Academic literature on the topic 'Elemental sulphur oxidation'

Sewage sludge and elemental sulphur (S°) were combined and incubated under controlled conditions. Sulphur oxidation was enhanced by sewage sludge, though acidification of the mixtures prevented more than 4% of the S° from being converted to sulphate. When introduced to the soil environment, over 50% of the S° from these mixtures oxidized within 6 wk, compared with about 20% oxidation of S° applied without sewage sludge. Key words: Elemental sulphur, sulphur oxidation, sewage sludge

The volumetric oxygen transfer coefficient (kLa) was used to define the conditions necessary for minimum aeration and to eliminate potential oxygen limitation in bioleaching cultures ofAcidithiobacillus ferrooxidans. The Michaelis constants for oxygen were 1.07 and 0.71 μmol O2l-1for the oxidation of ferrous iron and elemental sulphur, respectively. The critical oxygen concentration, below which oxygen limitation occurred, was determined to be 6.25 and 3.125 μmol O2l-1for the oxidation of ferrous iron and elemental sulphur, respectively. The (kLa)critvalues required to maintain oxygen-unlimited substrate oxidation for ferrous iron and elemental sulphur were 7.70 and 4.88 h-1, respectively.

The effect of particle size, surface area per unit weight, and molecular composition of S0 on the rate of S0 oxidation by Thiobacillus albertis was studied. Spherical S0 prills varying in size and surface areas were prepared and added as the sulphur source to synthetic salts medium. The rate of S0 oxidation by T. albertis was found to be a function of surface area/unit weight of sulphur. In all these experiments [Formula: see text] was produced in a linear manner with time indicating sterically favorable cell–sulphur oxidation binding sites for bacterial growth. Different powdered forms of S0 (high-purity orthohombic, high-purity polymeric, and mixed molecular sulphur) were oxidized at a significantly faster rate than the prilled S0. Also the initial oxidation was exponential up to 3 days at which point [Formula: see text] production from mixed molecular sulphur utilization fell off substantially with time as compared with similar [Formula: see text] rate curves obtained with high-purity orthorhombic and high-purity polymeric oxidation. It was implied that the increased Sx content in mixed molecular sulphur was responsible for the slower oxidation rate by altering the sulphur crystal lattice formation which affected the number of sterically favorable oxidation binding sites for T. albertis growth. Thiobacillus albertis was shown to colonize S0 surfaces as microcolonies. It was concluded that particle size, surface area/unit weight, and the crystal microstructure of S0 affects the oxidation rate of S0 by T. albertis.

The dissolution of gold-bearing pyrite plays an important role in bioleaching of gold. This paper describes a fundamental study on the electrochemical behavior and reaction mechanisms of gold-bearing pyrite leaching in the form of Carbon Paste Electrode (CPE) with and without microorganisms using Cyclic Voltammetry (CV) and polarization curve. A two step process was suggested from Cyclic voltammetry. Electrode passivation by elemental sulphur was observed below 700mV (vs. SCE), elemental sulphur was then oxidized to sulphate when the electrode potential further increased from 700mV. The polarization current density of CPE and the oxidation rate of pyrite are further enhanced by the presence of microorganisms. Analyses of EDS and XPS confirmed the formation of elemental sulphur and sulphate. This electrochemical method successfully showed its simplicity and reliability to measure oxidation rate of gold bearing pyrite.

South Africa (SA) currently faces a major pollution problem from mining impacted water, including acid rock drainage (ARD), as a consequence of the mining activities upon which the economy has been largely built. The environmental impact of ARD has been further exacerbated by the country's water scarce status. Increasingly scarce freshwater reserves require the preservation and strategic management of the country's existing water resources to ensure sustainable water security. In SA, the primary focus on remediation of ARDcontaminated water has been based on established active technologies. However, these approaches are costly, lead to secondary challenges and are not always appropriate for the remediation of lower volume discharges. Mostly overlooked, ARD discharges from diffuse sources, associated with the SA coal mining industry, have a marked impact on the environment, similar to those originating from underground mine basins. This is due to the large number of deposits and their broad geographic distribution across largely rural areas of SA. Semi-passive ARD treatment systems present an attractive alternative treatment approach for diffuse sources, with lower capital and operational costs than active systems as well as better process control and predictability than traditional passive systems. These semi-passive systems typically target sulphate salinity through biological sulphate reduction catalysed by sulphate reducing bacteria (SRB). These anaerobic bacteria reduce sulphate, in the presence of a suitable electron donor, to sulphide and bicarbonate. However, the hydrogen sulphide product generated is highly toxic, unstable, easily re-oxidised and poses a significant threat to the environment and human health, so requires appropriate management. An attractive strategy is the reduction of sulphate to sulphide, followed by its partial oxidation to elemental sulphur, which is stable and has potential as a value-added product. A promising approach to achieve partial oxidation is the use of sulphide oxidising bacteria (SOB) in a floating sulphur biofilm (FSB). These biofilms develop naturally on the surfaces of sulphide rich wastewater streams. Its application in wastewater treatment and the feasibility of obtaining high partial oxidation rates in a linear flow channel reactor (LFCR) has been described. The use of a floating sulphur biofilm overcomes many of the drawbacks associated with conventional sulphide oxidation technologies that are costly and require precise operational control to maintain oxygen limiting conditions for partial oxidation. In the current study a hybrid LFCR, incorporating a FSB with biological sulphate reduction in a single reactor unit, was developed. The integration of the two biological processes in a single LFCR unit was successfully demonstrated as a ‘proof of concept'. The success of this system relies greatly on the development of discrete anaerobic and microaerobic zones, in the bulk liquid and at the airliquid interface, that facilitate sulphate reduction and partial sulphide oxidation, respectively. In the LFCR these environments are established as a result of the hydrodynamic properties associated with its design. Key elements of the hybrid LFCR system include the presence of a sulphate-reducing microbial community immobilised onto carbon fibres and the rapid development of a floating sulphur biofilm at the air-liquid interface. The floating sulphur biofilm consists of a complex network of bacterial cells and deposits of elemental sulphur held together by an extracellular polysaccharide matrix. During the Initial stages of FSB development, a thin transparent biofilm layer is formed by heterotrophic microorganisms. This serves as ‘scaffolding' for the subsequent attachment and colonisation of SOB. As the biofilm forms at the air-liquid interface it impedes oxygen mass transfer into the bulk volume and creates a suitable pH-redox microenvironment for partial sulphide oxidation. Under these conditions the sulphide generated in the bulk volume is oxidised at the surface. The biofilm gradually thickens as sulphur is deposited. The produced sulphur, localised within the biofilm, serves as an effective mechanism for recovering elemental sulphur while the resulting water stream is safe for discharge into the environment. The results from the initial demonstration achieved near complete reduction of the sulphate (96%) at a sulphate feed concentration of 1 g/L with effective management of the generated sulphide (95-100% removal) and recovery of a portion of the sulphur through harvesting the elemental sulphur-rich biofilm. The colonisation of the carbon microfibres by SRB ensured high biomass retention within the LFCR. This facilitated high volumetric sulphate reduction rates under the experimental conditions. Despite the lack of active mixing, at a 4-day hydraulic residence time, the system achieved volumetric sulphate reduction rates similar to that previously shown in a continuous stirred-tank reactor. The outcome of the demonstration at laboratory scale generated interest to evaluate the technology at pilot scale. This interest necessitated further development of the process with a particular focus on evaluating key challenges that would be experienced at a larger scale. A comprehensive kinetic analysis on the performance of the hybrid LFCR was conducted as a function of operational parameters, including the effect of hydraulic residence time, temperature and sulphate loading on system performance. Concurrently, the study compared the utilisation of lactate and acetate as carbon source and electron donor as well as the effect of reactor configuration on system performance. Comparative assessment of the performance between the original 2 L LFCR and an 8 L LFCR variant that reflected the pilot scale design with respect to aspect ratio was conducted. Pseudo-steady state kinetics was assessed based on carbon source utilisation, volumetric sulphate reduction, sulphide removal efficiency and elemental sulphur recovery. Additionally, the hybrid LFCR provided a unique synergistic environment for studying the co-existence of the sulphate reducing (SRB) and sulphide oxidising (SOB) microbial communities. The investigation into the microbial ecology was performed using 16S rRNA amplicon sequencing. This enabled the community structure and the relative abundance of key microbial genera to be resolved. These results were used to examine the link between process kinetics and the community dynamics as a function of hydraulic residence time. Results from this study showed that both temperature and volumetric sulphate loading rate, the latter mediated through both sulphate concentration in the feed and dilution rate, significantly influenced the kinetics of biological sulphate reduction. Partial sulphide oxidation was highly dependent on the availability and rate of sulphide production. Volumetric sulphate reduction rates (VSRR) increased linearly as hydraulic residence time (HRT) decreased. The optimal residence time was determined to be 2 days, as this supported the highest volumetric sulphate reduction rate (0.21 mmol/L.h) and conversion (98%) with effective sulphide removal (82%) in the 2 L lactate-fed LFCR. Lactate as a sole carbon source proved effective for achieving high sulphate reduction rates. Its utilisation within the process was highly dependent on the dominant metabolic pathway. The operation at high dilution rates resulted in a decrease in sulphate conversion and subsequent increase in lactate metabolism toward fermentation. This was attributed to the competitive interaction between SRB and fermentative bacteria under varying availability of lactate and concentrations of sulphate and sulphide. Acetate as a sole carbon source supported a different microbial community to lactate. The lower growth rate associated with acetate utilising SRB required longer start-up period and was highly sensitive to operational perturbations, especially the introduction of oxygen. However, biomass accumulation over long continuous operation led to an increase in performance and system stability. Microbial ecology analysis revealed that a similar community structure developed between the 2 L and 8 L lactate-fed LFCR configurations. This, in conjunction with the kinetic data analysis, confirmed that the difference in aspect ratio and scale had minimal impact on process stability and that system performance can be reproduced. The choice of carbon source selected for distinctly different, highly diverse microbial communities. This was determined using principle co-ordinate analysis (PCoA) which highlighted the variation in microbial communities as a function of diversity and relative abundance. The SRB genera Desulfarculus, Desulfovibrio and Desulfomicrobium were detected across both carbon sources. However, Desulfocurvus was found in the lactate-fed system and Desulfobacter in acetate-fed system. Other genera that predominated within the system belonged to the classes Bacteroidetes, Firmicutes and Synergistetes. The presence of Veillonella, a lactate fermenter known for competing with SRB, was detected in the lactate-fed systems. Its relative abundance corresponded well with the lactate fermentation and oxidation performance, where an apparent shift in the dominant metabolic pathway was observed at high dilution rates. Furthermore, the data also revealed preferential attachment of selective SRB onto carbon microfibers, particularly among the Desulfarculus and Desulfocurvus genera. The microbial ecology of the floating sulphur biofilm was consistent across both carbon sources. Key sulphur oxidising genera detected were Paracoccus, Halothiobacillus and Arcobacter. The most dominant genera present in the FSB were Rhizobium, well-known nitrogen fixing bacteria, and Pannonibacter. Both genera are members of the class Alphaproteobacteria, a well-known phylogenetic grouping in which the complete sulphur-oxidising, sox, enzyme system is highly conserved. An aspect often not considered in the operation of these industrial bioprocess systems is the microbial community dynamics within the system. This is particularly evident within biomass accumulating systems where the proliferation of non-SRB over time can compromise the performance and efficiency of the process. Therefore, the selection and development of robust microbial inoculums is critical for overcoming the challenges associated with scaling up, particularly with regards to start-up period, and long-term viability of sulphate reducing bioreactor systems. In the current study, long-term operation demonstrated the robustness of the hybrid LFCR process to maintain relatively stable system performance. Additionally, this study showed that process performance can be recovered through re-establishing suitable operational conditions that favor biological sulphate reduction. The ability of the system to recover after being exposed to multiple perturbations, as explored in this study, confirms the resilience and long-term viability of the hybrid process. A key feature of the hybrid process was the ability to recover the FSB intermittently without compromising biological sulphate reduction. The current research successfully demonstrated the concept of the hybrid LFCR and characterised sulphate reduction and sulphide oxidation performance across a range of operating conditions. This, in conjunction with a clearer understanding of the complex microbial ecology, illustrated that the hybrid LFCR has potential as part of a semi-passive approach for the remediation of low volume sulphate-rich waste streams, critical for treatment of diffuse ARD sources.

The oxidative dissolution of chalcopyrite in ferric media often produces incomplete copper recoveries. The incomplete recoveries have been attributed to inhibition caused by the formation of a metal deficient sulphide and the deposition of elemental sulphur and jarosite. Although these phases have been qualitatively identified on the surface of chalcopyrite, none have been quantitatively identified. The aim of the project was to quantitatively analyse the surface before and after oxidative dissolution, with X-ray photoelectron spectroscopy (XPS), and to use the phases identified as the basis for mechanisms of dissolution and inhibition.XPS analysis was performed on chalcopyrite massive fractured under anaerobic atmosphere and chalcopyrite massive and concentrate oxidised in 0.1 M ferric sulphate (pH 1.9) and 0.2 M ferric chloride (pH 1.6) at 50, 65 and 80ºC. Quantitative XPS analysis of the chalcopyrite surfaces required the development of programs that accounted for the observed XPS spectra. The output of these programs was used to construct profiles of the chalcopyrite surfaces and the deposited phases. These surface profiles were correlated with copper recoveries determined for chalcopyrite concentrate dissolution under the same conditions.The surface of chalcopyrite before oxidative dissolution reconstructs to form a `pyritic' disulphide phase. This phase is oxidised in ferric media to form thiosulphate via the incorporation of oxygen atoms from the hydration sphere. The thiosulphate reacts in the oxidising conditions of low pH to form elemental sulphur, sulphite and sulphate. The sulphate complexes with ferric to produce hydronium jarosite. This reaction occurs at the surface during the initial stages of dissolution and in the bulk solution during the latter stages. This precipitation of hydronium jarosite during the latter stages of dissolution corresponds to inhibition of the dissolution reaction. It is therefore concluded hydronium jarosite is responsible for inhibiting the oxidative dissolution of chalcopyrite in ferric media.The identification of hydronium jarosite as the inhibiting phase is consistent with the industrial practice of removing `excess' iron from the ferric solution before oxidative dissolution. However, additional iron and sulphate are generated at the chalcopyrite surface during oxidative dissolution. These high iron and sulphate concentrations combine with the low pH and high temperatures favoured for the oxidative dissolution of chalcopyrite to produce ideal conditions for jarosite precipitation. Therefore, pH must be lowered further to prevent jarosite precipitation and enhance copper recoveries from chalcopyrite in ferric media.

The oxidative dissolution of chalcopyrite in ferric media often produces incomplete copper recoveries. The incomplete recoveries have been attributed to inhibition caused by the formation of a metal deficient sulphide and the deposition of elemental sulphur and jarosite. Although these phases have been qualitatively identified on the surface of chalcopyrite, none have been quantitatively identified. The aim of the project was to quantitatively analyse the surface before and after oxidative dissolution, with X-ray photoelectron spectroscopy (XPS), and to use the phases identified as the basis for mechanisms of dissolution and inhibition.
XPS analysis was performed on chalcopyrite massive fractured under anaerobic atmosphere and chalcopyrite massive and concentrate oxidised in 0.1 M ferric sulphate (pH 1.9) and 0.2 M ferric chloride (pH 1.6) at 50, 65 and 80ºC. Quantitative XPS analysis of the chalcopyrite surfaces required the development of programs that accounted for the observed XPS spectra. The output of these programs was used to construct profiles of the chalcopyrite surfaces and the deposited phases. These surface profiles were correlated with copper recoveries determined for chalcopyrite concentrate dissolution under the same conditions.
The surface of chalcopyrite before oxidative dissolution reconstructs to form a `pyritic' disulphide phase. This phase is oxidised in ferric media to form thiosulphate via the incorporation of oxygen atoms from the hydration sphere. The thiosulphate reacts in the oxidising conditions of low pH to form elemental sulphur, sulphite and sulphate. The sulphate complexes with ferric to produce hydronium jarosite. This reaction occurs at the surface during the initial stages of dissolution and in the bulk solution during the latter stages. This precipitation of hydronium jarosite during the latter stages of dissolution corresponds to inhibition of the dissolution reaction. It is therefore concluded hydronium jarosite is responsible for inhibiting the oxidative dissolution of chalcopyrite in ferric media.
The identification of hydronium jarosite as the inhibiting phase is consistent with the industrial practice of removing `excess' iron from the ferric solution before oxidative dissolution. However, additional iron and sulphate are generated at the chalcopyrite surface during oxidative dissolution. These high iron and sulphate concentrations combine with the low pH and high temperatures favoured for the oxidative dissolution of chalcopyrite to produce ideal conditions for jarosite precipitation. Therefore, pH must be lowered further to prevent jarosite precipitation and enhance copper recoveries from chalcopyrite in ferric media.

Sulphur (S) is one of the essential nutrients for plant growth. Over the last few decades, soil S deficiency has become more common in many countries primarily due to the application of high analysis S-free fertilisers and stricter regulations for industrial S dioxide emissions. To ameliorate soil S deficiency, elemental S (ES) as a fertiliser source is of great interest as ES is cost-effective and less susceptible to leaching than sulphate sources. However, ES has to be oxidised to sulphate to become available for plants. Sulphur oxidation is a biological process and depends on many factors affecting the size (genetic potential) and activity of the microbial population, but the predictability of ES oxidation by S-oxidising organisms has not been studied in soil. This work aimed to 1) examine the relationship between the genetic potential of a soil to oxidise ES and the oxidation rate of ES; and 2) investigate causes for the slower oxidation of granular ES compared to powdered ES. The relationship between the oxidation rate of ES, and soil physico-chemical properties and microbial populations (indicated by gene abundances) was investigated in ten Australian cropping soils covering a wide range of soil physico-chemical properties in a laboratory incubation experiment. The oxidation rate of ES, estimated from decreases in ES concentrations, varied greatly from 5.1 to 51.7 μg cm-2 d-1 across soils and was positively correlated with the initial soil pH (R2 = 0.54, P < 0.05). A regression equation including pH and organic C content as independent variables explained 79% of the variation in the oxidation rate (P < 0.01). The copies numbers of a functional gene soxB was quantified to indicate the abundance of Soxidising bacteria, and 16S ribosomal ribonucleic acid (16S rRNA) and 18S ribosomal ribonucleic acid (18S rRNA) to indicate the abundance of total bacteria and fungi, respectively. The abundances of soxB and 16S rRNA were positively correlated (P < 0.05) with ES oxidation rate (R2 = 0.67 for soxB and 0.66 for16S rRNA), but no significant correlation was observed between the oxidation rate and 18S rRNA abundance. This suggests that ES oxidation is dependent primarily on bacterial populations in soils. A combination of bacterial gene abundance (soxB or 16S rRNA) and soil pH could explain more than 80% of the variation in ES oxidation rate (P < 0.01). A distribution of soxB gene across diverse taxonomic and physiological bacterial groups was observed in the soils, which explains the strong relationship between soxB and 16S rRNA abundances (R2 = 0.99, P < 0.01). Elemental S is often combined with macronutrient fertilisers and this is generally found to reduce the ES oxidation rate as compared to ES in powdered form. We hypothesised that this reduction may be due to 1) acidification in the soil around the granule (in addition to ES oxidation, acidification can also be induced by monoammonium phosphate with which ES is often co-granulated); or 2) increased ionic strength of the soil solution in the vicinity of the granule from water-soluble fertilisers. Therefore, the effect of increases in acidity or ionic strength on ES oxidation in a sandy soil was studied. Interestingly, neither increases in acidity nor in ionic strength significantly affected ES oxidation in this soil, even though significant shifts in bacterial abundance and community composition were observed due to these changes. An additional experiment carried out at two ES application rates with two different soils showed similar results. This indicates that changes in bacterial abundance and community composition brought about by temporary changes in pH and ionic strength do not necessarily affect ES oxidation. The lack of agreement between bacterial population and ES oxidation might be due to the measurement of the total populations of bacteria, including dormant ones. The consistent ES oxidation (%ES oxidised) across treatments in this experiment suggests that there were sufficient active populations of S-oxidisers even at high acidity and ionic strength levels. Furthermore, while soil pH related to ES oxidation rate across soils as indicated by our previous study, no relationship was found in the soil acidified for < 15 weeks. This inconsistent effect of pH on the oxidation of ES (across soils versus within a soil) can be reconciled by the fact that pH differences across soils are associated with differences in many soil chemical and biological properties, which is not the case for short-term acidification. As the slower oxidation for co-granulated ES, compared to powdered ES, is likely not related to the chemical changes (pH, ionic strength) around the granule, we speculated that the slower oxidation is due to a reduction in the surface area of ES exposed to S-oxidisers in soil. To test this hypothesis, an experiment was conducted in which ES oxidation, soil chemical properties and bacterial abundance and community composition were compared between powdered (mixed through soil) and granular fertiliser (diammonium phosphate +10% ES). Soil in the vicinity of the granule including the granule was sampled for analysis. Oxidation of the cogranulated ES was much slower than for the powdered ES, with 36% oxidised for the former and 95% for the latter by the end of 20 weeks incubation. This difference was not related to differences in soil pH, bacterial abundances and community composition between these two treatments. Instead, the difference in ES oxidation rate between the two treatments corresponded to the difference in surface area of the granule and that of the individual ES particles, strongly suggesting that the slower oxidation rate for co-granulated ES was due to a reduction in the effective surface area available for S-oxidisers to colonise. Hence, oxidation of ES is not limited by the population of ES-oxidising bacteria in soil, but by the amount of ES exposed to soil organisms. This work shows that ES oxidation is influenced by both soil biological and physico-chemical properties across soils, and it could be well predicted by two variables i.e. soil pH and bacterial gene abundance under a steady environment. However, alterations in the abundance and community composition of bacteria resulted from temporary ambient changes within a soil do not necessarily affect ES oxidation, which suggests that the slow oxidation of ES in granules is not related to chemical changes but due to the low degree of dispersion of granules in soil. Therefore, in an effort to improve the effectiveness of granular ES, it is key to improve the exposure of ES to soil microorganisms, e.g. by technically improving granule dispersion in soil or by inoculating S-oxidisers into the granule.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Agriculture, Food and Wine, 2016.

A wide range of trace gases, including dimethyl sulphide (DMS) and organohalogens, are formed in the surface oceans via biological and/or photochemical processes. Consequently, these gases become supersaturated in seawater relative to the overlying marine air, leading to a net flux to the atmosphere. Upon entering the atmosphere, they are subject to rapid oxidation or radical attack to produce highly reactive radical species which are involved in a number of important atmospheric and climatic processes. Organohalogens can affect the oxidizing capacity of the atmosphere by interacting with ozone, with implications for air quality, stratospheric ozone levels, and global radiative forcing. DMS and iodine-containing organohalogens (iodocarbons) can both contribute to direct and indirect impacts of aerosols on climate through the production of new particles and cloud condensation nuclei (CCN) in the clean marine atmosphere. Therefore, marine trace gases are considered a vital component of the earth’s climate system, and changes in the net production rate and subsequent sea-to-air flux could have an impact on globally important processes. In recent years, attention has turned to the impact that future ocean acidification may have on the production of such gases, with the greatest focus on DMS and organohalogens. In this chapter, the current state-of-the-art in this growing area of research is outlined. The oceans are a major source of sulphur (S), an element essential to all life, and marine emissions of the gas DMS (chemical formula (CH3)2S) represent a key pathway in the global biogeochemical sulphur cycle. The surface oceans are supersaturated with DMS relative to the atmosphere, resulting in a oneway flux from sea to air (Lovelock et al. 1972; Watson and Liss 1998). DMS is a breakdown product of the biogenically produced dimethyl sulphoniopropionate (DMSP): . . . (CH3)2S+CH2CH2COO- → (CH3)2S + CH2CHCOOH (acrylic acid) (11.1) . . . Single-celled marine phytoplankton are the chief producers of DMSP, and this reaction is catalysed intra- and extracellularly by the enzyme DMSP-lyase (Malin et al. 1992; Liss et al. 1997). The capacity of phytoplankton to produce DMSP varies between species, with prymnesiophytes considered to be the most prolific (Malin et al. 1992 ; Liss et al. 1997 ; Watson and Liss 1998).

Abstract This study is aiming to conclude the root cause of elemental sulfur formation in the Gas handling facilities for an Oil field development facilities. The study focuses on supporting the concluded root cause by actual field trials. Practical short-term, midterm and long term solutions were studied and recommended including an optimization strategy to maximize utilization of existing facilities. The lessons learned for future projects were listed to overcome and manage the elemental sulfur formation issue. It was suspected that the root cause is related to potential oxidation of H2S due to the oxygen ingress associated with the generated nitrogen in the recycled low pressure gases. The study findings were achieved using actual field trials by either increasing the purity of the nitrogen source or by flaring (i.e. not recovering) the low pressure gases and monitoring changes in the operating conditions and the tendency of elemental Sulfur deposition for different N2 Purity levels. Accordingly, the mitigation measures were studied, assessed and the required modifications to overcome the problem are recommended. The first field trial was conducted considering flaring low pressure gases and increasing the nitrogen purity from 97 % to 99.8 %. The second field trial was conducted considering only increasing the nitrogen purity to 99.8% without flaring. For both field trials the tendency of Sulphur deposition was monitored in the Gas lift system and findings were recorded. The nitrogen purity was reduced gradually from 99.8 % to test implications on operation and note the nitrogen purity level at which Gas lift choke valves and Gas lift/ gas injection compressors are chocked by the elemental sulfur formation. According to the results of the field trials, the H2S oxidation due to the oxygen levels in the nitrogen stream was confirmed as the root cause for the elemental sulfur formation. All the lessons learnt to be considered at different stages of any project were captured and summarized in a typical checklist for the design of similar facilities at each project stage.

In the present work, pure iridium oxide (IrO2), and ternary catalysts (IrSnSb-Oxides and RuIrTi-Oxides) are investigated to be used as anode electrocatalysts in The Direct Methanol Fuel Cells (DMFC). Investigations of Methanol Oxidation and Hydrogen Evolution over the catalysts are measured in sulphuric acid as a supportive electrolyte using cyclic voltammetry technique at room temperature (25°C). A specific comparison between the electrocatalytic activities of IrSnSb-Oxides and RuIrTi-Oxides systems is conducted. A comprehensive examination of IrSnSb-Oxides and RuIrTi-Oxides catalysts containing different fractions of the alloying elements are performed to study the effect of varying Iridium Ir content (%) in IrSnSb-Oxides and Ruthenium Ru content (%) in RuIrTi-Oxides on the catalytic activity of ternary catalysts and on the performance of DMFC. It is observed that the electrocatalytic performance of ternary oxides catalysts is strongly dependent on the Ir and Ru content. The generated IrO2 and 33.36% Ru – 1%Ir – 65.64%Ti – Oxides catalysts prove high stability for oxidation of methanol and more proficient electrochemical activity as an anodic electrocatalyst in DMFC at 25°C. The electrochemical measurements of the Hydrogen Evolution Reaction (HER) for metal oxides show that 46.65%Ir – 40.78%Sn – 12.57%Sb sample and 18.75%Ru – 9.35%Ir – 71.9%Ti sample are the superior hydrogen evolution catalysts at 25°C.

Abstract Problems arising from uranium dispersion from mines and mine tailings, and the remediation of uranium contaminated areas, are discussed in this paper. In an experimental remediation study, a mixture of 70 vol.% of uraniferous mining wastes and 30 vol.% of a natural ceramic were used. The preliminary observations are discussed, and a model is proposed for the long term stabilization of mining tailings. Observations and monitoring of contaminated sites carried out during the last 25 years have revealed local impacts of uranium on the environment in Lower Silesia, Poland. Uranium pollution is limited to waste dumps, mine tailings, and their close vicinities at Kowary Podgórze, Radoniów, Kopaniec and Kletno. Uranium dispersion takes place mechanically due to transport by river waters, chemically by rain and ground waters, and anthropogenically when the wastes are utilized in construction. Floods are an additional mechanism responsible for the mechanical dispersion of uranium. As a result of these uranium transport mechanisms, in order to minimize the impacts of uranium on the environment, the covering of dumps with non-radioactive material is suitable only for sites located away from populated areas. Redox reactions have been observed at the Kowary tailings. During these reactions, iron hydroxide (goethite), hematite, and gypsum, are precipitated as solids. These observations provide a good prognosis for the long-term stabilization of radionuclides which can be incorporated into proposals for the construction of tailings sites. Using Eh-pH diagrams (system U-C-O-H, 25°C, 1 bar), UO2 is stable over the whole range of naturally occurring pHs, and is affected by Eh only in the range −0.4 to +0.1 volts in acidic environments, and below −0.4v in basal environments. BaSO4 and RaSO4 are stable under almost the same conditions as UO2. An environmentally significant redox boundary (FeS2 versus Fe2O3) occurs in the middle of the UO2 stability field. The geochemical and environmental behaviour of the elements discussed above suggest a mechanism for stabilizing radionuclides within stored wastes. The solidification of wastes should occur concurrently with naturally occurring redox reactions. During oxidation, an active iron-hydroxide gel is produced. This gel is then dehydrated and converted into limonite (a mixed compound), a monohydrate (goethite), hydro-hematite (Fe2O3·1/2H2O) and hematite (Fe2O3). This reaction occurs in neutral or weakly acidic environments. A key problem in the proposed remediation project, therefore, is pH stabilization in order to maintain the required environment for oxidation and cementation reactions. In order to achieve such an environment and to stabilize the reactions, a construction method is proposed for new waste storage systems, based on mixed layers of waste and barrier components composed of natural materials. The presence of CaO or Ca(OH)2 and anhydrite in the proposed internal membrane will reduce the vertical migration of sulphates. Redox reactions will be responsible for the secondary precipitation (reduction) of uranyl. These same reactions occur naturally during the precipitation of uranium ores. Iron oxidation is the other process in the redox pair required to reduce [UO2]+2 to UO2. The resultant pitchblende is insoluble in normal oxidizing environments. To minimize the dissolution of UO2 by sulphuric acid generated during the iron oxidation reaction, the construction of pH active membranes containing calcium oxide or hydroxide are recommended. These compounds will react with the free acid to precipitate gypsum. Although several elements can be mobilized as a result of oxidation, radium remains in insoluble solid phases such as the common Ca, Ba and Sr sulphates.