http://196.220.128.81:8080/xmlui/handle/123456789/183 2026-09-01T13:23:02Z 2026-09-01T13:23:02Z Iyiola, Olatunji Ogunniyi http://196.220.128.81:8080/xmlui/handle/123456789/6043 2026-08-20T16:41:56Z 2009-09-01T00:00:00Z

INVESTIGATION INTO FROTH FLOTATION FOR THE BENEFICIATION OF PRINTED CIRCUIT BOARD COMMINUTION FINES Iyiola, Olatunji Ogunniyi In resource recovery from end-of-life printed circuit board (PCB), the physical processing route is considered most environmentally friendly. The-75µm fraction generated-during the comminution assays well above many precious and base metal deposits, but contributes overall drop in value recovery. This investigation was aimed at exploiting the versatility of froth flotation for beneficiation of the PCB comminution fines. Characterization work shows wet assay of constituents in the sample vary with digestion condition. Absolute assays as for hazardous constituent thus require comparison of data from more than one digestion conditions. Comparative assaying of samples from beneficiation treatments can however use aqua regia digestion which gives less hazardous procedure compared to hydrogen fluoride plus microwave and nitric acid treatment. It also gives leach liquor from which all constituent elements can be analysed, compared to that from total digestion via sodium peroxide fusion. For this sample total digestion will therefore not always give better results compared to partial digestion. Findings also show that thermogravimetric analysis may not be recommended in PCB characterization. It gave no distinct inflexion point to characterize sample any constituent. This is due to the very diverse material constituents of the. Further on characterization, the sample gave loose bulk density lighter than water, and true density of 3 g/cm3. This coupled with surface hydrophobicity observed necessitates that pulping the sample must be done under water. Light optical and scanning electron microscopy showed particle liberation was very high, but not total. Unliberated fraction at-75µm can be put at 5000 particles per million. Morphology of the metallic particles was very diverse, with average circularity shape factor of 0.63. This coupled with the material diversity is a major constraint in sub-sieve size analysis of the sample. As shown by scanning electron microscopy energy dispersive x-ray spectroscopy, the liberated particles themselves contain more than one chemical element, being alloys. Beneficiation operation therefore cannot attempt to separate such particles into constituent elements but some bulk collection of metallic values into a concentrate. Reverse flotation of metallic values based on a scheme described as natural hydrophobic response (NHR) was found successful. Favorable kinetics under the scheme gave about 500 rpm and 500 ml/min aeration rate, at 300 g sample in a 3.5/ Leeds cell. Without the use of a collector, natural hydrophobic response was observed. The system also gave stable froth without the aid of a frother. Investigations (surface tension and dynamic froth stability height measurements, with general literature) show the NHR froth is a fine particle stabilized froth, and not surfactant stabilized. Au and Pd, were among the elements best enriched into the sink; 64 % recovery for Au at enrichment ratio of three. Flotation over narrower and coarser fraction (+106- 75 11m) shows the NHR scheme can be successfully applied at this size. Chemical conditioning schemes investigated shows very minimal responses to reagents. Potassium amyl xanthate (PAX) did not condition the metallic particles for flotation remarkably as it does with native metals. Sulphidation with sodium hydrogen sulphide shows a little improvement in response to PAX. Sodium mercaptobenzothiazole- a selective collector for tarnished copper and lead minerals- did not show such selectivity in the PCB comminution fines pulp. Some cationic pull with tetra butyl ammonium chloride towards selective pull of non metallic values after NHR pull has subsided was observed, although very little also. Macromolecular depression with carboxyl methyl cellulose did not subdue the natural hydrophobic response up to profuse percentage dosages. Depression by lowering surface tension, described as gamma depression, using Betamin 127A (active constituent: ethoxy nonyl phenol) was effective to wet hydrophobic particles, but still not helpful for selective pull after chemical conditioning. At the lowered surface tension, frothing sets in with entrainment. Probable causatives for the poor response to reagents are surface oxidation of the metallic particles and depression by calcium ions in pulp. Surface studies with field emission scanning electron microscope and auger electron spectroscopy composition depth profiling, show presence of organic layers on the surface of the metallic particles. The surfaces were also found to be oxidized down to about 340 nm depth profiled. None of the surface is pure alloy, but occurring in forms that will be relatively inert to reagents. Beside these, from aqua regia wet assaying, the sample contains about 7 % calcium by mass, and ICP-MS trace element analysis of the process water confirms calcium presence up to 7 ppm equilibrium concentration in the pulp. Judging from the responses, the natural hydrophobic response scheme can be well recommended for PCB comminution fines flotation. Optimization of the performance of the scheme responds remarkably well to kinetic parameters variation. With the generally low impeller energy and aeration rate found favourable for PCB CF flotation, and the zero reagent cost (no collector, no frother) of the NHR scheme, PCB comminution fines flotation shows good prospects. xviii, 198p. : ill. ;30cm

2009-09-01T00:00:00Z OMOTOYINBO, JOSEPH AJIBADE http://196.220.128.81:8080/xmlui/handle/123456789/6042 2026-08-20T16:15:49Z 2008-02-01T00:00:00Z

EFFECTS OF THERMOMECHANICAL PROCESSING ON THE MICROSTRUCTURE, TENSILE STRENGTH AND PLASTICITY INDICES OF 6063 ALUMINIUM ALLOY OMOTOYINBO, JOSEPH AJIBADE An investigation has been carried out on the effect of the variation of thermomechanical processing parameters on the microstructure, tensile strengths and plasticity indices of 6063 Aluminium alloy. It is intended to determine the possibility of developing a high tensile strength plasticity indices alloy through refining of microstructure by thermomechanical ageing route, thereby expanding the horizon of its applications in machine building, automobile, architecture and civil engineering industries. The as received alloy samples were solution heat treated (SHT) at 530°C for 2hours and quenched in water to room temperature. The study involved initial characterization of the thermoplastically worked AI-Mg-Si alloy, after solution heat treatment, as a singular operation employing varying degrees of plastic deformation (10%-50%) at different working temperatures (28°C, 160°C, 180°C, 200°C, 220°C and 240°C). Similarly, artificial ageing of the solution heat treated alloy samples was carried out at different ageing times (1-20hrs) and temperatures (160oC, 180°C, 200°C, and 220°C), followed by the characterization of the aged alloy samples. Both thermoplastic working and artificial ageing were carried out as preliminary studies. Finally, the solution heat treated alloy was subjected to various thermomechanical ageing treatments in order to give room for a exhaustive assessment of the effects of process variables (degree of preageing, % deformation, deformation temperature, final ageing time and temperature) on the microstructure, tensile strengths and plasticity indices of the 6063 Aluminium alloy. Tensile and impact tests were carried out on the processed alloy samples as means of property assessment, as well as microstructural examinations using the optical and transmission electron microscopes. Attempt was also made to develop mathematical models capable of relating tensile strength and plasticity as a function of processing parameters. The results show that thermomechanical processing has significant effect on the microstructure, tensile strengths and plasticity of the alloy. Precisely the properties were enhanced within certain ranges of the values of the processing parameters, while same properties were impoverished within some ranges of the values of the processing variables. However, thermomechanical ageing processing route TMAIIIC(9hrs preageing time, 30% warm deformation, 10hrs final ageing time and water quenched to room temperature), produced the best results in terms of tensile strength-plasticity indices of the alloy. It is therefore concluded that thermomechanical ageing techniques could be a highly useful tool for developing higher strength-plasticity property in age-hardenable alloys, as demonstrated in the studied 6063 Aluminium alloy. Likewise, improved understanding of the fundamental mechanisms of alloy strengthening by thermomechanical ageing can by appropriate process control, help in the creative task of alloy development. The success of an alloy development effort, of course, always depends on the competition with existing materials, and on the search for new demanding applications on the part of industrial alloy users. Scientifically and technologically, thermomechanical ageing is ready for such a challenge, in particular for age hardenable alloys. xxxi, 197p. : ill. ; 30cm

2008-02-01T00:00:00Z ADEWUYI, BENJAMIN OMOTAYO http://196.220.128.81:8080/xmlui/handle/123456789/6041 2026-08-20T15:48:31Z 2002-11-01T00:00:00Z

DEVELOPMENT OF AUSTEMPERED DUCTILE IRON FOR AUTOMOBILE AND MACHINE PARTS ADEWUYI, BENJAMIN OMOTAYO An investigation has been carried out on the effect of silicon level on austempered ductile iron in order to determine the suitability of the material in the development of structural materials that can be used in the production of automobile and machine parts that undergo constant cyclic loading. This is in response to pressures on engineering and automobile industries to produce components that provide improved properties and save energy cost or reductions in overall manufacturing cost and also to further increase the opportunity for wider commercial exploitation of cast irons. The study involved initial production of three ductile iron alloys containing different levels of silicon. The effect of austenitising temperature (850,900 and 950°C for 1hour) and rapid quenching and holding in a salt bath maintained at austempering temperature (280, 300 or 350°C for different time intervals 15,30,60,90,or 120) subsequently investigated. The silicon level sensitivity on the fatigue strength, impact toughness and the hardness properties of the three alloys containing increasing silicon levels (2.0%, 2.6%, 3.0%) were characterized using optical micrography and the results were used to correlate the phase relationship with the mechanical properties. Computer modeling was used to measure the volume fraction of retained austenite. The austempering applied to the ductile cast iron alloys produced different bainitic structures, as a function of heat treatment conditions that led to an attractive combination of mechanical properties. These render the low silicon, medium silicon and the high silicon austempered ductile iron useful in the production of automobile and machine parts as an economical substitute for high strength steels. While the bainitic transformation in steels gave a mixture of ferrite and carbides, the presence of silicon in the ductile iron led to significant austenite volume fractions being retained in the microstructure. The best overall results were obtained from a high silicon alloy austenitised at 950°C and austempered at 350°C while optimum impact energy of 70 and 115 Joules respectively was obtained from the medium silicon alloys and high silicon alloys austenitise at 950°C and austempered at 350°C. Both alloys have the same optimum values for fatigue limits, 450Nmm-2 at these austempering conditions. The results show that alloys of different silicon levels can be used to produce machine parts by altering the austempering parameters. The model developed to predict the fatigue limit from the impact toughness value and the opening and closure of the processing window can be used to optimize production processes in foundries. xviii,155p. : ill. ; 30cm

2002-11-01T00:00:00Z OKPALA, ALEXANDER NWACHUKWU http://196.220.128.81:8080/xmlui/handle/123456789/6040 2026-08-20T14:38:37Z 1997-01-01T00:00:00Z

THE EFFECT OF SURFACE FINISH ON THE EFFICIENCY OF INHIBITORS FOR STEELS CORRODING IN 3% NACL OKPALA, ALEXANDER NWACHUKWU Investigations were carried out to study the effects of surface finish on the efficiency of inhibitors for Steels Corroding in 3 % NaCl. This study was carried out owing to its importance in the drive towards curtailing the menace of corrosion in industries where varieties of steels are used for production structures, Installed offshore. particularly when these structures are in the course of the study, different grades of steel samples were- polished with emery papers of various grades and then subjected to electrochemical corrosion study by total immersion technique and methods, the corrosion media used was 3% NaCl solution containing 0.2% of sodium nitrite, sodium nitrate, sodium benzoate or sodium dichromate as inhibitors. results The most prominent conclusions drawn from the results were that the inhibition efficiency of the inhibitors generally rose with surface roughness, where higher concentration but fell at a certain critical surface roughness of the inhibitor in use was required and that corrosion of carbon steels in 3%NaCl increased with increase in the carbon content of the steel. xiii, 86p. : ill. ; 30cm

1997-01-01T00:00:00Z