Applied Geochemistry (v.70, #C)

Sources of environmental sulfur in the groundwater system, southern New Zealand by Rosalie Tostevin; Dave Craw; Robert Van Hale; Matthew Vaughan (1-16).
Sulfide minerals commonly occur in sediments and basement rocks in southern New Zealand, as authigenic precipitates from groundwater below the oxygenated surface zone. There are two principal potential sources for sulfur in the groundwater system: weathering of sulfide minerals in the metamorphic basement and rainwater-derived marine aerosols. We present data for these two key sulfur sources: metamorphic sulfide and associated hydrothermal Au-bearing veins within the Otago Schist (average δ 34S = −1.8 ± 2.4‰), and an inland saline lake (S derived entirely from rainwater, δ 34S = 21.4 ± 0.8‰). We use these two end member δ 34S values to estimate the contributions of these sources of sulfur in authigenic groundwater sulfide minerals and in waters derived from oxidation of these sulfide minerals, across a range of environments. We show that authigenic groundwater pyrite along joints in the Otago schist is derived primarily from metamorphic basement sulfur. In contrast, authigenic groundwater pyrite cementing Miocene-Recent aquifers shows a substantial marine aerosol component, and represents a distinct hydrogeological system. We suggest that marine aerosols represent a significant flux to the terrestrial sulfur cycle that has been present through the groundwater system in Otago over the past 20 million years.
Keywords: Sulfur isotopes; Sulfur cycle; Mine waters; Pyrite; Marine aerosols; Groundwater;

Effect of NO2 in exhaust gas from an oxyfuel combustion system on the cap rock of a proposed CO2 injection site by Kosuke Tanaka; Hirokazu Okawa; Keiichiro Hashimoto; Ryohei Takahashi; Akira Imai; Katsuyasu Sugawara (17-26).
A laboratory geochemical study was conducted using a drill core sample of cap rock from the Surat Basin, Australia, to investigate the effect of NO2 contained in the CO2 gas exhausted from the oxyfuel combustion process (oxyfuel combustion CO2) on the cap rock. A gas (CO2 containing NO2) was prepared to simulate the exhaust gas produced from the oxyfuel combustion process. Two types of gases (pure CO2 and CO2 containing SO2) were also prepared as reference gases. The effect of NO2 on cap rock was studied experimentally using these gases. No differences in the amounts of leached ions and pH changes for CO2 containing NO2 (36 ppmv), pure CO2, and CO2 containing SO2 (35 ppmv) existed. The pH values decreased immediately after CO2 gas injection but increased with time as a result of mineral buffering. Leaching of Fe, Mg, Ca, and K was suggested to have occurred as the result of dissolution of Fe-chlorite, prehnite and illite-smectite mixed layer clay in the shale sample. The amounts of Ca, Fe, and Mg leached with CO2 containing NO2 (318 ppmv) were higher than those for pure CO2. For the mixture containing 318 ppmv NO2, the pH increased more than that for the other gas conditions immediately after the pH fall at the start of the experiment, because oxidation-reduction reactions occurred between Fe2+ and NO3 . Moreover, the results indicated that some of the leached Ca and Fe were deposited on the shale sample because of the pH increase. Therefore, we concluded that the effects of NO2 on mineral dissolution and pH changes of formation water are negligible when oxyfuel combustion CO2 containing about 30 ppmv of NO2 is injected into an underground aquifer. In addition, even if about 300 ppmv NO2 is accidentally injected into the underground aquifer, mineral dissolution is suppressed due to the buffering of pH decrease after gas injection.Display Omitted
Keywords: Carbon capture and storage; Supercritical CO2; NO2; Cap rock; Oxyfuel combustion process;

Alteration of nuclear glass in contact with iron and claystone at 90 °C under anoxic conditions: Characterization of the alteration products after two years of interaction by Michel L. Schlegel; Christelle Martin; Florence Brucker; Christian Bataillon; Cécile Blanc; Matthieu Chorro; Patrick Jollivet (27-42).
The present study investigates the alteration of a fractured glass block in contact with iron and Callovo-Oxfordian claystone at 90 °C under anoxic and water-saturated conditions. The alteration rates and the nature of glass alteration products at the different compact interfaces (glass-clay, glass-iron) and in cracks were assessed by solution chemistry and microscopic-scale techniques (scanning electron microscopy coupled with energy-dispersive X-ray microscopy, microRaman spectroscopy, and X-ray absorption fine structure spectroscopy). A significant but modest (two-fold) increase in glass alteration in contact with steel was observed, leading to an average alteration rate over the experiment of about 0.007–0.014 g/m2/d. This rate is significantly lower than forward rate r0 in clay-equilibrated groundwater (1.7 g/m2/d), indicating that a decrease of the alteration rate was not hindered by the steel presence. The corrosion–alteration interface was made up of successive layers of corrosion products in contact with iron, a layer of Fe silicates, and an altered glass layer enriched in Fe. Characterization of the glass block in direct contact with claystone revealed that the thickness of altered glass was much more important than at the glass-iron interface. The altered glass layer in contact with clay was slightly enriched in Fe and Mg, and depleted in alkali cations. Altered glass layers in cracks were usually limited to fringes thinner than 2 μm, with a thickness decreasing from the crack mouth, indicating that alteration is controlled by transport in the cracks. The fractures were partially filled with calcite and lanthanide hydroxocarbonate precipitates. These results contribute to the understanding of nuclear vitrified waste-iron-corrosion products interactions in a deep geological repository.
Keywords: Nuclear glass; Iron; Clay; Alteration; Nuclear waste repository; Fractures; Fe; Mg; Corrosion products;

Long-term immobilisation of Cd2+ at the Tulul Al Hammam natural analogue site, central Jordan by Ella V. Sokol; Svetlana N. Kokh; Hani N. Khoury; Yurii V. Seryotkin; Sergei V. Goryainov (43-60).
The Tulul Al Hammam area in central Jordan is a natural analogue site where to study long-term Cd2+ retention during the weathering of Cd-enriched combustion-metamorphic marbles with clinker-like mineralogy. Natural Cd-rich portlandite (Ca0.67−0.45Cd0.33−0.55)[OH]2 was discovered and characterised by single-crystal XRD, SEM/EDS, and microprobe analyses, and Raman spectroscopy. The Ca[OH]2 – Cd[OH]2 solid solution ((Ca1−xCdx)[OH]2) is isostructural with Ca[OH]2 and β-Cd[OH]2 crystals in the CdI2-type of structure. Cd-rich portlandite is a common secondary phase in slightly altered massive marbles, where it replaces and rims single-crystals of the high-temperature precursor (Ca1−xCdx)O. The Cd:Ca molar ratios of (Ca1−xCdx)[OH]2 are inherited from the precursor phase (Ca1−xCdx)O. Reliable long-term immobilisation of Cd in (Ca1−xCdx)[OH]2 is assumed for pore water pH values from 10.5 up to 12 buffered by C-S-Hs formed mainly during spurrite hydration. The Tulul Al Hammam site may have some bearing on long-term Cd2+ retention in the concrete matrix.
Keywords: Cd-rich portlandite; Long-term Cd retention; Natural analogue; Cement; Waste management; Central Jordan;