Applied Geochemistry (v.43, #C)

Geochemical characterisation of Fika Formation in the Chad (Bornu) Basin, northeastern Nigeria: Implications for depositional environment and tectonic setting by Adebanji Kayode Adegoke; Wan Hasiah Abdullah; Mohammed Hail Hakimi; Babangida M. Sarki Yandoka (1-12).
Late Cretaceous shales of the Fika Formation in the Chad (Bornu) Basin, northeastern Nigeria, were analysed to define paleoenvironment and source of the organic matter, and their relation to tectonic setting. The organic carbon and sulphur contents of Fika shale samples are in the range of 0.51–2.13 and 0.31–1.65 wt.%, respectively, pointing that these shales were deposited in suboxic-anoxic marine conditions. The biomarker and chemical compositions provide evidence for a major contribution of aquatic algae and microorganisms with minor terrigenous organic matter input. Moderate salinity stratification and relatively anoxic-suboxic bottom water conditions are also likely in the Fika shales. Therefore, stratified water column with moderate salinity and relatively anoxic-suboxic bottom water conditions have contributed to organic matter (OM) preservation in the Fika shale layer. Fika shale samples are rich in SiO2 (54.80 wt.%), followed by Al2O3 (23.75 wt.%) and Fe2O3 (10.19 wt.%). Compared with average shale, the analysed shale samples are obviously enriched in Al2O3 (23.75 wt.%), TiO2 (1.34 wt.%), and P2O5 (0.30 wt.%), indicating that these sediments are rich in clay minerals and represent a good possibility for enhanced organic matter production and enrichment.Plots of Fika shale on bivariate discriminant function diagram suggest an active continental margin setting for the provenance. The inferred tectonic setting for the late Cretaceous shales of the Fika Formation of the Chad (Bornu) Basin is in agreement with the tectonic evolutionary history of the west and central Africa during the Cretaceous period.

Deep-sea ferromanganese deposits contain a wide range of economically important metals. Ferromanganese crusts and nodules represent an important future resource, since they not only contain base metals such as Mn, Ni, Co, Cu and Zn, but are also enriched in critical or rare high-technology elements such as Li, Mo, Nb, W, the rare earth elements and yttrium (REY). These metals could be extracted from nodules and crusts as a by-product to the base metal production. However, there are no proper separation techniques available that selectively extract certain metals out of the carrier phases. By sequential leaching, we demonstrated that, except for Li, which is present in an easily soluble form, all other high-tech metals enriched in ferromanganese nodules and crusts are largely associated with the Fe-oxyhydroxide phases and only to subordinate extents with Mn-oxide phases. Based on this fact, we conducted selective leaching experiments with the Fe-specific organic ligand desferrioxamine-B, a naturally occurring and ubiquitous siderophore. We showed by leaching of ferromanganese nodules and crusts with desferrioxamine-B that a significant and selective extraction of high-tech metals such as Li, Mo, Zr, Hf and Ta is possible, while other elements like Fe and the base metals Mn, Ni, Cu, Co and Zn are not extracted to large extents. The set of selectively extracted elements can be extended to Nb and W if Mn and carbonate phases are stripped from the bulk nodule or crust prior to the siderophore leach by e.g. a sequential leaching technique. This combination of sequential leaches with a siderophore leach enhanced the extraction to 30–50% of each Mo, Nb, W and Ta from a mixed type Clarion-Clipperton Zone (CCZ) nodule and 40–80% from a diagenetic Peru Basin nodule, whilst only 5–10% Fe and even less Mn are extracted from the nodules. Li is extracted to about 60% from the CCZ nodule and a maximum of 80% Li is extracted from the Peru Basin nodule.Our pilot work on selective extraction of high-tech metals from marine ferromanganese nodules and crusts showed that specific metal-binding organic ligands may have promising potential in future processing technologies of these oxide deposits.

Numerical modeling of geochemical transport processes is necessary to investigate long-term CO2 storage in deep saline formations, because aluminosilicate mineral alteration is very slow under ambient deep-formation conditions and is not amenable to experimental study. Geochemical transport modeling can solve many problems and answer questions related to CO2 geological sequestration. The numerical modeling provides valuable insights regarding the physical and chemical consequences of CO2 injection in the subsurface environment. However, the reliability and applicability of the models need to be tested and validated if they are applied for CO2 geological sequestration. Issues on model validations are important if CO2 injection technologies are to be implemented safely, efficiently, and predictably. Validation of geochemical transport models could be different from conventional model validation methods for groundwater flow and solute transport. For the short-term behaviors, the models can be validated using laboratory and field experiments. For the long-term mineral alteration and CO2 sequestration, the natural analogue using high-pressure CO2 reservoirs could be a best way to validate the model. In this paper, a natural CO2 reservoir in southern Songliao Basin of China, which is past accumulations of CO2 in geological formation associated with magmatic or volcanic activity, was selected. Although the length of CO2 exposure and hence the rates of reaction for the natural system is not known in detail, we have shown that it is indeed possible to use observation data of mineral alteration in the natural CO2 reservoir to constrain thermodynamic and kinetic data of minerals used in the model, and to confine conditions of temperature, pressure, salinity, and primary mineral composition.

Biochar application to hardrock mine tailings: Soil quality, microbial activity, and toxic element sorption by Charlene N. Kelly; Christopher D. Peltz; Mark Stanton; David W. Rutherford; Colleen E. Rostad (35-48).
Waste rock piles from historic mining activities remain unvegetated as a result of metal toxicity and high acidity. Biochar has been proposed as a low-cost remediation strategy to increase soil pH and reduce leaching of toxic elements, and improve plant establishment. In this laboratory column study, biochar made from beetle-killed pine wood was assessed for utility as a soil amendment by mixing soil material from two mine sites collected near Silverton, Colorado, USA with four application rates of biochar (0%, 10%, 20%, 30% vol:vol). Columns were leached seven times over 65 days and leachate pH and concentration of toxic elements and base cations were measured at each leaching. Nutrient availability and soil physical and biological parameters were determined following the incubation period. We investigated the hypotheses that biochar incorporation into acidic mine materials will (1) reduce toxic element concentrations in leaching solution, (2) improve soil parameters (i.e. increase nutrient and water holding capacity and pH, and decrease compaction), and (3) increase microbial populations and activity. Biochar directly increased soil pH (from 3.33 to 3.63 and from 4.07 to 4.77 in the two materials) and organic matter content, and decreased bulk density and extractable salt content in both mine materials, and increased nitrate availability in one material. No changes in microbial population or activity were detected in either mine material upon biochar application. In leachate solution, biochar increased base cations from both materials and reduced the concentrations of Al, Cd, Cu, Pb, and Zn in leachate solution from one material. However, in the material with greater toxic element content, biochar did not reduce concentrations of any measured dissolved toxic elements in leachate and resulted in a potentially detrimental release of Cd and Zn into solution at concentrations above that of the pure mine material. The length of time of effectiveness and specific sorption by biochar is variable by element and the toxic element concentration and acidity of the initial mine material.

Display OmittedSecondary uranium encrustations are hosted in thick travertine and calcrete deposits of Pleistocene–Recent age in central Jordan. The central Jordan varicolored marble and travertine are equivalent to the active metamorphic area in Maqarin, north Jordan. More than 100 samples were collected from the outcrops of the varicolored marble, travertine, calcrete, and the yellow uranium encrustations. The secondary yellow encrustations are mainly composed of uranyl vanadate complexes. Tyuyamunite Ca ( UO 2 ) 2 V 2 5 + O 8 · 3 ( H 2 O ) –strelkinite Na2(UO2)2V2O8·6(H2O) solid solution series are the major components and their composition reflects changes in the Ca/Na ratio in solution. Potentially, new vanadium free calcium uranate phases (restricted to the varicolored marble) were identified with CaO:UO3 ratios different from the known mineral vorlanite (CaU6+)O4.Carbon and oxygen isotope data from calcite in the varicolored marble are characterized by Rayleigh-type enrichment in light isotopes associated with release of 13C and 18O enriched CO2 by high temperature decarbonation during combustion of the bituminous marl. Stable isotope results from uranium hosted travertine and calcrete varieties exhibit a wide range in isotopic values, between decarbonated and normal sedimentary carbonate rocks. The depleted δ13C and δ18O values in the travertine are related to the kinetic reaction of atmospheric CO2 with hyperalkaline Ca(OH)2 water. The gradual enrichment of δ13C and δ18O values in the calcrete towards equilibrium with the surrounding environment is related to continuous evaporation during seasonal dry periods.Uranium mineralization in central Jordan resulted from the interplay of tectonic, climatic, hydrologic, and depositional events. The large distribution of surficial uranium occurrences hosted in travertine and calcrete deposits is related to the artesian ascending groundwater that formed extensive lakes along NNW–SSE trending depressions. Fresh groundwater moved upward through the highly fractured phosphate, bituminous marl and varicolored marble to form unusual highly alkaline water (hydroxide–sulfate type) enriched with sensitive redox elements among which were U and V.

Display OmittedReactive mixtures to be used in a permeable reactive barrier (PRB) for the treatment of low quality groundwater derived from a mine waste rock storage site were evaluated. Low pH drainage water from the site contained high concentrations of sulfate and dissolved metals, including Al, Co, Ni, and Zn. Column experiments were conducted to evaluate whether mixtures containing either peat moss (as an organic carbon source) or a mixture of peat moss and granular zero-valent iron (ZVI) filings, in addition to small amounts of lime and/or limestone, were suitable treatment materials for removing these metals from the water. The experimental results showed that the mixtures promote bacterially-mediated sulfate reduction and metal removal by precipitation of metal sulfides, metal carbonate/hydroxide precipitation, and adsorption under relatively high pH conditions (pH of 7–8). Both reactive mixtures removed influent dissolved metals to near or below the limit of detection in the effluent throughout the experiment; however, influent-level concentrations of the metals of interest gradually moved through the column containing peat alone, as the pH neutralizing ability in the mixture was consumed. In contrast, the column containing both peat and ZVI showed very little breakthrough of the influent metals, suggesting that the longevity of the mixture including ZVI will be much longer than the mixture containing peat alone. The results show that both reactive mixtures should be effective in a PRB installation as long as neutral pH conditions and microbial activity are maintained. The cost to performance ratio of the two reactive mixtures will be a key factor in determining which mixture is best suited for a particular site.

Isotopic tracing of perchlorate sources in groundwater from Pomona, California by Neil C. Sturchio; Abelardo Beloso; Linnea J. Heraty; Stephen Wheatcraft; Rina Schumer (80-87).
The groundwater of Pomona, California, is contaminated with perchlorate ( ClO 4 - ). This water is treated to reduce the ClO 4 - concentration to less than 6 μg L 1 for compliance with California Department of Public Health drinking water regulations. A study of the isotopic composition of oxygen and chlorine in ClO 4 - has been conducted to determine the source of the contamination. Isotopic compositions were measured for ClO 4 - samples extracted from 14 wells, yielding ranges of δ18O values from −10.8‰ to −8.0‰, Δ17O values from +4.6‰ to +7.5‰, and δ37Cl values from −12.8‰ to −8.9‰. Evaluation of mixing proportions using published isotopic data for three ClO 4 - end-members (synthetic, Atacama, and indigenous natural ClO 4 - ) indicates that contamination is dominantly (85–89%) Atacama ClO 4 - derived from past use of imported Chilean nitrate fertilizer in citrus cultivation. This interpretation is consistent with (1) aerial photography archives showing extensive citrus fields surrounding Pomona in the early- to mid-20th century, (2) mass-balance estimates for ClO 4 - , and (3) numerical hydrologic models yielding travel-times for ClO 4 - from fields to wells that are in the range of 15 to >100 years. The hydrologic models predict that ClO 4 - contamination of Pomona groundwater will persist for decades into the future.

Developing protocols for geochemical baseline studies: An example from the Coles Hill uranium deposit, Virginia, USA by Denise M. Levitan; Madeline E. Schreiber; Robert R. Seal; Robert J. Bodnar; Joseph G. Aylor (88-100).
In this study, we determined baseline geochemical conditions in stream sediments and surface waters surrounding an undeveloped uranium deposit. Emphasis was placed on study design, including site selection to encompass geological variability and temporal sampling to encompass hydrological and climatic variability, in addition to statistical methods for baseline data analysis. The concentrations of most elements in stream sediments were above analytical detection limits, making them amenable to standard statistical analysis. In contrast, some trace elements in surface water had concentrations that were below the respective detection limits, making statistical analysis more challenging. We describe and compare statistical methods appropriate for concentrations that are below detection limits (non-detect data) and conclude that regression on order statistics provided the most rigorous analysis of our results, particularly for trace elements. Elevated concentrations of U and deposit-associated elements (e.g. Ba, Pb, and V) were observed in stream sediments and surface waters downstream of the deposit, but concentrations were below regulatory guidelines for the protection of aquatic ecosystems and for drinking water. Analysis of temporal trends indicated that concentrations of major and trace elements were most strongly related to stream discharge. These findings highlight the need for sampling protocols that will identify and evaluate the temporal and spatial variations in a thorough baseline study.

In nuclear waste repositories concrete and bentonite are used, sometimes in contact with each other. The rate of mutual degradation of concrete and bentonite by alkaline fluids from concrete is explored using a simple model. The model considers dissolution of a soluble compound in the concrete (e.g. portlandite), which is gradually dissolved as the solubilised hydroxide and the cation(s) diffuse towards and into the bentonite in which smectite degrades by interaction with the solutes. Accounting for only the diffusion resistances in concrete and clay, the solubility of the concrete compound and the hydroxide consumption capacity of the smectite, results in a very simple analytical model. The model is tested against several published modelling results that account for reaction kinetics, reactive surface, and equilibrium data for tens to many tens of different secondary minerals. In the models that include several specified minerals often assumptions need to be made on which minerals can form. This introduces subjective assumptions. The degradation rates using the simple model are within the range of results obtained by the complex models. In the studies of the data used in these models it was found that the uncertainties in thermodynamic data are considerable and can give contradictory information on under what conditions smectite degrades. Some smectite models and thermodynamic data suggest that smectite will transform to other minerals spontaneously if there were no kinetic restrictions.

Lead isotopic signatures of saprotrophic macrofungi of various origins: Tracing for lead sources and possible applications in geomycology by Jan Borovička; Martin Mihaljevič; Milan Gryndler; Jaroslava Kubrová; Anna Žigová; Hana Hršelová; Zdeněk Řanda (114-120).
Four saprotrophic species of macrofungi (Leucoagaricus leucothites, Agaricus bernardii, Agaricus campestris and Agaricus xanthodermus) were collected from 4 sites in the Czech Republic and analyzed for Pb content and Pb isotopic composition. Lead concentrations were relatively high in L. leucothites (up to 130 mg kg−1) collected in site heavily polluted by a lead smelter, but much lower (0.2–6.5 mg kg−1) in samples of the Agaricus species collected from urban, rural and pristine areas, respectively. The 206Pb/207Pb isotopic ratio in fruit bodies had a wide range of variation, and except for the smelter-polluted site in Příbram, did not reflect that in the organomineral topsoil horizons at particular sites. In the urban area of Prague, a detailed study of Pb uptake was conducted. The 206Pb/207Pb isotopic ratio in 19 samples of A.bernardii varied in a surprisingly wide range, from 1.124 to 1.175. In 5 specimens, the majority of “accumulated” Pb was undoubtedly transported from the topsoil layers (0–5 cm) characterized by low 206Pb/207Pb isotopic ratios, corresponding with gasoline-derived Pb from traffic emissions. In most samples, however, lead must have been transported from lower depths. Since the mycelium of A. bernardii was not restricted to the topsoil but could be detected both visually and using specific PCR even in a depth of 30 cm, such uptake appears to be possible. At suitable sites, Pb isotopes might represent an interesting tool for tracing the fungal uptake and transport of Pb in soils.

Sulfates are commonly considered to oxidize hydrocarbons to form acid natural gas, whereas the direct oxidants in this process remain controversial. To understand the relation between the initiation of TSR and the speciation of aqueous sulfate, a series of gold-tube hydrous pyrolysis experiments and in situ Raman detections were conducted. The results from hydrous pyrolysis using various sulfate solutions revealed that free SO 4 2 - in the formation waters was not able to initiate the direct oxidation of hydrocarbons. The variations of the Raman spectra of MgSO4(aq) with temperature indicated that CIP was formed at temperatures lower than 250 °C; however, a sudden precipitation of magnesium–hydroxide–sulfate–hydrate and an abrupt decrease of the CIP content in solution occurred at higher temperatures (T  > 300 °C). This demonstrates that the dominant species of sulfate in solution are CIP and HSO 4 - in geological and experimental conditions, respectively. Meanwhile, two different mineral buffers, including silica gel and brucite, played distinct roles in the occurrence of TSR involving Mg2 +–Na+– SO 4 2 - , i.e., the redox reaction was accelerated or inhibited with the presence of silica gel or brucite, respectively. This confirms that CIP is insufficient for initiating TSR and HSO 4 - is the dominant oxidant for the onset of TSR at the experimental temperature. Moreover, TSR shows more intensive at higher concentration of HSO 4 - . The effect of additional salts on TSR was also investigated. Raman observations demonstrated that the presence of Mg2+ can promote the formation of CIP in the subsurface. The gold-tube pyrolysis results indicate that dissolved salts play a positive role in the initiation of TSR in the experimental conditions. Hence, CIP was formed, and directly oxidized hydrocarbons or oils in carbonate reservoirs and high concentrations of dissolved salts or cations (especially Mg2+) may account for the low onset temperature of TSR in the subsurface.

Variability of crystal surface reactivity: What do we know? by Cornelius Fischer; Inna Kurganskaya; Thorsten Schäfer; Andreas Lüttge (132-157).
A multitude of natural processes and technical applications require our ability to provide a reliable prediction of crystal surface reactivity. During the last decades, the detailed analysis of crystal surface reactions revealed the existence of intrinsic variability in surface reactivity. This reactivity acts in addition to extrinsic factors, such as inhibitors, background electrolytes, or pH variations. The nature of this intrinsic variability is poorly understood. In any case, it must represent complex energetic contributions from and interactions between reacting mineral surfaces and dissolved and particulate materials in the fluid.Consequently, single rate constants and homogeneous surface area normalization are problematic constraints for the explanation and prediction of surface reactions of both, natural and artificial materials. Here, we review various aspects of intrinsic variability of crystal surface reactivity from experimental and modeling results including the fundamental role of microscopic kink site distribution. Important reaction processes include crystal dissolution and sorption of small particles, i.e., nanoparticles and colloids.A key means of understanding these variations lies in understanding the relationship between surface energy distribution and surface roughness. Rough surfaces are well-known to control the retention of colloids and nanoparticles under unfavorable adsorption conditions. This review provides an integrated view on an important feedback process that includes surface reactivity, kink site distribution, surface roughness, particle retention, and surface inhibition as critical components. Also, we review briefly the methods used to quantify surface roughness variability over a wide range of scales. It is our goal to highlight the multiple facets that may both reflect or influence the intrinsic variability of reactions over time.