The discharge of poorly treated wastewater containing persistent organic contaminants, such as phenol, into water bodies is a major contributor to water pollution. This is of great concern as it poses health threats to human beings, aquatic species and the ecosystem as a whole. Amongst the water treatment technologies available, adsorption is highly recommended because of its ease of operation, simple design and economic viability. Commercial activated carbon (CAC) has previously been utilised as an adsorbent for remediation of recalcitrant pollutants from wastewater. However, high costs and the complexity of regenerating spent carbon has resulted in the need for economically viable adsorbents. The current research focused on the use of layered double hydroxide (LDH) clays for removal of phenol from contaminated water. The work is divided into two sections whereby the initial phase focuses on the use of commercial LDH clays, while the second phase is based on the in-house synthesised LDH clays guided by the performance of the commercial clays. Six commercial clays were sourced from different suppliers for the first phase, namely: DHT ̵ 4A and Alcamizer 1 from Kisuma Chemicals (Netherlands), Sorbacid 944, Sorbacid 911 and Hycite 713 from Clariant (Germany) and GF ̵ 450 from Greenfield additives (South Africa). Sorbacid 944 was the only clay which had three metallic constituents, magnesium Mg), zinc (Zn) and aluminium (Al) and was quantified to be 100% hydrotalcite; other clays had a substantial amount of impurities, such as calcite, boehmite and silica. Screening tests on the commercial clays were done by contacting 10 g L-1 of each clay with 40 mg L-1 synthetic phenol solution over 108 h. All the clays produced an adsorption efficiency of less than 10%. However, three clays which showed better adsorption efficiencies, namely: GF ̵ 450 (9%), Sorbacid (6%) and DHT ̵ 4A (3%) were utilised for further assessment. The three clays were thermally treated at 500°C for 4 h to produce mixed metal oxides (MMO), which are known to be good adsorbents. Calcination of the clays resulted in an increase in phenol adsorption efficiency over 24 h on Sorbacid 944 (87%) and DHT ̵ 4A (52%) while GF ̵ 450 remained below 10%. Having produced a higher adsorption efficiency, Sorbacid 944 was further assessed for optimisation of phenol removal process. The initial pH of the solution was established to have an inverse proportionality relationship with phenol adsorption. Elevated pH resulted in an increase in the concentration of hydroxyl ions (OH-) which increased the reformation rate of calcined LDH (CLDH) and reduced the adsorption efficiency, while acidic pH was not evaluated as it is known to cause dissolution of LDH. Neutral pH was established to be the optimum pH for phenol adsorption. An increase in operational temperature resulted in a faster phenol adsorption rate from 2 x 10-4 g mg-1min-1 at 25 °C to 3.8 x 10-3 g mg-1min-1at 65 °C. The optimum clay loading was 10 g L-1 and the clay proved to be effective over three cycles. The Freundlich equilibrium isotherm best fitted the phenol adsorption equilibrium data, with a maximum adsorption capacity of 16.6 mg g-1. The change in enthalpy of the adsorption process was determined to be ca.20 kJ mol-1 indicating an endothermic process dominated by physical adsorption. The changes in Gibbs free energy over the evaluated temperatures ranged between -12 kJ mol-1 and -16 kJ mol-1. This showed that the adsorption process was spontaneous irrespective of the operating temperature. The second phase of the study involved the synthesis of eight LDH clays containing varying compositions of Mg, Zn and Al with a carbonate interlayer anion. The clay which contained molar ratios of Mg (60%), Zn (20%) and Al (20%) (Mg0.6Zn0.2Al0.2) was found to possess higher adsorption efficiencies upon calcination at 450 °C for 4 h. Clays which had a Zn/Mg molar ratio greater than 1, Mg0.4Zn0.4Al0.2, Mg0.25Zn0.5Al0.25 and Zn0.75Al0.25 showed lower phenol adsorption efficiencies of 63%, 65% and 50% respectively. Clays with a Zn/Mg ratio less than 1, Mg0.6Zn0.2Al0.2 and Mg0.5Zn0.25Al0.25 showed optimal ratio of acidic and basic sites hence higher phenol adsorption efficiencies of 89% and 80% respectively. A higher aluminium content in the clay increased the spinel content (MgAl2O4) upon calcination resulting in a decrease in phenol adsorption. Phenol adsorption equilibrium data and kinetics for clay Mg0.6Zn0.2Al0.2 were comparable with those of Sorbacid 944. Column reactor configurations should be investigated for industrial applications. Furthermore, real wastewater matrices containing multi-contaminants should be used instead of synthetic wastewater with a few pollutants. This will provide insight in the applicability of LDH for impurity removal from wastewater on an industrial scale. / Dissertation (MEng (Water Utilisation))--University of Pretoria, 2021. / Technology and Human Resources for Industrial Support (THRIP) / Chemical Engineering / MEng (Water Utilisation) / Unrestricted

Le développement de nouveaux adsorbants écologiques et efficaces pour la séparation du CO2 nécessite un lien quantitatif entre les propriétés des adsorbants et ses propriétés d'adsorption. Dans ce travail, nous développons une méthodologie qui prend en compte explicitement les propriétés des adsorbants, tels que le diamètre de pore, la densité, la forme de pore et la composition chimique. L'objectif est d'établir des corrélations quantitatives entre les paramètres mentionnés ci-dessus et les forces qui gouvernent la physisorption dans les milieux poreux, c'est à dire les interactions van der Waals et les interactions électrostatiques. Ainsi, les propriétés optimales des adsorbants pour la séparation du CO2 sont identifiées. En parallèle à ces études théoriques, une série d'adsorbants potentiellement intéressants pour la séparation du CO2 par PSA ont été testées expérimentalement. Une étude systématique de l'influence du centre métallique sur les séparations de mélanges CO2/CH4 et CO2/CH4/CO a été réalisée sur MOFs présentant sites coordinativement insaturés. Dans le cas des zéolithes, l'effet de la composition chimie (rapport Si / Al) sur les propriétés de séparation a été étudiés. Les capacités cycliques et des sélectivités ont été déterminées par des expériences de perçage. Les matériaux présentant un bon compromis entre la sélectivité et la capacité de travailler dans les conditions typiques de PSA ont été identifiés. Finalement, une comparaison entre la prédiction du modèle d'adsorption et les expériences a été faite / The design of new environmentally friendly and efficient adsorbents for CO2 separation requires a quantitative link between the adsorbent properties and adsorption capabilities. In this work we develop a methodology, which explicitly takes into account the adsorbent properties, such as the pore diameter, density, pore shape and chemical composition. The objective is to establish quantitative correlations between the above-mentioned parameters and the forces that govern physisorption in porous media, i.e. van der Waals forces and electrostatic interactions. Thus, the optimal properties of the adsorbent for CO2 separation are identified. In parallel to these theoretical studies, a series of potentially interesting adsorbents for CO2 separation by PSA were tested experimentally. A systematic study of the influence of the metal center on the separations of CO2/CH4 and CO2/CH4/CO mixtures was carried out on MOFs presenting coordinatively unsaturated sites. In the case of zeolites, the effect of the framework composition (Si/Al ratio) on the separation properties was studied. The cyclic capacities and selectivities were determined by breakthrough experiments. Materials presenting a good compromise between selectivity and working capacity under typical PSA conditions were identified. Finally, a comparison between the prediction of the adsorption model and the breakthrough experiments is carried out