SUNScholar - Browsing by Author "Akdogan, G."

Browsing by Author "Akdogan, G."

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The application of activated carbon for the adsorption and elution of platinum group metals from dilute cyanide leach solutions
(Southern African Institute of Mining and Metallurgy, 2013) Snyders, C. A.; Mpinga, C. N.; Bradshaw, S. M.; Akdogan, G.; Eksteen, J. J.
ENGLISH ABSTRACT: The research presented in this paper investigated the practical aspects of the recovery of platinum group metals (PGMs) from a dilute cyanide leach solution containing base metals, in a manner similar to that used for gold extraction in a typical CIP process, and focuses on both the adsorption and elution stages. The carrierphase extraction of precious metals using activated carbon offers significant advantages over other processes in terms of simplicity, the high pre-concentration factor, rapid phase separation, and relatively low capital and operating costs. As a sorbent, activated carbon is still by far the most important material because of its large surface area, high adsorption capacity, porous structure, negligible environmental toxicity, low cost, and high purity standards. Adsorption tests were conducted on a pregnant alkaline leach solution (0.15 ppm Pt, 0.38 ppm Pd, 0.1 ppm Au) resulting from cyanide extraction performed in column leach tests. The initial adsorption rates of Pt, Pd, and Au were very fast and recoveries of these three metals were approximately 90 per cent after 2 hours, and 100 per cent for Pt, 97.4 per cent for Pd, and 99.9 per cent for Au after 72 hours. The parameters that influence the extraction of PGMs and Au were examined to assess their relative importance during the adsorption process in order to provide the basis for process optimization. The concentration of thiocyanate was not identified as significant factor for PGMs adsorption, while Ni concentration was the most significant extraction process parameter. Base metal cyanide complexes adsorb and compete with the PGM complexes for sites on activated carbon, and while copper adsorption can be minimized by adjusting the residence time, Ni adsorbs at approximately the same rate as the PGMs, influencing the loading capacity and adsorption kinetics of the PGMs. The feasibility of eluting platinum and palladium cyanide complexes from activated carbon using an analogue of the AARL process was investigated. Platinum and palladium elute from activated carbon almost to completion in 4 to 5 bed volumes at 80°C, while the elution of gold at this temperature is slow, with a significant amount of gold still to be eluted after 16 bed volumes. The equilibrium loading of gold is exothermic in nature (Fleming and Nicol, 1984) which will result in an increase in gold elution kinetics with an increase in temperature at similar pre-treatment conditions. A similar result was found for the elution of Pt and Pd. Cyanide pre-treatment was found to have a significant influence on PGM elution. Higher cyanide concentration in the pre-treatment step results in more efficient elution up to a point, and results suggest the possibility of an optimum cyanide concentration, beyond which elution efficiency starts decreasing due to increased ionic strength.
The development of experimental machines in order to understand the demands of incremental sheet forming of titanium
(Industrial Engineering, Stellenbosch University, 2011-09) Oosthuizen, G. A.; Nortje, H.; Herselman, E. J.; Akdogan, G.; Sacks, N.
Titanium sheet-metal is extensively used for aerospace and biomedical applications. The diversified customer's demands have created a recent trend towards the small batch production. In this context incremental forming has attained great attention. Therefore, experimental machines are designed and manufactured to simulate the harsh forming conditions. In the fretting machine the combination of a normal force and small vibrations may constitute a wear phenomenon known as fretting wear. The friction and wear properties of the tool, lubrication and work piece materials are tested using the sliding test machine. The steps to evaluate and develop these machines as research tools are illustrated and discussed. The fretting- and sliding machines help to investigate suitable forming tools, forming parameters and lubricant strategies for incremental forming of titanium. It is concluded that these simulation tools provide more efficient and cost effective ways to understand the effects of changing the forming conditions.
Expanding the semantic range to enable meaningful real-world application in chemical engineering
(HESA, 2019) Dorfling, C.; Wolff, K.; Akdogan, G.
ENGLISH ABSTRACT: Legitimation Code Theory has proven to be useful in analysing the relationship between theory and practice. Semantic gravity can be used to illustrate teaching and learning processes that move between different levels of abstraction and context-dependency. Effective engineering education entails moving both up and down the semantic range in a way that enables students to apply concepts to contextual practices. However, students seldom engage at the strongest level of semantic gravity. This study investigated the contextualisation of theory in a chemical engineering programme through industrial site visits. Final-year chemical engineering students participated in a voluntary field trip to visit industrial sites. Data obtained through written surveys showed that visits allowed participants to develop a better appreciation for the relevance of taught material to industrial applications and to better understand relationships between different modules and problem solving. Site visits were found to be an effective way of expanding the semantic range.
Gold CIP and CIL process optimization in a capital constraint environment
(The Southern African Institute of Mining and Metallurgy, 2017-05) Snyders, C. A.; Akdogan, G.; Bradshaw, S. M.; Van Wyk, A. P.
ENGLISH ABSTRACT: This article focuses on the use of a model in combination with economic analysis to extract maximum value out of current gold operations, without the need for additional capital. Two South African case studies (CIP and CIL) are presented to show that an optimum point of operation exists. This optimum point of operation, however, depends on several economic factors such as the gold price, exchange rate, and utility costs in combination with plant conditions such as the feed rate and Au grade. As these parameters fluctuate, the operating conditions will have to be adjusted to achieve the maximum value. Operating at a maximum will require regular decisionmaking and adjusting of operating conditions, especially in times of a constrained economy.
Investigating of eco- and energy-efficient lubrication strategies for the drilling of light metal alloys
(Southern African Institute for Industrial Engineerg, 2010) Treurnicht, N. F.; Joubert, H. J.; Oosthuizen, G. A.; Akdogan, G.
ENGLISH ABSTRACT: Energy use will be one of the main drivers for the achievement of more eco-efficient drilling processes in the automotive industry. Industry awareness of the environmental impact of used cutting emulsions, and the negative effect on worker health, has increased sharply. This has led to innovative lubrication methods such as through-spindle minimal quantity lubrication (MQL) for drilling aluminium-silicon alloys. In this work the performance of MQL at different cutting speeds and feed rates has been investigated using infrared temperature measurements. The results indicate that MQL is a feasible eco-efficient alternative to conventional flood cooling when drilling aluminium-silicon alloys.
Investigating the behaviour of PGEs during first-stage leaching of a Ni-Fe-Cu-S converter matte
(Southern African Institute of Mining and Metallurgy, 2018) Snyders, C. A.; Akdogan, G.; Thompson, G.; Bradshaw, S. M.; Van Wyk, A. P.
ENGLISH ABSTRACT: In a first-stage atmospheric leach in a Sherritt Ni-Cu matte leach process, a Ni-Cu-Fe-S Peirce-Smith converter matte is contacted with recycled aqueous copper sulphate/sulphuric acid solution (spent solution) with the purpose of dissolving nickel, while simultaneously removing copper (via metathesis and cementation reactions) from solution. While the iron content has been found to have a significant impact on the first-stage leach, a previously expected relationship between copper and PGM behaviour has not been established clearly. For this study, a converter matte consisting mainly of heazlewoodite (Ni3S2), chalcocite (Cu2S), and awaruite (Ni3Fe) was leached in a laboratory-scale batch reactor. The temperature, acid, and copper concentration under both oxidative and non-oxidative conditions were varied, while the copper, iron, and PGEs were tracked and the pH and Eh measured. Palladium was generally found to be closely related to the behaviour of copper, while platinum did not leach. The other platinum group metals such as iridium and rhodium were found to precipitate only with accelerated precipitation being observed during Fe precipitation reactions.
Investigation of flow regime transition in a column flotation cell using CFD
(Southern African Institute of Mining and Metallurgy, 2019-02) Mwandawande, I.; Akdogan, G.; Bradshaw, S. M.; Karimi, M.; Snyders, N.
ENGLISH ABSTRACT: Flotation columns are normally operated at optimal superficial gas velocities to maintain bubbly flow conditions. However, with increasing superficial gas velocity, loss of bubbly flow may occur with adverse effects on column performance. It is therefore important to identify the maximum superficial gas velocity above which loss of bubbly flow occurs. The maximum superficial gas velocity is usually obtained from a gas holdup versus superficial gas velocity plot in which the linear portion of the graph represents bubbly flow while deviation from the linear relationship indicates a change from the bubbly flow to the churn-turbulent regime. However, this method is difficult to use when the transition from bubbly flow to churn-turbulent flow is gradual, as happens in the presence of frothers. We present two alternative methods in which the flow regime in the column is distinguished by means of radial gas holdup profiles and gas holdup versus time graphs obtained from CFD simulations. Bubbly flow was characterized by saddle-shaped profiles with three distinct peaks, or saddle-shaped profiles with two near-wall peaks and a central minimum, or flat profiles with intermediate features between saddle and parabolic gas holdup profiles. The transition regime was gradual and characterized by flat to parabolic gas holdup profiles that become steeper with increasing superficial gas velocity. The churn-turbulent flow was distinguished by steep parabolic radial gas holdup profiles. Gas holdup versus time graphs were also used to define flow regimes with a constant gas holdup indicating bubbly flow, while wide gas holdup variations indicate churn-turbulent flow.
Modelling of fluid flow phenomena in Peirce-Smith copper converters and analysis of combined blowing concept
(The Southern African Institute of Mining and Metallurgy, 2015) Chibwe, D. K.; Akdogan, G.; Taskinen, P.; Eksteen, J. J.
ENGLISH ABSTRACT: This investigation consists of a numerical and physical modelling exercise on flow patterns, mixing, solid-liquid mass transfer, and slag-matte phase distribution in a 0.2-scale cold model of an industrial Peirce-Smith converter (PSC). Water, kerosene, air, and sintered benzoic acid compacts were used to simulate matte, slag, injected gas, and solid additions into the PSC. The 2D and 3D numerical simulations were carried out using volume of fluid (VOF) and realizable k-ε (RKE) turbulence models to account for the multiphase and turbulence nature of the flow respectively. These models were implemented using the commercial computational fluid dynamics numerical code FLUENT. Numerical and physical simulations were able to predict, in agreement, the mixing and dispersion characteristics of the system in relation to various blowing conditions. Measurement of mass transfer indicated that fluid flow in the PSC is stratified. Blowing configurations and slag volume both had significant effects on mixing propagation, wave formation, and splashing. As a potential process alternative to increase conversion efficiency, we propose a combined blowing configuration using top lance and lateral nozzles. The numerical simulations were conducted on combined as well as lateral blowing conditions, and the results of the combined concept are encouraging.
Modelling the dynamics of granular particle interactions in a vortex reactor using a coupled DPM-KTGF model
(Elsevier, 2020) Oyegbile, B.; Akdogan, G.; Karimi, M.
ENGLISH ABSTRACT: In this work, a shear-driven two-phase particulate flow of monodispersed and polydispersed granular materials has been studied experimentally and numerically as a function of solids concentration and restitution coefficients for different operating speeds N (70 -130 rpm) in a lab-scale rotor-stator agglomeration reactor. A coupled computational fluid-particle dynamics (CFPD) model was developed consisting of a steady-state flow field of the continuous phase coupled to a transient particle tracking of the discrete phase. This was achieved via a one-way coupling between the continuous and the discrete phase by including the effect of drag, lift, pressure gradient, virtual mass forces, as well as granular collisional forces in describing the particle-particle, particle-wall and the fluid-particle interactions. The spatiotemporal evolution of the flow pattern, discrete phase properties, and influence of the operating conditions on the granular properties were characterized. The validation of the numerical model developed in this study was carried out based on the theoretical analysis of the rotor-stator flow and the PIV flow measurements. The results showed that the particle sizes were uniformly distributed within the reactor after steady-state conditions, while a small region of high particle concentration was observed near the rotor due to low vorticity and turbulent intensity around the region. In terms of the operating conditions, the restitution coefficients and the operating speeds do not have a significant influence on the granular properties apart from the small region around the shaft where there is a correlation between these parameters. The particle sizes, however, show a positive correlation with the granular properties. Also, a wider particle size distribution was observed axially towards the stator, which might be attributed to the pumping effect of the Batchelor flow in this direction. It was also concluded that the discrete phase velocity does not seem to vary significantly with the restitution coefficients. Furthermore, the vertical velocity and vorticity profiles give a reasonably good agreement between the CFPD model predictions and PIV measurements. The minor observed deviations were mainly due to some of the experimental limitations rather than the robustness of the CFPD model or the numerical code.
Numerical and physical modelling of tundish slag entrainment in the steelmaking process
(The Southern African Institute of Mining and Metallurgy, 2017-05) Mabentsela, A.; Akdogan, G.; Bradshaw, S.
ENGLISH ABSTRACT: Physical and numerical modelling methods were followed to identify mechanism(s) for tundish slag entrainment in a bare tundish and one with a flow control device (FCD). The physical and numerical models made use of water and paraffin to model steel and slag respectively. Observations from the physical model showed that the steel-slag interface remains immobile in both cases. Entrained paraffin formed droplets approximately 1 mm in diameter. Results from both models (numerical and physical) showed that in both cases (bare and FCD case), areas of high entrained slag concentration exist near the inlet region. The entrained slag concentration decreases towards the tundish endwalls. Flow patterns and velocities tangential to the steel-slag interface from the numerical model showed that slag entrainment in both the bare tundish and tundish with a FCD possibly takes place via two mechanisms. First, the slag moves across the steel-slag interface via mass transfer; secondly small velocities tangential to the interface at depths greater than 10 mm below the interface carry the already ‘entrained’ slag into the bulk steel phase. These tangential flow patterns are dominant in the inlet region, hence the high concentration of entrained slag in this region.
Physical and numerical modelling of a four-strand steelmaking tundish using flow analysis of different configurations
(The Southern African Institute of Mining and Metallurgy, 2015) Cloete, J. H.; Akdogan, G.; Bradshaw, S. M.; Chibwe, D. K.
ENGLISH ABSTRACT: Modern tundishes have evolved as vessels to serve as the final step in refining of molten steel by removing inclusions and promoting thermochemical homogeneity. In this study the flow behaviour in a four-strand tundish was investigated by means of a ½-scale water model as well as numerical modelling. The numerical and physical models were used to characterize residence time distribution and calculate properties pertaining to tundish flow regime. Three different tundish configurations were investigated: a bare tundish with no flow control devices, a tundish with a turbulence inhibitor, and a tundish with both a turbulence inhibitor and a dam. The physical and numerical models showed that a tundish without flow control devices is prone to significant short-circuiting. A tundish with a turbulence inhibitor was shown to be successful in preventing shortcircuiting and provided surface-directed flow that might assist the removal of inclusions from the melt. However, it was also observed that the upward-directed flow caused the maximum turbulence kinetic energy near the surface to increase dramatically. The potential for slag entrainment should therefore be considered during the design and operation of tundishes with turbulence inhibitors.
Prediction of gas holdup in a column flotation cell using computational fluid dynamics (CFD)
(The Southern African Institute of Mining and Metallurgy, 2019-01) Mwandawande, I.; Akdogan, G.; Bradshaw, S. M.; Karimi, M.; Snyders, N.
ENGLISH ABSTRACT: Computational fluid dynamics (CFD) was applied to predict the average gas holdup and the axial gas holdup variation in a 13.5 m high cylindrical column 0.91 m diameter. The column was operating in batch mode. A Eulerian-Eulerian multiphase approach with appropriate interphase momentum exchange terms was applied to simulate the gas-liquid flow inside the column. Turbulence in the continuous phase was modelled using the k- realizable turbulence model. The predicted average gas holdup values were in good agreement with experimental data. The axial gas holdup prediction was generally good for the middle and top parts of the column, but was over-predicted for the bottom part of the column. Bubble velocity profiles were observed in which the axial velocity of the air bubbles decreased with height in the column. This may be related to the upward increase in gas holdup in the column. Simulations were also conducted to compare the gas holdup predicted with the universal, the Schiller-Naumann, and the Morsi-Alexander drag models. The gas holdup predictions for the three drag models were not significantly different.
The recovery of platinum group metals from low-grade concentrates to an iron alloy using silicon carbide as reductant
(The Southern African Institute of Mining and Metallurgy, 2015) Malan, W.; Akdogan, G.; Bradshaw, S.; Bezuidenhout, G. A.
The purpose of the study was to investigate the feasibility of SiC reduction of low-grade concentrates from Lonmin’s Rowland and Easterns operations with respect to metal fall and PGM recovery. These concentrates are rich in SiO2 and MgO with low concentrations of chalcopyrite and Cr2O3. Pd is the most abundant of the PGMs. SiC reduction of samples was conducted at 1600℃ with 2.5–3.5 kg SiC per 100 kg concentrate. PGM recoveries for Easterns concentrate were better than for Rowland. More than 85% of the Ir and Pd and almost 60% of the Pt were recovered with 3.5 kg SiC per 100 kg concentrate. SEM of slag samples showed little entrainment of metallic prills compared to Rowland samples. This was attributed to the relatively higher melt viscosities of the Rowland concentrate. In order to decrease slag viscosity and to enhance PGM recovery, the FeO content of the Easterns concentrate was increased with the addition of 10 kg converter slag per 100 kg concentrate. Ir and Pd recoveries were increased to about 95%, while Pt recovery was around 70%. On the basis of these results an optimum feed ratio between Easterns and Rowland concentrates and converter slag is proposed. Carbothermic reduction of the optimum charge was also compared to SiC reduction. Carbothermic reduction yielded a marginally higher metal fall; however, the calculated gas emissions and energy requirements were higher than for SiC reduction.
Sonic injection into a PGM Peirce-Smith converter : CFD modelling and industrial trials
(The Southern African Institute of Mining and Metallurgy, 2015) Chibwe, D. K.; Akdogan, G.; Bezuidenhout, G. A.; Kapusta, J. P. T.; Bradshaw, S.; Eksteen, J. J.
ENGLISH ABSTRACT: Peirce-Smith converters (PSCs) are extensively used in the copper, nickel, and platinum group metals industries. The typical converting operation involves lateral purging of air into molten matte through a bank of tuyeres. This blowing operation occurs at low pressure from the blowers, resulting in a bubbling regime that is considered inefficient from both a process and an energy utilization perspective. Inherent drawbacks also include recurrent tuyere blockage, tuyere punching, and low oxygen efficiency. Western Platinum embarked on a full-scale industrial evaluation of generating a jetting regime by using sonic injection. Prior to industrialscale tests, a numerical assessment to ascertain the feasibility of implementing sonic injection into a PSC was conducted. The work included flow characterization at high-pressure injection achieving sonic velocity at the tuyere exit. The 2D and 3D simulations of the three-phase system were carried out using the volume of fluid method together with the RKE turbulence model to account for the multiphase and turbulent nature of the flow. This paper discusses the key findings in understanding plume extension, velocity distribution, shear wall stress analysis, and phase distribution characteristics in the system. Plant trials are also discussed with reference to the commercial aspects of a full-scale implementation of sonic injection in the smelter.

Browsing by Author "Akdogan, G."

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