Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> http://www.scielo.org.za/rss.php?pid=0038-223X20100004&lang=pt vol. 110 num. 4 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Educating entrepreneurs</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400001&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>Blast optimization at Kriel Colliery</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400002&lng=pt&nrm=iso&tlng=pt Kriel Colliery has experienced some sub-standard blast results on the overburden. Blast results are considered poor when the fragmentation is too big, back break into the new highwall, capping is experienced and/or excess overburden material is thrown into the void. Poor blasting leads to lower productivity, equipment breakdowns, and poor drilling and blasting results on the adjacent blast, contamination of coal or loss of coal. A simulation was developed in Microsoft Excel to model blasting results while changing various parameters. From the simulation results, it could be seen that a change of blast design could be beneficial. As an example, smaller drilling patterns were simulated (10 m x 10 m to 8 m x 8 m, and 8 m x 8 m to 7 m x 7 m in Pit 5 and Pit 6 respectively) in combination with changes in explosives (P700 emulsion vs. ANFO) and drill bit diameter (311mm vs. 251mm). The results show that each of the options has a specific scenario that will be most beneficial to the mine. These results are quite specific and subject to variable inputs. The purpose of the example is to demonstrate how the simulation can be used as a tool to asses blast design variations <![CDATA[<b>Optimizing yield of metallic zinc tapped from a zinc smelter by studying factors causing zinc losses to dross</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400003&lng=pt&nrm=iso&tlng=pt Zincor experienced significant losses of metallic zinc to dross during the melting of zinc cathode plates. In this study five factors affecting the formation of dross are identified from literature. Dross from both the plant and that produced in the laboratory is characterized using XRD. An empirical model, based on laboratory-scale investigations, was developed to quantify the effect these factors on their own or in combination with each other has on the amount of zinc loss to dross. The predictive capability of the model is evaluated based on the laboratory-scale investigations. Predictions are made on the effects that heat treating the cathode plates prior to melting, increasing the cathode plate thickness, washing and drying prior to melting, and loading the furnace in a controlled manner have on the amount of zinc loss to dross. <![CDATA[<b>A novel approach to reagent selection for coal flotation</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400004&lng=pt&nrm=iso&tlng=pt Zincor experienced significant losses of metallic zinc to dross during the melting of zinc cathode plates. In this study five factors affecting the formation of dross are identified from literature. Dross from both the plant and that produced in the laboratory is characterized using XRD. An empirical model, based on laboratory-scale investigations, was developed to quantify the effect these factors on their own or in combination with each other has on the amount of zinc loss to dross. The predictive capability of the model is evaluated based on the laboratory-scale investigations. Predictions are made on the effects that heat treating the cathode plates prior to melting, increasing the cathode plate thickness, washing and drying prior to melting, and loading the furnace in a controlled manner have on the amount of zinc loss to dross. <![CDATA[<b>Improving the quality of tinplated steel using a novel technique to study the effect of industrial process parameters</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400005&lng=pt&nrm=iso&tlng=pt Tin plating operations are of a complex nature due to the many operational variables that need to be controlled in order to create a product of required quality. The work in this report lays the basics for the control of a halogen plating operation based on the DuPont tinplating set-up with regard to the chemical make-up of the plating solution, as well as operational variables such as temperature and current density. To evaluate these aspects of the process, a rotating cathode Hull-cell set-up was used. This allowed for a laboratory scale plating arrangement that simulates industry closely with regard to chemical and hydro-dynamic considerations. Typical industry accepted standards were obtained for the values of operational variables and a 'baseline' test was conducted employing these standards. All subsequent tests conducted were benchmarked against this baseline result. A large suite of results was obtained in which it was found that changes could be made to the industry accepted norm which would improve on the stability of the operation and therefore the quality of the final tin-plated product. Examples of these results are: an increase in stannous tin concentration, an increase in sodium chloride concentration and a slightly elevated plating temperature. In addition, conditions were found that must be avoided to prevent instability and poor product quality <![CDATA[<b>Acid leaching of heavy metals from bentonite clay, used in the cleaning of acid mine drainage</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400006&lng=pt&nrm=iso&tlng=pt Heavy metals and sulphates in acid mine drainage (AMD) can be adsorbed onto bentonite clay, leaving clean water and a heavy metal loaded clay precipitate as products. Due to the toxicity of heavy metals, the clay could not be disposed of safely in the past. A method was thus required to remove the heavy metal content from the clay. Acid leaching was proposed to liberate the heavy metals from the loaded clay. Sulphuric, nitric and hydrochloric acid were considered as lixiviants. Loaded clay samples were leached over a range of pH values from 1 to 3.5 to identify an optimum leaching condition. From the results it was found that metals can be recovered from loaded bentonite clay by means of acid leaching and the optimum pH for heavy metal liberation was found to be 2.5, with uranium as an exception, being optimally leached at a pH of 3. This allows for the possibility of selective leaching. Furthermore, X-ray diffraction analyses indicated that the clay structure did not deteriorate significantly during acid leaching, suggesting that the bentonite could be reused. The treatment of AMD with bentonite clay, and subsequent acid leaching of the clay, is a sustainable solution, and current outcomes could possibly lead to industrial implementation of the process during water purifying and metal recovery from waste streams. <![CDATA[<b>Coal clearance system at Zondagsfontein Colliery</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2010000400007&lng=pt&nrm=iso&tlng=pt The purpose of the project was to propose a coal clearance system (coal transportation system from the mining face to the plant) that could be used for the planned underground operations at Zondagsfontein Colliery. Components of the current coal clearance system were overlooked during feasibility studies. Subsequent studies of the coal clearance system revealed that the combined capacity of the two trunk belts does not match that of the shaft (main) belt. As a result production downtimes will be encountered due to bottlenecks in the system. Ways of addressing this challenge were analysed by weighing both advantages and disadvantages and ultimately a surge bin option was selected. Belt conveyor simulations were conducted in order to determine the optimum capacity of the surge bin. The configuration of the surge bin in relation to the two trunk belts was chosen by considering development cost, advantages, and disadvantages of each option. It was concluded and recommended that a 500 tonnes capacity surge bin is required to remove the bottleneck from the system.