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Volatile organic compounds – biphenyl thermodynamic interactions

  • Authors: Muzenda, Edison
  • Date: 2014
  • Subjects: Absorption , Activity coefficient , Phase equilibrium , Volatile organic compounds , Thermodynamics
  • Type: Article
  • Identifier: uj:4989 , ISSN 2078-0966 , http://hdl.handle.net/10210/13124
  • Description: This work focused on the thermodynamic interactions involving volatile organic compounds (VOCs) and biphenyl. The solubility of 60 VOCs in biphenyl was studied using group contribution methods. The modified UNIFAC Dortmund and Lyngby were used to compute the required phase equilibrium in the form of infinite dilution activity coefficients. Six family groups were studied mainly alkanes, alkenes, alkynes, aldehydes, alcohols, and carboxylic acids. The Modified UNIFAC Dortmund performed better than the Modified UNIFAC Lyngby. Biphenyl showed excellent absorption affinity for all VOCs in particular for alkynes and aldehydes. The solubility decreased with increase in VOC molecular weight.
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The status of used vegetable oil (UVO) biodiesel production in South Africa

  • Authors: Mbohwa, Charles , Mudiwakure, Alexander
  • Date: 2013
  • Subjects: Oil-derived biodiesel , Biodiesel production technology - South Africa , Biodiesel technology benchmarking
  • Type: Article
  • Identifier: uj:6040 , ISSN 2078-0966 , http://hdl.handle.net/10210/10440
  • Description: This paper discusses the status of used oil derived biodiesel production in South African. It highlights the positives and shortcomings of the technology used and identifies the potential for improvement. All known South African used oil biodiesel producers were targeted. The response rate was 40% out of 200 producers. Technology used was benchmarked with established advanced biodiesel producing countries such as Germany, Brazil and the USA. Production rate, yield, product quality were the key performance indicators assessed. Results show that biodiesel production in South Africa is still in its infancy and production rates are low ranging from 100litres/day to a maximum 8000litres/day. Most plants are locally manufactured. Imports from India, China and Australia make up the remainder. Batch reactors are favoured over continuous reactors because of low acquisition cost, simple design and ease of operation. They allow for phase to phase quality control. This has resulted in low volume production militating against economies of scale. Yields, at up to 94% are acceptable and competitive. The products are contaminated with methanol and free fatty acids. The standards set for biodiesel quality were found to be restrictive and prohibitive but prospects for sustainable production are excellent.
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Synthesis and characterization of new nitrogen donor ligands

Synthesis and characterization of new nitrogen donor ligands

Subsidy and revenue maximization in developing countries

  • Authors: Sumbwanyambe, Mbuyu , Nel, A. L.
  • Date: 2012
  • Subjects: Information technology , Subsidized communication services
  • Type: Article
  • Identifier: uj:6281 , ISSN 2078-0966 , http://hdl.handle.net/10210/9884
  • Description: Developing countries have embarked on the promotion of “ICT access for all” through subsidized Information and Communication Technologies (ICTs), especially in underserviced areas of such countries. The main aim of the “ICT access for all” is to extend the communication services to the large areas of underserviced regions through subsidized communication services. In some instances, subsidies may lead to high ICT penetration and high resource utilization while in some instances unsubsidized services may lead to low utilization of resources and low ICT penetration, which may eventually lead to market failure and destroy market efficiency. With explicitly defined objectives, regarding subsidy policy, however, developing countries always fall short on the implementation of such subsidy policy due to economic reasons and unrealistic subsidy driven pricing models. In this paper we investigate the impact of subsidy driven pricing model on resource utilization and revenue maximization in a developing country. In this paper we try to find a middle ground between promoting “ICT access for all” (given a subsidy and diverse income variations between the groups) and resource utilization in a network.
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Sizing of an anaerobic biodigester for the organic fraction of municipal solid waste

  • Authors: Kigozi, R. , Aboyade, A. O. , Muzenda, Edison
  • Date: 2014
  • Subjects: Anaerobic digestion , Biogas digesters , Clean energy , Municipal solid waste management
  • Type: Article
  • Identifier: uj:4982 , ISSN 2078-0966 , http://hdl.handle.net/10210/13114
  • Description: The anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) for biogas production is a potential solution to the growing challenges associated with municipal solid waste (MSW) management while simultaneously providing an alternative clean energy source. Biogas is produced by the anaerobic digestion (AD) of biomass using microorganisms in specifically designed plants called biogas digesters under controlled conditions or naturally in marshes and landfills. It is a rather clean and versatile fuel as opposed to fossil fuels. To design an efficient AD system, a proper understanding of the quality and quantity of available feedstock must be made as well as prevailing operating conditions. This paper represents steps that were taken to come up with an optimal size of biodigester to treat OFMSW produced at the University of Johannesburg’s Doornfontein Campus in downtown Johannesburg. The campus generates 232.2kg of OFMSW per day which required 30m3 of biodigester capacity.
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Simulated metamorphosis - a novel optimizer

  • Authors: Mutingi, Michael , Mbohwa, Charles
  • Date: 2014
  • Subjects: Metamorphosis , Evolution , Optimization , Algorithm , Metaheuristics , Simulated metamorphosis
  • Type: Article
  • Identifier: uj:4972 , ISSN 2078-0966 , http://hdl.handle.net/10210/13073
  • Description: This paper presents a novel metaheuristic algorithm, simulated metamorphosis (SM), inspired by the biological concepts of metamorphosis evolution. The algorithm is motivated by the need for interactive, multi-objective, and fast optimization approaches to solving problems with fuzzy conflicting goals and constraints. The algorithm mimics the metamorphosis process, going through three phases: initialization, growth, and maturation. Initialization involves random but guided generation of a candidate solution. After initialization, the algorithm successively goes through two loops, that is, growth and maturation. Computational tests performed on benchmark problems in the literature show that, when compared to competing metaheuristic algorithms, SM is more efficient and effective, producing better solutions within reasonable computation times.
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Review of silver recovery techniques from radiographic effluent and x-ray film waste

  • Authors: Masebinu, Samson O. , Muzenda, Edison
  • Date: 2014
  • Subjects: Hydrometallurgy , Pyro-metallurgy , Radiographic waste , Silver recovery
  • Type: Article
  • Identifier: uj:5006 , ISSN 2078-0966 , http://hdl.handle.net/10210/13146
  • Description: This paper highlights the techniques for silver recovery from radiographic waste; effluent and X-ray films. The decline in silver natural resource has increased the cost of sourcing for pure silver. The ecological problems caused by the disposal of radiographic waste is a huge motivation for increased recovery, regeneration and recycling process. The negative impact of pure silver on human and the environment is low but its soluble salt and emission from its recovery process pose a great risk to the ecosystem. Pyro-metallurgical processes of silver recovery requires heat >950°C which also destroys the polymer substrate. Hydrometallurgical processes such as electrolysis, metallic replacement, chemical precipitation and adsorption, are often used and provides high purity and efficiency. A proposed research work for silver recovery based on chemical precipitation using oxalic acid has been presented.
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Reflecting on waste management strategies for South Africa

  • Authors: Muzenda, Edison , Belaid, Mohamed , Mollagee, Mansoor , Motampane, Ntemi , Ntuli, Freeman
  • Date: 2011
  • Subjects: Waste management - South Africa
  • Type: Article
  • Identifier: uj:4710 , ISSN 2078-0966 , http://hdl.handle.net/10210/10956
  • Description: The energy crisis, global warming and a cleaner environment are arguably amongst the most pressing issues at present facing modern society. Before devising a suitable strategy to convert a proportion of the waste into useful product, categorization of waste types is of great significance to any more detailed study. The population of the world continues to grow, as does the average standard of living, increasing demand for food, water and energy which places increasing pressure on the environment. This paper attempts to parameterize waste generation within a South African context in order provide a theoretical foundation for such work to take place. Organic materials, which includes wood, leaves, grass, food, paper, plastic, cotton, synthetic fabrics, sewage sludge, animal remains, bacteria, any carbohydrates or hydrocarbons. These are all materials sent to landfills (with the exception of metal, ceramics and glass). The Gauteng province was chosen for this preliminary study as it constituted 42% of SA’s waste in 2010 making it by far the country’s biggest waste generator. The types of waste that were particularly targeted in lieu of the downstream research endeavoured were medical waste, plastics, tyres and sewage sludge.
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Process intensification of zinc oxide leaching process using sulphuric acid

  • Authors: Napo, P. , Ntuli, Freeman , Muzenda, Edison , Mollagee, Mansoor
  • Date: 2011
  • Subjects: Leaching , Zinc oxide ores
  • Type: Article
  • Identifier: uj:4705 , ISSN 2078-0966 , http://hdl.handle.net/10210/10948
  • Description: This study investigated methods of intensifying the leaching of zinc oxide ore using sulphuric acid for the improvement of zinc recovery. The factors that were investigated in this study were agitation speed, acid concentration and the feeding mechanism of reactants into the reactor (batch and semi-batch processes). Analysis of the elemental composition of the ore was performed using XRF prior to leaching and an Atomic Absorption Spectrometer (AAS) was used to determine the amount of zinc recovered. The results obtained, showed that increasing the acid concentration results in a significant increase zinc recovery...
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Non-destructive testing of dissimilar friction stir welds

  • Authors: Akinlabi, Esther Titilayo , Levy, Adrian C. S. , Akinlabi, Stephen A.
  • Date: 2012
  • Subjects: Friction stir welding , Non-destructive testing , Aluminum alloys , Copper
  • Type: Article
  • Identifier: uj:5333 , ISSN 2078-0966 , http://hdl.handle.net/10210/8876
  • Description: friction stir welds between 5754 aluminium alloy and C11000 copper. The Friction stir welds of 5754 aluminium alloy and C11000 copper were produced at different tool rotational speeds and feed rates. The tool rotational speed was varied between 600 and 1200 rpm while the feed rate was varied between 50 and 300 mm/min. The visual inspection and the x-ray radiographic testing techniques were employed to conduct the tests; these tests were conducted on the welds to ascertain the joint integrity before characterization to have an idea of the quality of the welds. No visual defects were observed on all the welds considered but the x-ray radiography technique revealed the presence of wormhole defects and discontinuities in some of the welds. It was found that the welds produced at 950 rpm with varied feed rates were the best quality welds produced and this was substantiated with the microstructural evaluation of the joint interface. It was found that these welds have good mixing and metallurgical bonding at the interfaces.
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Microstructure and mechanical properties of ultra-fine grained copper processed by equal channel angular pressing technique

  • Authors: Sanusi, Kazeem O. , Afolabi, Ayo S. , Muzenda, Edison
  • Date: 2014
  • Subjects: Tensile properties , Equal channel angular pressing technique , Grain refinement , Ultra-fine grained copper
  • Type: Article
  • Identifier: uj:5005 , ISSN 2078-0966 , http://hdl.handle.net/10210/13145
  • Description: The equal channel angular pressing (ECAP) technique is now recognised for achieving very significant grain refinement of ultra-fine grained materials which, at present produce unique mechanical properties. This study reports the results of the tensile tests and the microstructural analysis carried out on the specimens of ultra-fine grained (UFG) copper processed by ECAP technique at room temperature using a die with a 126o between the die channels. The copper samples used in this work were subjected to six and twelve passes during the ECAP processing. Tensile tests were conducted for samples cut out in two different directions; in the parallel and perpendicular direction at room temperature to evaluate the mechanical properties after the ECAP at these two directions. The microstructural characterization was carried out using optical electron microscope (OEM) and scanning electronic microscope (SEM). The results show ECAP technique introducing significant grain refinement and produced ultrafine grains in copper and there is a potential for achieving high ductility in the copper alloy after processing. The tested sample is characterized by significant differences of strength properties depending on the direction.
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Friction stir welding of dissimilar materials – statistical analysis of the weld data

  • Authors: Akinlabi, Esther Titilayo , Akinlabi, Stephen A.
  • Date: 2012
  • Subjects: Friction stir welding
  • Type: Article
  • Identifier: uj:5336 , ISSN 2078-0966 , http://hdl.handle.net/10210/8879
  • Description: This paper reports the results of statistical analysis conducted on the weld data obtained from friction stir welding of aluminium and copper. The welds were produced by varying the process parameters; the rotational speed was varied between 600 to 1200 rpm and the welding speed varied between 50 and 300 mm/min. The Statistica (version 9.0) statistical analysis software package was used to generate the scatter and surface plots relative to the experimental results obtained from the tensile testing and the FSW data. Regression analysis was also done on the weld data. It was found that the downward vertical force has a significant effect on the Ultimate Tensile Strength of the weld and a strong relationship exist between the heat input into the welds and the measured electrical resistivities of the welds.
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Friction stir welding of aluminium and copper : fracture surface characterizations

  • Authors: Akinlabi, Esther Titilayo , Akinlabi, Stephen A.
  • Date: 2014
  • Subjects: Aluminium , Copper , Fracture surfaces , Friction stir welding
  • Type: Article
  • Identifier: uj:4745 , ISSN 2078-0966 , http://hdl.handle.net/10210/11731
  • Description: Butt welds of aluminium alloy and copper alloy were produced by Friction Stir Welding by varying the feed rate and keeping all other parameters constant. The final weld matrix was composed of welds produced by a constant rotational speed of 600 rpm and the feed rate varied between 50 and 300mm/min. The microstructure and fracture surfaces of the joint interfaces were investigated. The results revealed that the joint interface was characterised with mixed layers of both materials joined. The strongest weld was produced at the highest feed rate employed at 300 mm/min. The fracture surfaces were characterised with thin layers of intermetallic compounds and can be considered fit for practical applications.
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Experimental investigation of laser beam forming of titanium and statistical analysis of the effects of parameters on curvature

  • Authors: Akinlabi, Stephen A. , Akinlabi, Esther Titilayo
  • Date: 2013
  • Subjects: Laser beam forming , Titanium alloys
  • Type: Article
  • Identifier: uj:4746 , ISSN 2078-0966 , http://hdl.handle.net/10210/11732
  • Description: Laser beam forming, a non-contact manufacturing process has become a viable manufacturing process for shaping metallic components. The capability of laser beam forming and bending demands more experimental studies to identify an optimized parameter setting and the likely parameters influencing the formed curvature. This paper investigates experimental laser beam forming of Ti6Al4V titanium alloy using a 4.4 kW Nd: YAG laser and studied the effects of the process parameters on the formed curvature. It was established that an increase in both the laser beam power and the number of scan tracks reduces the radius of curvature in the formed sheets having a more dome shape. The scan speed on the other hand, achieved the same good curvature at a slower or reduced scan speed to allow enough laser – material interaction. Furthermore, both the ANOVA and the regression analysis confirmed the repeatability of the experimental data. A simple regression model was developed based on the known active parameters to determine approximate curvatures instead of running a series of experiments.
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Effect of pH on the recovery and grade of base metal sulphides (PGMs) by flotation

  • Authors: Muzenda, Edison , Afolabi, Ayo S. , Abdulkareem, Ambali S. , Ntuli, Freeman
  • Date: 2011
  • Subjects: Platinum Group Metals , Metal sulphides , Flotation
  • Type: Article
  • Identifier: uj:4713 , ISSN 2078-0966 , http://hdl.handle.net/10210/10959
  • Description: This study investigated the effect of pH on the recovery and grade of the Platinum Group Metals (PGMs) and base metal sulphides from the UG2 ore of the Bushveld Complex. This was achieved through running a series of test work in a Denver flotation cell at varying pH 6-11 at constant reagent dosage. The UG-2 reef is characterized by two predominant gangue phases i.e. chromite and silicate, that have significantly different physical and chemical properties. The test work was aimed at evaluating which pH gives best recoveries, and finding the effect of the chrome content in these recoveries. A pH of 9 gave the highest recovery compared to other pH ranges. However, the highest PGM grade was attained at a pH of 6 which is slightly acidic. Ideally this trend could be expected since the collectors (xanthates) are more stable in alkaline medium. The higher PGM recovery was also accompanied by higher chrome content as a result of their similar chemical properties.
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Design of a support system for a re-configured milling machine to achieve friction stir welds

Cu (II) removal from synthetic waste water by ion exchange process

  • Authors: Muzenda, Edison , Kabuba, John , Ntuli, Freeman , Mollagee, Mansoor , Mulaba-Bafubiandi, Antoine F.
  • Date: 2011
  • Subjects: Clinoptilolite , Ion exchange , Synthetic waste water , Waste water treatment , Heavy metals - Removal
  • Type: Article
  • Identifier: uj:4708 , ISSN 2078-0966 , http://hdl.handle.net/10210/10953
  • Description: The objective of this study was to investigate the potential of acid activated South Africa clinoptilolite as an adsorbent in the ion-exchange process for the removal of cations from aqueous solutions. The kinetic parameters affecting the adsorption of Cu (II) ions were studied. The adsorption of Cu (II) from synthetic waste water was found to be dependent on pH, temperature, contact time and initial adsorbate concentration. The pH was varied from 2.5 to 6 and the optimum pH for Cu (II) removal was found to be 4.0. The removal of Cu (II) ions increased with time and attained saturation in about 60-70 min. The equilibrium data showed that the adsorption was endothermic nature. Kinetics data showed that at higher temperatures, the rate of adsorption is higher for the clinoptilolite natural zeolite and that Langmuir equation successfully described the adsorption process.
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Characterizing the effect of processing parameters on the porosity of laser deposited titanium alloy powder

  • Authors: Mahamood, Rasheedat M. , Akinlabi, Esther Titilayo , Shukla, Mukul , Pityana, Sisa
  • Date: 2014
  • Subjects: Laser metal deposition , Medical implants , Porosity , Processing parameters , Titanium alloy
  • Type: Article
  • Identifier: uj:4739 , ISSN 2078-0966 , http://hdl.handle.net/10210/11725
  • Description: Laser Metal Deposition (LMD) is an additive manufacturing technique that produces parts layer by layer directly from the Computer Aided Design (CAD) file. Highly customized parts with complex shapes such as medical implants can well be manufactured using the LMD process. LMD has been used to produce a wide range of patient specific (customized) parts. Porous parts are of particular importance as medical implants because they can potentially aid the healing process and proper integration of the implant with the body tissues. In this research porous samples of titanium alloy (Ti6Al4V) were produced using the LMD process. Spherical shaped Ti6Al4V powder of particle size ranging between 150 to 200 μm was used. The effect of laser power and scanning speed on the shape, size and degree of porosity of the deposited tracks was investigated. The results showed that as the laser power was increased and the scanning speed decreased, the degree of porosity was reduced. The size of the porosity was also found to reduce as the laser power was increased.
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Bio-methane generation from organic waste : a review

  • Authors: Muzenda, Edison
  • Date: 2014
  • Subjects: Anaerobic digestion , Biodegradable material , Biogas
  • Type: Article
  • Identifier: uj:4987 , ISSN 2078-0966 , http://hdl.handle.net/10210/13119
  • Description: Anaerobic digestion of organic waste can address both energy recovery and pollution control. A variety of agricultural, industrial and domestic wastes can be anaerobically digested as they contain easily biodegradable material. Biogas contains 50 -70% methane and 30-50% carbon dioxide as well as small a amounts of other gases with calorific value of about 21-24 MJ/m3. This paper reviews the history of biogas, biogas production stages and operating parameters. The anaerobic digestion configuration and potential substrates for biogas production are also considered.
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