Papers by Jacobus Eksteen
International Journal of Mineral Processing, 2008
The influence of microwave radiation on the liberation of the valuable minerals in a massive sulf... more The influence of microwave radiation on the liberation of the valuable minerals in a massive sulfide ore is presented. In general, sphalerite shows the highest degree of liberation with a maximum value of 84%. Sphalerite is followed by galena with 73% liberation and chalcopyrite with 63% liberation. Afine feed size and a high microwave power are the two common requirements for the liberation of the valuable metalbearing minerals in the are. Some of the valuable base-metal minerals show slightly different degrees of sensitivity to microwave irradiation. Therefore, process efficiency and economics should be considered in deciding the applicable level of heating. Chalcopyrite and galena, which are readily affected by microwave radiation, show a tendency to generate high amounts of locked particles, due presumably to randomfracture, partial (non-uniform) particle transformation and irregular particle shape.
Biofilm formation on the surface of monazite and xenotime during bioleaching
Microbial biotechnology, Jun 8, 2023
Microbial attachment and biofilm formation is a ubiquitous behaviour of microorganisms and is the... more Microbial attachment and biofilm formation is a ubiquitous behaviour of microorganisms and is the most crucial prerequisite of contact bioleaching. Monazite and xenotime are two commercially exploitable minerals containing rare earth elements (REEs). Bioleaching using phosphate solubilizing microorganisms is a green biotechnological approach for the extraction of REEs. In this study, microbial attachment and biofilm formation of Klebsiella aerogenes ATCC 13048 on the surface of these minerals were investigated using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). In a batch culture system, K. aerogenes was able to attach and form biofilms on the surface of three phosphate minerals. The microscopy records showed three distinctive stages of biofilm development for K. aerogenes commencing with initial attachment to the surface occurring in the first minutes of microbial inoculation. This was followed by colonization of the surface and formation of a mature biofilm as the second distinguishable stage, with progression to dispersion as the final stage. The biofilm had a thin‐layer structure. The colonization and biofilm formation were localized toward physical surface imperfections such as cracks, pits, grooves and dents. In comparison to monazite and xenotime crystals, a higher proportion of the surface of the high‐grade monazite ore was covered by biofilm which could be due to its higher surface roughness. No selective attachment or colonization toward specific mineralogy or chemical composition of the minerals was detected. Finally, in contrast to abiotic leaching of control samples, microbial activity resulted in extensive microbial erosion on the high‐grade monazite ore.
Separation and Purification Technology, Mar 1, 2019
Cyanide-starved alkaline glycine solutions have been shown to have distinct advantages in terms o... more Cyanide-starved alkaline glycine solutions have been shown to have distinct advantages in terms of lower reagent consumption and detoxification needs, or leach rate and recovery, over cyanide-only and glycine-only leach systems respectively for gold ores with nuisance copper. Activated carbon has been shown to be suitable for gold adsorption from alkaline glycine systems, and is well established for cyanide based systems. Activated carbon being an effective substrate for the adsorption of gold thus offers a possible downstream carbon-in-pulp (CIP) recovery route for alkaline glycine leach systems and hybrid systems in the presence of cyanide. Given the frequent occurrence of gold deposits with high levels of nuisance copper, the equilibrium loading of gold and copper onto activated carbon from cyanide-starved alkaline glycine solutions containing copper and gold has been studied. Adsorption efficiency was studied in terms of equilibrium loading isotherms. Results showed that while copper adsorption is more sporadic based on goodness of fit, gold adsorption is more consistent and clearly follows the Freundlich isotherm model (good linear correlation of log Q vs log C values). The adsorption isotherms were obtained using a gold concentration of 2 ppm. In the presence of copper, the equilibrium gold loading increases with increasing glycine and calcium ion concentrations, decreases with increasing cyanide concentration and is not affected by initial gold concentration. The cuprous cyanide and cupric glycinate complexes lowered gold loading through a competitive adsorption with the copper (I) cyanide complexes adsorbing more rapidly on the carbon than their glycinate counterparts. The equilibrium gold loading capacity in cyanide-starved glycine solutions containing 2 ppm Au and 300 ppm Cu, at pH 11 was found to be 9.95 kg Au / ton carbon in 24 h, which is almost four times higher than the gold loading capacity in a pure cyanide system (2.7 kg Au /ton carbon) under similar conditions. The study revealed that activated carbon was an effective adsorbent for removal gold from cyanide-glycine aqueous solutions.
Analysis of natural licks at Loskop Dam and Suikerbosrand Nature Reserves
South African Journal of Wildlife Research, 1990
Natural licks at Loskop Dam and Suikerbosrand Nature Reserves were analysed to determine why thes... more Natural licks at Loskop Dam and Suikerbosrand Nature Reserves were analysed to determine why these soils were selected by wildlife (ungulates). Samples were taken of the lick sites, and soils surrounding these sites, for comparison. All samples were analysed for percentage clay, pH, P, Na, K, Ca, Mg, carbonates, chlorides, and electrical resistance. All the licks had significantly higher Na values than the surrounding soils, and also higher pH values and salt content, but low P values. The alkaline licks have higher Ca and Mg values, and show higher clay content than surrounding soils. The importance of these natural licks to wildlife needs further research.
Microorganisms, May 18, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Separation and Purification Technology, Jul 1, 2019
Recently, a novel leach process for treating gold-copper ores and concentrates by glycine in the ... more Recently, a novel leach process for treating gold-copper ores and concentrates by glycine in the presence of starved cyanide in solutions were investigated where the Cu species are present as cuprous cyanide and cupric glycinate. Often Cu-levels in these gold ores are insufficient to economically justify solvent extraction with electrowinning, and sulfide precipitation is often preferred. This research reports the precipitation behaviour of Cu and Au from glycine-cyanide solutions by adding NaHS. Contrary to conventional cyanide-only systems, where all the copper is present as cuprous cyanide and alkaline precipitation of copper by sulfide addition is not feasible, the synergistic lixiviant system leads to a cupric-dominant system where copper can be precipitated. As the leach solution mainly contains glycine(Gly), cyanide(CN −) and copper in alkaline environment, the effect of glycine concentration [Gly], [HS − ]: [Cu T ] and [CN − ]: [Cu T ] molar concentration ratios, pH, temperature and reaction time on the Cu and Au precipitation have been studied, where [Cu T ] = [Cu + ] + [Cu 2+ ]. The results show that CuS precipitation (covelite) increased slightly with moderately elevated temperature, but decreased significantly with increasing [CN − ]:[Cu T ] molar ratio. CuS precipitation was found to be insensitive to [HS − ]: [Cu T ] molar ratio, glycine concentrations, pH and reaction time. Pre-oxidation of cuprous Cu + to cupric Cu 2+ was carried out using H 2 O 2 to confirm the effect of oxidation state on copper precipitation. The kinetics of preoxidation was fast and above 95% of Cu + were oxidized to Cu 2+ in 5 min. The optimal [H 2 O 2 ]:[Cu + ] molar ratio was found to be 5:1 and 4:1 at [CN − ]:[Cu T ] molar ratio of 2:1 and 1:1 respectively, implying significant reagent consumption to complete the reaction. With pre-oxidation and oxygen removal by nitrogen gas stripping, a Cu recovery as high as 96.5% was achieved with the addition of 1.4 mol of sulfide per mole Cu T for 5 min at [Cu]:[CN − ]:[Gly] molar ratio of 1:2:3 and pH 10.5. No Au co-precipitation was observed after precipitation for most of tested conditions. This study showed that a high level of Cu and Au separation can be obtained by sulphide precipitation with H 2 O 2 pre-oxidation from CN-starved glycine solutions and allowing Au to be subsequently removed by activated carbon.
IFAC Proceedings Volumes, 2007
In this investigation the development of nonlinear control system for an autogenous mill was cons... more In this investigation the development of nonlinear control system for an autogenous mill was considered. A symbiotic adaptive neuroevolution algorithm was used in conjunction with a dynamic multilayer perceptron model fitted to actual plant data to evolve neurocontrol systems. Simulation studies established the potential of the approach, which yielded satisfactory results, despite having had to learn from a model that covered part of the state space only.
Minerals Engineering, Jun 1, 2011
The presence of chrome in electric arc furnaces smelting platinum group metals (PGM's) has a numb... more The presence of chrome in electric arc furnaces smelting platinum group metals (PGM's) has a number of potentially negative consequences. In cases where the slag chrome content is above the saturation limit the existence of near-stagnant conditions near the slag/matte interface increases the risk of chromite spinels settling and consolidating into a ''mushy layer'', a three-phase suspension of slag, chromite and matte. The holdup of matte above the elevation of the slag/matte interface can lead to the attack of freeze linings and copper cooling elements potentially causing failures of the furnace lining and significant downtimes as well as major safety risks. This paper investigates the relationship between typical furnace operating parameters and the behavior of the slag bath with respect to the formation of the ''mushy'' layer at the slag/matte interface using computational fluid dynamics (CFD). The extent of the potential ''mushy'' layer is seen to increase with decreasing electrode immersion and furnace power. Electrode immersion is, however, a considerably stronger driver is this regard. The CFD modelling results have aided in selecting appropriate furnace electrode immersion/power combinations intended to minimize ''mushy'' layer formation.
Systems modelling of furnaces using industrial data and fundamental submodels to predict the matte chanmistry dynamics in an ausmelt converter
Canadian Metallurgical Quarterly, May 15, 2019
The purpose of this study was to investigate the role of grinding media type, water chemistry and... more The purpose of this study was to investigate the role of grinding media type, water chemistry and pyrite mineralogy on the galvanic interaction between grinding media and pyrite during grinding of a gold ore. The galvanic current between pyrite and grinding media increased with the electrochemical activity of the grinding media, while it decreased as a function of increasing chromium content in the media. Furthermore, changing the pyrite-based electrode from pure pyrite to a gold-bearing pyrite electrode increased the galvanic current between the pyrite and the grinding media electrodes; therefore, the gold-bearing pyrite electrode is more active than the pure pyrite one. In addition, using process water instead of tap water increased the galvanic current density between pyrite and the high-chromium grinding media electrode (30% chromium). However, when the forged steel or the low-chromium grinding media electrodes were used, the galvanic current decreased compared to the tap water condition. In addition, the results obtained from SEM-EDX analysis showed that in both tap and process water conditions, oxide species were identified on the surface of the forged steel and low chromium electrodes. However, no oxygen was detected on the surface of the 30% chromium grinding media. RÉSUMÉ Le but de cette étude consistait à examiner le rôle du type de corps broyant, de la chimie de l'eau et de la minéralogie de la pyrite sur l'interaction galvanique entre le corps broyant et la pyrite lors du broyage humide d'un minerai d'or réfractaire. Tous ces facteurs affectent fortement le courant galvanique entre les minéraux et le corps broyant. Le courant galvanique entre la pyrite et le corps broyant augmentait avec l'activité électrochimique du corps broyant, alors qu'il diminuait en fonction de l'augmentation de la teneur en chrome du corps broyant. En outre, le changement de l'électrode à base de pyrite de pyrite pure à une électrode de pyrite porteuse d'or augmentait le courant galvanique entre la pyrite et les électrodes du corps broyant; par conséquent, l'électrode de pyrite porteuse d'or est plus active que celle de pyrite pure. De plus, l'utilisation de l'eau traitée au lieu de l'eau du robinet augmentait la densité de courant galvanique entre la pyrite et l'électrode de corps broyant à haute teneur en chrome (30% chrome). Cependant, lorsqu'on utilisait les électrodes de corps broyant en acier forgé ou à basse teneur en chrome, le courant galvanique diminuait par rapport à l'utilisation d'eau du robinet. De plus, les résultats obtenus avec l'analyse de SEM-EDX ont montré qu'avec l'eau du robinet comme avec l'eau traitée, les espèces d'oxydes étaient identifiées à la surface des électrodes en acier forgé et à basse teneur en chrome. Cependant, on n'a pas détecté d'oxygène à la surface du corps broyant à 30% en chrome.
Bioleaching of Mt.Weld monazite by phosphate solubilisation: Evidences of induced dissolution of rare earth elements
Journal of The South African Institute of Mining and Metallurgy, Apr 1, 2004
Paper written on project work carried out in partial fulfilment of Phd. (Process Engineering) deg... more Paper written on project work carried out in partial fulfilment of Phd. (Process Engineering) degree* Synopsis The recovery of cobalt and copper from waste slag was studied in a plasma DC-arc furnace in reducing conditions. Three fluxes, CaO, CaF 2 , and TiO 2 , were investigated for their influence on selective recovery of cobalt into an iron-rich alloy. A further investigation on the influence of furnace power on the reduction of slag to recover cobalt to the alloy showed that a change in power setting had an unexpected effect on the recovery of metals to the alloy, in that selectivity of base metal recovery over iron recovery decreased at an increased power level.
Kinetics of RH, RU, and IR dissolution during the sulphuric acid pressure leaching of first stage leach residue
IngenieursweseProsesingenieurswesePlease help us populate SUNScholar with the post print version ... more IngenieursweseProsesingenieurswesePlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: scholar@sun.ac.z
Mineral processing and extractive metallurgy, Sep 27, 2019
The dense media cyclone (DMC) has had wide application in beneficiation of coal, iron ore, diamon... more The dense media cyclone (DMC) has had wide application in beneficiation of coal, iron ore, diamonds and base metals, with limited applications in preconcentrating precious metals such as gold. This paper reports and discusses data from experimental evaluations of the DMC for preconcentrating gold ores. Two ore types were tested in the particle size range from 0.3 mm to 4.75 mm which was considered a pumpable size range. A DMC with a diameter of 100 mm was used to separate the gold ores at separation densities ranging from 2.55 g/cm³ to 2.95 g/cm³. Evaluation of the data confirms the potential of the DMC for gold ore preconcentration, with some ores being more amenable to gangue rejection than others. An optimum density of separation is required for a given type of ore in order to achieve balance between overall mass rejected and gold recovery.
IFAC Proceedings Volumes, Aug 1, 1995
In this study image features extracted from froth images by an on-line machine vision system in a... more In this study image features extracted from froth images by an on-line machine vision system in an industrial platinum flotation plant were used to relate froth characteristics and flotation performance by using neural networks. It has been shown that a considerable amount of data can be extracted from flotation surface froths and that both novel feedback control procedures and feedback control as a complement to conventional feedforward systems are made possible. Feature measures such as chromatic information, average bubble size, froth texture, froth stability and mobility of surface froths were used in the on-line classification of flotation froths. This intelligent vision system constitutes a powerful research tool for the investigation and interpretation of the effect of various flotation parameters. This paper shows how the rapid development in computer technology and neural networks can be used to transform recently developed concepts and available technology into a new generation of intelligent automation systems.
Minerals Engineering, Oct 1, 2013
A prior application of mineralogy to the analysis of nickel converter matte was based on two dime... more A prior application of mineralogy to the analysis of nickel converter matte was based on two dimensional in-plane projections of three dimensional phase structures. Recent developments in electron microscopy have established suitable techniques to base further analysis on actual three dimensional projections. Focused ion beam scanning electron microscopy tomography in arrangement with transmission electron microscopy was considered suitable in acquiring three dimensional projections of nickel converter matte phase structures at the mesoscale with subsequent reconstruction for 3D visualization and analysis. Transmission electron microscopic section analysis was particularly useful in signifying that phase structures were geometrically arranged within an underlying nickel-sulfide microtexture. Tomography reconstruction and rendering of a rectangular particle volume allowed for color and grayscale based 3D visualization of the nickel-sulfide microtexture, copper-sulfide and NiCu-alloy phase structures. Color based 3D visualization was specifically effective in assigning a cubic morphology to smaller alloy phase structures. Grayscale based 3D visualization of alloy phase structures illustrated compositional zones correlating to the presence of bright Pt-dominant cores and darker Ni-dominant rims. High-fidelity reconstruction of developed Pt-dominant lobes was produced illustrating insightful morphological detail. It would be important to consider the three dimensional insights gained to the downstream metallurgy of nickel converter matte.
Minerals Engineering, Aug 1, 2006
A methodology is presented and evaluated to model the metallurgical dynamics of DC plasma arc sme... more A methodology is presented and evaluated to model the metallurgical dynamics of DC plasma arc smelting, using high carbon ferrochrome production as a case study. The model type is called an Equilib-ARMAX model as it integrates fundamental thermodynamic models with dynamic models. The Equilib-ARMAX model takes into account the inherently uncertain nature of smelter plant data, as well as the process dynamics and the moving chemical equilibrium target. The model structure, modelling performance, and model limitations of this model type are presented. The model could predict the metallurgical dynamics well within the inherent uncertainty of the process data.
Minerals Engineering, Nov 1, 2013
In this study, the application of models to predict the steady state and dynamic behaviour of the... more In this study, the application of models to predict the steady state and dynamic behaviour of the pressure leaching stages at a Base Metal Refinery (BMR) is discussed. Part I of this communication provides background about the context of the study, and presents a complete overview of the process concerned and the model development strategy. The steady state model allows the prediction of the operating temperature and the slurry composition in the different autoclave compartments as a function of pressure, feed rates, and the flow rate of the flash recycle stream. The dynamic response of the temperature and stream compositions to changes in the above mentioned process variables can also be predicted. It has been illustrated how interdependencies between process variables can be determined and an improved understanding of the process can be developed by means of the process models. The importance of controlling the relative leaching rates of digenite and covellite to minimise precious metal leaching, for example, was illustrated by modelling the system behaviour at different operation conditions.
Hydrometallurgy, Sep 1, 2020
The synergistic leaching system using glycine as the main lixiviant with low levels of cyanide as... more The synergistic leaching system using glycine as the main lixiviant with low levels of cyanide as a catalyst has been shown to be an effective approach to leach gold-copper ores and concentrates, allowing the consumption of cyanide to be remarkably reduced. The recovery of gold from the synthetic cyanide-starved glycine leachate in the presence of copper has been investigated using. It was found that the adsorbed copper was mostly cuprous cyanide. The effects of [CN − ]:[Cu T ] and [Gly]: [Cu T ] molar ratios were not significant on the adsorption of gold and copper using IXOS-AuC resin. The gold recovery increased, while the copper recovery decreased with the increasing initial gold concentration. The equilibrium and kinetics studies were undertaken, and the experimental adsorption equilibrium and rate data showed an excellent fit using the Freundlich isotherm and pseudosecond-order models respectively. Elution tests showed that the loaded copper can be selectively pre-eluted over gold by 0.4 M NaCN at pH 11.5. Gold can be effectively eluted by either acidic thiourea or alkaline thiocyanate. The multi-cycle adsorption/elution tests showed that the resin can be effectively regenerated by both acidic thiourea and alkaline thiocyanate, with an insignificant decrease in adsorption and elution efficiency over 3 adsorption/elution cycles. From SEM analysis, the change of surface morphology of the resin was not significant after adsorption and the adsorption/elution cycles.
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Papers by Jacobus Eksteen