Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> vol. 108 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Soil quality as a key success factors in sustainable rehabilitation of kimberlite mine waste</b>]]> 'Soil quality is the capacity of a soil to function, within ecosystem and land use boundaries, to sustain biological productivity, maintain environmental quality, and promote plant, animal and human health'. In the long-term, vegetative rehabilitation of mining wastes aims at, as far as possible, the proper ecological integration of the reclaimed area into the surrounding landscape, which is sustainable and requires minimal maintenance. A certain succession pattern is therefore needed. Recent ecological concepts recognize the role of the substrate's quality and nutrients in affecting the rates and directions of succession patterns. Although pedogenesis and eventually soil quality in mine waste are not well known, monitoring of soil quality parameters in kimberlite mine tailings reveal a remarkable establishment and or improvement of specific soil quality indicators. During the same time the vegetative cover's total functionality as well as reproductive ability improved. Functions of soil, and thus soil quality, can be assessed at the field, farm, ecosystem, pedosphere, and global scale. It is recognized, however, that management of soil becomes increasingly difficult at larger scales, but for demarcated mine waste sites it is possible to ameliorate and manage and assess soil functions and quality. Therefore the significance of the study is the following: soil functions and quality become inseparable from the idea of system sustainability, and are considered as key indicators of ecosystem sustainability on rehabilitated mine tailings material. <![CDATA[<b>Computer simulation of air and methane flow following an outburst in transport gallery D-6, bed 409/4</b>]]> This article outlines the results of a computer simulation reproducing the transport of a mixture of air and methane following the outburst on 25 November, 2005 in transport gallery D-6, bed 409/4, at the 'Zofiówka' hard coal mine. Based on a mathematical model, numerical method and boundary conditions from the disturbance caused by the outburst, the Ventgraph system of computer simulation programs was adopted for the study. We performed a computer simulation of the influence exerted by the outburst on the propagation of the air and methane mixture, and compared the results of this simulation with those of the actual event as registered by sensors of the mine monitoring system. A validation of the model allowed us to present temporal changes in the concentration of methane and air along flow routes. <![CDATA[<b>A simple process control model for spiral concentrators</b>]]> Spiral concentration forms a crucial part of gravity separation circuits. The application of process models in the operation of gravity separation circuits offers significant benefits in recoveries and grade control. Significant strides in the modelling of spiral concentrators have been made during the last couple of decades. Despite these advances in modelling techniques and models, application in industrial processes is not fully optimized. The adjustment of splitter positions to accommodate changes in the feed parameters is impractical and difficult, resulting in losses. In this work an optical method is employed to detect the concentrate band position as a function of operating variables. As expected, the results indicate a strong influence of the solids content and total heavy mineral (THM) feed grade on the predicted gangue-mineral interface. Viscosity modifiers indicated the band position to be sensitive to viscosity and therefore the slimes content. Validation on an industrial sample indicated the possibility of using this model in feed-forward control application. <![CDATA[<b>Prevention of chemical contamination of groundwater by mine water</b>]]> In this paper, which is aimed to serve as a review article, first of all a breakdown of the earth's total water reserves is given. The usage areas of water in the mining industry are mentioned and these uses are briefly outlined, together with the main pollution potential of each. According to this, most of the water (almost 80% of it) is utilized in processing. Later on, probable damages that the mining would give to groundwater as a result of acid mine drainage, heavy metal pollution, euthrophication and deoxygenation is described. Finally, the measures and controls that should be taken against water contamination in mines are presented. <![CDATA[<b>Can we decrease the ecological footprint of base metal production by recycling?</b>]]> Sustainability and the environment are important and topical themes currently. There is a generally growing awareness of resource consumption, possible resource depletion, and the polluting effects of indiscriminate dumping at the end of the useful life of an item, as well as of the pollution caused by producing items and making them available to the end user. The issues are complex and interlinked. In order to improve understanding, it is important to obtain holistic and quantitative perspectives. To help in quantification, concepts such as the ecological and carbon footprints have been defined and are in common use. This paper introduces the concept of a material footprint to help quantify the material resource usage in an item, in terms of globally available resources. It allows comparison of various items to one another in terms of their use of material resources. Thus the types of items available for recycling can be ranked to determine recycling priorities. The material footprint can also help in determining recycling priorities for the various materials in the items. Several examples are used as illustration. It is shown that recycling of printed circuit boards is especially worthwhile. Printed circuit boards are complex and heterogeneous from a materials recycling perspective. The paper describes the complexities of recycling these boards, but also points out the benefits. An overview is given of currently available metallurgical technologies for such recycling. It is shown that in these processes there are many factors that affect the environment. It thus remains difficult to determine the total impact of recycling on the environment holistically. Possibly some benefits are to be gained in the Southern African context by better integration between secondary material processors and primary metal producers. <![CDATA[<b>Recovery of unburned carbon by conventional flotation of bottom ashes from Tuncbilek Thermal Power Plant</b>]]> This research study includes studies carried out on the recovery of unburned carbon in the ashes of Tuncbilek Thermal Power Plant. Bottom ashes have been identified by X-ray diffraction and X-ray fluorescence. These samples are potentially of class F type and have significant amounts of unburned coal. According to the ash amount that units in the thermal power plant produce, and the analyses of the samples mixed, which used certain amounts in flotation tests, it was found that the bottom ash includes 91.47% ash in dry form and 8.53% combustible matter, and the lower calorific value is 491 kcal/kg. Optimum flotation conditions to get the unburned carbon were subsequently determined by examination of the optimum flotation grain size, pulp density, collector type and amount, depressant type and amount, frother type and amount, agitation speed, and froth-taking time. While the lower calorific value of the thermal power plant bottom ashes of the 3rd , 4th and 5th units and the mixed bottom ash sample was, respectively, 959, 469, 279 and 491 kcal/kg in dry form, it increased to 2490, 1312, 786 and 1348 kcal/kg in the product obtained as a result of flotation in optimum conditions. <![CDATA[<b>Computational fluid dynamic modelling of a waste-heat boiler associated with flash smelting of base metal sulphides</b>]]> The waste-heat boiler is used within the Sulphide flash smelting process as the main dust and energy recovery unit. The large volume of off-gas discharged from the flash smelter is at a very high temperature (1350°C) and contains a significant dust load that subjects the downstream waste-heat boiler to tough and demanding conditions. The boiler cavity is especially prone to dust accretions, fouling, and corrosion caused by accumulation of molten particles and precipitation of sulphuric acid. Computational fluid dynamics (CFD) is applied within a qualitative study to model the flow and heat transfer distribution throughout the waste-heat boiler. The commercial CFD package, Fluent 6.2.16, was applied to a modified waste-heat boiler (23 m × 11 m × 5.4 m) within the Outokumpu flash smelting process. This investigation focuses on the geometric modifications to the typical boiler design, which includes elevation of the ceiling, placement of flow-obstructing baffles and radiation plates parallel within the flow path. Also investigated were various boiler operating conditions such as the circulation of process off-gas, air leakage from the dust discharging hoppers and variation in inlet gas composition. The geometric modifications had the desired effect of increasing the volumetric utilization and therefore enhancing heat transfer between the boiler surface and the gas stream and dust segregation. Introducing circulated off-gas at a rate of 20 m/s and at a 45° angle to the front of the waste boiler further enhanced cooling while reducing the high impact of the furnace-uptake gas-stream on the boiler ceiling. The placement of radiation plates was found to be very effective in enhancing the heat transfer surface and distributing gas flow within the boiler. These results present recommendations towards an improved waste-heat boiler design.