Theoretical study on reactivity of different sulfide collectors and their binding affinity toward Cu(II), Zn(II) and Pb(II) ions.

  • Author / Creator
    Chowdhry, Manjeet
  • Collectors are one of the most important ingredients of froth flotation in mineral processing, as they selectively render the desired minerals more hydrophobic than others. Current crop of sulfide collectors interact with almost all sulfide minerals. This necessitates the use of complicated reagent schemes to ensure efficient processing of typical polymetallic sulfide ores. Given the routine variability in ore composition and other operational parameters, these schemes are often very difficult to implement. For efficient and economical processing of lean grade, finely disseminated, and mineralogical complex future ore bodies, new collectors exhibiting superior collecting power and enhanced mineral selectivity need to be developed. However, till now no definitive criterion has been developed to guide us in design of such reagents. Mineral selectivity of collectors is a function of their molecular structure and specifications of mineral surfaces. Thus, establishing a comprehensive framework to guide us in determining the structural requirements for a collector to be selective towards a particular mineral, or to be used in a given scenario, is the most logical way to go ahead. However, it is very hard to relate structural features of a collector to its reactivity and binding ability through use of experimentally based approaches. In comparison, computational chemistry methods, such as density functional theory, are much more suitable for this purpose. Majority of sulfide collectors adsorb on minerals via chemical reactions with metal ions on the mineral surface or in the bulk solutions. Therefore, modeling the interaction of collectors with metal ions instead of mineral surfaces as a first approximation is more appropriate, as it is relatively fast and computationally economic. In this work, interactions of three important collector classes, namely, anionic thiol collectors, neutral collectors, and mercapto azole reagents, were modeled with three common heavy metal ions, namely, Cu, Pb and Zn. Reactivity of individual collector molecules is expressed quantitatively as well as qualitatively through use of: (i) theoretically calculated parameters (partial charges, spatial distribution and hybridization of frontier molecular orbitals, and geometrical parameters), and (ii) well-established reactivity descriptors (chemical potential, hardness, and global electrophilicity). The predicted orders of reactivity are linked to differences in the structures of collector molecules. Interaction energies for metal-collector complexes were calculated to assess the binding ability of collectors. Azole reagents were predicted to be most reactive, followed by anionic thiols. All collectors showed higher preference for Cu followed by Pb. Anionic thiol collectors were found to bind metal atoms in a bidentate fashion. Their reactivity and binding ability follow the order: dithiocarbamate > xanthate > dithiocarboxylate > trithiocarbonate > dithiophosphate. Neutral collectors interact with metal ions mainly through S atom of the thio-carbonyl group. The order of reactivity and binding ability is: thiourea > thionocarbamate > monothiocarbonate > dithiocarbonate > trithiocarbonate. Among the mercapto azole reagents, collectors of imidazole series were predicted to be most reactive, followed by thiazole series. These reagents interact with metals through exocyclic S and endocyclic imine N atom, and form chelate rings at metal centers. The predicted order of reactivity and binding abilities agree well with the experimental observations reported in the past. This study, thus, establishes that a relationship between structure of flotation collectors and their reactivity towards different minerals could be formulated by considering metal-reagent interactions. The results obtained for neutral collectors and heterocyclic aromatic reagents eliminate the existing ambiguity in literature regarding their binding mechanism. This study shows that computational studies are very helpful in clarifying some of the unexplainable observations in experimental flotation, such as a very weak flotation efficiency of trithiocarbonate reagent compared to xanthates and dithiocarbamate reagents.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.