Date of Award


Degree Type


Degree Name

Doctor of Philosophy


This thesis examines the interactions of the aqueous species {dollar}\rm Ag\sp+,\ AgCl\sb{lcub}x{rcub}\sp{lcub}1-x{rcub},\ AuCl\sb4\sp-{dollar} and AuSH with the surfaces of PbS, (Zn,Fe)S and FeS{dollar}\sb2{dollar} with the aim of better understanding the role that sulphide minerals play in concentrating precious metals from solution. Through the use of surface (XPS, AES, SEM) and conventional (AAS, IC, electrochemistry) analytical techniques, insight into mineral modification, metal chemistry and morphology, alloy composition and solution chemistry is obtained.;Reactions of Ag{dollar}\sp+{dollar} and the three minerals resulted in the presence of Ag{dollar}\sb2{dollar}S and Ag(0) being observed on all mineral surfaces, in a 2 step process where Ag{dollar}\sb2{dollar}S, then Ag(0) forms. The presence of polysulphides on the PbS and (Zn,Fe)S indicated that sulphur is the reducing agent. From the AgCl/PbS interactions it was determined that: (a) the process was a diffusion limited ion-exchange process; (b) there is a direct relationship between the amount of silver on the surface and the chloride concentration; and (c) the presence of Ag{dollar}\sb2{dollar}S was found on the PbS surfaces regardless of metal ion concentration. For the AgCl/FeS{dollar}\sb2{dollar} interactions, an inverse relationship with Cl{dollar}\sp-{dollar} seems to occur and if a critical value of the free silver ion is not exceeded, no deposition will occur.;When considering the mixed Ag-Au chloride system, it was determined that: (a) aqueous gold species are preferentially reduced on both the PbS and FeS{dollar}\sb2;{dollar} (b) it is possible to increase the amount of silver present on the FeS{dollar}\sb2{dollar} surface if gold is present in solution; and (c) gold-silver alloys akin to those found in nature were formed on the pyrite surface.;Reactions of gold bisulfide with pyrite have revealed the presence of bulk metallic gold as well as adsorbed gold(I) present on the surface. For both the chloride and bisulphide systems, an increase in either pH or temperature results in an increase in the amount of gold on the surface. It has been shown that crystal morphology similar to that found in nature is reproduced in these laboratory studies.



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