Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Zeolites have found applications as heterogeneous or solid catalyst in the petrochemical and refining industries. Zeolite ZSM-5 in particular is a highly siliceous solid catalyst with a porous network that consists of medium pore structure (pore openings 5-5.5 A). The solid catalyst (ZSM-5) is well known for its high temperature stability and strong acidity, which makes it an established catalyst used for different petrochemical processes such as Methanol-To-Gasoline (MTG), isomerisation, disproportionation, and cracking. Unlike in the past, the synthesis of zeolite ZSM-5 from other sources that contains silica (Si) and alumina (Al) with the addition of a template (TPBr) as a structure-directing agent is eminent. Its synthesis can be achievable from coal fly ash that is a waste material and a cheap source of Si and Al. Coal fly ash is a waste material that is produced during the combustion of coal to generate electricity. The elemental composition of coal fly ash consists of mostly SiO2 and Al2O3 together with other significant and trace elements. Zeolite ZSM-5 catalyst synthesised from coal fly ash by previous authors required an excessive amount of additional source of silica even though the XRD spectra still show the presence of quartz and mullite phase in the final products. These phases prevented the use of fly ash (solid) as a precursor to synthesise zeolite ZSM-5 products. However, the synthesis of high purity zeolite ZSM-5 products by extracting silica and alumina from South African fly ash and then using it with small amounts of fumed silica was investigated This aim was achieved by fusing fly ash (FA) with sodium hydroxide (NaOH) under hydrothermal condition set at 550 oC for 1 hour 30 minutes. The quartz and mullite phase observed by previous authors was digested by the fusion process. Thereafter, the treatment of fused fly ash filtrate (FFAF) with concentrated H2SO4 (98-99%), precipitated silica and removed Al that therefore increased the Si/Al ratio from 1.97 in fly ash (FA) to 9.5 in the silica extract (named fused fly ash extract). This route was designed to improve the quality of the final products and reduced the amount of fumed silica added to the synthesis mixture prior to hydrothermal synthesis. In this line of investigation, the process of adding fumed silica to the hydrothermal gel was optimised. H-FF1 with a Si/Al ratio of 9.5 was synthesised using the silica extract without the addition of fumed silica. Its XRD, SEM and relative crystallinity results proved that H-FF1 was inactive and hence was not further characterised and utilised in the conversion of methanol to hydrocarbons (MTH). Purer phase zeolite ZSM-5 products (H-FF2 and H-FF3) that were synthesised from silica extract with the addition of small amounts of fumed silica were characterised and successfully used in the methanol to hydrocarbons (MTH) reaction. The synthesised ZSM-5 products had different Si/Al ratio, different morphology, crystal size, BET surface area, and relative crystallinity as well as different trends in the MTH reaction. It was also observed that H-FF2 and H-FF3 (pure phase) solid catalyst deactivated faster than the commercial H-ZSM-5 in the MTH reaction. However, the MTH conversion over H-FF2 competed with that of the commercial H-ZSM-5 within 3 hours of time on stream (TOS) but later deactivated at a faster rate. This was caused by the large crystal size and reduced BET surface area of H-FF2 when compared to the commercial H-ZSM-5. However, H-FF2 performed better than H-FF3 on stream (MTH reaction) due to its smaller crystal size and higher BET. This study has successfully utilised a route that synthesised high purity zeolite ZSM-5 products from the South African fused fly ash extract (FFAE) with the addition of small amounts of fumed silica. The properties of the synthesised zeolite ZSM-5 products (H-FF2 and H-FF3) were similar to that of the commercial H-ZSM-5 as well as active in the MTH reaction. This promoted the utilisation of a waste material (coal fly ash) to synthesise highly siliceous zeolite ZSM-5 products that avoided the presence of mineral phases from fly ash in the final products.

Thesis (M.Eng.). / Written for the Dept. of Mining, Metals and Materials Engineering. Title from title page of PDF (viewed 2009/06/15). Includes bibliographical references.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / Coal fly ash waste produced from the coal combustion process is becoming an ever increasing concern. It is produced in such abundance due to not only South Africa, but the whole of the world relying mainly on coal combustion for the main source of energy production. With the growing rate of the human population this energy production is ever increasing. The current methods of disposal of this fly ash is not sustainable, it is being dumped in ash dumps, and poses a risk to the surrounding environment and human population. Therefore, processes need to be developed to take this waste and turn it into useful materials. This would not only solve the problem of its disposal but also create useful products that can be applied to further protect the environment. It was discovered that one of the useful materials that can be synthesised from fly ash are zeolites. These nano-porous structures have a wide variety of uses. Therefore, many studies have been conducted around optimising the synthesis of various zeolites from coal fly ash. More recently these studies have focused on the scale-up conditions needed to synthesise these zeolites on the large industrial scale, regarding the sheer volume of fly ash produced annually. The most robust and widely used technique for zeolite synthesis involves a pre-synthesis fusion of the fly ash with sodium hydroxide at a temperature of 550 0C. This would not be feasible to scale-up to industrial scale because of the energy intensity. Therefore, alternative pre-synthesis techniques have been proposed. One of those techniques involves using a sonochemical treatment as a pre-synthesis. It can be argued that this technique may not be able to be easily scaled. To solve this problem, another alternative technique was investigated within this study. It involves the use of a jet loop pilot plant mixing system, which can be scaled-up very readily to industrial scale.

About 27 million metric tons of municipal solid waste are used annually as fuel in U.S. Waste-to-Energy (WTE) power plants, which annually generate seven million tons of bottom ash (BA) and fly ash (FA). In the U.S., bottom ash and fly ash residues are mixed to “combined ash” (CA) in the approximate ratio of 6 to 1, and are disposed in landfills after metal separation. The disposal of WTE ash is a significant cost and land use item of waste management. This dissertation aims to (i) comprehensively understand the characterization and properties of WTE ash; (ii) provide practical and economic stabilization technologies to reduce the leachability of heavy metals in WTE ash and assessing whether it can be further beneficially used as secondary materials; (iii) utilize the stabilized/processed WTE ash as secondary construction materials in civil engineering applications, thus diverting materials from landfills and contributing to the circular economy. The Characterization section provides a comprehensive assessment of WTE bottom ash, fly ash, and combined ash, including chemical composition (XRF, ICP-OES, IC), mineral composition (X-ray diffraction-XRD quantification), thermogravimetric analysis (TGA), particle size distribution, and scanning electron microscopy (SEM). The physical properties of WTE residues were also investigated, including moisture, bulk density, specific gravity, void content, and water absorption. Leaching Environmental Assessment Framework (LEAF) Method 1313 of the U.S. Environmental Protection Agency (EPA) was used to understand the effect of eluate pH on the leachability of heavy metals. Combination of the above methods was applied to quantify the crystalline and amorphous phases present in WTE residues and produced specimens. In the U.S., WTE BA is discharged from the combustion chamber into a water tank. The BA includes 50-70% mineral fraction, 15-30% glass and ceramics, 5-13% ferrous metals, 2-5% non-ferrous metals, and 1-5% unburned organics. This thesis received the BA samples after ferrous and non-ferrous metal recycling. The major chemical composition includes SiO2 (34%), CaO (21%), Al2O3 (9%), and Fe2O3 (11%). According to XRD quantification results, BA consists of 76% amorphous phases (glass and metastable minerals), and the dominant crystalline mineral is quartz (SiO2, 12%). The calcium silicate (aluminate) hydrates (C-S-(A)-H) gel formed during the water quenching process embeds fine particles in the amorphous phases. The U.S. WTE air pollution control systems commonly include semi-dry scrubbers, with a few plants using dry scrubbers. FA consists of two kinds of particles: the furnace particles carried in the process gas and the newly-formed particles in the scrubber. The major chemical composition in FA includes CaO (40%), Cl (15%), SO3 (8%), CO2 (8%), and activated carbon/organic matter (3%) due to the injection of absorbents (hydrated lime and activated carbon) and the effects of flue gas scrubbing. The empirical formulae of the constituent crystalline (40-50%) and amorphous (50-60%) phases were derived. The excess water in semi-dry scrubbers improved the hydration reaction between newly-formed particles and furnace particles and resulted in the transformation of amorphous phase to calcium silicate hydrates (C-S-H) phase. The hydration products of semi-dry FA immobilized some heavy metals and reduced their leachability to below the levels of the Resource Conservation and Recovery Act (RCRA) by Toxic Characteristic Leaching Procedure (TCLP) test, as compared to dry scrubber FA, which exceeded the limits of RCRA. The U.S. combined ash can pass the TCLP test and comply with the RCRA standards for non-hazardous landfill disposal. The Stabilization section examines the effects of processing combined ash. CA undergoes water washing, crushing, and size separation processes to three fractions: coarse (27%, CCA, 9.5-25 mm), medium (37%, MCA, 2-9.5 mm), and fine (25%, FCA, < 2 mm), identified by particle size distribution results. The by-products of the washing process are extra fine filter cake ash (EFFCA, 8% of CA) collected from the water treatment system and ash dissolved in the wastewater (3% of CA). The characterization (chemical composition, mineral composition, and leachability) of ash the fractions (CCA, MCA, and FCA) showed that their mineral changed during the processing and exhibited significantly lower leachability (LEAF Method 1313-pH dependence), in comparison to as-received CA. The processed ash fractions with reduced leachability of heavy metals, can be further beneficially used as secondary materials. The effect of pH of the washing agents (water, acid and alkaline solutions) on the chemical/mineral transformation and the heavy metals leachability of the FA, BA, and CA was assessed. A novel technique of determining the distribution of various elements in washed ash (product), filter cake (by-product), and wastewater (dissolution) during ash processing was developed to compare the effectiveness of the washing process, which is dominated by dissolution and precipitation reactions. As-received FA, BA, and CA contained 50-75% of amorphous phases in metastable status, which are transformed to crystalline phases during the washing process. It was concluded that water washing is the most practical method for transforming WTE CA to construction material. The Utilization section examined the use of WTE ash in civil engineering applications, i.e. (i) Using the CCA and MCA fractions as stone aggregate substitute in structural concrete; (ii) Using FCA as sand substitute or using the milled FCA (MFCA) powder as mineral addition in cement mortar; (iii) Using FCA and EFFCA powder as metakaolin substitute in artificial aggregate; (iv) Using FA and phosphate FA (PFA) as cement substitute in cement mortar. In conclusion, the CA size fractions, i.e., MCA and CCA, are suitable for use as aggregate substitutes in the production of structural concrete. Up to 100 wt.% of stone aggregate in concrete can be substituted by MCA and CCA. The compressive strength of the optimal products exceeds 28 MPa after 28 days of curing, which is comparable to commercial concrete products using natural stone aggregate. The optimum concrete mixture composition was 40 wt.% of MCA or CCA, 30 wt.% sand, 20 wt.% cement, 10 wt.% water, and superplasticizer, with compressive strength of 28-30 MPa and elastic modulus of 6,300-6,600 MPa. The optimal products complied with stringent leaching standards, and the properties of the final products were comparable to the conventional civil engineering materials. All FCA or MFCA products were effectively stabilized/solidified and transformed to non-hazardous material that can be used in construction. The main challenge in the utilization of FCA or MFCA in cement mortar is the cementitious phase expansion due to the metallic aluminum present in FCA or MFCA. It was concluded that up to 50 vol.% of sand in cement mortar can be directly substituted by FCA, and up to 25 vol.% of MFCA can be utilized as mineral addition to replace cement in the production of cement mortar. In the production of artificial aggregates, up to 15% of FCA or up to 10% of EFFCA can replace metakaolin by volume. The produced samples indicated crushing strength of 4 and 1.5 MPa, respectively. The specific gravity and water absorption of optimal ash aggregate is 1.3 and 30%. The FCA and EFFCA aggregates exhibited good chemical stability and reduced the cracks observed in the fire resistance test. The ash aggregates can be used as a lightweight aggregate for non-structural applications. FCA can improve the workability of the metakaolin mixture and extend the setting time, which is beneficial for geopolymer aggregate manufacturing. The heavy metals from FCA and EFFCA can be effectively stabilized/solidified in artificial aggregate. Phosphoric acid can effectively stabilize the as-received FA, so that the dry scrubber FA passes the TCLP test and complies with the RCRA standards. The mineral transformations of individual ash and ash-cement paste were investigated by the XRD quantification analysis. FA and PFA enhanced the hydration degree of cement, and received higher mechanical performance than reference in 0-25 vol.% cement replacement. The leachability of heavy metals was effectively reduced in a wide leaching range (eluate pH 0-12.5), realized the stabilization/solidification purposes under restricted non-hazardous landfill standards.

Les Cendres Volantes d’Electrofiltres (CVE) d’incinération d’ordures ménagères sont considérées comme des déchets dangereux et mises en décharges après une phase de stabilisation et de solidification par un liant hydraulique. Leur utilisation dans des matériaux cimentaires permet l’élimination d’un déchet en diminuant la demande de matériaux de construction. Cependant, avant leur incorporation dans des matériaux cimentaires, les CVE doivent subir plusieurs traitements. Premièrement, un lavage à l’eau permet de diminuer fortement la concentration en chlorures. Dans un deuxième temps, une séparation granulométrique des CVE est appliquée afin de ne sélectionner que la fraction la moins contaminée en métaux lourds, notamment en plomb et en zinc, ces métaux lourds étant connus comme retardateurs de prise. Enfin, une troisième étape consiste à oxyder l’aluminium métallique présent dans les CVE à l’aide d’un lavage basique à l’hydroxyde de sodium. S’il n’est pas oxydé durant la phase de traitement, l’aluminium métallique se transforme en aluminates dans la matrice cimentaire tout en produisant de l’hydrogène, responsable de l’apparition de vides et de fissures endommageant ainsi le matériau. Une fois traitées, les CVE peuvent alors être utilisées en substitution partielle du ciment pour une étude de leur réactivité potentielle. Les résultats de cette étude ont montré que l’activité des CVE traitées à l’hydroxyde de sodium est principalement d’origine physique (granulométrique et surface développée). Les CVE ne présentent pas de nature pouzzolanique. Les essais de lixiviation ont montré une durabilité équivalente et une très bonne stabilisation du chrome, du plomb et du zinc, qui permet de respecter les normes environnementales européennes./Municipal Solid Waste Incineration (MSWI) Electrofilter Fly Ash (EFA) is considered as hazardous waste and landfilled after stabilisation and solidification with a hydraulic binder. Its use in cementitious materials allows the elimination of a waste and a decrease of construction materials use. However, before its incorporation in cementitious materials, EFA has to be treated. Firstly, a water washing allows an important decrease in chloride concentration. In a second time, size-based separation is used to select the less heavy metals contaminated fraction, especially in lead and zinc. Indeed, these heavy metals are knows as setting retarders. Finally, a third step involves oxidizing of metallic aluminium contained in EFA during a basic washing with sodium hydroxide. Indeed, if it is not oxidize during the treatment, metallic aluminium converts in aluminates in the cementitious material, and produces hydrogen, generating cracking and voids, and damaging the cementitious material. After the treatment step, a study of the potential reactivity of EFA used in partial replacement of cement is carried out. Results show the activity of EFA treated with sodium hydroxide is mainly physical (grading and developed surface). EFA presents not pozzolanic effect. Leachability tests show an equivalent durability and a very efficient stabilisation of chrome, lead and zinc, allowing the respect of the European environmental standard. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

D’après les limites d’acceptation pour la mise en décharge des déchets, les REFIOM (Résidus d’Epuration des Fumées d’Incinération d’Ordures Ménagères) sont considérés comme déchets dangereux, car ils libèrent des quantités importantes de chlorures et de métaux lourds lorsqu’ils entrent en contact avec de l’eau. Ces solides doivent par conséquent être traités avant leur mise en décharge. A côté des traitements visant l’acceptabilité des REFIOM en décharge, quelques recherches entrevoient la possibilité de valoriser ces résidus, notamment dans des matériaux cimentaires. <p>Les recherches présentées ici s’inscrivent dans cette tendance nouvelle et visent l’élaboration d’un procédé combinant traitement et valorisation des REFIOM. <p>Les REFIOM représentent en fait différents types de résidus provenant des installations que rencontrent les fumées issues de l’incinération des déchets. La composition des résidus diffère selon leur origine. Il est dès lors apparu essentiel de considérer chaque type de résidu séparément et de poursuivre l’élaboration d’un traitement sur un seul type de REFIOM. Nous avons choisi de concentrer les recherches sur les Cendres Volantes de Chaudière (CVC), ces résidus se retrouvant dans tout incinérateur. <p>Le traitement des CVC est basé sur l’extraction de fractions valorisables et la séparation de fractions contaminées, permettant d’obtenir des résidus acceptables en décharge ou, idéalement eux-mêmes valorisables. <p>Une séparation magnétique permet d’extraire environ 10% en poids des CVC mais ne semble pas exploitable dans le cadre du traitement des CVC car les particules magnétiques contiennent des impuretés (composés non magnétiques) et que le résidu final reste contaminé. <p>Une étude de la répartition des éléments en fonction de la taille des particules (granulochimie) est effectuée sur les CVC. Il apparaît intéressant de séparer la fraction inférieure à 38 µm obtenue lors d’une séparation granulométrique, effectuée en voie humide en utilisant une solution dense. En effet, cette fraction semble être nettement plus contaminée en Pb (soluble) que le reste des CVC. Une telle séparation constitue dès lors la première étape du traitement des CVC. Elle est suivie par des étapes de lavage des fractions obtenues, visant à extraire les sels solubles (chlorures et métaux). Les lavages sont envisagés à contre-courant afin d’utiliser au mieux l’eau de lavage. Une recirculation interne des solutions est également prévue, de sorte que, théoriquement, le procédé ne génère pas d’effluents liquides. Une étape de précipitation de composés métalliques (PbS dans ce cas-ci) est prévue après le lavage des boues. <p>Le procédé de traitement des CVC produirait ainsi des boues et des granulats décontaminés, des sels et des précipités métalliques. Seules certaines étapes du procédé ont été investiguées en laboratoire ;des essais supplémentaires sont encore nécessaires pour optimiser chaque étape, comprendre les phénomènes physico-chimiques qui se produisent et assurer des filières de valorisation. <p>/<p>Municipal Solid Waste Incineration (MSWI) fly ashes and Air Pollution Control (APC) residues are considered as hazardous waste according to the limits for the acceptance of waste at landfills, because high amounts of chlorides and heavy metals leach from the solids when those are in contact with water. These residues have thus to be treated before they can be accepted in landfill. Several treatments aim to limit the leaching of the residues. Beside these treatments, some research works go further the treatment and consider the valorisation of MSWI fly ashes and APC residues, e.a. in cementitious materials. <p>The present work follows the new trend and aims to build up a process that combines treatment and valorisation of MSWI fly ashes and APC residues. <p>MSWI fly ashes and APC residues come from the devices encountered by the flue gases from waste incineration. The residues composition differs according to their origin. It seems thus essential to consider each type of residues separately and to develop the treatment only on one sort of residue. Boiler Fly Ashes (BFA) were chosen because they exist in every modern MSWI plant. <p>The BFA treatment is based on the extraction of valorisable fractions and on the separation of contaminated fractions, which makes the final residues less hazardous; these final residues would then be acceptable in landfill, or, even better, be valorisable. <p>A magnetic sorting extracts ~10% (wt.) of BFA; however, such a separation would not be useful in a treatment process because the magnetic particles contain some impurities (non magnetic particles) and the final residue is still hazardous. <p>The repartition of the elements according to the particles size has been studied on BFA. It seems interesting to separate the BFA at 38 µm by a wet sieving process using a dense solution. The lower fraction presents a higher contamination in Pb (soluble) than the larger. Consequently, the first step of the BFA treatment consists of a wet sieving. Washing steps follow the sieving and aim to extract soluble salts (chlorides, heavy metals). These washings work in a counter-current way to optimise the use of water. The solutions are recycled in the process, which implies the absence of liquid effluents. A precipitation step of some metallic compounds (PbS in this case) is foreseen after the washing of the lower fraction. <p>The BFA treatment process would produce decontaminated sludge and coarse fractions, salts and metallic compounds. Some steps of the process have been investigated at lab-scale; further studies are necessary to optimise each step, to understand the observed reactions and to guarantee valorisation channels. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished