Applied Geochemistry (v.64, #C)

Applied Geochemistry special issue on Environmental impacts of mining and smelting by Vojtěch Ettler; Cécile Quantin; Michael Kersten (1).

Natural ferrihydrites (Fh) often contain impurities such as aluminum, especially in acid mine drainage, and these impurities can potentially impact the chemical reactivity of Fh with respect to metal (loid) adsorption. In the present study, we have investigated the influence of aluminum on the sorption properties of ferrihydrite with respect to environmentally relevant aqueous arsenic species, arsenite and arsenate. We have conducted sorption experiments by reacting aqueous As(III) and As(V) with synthetic Al-free and Al-bearing ferrihydrite at pH 6.5. Our results reveal that, when increasing the Al:Fe molar ratio in Fh, the sorption density dramatically decreased for As(III), whereas it increased for As(V). Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy analysis at the As K-edge indicated that the AsIIIO3 pyramid binds to FeO6 octahedra on both Al-free Fh and Al-bearing Fh, by forming bidentate mononuclear edge-sharing (2 E) and bidentate binuclear corner-sharing (2 C) surface complexes characterized by As–Fe distances of 2.9 Å and 3.4 Å, respectively. The decrease in As(III) sorption density with increasing Al:Fe ratio in Fh could thus be explained by a low affinity of the As(OH)3 molecule for Al surface sites compared to Fe ones. In contrast, on the basis of available literature on As(V) adsorption mechanisms, we suggest that, in addition to inner-sphere 2 C arsenate surface complexes, outer-sphere arsenate surface complexes forming hydrogen bonds with both =Al–OH and =Fe–OH surface sites could explain the enhancement of As(V) sorption onto aluminous Fh relative to Al-free Fh, as observed in the present study. The presence of aluminum in Fh may thus enhance the mobility of arsenite with respect to arsenate in Acid Mine Drainage impacted systems, while mixed Al:Fe systems could present an alternative for arsenic removal from impacted waters, provided that As(III) would be oxidized to As(V).Display Omitted
Keywords: Aluminous ferrihydrite; Arsenic; Acid mine drainage; Sorption; EXAFS;

Arsenic and lead mobility: From tailing materials to the aqueous compartment by Alexandra Courtin-Nomade; Thomas Waltzing; Catherine Evrard; Marilyne Soubrand; Jean-François Lenain; Emmanuelle Ducloux; Sonda Ghorbel; Cécile Grosbois; Hubert Bril (10-21).
This study concerns the mineralogy of the tailings of a former Ag–Pb mine (Auzelles district, France) and the contribution of the waste materials to the heavy metal dissemination in the environment. Accumulation of metals in fish flesh was reported and this pollution is attributed to past mining activities. Tailings were studied to establish the major transfer schemes of As and Pb in order to understand their mobility that leads to contamination of a whole ecosystem. Mineralogical investigation, solubility and compliance tests were performed to assess the stability of the metal-bearing phases. Among the various metallic elements measured, As and Pb show the highest bulk concentrations (up to 0.7% and 6.3% respectively) especially for samples presenting near neutral pH values. According to X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDX), Electron Probe Micro-Analysis (EPMA) and micro-Raman spectrometry (μRS), tailings mineralogy still contain primary minerals such as sulfides (e.g., galena, pyrite), phosphates (monazite, apatite) and/or carbonates (e.g., (hydro-)cerussite, dolomite, siderite). Sulfates (e.g., anglesite, lanarkite, plumbojarosite and beudantite) are the main secondary metal-bearing phases with other interesting phases accounting for metals mobility such as Fe and/or Pb and/or Mn oxides (e.g., lepidocrocite, goethite -up to 15 wt% of Pb was measured-, plumboferrite-type phase, mimetite). The lowest Pb solubilities were obtained at pH 8–9 and at a larger range than for As for which the lowest solubilities are reached around pH 6–7. At this minimum solubility pH value, Pb concentrations released still over exceed the National Environmental Quality Standards (NEQS), whatever the samples. The highest solubility is reached at pH 2 for both elements whatever the considered sample. This represents up to 51% of total Pb and up to 46% of total As remobilized and concentrations exceeding the NEQS. As and Pb released mainly depends on the Fe/Mn oxides (e.g., goethite, lepidocrocite) and carbonates (cerussite) which are the less stable phases. Compliance tests also show that Pb concentrations released are higher than the upper limit for hazardous waste landfills. Determination of the mineralogy allows understanding both the solubility and leaching test experiments results, as well as to forecast the impact of the residues on the water quality at a mid-term scale.
Keywords: Tailings; Lead; Arsenic; Mineralogy; Leaching tests;

The Cu hydroxy mineral, atacamite, is commonly associated with saline environments and is generally thought to dissolve rapidly in the presence of fresh water. A Cu contaminated soil from the arid Namaqualand region, South Africa, shows atacamite as the dominant Cu containing mineral. The stability of the Cu phase in this soil was determined through equilibrium and leaching studies using both deionised water (DI) and a concentrated (0.5 M) NaCl solution. Initially a high concentration of exchangeable Cu was released from the soils leached with NaCl. Continued leaching with NaCl resulted in a substantial decrease in Cu release as atacamite equilibria started to control dissolved Cu. This suggests that an initial spike of Cu laden water will leach from the soils at the onset of a large rainfall event. Further additions of water will result in a lower but sustained release of Cu from the soil. The Cu contaminated soils are exposed to acidic sulphate leachate thus the dissolution kinetics of synthetic atacamite in the acidic range (pH 5.5–4.0) was determined in both NaCl and DI solutions. The kinetic data showed that atacamite dissolution rates are significantly higher in DI than in NaCl but the rates converge at pH 4. In comparison to common acid soluble minerals, atacamite displays a moderate dissolution rate (10−9.55–10−7.14 mol m−2 s−1) within the acid range (pH 5.5–4.0). The atacamite dissolution reaction order with respect to pH is 1.3 and 1.6 in DI and NaCl solutions, respectively, suggesting that dissolution rates of atacamite are highly pH dependent in the acid range. The type of acid used to lower the pH had no effect on the reaction kinetics, with HNO3 and H2SO4 resulting in comparable dissolution rates of atacamite at pH 4.5.
Keywords: Paratacamite; Reaction kinetics; Buffels river; Spektakel mine;

Models of geochemical controls on elements of concern (EOCs; e.g., As, Se, Mo, Ni) in U tailings are dominated by ferrihydrite. However, the evolution of aqueous concentrations of Al and Mg through the Key Lake (KL) U mill bulk neutralization process indicates that secondary Al and Mg minerals comprise a large portion of the tailings solids. X-ray diffraction, Al K-edge XAS, and TEM elemental mapping of solid samples collected from a pilot-scale continuous-flow synthetic raffinate neutralization system of the KL mill indicate the secondary Al–Mg minerals present include Mg–Al hydrotalcite, amorphous Al(OH)3, and an amorphous hydrobasaluminite-type phase. The ferrihydrite present contains Al and may be more accurately described as Al–Fe(OH)3. In the final combined tailings sample (pH 10.5) collected from the model experiments using raffinate with Al, Mg, and Fe, solid phase EOCs were associated with Al–Fe(OH)3 and Mg–Al hydrotalcite. In model experiments using raffinate devoid of Fe, aqueous EOC concentrations decreased greatly at pH 4.0 (i.e., where ferrihydrite would precipitate) and largely remained in the solid phase when increased to the terminal pH of 10.5; this suggests Al–Mg minerals can control aqueous concentrations of EOCs in the raffinate in the absence of Fe. Maximum adsorption capacities for individual and mixtures of adsorbates by Mg–Al hydrotalcite were determined. A revised model of the geochemical controls in U mill tailings is presented in which Al and Mg minerals co-exist with Fe minerals to control EOC concentrations.
Keywords: Tailings; Uranium; Aluminum; Magnesium; Arsenic; Nickel;

Assessment of soil metal distribution and environmental impact of mining in Katanga (Democratic Republic of Congo) by Olivier Pourret; Bastien Lange; Jessica Bonhoure; Gilles Colinet; Sophie Decrée; Grégory Mahy; Maxime Séleck; Mylor Shutcha; Michel-Pierre Faucon (43-55).
Metal and metalloid (As, Cd, Co, Cu, Pb and Zn) distribution in soils from the Katanga Copperbelt (Democratic Republic of Congo) is investigated in order to characterize the environmental impacts of mining and smelting activities in that area. The concentrations of Cu, Co, As, Zn, Pb and Cd in soils from mining sites are higher than in non-metalliferous sites and above permissible metal and metalloid concentrations in soils. Moreover, the fractionation and mobility of Co, and Cu in such environment is assessed using the application of both ammonium acetate-EDTA extraction and speciation modeling (WHAM 6). The resulting data set covers wide range of environmental conditions (pH, trace metals concentration, natural soils and soils affected by mining and ore processing). These extractions show that only a small fraction of Cu and Co is mobile, with variation depending on sites: mobility is higher in soils affected by mining and ore processing. The strong affinity of Mn-oxides for Co may explain lower Co mobility in Mn-rich soils. The high Mn and Fe contents of Cu–Co soils from Katanga may actually exert a protective effect against the toxic effects of Co. Finally, Cu–Co speciation modeling of contaminated sites emphasizes that organic matter strongly sorb Cu whereas Co speciation is mostly by Mn content. This type of study leads to a better understanding of metal fractionation and can guide to define different practices of phytoremediation.
Keywords: Metals; Co; Cu; Soils; Rhizopshere; Statistics; Katanga; Guide reference;

This review summarizes over 160 studies focused on soil contamination near non-ferrous metal smelters. The methods of these investigations were examined with an emphasis on the combinations of traditional (geo)chemical approaches with various mineralogical and metal isotope techniques that are particularly helpful for depicting the fate of smelter-derived contamination in the soil. Differences in the distributions and binding of metal(loid)s in smelter-affected soils from temperate and (sub)tropical climatic zones indicate the greater vulnerability of the latter. Prevailing wind direction is a key factor affecting the dispersion of smelter emissions and their subsequent deposition into the soils, with greater importance found especially in arid areas. Whereas the greatest contamination is generally observed in the surface soil layers, downward migration of metal(loid)s in the soil profiles has been documented at numerous sites. Contamination of smelter soils significantly affects both plants and soil organisms, but suitable remediation techniques (such as chemical stabilization of soils by amendments) can be used for reducing the bioavailability of contaminants.Display Omitted
Keywords: Soil; Non-ferrous metal smelting; Pollution; Metal(loid)s;

Contamination of soil and grass in the Tsumeb smelter area, Namibia: Modeling of contaminants dispersion and ground geochemical verification by Bohdan Kříbek; Vladimír Majer; Ilja Knésl; Josef Keder; Benjamin Mapani; Frederick Kamona; Martin Mihaljevič; Vojtěch Ettler; Vít Penížek; Aleš Vaněk; Ondra Sracek (75-91).
The area of the city of Tsumeb in northern Namibia is strongly affected by gaseous emissions and by dust fallout from the local smelter. This is also reflected in increased concentrations of lead and arsenic in blood and urine of the residents. Consequently, modeling of the dispersion of dust and SO2 emissions from the smelter was used in this study to delineate the contaminated area and to assess the health risks. The modeling results were verified by ground-based geochemical survey of soil and grass in the area. The results of modeling revealed that the concentrations of SO2 in the Tsumeb town were relatively low, whereas the highest dust fallout concentrations were found around the Tsumeb smelter. The Tsumeb town residential area was less affected due to favorable landscape morphology between the smelter and the city (the Tsumeb Hills).The results of modeling of dust fallout and geochemical survey coincided very well. Since the anthropogenic contamination was bound only to the surface layer of soil, the local soils were sampled at two depth horizons: topsoil and the deeper soil horizon. This enabled us to distinguish between the anthropogenic contamination of soil surface from natural (geogenic) concentrations of studied metals in the deeper part of the soil profile. Concentrations of metals in grass correlated with the concentration of metals in topsoil.In contrast to a good conformity with the modeling of dust fallout from the smelter and geochemical survey, the results of modeling of SO2 contents in the air, and total sulfur content in soils were different. Differences can be explained by additional sources of contamination, as for example a sulfate-rich dust fallout from local tailings ponds and slag dumps that were not considered in the SO2 dispersion model.The results of the present investigation can be used by the mining companies in the management of air quality, assessment of the efficacy of applied remediation measures, and in reducing the impact of dust fallout on the local ecosystem. The Municipal Administration may use these results to plan further development of the city of Tsumeb, especially in terms of further expansion of housing construction.
Keywords: Metals; Contamination; Soil; Grass; Dust dispersion modeling; Smelter;

Bacterially-mediated weathering of crystalline and amorphous Cu-slags by Anna Potysz; Malgorzata Grybos; Jakub Kierczak; Gilles Guibaud; Piet N.L. Lens; Eric D. van Hullebusch (92-106).
Two types of Cu-slags (CS: crystalline massive slag and GS: granulated amorphous slag) exhibiting a different chemical and mineral phase composition were compared with respect to their susceptibility to bacterial weathering using Pseudomonas aeruginosa (n° CIP 105094). Abiotic conditions e.g. sterile growth medium and ultrapure water were used for comparison. The experiments were extended up to 112 days with a systematic liquid phase renewal every 14 days. The results revealed significant release of elements in the bacterially mediated weathering experiments. Concentrations of elements (Si, Fe, Cu, Zn and Pb) in the biotic solutions were increased at least by 20% up to 99% compared to abiotic ones. From 3 to 77% of the leached elements were associated to the fraction >0.22 μm. Scanning electron microscope observations demonstrated greater weathering of mineral phases in biotic experiments than in abiotic ones which is in accordance with the solution chemistry exhibiting higher concentrations of elements leached in biotic set-ups. In the case of CS, glass and sulfides weathering was yet observed in abiotic experiment, whereas partial dissolution of fayalite (Fe2SiO4) was solely affected by the presence of bacteria. GS having a higher bulk content of metallic elements was found to be more stable than sulfide-bearing CS, while its (GS) glass matrix was found to weather easier under biotic conditions.
Keywords: Cu-slags; (Bio)weathering; Pseudomonas aeruginosa; Leaching (Si, Fe, Cu, Zn, Pb);

Natural weathering of slags from primary Pb–Zn smelting as evidenced by Raman microspectroscopy by S. Sobanska; D. Deneele; J. Barbillat; B. Ledésert (107-117).
Lead (Pb) and zinc (Zn) smelters produce high amount of granulated slags which are currently stored on unconfined slag heaps and exposed to weathering. The environmental risk related to slags disposals can be estimated through the results of a variety of characterization methods coupled with laboratory leaching experiments and in situ monitoring. The present study is focused on the Raman characterization and distribution at a microscopic scale of secondary products resulting to the alteration of glassy slags exposed to natural weathering for at least ten years. The slag alteration is characterized by the formation of a crack network around iron sulfide inclusions and Pb droplets embedded in the glassy matrix. The Raman images clearly point out the gradually weathering processes. The dissolution of the FeS species lead to the formation of Fe (oxy-hydr)oxide phases. The successive layer formation highlights a probable local pH/Eh changes. The fluids-containing sulfates issued from the alteration of sulfide species are conveyed in the crack network inducing a local alteration of the crack edges together with the formation of (Al,Fe)-hydroxide phases. The fluids-containing sulfates when in contact with Pb droplets induce a progressive dissolution of the droplets from the edge to the core to form Pb sulfate species (mainly basic lead sulfates) and Pb oxides in complex mixture. In a last step, carbonation occurs with local increasing pH due to the presence of CO2 from air or HCO 3 − / CO 3 2 − in fluids originating from glassy matrix alteration.Display Omitted
Keywords: Slag wastes; Alteration processes; Raman imaging;

Leaching behaviour of slag and fly ash from laterite nickel ore smelting (Niquelândia, Brazil) by Vojtěch Ettler; Jindřich Kvapil; Ondřej Šebek; Zdenek Johan; Martin Mihaljevič; Gildas Ratié; Jérémie Garnier; Cécile Quantin (118-127).
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.Display Omitted
Keywords: Laterite ore nickel smelting; Slag; Fly ash; Mineralogy; Leaching; Brazil;

Application of Zn isotopes in environmental impact assessment of Zn–Pb metallurgical industries: A mini review by Nang-Htay Yin; Yann Sivry; Marc F. Benedetti; Piet N.L. Lens; Eric D. van Hullebusch (128-135).
Zn and Pb smelters are the major contributors to Zn and Pb emissions among all anthropogenic sources, thus, it is essential to understand Zn isotopic variations within the context of metallurgical industries, as well as its fractionation in different environments impacted by smelting activities. This mini review outlines the current state of knowledge on Zn isotopic fractionation during the high-temperature roasting process in Zn and Pb refineries; δ66Zn values variations in air emissions, slags and effluents from the smelters in comparison to the geogenic Zn isotopic signature of ores formation and weathering. In order to assess the environmental impact of these smelters, the available and measured δ66Zn values are compiled for smelter impacted natural water bodies (groundwater, stream and river water), sediments (lake and reservoir) and soils (peat bog soil, inland soil). Finally, the discussion is extended to the fractionation induced during numerous physicochemical reactions and transformations, i.e. adsorption, precipitation as well as both inorganic and organic surface complexation.Display Omitted
Keywords: Zn isotopes; Fractionation; Pb–Zn smelters; Metallurgical slags; Contamination sources;

Nickel isotope fractionation during laterite Ni ore smelting and refining: Implications for tracing the sources of Ni in smelter-affected soils by G. Ratié; C. Quantin; D. Jouvin; D. Calmels; V. Ettler; Y. Sivry; L. Cruz Vieira; E. Ponzevera; J. Garnier (136-145).
Nickel isotope ratios were measured in ores, fly ash, slags and FeNi samples from two metallurgical plants located in the Goiás State, Brazil (Barro Alto, Niquelândia). This allowed investigating the mass-dependent fractionation of Ni isotopes during the Ni-laterite ore smelting and refining. Feeding material exhibits a large range of δ60Ni values (from 0.02 ± 0.10‰ to 0.20 ± 0.05‰, n = 7), explained by the diversity of Ni-bearing phases, and the average of δ60Nifeeding materials was found equal to 0.08 ± 0.08‰ (2SD, n = 7). Both δ60Ni values of fly ash (δ60Ni = 0.07 ± 0.07‰, n = 10) and final FeNi produced (0.05 ± 0.02‰, n = 2) were not significantly different from the feeding materials ones. These values are consistent with the very high production yield of the factories. However, smelting slags present the heaviest δ60Ni values of all the smelter samples, with δ60Ni ranging from 0.11 ± 0.05‰ to 0.27 ± 0.05‰ (n = 8). Soils were also collected near and far from the Niquelândia metallurgical plant, to evaluate the potential of Ni isotopes for tracing the natural vs anthropogenic Ni in soils. The Ni isotopic composition of the non-impacted topsoils developed on ultramafic rocks ranges from −0.26 ± 0.09‰ to −0.04 ± 0.05‰ (n = 20). On the contrary, the Ni isotopic composition of the non-ultramafic topsoils, collected close to the plant, exhibit a large variation of δ60Ni, ranging from −0.19 ± 0.13‰ up to 0.10 ± 0.05‰ (n = 4). This slight but significant enrichment in heavy isotopes highlights the potential impact of smelting activity in the surrounding area, as well as the potential of Ni isotopes for discerning anthropogenic samples (heavier δ60Ni values) from natural ones (lighter δ60Ni values). However, given the global range of published δ60Ni values (from −1.03 to 2.5‰) and more particularly those associated to natural weathering of ultramafic rocks (from −0.61 to 0.32‰), the use of Ni isotopes for tracing environmental contamination from smelters will remain challenging.
Keywords: Nickel; Isotope; Smelting; Refining; Source; Soil;

Study of Ni exchangeable pool speciation in ultramafic and mining environments with isotopic exchange kinetic data and models by I. Zelano; Y. Sivry; C. Quantin; A. Gélabert; M. Tharaud; S. Nowak; J. Garnier; M. Malandrino; M.F. Benedetti (146-156).
Soils and ore samples influenced by mining and metallurgical activity were collected in ultramafic soils (UM) complexes of Barro Alto and Niquelândia, in order to determine the contribution of each Ni bearing phases to the total exchangeable pool of Ni, and to point out if this pool was affected by anthropic activities. For this purpose, the IEK-model previously developed by the group (Zelano et al., submitted) was applied, on the basis of IEK experiments performed on pure typical Ni scavengers (serpentines, chlorite, smectite and iron oxydes) from ultramafic systems. For each typical scavenger, this model describes the percentage of Ni associated to exchangeable pool(s) as well as their corresponding kinetic constant(s) of exchange. The mineralogical composition of soil and ore samples and Ni solid speciation were first determined, and the IEK-model was applied on these bases. In almost all samples, an important contribution of serpentine to Ni exchangeable pool was highlighted, ranging between 10% and 45%. The important amount of organic matter (OM) in one of the studied soil samples, allowed to extrapolate generic OM E Ni and k parameters, which were introduced in the IEK-model to improve its predictive capability. Obtained results provided evidences of how even a small content (3 wt%) of organic carbon (OC), can represent an important contribution of OM to the total ENi pool (60%). In the investigated ore samples, up to the 60% of E Ni was attribute to smectite, responsible for fast E Ni pool kinetic evolution. In addition, the model highlighted the role of the Fine Black Ash (FBA), by-products of the pyrometallurgical activity, detected into a soil sample, that is responsible for the 15% of E Ni. This approach allowed to determine, for the first time, the relative contribution of each Ni bearing phase to the total exchangeable pool, in terms of concentration and kinetics.Display Omitted
Keywords: Ultramafic soils; Isotopic exchange kinetics; Solid speciation; Mine waste; Nickel-availability; Modeling;

Exploring Cd, Cu, Pb, and Zn dynamic speciation in mining and smelting-contaminated soils with stable isotopic exchange kinetics by Zong-ling Ren; Yann Sivry; Jun Dai; Mickaël Tharaud; Laure Cordier; Isabella Zelano; Marc F. Benedetti (157-163).
The exchange kinetics of Cd, Cu, Pb, and Zn in seven mining and smelting-contaminated soils and the other two anthropogenically contaminated soils was investigated by using multi-elementary stable isotopic exchange kinetic (SIEK) method, and the experimental results were successfully interpreted by modelling using a sum of pseudo first order kinetics equations. SIEK results show that in the studied soils the isotopic exchange of Cd is a relatively fast process, and the exchange almost reaches an apparent plateau after 3-d equilibration; whereas for Cu, Pb, and Zn, the exchange is more sluggish, suggesting that it is important to understand the time-dependent metal mobility for risk assessment and management of contaminated soils. In most of the soils, the total isotopically exchangeable pool is divided, for all the metals, into two distinct pools: a fast exchangeable pool (E 1) with a kinetic rate constant k 1 having values around 1 min−1 and a much slower exchangeable pool (E 2) with k 2 ranging from 0.0001 min−1 to 0.001 min−1. The distribution of the two exchangeable pools varies significantly among metals. The amount of isotopically exchangeable Cd related to the fast pool is dominant, accounting for on average 60% of total isotopically exchangeable pool in the soils; whereas this pool is smaller for Cu, Zn, and Pb. The sequence of average k 1 values is Cd > Pb ≈ Zn > Cu, consistent with the reported sequence of stability constants of metal-humic substances (HS) complexes while the average k 2 values follow the order: Cd > Pb > Cu > Zn, probably controlled by the slow desorption of metal ions associated with soil organic matter (SOM) fraction. Our results imply that further study on the exchange kinetics of metals on each individual sorption surface in soils, especially SOM, is critical to help understanding the overall exchange kinetics of heavy metals in whole soils.

Mitrovica, northern Kosovo, is the site of some of the highest Pb concentrations reported in human populations; exemplified by Pb concentrations in scalp hair of up to 130 μg g−1 and widely-publicized of Pb-related ill-health and mortality amongst internally displaced populations. High human Pb burdens are accompanied by elevated concentrations of potentially harmful elements (PHEs) in soils and house dust within the city, which has a long history of mining and metallurgy. In this study enrichment-levels for PHEs in soils are quantified and compared to environmental quality guidelines and a statistically-derived estimation of background concentration. In addition, Pb isotopes (207Pb/206Pb, 208Pb/206Pb) are used to characterise the isotopic signatures of potential point sources of Pb and a mixing model employed to quantify the contribution of sources to Pb present in soils, house dust, and the scalp hair of children and young people. Pb isotopic evidence suggests that Pb in surface soils and house-dust is predominantly sourced from historical deposition of Pb-containing aerosols from metal smelting, with lower contributions from wind-blown dispersal of metalliferous waste. Pb present in scalp hair is interpreted as the result of non-occupational exposure and the ingestion and/or inhalation of Pb-enriched surface soil and house dust. This study represents one of the very few instances where this type of geochemical tracing technique has been successfully applied to definitively identify the source of Pb present within biological samples. The results of this study are of particular relevance to environmental management and highlight the human health risk posed by the legacy of now inactive mining and metallurgy in addition to the challenge posed in mitigating the risk posed by diffuse soil pollution.
Keywords: Lead isotopes; Mixing model; Metals; Soil; Scalp hair;