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.     

Stability and leaching of cobalt smelter fly ash

The leaching behaviour of fly ash from a Co smelter situated in the Zambian Copperbelt was studied as a function of pH (5–12) using the pH-static leaching test (CEN/TS 14997). Various experimental time intervals (48 h and 168 h) were evaluated. The leaching results were combined with the ORCHESTRA modelling framework and a detailed mineralogical investigation was performed on the original FA and leached solid residues. The largest amounts of Co, Cu, Pb and Zn were leached at pH 5, generally with the lowest concentrations between pH 9 and 11 and slightly increased concentrations at pH 12. For most elements, the released concentrations were very similar after 48 h and 168 h, indicating near-equilibrium conditions in the system. Calcite, clinopyroxenes, quartz and amorphous phases predominated in the fly ash. Various metallic sulfides, alloys and the presence of Cu, Co and Zn in silicates and glass were detected using SEM/EDS and/or TEM/EDS. The leaching of metals was mainly attributed to the dissolution of metallic particles. Partial dissolution of silicate and glass fractions was assumed to significantly influence the release of Ca, Mg, Fe, K, Al and Si as well as Cu, Co and Zn. The formation of illite was suggested by the ORCHESTRA modelling to be one of the main solubility-controlling phases for major elements, whereas Co and Zn were controlled by CoO and zincite, respectively. Sorption of metals on hydrous ferric oxides was assumed to be an important attenuation mechanism, especially for the release of Pb and Cu. However, there is a high risk of Co, Cu, Pb and Zn mobility in the acidic soils around the smelter facility. Therefore, potential local options for “stabilisation” of the fly ash were evaluated on the basis of the modelling results using the PHREEQC code.     

Distribution and speciation of metals,phosphorus, sulfate and organic material in brackish estuary water affected by acid sulfate soils

Dissolved (<1 kDa) and colloidal (1 kDa-0.45 μm) size fractions of sulfate, organic carbon (OC), phosphate and 17 metals/metalloids were investigated in the acidic Vörå River and its estuary in Western Finland. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these waters. The sampling was carried out during high-water flow in autumn and in spring when the abundantly occurring acid sulfate (AS) soils in the catchment area are extensively flushed. Based on the high concentrations of sulfate, acidity and several metals, it is clear that the Vörå River and its estuary is strongly affected by AS soils. The high dissolved form of metals limits also the existence of fish and other organisms in this estuary, and certainly also in other similar shallow brackish estuaries elsewhere in the Gulf of Bothnia. However, generally already <20% saline sea water reduces the concentration for OC and several elements (Al, Cu, Cr, Fe, Pb, PO₄ and U) by half and c. 20–30% saline sea water is needed to halve concentrations of Cd, Co, Mn, Ni and Zn. Consequently, these elements as well as organic matters were rapidly precipitated in the estuary, even after mixing with fairly small amounts of the alkaline brackish sea water. Aluminium, Cu, Fe and U most likely precipitate together with organic matter closest to the river mouth. Manganese is relatively persistent in solution and, thus, precipitates further down the estuary as Mn oxides, which concomitantly capture Ba, Cd, Co, Cu, Ni and Zn. In the inner estuary, the high contents of Al is as important than Fe in removing PO₄ and, thus, also reducing the risk of algae blooms in near coastal areas influenced by AS soils in the Gulf of Bothnia. Moreover, the dispersion of metals far out in the estuary is dependent on hydrological conditions, i.e. with high flows the plume of metal-rich water will spread further out in the estuary. Furthermore, the extensive drainage of the catchment and subsequent artificial enlargement of the river channel during recent decades has not only enabled oxidation of sulfidic sediments, but strongly increased flow peaks that reach further out in the estuary.     

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.     

Geochemical challenges of diverse regolith-covered terrains for mineral exploration in China

In recent years mineral exploration has concentrated on concealed deposits in regolith-covered terrains. In China, the regolith-covered landscapes mainly include desert windblown sand basins, desert peneplains, semi-arid grassland, loess plateaus, forestry land, alluvial plains and laterite terrains. These diverse regolith-covered areas represent geochemical challenges for mineral exploration in China. This paper provides an overview of recent progress on mechanisms of metal dispersion from the buried ore deposits through the transported cover to the surface and penetrating geochemical methods to detect the anomalies. Case studies show that, in arid and semi-arid desert sand-covered terrains, sampling of fine-fraction (− 120 mesh, < 0.125 mm) clay-rich horizon soil is cost-effective for regional geochemical surveys for sandstone-type uranium, gold, and base metal deposits. Fine-fraction sampling, selective-leaching and overburden drilling geochemical methods can effectively indicate the 210 gold ore body at Jinwozi goldfield. In alluvium-covered terrains, fine-grained soil sampling (− 200 mesh, < 0.074 mm) combined with selective leaching geochemistry shows clear ring-shaped anomalies of Cu and Ni over the Zhouan concealed Cu–Ni deposit. In laterite-covered terrains, the anomalies determined by the fine-fraction soils and selective leaching of absorbed metals on coatings of Fe–Mn oxides coincide well with the concealed deposit over the Yueyang ore deposits at the Zijin Au–Cu–Ag field. Nanoparticles of hexagonal crystals mainly native copper, gold and alloys of Cu–Fe, Cu–Fe–Mn, Cu–Ti, and Cu–Au were observed in gases, soils and ores using a transmission electron microscope (TEM). The findings imply that nanoparticles of gold and copper may migrate through the transported cover to the surface. Uranium is converted to uranyl ions [UO₂^2 +] under oxidizing conditions when migrating from ore bodies to the surface. The uranyl ions are absorbed on clay minerals, because clay layers have a net negative charge, which needs to be balanced by interlayer cations. Nanoparticles of Au and Cu and ion complexes of U are more readily absorbed onto fine fractions of soils containing clays, colloids, oxides and organic matters. Thus, fine-grained soils enriched with clays, oxides and colloids are useful media for regional geochemical surveys in regolith-covered terrains and in sedimentary basins. Fine-fraction soil sampling combined with selective leaching geochemistry is effective for finding concealed ore bodies in detailed surveys. Penetrating geochemistry at surface sampling provides cost-effective mineral exploration methods for delineation of regional and local targets in transported cover terrains.     

Effect of low-molecular-weight organic acids on the distribution of mobilized Al between soil solution and solid phase

Low-molecular-weight (LMW) organic acids occur widely in soils. Results in pure mineral systems and podzols suggest that LMW organic acids can promote the dissolution of Al from kaolinite, Al oxides and soils, but limited information is available concerning the role of these organic acids on Al mobilization in variable charge soils as yet. This paper deals with the effect of LMW organic acids on Al mobilization and mobilized Al distributed between the solution phase and exchangeable sites in two acidic variable charge soils. The results indicated that LMW organic acids accelerated Al mobilization through proton- and ligand- promoted reactions. The ability of different organic acids to mobilize Al followed the order: citric acid > oxalic acid > malonic acid > malic acid > tartaric acid > salicylic acid > lactic acid > maleic acid. This order was in general agreement with the magnitude of the stability constants of Al–organic acid complexes. The ratio of soluble Al to exchangeable Al also increased as the stability constants increased. These results showed that the organic acids with strong Al-complexation capacity were most effective in Al mobilization, whereas the weak organic acids promoted the retention of mobilized Al by the soil exchangeable sites. Increase in both organic acid concentration and solution pH promoted Al mobilization and also increased the ratio of soluble Al to exchangeable Al due to the increase in the concentration of the effective organic ligands, especially in the strong organic acid systems. These findings may have their practical significance for establishing more effective amelioration procedures for variable charge soils with increased acidity and higher mobility of Al.     

Influence of a CO2 long term exposure on the mobilisation and speciation of metals in soils

This study investigates the potential risks associated with high levels and long term exposure of carbon dioxide (CO₂) on the mobility and speciation of exchangeable metals in soils. CO₂ incubation batch experiments at high pressure and temperature coupled with geochemical modelling were carried out to elucidate the behaviour and mobilisation of metals and the response of soil chemical parameters as a result of long term CO₂ exposure. A t-Student analysis was performed to ascertain whether differences in the mean concentration of exchangeable metals in soils before and after CO₂-incubations are attributable to increase of metal molibilisation because of the long term CO₂ exposure. The t-Student revealed the CO₂ long term incubation was statistically significant (p < 0.05) for the exchangeable concentration of Ni, Zn, and Pb. The CO₂-soil incubation induces the acidification of the pore water of soils via CO₂ hydrolysis and as a consequence, it increases the exchangeable concentration of Ni, Zn, and Pb in the soils. As, Al, Cr, Cu, and Fe show a different mobilisation pattern depending on the moisture content in soils. Al³⁺, Fe²⁺, Cr³⁺, and Cu²⁺ as free cations, As as HAsO₂, Pb²⁺and PbHCO₃⁻, Zn²⁺ and ZnHCO₃⁻, are predicted to be the predominant aqueous complexes in the pore water of the incubated soils.     

Spectroscopic investigation on the chemical forms of Cu during the synthesis of zeolite X at low temperature

The direct synthesis of zeolites in polluted soils has proved to be a promising process for the stabilization of metals inside these minerals. Nevertheless, more detailed information about this process is still needed in order to better foresee the fate of metals in treated soils. In this work, zeolite X has been synthesized under alkaline conditions in an aqueous solution containing 2500 mg kg⁻¹ of Cu, starting from Na silicate and Al hydroxide at 60 °C. Aluminium, Si and Cu concentrations in the aqueous phase, during zeolite synthesis, were measured over a period of 160 h. The solid products have been characterized over time by XRD, SEM-EDX, ESR, FT-IR, and synchrotron radiation X-ray microbeam absorption near edge structure (μ-XANES) and extended X-ray absorption fine structure (μ-EXAFS) spectroscopy. It appears that the marked reduction of Cu concentration in solution is not only due to a simple precipitation effect, but also to processes connected with the formation of zeolite X which could entrap, inside its porous structure, nano- or micro-occlusions of precipitated Cu hydroxides and/or oxides. In addition, EXAFS observations strengthen the hypothesis of the presence of different Cu phases even at a short-range molecular level and suggest that some of these occlusions could be even bound to the zeolite framework. The results suggest that zeolite formation could be used to reduce the availability of metals in polluted soils.     

Net alkalinity and net acidity 2: Practical considerations

The pH, alkalinity, and acidity of mine drainage and associated waters can be misinterpreted because of the chemical instability of samples and possible misunderstandings of standard analytical method results. Synthetic and field samples of mine drainage having various initial pH values and concentrations of dissolved metals and alkalinity were titrated by several methods, and the results were compared to alkalinity and acidity calculated based on dissolved solutes. The pH, alkalinity, and acidity were compared between fresh, unoxidized and aged, oxidized samples.Data for Pennsylvania coal mine drainage indicates that the pH of fresh samples was predominantly acidic (pH 2.5–4) or near neutral (pH 6–7); ≈ 25% of the samples had pH values between 5 and 6. Following oxidation, no samples had pH values between 5 and 6.The Standard Method Alkalinity titration is constrained to yield values >0. Most calculated and measured alkalinities for samples with positive alkalinities were in close agreement. However, for low-pH samples, the calculated alkalinity can be negative due to negative contributions by dissolved metals that may oxidize and hydrolyze.The Standard Method hot peroxide treatment titration for acidity determination (Hot Acidity) accurately indicates the potential for pH to decrease to acidic values after complete degassing of CO₂ and oxidation of Fe and Mn, and it indicates either the excess alkalinity or that required for neutralization of the sample. The Hot Acidity directly measures net acidity (= −net alkalinity). Samples that had near-neutral pH after oxidation had negative Hot Acidity; samples that had pH < 6.3 after oxidation had positive Hot Acidity. Samples with similar pH values before oxidation had dissimilar Hot Acidities due to variations in their alkalinities and dissolved Fe, Mn, and Al concentrations. Hot Acidity was approximately equal to net acidity calculated based on initial pH and dissolved concentrations of Fe, Mn, and Al minus the initial alkalinity. Acidity calculated from the pH and dissolved metals concentrations, assuming equivalents of 2 per mole of Fe and Mn and 3 per mole of Al, was equivalent to that calculated based on complete aqueous speciation of Fe^II/Fe^III. Despite changes in the pH, alkalinity, and metals concentrations, the Hot Acidities were comparable for fresh and most aged samples.A meaningful “net” acidity can be determined from a measured Hot Acidity or by calculation from the pH, alkalinity, and dissolved metals concentrations. The use of net alkalinity = (Alkalinity_measured − Hot Acidity_measured) to design mine drainage treatment can lead to systems with insufficient Alkalinity to neutralize metal and H⁺ acidity and is not recommended. The use of net alkalinity = −Hot Acidity titration is recommended for the planning of mine drainage treatment. The use of net alkalinity = (Alkalinity_measured − Acidity_calculated) is recommended with some cautions.     

Trace metal speciation in sea and pore water of the Gotland Deep,Baltic Sea, 1994

Studies on the speciation (particulate, colloidal, anionic and cationic forms) of trace metals (Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Zn) in the water column and in pore waters of the Gotland Deep following the 1993/94 salt-water inflows showed dramatic changes in the total “dissolved” metal concentrations and in the ratios between different metal species in the freshly re-oxygenated waters below 125 m. Changes in concentrations were greatest for those metals for which the solubility differs with the redox state (Fe, Mn, Co) but were also noted for those metals which form insoluble sulphides (Cd, Pb, Cu, Zn) and/or stable complexes with natural ligands (Cu). Pore water data from segmented surface muds (0–200 mm) indicated that significant redox and related metal speciation changes took place in the surface sediments only a few weeks after the inflow of the oxygenated sea water into the Gotland Deep.     

Contaminant removal from acidic mine pit water via in situ hydrotalcite formation

Remediation of 56 ML of acidic, contaminant-laden Baal Gammon mine pit water was undertaken using in situ hydrotalcite formation. The pit water composition was modified via the addition of MgCl₂·6H₂O to form a 2.5:1 M²⁺:M³⁺ metal ion ratio followed by the addition of NaOH to increase the pH 10 to induce spontaneous hydrotalcite precipitation. As a result of the in situ hydrotalcite precipitation a broad spectrum of elements of environmental concern including Al, Cd, Co, Cr, Cu, Fe, In, Mn, Mo, Ni, V and Zn were removed from solution. Significantly, an ore grade hydrotalcite precipitate containing Cu (8.0 ± 1.0%) and Zn (3.9 ± 0.5%) was produced directly from the mine pit water column allowing for potential recovery of valuable metals to offset remediation costs. The final water quality produced after in situ remediation was of a simple Na–Cl–SO₄ type.     

Hydrochemistry,mineralogy and sulfur isotope geochemistry of acid mine drainage at the Mt. Morgan mine environment,Queensland, Australia

Mineralogical, hydrochemical and S isotope data were used to constrain hydrogeochemical processes that produce acid mine drainage from sulfidic waste at the historic Mount Morgan Au–Cu mine, and the factors controlling the concentration of SO₄ and environmentally hazardous metals in the nearby Dee River in Queensland, Australia. Some highly contaminated acid waters, with metal contents up to hundreds of orders of magnitude greater than the Australia–New Zealand environmental standards, by-pass the water management system at the site and drain into the adjacent Dee River.Mine drainage precipitates at Mt. Morgan were classified into 4 major groups and were identified as hydrous sulfates and hydroxides of Fe and Al with various contents of other metals. These minerals contain adsorbed or mineralogically bound metals that are released into the water system after rainfall events. Sulfate in open pit water and collection sumps generally has a narrow range of S isotope compositions (δ³⁴S = 1.8–3.7‰) that is comparable to the orebody sulfides and makes S isotopes useful for tracing SO₄ back to its source. The higher δ³⁴S values for No. 2 Mill Diesel sump may be attributed to a difference in the source. Dissolved SO₄ in the river above the mine influence and 20 km downstream show distinctive heavier isotope compositions (δ³⁴S = 5.4–6.8‰). The Dee River downstream of the mine is enriched in ³⁴S (δ³⁴S = 2.8–5.4‰) compared with mine drainage possibly as a result of bacterial SO₄ reduction in the weir pools, and in the water bodies within the river channel. The SO₄ and metals attenuate downstream by a combination of dilution with the receiving waters, SO₄ reduction, and the precipitation of Fe and Al sulfates and hydroxides. It is suggested here that in subtropical Queensland, with distinct wet and dry seasons, temporary reducing environments in the river play an important role in S isotope systematics.     

Assessment of trace metal and rare earth elements contamination in rivers around abandoned and active mine areas. The case of Lubumbashi River and Tshamilemba Canal,Katanga, Democratic Republic of the Congo

Active and abandoned mine activities constitute the sources of deterioration of water and soil quality in many parts of the world, particularly in the African Copperbelt regions. The accumulation in soils and the release of toxic substances into the aquatic ecosystem can lead to water resources pollution and may place aquatic organisms and human health at risk. In this study, the impact of past mining activity (i.e., abandoned mine) on aquatic ecosystems has been studied using ICP-MS analysis for trace metals and Rare Earth Elements (REE) in sediment samples from Lubumbashi River (RL) and Tshamilemba Canal (CT), Katanga, Democratic Republic of the Congo (DRC). Soil samples from surrounding CT were collected to evaluate trace metal and REE concentrations and their spatial distribution. The extent of trace metal contamination compared to the background area was assessed by Enrichment Factor (EF) and Geoaccumulation Index (I_geo). Additionally, the trace metal concentrations probable effect levels (PELs) for their potential environmental impact was achieved by comparing the trace metal concentrations in the sediment/soil samples with the Sediment Quality Guidelines (SQGs). Spearman's Rank-order correlation was used to identify the source and origin of contaminants. The results highlighted high concentrations of trace metals in surface sediments of CT reaching the values of 40152, 15586, 610, 10322, 60704 and 15152 mg kg⁻¹ for Cu, Co, Zn, Pb, Fe and Mn, respectively. In the RL, the concentrations reached the values of 24093, 2046, 5463, 3340, 68290 and 769 mg kg⁻¹ for Cu, Co, Zn, Pb, Fe and Mn, respectively. The ΣREE varied from 66 to 218 and 142–331 mg kg⁻¹ for CT and RL, respectively. The soil samples are characterized by variable levels of trace metals. The EF analysis showed “extremely severe enrichment” for Cu and Co. However, no enrichment was observed for REE. Except for Mo, Th, U, Eu, Mo, Ho and Tm for which Igeo is classified as “moderately polluted and/or unpolluted”, all elements in different sites are classified in the class 6, “extremely polluted”. The trace metal concentrations in all sampling sites largely exceeded the SQGs and the PELs for the Protection of Aquatic Life recommendation. Cu and Co had positive correlation coefficient values (r = 0.741, P < 0.05, n = 14). This research presents useful tools for the evaluation of water contamination in abandoned and active mining areas.     

Colloidal and truly dissolved metal(oid) fractionation in sediment pore waters using tangential flow filtration

The partitioning of trace metal(oid)s between colloidal and “truly” dissolved fractions in sediment pore waters is often overlooked due to the analytical challenge; indeed, only small volumes are available and filtration membranes are rapidly clogged. Moreover, metal(oid)s are subject to co-precipitate with Fe. In this study, tangential flow filtration (TFF) was assessed for the fractionation of Fe, Mn, Cu, As, Co, Ni, Zn and Cd in sediment pore waters with a 5 kDa cut-off size membrane. Five natural sediments were collected and used for different tests. Results on blank samples showed that this technique was appropriate for Fe, Mn, Co, Zn, As and Cd. Although the applied concentration factors (CF) were low (<7.4) due to the small available volume of pore waters (50 mL), it was shown that colloidal concentrations obtained from the TFF procedure were similar whatever the applied concentration factor. The mass balance approach showed satisfying results (100 ± 25%) for Mn, Co, Zn and As. Mass balances were higher than 130% and highly variable for Cd, Ni and Cu. For Fe, mass balance was reproducible but low (71 ± 10%), probably due to sorption of positively charged Fe oxides on the membrane. Applying this method to five contrasting metal(oid)-contaminated sediments, it was shown that Mn, As, Co and Fe were mainly present in the “truly” dissolved phase (<5 kDa). This technique is a necessary step to assess sediment toxicity and bioavailability of metal(oid)s and could be of great interest for emergent pollutants such as nanometals.     

Fe(III) mobilisation by carbonate in low temperature environments: Study of the solubility of ferrihydrite in carbonate media and the formation of Fe(III) carbonate complexes

The linkage between the iron and the carbon cycles is of paramount importance to understand and quantify the effect of increased CO₂ concentrations in natural waters on the mobility of iron and associated trace elements. In this context, we have quantified the thermodynamic stability of mixed Fe(III) hydroxo-carbonate complexes and their effect on the solubility of Fe(III) oxihydroxides. We present the results of carefully performed solubility measurements of 2-line ferrihydrite in the slightly acidic to neutral–alkaline pH ranges (3.8–8.7) under constant pCO₂ varying between (0.982–98.154 kPa) at 25 °C.The outcome of the work indicates the predominance of two Fe(III) hydroxo carbonate complexes FeOHCO₃ and Fe(CO₃)₃³⁻, with formation constants log^*β°_1,1,1 = 10.76 ± 0.38 and log β°_1,0,3 = 24.24 ± 0.42, respectively.The solubility constant for the ferrihydrite used in this study was determined in acid conditions (pH: 1.8–3.2) in the absence of CO₂ and at T = (25 ± 1) °C, as log^*K_s,0 = 1.19 ± 0.41.The relative stability of the Fe(III)-carbonate complexes in alkaline pH conditions has implications for the solubility of Fe(III) in CO₂-rich environments and the subsequent mobilisation of associated trace metals that will be explored in subsequent papers.     

Metal contamination and solid phase partitioning of metals in the stream and bottom sediments in a reservoir receiving mine drainage

This study was conducted to assess the anthropogenic impact on metal concentrations in the bottom sediments of the Juam reservoir, Korea, and in stream sediments in its catchment, and to estimate the potential mobility of selected metals (Fe, Mn, Cu, Ni, Pb and Zn) using sequential extraction. A comparison of the metal concentrations in the stream sediments with mean background values in sediments collected from first- or second-order creeks shows that Pb, Cu and Ni are the most affected by anthropogenic inputs. The ²⁰⁶Pb/²⁰⁷Pb ratios of the bottom and core sediments (means: 1.2320 ± 0.0502 and 1.2212 ± 0.0040, respectively) suggest that Pb contamination is mainly due to the waste discharge of abandoned coal and metal mines rather than industrial and airborne sources. Considering the proportion of metals bound to the exchangeable, carbonate and reducible fractions, the comparative mobility of metals is suggested to decrease in the order Mn > Pb > Zn > Ni > Fe ≫ Cu.     

Evaluation of the dissolved contaminant load transported by the Tinto and Odiel rivers (South West Spain)

The Tinto and Odiel rivers are heavily affected by acid mine drainage (AMD). However, the exact quantities of contaminants transported into the Huelva estuary and the Gulf of Cadiz are unknown. The existing previous investigations are, in general, based on studies with few data or incorrect methodology, and are therefore unreliable. This study aims to present a reliable estimation of the dissolved contaminant load transported by both rivers for the periods 1995/96 to 2002/03. The methodology used is based principally on the correlation between contaminant concentration and flow rate. The results show that both rivers transport enormous quantities of dissolved contaminants: 7900 t a⁻¹ of Fe, 5800 t a⁻¹ Al, 3500 t a⁻¹ Zn, 1700 t a⁻¹ Cu, 1600 t yr⁻¹ Mn and minor quantities of other metals. These values represent 60% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 17% of the global gross flux of dissolved Cu.     

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.     

Magnetite geochemistry of the Longqiao and Tieshan Fe–(Cu) deposits in the Middle-Lower Yangtze River Belt: Implications for deposit type and ore genesis

Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong ore district) and Tieshan Fe–(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China.Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe–(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate).Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid–rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and fO₂, may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of fO₂, but lower fluid–rock interactions and ore-forming temperature than the Longqiao deposit. The TiO₂–Al₂O₃–(MgO + MnO) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe–(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed.     

New insights on mobility and bioavailability of heavy metals in soils of the Padanian alluvial plain (Ferrara Province,northern Italy)

Heavy metals having both natural and anthropogenic origin are common contaminants in soils and sediments, and can be transferred and bioaccumulated at all levels of the food chain, posing serious environmental concern to the local population. In this paper, agricultural soils from the Province of Ferrara (easternmost part of the Padanian Plain, northern Italy) were investigated to assess the levels of potentially toxic metals in relation to their phytoavailability. Agricultural soils have been sampled in order to identify the origin, mobility and bioavailability of heavy metals, collecting superficial and deeper (depths of 20–30 and 100–120 cm, respectively) horizons. The “total” XRF analyses properly elaborated with a statistical approach reveal that soils evolved from two distinct types of alluvial sediments, in turn related to the Po and Reno rivers; the former type is distinctively enriched in heavy metals (particularly Cr and Ni), reflecting the presence of femic and ultrafemic rocks in the hydrological basin of River Po. The absence of Top Enrichment Factors for Ni, Co, Cr, V, and Pb suggests that the content of these elements is natural and unaffected by contamination, whereas superficial enrichments of Cu (and Zn) is ascribed to anthropogenic inputs related to agricultural activities. Multiple extraction tests using variously aggressive reactants (aqua regia, DTPA, EDTA, NH₄NO₃, and H₂O) analyzed by ICP gave insights on the specific mobility of the distinct elements, which decreases in the following order: Pb > Cu > Cd > Co > >Ni > Cr. Taking into consideration the elements that are inducing the main concerns, Cr appears scarcely mobile, whereas Ni could be more phytoavailable and has to be monitored in the local agricultural products. Cd although scarcely abundant has to be monitored for its mobility and toxicity, whereas Cu although abundant and extremely mobile doesn’t induce concerns as it is not hazardous for the living receptors.