Sequential Extraction Data Research Articles

Geochemical and mineralogical characterization of tailings of the Dexing copper mine, Jiangxi Province, China

The Dexing copper mine is the largest open pit copper mines in Asia, with mining and beneficiation history stretching back more than half a century; consequently it has large amounts of ore tailings. The mineralogy, chemical composition and distribution of elements in the impounded tailings are of great significance to the future utilization and reclamation of the tailings ponds. In total, 1400 tailing samples from 35 drill cores were collected from the 1 tailings pond at the Dexing copper mine. All samples were analyzed to determine their chemical composition. The particle size, XRD, pH and sequential extraction fractions of selected samples were determined. The silt-size fraction dominates the grain-size distribution. Quartz and sericite are the most abundant gangue minerals in the tailings, with medians of 54.3 and 23.7%, respectively. 3D modeling of the tailings pond suggests that the distribution of particle size, minerals and elements is mainly controlled by the gravitational separation during tailings discharge. Silica, Cu, Mo and Ti are enriched in the dam area of the tailings pond, whereas Al 2 O 3 and K 2 O are enriched in the impoundment area. The potential Cu, Ti and sericite reserves in the tailings pond were estimated at 38 149 tons, 142 175 tons and 8.15 million tons, respectively. The tailings are not significantly oxidized and so their environmental risk is low under the present circumstances. Their weak alkalinity and presence of carbonate minerals provide the tailings buffering capacity to weak acids. Sequential extraction data suggest that the mobility of elements in the tailings pond is low; however, about 6040 tons of Cu, 428 tons of Zn, 252 tons of Mo, 145 tons of As and 66 tons of Pb, may be released if the physicochemical conditions change and the tailings become acidic.

Evaluation of the dynamic mobilization of vanadium in tributary sediments of the Three Gorges Reservoir after water impoundment

The Three Gorges Reservoir (TGR) is the largest water resource protection zone in China, and environmental safety is crucial to its operation. For both aqueous and sediment phases, diffusive gradients in thin films (DGT), total vanadium (V) concentration (CTotal-V), and community Bureau of Reference (BCR) sequential extraction data were used to measure the pollution characteristics, horizontal and vertical distributions of DGT-labile V, and the dynamic mobilization of V in a typical tributary (the Meixi River) of the TGR. The results showed that CTotal-V in the surface sediments were obviously higher than the background values in sediment and soil, indicating a potential anthropogenic input of V in this area. A positive relationship was found between total organic carbon (TOC) and CTotal-V in the sediments, indicating that the pollution characteristics of V were associated with TOC. In addition, horizontal and vertical distributions of the fluxes of DGT-labile V (FDGT-V) varied among the four DGT probes. In the same DGT probe, the horizontal distributions (0–6mm, 6–12mm and 12–18mm) of FDGT-V were similar in the overlying water; however, the values showed a poor coincidence with those recorded in the sediment. The vertical distribution of FDGT-V in the same DGT probe showed similar tendencies. In fact, CDGT-V is significantly negatively correlated with CDGT-Fe, demonstrating that V had an inversely diffusive tendency with Fe. Moreover, diffusion fluxes of V at the sediment-water interface illustrated that the release characteristics of V varied among the sampling sites. In addition, the BCR fraction of V in the surface sediments of the four sampling sites showed that V mainly existed in the residual fraction (88.04–88.57%). The concentrations of DGT-labile V (CDGT-V) were considerably lower than the non-residual fractions (the sum of exchangeable, reducible, and oxidizable fractions) measured by BCR sequential extraction. Correlation analysis showed that CDGT-V had no correlation with non-residual V fractions, indicating that it is doubtful whether BCR extraction alone can be used to predict the bioavailability of V in this study.

Importance of chemical binding type between As and iron-oxide on bioaccessibility in soil: Test with synthesized two line ferrihydrite

Bioaccessible concentrations of As associated with Fe oxide as different chemical binding types were determined in soils using the in vitro Physiologically Based Extraction Test (PBET). When compared to the five-step sequential extraction data, most of the As extracted by in vitro PBET originated from the amorphous Fe oxide-bound fraction, and more importantly, the bioaccessibility of As ranged from 0 to 58.8% in 24 soil samples. Two batches of ferrihydrite were synthesized separately. For one batch, As was adsorbed onto the ferrihydrite after synthesis; for the other one, As was added while synthesizing ferrihydrite to co-precipitate. The bioaccessible concentration of As determined by in vitro PBET of the former was 415mg of As/kg of ferrihydrite and that of the latter was 67mg of As/kg of ferrihydrite. X-ray photoelectron spectra (XPS) analysis indicated that As–O–Fe bonds were evident in As-associated ferrihydrite sample and especially, As was found within the Fe oxide lattice in the co-precipitated sample. Our data suggest that binding type between As and Fe oxide should be considered when determining the bioaccessibility of As in soil, which, in turn, greatly influences the realistic risk of As present in soil.

Sorption of Pb, Cu, Cd, and Zn by Municipal Solid Waste Composts: Metal Retention and Desorption Mechanisms

In this study, the ability of two municipal solid waste composts to adsorb Pb, Cu, Cd, and Zn ions (Me(II)) from aqueous solutions was investigated. Sorption experiments, carried out at pH 4.5 to simulate acidic Me(II)‐polluted environments, showed for both composts higher affinity for Pb (∼0.45 mmol g−1) and Cu (∼0.31 mmol g−1) compared to Cd (∼0.25 mmol g−1) and Zn (∼0.10 mmol g−1). The sorption isotherms data fitted the Freundlich model better than the Langmuir in both composts, suggesting the presence of heterogeneous Me(II) adsorption sites. The humic acids (HA) extracted from composts contributed to 16, 23, 17, and 20% in the sorption of Pb, Cu, Cd, and Zn, respectively, while the compost water‐soluble‐fractions hardly affected the sorption/precipitation of the Me(II) (<5%). The Fourier transform infrared (FT‐IR) spectra of the different Me(II)–HA systems also indicated that the carboxylate groups of HA mainly interacted with Pb(II) and Cu(II) by forming monodentate and bidentate complexes, respectively. The sequential extraction data showed that a significant amount of Cd and Zn was retained by composts through electrostatic interactions (>65% of the respective total amounts sorbed) while most of Cu and Pb (40 and 54%) was strongly complexed and/or precipitated. The treatment of the Me(II)‐composts with citric and malic acids favored the release of >78 and 48% of Zn, 65 and 30% of Cu, and 40 and 30% of Cd, sorbed by both composts, respectively. This release was lower for Pb (<20%) as the cation more strongly retained by the organic or inorganic components of composts.

Experimental determination of nonequilibrium transport parameters reflecting the competitive sorption between Cu and Pb in slag-sand column

Competitive sorption and resulting nonequilibrium transport of Cu and Pb were investigated using slag as a primary sorbent. A series of estimation models were applied based on the equilibrium, and nonequilibrium sorption respectively, and finally calibrated by incorporating the experimentally determined batch kinetic data. When applied individually, the behavior of metals in slag-sand column were well predicted by both equilibrium and nonequilibrium models in CXTFIT code. However, coexisting Cu and Pb exhibited competition for sorption sites, generating an irregular breakthrough curves such as overshoot (higher concentration in effluent than the feed concentration) of Cu and corresponding earlier peak of Pb followed by gradual re-rising. Although two-site nonequilibrium model further considers coupled hydrochemical process, desorption of the Cu from competition made the model prediction inaccurate. However, the parameter estimation could be improved by incorporating the experimentally determined mass transfer rate, ωexp from batch kinetics. Based on the calibrated model, the fraction of instantaneous retardation, βexp of Pb decreased from 0.41 in the single system to 0.30 in the binary system, indicating the shift from equilibrium to nonequilibrium state, where which of Cu increased from 0.39 to 0.94, representing the shift towards equilibrium. The modified results were also compared with five-step sequential extraction data, confirming that the shift of particular metal fractions from the competition triggered the nonequilibrium transport.

Effect of aging on bioaccessibility of arsenic and lead in soils

The effect of aging on the bioaccessibility of As and Pb in three soils spiked with As (40 or 400 mg kg−1), Pb (150 or 1500 mg kg−1) or As + Pb (40 mg kg−1 As and 150 mg kg−1 Pb) were investigated using the physiologically based extraction test (PBET). Prolonged aging in soils resulted in a decrease in As/Pb bioaccessibility, especially within the first month. After 76 weeks, As/Pb bioaccessibility in soils decreased to a stable level, with 48–84% and 8–34% for bioaccessible As and Pb respectively in the intestinal phase, illustrating that As in spiked soils was much more bioaccessible than Pb. Correlation analysis between sequential extraction data and PBET results showed that the non-specifically sorbed As contributed the most to bioaccessible As, while Pb bound with carbonates and exchangeable fractions were the source for bioaccessible Pb. For future work, minerals containing As and/or Pb instead of their soluble salts can be added to uncontaminated soils to better simulate the natural aging processes.

Effects of biosolids and compost amendment on chemistry of soils contaminated with copper from mining activities.

Several million metric tons of mining wastes, called stamp sands, were generated in the Upper Peninsula of Michigan during extensive copper (Cu) mining activities in the past. These materials, containing large amounts of Cu, were discharged into various offshoots of Lake Superior. Due to evidences of Cu toxicity on aquatic organisms, in due course, the materials were dredged and dumped on lake shores, thus converting these areas into vast, fallow lands. Erosion of these Cu-contaminated stamp sands back to the lakes is severely affecting aquatic life. A lack of uniform vegetation cover on stamp sands is facilitating this erosion. Understanding the fact that unless the stamp sands are fertilized to the point of sustaining vegetation growth, the problem with erosion and water quality degradation will continue, amending the stamp sands with locally available biosolids and composts, was considered. The purpose of the reported study was to assess potential effects of such organic fertilizer amendments on soil quality. As the first step of a combined laboratory and greenhouse study, a 2-month-long incubation experiment was performed to investigate the effects of biosolids and compost addition on the soil nutrient profile of stamp sands and organic matter content. Results showed that both biosolids and compost amendments resulted in significant increase in nitrogen and phosphorus concentrations and organic matter contents of stamp sands. Sequential extraction data demonstrated that Cu was mostly present as bound forms in stamp sands, and there was no significant increase in the plant available fraction of Cu because of fertilizer application.

Potential ecological impacts of trace metals on aquatic biota within the Upper Little Tennessee River Basin, North Carolina

The Upper Little Tennessee River (ULTR) possesses one of the most diverse assemblages of aquatic biota in North America, including the endangered Appalachian elktoe mussel (Alasmidonta raveneliana). Populations of the Appalachian elktoe significantly declined along with other species following an extreme flood in 2004. This paper examines the potential role that four toxic trace metals (Cu, Cr, Ni, and Zn) played in the population declines. Dissolved and total-recoverable concentrations of Cr and Ni measured during three flood events were below USEPA and North Carolina freshwater guidelines for potential impacts on aquatic biota, respectively. In contrast, 58% of the samples exceeded NC guideline values for total-recoverable concentrations of Cu and Zn. In general, metal concentrations increased with increasing discharge and suspended sediment concentrations (SSC). These relationships, combined with sequential extraction data from sediments, suggest that most metals were transported in the particulate form and were not readily bioavailable. During individual events, metal concentrations for a given discharge were influenced by a “first flush” hysteresis effect. Rapid increases in metal concentrations during the early stages of an event appear to be related to the entrainment of fine sediment, including particulate Fe to which the metals are sorbed. Instantaneous metal loads calculated for nine tributaries to the ULTR, combined with previously collected data, suggest that the majority of the metals were derived from the erosion of sediment and particulate Fe from subsurface soil horizons developed in bedrock containing sulfidic layers. The erosion was particularly pronounced in tributary basins in poor to moderate ecological condition. While a fraction of the Cu may have been derived from Cu-based pesticides and was periodically elevated above guideline values in river waters, the data in total suggest that toxic trace metals were unlikely to play a major role in the decline of elktoe populations.

Sorption of Cadmium(II) and Zinc(II) from Aqueous Solution by Water Treatment Residuals at Different pH Values

Here, we report on the ability of two different water treatment residues, a Fe-based (Fe-WTR) and an Al-based (Al-WTR) ones, to accumulate Cd(II) and Zn(II) from aqueous solutions at different pH values (pH 4.5, 5.5, and 7.0). Fe-WTR showed a greater Zn(II) and Cd(II) sorption capacity than Al-WTR at all the pH values investigated, in particular at pH 7.0 (e.g., ∼0.200 and ∼0.100 mmol g−1 of Me(II) sorbed by Fe- and Al-WTR at pH 7.0, respectively). The greater capacity of the Fe-WTR to accumulate Me(II) seems to be linked to its higher content of iron and manganese ions and to its higher CEC value compared to Al-WTR. The role of the inorganic and organic fractions of WTRs in metal sorption was also assessed. A higher affinity of Cd(II) with respect to Zn(II) toward functional groups of the organic matter of both WTRs was observed, while Zn(II) showed a stronger association with the inorganic phases. The sorption of both metal ions appeared mainly governed by the formation of inner-sphere surface complexes with the inorganic and organic phases of WTRs, as suggested by the sequential extraction data.

Total concentration, speciation and mobility of potentially toxic elements in soils around a mining area in central Iran

The current study was designed to investigate the extent and severity of contamination as well as the fractionation of potentially toxic elements (As, Cd, Cr, Cu, Pb, Zn, Ni) in minesoils and agricultural soils around a Pb–Zn mine in central Iran. For this purpose, 20 agricultural soils and eight minesoils were geochemically characterized. Results showed that minesoils contained elevated concentrations of As (12.9–254mgkg−1), Cd (1.2–55.1mgkg−1), Pb (137–6239mgkg−1) and Zn (516–48,889mgkg−1). The agricultural soils were also polluted by As (5.5–57.1mgkg−1), Cd (0.2–8.5mgkg−1), Pb (22–3451mgkg−1) and Zn (94–9907mgkg−1). The highest recorded concentrations for these elements were in soils influenced directly by tailing ponds. Chromium, Cu and Ni content in agricultural soils (with average value of 74.1, 34.6 and 50.7mgkg−1, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4mgkg−1, respectively). Sequential extraction data indicated that there were some differences between the speciation of PTEs in soil samples. In the agricultural soils, Zn and Cd were mainly associated with carbonate bound fraction, As and Pb with reducible fraction, Cu with oxidisable fraction and Cr and Ni with residual phase. With respect to mobility factor values, Zn and Cd in the agricultural soils have been found to be the most mobile while As mobility is negligible. Also, the mobility factor of As, Cd and Pb in agricultural soils adjoining tailing ponds was high. In minesoil sample Cd was most abundant in the carbonate form, whereas other studied elements were mainly present in the reducible and residual fractions; therefore, despite the high total concentrations of As, Pb and Zn in the minesoils, the environmental risk of these elements was low. Based on the obtained data, a portion of Cu, Cr and Ni input was from agricultural activities.

Binding intensity and metal partitioning in soils affected by mining and smelting activities in Minas Gerais, Brazil.

Mining and smelting activities are potential sources of heavy metal contamination, which pose a threat to human health and ecological systems. This study investigated single and sequential extractions of Zn, Pb, and Cd in Brazilian soils affected by mining and smelting activities. Soils from a Zn mining area (soils A, B, C, D, E, and the control soil) and a tailing from a smelting area were collected in Minas Gerais state, Brazil. The samples were subjected to single (using Mehlich I solution) and sequential extractions. The risk assessment code (RAC), the redistribution index (U ts ), and the reduced partition index (I R ) have been applied to the sequential extraction data. Zinc and Cd, in soil samples from the mining area, were found mainly associated with carbonate forms. This same pattern did not occur for Pb. Moreover, the Fe-Mn oxides and residual fractions had important contributions for Zn and Pb in those soils. For the tailing, more than 70% of Zn and Cd were released in the exchangeable fraction, showing a much higher mobility and availability of these metals at this site, which was also supported by results of RAC and I R . These differences in terms of mobility might be due to different chemical forms of the metals in the two sites, which are attributable to natural occurrence as well as ore processing.

Measuring the solid-phase fractionation of lead in urban and rural soils using a combination of geochemical survey data and chemical extractions.

The study used 276 urban soils and 447 rural soils collected from in and around the UK town of Northampton and focussed on the fractionation of Pb. The Pb fractionation obtained from total element data was compared to the fractionation of Pb in a subset of 10 urban soils obtained using a sequential extraction method. The fractionation of the Pb from the total element data and from the sequential extractions was estimated using a self-modelling mixture resolution statistical model. The bioaccessibility of Pb in a subset of 50 of the urban soils, as measured using the unified BARGE method, was shown to be quantitatively linked with Pb fractionation from both the total element and the sequential extraction data. Three intrinsic soil components from the regional total element data model and one physico-chemical component from the sequential extraction data model were identified as the sources of bioaccessible Pb. The source of bioaccessible Pb in both rural and urban soils was tentatively identified as a fine-grained pyromorphite mineral.

Environmental mineralogy of Cu-porphyry mine tailings, a case study of semi-arid climate conditions, Sarcheshmeh mine, SE Iran

Sarcheshmeh porphyry copper mine is located in semiarid clime conditions, in the Central Iranian Volcano-Plutonic Copper Belt. Hydro-geochemical and climatological conditions produce suites of secondary mineral assemblages in the Sarcheshmeh mine tailings, which are very interesting and important from the environmental point of view. Solid samples were collected from the fresh and weathered tailings and also from the surface evaporative layer formed on top of the old impoundments. Samples were investigated by using X-ray diffraction (XRD), ore microscopy and chemical fractionation methods. The primary mineralogy of fresh tailings, which is controlled by alteration/mineralization in the Sarcheshmeh mine, was mainly composed of quartz, pyrite, muscovite (sericite), albite, orthoclase, ±clinochlore±chalcopyrite and±illite. This mineral assemblage was subjected to the oxidation/weathering reactions in dried impoundments. Acidic conditions of the weathering zone were compatible with the precipitation of jarosite [KFe3+3(SO4)2(OH)6], hydronium jarosite [(H3O)Fe3+3(SO4)2(OH)6], natrojarosite [NaFe3+3(SO4)2(OH)6], alunite [KAl3(SO4)2(OH)6], butlerite [Fe3+(SO4)(OH)2H2O] and gypsum [CaSO4 2H2O]. A great variety of soluble secondary minerals, typical of arid and semiarid environment, were distinguished in the well-developed evaporative layer on top of the old weathered tailings. These minerals, which are formed due to the upward migration of multi-elemental contaminated waters enriched in Al, Ca, Cl, Cu, Fe2+, Fe3+, H, K, Mg, Mn, Na, O, S, and Zn, were mainly from: (1) simple hydrated sulfate salts of the divalent metal cations (gypsum, hexahydrite, kieserite, leonite, poitevinite, and Zinc-melanterite); (2) simple hydrated salts of the trivalent ions (alunogen, kalinite, and tamarugite); (3) mixed divalent–trivalent salts (lishizhenite, römerite, and Zincobotryogen); and (4) chloride containing minerals (eriochalcite, halite, and mitscherlichite). Secondary minerals in the evaporative zone were found in several unique mineral assemblages such as poitevinite–tamarugite–alunogen–hexahydrite. Formation, transformation, and dissolution of evaporative minerals are induced by the wetting/drying cycles. Mineralogical results, which are supported by the hydro-geochemical and sequential extraction data, are useful for the prediction of contamination potential of tailings, the fate of environmental contaminants, and also the possible remediation strategies.

Redox transformation, solid phase speciation and solution dynamics of copper during soil reduction and reoxidation as affected by sulfate availability

In periodically flooded soils, interactions of Cu with biogenic sulfide formed during soil reduction lead to the precipitation of sparingly soluble Cu-sulfides. In contaminated soils, however, the amounts of Cu can exceed the amount of sulfate available for microbial reduction to sulfide. In laboratory batch experiments, we incubated a paddy soil spiked to ∼4.4mmolkg-1 (280mgkg−1) Cu(II) to monitor temporal changes in the concentrations of dissolved Cu and the speciation of solid-phase Cu during 40days of soil reduction and 28days of reoxidation as a function of initially available reducible sulfate (0.06, 2.09 or 5.92mmolkg−1). Using Cu K-edge EXAFS spectroscopy, we found that a large fraction of Cu(II) became rapidly reduced to Cu(I) (23–39%) and Cu(0) (7–17%) before the onset of sulfate reduction. Combination with results from sequential Cu extraction and chromium reducible sulfur (CRS) data suggested that complexation of Cu(I) by reduced organic S groups (Sorg) may be an important process during this early stage. In sulfate-depleted soil, Cu(0) and Cu(I)–Sorg remained the dominant species over the entire reduction period, whereas in soils with sufficient sulfate, initially formed Cu(0) and (remaining) Cu(II) became transformed into Cu-sulfide during continuing sulfate reduction. The formation of Cu(0), Cu(I)–Sorg, and Cu-sulfide led to an effective decrease in dissolved Cu concentrations. Differences in Cu speciation at the end of soil reduction however affected the dynamics of Cu during reoxidation. Whereas Cu(0) was rapidly oxidized to Cu(II), more than half of the S-coordinated Cu fraction persisted over 14days of aeration. Our results show that precipitation of Cu(0) and complexation of Cu(I) by reduced organic S groups are important processes in periodically flooded soils if sulfide formation is limited by the amount of available sulfate or the duration of soil flooding. The speciation changes of Cu described in this study may also affect the speciation and solubility of other chalcophile metals in redox-dynamic wetland soils.

The method of definition of the effective thermodynamic parameters of trace metals sorbed forms in bottom sediments from sequential extraction data

Citation: Lipatnikova, O.A., D. V. Grichuk, O. V. Sokolova (2011), The method of definition of the effective thermodynamic parameters of trace metals sorbed forms in bottom sediments from sequential extraction data, Vestn. Otd. nauk Zemle, 3, NZ6065, doi:10.2205/2011NZ000195. Application of thermodynamic modeling to forecast of trace metals migration in water ecosystems is difficult because bottom sediments composition in reservoirs is very changeable and uncertain. We offer the alternative approach for solving similar problems. It is based on use of empirical information about distribution of mobile and potentially mobile forms of trace elements. Such type of information can be received using sequential extraction scheme (for example Tessier scheme). Effective thermodynamic parameters for certain object are calculated from this data. System «pore water – solid phase» of bottom sediments is considered as multicomponent system in thermodynamic model. It includes aqueous phase, individual solid phases and principal sorbing phases (clay minerals, iron and manganese hydroxides and organic matter) assumed as ideal solid solutions. The coefficients of trace metals selectivity with respect to calcium for the main sorbed forms were calculated based on the results of the analysis of extracts from the solid phase of bottom sediments and pressed pore waters. Based on these coefficients, the imaginary increments of the Gibbs free energy Δg°(T) for the sorbed forms were calculated. The quantity Δg°(T) CaX=0 was taken as a reference point of the imaginary Δg°. We performed the calculation of metal distribution between sorbents and pore solution using the calculated effective thermodynamic parameters. The thermodynamic calculations accurately reproduce the empirically obtained trace metals distribution in bottom sediments.

Controls on the geochemistry of rare earth elements in sediments and groundwaters of the Aquia aquifer, Maryland, USA

Groundwater samples were collected along two flow paths from the Aquia aquifer in Maryland, USA to investigate the rare earth element (REE) geochemistry of the flow system as a function of evolving groundwater composition. Neodymium (Nd) concentrations of Aquia aquifer groundwater range from 56.6 to 71.4 pmol kg − 1 along the Eastern Shore flow path (i.e., Eastern Shore of the Chesapeake Bay), and from 41.5 to 77.9 pmol kg − 1 on the Western Shore flow paths, and consequently fall within the range reported for other circumneutral to alkaline pH groundwaters. Shale-normalized REE patterns of Eastern and Western Shore Aquia groundwaters are similar (i.e., relatively flat) and do not vary substantially along either flow path. For example, (Yb/Nd) NASC for Aquia aquifer groundwaters exhibit a limited range between 0.7 and 1.1. Aquia aquifer sediments were analyzed for REEs following a sequential extraction procedure. Neodymium concentrations for the bulk aquifer sediment range from 26 to 70 μmol kg − 1 (3.7 to 10.1 ppm), or a factor of 2.5 to 7 lower than the Nd content of the upper continental crust. The sequential extractions reveal that the majority of the REEs in the aquifer sediments occur associated with the abundant carbonate shell fragments that are ubiquitous within the Aquia aquifer sediments. Furthermore, the sequential extraction data indicate that the light REEs (LREE) are more readily exchangeable (i.e., outer sphere surface complexed) on aquifer mineral surfaces than the heavy REEs (HREE), and the HREEs and middle REEs (MREE) exhibit a greater association with Fe/Mn oxides/oxyhydroxides within the sediments. Analysis of the abundant glauconite pellets within Aquia aquifer sediments indicates an overall enrichment in the HREEs relative to the LREEs for this mineral, compared to shale. Our data suggest that the chief source of REEs to Aquia aquifer groundwater is dissolution of carbonate biominerals (shell fragments) that occurs in the recharge zone and before groundwaters become saturated with respect to calcite and aragonite. Additionally, weakly sorbed REEs (outer sphere surface complexed) contribute LREEs and MREEs to Aquia aquifer groundwater as pH increases above 8, leading to the relatively flat, shale-normalized REE patterns that characterize Aquia aquifer groundwaters. Once released to the solution, REE form strong aqueous complexes with carbonate ions, LnCO 3 + and Ln(CO 3) 2 −, with the dicarbonato complexes (i.e., Ln(CO 3) 2 −) predominating. The REE are subsequently transported with flowing groundwater in the Aquia aquifer as the negatively charged dicarbonato complexes exhibit a low affinity to sorb to negatively charged mineral surfaces in the aquifer sediments.

Binding strength-associated toxicity reduction by birnessite and hydroxyapatite in Pb and Cd contaminated sediments

In situ stabilization of sediment-bound heavy metals has been proposed as an alternative to ex situ treatment due to the concerns on ecosystem disturbance and remediation cost. The present study was conducted to test the performance of birnessite, hydroxyapatite, and zeolite as stabilizing agents for Pb and Cd in sediment. The heavy metal binding capacity and strength of the stabilizing agents were determined by analyzing Langmuir model parameters. The three agents showed the similar binding capacity (i.e., maximum monolayer sorption constant, Ka) ranging from 1.13 to 3.62×105mg/kg for Pb and 1.07 to 1.33×105mg/kg for Cd. In contrast, binding strength (i.e., binding energy constant, b) of birnessite and hydroxyapatite was about one order higher than that of zeolite. This is further supported by five-step sequential extraction data: more than 99 and 70% of freshly spiked Pb and Cd were present as not-readily extractable fractions in birnessite and hydroxyapatite, respectively while the fractions were 17.9 and 14.1% in zeolite. Toxicity Characteristic Leaching Procedure (TCLP) test was also conducted to verify the effectiveness of the heavy metal-stabilizing ability of birnessite and hydroxyapatite. Birnessite successfully retained both Pb and Cd against the leaching solution, satisfying the TCLP extract concentration limits (i.e., 5 and 1mg/L, respectively). However, hydroxyapatite released about 223.7mg/L of Cd into the solution, which greatly exceeded the limit. The toxicity test with Hyalella azteca showed that their survival rate increased by 92.5–100% when birnessite or hydroxyapatite was added to Pb- or Cd-spiked sediment as a stabilizing agent. Our data demonstrate the potential use of birnessite and hydroxyapatite as an effective in situ remediation means for heavy metal-contaminated sediment with minimal risk to the aquatic ecosystem.

On metal diagenesis in contaminated sediments of the Deûle river (northern France)

The objective of the present work was to assess depth-related variations in the (bio)geochemical processes involved in anoxic sediments from the Deûle river, and to examine particularly their impacts on the distribution of anthropogenically sourced metals. Anoxic sediment samples were sliced and analyzed to determine total concentrations vs. depth of elements and corresponding pore waters were analyzed to determine concentration profiles with depth of pH, Eh, alkalinity, O2, dissolved organic carbon (DOC), and main inorganic anions and cations present in the medium. It was shown that rapid depletions of O2, NO3- and SO42-, accompanied with HCO3- generation and a sharp decrease in the redox potential occurred within the first centimeters of the surface sediment as a consequence of early diagenesis. Bacterial reductive dissolution of Mn(III and IV) and Fe(III) oxides/hydroxides to Mn(II) and Fe(II) accompanied by microbial degradation of organic matter took place as well, and resulted in trace metal increases in the pore water at levels that raised the possibility of mineral generation. Thermodynamic calculations predicted removal of metals from interstitial waters through combinations with carbonates and/or sulfides. These took place either by direct precipitation to form pure crystals, or by coprecipitation/sorption with/into calcite and with pyritic compounds. Chemical sequential extraction data were useful in this work to support, at least partially, some thermodynamic predictions concerning the existence of interactions between trace metals and carbonate and sulfide ions to generate (co)precipitates. Electron paramagnetic resonance (EPR) studies on Deûle sediments revealed the presence of Mn(II) adsorbed onto sedimentary calcite surfaces. X-ray diffractograms of heavy minerals from Deûle sediments extracted with CHBr3 by density separation exhibited peaks ascribed to galena, sphalerite and pyrite. In addition to these compounds, using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), micro-analyses of sedimentary heavy minerals confirmed successfully the existence of other thermodynamically predicted associations: covellite; chalcopyrite, greenockite and/or amorphous CdS.

Primary sink and source of geogenic arsenic in sedimentary aquifers in the southern Choushui River alluvial fan, Taiwan

Abstract This work characterized the sink and source/mobility of As in the As-affected sedimentary aquifers of the southern Choushui River alluvial fan, central Taiwan. Major mineral phases and chemical components were determined by XRD and X-ray photoelectron spectroscopy (XPS). The partitioning of As and Fe among cores were determined by sequential extraction. Based on XPS results, the primary forms of Fe were hematite, goethite and magnetite. Sequential extraction data and the XRF analysis indicated that Fe oxyhydroxides and sulfides were likely to be the major sinks of As, particularly in the distal-fan. Furthermore, Fe oxyhydroxides retained higher As contents than As-bearing sulfides. The reductive dissolution of Fe oxyhydroxides, which accompanied high levels of HCO 3 - and NH 4 + concentrations, was likely the principal release mechanism of As into groundwater in this area. The dual roles of Fe oxyhydroxides which are governed by the local redox condition act as a sink and source in the aquifer. Ionic replacement by PO 4 3 - and HCO 3 - along with seasonal water table fluctuation, caused by monsoons and excessive pumping, contributed specific parts of As in the groundwater. The findings can be used to account for the inconsistency between Fe and As concentrations observed in groundwater.

A conceptual model describing the fate of sulfadiazine and its metabolites observed in manure-amended soils

Sulfadiazine (SDZ) belongs to the chemical class of sulfonamides, one of the most important groups of antibiotics applied in animal husbandry in Europe. These antibiotics end up in the soil after manure from treated animals is applied as fertilizer. They can inhibit soil microbial functions and enhance the spread of resistance genes among soil microorganisms. In order to assess the exposure of soil microorganisms to SDZ, a conceptual kinetic model for the prediction of temporally resolved antibiotic concentrations in soil was developed. The model includes transformation reactions, reversible sequestration and the formation of non-extractable residues (NER) from SDZ and its main metabolites N 4-acetyl-sulfadiazine (N-ac-SDZ) and 4-hydroxy-sulfadiazine (OH-SDZ). The optimum model structure and rate constants of SDZ kinetics and its metabolites were determined by fitting different model alternatives to sequential extraction data of a manure-amended Cambisol soil. N-ac-SDZ is degraded to SDZ with a half-life of 4 d, whereas OH-SDZ is not. Though, based on the available data, the hydroxylation of SDZ seems to be negligible, it is still included in the model structure since this process has been observed in recent studies. Sequestration into a residual fraction has similar kinetics for SDZ, N-ac-SDZ and OH-SDZ and is one order of magnitude faster than the reverse translocation. The irreversible formation of NER is restricted to SDZ and OH-SDZ. The model shows good agreement when applied to extraction data measured independently for a Luvisol soil. The combination of sequential extraction data and the conceptual kinetic model enables us to gain further insight into the long-term fate and exposure of sulfonamides in soil.