Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> http://www.scielo.org.za/rss.php?pid=0038-223X20160001&lang=en vol. 116 num. 1 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Furnace Tapping 2014</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100001&lng=en&nrm=iso&tlng=en <![CDATA[<b>Mining Heritage</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100002&lng=en&nrm=iso&tlng=en <![CDATA[<b>Correspondence between J. Freer and R.E. Robinson</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100003&lng=en&nrm=iso&tlng=en <![CDATA[<b>A tribute to Prof. Robinson from his daughter</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100004&lng=en&nrm=iso&tlng=en <![CDATA[<b>Erratum</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100005&lng=en&nrm=iso&tlng=en <![CDATA[<b>Tap-hole monitoring technologies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100006&lng=en&nrm=iso&tlng=en This paper provides a progress update on three tap-block monitoring technologies that Hatch has been developing with our clients for non-ferrous smelting furnaces. The Tapblock Diagnostic System (TDS) is an advanced on-line monitoring system that uses temperature data along with embedded thermal model results to evaluate the condition of a tap-block over its campaign life. Hatch recently installed a second TDS and this paper provides some details on this second installation. The Taphole Acoustic Monitoring (TAM) system is installed on water-cooled copper tap-blocks and uses the noise from the tapping channel to provide a qualitative indication of wear and deterioration of the tapping channel refractory. In addition, TAM can be used to monitor drilling and lancing performance and potentially could also be used in the future as a guide for automatic drilling and lancing systems. The third technology is the use of fibre optic sensors to measure temperature on the hot face and in the tapping channel of a tap-block. Fibre optic technology allows installation of numerous sensors in key locations where they are very sensitive to tap-block condition, and also provide more extensive spatial coverage than is possible with traditional instruments. This paper provides an update on our efforts to address issues with premature failure of the sensor cables due to corrosion, and also to turn the vast amount of data from the sensor cable into information that can be used by furnace operators. <![CDATA[<b>Tapping of PGM-Ni mattes: An industry survey</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100007&lng=en&nrm=iso&tlng=en Matte tapping is one of the most critical operations of a matte smelter. Every smelter has developed particular matte tapping practices and tap-hole repair strategies that are often based on the experience of the smelter personnel. As a result, very little information has been published on these critical topics. This paper aims at providing the information gathered from a survey conducted in the PGM and Ni matte industries on matte tapping practices and tap-hole maintenance strategies for different PGM-Ni matte smelting operations. <![CDATA[<b>Monitoring, repair, and safety practices for electric furnace matte tapping</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100008&lng=en&nrm=iso&tlng=en The smelter at Sudbury Integrated Nickel Operations, located in Sudbury, Ontario, operates a single AC electric furnace. This furnace treats nickel sulphide concentrates produced by Glencore and third-party feeds, and as such its performance is critical to the company's nickel supply chain. Currently the plant has two shutdowns per year in order to carry out significant repairs on the matte tap-holes. Improved monitoring systems that enable better prediction of tap-hole wear have been a continued focus. The electric furnace is an essential part of the smelter flow sheet, requiring planned tap-hole maintenance together with robust systems to manage to this plan. The ability to meet our goal of zero harm depends on ensuring that safe practices are in place. Detailed procedures and cool-down practices have been implemented to ensure that the required matte chemistry and temperature criteria are met prior to a shutdown for tap-block maintenance. A major repair of the furnace will take place in 2015. During this rebuild, the sidewalls and matte endwall will be replaced. There is work underway to improve wall and matte end performance in an attempt to extend the time between rebuilds. This paper reviews the approach taken. <![CDATA[<b>SlagFlo<sup>TM</sup>: Modulating the flow in the tap-hole</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100009&lng=en&nrm=iso&tlng=en Tenova Pyromet's SlagFloTM control valve is designed to throttle the flow of molten slag in order to control the tapping rate. In addition, the SlagFloTM valve has proved to be a reliable tool for remotely closing the slag tap-hole during normal operation, as well as emergency conditions. This piece of equipment makes use of a water-cooled copper element that is hydraulically operated and attached directly to the slag tap-hole. The equipment is compact, simple to maintain, and cost-effective to purchase and install. It can be retrofitted to most existing slag tap-holes with minimal modifications. During the development phase, finite element method (FEM) and computational fluid dynamics (CFD) software was extensively used to model predicted operating conditions and to optimize the design. By using CFD, it was possible to understand the flow patterns inside the copper element and to optimize these to improve overall performance. The SlagFloTM valve was installed and commissioned in 2011/2012 on a 12 MW furnace as part of a new mineral wool plant built in the USA. It has performed well since its installation, despite operating under conditions in excess of the original design criteria. During the first 6 months of operation it quickly became the preferred method of closing the furnace, although the design intent was for occasional use during emergency shut down conditions only. Since replacing the mudgun as the main method of closing the tap-hole, a few minor changes were made to the installation in order to cope with the increased heat load and much higher frequency of use. The SlagFloTM valve has also been installed in South Korea, on two mineral wool furnaces designed and supplied by Tenova Pyromet in 2015. Both furnaces are scheduled to be in full production by the second quarter of 2016. Tenova Pyromet is investigating modifications needed to suit other commodity furnaces with more aggressive slag chemistries. <![CDATA[<b>An overview of the design, operation, and maintenance practices relating to tap-hole management on a PGM smelting furnace</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100010&lng=en&nrm=iso&tlng=en Tenova Pyromet's SlagFloTM control valve is designed to throttle the flow of molten slag in order to control the tapping rate. In addition, the SlagFloTM valve has proved to be a reliable tool for remotely closing the slag tap-hole during normal operation, as well as emergency conditions. This piece of equipment makes use of a water-cooled copper element that is hydraulically operated and attached directly to the slag tap-hole. The equipment is compact, simple to maintain, and cost-effective to purchase and install. It can be retrofitted to most existing slag tap-holes with minimal modifications. During the development phase, finite element method (FEM) and computational fluid dynamics (CFD) software was extensively used to model predicted operating conditions and to optimize the design. By using CFD, it was possible to understand the flow patterns inside the copper element and to optimize these to improve overall performance. The SlagFloTM valve was installed and commissioned in 2011/2012 on a 12 MW furnace as part of a new mineral wool plant built in the USA. It has performed well since its installation, despite operating under conditions in excess of the original design criteria. During the first 6 months of operation it quickly became the preferred method of closing the furnace, although the design intent was for occasional use during emergency shut down conditions only. Since replacing the mudgun as the main method of closing the tap-hole, a few minor changes were made to the installation in order to cope with the increased heat load and much higher frequency of use. The SlagFloTM valve has also been installed in South Korea, on two mineral wool furnaces designed and supplied by Tenova Pyromet in 2015. Both furnaces are scheduled to be in full production by the second quarter of 2016. Tenova Pyromet is investigating modifications needed to suit other commodity furnaces with more aggressive slag chemistries. <![CDATA[<b>Response surface optimization of process parameters for the removal of F and Cl from zinc oxide fume by microwave sulphating roasting</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100011&lng=en&nrm=iso&tlng=en Microwave sulphating roasting was applied to zinc oxide fume from a fuming furnace for the removal of F and Cl. The effect of important parameters such as roasting temperature, holding time. and vapour flow were investigated and the process conditions were optimized using response surface methodology. The results showed that the effects of roasting temperature and holding time on the removal efficiency of F and Cl were most significant, and the effect of vapour flow is of much lower importance. The defluorination and dechlorination efficiency increased rapidly as the roasting temperature and holding time increased, while the vapour flow had little effect. The defluorination efficiency could reach 91.3% while the dechlorination efficiency could reach 89.5%, under the process conditions of roasting temperature 655°C, holding time 65.2 minutes, and vapour flow of 6.8 ml/min. The results showed that the removal of F and Cl from zinc oxide fume using a microwave direct roasting process is feasible and reliable. <![CDATA[<b>Application of finite element method and artificial neural networks to predict the rolling force in hot rolling of Mg alloy plates</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100012&lng=en&nrm=iso&tlng=en A computational model combining a finite element method (FEM) with an artificial neural network (ANN) was developed to predict the rolling force in the hot rolling of Mg alloy plates. FEM results were compared with experimental data to verify the accuracy of the finite element model. Numerous thermomechanical finite element simulations were carried out to obtain a database for training and validation of the network. The input variables were initial thickness, thickness reduction, initial temperature of the plate, friction coefficient in the contact area, and rolling speed. The optimal ANN model was obtained after repeated training and studying of the samples. The trained network gave satisfactory results when comparing the ANN predictions and FEM simulation results. A comprehensive validation of the prediction model is presented. The resulting ANN model was found to be suitable for online control and rolling schedule optimization in the hot rolling process of Mg alloy plate. <![CDATA[<b>Effects of rolling and cooling process on mechanical properties and microstructure of 600 MPa microalloyed dual-phase steel produced by compact strip production</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100013&lng=en&nrm=iso&tlng=en The effects of finishing temperature, cooling method, and coiling temperature on the mechanical properties and microstructure of DP600 dual-phase steel produced by compact strip production (CSP) were investigated. Optical microscopy, scanning electron microscopy, transmission electron microscopy, and tensile testing were used to study the microstructure and mechanical properties. The results show that the appropriate microstructure is acquired by decreasing the finishing temperature, accelerated cooling and stage-cooling method, and controlling the coiling temperature below the start temperature of martensite transformation of 352°C. The DP steel produced by CSP contains 81% ferrite and 19% martensite, and the yield strength, tensile strength, and elongation are 350 MPa, 680 MPa, and 29.5%, respectively. The fine polygonal ferrite grain, high density of dislocations, and martensitic laths among the ferrite grains contribute to the excellent microstructure and mechanical properties. <![CDATA[<b>An algorithm for determining kinetic parameters for the dissociation of complex solid fuels</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100014&lng=en&nrm=iso&tlng=en An established distributed activation energy model (DAEM)-based algorithm for the dissociation of complex fuels obeying linear kinetics was modified to determine the kinetic parameters of materials reacting in a CO2 gas stream by incorporating the random pore reaction model (RPM). The algorithm was adapted to the RPM and was able to derive the activation energy, E, the grouped pre-exponential factor, A, and the number of reactions occurring in the thermal conversion process. Furthermore, the mass fraction associated with each unique reaction was obtained. The ability to accurately determine multiple reactions and changes in the kinetic parameters during the reaction distinguishes the algorithm as a unique and robust method for determining kinetic parameters for the pyrolysis of complex fuels. The novelty in this research was the adaptation of the RPM and other reaction models to the DAEM algorithm, and hence to other conversion processes. The algorithm was tested on simulated conversion data and experimental data from thermogravimetic analysis of the dissociation of a South African coal char and a 50:50 (wt%) coal-biomass blend char under CO2 atmosphere. The specific mass fraction of the reactive material dissociating under a particular set of kinetic parameters was determined, and all sets of data were successfully modelled to high accuracy. <![CDATA[<b>New gas nitriding technique using the interior of the nitrided pressure vessel as the process chamber</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100015&lng=en&nrm=iso&tlng=en The need to nitride the interior of large machine housings, which are also pressure vessels, for use in a high-temperature gas reactor resulted in the development of a suitable new nitriding technique whereby the vessel interior is used as a process chamber while being heated in a conventional top-hat heat treatment furnace. However, this new concept introduced several mechanical design challenges, such as an extended-length fan shaft, a high-temperature bearing, and sealing flanges for operation under extremely high temperatures. A prototype nitriding plant was constructed and operated to verify the design. The different tunnels machined inside the forged vessel were nitrided evenly by measuring and balancing the gas flow through each tunnel. Test specimens placed at different positions in the housing were also nitrided during the process. The nitrided specimens were subjected to microhardness and layer thickness tests. Measured gas flow rates and other operational data confirmed the inverse proportionality between ammonia supply flow rate and measured crack ratio, as well as a crack ratio temperature dependence, typical of conventional gas nitriding processes. The design and operation of the nitriding plant were successful and a nitride layer thickness of 400 μηι and a hardness of approximately 1100 VHN were achieved. This proves that a large pressure vessel can be successfully nitrided using the vessel's interior as a process chamber <![CDATA[<b>Statistical analysis of coal mining safety in China with reference to the impact of technology</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100016&lng=en&nrm=iso&tlng=en This paper presents a statistical analysis of coal mining safety which shows a positive relationship between technological innovation and the state of safety in Chinese coal mines. Fatalities per million tons, labour productivity, and fatalities per 10 000 exposure hours are the indicators used to analyse the situation of Chinese coal mining safety during the years 2001-2010. A correlation analysis is provided using Statistics Package for Social Science (SPSS). The results show that during this period, there was a positive correlation between technological development, financial investment in safety, and coal mine safety in China. The Huainan Mining Group is taken as an example to illustrate the improvement in coal mine safety due to technological development. Finally, some suggestions are proposed to further improve safety in Chinese coal mines from the perspective of risk assessment, an interdisciplinary approach, and safety culture. <![CDATA[<b>Coal seam fracturing by a high-pressure waterjet technique to increase efficiency of coal mine gas drainage</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100017&lng=en&nrm=iso&tlng=en In an effort to eliminate the hazard posed by coal seam gas and increase the efficiency of coal seam gas drainage in an underground coal mine, a high-pressure waterjet fracturing technique has been developed, optimized experimentally and numerically, and trialled underground. Numerical and laboratory results indicate that the slotting capacity of the high-pressure waterjet fracturing system can be improved by optimizing the geometrical structure and parameters of the nozzle. The results from field investigation showed that the gas production rate can be more than doubled by using the high-pressure waterjet-assisted method before and during longwall extraction. <![CDATA[<b>Virgin rock temperature study of Venetia diamond mine</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100018&lng=en&nrm=iso&tlng=en Temperature surveys in 13 boreholes at Venetia diamond mine, Limpopo Province, South Africa, in 1994 (shortly after the mine opened) and in 2006 (during the feasibility phase of the Venetia underground project) have resulted in a comprehensive database of rock temperatures and geothermal gradients. The database permits clear identification of some factors that perturb rock temperatures, the most important being underground flow of water and recent climate change, and identification of depth intervals showing linear temperature trends that are useful for establishing geothermal gradients. The Venetia data demonstrates the value of such detailed virgin rock temperature studies for mine refrigeration purposes. The average ground surface temperature, estimated by upward extrapolation of the borehole data, is 25.9±0.5°C, and the geothermal gradient, estimated by averaging the gradients in linear sections of the boreholes, is 19.5±1.0 K/km. A plot of unperturbed borehole temperature versus depth below mine datum (696 m above mean sea level) yields a linear array with an intercept of 25.3°C and a slope of 20.1 K/km, which are compatible with the above averages. The average thermal conductivity of Limpopo Belt rocks of similar composition and metamorphic grade to the country rocks at Venetia is 3.01±0.55 W m-1 K-1. The geothermal heat flux calculated from this value and the measured geothermal gradients is 58±3 mW m-2. <![CDATA[<b>Solvent extraction and separation of hafnium from zirconium using Ionquest 801</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100019&lng=en&nrm=iso&tlng=en The solvent extraction (SX) characteristics of Ionquest 801 were investigated to determine if the selective extraction of hafnium (Hf) over zirconium (Zr) is possible. Firstly, Ionquest 801 was screened for its suitability as a function of acid concentration. The solvent consisted of 5wt % extractant, corresponding to a extractant to metal ratio (E:M Zr) of 14:1, in cyclohexane with 5% v/v 1-octanol added as modifier. Aqueous solutions of ZrCl4 with 3 wt% HfCl4 were prepared by dissolution of the salts in HNO3 to obtain 1.0 g/l Zr(Hf)Cl4(aq) feed solutions (aged 24 hours). Subsequently, the extractant concentration was varied at optimal acid molarities. The most favourable extraction percentages were attained at 0.7 M HNO3 and an E:M Zr ratio of 5:1. Artifices in the form of aqueous additives were used to maximize the Hf selectivity at these optimal conditions. These included the addition of 1.5 M NaCl, NaNO3, Na2SO4, and NaClO4.H2O, as well as tartaric, oxalic, mandelic, and citric acid with and without the addition of 6 wt% hydrogen peroxide (H2O2). Exploratory studies on the influence and usability of the most promising factors such as [SO-4²], [H2O2], and combinations thereof in a SX system were undertaken. <![CDATA[<b>Insights into the potential for reduced refractory wear in silicomanganese smelters</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2016000100020&lng=en&nrm=iso&tlng=en Excavation of an industrial-scale submerged arc furnace, utilized in the production of silicomanganese, identified two high-wear areas in the refractory lining: the tap-hole, built with cold rammed carbon paste and SiC bricks, and the hearth, built with cold rammed carbon paste. To obtain insight into the potential causes of wear, thermodynamic calculations were conducted on eight sets of data, obtained for seven furnaces on three plants based in South Africa. FACTsage software and associated databases - FACTPS, FToxid, and FSstel - as well as the Mn-Fe-Si-C database of Tang and Olsen (2006), were applied. Theoretical indications are that chemical reaction between carbon refractory and slag, as well as dissolution of carbon and SiC refractory in metal, contributed to tap-hole refractory wear; and dissolution of carbon in metal contributed to hearth refractory wear.