Reactive Sulfide Research Articles

Volunteer Revegetation of Waste Rock Surfaces at the Bingham Canyon Mine, Utah

Voluntary recolonization of sulfide-bearing waste rock dumps by native vegetation is inhibited by the harsh chemical and physical conditions. The success of volunteer vegetation on the waste rock surfaces at the Bingham Canyon (Utah) porphyry copper deposit is most strongly dependent on the soil pH and salinity, and to a lesser extent on physical characteristics such as compaction and distance from seed source. Vegetation cover and richness both decline below a paste pH of about 6 and above a paste conductivity of about 0.7 dS/m (for a 1:1 soil to water mixture). No significant vegetation establishment occurs below a soil pH of about 4.5. Young sulfide-bearing waste rock surfaces at Bingham Canyon have high salinity, but as reactive pyrite is depleted and salts are flushed from the soil, the salinity eventually declines, allowing volunteer native vegetation to become established on surfaces with a circumneutral pH. Under natural conditions, the pH of older acidic weathered surfaces will recover very slowly, but it can be rapidly raised by adding relatively small amounts of limestone because there are few intact reactive sulfides. For uncompacted waste rock surfaces with favorable chemical conditions, less than 90% gravel content, and that are located near a native seed source, the arithmetic mean volunteer vegetation cover was 56 +/- 24% and the mean species richness was 17 +/- 5. These data indicate that with adequate surface preparation and limestone addition, direct planting of older, acidic, but low salinity waste rock surfaces can greatly accelerate natural revegetation.

Diagenetic reactivity of the plutonium in marine anoxic sediments (Cumbrian mud patch - eastern Irish Sea)

An extensive diagenetic study carried out on a sediment core collected in the Cumbrian mud patch off the Sellafield nuclear reprocessing plant, is presented. Sequential leaching data, using a thoroughly validated protocol specifically designed to prevent any resorption of the released plutonium in the course of the extraction, demonstrate that a significant proportion of the plutonium is loosely bound to sites that readily exchange with seawater, oxidise upon oxygenated water contact (reactive sulphides) or easily dissolve upon changes in pH. Such a result contradicts many previous sequential extraction studies which have reported that little of the plutonium in Irish Sea sediments is in a readily available form. The profile of dissolved plutonium in pore waters indicates an active uptake process at depth, probably linked to sulphide (Acid Volatile Sulphide) precipitation. These reactive sulphides are liable to act as source of plutonium to the overlying water if they are brought close the interface by bioturbation or in contact with oxygenated seawater by burrowing activity.

Silver accumulation in Daphnia magna in the presence of reactive sulfide

Previously, we demonstrated a higher silver body burden when Daphnia magna were exposed to silver in the presence of environmentally relevant concentrations (25 nM) of reactive sulfide, but the explanation was unclear. In the present study, D. magna were exposed to AgNO 3 (0.93 μg Ag/L = 8.6 nM as a mixture of cold Ag and 110mAg) in synthetic water in either the presence or absence of 25 nM sulfide as zinc sulfide clusters. After 1-h exposure, daphnids were transferred to clean water for up to 5-h depuration. At different times of Ag exposure and depuration, daphnids were randomly sampled for whole body silver burden. Also, after 1 h, daphnids were sampled for silver accumulation in “gills” (small organs on the thoracic appendages), digestive tract, and carcass. Other groups were exposed to the same silver and sulfide concentrations for 1 h and then sampled for whole-body autoradiography. Silver body burden was about two-fold higher in the presence of sulfide. A two-fold increase in silver burden in “gills” and digestive tract, but not in carcass, was also observed in the presence of sulfide. Absolute differences due to sulfide were greatest in digestive tract and explained most of the difference in whole body burden. Transfer to clean water caused a significant drop in silver concentration in whole body and all compartments to similar levels in the two groups after 5-h depuration. These results indicate that the higher silver body burden observed in the presence of sulfide is mainly due to sulfide-bound silver in the digestive tract of the daphnids. This conclusion is supported by autoradiography, which showed a high concentration of silver in the digestive tract of daphnids exposed to Ag/sulfide.

Reactive sulfide relationships with trace metal extractability in sediments from southern Moreton Bay, Australia

Anthropogenic contaminants introduced into the aquatic environment can eventually accumulate in benthic sediments. Sediment quality assessment is therefore an important consideration in ensuring the ecological sustainability of coastal regions. An important research focus associated with sediment quality assessment is determining whether sediments enriched with trace metals actually exert an adverse effect on aquatic ecosystems (Ankley et al., 1994). This issue is complicated because trace metal bioavailability in sediments is controlled by sorption to several solid-phases (such as iron oxyhydroxides, organic matter and reactive sulfide species; Chapman et al., 1998). Furthermore, total metal analysis often provides a poor indication of bioavailability and potential mobility (ANZECC/ARMCANZ, 2000). As such, the use of partial extractions potentially provides a more accurate representation of the concentration of reactive, bioavailable metal species (Burton et al., 2005).

Evaluation of the protective effects of reactive sulfide on the acute toxicity of silver to rainbow trout (Oncorhynchus mykiss).

Acute 96-h toxicity tests were performed with juvenile rainbow trout (Oncorhynchus mykiss) exposed to AgNO3 in either the absence or the presence of 100 nM reactive sulfide to evaluate the protective effect of aqueous sulfides against ionic Ag toxicity. The sulfide was presented in the form of zinc sulfide (ZnS) clusters under oxic conditions. Silver was lost from the water column during the course of the experiment, so mean measured Ag concentrations were used to generate all median lethal concentration (LC50) data. The system was complicated in that Ag2S precipitated because of the need for large amounts of Ag to obtain lethal effects in the presence of ZnS. Some of the losses of Ag could be explained by complexation with ZnS and formation of solid Ag2S. Other losses were probably the result of partial adsorption to exposure-chamber walls or to complexation with ligands or functional groups within organic material produced by the fish. The LC50 (95% confidence interval) values generated using measured concentrations for total Ag were 139 (122-162) nM in the absence of sulfide and 377 (340-455) nM in the presence of 100 nM sulfide. The LC50 values generated using measured concentrations from filtered (pore size, 0.45 microm) water samples were 122 (105-145) nM in the absence of sulfide and 225 (192-239) nM in the presence of 100 nM sulfide. These results suggest a stoichiometric protection of sulfides up to a 2:1 ratio of Ag:sulfide. Greater accumulation of Ag at the gills was measured in fish exposed to AgNO3 in the presence of sulfide.

Reactive sulfides relationship with metals in sediments from an eutrophicated estuary in Southeast Brazil

The potential association of acid-volatile sulfides (AVS) and reactive (HCl soluble) Fe with the distribution of reactive trace metals (Cu, Cd, Ni, Pb and Zn) was investigated in sediment cores collected in the Iguaçu river estuarine system (Guanabara bay, Brazil), within the river (core R) and the bay (core B) areas. Moderate to extremely high AVS concentrations (33–314 μmol g −1) were found in the rapidly-accumulated sediments of this eutrophicated estuary. AVS showed significant correlations with Fe, Ni and Pb in core B, whereas no correlation between AVS and metals was observed in core R. Results suggest that the AVS:Fe molar ratio may often reflect the diagenetic conditions controlling the distribution of Cd and Cu in core B better than AVS and Fe levels themselves. A shift in the biogeochemical controls of metal distribution from the river to the open bay sediments is suggested, with a greater association of most metals with AVS and Fe in bay sediments.

Finite Element Modelling of Three-Dimensional Steady-State Convection and Lead/Zinc Mineralization in Fluid-Saturated Rocks

We use the finite element method to model three-dimensional steady-state convective pore-fluid flow and the relevant mineralization in fluid-saturated rocks when they are heated from below. In particular, we investigate lead/zinc precipitation and dissolution patterns caused by the reactive sulfide and sulfate fluids mixing in three-dimensional hydrothermal systems. The related numerical results demonstrated that: (1) The finite element method is useful in and applicable to the modelling of three-dimensional ore body formation and mineralization problems in fluid-saturated porous rocks; (2) The mixing of reactive sulfide and sulfate fluids is an important mechanism to generate high-grade lead/zinc deposits in three-dimensional hydrothermal systems in the upper crust of the Earth.

Water Cover Over Mine Tailings and Sludge: Field Studies of Water Quality and Resuspension

Flooding is considered one of the best available technologies for long term storage of acid generating mine waste when suitable site-specific conditions exist. There is, however, a concern that oxidation may still occur. In cases where lime neutralization sludge and reactive sulfide tailings are co-disposed in the tailings pond, wind-induced waves could resuspend the waste and negatively impact the quality of the water cover. Studies were undertaken at the Noranda Inc. Heath Steele Lower Cell tailings impoundment, located in northeastern New Brunswick, Canada, 50 km northwest of city of Miramichi. The stored material in the cell consisted of unoxidized tailings with small amounts of sludge. The 90 ha impoundment acted as a polishing pond, prior to the discharge of final effluent. The pond was keptalkaline (pH of 8.5-10.5) in order to meet regulated discharge limits. On some windy days when the Lower Cell experienced turbulent water conditions, the final effluent exceeded the suspended solids water quality standard of 25 mg/L. The dry mass of suspended sediment measured in 1999 ranged from 1.5 to 434 mg with relatively more material (> 100 mg) being suspended under shallow water cover (= 1 m). Both x-ray diffraction and scanning electron microscopy analyses indicated that the suspended material was mostly lime neutralization sludge and other material composed primarily of calcite and brucite and coatings of aluminum, iron, zinc and manganese hydroxides. Solubility considerations of the carbonate system confirmed that the water cover was supersaturated with respect to calcite. The results suggest that sludge and tailings re-suspension and precipitation of solid phases in the water cover likely combined to produce the observed, occasionally high total suspended solids concentration.

Evaluation of the effect of reactive sulfide on the acute toxicity of silver (I) to Daphnia magna. Part 1: Description of the chemical system

Experiments were designed to assess the potential protective effect of the presence of sulfide against the acute (48-h) toxicity of silver(I) to Daphnia magna. Tests were conducted in borosilicate glass beakers (250 ml) in moderately hard synthetic water. Toxicity solutions were replaced after 24 h by static renewal method. This paper describes the chemical system, and the acute toxicity results are presented in a companion paper. Sulfide was below detection limit (<5 nM) in controls with no sulfide added. Sulfide, added as zinc sulfide clusters at approximately 35- or approximately 350-nM concentration, dropped in concentration to approximately 25 and 250 nM, respectively, over the 24-h period of measurements. Silver also decreased in concentration during the experiment (up to 59%), and the rate of loss was greater in the absence of sulfide compared with the presence of sulfide. A filtration experiment indicated a 1:1 binding ratio of silver to sulfide and a conditional stability constant for the Ag(I)-zinc sulfide complex of log K' = 8.9. The losses of sulfide and silver during the experiments highlighted the need for regular monitoring of the important chemical components of the system, even during short (48-h) toxicity tests.

Evaluation of the effect of reactive sulfide on the acute toxicity of silver (I) to Daphnia magna. Part 2: Toxicity results

The protective effect of reactive sulfide against AgNO3 toxicity to Daphnia magna neonates was studied. Acute (48-h) toxicity tests were performed in the absence (<5 nM) and presence of low (approximately 25 nM) and high (approximately 250 nM) concentrations of zinc sulfide clusters under oxic conditions. In both the presence and the absence of sulfide, lower mean lethal concentration (LC50) values were observed when measured as opposed to nominal silver concentrations were used in calculations. This reflected the fact that measured total silver concentrations were lower than nominal concentrations due to losses of silver from solution observed during the experiment. High concentration (approximately 250 nM) of sulfide completely protected against toxicity up to the highest silver concentration tested (2 microg/L [19 nM]) with measured silver data. In the presence of environmentally realistic levels of sulfide (approximately 25 nM) in receiving waters, acute silver toxicity was reduced by about 5.5-fold. However, when filtered (0.45 microm) silver concentrations alone were considered, toxicity (48-h LC50) was similar in the absence (0.22 microg/L) and presence (0.28 microg/L) of sulfide. The difference between measured total and filtered silver was attributed to chemisorption of the metal sulfide onto the membrane filter and provides evidence that the toxic fraction of silver is that which is unbound to sulfide. Accumulation of silver was greater in daphnids exposed to silver in the presence of sulfide than in its absence, even though a toxic effect was not observed under these conditions. In this case, silver appears to be incorporated by daphnids rather than merely adsorbed on the surface. Our results point out the need to incorporate sulfide into the acute biotic ligand model and to assess its potentially large role in preventing chronic toxicity.

Finite element modelling of reactive fluids mixing and mineralization in pore‐fluid saturated hydrothermal/sedimentary basins

We present the finite element simulations of reactive mineral‐carrying fluids mixing and mineralization in pore‐fluid saturated hydrothermal/sedimentary basins. In particular we explore the mixing of reactive sulfide and sulfate fluids and the relevant patterns of mineralization for lead, zinc and iron minerals in the regime of temperature‐gradient‐driven convective flow. Since the mineralization and ore body formation may last quite a long period of time in a hydrothermal basin, it is commonly assumed that, in the geochemistry, the solutions of minerals are in an equilibrium state or near an equilibrium state. Therefore, the mineralization rate of a particular kind of mineral can be expressed as the product of the pore‐fluid velocity and the equilibrium concentration of this particular kind of mineral. Using the present mineralization rate of a mineral, the potential of the modern mineralization theory is illustrated by means of finite element studies related to reactive mineral‐carrying fluids mixing problems in materially homogeneous and inhomogeneous porous rock basins.

Influence of reactive sulfide (AVS) and supplementary food on Ag, Cd and Zn bioaccumulation in the marine polychaete Neanthes arenaceodentata

A laboratory bioassay determined the relative contribution of various pathways of Ag, Cd and Zn bioaccumulation in the marine polychaete Neanthes arenaceodentata exposed to moder- ately contaminated sediments. Juvenile worms were exposed for 25 d to experimental sediments con- taining 5 different reactive sulfide (acid volatile sulfides, AVS) concentrations (1 to 30 µmol g -1 ), but with constant Ag, Cd, and Zn concentrations of 0.1, 0.1 and 7 µmol g -1 , respectively. The sediments were supplemented with contaminated food (TetraMin ® ) containing 3 levels of Ag-Cd-Zn (unconta- minated, 1 × or 5 × metal concentrations in the contaminated sediment). The results suggest that bioaccumulation of Ag, Cd and Zn in the worms occurred predominantly from ingestion of contami- nated sediments and contaminated supplementary food. AVS or dissolved metals (in porewater and overlying water) had a minor effect on bioaccumulation of the 3 metals in most of the treatments. The contribution to uptake from the dissolved source was most important in the most oxic sediments, with maximum contributions of 8% for Ag, 30% for Cd and 20% for Zn bioaccumulation. Sediment bioas- says where uncontaminated supplemental food is added could seriously underestimate metal expo- sures in an equilibrated system; N. arenaceodentata feeding on uncontaminated food would be exposed to 40-60% less metal than if the food source was equilibrated (as occurs in nature). Overall, the results show that pathways of metal exposure are dynamically linked in contaminated sediments and shift as external geochemical characteristics and internal biological attributes vary.

Prediction of the life expectancy of organic covers

The present paper aims to predict the life expectancy of organic covers, under various climatic conditions, when established over reactive sulphide wastes. Prediction is enabled with the use of a computer program that analyzes and interprets experimental data derived from laboratory tests, regarding the application of an organic cover over reactive unoxidized arsenopyrite concentrate. The life expectancy of organic covers can be predicted by establishing their potential to prevent influx of air into the underlying reactive sulphide mass. Influx of air can be calculated by recording O 2 concentration in pore air, which is directly related to the moisture content (m) within the organic material. The moisture content, in each area under study, depends mainly on rainfall rate (w) and on organic material width (h). By correlating these two parameters, provided that the initial moisture content is known, the moisture content within the organic mass, as well as its monthly variations, can be accurately predicted over long periods of time. The methodology used for the prediction of the life expectancy was based on the study of the relationships, which are considered as critical for the effective operation of an organic cover, namely (a) monthly moisture content change vs. monthly rainfall rate and width of the organic cover and (b) O 2 concentration vs. moisture content. Finally, two case studies examining the application of organic covers over reactive sulphide materials are presented and discussed.

Turbulence-Driven Metal Release from Resuspended Pyrrhotite Tailings

The use of shallow water covers (up to 2 m) to flood reactive sulfide mine tailings is a common method of reducing the environmental impact of mining. It relies on the low solubility and diffusivity of oxygen in water. In actual tailings ponds, however, wind-induced waves and turbulent mixing can lead to tailings resuspension and increased oxygen transfer. Laboratory experiments and numerical modeling were performed to examine the impact of resuspension on metal release from sulfide mine tailings, and to elucidate the nature of the flow field. The results indicated that resuspended tailings oxidized and released acidity and metals considerably more than tailings at rest. The oxidation and metal release rates increased with an increase in the degree of turbulence-induced mixing in the water cover. Computed wall shear stresses on the surface of the tailings ranged from 0.14 to 0.42 N/m², which were close to, but slightly above, the critical shear stresses of the tailings (0.12–0.17 N/m²). The flow energy was found to be positively correlated to the cumulative release of metals (zinc, nickel, copper, and ferric iron) and sulfate.

Competitive displacement reactions of cadmium, copper, and zinc added to a polluted, sulfidic estuarine sediment

AbstractThe competitive displacement reactions occurring after the addition of Cd, Cu, and Zn to a polluted, sulfidic estuarine sediment were studied. Pore‐water metal measurements indicated that added Cd and Zn reacted quantitatively with the acid‐volatile sulfide (AVS) fraction (primarily FeS) of the sediments to form CdS and ZnS, whereas Cu reacted to form Cu2S, not CuS as is often assumed. The titration of a synthetic FeS phase, with Cu(II) in a strictly oxygen‐free environment was used to provide a mechanistic illustration of the formation of Cu2S involving the reduction of Cu(II) to Cu(I) by Fe(II). Although this reduction reaction is not thermodynamically favorable in acidic solutions, in near‐neutral pH environments the dual precipitation of Cu2S (reduced phase) and FeOOH (oxidized phase) is the driving force for the reaction. Only when the sedimentary AVS (FeS) phase had been exhausted did the added Cu displace Zn and Cd ions from their respective binding phases. Likewise, Cd added in excess of the molar AVS (FeS) concentration displaced Zn from less stable solid phases. These observations, although commonly predicted by thermodynamics, have seldom been demonstrated in real sediments and provide evidence that AVS (FeS) is the most reactive phase in anoxic sediments. The metal additions caused large disturbances to the sediment redox potential. This was attributed to disruption of the HS‐/SO redox equilibrium position by precipitation of HS− as metal sulfide phases. Although these redox changes did not seem to affect the partitioning of Cd, Cu, or Zn to the reactive sulfide phase (AVS), significant changes to the pore‐water metal speciation may be expected. The effects of these observations on metal bioavailability for sediment toxicology studies that utilize metal‐spiked sediments during method development are discussed.

Use of organic covers for acid mine drainage control

Organic covers may be used to prevent diffusion of oxygen into reactive sulphide wastes and subsequently to eliminate sulphide compounds oxidation and generation of acidic waters. The main advantages over other types of covers are related with their low hydraulic permeability, high cation exchange capacity and high alkalinity. In addition, the establishment of organic covers, which is considered as a low cost solution for the prevention of acid mine drainage generation, does not disturb the natural environment, since they consist of industrial wastes rather than natural materials and allow the development of vegetation, which improves the aesthetics of the reclaimed areas. However, treatment of municipal sewage sludge is necessary prior to discharge, in order to minimize potential health and environmental risks, resulting from the presence of toxic elements. In the present paper, all processes associated with the function of an organic cover are described and discussed, including potential health and environmental risks resulting from land application of municipal sewage sludge. In addition, preliminary laboratory data, derived from the application of organic covers over reactive sulphidic concentrates are presented and discussed, in order to evaluate the performance of the covers and to determine the critical factors affecting their performance. The final aim of this research work is the development of an experimental model, that predicts the performance of an organic cover, by taking into account critical parameters such as annual rainfall rate, organic material height, initial moisture and moisture under saturation conditions.

Influences of dietary uptake and reactive sulfides on metal bioavailability from aquatic sediments.

Understanding how animals are exposed to the large repository of metal pollutants in aquatic sediments is complicated and is important in regulatory decisions. Experiments with four types of invertebrates showed that feeding behavior and dietary uptake control bioaccumulation of cadmium, silver, nickel, and zinc. Metal concentrations in animal tissue correlated with metal concentrations extracted from sediments, but not with metal in porewater, across a range of reactive sulfide concentrations, from 0.5 to 30 micromoles per gram. These results contradict the notion that metal bioavailability in sediments is controlled by geochemical equilibration of metals between porewater and reactive sulfides, a proposed basis for regulatory criteria for metals.

Iron and Aluminum Hydroxysulfates from Acid Sulfate Waters

Acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite, chalcopyrite, pyrrhotite, and marcasite in rocks, soils, sediments, and industrial wastes. This spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits, the formation of acid sulfate soils, and the mobilization and release of acidity and metals to surface and ground waters. The purely natural process of “acid rock drainage” is often intensified by human activities related to mining, mineral processing, construction, soil drainage, and dredging. Geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water, and to microbes that catalyze the reaction process. Large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing. Acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation, hydrolysis, and neutralization. The objective of this chapter is to describe the formation, properties, fate, and environmental implications of the nano- to microphase hydroxy-sulfates of Fe and Al that are precipitated from acid sulfate waters. These minerals are commonly of poor crystallinity and difficult to characterize. Much remains to be learned about their occurrence, formation, and properties. ### Mine drainage The best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited (Ash et al. 1951, Barton 1978, Nordstrom 1982a, Rose and Cravotta 1998, Nordstrom and Alpers 1999). There may be as many as 500,000 inactive or abandoned mine sites in the United States alone (Lyon et al. 1993). Although most of these pose no immediate water-quality problem, Kleinmann (1989) estimated that about 19,300 km of streams and more than 72,000 ha of lakes and reservoirs have been …

Modification of iodometric determination of total and reactive sulfide in environmental samples

In iodometric determination of sulfide two reactions are taking place when alkaline solution is added to HCl acid–iodine. The main oxidation reaction (1), H 2S+I 2=2HI+S; and side reaction of sulfide (2), S −2+4I 2+8OH −=SO 4 2−+8I −+4H 2O. Preference of reaction (2) over (1) is dependent on pH increasing to >7. When sulfide solution of pH 9 was mixed with HCl acid–iodine, the recovery exceeded 120%, but the recovery of a solution with a pH of 13 exceeded 200%. To eliminate the side reaction in iodometric titration, the sulfide solution must be acidic when it is mixed with HCl–iodine. To avoid the side reaction (2), the pH of sulfide solutions were adjusted with acetic acid to pH 5.5, mixed with HCl–iodine solution and then titrated with standard thiosulfate with precision and accuracy <±3%.

The development and performance characteristics of mixed flowing gas test environment

Three flowing mixed gases have been developed to achieve realistic simulation through the synergistic effects of (1) low concentrations of relevant pollutants, (2) humidity, and (3) temperature. The authors have demonstrated the importance of incorporating the sulfide-chloride synergisms into reproduced indoor field environments in order to simulate the observed corrosion response. By adjusting these variables, large differences can be found in materials reaction rates, corrosion mechanisms, and chemistries. Data were taken that demonstrate the effects of critical variables on corrosion processes. Relative humidity, reactive chloride concentration, and reactive sulfide concentration were consistently identified as the most important in all cases. Temperature, gas velocity, and NO/sub 2/ concentration were found to be far less critical. Sulfur dioxide was relatively unimportant for either indoor, field, or laboratory mixtures. It is concluded that three-component mixtures based on low levels of H/sub 2/S, NO/sub 2/, and Cl/sub 2/ can be used to simulate all reactive environment classes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>