Olanrewaju Fatoba

The leaching behaviour and geochemical fractionation of trace elements in hydraulically disposed weathered coal fly ash

A five-step sequential extraction (SE) procedure was used to investigate the leaching behaviour and geochemical partitioning of the trace elements As, Zn, Pb, Ni, Mo, Cr and Cu in a 20-year-old fly ash (FA) dump. The weathered FA, which was hydraulically co-disposed with salt laden brine in slurry form (FA: brine ratio of 1:5), was analyzed and compared with fresh FA. The weathered FA samples were collected from three cores, drilled at a coal-fired power station in the Republic of South Africa while the fresh FA sample was collected from the hoppers in the ash collection system at the power station. The FA samples were sequentially leached using: ultrapure water; ammonium acetate buffer solution (pH 7); ammonium acetate buffer solution (pH 5); hydroxylamine hydrochloride in nitric acid (pH 2) and finally the residues were digested using a combination of HClO4: HF: HNO3 acids. Digestion of as received (unleached) FA samples was also done using a combination of HClO4: HF: HNO3 acids in order to determine the total metal content. The trace element analysis was done using ICP-OES (Varian 710-ES). The SE procedure revealed that the trace elements present in the fresh FA and the weathered FA samples obtained from the three cores could leach upon exposure to different environmental conditions. The trace elements showed continuous partitioning between five geochemical phases i.e., water soluble fraction, exchangeable fraction, carbonate fraction, Fe and Mn fraction and residual fraction. Although the highest concentration of the trace elements (ranging 65.51%–86.34%) was contained in the residual fraction, a considerable amount of each trace element (ranging 4.42%–27.43%) was released from the labile phases (water soluble, exchangeable and carbonate fractions), indicating that the trace species readily leach from the dumped FA under environmental conditions thus pose a danger to the receiving environment and to groundwater.

Electrospinning: Polymer Nanofibre Adsorbent Applications for Metal Ion Removal

In recent decades, electrospun nanofibres have been applied to different potential fields such as sensor devices, tissue engineering scaffolds, wound dressing, filtration, drug delivery, etc. and significant review papers have been published in these fields. However, the use of electrospun nanofibres in metal ion adsorption is emerging and comparatively innovative. Nanofibre materials hold great potential in advancing the growth of metallurgical technologies and progress for the separation of metallic ions from various sources. The physico-chemical removal processes of adsorption use nanofibres due to their large surface area to volume ratio and the availability of a wide variety of chemical and morphological modification methods. In this review paper, research and developments related to electrospun polymer nanofibre for metal ion removal is presented. The review highlights the emerging and increasing use of electrospun nanofibres for metal ion adsorption especially for hazardous metals. Fundamental understanding of the electrospinning fabrication process, working parameters as they affect fibre morphologies, solvents and polymers used in electrospinning is discussed. This work summarizes the current status of process technique development and ideas in the research and use of electrospun nanofibres in heavy metal ion adsorption to address environmental problems from contaminated water.

Surface-modified polyacrylonitrile nanofibres as supports

Polyacrylonitrile nanofibres (PAN-nfs) are one of the most studied nanofibres because of their excellent characteristics, such as good mechanical strength, chemical resistance, and good thermal stability. Due to the easy dissolution in polar organic solvents, PAN-nfs are mostly produced via electrospinning technique. The electrospun PAN-nfs surfaces are relatively in-active and hydrophobic, and, therefore, hinder some potential applications; however, chemical surface modification reactions, such as amination, reduction, hydrolysis, and amidoximation, have been carried out on them. These reactions bring about functional groups, such as amine, hydroxyl, carboxylic, imine etc, to the surface PAN-nfs and invariably make their surfaces active and hydrophilic. The surface-modified PAN-nfs have been used as supports for organic compounds, enzymes, and antibodies in biological studies. They have also been used for immobilization of various organic ligands for adsorption of metal ions in water. Furthermore, because of their ability to complex metal ions, several surface-modified PAN-nfs have also been used as supports for transition metal catalysts in Fenton’s chemistry.

Review of the methods for determination of reactive oxygen species and suggestion for their application in advanced oxidation induced by dielectric barrier discharges

Advanced oxidation processes (AOPs) particularly non-thermal plasmas based on electrical discharges have been widely investigated for water and wastewater treatment. Dielectric barrier discharges (DBDs) generate large amounts of selective and non-selective reactive oxygen species (ROS) such as ozone, hydrogen peroxide, atomic oxygen, superoxide molecular anions and hydroxyl radicals, having been proved to be efficient for water decontamination among various forms of electrical discharge systems. The detection and quantification methods of these oxygen species in non-thermal plasmas have been reviewed. However, their application in dielectric barrier discharge has not been well studied. It is therefore imperative to summarise the various detection and quantification methods for oxygen-based species determination in AOPs, aqueous systems and non-thermal plasma processes. Thereafter, reviewed methods are suggested for the determination of ROS in DBD configurations to understand the consumption trend of these oxidants during treatment of water effluents and to evaluate the performance of the treatment reactor configuration towards the degradation of targeted pollutants.

Synthesis, characterization and photocatalytic activity of Ag metallic particles deposited carbon-doped TiO2 nanocomposites supported on stainless steel mesh

In this present work, post deposition of metallic Ag nanoparticles on carbon-doped TiO2 nanocomposites supported on stainless steel mesh was achieved via a combination of sol–gel and thermal evaporation techniques. Poly acrylonitrile dissolved in dimethyl formamide and titanium tetra chloride was used as a carbon and titanium precursor, respectively. The photocatalytic activity of the prepared supported catalysts was evaluated by the degradation of an aqueous solution of methylene blue as a model pollutant under ultra-violet light irradiation. The prepared photocatalysts were characterized by several analytical techniques such as high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, Brunauer–Emmett–Teller measurements, X-ray photoelectron spectroscopy and X-ray diffraction. The XRD patterns and HRTEM micrographs confirmed the formation of a highly crystalline pure anatase TiO2 phase irrespective of the deposited metallic Ag particles. The Brunauer–Emmett–Teller N2 adsorption–desorption analysis revealed that the specific surface area of supported carbon-doped TiO2 nanocomposites without silver was 152 and 160 m2/g for metallic Ag deposited carbon-doped TiO2 nanocomposites. The X-ray photoelectron spectroscopy profile of the photocatalysts revealed the existence of Ti in oxidation state of +4 and metallic Ag in zero state, respectively. The results revealed that the percentage methylene blue removed was dependent on the amount of silver deposited and the catalyst surface area. The supported metallic Ag particles deposited carbon-doped TiO2 nanocomposites demonstrated 10.8% higher activity than the carbon-doped TiO2 nanocrystals without metallic Ag. The excellent reusability and stability of the Ag deposited carbon-doped TiO2 nanocomposites and high photocatalytic behavior after four consecutive applications was determined and methylene blue removal rate was maintained.Graphical Abstract

Elemental composition of fly ash: a comparative study using nuclear and related analytical techniques / Skład pierwiastkowy popiołów lotnych: studium przypadku z wykorzystaniem metod nuklearnych i analitycznych

Abstract Epithermal neutron activation analysis along with ICP-OES, LA ICP-MS, and XRF were used to determine the elemental composition of coal fly ash from the Malta coal power station in the Mpumalanga province of South Africa. A total of 54 major, trace and rare earth elements were obtained by the four analytical techniques. The results were compared and the discrepancies discussed to show the merits and drawbacks of each of the techniques. It was shown that the elemental content of this particular coal fly ash are of the same order as the NIST standard reference material Coal Fly Ash 1633b. Abstrakt W celu określenia składu pierwiastkowego popiołów lotnych z elektrowni węglowej Malta w prowincji Mpumalanga w Republice Południowej Afryki wykorzystano epitermalną, neutronową analizę aktywacyjną oraz ICP-OES, LA ICP-MS i XRF. Za pomocą czterech techniki analitycznych oznaczono stężenia 54 głównych i śladowych pierwiastków oraz pierwiastków ziem rzadkich. Wyniki porównano, a także opisano różnice pokazujące zalety oraz wady każdej z wykorzystanych metod. Wykazano, że skład pierwiastkowy popiołu lotnego jest porównywalny ze składem standardowego materiału odniesienia NIST Węgiel Popiół Lotny 1633b.

Long-term brine impacted fly ash, Part II: Mobility of major species in the ash residues

The leaching of major species from fly ash is a function of the pH of the solution in contact with the fly ash. The aim of this study was to determine the effect of the pH of the leachant on the leaching of species from the ash residues recovered after the long-term fly ash–brine interactions. Acid neutralization capacity (ANC) tests using solutions of different pH values ranging from the initial pH of the ash residues (11–12) to pH 4 were employed in the leaching experiments. The ANC tests revealed that the release of major species from the ash residues depended on the pH of the leachants except for Na and Cl, where the significant concentrations leached were independent of the solution pH. The concentrations of Al and Si in the ANC leachates were very high at pH below 6 while Ca, K, Sr, Mg and B were immediately mobilized from the brine impacted fly ash when in contact with de-ionized water, and leaching increased as the pH decreased. The concentration of SO4 leached from the brine impacted ash residues at high pH was high, and the leaching increased with decrease in the pH of the leachant. This study shows that most of the major elements captured in the ash residues could be mobilized when in contact with aqueous solutions of various pH. This reveals that the co-disposal of fly ash and brine may not be the best practice as the major elements captured in the ash residues could leach over time.