The generation of power within Southern Africa is reviewed. A study is described in which the emission factors for CO 2 and NO x were determined experimentally across a wide range of power stations and technologies, and compared to the IPCC default factors. It was found that the CO 2 emission factors tended to be at the upper end of the IPCC default range, whereas the NOx emission factors were generally below the low end. The results from South Africa tend to dominate the regional picture at present, but this is likely to change in the near future, as Botswana has announced plans to introduce over 4 000 MWe of coal-fired power stations.
SYNOPSIS The quest for efficiency in comminution is an ongoing concern as comminution usually constitutes a major cost component in the metal production industry. Such improvements can be made by circuit optimization or development of more efficient equipment. A novel crusher, known as the rotary offset crusher (ROC), promises to deliver in this space. The ROC was invented in 2002 by Michael Hunt, Henry Simonsen, and Ian Sinclair, but failed to garner enough support to progress to production. The original design concept was recently rekindled, and a laboratory version of the crusher has been built and commissioned at the University of the Witwatersrand. The crusher is simple in design, with two cylindrical discs that are parallel to each other, and, as the name implies, there is an offset between the vertical axes of the discs. The top disc has a conical section on its lower face, and this creates a crushing zone between the opposite faces of the two spinning discs. Centrifugal motion transports particles through the crushing zone. Batch experiments have been conducted with quartz at various crusher settings (discs offset, rotational speed, and vertical exit gap) for various feed size distributions. The indications so far suggest that the disc speed is a key factor affecting the performance. Size reduction ratios as high as 11 were recorded from experiments with quartz at a speed of 830 r/min. Keywords: rotary offset crusher, comminution, throughput.
The cyanidation process for refractory gold ores has been the subject of numerous investigations aimed at improving gold recovery and leaching kinetics. From recent literature investigations, hydrodynamic cavitation has been found to be a promising new approach which may modify the cyanidation processes. In this study, this approach results in the enhancement of mass transfer kinetics in multiphase fluid streams due to impacting two pulps streams against one another in a vessel called the Jetleach reactor. In this work, the Jetleach reactor was applied to a flotation concentrate from a South African gold tailings processing plant (Ergo) where an improvement of almost 10% in gold recovery was obtained while decreasing cyanide and oxygen consumption by almost 8% and 50%, respectively. The main reason for the improvement is surmised to be due to the generation of micro-cavitation which improves the mass transfer of oxygen and cyanide within the slurry.
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