Effect of temperature on specific retention volumes of selected volatile organic compounds using the gas-liquid chromatographic technique revisited

This paper is a continuation of our interest in the influence of temperature on specific retention volumes and the resulting infinite dilution activity coefficients. This has a direct effect in the design of absorption and stripping columns for the abatement of volatile organic compounds. The interaction of 13 volatile organic compounds (VOCs) with polydimethylsiloxane (PDMS) at varying temperatures was studied by gas liquid chromatography (GLC). Infinite dilution activity coefficients and specific retention volumes obtained in this study were found to be in agreement with those obtained from static headspace and group contribution methods by the authors as well as literature values for similar systems. Temperature variation also allows for transport calculations for different seasons. The results of this work confirm that PDMS is well suited for the scrubbing of VOCs from waste gas streams

Effect of oxygen and micro-cracking on the flotation of low grade nickel sulphide ore

This study investigated the effect of oxygen and micro-cracking on the flotation of low grade nickel sulphide ore. The ore treated contained serpentine minerals which have a history of being difficult to process efficiently. The use of oxygen as a bubbling gas has been noted to be effective because it increases the pulp potential. The desired effect of micro cracking the ore is that the nickel sulphide minerals will become activated and this activation will render these minerals more susceptible to react with potassium amyl xanthate collectors, resulting in a higher recovery of nickel and hinder the recovery of other undesired minerals contained in the ore. Higher nickel recoveries were obtained when pure oxygen was used as a bubbling gas rather than the conventional air. Microwave cracking favored the recovery of nickel

Reagent optimization across a UG2 plant

Reagent optimization is very important in the recovery of valuable metals from their ore via flotation. This is particularly important for large platinum operations where correct reagent regime and addition system can provide improvement opportunities in recovery and grade. Also reagent optimization can reduce reagent costs for the rougher, scavenger and cleaner flotation units. Reagents were optimized in the flotation of hot floats from the plant at laboratory scale. It was found that in order to save cost, the collector and depressant must be reduced in the roughers and cleaners respectively. This report presents results and some practical considerations that must be taken into account to optimise reagent usage

Effect of pH on the recovery and grade of base metal sulphides (PGMs) by flotation

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

Emergence and spread of two SARS-CoV-2 variants of interest in Nigeria.

Identifying the dissemination patterns and impacts of a virus of economic or health importance during a pandemic is crucial, as it informs the public on policies for containment in order to reduce the spread of the virus. In this study, we integrated genomic and travel data to investigate the emergence and spread of the SARS-CoV-2 B.1.1.318 and B.1.525 (Eta) variants of interest in Nigeria and the wider Africa region. By integrating travel data and phylogeographic reconstructions, we find that these two variants that arose during the second wave in Nigeria emerged from within Africa, with the B.1.525 from Nigeria, and then spread to other parts of the world. Data from this study show how regional connectivity of Nigeria drove the spread of these variants of interest to surrounding countries and those connected by air-traffic. Our findings demonstrate the power of genomic analysis when combined with mobility and epidemiological data to identify the drivers of transmission, as bidirectional transmission within and between African nations are grossly underestimated as seen in our import risk index estimates

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 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

Optimization and characterization of biofuel from waste cooking oil

Abstract: Waste cooking oil (WCO) is regarded as one of the cheapest feedstock for the production of biodiesel. The waste cooking oil used in this study was prepared in the laboratory by adding 5 wt. % of oleic acid into 95 wt. % of soybeans oil. 10 wt. % of titania-supported-magnesium oxide catalyst (MgO/TiO2) used was prepared by incipient wetness impregnation and characterized using XRF and XRD. These materials were tested and used as catalyst for the conversion of waste vegetable oil to biodiesel in the presence of methanol and hexane as co-solvents. Methanol to hexane mole ratio of 1:1 was employed in the transesterification process. The effects of reaction time, reaction temperature and hexane co-solvent on the waste vegetable oil conversion have been established. The 1HNMR analysis was used to estimate the waste vegetable oil conversion and the average molecular formula of fatty acid methyl esters (FAME) produced. It was observed that the oil conversion increased with the increase in reaction time, reaction temperature and use of hexane as co-solvent