SHAM blockade of cyanide or sulfide-insensitive oxygen flux is often used to identify the presence of an alternative oxidase. Mitochondrial respiration in the soil amoeba Acanthamoeba castellanii is stimulated by low concentrations of sulfide and is only partially suppressed at higher concentrations; however, in the presence of SHAM, sulfide inhibition is enhanced at both low and high concentrations (Lloyd et al., 1981). In the lugworm A. marina, cytochrome c oxidase is sensitive to sulfide (Völkel and Grieshaber, 1997). At low or subinhibitory concentrations, the oxidation of sulfide to thiosulfate supplies reducing equivalents to the electron transport system at the level of ubiquinone/ubiquinol, before complex III, for ATP production. This path utilizes cytochrome c oxidase, and the resultant ATP production is unaffected by SHAM. However, if cytochrome c oxidase is inhibited by high sulfide concentrations, sulfide oxidation continues as electrons flow through a SHAM-sensitive sulfide-insensitive alternative terminal oxidase. In this case, sulfide oxidation is primarily a detoxification process and does not yield ATP, even though the alternative oxidase branch point is hypothesized to be after complex III (Völkel and Grieshaber, 1997).
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electrodes and they speculated that the phenomena are caused by the periodic formation/removal of sulfur from the electrode surface [12,13]. Similar behavior occurs at platinum anodes [14,15]. It has been found that potential oscillations play a detrimental impact on the electrode lifetime . The electro-oxidation process of S 2- S is a way for us to recovery sulfur , but the sulfur will deposit on the surface of the anode quickly. The passive film of sulfur can make the cell potential increase sharply, and then put the process into trouble. In this case, the electro-oxidation process of S 2- SO 4 2-
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According to Reaction (R1) ND-SO could account to one- third of the HS − oxidation, despite the flux of NO − 3 towards the redoxcline is around 1 order of magnitude lower than the HS − flux (Fig. 8). Furthermore ND-SO is proton-consuming and sulfide oxidation to elemental sulfur is more acid proton- consuming than the full sulfide oxidation to sulfate (see also Visscher and Stolz, 2005). The abundance of elemental sul- fur particles found in the turbid layer filtrate (Fig. 7) indicates that sulfide oxidation to elemental sulfur is predominant. Full oxidation of sulfide to sulfate is less likely as no increase of sulfate is observed in the redoxcline (Fig. 3c). Maxima in pH are known to occur when sulfide is oxidized to ele- mental sulfur with nitrate as the electron acceptor (Kamp et al., 2006). Consequentially, the minimum amount of nitrate in the redoxcline and the slight alkaline pH shift, indicate that ND-SO is a relevant process in the redoxcline (Figs. 3b and c, 8). Therefore, the proton-consuming ND-SO could be the biogeochemical process in the redoxcline creating a dis- equilibrium in the carbonate dissolution–precipitation reac- tion, favoring calcite precipitation. This mechanism was re- cently reported for the formation of stromatolites below the photic zone of the Arabian Sea. There, a collective effect of proton-consuming ND-SO and alkalinity-producing sulfate- driven oxidation of CH 4 (SD-OM) leads to authigenic car-
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concentration measured during the mixis of the lake (Fig- ure 4) and then decreased back to <10% of the epilimnetic sulfate concentration on January 17. Simultaneously, iron concentrations were rather low in the water column. These findings suggest that significant oxidation of sulfide is ongoing at the chemocline. Of the different sulfide oxi- dation intermediates, the presence of thiosulfate, sulfite, and zero-valent sulfur was documented in the water column of the lake, while concentrations of inorganic polysulfides, tetrathionate, and thiocyanate were below the detection limit. During the early stage of the strati- fication (May and July), sulfur oxyanions (e.g. thiosulfate and sulfite) were the main products of the incomplete oxidation of hydrogen sulfide. During the stable stratifi- cation and mixing periods, however, zero-valent sulfur prevailed over sulfur oxyanions (Table 2). These findings indicate that the lack of mixing between the epilimnion and hypolimnion and the relatively small concentrations of hydrogen sulfide in the spring limited the buildup of sulfide oxidation intermediates. In autumn, the mixing of hydrogen sulfide and dissolved oxygen increase and the concentration of hydrogen sulfide was much higher which led to the formation of more reduced sulfide oxi- dation intermediates (e.g. ZVS). On the other hand we cannot rule out that changing bacterial community affected consumption rates of various sulfur species lead- ing to a shift in sulfur speciation . During the terminal stage of lake water column mixing (January), the water column inventory in sulfide oxidation intermediates was even higher than the hydrogen sulfide inventory.
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Nickel nitroprusside (NiNP) complex has been synthesized from two procedures i.e. drop by drop (DbD) and bulk mixing methods. Surface morphology, size and shape of the complex resulted from the two procedures has been compared using scanning electron microscopy (SEM) images. X-ray diffraction (XRD) patterns were used to understand the phase purity and particle size of the complex particles obtained from two procedures. Presence of characteristic functional groups in the complex was examined using IR spectroscopy. From the studies it was clear that, size of the complex particles (n-NiNP) prepared from DbD method was considerably reduced. Carbon paste electrodes (CPEs) were constructed using NiNP complex prepared from DbD and bulk mixing methods to examine their electrocatalytic activity for the oxidation of sulfide. Obviously n-NiNP modified CPE showed enhanced electrocatalytic activity toward the oxidation of sulfide. Attempt has been made to use the n- NiNP modified CPE as an electrochemical sensor for sulfide estimation. It showed a linear response over 2 – 14 x10 -5 M and 0.2 – 1.4 mM of sulfide. Limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.1 x 10 -5 M and 0.43 x10 -4 M sulfide respectively for the lower end calibration graph. Interference of various cations and anions generally present along with sulfide in water matrices was studied. Proposed electrochemical sensor has been applied for the estimation of sulfide in sewage and water samples. Good agreement between the results obtained from the proposed electrochemical sensor and standard Methylene blue method was observed.
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The finding that the AOX activity in lugworm mitochondria strongly depends on the redox state serves to resolve a discrepancy detected during former studies that obscured the exact position of the AOX in the respiratory chain. Sulfide oxidation via the alternative pathway was inhibited by antimycin A; therefore, complex III was thought to be involved in this pathway without any proton translocation taking place (Völkel and Grieshaber, 1996; Völkel and Grieshaber, 1997). In contrast to myxothiazole, antimycin A stimulates ROS production at complex III, which in turn evidently inhibits the AOX (Andreyev et al., 2005). Therefore, the addition of antimycin A can indirectly inhibit sulfide oxidation via the AOX, although complex III is not involved in the reaction. DHA selectively activates the energy-conserving sulfide oxidation pathway in lugworm mitochondria, probably by preventing the inhibition of cytochrome oxidase. However, the mechanism of this reaction does not exclusively depend on the cellular redox state, as GSSG had no activating effect. A non-enzymatic oxidation of sulfide by DHA can by excluded since hardly any ascorbate was detectable in the assay. Furthermore, the ratio of oxygen consumed and thiosulfate produced per molecule of sulfide oxidized was comparable in the presence and in the absence of DHA (Hildebrandt and Grieshaber, 2008), whereas less oxygen would be consumed if DHA was used as an electron acceptor.
measured even at 0.5 molar ratio, confirming their hydrophil- ic surfaces. This result accords with the surface mineralogy change investigated in subsection 3.2 (i.e., that oxygen-asso- ciated species with greater polarity reduce the floatability and also the contact angle). Interestingly, at floatabilities be- low 50%, the contact angles of the mineral samples de- creased too abruptly for measurement. This sharp decrease may reflect the close correlation between floatability and the sulfide fraction on the mineral surface, which directly affects the contact angle. This assumption should be verified in fur- ther study.
In this study, we report on the use of waste glycerol (WG), a byproduct of biodiesel production, to reduce release of metals, sulfate, and acidity from unsaturated tailings at the Ore Knob Mine, a former copper–zinc mine located in western North Carolina. From 1957 to 1962, Appalachian Sulphides, Inc. operated a mine and processing facility at the site. Most waste tailings were pumped to an impoundment located on Ore Knob Branch, eventually forming a 9 ha tailings pile with a maximum tailings depth of 21 m at the center of the embankment face. The hydrological and geochemical characteristics of the pile have been described by Behrooz and Borden (2012). Oxidation of pyrrhotite and related sulfide minerals in the vadose zone of the Ore Knob Mine tailings pile produces AMD, which is rapidly transported through the pile by infiltrating surface water. Annual pollutant loads (kg/yr) released by the pile are estimated to be 220,000 acidity, 100,000 Fe, 370,000 SO 4 ,
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Tubing, casing, and equipment made of steel are good electric conductors. Va rious salts or CO2 and H2S, and so on, are dissolved in the water that oil and gas well fluid produced contains. When steel contacts the aforementioned med ia, the protective meta l-o xide film that has been formed in air may be dis solved in an electro lyte solution. When meta l is e xposed, the meta l as a good electric conductor and the solution as a good ionic conductor form a return circuit. Fe rrous ions with positive charges tend to dissolve in electrolyte solution and form ferrous salts. Electrons tend to congregate at the metal end and a certain e lectric potential difference is formed. Electrons flow toward the solution. This is an oxidation reaction process and is known as anodic reaction. The metal end is known as the anodic area. In addition, the electrons that enter solution are bound with hydrogen ion, and hydrogen molecules are formed. This is a reduction react ion process and is known as cathodic react ion. The solution end is known as the cathodic area. In an aerobic environment, hydroxide radicals are formed.
The main metal oxide mineral were cerussite,smithsonite, hemimorphite, sardinianite, limonite, fiber,and so on. The content of metal sulfide mineral was small ,these were galena, sphalerite, pyrite and pyrrhotite, etc. Nonmetallic minerals were quartz, chlorite, carbonate, silicon line stone, sericite, cordierite, epidote, barite, etc. The valuable components were cerussite, sphalerite and oxide minerals of zinc. Metal minerals mainly exist in colloidal structure and honeycomb structure.The metasomatic phenomenon was obvious between metal mineral.
This paper presents a method for externalising and formalising knowledge involving the selection of hydrometallurgical process flowsheets for gold extraction from ores. A case-based reasoning (CBR) sys- tem was built using an open source software myCBR 3.0. The aim of the systems is to recommend flow- sheet alternatives for processing a potential gold ore deposit. Nine attributes: Ore type, Gold ore grade, Gold distribution, Gold grain size, Sulfide present, Arsenic sulfide, Copper sulfide, Iron sulfide and Clay present were modelled and several literature sources of actual gold mines and processes were used for acquiring cases for the system. After preliminary testing, functional evaluation of the built CBR system was carried out by using five real mining projects as test cases. Additionally, human experts in the field of gold hydrometallurgy were interviewed to demonstrate the benefits of the CBR system as it holds no human biases towards any processing techniques. It was found that the suggestions of the CBR system provided useful information and direction for further process design and performed well compared to the inter- viewed human experts, thus confirming that the system is of practical relevance to the process engineer designing an industrial gold processing plant. The current model was found to be a functioning basis for further development through additional attributes, adjusted attribute weighting and increased number of cases.
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Figure 5 shows the polarization curves and power density curves of all AFCs constructed on days 1-7. The results demonstrate the relationship between the OCVs and sulfide concentrations in the influent. The higher the sulfide concentration, the higher the OCV achieved. The OCVs in AFCs also decreased over time, similar to the observation in MFC operation, which was probably due to the deterioration of the cathode electrode as discussed in the previous section. Moreover, the results from polarization curves suggest an increase in voltage losses in AFC1 and AFC3 over time, resulting in a decrease in the maximum power densities in these AFCs. In contrast, AFC6 appears to have lower voltage losses compared to AFC1 and AFC3, which was likely due to less sulfide removal in AFC6, resulting in less sulfur accumulation on the anode electrodes of AFC6 compared to those of AFC1 and AFC3.
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The best matching cases for Query T4 are the two Barneys Canyon cases and the Joutel project, with global similarity values of 0.88. The ores in all cases are refractory iron sulfides, in which the gold grains are enclosed in mineral. The ores contain sulfides, of which pyrite and arsenopyrite are mentioned. Joutel differs from T4 in gold grain size and the Barneys Canyon ores contain clay, unlike T4. However, the process flowsheet of Joutel is much more similar to T4 than the Barneys Canyon cases. In T4 and Joutel the ores are pretreated, by pressure oxidation and preaeration respectively, before cyanide leaching. In the dissimilar Barneys Canyon cases the ore is heap leached without any pretreatment. This underlines the benefit of CBR, as it provides several options for the user to compare.
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Reduced iron sulfides in coastal sediments rapidly undergo a redox transition to Fe(III) phases upon exposure to oxygen (Burns 2011). The iron can continue to cycle between Fe(II) and Fe(III) phases or some iron can leave the cycle through the formation of solids, typically iron oxide, potentially in the nanoscale (Guo 2013; Charette 2002; Burns 2011; Rose 2003). The resultant colloidal (nano) ferric oxide phases adsorb metal cations mobilized by the phase sulfide oxidation. It has been shown that iron oxides are capable of adsorbing metals under environmentally relevant pH and ionic strength ranges and that natural organic matter (specifically, humic acid (HA) as representative of NOM) is also capable of adsorbing both metals and iron oxides (Lion 1982; Lowry 2012; Baalousha 2008; Maurer-Jones 2013; Jirsa 2013). It has even been shown that humic acid complexed with iron oxides can still bind metals (Kretzschmar 2005; Manciulea 2009). A study conducted by Plathe and colleagues (2013) concluded that approximately 80% of nanoparticles analyzed in a river system were associated with heavy metals and that iron oxides represented the largest portion of this percent. Thus, association and transport of these iron phases are critical to the mobility of heavy metals in these systems.
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therefore significantly reduces the amount of dimethyl sulfide in the mixed surface layer that is available for sea-to-air transfer. Growth on dimethyl sulfide as a carbon source has been described for a range of prokaryotyes, including anaerobic degradation by methanogens 9 and sulfate-reducing bacteria. 10 In the
Acid mine water (AMW) is an environmental concern for coal mining throughout the world. AMW occurs during mining processes when metal sulfides in coal and over burden rocks are exposed to oxygen and water, causing a rapid oxidizing reaction. Oxidation of metal sulfide, especially pyrite, has the potential to produce sulfate, which may turn into sulfuric acid 1 . Subsequently, it may be dissolved
gene set (Table S2). On the basis of these genomic data and the observation that all of the key genes for sulfate reduction are highly expressed by D. alkaliphilus during growth by sulﬁde oxidation (Fig. 1B), we propose a novel, DSR-mediated pathway for sulﬁde oxidation, with reductive-type Dsr proteins as key elements (Fig. 2B). One possible scenario is the reversal of the pathway proposed by Santos et al. (7) and begins by DsrC directly interacting with sulﬁde to form the oxidized key intermediate DCT. However, neither D. thermophilus nor T. dismutans, which both possess the genes of the complete sulfate reduction pathway, including DsrC, can grow by sulﬁde oxidation, but both require elemental sulfur as an electron donor (12). This incapacity indicates that DsrC alone may not be sufﬁcient for the initial sulﬁde oxidation. The DSR-mediated sulﬁde oxidation pathway would then start with the initial formation of elemental sulfur (Fig. 2B), as originally proposed for sulﬁde oxidation by SRMs (2). The initial oxidation of sulﬁde to sulfur without the involvement of DsrC would bypass the membrane- bound DsrMKJOP complex that donates electrons to DCT and regenerates DsrC. Nevertheless, all of the genes involved in this complex were highly expressed in our study. This leaves us with a puzzle concerning the initial oxidation of sulﬁde, which we have not conclusively resolved yet. Interestingly, Fuseler et al. (2) could not measure sulﬁte reductase activity, which is in contrast to the high level of expression of all of the Dsr-encoding genes that we observed. On the basis of their observations, they con- cluded that sulfur oxidation during disproportionation is not a reversal of the sulfate reduction pathway (Fig. 2B). In agreement with Fuseler et al. (2), we also observed the production of elemental sulfur (measured as S 8 ) and polysulﬁdes (S 8 , 0.98 to 3.6 M;
Several experimental designs have been considered for studying such models and central composite design (CCD) was selected. For this study, a full factorial central composite design with eight star points and six replicates at the central points were employed to fit the second order polynomial model, and 32 experiments were required for this procedure. STATISTICA by Stat Soft Inc. software was used for regression and graphical analysis of the data obtained. In order to search for the optimum combination of major critical parameters of the sodium alginate immobilization method for the sulfide oxidation, experiments were performed according to the CCD experimental plan shown in Table 2.
ABSTRACT: Nineteen (19) groundwater samples were collected and analysed for a wide range of elements. The study aimed at determining the mineral saturation index and hydrogeochemical characteristics of the groundwaters within the study area. Geochemical processes were elucidated using PHREEQC software. Oxidation of Fe-bearing sulfide minerals, Silicate & Carbonate weathering are the most dominant hydrogeochemical processes influencing the groundwater chemistry in the study area.
Later it was found that the Method 8131 - Methylene Blue Method (Hach Company, 1992) was underestimating the sulfide concentration. To solve this problem, an Iodometric Method was used to measure remaining sulfide concentration after the different chemicals are added at given reaction times. In the Iodometric Method, chlorine liberates free iodine from potassium iodide (KI) solutions at pH 8 or less. The liberated iodine and the solution containing sulfide is titrated with a standard solution thiosulfate (Na 2 S 2 O 3 ) with starch as indicator as
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