Polymeric depressants for selective mineral flotation and the interaction mechanisms

• 有机抑制剂在矿物浮选分离中的应用及其作用机理

• Author / Creator

  Yuan, Duowei

• In nature, the molybdenite ores are frequently associated with copper sulfide minerals such as chalcopyrite, and the flotation separation of copper-molybdenum (Cu-Mo) sulfides largely relies on the use of toxic and hazardous depressants such as cyanides, Na2S/NaHS. It is desired to replace these toxic chemicals with more environmentally benign depressants. In addition, talc, a problematic gangue mineral, also frequently occurs in the Cu-Mo sulfide ores. As an inherent hydrophobic magnesium silicate, talc can easily report to the Cu-Mo bulk concentrates in the flotation, reducing the grade of concentrates and strongly affects the subsequent smelting operations. Therefore, economic beneficiation of these Cu-Mo sulfide ores could not be achieved without proper depressants and the efficient removal of talc.
  Humic acids (HA), a primary constituent of humic substances or humus (organic fraction of soil), has a wide range of technological and practical applications owing to its abundance and low-cost. In this work, humic acids and its analogues have been studied as depressants for the Cu-Mo sulfides separation and molybdenite-talc separation. The flotation results indicated that HA is a selective depressant for molybdenite while the flotation of chalcopyrite or talc is barely affected. Besides, the depression and adsorption mechanisms of HA were also investigated by a range of different techniques such as zeta potential measurements, infrared spectroscopy, Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Quartz crystal microbalance with dissipation (QCM-D). The experimental results demonstrated that HA strongly adsorbs onto molybdenite basal planes through hydrophobic interaction, while chemical interactions were not involved. In contrast, the adsorption of HA on talc basal planes was hindered by electrostatic repulsion. Besides, HA could also adsorb onto chalcopyrite surfaces, and the interactions are likely to be electrostatic in nature. However, the addition of xanthate collector could potentially desorb the attached HA and restore the floatability of chalcopyrite.
  In addition, O-Carboxymethyl chitosan (O-CMC), a derivative of the second most abundant natural polysaccharide—chitin, was also investigated as a depressant for the Cu-Mo sulfides separation. The flotation tests indicate that O-CMC selectively depresses molybdenite during molybdenite-chalcopyrite separation over a broad range of pH. Moreover, the adsorption characteristics and mechanisms of O-CMC on molybdenite and chalcopyrite were systematically investigated by electrokinetic study, infrared spectroscopy, AFM, XPS, and ToF-SIMS characterizations. The experimental results demonstrated that O-CMC adsorbed on both mineral surfaces. However, the interactions between O-CMC and chalcopyrite are mostly weak physical interactions such as electrostatic interaction etc., and the adsorbed O-CMC can be readily removed by rinsing or displaced by xanthate. In comparison, the adsorption of O-CMC on molybdenite basal planes is dictated by hydrophobic attraction and electrostatic repulsion and is barely affected by rinsing or xanthate addition. Therefore, the strong interaction between O-CMC and molybdenite is responsible for the depression of molybdenite and selective separation of two minerals in the flotation. The research also showed that no strong chemical interactions were involved during the adsorption of O-CMC on both mineral surfaces.
  The results of this work shed light on the fundamental understanding of the interaction mechanisms between polymeric depressants and mineral surfaces under different solution conditions, and provided valuable guidance for the selection of polymeric depressants and directions for the development of many other polymeric depressants or flocculants. This research also provides important implications for the beneficiation and separation of many other mineral systems and related technological and industrial processes such as wastewater treatment.

• Subjects / Keywords

  • Depressant
  • Molybdenite
  • Humic acids
  • Flotation
  • Chalcopyrite
  • Separation
  • Talc
  • adsorption
  • Chitosan
  • O-Caroboxymethyl chitosan

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-se19-ve32

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.