No description available.

South Africa mines coal to supply in the growing energy demands of the country. A majority of these mines are opencast resulting in back filled pits and above ground disposal facilities. Leachate emanating from these disposal sites are saline and in most cases highly acidic. Currently the standard testing procedure to quantify expected leachate qualities include Acid Base Accounting (ABA), Net-acid Generating test (NAG), static-and kinetic leaching. The aim of this study is to model standard humidity cell leach tests performed using the PHREEQC code. This model can then be scaled up to field conditions to model 1D reactive transport. It is commonly accepted that the rate of pyrite oxidation in backfilled pits and waste storage facilities is governed by the rate of oxygen ingress and that no pyrite oxidation take place in the saturated zone. This is not the case for humidity cells, as sufficient oxygen is available for reaction. Pyrite reactions rates in humidity cells is expected to be governed by a combination of available reaction surface and ash layer resistance. This is modelled in PHREEQC (Parkhurst & Appelo, 2003) using the KINETIC block. Leachate composition is then modelled in the column by making use of the TRANSPORT block. The experimental data is fitted by using the reactive surface and ash layer diffusion coefficient as a fitting parameter. PHREEQC does not have a gas transport module to model oxygen diffusion through the column. Due to this shortfall of PHREEQC, the influence of oxygen ingress in the system can not be directly modelled under kinetic conditions. Davis and Ritchie (1986a) proposed an anlylitical solution in which the integrated sulphate production rate can be calculated for a waste heap dump. This rate takes into account the influence of oxygen ingress and the development of an ash layer resistance to the pyrite oxydation rate. This intergrated rate can then be defined in a RATES block in PHREEQC. The Aproximate Analytical Solution (AAS) model proposed by Davis and Ritchie (1986a) is used to scale up the model used for the humidity leach cell experiment. It was found from the modelling results and comparison with PYROX that the model under predicts the integrated sulphate production rate in the initial stages of the reacting waste heap dump. It does however show results that are in close agreement with the results obtained from PYROX in later stages of the lifespan of the waste heap dump. This highlight limitations to the AAS model’s applicability on geochemical problems. The model can only be applied to describe waste heap dumps where the particles at the top of the heap are fully oxidized. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

South Africa mines coal to supply in the growing energy demands of the country. A majority of these mines are opencast resulting in back filled pits and above ground disposal facilities. Leachate emanating from these disposal sites are saline and in most cases highly acidic. Currently the standard testing procedure to quantify expected leachate qualities include Acid Base Accounting (ABA), Net-acid Generating test (NAG), static-and kinetic leaching. The aim of this study is to model standard humidity cell leach tests performed using the PHREEQC code. This model can then be scaled up to field conditions to model 1D reactive transport. It is commonly accepted that the rate of pyrite oxidation in backfilled pits and waste storage facilities is governed by the rate of oxygen ingress and that no pyrite oxidation take place in the saturated zone. This is not the case for humidity cells, as sufficient oxygen is available for reaction. Pyrite reactions rates in humidity cells is expected to be governed by a combination of available reaction surface and ash layer resistance. This is modelled in PHREEQC (Parkhurst & Appelo, 2003) using the KINETIC block. Leachate composition is then modelled in the column by making use of the TRANSPORT block. The experimental data is fitted by using the reactive surface and ash layer diffusion coefficient as a fitting parameter. PHREEQC does not have a gas transport module to model oxygen diffusion through the column. Due to this shortfall of PHREEQC, the influence of oxygen ingress in the system can not be directly modelled under kinetic conditions. Davis and Ritchie (1986a) proposed an anlylitical solution in which the integrated sulphate production rate can be calculated for a waste heap dump. This rate takes into account the influence of oxygen ingress and the development of an ash layer resistance to the pyrite oxydation rate. This intergrated rate can then be defined in a RATES block in PHREEQC. The Aproximate Analytical Solution (AAS) model proposed by Davis and Ritchie (1986a) is used to scale up the model used for the humidity leach cell experiment. It was found from the modelling results and comparison with PYROX that the model under predicts the integrated sulphate production rate in the initial stages of the reacting waste heap dump. It does however show results that are in close agreement with the results obtained from PYROX in later stages of the lifespan of the waste heap dump. This highlight limitations to the AAS model’s applicability on geochemical problems. The model can only be applied to describe waste heap dumps where the particles at the top of the heap are fully oxidized. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Recently, a particular interest has been devoted to “smart”/stimuli-responsive amphiphilic polymeric materials. Strictly speaking, such structures do not present an amphiphilic character but can be transformed as such by external stimuli within their close environment, e.g., pH, temperature, light, ionic strength, ... and are then able to produce reversible self-assemblies greatly attractive in the biomedical field as drug delivery systems. The originality of this thesis relies upon the synthesis of “intelligent” hydrophilic triblock copolymers containing acrylamide and acrylate-based monomers presenting both thermo- and pH-responsiveness. The applied synthetic strategy aimed at performing the controlled copolymerization reactions entirely in aqueous conditions and in a “one-pot process” via Atom Transfer Radical Polymerization (ATRP). This synthetic approach represents a real challenge knowing that ATRP of (meth)acrylamide comonomers is difficult to control in aqueous medium. However, by the help of kinetic studies and related theoretical modeling, a fine control over the copolymerization process has been made available allowing the synthesis of polyacrylamide-based triblock copolymers with different charge states. Ultimately, all series of triblock copolymers have been investigated for forming polyelectrolyte complexes potentially useful as drug delivery (nano)systems. The first part of the thesis aims at reporting the control and the understanding of the aqueous ATRP of N-isopropylacrylamide (NIPAAm) initiated by a model low molecular weight initiator. The NIPAAm polymerization has been kinetically studied varying different parameters. Correlated with a theoretical modeling, the reactions involved in the ATRP process have been identified highlighting the importance of molecular diffusion limitations. This step was crucial in view to extrapolate to the synthesis of poly(N-isopropylacrylamide)-based copolymers. The second part focuses on the controlled synthesis of poly(ethylene oxide)-b-poly(N- isopropylacrylamide) diblock copolymers using the macroinitiator method. Different conditions such as solvent mixture, nature of the catalyst and of macroinitiator, i.e., poly(ethylene oxide), have been studied ultimately yielding well-tailored polyacrylamide-based triblock copolymers based on NIPAAm, N,N-dimethylaminoethyl acrylate and 2-acrylamido-2-methyl-1-propane sodium sulfonate comonomers The “smart” character of the resulting triblock copolymers has been investigated affording in specific conditions micellar self-assemblies. Last but not least, polyelectrolyte complexes have been prepared by coulombic interactions between the resulting triblock copolymers, e.g., poly(ethylene oxide)-b-poly(N- isopropylacrylamide)-b-poly(N,N-dimethylaminoethyl acrylate) and poly(ethylene oxide)-b- poly(N-isopropylacrylamide)-b-poly(2-acrylamido-2-methyl-1-propane sodium sulfonate) whose the thermo-responsiveness could be highlighted. The so-formed polyelectrolyte complex nanoparticles constitute promising nanovectors of the third generation able to kinetically tune the drug release in function of local temperature variation.

No description available.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Recent developments in the atmospheric treatment of low-grade nickel laterite ores at Anglo American plc has culminated in the conceptual iron-focused laterite (ARFe) process. In addition to the recovery of nickel and cobalt from laterite ore, this process uniquely aims to recover iron as a saleable by-product. The reduction of soluble iron(III) (Fe(III)) by sulfur dioxide gas (SO2) is central to the ARFe concept and represents a complex, multiphase system involving simultaneous gas-liquid mass transfer, thermodynamic speciation and chemical reaction. The chemistry of iron-containing systems is generally poorly understood and accurately predicting their behaviour is challenging, especially under aggressive hydrometallurgical conditions. The primary objective of this work is the development of an engineering model capable of describing the rate and extent of ferric reduction with SO2 under conditions typical of the ARFe process. Thermodynamic considerations provide a rigorous framework for the interpretation of chemical reactions, however little experimental data are openly available for the associated solution species in acidic iron sulfate systems. A key contribution of this work, and critical for the development of the overall model, is the direct measurement of speciation in iron sulfate solutions. Raman and UV-vis spectroscopy were utilised to make direct speciation measurements in the various subsystems of the Fe2(SO4)3-FeSO4-H2SO4-H2O system that were previously unavailable in the open literature. The FeSO+4 and Fe(SO4)– 2 species were explicitly identified and measurements were supported and rationalised by static computational quantum mechanical calculations and ultimately permit the calibration of a robust, ion-interaction solution model with the explicit recognition of the important solution species up to 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 over 25 – 90 C. Batch and continuous Fe(III) reduction kinetics were measured and the effects of initial Fe2(SO4)3 and H2SO4 concentrations, temperature and in-situ neutralisation quantified. The retardation effect of sulfuric acid was observed to be the most significant factor influencing the initial reaction rate and the achievable extent of reduction at fixed residence time, which varied between about 20 and 80 % after 180 minutes of reaction. A reaction mechanism that is limited by the slow ligand-to-metal electron transfer in the FeIIISO+3 solution species’ decomposition is proposed and spectroscopic measurements and computational quantum mechanical calculations are used to support this mechanism. A kinetic model, comprising a system of differential mass-balance equations, is incorporated into the thermodynamic framework. This reaction model permits the prediction of kinetic profiles over the full range of experimental conditions and can be incorporated into more elaborate simulation models of the ARFe circuit. The specific original contributions of this work are • The direct measurement of aqueous speciation in the Fe2(SO4)3-H2SO4-H2O system by Raman and UV-vis spectroscopy • The development of a modelling framework to characterise speciation, activity coefficients and solubility in the mixed Fe2(SO4)3-FeSO4-H2SO4-H2O system. • The measurement of Fe(III) reduction kinetics using SO2 in concentrated sulfate solutions as a function of initial composition and temperature. • The development of a solution reaction model of Fe(III) reduction with SO2 that accurately predicts the solution speciation and reaction rate with time as a function of composition and temperature. Lastly, the vast complexity of industrial systems will nearly always result in a lack of specific experimental data that are required for the development of phenomenological models. This work emphasises the crucial role that engineering studies hold in the generation of such data to derive maximum practical value for industrial process development and optimisation. / AFRIKAANSE OPSOMMING: Onlangse ontwikkelinge in die atmosferiese behandeling van lae-graad nikkel lateriet erts by Anglo American plc het gelei tot die konseptuele yster gefokus lateriet (ARFe) proses. Bykommend tot die herwinning van nikkel en kobalt uit laterite erts is hierdie proses uniek en daarop gemik om yster te herwin as ’n verkoopbare by-produk. Die vermindering van oplosbare yster(III) (Fe(III)) met swaeldioksied (SO2) is sentraal tot die ARFe konsep en verteenwoordig ’n komplekse, multifase stelsel wat gelyktydige gas-vloeistof massa-oordrag, termodinamiese spesiasie en chemiese reaksie behels. Die oplossingschemie van ysterstelsels word, oor die algemeen, swak verstaan en om hul gedrag akuraat te voorspel is ’n uitdaging, veral onder aggressiewe hidrometallurgiese kondisies. Die primêre doel van hierdie werk is die ontwikkeling van ’n ingenieursmodel wat die tempo en omvang van yster(III) vermindering met SO2 onder tipiese ARFe proses toestande beskryf. Termodinamiese oorwegings stel ’n streng raamwerk voor vir die interpretasie van chemiese reaksies, alhoewel daar egter min eksperimentele data openlik beskikbaar is vir die gepaardgaande oplossing spesies in suur yster(III) sulfaat stelsels. ’n Belangrike bydrae van hierdie werk, en van kritieke belang vir die ontwikkeling van die algehele model, is die direkte meting van spesiasie in yster(III) sulfaat oplossings. Raman en UV-vis spektroskopie is gebruik om direkte spesiasie metings te maak in die verskillende subsisteme van die Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel wat voorheen nie in die oop literatuur beskikbaar was nie. Die FeSO+4 en Fe(SO4)– 2 spesies is ekplisiet geïdentifiseer, terwyl die metings ondersteun en gerasionaliseer is deur statiese kwantummeganiese berekeninge wat uiteindelik die kalibrasie van ’n robuuste, ioon-interaksie model tot gevolg hê wat ook die belangrike oplossingspesies duidelik beklemtoon tot en met 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 en tussen 25 – 90°C. Enkellading en kontinue yster(III) verminderingskinetika is gemeet en die gevolge van die aanvanklike Fe2(SO4)3 en H2SO4 konsentrasies, temperatuur en in-situ neutralisasie is gekwantifiseer. Die waargeneemde vertragingseffek van swaelsuur is die mees beduidende faktor wat die aanvanklike reaksietempo en die haalbare reaksie omvangsvermindering na ’n vaste residensietyd van 180 minute bepaal, wat wissel tussen ongeveer 20 en 80%. ’n Reaksiemeganisme word voorgestel wat beperk word deur die stadige ligand-totmetaal elektronoordrag in ontbinding van die Fe(III)SO+3 oplossing-spesies en wat verder deur spektroskopiese metings en kwantummeganiese berekenings ondersteun word. A kinetiese model, wat bestaan uit ’n stelsel van gedifferensieerde massa-balans vergelykings, is in die termodinamiese raamwerk geïnkorporeer. Hierdie reaksie-model laat die voorspelling van kinetiese profiele toe oor die volle omvang van die eksperimentele toestande en kan in meer uitgebreide simulasie modelle van die ARFe proces geinkorporeer word. Die spesifieke en oorspronklike bydraes van hierdie werk is • Die direkte meting van die spesiasie in die Fe2(SO4)3-H2SO4-H2O stelsel deur Raman en UV-vis spektroskopie • Die ontwikkeling van ’n modelraamwerk om spesiasie, aktiwiteitskoëffisiënte en oplosbaarheid in die gemengde Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel te karakteriseer. • Die meting van yster(III) vermideringskinetieka deur SO2 in gekonsentreerde sulfate oplossings te gebruik as ’n funksie van die aanvanklike samestelling en temperatuur. • Die ontwikkeling van ’n oplossingsreaksie-model van yster(III) vermindering met SO2 wat die oplossing-spesiasie en reaksietempo met die tyd as ’n funksie van samestelling en temperatuur akkuraat voorspel. Laastens, die oorgrote kompleksiteit van industriële stelsels sal byna altyd lei tot ’n gebrek van spesifieke eksperimentele data wat nodig is vir die ontwikkeling van fenomenologiese modelle. Hierdie werk beklemtoon die belangrike rol wat ingenieursstudies speel in die generasie van data wat sodanig tot maksimum praktiese waarde vir industriële prosesontwikkeling en optimalisering lei.

Óxido e fosfato de nióbio, calcinados em diferentes temperaturas, foram usados como catalisadores na reação de desidratação de 1-butanol, onde o efeito da temperatura de reação, da massa de catalisador e da vazão de butanol sobre a conversão e seletividade a butenos foram avaliadas através de um plano experimental. Foram caracterizadas as propriedades cristalográficas dos catalisadores. A maioria dos catalisadores apresentaram uma estrutura amorfa, mas algumas amostras apresentaram uma estrutura cristalina quando calcinadas em maiores temperaturas, 500 e 850 °C para o NbO e NbP, respectivamente. Nos testes reacionais, observou-se que o aumento da temperatura de calcinação dos catalisadores reduziu a conversão de 1-butanol. O catalisador fosfato de nióbio apresentou maior atividade, já que foi obtida uma conversão similar à do óxido de nióbio com uma massa 5 vezes menor, indicando a presença de sítios ácidos mais ativos. Além disso, a variável reacional que teve maior efeito na conversão foi a vazão de alimentação de 1-butanol; e seu aumento causou um decréscimo nos valores de conversão. Este comportamento indicou que a ordem aparente da reação é menor que um, o que foi confirmado por um modelo cinético baseado em lei de potência, o qual ajustado aos dados experimentais resultou em uma ordem aparente em torno de zero Equações fenomenológicas de velocidade de reação baseadas no modelo LHHW foram desenvolvidos. O teste estatístico F de Fisher foi utilizado para comparar os modelos fenomenológicos obtidos: para o óxido de nióbio calcinado em 400 °C o modelo heterogêneo que leva em conta apenas a adsorção de butanol foi considerado o mais adequado; para o fosfato de nióbio calcinado em 400 °C o modelo heterogêneo que leva em conta a adsorção de butanol e de água foi o mais adequado. Para ambos os catalisadores, com exceção do NbO calcinado em 500 °C, foi observada uma significativa isomerização de 1-buteno a 2-buteno, principalmente nas condições que foi obtida uma maior conversão de butanol. Este fato comprova a elevada força ácida destes catalisadores. A seletividade a 2-buteno foi maior ou igual a 1-buteno em todas as temperaturas e condições de reação com fosfato de nióbio. Para o óxido de nióbio, a seletividade a 2-buteno foi maior em poucas condições reacionais. / Niobium oxide and phosphate, calcined at different temperatures, were used as catalysts in the 1-butanol dehydration reaction, where the effect of reaction temperature, catalyst mass and butanol flow rate on conversion and selectivity to butenes were evaluated through an experimental design. The catalysts crystallographic properties were characterized. Most catalysts presented an amorphous structure, but some samples presented a crystalline structure when calcined at higher temperatures, 500 and 850 °C for NbO and NbP, respectively. In the reaction testes, it was observed that the increase in the catalysts calcination temperature decreased the 1-butanol conversion. The niobium phosphate catalyst presented higher activity, since it was obtained a similar conversion to that of niobium oxide with a mass 5 times lower, indicating the presence of more active acidic sites. Furthermore, the reaction variable that had the highest effect on the conversion was in the 1-butanol feeding flow rate; and its growth caused a decrease in the conversion values. This behavior indicated that the apparent reaction order is lower than one, which was confirmed through a kinetic model based on power law, which adjusted to the experimental data resulted in an apparent order around zero Phenomenological equations of reaction rate based on the LHHW model were developed. The Fisher statistical test was used to compare the phenomenological models obtained: for the niobium oxide calcined at 400 °C the heterogeneous model that takes into account only the adsorption of butanol was considered the most adequate; for the niobium phosphate calcined at 400 °C the heterogeneous model that takes into account the adsorption of butanol and of water was the most adequate. For both catalysts, with the exception of NbO calcined at 500 °C, a significant isomerization of 1-butene to 2-butene was observed, mainly in the conditions that were obtained a higher conversion of butanol. This fact proves the elevated acid strength of these catalysts. The selectivity to 2-butene was higher or equal to 1-butene at all reaction temperature and conditions where niobium phosphate was employed. For the niobium oxide, the selectivity to 2-butene was higher in a few reaction conditions.

Pecan nuts might become contaminated with foodborne pathogens, such as Salmonella and E. coli., through birds and other potential sources of contamination that can lead to serious illness or even death, as well as financial losses. For example, the outbreak of Salmonella in pecan products in Texas caused major product recalls in 2010. Irradiation with electron beams could be an effective method of preventing potential outbreaks without changing the pecans' taste, color and flavor and without causing any risk of recontamination before the product reaches the consumer. However, when irradiation is applied alone, the shelf life of the product is decelerated because of the detrimental effect of lipid oxidation. Therefore, to extend the shelf of the pecans while assuring their safety, irradiation of pecans under modified atmosphere packing (MAP) conditions could be a viable option. This research showed that when treated with electron beams, surrogates of Escherichia coli (a cocktail of BAA-1427, BAA-1428, and BAA-1430), and Salmonella (S. Typhimurium LT2) were more resistant to ionizing radiation (higher D10 values) when packed under vacuum (VP) than under air or other MAP conditions. This research also showed that lipid oxidation in pecans (due to exposure to ionizing radiation) shows a lag phase, probably due to the antioxidants present in pecan nuts. The lag phase represents a delay period before the pecan nuts start to get rancid (increase in PV formation), and it is best described by a modified Gompertz model. Kinetic evaluation of the lipid oxidation reaction suggests that the dose level has a more drastic effect in PV formation than the type of package used during the irradiation treatment, e.g., vacuum packed versus nitrogen-packed. Moreover, accelerated shelf life studies (4 weeks at 48.9oC) showed that vacuum-packed (VP) pecans can be stored at -25 degrees C up to three years, while irradiated (at 3.0 kGy) VP pecans can be stored only for eight months, without the detrimental effects of lipid oxidation. Therefore, irradiation of pecans under air at 3.0 kGy reduces the shelf life of the nuts in terms of rancidity, but vacuum-packaging can be used to extend their shelf-life. Irradiation in oxygen packaging increases rancidity and the oxidation reaction rate accelerates with increasing dose. Irradiation under nitrogen packaging requires lower doses to achieve the almost same number of log reductions in microbial population. The use of nitrogen packaging also inhibits the oxidative reaction leading to rancidity in pecans. Although there are some drawbacks to the application of nitrogen packaging in an irradiation plant (special machinery and packaging films (permeability specifications for N2 gas)), the savings induced by avoiding recalls may make this technology worthy of consideration.

No description available.

Positron emission tomography (PET) is a widely used molecular imaging modality,which offers quantitative information about many biochemical processes in vivo. In particular, the dynamic PET data provide physiologically meaningful parametricimages after the estimation of the parameters of a model that best describes thekinetic behaviour of the injected radiotracer. Spatiotemporal 4D image reconstructionalgorithms estimate these physiological parameters directly from the raw sinogramdata, where the noise distribution can be more accurately modelled and thus leading tostatistically more reliable parameter estimates. In this thesis a novel direct parametricimage reconstruction algorithm is introduced, which is based on the expectationmaximisation (EM) framework and is applicable to any spatiotemporal model. Themethod is evaluated for the spectral analysis model, which is a linear temporal modeland a two-tissue compartment model, which is a nonlinear temporal model. Inaddition, the method is evaluated for a linear spatial model and in particular the modelthat is normally used to describe the blurring components in image-based resolutionmodelling. Finally, the performance of gradient-based 3D reconstruction algorithmswas also assessed as an alternative to the well-established EM-based algorithms.