorescence modeled through parallel factor analysis (EEM-PARAFAC). DOM in both surface and groundwater from the eastern Everglades S332 basin reflected a terrestrial-derived fingerprint through dominantly higher abundances of humic-like PARAFAC components. In contrast, surface water DOM from northeastern Florida Bay featured a microbial-derived DOM signature based on the higher abundance of microbial humic-like and protein-like components consistent with its marine source. Surprisingly, groundwater DOM from northeastern Florida Bay reflected a terrestrial-derived source except for samples from central Florida Bay well, which mirrored a combination of terrestrial and marine end-member origin. Furthermore, surface water and groundwater displayed effects of different degradation pathways such as photodegradation and biodegradation as exemplified by two PARAFAC components seemingly indicative of such degradation processes. Finally, Principal Component Analysis of the EEM-PARAFAC data was able to distinguish and classify most of the samples according to DOM origins and degradation processes experienced, except for a small overlap of S332 surface water and groundwater, implying rather active surface-to-ground water interaction in some sites particularly during the rainy season. This study highlights that EEM-PARAFAC could be used successfully to trace and differentiate DOM from diverse sources across both horizontal and vertical flow profiles, and as such could be a convenient and useful tool for the better understanding of hydrological interactions and carbon biogeochemical cycling.

The patterns of dissolved inorganic C (DIC) and aqueous CO2 in rivers and estuaries sampled during summer and winter in the Australian Victorian Alps were examined. Together with historical (1978–1990) geochemical data, this study provides, for the first time, a multi-annual coverage of the linkage between CO2 release via wetland evasion and CO2 consumption via combined carbonate and aluminosilicate weathering. δ13C values imply that carbonate weathering contributes ∼36% of the DIC in the rivers although carbonates comprise less than 5% of the study area. Baseflow/interflow flushing of respired C3 plant detritus accounts for ∼50% and atmospheric precipitation accounts for ∼14% of the DIC. The influence of in river respiration and photosynthesis on the DIC concentrations is negligible. River waters are supersaturated with CO2 and evade ∼27.7 × 106  mol/km2/a to ∼70.9 × 106  mol/km2/a CO2 to the atmosphere with the highest values in the low runoff rivers. This is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds. Evaded CO2 is not balanced by CO2 consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived H2CO3. The results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived DIC concentrations are not directly connected to high carbonate and aluminosilicate weathering rates.

Application of multi-isotope ratios to study the source and quality of urban groundwater in Metro Manila, Philippines by Takahiro Hosono; Fernando Siringan; Tsutomu Yamanaka; Yu Umezawa; Shin-ichi Onodera; Takanori Nakano; Makoto Taniguchi (900-909).
To characterize water quality in terms of dissolved elements and to investigate both the origin of the water and the source and behavior of groundwater contaminants in Metro Manila, 33 water (groundwater and surface water) samples were analyzed for ion and element concentrations, H and O isotope ratios (δD-H2O and δ18O-H2O), SO 4 2 - isotope ratios (δ34S- SO 4 2 - and δ18O- SO 4 2 - ), and Sr isotope ratio (87Sr/86Sr). The chemical measurements showed that the primary important environmental concerns within Metro Manila are groundwater salinization for both shallow and deep aquifers, and As concentrations (up to 22.5 μg/L) in shallow groundwaters. Comparison of SO 4 2 - and Sr isotope values with possible source materials revealed that contamination by man-made materials such as fertilizers and detergents are present in some shallow groundwaters. Shallow groundwater having higher δD-H2O and δ18O-H2O values (av. −44‰ ± 5.6‰ and −6.8‰ ± 0.6‰, respectively, n  = 15) than deep groundwater (av. −48‰ ± 4.4‰ and −7.4‰ ± 0.7‰, respectively, n  = 7) suggests that the origins of H2O in both groundwaters are different from each other. Since the mixing of shallow and deep groundwater does not commonly occur under Metro Manila, the contaminants in the shallow aquifers are unlikely to be transported into the deep aquifers. Sulfate reduction by bacterial activity was observed for some groundwaters, resulting in a maximum elevation in δ34S- SO 4 2 - values of around 10‰. By using SO 4 2 - isotope ratios as an indicator of changes in redox conditions and Sr isotope ratio as a source indicator, it was shown that As was dissolved from unconsolidated sedimentary deposits of volcanic origin which enclose shallow unconfined aquifers, but was not the result of changes in redox conditions. The study demonstrated that multi-isotope ratios are useful for evaluating water quality problems in urban groundwaters.

A prolonged drought in the High Plains of Nebraska prompted the use of groundwater for cooling at the largest coal-fired power plant in the State. Prior to the drought, groundwater was used primarily for irrigation and the power plant relied exclusively on surface water stored in a nearby reservoir for cooling. Seepage from the reservoir system during the past ∼75 a has resulted in the buildup of a large mound of water in the underlying unconfined aquifer. A well field was installed during the drought for the purpose of tapping the groundwater mound as a supplemental source of water for cooling. Concentrations of dissolved Cl and SO 4 2 - indicate 65–100% of shallow groundwater and 0–100% of deep groundwater (saturated thickness ∼115 m) in the immediate vicinity of the reservoir was from seepage out of the reservoir system. Hydrogen and O isotopic data indicate most surface-water seepage occurred in the late spring and early summer when reservoir stage was at its highest level. Tritium/3He apparent groundwater ages imply horizontal flow velocities from the reservoir were on the order of 60–600 m/a. These diverse data provided information regarding the spatial distribution, timing, and rate of seepage from the reservoir that could not have been obtained from the available geologic, hydraulic head, and conductivity data. In particular, mixing fractions of surface water and regional groundwater in the aquifer could not have been determined using hydraulic information. Mixing fractions were of special interest in this study because of the management objective to maximize the capture of surface-water seepage in the cooling water wells. Groundwater-flow models developed as well-field management tools were calibrated using inverse modeling techniques and observations of groundwater age, surface-water flow, reservoir stage, and groundwater levels. The age data only accounted for 6 of the 2574 field observations used to calibrate the groundwater-flow models, yet they were among the most influential for refining estimates of hydraulic conductivity, recharge, and seepage from the reservoir. Results from this study demonstrate the benefits of using geochemical, isotopic, and age tracer data to develop conceptual and numerical models of groundwater flow for the purpose of water management.