No description available.

No description available.

The Platreef has been the site of platinum mining since the 1920’s. The reef itself comprises a series of pyroxenites, gabbronorites and norites that contain xenoliths/rafts of footwall rocks. The Platreef is irregularly mineralised with PGE, Cu and Ni, and has a greater abundance of sulphides than the Merensky Reef. The main base metal sulphides within the Platreef are pyrrhotite, pyrite, pentlandite, and chalcopyrite. Extremely varied platinum group minerals occur as tellurides, bismuthotellurides, antimonides and arsenides. This study aimed to gain a clearer understanding of the formation of sulphides within the Platreef. In order to do this, cores from both the northern and southern sectors of the Platreef were sampled. A detailed study of the sulphides within these cores was conducted to identify different styles of mineralisation and their occurrences. Four different styles of mineralisation were identified: massive, net-textured, blebby and interstitial. In general, sulphides in the southern sector of the Platreef are concentrated in the lower portion of the package, whereas in the northern sector they are concentrated in the upper part although in both sectors the sulphide occurrences are associated with metasedimentary xenoliths. Conventional and multiple sulphur isotope analyses were undertaken on sulphides from cores from both the southern and the northern sectors. This was done in order to determine the source of the sulphur. These analyses were also conducted to examine sulphur isotope variations with changing footwall. Previous sulphur isotope data predominantly obtained from the central sector of the Platreef indicated a crustal contribution to the sulphur budget but did not provide much data on footwall sulphides so the nature of the crustal component was only implied. In this thesis sulphur from an external source was identified as having contributed to the formation of sulphides in both the southern and the northern sectors of the Platreef, especially for sulphides in proximity to metasedimentary xenoliths. In the southern sector of the Platreef this source was identified as most likely being pyritic shales of the Lower Duitschland Formation. In the northern sector, Malmani dolomites, which are suggested to have collapsed from the roof of the Platreef, are the most likely source of sulphur. Importantly, in the northern sector no sulphur is thought to have come from the Archaean granite footwall. Oxygen isotope analyses were conducted on samples from the southern sector of the Platreef to verify the presence of crustal contamination. Data collected indicated that there had been a crustal oxygen component involved in the formation of silicates that led to their partial recrystallisation. When compared to oxygen isotope data from the central sector of the Platreef it appears that there are variations along strike that most likely result due to the changing footwall. This data indicates a major contribution of oxygen-, sulphur- and other volatile-rich fluids to the Platreef. This led to the partial re-crystallisation of silicates, and in areas in close proximity to sulphur-bearing metasedimentary xenoliths aided in the formation of sulphides. These volatile-rich fluids most likely originated from metasedimentary xenoliths during metamorphism that then migrated through the Platreef package. When the observations from both the southern and northern sectors of the Platreef are compared and combined with pre-existing data for the central sector, several general observations can be made. 1. The entire length of the Platreef has been affected by contamination from crustal sulphur sources to some degree. This contamination is suggested to be from volatile-rich fluids which were released from metasedimentary crustal xenoliths and footwall during metamorphism. 2. The proximity between sulphide enrichment and sulphur-bearing sediments (as footwall or xenoliths) is important and indicates the source of the sulphur which led to sulphide formation. 3. Contamination occurred on a localised scale, depending on the composition of the sedimentary lithologies and the proximity of the contaminant to the magma. In the southern sector of the Platreef the source of the sulphur is almost certainly pyritic shales of the Lower Duitschland Formation. In the central sector, sulphur has most likely come from sulphur-rich dolomites and evaporites from the Malmani dolomites. In the northern sector, sulphur-rich fluids were released from Malmani dolomite rafts that collapsed from the roof into the magma during the emplacement of the Platreef. The Archaean footwall in this area has had little or no control on the formation of the sulphides within the Platreef.

Weyerhaeuser's Paper Mill in Albany, Oregon has been experiencing frequent ring formation in the #3 rotary lime kiln. Rings form when lime mud (CaCO₃) or product lime (CaO) particles adheres to the walls of the lime kiln and become resistant to the abrasive action of the sliding motion of product lime particles (Notidis, 1994). Ring formation has resulted in frequent shut downs to remove (blast) the rings and caused a significant loss of productivity and revenue to the company. A careful analysis of the production process in the mill revealed that concentration of sodium was high and that of sulfur low in the lime mud. The high sodium was due to the low sulfur input to the kiln resulting in high sodium to sulfur ratio. The use of natural gas as a fuel source in the kiln partly causes low sulfur levels in the mud. This study examines the effects of burning emulsified sulfur in the #3 rotary lime kiln to reduce sodium enrichment in the solids, and examine its effect on kiln operation and SO₂ emissions from the #3 rotary lime kiln. A four day trial of burning emulsified sulfur to reduce sodium concentration in the #3 rotary lime kiln was planned. Tote bins of 70% solution of emulsified sulfur was fed into the #3 rotary lime kiln. The sulfur feed was controlled to ensure an excess of sulfur by observing the SO₂ concentration in the kiln stack and maintaining a concentration above 100 ppm corrected to 10% oxygen. The results show that while burning emulsified sulfur had no significant effect on kiln operation, it resulted in a high reduction of sodium in the dust caught in the electrostatic precipitator and an increase SO₂ emission from the stack. The reduction of sodium in the dust was 50%, which is an enrichment factor of 2. Although lime can effectively remove SO₂, the removal efficiency decreased from 96.0% to 73.0% when emulsified sulfur was burned in the #3 rotary lime kiln. The results of this trial are promising, since it demonstrates that burning emulsified sulfur significantly lowers the sodium enrichment in the kiln. The reduced levels of sodium can potentially lead to a reduction in ring formation in the #3 rotary lime kiln in the Albany Paper Mill. / Graduation date: 2004

Graduation date: 2003

The controls of water and O2 availability, microbial activity and temperature on acid (H2SO4) production rates in commercial-scale sulphur (S0) blocks were quantified and recommendations were made for minimizing H2SO4 production in S0 blocks. Acidic drainage from the S0 blocks (pH 0.4-1.0) was attributed to mixing of fresh infiltrating water and low-pH resident water (mean pH=-2.1) with resident water comprising ~4-8% of the drainage. Although clean S0 is strongly hydrophobic, preferential water infiltration occurred rapidly through fractured S0 blocks in which the bulk hydraulic conductivity was estimated to be similar to gravel or clean sand (Ks=1x10-1 to 1x10-3 m/s). Microbial colonization of fracture faces generated localized hydrophilic conditions that helped create preferential pathways for water infiltration. Liquid water contact (compared to water vapour) was essential for S0 oxidation (i.e., H2SO4 production), therefore H2SO4 production in the S0 blocks was limited to fractures and friable S0 through which water flowed. H2SO4 production was greatest in the upper 1 m of the S0 block (70 to >97% of annual H2SO4 production) and the result of autotrophic microbial S0 oxidation.<p> S0 oxidation rates were very sensitive to temperature and increased by a factor of 4.3 for a temperature increase of 10°C (Q10). Therefore minimizing temperature (<5°C) in S0 blocks would be an effective strategy for controlling H2SO4 production. Heat released during S0 oxidation did have a measurable effect on in situ temperatures and should be considered in the design of insulated cover systems. Although autotrophic microbial activity was insensitive to O2 concentrations when they were >1 vol.%, the total mass production rate of H2SO4 is approximately proportional to the O2 concentration at the surface of the S0 block (assuming in situ O2 concentrations decrease to <1 vol. %). Therefore, cover systems that minimize the surficial O2 concentration are recommended.<p> Cover systems limiting H2O infiltration would be effective for minimizing the volume of acidic drainage, but may have no impact on H2SO4 production rates within the block. In this study, H2O infiltration through a typical soil cover (~95% efficiency) would easily satisfy the annual H2O demand for H2SO4 production (2.6 mm/m2 in the upper 1 m). Greater near-surface H2SO4 production rates may appear to make surficial biocide application an attractive option for minimizing S0-oxidizing microbial activity, however, this approach might simply drive the zone of H2SO4 production to greater depths and have no affect on the total mass production of H2SO4.

The ability to effectively remove sulphur from sulphur-poisoned NOx storage/reduction (NSR) catalysts, while minimizing associated fuel penalties and thermal degradation, is important for commercial application of NSR catalysts. As long as sulphur remains in the fuel or lubrication oil formulations, deactivation of NSR catalysts will persist. In an attempt to more fully understand the mechanism of sulphur removal and the associated operating conditions necessary to efficiently decompose sulphates, various gas compositions, temperatures and desulphation methodologies were applied to a commercially supplied catalyst. Experiments were conducted using a pilot scale plug flow catalytic reactor. FTIR spectroscopy and mass spectrometry were used to measure key sulphur species concentrations. Three groups of experiments were conducted. In the first, the effect of gas composition on the amount of sulphur removed from the catalyst was evaluated. In the latter two, high flow cycling desulphation and low flow cycling desulphation were compared. The most effective desulphation gas composition was achieved through the combination of high concentrations of H2, CO and C3H6 and also the inclusion of CO2 and H2O, which released up to 91% of the stored sulphur. The commercial catalyst tested is designed for a dual-leg process. Dual-leg systems are advantageous over single-leg systems in that engine modifications are unnecessary for catalyst regeneration, thereby minimizing losses in vehicle performance. It was found that under conditions appropriate for that application, catalyst desulphation is dominated by the amount of residual surface oxygen. Through the use of short lean phase cycling, to prevent oxygen saturation, the dual-leg application proved effective for sulphate removal, inducing 69% sulphur release compared to 51% when the surface was saturated with oxygen. Multiple stabilities of sulphur exist on the catalyst, which led to residual catalyst sulphates after many desulphations.

The ability to effectively remove sulphur from sulphur-poisoned NOx storage/reduction (NSR) catalysts, while minimizing associated fuel penalties and thermal degradation, is important for commercial application of NSR catalysts. As long as sulphur remains in the fuel or lubrication oil formulations, deactivation of NSR catalysts will persist. In an attempt to more fully understand the mechanism of sulphur removal and the associated operating conditions necessary to efficiently decompose sulphates, various gas compositions, temperatures and desulphation methodologies were applied to a commercially supplied catalyst. Experiments were conducted using a pilot scale plug flow catalytic reactor. FTIR spectroscopy and mass spectrometry were used to measure key sulphur species concentrations. Three groups of experiments were conducted. In the first, the effect of gas composition on the amount of sulphur removed from the catalyst was evaluated. In the latter two, high flow cycling desulphation and low flow cycling desulphation were compared. The most effective desulphation gas composition was achieved through the combination of high concentrations of H2, CO and C3H6 and also the inclusion of CO2 and H2O, which released up to 91% of the stored sulphur. The commercial catalyst tested is designed for a dual-leg process. Dual-leg systems are advantageous over single-leg systems in that engine modifications are unnecessary for catalyst regeneration, thereby minimizing losses in vehicle performance. It was found that under conditions appropriate for that application, catalyst desulphation is dominated by the amount of residual surface oxygen. Through the use of short lean phase cycling, to prevent oxygen saturation, the dual-leg application proved effective for sulphate removal, inducing 69% sulphur release compared to 51% when the surface was saturated with oxygen. Multiple stabilities of sulphur exist on the catalyst, which led to residual catalyst sulphates after many desulphations.

The controls of water and O2 availability, microbial activity and temperature on acid (H2SO4) production rates in commercial-scale sulphur (S0) blocks were quantified and recommendations were made for minimizing H2SO4 production in S0 blocks. Acidic drainage from the S0 blocks (pH 0.4-1.0) was attributed to mixing of fresh infiltrating water and low-pH resident water (mean pH=-2.1) with resident water comprising ~4-8% of the drainage. Although clean S0 is strongly hydrophobic, preferential water infiltration occurred rapidly through fractured S0 blocks in which the bulk hydraulic conductivity was estimated to be similar to gravel or clean sand (Ks=1x10-1 to 1x10-3 m/s). Microbial colonization of fracture faces generated localized hydrophilic conditions that helped create preferential pathways for water infiltration. Liquid water contact (compared to water vapour) was essential for S0 oxidation (i.e., H2SO4 production), therefore H2SO4 production in the S0 blocks was limited to fractures and friable S0 through which water flowed. H2SO4 production was greatest in the upper 1 m of the S0 block (70 to >97% of annual H2SO4 production) and the result of autotrophic microbial S0 oxidation.<p> S0 oxidation rates were very sensitive to temperature and increased by a factor of 4.3 for a temperature increase of 10°C (Q10). Therefore minimizing temperature (<5°C) in S0 blocks would be an effective strategy for controlling H2SO4 production. Heat released during S0 oxidation did have a measurable effect on in situ temperatures and should be considered in the design of insulated cover systems. Although autotrophic microbial activity was insensitive to O2 concentrations when they were >1 vol.%, the total mass production rate of H2SO4 is approximately proportional to the O2 concentration at the surface of the S0 block (assuming in situ O2 concentrations decrease to <1 vol. %). Therefore, cover systems that minimize the surficial O2 concentration are recommended.<p> Cover systems limiting H2O infiltration would be effective for minimizing the volume of acidic drainage, but may have no impact on H2SO4 production rates within the block. In this study, H2O infiltration through a typical soil cover (~95% efficiency) would easily satisfy the annual H2O demand for H2SO4 production (2.6 mm/m2 in the upper 1 m). Greater near-surface H2SO4 production rates may appear to make surficial biocide application an attractive option for minimizing S0-oxidizing microbial activity, however, this approach might simply drive the zone of H2SO4 production to greater depths and have no affect on the total mass production of H2SO4.

No description available.