OpenUCT :: Browsing by Author "Hansford, Geoffrey Spearing"

Browsing by Author "Hansford, Geoffrey Spearing"

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Open Access
Activated sludge process : effects of feed concentration on effluent COD
(1977) Baskir, Cyril Isadore; Hansford, Geoffrey Spearing
The concentration of substrates in the feed to an activated sludge process was found to exert a significant effect upon its effluent COD. A mathematical model was proposed to explain this effect and was successful in correlating the data of this study. The model was based on the hypothesis that COD measures both substrate and product concentrations. It was found that an optimum sludge age exists for achieving minimum effluent COD. At sludge ages longer than the optimum, effluent COD increased due to product formation; at shorter sludge ages the effluent COD increased due to an increased concentration of degradable substrate.
Open Access
An assessment of oxygen availability, iron build-up and the relative significance of free and attached bacteria, as factors affecting bio-oxidation of refractory gold-bearing sulphides at high solids concentrations
(1994) Bailey, Andrew Douglas; Hansford, Geoffrey Spearing
Bacterial oxidation is currently finding significant application for the oxidative pretreatment of refractory gold-bearing sulphides. Plants processing sulphide concentrates have commonly been operated at solids concentrations of between 18 and 20 per cent (m/v) (Le 180 and 200 kg.m-3). At higher concentrations, a decline in the bio-oxidation rate has been observed. Other metallurgical processes, such as chemical leaching and cyanidation, are performed at higher solids concentrations of between 40 and 50 per cent (400 and 500 kg.m-3), providing an incentive to increase the solids concentration at which bio-oxidation plants are operated. A review of literature indicated the following factors to be potential causes of reduced bio-oxidation rates at high solids concentrations: oxygen and carbon dioxide mass transfer; a low bacteria-to-solids ratio; mechanical damage of the bacte.ria; and the build-up of inhibitory oxidation products. Interaction of these factors in the completely-mixed reactors that are commonly used for biooxidation, has confounded the interpretation of the effects of individual factors. Analysis of literature data revealed a link between the sulphide grade of a particular material and the highest solids concentration at which the bacterial oxidation rate was maximal. The oxygen demand is directly proportional to the sulphide concentration in the reactor. Correlations were used to predict the oxygen transfer potential in the experimental reactors and it was found that as long as the oxygen transfer potential exceeded the oxygen demand, the biooxidation rate was proportional to the solids concentration for a specific material. Wh~n the oxygen demand equalled or exceeded the oxygen transfer potential, then the bacterial oxidation rate was limited by oxygen availability. The sulphide grade is characteristic of a particular ore or concentrate and from the data analysis oxygen availabiiity appeared to be the underlying reason why low grade materials could be oxidised at the maximum specific bio-oxidation rate at far higher solids concentrations than high-grade f!laterials. Abstract ii The experiments performed in this study were designed to further investigate the apparent relationship, identified by analysis of literature data, between sulphide grade and the solids concentration at which the bacterial oxidation rate was maximal. The effect of both solids concentration and sulphide grade on the biooxidation rate was investigated and related to the oxygen availability in the reactor.
Open Access
The batch and continuous bacterial leaching kinetics of a refractory gold-bearing pyrite concentrate
(1989) Chapman, J T; Hansford, Geoffrey Spearing
The recent focus on bacterial leaching as a preoxidation step in the treatment of refractory gold bearing sulphide ores and concentrates, has created the need for kinetic models to adequately describe bacterial leaching reactor performance. This work is a kinetic study of the bacterial leaching of a refractory gold bearing, pyrite concentrate. The study includes the presentation of two mechanistically based, the shrinking particle and propagating pore (Hansford and Drossou, 1986), batch reactor kinetic models. These models are derived for single stage continuous reactor description. In addition, the empirical logistic growth model (Pinches et al., 1987) is presented for both batch and continuous reactor description. The models are correlated with the experimental data. Three narrow size fractions of the pyrite concentrate were subjected to batch and continuous bacterial oxidation, using a Thiobacillus ferrooxidans culture. Time profile data of the pyrite oxidation were obtained for the batch reactor study. Similarly, retention time profile data of pyrite oxidation was obtained for the single stage continuous reactor. The .gold extraction as a function of sulphide oxidation as well as fraction arsenic leached, was established.
Open Access
Biooxidation of a gold bearing arsenopyrite/pyrite concentrate
(1990) Miller, D M; Hansford, Geoffrey Spearing
The objectives of this project have been to characterise the biooxidation of an auriferous pyrite/arsenopyrite flotation concentrate, and to interpret laboratory batch and continuous pilot plant data in the light of the logistic model. Furthermore, the possibility of predicting continuous biooxidation plant performance from batch data was considered. The batch testing was carried out on five narrowly sized fractions of Fairview concentrate, as well as on the bulk concentrate. Extents of removal of iron, arsenic and sulphide-sulphur were described by the logistic equation and values of the kinetic parameters obtained. Maximum rates of removal of these components, predicted by the logistic parameters, correlated well with experimentally determined rates of removal obtained from the linear portions of the fractional removal versus time curves. Bibliography: pages 93-98.
Open Access
Disruption of microorganisms due to agitation in slurries of fine particles
(1993) Pearce, Sarah Jane Amanda; Harrison, STL; Hansford, Geoffrey Spearing
This dissertation presents the results of an investigation into the disruption of microorganisms when agitated in slurries of fine particles in a stirred tank. The most widely used industrial process involving agitation of microorganisms in slurries of particles in stirred tanks is the biooxidation process. Mixed cultures of thiobacilli are used in stirred tank reactors for the biooxidation of sulphide minerals. In addition to operating conditions, the efficiency of biotechnological processes is dependent on the growth and metabolism of the microorganisms. The microorganisms are sensitive to the hydrodynamic conditions generated in the processes. In response to adverse hydrodynamic conditions there may be changes in the growth rate of the microorganisms, the nutrient uptake rate, the product formation rate and morphology of the microorganisms. Under extreme conditions cell damage and disruption may ensue. The presence of particulates in bioprocesses, in the form of solid substrates or support systems for attached growth, further complicate the hydrodynamic conditions. The knowledge of the effect of particulates on microorganisms is an important priority.
Open Access
The effects of solution conditions on the kinetics of microbial ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture
(2008) Ojumu, Tunde Victor; Petersen, Jochen; Hansford, Geoffrey Spearing
The objective of this work was to investigate the effects of a wide range of solution conditions,namely: temperature, pH, dissolved Al and Mg, and the effect of total iron concentration on the kinetics of microbial ferrous-iron oxidation by Leptospirillum ferriphilum, with a view to developing a comprehensive rate equation.
Open Access
Ethanol inhibition of continuous anaerobic yeast growth
(1981) Hoppe, Gerhard Klaus; Hansford, Geoffrey Spearing
The growing interest in fermentation and fermentation technology as a means to produce chemicals has led to the investigation of different aspects of many fermentations. In this work, the inhibitory effects of the product ethanol on the yeast Saccharomy cescerevisiae ATCC 4126 have been studied during the conversion of the substrate glucose. Continuous culture techniques under anaerobic conditions (the medium was not deaerated) were used where high concentrations of ethanol were produced by the yeast itself. This was in contrast to previous studies in the literature where ethanol was added to the culture.
Open Access
An experimental and theoretical study of the flow about spheres and discs rotating slowly in viscoelastic fluids
(1974) Cairncross, Eugene Kenneth; Hansford, Geoffrey Spearing
An analysis of the flow about a sphere rotating slowly in a Rivlin-Ericksen fluid contained in a stationary outer concentric sphere is presented. An application of the conformal mapping technique is proposed. The technique is used to obtain the radial and axial velocity components for the flow about a disc rotating within an outer oblate spheroidal shell from the solution to the corresponding problem of the flow about a sphere rotating within an outer spherical shell. The results are compared with an existing rigorous analysis for a disc rotating in an infinite sea of the Third Order fluid. They are also used to estimate wall effects in experimental situations. Tangential and radial velocity profiles are measured for the flow about a sphere rotating slowly in a Newtonian liquid. Velocities are determined from enlarged streak photographs of aluminium particles moving in a collimated 'sheet' of light, at several planes throughout the flow field. Similar velocity profiles are measured for the flow of a 1,50% Natrosol 250 H solution about two spheres of different diameters rotating in tanks with different dimensions. A set of velocity distributions is also measured for a sphere rotating in a 0,9% Natrosol 250 H solution; a dye tracer study of the flow about a sphere rotating in this liquid is presented as well. Velocity profiles are presented for the flow of the 1,50% Natrosol solution about a rotating disc and the flow of the 0,9% solution about a second rotating disc of different diameter. Both Natrosol solutions exhibited viscoelastic behaviour in all cases. The Newtonian fluid study is at a Reynolds number of 1,2: all viscoelastic fluid studies are within the range of Reynolds numbers of 0,05 to 1,24. The zero shear viscosities of the Natrosol solutions are measured using the falling sphere method. The non-Newtonian material parameters are obtained by fitting the theoretical curves to the measured velocity data. The values of the elastic and shear thinning parameters for the two fluids obtained in the different geometrical and dynamical systems are compared.
Open Access
The feasibility of reverse osmosis as a water reclamation process with special reference to the rejection of organic compounds
(1986) Schutte, Christiaan Frederik; Hansford, Geoffrey Spearing
This thesis deals with water reclamation and water reuse in the South African water supply context. The overall objective of the study is to assess the potential role and feasibility of reverse osmosis as a water reclamation process. In order to achieve this objective a number of separate desk, laboratory and pilot plant studies were conducted. It was concluded from the first desk study that a significant potential role exists for reverse osmosis in the South African water economy, mainly for the treatment of industrial effluents and, in the longer term, for the reclamation of water from sewage effluents and for the treatment of effluents and recycled water in indirect water reuse situations. A cost analysis showed that reverse osmosis could become economically viable in some water reuse situations in the near future provided that a productive membrane life of about three years can be achieved and that membrane fluxes can be maintained at design rates. These findings indicated the need for a pilot plant study to determine the effects of pretreatment and membrane cleaning on flux levels and rejection. A 50 m³/d pilot plant was designed and operated for a period of about six months from which it was concluded that acceptable flux levels can be maintained in tubular reverse osmosis plants treating well-oxidized activated sludge effluent with and without extensive pretreatment, provided both chemical and physical cleaning methods are employed. The desk study on the rejection of contaminants by reverse osmosis membranes indicated the need for a simple model that can be used to predict the removal of organic compounds of interest in water reclamation applications. It was concluded from a fundamental laboratory study, which included the evaluation of existing membrane models against laboratory data, that the solvophobic theory can be adapted in a simplified form to predict the transport of dissolved organic compounds in relatively non-polar reverse osmosis membranes. Based on reverse osmosis, diffusion, sorption and desorption data a mechanism is, furthermore, proposed for the transport of phenol in different membranes.
Open Access
The ferric leaching of pyrite
(1997) May, Noelene; Hansford, Geoffrey Spearing
The bioleaching of pyrite has been found to occur via an indirect mechanism. Ferric iron leaches the pyrite, and is reduced to ferrous iron. Bacteria such as Thiobacillus ferrooxidans oxidise the ferrous iron to ferric iron, thus maintaining a high redox potential. In this thesis, the effect of the redox potential on the ferric leach rate was investigated by examining previously published data and by developing an experimental technique where dynamic redox potential measurements were used to study the kinetics of the sub-process. The ferric leach rate of pyrite was found to be of the order of 5 x 10⁻⁷ moles pyrite per mole pyrite per second, which is of the same order of magnitude as rates reported for the bioleaching of pyrite over similar ranges of redox potential. The rate decreased as the redox potential decreased, in what appeared to be a Butler-Volmer-like manner. This, along with the observation that there was no significant effect of the total iron concentration, suggested the likelihood of an electrochemical mechanism being operative, with charge transfer at the pyrite surface being rate limiting.
Open Access
An investigation into the ferric leaching of chalcopyrite : a sub-process in the bioleaching of chalcopyrite
(2001) Jeevaratnam, Elizabeth Geethika; Hansford, Geoffrey Spearing
The current focus of research in the UCT Minerals Bioprocessing Research Unit is to develop an understanding of the chalcopyrite bioleaching sub-processes. This thesis forms part of the greater study on bioleaching, investigating the ferric leaching subprocess. The objective of this thesis was two-folds. Firstly, a detailed literature review was undertaken to develop a better understanding of the ferric leaching of chalcopyrite and the cause of passivation during chalcopyrite leaching. Secondly, leach experiments on pyrite were used to establish the applicability and reproducibility of measuring the rate of ferric leaching at a constant redox potential, using the methodology developed by Kametani and Aoki (1985). Following this, chalcopyrite ferric leach experiments were conducted to obtain the redox potential range where chalcopyrite leaching occurs. The rate of chalcopyrite leaching in a sulfate media decreases with time due to the formation of a passivating layer. This has been described by many researchers as parabolic kinetics (Dutrizac, 1982; Beckstead et al., 1976; Munoz et al., 1979 and Dutrizac and Mac Donald, 1974). The nature of the passivating layer is still under considerable debate. Current theories of passivation include either the formation of jarosite, ferric hyroxy sulfate, sulfur or iron deficient polysulfide like covellite (Klauber et al. , 2001 , Parker et al., 1981 , Munoz et al, 1976, Warren et al., 1985 and Parker et al., 1981). Recent research has suggested that different passivating layers are formed during the various stages of chalcopyrite leaching. These include a ferric hydroxy sulfate layer followed by jarosite over extended period of time (Klauber etal., 2001 and Parker et al., 2001 ). Current investigations are underway to establish whether semiconductor properties of the mineral affects the type of passivating layer formed. To date, most of the work has been performed at temperatures higher than those at which chalcopyrite bioleaching occurs and with varying pH and redox potentials. There has been little consideration of the potential difference between the suspended particles surface and the solution. This problem can be overcome by conducting experiments at a constant solution redox potential. Kametani and Aoki (1985) first presented a method of maintaining a constant redox potential by using potassium permanganate as an oxidant to continuously re-oxidise ferrous-iron to ferric-iron. This method was then adopted by our research group to determine the initial rates of chalcopyrite leaching. Preliminary rates of chalcopyrite leaching were presented in the thesis by Furamera (2000). Further work was required to firmly establish the rates of chalcopyrite leaching and the optimal redox potential range within which chalcopyrite leach occurs. This involved optimising the redox potential control system to obtain better redox potential control during the chalcopyrite leach experiment.
Open Access
An investigation into the mechanism of bioleaching of a predominantly-chalcopyrite concentrate with mesophiles
(2002) Jaffer, Ashraf; Hansford, Geoffrey Spearing
Bioleaching is an established technology for the treatment of refractory gold ores and concentrates. The bioleaching of sulphide minerals is a complex process in which bacterial and chemical oxidation processes occur simultaneously. Recent studies has provided convincing evidence that the bioleaching of pyrite occurs via a two-step mechanism (Boon, 1996).
Open Access
An investigation into the use of batch experiments in the determination of the kinetics of ferrous-iron oxidation by Leptospirillum ferrooxidans
(2000) Dempers, Christian John Nicholas; Hansford, Geoffrey Spearing
The objectives of this research were to investigate the effect of temperature and pH on the bacterial ferrous-iron oxidation by Leptospirillum ferrooxidans in batch culture and compare these results with those previously obtained in continuous culture. An additional objective was to assess the validity of a variable maintenance equation by a re-evaluation of previously published literature and to evaluate this equation for use during bacterial ferrous-iron oxidation with more than one limiting factor. The ferrous-iron oxidation kinetics of a predominantly Leptospirillum ferrooxidans culture were studied in batch bioreactors. The inoculum for the batches was obtained from steady state continuous cultures of predominantly Leptospirillum ferrooxidans grown on ferrous-iron medium at a dilution rate of 0.04 h-¹. The continuous cultures were grown at the conditions (temperature and pH) at which the batches were operated. The batches were started with a inoculum of 500 ml and 500 ml of a salts medium containing 12g.l-¹ ferrous-iron. The batches were run at temperatures ranging from 30 to 40°C and pH values ranging from pH 1.10 to pH 1.70. The growth rate and the oxygen and ferrous-iron utilisation rates of the bacteria were monitored by means of off-gas analysis and redox potential measurement. The re-evaluation of previously published data proved that the bio-oxidation of ferrous-iron can be represented using a variable maintenance equation proposed by Pirt (1982). An estimation of the maximum bacterial specific ferrous-iron utilisation rate and the maximum bacterial specific growth rate can be obtained from batch or continuous experiments that have been limited by more than one factor e.g. ferrous-iron, arsenic, ammonia, phosphate, sulfate, growth rate. The maximum bacterial specific ferrous-iron utilisation rates and the maximum bacterial specific growth rates calculated from the variable maintenance model are very similar to those values previously published and affirms the validity of the equation. The batch growth curves follow expected trends and have a very long exponential phase and a very short deceleration phase. The bacterial growth during the exponential phase follows first order kinetics with respect to biomass concentration and is independent of the substrate concentration. It was not possible to determine the maximum bacterial yields and the maintenance coefficients during the batch bacterial ferrous-iron oxidation using the constant maintenance energy equation of Pirt (1965). The reason for this is that at the beginning of a batch the ferrous-iron concentration is very high and the culture is limited by the growth rate, while at the end of a batch it is limited by ferrous-iron and inhibited by the ferric-iron product. A variable maintenance energy equation, proposed by Pirt (1982), had to be used to calculate the maximum bacterial yields and the constant-and variable maintenance coefficients. The maximum bacterial yields on ferrous-iron and oxygen and the respective constant, and variable maintenance coefficients did not vary significantly with temperature or pH. The average maximum yield and constant maintenance coefficient calculated were similar to those reported previously for Leptospirillum ferrooxidans in continuous culture and for Acidithiobacillus ferrooxidans in continuous and batch culture. The maximum bacterial specific ferrous-iron utilisation rate and the maximum bacterial specific growth rate calculated from the variable maintenance equation are very similar to those previously published. The constant maintenance equation is only valid for bacterial ferrous-iron oxidation if the culture is only limited by the substrate during the whole experiment. If at any stage the culture is limited by another factor then the bioenergetics must be represented using the variable maintenance equation. The variable maintenance equation should therefore replace the constant maintenance equation when quantifying the bioenergetics of bacterial ferrous-iron oxidation and the bioleaching of sulfide minerals. The variable maintenance equation is especially relevant to the bioleaching of sulfide minerals at low redox potentials (high ferrousiron concentrations) where the bacterial culture may not be limited by the energy source (ferrous-iron). The growth rate during the deceleration phase in a batch culture is limited by the substrate, ferrous-iron, and follows Michaelis-Menten based kinetics. The kinetic parameters calculated from batch experiments were very similar to those calculated by previous researchers in continuous experiments. The variation of temperature and pH, however produced different results in batch and continuous experiments. The continuous experiments are more accurate for representing bacterial ferrous-iron oxidation kinetics limited by ferrous-iron because batch experiments have transient conditions and the limitation by ferrous-iron occurs over a very short time, hence a limited number of data points can be obtained. Batch experiments, however are useful for initial short-term analysis of a system and to provide an initial indication of the kinetic modelling parameters.
Open Access
An investigation of the kinetics of thermophilic microbial ferrous iron oxidation in continuous culture
(2006) Searby, Giles Edward; Hansford, Geoffrey Spearing
The potential of thermophilic micro-organisms to bioleach primary copper sulfides and other minerals has led to the need to develop a fundamental understanding of the mechanistic process involved. Ferrous iron oxidation has been established as a key step in bioleaching and is understood to be achieved largely by microbial action. The objective of this work was to determine an appropriate set of kinetic expressions that describe the rates of microbial growth and ferrous iron oxidation of a thermophilic archeal culture grown in continuous culture on ferrous iron between 60 and 80°C.
Open Access
Kinetics of the ferric sulphate leaching of sphalerite and sphalerite/pyrite mixtures : a study of the chemical leaching of base metal minerals under conditions similar to that of bio-leaching by thiobacilli
(1996) Fowler, Terry-Ann; Hansford, Geoffrey Spearing
The work presented in this dissertation is an investigation of-the ferric leaching of zinc from sphalerite. A further aspect of this study was an investigation of the influence of pyrite on the dissolution rate of sphalerite due to possible galvanic interactions. This study is one component of a larger study of the sub-processes involved in the bioleaching of sulphide minerals in which the ferric leaching of the sulphide mineral is assumed to be a chemical step with the bacteria oxidising ferrous iron to ferric iron and elemental sulphur, if formed, to sulphate. The literature showed that two types of model have been used to describe the ferric leaching of the sphalerite. The first type was a shrinking-particle model in which there action was described by first order kinetics or an electrochemical mechanism. The second type included a mass transfer resistance in terms of a shrinking-core model described by half-order kinetics or a decaying diffusion coefficient. All four of these models were tested for their ability to predict published data for the ferric leaching of sphalerite. It was found that the models fitted the data for the initial period of a leach up to conversions of about 50%. However, no one of the models was found to be successful in predicting the data for prolonged leaching to high conversions.
Open Access
A laboratory study on the anaerobic digestion of yeast waste
(1973) Richter, Harold Ian Henry; Hansford, Geoffrey Spearing
This thesis reports the establishment of a new type of internally clarified digester as a means of treating a strong industrial waste. Factors pertaining to both the system and the waste itself were investigated. A batch system was used to determine the susceptibility of the waste chosen, viz. that from the first separator of a local yeast factory, to anaerobic digestion. The reactor-clarifiers were constructed and operated at a wide range of loadings. A constant hydraulic retention time was maintained for each of the digesters and sufficient sludge withdrawn daily to maintain a constant sludge concentration over the range of loadings used. The ability of each of the parameters used to monitor digestion, to predict periods of digester imbalance was investigated. A mathematical model was derived to describe the process and the kinetic parameters related to the anaerobic digestion of yeast waste evaluated. Possible inhibitory substances present in the waste and/or generated during digestion and their influence on the system were investigated.
Open Access
The modelling of a falling sludge bed reactor using AQUASIM
(1999) Ristow, Neil E; Hansford, Geoffrey Spearing
This dissertation details the modelling of a Falling Sludge Bed Reactor (FSBR) using AQUASIM. This study is one of the first of a series of projects investigating the design and use of this novel bioreactor for enhanced hydrolysis of particulate organic matter. The main feature of this bioreactor is the increased solids retention time obtained by allowing the solid matter to settle into three valleys, while the aqueous phase exits with a relatively short retention time. The main aim of this project was to identify the state of the art regarding mathematical modelling of anaerobic digestion and biological sulfate reduction, to select rate equations from the literature that would simulate the various interactions taking place in the FSBR being fed a mixture of organic matter and acid mine drainage, and to investigate the trends obtained from the an AQUASIM model of the system. This would then serve as a basis for further projects, which would include identification of the enzymatic interactions in the FSBR, kinetic studies of critical processes not available in the current literature, and the development of a more complex mathematical model that would include factors other than the biological processes.
Open Access
Modelling of batch and fed-batch ethanol fermentation
(1989) Glyn, Julian E H; Hansford, Geoffrey Spearing
Two series of batch and fed-batch fermentations were carried out using S.cerevisiae in a semi-defined medium containing 200 gl-1 glucose as limiting substrate. Growth rates were calculated and the data used to test the applicability of eight empirical kinetic models. The form proposed by Levenspiel, combining the concept of a limiting ethanol concentration with a power-law form, gave the best results with these data. Glucose concentration was found to have a far smaller, though not negligible, effect on growth rate under these conditions. It was also observed that in fed-batch fermentations the total substrate uptake rate of the broth became constant soon after commencement of feeding, without cessation of growth. It is suggested that ethanol inhibits the synthesis of a rate-controlling enzyme in the glycolyti·c chain, but no previous work could be found to support or refute this explanation. A quasi-mechanistic model of growth under the condition of constant substrate consumption rate is formulated and discussed.
Open Access
A Preliminary investigation of the ferric leaching of a mixed sulphide copper concentrate at controlled redox potentials
(2000) Furamera, Tendai Attan; Hansford, Geoffrey Spearing
This thesis is part of the greater study and looks into understanding the ferric leaching sub-process by establishing an effective way of measuring the rate of the chemical leach process.
Open Access
A Preliminary investigation of the kinetics of biological sulphate reduction using ethanol as a carbon source and electron donor
(2000) Erasmus, Clive L; Harrison, STL; Hansford, Geoffrey Spearing
Bibliography: leaves 106-113.