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The adsorption of gold from iodide solutions
Author(s)
Teirlinck, Peter Albert Maria
Date Issued
1996
Type
Thesis
Publisher
Cape Technikon
Abstract
With the increasing awareness ofpreserving the environment, the need for other
lixiviants in leaching processes has escalated. The investigation for lixiviants,
especially for gold, has entailed mostly the halogen group. From halogens, iodine
forms the most stable gold complex. The aim ofthis study was to investigate the
adsorption characteristics of gold-iodide onto a coconut shell based activated carbon.
In the first part of this study, the factors influencing the adsorption kinetics and
equilibrium were investigated. Mixing experiments and interruption tests indicated
clearly that the principal adsorption mechanism is by first order film diffusion. When
the initial gold concentration was changed, the adsorption kinetics and equilibrium
decrease viith an increase in gold concentration. This is due to the shielding effect by
the adsorbed gold as it is partly reduced on the carbon surface. The concentration of
iodide increased the adsorption kinetics and equilibrium. The increase in
concentration of iodine leads to an increase in concentration ofthe principal oxidising
agent, tri-iodide, thereby decreasing the adsorption parameters as the gold gets redissolved
from the carbon surface. Furthermore, iodine and trio-iodide adsorbs
competitively, thereby decreasing the rate ofadsorption ofthe gold complex. This is
further iterated by experiments where the carbon was pre-treated v.ith a iodine/iodide
solution. In acidic solutions, none, or a minimal amount ofthe gold is red11ced on the carbon
surface, adsorption is only in the complex form, while in a alkaline solution, the gold
is partly adsorbed and partly reduced.
In the second section, the adsorption is approached from a basic electrochemical
perspective. Here, depending on the pH ofthe solution, it is shown that the potential
ofthe solution dictates the species of iodine and gold-iodide complex in solution, it
affects the adsorption characteristics ofthe activated carbon.
lixiviants in leaching processes has escalated. The investigation for lixiviants,
especially for gold, has entailed mostly the halogen group. From halogens, iodine
forms the most stable gold complex. The aim ofthis study was to investigate the
adsorption characteristics of gold-iodide onto a coconut shell based activated carbon.
In the first part of this study, the factors influencing the adsorption kinetics and
equilibrium were investigated. Mixing experiments and interruption tests indicated
clearly that the principal adsorption mechanism is by first order film diffusion. When
the initial gold concentration was changed, the adsorption kinetics and equilibrium
decrease viith an increase in gold concentration. This is due to the shielding effect by
the adsorbed gold as it is partly reduced on the carbon surface. The concentration of
iodide increased the adsorption kinetics and equilibrium. The increase in
concentration of iodine leads to an increase in concentration ofthe principal oxidising
agent, tri-iodide, thereby decreasing the adsorption parameters as the gold gets redissolved
from the carbon surface. Furthermore, iodine and trio-iodide adsorbs
competitively, thereby decreasing the rate ofadsorption ofthe gold complex. This is
further iterated by experiments where the carbon was pre-treated v.ith a iodine/iodide
solution. In acidic solutions, none, or a minimal amount ofthe gold is red11ced on the carbon
surface, adsorption is only in the complex form, while in a alkaline solution, the gold
is partly adsorbed and partly reduced.
In the second section, the adsorption is approached from a basic electrochemical
perspective. Here, depending on the pH ofthe solution, it is shown that the potential
ofthe solution dictates the species of iodine and gold-iodide complex in solution, it
affects the adsorption characteristics ofthe activated carbon.
Additional information
Thesis (Masters Degree (Chemical Engineering)) - Cape Technikon, Cape Town, 1996
Subjects
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