La stabilité structurale et chimique de céramiques bien densifiées candidates pour leur utilisation comme électrolyte ou matériau d'électrode de piles à combustible, électrolyseur H2/air ou même de convertisseur CO2/Hydrocarbures a été étudiée vis-à-vis de l'eau sous pression (autoclave, eau pauvre ou saturée en CO2). La pressurisation maximise l'efficacité des dispositifs. Quatre familles de pérovskites ont été considérées: BaCe0.4Zr0.5Y0.1Zn0.04O3- (BCZYZ), SrZr0.9Er0.1O3- (SZE), Ln2NiO4+ (LNO, Ln = La, Pr, Nd), and La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428). Les céramiques denses sont traitées à 550°C en autoclave plusieurs jours à plusieurs semaines, soit dans des conditions de fonctionnement ( 20 bar, eau sans CO2, 550°C), soit en vieillissement accéléré ( 40 bar eau sans ou saturée de CO2, 550°C). Les céramiques ont été analysées avant et après 'protonation' par Microscopie Optique, Thermogravimétrie, Expansion Thermique, (micro/macro) ATR FTIR, Raman micro-Spectroscopie, diffraction des rayons X et des neutrons. En condition de fonctionnement ( 20 bar), la stabilité des matériaux d'électrodes LNO/LSCF6428 et de l'électrolyte SZE est bonne, alors que la céramique BCZYZ se corrode. La céramique LSFC6428 soumis à des conditions sévères (eau saturée en CO2, 40 bar) est 5 à 30 fois moins corrodée que les composés LNO and SZE. La corrosion s'initie en surface, aux joints de grains. La protonation modifie plus ou moins la symétrie, le volume et les paramètres de la maille unitaire ainsi que les transitions de phase en relation avec la modification de la distribution/organisation des lacunes d'oxygène. Le niveau de dopage en proton des différents matériaux est aussi discuté. / The chemical and structural stability of well-densified ceramics potentially used as H2/air fuelcell/electrolyzer (and perhaps in CO2/Hydrocabons Converter) electrolyte or electrodes vs. CO2-free/saturated pressurized water has been studied. The pressurization maximizes the efficiency of theenergy conversion systems. Four types of pervoskite-related oxide ceramics were concerned:BaCe0.4Zr0.5Y0.1Zn0.04O3-d (BCZYZ), SrZr0.9Er0.1O3-d (SZE), Ln2NiO4+d (LNO, Ln = La, Pr, Nd), andLa0.6Sr0.4Co0.2Fe0.8O3-d (LSCF6428). Dense ceramic samples were exposed at 550°C to water vaporpressure in an autoclave for days to weeks. The protonation treatments were performed in twodifferent conditions: operating condition (£20 bar of CO2-free water pressure, 550°C) and acceleratedaging conditions (³40 bar of CO2-free/CO2-saturated water pressure, 550°C). The pristine and‘protonated’ samples were characterized using various analysis techniques: Optical Microscopy,Thermogravimetry, Thermal Expansion, (micro/macro) ATR FTIR, Raman micro-spectroscopy, X-rayand Neutron Scattering. The study reveals that under the operating condition (£20 bar), the stability ofLNO/LSCF6428 electrode materials and of SZE electrolyte appears good, while the BCZYZelectrolyte exhibit significant corrosion. The superior stability of LSFC6428 exposed in extreme CO2-water vapor atmosphere was demonstrated about 5 to 30 times better than LNO and SZE homologues.The surface secondary phases form at the grain boundary. The protonation modifies more or less thestructure symmetry, the unit-cell volume/parameter and the phase transition sequence in relation withthe modification of the oxygen vacancy distribution. The proton doping level for different samples isalso discussed.

Out-of-Autoclave (OoA) processes for manufacturing aerospace-grade parts needs to be better understood to further the development and success of industries that are manufacturing reusable launch vehicles, military and commercial aircraft, and spacecraft. Overcoming the performance limitations associated with OoA, also known as low-pressure prepreg curing, methods (void count, energy absorption, etc.) will help decrease the costs associated with aerospace composite manufacturing and the negative environmental effects correlated with high-pressure composite curing methods. Experimental, theoretical, and numerical approaches are used to explore both low and high-pressure curing cycles and how the two different processes affect final cured parts. Quasi-static uniaxial compression tests on 33mm diameter tubular specimens concluded that the high-pressure curing methods (up to 90 psi) increased the likelihood of a final part with increased stiffness compared to the lower atmospheric-pressure methods (14.7 psi) on an order of 22%. After further extension and deformation past the linear elastic region, tests concluded that although the autoclaved specimens may have been higher-quality parts, the low-pressure-cured specimens performed more efficiently with respect to energy absorption. Considering the specific energy absorption (SEA) and crush force efficiency (CFE) are both on average around 6% higher for the low-pressure specimens, it is concluded that they can perform similarly to the high-pressure specimens and possibly even more efficiently depending on the loading conditions and desired purpose of the structure.

Objectives: Dental instrument sterilization with steam autoclaves is critical to maintaining infection control standards in dental practice, and preventing patient-to-patient transmission of pathogenic bacteria and viruses. The American Dental Association and the United States Centers for Disease Control and Prevention recommend, and many state dental laws require, weekly use of biological spore tests to verify dental instrument sterilization outcomes. However, the most widely used biological spore test needs microbial culture incubation for 2 days after autoclave exposure, which limits swift identification of sterilization failure. To address this issue, this study evaluated the reliability of a new rapid biological spore test for determining the sterilization efficacy of dental steam autoclaves within 20 minutes. Methods: Two commercial biological spore tests were evaluated in Temple University dental school steam autoclaves, 1.) the Steris Celerity 20 Steam Biologic Indicator with a 20-minute outcome time requirement, and 2.) the 3M Attest 1262 Biological Indicator with a 48-hour outcome time requirement. Both biological spore tests employed live thermoresistant Geobacillus stearothermophilus spores as an indicator of whether sterilization conditions in steam autoclaves were met or not. To compare their efficacy, a total of 157 pairs of the two biological spore tests were placed into dental steam autoclaves with dental instrument cassettes, and subjected to manufacturer-recommended steam autoclave temperature and air pressure operating conditions for an adequate sterilization time of 15 minutes. Two additional groups of 10 pairs each of the two biological indicators were subjected to appropriate steam autoclave temperature and air pressure settings, but only for aborted non-sterilizing time periods of 10 and 5 minutes, respectively. Subsequent aseptic processing and laboratory incubation of both biological indicators was initiated within 2-24 hours, and followed manufacturer recommendations. After autoclave exposure, Steris Celerity 20 Steam Biologic Indicator test ampoules were incubated in a specialized instrument for 20 minutes at 57 °C, which also spectrophotometrically evaluated the microbial culture medium for fluorescent α- glucosidase enzyme signal changes. No change in fluorescent intensity represented successful sterilization, whereas increased fluorescence indicated survival of viable G. stearothermophilus spores germinating into vegetative bacterial cells after failed sterilization. 3M Attest 1262 Biological Indicator ampoules were incubated for 48 hours in a laboratory heating block at 57 °C, after which a pH-based color change in the microbial culture broth was visually assessed. No change in the color of the culture broth (purple color remains) indicated successful sterilization, whereas development of a yellow color in the culture broth, as a result of viable G. stearothermophilus spore germination into vegetative bacterial cells, denoted failed sterilization. Results: A total of 354 biological indicators were exposed to dental steam autoclaves sterilization cycles, incubated for either 20 minutes or 48 hours, and evaluated for G. stearothermophilus spore growth. The Steris Celerity and 3M Attest biological spore tests both uniformly detected successful sterilization, with no G. stearothermophilus spore growth, after 15 minutes of steam autoclave exposure at manufacturer recommended steam autoclave temperature and air pressure operating conditions. This provided 100% agreement, and no statistically significant difference in the prevalence of successful sterilization outcomes, between 157 pairs of both biological indicator types after 15 minutes of steam autoclave exposure. Similarly, both biological spore test systems were also in complete agreement after only 5 minutes of steam autoclave exposure, with 100% of both biological indicators positive for G. stearothermophilus spore growth, indicating failed sterilization. In contrast, after 10 minutes of steam autoclave exposure, there was a complete lack of agreement between the two types of biological indicators. All 10 Steris Celerity spore tests were positive, whereas all 10 3M Attest ampoules were negative, for G. stearothermophilus spore growth after 10 minutes of steam autoclave exposure. Relative to this disagreement, a non-biological chemical indicator strip that was part of the Steris biological indicator test system failed to have a darkened bar develop and extend into the “Accept (OK)” portion of the strip for all Steris Celerity spore tests exposed to either 5 minutes or 10 minutes of steam autoclave exposure, indicating that adequate autoclave steam, temperature and/or time parameters had not been attained for sterilization. Conclusions: The Steris Celerity biological spore test was successful in rapidly determining the sterilization efficacy of dental steam autoclaves within only a 20-minute incubation time period, as compared to 48 hours of incubation required by the widely-used 3M Attest biological spore test. As a result, this rapid assay offers earlier detection of steam autoclave sterilization failure before potentially contaminated dental instruments are used in clinical patient care. The alarming failure of 3M Attest biological spores to grow after a non-sterilizing 10-minute steam autoclave exposure time warrants further product evaluation. / Oral Biology

The non-profit organization Project Vita has recently built a maternity clinic in Linga Linga, where the medical instruments to be sterilized are boiled in water for an hour. The fuel needed to boil the water is wood, which is a scarce resource. This is why, according to the healthcare worker that was interviewed in Mozambique, it is desirable to have an electric-powered solution to sterilise the medical instruments. After research on the different sterilization techniques that exist, the conclusion was drawn that the safest way to sterilise is by the use of an autoclave. However, it would be difficult to implement and maintain an autoclave in Linga Linga. Therefore, it was proposed to build an autoclave using a pressure cooker. Through experimentation, different programs, times and pressures were tested to find out if a pressure cooker could sterilise a common object. It could be concluded that theoretically, it seems that the pressure cooker reached a temperature of over 121 degrees Celsius. However, the pressure could not be measured nor was a biological indicator, that could indicate if an autoclave or pressure cooker does sterile, used.  This project was to be done in Mozambique, but because of COVID-19, a travel ban was set in motion and universities and laboratories had limited access, thus limiting the project. As a result, it is still unclear if a pressure cooker can be used to sterilize medical instruments. / Detta arbete ingår som en del av Project Vitas arbete med en förlossningsklinik i Linga Linga, Moçambique.

Les infections bactériennes lorsqu’elles se développent à partir d’implants sont très difficiles à traiter, l’issue courante étant un retrait pur et simple de l’implant incriminé. Dans ce cadre, les revêtements des biomatériaux ont un rôle important à jouer pour, d’une part, prévenir l’adhésion bactérienne et d’autre part, éliminer les bactéries présentes. Ces revêtements antibactériens doivent par ailleurs permettre une intégration tissulaire des biomatériaux aux cellules rencontrées sur le site de l’implantation. Dans ce travail une nouvelle famille de revêtements antibactériens a été développée. Ils contiennent et libèrent de manière contrôlée un agent bioactif. Ils sont constitués de multicouches de polymère plasma d'anhydride maléique déposées à la surface de fibres de polypropylène tressées et constituant le matériau à implanter. Entre chaque dépôt de polymère plasma (agissant comme couche barrière), des nanoparticules d'argent sont piégées formant ainsi des réservoirs d’agent antibactérien. En raison des différences de propriétés mécaniques entre les films minces plasma et le substrat massique élastique (i.e. tissu de fibre de polypropylène), la résistance à la traction génère des fissures dans les couches polymère plasma, qui sont utilisées comme canaux de diffusion pour les substances bioactives (dans notre cas les ions argent). Avant étirement, la libération spontanée des ions argent par simple diffusion aux travers des couches barrières peut être contrôlée en jouant sur le taux de réticulation des couches plasma. Au cours de l'étirement, le contrôle réversible de l'ouverture des fissures permet une libération maîtrisée des ions argent. Dans le domaine des textiles et d'autres biomatériaux souples, cette stratégie est prometteuse en raison des contraintes mécaniques qui se produisent naturellement sur le site de l'implantation.L'impact de différents types de procédures de stérilisation couramment utilisés (autoclave et irradiation par faisceau d’électrons) sur les propriétés du matériau développé a également été étudié. En particulier, l’incidence sur la chimie de surface, la dispersion des nanoparticules d'argent et la formation de fissures sous étirement a été regardée. La méthode de stérilisation par faisceau d’électrons permet de conserver les propriétés finales recherchées. Enfin, les propriétés antibactériennes du nouveau matériau ont été étudiées. L'effet du relargage des ions argent sur des bactéries Escherichia coli planctoniques, l'adhésion bactérienne et la formation de biofilm sur le système étiré et non-étiré a été évalué. L’intégrité membranaire des bactéries adhérées et des bactéries dans les biofilms a été suivie au cours de l'étude comme indicateur de l’état physiologique des bactéries. Les résultats ont suggéré que la sensibilité des bactéries aux concentrations faibles d'ions d'argent libérés aboutit à la formation de différents types de structures de biofilms sur les matériaux étudiés. L’ensemble des résultats obtenus donne une base solide pour le développement de matériaux intelligents capables de contrôler la libération du principe actif sur le site de l'infection. Nos résultats montrent qu’une faible dose d’argent peut suffire à contrôler l’infection en agissant sur la structure des biofilms formés. / Despite strict operative procedures to minimize microbial contaminations, bacterial infection of implants significantly raises postoperative complications of surgical procedures. One of the promising approaches is to adjust and control antimicrobial properties of the implant surface. New types of antibacterial coatings prepared via plasma polymer functionalization step have been developed. These coatings contain and release in a control way a bioactive agent. Controlled release was achieved by the fabrication of plasma polymer multilayer systems, which consist of two layers of Maleic Anhydride Plasma Polymer deposited on the surface of Polypropylene made surgical mesh. In between plasma polymer layers, silver nanoparticles are trapped as an antibacterial agent reservoir. Owing to differences between mechanical properties of the plasma-polymer thin films and the elastic bulk substrates, tensile strengths generate cracks within the plasma polymer, which might be used as diffusive channels for bioactive substances, here silver ions. The cracks can be controlled mechanically in a reversible way. The tailoring of the spontaneous release of bioactive agent is achieved by the modification of the second plasma polymer deposition conditions. In addition, during mechanical stimulation of the designed material, control over silver ion release is achieved through an elongation-dependent releasing process allowed by the reversible control of the cracks. In the field of textiles and other soft biomaterials, this strategy is promising due to the mechanical stresses that naturally occur at the implant location. In regard of possible application of the developed system as a future biomaterial, the impact of different types of commonly used sterilization procedures on the properties of developed material was studied. The effects of autoclaving and electron beam sterilization methods on the surface chemistry, the dispersion of embedded silver nanoparticles in the plasma polymer and the cracks formation of the developed material was verified. Results showed the compatibility of the developed system with electron beam sterilization method. The antibacterial properties of the new material have been evaluated. The effect of developed system on planktonic bacteria, bacterial adhesion and biofilm formation on stretched and unstretched system was studied. The membrane integrity of the adhered bacteria and bacteria in biofilms was followed during the study as an indicator of the physiologic state of bacteria. Results suggested that the sensitivity of bacteria to low concentrations of released silver ions resulted in the formation of different types of structures of the biofilms on the studied materials. The results give a strong base on the future of intelligent, silver containing materials that control the release at the site of infection. Our results show that low doses of silver may be sufficient to control infection by acting on the structure of bacterial biofilms.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Thermoplastic composites (TPCs) have shown significant advantages over thermosetting composites. They have only been put into use recently and global knowledge in TPCs is often proprietary, therefore a study into the application, processing and properties is of importance. The aim of the study is to contribute knowledge in TPCs for South African industry and academic institutions. This thesis studies continuous fibre reinforced thermoplastics (CFRTPs), focussing on the autoclave processing of commingled CFRTPs. A literature study provided background knowledge to CFRTPs regarding processing techniques and mechanics. Flexural testing and impact testing were performed on a variety of CFRTPs and thermosetting composites (TSCs). These tests were performed to further understand CFRTPs as well as to compare CFRTPs and TSCs. The flexural testing revealed that CFRTPs have comparable strength and stiffness to the TSCs that were tested. They also revealed that pre-consolidated sheets showed better and more consistent properties than sheets made from commingled fabric. The impact testing revealed that the tested CFRTPs and TSCs had similar impact resistance even though thermoplastic composites are supposed to be more impact resistant. The tests also showed that thick unreinforced thermoplastics had much higher impact resistance than the reinforced materials. Manufacturing experiments were performed to establish sound processing methods of CFRTPs. It was realised here that the high temperatures required to process the materials require specific processing consumables and tooling. The experiments began by processing flat panels in a convection oven with vacuum bagging techniques. They then progressed to autoclave processing of parts with complex geometry. An airline seat backrest was chosen as the case study in the application of CFRTPs. This application requires structural strength and stiffness and also has strict fire, smoke, toxicity and heat release (FSTH) requirements. Its geometry was sufficiently complex to demonstrate the use of commingled CFRTP material. Backrests were made from both CFRTPs and TSCs so that a comparison could be made between the two types. The backrest was modelled using finite element methods (FEM) to determine an adequate lay-up. This lay-up was then used for both the CFRTP and TSC backrests to ensure similarity between the backrests of both materials. LPET (modified polyethylene terephthalate) was the chosen thermoplastic matrix as it was more attainable than PPS (polyphenylene sulphide) CFRTPs. The backrests of both materials were manufactured in an autoclave with a vacuum bag method and then assembled using adhesives and bonding jigs. Testing revealed that the stiffness and mass of the CFRTP backrests were very similar to the epoxy backrests. This implies that commingled CFRTPs can replace the use of TSCs in similar applications. A basic cost comparison was also performed to compare the manufacture of CFRTP backrests to TSC backrests. Further work is needed to optimise processing time of these materials to make them more competitive with TSCs. The processing time of commingled materials will probably never be as quick as that of press formed pre-consolidated sheets. Their ability to be formed into more complex parts does however make their use advantageous. / AFRIKAANSE OPSOMMING: Termoplastiese saamgestelde materiale (Engels: thermoplastic composites (TPCs)) toon beduidende voordele bo termoverhardbare saamgestelde materiale. Hulle word eers sedert onlangs benut en algemene kennis in TPCs is dikwels patentregtelik, dus is ’n studie van die aanwending, prosessering en eienskappe daarvan van belang. Die doel van hierdie studie is om ’n bydrae te lewer tot die kennis van TPCs vir die Suid-Afrikaanse industrie en akademiese instellings. Hierdie tesis ondersoek kontinue veselversterkte termoplastieke (Engels: continuous fibre reinforced thermoplastics (CFRTPs)) en fokus op die outoklaafprosessering van vermengde (Engels: commingled) CFRTPs. ’n Literatuurstudie het die agtergrondkennis rakende die prosesseringstegnieke en meganika van CFRTPs verskaf. Buigtoetsing en impaktoetsing is op ’n verskeidenheid CFRTPs en termoverhardbare saamgestelde materiale (Engels: thermosetting composites (TSCs)) uitgevoer. Hierdie toetse is uitgevoer om CFRTPs beter te verstaan asook om CFRTPs en TSCs te vergelyk. Die buigtoetsing het onthul dat CFRTPs ooreenstemmende sterkte en styfheid het as die TSCs wat getoets is. Dit het ook getoon dat vooraf-gekonsolideerde plate beter en meer konsekwente eienskappe getoon het as plate wat van vermengde materiaal gemaak is. Die impaktoetsing het onthul dat die CFRTPs en TSCs wat getoets is soortgelyke impakweerstand gehad het, selfs al is termoplastiese saamgestelde materiale veronderstel om meer impakweerstand te toon. Die toetse het ook getoon dat dik onversterkte termoplastieke veel hoër impakweerstand gehad het as die versterkte materiale. Vervaardigingseksperimente is uitgevoer om betroubare prosesseringsmetodes vir CFRTPs vas te stel. Daar is besef dat die hoër temperature wat vereis word om die materiale te prosesseer ook spesifieke prosesseringsverbruiksware en -gereedskap benodig. Die eksperimente het begin met die prosessering van reguit panele in ’n konveksie-oond met vakuumsaktegnieke. Daar is toe aanbeweeg na die outoklaafprosessering van onderdele met komplekse geometrie. Die rugleuning van ’n vliegtuigsitplek is gekies as die gevallestudie in die gebruik van CFRTPs. Hierdie toepassing vereis strukturele sterkte en styfheid en is ook onderhewig aan streng vereistes t.o.v. brand, rook, toksisiteit en hittevrystellimg (Engels FSTH). Die geometrie daarvan was kompleks genoeg om die gebruik van vermengde CFRTP-materiaal te demonstreer. Rugleunings is gemaak van beide CFRTPs en TSCs sodat ’n vergelyking tussen die twee tipes gemaak kon word. Die rugleuning is gemodelleer deur eindige element metodes (EEM) te gebruik om ’n aanvaarbare oplegging te bepaal. Hierdie oplegging is toe gebruik vir beide die CFRTP en TSC rugleunings om die gelykvormigheid tussen die rugleunings van beide materiale te verseker. LPET (Engels: modified polyethylene terephthalate) was die gekose termoplastiese matriks aangesien dit meer verkrygbaar was as PPS (Engels: polyphenylene sulphide) CFRTPs. Die rugleunings van beide materiale is vervaardig in ’n outoklaaf met ’n vakuumsakmetode en toe geintegreer deur die gebruik van kleefstowwe en setmate. Toetsing het getoon dat die styfheid en massa van die CFRTP rugleunings baie soortgelyk was aan die epoksie rugleunings. Dit impliseer dat vermengde CFRTP die plek van TSCs in soortgelyke gebruike kan inneem. ’n Basiese kostevergelyking is ook gedoen om die vervaardiging van CFRTP-rugleunings teenoor TSC-rugleunings te vergelyk.

Composite materials have traditionally been used in high-end aerospace parts and low-end consumer parts. The reason for this separation in markets is the wide gap in technology between pre-preg materials processed in an autoclave and chop strand fiberglass blown into an open mold. Liquid composite molding has emerged as a bridge between inexpensive tooling and large, technical parts. Processes such as vacuum infusion have made it possible to utilize complex layups of reinforcement materials in an open mold style set-up, creating optimal conditions for composites to penetrate many new markets with rapid innovation. Flow simulation for liquid composite molding is often performed to assist in process optimization, and requires the permeability of the reinforcement to be characterized. For infusion under a flexible membrane, such as vacuum infusion, or for simulation of a part with non-uniform thickness, one must test the permeability at various levels of compaction. This process is time consuming and often relies on interpolation or extrapolation around a few experimental permeability measurements. To accelerate the process of permeability characterization, a small number of methodologies have been previously presented in the literature, in which the permeability may be tested at multiple fiber volume contents in a single test. Some of the methods even measure the permeability over a continuous range of thicknesses, thus requiring no later interpolation of permeability values. A novel method is presented here for the rapid measurement of permeability over a continuous range of fiber volume content, in a single unidirectional vacuum infusion flow experiment. The thickness gradient across the vacuum bag, as well as the fluid pressure at several locations in the mold, were concurrently measured to calculate the fabric compressibility. An analytical flow model, which accounts for the compressibility, is then used by iterating the fitting constant in a permeability model until the predicted flow front progression matches empirical measurement. The method is demonstrated here for two reinforcement materials: 1) a fiberglass unbalanced weave and 2) a carbon bi-ax non-crimped fabric. The standard deviation of calculated permeabilities across the multiple infusion experiments for each material and flow orientation ranged from 12.8% to 29.7%. Validation of these results was performed by comparing the resulting permeability with multiple non-continuous permeability measurement methods.

In the production of base metals by smelting of sulphide ore concentrates, large amounts of iron are rejected with iron silicate slags. These slags contain Ni, Cu and Co in concentrations up to several percent units. Extraction of the entrapped base metals using high pressure oxidative acid leaching (HPOXAL) was investigated in this work. Crystalline slags containing fayalite (Fe2SiO4), magnetite (Fe3O4), silica (SiO2) and matte (MeSn<1) were found to be highly amenable to leaching at 250°C, 90 psi (6.2 bar) O2 partial pressure and 70 g/L initial H2SO4. Extractions of Ni, Co and Cu exceeded 90% within 15-20 min and arrived at 95-97% after 45 min. The residues of leaching were identified as aggregates of crystalline hematite (Fe2O3) and amorphous silica. Dissolution of fayalite and magnetite was shown to be acid driven. Since HPOXAL operates with substoichiometric additions of sulphuric acid (10-20% of the stoichiometric requirement), acid regeneration facilitated by iron oxidation and hydrolysis is crucial to high rates of leaching. Low acidities (<10 g/L) were shown to cause precipitation of ferrous sulphate, slowing acid regeneration and slag dissolution. Elevated acidities (>70 g/L) result in excessive concentrations of Fe(III) in the leach solution, complicating downstream processing. The use of pyrrhotite tailings, an environmentally hazardous waste, as a substitute of sulphuric acid in slag leaching was investigated. Oxidative co-leaching of pyrrhotite tailings with naturally cooled converter slag at 250°C, 90 psi (6.2 bar) O2, 68 g/L equivalent H2SO4 was shown to have kinetics comparable to adding sulphuric acid with final extractions reaching 95-97% in 45 min. Granulation of slag melt can produce an amorphous solid solution of SiO2 and metal oxides. Amorphous slag is not amenable to HPOXAL due to the formation of a passive layer of silica. Leaching of amorphous slag at low temperatures was shown to proceed nearly to completion. The difference in the leachability of amorphous slag at high and low temperatures is explained in terms of the rate of silicic acid re-polymerization leading to closure of pores in the leached layer.

Pressure oxidation of refractory gold ores containing carbonate minerals is conducted under neutral/alkaline conditions in order to promote fast kinetics, reduced reagent consumption and suppressing the formation of elemental sulphur and CO2 (which reduces the effectiveness of the process). In this work, both the addition of sodium carbonate and the presence of silica were investigated during the pressure oxidation of pyrite in the presence of calcium carbonate. It was found that the shift to an alkaline leaching environment favours the formation of soluble sulphate products over anhydrite (an industrial scale), but that the increase in kinetics is likely due to an increase in pH and carbonate/bicarbonate concentrations. The presence of silica in the autoclave induces the formation of an in situ iron oxyhydroxide silicate coating and a significant reduction in pyrite oxidation, which was minimized by addition of sodium carbonate.

In the production of base metals by smelting of sulphide ore concentrates, large amounts of iron are rejected with iron silicate slags. These slags contain Ni, Cu and Co in concentrations up to several percent units. Extraction of the entrapped base metals using high pressure oxidative acid leaching (HPOXAL) was investigated in this work. Crystalline slags containing fayalite (Fe2SiO4), magnetite (Fe3O4), silica (SiO2) and matte (MeSn<1) were found to be highly amenable to leaching at 250°C, 90 psi (6.2 bar) O2 partial pressure and 70 g/L initial H2SO4. Extractions of Ni, Co and Cu exceeded 90% within 15-20 min and arrived at 95-97% after 45 min. The residues of leaching were identified as aggregates of crystalline hematite (Fe2O3) and amorphous silica. Dissolution of fayalite and magnetite was shown to be acid driven. Since HPOXAL operates with substoichiometric additions of sulphuric acid (10-20% of the stoichiometric requirement), acid regeneration facilitated by iron oxidation and hydrolysis is crucial to high rates of leaching. Low acidities (<10 g/L) were shown to cause precipitation of ferrous sulphate, slowing acid regeneration and slag dissolution. Elevated acidities (>70 g/L) result in excessive concentrations of Fe(III) in the leach solution, complicating downstream processing. The use of pyrrhotite tailings, an environmentally hazardous waste, as a substitute of sulphuric acid in slag leaching was investigated. Oxidative co-leaching of pyrrhotite tailings with naturally cooled converter slag at 250°C, 90 psi (6.2 bar) O2, 68 g/L equivalent H2SO4 was shown to have kinetics comparable to adding sulphuric acid with final extractions reaching 95-97% in 45 min. Granulation of slag melt can produce an amorphous solid solution of SiO2 and metal oxides. Amorphous slag is not amenable to HPOXAL due to the formation of a passive layer of silica. Leaching of amorphous slag at low temperatures was shown to proceed nearly to completion. The difference in the leachability of amorphous slag at high and low temperatures is explained in terms of the rate of silicic acid re-polymerization leading to closure of pores in the leached layer.