The aim of this work was to determine whether a mechanism exists for bacterial oxidation of covellite (CuS) other than that involving cyclic reduction and oxidation of soluble iron, and to describe any such mechanism.It was thought likely that mechanisms of bacterial attack on CuS would also apply to other metal sulphides. High purity covellite was synthesized by the thermal reaction of sulphur and copper. Thiobacillus cultures were obtained from other workers and from the natural environment, and enriched for sulphide oxidizing capability. Oxygen consumption was monitored polarographically. Soluble copper, sulphate and total iron were assayed by Atomic Absorption Spectrophotometry while ferrous ion was determind spectrophotometrically as a complex with orthophenanthroline. By rapid specific inhibition of biological activity during sulphide oxidation, the contribution of bacteria to the stoichiometry of oxidation was determined. At pH 2.5 the product of either biological (Thiobaccillus ferrooxidans) or non-biological oxidation was CuSO4, the biological rate exceeding the non-biological rate about a hundredfold. At pH 4.5 T.thioparus was incapable of oxidizing CuS itself but catalysed attack by oxygen (about fivefold) by oxidizing a sulphur passivation film which formed by reaction of CuS with oxygen. The nett result was again CuSO4 production. At pH 2.5 three strains of T. ferrooxidans oxidized CuS itself without the aid of ferric ion; a fourth strain (BJR-V-1) was completely dependent on ferric ion or dissolved oxygen to oxidize CuS to sulphur. In situations where dissolved oxygen initiated the oxidation of CuS, the oxidation rate was approximately first order with respect to dissolved oxygen, while zero order kinetics were observed when other mechanisms predominated. In dilution experiments designed to demonstrate the dependence of sulphide oxidation (to sulphate) on physical contact between bacteria and mineral surfaces, no dependence was observed. It was concluded that water soluble intermediate were involved in CuS oxidation by T. ferrooxidans and in sulphur transport to the cells of T. ferrooxidans and T. thioparus. Arguments were advanced suggesting that the intermediates were inorganic and the concentration of intermediates was estimated from experimental results and the theory if diffusion. The process of CuS passivation was studied; consumption of oxygen and acid, and production of cupric ion and sulphate were measured, the results indicating that passivation resulted from the accumulation of approximately 30 micromole of elemental sulphur per square metre of CuS. Oxygen consumed during depassivation by thiobacilli supported this conclusion. Assuming an even distribution of sulphur over the surface, the film was calculated to be one or two atoms thick. From consideration of the results of this study it was proposed that polythionates may be involved both in CuS oxidation by bacteria and in transport of sulphur into bacterial cells. The role of iron was investigated. Chemically synthesized ferric ion was less effective in CuS oxidation than was ferric ion produced by T. ferrooxidans strain BJR-V-1 through oxidation of ferrous ion. The half saturation ferrous ion concentration with respect to oxidation by each of the T. ferrooxidans strains was approximately 10-5 molar, in contrast to values of 10-2 molar reported by others. Further ferrous oxidation kinetic experiments with strain BJR-V-1 indicated that the major substrate for the rate limiting reaction in ferrous oxidation was a ferrous phosphate complex; a sulphate complex also played a part.

Hydrogen sulphide (H2S) is a serious problem for many industries, including oil production and processing, pulp and paper, and wastewater treatment. In addition, H2S is usually present in natural gas and biogas. It is necessary to control the generation and release of H2S into the environment because H2S is corrosive, toxic, and has an unpleasant odour. In addition, the removal of H2S from natural gas and biogas is essential for preventing the emission of SO2 upon combustion of these gases. Physicochemical processes have been developed for the removal of H2S. These processes employ techniques such as chemical or physical absorption, thermal and catalytic conversion, and liquid phase oxidation. In comparison, biological processes for the removal of sulphide typically operate at ambient temperature and pressure, with the feasibility for the treatment of smaller streams, and the absence of expensive catalysts. The objective of the present work was to study the biooxidation of sulphide under denitrifying conditions in batch system and a continuous immobilized cell bioreactor using a mixed microbial culture enriched from the produced water of a Canadian oil reservoir. <p>In the batch experiments conducted at various initial sulphide concentrations, an increase in the sulphide oxidation and nitrate reduction rates was observed as the initial sulphide concentration was increased in the range 1.7 to 5.5 mM. An extended lag phase of approximately 10 days was observed when sulphide concentrations around or higher than 14 mM were used. This, when considered with the fact that the microbial culture was not able to oxidize sulphide at an initial concentration of 20 mM, indicates the inhibitory effects of sulphide at high concentrations.<p>The effect of the initial sulphide to nitrate concentrations ratio (ranging from 0.3 to 4.0) was also studied. As the initial sulphide to nitrate ratio decreased, the sulphide oxidation rates increased. The increasing trend was observed for initial nitrate concentrations in the range of 1.3 to 7.3 mM, corresponding to ratios of 4.08 to 0.83. The increase in nitrate reduction rates was more pronounced than that of the sulphide oxidation rates. However at nitrate concentrations higher than 7.3 mM (ratios lower than 0.83) the nitrate reduction rate remained constant. The percentage of sulphide that was oxidized to sulphate increased from 2.4% to 100% as the initial sulphide to nitrate ratio decreased from 4.08 to 0.42. This indicated that at ratios lower than 0.42, nitrate would be in excess and at ratios exceeding 4.08, nitrate would be limiting. In the continuous bioreactor systems, at sulphide loading rates ranging from 0.26 to 30.30 mM/h, sulphide conversion remained in the range of 97.6% to 99.7%. A linear increase in the volumetric oxidation rate of sulphide was observed as the sulphide loading rate was increased with the maximum rate being 30.30 mM/h (98.5% conversion). Application of immobilized cells led to a significant increase in oxidation rate of sulphide when compared with the rates obtained in a bioreactor with freely suspended cells. At nitrate loading rates ranging from 0.19 to 24.44 mM/h, the nitrate conversion ranged from 97.2% to 100% and a linear increase in volumetric reduction rate was observed as the nitrate loading rate was increased, with the maximum rate being 24.44 mM/h (99.7% conversion). <p>A second bioreactor experiment was conducted to investigate the effects of sulphide to nitrate concentrations ratio on the performance of the system. Sulphide conversion was complete at sulphide to nitrate ratios of 1.1 and 1.3, but decreased to 90.5% at the ratio of 3.1 and 65.0% at the ratio of 5.0, indicating nitrate was limiting for sulphide to nitrate ratios of 3.1 and 5.0. The increase in the sulphide to nitrate ratio (and the resulting limitation of nitrate) caused a decrease in the volumetric reaction rate of sulphide.<p>Nitrate conversion was complete at sulphide to nitrate ratios of 1.3, 3.1, and 5.0; however, at a ratio of 1.1, the conversion of nitrate dropped to 59.6%, indicating that nitrate was in excess, and sulphide was limiting. The volumetric reaction rate of nitrate decreased as the sulphide to nitrate ratio increased for ratios of 1.3, 3.1, and 5.0; this was due to the decrease in the nitrate loading rate. For sulphide to nitrate ratios of 1.1 and 1.3, 7.2% and 19.6% of the sulphide was converted to sulphate, respectively. At ratios of 3.1 and 5.0, no sulphate was generated. For ratios between 1.3 and 5.0, an increase in the ratio caused a decrease in the generation of sulphate.

Although iron-based permeable reactive barriers are gaining importance in the treatment of groundwater contaminants, there have been field observations indicating that sulphide may affect the degradation rates of certain chlorinated ethenes. Previous observations suggest that sulphide has little effect on TCE degradation rates but can cause a significant decline in the rate of degradation of cis-DCE. This study was conducted to systematically test the effects of S2- on TCE, cis-DCE, trans-DCE, 1,1-DCE and VC. Two different concentrations of sulphide (5 and 50 mg/L) were used in the column experiments. The results showed that the rate of TCE degradation was only slightly reduce in the presence of sulphide, while there was substantial reduction in the rates of degradation of cis-DCE, 1,1-DCE and VC. Trans-DCE was affected by sulphide, however, not as severely as cis-DCE, 1,1-DCE and VC. Raman Spectra showed the presence of a small amount of sulphide precipitates, and corrosion potential measurements showed that sulphide shifted the corrosion potential of the iron to less negative values by approximately 70 mV, suggesting that the change in corrosion potential was not responsible for the preferential degradation of TCE relative cis-DCE and VC. The dominant pathway for TCE degradation is β-elimination, while that for cis-DCE and VC is generally considered to be hydrogenolysis, though there is also evidence in the literature indicating that cis-DCE and VC can also degrade by catalytic hydrogenation. The results indicate that sulphide does not inhibit β-elimination but severely limits the hydrogenolysis/catalytic hydrogenation pathway. The fact that sulphide inhibited the conversion of ethene to ethane, a known catalytic reaction, indicated that sulphide is acting as a catalyst poison. It is therefore concluded that the primary mechanism for the transformation of cis-DCE to VC and for VC to ethene is catalytic hydrogenation, and that sulphide inhibits these transformations through its role as a catalyst poison.

Although iron-based permeable reactive barriers are gaining importance in the treatment of groundwater contaminants, there have been field observations indicating that sulphide may affect the degradation rates of certain chlorinated ethenes. Previous observations suggest that sulphide has little effect on TCE degradation rates but can cause a significant decline in the rate of degradation of cis-DCE. This study was conducted to systematically test the effects of S2- on TCE, cis-DCE, trans-DCE, 1,1-DCE and VC. Two different concentrations of sulphide (5 and 50 mg/L) were used in the column experiments. The results showed that the rate of TCE degradation was only slightly reduce in the presence of sulphide, while there was substantial reduction in the rates of degradation of cis-DCE, 1,1-DCE and VC. Trans-DCE was affected by sulphide, however, not as severely as cis-DCE, 1,1-DCE and VC. Raman Spectra showed the presence of a small amount of sulphide precipitates, and corrosion potential measurements showed that sulphide shifted the corrosion potential of the iron to less negative values by approximately 70 mV, suggesting that the change in corrosion potential was not responsible for the preferential degradation of TCE relative cis-DCE and VC. The dominant pathway for TCE degradation is β-elimination, while that for cis-DCE and VC is generally considered to be hydrogenolysis, though there is also evidence in the literature indicating that cis-DCE and VC can also degrade by catalytic hydrogenation. The results indicate that sulphide does not inhibit β-elimination but severely limits the hydrogenolysis/catalytic hydrogenation pathway. The fact that sulphide inhibited the conversion of ethene to ethane, a known catalytic reaction, indicated that sulphide is acting as a catalyst poison. It is therefore concluded that the primary mechanism for the transformation of cis-DCE to VC and for VC to ethene is catalytic hydrogenation, and that sulphide inhibits these transformations through its role as a catalyst poison.

Hydrogen sulphide (H2S) is a serious problem for many industries, including oil production and processing, pulp and paper, and wastewater treatment. In addition, H2S is usually present in natural gas and biogas. It is necessary to control the generation and release of H2S into the environment because H2S is corrosive, toxic, and has an unpleasant odour. In addition, the removal of H2S from natural gas and biogas is essential for preventing the emission of SO2 upon combustion of these gases. Physicochemical processes have been developed for the removal of H2S. These processes employ techniques such as chemical or physical absorption, thermal and catalytic conversion, and liquid phase oxidation. In comparison, biological processes for the removal of sulphide typically operate at ambient temperature and pressure, with the feasibility for the treatment of smaller streams, and the absence of expensive catalysts. The objective of the present work was to study the biooxidation of sulphide under denitrifying conditions in batch system and a continuous immobilized cell bioreactor using a mixed microbial culture enriched from the produced water of a Canadian oil reservoir. <p>In the batch experiments conducted at various initial sulphide concentrations, an increase in the sulphide oxidation and nitrate reduction rates was observed as the initial sulphide concentration was increased in the range 1.7 to 5.5 mM. An extended lag phase of approximately 10 days was observed when sulphide concentrations around or higher than 14 mM were used. This, when considered with the fact that the microbial culture was not able to oxidize sulphide at an initial concentration of 20 mM, indicates the inhibitory effects of sulphide at high concentrations.<p>The effect of the initial sulphide to nitrate concentrations ratio (ranging from 0.3 to 4.0) was also studied. As the initial sulphide to nitrate ratio decreased, the sulphide oxidation rates increased. The increasing trend was observed for initial nitrate concentrations in the range of 1.3 to 7.3 mM, corresponding to ratios of 4.08 to 0.83. The increase in nitrate reduction rates was more pronounced than that of the sulphide oxidation rates. However at nitrate concentrations higher than 7.3 mM (ratios lower than 0.83) the nitrate reduction rate remained constant. The percentage of sulphide that was oxidized to sulphate increased from 2.4% to 100% as the initial sulphide to nitrate ratio decreased from 4.08 to 0.42. This indicated that at ratios lower than 0.42, nitrate would be in excess and at ratios exceeding 4.08, nitrate would be limiting. In the continuous bioreactor systems, at sulphide loading rates ranging from 0.26 to 30.30 mM/h, sulphide conversion remained in the range of 97.6% to 99.7%. A linear increase in the volumetric oxidation rate of sulphide was observed as the sulphide loading rate was increased with the maximum rate being 30.30 mM/h (98.5% conversion). Application of immobilized cells led to a significant increase in oxidation rate of sulphide when compared with the rates obtained in a bioreactor with freely suspended cells. At nitrate loading rates ranging from 0.19 to 24.44 mM/h, the nitrate conversion ranged from 97.2% to 100% and a linear increase in volumetric reduction rate was observed as the nitrate loading rate was increased, with the maximum rate being 24.44 mM/h (99.7% conversion). <p>A second bioreactor experiment was conducted to investigate the effects of sulphide to nitrate concentrations ratio on the performance of the system. Sulphide conversion was complete at sulphide to nitrate ratios of 1.1 and 1.3, but decreased to 90.5% at the ratio of 3.1 and 65.0% at the ratio of 5.0, indicating nitrate was limiting for sulphide to nitrate ratios of 3.1 and 5.0. The increase in the sulphide to nitrate ratio (and the resulting limitation of nitrate) caused a decrease in the volumetric reaction rate of sulphide.<p>Nitrate conversion was complete at sulphide to nitrate ratios of 1.3, 3.1, and 5.0; however, at a ratio of 1.1, the conversion of nitrate dropped to 59.6%, indicating that nitrate was in excess, and sulphide was limiting. The volumetric reaction rate of nitrate decreased as the sulphide to nitrate ratio increased for ratios of 1.3, 3.1, and 5.0; this was due to the decrease in the nitrate loading rate. For sulphide to nitrate ratios of 1.1 and 1.3, 7.2% and 19.6% of the sulphide was converted to sulphate, respectively. At ratios of 3.1 and 5.0, no sulphate was generated. For ratios between 1.3 and 5.0, an increase in the ratio caused a decrease in the generation of sulphate.

One of the major technical challenges towards a viable H2S//Air SOFC is to identify and develop anode materials that are electronically conductive, chemically and electrochemically stable, and catalytically active when exposed to H2S-rich environments. The corrosive nature of H2S renders most traditional state-of-the-art SOFC anode materials (Ni, Pt, Ag) useless for long-term cell performance even at very low sulfur concentrations. In my doctoral thesis work, a new class of perovskite-based anodes was developed for potential use in SOFCs operating with H2S and sulfur-containing fuels. Cermets from this family of materials have shown excellent chemical stability and electrochemical performance at typical SOFC operating conditions. As an added benefit, they appear to preferentially oxidize H2S over hydrogen, as suggested by open circuit voltage, impedance spectra, and cell performance measurements obtained using various H2S-H2-N2 fuel mixtures. Cell power output values were among the highest reported in the literature and showed no significant deterioration during 48-hour testing periods. Impedance measurements indicated overall cell resistances decreased with increasing temperature and H2S content of the fuel. This behavior is starkly different from that of contemporary SOFC anodes, where the presence of H2S usually increases overall polarization resistance and ultimately destroys the cell. Results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC power systems.

Seismic imaging of shallow sediment hosted massive sulphides has not been studied in detail. In this research two shallow sediment hosted massive sulphide deposits (one deeper and larger than the other) were modeled and synthetic seismic data generated using a 2D elastic wavefield finite difference code. F-k filtering can be used to attenuating surface waves (conventional processing). This requires small trace spacing so that spatially aliasing of energy is avoided. An alternative to this involves avoiding the surface wave using an optimum offset window technique. Both of these approaches, attenuation and avoidance, produce a high amplitude image of the deeper larger orebody. For the smaller, shallower orebody, conventional processing produced only a weak image of the orebody. However, there is a significant amount of shear wave energy from this target, and therefore multicomponent geophones should be used to capture this energy.

Seismic imaging of shallow sediment hosted massive sulphides has not been studied in detail. In this research two shallow sediment hosted massive sulphide deposits (one deeper and larger than the other) were modeled and synthetic seismic data generated using a 2D elastic wavefield finite difference code. F-k filtering can be used to attenuating surface waves (conventional processing). This requires small trace spacing so that spatially aliasing of energy is avoided. An alternative to this involves avoiding the surface wave using an optimum offset window technique. Both of these approaches, attenuation and avoidance, produce a high amplitude image of the deeper larger orebody. For the smaller, shallower orebody, conventional processing produced only a weak image of the orebody. However, there is a significant amount of shear wave energy from this target, and therefore multicomponent geophones should be used to capture this energy.

No description available.

No description available.