R. O. Akinyeye

Synthesis and Characterization of Sulfonated Polyanilines and Application in Construction of a Diazinon Biosensor

A series of sulfonated polyaniline/derivatized polyaniline nanocomposites was chemically synthesized in the presence of anthracene and naphthalene sulfonic acids. UV-vis and FTIR results indicated the emergence of new bands at 420 and 700 nm and 1100 cm−1 in their spectra, respectively, meaning the dopant/polymer intercalations involved electronic interactions between dopant/polymer sub-lattices. The electroactive composites displayed moderately fast electrode kinetics. A composite-based biosensor for hydrogen peroxide reached a steady state current of 9.2 and 5.3 µA, and when fine-tuned for diazinon detection gave % inhibitions to be 41 and 81% for the polyaniline and poly-o-methoxyaniline biosensors, respectively.

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.

Natural weathering in dry disposed ash dump: Insight from chemical, mineralogical and geochemical analysis of fresh and unsaturated drilled cores

Some existing alternative applications of coal fly ash such as cement manufacturing; road construction; landfill; and concrete and waste stabilisation use fresh ash directly collected from coal-fired power generating stations. Thus, if the rate of usage continues, the demand for fresh ash for various applications will exceed supply and use of weathered dry disposed ash will become necessary alternative. As a result its imperative to understand the chemistry and pH behaviour of some metals inherent in dry disposed fly ash. The bulk chemical composition as determined by XRF analysis showed that SiO2, Al2O3 and Fe2O3 were the major oxides in fresh ash and unsaturated weathered ashes. The unsaturated weathered ashes are relatively depleted in CaO, Fe2O3, TiO2, SiO2, Na2O and P2O5 due to dissolution and hydrolysis caused by chemical interaction with ingressing CO2 from the atmosphere and infiltrating rain water. Observed accumulations of Fe2O3, TiO2, CaO, K2O, Na2O and SO3 and Zn, Zr, Sr, Pb, Ni, Cr and Co in the lower layers indicate progressive downward movement through the ash dump though at a slow rate. The bulk mineralogy of unsaturated weathered dry disposed ash, as determined by XRD analysis, revealed quartz and mullite as the major crystalline phases; while anorthite, hematite, enstatite, lime, calcite, and mica were present as minor mineral phases. Pore water chemistry revealed a low concentration of readily soluble metals in unsaturated weathered ashes in comparison with fresh ash, which shows high leachability. This suggests that over time the precipitation of transient minor secondary mineral phases; such as calcite and mica might retard residual metal release from unsaturated weathered ash. Chloride and sulphate species of the water soluble extracts of weathered ash are at equilibrium with Na+ and K+; these demonstrate progressive leaching over time and become supersaturated at the base of unsaturated weathered ash. This suggests that the ash dump does not encapsulate the salt or act as a sustainable salt sink due to over time reduction in pore water pH. The leaching behaviours of Ca, Mg, Na+, K+, Se, Cr and Sr are controlled by the pH of the leachant in both fresh and unsaturated weathered ash. Other trace metals like As, Mo and Pb showed amphoteric behaviour with respect to the pH of the leachant. The precipitation of minor quantities of secondary mineral phases in the unsaturated weathered ash has significant effects on the acid susceptibility and leaching patterns of chemical species in comparison with fresh ash. The unsaturated weathered ash had lower buffering capacity at neutral pH (7.94-8.00) compared to fresh (unweathered) ash. This may be due to the initial high leaching/flushing of soluble basic buffering constituents from fly ash after disposal. The overall results of the acid susceptibility tests suggest that both fresh ash and unsaturated weathered ash would release a large percentage of their chemical species when in contact with slightly acidified rain. Proper management of ash dumps is therefore essential to safeguard the environmental risks of water percolation in different fly ashes behaviour.

The Leachability of Major Elements at Different Stages of Weathering in Dry Disposed Coal Fly Ash

Large quantities of solid residue are generated by coal-fired power stations in many parts of the World. The disposal and management of the unused fly ash remains a major problem to the environment. The weathered dry disposed ash cores comprise of major element constituents such as Al, Si, Ca, Mg, Fe, Mn, Na and K. The mobility patterns and mineralogical associations of major elements in weathered dry disposed ash dumps aged 1-year-old, 8-year-old and 20-year-old from a coalfired power station in South Africa were investigated using a modified sequential extraction scheme. The extraction sequence was as follows: (1) water soluble, (2) exchangeable, (3) carbonate, (4) Fe and Mn and (5) residual. A total acid digestion was carried out on the original sample prior to extraction to validate the extraction procedure. The distribution of Si, Fe, Mn, Ca, Mg, Na, and K in 59 drilled ash core samples was determined by inductively coupled plasma mass spectrometry. The leachability of the seven elements from different fractions proved to be different; so various distribution patterns have been achieved. The highest concentration of analytes is recorded in the water soluble, exchangeable, and carbonates of 1-year-old ash cores hence it is the least leached. The concentration of each element in each fraction was calculated as a percentage of the total metal content for the 1-year-old ash cores. The average amount of the major elements in the easily soluble fractions of 1-year-old ash core samples are: water soluble: Na (21%) . Ca (10.2%) . Mn (8.4%) . Si (4.0%) . K (2.58%) . Mg (0.05%) . Al (0.003%) . Fe (0.001%), exchangeable: Ca (37.04%) . Mg (12.6%) . Na (11.26%) . Mn (10.3%) . K (3.17%) . Si (1.6%) . Al (0.27%) . Fe (0.33%), carbonate: Mn (41.21%) . Ca (37.9%) . Mg (32.9%) . Al (29.25%) . Si (25.39%) . Fe (21.39%) . Na (2.6%) . K (2.23%). The mobility of major elements in the weathered ash dumps are influenced by heterogeneity in the ash dump, inhomogeneous continuous brine irrigation and chemical interaction of ash cores with ingressed CO2 from atmosphere and percolating rain water. f 2011 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 15 March 2011; Received in revised form 30 May 2011; Accepted 2 June 2011

Chemical Synthesis and Morphology of β–Naphthalene Sulfonic Acid‐Doped Polypyrrole Micro/Nanotubes

Abstract A preliminary result of the morphology and yield of chemically synthesized polypyrrole (PPY) using β–naphthalene sulfonic acid (NSA) and ammonium peroxodisulphate (APS) in aqueous medium is presented. Various micro/nanotubes were obtained using different dopant/monomer (D/M) ratios and temperature settings. Similar but shorter and sheet‐like nanostructures were obtained without the use of surfactant NSA; with a fibre‐like, loose and admixed physical outlook. The percentage yield (m/v) of the doped PPY was greater than that from the undoped, being 27–44 and 18–20, respectively with higher values obtained from the low temperature synthesis. The highest percentage yield of 44 was obtained from a D/M ratio of 0.8.

Distributional Fate of Elements during the Synthesis of Zeolites from South African Coal Fly Ash

The synthesis of zeolites from South African coal fly ash has been deemed a viable solution to the growing economical strain caused by the disposal of ash in the country. Two synthesis routes have been studied thus far namely the 2-step method and the fusion assisted process. Fly ash contains several elements originating from coal which is incorporated in the ash during combustion. It is vital to determine the final destination of these elements in order to unveil optimization opportunities for scale-up purposes. The aim of this study was to perform a material balance study on both synthesis routes to determine the distributional fate of these elements during the synthesis of zeolites. Zeolites were first synthesized by means of the two synthesis routes. The composition of all raw materials and products were determined after which an overall and elemental balance were performed. Results indicated that in the 2-step method almost all elements were concentrated in the solid zeolite product while during the fusion assisted route the elements mostly report to the solid waste. Toxic elements such as Pb, Hg, Al, As and Nb were found in both the supernatant waste and washing water resulting from each synthesis route. It has also been seen that large quantities of Si and Al are wasted in the supernatant waste. It is highly recommended that the opportunity to recycle this liquid waste be investigated for scale-up purposes. Results also indicate that efficiency whereby Si and Al are extracted from fused ash is exceptionally poor and should be optimized.

Mineralogy and Mobility Pattern of Trace Metals in Brine Irrigated Dry Disposed Weathered Coal Fly Ash

This study determines mineralogical association of trace elements in the ash core samples and provides insight into various factors that promote their mobility and eventual release into surface and groundwater systems. Fly ash from a power station ash dump in Mpumalanga Province (South Africa) was characterized using X-ray diffraction and X-ray fluorescence. A five-step sequential extraction procedure was used to determined mineralogical association of elements as a function of depth in the ash dump. The dry disposed ash cores are sialic in chemical composition. The mineral peak height as revealed by X-ray diffraction analysis showed variations due to heterogeneity in the ash dump and in homogenous continuous brine irrigation. The sequential extraction results showed that some trace elements are moving in a leaching pathway through the fly ash in the water soluble fraction. Toxic analytes are present in water soluble, exchangeable, and carbonate fractions. Observed Pb concentration maxima in the carbonate fraction of ash cores suggests mobility due to reduction in the pore water pH. A relatively high concentration of As and Se in the exchangeable fraction indicates their possible release when fly ash comes in contact with slightly acidic rain water. This is of major environmental concern for possible contamination of surface and groundwater systems. The relative enrichment of As and Se in the residual fraction suggests that the dust from 8-year-old brine irrigated ash dump would be toxic to human health. This investigative study demonstrates that reduction in pore water pH, inhomogeneity in the ash dump, continuous brine irrigation, leachate from topsoil, moisture content level, ingressed CO2 from atmosphere, and percolating rain water are factors that promote trace metal mobility and leaching in the brine irrigated dry disposed ash dump.

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.

Laboratory Study on the Mobility of Major Species in Fly Ash-Brine Co-disposal Systems: Up-flow Percolation Test

Apart from the generation of fly ash, brine (hyper-saline wastewater) is also a waste material generated in South African power stations as a result of water re-use. These waste materials contain major species such as Al, Si, Na, K, Ca, Mg, Cl and SO4. The co-disposal of fly ash and brine has been practiced by some power stations in South Africa with the aim of utilizing the fly ash to capture the salts in brine. The effect of the chemical interaction of the species contained in both fly ash and brine, when co-disposed, on the mobility of species in the fly ash–brine systems is the focus of this study. The up-flow percolation test was employed to determine the mobility of some major species in the fly ash–brine systems. The results of the analysed eluates from the up-flow percolation tests revealed that some species such as Al, Ca and Na were leached from the fly ash into the brine solution while some species such as Mg, Cl and SO4 were removed to some extent from the brine solution during the interaction with fly ash. The pH of the up-flow percolation systems was observed to play a significant role on the mobility of major species from the fly ash–brine systems. The study showed that some major species such as Mg, Cl and SO4 could be removed from brine solution using fly ash when certain amount of brine percolates through the ash.

Chemical Partitioning and Mobility of Trace Elements in Dry Disposed Weathered Ash Conditioned with high-Saline Effluents

We investigated the mobility of inorganic elements in the ash dump due to chemical interaction of weathered dry disposed ash conditioned with high-saline effluents and ingressed CO2 from atmosphere and percolating rainwater. Drilled ash core samples collected from dry disposed ash dump at a South African coal-burning power station were characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. A modified sequential extraction procedure was selected to determine the mineralogical association of the investigated elements in the 1-year-old drilled ash cores. Major mineral phases are quartz and mullite and other minor phases included hematite, lime, calcite, anorthite, mica, and enstatite. Mica and calcite in the ash cores is attributed to carbonation process, which led to long-term reduction in pore water pH. The 2-week-old ash cores are sialic but the 1-year-old ash cores were both sialic and ferrocalsialic in chemical composition. The ferrocalsialic nature of 1-year-old ash cores could be attributed to drastic changes in feed coal in the power station. The chemical index of alteration (CIA) and chemical index of weathering (CIW) values suggest a relatively high degree of weathering. The changes in CIA and CIW values in the ash cores depend on the pore water pH, leaching rate, carbonation process, and possibly the conversion of the alkali and alkali earth metals into carbonates. Multivariate analysis results suggest that the major oxides and carbon percent show differences and have a greater contribution to the differentiation in the 1-year-old ash cores. Trace elements such as Mo, Cr, and Se show high mobility but As, B, and Pb exhibit fairly low mobility in the water-soluble fraction. A considerable mobility of trace elements in the exchangeable and carbonate fractions is attributed to the alkaline nature and pore water pH. A decreasing response of As, Mo, Cr, and Pb in the reducible fraction with depth suggests immobility attributed to coprecipitation with the Feand Mn-oxide phases. On the contrary, the increasing response of Pb, Mo, and B in the carbonate fraction with depth implies mobility due to dissolution and flushing of soluble major chemical phases, as evident in the pore water pH. A considerable amount of B and Pb are concentrated in the residual fraction of 1-year-old ash cores. This suggests that, under natural settings, these elements will not be released in solution over a long time; therefore, they are not considered to be an environmental risk. f 2013 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 16 March 2013; Received in revised form 16 September 2013; Accepted 17 September 2013