Gold tailings as a source of waterborne uranium contamination of streams - the Koekemoerspruit (Klerksdorp goldfield, South Africa) as a case study - part I of III: uranium migration along the aqueous pathway

Tailings deposits from gold and uranium (U) mining in the Witwatersrand basin often contain elevated levels of radioactive and chemo-toxic heavy metals. Through seepage, dissolved U and other metals migrate from tailings deposits via groundwater into adjacent fluvial systems. The subsequent transport through flowing surface water is one of the most effective pathways of distributing contaminants throughout the biosphere. Mechanisms of diffuse stream contamination, as well as the aqueous transportation of U were investigated. In this paper, geochemical data of water and sediment samples from the Koekemoerspruit (a typical example of a stream affected by gold and U mining in South Africa) are analysed with regards to possible transport and immobilisation mechanisms of U migrating in solution. Ratios between dissolved and solid phases of U for various water-sediment-systems along the aqueous pathway indicated, unexpectedly, significantly lower mobility of U in flowing surface water than in the groundwater system of the floodplain. Correlation of various geochemical parameters suggests co-precipitation of U along with calcium carbonate and iron/ manganese-compounds as the main reason for the higher immobilisation rate in the flowing water systems. Owing to redoxinitiated precipitation at the interface of reducing groundwater and oxygenated stream water within the bottom sediments, the latter act as a sink and geochemical barrier for U from groundwater sources. The low retention of U in the highly sorptive floodplain sediments on the other hand is explained by the formation of neutral uranyl-sulphate-complexes, which prevent the positively charged U ion from adsorbing onto negative surfaces of clay minerals and organic substances in the floodplain. Evidence for such complexes are sulphate crusts with extremely high U concentrations, which form on topsoil due to capillary fringe effects in dry periods. Due to their high solubility, these crusts are easily dissolved by rain, resulting in concentration peaks of dissolved U in surface runoff. WaterSA Vol.30 (2) 2004: 219-22

Charting a New Sustainability Course for Luxury Game Lodges in Africa: A Hybrid Analytical Framework for Analysing the Key Coupled Human and Natural System Components

This paper introduces a hybrid analytical framework to comprehensively assess luxury game lodges within protected areas such as Coupled Human and Natural Systems (CHANS). The framework, developed through a synthesis of diverse Social-Ecological Systems (SES) models and tools, encompasses eight key steps, from sustainability context assessment to creating a tailored managerial-ecology model. By systematically analysing ecological, social, and economic dimensions, this framework empowers stakeholders to make informed decisions that balance biodiversity conservation, sustainability, and community engagement in luxury game lodge operations. Its practical application promises to advance the coexistence of ecotourism and environmental protection, fostering the long-term viability of these vital tourism destinations within protected areas

Pyrolysis and gasification of 5–20 mm tyre rubber cubes under carbon dioxide flow

The thermal behaviour of waste tractor tyre tread was investigated using 5-, 10-, 15- and 20 mm cubes and video recording of the process – an experimental approach for which no precedent could be found in the literature. Pyrolysis and gasification under CO2 flow in the range of 400 °C to 1000 °C were studied using a pre-heated tube furnace under near-isothermal reaction conditions. The video-graphic timeline and thermal history observations were used to correlate the results with first-order heat-transfer calculations and TGA-derived kinetics published previously. For pyrolysis, heat-transfer becomes the rate limiting step in the region 800–900 °C and above. Experimental evidence shows that the full pyrolysis time may be estimated from the algebraic sum of the local kinetic component and a heat-transfer component. The pressure build-up due to the release of gaseous products results in shattering of the solid into sub-millimetre char fragments. The kinetics of the reverse-Boudouard reaction can be described by a standard gas–solid shrinking particle model; however the character of the charred remains complicates this. Mass transfer limits are predicted only to become significant above 1200 °C, for a well-characterised char surface.The University of Pretoria and Suid-Afrikaanse Akademie vir Wetenskap en Kuns.https://pubs.rsc.org/en/journals/journal/rehj2024Chemical EngineeringNon

Treatment of TRISO-coated particles with CF4 in a low temperature plasma

An alternative recovery method to the mechanical crushing of off-specification tri-structural-isotropic (TRISO) coated fuel microspheres is demonstrated. It is shown that the inert SiC layer can be completely removed by etching with the active fluorine species from an inductively coupled radio-frequency CF4 glow-discharge impinging a static bed from the top, at a working pressure of 1 kPa. At this pressure mass transport does not have a rate limiting role and the chemical reaction itself is rate determining. A treatment time of roughly 4 h is required for the conditions reported hereThe South African National Research Foundationhttp://www.elsevier.com/locate/jnucmatai201

Recovery of valuable products from polytetrafluoroethylene (PTFE) waste

Thesis (Ph.D. (Chemistry))--North-West University, Potchefstroom Campus, 2008.The disposal of PTFE waste presents a global problem from both an ecological and economical perspective. This study was performed to address this problem as well as to understand the mechanism according to which PTFE is depolymerised to form the different products, namely C2F4, C2F6, C3F6, C3F8 and c-C4F8. Different conceptual reactors were designed and built for different tests on filled and unfilled PTFE. These included a laboratory scale Rotating-kiln Reactor for testing the depolymerisation properties in a horizontal reactor, a Drop-tube Reactor for the continuous depolymerisation of unfilled PTFE, a Paddle Reactor for the continuous depolymerisation of filled as well as unfilled PTFE and a Vibrating Reactor for the evaluation of other fluoropolymers like THV, HTE, ETFE and PFA. Analytical techniques such as GC, GC/MS, TGA and SEM were used to evaluate the different types of PTFE and analyse the gaseous products from the depolymerisation process. A mechanism by which depolymerisation and product formation takes place was proposed on the basis of experimental data obtained during experimentation on various PTFE depolymerisation systems, utilising different analytical techniques, including a thermodynamic study, a kinetic study and molecular modeling. For the product formation mechanism a two-route approach was proposed. Route 1 dominated at temperatures < 700 °C, producing mainly C2F4, C3F6 and c-C4F8. Route 2 dominated at temperatures between 700 and 900 °C, producing mainly C2F4) C2F6, C3F6, C3F8, PFIB and c-C4F8. A thermodynamic study and molecular modeling was used to evaluate possible product formation reactions in order to propose scientifically sound mechanisms for Routes 1 and 2. A kinetic study revealed that the order of the depolymerisation reaction is 0.54, and that the reaction proceeds at a rate of 4.03 x 10"3 s"1 at 600 °C. The activation energy for the depolymerisation process was calculated to be 260 kJ-mol"1. A Rotating-kiln Plant was designed for the production of HFP from PTFE on a commercial scale. An economic analysis indicated that a 500 kg-h"1 filled PTFE depolymerisation plant, selling HFP as a product at R55 per kg, is highly profitable.Doctora

Gold tailings as a source of waterborne uranium contamination of streams - the Koekemoerspruit (Klerksdorp goldfield, South Africa) as a case study - part II of III: dynamics of groundwater-stream interactions

Dissolved uranium (U) from the tailings deposits of various gold mines in South Africa has been found to migrate via seepage and groundwater into adjacent streams. The extent of the associated non-point pollution depends on the concentration of U in the groundwater as well as the volume and rate of groundwater seepage into the stream channel. Whilst the U concentration in groundwater is relatively constant and comparatively easy to determine, the same is not true for the flux of groundwater into the stream. In order to track the water exchange at the groundwater-stream interface, real-time in situ measurements by data-logger controlled probes for gauging heights and electrical conductivity (EC) were taken at 10 min intervals. As a result of a steep hydraulic gradient between water-saturated tailings deposits and the receiving watercourse, exfiltration (base-flow) of contaminated groundwater generally dominates. However, short-term inversions of the flow direction (infiltration of stream water into the groundwater) were also observed. These are attributed to an artificial flow regime of the Koekemoerspruit, which results from a pumping scheme that discharges groundwater from underground mine workings into the stream. Differences in pumping rates lead to pronounced diurnal fluctuations of gauging heights in the stream, which in turn cause even higher fluctuations of the associated groundwater table. The hydraulic mechanisms of the stream-groundwater interaction, as well as implications for the aqueous transport of U are discussed. WaterSA Vol.30 (2) 2004: 227-23

The relationship between moral intervention strategies and the stigmatisation of people living with HIV – A Christian perspective

One of the ways in which sexual transmission of AIDS is addressed is through moral interventions by organisations affiliated with Christian churches. However, this approach has been heavily criticised in recent literature, implying that moral interventions by church-affiliated organisations generally lead to stigmatisation which is one of the major obstacles to their involvement in HIV prevention. This article explores the origin of this accusation and discusses the Christian-ethical aspects related to HIV or AIDS. The conclusion is that the fact that churches take the Word of God and Christian morality as point of departure in HIV or AIDS intervention programmes does not imply that people who transgressed religious moral teachings may be condemned. On the contrary, the church preaches Christian forgiveness, mercy and empathy. Churches and organisations affiliated with churches should therefore be regarded as valuable partners in the fight against AIDS, for while propagating a normative lifestyle, they also preach love, compassion and support for people living with HIV

Gold tailings as a source of water-borne uranium contamination of streams - the Koekemoerspruit (South Africa) as a case study - part III of III: fluctuations of stream chemistry and their impacts on uranium mobility

Once dissolved uranium (U) from tailings deposits enters adjacent streams, subsequent downstream transport is affected by the rate at which U is immobilised in sediments, thereby lowering its concentration in stream water. For aqueous phases immobilisation includes adsorption onto sediments and suspended solids, as well as precipitation and co-precipitation as insoluble compounds, all mechanisms being largely controlled by pH and redox potential (Eh) of the stream water. Using real-time in situ measurements pronounced diurnal oscillations of both parameters were found at the site described here. The influence of the position of probes in detecting such short-term variations of stream-water quality are analysed by comparing in-house with in-stream measurements. Diurnal pH-oscillations are mainly caused by photosynthesis-based shifts of the calcium carbonate - carbon dioxide equilibrium in the stream that, in turn, is influenced by geological features of the catchment, biological activity as well as meteorological factors. These oscillations are likely to affect the mobility of dissolved U as well as the rate and distance of the downstream transport of U and other heavy metals significantly. Apart from this, event-related changes of stream chemistry, such as a sudden fall in pH in response to acid rain, were also observed. The dynamics and possible impacts on re-mobilisation of U from contaminated sediments back into the stream water are explored. WaterSA Vol.30 (2) 2004: 233-23