Thesis(Ph.D.(Physics)) -- University of Limpopo, 2020 / Surface properties of pyrite (FeS2), chalcopyrite (CuFeS2), galena (PbS) and
sphalerite (ZnS) most thermodynamically stable surfaces have been studied using first
priniciples density functional theory. The most stable surfaces showed the highest
surface exposure as it covered a higher percentage of the surface area on
morphologies. The interaction of water with such sulphide surfaces was also
investigated; the structures of sulphide minerals surfaces were changed in the
presence H2O molecules. The surfaces of FeS2 and ZnS relax most while those of
CuFeS2 and PbS surfaces change slightly in the presence of H2O molecules.
The results on the effect of chain length of DTPs and DTCs on the enthalpies of
adsorption on pyrite, galena, chalcopyrite and sphalerite have shown that an increase
in chain length of the DTPs resulted in an increase in the enthalpies of adsorption
trend for pyrite, galena and sphalerite. This is an important observation since the
ligand is the same in all cases and therefore the effect is due to the role of the alkyl
group Moreover, we noted a decrease of enthalpies of adsorption with an increase of
DTCs chain lengths on pyrite, galena, chalcopyrite and sphalerite.
The effect of the branching of the hydrocarbon chain length of the dithiocarbamates
on the enthalpy of adsorption of pyrite was investigated. The results show that the
configuration of the alkyl chain length of the same carbon number has an influence on
the enthalpy of adsorption. Furthermore, the results indicate that there was minimal
enthalpy of adsorption when DeDTP was dosed to galena, chalcopyrite and sphalerite
minerals as compared to DeDTC and ethyl xanthate. On the other hand, the enthalpies
of adsorption of DeDTP on pyrite were very high which represented a greater
exothermic reaction than for any of the DeDTC and ethyl xanthate. The bond distance
between thiol collector and the surface is consistent with the corresponding calculated
adsorption energies.
The Mulliken population of S-Fe/S-Pb/S-Zn bond for the adsorption of eX on
CuFeS2 surface are high compared to PbS and ZnS surfaces, which indicated that
there is a strong covalent bond between S and Fe atoms as compared to S-Pb and
Pb-Zn bonds. Such observations are consistent with results of other thiol collectors. It
was seen that the Mulliken atomic charges populations of CuFeS2, PbS and ZnS
surface layers are different before and after DTPs adsorption. The charges of Fe atom
reduce, which indicates that the Zn and Pb atoms become more positive and the Fe
atom becomes more negative. In addition, there are changes in the charges of S atoms in ZnS and PbS surface layers before and after H2O absorption, suggesting that the
presence of water would affect the adsorption of thiol collector.
The densities of states (DOS) of the thiol collectors on surfaces of sulphide
minerals have shown a strong hybridisation between the S 3p-orbital HOMO, metals
(Fe, Pb, Zn) 3d-orbital for pyrite and chalcopyrite, 6p-orbital for galena and (3d and
4s)-orbitals for sphalerite. The collector S 3p-orbital reduces to zero states on the
surfaces of Fe, Pb and Zn atoms. The Fe-S bond population for DeDTP is lower than
that of DispDTP and DbDTP in pyrite, respectively. For chalcopyrite the DeDTP Fe-S
population is higher than both DispDTP and DbDTP: similar trends were observed for
Pb-S and Zn-S, however, the Pb-S bonding was less covalent as compared to the Fe S in chalcopyrite. The DTPs Fe-S bond population is generally higher in chalcopyrite
than in pyrite. Mulliken charges analysis indicated that the DTPs S atoms lost charges
and the metals gained with a decreasing DTPs chain length for pyrite: a similar trend
was observed for chalcopyrite. The DTPs gained electrons from galena and sphalerite
surface. For DTCs pyrite and chalcopyrite surface Fe atoms gain more electrons in
the presence of DeDTP than other DTPs, while galena and sphalerite lost most
electrons in the presence of DbDTC than other DTCs. As for xanthate, the Mulliken
bond charges indicated that the S atoms and the metals lost charges, suggesting that
some charges reside at the internuclear region between the metals and sulphurs (M–
S). These show that electron charges are collector and mineral dependent; collector
would be an electron acceptor or donor depending on the mineral makeup.
A comparison of the computational results, isothermal titration calorimetry (ITC) and
microfloatation experiments for the interaction of DeDTP, DeDTC and eX with pyrite
and galena was made. The calculated adsorption energies between thiol collectors
and mineral surfaces were always more exothermic than the experimentally
determined ones. In computational calulations, water adsorption was found to reduce
the reactivity of Fe and Pb atom for the interaction with thiol collectors and bring the
adsorption energies closer to the magnitude of the experimental values. FeS2 (100)
surface heat of adsorption depict similar trends to experimental recoveries from
microfloation for DeDTP, DeDTC and eX, while FeS2 (111) heats of adsorptions for
DeDTP and DeDTC are consistent with ITC experimental results. Lastly, calculated
DeDTP and DeDTC adsorptions on the PbS (100) are also consistent with
experimental recoveries. / National Research Foundation (NRF),
South African Minerals of Metal Institution (SAMMRI) and
University of Limpopo (UL)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3386 |
| Date | January 2020 |
| Creators | Mulaudzi, Masilu Godfrey |
| Contributors | Ngoepe, P. E. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xx,187 leaves |
| Relation |
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