Applied Geochemistry (v.56, #C)

Display OmittedBauxite refinery residues (BRR) remain the single largest environmental problem for the alumina industry, because of the fine-grained nature (>90% at <10 μm), high pH (>13), high sodicity (>50 g/kg), and high alkalinity (typically ≈30 g/kg as equivalent CaCO3). However, neutralisation of BRR provides a geochemically engineered solution, with potential re-use options. Hence, we compare the geochemistry of 4 BRRs: the un-neutralised raw red mud (UNRM), a CO2-neutralised red mud (CNRM), a Basecon™-neutralised (Basecon™) red mud, and a CO2-neutralisation followed by a Basecon™-neutralisation (Hybrid) material from a common source for reuse potential. Compositional changes, including acid neutralising capacity, trace-metal and phosphorous binding capacities, and toxicity leaching characteristics (TCLP) show that different neutralisations produce two geochemically distinct solids, those without alkalinity precipitation, and those with solid alkalinity. From the work completed, both Basecon™-neutralised and Hybrid materials have a significantly higher reuse potential for environmental remediation programs, such as acid rock drainage neutralisations, wastewater treatment, and/or artificial soil construction.

Coupling geochemical tracers and pesticides to determine recharge origins of a shallow alluvial aquifer: Case study of the Vistrenque hydrogeosystem (SE France) by Lara Sassine; Mahmoud Khaska; Sophie Ressouche; Roland Simler; Joël Lancelot; Patrick Verdoux; Corinne Le Gal La Salle (11-22).
The objective of this study is to identify the origin of groundwater in a shallow alluvial aquifer, using a multi-tracer approach including δ18O, δ2H, major elements and 87Sr/86Sr. In addition, triazines are used as a tracer of water draining agricultural areas.Four potential recharge sources are evidenced in the alluvial groundwater: rainfall, karst water from adjacent aquifer, imported Rhône river water and local stream water.Strontium isotopes are used to highlight the adjacent karst water input (Sr = 6.4–17.6 μmol L−1; 87Sr/86Sr = 0.7076–0.7078) showing a contrasting signature with the pristine alluvial groundwater (Sr = 3.4 μmol L−1; 87Sr/86Sr = 0.7088–0.7092). Lateral karst recharge is observed, with high proportions reaching 100%, all along the North Western border of the aquifer. This lateral recharge implies a dilution in triazines content of the Vistrenque groundwater as the karst area is not used for agriculture.Oxygen-18 and deuterium signatures of local rainwater (δ2H = −43.5‰) and imported Rhône River water (δ2H = −72.5‰) differ significantly which allows to quantify the influence of imported water on the alluvial groundwater. Such influence is observed only locally in this study. Contribution of local stream water, influenced by wastewater treatment plant effluents, is also locally detected in the alluvial aquifer, using Cl, K, and Na contents.High triazines, NO3, and Cl concentrations underline the vulnerability of this shallow alluvial aquifer to surface contaminations. Finally, the results of this environmental multi-tracer approach are statistically supported by principal component analyses.

Modelling of phase equilibria in CH4–C2H6–C3H8nC4H10–NaCl–H2O systems by Jun Li; Zhigang Zhang; Xiaorong Luo; Xiaochun Li (23-36).
A thermodynamic model is presented for the mutual solubility of CH4–C2H6–C3H8nC4H10–brine systems up to high temperature, pressure and salinity. The Peng–Robinson model is used for non-aqueous phase fugacity calculations, and the Pitzer model is used for aqueous phase activity calculations. The model can accurately reproduce the experimental solubilities of CH4, C2H6, C3H8 and nC4H10 in water or NaCl solutions and H2O solubility in the non-aqueous phase. The experimental data of mutual solubility for the CH4–brine subsystem are sufficient for temperatures exceeding 250 °C, pressures exceeding 1000 bar and NaCl molalities greater than 6 molal. Compared to the CH4–brine system, the mutual solubility data of C2H6–brine, C3H8–brine and nC4H10–brine are not sufficient. Based on the comparison with the experimental data of H2O solubility in C2H6-, C3H8- or nC4H10-rich phases, the model has an excellent capability for the prediction of H2O solubility in hydrocarbon-rich phases, as these experimental data were not used in the modelling.Predictions of hydrocarbon solubility (at temperatures up to 200 °C, pressures up to 1000 bar and NaCl molalities greater than 6 molal) were made for the C2H6–brine, C3H8–brine and nC4H10–brine systems. The predictions suggest that increasing pressure generally increases the hydrocarbon solubility in water or brine, especially in the lower-pressure region. Increasing temperature usually decreases the hydrocarbon solubility at lower temperatures but increases the hydrocarbon solubility at higher temperatures. Increasing water salinity dramatically decreases the hydrocarbon solubility.The experimental solubility data for hydrocarbon mixtures in water are not sufficient or systematic. Comparisons were made between the experimental data and the results of the model calculations. Most of the experimental data can be well predicted by this model with slightly higher discrepancies. More systematic experimental studies are needed to improve the model.

The chemical composition of volatile organic compounds (VOCs) in soil gases from the Solfatara crater (Campi Flegrei, Italy) was analyzed to investigate the effects of biogeochemical processes on gases discharged from the hydrothermal reservoir and released into the atmosphere through diffuse degassing. The chemistry of fluids from fumarolic vents, which represent preferential pathways for fluid uprising, was also reported for comparison. Oxidation–reduction and hydration–dehydration reactions, as well as microbial activity, strongly affected the composition of C4–C9 alkanes, alkenes, S-bearing compounds and alkylated aromatics, especially in those sites where the soil showed relatively low permeability to uprising fluids. Other endogenous organic compounds, such as benzene, phenol and hydrofluorocarbons were able to transit through the soil almost undisturbed, independently on the gas emission rate. Products of VOC degradation mainly consisted of aldehydes, ketones, esters, ethers and, subordinately, alcohols. Cyclic compounds revealed the occurrence of VOCs produced within sedimentary formations overlying the hydrothermal reservoir, whereas the presence of chlorofluorocarbons (CFCs) was likely related to air contamination. The results of the present study highlighted the strict control of biogeochemical processes on the behavior of hydrothermal VOCs that, at least at a local scale, may have a significant impact on air quality. This information could be improved by laboratory experiments conducted at specific chemical–physical conditions and in presence of different microbial populations.

Fluoride is considered beneficial to teeth and bones when consumed in low concentrations, but at elevated concentrations it can cause dental and skeletal fluorosis. Most fluoride-related health problems occur in poor, rural communities of the developing world where groundwater fluoride concentrations are high and the primary sources of drinking water are from community hand-pump borehole drilled wells. One solution to drinking high fluoride water is to attach a simple de-fluoridation filter to the hand-pump; and indigenous materials have been recommended as low-cost sorbents for use in these filters. In an effort to develop an effective, inexpensive, and low-maintenance de-fluoridation filter for a high fluoride region in rural northern Ghana, this study conducted batch fluoride adsorption experiments and potentiometric titrations to investigate the effectiveness of indigenous laterite and bauxite as sorbents for fluoride removal. It also determined the physical and chemical properties of each sorbent. Their properties and the experimental results, including fluoride adsorption capacity, were then compared to those of activated alumina, which has been identified as a good sorbent for removing fluoride from drinking water. The results indicate that, of the three sorbents, bauxite has the highest fluoride adsorption capacity per unit area, but is limited by a low specific surface area. When considering fluoride adsorption per unit weight, activated alumina has the highest fluoride adsorption capacity because of its high specific surface area. Activated alumina also adsorbs fluoride well in a wider pH range than bauxite, and particularly laterite. The differences in adsorption capacity are largely due to surface area, pore size, and mineralogy of the sorbent.

Black shales contain high concentrations of trace elements, which may be liberated to the environment as a result of natural weathering and, potentially, during shale gas development and future mining of black shales for extraction of shale oil. The Sunbury Shale is one of the youngest units making up the thick Devonian and Mississippian black shale sequence in the Appalachian Basin. This study compares the trace element geochemistry of samples collected from two exposures of Sunbury Shale located <8 km apart in northeastern Kentucky, one a fresh excavation, the second, a roadcut exposed for 50 years, wherein the shale was visibly weathered. Core samples obtained from sites ∼40 km NE and ∼60 km SW of the exposures were also analyzed. The 50-year period of surface weathering resulted in significant loss of some trace elements, particularly Mn and elements associated with sulfides (e.g., Cd, Cu, Ni, and Zn). It is expected that Mn would be maintained in its soluble reduced form in the presence of sulfides and our results suggest Mn is a particularly sensitive indicator of weathering in carbonate-poor black shales. The relative immobility of As, Sb, and Se, also found in sulfides, reflects preferential sorption of oxyanions under the locally acidic conditions resulting from sulfide oxidation. Leaching experiments show waters in contact with the shale may, nonetheless, acquire concentrations of As and Se well in excess of water quality standards. No significant differences were found in the concentrations of Cr, Mo, or V that are associated with refractory phases.

Reflections of the geological characteristics of Cyprus in soil rare earth element patterns by Limin Ren; David R. Cohen; Neil F. Rutherford; Andreas M. Zissimos; Eleni G. Morisseau (80-93).
Display OmittedRare earth elements (REEs) are used as indicators or proxies for a range of geological and mineralogical processes due to their unique geochemical characteristics. Total and aqua regia-extractable concentrations of REEs and 57 other elements have been determined for 5350 soil samples as part of the high sampling density Geochemical Atlas of Cyprus. The bedrock geology of Cyprus is dominated by the sequence of ultramafic to mafic units formed at a spreading ridge and subsequently obducted to form the Troodos Ophiolite (TO), and the surrounding carbonate-rich Circum-Troodos Sedimentary Sequence (CTSS) deposited in environments ranging from deep marine to sub-aerial. Total and aqua regia-extractable REE patterns are similar for each element and are largely controlled by parent lithology. Soil-to-rock REE ratios are generally elevated in the TO units (>4 for LREEs and 1.5–3 for HREEs) due to loss of more mobile elements during weathering but are close to 1 in the CTSS units. HREEs are more elevated than LREEs in soils derived from TO units with upper continental crust-normalised patterns indicating the main source to be pyroxenes and zircon. Trace element trends indicate REEs in the CTSS were largely derived from detrital material shedding off the TO and deposited in progressively shallowing basins under largely anoxic conditions (absence of Ce4+ anomalies), with a minor contribution from seawater via adsorption onto secondary Fe + Mn oxides or co-precipitation with carbonates. Heavy mineral-associated elements such as Zr and Th display a relative consistent ratio in the CTSS soils. Peak HREE concentrations occur in the mafic cumulates and intrusives where the median LaUCC/YbUCC is ∼0.12, whereas in CTSS units the LREEs are more elevated with a median LaUCC/YbUCC ∼0.7. Due to the strong lithogeochemical controls, soil REE spatial patterns reflect even subtle mineralogical variations within the various TO units, the location of major transform faults and other structures, and areas that have been affected by hydrothermal alteration.

Groundwater transport of Cu in laterites in Zambia by Charity Lweya; Søren Jessen; Kawawa Banda; Imasiku Nyambe; Christian Bender Koch; Flemming Larsen (94-102).
Display OmittedThe risk of transporting copper (Cu) in near surface laterite with acid groundwater was studied down gradient of a newly constructed open mine in the North Western Province of Zambia. The assessment was based on results obtained from field and laboratory work and geochemical modeling. Large seasonal variations in the groundwater elevation is changing the subsurface water flow from a dominating Darcy flow in the laterite during the rainy season to a dominating fracture flow in the deeper, fractured gneiss in the dry season. As the major groundwater flow occurs in the laterite, and the low pH of the groundwater is also observed in the laterite, mineralogical and sorption experiments were confined to this unit where the risk of a Cu groundwater transport is highest. The mineralogy of the laterite was studied using X-ray analysis, infrared and Mössbauer spectroscopy, and results revealed a homogeneous composition of strongly weathered primary silica minerals, mainly quartz, muscovite, biotite and feldspars, and secondary minerals dominated by disordered kaolinite, iron oxide (goethite/hematite mixtures or solely goethite) and minute amounts of vermiculite. Cu sorption to the laterite was determined from batch experiments using initial Cu concentrations between 10 and 400 mg/L and pH of 2.8 and 4.5. At pH 4.5 a maximum sorption capacity of 239 mg/kg was found for aqueous equilibrium Cu concentrations of 150 mg/L. For aqueous Cu concentrations below 150 mg/L, a nearly linear sorption was observed with Kd value of 18. Cu sorption to the laterite is negligible for pH 2.8. The mineralogical study of the laterite suggests that Cu predominately sorbs to the minerals iron oxides and kaolinite.