Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1909. / Year degrees were granted determined from "Forty-First Annual Catalogue. School of Mines and Metallurgy, University of Missouri". The entire thesis text is included in file. Typescript. Illustrated by authors. Title from title screen of thesis/dissertation PDF file (viewed )

Cyanide is produced throughout a plant's life cycle alongside the hormone ethylene by oxidation of 1-aminocyclopropane-1-carboxylic acid. Production increases during certain developmental stages such as seed germination, seedling elongation, fruit ripening and senescence. Abiotic stresses increase ethylene production giving rise to `stress cyanide'. Cyanide also comes from metabolism of cyanogenic compounds. Cyanide is however, a toxic chemical which readily binds to metallo-enzymes inhibiting primary metabolic processes. Plants have mechanisms to maintain cyanide homeostasis such as the β-cyanoalanine pathway whereby cysteine reacts with cyanide forming β--cyanoalanine, mediated by β-cyanoalanine synthase and cysteine synthase. A dual nitrilase 4 enzyme then converts the β-cyanoalanine into asparagine or aspartate and ammonium. Studies have suggested that the physiological function of the pathway is not restricted to detoxification and assimilation of excess cyanide. The overall research goal was to investigate the role of the pathway in plant tolerance to water deficit and exogenous cyanide exposure in Arabidopsis thaliana. The first objective was to investigate responsiveness of the pathway to duration and intensity of water deficit and cyanide exposure. The second was to investigate the contribution of enzymes associated with the pathway to cyanide metabolism. The questions addressed were whether there is enzymatic redundancy in enzymes associated with the first step of cyanide detoxification and whether there is pathway redundancy between the β-cyanoalanine and an alternative sulfurtransferase pathway. A. thaliana Col-0 and three SALK-line mutants with a T-DNA insertion for the genesAtCysA1, AtCysC1 and AtNIT4 were grown and exposed to water stress. Physiological and biochemical measurements were taken. The results showed a transient increase in cyanide concentration and β-cyanoalanine synthase activity on exposure to stress. The response pattern was similar regardless of intensity or duration of stress. Knocking out AtCysA1 or AtCysC1 did not impair the ability of plants to metabolize cyanide and tolerate stress i.e the enzymes were functionally redundant. The AtNIT4 mutant however, was impaired in cyanide metabolism and exhibited a sensitive phenotype under both stresses, suggesting that the cyanoalanine pathway is the sole pathway in cyanide detoxification. The results show that the pathway may be an important tool in improvement of plant tolerance to abiotic stress.

Thesis (MTech (Chemical Engineering))--Cape Technikon, Cape Town, 2001. / Carbon-in-pulp technology is used extensively in the mining industry to recover metal cyanides from solution. Also this technology has found increasing application in the gold mining sector, replacing the less efficient zinc precipitation procedure. The extensive use of carbon in such processes have prompted many researchers to investigate the mechanism of metal cyanide adsorption. Not only has this provided many viable theories in the understanding of the mechanism, but has also led to an improved understanding of the effects of the various operating conditions on the ClP circuit. Also the modelling of this process has resulted in proposed rate equations of which the famous "kn" model is the most widely used in design. This is a single rate equation that could result in significant errors and hence a dual resistance model was developed. However this model is mathematically complex. Recently in an attempt to overcome the shortcomings of previous models, empirical calculations to accurately describe adsorption kinetics were developed at the Cape Technikon. These correlations were derived using batch experimental data. In this study the focus was on modeling the adsorption process on a continuous scale using a laboratory scale cascade system. This study utilized the fact that solution concentration is the main driving force for aurocyanide adsorption onto activated carbon and that carbon loading has an indirect effect on adsorption kinetics. The metal was ultimately tested against actual plant data and provided very accurate results.

Thesis (MTech(Chemical engineering))--Cape Technikon, Cape Town, 2001 / Over the years the carbon-in-pulp technology has been refined to become the highly efficient process that is used in our present-day system of recovering dissolved gold from cyanide leached pulps. The efficiency of a CIP circuit mainly depends on the effectiveness ofthe adsorption section as it not only determines the amount of soluble gold lost in the residues, but also indirectly affects the function of the other processes in the plant. Research in this area has declined over the past few years as a result of a decrease in the gold price. It is now more than ever important to investigate the operating conditions ofthe adsorption process to ensure that a highly effective system is maintained.The adsorption of gold cyanide onto activated carbon is to a large extent dependent on maintaining operating conditions well above those of equilibrium. The Freundlich and the Langmuir isotherms have been used by many researchers to describe the equilibrium conditions of the adsorption process. The general practice in the carbonin- pulp technology is to use an isotherm for the prediction of a circuit's performance. As confidence has increased in the reliability of these predictions, it has become important to acquire knowledge of the equilibrium condition that is driving the process. Previous research findings have indicated that the equilibrium isotherm of gold cyanide adsorption onto activated carbon is influenced by changes in the adsorption conditions down the adsorption train. This equilibrium or isotherm shift may lead to errors in the prediction of gold adsorption rates, which results in the filct that the simulations of the performance of the CIP circuits are not reliable. In this study the aim was to investigate the combined influence of various operating conditions on the adsorption equilibrium

Thesis (MTech (Chemical Engineering))--Cape Technikon, Cape Town, 2000 / Due to equilibrium constraints and the relatively slow kinetics of the cyanidation of gold ores, calcium or potassium cyanide is added to the leaching stage in excess to that required theoretically. This, in many situations, result in large concentrations of free cyanide present in the effluent streams from gold plants. In view of the toxicity of cyanide and the fact that cyanide is fatal in small dosages, authorities have been forced to tigl1ten up plant discharge regulations. Therefore, it is vital to remove cyanide from industrial effluent, not only to meet standard requirements, but also to recover the cyanide as a means of reducing chemical costs. The aim of this study is to recover, rather than destroy, free cyanide from effluent streams via a metal impregnated carbon-in-column configuration. The first part of the study focused on the mechanism of free cyanide recovery by metal impregnated carbon and the factors influencing the kinetics of the process in a batch reactor. The second part concentrates on the optimisation of such a process m a column configuration, and subsequently to recover the cyanide from the carbon. In the batch experiments it was found that impregnated metal carbon outperformed virgin carbon for free cyanide removal both from a kinetic and equilibrium point of view. Furthermore: the presence of other metal cyanides in solution with free cyanide has a negligible effect on the performance of the metal (silver) impregnated activated carbon to remove free cyanide. Moreover, scanning electron micrographs revealed distinct differences in appearance of metal impregnated carbons, which ultimately responds differently to the removal of free cyanide. Although the kinetics of adsorption in the column experiments was found to be slower when compared to that experienced in a batch reactor, preliminary results show that a column configuration could be suitable for a free cyanide recovery on a large scale. Furthemore, a sensitivity analysis using the kinetics of adsorption and equilibrium cyanide loading as criteria, has been conducted on the column configuration. In these studies the effects of different bed volumes, competitive adsorption with other species present, different flow rates, different column diameters and initial cyanide concentrations on the process have been evaluated. These results were plotted as break-through curves, and the mass transfer zone (MTZ) was determined. It was found that impregnation in an air atmosphere yields a product with a higher capacity than in a nitrogen atmosphere, compromising carbon through combustion. Under a nitrogen atmosphere a more robust product is formed. As can be expected, lower linear velocities and/or larger bed volumes as well as lower initial free cyanide concentrations improve the fraction of cyanide removed in a column configuration.

Thesis (MTech (Chemical engineering)--Cape Technikon, Cape Town, 2001 / Over the years the carbon-in-pulp technology has been refined to become the highly efficient process that is used in our present-day system of recovering dissolved gold from cyanide leached pulps. The efficiency of a CIP circuit mainly depends on the effectiveness ofthe adsorption section as it not only determines the amount of soluble gold lost in the residues, but also indirectly affects the function of the other processes in the plant. Research in this area has declined over the past few years as a result of a decrease in the gold price. It is now more than ever important to investigate the operating conditions ofthe adsorption process to ensure that a highly effective system is maintained. The adsorption of gold cyanide onto activated carbon is to a large extent dependent on maintaining operating conditions well above those of equilibrium. The Freundlich and the Langmuir isotherms have been used by many researchers to describe the equilibrium conditions of the adsorption process. The general practice in the carbonin- pulp technology is to use an isotherm for the prediction of a circuit's performance. As confidence has increased in the reliability of these predictions, it has become important to acquire knowledge of the equilibrium condition that is driving the process. Previous research findings have indicated that the equilibrium isotherm of gold cyanide adsorption onto activated carbon is influenced by changes in the adsorption conditions down the adsorption train. This equilibrium or isotherm shift may lead to errors in the prediction of gold adsorption rates, which results in the filct that the simulations of the performance of the CIP circuits are not reliable.

Please read the abstract in the front section of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

Cyanide was rapidly removed when added to culture supernatants of seven different Pseudomonas. The ability to remove cyanide was correlated with the accumulation of α-keto acids (pyruvate and α-ketoglutarate). These compounds react with cyanide forming less toxic cyanohydrins, thus conferring a mechanism for bacterial cyanide tolerance. When added to growth media the α-keto acids were shown also to serve as effective cyanide antagonists. While all bacteria tested accumulated α-keto acids, only those capable of utilizing cyanide as a nutritional nitrogen source were able to metabolize cyanohydrins. In P. fluorescens NCIMB 11764, the same enzyme (cyanide oxygenase) shown previously to be involved in cyanide metabolism appears responsible for cyanohydrin transformation. Keto acid excretion is believed to represent a new mechanism of bacterial cyanide detoxification with further enzymatic metabolism of the cyanohydrins helping to explain how cyanide can satisfy the nitrogen requirement in cyanide-utilizing bacteria.

Utilization of cyanide as the sole nitrogen source by Pseudomonas fluorescens NCIMB 11764 (Pf11764) occurs via oxidative conversion to carbon dioxide and ammonia, the latter satisfying the nitrogen requirement. Substrate attack is initiated oxygenolytically by an enzyme referred to as cyanide oxygenase (CNO), which exhibits properties of a pterin-dependent hydroxylase. The pterin requirement for Pf11764 CNO was satisfied by supplying either the fully (tetrahydro) or partially (dihydro) reduced forms of various pterin compounds at catalytic concentrations (0.5 µM). These compounds included, for example, biopterin, monapterin and neopterin, all of which were also identified in cell extracts. A related CNO-mediated mechanism of cyanide utilization was identified in cyanide-degrading P. putida BCN3. This conclusion was based on (i) the recovery of CO2 and NH3 as enzymatic reaction products, (ii) the dependency of substrate conversion on both O2 and NADH, and (iiii) utilization of cyanide, O2 and NADH in a 1:1:1 reaction stoichiometry. In contrast to findings reported for Pf11764, it was not possible to demonstrate a need for exogenously added pterin as a cofactor for the PpBCN3 enzyme system. However, results which showed that cells of PpBCN3 contained approximately seven times the amount of pterin as Pf11764 (of which a significant portion was protein-bound) were interpreted as indicating that sufficient bound CNO-cofactor exists, thus eliminating any need for a supplemental source.

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