Pretoria, South Africa
Pretoria, South Africa

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Moodley S.,Exxaro Resources | Bessinger D.,Exxaro Resources | Kucukkaragoz C.,University of Witwatersrand | Eric R.H.,University of Witwatersrand
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2012

In the chloride process for TiO2 pigment production, various titania feedstocks (i.e. rutile, synthetic rutile, slag, and upgraded titania slag (UGS)) are chlorinated in a fluidized bed reactor with petroleum coke at temperatures between 1000°C and 1100°C to yield gaseous metal chlorides. Although feedstock preference is largely based on TiO2 content, feedstock physical properties (i.e. density, sphericity, size distribution, and porosity) differ; these differences will affect fluidization behaviour and can inadvertently affect conversion efficiency. For example, a high carryover from the reactor reduces particle residence time and decreases conversion rates. Owing to dwindling rutile reserves in the world, most chloride producers are forced to feed blends of feedstocks to their chlorinators; and so it becomes important to understand whether blends have an effect on the hydrodynamic properties of the bed. This paper describes the physical characterization of different feeds and the determination of the elutriation constants for slag, rutile, synthetic rutile, and a blend (i.e. 50 wt% rutile, 50 wt% slag). A common feature of the tests was that particles finer than 75 μm tended more than any other size to be elutriated. The tested rutile, classified as a Geldart Group B material, had the lowest carryover, whereas the slags had the highest. Interestingly, the elutriation constant (ki *) of the blend is lower than those of either of its individual components. © The Southern African Institute of Mining and Metallurgy, 2012.

Meyer E.J.,Exxaro Resources | Craig I.K.,University of Pretoria
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2010

Often the most difficult step in establishing a control system is the development of a suitable dynamic process model. As such a model is not available elsewhere, a first principle dynamic mathematical model was developed for a coal dense medium separation circuit. Each unit operation was modelled individually and then integrated together to form a complete nonlinear state space model for the circuit. This model was used to simulate the process and it was validated using real process data derived from a plant experiment. © 2010 IFAC.

Maharajh S.,Exxaro Resources | Muller J.,Exxaro Resources | Zietsman J.H.,University of Pretoria
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2015

In the chlorination process for TiO2 pigment production, blends of titania feedstocks such as ilmenite, synthetic rutile (SR), natural rutile, upgraded slag, and chloride-grade slag are reacted with coke and chlorine at a temperature of around 1000°C to form TiCl4 (the main product) and other waste metal chlorides. The TiCl4 is the main feed material for the TiO2 pigment-making process. Feeding different titania materials to the chlorinator affects the amount of coke and chlorine required for the process, the amount of waste generated, waste disposal costs, the amount of TiCl4 produced, and bed build-up rates. These factors influence the value of the feedstock. Generally, a higher TiO2 feedstock is more valued since less waste is generated and less reagents are consumed. To quantify the impact of different feedstocks on the chlorinator, a techno-economic model was developed to describe the chlorination process and estimate process variables at steady state. This paper describes the development of the model and studies in which the model has been used to quantify effects of using different feedstocks. © The Southern African Institute of Mining and Metallurgy, 2015.

Meyer E.J.,Exxaro Resources | Craig I.K.,University of Pretoria | Alvarado V.,Exxaro Resources
IFAC-PapersOnLine | Year: 2015

This paper describes the application of an unscented Kalman filter to a coal run-of-mine bin. A dynamic model of the bin is derived using the principle of mass conservation. The dynamic model is nonlinear with unknown parameters that are identified using actual plant production data. The identified dynamic model is used by an unscented Kalman filter to update the states of the system to improve model output accuracy. The derived bin model with and without an unscented Kalman filter is compared with actual plant data. Results show that the unscented Kalman filter can significantly improve the plant outputs estimated by the bin model on its own. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

Brink G.,Exxaro Resources | Heymann G.,University of Pretoria
Journal of the South African Institution of Civil Engineering | Year: 2014

The behaviour of collapsible soil is often quantified by conducting a Collapse Potential Test or double oedometer test. However, these tests interpret the soil behaviour in terms of total stress, while it is well known that the behaviour of soil is governed by its effective stress. This article shows the results of a test conducted on undisturbed residual granite to study the collapse of the soil in terms of effective stress. The test was conducted in a modified oedometer which allowed the incremental addition of water to the sample during the test. The matric suction was quantified as a function of the moisture content of the soil during the test. The results indicate that the reduction in effective stress plays an important role during soil collapse. In addition it was found that much of the collapse settlement may be due to creep which occurs after the reduction in effective stress. © 2014, South African Institute of Civil Engineers. All rights reserved.

Fowler M.,Exxaro Resources | Morkel J.,University of Pretoria
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2010

A high volume of slimes which are separated out during the mining of heavy mineral sands has a high environmental impact and results in great capital as well as operational expenses. The presence of clay minerals drastically increases the slimes volume that needs to be catered for due to its low settling capability as well as swelling characteristics. By adding coagulants in the form of cations and organics, one can improve the settling rate of the minerals as well as the degree of solid bed compaction. The addition of flocculant, which is currently used in industry to improve settling rate, is detrimental to solid bed compaction. By combining the cations and flocculant one can dramatically improve the solid bed compaction. This combination is, however, detrimental to the settling rate of kaolinite-rich slimes but improves the settling rate of smectite-rich slimes. Organics can also be used to produce a clear supernatant and improve the settling rate. © The Southern African Institute of Mining and Metallurgy, 2010.

Meyer E.J.,Exxaro Resources | Craig I.K.,University of Pretoria
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2011

A partition curve is used in dense medium separation to determine the efficiency of the separation of clean coal from discard. The method used to determine a partition curve in coal beneficiation is float and sink analysis. The float and sink dry masses are determined at each density fraction only after complete separation of the material has taken place. This means that the partition curve is a form of a steady-state model. A dynamic model for a dense medium separation circuit is available from first principles. This paper shows how a steady-state model is derived from the dynamic model to generate a partition curve. This partition curve is compared with plant measurements taken from a plant operation. © 2011 IFAC.

Steenkamp J.D.,Mintek | Pistorius P.C.,Carnegie Mellon University | Muller J.,EXXARO Resources
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2016

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. © The Southern African Institute of Mining and Metallurgy, 2016.

Jordan P.,Exxaro Resources
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2011

The practice of ilmenite smelting in electric arc furnaces has been researched and published over the last few decades. An issue that has not been addressed is the understanding of the properties of ilmenite smelting reductants, and linking these properties to the subsequent smelting behaviour in the furnace. The reduction mechanism of ilmenite smelting is not fully understood, but it is believed that the Boudouard reaction plays a role. This paper investigates the behaviour of a number of reductants when reacted with CO2 at different temperatures. © The Southern African Institute of Mining and Metallurgy, 2011.

Grobler J.D.,Exxaro Resources | Bosman J.B.,PESCO
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2011

In a gravity separation device, particle shape, size and density all play a role. The combination of these determines where each individual particle reports to in the viscous fluid, where particle crowding (solids to water ratio) also plays a role. To understand the performance of gravity separation devices in the heavy mineral industry, these particle characteristics need to be measured. There are various challenges in analysing particle density and particle size simultaneously for the purpose of quantifying gravity separator performance, not to mention particle shape. These analytical challenges include the high cost of high-density sink-float fractionation, toxicity of high-density sink-float media, inability of sink-float media to fractionate at densities greater than 4.0 g/cm3, and the time-intensive nature of these fractionations. The use of the detailed particle-by-particle output from Qemscan® particle mineral analyses (PMA) as a fast and cost-effective alternative is evaluated. The size and density outputs from the Qemscan® were employed to characterize the performance of a heavy mineral spiral concentrator as an example. Critical analytical requirements are to be addressed before the Qemscan® output data can be utilized. © The Southern African Institute of Mining and Metallurgy, 2011.

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