Ayo Samuel Afolabi

Effect of pH on the Floatability of Base Metal Sulphides PGMs

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 produces the best recoveries, and finding the effect of the chrome content in these recoveries. A pH of 9 produced the highest recovery compared to other pH values. 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.

Kinetics Studies of Adsorption and Desorption of South African Fly Ash for Some Phenolic Compounds

The extent of adsorbability and desorbability of an unclassified South African coal fly ash (SACFA) from the Lethabo power plant was evaluated in the treatment of phenol, 2-nitrophenol, and 4-nitrophenol from aqueous solutions. Batch studies were performed to evaluate the effects of various experimental parameters such as adsorbent dosage, initial pH (pHo), and contact time on the removal of these three adsorbates. The adsorption isotherm indicates that the Freundlich model correctly fits the experimental data for the adsorbates better than the Langmuir model, with fly ash having the highest adsorption capacity of 6.51 × 10−2 mg/g for 4-nitrophenol, 2-nitrophenol 6.00 × 10−2 mg/g, and phenol 6.31 × 10−2 mg/g. SACFA was found to adsorb 90.2% of phenol, 88.9% of 2-nitrophenol, and 92.6% of 4-nitrophenol at an initial concentration of 20 mg/l. The desorption of the adsorbates from the surface of the fly ash was achieved using 30 ml of distilled water at 307 K. The analyses of the results obtained revealed that the desorption of 4-nitrophenol was the most difficult of the three adsorbates to be desorbed. The desorption efficiencies obtained were 17.9% for phenol, 18.8% for 2-nitrophenol, and 10.2% for 4-nitrophenol.

Development of Adsorbent from Banana Peel for Wastewater Treatment

This study investigated the development and application of banana peel for the remediation of heavy metals (Pb, Zn and Cr). Batch experimental processes as well as conditions that might influence the sorption of the metals were investigated. These conditions include effects of pH, contact time, adsorbent dose, and particle size. The applicability of the sorption process was tested on wastewater. The adsorbent activated with 0.5 M H2SO4 showed the highest percentage removal of chromium ion (88.9 %) at a pH of 6. It has been found that particle size has no effect on the removal of zinc ion and it has also been found that the removal efficiency of lead and chromium ion decreased with increase in contact time and particle size. Also, it can be seen from the results that untreated banana peel waste increases the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) values of wastewater. The results from the optimized method revealed the applicability of the method to environmental water samples. This study therefore confirms that banana peel is a promising adsorbent for the removal of chromium from industrial effluent.

Effect of Treatment Methods on Used Lubricating Oil for Recycling Purposes

The need to treat used lubricating oil for possible reuse has arisen due to concern for the environment, scarcity, price stability, and increasing dependence on this product for many industrial applications. Various methods, such as distillation/clay, acid/clay, acid, and activated charcoal/clay treatment methods, were employed in this study for the treatment of used Mobil and Total lubricating oil samples with the aim of improving their qualities for reuse. The characteristics of the fresh, used, and treated oil are tested for water content, specific gravity, kinematic viscosity, viscosity index, flash point, pour point, sulphur content, and concentrations of heavy metals (aluminum, iron, and lead). The results obtained showed that the usage of the lubricant oil affects the qualities of oil, for instance the sulphur of both brands of the oil samples was below the detectable limit, while the sulphur contents of the used oil are 0.80 and 0.69% for the used Mobil and Total oil samples, respectively. The results also revealed that treatments employed in this work were able to improve the characteristics of the used oil samples after treatment. The analyses of the results showed that the acid/clay method was the most effective method of treatment that brings the characteristics of the treated oil close to the fresh oil sample, while the distillation/clay and activated/charcoal methods were the best in terms of recovery of the oil after treatment. These two methods also recovered about 80% of the used lube oil samples compared to acid and acid/clay treatment methods, where the oil recovered was about 50% of the charge used oil sample.

Parametric effects on leaching behavior of nickel-copper matte in ammonia

Leaching, which is described as the extraction of soluble constituents from a solid by means of a solvent, is an important separation technique in the refining of precious metals from their matte. It is, therefore, important to investigate the extraction behavior of metals from the matte, which is the focus of this study. This study reports the influence of concentration of the solvent (ammonia), leaching temperature, leaching time, and pH on the recovery of nickel and copper from the matte. The elemental composition analysis of the matte indicated that it contains 23% copper, 37% nickel and 1.1% ferrous compound. The analysis also showed that the major mineral phases present in the matte were heazlewoodite (Ni3S2), chalcocite (Cu2S), djurleite (Cu1.9S), and nickel alloy. The leaching parameters studied were concentration of ammonia (1.5, 2.0, 2.5, and 3.0 M), leaching time (0–270 min, at 15 min sampling interval), leaching temperatures (50°C, 60°C, and 70°C), and pH (9.3–11.2). The results obtained revealed that the recovery of nickel and copper from the matte was greatly influenced by the concentration of ammonia, leaching time, leaching temperature, and pH. It was established from this study that the highest dissolution of nickel and copper was obtained at 3 M and 2 M ammonia concentration, respectively. The results also revealed that a decrease in the pH of the solution resulted in a decrease in both nickel and copper recovery, with maximum leaching time of 270 min. It was observed that less than 50% of both nickel and copper was leachable due to the presence of metal alloys. The analyses of the results also showed that as the leaching temperature increased from 50°C to 60°C, the amount of nickel and copper that was recovered from the matte significantly increased. However, there was reduction in the amount of nickel and copper recovered from the matte as the temperature was increased from 60°C to 70°C, due to loss of ammonia by evaporation. The shrinking core model was used to explain the behavior of the recovery of these metals at different temperatures, and both metals were found to be favored by diffusion controlled reaction.

Effect of reverse flotation on magnetic separation concentrates

Reverse flotation studies on magnetite samples have revealed that the use of starch as a depressant of Fe-oxides has a hydrophilic effect on the surface of Fe-bearing silicates and significantly decreases Fe in the silica-rich stream when used in combination with an amine (Lilaflot D817M). In this study, the effect of reverse flotation on the optimization of products obtained from magnetic separation was investigated. Two different magnetic samples, zones 1 and 2, were milled to <75 μm and then subjected to low intensity magnetic separation (LIMS). The LIMS test conducted on the <75 μm shown an upgrade of 46.40wt% Fe, 28.40wt% SiO2 and 2.61wt% MnO for zone 1 and 47.60wt% Fe, 29.17wt% SiO2 and 0.50wt% MnO for zone 2. Further milling of the ore to <25 μm resulted in a higher magnetic-rich product after magnetic separation. Reverse flotation tests were conducted on the agitated magnetic concentrate feed, and the result shows a significant upgrade of Fe compared to that obtained from the non-agitated feed. Iron concentrations greater than 69%, and SiO2 concentrations less than 2% with overall magnetite recoveries greater than 67% and 71% were obtained for zones 1 and 2, respectively.

Effect of austempering temperature and time on corrosion behaviour of ductile iron in chloride and acidic media

Purpose – The aim of this paper is to study the effect of heat treatment temperature and time on the corrosion behavior of ductile iron in 0.5 M NaCl and 0.5 M H2SO4.Design/methodology/approach – Ductile iron samples of known composition were austenized at temperatures 800°C and 850°C, and austempered at 300°C and 350°C for periods of 30, 45 and 60 min to convert them to austempered ductile iron (ADI). The corrosion behavior of these ADI samples in 0.5 M NaCl and H2SO4 was measured using the conventional weight loss method. The metallographic examination of the samples was carried out to study the morphology of their corroded surfaces.Findings – Ductile iron is susceptible to corrosion in both acidic and chloride media, while attack by acid media is mainly at the grain boundaries, that from the chloride is pitting. The corrosion behavior of the material is affected by the compositional structures of the materials as well as the austempering temperature and time it was subjected to.Practical implications –...

A Predictive Model for the Energy Analysis of a Proton Exchange Membrane Fuel Cell by Computer Simulation

The energy analysis of proton exchange membrane fuel cell was examined using MathCAD software in this study. The results obtained from the experimental testing of the fabricated membrane electrode assembly in a single cell stack revealed that the fabricated membrane electrode assembly can produce an open circuit voltage of 0.745 V, and a power density of 0.0669 w/cm2. The simulation of the developed model for the energy analysis in a fuel cell shows that an increase in hydrogen partial pressures resulted in an increment in the voltage of the fuel cell. The results also show that the flow rate of oxygen had less effect on the fuel cell performance, whereas that of hydrogen enhanced its performance. The temperature effects on the fuel cell performance were of negative impact for the cathodic reaction, thus increasing temperature decreases the forward reaction voltage. The comparison of the experimental with the simulated results shows some variations with correlation coefficient of 0.77 and standard deviation of 24%. These variations are attributed to some of the assumptions made during the conceptualization of the model equation.

Predictive mathematical modeling and computer simulation of direct ethanol fuel cell.

ABSTRACT The challenges of finding a better substitute of energy as well as the shortcomings identified with direct ethanol fuel cell, includes high anode over potential and crossover necessitate the need to investigate the influence operating parameters on the performance of fuel through computer simulation. This study focus on the development of a predictive mathematical modeling for direct ethanol fuel cell for the purpose of investigating the influence pressure, temperature cathode, and reactants concentration on the performance, efficiency, and heat generated by the cell. Results obtained indicate that an increase in operating temperature led to a decrement in output voltage and cell efficiency, while the same condition of increasing the temperature positively favors the heat generated from the cell. Simulated results also show that cell performance is improved with an increase in concentration of the fuel (ethanol) and oxidant (oxygen). It can be inferred from this study that the cell performance of DEFC can be theoretically predicted with the developed model.

Microstructure and Mechanical Properties of Ultra-fine Grained Copper Processed by Equal Channel Angular Pressing Technique

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 126 o 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.