Research Articles (ENS)

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Synthesis of hydroxy sodalite from coal fly ash for biodiesel production from waste-derived maggot oil
(MDPI, 2019) Shabani, Juvet Malonda; Babajide, Omotola; Petrik, Leslie
Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents conventionally used as feedstocks. In the current study, hydroxy sodalite (HS) zeolite samples were synthesised from coal fly ash feedstock by a direct hydrothermal synthesis method. The effects of hydrothermal crystallisation synthesis time on phase crystallinity, crystal size, and morphology of the formed HS were investigated. The prepared samples were characterised using XRD, SEM, EDS and FT-IR techniques. The XRD results of the samples prepared with varying synthesis times confirmed the formation of HS from low to high phase purity and crystallinity from 11 to over 98%. The SEM results reflected gradual variation in crystal morphology, of which highly crystalline HS samples were associated with hexagonal-cubic and cubic-platelet crystals.
Hall measurements on carbon nanotube paper modified with electroless deposited platinum
(Springer, 2010) Petrik, Leslie; Ndungu, Patrick; Iwuoha, Emmanuel
Carbon nanotube paper, sometimes referred to as bucky paper, is a random arrangement of carbon nanotubes meshed into a single robust structure, which can be manipulated with relative ease. Multi-walled carbon nanotubes were used to make the nanotube paper, and were subsequently modified with platinum using an electroless deposition method based on substrate enhanced electroless deposition. This involves the use of a sacrificial metal substrate that undergoes electro-dissolution while the platinum metal deposits out of solution onto the nanotube paper via a galvanic displacement reaction. The samples were characterized using SEM/EDS, and Hall-effect measurements. The SEM/EDS analysis clearly revealed deposits of platinum (Pt) distributed over the nanotube paper surface, and the qualitative elemental analysis revealed co-deposition of other elements from the metal substrates used.
Fusion-assisted hydrothermal synthesis and post-synthesis modification of mesoporous hydroxy sodalite zeolite prepared from waste coal fly ash for biodiesel production
(MDPI, 2022) Shabani, Juvet Malonda; Ameh, Alechine E.; Petrik, Leslie
Increases in biodiesel prices remains a challenge, mainly due to the high cost of conventional oil feedstocks used during biodiesel production and the challenges associated with using homogeneous catalysts in the process. This study investigated the conversion of waste-derived black soldier fly (BSF) maggot oil feedstock over hydroxy sodalite (HS) zeolite synthesized from waste coal fly ash (CFA) in biodiesel production. The zeolite product prepared after fusion of CFA followed by hydrothermal synthesis (F-HS) resulted in a highly crystalline, mesoporous F-HS zeolite with a considerable surface area of 45 m2/g. The impact of post-synthesis modification of the parent HS catalyst (F-HS) by ion exchange with an alkali source (KOH) on its performance in biodiesel production was investigated. The parent F-HS zeolite catalyst resulted in a high biodiesel yield of 84.10%, with a good quality of 65% fatty acid methyl ester (FAME) content and fuel characteristics compliant with standard biodiesel specifications. After ion exchange, the modified HS zeolite catalyst (K/F-HS) decreased in crystallinity, mesoporosity and total surface area.
A comparative review of decision support tools routinely used by selected transboundary River Basin Organisations
(Taylor and Francis, 2021) Brown, Cate; Hassan, Bukhari
As human pressures on water resources increase, the data and decision support (DS) tools used in the governance, development and management of transboundary rivers are likely to become increasingly important. There are no universal, standardised selection processes or designs for these tools, and so it is up to individual River Basin Organisations (RBOs) to decide what to include in their capacities. This desktop study provides a broad comparative analysis of the suites of DS numerical modelling tools developed and utilised by five intergovernmental transboundary RBOs that advise their member states in the management of their shared water resources: the Permanent Okavango River Basin Water Commission; the Orange-Senqu River Commission; the Nile Basin Initiative; the Zambezi Watercourse Commission; and the Mekong River Commission. These DS tools were reviewed against the information required to enable the kinds of comprehensive assessments of proposed basin management and development plans defined in their respective agreements, which include not only hydrological parameters, but also environmental and social considerations. A review of the model development timelines showed that prior to 2000, little capacity existed in modelling of hydrological, ecosystem, and social components of the river, but that these gaps have been addressed in recent years.
Organic nanostructured materials for sustainable application in next generation solar cells
(MPDI, 2021) Mabindisa, Rorisang; Tambwe, Kevin; Mciteka, Lulama
Meeting our current energy demands requires a reliable and efficient renewable energy source that will bring balance between power generation and energy consumption. Organic photovoltaic cells (OPVs), perovskite solar cells and dye-sensitized solar cells (DSSCs) are among the next-generation technologies that are progressing as potential sustainable renewable energy sources. Since the discoveries of highly conductive organic charge-transfer compounds in the 1950s, organic semiconductors have captured attention. Organic photovoltaic solar cells possess key characteristics ideal for emerging next-generation technologies such as being nontoxic, abundant, an inexpensive nanomaterial with ease of production, including production under ambient conditions. In this review article, we discuss recent methods developed towards improving the stability and average efficiency of nanostructured materials in OPVs aimed at sustainable agriculture and improve land-use efficiency. A comprehensive overview on developing cost-effective and user-friendly organic solar cells to contribute towards improved environmental stability is provided. We also summarize recent advances in the synthetic methods used to produce nanostructured active absorber layers of OPVs with improved efficiencies to supply the energy required towards ending poverty and protecting the planet
The H I intensity mapping bispectrum including observational effects
(2021-07-30) Cunnington, Steven; Watkinson, Catherine; Pourtsidou, Alkistis
The bispectrum is a three-point statistic with the potential to provide additional information beyond power spectra analyses of survey data sets. Radio telescopes that broadly survey the 21-cm emission from neutral hydrogen (H I) are a promising way to probe LSS and in this work we present an investigation into the H I intensity mapping (IM) bispectrum using simulations. We present a model of the redshift space H I IM bispectrum including observational effects from the radio telescope beam and 21-cm foreground contamination. We validate our modelling prescriptions with measurements from robust IM simulations, inclusive of these observational effects. Our foreground simulations include polarization leakage, on which we use a principal component analysis cleaning method. We also investigate the effects from a non-Gaussian beam including side-lobes. For a MeerKAT-like single-dish IM survey at z = 0.39, we find that foreground removal causes an 8 per cent reduction in the equilateral bispectrum’s signal-to-noise ratio, whereas the beam reduces it by 62 per cent. We find our models perform well, generally providing χ2 dof ∼ 1, indicating a good fit to the data. Whilst our focus is on post-reionization, single-dish IM, our modelling of observational effects, especially foreground removal, can also be relevant to interferometers and reionization studies.
Rare earths’ recovery from phosphogypsum: An overview on direct and indirect leaching techniques
(MDPI, 2021) Mukaba, J.-L.; Eze, C.P.; Pereao, O.; Petrik, Leslie
The need for rare earth elements (REEs) in high-tech electrical and electronic-based materials is vital. In the global economy, deposits of natural REEs are limited except for countries such as China, which has prompted current attempts to seek alternative resources of REEs. This increased the dependence on major secondary rare earth-bearing sources such as scrap alloy, battery waste, spent catalysts, fly ash, spent magnets, waste light-emitting diodes (LEDs), and phosphogypsum (PG) for a substantial recovery of REEs for use. Recycling REEs from these alternative waste sources through hydrometallurgical processes is becoming a sustainable and viable approach due to the low energy consumption, low waste generation, few emissions, environmental friendliness, and economic feasibility. Industrial wastes such as the PG generated from the production of phosphoric acid are a potential secondary resource of REEs that contains a total REE concentration of over 2000 mg/kg depending upon the phosphate ore from which it is generated. Due to the trace concentration of REEs in the PG (normally < 0.1% wt.) and their tiny and complex occurrence as mineral phases the recovery process of REE from PG would be highly challenging in both technology and economy. Various physicochemical pre-treatments approaches have been used up to date to up-concentrate REEs from PG prior to their extraction. Methods such as carbonation, roasting, microwave heating, grinding, or recrystallization have been widely used for this purpose. This present paper reviews recent literature on various techniques that are currently employed to up-concentrate REs from PG to provide preliminary insight into further critical raw materials recovery. In addition, the advantages and disadvantages of the different strategies are discussed as avenues for the realization of REE recovery from PG at a larger scale. In all the different approaches, recrystallization of PG appears to show promising advantages due to both high REE recovery as well as the pure PG phase that can be obtained. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Chitosan/PEO nanofibers electrospun on metallized track-etched membranes: fabrication and characterization
(Elsevier, 2021) Pereao, O; Uche, C; Bublikov, P.S
The development of next-generation adsorption, separation, and filtration materials is growing with an increased research focus on polymer composites. In this study, a novel blend of chitosan (CS) and polyethylene oxide (PEO) nanofiber mats was electrospun on titanium (Ti)-coated polyethylene terephthalate (PET) track-etched membranes (TMs) with after-treatment by glutaraldehyde in the vapor phase for enhancing the nanofiber stability by crosslinking. The prepared composite, titanium-coated track-etched nanofiber membrane (TTM-CPnf) was characterized by Fourier transform infra-red (FTIR), water contact angle, and scanning electron microscopy (SEM) analyses. Smooth and uniform CS nanofibers with an average fiber diameter of 156.55 nm were produced from a 70/30 CS/PEO blend solution prepared from 92 wt. % acetic acid and electrospun at 15 cm needle to collector distance with 0.5 mL/h flow rate and an applied voltage of 30 kV on the TTM-CPnf. Short (15 min) and long (72 h)-term solubility tests showed that after 3 h, crosslinked nanofibers were stable in acidic (pH = 3), basic (pH = 13), and neutral (pH = 7) solutions. The crosslinked TTM-CPnf material was biocompatible based on the low mortality of freshwater crustaceans Daphnia magna. The composite membranes comprised of electrospun nanofiber and TMs proved to be biocompatible and may thus be suitable for diverse applications such as dual adsorption–filtration systems in water treatment.
Treatment of persistent organic pollutants in wastewater using hydrodynamic cavitation in synergy with advanced oxidation process
(Springer, 2017) Badmus, Kassim Olasunkanmi; Tijani, Jimoh O.; Massima, Emile; Petrik, Leslie
Persistent organic pollutants (POPs) are very tenacious wastewater contaminants. The consequences of their existence have been acknowledged for negatively affecting the ecosystem with specific impact upon endocrine disruption and hormonal diseases in humans. Their recalcitrance and circumvention of nearly all the known wastewater treatment procedures are also well documented. The reported successes of POPs treatment using various advanced technologies are not without setbacks such as low degradation efficiency, generation of toxic intermediates, massive sludge production, and high energy expenditure and operational cost. However, advanced oxidation processes (AOPs) have recently recorded successes in the treatment of POPs in wastewater. AOPs are technologies which involve the generation of OH radicals for the purpose of oxidising recalcitrant organic contaminants to their inert end products. This review provides information on the existence of POPs and their effects on humans. Besides, the merits and demerits of various advanced treatment technologies as well as the synergistic efficiency of combined AOPs in the treatment of wastewater containing POPs was reported. A concise review of recently published studies on successful treatment of POPs in wastewater using hydrodynamic cavitation technology in combination with other advanced oxidation processes is presented with the highlight of direction for future research focus.
Quantification of radicals generated in a sonicator
(Iranian Chemical Society, 2016) Fatoba, Ojo O.; Badmus, Kassim Olasunkanmi; Tijani, Jimoh O.; Eze, C.P.
The hydroxyl radical (OH•) is a powerful oxidant produced as a consequence of cavitation in water. It can react nonspecifically in breaking down persistent organic pollutants in water into their mineral form. It can also recombine to form hydrogen peroxide which is very useful in water treatment. In this study, terephthalic acid (TA) and potassium iodide dosimetry were used to quantify and investigate the behaviour of the generated OH radical in a laboratory scale sonicator. The 2-hydroxyl terephthalic acid (HTA) formed during terephthalic acid dosimetry was determined by optical fibre spectrometer. The production rate of HTA served as a means of evaluating and characterizing the OH• generated over given time in a sonicator. The influence of sonicator power intensity, solution pH and irradiation time upon OH• generation were investigated. Approximately 2.2 x 10-9 M s-1 of OH radical was generated during the sonication process. The rate of generation of the OH radicals was established to be independent of the concentration of the initial reactant. Thus, the rate of generation of OH• can be predicted by zero order kinetics in a sonicator.
Desalination and seawater quality at Green Point, Cape Town: A study on the effects of marine sewage outfalls
(Academy of Science of South Africa (ASSAf), 2017) Petrik, Leslie; Green, Lesley; Abegunde, Adeola P.; Zackon, Melissa; Sanusi, Cecilia Y.; Barnes, Jo
This paper presents our collection methods, laboratory protocols and findings in respect of sewage pollution affecting seawater and marine organisms in Table Bay, Cape Town, South Africa, then moves to consider their implications for the governance of urban water as well as sewage treatment and desalination. A series of seawater samples, collected from approximately 500 m to 1500 m offshore, in rock pools at low tide near Granger Bay, and at a depth under beach sand of 300–400 mm, were investigated for the presence of bacteriological load indicator organisms including Escherichia coli and Enterococcus bacteria. A second series of samples comprised limpets (Patella vulgata), mussels (Mytilus galloprovincialis), sea urchins (Tripneustes ventricosus), starfish (Fromia monilis), sea snails (Tegula funebralis) and seaweed (Ulva lactuca), collected in rock pools at low tide near Granger Bay, and sediment from wet beach sand and where the organisms were found, close to the sites of a proposed desalination plant and a number of recreational beaches. Intermittently high levels of microbial pollution were noted, and 15 pharmaceutical and common household chemicals were identified and quantified in the background seawater and bioaccumulated in marine organisms. These indicator microbes and chemicals point to the probable presence of pathogens, and literally thousands of chemicals of emerging concern in the seawater. Their bioaccumulation potential is demonstrated.
Application of nano zinc oxide (nZnO) for the removal of triphenyltin chloride (TPT) from dockyard wastewater
(Water Research Commission, 2014) Ayanda, Olushola S.; Fatoki, Olalekan S.; Adekola, Folahan A.; Petrik, Leslie; Ximba, Bhekumusa J.
The use of triphenyltin chloride (TPT), a persistent organic pollutant, as a biocide has led to serious contamination of the marine environment. The potential of nano zinc oxide (nZnO) for the removal of TPT from contaminated dockyard wastewater was investigated. The adsorption of TPT onto nZnO has been found to depend on the adsorbent dose, contact time, pH, stirring speed, and temperature. Equilibrium data fitted well with the Freundlich model and the experiments showed that 97.0% TPT removal was achieved by treating 0.643 mg·l-1 TPT contaminated dockyard wastewater with 0.5 g nZnO at optimal conditions. The kinetic data for the adsorption process obeyed a pseudo second-order kinetic model, suggesting that the adsorption process is chemisorption. The nZnO investigated in this study showed good potential for the removal of TPT from contaminated dockyard wastewater systems.
Synthesis of zeolites Na-P1 from South African coal fly ash: effect of impeller design and agitation
(MDPI, 2013) Mainganye, Dakalo; Ojumu, Tunde V.; Petrik, Leslie
South African fly ash has been shown to be a useful feedstock for the synthesis of some zeolites. The present study focuses on the effect of impeller design and agitation rates on the synthesis of zeolite Na-P1 which are critical to the commercialization of this product. The effects of three impeller designs (4-flat blade, Anchor and Archimedes screw impellers) and three agitation speeds (150, 200 and 300 rpm) were investigated using a modified previously reported synthesis conditions; 48 hours of ageing at 47 °C and static hydrothermal treatment at 140 °C for 48 hours. The experimental results demonstrated that the phase purity of zeolite Na-P1 was strongly affected by the agitation rate and the type of impeller used during the ageing step of the synthesis process. Although zeolite Na-P1 was synthesized with a space time yield (STY) of 15 ± 0.4 kg d−1m−3and a product yield of 0.98±0.05 g zeolites/g fly ash for each impeller at different agitation speeds, zeolite formation was assessed to be fairly unsuccessful in some cases due the occurrence of undissolved mullite and/or the formation of impurities such as hydroxysodalite with the zeolitic product. This study also showed that a high crystalline zeolite Na-P1 can be synthesized from South African coal fly ash using a 4-flat blade impeller at an agitation rate of 200 rpm during the ageing step at 47 °C for 48 hours followed by static hydrothermal treatment at 140 °C for 48 hours.
Waste minimization protocols for the process of synthesizing zeolites from South African coal fly ash
(MDPI, 2013) Du Plessis, Pieter W.; Ojumu, Tunde V.; Petrik, Leslie
Production of a high value zeolite from fly ash has been shown to be an avenue for the utilization of South African fly ash which presently constitutes a huge disposal problem. The synthesis of zeolites Na-P1 and analcime on a micro-scale has been successful and preliminary investigation shows that scale-up synthesis is promising. However, the post-synthesis supernatant waste generated contains high levels of NaOH that may constitute a secondary disposal problem. A waste minimization protocol was developed to reduce the volume of waste generated with a view to enhancing the feasibility of the scale synthesis. Series of experiments were conducted in 100 mL jacketed batch reactors. Fly ash was reacted with 5 Mol NaOH on a 1:1 mass basis during the aging step, followed by hydrothermal treatment in which ultrapure water was added to the slurry. This study shows that by re-introducing the supernatant waste into the experiments in such a way that it supplies the required reagent (NaOH) for the zeolite synthesis, zeolite Na-P1 and analcime can be synthesized. It also shows that the synthesis process can be altered to allow up to 100% re-use of the supernatant waste to yield high value zeolitic products. This study effectively constructed two protocols for the minimization of waste generated during the synthesis of zeolites from South African coal fly ash. This result could be used to establish a basis for legal and environmental aspects involved in the commission of a full-scale plant synthesizing zeolites NaP1 and analcime.
Synthesis and characterization of carbon doped TiO2 photocatalysts supported on stainless steel mesh by sol-gel method
(Korean Carbon Society, 2017) Tijani, Jimoh O.; Fatoba, Ojo O.; Totito, T. C.; Roos, W. D.; Petrik, Leslie
This study synthesized pure anatase carbon doped TiO2 photocatalysts supported on a stainless steel mesh using a sol-gel solution of 8% polyacrylonitrile (PAN)/dimethylformamide (DMF)/TiCl4. The influence of the pyrolysis temperature and holding time on the morphological characteristics, particle sizes and surface area of the prepared catalyst was investigated. The prepared catalysts were characterized by several analytical methods: high resolution scanning electron microscopy (HRSEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS). The XRD patterns showed that the supported TiO2 nanocrystals are typically anatase, polycrystalline and body-centered tetragonal in structure. The EDS and XPS results complemented one another and confirmed the presence of carbon species in or on the TiO2 layer, and the XPS data suggested the substitution of titanium in TiO2 by carbon. Instead of using calcination, PAN pyrolysis was used to control the carbon content, and the mesoporosity was tailored by the applied temperature. The supported TiO2 nanocrystals prepared by pyrolysis at 300, 350, and 400°C for 3 h on a stainless steel mesh were actual supported carbon doped TiO2 nanocrystals. Thus, PAN/DMF/TiCl4 offers a facile, robust sol-gel related route for preparing supported carbon doped TiO2 nanocomposites.
Plasmonic metal decorated titanium dioxide thin films for enhanced photodegradation of organic contaminants
(Elsevier, 2017) Nyamukamba, Pardon; Tichagwa, Lilian; Ngila, Jane Catherine; Petrik, Leslie
Photocatalysis using titanium dioxide as photocatalyst is an efficient way for the removal of organic contaminants in water using solar energy. In this study, thin films of copper and silver were deposited on fused silica using the thermal evaporation technique. A 100 nm film of titanium dioxide (TiO2) was then deposited on the plasmonic metal films using a sputter coating technique. The opposite order of deposition of the film was also explored. The prepared thin films were fully characterized using high resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS). The effect of plasmonic metal film thickness, order of deposition and the use of bimetallic layers on the photocatalytic activity of the TiO2 photocatalyst was evaluated using methyl orange as a model pollutant. It was shown that, the increase in Ag film thickness underneath the TiO2 film increased the photocatalytic activity of the TiO2 photocatalyst until an optimum film thickness of 20 nm was attained. In the case of copper, the increase in film thickness above 5 nm led to reduced photocatalytic activity. Silver was found to be a better plasmonic metal than copper in enhancing the photocatalytic activity of TiO2 under UV light illumination. Cu was found to perform better when deposited underneath the TiO2 film whereas Ag performed better when deposited on top of the TiO2 photocatalyst film. The use of bimetallic layers was found to enhance TiO2 photocatalytic activity more than monometallic layers.
Silver/carbon codoped titanium dioxide photocatalyst for improved dye degradation under visible light
(Hindawi Publishing Corporation, 2017) Nyamukamba, Pardon; Tichagwa, Lilian; Mamphweli, S.; Petrik, Leslie
Herein, we report the synthesis of quartz supported TiO2 photocatalysts codoped with carbon and silver through the hydrolysis of titanium tetrachloride followed by calcination at 500°C. The prepared samples were characterized by UV-Vis diffuse reflectance spectroscopy, high resolution scanning electron microscopy (HRSEM), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Codoping of TiO2 with Ag and carbon resulted in an increase in the surface area of the photocatalyst and altered the ratio of the anatase to rutile phase. The absorption edge of all the doped TiO2 photocatalysts redshifted and the band gap was reduced. The lowest band gap of 1.95 eV was achieved by doping with 0.5% Ag. Doping TiO2 using carbon as the only dopant resulted in a quartz supported photocatalyst that showed greater photocatalytic activity towards methyl orange than undoped TiO2 and also all codoped TiO2 photocatalysts under visible light irradiation.
Polyester sulphonic acid interstitial nanocomposite platform for peroxide biosensor
(MDPI, 2009) Al-Ahmed, Amir; Ndangili, Peter M.; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.
A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (~90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 μA (μM)-1 and a detection limit of 0.185 μM for H2O2. Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C.
Amphibious Horses: Beings in the Littoral and Liminal Contact Zones
(2013) Woodward, Wendy
Horses galloping in littoral zones are represented as embodying wildness, freedom and a prelapsarian quality. Roy Campbell’s ‘The Horses of the Camargue’ includes themes which recur in texts about littoral horses: the romanticising segue between the horses and the environment they inhabit, the ramifications of wild horse and human entanglement and the unavoidable loss of littoral equine ‘freedom’ when he is trained and/or taken from the sea. Yet Campbell’s poem is dedicated to AF Tschiffely who rode two Criollo horses from Buenos Aires to Washington in 1925. If horses, generally, who cross boundaries between the wild and the tame, answer to those parts of ourselves which long for an uncomplicated connection with wildness, they also embody the potential for cross-species relationships based on training. Wolraad Woltemade’s horse exemplifies equine trusting of a rider; Edwin Muir’s poem, ‘The Horses’, stresses their desires for human connection. This paper will then take a serendipitous journey in the company of threshold beings who whinny littorally through childhood adventure stories, Misty of Chincoteague, and Big Black Horse, and the more sombre tale, The Homecoming, to fetch up on the edges of a dam in Tokai where a herd of horses, and one in particular, surpass youthful fable. Horses are luminous beings who exist liminally as well as literally— in personal myth and in grounded, horse-human relationships on the sandy dressage arena as they teach the rider the stability to connect symbol and ‘reality’, heaven and earth.
Statistical testing of input factors in the carbonation of brine impacted fly ash
(Taylor & Francis, 2012) Muriithi, Grace; Gitari, Wilson; Petrik, Leslie
A D-optimal design was applied in the study of input factors: temperature, pressure, solid/liquid (S/L) ratio and particle size and their influence on the carbonation of brine impacted fly ash (FA) determined. Both temperature and pressure were at two levels (30◦C and 90◦C; 1 Mpa and 4 Mpa), S/L ratio was at three levels (0.1, 0.5 and 1) while particle size was at 4 levels (bulk ash, <20 μm, 20 μm −150 μmand >150 μm). Pressure was observed to have a slight influence on the % CaCO3 yield while higher temperatures led to higher percentage CaCO3 yield. The particle size range of 20 μm – 150 μm enhanced the degree of carbonation of the fly ash/brine slurries. This was closely followed by the bulk ash while the >150 μm particle fraction had the least influence on the % CaCO3. The effect of S/L ratio was temperature dependent. At low temperature, the S/L ratio of 1 resulted in the highest % CaCO3 formation while at high temperature, the ratio of 0.5 resulted in the highest percentage CaCO3 formation. Overall the two most important factors in the carbonation of FA and brine were found to be particle size and temperature.

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