Peter Apata Olubambi

Role of Ore Mineralogy in Optimizing Conditions for Bioleaching low-grade Complex Sulphide Ores

The role that ore mineralogy plays in understanding and optimizing the conditions favouring the bioleaching of complex sulphide ore containing high amounts of siderite was studied using mixed cultures of mesophilic bacteria, with emphasis on zinc, lead and copper recoveries. The influencing parameters investigated include particle size, stirring speed, volume of inoculum, pulp density, and pH. The results show that the mixed mesophilic cultures can extract about two and a half times the amount of zinc than copper over an equivalent period of time. The highest zinc and copper recoveries of 89.2% and 36.4% respectively are obtained at particle size of 75 μm, stirring speed of 150 r/min, pulp density of 10% (w/v), 12% (v/v) inoculum concentration, and a pH of 1.6. Variations in elemental composition within different particle sizes resulting from the mineralogy of the ore account for the bioleaching behaviour at varying particle sizes. The dissolution at varying pulp density, volume of inoculum, solution pH and the low solution potential observed are also influenced by ore mineralogy.

Influence of spark plasma sintering on microstructure and wear behaviour of Ti-6Al-4V reinforced with nanosized TiN

Abstract Ti-6Al-4V/TiN composites were successfully consolidated by spark plasma sintering (SPS). TiN addition to Ti-6Al-4V was varied from 1% to 5% (volume fraction). The effect of TiN addition on the densification, microstructure, microhardness and wear behaviour of Ti-6Al-4V was studied. Experimental results showed reduction in sintered density of the compacts from 99% to 97% with increase in TiN content. However, an increase in microhardness value was recorded from HV0.1 389 to HV0.1 488. X-ray diffraction (XRD) analysis showed that the intensity of diffraction peaks of TiN phase in the composites increased also with formation of small amount of secondary Ti2N phase. SEM analysis of SPS sintered nanocomposites possessed a refinement of α/β phase microstructure in Ti-6Al-4V with the presence of uniformly dispersed TiN particles. The worn surface of the composite showed improved abrasive wear resistance with non-continuous grooves as compared to the sintered Ti-6Al-4V without TiN addition.

Effect of TiN and TiCN additions on spark plasma sintered Ti–6Al–4V

Abstract In this study, the microstructural and densification behavior of titanium nitride (TiN) and titanium carbonitride (TiCN) reinforced Ti-6Al-4V were investigated under an applied pressure of 50 MPa, sintering temperatures of 1000–1100 °C, heating rate of 100 °C/min and dwell time of 10–20 min through spark plasma sintering technique. Results show that the microstructural transformation of the titanium matrix composite comprises of a mixture of lamellar colonies with β grain boundaries and nanoparticles with an average grain size range of 4.5–6.0 μm. Furthermore, an addition of nanoceramics TiN/TiCN resulted in microstructural transformation, uniform particle distribution within the metal matrix and along the grain boundary. However, the sintered relative density of the composites decreased with the percentage increase in TiCN, while fully dense composites were obtained at a sintering temperature of 1100 °C. Microhardness values of the sintered composites reach a greater level in comparison to Ti-6Al-4V alloy while fracture morphology of the sintered composites with addition of nanoceramics (TiN/TiCN) displayed a transgranular transformation within the matrix accompanied with fine dimple features.

Influence of Shear Stress on Erosion–Corrosion of Stainless Steels in Simulated Mine Water

This study provides information on the performance of three stainless steels at various shear stresses and presence of silica sand particles in simulated mine water. The materials employed were two duplex stainless steels (UNS S32205 and UNS S32750) and one austenitic stainless steel (UNS 30403). The rotating cylinder electrode system produced shear stresses to evaluate the flow-induced and erosion–corrosion tests by open-circuit potential and potentiodynamic polarization techniques. Hardness tests were used to examine the performance of the degraded samples, and scanning electron microscopy was used to characterize the surface morphology. UNS S32750 displayed nobler OCP compared with UNS S32205 with austenitic steel having the least potential irrespective of the shear stresses and with/without silica sand. Work hardening of the duplex stainless steels promoted variable behavior in the hardness results. The current density results revealed that UNS S32705 had the best corrosion performance in the studied environments. The SEM images showed plastic deformation, material dissolution and pitting corrosion as the shear stress increased and on the introduction of silica sand.

Improving the Tribological Properties of Ti6Al4V Alloy with Multi-walled Carbon Nanotube Additions

The effects of varied weight fractions of multi-walled carbon nanotubes (MWCNTs) on the dry sliding wear characteristics of Ti6Al4 V were investigated in this study. Dry sliding wear tests were conducted at three applied load levels of 5, 15 and 25 N on spark plasma sintered unreinforced Ti6Al4V alloy and MWCNTs reinforced Ti6Al4V composites containing 1, 2 and 3 wt% MWCNTs respectively sintered at 1000 °C. The ball-on-flat test configuration with tungsten carbide (WC) as the counterface material was used during the tests. Wear scars and debris were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) techniques. It was observed that the wear resistances and coefficients of friction for the composites were significantly improved over that of the unreinforced Ti6Al4V alloy. Worn surface analysis showed the prevalent wear mechanisms at low and high applied loads were adhesive and abrasive wears respectively. Wear debris analysis by EDX showed the presence of tungsten (W), which suggests a transfer layer of the counterface material. Wear resistance enhancement in the composites was directly related to the extent of MWCNTs dispersion within Ti6Al4V matrix, the interfacial bond strength between the matrix and the reinforcement, as well as the presence of hard TiC interfacial product.

Synthesis of Ti-6Al-4V alloy with nano-TiN microstructure via spark plasma sintering technique

The effect of nano-TiN dispersion strengthened Ti-6Al-4V via spark plasma sintering method has been investigated. Ti-6Al-4V with 4 vol. percent of nano-TiN were mixed in a Turbula shaker mixer for 8 h at a speed of 49 rpm and the admixed powders were sintered at sintering temperature range of 1000 - 1100 °C, holding time of 10-30 mins, heating rate of 100 °C/min under an applied pressure of 50 MPa. The morphology of the as-received and sintered compacts was examined by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and phase analysis was done by X-ray diffractometry (XRD). The sintered compacts without nano-TiN reveal lamellar structure while reinforced Ti-6Al-4V with nano-TiN shows a bimodal structure and titanium nitride has a great influence on a grain growth at high temperature. Furthermore, the microstructural formation mechanism was investigated. With the addition of the content of Ti-6Al-4V with 4 vol.% of nano-TiN, the micro-hardness also improved and this was due to homogenous distribution of TiN in Ti-6Al-4V matrix.

Effectiveness of biohydrometallurgy for sustainable development in the African minerals industry: a case study with a low grade ore from Nigeria

Abstract The effectiveness of the application of biohydrometallurgical processes in the sustainable development of the minerals industry is discussed with specific reference to the Nigerian minerals industry. The state of the Nigerian minerals industry is evaluated. Assessment of available processing and recovering routes is made, and the influencing factors for the adoption of the biohydrometallurgical processing approach are reviewed. A case study of the biohydrometallurgical processing of a bulk complex sulphide ore from Ishiagu, in the South Eastern part of Nigeria, is presented. Results showed that a biohydrometallurgical approach is suitable and effective for processing the ore and can therefore be considered, applied and adopted to processing of other ore deposits from Africa.