Dissolution Of Metal Sulfides Research Articles

Recovery and enrichment of valuable metals from zinc oxide dust and mitigation of toxicity based on tartaric acid and hydrogen peroxide

Considering the lack of some valuable metal resources and the toxicity of zinc oxide dust. In this study, firstly, sulfuric acid and tartaric acid were used as solvents to dissolve zinc, germanium, indium, and tin or produce soluble complex dissolution under the action of ultrasonic wave. In addition, the introduction of tartaric acid can not only effectively decompose zinc ferrite, release germanium and indium in its lattice, but also reduce Fe3+ (Ferri ion, Ⅲ) and overcome the defects of Fe3+ hydrolysis-coprecipitation. Then, sulfuric acid and hydrogen peroxide were used to promote the dissolution of metal sulfides, thereby improving the comprehensive recovery rate of metals. The study demonstrates that the final recovery rate of metals was 97.44 %, 97.01 %, 91.26 %, and 90.86 %, respectively, and the slag rate was 30.36 % under optimal conditions. The grade of lead and argentum in the residue were increased to 50.68 % and 691.63 g·t−1. During the reaction, about 50 % of arsenic and 95 % of cadmium entered the solution and were removed. Compared with the enterprise, this process shortens the total leaching time to 90 min, greatly reduces the amount of sulfuric acid, significantly improves the recovery rate of valuable metals, and reduces the toxicity of slag.

Removal of heavy metals from mine tailings by in-situ bioleaching coupled to electrokinetics

This work utilizes a combined biological-electrochemical technique for the in-situ removal of metals from polluted mine tailings. As the main novelty point it is proposed to use electrokinetics (EK) for the in-situ activation of a bioleaching mechanism into the tailings, in order to promote biological dissolution of metal sulphides (Step 1), and for the subsequent removal of leached metals by EK transport out of the tailings (Step 2). Mine tailings were collected from an abandoned Pb/Zn mine located in central-southern Spain. EK-bioleaching experiments were performed under batch mode using a lab scale EK cell. A mixed microbial culture of autochthonous acidophilic bacteria grown from the tailings was used. Direct current with polarity reversal vs alternate current was evaluated in Step 1. In turn, different biological strategies were used: biostimulation, bioaugmentation and the abiotic reference test (EK alone). It was observed that bioleaching activation was very low during Step 1, because it was difficult to maintain acidic pH in the whole soil, but then it worked correctly during Step 2. It was confirmed that microorganisms successfully contributed to the in-situ solubilization of the metal sulphides as final metal removal rates were improved compared to the conventional abiotic EK (best increases of around 40% for Cu, 162% for Pb, 18% for Zn, 13% for Mn, 40% for Ni and 15% for Cr). Alternate current seemed to be the best option. The tailings concentrations of Fe, Al, Cu, Mn, Ni and Pb after treatment comply with regulations, but Pb, Cd and Zn concentrations exceed the maximum values. From the data obtained in this work it has been observed that EK-bioleaching could be feasible, but some upgrades and future work must be done in order to optimize experimental conditions, especially the control of soil pH in acidic values.

Gallionella and Sulfuricella populations are dominant during the transition of boreal potential to actual acid sulfate soils

Acid sulfate soils release metal laden, acidic waters that affect the environment, buildings, and human health. In this study, 16S rRNA gene amplicons, metagenomes, and metatranscriptomes all demonstrated distinct microbial communities and activities in the unoxidized potential acid sulfate soil, the overlying transition zone, and uppermost oxidized actual acid sulfate soil. Assembled genomes and mRNA transcripts also suggested abundant oxidized acid sulfate soil populations that aligned within the Gammaproteobacteria and Terracidiphilus. In contrast, potentially acid tolerant or moderately acidophilic iron oxidizing Gallionella and sulfur metabolizing Sulfuricella dominated the transition zone during catalysis of metal sulfide oxidation to form acid sulfate soil. Finally, anaerobic oxidation of methane coupled to nitrate, sulfate, and ferric reduction were suggested to occur in the reduced parent sediments. In conclusion, despite comparable metal sulfide dissolution processes e.g., biomining, Gallionella and Sulfuricella dominated the community and activities during conversion of potential to actual acid sulfate soils.

Microbial controls on heavy metals and nutrients simultaneous release in a seasonally stratified reservoir.

The eutrophication of reservoirs can change the physicochemical parameters of water, thus affecting the migration and transformation of heavy metals. At present, there is insufficient research on the coupling mechanisms between nutrients and heavy metals, especially between heavy metals in suspended particles. In this paper, spatial and temporal distribution characteristics of nutrients dissolved heavy metals, and heavy metals in suspended particles were analyzed in a seasonally stratified reservoir. Combined with the nitrogen and phosphorus biogeochemical process, the coupling mechanisms between heavy metals and nutrients were discussed. The results showed that the Aha Reservoir had temperature and dissolved oxygen stratification in April and July. The reduction and dissolution of Fe and Mn oxide/hydroxide and the resuspension of sediments might result in a simultaneous increase in the concentrations of nutrients, dissolved heavy metals and heavy metals in suspended particles in hypolimnion in July and October. In the presence of dissimilatory iron-reducing bacteria (DRIB), the dissolution of iron-bound phosphorus in sediments and suspended particulate matter (SPM) might lead to the simultaneous release of iron and phosphorus into the water. The dissolution of metal sulfides in the sediments and SPM under the action of dissimilatory nitrate reduction to ammonium (DNRA) bacteria might lead to the simultaneous release of ammonia nitrogen and heavy metals into the water. Due to the coupling between nitrogen and phosphorus and heavy metals, seasonal stratified reservoir may face the risk of periodic simultaneous pollution of eutrophication and heavy metals in summer and autumn. This research provides theoretical support for the treatment of heavy metal and eutrophication combined pollution in karst areas.

Influence of UVA radiation on growth, biofilm formation and bioleaching capacity of Leptospirillum ferrooxidans

Ultraviolet-A (UVA) radiation is one of the most stressful oxidative agents that bacteria have to face in natural environments. The effect of this radiation on growth, survival, biofilm formation, and bioleaching activity of two Leptospirillum ferrooxidans strains was studied, comparing the collection strain DSM2705 with FAM-RA2, a strain recently isolated from Famatina (La Rioja, Argentina), at 3869 m above sea level (ma.s.l.). We demonstrated that the isolate FAM-RA2 was more UVA resistant than the collection strain DSM2705 in kinetic growth and biofilm formation assays. However, both strains presented a similar behavior in their bioleaching capacity. Higher levels of intracellular reactive oxygen species (ROS) after UVA exposure were detected in DSM2705 strain, suggesting the presence of stronger defensive mechanisms against oxidative stress in FAM-RA2 strain. Assays of biofilm formation showed that UVA radiation induced cell adhesion and extracellular polymeric substance (EPS) production in the collection strain DSM2705, but not in the FAM-RA2 strain. The ability of UVA radiation to increase biofilm formation in DSM2705 led us to suppose that this agent could promote its bioleaching activity; however, under these studied conditions, this stress agent did not enhance metal sulfide dissolution. This study provides first insights into the effects of UVA radiation on the physiological features of acidophilic microorganisms.

Size speciation of dissolved trace metals in hydrothermal plumes on the Southwest Indian Ridge

Determining the size speciation and chemical transformation of trace metals is of paramount in order to better assess the impact of hydrothermal activities on the ocean metal budgets. In this study, we examined the concentration and size speciation of dissolved trace metals (i.e. Mn, Fe, Cu, Ni, Mo, As, Pb, Cd) in the hydrothermal plumes of two vent fields (i.e. Longqi and Tiancheng) on the Southwest Indian Ridge. The majority of dissolved Mn (75–100%) in the buoyant and non-buoyant plumes were presented as soluble Mn (<1 kDa), while dissolved Fe in the buoyant plume contained considerable colloidal Fe (54–95%). More than 66% of hydrothermally dissolved Fe was removed in the buoyant plume within a short distance of dispersion. Except for the samples most proximal to the fluid source, concentrations of Cu, Ni and Mo in the plumes were comparable to those of the background seawater and independent of the plume dilution. Concentrations of dissolved As and Pb in the buoyant plume of the Tiancheng field were higher than those of the Longqi field, resulting from the scavenging of As in the Longqi field and the release of Pb from metal sulfide dissolution in the Tiancheng field. Concentrations of dissolved Cd in the non-buoyant plume were nearly identical to the background seawater and soluble Cd was dominant (75–92%) in the soluble phase. In contrast, 33–96% (or 0.024–0.085 μg/kg) of dissolved Cd was removed in the buoyant plume and the remaining dissolved Cd was mainly in colloidal phase (up to 96%), suggesting that hydrothermal plume was likely an important sink of oceanic Cd and colloidal ligands played an important role in the stabilization of hydrothermal Cd. Our study has demonstrated the very dynamic nature of trace metal speciation in hydrothermal vent fluids.

Dissolution of PbS, CuS, and ZnS in oxic waters: effects of adsorbed natural organic matter.

Metal sulfides serve as sinks of toxic heavy metals in anoxic sediments. Suspension of metal sulfides to oxic water columns may cause their oxidative dissolution, leading to the release of toxic heavy metal ions. Ubiquitous natural organic matter (NOM) could adsorb on the surfaces of metal sulfides and influence their dissolution. In this study, the dissolution of suspended PbS, CuS, and ZnS with different levels of adsorbed NOM was investigated. The rates of metal release showed the following order after normalization by the available surface areas: PbS > CuS > ZnS. The adsorbed NOM was found to inhibit the oxidative dissolution of PbS and ZnS; the degree of inhibition was enhanced by increased levels of NOM adsorption. In contrast, the dissolution of CuS was found to increase and then decrease with increased levels of NOM adsorption. These results show that adsorbed NOM can promote metal release via ligand-induced dissolution, as well as inhibit metal release by forming a barrier against oxygen and proton attacks. The relative importance of these processes is metal specific and governs the overall impacts of NOM adsorption on the dissolution of metal sulfides. The results imply that remobilization of heavy metals from contaminated sediments during intensified storm events should be carefully evaluated in terms of metals of concern and levels of organic matter adsorption.

Systems biology of acidophile biofilms for efficient metal extraction

Society’s demand for metals is ever increasing while stocks of high-grade minerals are being depleted. Biomining, for example of chalcopyrite for copper recovery, is a more sustainable biotechnological process that exploits the capacity of acidophilic microbes to catalyze solid metal sulfide dissolution to soluble metal sulfates. A key early stage in biomining is cell attachment and biofilm formation on the mineral surface that results in elevated mineral oxidation rates. Industrial biomining of chalcopyrite is typically carried out in large scale heaps that suffer from the downsides of slow and poor metal recoveries. In an effort to mitigate these drawbacks, this study investigated planktonic and biofilm cells of acidophilic (optimal growth pH < 3) biomining bacteria. RNA and proteins were extracted, and high throughput “omics” performed from a total of 80 biomining experiments. In addition, micrographs of biofilm formation on the chalcopyrite mineral surface over time were generated from eight separate experiments. The dataset generated in this project will be of great use to microbiologists, biotechnologists, and industrial researchers.

Effect of biogenic jarosite on the bio-immobilization of toxic elements from sulfide tailings

The discharge of toxic elements from tailings soils in the aquatic environments occurs chiefly in the presence of indigenous bacteria. The biotic components may interact in the opposite direction, leading to the formation of a passivation layer, which can inhibit the solubility of the elements. In this work, the influence of jarosite on the bio-immobilization of toxic elements was studied by native bacteria. In batch experiments, the bio-immobilization of heavy metals by an inhibitory layer was examined in the different aquatic media using pure cultures of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. A variety of analyses also investigated the mechanisms of metals bio-immobilization. Among different tests, the highest metal solubility yielded 99% Mn, 91% Cr, 95% Fe, and 78% Cu using A. ferrooxidans in 9KFe medium after ten days. After 22 days, these percentages decreased down to 30% Mn and about 20% Cr, Fe, and Cu, likely due to metal immobilization by biogenic jarosite. The formation of jarosite was confirmed by an electron probe micro-analyzer (EPMA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The mechanisms of metal bio-immobilization by biogenic jarosite from tailings soil confirmed three main steps: 1) the dissolution of metal sulfides in the presence of Acidithiobacillus bacteria; 2) the nucleation of jarosite on the surface of sulfide minerals; 3) the co-precipitation of dissolved elements with jarosite during the bio-immobilization process, demonstrated by a structural study for jarosite. Covering the surface of soils by the jarosite provided a stable compound in the acidic environment of mine-waste.

Intensification of Sulfuric Acid Leaching of Copper from Sulfide Concentrates Using Ozone and Iron Ions

Studies have been conducted to establish the patterns of sulfuric acid dissolution of metal sulfides in the presence of environmentally friendly oxidizing agents, ozone and iron(III) ions; determine the parameters and modes of intensified extraction of metals into solution; reduce the consumption of oxidizing agents; and develop the least environmentally intense and most cost-effective methods for the extraction of nonferrous metals from sulfide ores, concentrates, and industrial wastes. A copper sulfide concentrate with a grain size of 0.074 mm (90%) and a copper content of 24.5% obtained by the flotation concentration of ore from the Udokan deposit and ozone with a concentration of 80–180 mg/L in a mixture with oxygen are used for the study. The concentrate is fed into a stirred reactor at a rate of 1–5 mL/s. Patterns are studied within the sulfuric acid concentration range 20–100 g/L and a Fe(III) ion concentration of 7.8–29.2 g/L at a solid phase to liquid phase ratio 1.1–1.5 at a temperature of 18–60°C. It has been established that the use of Fe(III) ions and ozone can significantly intensify the recovery of copper from sulfides in sulfuric acid solutions. The extraction of copper from sulfides increases in proportion to the 2.4-fold increase in the concentration of Fe(III) from 7.8 to 29.25 g/L. Ozone effectively oxidizes Fe(II) and regenerates the oxidizing agent, Fe(III) ions. With an increase in the temperature and iron concentration, the consumption of ozone for oxidation increases; namely, 0.22 mol of O3 is consumed per 1 mol of Fe, which is higher than a theoretical value of 0.17. An increase in the rate of the ozone-assisted extraction of copper from sulfides is achieved by increasing the temperature from 20 to 50°C (by 1.4 times), the concentration of ozone from 85 to 180 mg/L (3 times), the feed rate of the ozone–oxygen gas mixture from 1 to 5 mL/s (2.7 times at 20°C and 3.9 times at 50°C), and by the addition of Fe(III) ions by ~1.5 times at 50°C and [Fe(III)] = 10 g/L. The largest oxidizing activity in the sulfuric acid solution is provided by ozone decomposition products at a temperature of 50°C when the solubility of ozone decreases. The ozone utilization coefficient and specific ozone consumption rate for extracted copper decrease with an increase in the feed rate of the ozone–oxygen gas mixture from 1 to 5 mL/s by 1.42 times at 20°C and by 1.16 times at 50°C and increase with an increase in the temperature and concentration of Fe(III) due to the rapid decomposition of ozone and its unproductive use for the oxidation of iron.

Intensification of sulfuric acid leaching of copper from sulfide concentrates with the use of ozone and iron ions

The studies were carried out in order to establish the patterns of sulfuric acid dissolution of metal sulfides with the participation of environmentally friendly oxidizing agents – ozone and iron (III) ions, to determine the parameters and intensification modes of metal extraction into the solution, reduce oxidizing agent consumption. The purpose of the studies was to develop the least environmentally intense, cost-effective methods for extracting non-ferrous metals from sulfide ores, concentrates and industrial waste. For study, we used copper sulfide concentrate of flotation concentration of ore from the Udokan deposit with a grain size of 90 % –0.074 mm with a copper content of 24.5 %, ozone with a concentration of 80–180 mg/l in a gas mixture with oxygen, fed to the reactor at a speed of 1–5 ml/s. Patterns were studied in the range of sulfuric acid concentration of 20–100 g/l, Fe(III) ion concentration of 7.8–29.2 g/l, temperature of 18–60 °C in stirred reactors with the solid-to-liquid ratio of 1.1 ÷ 1.5. It was found that the use of Fe(III) ions and ozone can significantly intensify copper recovery from sulfides to the sulfuric acid solution. Copper extraction from sulfides increases in proportion to the 2.4-fold increase in the concentration of Fe(III) from 7.8 to 29.25 g/l. Ozone effectively oxidizes Fe(II) and regenerates Fe(III) ions. With the rising temperature and iron concentration, ozone consumption for oxidation increases:0.22 mol of O 3 is consumed per 1 mol of Fe that is more than the theoretical value of 0.17. An increase in the rate of copper extraction from sulfides using ozone is achieved by increasing the temperature from 20 to 50 °C (1.4 times), ozone concentration from 85 to 180 mg/l (3 times), feed rate of ozone-oxygen mixture from 1 to 5 ml/s (2.7 times at 20 °C, 3.9 times at 50 °C), by adding Fe(III) ions (~1.5 times at 50 °C [Fe(III)] = 10 g/l). The highest oxidizing activity in a sulfuric acid solution is provided by ozone decomposition products at a temperature of 50 °C when its solubility decreases. Ozone utilization coefficient and specific ozone consumption for extracted copper decrease with an increase in the ozone-oxygen mixture supply rate with oxygen from 1 to 5 ml/s (1.42 times at 20 °C, 1.16 times at 50 °C) and increase with rising temperature and Fe(III) concentration due to the rapid ozone decomposition and unproductive use for iron oxidation.

Microstructure evolution of low-grade chalcopyrite ores in chloride leaching - A synchrotron-based X-ray CT approach combined with a data-constrained modelling (DCM)

The dissolution of metal sulfides, especially chalcopyrite and the development of porosity in samples of two different low-grade ores during chloride leaching have been studied by synchrotron-based micro-CT. Quantitative analysis of the changes was achieved by using a data-constrained modelling (DCM) approach. The result indicated that void spaces developed from the surface gradually into the core of a sample, which increased from 0.08% to as much as 11.1% in the Chilean ore, and from 0.05% to 0.93% in the Mongolian ore. Combining the results of DCM modelling and CsCl distribution test, no pore structure stretching into the core of the samples was found. As a result, the leaching of metal sulfide mostly happened in the out rim of both samples, where the mineral is directly exposed to the solution. For the Chilean ore, the volume fraction of metal sulfide decreased from 4.45% to 4.06% in 17 h in the sample as a whole, and from 1.23% to 1.2% in the core. For the Mongolian ore, the volume fraction of metal sulfide decreased from 0.23% to 0.21% in the same time span. This study provides clear evidence that contact of the target mineral with leaching solution is the primary premise for metal dissolution to happen. It also demonstrates that the combination of synchrotron CT and DCM is a useful approach for mineral micro-structure analysis.

Sphalerite bioleaching comparison in shake flasks and percolators

Bioleaching experiments with a mixed Acidithiobacillus-culture were carried out in shake flasks as well as in column percolators with crushed and sieved sphalerite-rich ore from a former mine in the German Harz Mountains. Efficient sphalerite dissolution in the bioleaching assays was observed in contrast to the chemical leaching experiments. The redox potential was higher in the bioleaching than in the chemical control assays. Total cell counting and most-probable-number cultivation congruently exhibited high cell numbers at the end of the bioleaching experiments of about one month. The kinetics of sphalerite bioleaching showed a linear increase of the zinc concentration in solution with time and exhibited similar sphalerite surface related reaction rates for percolators and shake flasks indicating that the overall sphalerite dissolution rate was mainly controlled by the total mineral surface. Maximal zinc bioleaching efficiency with up to 10 g/L zinc in the pregnant leach solution was achieved at a low starting pH 1.8 and addition of 2 g/L ferrous iron. Besides zinc, up to 1 mg/L gallium as trace element was extracted. Electrochemical analysis of leaching residues was performed as well to analyze potential surface related limitations for metal sulfide dissolution.

Effects of resuspension on the mobility and chemical speciation of zinc in contaminated sediments.

Identifying and quantifying the processes governing the mobilization of metals during resuspension events is key to assessing long-term metals efflux from sediments and associated ecological impacts. We investigated the effects of sediment resuspension on the mobilization and chemical speciation of zinc in two-week-long batch experiments using metal-contaminated sediments from Lake DePue (IL, USA). Measurements of dissolved zinc and sulfate allowed us to characterize the kinetics of metal sulfide dissolution and the resulting net release of zinc to the aqueous phase. X-ray absorption spectroscopy (XAS) provided direct insights into the chemical speciation of iron and zinc and their dynamic transformations during resuspension. While ZnS rapidly oxidized during resuspension, dissolved zinc increased only after two days of resuspension. We proposed a kinetic model to explain changes in the chemical speciation of zinc during these experiments as constrained by the dissolved species concentrations and chemical speciation as informed by XAS. Only 15% of the zinc mobilized was released to the aqueous phase while the remaining fraction repartitioned the solid phase either as a carbonate precipitate or as a sorbed species. Our results show that zinc sorption onto particle surfaces and reprecipitation of zinc minerals limit zinc solubility during resuspension of metal-sulfide sediments.

Automated Microscopic Analysis of Metal Sulfide Colonization by Acidophilic Microorganisms.

Industrial biomining processes are currently focused on metal sulfides and their dissolution, which is catalyzed by acidophilic iron(II)- and/or sulfur-oxidizing microorganisms. Cell attachment on metal sulfides is important for this process. Biofilm formation is necessary for seeding and persistence of the active microbial community in industrial biomining heaps and tank reactors, and it enhances metal release. In this study, we used a method for direct quantification of the mineral-attached cell population on pyrite or chalcopyrite particles in bioleaching experiments by coupling high-throughput, automated epifluorescence microscopy imaging of mineral particles with algorithms for image analysis and cell quantification, thus avoiding human bias in cell counting. The method was validated by quantifying cell attachment on pyrite and chalcopyrite surfaces with axenic cultures of Acidithiobacillus caldus, Leptospirillum ferriphilum, and Sulfobacillus thermosulfidooxidans. The method confirmed the high affinity of L. ferriphilum cells to colonize pyrite and chalcopyrite surfaces and indicated that biofilm dispersal occurs in mature pyrite batch cultures of this species. Deep neural networks were also applied to analyze biofilms of different microbial consortia. Recent analysis of the L. ferriphilum genome revealed the presence of a diffusible soluble factor (DSF) family quorum sensing system. The respective signal compounds are known as biofilm dispersal agents. Biofilm dispersal was confirmed to occur in batch cultures of L. ferriphilum and S. thermosulfidooxidans upon the addition of DSF family signal compounds.IMPORTANCE The presented method for the assessment of mineral colonization allows accurate relative comparisons of the microbial colonization of metal sulfide concentrate particles in a time-resolved manner. Quantitative assessment of the mineral colonization development is important for the compilation of improved mathematical models for metal sulfide dissolution. In addition, deep-learning algorithms proved that axenic or mixed cultures of the three species exhibited characteristic biofilm patterns and predicted the biofilm species composition. The method may be extended to the assessment of microbial colonization on other solid particles and may serve in the optimization of bioleaching processes in laboratory scale experiments with industrially relevant metal sulfide concentrates. Furthermore, the method was used to demonstrate that DSF quorum sensing signals directly influence colonization and dissolution of metal sulfides by mineral-oxidizing bacteria, such as L. ferriphilum and S. thermosulfidooxidans.

Comparative Analysis of Attachment to Chalcopyrite of Three Mesophilic Iron and/or Sulfur-Oxidizing Acidophiles

Adhesion plays an important role in bacterial dissolution of metal sulfides, since the attached cells initiate the dissolution. In addition, biofilms, forming after bacterial attachment, enhance the dissolution. In this study, interactions between initial adhesion force, attachment behavior and copper recovery were comparatively analyzed for Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans during bioleaching of chalcopyrite. The adhesion forces between bacteria and minerals were measured by atomic force microscopy (AFM). L. ferrooxidans had the largest adhesion force and attached best to chalcopyrite, while A. ferrooxidans exhibited the highest bioleaching of chalcopyrite. The results suggest that the biofilm formation, rather than the initial adhesion, is positively correlated with bioleaching efficiency.

Influence of Structural Defects on Biomineralized ZnS Nanoparticle Dissolution: An in-Situ Electron Microscopy Study.

The dissolution of metal sulfides, such as ZnS, is an important biogeochemical process affecting fate and transport of trace metals in the environment. However, current studies of in situ dissolution of metal sulfides and the effects of structural defects on dissolution are lacking. Here we have examined the dissolution behavior of ZnS nanoparticles synthesized via several abiotic and biological pathways. Specifically, we have examined biogenic ZnS nanoparticles produced by an anaerobic, metal-reducing bacterium Thermoanaerobacter sp. X513 in a Zn-amended, thiosulfate-containing growth medium in the presence or absence of silver (Ag), and abiogenic ZnS nanoparticles were produced by mixing an aqueous Zn solution with either H2S-rich gas or Na2S solution. The size distribution, crystal structure, aggregation behavior, and internal defects of the synthesized ZnS nanoparticles were examined using high-resolution transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectroscopy. The characterization results show that both the biogenic and abiogenic samples were dominantly composed of sphalerite. In the absence of Ag, the biogenic ZnS nanoparticles were significantly larger (i.e., ∼10 nm) than the abiogenic ones (i.e., ∼3-5 nm) and contained structural defects (e.g., twins and stacking faults). The presence of trace Ag showed a restraining effect on the particle size of the biogenic ZnS, resulting in quantum-dot-sized nanoparticles (i.e., ∼3 nm). In situ dissolution experiments for the synthesized ZnS were conducted with a liquid-cell TEM (LCTEM), and the primary factors (i.e., the presence or absence structural defects) were evaluated for their effects on the dissolution behavior using the biogenic and abiogenic ZnS nanoparticle samples with the largest average particle size. Analysis of the dissolution results (i.e., change in particle radius with time) using the Kelvin equation shows that the defect-bearing biogenic ZnS nanoparticles (γ = 0.799 J/m2) have a significantly higher surface energy than the abiogenic ZnS nanoparticles (γ = 0.277 J/m2). Larger defect-bearing biogenic ZnS nanoparticles were thus more reactive than the smaller quantum-dot-sized ZnS nanoparticles. These findings provide new insight into the factors that affect the dissolution of metal sulfide nanoparticles in relevant natural and engineered scenarios, and have important implications for tracking the fate and transport of sulfide nanoparticles and associated metal ions in the environment. Moreover, our study exemplified the use of an in situ method (i.e., LCTEM) to investigate nanoparticle behavior (e.g., dissolution) in aqueous solutions.

Effects of dissolved oxygen, pH, salinity and humic acid on the release of metal ions from PbS, CuS and ZnS during a simulated storm event

Metal sulfides serve as the sinks of toxic heavy metals in anoxic sediments. Once exposed to fluctuations in environmental conditions, dissolution of metal sulfides can occur and release toxic heavy metal ions into water column. In this study, we investigated the effects of dissolved oxygen (DO), pH, salinity and humic acid (HA) on the dissolution of CuS, PbS and ZnS using batch experiments with continuous aeration to simulate the re-suspension of these metal sulfides during a storm event. Experimental results indicated that oxidative dissolution of CuS, PbS and ZnS occurred in the presence of DO. The rate was the fastest for PbS, followed by CuS and ZnS. Soluble metal concentrations also increased with decreasing pH under oxic conditions. Compared to metal sulfides dissolution rates in freshwater without HA, the presence of saline conditions and HA generally accelerated the dissolution of CuS but inhibited the dissolution of PbS and ZnS. A higher saline or HA concentration, however, did not always lead to a stronger enhanced or inhibited dissolution rate, which could be a collective effect resulting from ligand-enhanced dissolution, complexation, and decreased oxygen and proton attacks due to HA adsorption on the metal sulfide surfaces.

Significant seasonal variations of microbial community in an acid mine drainage lake in Anhui Province, China

Acid mine drainage (AMD),characterized by strong acidity and high metal concentrations, generates from the oxidative dissolution of metal sulfides, and acidophiles can accelerate the process significantly. Despite extensive research in microbial diversity and community composition, little is known about seasonal variations of microbial community structure (especially micro eukaryotes) in response to environmental conditions in AMD ecosystem. To this end, AMD samples were collected from Nanshan AMD lake, Anhui Province, China, over a full seasonal cycle from 2013 to 2014, and water chemistry and microbial composition were studied. pH of lake water was stable (∼3.0) across the sampling period, while the concentrations of ions varied dramatically. The highest metal concentrations in the lake were found for Mg and Al, not commonly found Fe. Unexpectedly, ultrahigh concentration of chlorophyll a was measured in the extremely acidic lake, reaching 226.43–280.95 μg/L in winter, even higher than those in most eutrophic freshwater lakes. Both prokaryotic and eukaryotic communities showed a strong seasonal variation. Among the prokaryotes, “Ferrovum”, a chemolithotrophic iron-oxidizing bacterium was predominant in most sampling seasons, although it was a minor member prior to September, 2012. Fe2+ was the initial geochemical factor that drove the variation of the prokaryotic community. The eukaryotic community was simple but varied more drastically than the prokaryotic community. Photoautotrophic algae (primary producers) formed a food web with protozoa or flagellate (top consumers) across all four seasons, and temperature appeared to be responsible for the observed seasonal variation. Ochromonas and Chlamydomonas (responsible for high algal bloom in winter) occurred in autumn/summer and winter/spring seasons, respectively, because of their distinct growth temperatures. The closest phylogenetic relationship between Chlamydomonas species in the lake and those in Arctic and Alpine suggested that the native Chlamydomonas species may have been both acidophilic and psychrophilic after a long acclimation time in this extreme environment.

Electrochemical Applications in Metal Bioleaching.

Biohydrometallurgy comprises the recovery of metals by biologically catalyzed metal dissolution from solids in an aqueous solution. The application of this kind of bioprocessing is described as "biomining," referring to either bioleaching or biooxidation of sulfide metal ores. Acidophilic iron- and sulfur-oxidizing microorganisms are the key to successful biomining. However, minerals such as primary copper sulfides are recalcitrant to dissolution, which is probably due to their semiconductivity or passivation effects, resulting in low reaction rates. Thus, further improvements of the bioleaching process are recommendable. Mineral sulfide dissolution is based on redox reactions and can be accomplished by electrochemical technologies. The impact of electrochemistry on biohydrometallurgy affects processing as well as analytics. Electroanalysis is still the most widely used electrochemical application in mineralogical research. Electrochemical processing can contribute to bioleaching in two ways. The first approach is the coupling of a mineral sulfide to a galvanic partner or electrocatalyst (spontaneous electron transfer). This approach requires only low energy consumption and takes place without technical installations by the addition of higher redox potential minerals (mostly pyrite), carbonic material, or electrocatalytic ions (mostly silver ions). Consequently, the processed mineral (often chalcopyrite) is preferentially dissolved. The second approach is the application of electrolytic bioreactors (controlled electron transfer). The electrochemical regulation of electrolyte properties by such reactors has found most consideration. It implies the regulation of ferrous and ferric ion ratios, which further results in optimized solution redox potential, less passivation effects, and promotion of microbial activity. However, many questions remain open and it is recommended that reactor and electrode designs are improved, with the aim of finding options for simplified biohydrometallurgical processing. This chapter focuses on metal sulfide dissolution via bioleaching and does not include other biohydrometallurgical processes such as microbial metal recovery from solution.