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Equilibrium shift of gold adsorption in a batch reactor

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dc.creator Burnett, Hannelene Jo-Anne
dc.date 2012-09-26T13:06:33Z
dc.date 2012-09-26T13:06:33Z
dc.date 2001
dc.date.accessioned 2017-05-10T10:21:30Z
dc.date.available 2017-05-10T10:21:30Z
dc.identifier http://hdl.handle.net/11189/465
dc.identifier.uri http://hdl.handle.net/11189/465
dc.description Thesis (M.Tech-Chemical engineering)--Cape Technikon, Cape Town, 2001. Includes bibliographical references
dc.description 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.Experiments were carried out where the change in pH, oxygen and cyanide concentration, ionic strength in solution and competing ions were investigated simultaneously. In order to investigate the influence ofchanges in these experimental conditions, equilibrium isotherms were determined by using standard synthetic soiutions prepared in 1 litre batch reactors with different concentrations of potassium gold cyanide. Through factorial design the three most sensitive factors were determined. Further experiments were then carried out to test the effect of changes in free cyanide concentration, pH and competing ions (50 ppm nickel) on the equilibrium isotherm as well as the adsorption profile. A relationship was postulated between the cyanide profile in the adsorption circuit and the initial cyanide concentration, which yielded an expression for a first order decay in free cyanide. A linear relationship was also established between the free cyanide concentration and the equilibrium A parameter at a solution pH of 10.5. This resuhed in a modified A parameter when the two proposed expressions were combined. The modified A parameter can be substituted in the existing Freundlich isotherm which will modify the isotherm. A surface diffusion/film diffusion model was fitted to the experimental data to estimate the adsorption profile. The modified A parameter was incorporated into the model and it proved that a better fit (51 % improvement) could be obtained when a change in pH and free cyanide concentration was accounted for. As a result oflirnited experimental data the competition factor for gold and nickel could not be determined. It is suggested that future work should include the effect of competing ions, in order to include this factor in the modified Freundlich isotherm. It is assumed that if this additional effect were added to the model, an even greater fit ofthe model predictions would be obtained.
dc.language en
dc.rights http://creativecommons.org/licenses/by-nc-sa/3.0/za/
dc.subject Adsorption
dc.subject Cyanide process
dc.subject Gold -- Metallurgy
dc.subject Carbon-in-pulp process
dc.subject Chemical engineering
dc.title Equilibrium shift of gold adsorption in a batch reactor
dc.type Thesis


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