Insoluble Metal Sulfides Research Articles

Inhibition of sulfate-reducing bacteria by metal sulfide formation in bioremediation of acid mine drainage.

Acid mine drainage (AMD) containing high concentrations of sulfate and heavy metal ions can be treated by biological sulfate reduction. It has been reported that the effect of heavy metals on sulfate-reducing bacteria (SRB) can be stimulatory at lower concentrations and toxic/inhibitory at higher concentrations. The quantification of the toxic/inhibitory effect of dissolved heavy metals is critical for the design and operation of an effective AMD bioremediation process. Serum bottle and batch reactor studies on metal toxicity to SRB indicate that insoluble metal sulfides can inhibit the SRB activity as well. The mechanism of inhibition is postulated to be external to the bacterial cell. The experimental data indicate that the metal sulfides formed due to the reaction between the dissolved metal and biogenic sulfide act as barriers preventing the access of the reactants (sulfate, organic matter) to the necessary enzymes. Scanning electron micrographs of the SRB cultures exposed to copper and zinc provide supporting evidence for this hypothesis. The SRB cultures retained their ability to effect sulfate reduction indicating that the metal sulfides were not lethally toxic to the SRB. This phenomenon of metal sulfide inhibition of the SRB has to be taken into account while designing a sulfate-reducing bioreator, and subsequently an efficient biotreatment strategy for AMD. Any metal sulfide formed in the bioreactor needs to be removed immediately from the system to maintain the efficiency of the process of sulfate reduction.

Chemical binding of heavy metals in anoxic river sediments

Acid volatile sulfides (AVS) in sediments are available for binding with divalent cationic metals through the formation of insoluble metal–sulfide complexes, thereby controlling the metal bioavailability and subsequent toxicity to benthic biocommunities. However, when the molar concentrations of simultaneously extracted metals (SEM) were greater than AVS, the unexpectedly low or nondetectable levels of metal in pore water could also be found. Thus, except AVS, additional binding phases in sediments were supposed to provide the binding sites for SEM. The aims of this study are to realize the spatial distribution of AVS, SEM, and other binding phases of heavy metals in anoxic sediments of the Ell-Ren river and to elucidate what may be the main additional binding phases except AVS in the anoxic river sediments. By comparing the spatial distributions of SEM/AVS ratio with various binding phases in extremely anoxic sediments (redox potential was between −115 and −208 mV), both organic matter and carbonates could be considered to be the main additional binding phases of SEM other than AVS. In addition, AVS appeared to have the priority to bind with SEM. By comparing the binding phases of heavy metals before and after AVS extraction, it could be found that Fe-oxides could also be considered to be the main additional binding phase associated with Zn in slightly anoxic sediments (redox potential was between −50 and −130 mV), while organic matter with Cu being the next.

Analysis of Acid Volatile Sulphide and Pyrites Using Microdiffusion

The microdiffusion method published by Brouwer and Murphy[1] for analysis of acid volatile sulphide (AVS-chiefly FeS) has been extended to both AVS and FeS2in a two step process. For the first step (AVS analysis), excellent recoveries (∼100%) are obtained for Na2S, FeS, PbS, CdS, and ZnS provided diffusion times are long enough. Recovery from other insoluble metal sulphides (Ag2S and HgS) were low, while for CuS were variable. In the second step, recoveries were ∼100% for ground, crystalline FeS2. This work re-emphasises the importance of adding a sufficiently strong reducing agent during AVS determination in sediments to prevent oxidation of S2− by Fe3+ produced in the acid dissolution of ferric phases. The method is amenable to adoption to different apparatus provided recoveries and reaction times are checked with suitable standards.

Landfill Bioreactor Cells as Ecofilters for Extraction of Bio-energy and Nutrients from Solid Wastes

This paper describes a modified, ecologically based waste treatment technique, where municipal solid waste is anaerobically treated in landfill reactorcells in a way that both bio-energy and nutrients can be recovered. The controlled landfill reactorcell ('bioreactor-cell') serves as an anaerobic filter, where energy is extracted as biogas while nutrients are recovered through the leachates. The leachates can be used as fertilizer in e.g. energy forests within the controlled landfill area, and thus nutrients can be brought back into an ecocycle. At the same time anaerobic conditions result in an effective immobilization of heavy metals and other pollutants, e.g. through complexation to organic matter or as insoluble metal sulphides, which are immobilized in the fermentation residue. The long-lived organic fraction, remaining after the fermentation process has declined, containing a high content of lignine, serves as a water-holding matrix. Thus it helps to enforce a sustainable high moisture level, resulting in sustainable anaerobic conditions with heavy metals retained on a long-term basis. Also non-degradable products, like plastics, help to shield off oxygen and maintain reliable anaerobic conditions. Landfilling of organic matter under anaerobic conditions is a measure to counteract increasing concentrations of CO2 in the atmosphere, resulting from human activities. A small fraction of the organic matter is long-term accumulated in the landfill, and the processes can be compared to those of natural wetlands.

Immobilizatoin of Lead Compounds in Fly Ash by Mixing with Asphalt, Sulfur and Sodium Hydroxide.

The present paper is concerned with a novel heavy metal immobilization by mixing with additives of asphalt, sulfur and sodium hydroxide. To immobilize heavy metals, fly ash were mixed with each additive by using a bi-axial kneader heated at 403 K. Then the dissolution test was carried out based on the Japan Environment Agency notification No. 13. Seven samples of fly ash discharged from the melting process of MSW incineration fly ash were employed. The present immobilization of heavy metal were considered to consist of the conbination of the following two advantages; (1) common advantage of asphalt solidification, (2) additional advantage of low solubility by metal sulfuration. Results of the experiment show that the lead concentration in the eluted solution of the treated sample satisfied Japan's lead emission standard of 0.3 mg/l. It was considered that sodium sulfides, which were produced from the reaction of sulfur and sodium hydroxide, react with heavy metals to form insoluble metal sulfides. The minimum amounts of sulfur and sodium hydroxide needed to achieve the allowable limit had a linear relationship with the heavy metal content in fly ash.

Bioaccumulation and localization of exogenous cadmium in a teleost by electron microscopy (TEM) and its specific quantitation by electron probe X-ray microanalysis (EPMA)

A cadmium bioconcentration study was carried out in a fresh water teleost, Colisa fasciatus, to study the bioaccumulation kinetics and fate of exogenous cadmium (Cd) in biological tissues. Study shows that on exposure of the fish to a sublethal concentration of cadmium in test water, Cd uptake results in its bioconcentration in gills, liver and muscle tissues. To explore whether the accumulated Cd reaches the membranes or inside the cells, transmission electron microscopy (TEM) of the thin sections of tissues was done after histochemical localization of Cd in cells by modified SST method. TEM studies of sections of gills, liver and muscle tissues showed the deposits of exogenous Cd (visualized as dense clouds) in biological cells. This suggests the presence of free or loosely bound Cd on the membranes and inside the cells, which in the presence of Na2S is converted into insoluble metal sulfides. Electron probe X-ray microanalysis (EPMA) studies confirmed the presence of Cd on the membrane surface as well as inside the cells of bioindicator organs suggesting involvement of membrane transport of exogenous Cd inside the cells and its deposition as loosely bound insoluble metal complexes.

Biological implications of sulfide in sediment—a review focusing on sediment toxicity

AbstractThe biological implications of sulfide in sediment are poorly understood and all too often ignored despite the fact that sulfide can be extremely important in determining sediment toxicity to resident biota. Sulfide influences sediment toxicity in three major ways, which are reviewed in detail: as a toxicant in its own right; by reducing metal toxicity by forming insoluble metal sulfide solids and/or by forming metal sulfide complexes; and by affecting animal behavior, which in turn can alter the toxicity of not just the sulfide but also other sediment contaminants. Our present limited understanding of sulfide in sediments represents two major problems related to determining the toxicity of sediments, both in the laboratory and the field, and the causative agents of such toxicity. First, we do not know how important sulfide toxicity is to resident populations. Second, by not adequately considering sulfide toxicity, we risk underestimating toxicity and misidentifying the causative agents. Generic and specific recommendations related to resolving these problems are provided, including appropriate measurement and monitoring of sulfide in the laboratory and the field, determination of toxicity thresholds and tolerances for a wide range of sediment‐dwelling organisms, further development of toxicity identification evaluation procedures, further research into sulfide effects on metal toxicity, and determination of the influence of sulfide on bioirrigation.

Electron transfer process: 1. Removal of organic sulphur from high sulphur Indian coal

A novel experiment was carried out for the removal of organic sulphur from high sulphur Indian coal using the electron transfer process. The process involves initial formation of naphthalene radical anion by the interaction of naphthalene, dissolved in ethanol, with a metal ion (Cu+, Co2+, Ni2+, Sn2+ or Sb3+) of variable valence state which subsequently transfers electron to organic sulphur compound. A mechanism is proposed in which cleavage of C–S bonds occur by the metal naphthalenide forming soluble metal–organic sulphur compounds. Maximum amount of leached out sulphur is found to be 9.4% of the total organic sulphur with Sb3+ ion (without naphthalene) revealing that a particular type of organic sulphur was removed by this process. Aliphatic sulphur compound is believed to have leached out from coal and was found to be effective with metal ions having highly negative oxidation potentials. In case of metal ions with low negative oxidation potentials, e.g. Cu+ and Sn2+, although organic sulphur is removed, however, these ions rapidly form insoluble metal sulphides. This work provides a novel breakthrough of desulphurization of organic sulphur from coal.

MarinevsFluvial Suspended Matter in the Scheldt Estuary

The ratio of marine to fluvial suspended matter in the Scheldt Estuary was calculated by applying factor analysis to a data set of elemental concentrations. The data set consisted of 98 samples collected under various river discharge conditions. Each sample was analysed for the concentration of Cr, Pb, Fe, Mn, Ni, Co, Ba, Zn, Cu, Cd, S, Ca, Sr, Ag, Sn and Na. Five linearly independent processes were found to describe the variability of the elemental concentrations: (1) the supply of fluvial material to the mixing zone; (2) manganese oxidation in the transition area between the anoxic upper estuary and the oxic lower estuary; (3) the supply of marine material to the mixing zone; (4) a phytoplankton bloom in the lower estuary; and (5) the formation of insoluble metal sulphides in the anoxic high-turbidity zone. Scores of the first and third factor were used to calculate the ratio of marine to fluvial suspended matter in the mixing zone. Information on the origin of both the inorganic and organic fraction of suspended matter was obtained in this way.

X-ray Absorption Spectroscopy of Lead and Zinc Speciation in a Contaminated Groundwater Aquifer

The formation of insoluble metal sulfides in the environment may reduce the mobility and bioavailability of heavy metal contaminants and potentially eliminate the need for ex situ remediation of certain hazardous waste sites. To assist in assessing remediation strategies for the Bypass 601 Superfund site, groundwater aquifer samples were analyzed using synchrotron X-ray absorption spectroscopy (XAS) to determine whether lead and zinc sulfides were dominant mineral phases. Moist aquifer solids contained between 150 and 1800 mg of Pb/kg and between 100 and 250 mg of Zn/kg. Lead sulfide was not dominant in any of the samples analyzed, including one sample collected from a well in a flood plain that contained 70% of zinc bonded to sulfur, probably as ZnS. This portion of the aquifer had apparently been under reducing conditions. In all other samples, first-shell bonding of Pb and Zn was predominantly to oxygen. Data indicated that PbO, PbCO3, PbSO4, and ZnO were not dominant metal species. The XAS analyses sh...

Bioleaching: metal solubilization by microorganisms

Bioleaching is a simple and effective technology for metal extraction from low-grade ores and mineral concentrates. Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. thiooxidans, which convert insoluble metal sulfides into soluble metal sulfates. Non-sulfide ores and minerals can be treated by heterotrophic bacteria and by fungi. In these cases metal extraction is due to the production of organic acids and chelating and complexing compounds excreted into the environment. At present bioleaching is used essentially for the recovery of copper, uranium and gold, and the main techniques employed are heap, dump and in situ leaching. Tank leaching is practised for the treatment of refractory gold ores. Bioleaching has also some potential for metal recovery and detoxification of industrial waste products, sewage sludge and soil contaminated with heavy metals.

Evaluation of metal/acid‐volatile sulfide relationships in the prediction of metal bioaccumulation by benthic macroinvertebrates

AbstractRecent studies have demonstrated that the toxicity of divalent cationic metals (cadmium, copper, lead, nickel, and zinc) in sediments can be controlled through binding to acid‐volatile sulfide (AVS). When the molar concentration of AVS exceeds that of the metals (i.e., the metal/AVS ratio is less than unity), they exist predominantly as insoluble metal sulfides, which presumably are not biologically available. Thus, at metal/AVS ratios less than 1, toxicity of sediment‐associated metals to benthic macroin‐vertebrates has not been observed. However, bioaccumulation may provide a more direct assessment of contaminant bioavailability than the presence or absence of toxicity. The purpose of this report is to comprehensively review available literature on metal bioaccumulation versus sediment metal/AVS relationships to further examine the tenet that AVS controls metal bioavailability. In all, 12 studies were evaluated; these ranged from short‐term (10‐d) laboratory experiments with metal‐spiked or field‐collected sediments containing cadmium, copper, lead, nickel, and/or zinc to long‐term (> 1‐year) field studies with sediments spiked with cadmium or zinc. Test organisms included mollusks, oligochaetes, polychaetes, amphipods, and midges. The preponderance of studies indicated reduced accumulation of metals at sediment metal/AVS ratios of less than 1. However, there were exceptions to this general observation, two of which occurred in short‐term laboratory experiments with cadmium‐ or nickel‐spiked sediments. In these studies there appeared to be a linear accumulation of metals with increasing sediment metal concentrations irrespective of the metal/AVS ratio. Although there is experimental evidence suggesting that significant bioaccumulation of metals does not occur when there is sufficient AVS available to bind them, the existence of at least some data to the contrary indicates the need for further research relative to factors controlling the bioaccumulation of metals from sediments.

Full-scale plant study on fly ash treatment by the acid extraction process

Fly ash discharged from a municipal refuse incineration plant is regulated, by 1992 legislation, to be treated to prevent leaching of heavy metals before final disposal. We have developed a stable and simple fly ash treatment method “Acid Extraction-Sulfide Stabilization Process (AES Process)”, in which the fly ash is acid-extracted and stabilized by NaHS to change the residual heavy metal into insoluble heavy metal sulfide. The results of many fundamental experiments and pilot tests indicate that it is important to consider the characteristics of fly ash (fine, scattering, moisture-absorbing, etc.) in designing the AES Process. Since 1977, seven municipal incineration plants with AES Process have been constructed. At one of these plants, the fly ash and waste water is treated together by the AES Process and evaporation/crystallization process. The fly ash is discharged as stabilized cake for final landfill disposal; solid salt is recycled to soda production plants and condensed water is recycled in the plant as cooling water. This plant discharges no waste water. Operating results of the AES Process is that the stabilized cake conforms to the standard for landfill disposal in T-Hg, Cd and Pb, and the recovered solid salt contains approximately 99% NaCl. The operation cost per ton of the fly ash is ¥3,840 per ton.

Health effects of metals: a role for evolution?

Metals have been mined and used since ancient times. The industrial era has seen a sharp increase in both the amounts and variety of metals that find applications in industry. The inadvertent release of metals, such as from fossil fuel consumption, also adds to the global burden. A number of catastrophic outbreaks have alerted us to the occupational and environmental health risks. Life on this planet has evolved in the presence of metals. Cells learned to make use of the more abundant metals in the Archean oceans as an integral component in their structure and function. Today, we inherit these as the essential metals. At the same time, evolving life must have developed means of coping with the potentially toxic actions of metals. The appearance of oxygen in the atmosphere in the Precambrian period also resulted in cells both using and developing protective mechanisms against what must have been a highly toxic, reactive gas. Atmospheric oxygen must have increased the solubility of many metals as insoluble metal sulfides were oxidized to the more soluble sulfates. It may be no coincidence that the protective mechanisms for oxygen are also used to protect against a number of toxic metals. Selected examples are given on the role of evolution in metal toxicology, specifically, examples where the normal function of essential metals is deranged by competition with nonessential metals. Examples are also given of protective mechanisms that involve enzymes or cofactors involved in the oxygen defense system.

Biogeochemical cycling of nutrients and trace metals in anoxic freshwater sediments of the Neckar River, Germany

Pore-water components (SO42-, Fe2+, Mn2+), including nutrients (NH4+:, NO3-, PO43-), alkalinity and pH were determined at three sites in the Neckar River. Sequential extraction procedures and trace metals in both pore waters and sediments are reported in order to evaluate the mobility of trace metals in contaminated sediments. The results show that the mineralization of organic matter plays an important role in the cycling of nutrients and trace metals. Pore-water profiles (Zn, Cu, Pb, Cd) suggest that the element maximums at the sediment-water interface are caused by the decomposition of biomass. Low concentrations of dissolved Zn, Cu, Pb and Cd in the anoxic sediments can be explained by a sharp decrease of SO42- in pore water concomitant with HS- production. This leads to the formation of highly insoluble metal sulfides. Solubility calculations show that the sediments act as a sink for trace metals with respect to trace metal sulfides. The organic/sulfidic-bound fraction accounts for 64-81% of Cd in the sediment cores, 36-67% of Pb and 51-69% of Cu. In contrast, Cr in pore water increases with depth because of its release from Fe/Mn oxides. NH4+ and PO43- are also released into the pore water owing to the mineralization of organic matter. No significant fluxes of NH4+ and PO43- into overlying water were found because of the existence of an oxic surface layer.

Treatment of metal‐contaminated water using bacterial sulfate reduction: Results from pilot‐scale reactors

Simple anaerobic reactors were installed to treat metal-contaminated water in an underground coal mine and at a smelting residues dump in Pennsylvania. The reactors consisted of barrels and tanks filled with spent mushroom compost, within which bacterial sulfate reduction became established. Concentrations of Al, Cd, Fe, Mn, Ni, and Zn were typically lowered by over 95% as contaminated water flowed through the reactors. Cadmium, Fe, Ni, and some Zn were retained as insoluble metal sulfides following their reaction with bacterially generated H(2)S. Aluminum, Mn, and some Zn hydrolyzed and were retained as insoluble hydroxides or carbonates. Reactor effluents were typically circumneutral in pH and contained net alkalinity. The principal sources of alkalinity in the reactors were bacterial sulfate reduction and limestone dissolution. This article examines the chemistry of the reactor systems and the opportunities for enhancing their metal-retaining and alkalinity-generating potential.

Treatment of Metal-Contaminated Water Using Bacterial Sulfate Reduction: Results from Pilot-Scale Reactors

Simple anaerobic reactors were installed to treat metal-contaminated water in an underground coal mine and at a smelting residues dump in Pennsylvania. The reactors consisted of barrels and tanks filled with spent mushroom compost, within which bacterial sulfate reduction became established. Concentrations of Al, Cd, Fe, Mn, Ni, and Zn were typically lowered by over 95% as contaminated water flowed through the reactors. Cadmium, Fe, Ni, and some Zn were retained as insoluble metal sulfides following their reaction with bacterially generated H2S. Aluminum, Mn, and some Zn hydrolyzed and were retained as insoluble hydroxides or carbonates. Reactor effluents were typically circumneutral in pH and contained net alkalinity. The principal sources of alkalinity in the reactors were bacterial sulfate reduction and limestone dissolution. This article examines the chemistry of the reactor systems and the opportunities for enhancing their metal-retaining and alkalinity-generating potential. © 1992 John Wiley & Sons, Inc.

Aqueous Solubilities, Solubility Products and Standard Oxidation‐Reduction Potentials of the Metal Sulfides

Available thermodynamic data, incorporating a new free energy of formation for aqueous S2− of 111 (±2) kJ/mol at 25°C, indicate that solubility products of the insoluble metal sulfide salts are several orders of magnitude smaller than previously considered. Thermodynamic characterization for a variety of soluble and insoluble aqueous metal sulfide systems is reported. Trends in the aqueous solubilities of the alkali salts solubilities are compared and discussed. New aqueous solubility products, , and standard redox potentials, , for over forty metal sulfides are determined. The new values of and at 25°C include: , and . Significant free S2− occurs only in extremely alkaline media. The suitability of , rather than , based solubility products and redox potentials is discussed and these alternate values determined.

Pixe analysis of the platinum group elements preconcentrated from geological samples

A fast multi-elemental method of measuring the platinum group elements (PGEs) in geological samples is needed for the geochemical study and the commercial exploitation of these metals. The application of particle induced X-ray emission (PIXE) for the determination of ng-range concentrations of platinum, palladium, rhodium and ruthenium in terrestrial rocks is described. The PGEs are inhomogeneously distributed in sulphide ores and their host rocks, necessitating the analysis of large sample aliquots to obtain representative results. Preconcentration of the sample material is therefore essential for their analysis by PIXE. The noble metals are extracted from a 50 g sample by a modified nickel sulphide fire-assay technique. The resulting NiS button is partly dissolved in hydrochloric acid and the insoluble noble metal sulphides are retained on a Nuclepore filter membrane which is then used directly as a target for PIXE analysis. The method was evaluated by the analysis of serially diluted samples of a standard reference material of a platinum bearing ore. X-ray spectrum optimisation was investigated using differential X-ray absorbers. Detection limits of ∼ 0.5 ng/g were established for the elements Rh, Ru, Pd and Pt. The low detection limits and relative simplicity of analysis by PIXE compare favourably with other recently developed procedures.

Bacterial leaching of metals from sewage sludge

Thiobacillus thiooxidans is capable of oxidizing sulfur in digested sludge, while decreasing the pH value from about 5.5 to, say, 1.0 to 1.5. Insoluble metal sulfides can be solubilized through this acidification. Thiobacillus ferrooxidans oxidises pyritic ore in the presence of 6% centrifuged sludge if the pH value is adjusted to about 2.5. When mixing T. thiooxidans and T. ferrooxidans with sludge and 1% sulfur, the former acidifies the sludge and the latter oxidizes metal sulfides; together they solubilize more metal than T. thiooxidans alone. The following metals solubilized from their sulfides have been investigated so far: iron, copper, zinc, nickel, and cadmium. The possibility of recycling metals from sewage sludge with this method is discussed.