Browsing by Author "Hallbauer, D"

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    Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources.
    (Springer, 1999) Frimmel, H; Hallbauer, D
    Crush-leach data were obtained, using High Performance Gradient Ion-Chromatography and Capillary Electrophoresis, on individual generations of aqueous fluid inclusions in hydrothermal quartz from three different auriferous conglomerate horizons (reefs) in the late Archaean Witwatersrand Basin, South Africa. These data, supplemented by oxygen isotope analyses of hydrothermal quartz and in combination with microthermometric analyses, help to constrain the chemical composition, pH, temperature of formation and the possible source of the mineralizing fluid which, in places, was capable of mobilizing some of the primarily detrital gold in the fluvial Witwatersrand sediments. The dominant cations in the aqueous fluid inclusions are Na + and Ca 2+, with C1- or HCOj being the dominant anion, whereas K ÷, Mg 2+, and SOlare subordinate. Most fluid inclusions have elevated NH~- concentrations which are directly correlated with those of NO 3. In a number of samples small amounts of organic acids (formate, propionate, and acetate) were also detected. A largely meteoric source is inferred for the gold-mobilizing fluids in the Witwatersrand reefs because of a lack of Br- in the fluid, a composition distinctly different from that of seawater, the presence of organic acids, and ~18Ofluid values around 0%0. The fluids are ascribed to hydrothermal infiltration triggered by the 2020 Ma Vredefort impact which also created a secondary permeability in the form of a dense network of micro-fractures preferentially in the conglomerate beds of the already metamorphosed Witwatersrand rock sequence. This fluid differs from the regional metamorphic fluid in the basin by having a considerably higher pH (5.7-7.2). The difference in pH might explain why the older, fairly acidic metamorphic fluid was apparently less capable of mobilizing the gold as gold solubility reaches its peak at the pH calculated for the fluid ascribed to the impact.
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    Measurement and modelling of organic fouling deposition in ultrafiltration by ultrasonic transfer signals and reflections.
    (Elsevier, 2002) Li, Jianxin; Sanderson, R; Hallbauer, D; Hallbauer-Zadorozhnaya, V Y
    The development of a non-destructive, real-time observation technique to detect and monitor fouling during liquid separation processes is of great importance to the development of strategies to improve operating conditions. In this study ultrasonic time-domain reflectometry (UTDR) was used to measure organic fouling, in real time, during ultrafiltration (UF) with polysulfone (PS) membranes. The feed solution was a paper-mill effluent, which contains breakdown products of lignin or lignosulphonate, from a wastewater treatment plant. An asymmetric, composite PS membrane can be detected by UTDR. Experimental results showed that the ultrasonic signal response can be used to monitor fouling-layer formation and growth on the membrane in real-time. Traditional flux measurements and analysis of the membrane surface by microscopy corroborated the UTDR results. Further, the differential signal developed indicate the state and progress of the fouling layer and gives warning of advanced fouling during operation. Moreover, a predictive modelling program — ultrasonic reflection (USRF) was developed to model the fouling deposits. This contributed to a better understanding of the fouling layer formation and its recognition during ultrasonic testing. This modelling was applied to model the density and thickness of a fouling layer on a membrane surface so as to predict the fouling behavior. The modelling results were in a good agreement with the actual observations.