Leaching of metals from copper smelter flue dust (Mufulira,Zambian Copperbelt)

The leaching behaviour of electrostatic precipitator dust from the Mufulira Cu smelter (Copperbelt, Zambia) was studied using a 48-h pH-static leaching experiment (CEN/TS 14997). The release of metals (Cd, Co, Cu, Ni, Pb and Zn) and changes in mineralogical composition using X-ray diffraction and PHREEQC-2 modelling were investigated in the pH range of 3–7. The highest concentrations of metals were released at pH 3–4.5, which encompasses the natural pH of the dust suspension (～4.3). About 40% of the total Cu was leached at pH 3, yielding 107 g/kg. Chalcanthite (CuSO₄·5H₂O), magnetite (Fe₃O₄) and delafossite (CuFeO₂) represented the principal phases of the studied dust. In contact with water, chalcanthite was dissolved and hydrated Cu sulphates precipitated at pH 4–7. Gypsum (CaSO₄·2H₂O) and secondary Fe or Al phases were observed in the leached residues. Serious environmental impact due to leaching may occur in dust-contaminated soil systems in the vicinity of the smelting plants.     

The leaching of major and trace elements from MSWI bottom ash as a function of pH and time

In this paper, the leaching behaviour of major components (Al, Ca, SO₄, Mg, Si, Fe, Na and DOC) and trace elements (Ni, Zn, Cd, Cu, Pb, Mo and Sb) from MSWI bottom ash is studied as a function of time over a wide range of pH, under pH-controlled conditions. Equilibrium geochemical modelling using the modelling framework ORCHESTRA is used to enable a process-based interpretation of the results and to investigate whether ‘equilibrium’ is attained during the time scale of the experiments. Depending on the element and setpoint-pH value, net concentration increases or decreases of up to one order of magnitude were observed. Different concentration–time trends (increase or decrease) are observed in different pH ranges. The direction of the concentration–time trends depends on: (1) the shape of the ‘equilibrium’ solubility curve, and (2) the position of the setpoint-pH in the leaching test relative to the natural pH of the sample. Although the majority of the elements do not reach steady state, leached concentrations over a wide pH range have been shown to closely approach ‘equilibrium’ model curves within an equilibration time of 168 h. The different effects that leaching kinetics may have on the pH dependent leaching patterns have been identified for a wide range of elements, and can generally be explained in a mechanistic way. The results are in support of the currently prescribed equilibration time of 48 h in the European standard for the pH-static leaching test (TS14997). Finally, this study demonstrates that pH-static leaching experiments such as described in the European standards (TS14497 and TS14429), in combination with selective chemical extractions and a mechanistically based modelling approach, constitute a powerful set of tools for the characterization of leaching processes in waste materials over a wide range of conditions.     

Measuring reactive pools of Cd,Pb and Zn in coal fly ash from the UK using isotopic dilution assays

Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH < 11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH > 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO₃ and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash.     

Correlations between metals in tree-rings of Prosopis julifora as indicators of sources of heavy metal contamination

Heavy-metals (Cu, Pb and Zn) in tree-ring sequences of Prosopis juliflora, a tree species native to arid environments, were analyzed by ICP-MS. The tree-ring sequences were obtained from three specimens growing in an urban area previously reported as contaminated by the activity of a Cu smelter facility. The metal found in highest concentration in the wood was Zn, with concentrations up to 120 mg/kg and an enrichment factor up to 26; followed by Cu (up to 9.6 mg/kg, enrichment factor up to 8.6) and Pb (up to 1.4 mg/kg, enrichment factor up to 3). By assessing the correlation between different metal concentration trends, it was possible to infer two main pollution sources: vehicle traffic and Cu smelter emissions. Vehicle traffic is indicated by a correlation between Pb and Zn over time within individual trees, whereas contamination from the Cu-smelting facility is indicated by a correlation of Cu over time between trees. In tree A there was a significant within-tree correlation between Pb and Zn concentration trends (r = 0.856, P < 0.001), whereas Cu showed no correlation with the other metals. For tree B, there were no within-tree correlations between these metals, but when comparing the concentration–time trends between trees A and B, there was a significant correlation for Cu (r = 0.768, P < 0.01). The tree-ring sequence from tree C showed significant within-tree correlation for Cu:Zn (r = 0.430, P < 0.01) and for Pb:Zn (r = 0.753, P < 0.001). The highest enrichment values were found in tree A, located along the path of the growing-season dominant wind direction from the smelter facility, and not in the tree growing closer to the smelter (tree C), suggesting that the smelter’s emissions are dispersed to longer distances through the tall chimneys, attenuating the impact to the area directly closest to the smelter facility. It is concluded that Prosopis juliflora appears as a good bioindicator based on its metal accumulation capacity and lack of metal mobility among tree rings, thus providing information on the chronology and sources of heavy-metal pollution in urban and industrial areas.     

Metal mobility by de-icing salt from an infiltration trench for highway runoff

Soil from an infiltration trench for highway runoff was leached in columns alternately with NaCl and de-ionised water to simulate the runoff of de-icing salt into the trench followed by snowmelt or rainwater. Simultaneously, two columns with the same soil were leached with de-ionised water throughout the experiment. In addition, the groundwater below the infiltration trench was sampled on some occasions. The column leachate and groundwater were split into two sub samples, one was filtered though a 0.45 μm filter; both were analysed for Pb, Cd, Zn, Fe and total organic carbon (TOC). The column experiment showed clearly that an extensive mobilisation of Pb occurred in low electrolyte water leaching following NaCl leaching. The high Pb concentration coincided with peaks in Fe and TOC concentrations and implied colloid-assisted transport. Conversely, Cd and Zn concentrations were raised in the NaCl leachate and a high correlation with Cl showed that Cl complexes are important for the mobilisation, although a pH effect and ionic exchange cannot be excluded. Only 0.15% and 0.06% of the total amount of Pb was leached from the columns leached with alternating NaCl and deionised water confirming the usual hypotheses about the high immobility of Pb in soils. However, on one occasion when the ionic strength and pH was the lowest measured the concentration of Pb in groundwater sampled from 2.5 m depth was 27 μg L⁻¹ in the dissolved phase (<0.45 μm) and 77 μg L⁻¹ in the particle phase (>0.45 μm). These Pb concentrations are almost 3 and 8 times above the Swedish limit for drinking water quality. Accordingly, in spite of the immobility of Pb the accumulation in roadside soils is so large that groundwater quality is threatened. In conclusion, the study suggests that roadside soils impacted by NaCl from de-icing operations contribute Pb to groundwater by colloid-assisted transport.     

Laboratory study of calcite–gypsum sludge–water interactions in a flooded tailings impoundment at the Kristineberg Zn–Cu mine,northern Sweden

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.     

Cement–fly ash stabilisation/solidification of contaminated soil: Performance properties and initiation of operating envelopes

This study was aimed at evaluating the mechanical and pH-dependent leaching performance of a mixed contaminated soil treated with a mixture of Portland cement (CEMI) and pulverised fuel ash (PFA). It also sought to develop operating envelopes, which define the range(s) of operating variables that result in acceptable performance. A real site soil with low contaminant concentrations, spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, was treated with one part CEMI and four parts PFA (CEMI:PFA = 1:4) using different binder and water contents. The performance was assessed over time using unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. With binder dosages ranging from 5% to 20% and water contents ranging from 14% to 21% dry weight, the 28-day UCS was up to 500 kPa and hydraulic conductivity was around 10⁻⁸ m/s. With leachant pH extremes of 7.2 and 0.85, leachability of the contaminants was in the range: 0.02–3500 mg/kg for Cd, 0.35–1550 mg/kg for Cu, 0.03–92 mg/kg for Pb, 0.01–3300 mg/kg for Ni, 0.02–4010 mg/kg for Zn, and 7–4884 mg/kg for total petroleum hydrocarbons (TPHs), over time. Design charts were produced from the results of the study, which show the water and/or binder proportions that could be used to achieve relevant performance criteria. The charts would be useful for the scale-up and design of stabilisation/solidification (S/S) treatment of similar soil types impacted with the same types of contaminants.     

The nature and distribution of Cu,Zn, Hg,and Pb in urban soils of a regional city: Lithgow,Australia

This study investigates the concentration and spatial distribution of Cu, Zn, Hg and Pb in the surface (0–2 cm) soils of a regional city in Australia. Surface soils were collected from road sides and analysed for their total Cu, Zn, Hg and Pb concentrations in the <180 μm and <2 mm grain size fractions. The average metal concentration of surface soils, relative to local background soils at 40–50 cm depth, are twice as enriched in Hg, more than three times enriched in Cu and Zn, and nearly six times as enriched in Pb. Median surface soil metal concentration values were Cu – 39 mg/kg (682 mg/kg max), Zn – 120 mg/kg (4950 mg/kg max), Hg – 44 μg/kg (14,900 μg/kg max) and Pb – 46 mg/kg (3490 mg/kg max). Five sites exceeded the Australian NEPC (1999) 300 mg/kg guideline for Pb in residential soils. Strong positive correlations between Cu, Zn and Pb, coupled with the spatial distribution of elevated soil concentrations towards the city centre and main roads suggest traffic and older housing as major sources of contamination. No spatial relationships were identified between elevated metal loadings and locations of past or present industries.     

Measurement of labile metals in acid rock drainage springs,New Zealand: Field application of anodic stripping voltammetry

Spring waters were analysed in the field by anodic stripping voltammetry, using equipment which is sufficiently portable to be useful in a remote heavily forested area accessible by foot only. The equipment and techniques are capable of producing analyses on site to the μg/L level for labile metals. Field analysis avoids issues of sample storage and transport protocols that limit confidence in laboratory measurements of labile elements. Samples were taken as a feedback to immediate analysis resulting in a fine grid map of the geological site. Acid rock drainage emanates from a New Zealand historic mine site, with elevated concentrations of metals. However, ground water and surface water discharging naturally from mineralised rocks in the same area also have elevated levels of metals. This study quantifies natural metalliferous discharges from a single site, and compares this to the overall metal flux from the mine area. Acid (pH 3) metalliferous springs emanate from colluvium and bedrock in a young (months-old) landslide. Labile Cu, Pb, Zn and Cd are the environmentally most significant metals in the studied area. Labile metal concentrations observed in the natural springs are up to 24 μg/L Cu, up to 50 μg/L Pb, up to 5 μg/L Cd and up to 9 mg/L Zn. Labile Cu and Zn concentrations are similar to laboratory-determined total concentrations, whereas labile Pb and Cd concentrations are generally distinctly lower than total Pb and Cd concentrations. Four different spring water compositions occur within metres of each other: acid metalliferous water with high Pb, acid metalliferous water with low Pb, high Cu, Pb, Zn acid water and high pH water with elevated Cu. High metal concentrations in these waters are readily attenuated by adsorption to Fe oxyhydroxides (HFO), especially when rain raises spring water pH at the surface. Copper, Pb and Cd are >99% adsorbed, and Zn >95% adsorbed, during this rainfall dilution. Natural spring waters have potential to contribute up to 10% of the total Zn flux from the catchment, but negligible proportions of Cu, Pb and Cd.     

Bioavailability and mobility of trace metals in phosphogypsum from Aqaba and Eshidiya,Jordan

As, Cd, Cr, Cu, U, and Zn in Aqaba and Eshidiya phosphogypsum showed relative uniformity in particle size presented by coarse (>0.212 mm); medium (0.212–0.053 mm); and fine (<0.053 mm) in the stacks by age of deposition. Jordan phosphogypsum contains low concentrations of As, Cd, Cr, Cu, U, and Zn compared to those reported worldwide. The bioavailability and mobility of trace metals were estimated using aqua regia leaching experiments. Leaching results have shown that around 3% of the As, 1% of the Cd, 5% of the Cr, 9% of the Cu, 4% of the U, and 3% of the Zn are transferred to the surrounding aquatic environment and/or soils. Mobility of trace metals in phosphogypsum was classified into three degrees: elements with high mobility were Cu and U; those with moderate mobility were As and Zn; and those with low mobility were Cd and Cr. It can be concluded that As, Cd, Cr, Cu, U, and Zn were not only uniformly distributed in the stack, but they are not leached from the phosphogypsum stacks in any significant amount, and then they are not easily transferred to the surrounding aquatic environment and/or soils.     

Leaching behaviour of slag and fly ash from laterite nickel ore smelting (Niquelândia,Brazil)

The laterite nickel (Ni) ore smelting operation in Niquelândia (Goiás state, Brazil) produced large amounts of smelting wastes, stockpiled on dumps (slags) and in settling ponds (fly ash). In this study we present data on the chemistry, mineralogy and pH-dependent leaching behaviours of these two waste materials.Bulk chemical analyses indicated that both wastes contained significant amounts of potentially toxic elements (PTEs), with substantially higher concentrations in the case of the fly ash (up to 2.51 wt% Ni, 1870 mg/kg Cr and 488 mg/kg Co). The mineralogical investigations carried out using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and electron microprobe (EPMA) indicated that the slag was mainly composed of silicate glass, olivine and pyroxene. In contrast, the fly ash was composed of Ni-bearing serpentine-like phases (originating from the furnace feed), Ni-bearing glass, olivine, pyroxene and spinel. The pH-dependent leaching behaviour was performed according the EU standard experimental protocol (CEN/TS 14997) in the pH range of 3–12. The leaching was highly pH-dependent for both materials, and the highest releases of PTEs occurred at pH 3. The slag generally exhibited an U-shaped leaching behaviour of the PTEs as a function of pH, and was found to release up to 48.0 mg/kg Ni, 25.6 mg/kg Cr, and 1.42 mg/kg Co. The fly ash was significantly more reactive, and exhibited its highest leaching level of PTEs between pH 3 and 7. The maximum observed release corresponded to 5750 mg/kg Ni, 4.35 mg/kg Cr, and 112 mg/kg Co. The leached Ni concentrations after 24 h of leaching in deionized water exceeded the limit for hazardous waste by more than 100x according to the EU legislation (40 mg/kg Ni). X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structures (EXAFS) spectra indicated that Ni in the fly ash is predominantly bound in a serpentine-like phase, and during the fly ash experimental alteration it was mainly released from the second shell (corresponding to the atomic distances between Ni and Si, Mg, Fe in high-temperature silicates, glass, and partially dissolved serpentine). This study shows that disposal sites for the fly ash can represent a significant source of local pollution, and direct recycling of the fly ash in the smelting technology (as currently adopted at the Barro Alto new smelter and since few years also at the Niquelândia smelter) is the best environment-friendly option for handling of fly ash in the future.     

Ages of sediment-hosted Himalayan Pb–Zn–Cu–Ag polymetallic deposits in the Lanping basin,China: Re–Os geochronology of molybdenite and Sm–Nd dating of calcite

The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt of the Sanjiang Tethyan metallogenic province in China. Over 100 thrust-controlled, sediment-hosted, Himalayan base metal deposits have been discovered in this basin, including the largest sandstone-hosted Pb–Zn deposit in the world (Jinding), and several Cu ± Ag ± Co deposits (Baiyangping, Baiyangchang and Jinman). These deposits, with total reserves of over 16.0 Mt Pb + Zn, 0.6 Mt Cu, and 7000 t Ag, are mainly hosted in Meso-Cenozoic mottled clastic rocks, and strictly controlled by two Cenozoic thrust systems developed in the western and eastern segments of the Lanping basin.To define the metallogenic history of the study area, we dated nine calcite samples associated with copper sulfides from the Jinman Cu deposit by the Sm–Nd method and five molybdenite samples from the Liancheng Cu–Mo deposit by the Re–Os method. The calcite Sm–Nd age for the Jinman deposit (58 ± 5 Ma) and the molybdenite Re–Os age for the Liancheng deposit (48 ± 2 Ma), together with previously published chronological data, demonstrate (1) the Cu–Ag mineralization in the western Lanping basin mainly occurred in three episodes (i.e., ∼56–54, 51–48, and 31–29 Ma), corresponding to the main- and late-collisional stages of the Indo–Asian orogeny; and (2) the Pb–Zn–Ag (±Cu) mineralization in the eastern Lanping basin lacked precise and direct dating, however, the apatite fission track ages of several representative deposits (21 ± 4 Ma to 32 ± 5 Ma) may offer some constraints on the mineralization age.     

Impact of Changes in Redox Conditions on Leaching of Some Elements from MSW Fly Ash

Abstract. Oxidation and reduction processes can influence extent of leaching of elements from solid waste. Three samples of municipal solid waste combustion fly ash were subjected to oxidizing and reducing conditions in order to evaluate leaching of elements in the Milli-Q water and fly ash (liquid to solid ratio, 100) mixtures. Although the oxidizing and reducing conditions were applied for 6 hours only, elements like Cs, Li, Mg, Sb, Tl and V leached more under oxidizing condition than under reducing condition in the case of all three ash samples. Cadmium, Pb and Zn leached more from all samples under reducing condition than under oxidizing condition. Leaching of other elements like Al, Ba, Cr, Cu, Ni and Rb was inconsistent with oxidizing or reducing conditions and varied from sample to sample, suggesting that factors other than redox may be more important in controlling leaching of these elements. Strong acid neutralization capacity of the fly ash samples let the pH vary within a narrow range, and thus severely limited the extent of leaching during the course of the experiment. Lead and Zn were the most sensitive while K and Na were the least sensitive to changes in redox conditions.     

The use of vetiver grass (Vetiveria zizanioides) in the phytoremediation of soils contaminated with heavy metals

Recent research has shown that phytoextraction approaches often require soil amendments, such as the application of EDTA, to increase the bioavailability of heavy metals in soils. However, EDTA and EDTA–heavy metal complexes can be toxic to plants and soil microorganisms and may leach into groundwater, causing further environmental pollution. In the present study, vetiver grass (Vetiveria zizanioides) was studied for its potential use in the phytoremediation of soils contaminated with heavy metals. In the pot experiment, the uptake and transport of Pb by vetiver from Pb-contaminated soils under EDTA application was investigated. The results showed that vetiver had the capacity to tolerate high Pb concentrations in soils. With the application of EDTA, the translocation ratio of Pb from vetiver roots to shoots was significantly increased. On the 14th day after 5.0 mmol EDTA kg⁻¹ of soil application, the shoot Pb concentration reached 42, 160, 243 mg kg⁻¹ DW and the root Pb concentrations were 266, 951, and 2280 mg kg⁻¹ DW in the 500, 2500 and 5000 mg Pb kg⁻¹ soils, respectively. In the short soil leaching column (9.0-cm diameter, 20-cm height) experiment, about 3.7%, 15.6%, 14.3% and 22.2% of the soil Pb, Cu, Zn and Cd were leached from the artificially contaminated soil profile after 5.0 mmol EDTA kg⁻¹ of soil application and nearly 126 mm of rainfall irrigation. In the long soil leaching experiment, soil columns (9.0-cm diameter, 60-cm height) were packed with uncontaminated soils (mimicking the subsoil under contaminated upper layers) and planted with vetiver. Heavy metal leachate from the short column experiment was applied to the surface of the long soil column, the artificial rainwater was percolated, and the final leachate was collected at the bottom of the soil columns. The results showed that soil matrix with planted vetiver, could re-adsorb 98%, 54%, 41%, and 88% of the initially applied Pb, Cu, Zn, and Cd, respectively, which may reduce the risk of heavy metals flowing downwards and entering the groundwater.     

The geochemistry of trace elements in geothermal fluids,Iceland

Trace element geochemistry was studied in geothermal fluids in Iceland. The major and trace element compositions of hot springs, sub-boiling, and two-phase (liquid and vapor) wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth. Aquifer fluid temperatures ranged from 4 to 300 °C, pH values between 4.5 and 9.3, and fluids typically contained total dissolved solids <1000 ppm, except in geothermal areas that have seawater and seawater-meteoric water mixtures. Trace alkali elements Li, Rb and Cs are among the most mobile elements in aquifer fluids, with concentrations in the range of <1 ppb to 3.49 ppm Li, <0.01 to 57 ppb Cs, and <1 ppb to 3.77 ppm Rb. Their chemistry is thought to be dominated by rock leaching and partitioning into Na- and K-containing major alteration minerals. Arsenic, Sb, Mo and W are typically present in concentrations in the range of 1–100 ppb. They are relatively mobile, yet Mo may be limited by molybdenite solubility. The alkaline earth elements Ba and Sr are quite immobile with concentrations in the range of <0.1–10 ppb Ba and <1–100 ppb Sr in the dilute fluids, but up to 5.9 ppm Ba and 8.2 ppm Sr in saline fluids. These elements show a systematic relationship with Ca, possibly due to substitution for Ca in Ca-containing major alteration minerals like calcite, epidote and anhydrite. Incorporation into major Ca-minerals may also be important for Mn. Many metals including Fe, Cr, Ni, Zn, Cu, Co, Pb and Ag have low mobility and concentrations, typically <1 ppb for Ag, Cd, Co, Cr, Cu, Ni, and Pb, <10 ppb for Zn and < 100 ppb for Fe, although for some metals higher concentrations are associated with saline fluids. Based on the metals assessed, saturation is approached with respect to many sulfide minerals and in some cases oxide minerals but Cu, Ni and Pb minerals are slightly but systematically undersaturated, and Ag phases significantly undersaturated. Evaluation of mineral-fluid equilibria for these metals is problematic due to their low concentrations, problems associated with assessing the aqueous species distribution by thermodynamic calculations, and uncertainties concerning the exact minerals possibly involved in such reactions. Reaction path calculations, poor comparison of concentrations measured in the samples collected at the wellhead and published downhole data as well as boiling, cooling and mass precipitation calculations suggest removal of many metals due to changes upon depressurization boiling and conductive cooling of the aquifer fluids as they ascend in wells. These results imply that processes such as mass precipitation upon fluid ascent may be highly important and emphasize the importance of considering mass movement in geothermal systems.     

Geochemical associations for evaluating the availability of potentially harmful elements in urban soils: Lessons learnt from Athens,Greece

The estimation of potentially harmful element (PHE) availability in urban soil is essential for evaluating impending risks for human and ecosystem health. In the present study five single extraction procedures were evaluated based on the analysis of 45 urban top-soil samples from Athens, Greece. The pseudototal (aqua regia), potentially phytoavailable (0.05 M EDTA), mobilizable (0.43 M HAc), bioaccessible (0.4 M glycine) and reactive pools (0.43 M HNO₃) of PHEs were determined. In general, geogenic elements in Athens soil (Ni, Cr, Co, As) are relatively less available than typical tracers of anthropogenic contamination (Pb, Zn, Cu, Cd). Results of principal component analysis (PCA) indicate an association between available fractions of Pb, Cu, Zn, Cd and amorphous Fe oxides, whereas amorphous Mn oxides account for the available concentrations of Mn, Ni and Co. Empirical multiple linear regression models demonstrate that pseudototal concentration is the predominant explanatory factor of variability for the available pools of the anthropogenic elements. Major elemental composition and total organic carbon (TOC) improve the predictions for the geogenic group of elements, although the explained variability remains low. Dilute HNO₃ is a better predictor of Zn, Ni, As and Mn availability, whereas Pb and Cu available fractions are predicted more accurately by the classical aqua regia protocol. This study contributes to the international database on the environmental behavior of PHEs and provides additional knowledge that can be used toward the harmonization of chemical extraction methodology in urban soil.     

The use of water-extractable Cu,Mo, Zn,As, Pb concentrations and automated mineral analysis of flue dust particles as tools for impact studies in topsoils exposed to past emissions of a Cu-smelter

An exploratory study has been conducted to test the utility of automated mineral analysis observations to identify flue dust particles in topsoils exposed for several decades to emissions of a copper smelter. The methods used are readily available in mining countries. To identify the most impacted sites, the Cu, Zn, Pb, Mo and As levels in water and diluted sulphuric acid extractions of four topsoil size fractions (833–495 μm, 246–148 μm; 74–38 μm; <38 μm) were analysed. X-ray diffraction analyses were used to demonstrate the mineralogical degradation of smectite phases when approaching the smelter. Flue dust particles in different states of conservation in topsoils were directly observed by scanning electron microscopy (SEM) aided by energy dispersive detection of X-rays. Qemscan^® scanning of dispersed topsoil preparations (10,000 particles) pinpoints smelter particles by their density; flue dust pearls can be tracked by sorting particles according to their sphericity, clearly identifying them as pyrometallurgical products. When sorting soil particles by mineral groups (e.g. sulphides), an increase in this phase group can be observed when approaching the smelter. SEM resolution limits observations to particles larger than 2–3 μm. Smaller particles can be observed by transmission electron microscopy, although observer experience and the availability of equipment time are essential as is the case for SEM.     

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 (12.9–254 mg kg⁻¹), Cd (1.2–55.1 mg kg⁻¹), Pb (137–6239 mg kg⁻¹) and Zn (516–48,889 mg kg⁻¹). The agricultural soils were also polluted by As (5.5–57.1 mg kg⁻¹), Cd (0.2–8.5 mg kg⁻¹), Pb (22–3451 mg kg⁻¹) and Zn (94–9907 mg kg⁻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 50.7 mg kg⁻¹, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4 mg kg⁻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.     

Effects of acid-sulfate weathering and cyanide-containing gold tailings on the transport and fate of mercury and other metals in Gossan Creek: Murray Brook mine,New Brunswick,Canada

Gossan Creek, a headwater stream in the SE Upsalquitch River watershed in New Brunswick, Canada, contains elevated concentrations of total Hg (Hg_T up to 60 μg/L). Aqueous geochemical investigations of the shallow groundwater at the headwaters of the creek confirm that the source of Hg is a contaminated groundwater plume (neutral pH with Hg and Cl concentrations up to 150 μg/L and 20 mg/L, respectively), originating from the Murray Brook mine tailings, that discharges at the headwaters of the creek. The discharge area of the contaminant plume was partially delineated based on elevated pH and Cl concentrations in the groundwater. The local groundwater outside of the plume contains much lower concentrations of Hg and Cl (<0.1 μg/L and 3.8 mg/L, respectively) and displays the chemical characteristics of an acid-sulfate weathering system, with low pH (4.1–5.5) and elevated concentrations of Cu, Zn, Pb and SO₄ (up to 5400 μg Cu/L, 8700 μg Zn/L, 70 μg Pb/L and 330 mg SO₄/L), derived from oxidation of sulfide minerals in the Murray Brook volcanogenic massive sulfide deposit and surrounding bedrock. The Hg_T mass loads measured at various hydrologic control points along the stream system indicate that 95–99% of the dissolved Hg_T is attenuated in the first 3–4 km from the source. Analyses of creek bed sediments for Au, Ag, Cu, Zn, Pb and Hg indicate that these metals have partitioned strongly to the sediments. Mineralogical investigations of the contaminated sediments using analytical scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), reveal discrete particles (<1–2 μm) of metacinnabar (HgS), mixed Au–Ag–Hg amalgam, Cu sulfide and Ag sulfide.     

Some new data on the genesis of the Linghou Cu–Pb–Zn polymetallic deposit—Based on the study of fluid inclusions and C–H–O–S–Pb isotopes

The Linghou deposit, located near Hangzhou City of Zhejiang Province, eastern China, is a medium-sized polymetallic sulfide deposit associated with granitic intrusion. This deposit is structurally and lithologically controlled and commonly characterized by ore veins or irregular ore lenses. In this deposit, two mineralization events were identified, of which the former produced the Cu–Au–Ag orebodies, while the latter formed Pb–Zn–Cu orebodies. Silicification and calc-silicate (skarn type), phyllic, and carbonate alternation are four principal types of hydrothermal alteration. The early Cu–Au–Ag and late Pb–Zn–Cu mineralizations are characterized by quartz ± sericite + pyrite + chalcopyrite + bornite ± Au–Ag minerals ± magnetite ± molybdenite and calcite + dolomite + sphalerite + pyrite + chalcopyrite + galena, respectively. Calcite clusters and calcite ± quartz vein are formed during the late hydrothermal stage.The NaCl–H₂O–CO₂ system fluid, coexisting with NaCl–H₂O system fluid and showing the similar homogenization temperatures (385 °C and 356 °C, respectively) and different salinities (16.89–21.68 wt.% NaCl eqv. and 7.70–15.53 wt.% NaCl eqv.), suggests that fluid immiscibility occurred during the Cu–Au–Ag mineralization stage and might have given rise to the ore-metal precipitation. The ore-forming fluid of the Pb–Zn–Cu mineralization mainly belongs to the NaCl–H₂O–CO₂ system of high temperature (~ 401 °C) and mid-high salinity (10.79 wt.% NaCl eqv.).Fluids trapped in the quartz-chalcopyrite vein, Cu–Au–Ag ores, Pb–Zn–Cu ores and calcite clusters yielded δ¹⁸O_H2O and δD values varying from 5.54‰ to 13.11‰ and from − 71.8‰ to − 105.1‰, respectively, indicating that magmatic fluids may have played an important role in two mineralization events. The δ¹³C_PDB values of the calcite change from − 2.78‰ to − 4.63‰, indicating that the CO₃^2 − or CO₂ in the ore-forming fluid of the Pb–Zn–Cu mineralization was mainly sourced from the magmatic system, although dissolution of minor marine carbonate may have also occurred during the ore-forming processes. The sulfide minerals have homogeneous lead isotopic compositions with ²⁰⁶Pb/²⁰⁴Pb ranging from 17.958 to 18.587, ²⁰⁷Pb/²⁰⁴Pb ranging from 15.549 to 15.701, and ²⁰⁸Pb/²⁰⁴Pb ranging from 37.976 to 39.052, indicating that metallic elements of the Linghou deposit came from a mixed source involving mantle and crustal components.Based on geological evidence, fluid inclusions, and H–O–C–S–Pb isotopic data, the Linghou polymetallic deposit is interpreted as a high-temperature, skarn-carbonate replacement type. Two types of mineralization are both related to the magmatic–hydrothermal system, with the Cu–Au–Ag mineralization having a close relationship with granodiorite.