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This paper is a case study of a large-scale pillar collapse at the Everest Platinum Mine. A major contributing factor to the collapse was the presence of weak alteration layers in the pillars. These alteration layers are found in the Bushveld Complex in South Africa where the pyroxenite layers have been exposed to hydrothermal fluid flow, serpentinisation and layer-parallel shearing. The resulting clay-like material and the weak partings substantially reduce the pillar strength. From the literature survey, it is clear that weak seams in pillars reduce their strength and conventional pillar strength formulas overestimate the strength in these cases. As an alternative, a novel numerical modelling approach is proposed to study the pillar failure and to conduct a back analysis of the mine collapse. This consists of a limit equilibrium constitutive model implemented in a displacement discontinuity code. Two areas of the mine were simulated, namely part of the collapsed area and a second area, with larger pillars that is still stable. This allowed for a preliminary calibration of the limit equilibrium model. The model illustrated that a reduction in friction angle on the partings, owing to the presence of water in the collapse area, seems to be a factor that contributed to the collapse. Although encouraging results are obtained, calibration of the limit equilibrium model remains a challenge. Laboratory testing is required in future to determine the strengths of the weak partings and in particular, the difference in strength of the wet and dry alteration zone material. Highlights: Geological alterations substantially reduce the strength of hard rock pillars and the classical approach of using empirical pillar strength formulae for layout design does not work in these cases. A novel approach to simulate the pillar failure on a mine-wide scale is presented in this paper and this consists of a displacement discontinuity boundary element method using a limit equilibrium model to represent the pillar failure. The collapse of the Everest Platinum Mine in South Africa is described in the paper, it is used to test the proposed methodology, and it provides valuable data for researchers interested in case studies where pillar strength is reduced by weak layers. The proposed modelling methodology seems valuable to simulate the pillar failure and to design layouts for these types of ground conditions. Calibration of the limit equilibrium model remains a challenge, however. [ABSTRACT FROM AUTHOR]

Globally, the determinants of rangeland dynamics and sustainability have been debated for decades. This study sought to explain the drivers of rangeland ecosystems in semi-arid South Africa by examining the vegetation and soil conditions around animal drinking water points, and their implications for sustainable management and paradigm debates. For this purpose, we selected three land use systems (continuous-communal livestock farms, rotational-commercial livestock farms, and continuous-game reserves), with the livestock farms having either high or low stocking rates. Soil organic carbon (OC), bulk density (p < 0.05), and soil compaction (p < 0.0001) varied greatly at land scales, being greater in the communal farms or game reserves than the commercial farms. Within the communal farms, sites with high stocking rates showed higher (p < 0.05) soil OC and bulk density than sites with lower stocking rates, but in the commercial farms, sites with high stocking rates had lower soil OC. Above ground grass biomass, and the abundance of highly desirable grass species were greater (p < 0.001) in the commercial farms and game reserves. Our results conclude that equilibrium elements, importantly animal density and diversity, seemed to play a major role in soil and vegetation dynamics. We also observed variations in edaphic factors and rainfall across the land use systems and over seasons (rainfall). We assume that these non-equilibrium elements may also influence rangeland ecosystems. To confirm this, however, we recommend future studies to include comparable measures of the vegetation and soil, and their relations with edaphic and temporal long-term rainfall variability across the land use systems. [ABSTRACT FROM AUTHOR]

Most partial equilibrium models of the agricultural sector have not incorporated a dynamic and interlinked module for agricultural input expenditure. The South African Bureau for Food and Agricultural Policy (BFAP) model, which models a major share of agricultural output in South Africa, has also up to now not integrated input expenditure into the modelling framework. In most models, input costs are treated as exogenous and the recursive link between the input and output sides of the sector is overlooked in the models that attempt to incorporate input expenditures. This article addresses both issues by integrating agricultural input expenditures into the South African sectoral partial equilibrium model by endogenising input costs and recursively linking both the input and output sides of the agricultural sector. Thus, the impact of increasing the input cost may not only signal a fall in the gross value added and net farming income, but also a growth in subsequent years when the recursive effect of the impact is fully accounted for. [ABSTRACT FROM AUTHOR]

An excess level of nitrate in drinking water is responsible for methemoglobinemia, or 'blue baby' disease. Consequently, management of nitrate in drinking water is universally of public health interest. In this study, clinoptilolite functionalised with cationic surfactant hexadecyltrimethyl ammonium (HDTMA) was used for the removal of nitrate from drinking water. The effects of surfactant loading, adsorbent dosage, pH, coexisting ions, temperature and environmental water quality on the adsorption of nitrate were investigated. It was found that adsorption was optimum when the initial concentration of the functionalising surfactant was 3 000 mg·ℓ-1. An increase in adsorbent dosage raised the percentage removal of nitrate. The valency of the coexisting anion had a major effect on nitrate removal, with the presence of phosphate (a trivalent anion) leading to the lowest removal ability. Temperature and pH had negligible effects on adsorbent performance. Environmental water samples (natural groundwater samples from Limpopo Province, South Africa) were tested and it was found that the World Health Organisation (WHO) regulatory compliance can be achieved even when the initial concentration of nitrate exceeds 300 mg·ℓ-1. Equilibrium data was modelled using the Freundlich and Langmuir isotherms and the data conformed well to the Freundlich isotherm, indicating the heterogeneous nature of the active sites. Kinetically, nitrate adsorption was best described by the pseudo-second rate equation. [ABSTRACT FROM AUTHOR]

Abstract: Biological uranium reduction was investigated using bacteria isolated from a uranium mine in Limpopo, South Africa. Background uranium concentration in soil from the mine was determined to be 168mgkg−1 much higher than the typical background uranium concentration in natural soils (0.30–11.7mgkg−1). Therefore it was expected that the bacteria isolated from the site were resistant to U(VI) toxicity. Preliminary studies using a non-purified consortium from the mine soil showed that U(VI) [uranyl(VI) dioxide, ] was reduced and re-oxidized intermittently due to the coexistence of U(VI) reducers and U(VI) oxidisers in the soil. Results from U(VI) reduction by individual species showed that the purified cultures of Pantoea sp., Pseudomonas sp. and Enterobacter sp. reduced U(VI) to U(IV) [U(OH)4(aq)] under pH 5–6. Klebsiella sp. had to be eliminated from the cultures since these contributed to the remobilisation of uranium to the hexavelant form. The initial reduction rate determined at 50% point in 30mgL−1 batches was highest in Pseudomonas sp. at 30mgL−1, followed by Pantoea sp. Rapid reduction was observed in all cultures during the first 6h of incubation with equilibrium conditions obtained only after incubation for 24h. Complete U(VI) reduction was observed at concentrations as high as 200mgL−1 and up to 88% removal after 24h in batches with an initial added U(VI) concentration of 400mgL−1. [Copyright &y& Elsevier]

There has been some debate on the impact of exchange rate volatility and levels in South Africa. This is a particular concern as South Africa needs to dramatically expand sustainable employment and at the same time raise value-added in its production of goods and services. These are not necessarily complementary objectives for a mineral-exporting economy. Using a computable general equilibrium model, with the appreciation induced by a commodity price boom, this paper analyses the possible impact of an appreciation of the rand on employment. The intention is to identify the impact on both aggregate employment and sectoral output. Although the economy does well as a result of the commodity boom, the results indicate the potential for 'Dutch Disease'-type effects. Almost all traded sectors are negatively affected, while the non-traded sectors experience a boost as a result of the appreciation. [ABSTRACT FROM AUTHOR]

We describe the isolation of six tetranucleotide microsatellites from the Cape sugarbird ( Promerops cafer) using an enrichment protocol. All loci were highly variable with number of alleles ranging from nine to 26 and values of observed heterozygosity ranging from 0.534 to 0.931. All loci were in Hardy–Weinberg equilibrium with the exception of Pro66 and Pro86. Further analysis of Pro86 indicated it was Z-linked. All loci amplified and were variable in the congeneric Gurneys sugarbird ( Promerops gurneyi). These loci will be used in mating system and phylogeographic studies of Cape sugarbirds in South Africa. [ABSTRACT FROM AUTHOR]