Presence Of Jarosite Research Articles

Fractional precipitation of copiapite-halotrichite efflorescent salts on Au[sbnd]Cu mine tailings under semi-arid climates in northern Chile

The oxidation of pyrite involves a series of chemical reactions that, depending on climatic conditions, can give rise to different mineral phases and morphologies. When oxidation takes place in semi-arid climate, the development of efflorescent salts on the surface of mine tailings is characteristic. These salts are mainly composed of Fe, Al and Mg sulfates and may accumulate valuable metals liberated through the dissolution of tailing minerals.This research aims to describe the evolution of salt precipitation from the economic and environmental perspective. For this purpose, we sampled efflorescent salts formed during the summer season on the surface of a tailing impoundment located in the north of Chile. The materials underwent comprehensive characterization utilizing X-ray techniques and scanning electron microscopy.The findings reveal a fractional precipitation in the crystallized salts. In an advanced oxidation system, characterized by multiple seasons of crystallization, dissolution and oxidation, the dry season begins with the precipitation of sulfates from a highly acidic solution dominated by Fe3+. This solution results from the dissolution and oxidation of the previous season sulfates. This initial stage is characterized by the presence of jarosite and gypsum, which are subsequently replaced by ferricopiapite. Towards the progress of the dry season, copiapite becomes more magnesian and precipitates alongside coquimbite and alunogen. Finally, halotrichite and pickeringite begin to crystallize. Base metal cations such as Co, Cu, Mn, Ni and Zn are preferentially incorporated into halotrichite-pickeringite sulfates during the most advanced evaporation phase.

Thiourea leaching of gold in presence of jarosite and role of oxalate

The effect of jarosite generated from bio-oxidation on gold leaching in acidic thiourea solution was studied, and the role of the oxalate additive was also investigated. The biogenetic jarosite was found to markedly raise the thiourea consumption and hinder the gold dissolution. The dominant cause for the detrimental effect of jarosite is likely that iron ions were released from jarosite dissolution in the acidic solution and thus increased the solution potential, resulting in the accelerated decomposition of thiourea and the aggravated passivation of gold surface by the passivating species from thiourea decomposition. However, the addition of oxalate to solution was shown to be effective in weakening the adverse effect of jarosite manifested as much reduced thiourea consumption and enhanced gold dissolution. The possible acting mechanisms of oxalate were revealed by the analyses of solution potential, Zeta potential and XPS. Oxalate could not only weaken the interaction between Fe3+ and thiourea via complexing with Fe3+ but also prevent the passivation species from coating on gold surface through indiscriminate adsorption and electrostatic repulsion.

Jarosites: Formation, Structure, Reactivity and Environmental

Jarosite, beudantite and alunite are members of the alunite supergroup. Minerals like those have been detected in different environments on Earth. These jarosite-type compounds are common in acid rock drainage environments and acid sulfate soils, resulting from the weathering of sulfide ores; they are also present in bioleaching systems because they are found in cultures of iron-oxidizing microorganisms. Jarosite is also generated in hydrometallurgical circuits, mainly in zinc hydrometallurgy. These minerals can be used to immobilize different elements such as arsenic and lead, among others. Jarosite and alunite have also been detected on the surface of Mars; the presence of jarosite and alunite and other sulfates provides evidence for the existence of water on Mars. In this work, an exhaustive review of the natural formation, synthesis, structure, thermodynamics, and reactivity of jarosite, beudantite and alunite are included. The capacity of jarosites for the immobilization of the elements, such as lead and arsenic, and information about studies related to jarosite formation on Mars are also included.

Utilization of Jarosite waste for the development of sustainable concrete by reducing the cement content

In this work, the effects of using Jarosite as a partial replacement for cement were investigated. Jarosite is a waste material produced by the zinc manufacturing industry that has been utilized in concrete as a partial replacement for cement. Experimental studies have been carried out to understand the performance of Jarosite in concrete in terms of the microstructure, heat of hydration, thermogravimetric properties, and mechanical and durability properties. Laboratory investigations have confirmed that an increase in the percentage of Jarosite up to 15% resulted in an improvement in the mechanical properties of both ordinary Portland cement and pozzolanic Portland cement-based concretes. A relatively denser microstructure was observed and attributed to the fine grain structure of the Jarosite and the formation of secondary hydration products. Results of the heat of hydration and thermogravimetric analysis confirmed the occurrence of a secondary hydration reaction in the presence of Jarosite. Further, the durability characteristics of the Jarosite mixture demonstrated better performance relative to the control concrete mix. The leaching characteristics of the heavy metals in Jarosite-based concrete mixtures were predicted to be within permissible limits.

Mineral Formation under the Influence of Mine Waters (The Kizel Coal Basin, Russia)

The development of coal deposits is accompanied by negative environmental changes. In the territory of the Kizel coal basin (Perm Region, Russia), the problem of contamination of water sources by acid mine waters and runoff from rock dumps is particularly acute. Mine waters are acidic (pH 2–3), with high mineralization (up to 25 g/L) and significant content of sulfate ions, iron, aluminum, manganese, toxic trace elements (As, Co, Ni, Pb and Zn). They are formed as a result of the interaction of underground waters from flooded mines of the Kizel basin with coal and rocks of dumps with high sulfur content (15%). Uncontrolled inflow of mine water into rivers (about 22 million m3 annually) leads to significant amounts of iron and aluminum hydroxide precipitation. These precipitations are in active interaction with river water, polluting the rivers tens of kilometers downstream and are entering the Kama reservoir. Studies of alluvial precipitation can be considered as a method of control and predictors of technogenic water pollution. The mineral composition of river sediments was studied with the application of different methods, including studies of sand-gravel and silty-clayey sediments. The sandy-gravel grains in the bottom load are mainly composed by natural minerals and are represented by a significant number of particles of coal dumps, slags and magnetic spherules. The silty-clayey material, mixed with natural minerals, contains a significant number of amorphous phases with a predominance of iron-rich substances, which may actively concentrate toxic elements. The presence of jarosite, goethite, basaluminite, lepidorocite and copiapite in silty-clayey sediments are indicators of the influence of mine waters.

Red-bed bleaching in a CO2 storage analogue: Insights from Entrada Sandstone fracture-hosted mineralization

ABSTRACTImproving our ability to predict the interactions between CO2 and reservoir rocks at geological time scales is of key importance if carbon capture and storage (CCS) is to have a role in climate-change mitigation, particularly in the light of likely regulatory requirements. Understanding and identifying the relevant geological processes over long time scales can be obtained only at natural-analogue sites. At one such site, in the Salt Wash Graben area of Utah, USA, widespread bleaching affects the Middle Jurassic red-bed “wet dune” Entrada Sandstone. Previous work has proposed a genetic link between the bleaching and spatially concomitant recent and modern CO2-rich fluids. The results presented here challenge some of the previous models and come from a detailed petrographic examination of mineralized fractures in the Entrada Sandstone that are centered in vertical extensions to the bleaching. These fractures typically contain complex mineralization assemblages. Pyrite was a paragenetically early phase, identifiable from common pseudomorphs of mixed iron oxides and oxyhydroxides that rarely contain relict pyrite. The pyrite contains up to 3 wt% arsenic. The volume of fracture-adjacent bleached sandstone is sufficient to have been the source of iron for the pyrite originally present in the fracture. The pyrite pseudomorphs occur at the center of fracture- and pore-filling cements that comprise intergrowths of hematite–goethite–jarosite–gypsum, an assemblage that suggests that their formation resulted from the oxidative alteration of pyrite, a genetic link supported by the arsenic present in the iron-bearing minerals. The presence of jarosite and proximal removal of earlier, sandstone-hosted carbonates are consistent with, and indicative of, the low-pH conditions associated with pyrite oxidation reactions. Calcite- and gypsum-cemented fractures crosscut, and contain fragments of, the pyrite-pseudomorphic and -oxidation assemblages, proving that they postdate pyrite formation and its subsequent oxidation, and that pyrite oxidation was not a result of modern weathering reactions. In outcrop, some calcite- and gypsum-cemented fractures link with travertine deposits associated with the modern and recent CO2-rich fluids. The mineral assemblages observed here, and the paragenetic sequence that we have inferred, suggest that the fracture-associated bleaching patterns result from the fracture-fed movement of sulfur-bearing reducing fluids, with hydrogen sulfide the most likely bleaching agent. We conclude that bleaching adjacent to fractures is not genetically related to modern CO2-bearing fluids despite the spatial relationship. The bleaching was already present when the modern fluids utilized the same fracture-based fluid pathways. We suggest that the more widespread regional bleaching formed contemporaneously with the fracture bleaching and followed similar mechanisms. This study highlights the complexity of interpreting analogue sites and the importance of using field and petrographic observations to unravel textures and events that are juxtaposed spatially but not temporally.

Volcanic Conduits of the Chã das Caldeiras Caldera (Fogo Island, Cape Verde) – REE and Fe Crystalchemistry

Topsoils of pyroclastic materials collected on two volcanic conduits of the Chã das Caldeiras caldera of the oceanic Fogo Island (Cape Verde) were studied. Significant positive Eu anomalies were found in both pre-historic and historic cones, which together with the presence of jarosite, may be considered hydrothermal signatures that survived in this surficial semi-arid environment.

Arsenic Immobilization by Nanoscale Zero-Valent Iron / Immobilizacja Arsenu Przez Nanożelazo Na Zerowym Stopniu Utlenienia

Abstract Contaminated mine water from the Kank site (Czech Republic) containing arsenic at a concentration of approximately 85 mg/dm3 was tested in a reaction with elemental iron nanoparticles. In a reductive environment there was a reduction of As to the more soluble and toxic form of As(III) depending on the pH of the solution. Oxidation of elemental iron creates oxyhydroxides which incorporate As into their structure in the form of mixed complexes and thereby remove and bind dissolved As from the solution. The addition of 0.5 g/dm3 nZVI to the contaminated water leads to a significant decrease in ORP and concentrations of As to around the detection limit. The pH of the solution is not significantly affected by the addition of nZVI. The main competing anion for co-precipitation is represented by phosphates whose concentration after the addition of nZVI was reduced to 6.5% of the original value. The resulting precipitates were analyzed by XPS, XRF, XRD, SEM-EDX and Mössbauer spectroscopy. The presence of jarosite, Schwertmannite and also arsenic probably in the form of skorodite was confirmed

Thermal expansion of monoclinic natrojarosite

Jarosites and related minerals are of great interest to a range of mineral processing and research applications. In some industrial settings jarosite formation is encouraged; for example to aid the removal of iron species from solutions in hydrometallurgical processes. In other environments such as bioleaching, jarosite formation can hinder the process by creating a kinetic barrier, in the form of a passivation layer, to the desired reaction. Jarosites are a major component of acidic soils and are present in significant amounts in acid mine drainage environments. There has been a recent resurgence in interest in jarosite minerals since their detection on Mars by the MER rover Opportunity. In this context, the presence of jarosite has been recognised as a likely indicator of the presence of water on Mars in the past. It is hoped that study of their formation mechanisms, stability and thermoelastic properties will provide insight into the environmental history of Mars as well as informing terrestrial industrial concerns. To this end we are engaged in a program to study jarosites and their formation and stability behaviour over a range of conditions. This contribution describes in situ powder diffraction experiments to determine the thermal expansion of a deuterated natrojarosite. Data were collected on the HRPD beamline at the ISIS spallation source where the natrojarosite sample was heated from 10–700K, and at the powder diffraction beamline at the Australian synchrotron where the sample was heated from 80-700K. Isothermal neutron and synchrotron datasets were refined simultaneously. Analysis of the lattice parameter variation with temperature shows that all cell edges increase smoothly to ~500 K where there is a discontinuity. This discontinuity represents the initially non-stoichiometric monoclinic jarosite converting to a stoichiometric, rhombohedral phase, shortly after which FeOHSO4 peaks become visible. Thermal expansion coefficients have been fitted from 10-470K and show that there is most variation in the monoclinic c-axis. This direction is normal to the layers of sulphate tetrahedra and iron octahedra within the jarosite structure and contains more flexible hydrogen bond linkages which more easily accommodate expansion than the more rigid polyhedra. Details of the combined neutron-synchrotron diffraction approach will also be discussed.

Detection of copiapite in the northern Mawrth Vallis region of Mars: Evidence of acid sulfate alteration

The Mawrth Vallis region on Mars is associated with extensive layered deposits containing a stratigraphic sequence of Fe/Mg smectites overlain by Al phyllosilicates. Earlier studies have reported restricted exposures of the ferric sulfate mineral jarosite on top of the sequence. In this paper we have used CRISM data covering the northern portion of the Mawrth Vallis region to find a new jarosite exposure and multiple occurrences of the mixed valence Fe-sulfate mineral copiapite (Fe2+Fe3+4(SO4)6(OH)2·20(H2O)). HiRISE imagery indicate that the copiapite exposures lie on top of the Al phyllosilicates and thus post-date that unit either as a coating or as extensive veins. The presumed copiapite exposures are associated with high values of a “SINDX” parameter derived from CRISM data. Application of several spectral matching metrics over a spectral subsection indicated several candidates for the high SINDX phase including copiapite, ferricopiapite and metavoltine (another mixed valence Fe-sulfate mineral). Visible and near infrared CRISM spectra of the high SINDX areas are most consistent with the phase being copiapite. On Earth copiapite generally occurs as efflorescent coatings in acid mine drainage environments or in association with acid sulfate soils. The presence of jarosite and copiapite indicates the presence of acidic waters. Such acid waters could have contributed to the formation of the underlying Al phyllosilicate minerals. A possible mode of origin for these minerals in this region would involve a fluctuating ground water table and the weathering of Fe sulfide minerals.

Jarosite in a Pleistocene East African saline-alkaline paleolacustrine deposit: Implications for Mars aqueous geochemistry

[1] Jarosite occurs within altered tephra from the saline-alkaline paleolake deposits of Pliocene-Pleistocene Olduvai Gorge, Tanzania. Zeolites (mainly phillipsite), authigenic K-feldspar, and Mg/Fe-smectites dominate the mineral assemblage, indicating saline-alkaline diagenetic conditions (pH > 9). As jarosite is ordinarily an indicator of acidic conditions on Earth and Mars, its association with such undisputed high-pH indicators is unexpected. Of 55 altered tephra samples collected from the paleolake basin and margin deposits, eleven contained jarosite detectable by X-ray Diffraction (XRD) (>0.15%). Mössbauer spectroscopy, Fourier Transform Infrared Reflectance (FTIR), Electron Probe Microanalysis (EPMA), X-ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) analyses confirm the presence and nature of the jarosite. This paper documents this occurrence and presents mechanisms that could produce this unusual and contradictory mineral assemblage. We favor a mechanism by which jarosite formed recently, perhaps as modern ground and meteoric water interacted with and oxidized paleolacustrine pyrite, providing local and temporary acidic conditions. However, local groundwater (at modern springs) has a pH > 9. In recent studies of Mars, the presence of jarosite or other Fe or Mg sulfates is often used to indicate dominantly acidic conditions. Regardless, the current study shows that jarosite can form in sediments dominated by alkaline minerals and solutions. Its coexistence with Mg/Fe smectites in particular makes it relevant to recent observations of Martian paleolakes.

Mineralogy, geochemistry of altered tuff from Cappadocia (Central Anatolia) and its use as potential raw material for the manufacturing of white cement

The present study deals with mineralogy, geochemistry and uses of altered tuff from Cappadocia (Central Anatolia) as a potential raw material for the manufacturing of white cement. Mineralogical analyses show that altered tuffs are mainly composed of quartz and kaolinite. In some samples minerals such as jarosite, illite, smectite, sanidine and calcite have also been detected. A widespread, intensive hydrothermal alteration zone has developed across a NE–SW striking fault in the study area (Türkmenlik Hill). The field observations and the results of the analyses show that there are some changes in mineralogical and chemical composition across this fault zone. The central part of the fault zone shows an intensive silicification (> 85% SiO 2). The amount of kaolinite increases towards the outsides; the outermost zone is composed of smectite (illite) in association with quartz and kaolinite. This phase zonation supports the proposition that those minerals were probably formed by hydrothermal activity. The presence of jarosite in some samples indicates that the hydrothermal solution might have had acidic character. The geochemical analyses show that the major oxides such as K 2O, Na 2O, MgO, Fe 2O 3, CaO, MnO and P 2O 5 were leached out from parent rocks through hydrothermal alteration. The predominant number of the samples have very low concentrations (< 0.5%) of colouring elements such as Fe 2O 3 and MnO and thereby the material is very white. There is a strong correlation between Fe 2O 3 and whiteness-degree. The whiteness-degree value increases with decreasing Fe 2O 3 concentration ( r = − 0.9). Materials with Fe 2O 3 concentration lower than 0.5% have a whiteness-degree > 85%. These properties, which particularly depend on mineralogical and geochemical composition, allow the use of this rock as an industrial raw material for manufacturing white cement. The opportune geographical position of this material relative to the cement plants in Turkey offers very important advantages regarding transport cost, which can decrease the production cost of white cement by as much as 50%.

Modeling ferrous–ferric iron chemistry with application to martian surface geochemistry

The Mars Global Surveyor, Mars Exploration Rover, and Mars Express missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major recent mission findings are the presence of jarosite (a ferric sulfate salt), which requires formation from an acid-sulfate brine, and the occurrence of hematite and goethite on Mars. Recent ferric iron models have largely focused on 25 °C, which is a major limitation for models exploring the geochemical history of cold bodies such as Mars. Until recently, our work on low-temperature iron-bearing brines involved ferrous but not ferric iron, also obviously a limitation. The objectives of this work were to (1) add ferric iron chemistry to an existing ferrous iron model (FREZCHEM), (2) extend this ferrous/ferric iron geochemical model to lower temperatures (<0 °C), and (3) use the reformulated model to explore ferrous/ferric iron chemistries on Mars. The FREZCHEM model is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Ferric chloride and sulfate mineral parameterizations were based, in part, on experimental data. Ferric oxide/hydroxide mineral parameterizations were based exclusively on Gibbs free energy and enthalpy data. New iron parameterizations added 23 new ferrous/ferric minerals to the model for this Na–K–Mg–Ca–Fe(II)–Fe(III)–H–Cl–SO 4–NO 3–OH–HCO 3–CO 3–CO 2–O 2–CH 4–H 2O system. The model was used to develop paragenetic sequences for Rio Tinto waters on Earth and a hypothetical Martian brine derived from acid weathering of basaltic minerals. In general, model simulations were in agreement with field evidence on Earth and Mars in predicting precipitation of stable iron minerals such as jarosites, goethite, and hematite. In addition, paragenetic simulations for Mars suggest that other iron minerals such as lepidocrocite, schwertmannite, ferricopiapite, copiapite, and bilinite may also be present on the surface of Mars. Evaporation or freezing of the Martian brine led to similar mineral precipitates. However, in freezing, compared to evaporation, the following key differences were found: (1) magnesium sulfates had higher hydration states; (2) there was greater total aqueous sulfate (SO 4T = SO 4 + HSO 4) removal; and (3) there was a significantly higher aqueous Cl/SO 4T ratio in the residual Na–Mg–Cl brine. Given the similarities of model results to observations, alternating dry/wet and freeze/thaw cycles and brine migration could have played major roles in vug formation, Cl stratification, and hematite concretion formation on Mars.

Transformation of jarosite to hematite in simulated Martian brines

The presence of jarosite – a hydrous iron sulfate – at Meridiani Planum supports the past existence of water on Mars surface. Thermodynamic calculations suggest that jarosite should transform to ferric oxyhydroxides in aqueous media. Here we show that jarosite can transform directly to hematite – the iron oxide identified at Meridiani Planum – in simulated Martian brines. Our results are consistent with a short aqueous history, but also indicate that jarosite can persist in highly saline Martian brines. The formation of goethite, a common iron oxyhydroxide on Earth, is prevented by the low water activity and/or high phosphate concentration of Martian brines.

English

The presence of jarosite in soil or mining waste is an indicator of acidic sulfate-rich conditions. Physical and chemical properties of synthetic jarosites are commonly used as analogs in laboratory studies to determine solubility and acid-generation of naturally occurring jarosites. In our work we have mineralogically and chemically characterized both natural and synthetic jarosites. Analysis of 32 natural hydrothermal and supergene K- and Na-jarosites indicates no (< 5 mole %) solid solution between K and Na end members. Instead, our detailed study of cell dimensions and composition reveals discrete mixtures of K and Na end members. Hydronium-bearing jarosite was detected in only one natural sample, and it appears that hydronium-bearing jarosites are metastable. Although the presence of hydronium in jarosite cannot be directly measured, we found that when synthetic hydronium-bearing jarosites are heated at 120°C for 78 days or 240°C for 24 hours, Fe(OH)SO4 is formed. The Fe(OH)SO4 is easily detected by X-ray diffraction and, hence, can be used as a post-mortem indicator of the presence of hydronium jarosite. Results from our synthetic jarosite studies indicate that natural metastable hydronium-bearing jarosite or iron-deficient forms of natural jarosite likely play an important role in acid generation in some mining wastes, but are not accurately represented by synthetic jarosite prepared by commonly used methods. The widespread practice of heating to at least 110°C after jarosite synthesis appears to drive off structural waters from protonated hydroxyl sites, which changes the properties of the jarosite. Therefore, synthetic jarosite should not be heated above 95 o C if it is to be used as an analog

English

Rarely do rock pile characterization methods allow for examination and sampling of the interior of large rock piles in-situ. The regrading of the Goathill North (GHN) rock pile at the Questa mine provided a unique opportunity to examine and sample the interior of a large rock pile through the construction of trenches cut into the rock pile as earth-moving progressed. Maps of each bench were created to document the different stratigraphic units, including the thickness, dip, and extent of the units. Units were defined based on grain size, color, and other physical properties. Units were correlated between benches and downward through the series of successively excavated trenches. Typically, paste pH increased with distance from the outer, oxidized zone (west) towards the interior units (east) of the GHN rock pile. The outer zone was oxidized (weathered) based upon the white and yellow coloring, low paste pH, presence of jarosite and gypsum, and absence of calcite. However, the oxidation/reduction (weathering) state in the interior zone is not yet determined. The base of the rock pile closest to the bedrock/colluvium surface represents the oldest part of the rock pile since it was laid down first. Portions of the base appeared to be nearly or as oxidized (weathered) as the outer, oxidized zone, suggesting that air and water flow along the basal interface occurred and possibly was an active weathering zone. Analyses of samples from unweathered, unoxidized drill core samples and from the GHN rock pile are similar in clay mineralogy as determined by XRD and electron microprobe analyses, which suggests that the majority of clay minerals in the GHN samples were derived from the original, pre-mined hydrothermal alteration and not post-mining weathering.

Sulfide oxidation and the natural attenuation of arsenic and trace metals in the waste rocks of the abandoned Seobo tungsten mine, Korea

Mineralogical examinations were performed to characterize the formation of secondary minerals and natural removal process of dissolved As and trace metals (Pb, Zn and Cu) from sulfide oxidation. Laboratory-based leaching tests were also conducted to determine whether the concentrations of As and trace metals in the leachates from waste-rock materials and contaminated soil could be affected by the presence acids such as acid rainwater or acid mine drainage. Waste-rock materials and contaminated soil were compared by 4-day leaching tests using HNO 3 solutions of increasing acidity (0.00001–0.1 mole/L). Mineralogical studies of the waste rocks confirmed the presence of Fe-(oxy)hydroxides (e.g. goethite), jarosite, elemental S, Fe-sulfates, amorphous Fe–As phases, anglesite and covellite as secondary minerals. These secondary minerals act as mineralogical scavengers of dissolved trace metals, SO 4 2 - and acidity released by sulfide oxidation. Arsenic was attenuated by the adsorption on Fe-(oxy)hydroxides and/or the formation of an amorphous Fe–As phase, with a Fe/As ratio = 1 (maybe scorodite: FeAsO 4 · 2H 2O). Electron probe microanalyses data showed that the Fe-(oxy)hydroxides had high concentrations of Pb (up to 21 wt%), with appreciable amounts of As (up to 7.7 wt%), Zn (up to 4.6 wt%) and Cu (up to 2.5 wt%) indicating that dissolved metals were co-precipitated and adsorbed onto Fe-(oxy)hydroxides, Fe(Mn)-hydroxides and Fe-sulfates. The results of the leaching experiments within the pH-range 3.5–5.0 indicated that acidic rainstorms may leach minor amounts of Pb (ca. 1.7–4.0% of total), Zn (ca. 0.8–2.2% of total), Cu (ca. 0.0–0.2% of total) and As (ca. 0.02–0.1% of total) from waste rocks, including the dissolution of soluble secondary minerals previously formed during prolonged dry periods, while dissolution of these elements was negligible from the contaminated soil. In the pH-range 1.0–3.0, the leaching of Pb (ca. 2.4–31% of total) and As (ca. 0.1–5.8% of total) from the waste rocks was significant, which could influence the concentration of these metals in mine runoff. Strongly acidic solutions may also appreciably dissolve Zn (0.0–48% of total) and Cu (0.0–34% of total) in contaminated soil. Leach tests showed that the formation of less soluble secondary minerals had high retention of As, Pb, Zn and Cu, unless their solubilities were increased after the addition of strongly acidic solutions (pH of below 2.0). The precipitation of secondary minerals and the adsorption of trace metals are efficient mechanisms for decreasing the mobilities of As and other trace metals in the surface environment. Geochemical modeling indicated that the leach solutions were supersaturated with respect to goethite, hematite, and magnetite at pH greater than 2.9. Ferrihydrite, Fe(OH) 3, was not in equilibrium with the solution during the entire experiment, suggesting that amorphous Fe-hydroxide can only form in small amounts. X-ray analyses of Seobo mine-waste samples indicated the presence of jarosite and goethite, which retain As, Pb, Zn and Cu during precipitation and co-precipitation.

Internal iron biomineralization in Imperata cylindrica, a perennial grass: chemical composition, speciation and plant localization

* The analysis of metal distribution in Imperata cylindrica, a perennial grass isolated from the banks of Tinto River (Iberian Pyritic Belt), an extreme acidic environment with high content in metals, has shown a remarkable accumulation of iron. This property has been used to study iron speciation and its distribution among different tissues and structures of the plant. * Mossbauer (MS) and X-ray diffraction (XRD) were used to determine the iron species, scanning electron microscopy (SEM) to locate iron biominerals among plant tissue structures, and energy-dispersive X-ray microanalysis (EDAX), X-ray fluorescence (TXRF) and inductively coupled plasma emission spectroscopy (ICP-MS) to confirm their elemental composition. * The MS spectral analysis indicated that iron accumulated in this plant mainly as jarosite and ferritin. The presence of jarosite was confirmed by XRD and the distribution of both minerals in structures of different tissues was ascertained by SEM-EDAX analysis. * The convergent results obtained by complementary techniques suggest a complex iron management system in I. cylindrica, probably as a consequence of the environmental conditions of its habitat.

Acid sulfate soils in dredged materials from tidal Pocomoke Sound in Somerset County, MD, USA

Seepage and runoff waters from soils forming in sulfide-bearing dredge materials (SBDM) can have dramatic effects on water quality if they are placed adjacent to open water and do not have adequate containment. Soils forming in SBDM can produce large amounts of acidity upon sulfide oxidation and the oxidation and hydrolysis of released ferrous iron when they are drained or otherwise exposed to air. These soils, under certain environmental conditions, can produce low pH seepage and runoff waters containing large amounts of iron and aluminum, especially after heavy rain that follows a prolonged dry period. During the course of the soil survey update of Somerset County, Maryland (MD), USA, 2 areas of soils forming in SBDM of differing age were identified in close proximity to the sites of recent fish kills on the Pocomoke Sound in Somerset County. Both of these soil areas were initially contained by earthen berms. The dredge materials were deposited directly over the natural tidal marsh soil. Soils forming in SBDM that are approximately 60 years of age were classified as fine-silty, mixed mesic Sulfic Endoaquepts, while the second area of SBDM are 8 years of age and classified as fine-silty, mixed, mesic Typic Sulfaquepts, by Soil Taxonomy. The presence of jarosite was confirmed in both soils by X-ray diffraction, and the presence of ironstone (iron oxyhydroxides) was confirmed in both soils at the effluent discharge points. This is an indication that these soils have undergone intensive acid sulfate weathering (sulfuricization) and that they have released a large quantity of iron to waters leaving the sites. Studies have shown that the 2 mechanisms responsible for acid production from soils forming in SBDM are (i) the oxidation and hydrolysis of mobile ferrous iron; and (ii) the oxidation of the sulfur occurring in the form of pyrite. It is suggested that the resultant low pH, Fe- and Al-enriched water from these soils that entered the Pocomoke Sound may have made fish more susceptible to microbial predation by weakening mucous membranes and/or by promoting the growth of harmful cyannobacteria and flagellates. This paper reports the nature and classification of soils that developed in SBDM at 2 sites of differing age and of the possible environmental impacts of seepage and runoff from these sites entering the Pocomoke Sound.

Effect of acid mine drainage on the mineralogy of a dystric cambisol

Two natural soil profiles non-acidified and acidified with acid mine drainage (AMD) were selected for study. Interactions between acid mine drainage and the soil were evaluated by the changes in the mineral composition applying XRD, transmission electron microscopy (TEM), analytical electron microscopy (AEM), and selective area electron diffraction (SAED). The main differences between the acidified and the non-acidified soil were in the presence of jarosite and in the authigenesis of two types of amorphous and/or poorly crystalline matter (Fe-rich; Al, Si-rich). The most frequent Fe-rich matter was identified as ferrihydrite. It appears to be in two morphological varieties: “massive” (composed of spheroidal particles) and “mohair” (composed of layered particles).