Applied Geochemistry (v.81, #C)

The strontium isotope budget of the Warta River (Poland): Between silicate and carbonate weathering, and anthropogenic pressure by Mateusz Zieliński; Jolanta Dopieralska; Zdzislaw Belka; Aleksandra Walczak; Marcin Siepak; Michał Jakubowicz (1-11).
The Sr isotope composition (87Sr/86Sr) and Sr content of waters of the Warta River (central-western Poland) and its tributaries were used to fingerprint water sources and their interactions in space and time. Dissolved Sr in river water of the Warta is characterized by a relatively narrow range of the 87Sr/86Sr values, from 0.7090 to 0.7105, which contrasts with a strong variation in isotopic signatures of the tributaries, from 0.7080 to 0.7121. With the exception of three streams, which include inputs of mine waters, the waters of tributaries are more enriched in 87Sr than the master stream. The overall Sr budget of the Warta watershed is determined by the relative contributions of carbonate dissolution and silicate weathering. It can be accounted for by mixing between waters from three reservoirs: 1) groundwater charged with Sr through interaction with Sr-bearing clay minerals, 2) groundwater related to weathering (dissolution) of carbonate rocks, and 3) atmospheric waters charged with Sr from the near-surface weathering and wash-out of Quaternary glaciogenic deposits. Superimposed on the natural Sr isotope systematics is impact of mine waters and fertilizers. The former providing non-radiogenic Sr from the Permian/Mesozoic aquifers constitutes an important anthropogenic element of the Sr budget, whereas the impact of the latter is presumably common but of minor importance. The present-day Sr isotope systematics of the Warta is temporary and different from that of the pre-industrial times.Display Omitted
Keywords: Strontium isotopes; Water reservoirs; Weathering; Anthropogenic contamination; Warta river; Poland;

Coordination of arsenic and nickel to aluminum and magnesium phases in uranium mill raffinate precipitates by Jared Robertson; J. Essilfie-Dughan; J. Lin; M. Jim Hendry (12-22).
The Key Lake U mill uses a stepwise neutralization process (pH 4.0, 6.5, 9.5, and 10.5) to treat raffinate (acidic, metal-rich wastewater) prior to safely releasing effluent to the environment. This process generates a complex mixture of precipitates that are deposited to a tailings facility. In this study, the coordination environments of As and Ni with respect to Al-Mg phases precipitated in the presence and absence of Fe in mill-generated and synthetic precipitates were defined using bulk X-ray absorption spectroscopy complemented with bulk X-ray diffraction. In low pH (pH 4.0–4.6) samples, As(V) precipitates as ferric arsenate and adsorbs to AlOHSO4 (an amorphous hydrobasaluminite-like phase) and ferrihydrite via bidentate-binuclear complexes. Nickel(II) predominantly adsorbs to amorphous Al(OH)3 via edge-sharing bidentate-mononuclear complexes. In high pH (pH 9.5–9.9) samples, As(V) adsorbs to amorphous Al(OH)3, ferrihydrite, and MgAlFe-hydrotalcite (bidentate complex). Nickel(II) octahedra adsorb to amorphous Al(OH)3 and likely form a Ni-Al layered double hydroxide (LDH) surface precipitate on MgAlFe-hydrotalcite via Al dissolution-precipitation. In the final solids (blended low and high pH precipitates) discharged at ∼ pH 10.5, As(V) adsorbs to amorphous Al(OH)3, ferrihydrite, and MgAlFe-hydrotalcite. Nickel(II) adsorbs to amorphous Al(OH)3 and forms Ni-Al LDH surface precipitates on hydrotalcite. This study demonstrates that neutralization of chemically complex wastewater precipitates multiple phases capable of controlling dissolved As and Ni concentrations. Knowledge gained from this study will aid investigations in understanding the long-term fate of these potential contaminants in the environment and can be applied to other industries and environmental systems with similar conditions.
Keywords: Arsenic; Nickel; EXAFS; Uranium tailings; XAS;

The radial sand ridges (RSRs) in the southwestern Yellow Sea off the Jiangsu Coast, East China have been intensively studied at least since 1975. Despite decades of studies, the provenance of the RSR sediments remains uncertain. In this study, the Nd-Sr isotopic and REE geochemical compositions of residual sediments (i.e., the acid-insoluble fractions) were investigated to determine the provenance of the RSR sediments. The Nd isotopic composition, PAAS-normalized REE patterns and characteristic parameters (e.g., Sm/Nd, (La/Sm)N, (Gd/Yb)N) were merely associated with source rocks but not with particle sorting while the Sr isotopic composition and REE contents of residual sediments were affected by particle sorting in addition to source rocks. The onshore RSR sediments originated mainly from mixing of the fine-grained sediments from various parts of the offshore RSR in terms of REE geochemical and isotopic analyses. Isotopic and REE geochemical comparison further reveals that the RSRs off the Jiangsu Coast were fed chiefly by the dispersal of surface sediments from the Yangtze River Mouth. Surface sediments from the Yangtze River Mouth were directly dispersed to the RSRs along the Jiangsu Coast and significantly affected the seaward part of the offshore RSR and the old Yellow River Delta area by a northward branch of the Changjiang Diluted Freshwater Plume. Only minor quantities of surface sediments from the modern Yellow River Mouth were introduced into the RSRs by the Jiangsu Coastal Current and mainly contaminated the landward part of the offshore RSR area. Our findings highlighted the potential of the Nd isotopes with REE geochemistry to trace the provenance of coastal sediments.
Keywords: Nd-Sr isotopes; REE geochemistry; Sediment provenance; Radial sand ridges (RSRs); Jiangsu coast;

The Upper Rhine Graben (URG) is a Tertiary rift structure in central Europe offering favorable conditions for geothermal energy utilization. Relatively high heat flow combines with sufficiently high permeability of the hydrothermal reservoirs. One of the target stratigraphic levels is the lower Triassic sandstone formation (Buntsandstein), where hot water resources at temperatures up to 250 °C can be utilized. Extensional neotectonics and hydraulic stimulation form new fracture surfaces in the reservoir rocks (enhanced geothermal system, EGS). The exposed fresh rock fracture surface reacts with the highly saline reservoir brines (Na-Cl up to 200 g l−1) with consequences for the permeability of the reservoir.In order to better understand the dynamic evolution of fault systems caused by fluid-rock interaction, we conducted batch-type experiments in a stirred autoclave system and reacted arkosic sandstone with synthetic 2 molal Na-Cl solution at temperatures of 200 °C and 260 °C. After 45–55 days reaction time altered rock samples were compared with the starting material and the geochemical-mineralogical processes were deduced with the help of XRD, SEM methods and EMP measurements. Fluid compositions were examined by ICP-MS, ICP-OES and IC.The arkosic sandstones show a surprisingly high reactivity during the experiments. Quartz grain surfaces show deep dissolution features and all reaction fluids were saturated with respects to quartz. Illite and kaolinite from the primary sandstone cementation completely dissolved from the sample surface. Perfectly euhedral crystals of metastable analcime formed during the experiment as separate crystals on quartz, as groups or clusters and as surface covering mats. The overall net transfer process dissolves quartz + illite + kaolinite ± K-feldspar and precipitates analcime + chlorite ± albite. The process is accompanied by a total volume increase of the solids of 20–30 vol%. K-feldspar dissolution is hampered by albitization rims shielding K-feldspar and efficiently preventing an equilibration of the Na–K exchange with the fluid. The experiments show changes on the rock surface, leading to an increase of the aperture of a single fracture during the early phases of reaction and later to a decrease as the fluid-rock reaction progresses. Alteration of the fracture surface also generates loose fragments and altered minerals. This fine material may efficiently reduce the fracture aperture at narrow points along the fracture.
Keywords: Hydrothermal experiments; Water-rock interaction; Analcime; Sandstone reservoir; Geothermal energy; Fracture surfaces;

Rate equations for modeling carbon dioxide sequestration in basalt by Ryan M. Pollyea; J. Donald Rimstidt (53-62).
Dissolution rate equations are developed from published data for glassy and crystalline basalt to predict the silica release flux (J Si) as a function of hydrogen ion activity (2 < pH < 12) and temperature (0° < T < 100 °C). For glassy basalt the silica flux is J S i = ( 5.00 × 10 2 ) e ( − 39700 R ) 1 T a H + 1.01 + ( 5.26 × 10 − 5 ) e ( − 38400 R ) 1 T a H + − 0.258 and for crystalline basalt the silica flux is J S i = ( 7.40 ) e ( − 40100 R ) 1 T a H + 0.680 + ( 8.67 × 10 − 7 ) e ( − 32900 R ) 1 T a H + − 0.286 .These rate equations are implemented in TOUGHREACT to simulate a CO2 saturated solution reacting with glassy and crystalline basalt in batch and semibatch reactors. The crystalline basalt models are compared with a more complex basalt representation comprising a composite mixture of olivine, plagioclase and pyroxene dissolution rates. Results show that numerical models based on the newly developed rate equations make reasonable predictions. Batch reactor models initially contained a solution spiked with CO2. These models showed relatively rapid CO2 consumption followed by cessation of the reaction with the glassy and crystalline basalt after the CO2 was exhausted and a terminal pH near eight. The composite basalt model was less successful because the plagioclase continued to react after the CO2 was exhausted causing the pH to rise to an unreasonably high value near 12. Semibatch reactor models containing a solution continuously supplied with CO2 showed relatively rapid CO2 consumption until all basalt was consumed. Complete semibatch reaction produced a sodium and bicarbonate rich solution with a pH near eight for all three basalt compositions.
Keywords: CO2 sequestration; TOUGHREACT models; Glassy basalt rate equation; Crystalline basalt rate equation;

High-temperature geothermal systems hold an enormous capacity for generating geothermal energy. The Kangding area is a typical high-temperature geothermal field in the Himalayan Geothermal Belt. Hydrogeochemical, gas geochemical and isotopic investigations were performed to identify and qualify the main hydrogeochemical processes affecting thermal water composition, including mixing and degassing, and then to estimate a reliable reservoir temperature. Nine water samples and four geothermal gas samples were collected and analysed for chemical and isotopic components. The results demonstrate the alkaline deep geothermal water is the mixtures of approximately 75% snow-melt water and 25% magmatic water. It is enriched in Na, K, F, Li and other trace elements, indicating the granite reservoir nature. The shallow geothermal water is the mixtures of approximately 30% upward flow of deep geothermal water and 70% meteoric cold water. High concentrations of Ca, Mg and HCO3 indicate the limestone reservoir nature. There is no remarkable oxygen isotope shift in the geothermal water since the rapid circulation is difficult to trigger off strong water-rock interaction. CO2 is the predominant geothermal gas, accounting for more than 97% of total gases in volume percentage. The concentration of CO2 degassing ranged from 0.4 mol L−1 to 0.8 mol L−1 via geothermometrical modelling. As a result, the geothermal water pH increased from 6.0 to 9.0, and approximately 36% of the total SiO2 re-precipitate. The sources of CO2 are the metamorphism of limestone and magmatic degassing based on the composition of carbon isotope. The appropriate geothermometers of Na-K and Na-Li yield reservoir temperature of 280 °C. The geothermometrical modelling, developed to eliminate the effects of CO2 degassing, yields temperature of 250 °C. The silica-enthalpy mixing model yields temperature of 270 °C with no steam separation before mixing.
Keywords: High-temperature geothermal system; Fluid geochemistry; Mixing and degassing processes; Geothermometry applications; Reservoir temperature;

Rain-plume interactions at Nyiragongo and Nyamulagira volcanoes and associated rainwater hazards, East Africa by Charles M. Balagizi; Marcellin M. Kasereka; Emilio Cuoco; Marcello Liotta (76-89).
A rain-gauge network consisting of 13 stations was installed on the volcanic fields around Nyiragongo and Nyamulagira volcanoes, as well as in the surrounding villages and Goma city (DR Congo) from December 2013 to October 2015. The rain gauges were then sampled on a monthly basis in order to evaluate the influence of volcanic emissions on rain chemistry and rainwater quality. This is the first temporally distributed dataset of rain chemistry from this densely populated region, where the two Africa's most active volcanoes, 14 km apart, continuously eject gases and ash to the atmosphere and where rainwater represents an important water resource. The results revealed that volcanic emissions are the primary source of the dissolved loads. Wind-blown dust dissolution is in fact occasionally the dominant source of major cations at cities and villages that are remote with respect to the volcano summits. A few sites located in the forested Virunga National Park are neither significantly impacted by volcanic emissions nor wind-blown dust. The combined contribution of volcanic gases and the dissolution of volcanic ash and soil dust determined the pH of the rainwater. Thus, areas with limited volcanic impact showed higher pH values (up to 7.6), while those that experience major volcanic impact showed lower pH values (as low as 3.1), as a consequence of the continuous input of acidic volcanic gases. The chemical composition of rain varies according to location and was driven by changes in wind direction. Nearly all the sites showed prominent temporal variations in dissolved loads, which were essentially related to the variations in precipitation amount due to seasonal changes. The rain dissolved loads, the bulk atmospheric deposition fluxes (e.g., 0.5–24.6 t km−2 yr−1 for fluoride and 22.6–176.6 t km−2 yr−1 for total dissolved substances), and the spatial variations converged to show that localities to the west and southwest of Mt Nyiragongo are the most strongly impacted by volcanic emissions. These areas to the west and southwest, which experience higher rates of F deposition, also coincide with the locations of villages and small cities where endemic dental fluorosis occurs. Such a relationship is explained by the use of F-rich water in all domestic activities, including as drinking water, in the region.Display Omitted
Keywords: Nyiragongo volcanic plume; Rainwater chemistry; Acid-driven ash dissolution; Rainwater quality; Dental fluorosis;

Heterogeneous oxidation of Fe(II) in AMD by Jonathan M. Dietz; Brian A. Dempsey (90-97).
Laboratory and field experiments were used to measure the effects of several variables on the rate of heterogeneous oxidation in acid mine discharges (AMD). A wider range of variables were used compared to previously published studies, i.e., Fe(III) solid from 0.012 to 2.40 g L−1, pH 5.35 to 6.81, DO 0.11–0.36 mM, temperature 10.1–22.7 °C, and Fe(II) total 0.04–1.0 mM. The heterogeneous rate exceeded the predicted homogeneous rate for slightly acidic pH values when Fe(III) solid was greater than about 0.02 g L−1, with the cross-over concentration of Fe(III) solid a function of temperature. An equation for the heterogeneous oxidation rate was derived, d [ F e ( I I ) a q ] d t = − k h e t e r o [ F e ( I I ) a q ] [ F e ( I I I ) s o l i d ] { O 2 } { H + } n where n was 1.4 for pH from 6.0 to 6.8 and 2.0 for pH from 5.3 to 6.0. All previous studies reported n equal to 1.0. One earlier study reported that the rate of heterogeneous oxidation was constant for Fe(III) solid greater than 0.4 g L−1. In our experiments the rate remained linear to at least 2.4 g L−1 Fe(III) solid . The predicted rate constants along with DO, pH, Fe(III) solid , and temperature can be used to predict the removal of Fe(II) in existing facilities and for design of new reactors. Application can result in design of smaller reactors for slightly acidic pH values and in production of re-usable Fe(III) oxide solids.Display Omitted
Keywords: Ferrous iron oxidation; Heterogeneous iron oxidation; Acid mine discharges;

Helium evidences for mantle degassing in the groundwater of Madeira Island – Portugal by Helena I.F. Amaral; Carla Midões; Rolf Kipfer (98-108).
The Madeira Island is fed by an active hotspot, but there are no evidences of current volcanism and geothermal activity or, of a heat source at depth, which probably justifies why only low temperature and low TDS groundwater is found in Madeira. Nonetheless, Madeira is a relatively young island (≤7 Ma old), and a connection to the upper mantle through geological conduits, is likely to occur. To investigate whether such a connection exists, noble gases and stable isotopes were, so far as we know, for the first time measured in groundwater samples of the main (basal) aquifer of Madeira Is.Groundwater is the main supply of drinking water in Madeira Is., and the hydrogeology of the island has been well characterized in previous studies. In this study, groundwater was generically divided into ‘cold’ waters (<20 °C, near the coast) and ‘warm’ waters (20–25 °C, central part of the island). This division was based on field temperature, water chemistry and stable isotopic composition. Four ‘hot’ waters (23–25 °C) showed partly distinct characteristics. A bubbling spring was also sampled. Very low tritium values indicate groundwater recharged recently and/or mix with free-tritium waters. Groundwater is fed by rain recharged during autumn as indicated by δ18O and δ2H signatures. During infiltration, the waters dissolved soil CO2 that according to the back-calculated δ13C-CO2 compositions corresponds mainly to CO2 of biogenic origin. Nonetheless, a mantle CO2 component cannot be excluded from samples from the inner part of the island. The noblegas helium was the sole tracer indicating a deep gas contribution to the groundwater. A strong mantle signal was detected in the ‘hot’ and bubbling waters, as indicated by their He-Ra values of 8 (being Ra the atmospheric 3He/4He ratio), typical of the MORB. Thus, even if the last volcanic eruption occurred ca. 0,006 Ma, degassing of the upper-mantle was detected in the shallow cold waters of Madeira. The deep gas ascends without heat transport, through dikes and faults that cross, mainly, the central part of the island.
Keywords: Mantle helium; Deep gases; Stable isotopes; Volcanic hydrogeology; Madeira island;

A geochemical examination of humidity cell tests by Ann S. Maest; D. Kirk Nordstrom (109-131).
Humidity cell tests (HCTs) are long-term (20 to >300 weeks) leach tests that are considered by some to be the among the most reliable geochemical characterization methods for estimating the leachate quality of mined materials. A number of modifications have been added to the original HCT method, but the interpretation of test results varies widely. We suggest that the HCTs represent an underutilized source of geochemical data, with a year-long test generating approximately 2500 individual chemical data points. The HCT concentration peaks and valleys can be thought of as a “chromatogram” of reactions that may occur in the field, whereby peaks in concentrations are associated with different geochemical processes, including sulfate salt dissolution, sulfide oxidation, and dissolution of rock-forming minerals, some of which can neutralize acid. Some of these reactions occur simultaneously, some do not, and geochemical modeling can be used to help distinguish the dominant processes. Our detailed examination, including speciation and inverse modeling, of HCTs from three projects with different geology and mineralization shows that rapid sulfide oxidation dominates over a limited period of time that starts between 40 and 200 weeks of testing. The applicability of laboratory tests results to predicting field leachate concentrations, loads, or rates of reaction has not been adequately demonstrated, although early flush releases and rapid sulfide oxidation rates in HCTs should have some relevance to field conditions. Knowledge of possible maximum solute concentrations is needed to design effective treatment and mitigation approaches. Early flush and maximum sulfide oxidation results from HCTs should be retained and used in environmental models. Factors that complicate the use of HCTs include: sample representation, time for microbial oxidizers to grow, sample storage before testing, geochemical reactions that add or remove constituents, and the HCT results chosen for use in modeling the environmental performance at mine sites. Improved guidance is needed for more consistent interpretation and use of HCT results that rely on identifying: the geochemical processes; the mineralogy, including secondary mineralogy; the available surface area for reactions; and the influence of hydrologic processes on leachate concentrations in runoff, streams, and groundwater.
Keywords: Geochemical characterization; Mining; Humidity-cell tests; Geochemical modeling; Predictions;

Grain-size dependence of mercury speciation in river suspended matter, sediments and soils in a mercury mining area at varying hydrological conditions by Carluvy Baptista-Salazar; Jan-Helge Richard; Michael Horf; Mateja Rejc; Mateja Gosar; Harald Biester (132-142).
Suspended matter (SM) plays an important role in the transport of mercury (Hg) in aquatic systems. Information about Hg-species in this material is crucial to understand risk potential, especially for Hg methylation and bioavailability. In the Idrija Hg mine (Slovenia) cinnabar (α-HgS) was mined and processed for centuries. These activities caused contamination of the Idrijca river system by dumping of ore roasting residues, as well as atmospheric Hg deposition in soils attributed to excessive Hg emissions from the roasting plant. Cinnabar is the dominant Hg-species in the coarse-grained sediments of the Idrijca river where Hg methylation is generally low, whereas natural-organic-matter-bound Hg (NOM-bound) has caused intense Hg methylation in the Gulf of Trieste (GT), the final sink for Hg released from the Idrijca catchment. Hydrology of the Idrijca river is characterized by high discharge events during heavy rains and snowmelt, which transports large amounts of SM towards the GT. However, the dominant Hg-species transported in SM and their specific source under varying hydrological conditions is largely unknown, yet crucial to predict future transport of bioavailable Hg forms from the mining area to the GT.We analyzed Hg concentrations and Hg-species (Hg-thermo-desorption) in SM and different grain size fractions of soils from the Idrijca catchment to evaluate changes in solid phase Hg-species under low and high flow conditions. Concentrations of dissolved Hg did not change significantly during low and high flow (median: 21.3–28.1 ng L−1, respectively). Hg concentrations in SM in tributaries decreased with distance (∼30 km) from the mine from 32.7 to 0.47 mg kg−1 related to Hg concentrations in fine particulate soil fractions (0.45–20 μm) which ranged from 56.2 to 0.53 mg kg−1. Hg speciation in SM was dominated by NOM-bound Hg forms at low flow (median: 95.5%) which decrease during high flow conditions (median: 53.8%) attributed to increased mobilization of cinnabar from riverbanks and mine residues. Our results show that aqueous Hg transport in the Idrija mining area is dominated by heavy rain events and mobilization of NOM-bound Hg from soils indicating that the frequency of heavy rain events will control transport of bioavailable Hg to the marine environment.

Cement has been little investigated as a control for acid mine drainage, despite having advantages over cheaper alternatives. Leaching column experiments (set up in triplicate) investigated the effect of applying Portland cement slurries with three different water/cement (w/c) ratios (0.8, 1.0, 1.2) to pyrite-bearing waste rock from Brukunga mine in southeastern Australia. After application of the cement, leachate from the cemented columns showed a reduction in acidity compared to the control columns of ∼85% and 100% for w/c ratios of 0.8 and both 1.0 and 1.2 respectively. This was due to direct neutralisation of acidity by cement dissolution and encapsulation of the pyrite-bearing rock fragments by the cement (as shown by a reduction in oxygen consumption rates of up to 70%). In columns with the higher w/c ratios (1.0, 1.2), the cement slurry penetrated to the base of the columns and greatly decreased the permeability. The greater coverage of the waste rock by the cement and increased contact time between the leachate and cement meant that no acid drainage leached from these columns (pH 7–8, Fe, Al, Mn, Zn and Cu concentrations rarely above detection limits). In columns with a w/c ratio of 0.8, the cement slurry was mostly retained in the upper 30–50% of the waste rock, leaving a large fraction of the waste rock below without any cement coverage. Leachate drained relatively quickly from these columns, probably through a small number of pathways through the cement plug and carried relatively small loads of acidity and metals from uncemented waste rock beneath the cement. Thus cement may be a viable method for controlling acid mine drainage generation from waste rock dumps, and could be applied with both lower and higher w/c ratios could be used to achieve an optimal balance between deep penetration and surficial retention.Display Omitted
Keywords: Portland cement slurries; Acid mine drainage control; Oxygen consumption tests;

This paper presents a multiscale investigation on the viability of employing ground granulated blast-furnace slag (GGBS) alone and the slag activated with cement (C-GGBS) and MgO (M-GGBS) in stabilization/solidification (S/S) of zinc (Zn) contaminated clayey soil that may offer a range of environmental and economic benefits. The macro and micro level test results showed that the addition of GGBS up to 30 wt% will not successfully stabilize the kaolin sample even with low contents of Zn. The cement-slag treatment exhibits a higher sorption capability as compared to the GGBS application, but in this case, the acidic attack dramatically decreases the potential of Zn retention, leading to a marked increase in the needed amount of agent (by nearly 60%) to gain the acceptable leaching characteristics. Moreover, the physicochemical reactions of Zn with C-GGBS have negative impacts on the microstructure, and thus, the engineering properties of the treated material. MgO gives a better cementation structure-bonding and a more pH-buffering capacity to the slag-amended soil, two features which are found to alleviate the restructuring of S/S product upon contact with the metal ions or the aggressive environments. This can play a vital role in enhancing the geo-mechanical performance and Zn immobilization of M-GGBS system with a lower quantity of the agent (to about 50%) and shorter curing ages (21 days) than the C-GGBS blend. Overall, it seems that the activated slag can be used as an effective S/S binder. However, the optimum dosage of binder will be strongly influenced by the activator composition.
Keywords: Zn-contaminated soil; Activated slag; Cementing phases; Buffering capacity; Stabilization/solidification;