Thesis (MScEng.)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Slag cleaning has become a common practice at many smelters in the nonferrous industry to maximize recovery of valuable metals. However, during the carbothermic reduction of nonferrous slag to recover cobalt, in particular, iron is recovered predominantly. High iron levels present a problem for the subsequent treatment of the alloy as it may increase the solids loading to the filter and lead to increased reagent consumption during leaching. Finding an appropriate slag modifier that would selectively improve the recovery of cobalt against that of iron to the metallic alloy can solve this problem. In the present study the effects of lime (CaO), rutile (Ti02), and fluorspar (CaF2) on the recovery of cobalt from waste nonferrous slag have been investigated under reducing conditions at 1500°C. The selective recovery of cobalt compared to the recovery of iron at different levels of flux additions is discussed in this study, to show the selectivity of these fluxes. It is also shown in the study that the recovery of cobalt does not only depend on the oxygen partial pressure and temperature but on the slag composition as well. The slags used in the experiments were a) synthetic slag prepared from chemically pure reagents and its composition was derived from that of the industrial nonferrous slag composition typical of reverbaratory furnace and b) actual slag obtained from an old slag dump situated on the Zambian Copperbelt region. The investigation has shown that Ti02 addition leads to the most selective cobalt recoveries in all cases. On the other hand, both CaO and CaF2 lead to higher overall cobalt recoveries. The effect of Ti02 on the slag chemistry leads to the formation of iron titanate compounds in the slag unlike CaO, which displaces "FeO" from the fayalitic slag and thus increases the activity of FeO in the molten slag, which in tum affects the iron recoveries to the alloy product. CaF2 on the other hand, affects the fluidity of the slag leading to improved recoveries by improved settling of metals through the slag to the alloy product. A 44V/I100A DC-plasma arc furnace was used to reduce slag to recover cobalt at about 13.5kV A power input. The major part of the study was conducted in a tube furnace and the findings were applied to the extraction of cobalt from slag using the plasma-arc furnace. It was found that the synthetic slag experiments could be used as a guide to understand the behaviour of cobalt during the carbothermic recovery of cobalt from silica saturated fayalitic slags. Cobalt recoveries were higher in the DC furnace than the corresponding reduction experiments carried out in the tube furnace. However, significant amounts of silicon and carbon were detected in the metallic alloy product of the DC plasma-arc furnace. / AFRIKAANSE OPSOMMING: Slak suiwering is besig om standaard praktyk te word by vele smelters om die herwinning van waardevolle metale uit slak te maksimeer. Tydens die karbotermiese reduksie van slakke vanaf kopersmelters om kobalt te herwin, word beduidende hoeveelhede yster ook herwin. Hoë ystervlakke in die herwinde legering veroorsaak probleme met die stroom-af verwerking van die legering aangesien dit lei tot verhoogde reagensgebruik tydens loging en 'n verhoogde vastestof las of die filterstelsel. Die identifisering van 'n geskikte slak modifiseerder, wat die selektiwiteit van herwinning van kobalt relatief tot yster verhoog, sal hierdie probleem verminder. In hierdie tesis word die rol van kalk (CaO), rutiel (Ti02) en vloeispaat (CaF2) toevoeging tot die selektiewe herwinning van kobalt uit afvalslakke ondersoek. Die karbotermiese reduksie van die slak vind by 1500 °C plaas. Dit word getoon dat bo-en-behalwe die suurstofpotensiaal en die bedryfstemperatuur, die slakchemie 'n beduidende rol speel. Die slakke gebruik in hierdie studie is: a) 'n sintetiese slak gemaak van chemies-suiwer rou-materiale (waarvan die samestelling afgelei is van die samestelling van tipiese reverbereeroond slakke), en b) monsters van die ware slak verkry vanaf 'n slakhoop van die Zambiese Kopergordel. Die studie het getoon dat Ti02 toevoeging gelei het tot die hoogste selektiwiteit in alle gevalle. Daarteenoor het CaF2 en CaO gelei tot hoër algehele herwinnings van kobalt. Ti02 toevoeging lei tot die vorming van ystertitanaat komplekse in die slak, teenoor CaO wat die "FeO" uit die fajaliet struktuur verplaas en die aktiwiteit van FeO in die slak verhoog en dus gevolglik herwinning van yster tot die legering beïnvloed. CaF2 verhoog egter die vloeibaarheid van die slak wat lei tot verhoogde herwinning deurdat die legering druppels makliker uitsak deur die slak. 'n 44VIII OOAGelykstroom-plasmaboogoond is gebruik om die kobalt te herwin uit die slak teen ongeveer 13.5 kVA Die grootste gedeelte van die studie is gedoen in 'n buisoond en die bevindings was dan toegepas op die ekstraksie van kobalt uit slak in die plasmaboogoond. Dit was gevind dat die sintetiese slak eksperimente gebruik kan word as 'n voorlopige gids om die gedrag van kobalt in silika-versadigde slakke tydens karbotermiese reduksie te verstaan. Kobalt herwinnings was oor die algemeen hoër il) die plasmaboogoond as vir die ooreenstemmende reaksies in die buisoond. Daar het egter beduidende hoeveelhede silikon en koolstof In die legering opgelos tydens die plasmaboogoond eksperimente.

The influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics.

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Paraffin activation has practical implications in the replacement of current petrochemical feedstocks (olefins), by utilizing economical and easily accessible alkanes, which may result in more efficient strategies for fine chemical synthesis and the proficient use of energy. However, the chemical inertness of paraffins limits their conversion to more valuable products. Several pincer chelate complexes are utilized in stoichiometric and catalytic C–H activation. These pincer ligands have attained much interest in that they are part of a system, which displays high stability, activity and variability. In this study four aminodiphosphine (PNP) pincer ligands were successfully synthesized and characterized by NMR, IR and HRMS. To investigate the steric effects on the metal center, four different functional groups on the nitrogen atom were used, a cyclic ring (cyclohexyl (3.1)) branched chain (iso-propyl (3.2)); straight chain (pentyl (3.3)); and aromatic ring (benzyl (3.4)). The ligands were successfully complexed to the transition metals iridium and cobalt and characterized by elemental analyses, IR, HRMS and thermogravimetric measurements. The thermal behaviour of the ligands showed that ligands 3.1-3.3 displayed similar decomposition patterns. Similar fragmentation patterns were observed for the iridium and cobalt complexes containing ligands 3.1 and 3.3. The complexes were tested in the oxidation of n-octane in two solvent systems, DCM and MeCN with H2O2 and t-BuOOH as the oxidants. The optimum substrate to oxidant ratio was found to be 1:5. No conversion was observed with H2O2. The conversion in DCM for the iridium catalysts was much higher than that of the cobalt catalyst. However, higher conversion was obtained in MeCN for the cobalt catalysts. No conversion was observed for the iridium catalyst in MeCN. The selectivity to ketones was much higher than to the alcohols, with only the C(1) position being most selective to the alcohols. The in situ, single pot testing of n-octane using a ruthenium precursor and ligand 3.1- 3.4 undertaken in DCM showed no conversion, whilst in MeCN a conversion of 17% was observed. The selectivity was similar to that obtained by the cobalt catalysts in MeCN. All testing showed that the catalyst containing ligand 3.1 was the most active giving the highest conversions in different solvent systems, which is attributed to the bite angle effect. / Thesis (M. Sc.)-University of KwaZulu-Natal, Durban, 2011.

The cobalt-catalysed alkylative aldol cyclisations of α,β-unsaturated amides with an appendant ketone were studied using a range of trialkylaluminium reagents. Investigations revealed that Co(acac)2·2H2O acts as an effective precatalyst for this transformation and the reaction provides β-hydroxylactam products containing three contiguous stereocentres with high levels of diastereoselection. The substrate scope of the reaction was explored and attempts were made to develop an asymmetric variant of this process. Two plausible reaction mechanisms have been proposed; the first invokes a π-allylcobalt species as a key intermediate in the reaction mechanism and the second involves a radical-mediated pathway. A stereochemical rationale for the observed relative stereochemistry of the β-hydroxylactam products has been discussed. II. Rhodium-Catalysed Carbometallations of Ynamides in the Preparation of Multisubstituted Enamides A highly stereo- and regioselective rhodium-catalysed carbozincation of ynamides using organozinc reagents has been disclosed. A careful examination of ligand effects on the rhodium catalyst yielded a complementary set of hydrozincation conditions. The alkenylzinc intermediates produced during the course of these reactions have been harnessed in further transformations with electrophilic species and in cross-couplings, thus providing access to multisubstituted enamides in a stereo- and regioselective fashion. Additionally, a rhodium-catalysed tandem carbometallation−conjugate addition with ortho-boronate substituted cinnamic acid derivatives has been described. The enamide−indene products were obtained in good yields and regioselectivities. Preliminary work has been undertaken on an asymmetric variant of this transformation and the initial results have been reported.