Fundamental Study of Flotation Behaviors and Oxidation Mechanisms of Polymorphic Pyrrhotite and Pentlandite

  • Author / Creator
    Qi, Chao
  • This thesis is mainly concerned with understanding the flotation behaviors of the polymorphic pyrrhotite (Fe1-xS, 0 < x ≤ 0.125) and pentlandite ((Ni,Fe)9S8) to find better measures for their flotation separation. The flotation separation of pentlandite from pyrrhotite is a complicated issue due to the complex chemical environment of the real flotation system. To learn more about the complex chemical environment, we conducted two plant surveys in the Strathcona Mill to learn about the flotation performance of polymorphic pyrrhotite and pentlandite and to find factors that impacted their flotation performance (Chapter 3). Two important phenomena were noticed: 1. the hexagonal pyrrhotite showed higher floatability than the monoclinic pyrrhotite in the Strathcona Mill; 2. the copper adsorption enhanced the flotation recovery of pyrrhotite. For further understanding these phenomena, pyrrhotite oxidation and copper activation were studied in Chapter 4 and Chapter 6, respectively. Importantly, the flotation separation of pentlandite from pyrrhotite was achieved with selective oxidation using hydrogen peroxide, which is shown in Chapter 5.

    Pyrrhotite floatability is mainly related to its oxidation level. The oxidation rate of both pyrrhotites was investigated by cyclic voltammetry (CV) test, and oxidation level difference was evaluated with X-ray photoelectron spectroscopy (XPS) and Time-of-Flight secondary ion mass spectroscopy (ToF-SIMS). The CV tests demonstrated a higher oxidation rate of the monoclinic pyrrhotite than the hexagonal pyrrhotite, further explained by the different variations of the Fe-S bond strength. Investigations of the oxidized polymorphic pyrrhotite surfaces with ToF-SIMS showed that the Fe-S bond strength decreased gradually over a ‘defective layer’ under the surface. Over this ‘defective layer,’ the Fe-S bond strength of the monoclinic pyrrhotite declined more steeply than that of the hexagonal pyrrhotite, which is mainly due to the faster incorporation of the oxygen atoms into the monoclinic pyrrhotite than into the hexagonal pyrrhotite.

    For the flotation separation of the hexagonal pyrrhotite and pentlandite, hydrogen peroxide was employed to enlarge the oxidation difference between hexagonal pyrrhotite and pentlandite. The surface reactions of the hexagonal pyrrhotite and pentlandite towards the hydrogen peroxide conditioning were examined with electrochemical tests, XPS, ToF-SIMS, and dissolved oxygen (DO) studies. It was found that they responded differently towards the reduction reaction of hydrogen peroxide. On the hexagonal pyrrhotite, the reduction of the hydrogen peroxide was mainly balanced by the surface oxidation of the hexagonal pyrrhotite. While, on the pentlandite, the reduction of the hydrogen peroxide was balanced primarily by the oxidation of hydrogen peroxide. The more severe surface oxidation of the hexagonal pyrrhotite than the pentlandite rendered the hexagonal pyrrhotite lower floatability than the pentlandite.

    As a critical factor in the surrounding chemical environment, copper activation effects were firstly confirmed with micro-flotation studies. To fully understand copper activation effects on pyrrhotite flotation, copper’s effects on protecting pyrrhotite oxidation were investigated via the CV and XPS depth profile. It was found that copper protected pyrrhotite from severe oxidation by hindering the dissolution of sulfur. Meanwhile, the XPS depth profiles of the pyrrhotite showed that the Cu(I)S is the first and foremost copper activation species formed on pyrrhotite surfaces, which gradually oxidized to Cu(II)S and CuO as oxidation progresses. Cu(I)S is formed through the interaction between Cu2+ and surface reactive sulfur anions, which suggested that the copper adsorption can partially occupy the available sulfur anions to reduce the sulfur dissolution rate.

    In summary, this study explained the flotation performance of polymorphic pyrrhotite and pentlandite with their different oxidation behaviors under specific chemical environments. Such fundamental understandings revealed the challenges in the floatation separation of pentlandite from hexagonal pyrrhotite and are valuable for exploring for more effective measures.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • 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.