Applied Geochemistry (v.21, #7)

Peña del Hierro is an abandoned mine site located in the catchment area of the Tinto river (Pyrite Belt, SW Spain). As leaching from the spoils affect the quality of the stream water, the waste dumps have been characterized for mineralogy, geochemistry and granulometry to obtain an estimate of the potential pollution. Waste rock dumps in Peña del Hierro are very heterogeneous and are mainly composed of acid volcanic tuffs > gossan > shales > roasted pyrite ashes > floated pyrite. The volcanic tuffs, the gossan and the shales coexist in the same piles. The roasted pyrite ashes and the floated pyrite form more homogeneous dumps. The dissolution of pyrite concentrated in pyrite ashes and floated pyrite units can generate acid mine drainage. Nevertheless, acid volcanic tuffs, which are rich in pyrite and have no neutralizing minerals, are the main source of these acidic effluents. Only muscovite might partially neutralize the acidity, but the dissolution of this mineral is too slow to compensate for acidity. The occurrence of jarosite in the <2 mm fraction indicates that extreme acid mine drainage occurs. The gossan and roasted pyrite ashes have high contents of trace elements. According to their concentration, As (46–1710 ppm), Pb (113–3455 ppm) and Hg (0–53) are some of the most important toxic trace elements in these wastes. In dumps mainly composed of volcanic tuffs most of the trace elements derive from the gossan mixed in the piles. Gossan is stable in an oxidizing environment, but acidic effluents (pH < 2) can dissolve Fe oxyhydroxides from them and release high amounts of trace elements to the stream water. This research contributes to estimating the production of acid mine drainage and the actual contamination risk of potentially toxic elements in soils and waters of this area, and could be the base for possible future mitigation actions in other areas affected by mining wastes.

This study investigates a watershed influenced by acid mine drainage emanating from the former Leona Heights Sulfur Mine, located in Oakland, California. The primary factors that temporally controlled the magnitude of iron photoreduction included initial iron concentration, incident ultraviolet radiation, water temperature, biotic oxidation, flow rates, and the Fe(III) species present. Vegetation was not expected to seasonally influence the amount of incoming solar radiation reaching the water surface as the tree canopy contained significant cover during both the April and July monitoring events. Accordingly, it was anticipated that iron photoreduction would be greatest during the summer when both incoming ultraviolet radiation and dissolved iron were at a maximum. This was, however, not the case. A substantial decline in the apparent magnitude of iron photoreduction occurred during the summer/dry season (July) with respect to measurements taken during the spring/wet season (April). The primary reasons for the observed phenomenon were attributed to factors which may seasonally control the physical presence of iron oxidizing bacteria at the site and water temperature, which influences the optimum rate of bacterially mediated iron oxidation.

The chemical composition of natural waters is affected by the weathering of geologic materials at or near the surface of the Earth. Laboratory weathering experiments of whole-rock sulfide rocks from the Shoe-Basin Mine (SBM) and the Pennsylvania Mine (PM) from the Peru Creek Basin, Summit County, Colorado, indicate that the mineral composition of the sulfide rocks, changes in pH, the duration of the experiment, and the formation of sorbents such as Fe and Al oxyhydroxides affect the chemical composition of the resulting solution. Carbonate minerals in the rock from SBM provide buffering capacity to the solution, contribute to increases in the pH and enhance the formation of Fe and Al oxyhydroxides, which sorb cations from solution. The final solution pH obtained in the experiments was similar to those measured in the field (i.e., 2.8 for PM and 5.0 for SBM). At PM, acidic, metal-rich mine effluent is discharged into Peru Creek where it mixes with stream water. As a result, the pH of the effluent increases causing Fe and Al oxyhydroxide and schwertmannite to precipitate. The resulting solids sorb metal cations from the water thereby improving the quality of the water in Peru Creek.

Trace metal adsorption to suspended particulate matter (SPM) influences bioavailability and toxicity of trace metals in natural waters. For highly contaminated urban catchments in the greater Auckland (New Zealand) area, trace metal adsorption to SPM was assessed and compared to similar data from non-urban catchments in the Auckland region, to determine whether there was any difference in the ability of the SPM to adsorb Cu, Pb and Zn. The degree of trace metal adsorption onto the SPM was assessed by way of adsorption edge experiments. It was found that the ability of the Auckland urban SPM to adsorb trace metals decreased in the order Pb > Cu > Zn. Little difference in adsorption was observed between the non-urban Waikato and Kaipara River SPM and urban SPM, or between urban SPM from different flow regimes and seasons, despite some compositional differences in the SPM. This suggests that on the basis of a single surface-binding site, metal adsorption onto SPM could be readily predicted across a range of urban and non-urban catchments in the Auckland region. Adsorption edges were modelled with a diffuse layer, surface complexation model to assess the role of Fe-oxide in adsorption. The MINTEQA2 model was used, assuming Fe-oxide (as HFO) was the only adsorbing surface. There was generally good agreement between observed and modelled adsorption for Pb, indicating the importance of Fe-oxide surfaces for Pb adsorption. However, the model did not predict Zn or Cu adsorption as well. The TOC content of the SPM, and presence of dissolved ligands and organic matter in the water column, appeared to play an important role in Cu adsorption to the SPM. For Zn, the presence of adsorbing surfaces other than HFO appeared to influence adsorption.

Powder samples of two inactive borosilicate glasses (MW and SON68), used as references for vitrified nuclear waste in Switzerland, were leached statically in pure water over more than 12a at 90 °C. Solution aliquots were taken at regular intervals in order to investigate the glass dissolution kinetics and the retention of elements representing radionuclides. At 5.7 and 12.2a, single tests were interrupted to investigate the corroded samples.Boron and Li concentration data indicate that the glass corrosion kinetics of the MW glass is about 10 times faster than for the SON68 glass, both in the transient and asymptotic phase of the leaching process. The alteration products were studied by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM-STEM) coupled with energy dispersive spectrometry (EDS) analyses. Alteration of the MW glass produced abundant magnesian clay minerals, as well as nanoparticles of lanthanide and Zr phosphates, whereas only small amounts Ca–Zn–Fe–Ni clay minerals were formed as alteration product of SON68.Retention factors were above 99% for most trace elements, indicating almost quantitative fixation of many radionuclides in the secondary phases. Solution concentration data were used to calculate aqueous speciations and saturation indices of potential secondary solids. The solutions are close to saturation with respect to simple lanthanide phosphates (in agreement with the TEM data) and quartz. The presence of quartz in the altered SON68 samples is corroborated by XRD data.In conclusion, the corrosion and radionuclide retention properties of SON68 seem to be more favorable than those of the MW glass. A major finding of this investigation was that glass degradation may strongly depend on minor compositional changes in the glass composition. The presence of Mg in the MW glass triggers the nucleation of secondary clay minerals, thereby promoting glass corrosion via silica removal. In the Mg-free SON68 glass the formation of clays, and hence the glass degradation, were considerably slower.

Behaviour of boron and strontium isotopes in groundwater–aquifer interactions in the Cornia Plain (Tuscany, Italy) by Maddalena Pennisi; Gianluca Bianchini; Antonio Muti; Wolfram Kloppmann; Roberto Gonfiantini (1169-1183).
The Cornia Plain alluvial aquifer, in Tuscany, is exploited intensely to meet the demand for domestic, irrigation and industrial water supplies. The B concentration of groundwater, however, is often above the European limit of 1 mg L−1, with the result that exploitation of these water resources requires careful management. Boron and Sr isotopes have been used as part of a study on the origin and distribution of B dissolved in groundwater, and indirectly as a contribution to the development of appropriate water management strategies.The geochemistry of the Cornia Plain groundwater changes from a HCO3 facies in the inland areas to a Cl facies along the coastal belt, where seawater intrusion takes place. The B concentration of groundwater increases towards the coastal areas, while the 11B/10B ratio decreases. This indicates that there is an increasing interaction between dissolved B and the sediments forming the aquifer matrix, whose B content is in the order of 100 mg kg−1. Adsorption–desorption exchanges take place between water and the sediment fine fraction rich in clay minerals, with a net release of B from the matrix into the groundwater, and a consequent δ 11B shift from positive to negative values. The aquifer matrix sediments therefore seem to be the major source of B dissolved in the groundwater.The groundwater–matrix interactions triggered by the ionic strength increase caused by seawater intrusion can also be detected in the Ca–Na ion exchanges. Dissolved Sr follows a trend similar to that of Ca, while the 87Sr/86Sr ratio is equal to that of the exchangeable Sr of the aquifer matrix and therefore does not change significantly.These results have helped to define a new strategy for groundwater exploitation, with the final objective of reducing B concentration in the water extracted from the aquifer.

This paper examines the seasonal cycling of temperature and salinity in Dexter pit lake in arid northern Nevada, and describes an approach for modeling the physical processes that operate in such systems. The pit lake contains about 596,200 m3 of dilute, near neutral (pHs 6.7–9) water. Profiles of temperature, conductivity, and selected element concentrations were measured almost monthly during 1999 and 2000. In winter (January–March), the pit lake was covered with ice and bottom water was warmer (5.3 °C) with higher total dissolved solids (0.298 g/L) than overlying water (3.96 °C and 0.241 g/L), suggesting inflow of warm (11.7 °C) groundwater with a higher conductivity than the lake (657 versus 126–383 μS/cm). Seasonal surface inflow due to spring snowmelt resulted in lower conductivity in the surface water (232–247 μS/cm) relative to deeper water (315–318 μS/cm). The pit lake was thermally stratified from late spring through early fall, and the water column turned over in late November (2000) or early December (1999). The pit lake is a mixture of inflowing surface water and groundwater that has subsequently been evapoconcentrated in the arid environment. Linear relationships between conductivity and major and some minor (B, Li, Sr, and U) ions indicate conservative mixing for these elements.Similar changes in the elevations of the pit lake surface and nearby groundwater wells during the year suggest that the pit lake is a flow-through system. This observation and geochemical information were used to configure an one-dimensional hydrodynamics model (Dynamic Reservoir Simulation Model or DYRESM) that predicts seasonal changes in temperature and salinity based on the interplay of physical processes, including heating and cooling (solar insolation, long and short wave radiation, latent, and sensible heat), hydrologic flow (inflow and outflow by surface and ground water, pumping, evaporation, and precipitation), and transfers of momentum (wind stirring, convective overturn, shear, and eddy diffusion). Inputs to the model include the size and shape of the lake, daily meteorological data (short wave radiation, long wave radiation or cloud cover, air temperature, vapor pressure, wind speed, and rainfall), rates for water inputs and outputs, the composition of inflowing water, and initial profiles of temperature and salinity. Predicted temperature profiles, which are influenced by seasonal changes in the magnitude of solar radiation, are in good agreement with observations and show the development of a strong thermocline in the summer, erosion of the thermocline during early fall, and turnover in late fall. Predicted salinity profiles are in reasonable agreement with observations and are affected by the hydrologic balance, particularly inflow of surface and groundwater and, to a lesser degree, evaporation. Defining the hydrodynamics model for Dexter pit lake is the first step in using a coupled physical – biogeochemical model (Dynamic Reservoir Simulation Model-Computational Aquatic Ecosystem Dynamics Model or DYRESM-CAEDYM) to predict the behavior of non-conservative elements (e.g., dissolved O2, Mn, and Fe) and their effect on water quality in this system.

Understanding the fate of injected organic matter and the consequences of subsequent redox processes is essential to assess the viability of using reclaimed water in aquifer storage and recovery (ASR). A full-scale field trial was undertaken at Bolivar, South Australia where two ASR cycles injected approximately 3.6 × 105  m3 of reclaimed water into a carbonate aquifer over a 3-a period. Organic C within reclaimed water was predominantly in the dissolved fraction, ranging from 1 to 2 mmol L−1 (10–20 mg L−1), markedly higher than potable supply and stormwater previously reported as source waters for ASR. Between 20% and 24% of the injected dissolved organic C (DOC) was mineralised through reaction with injected O2 and NO3. Furthermore, this was achieved mainly within the first 4 m of aquifer passage. Despite the presence of residual DOC, SO4 reduction was not induced within the bulk of the injected plume. It was only near the ASR well during an extended storage phase where deeply reduced (methanogenic) conditions developed, indicating variable redox zones within the injectant plume. The quality of water recovered from the ASR well indicated that the organic C content of reclaimed water does not restrict its application as a recharge source for ASR.

Evaluation of phosphate fertilizers for ameliorating acid mine waste by David L. Harris; Bernd G. Lottermoser (1216-1225).
The aim of the study was to determine whether the application of bulk industrial chemicals (potassium permanganate and water-soluble phosphate fertilizer) to partly oxidized, polyminerallic mine wastes can inhibit sulfide oxidation, and metal and metalloid mobility. The acid producing waste rocks were metal (Pb, Zn, Cu) and metalloid (As, Sb) rich and consisted of major quartz, dickite, illite, and sulfide minerals (e.g., galena, chalcopyrite, tetrahedrite, sphalerite, pyrite, arsenopyrite), as well as minor to trace amounts of pre- and post-mining oxidation products (e.g., hydrated Fe, Cu, Pb, and alkali mineral salts). SEM-EDS observations of treated waste material showed that metal, metal–alkali, and alkali phosphate coatings developed on all sulfides. The abundance of phosphate phases was dependant on the fertilizer type and the availability of metal and alkali cations in solution. In turn, the release of cations was dependent on the amount of sulfide oxidation induced by KMnO4 during the experiment and the dissolution of soluble sulfates. Mn, Ca, Fe, and Pb phosphates remained stable during H2O2 leaching, preventing acid generation and metal release. In contrast, the lack of complete phosphate coating on arsenopyrite allowed oxidation and leaching of As to proceed. The mobilized As did not form phosphate phases and consequently, As displayed the greatest release from the coated waste. Thus, the application of KMnO4 and the water-soluble phosphate fertilizer Trifos (Ca(H2PO4)2) to partly oxidized, polyminerallic mine wastes suppresses sulfide oxidation and is most effective in inhibiting Cu, Pb, and Zn (Sb) release. However, the technique appears ineffective in suppressing oxidation of arsenopyrite and preventing As leaching.

Natural organic matter (NOM) from the Han River, Korea was fractionated into humic and non-humic fractions by absorbing onto XAD-7HP, and these fractions were analyzed using UV-absorption, and for dissolved organic C (DOC). The humic fraction (i.e. humic substances; HS) was extracted and its characteristics were compared to commercial humic materials using various spectroscopic methods such as Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR) and fluorescence spectroscopy. The humic fraction as organic C was 47.0% on the average, however, a rainfall event brought a higher humic fraction into Han River water. The molar ratios of H/C and O/C in the HS from Han River water (HRHS) were 1.40 and 0.76, respectively, and the ratio of aliphatic to aromatic protons in the HS (PAl/PAr ratio) was 5.8. Aromaticity and humification degree (i.e., degree of condensation) of HRHS were relatively lower than those from other humic materials, while the portion of oxygenated functional groups was relatively higher. FT-IR, 1H-NMR and fluorescence spectroscopy showed distinct differences between HRHS and the commercial humic materials. Commercial humic materials are not representative of HS extracted from Han River water. The fluorescence spectra, relatively simple measurements, were found to be most useful as fingerprints for humic materials from particular sources.

Elemental sulfur in drain sediments associated with acid sulfate soils by Edward D. Burton; Richard T. Bush; Leigh A. Sullivan (1240-1247).
This paper reports the abundance of elemental S in drain sediments associated with acid sulfate soils. The sediments exhibited near-neutral pH (5.97–7.27), high concentrations of pore-water Fe2+ (1.37–15.9 mM) and abundant oxalate-extractable Fe (up to 4300 μmol g−1). Maximum acid-volatile sulfide (AVS) concentrations in each sediment profile were high (118–1019 μmol g−1), with AVS often exceeding pyrite-S. Elemental S occurred at concentrations of 13–396 μmol g−1, with the higher concentrations exceeding previous concentrations reported for other sedimentary systems. Up to 62% of reduced inorganic S near the sediment/water interface was present as elemental S, due to reaction between AVS and oxidants such as O2 and Fe(III). Significant correlation (r  = 0.74; P  < 0.05) between elemental S and oxalate-extractable Fe(III) is indicative of elemental S formation by in situ oxidation of AVS. The results indicate that AVS oxidation in near-surface sediments is dynamic in acidified coastal floodplain drains, causing elemental S to be a quantitatively important intermediate S fraction. Transformations of elemental S may therefore strongly influence water quality in ASS landscapes.