Applied Geochemistry (v.20, #5)

Preface to the Ingerson Lecture by R.S. Harmon (817).

The flooding of two mine pit lakes (Lake St. Louis and Lake Fouthiaux) situated in the Blanzy–Montceau-les-Mines coal basin (Massif Central, France) has been under close scrutiny for 5 a. The aim was to understand: (i) what sources can influence the lake water geochemistry; (ii) what is the role of lake stratification on water chemistry; (iii) how the lake water chemistry evolves during flooding.To answer these questions, , conductivity, pH and Eh depth profiles were measured with a specific probe (Seabird®) in the lakes (seven surveys between July 1998 and February 2002).At the same time, water samples were collected every 5 m along the profiles and were analysed for Na+, Ca2+, K+, Mg2+, SO 4 2 - , NO 3 - , F, Cl, HCO 3 - , Fe, Cu, Ni, Zn, Co, Cd and Mn. The geological and hydrogeological contexts play a major role on the water chemistry of the lakes and three sources of influence have been distinguished : (i) the contribution of underlying mine groundwater, enriched in SO 4 2 - , due to the leaching of sulfide oxidation products from old flooded underground works; (ii) the seepage through coal mine spoils also containing sulfides; (iii) to a lesser extent Triassic formations, containing gypsum, present in the Fouthiaux area, which lead to a SO 4 2 - enrichment of lake waters. All these influences result in an enrichment in SO 4 2 - , showing essentially a neutralised acid mine drainage process, that is characterised by neutral to slightly alkaline waters, and an absence of high metal contents (except for Fe and Mn) which are non soluble at the pH and Eh conditions present in the lakes. The two studied lakes were initially meromictic and ions such as SO 4 2 - or Mn can show high concentrations at depth, in the lake layers which are not subject to winter mixing. During the studied period, Lake St. Louis remained meromictic and non removed elements continue to have high concentrations in deep zones. In contrast, Lake Fouthiaux, initially meromictic, became holomictic with time and the bottom layer did not maintain the enrichment in SO 4 2 - , Mn, and other elements shown at the beginning.

Electrokinetic remediation is an emerging technology that has generated considerable interest as a technique for the in situ remediation of clay-rich soils and sediments. Despite promising experimental results, however, at present there is no standardised universal electrokinetic soil/sediment remediation approach. Many of the current technologies are technically complex and energy intensive, and geared towards the removal of 90% or more of specific contaminants, under very specific field or laboratory-based conditions. However, in the real environment a low-tech, low-energy contaminant reduction/containment technique may be more appropriate and realistic. Such a technique, FIRS (Ferric Iron Remediation and Stabilisation), is discussed here. The FIRS technique involves the application of a low magnitude (typically less than 0.2 V/cm) direct electric potential between two or more sacrificial, Fe-rich, electrodes emplaced in, or either side of, a contaminated soil or sediment. The electric potential is used to generate a strong pH (and E h) gradient within the soil column (pH 2–13), and force the precipitation of an Fe-rich barrier or “pan” in the soil between the electrodes. Geochemical and geotechnical data for FIRS-treated sediments from the Ravenglass estuary, Cumbria, UK indicate that the technique can significantly reduce contaminant concentration in treated soil, by remobilisation of contaminants and concentration on, or around, the Fe-rich barrier. Arsenic, in particular, seems highly amenable to the FIRS treatment, due to its solubility under the high pH conditions generated near to the cathode, and its marked geochemical affinity with the freshly precipitated Fe oxides and oxyhydroxides in the Fe barrier. Geotechnical tests indicate that the Fe barrier produced by the technique is practically impervious (permeability = 10−9  m/s or less), and has moderate mechanical strength (UCS ∼11 N/mm2). Notably, a large increase in shear strength in the treated soil near to the anode electrode (due to Fe cementation and/or dewatering) is also observed, without significant loss of porosity. The data indicate that the FIRS technique shows considerable promise as an in situ method for contaminated land remediation and soil water containment, and for improving the mechanical properties of soils (contaminated or otherwise) for civil engineering purposes.

Single particle characterization of size-fractionated road sediments by Kouji Adachi; Yoshiaki Tainosho (849-859).
The relationship between particle distributions and chemical compositions of road sediments were investigated in Kobe, Japan. Road sediments are significant pollutants in urban areas, and their toxicity differs according to particle size. In the present study, the authors analyzed the distributions of particle size, chemical composition and particle type among size-fractionated road sediments. Road sediment samples were collected from road medians and street gutters. Chemical compositions of about 13,000 individual road sediment particles were characterized by scanning electron microscopy. They were classified into 7 types by cluster analysis, and their possible sources were estimated. The particle type distributions showed some relationships with the chemical composition distributions. This study showed that the chemical composition distributions among the road sediments were typical for each element in relation to the particle type distributions.

Natural tracers (major ions, δ 18O, and O2) were monitored to evaluate groundwater flow and transport to a depth of 20 m below the surface in fractured sedimentary (primarily shale and limestone) rocks. Large temporal variations in these tracers were noted in the soil zone and the saprolite, and are driven primarily by individual storm events. During nonstorm periods, an upward flow brings water with high TDS, constant δ 18O, and low dissolved O2 to the water table. During storm events, low TDS, variable δ 18O, and high dissolved O2 water recharges through the unsaturated zone. These oscillating signals are rapidly transmitted along fracture pathways in the saprolite, with changes occurring on spatial scales of several meters and on a time scale of hours. The variations decreased markedly below the boundary between the saprolite and less weathered bedrock. Variations in the bedrock units occurred on time scales of days and spatial scales of at least 20 m. The oscillations of chemical conditions in the shallow groundwater are hypothesized to have significant implications for solute transport. Solutes and colloids that adsorb onto aquifer solids can be released into solution by decreases in ionic strength and pH. The decreases in ionic strength also cause thermodynamic undersaturation of the groundwater with respect to some mineral species and may result in mineral dissolution. Redox conditions are also changing and may result in mineral dissolution/precipitation. The net result of these chemical variations is episodic transport of a wide range of dissolved solutes or suspended particles, a phenomenon rarely considered in contaminant transport studies.

The water–rock interaction processes occurring in the low-temperature, shallow volcanic aquifers of central-southern Italy were simulated by means of the EQ3/6 Software Package in reaction progress mode. In the investigation both the Roman Magmatic Province and Monte Amiata, which belongs to the Tuscan Magmatic Province, were included. The average K2O content of the volcanic rocks from the two areas is similar but the main K-bearing phases are leucite, in the Roman Magmatic Province, and sanidine, at Monte Amiata.Computed concentrations of major dissolved components and SiO2 are consistent with analytical data, suggesting that the results of the EQ3/6 runs are reliable simulations of the natural water–rock interaction processes. Hence, EQ3/6 results can be used to investigate the transfer of K from rocks to water.It turns out that the attainment of saturation with sanidine, during early stages of rock dissolution, limits K concentration in the Monte Amiata groundwaters to around an average of 2.9 ± 1.3 mg L−1 (1SD). In the silica undersaturated Roman Magmatic Province, saturation with leucite is not attained during the evolution of groundwaters and, consequently, K concentration reaches comparatively high levels, with an average of 24.6 ± 27.1 mg L−1 (1SD). Most of these unusually high K concentrations are due to natural weathering of silicates without any anthropogenic influence.

Aqueous alteration of nearly pure Nd-doped zirconolite (Ca0.8Nd0.2ZrTi1.8Al0.2O7), a passivating layer control by G. Leturcq; P.J. McGlinn; C. Barbe; M.G. Blackford; K.S. Finnie (899-906).
Neodynium-doped zirconolite was fabricated by hydrolysing a mixture of alkoxide with nitrate solutions followed by a series of drying, calcination, pressing and sintering steps. The material obtained was essentially zirconolite (99.5 vol% Ca0.8Nd0.2ZrTi1.8Al0.2O7) with a minor ZrTiO4 phase (0.5 vol%). The microstructure and composition of the zirconolite was characterised, before and after durability experiments, by SEM/EDS, SIMS, AFM and TEM. Chemical durability testing was carried out using the standard MCC-2 test at 150 °C for a series of four test durations - 1, 7, 28 and 84 days. The pH of the leachates was fairly constant with time (pH 5), and elemental releases reached apparent steady-state conditions within the first day of leaching. Thermodynamic calculations indicated that attainment of these steady-state conditions at this point could not be explained by thermodynamic equilibrium being reached between the leachates and the primary zirconolite phase. However, thermodynamic equilibrium between a possible layer of secondary hydroxides or a decalcified zirconolite and the leachates could explain the steady state of Ti, Zr and Al releases. Moreover, it is suggested that the steady-state conditions achieved by Nd, theoretically undersaturated in the leachates, is due to adsorption of Nd to this secondary layer, and is not a result of precipitation of a hydroxide form. Anatase, commonly observed during leaching of zirconotitanates, is also theoretically undersaturated in the leachates. When observed, it is possibly a product of local condensation of the hydroxide layer and not due to simply a dissolution/precipitation process. SEM and AFM investigations confirmed the formation of a passivation layer on the surface of the zirconolite. The layer was of the order of 10 nm, in accordance with the thickness calculated from leachate results.

Solutions draining the Alta Mine, Jefferson County, MT, were contaminated by acid sulfate waters (ASW) generated from anthropogenic exposure of meteoric waters to sulfidic underground mine workings and a waste-rock pile. In 1999, a remediation effort was initiated in an attempt to improve the quality of water draining the site through removal of the waste-rock pile with which these solutions come in contact. ASW were sampled in the mineshaft prior to entering the waste-rock pile and upon discharge from the waste-rock pile aquifer near the pile toe. ASW composition changed as solutions flowed through the waste-rock pile due to sulfide and silicate weathering and schwertmannite precipitation.Schwertmannite and goethite were both sampled in the waste-rock pile where a distinct field relation was observed between the two minerals. Schwertmannite was always in contact with actively flowing ASW, while goethite was never in direct contact with ASW and was generally above the waste-rock water table. Goethite is hypothesized to be re-dissolved/re-precipitated schwertmannite that was deposited under higher flow conditions and subsequently transformed to goethite through exposure to wet/dry cycling associated with seasonal fluctuations in the amount of water moving through the hydrogeologic system. Trace metal concentrations in ammonium oxalate extracts of these minerals provides the first published data on the behavior of multiple trace metals through this phase transformation, which has important ramifications for considering schwertmannite as a long term metal sink due to its known metastability with respect to goethite. A relative retention scale through this phase transformation of Pb > Zn, Mn > As, Al, Cu is potentially applicable to other ASW systems.

Results are presented from observation of dissolved metal concentrations and fluxes at 5 sites in the Lot–Garonne fluvial system known for its historic metal contamination. The contamination originates from the upstream Lot River where a small tributary (Riou-Mort River) drains a smelting-waste area. Unlike non-neutralised acid mine drainage systems, the Riou-Mort waters were not acidic (6.8 < pH < 8.0) due to application of alkaline reagents for neutralisation. Relatively high dissolved U concentrations (up to 1.1 μg L−1) were attributed to these reagents. High metal concentrations (e.g., up to 23 and 1190 μg L−1, for Cd and Zn, respectively) in the Riou-Mort water resulted from the oxidation of the sulphide phases within the smelting-wastes. Pyrite oxidation rate was estimated (5530 t a−1; 35.7 t km−2  a−1) from the total amount of SO 4 2 - discharged in the river water. The related dissolved metal inputs into the Lot River were, e.g., 0.55 and 35 t a−1 for Cd and Zn, respectively. The dissolved Cd fluxes in the Lot River corresponded to 65% of those in the downstream Garonne River. The dissolved Zn fluxes were even similar to those in the Garonne River. Mass balance calculations showed that, downstream the Riou-Mort/Lot River confluence, the exchange between dissolved and particulate phases accounted for the removal of 15% of Zn and 50% of Cd from the dissolved phase. The calculated annual dissolved metal fluxes at the outlet of the Lot–Garonne River system are significant at the global scale, as they represent 0.02–0.25% of the global river budget.

The authors present data for the chemical, stable isotope (13C/12C, 15N/14N and 34S/32S), and dissolved gas (N2, Ar, O2 and CH4) composition of groundwaters sampled in and around a landfill site in Cambridgeshire, England. Decomposition of 3 × 106  m3 of largely domestic waste, placed in unlined quarries, has given rise to the formation of an NH4-rich leachate dispersing as a plume into the surrounding Middle Chalk aquifer. In addition to identifying zones of methanogenesis and SO4 reduction, the data indicate processes of NH4 transformation by either assimilation or oxidation, and losses by formation of N2. Depending on the mixing ratio between leachate and background water, it may be possible to account for all NH4 loss by combined nitrification + denitrification in a system where there are abrupt temporal and spatial changes in redox conditions.

Arsenic readily released to pore waters from buried mill tailings by John Mahoney; Donald Langmuir; Neil Gosselin; John Rowson (947-959).
At the McClean Lake Operation in the Athabasca Basin of northern Saskatchewan, the untreated acid raffinate solutions associated with U mill tailings contain up to 700 mg/L dissolved As. To reduce the concentration of As and other contaminants in acid tailing slurries at the JEB mill at McClean Lake, ferric sulfate may be added to the acid raffinates to assure that their molar Fe/As ratio equals or exceeds 3. Tailings slurries are then neutralized with lime to pH 4, and subsequently to pH 7–8. The neutralized tailings contain minerals from the original ore, which are chiefly quartz, illite, kaolinite and chlorite, and precipitated (secondary) minerals that include gypsum, scorodite, annabergite, hydrobasaluminite and ferrihydrite. Most of the As is associated with the secondary arsenate minerals, scorodite and annabergite. However, a few percent is adsorbed and/or co-precipitated, mainly by ferrihydrite. Of major concern to provincial and federal regulators is the risk that significant amounts of As might be released from the tailings to pore waters after their subaqueous disposal in the tailings management facility. A laboratory study was performed to address this issue, measuring readily desorbed As using a method known as equilibrium partitioning in closed systems (EPICS). The EPICS method was selected because it employs a leaching solution that, except for its As concentration, is identical in composition to the neutralized raffinate in contact with the tailings. Laboratory experiments and modeling results demonstrated that the As that could be readily released to pore waters is about 0.2% of the total As in the tailings. Long-term, such releases may contribute no more than a few mg/L of dissolved As to tailings pore waters.

The temperature dependence of the self-diffusion of HTO, 22Na+ and 36Cl in Opalinus Clay (OPA) was studied using a through-diffusion technique, in which the temperature was gradually increased in the steady state phase of the diffusion. The measurements were done on samples from two different geological locations. The dependence of the effective diffusion coefficient on temperature was found to be of an Arrhenius type in the temperature range between 0 and 70 °C. A slight difference between the two locations could be observed. The average value of the activation energy of the self-diffusion of HTO in OPA was 21.1 ± 1.6 kJ mol−1, and 21.0 ± 3.5 and 19.4 ± 1.5 kJ mol−1 for 22Na+ and 36Cl, respectively. The measured values for HTO are slightly higher than the values found for the bulk liquid water (HTO: 18.8 ± 0.4 kJ mol−1). This indicates that the structure of the confined water in OPA might be slightly different from that of bulk liquid water. Also for Na+ and Cl, slightly higher values than in bulk liquid water (Na+: 18.4 kJ mol−1; Cl: 17.4 kJ mol−1) were observed.The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could not be used to describe the temperature dependence of the diffusion of HTO in OPA. This additionally indicates the slightly different structure of the pore water in OPA.

Laboratory study of calcite–gypsum sludge–water interactions in a flooded tailings impoundment at the Kristineberg Zn–Cu mine, northern Sweden by Anders Widerlund; Elena Shcherbakova; Erik Carlsson; Henning Holmström; Björn Öhlander (973-987).
Due to liming of acid mine drainage, a calcite–gypsum sludge with high concentrations of Zn (24,400 ± 6900 μg g−1), Cu (2840 ± 680 μg g−1) and Cd (59 ± 20 μg g−1) has formed in a flooded tailings impoundment at the Kristineberg mine site. The potential metal release from the sludge during resuspension events and in a long-term perspective was investigated by performing a shake flask test and sequential extraction of the sludge. The sequentially extracted carbonate and oxide fractions together contained ⩾97% of the total amount of Cd, Co, Cu, Ni, Pb and Zn in the sludge. The association of these metals with carbonates and oxides appears to result from sorption and/or coprecipitation reactions at the surfaces of calcite and Fe, Al and Mn oxyhydroxides forming in the impoundment. If stream water is diverted into the flooded impoundment, dissolution of calcite, gypsum and presumably also Al oxyhydroxides can be expected during resuspension events. In the shake flask test (performed at a pH of 7–9), remobilisation of Zn, Cu, Cd and Co from the sludge resulted in dissolved concentrations of these metals that were significantly lower than those predicted to result from dissolution of the carbonate fraction of the sludge. This may suggest that cationic Zn, Cu, Cd and Co remobilised from dissolving calcite, gypsum and Al oxyhydroxides were readsorbed onto Fe oxyhydroxides remaining stable under oxic conditions. In a long-term perspective (≳102  a), ⩾97% of the Cd, Co, Cu, Ni, Pb and Zn content of the sludge potentially is available for release by dissolution of calcite and reductive dissolution of Fe oxyhydroxides if the sludge is subject to a soil environment with lower dissolved Ca concentrations, pH and redox than in the impoundment.

Arsenic associations in sediments from the loess aquifer of La Pampa, Argentina by P.L. Smedley; D.G. Kinniburgh; D.M.J. Macdonald; H.B. Nicolli; A.J. Barros; J.O. Tullio; J.M. Pearce; M.S. Alonso (989-1016).
Groundwater from the Quaternary loess aquifer of La Pampa, central Argentina, has significant problems with high concentrations of As (up to 5300 μg L−1) as well as other potentially toxic trace elements such as F, B, Mo, U, Se and V. Total As concentrations in 45 loess samples collected from the aquifer have a range of 3–18 mg kg−1 with a mean of 8 mg kg−1. These values are comparable to world-average sediment As concentrations. Five samples of rhyolitic ash from the area have As concentrations of 7–12 mg kg−1. Chemical analysis included loess sediments and extracted porewaters from two specially cored boreholes. Results reveal a large range of porewater As concentrations, being generally higher in the horizons with highest sediment As concentrations. The displaced porewaters have As concentrations ranging up to 7500 μg L−1 as well as exceptionally high concentrations of some other oxyanion species, including V up to 12 mg L−1. The highest concentrations are found in a borehole located in a topographic depression, which is a zone of likely groundwater discharge and enhanced residence time. Comparison of sediment and porewater data does not reveal unequivocally the sources of the As, but selective extract data (acid-ammonium oxalate and hydroxylamine hydrochloride) suggest that much of the As (and V) is associated with Fe oxides. Primary oxides such as magnetite and ilmenite may be partial sources but given the weathered nature of many of the sediments, secondary oxide minerals are probably more important. Extract compositions also suggest that Mn oxide may be an As source. The groundwaters of the region are oxidising, with dissolved O2, NO3 and SO4 normally present and As(V) usually the dominant dissolved As species. Under such conditions, the solubility of Fe and Mn oxides is low and As mobilisation is strongly controlled by sorption–desorption reactions. Desorption may be facilitated by the relatively high-pH conditions of the groundwaters in the region (7.0–8.8) and high concentrations of potential competitors (e.g. V, P, HCO3). PHREEQC modelling suggests that the presence of V at the concentrations observed in the Pampean porewaters can suppress the sorption of As to hydrous Fe(III) oxide (HFO) by up to an order of magnitude. Bicarbonate had a comparatively small competitive effect. Oxalate extract concentrations have been used to provide an upper estimate of the amount of labile As in the sediments. A near-linear correlation between oxalate-extractable and porewater As in one of the cored boreholes investigated has been used to estimate an approximate K d value for the sediments of 0.94 L kg−1. This low value indicates that the sediments have an unusually low affinity for As.

Application of multi-element statistical analysis for regional geochemical mapping in Central Japan by Atsuyuki Ohta; Noboru Imai; Shigeru Terashima; Yoshiko Tachibana (1017-1037).
Some 434 stream sediment samples were collected in Central Japan for a nationwide geochemical mapping project. The resulting geochemical maps are compared with geological, mineral resource and land use maps. Spatial distribution patterns of elemental concentrations in stream sediments are determined mainly by surface geology. Elevated elemental concentrations of alkali elements, Be, Ga, Y, Cs, Ba, lanthanide (Ln), Tl, Th, and U are consistent with outcrop areas of granite, felsic volcanic rock, and accretionary complexes. High concentrations of MgO, Al2O3, P2O5, CaO, 3d transition metals, Zn, and Sr are present in sediments supplied from mafic volcanic rock, high pressure metamorphic rocks, and mafic-ultramafic rocks in accretionary complexes.A procedure is established and guidelines are set for a statistical test suite for geochemical mapping. Analysis of variance (ANOVA) and multiple comparison tests are effective for comparing means among the data subsets that are classified by parent lithological materials. Among the many procedures that have been proposed for multiple comparison tests, the Holm procedure was selected for this study. Multiple comparison statistically confirmed the correspondence of elemental abundance in stream sediments with surface geologies. However, visual interpretation of some elements is inconsistent with results of multiple comparison. According to the Holm procedure, the U content in stream sediments is affected not by granite, but by felsic volcanic rock. The Holm procedure clarifies that As, Sb, and Bi, that are not explained by the presence of mineral deposits, are enriched significantly in samples derived from accretionary complexes. Hydrothermal activity on the ocean floor might affect their levels of enrichment. Significant enrichment of Cu, Zn, Cd, Sn, Sb, Hg, and Pb observed in urban areas are also supported by the Holm procedure. The authors inferred that these sediment samples had been contaminated.