Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The adsorption of aqueous metal ions on various sulphide minerals was studied as a function of time, pH, surface composition and chemical speciation.;In the first part of this work (Chap. 3) the reaction between various types of gold solutions and several minerals was followed using XPS and SEM. Gold from chloro auric solutions was reduced quickly from Au(III) to Au(O) by every sulphide mineral studied. SEM showed the gold to be unevenly distributed on the surface in the form of agglomerates. Oxide minerals did not reduce gold to any great extent. The gold was shown to adsorb on the sulphide groups of the surface. An associative substitution (SN(,2)) mechanism was suggested for the adsorption step followed by reductive elimination of the gold complex. This work raises the possibility that adsorption/reduction of undersaturated gold solutions at low temperature could play an important role in the concentration of gold in natural systems.;In the second part of this work (Chap. 4) the adsorption of Hg(II), Cd(II), Zn(II) and Pb(II) on sulphide minerals was studied using XPS and AAS. The adsorption of all these ions was found to be dependent on hydrolysis. For these ions there is a critical pH at which adsorption increases from 0 to 100% over a narrow pH range. This pH is closely related to the pH of hydrolysis of the cation. Mercury is shown to be directly adsorbed on the sulphide groups present on the surface. The proposed adsorption mechanism is: adsorption of the hydrolyzed species on the sulphide groups (probably through hydrogen bonding) followed by dissociation of the hydroxyl groups and formation of a metal-sulphide type bond. These results show sulphide minerals to be good scavengers for heavy metals and suggest their utilisation to clean contaminated solutions.;In the last part of this work (Chap. 5) desorption methods of heavy metals from sulphide surfaces were perfected. Strong complexing ligands such as CN('-) or S('=) were found to completely desorb mercury from pyrrhotite surfaces. The rate of desorption was very fast, the reaction being complete after five minutes. The desorption study showed that a broad range of adsorption energies was present on the surface.



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