Probing Surface Heterogeneity, Electrochemical Properties and Bubble-Solid Interaction Mechanisms of Sulfide Minerals in Flotation

• Author / Creator

  Xie, Lei

• The colloidal stability governed by various surface interactions including van der Waals (VDW) interaction, electrical double layer (EDL) interaction, hydrophobic interaction, and some other interactions, plays an important role in a wide range of natural phenomena and engineering applications. The basic understanding of surface properties and interaction mechanisms of colloidal particles is of both fundamental and practical importance in many engineering processes such as mineral froth flotation. In this study, the surface characteristics of sulfide minerals, such as sphalerite, galena and molybdenite, were investigated in complex aqueous media using several complementary experimental techniques to better elucidate the surface heterogeneity, electrochemical properties and bubble-particle interaction mechanisms that contribute to various interfacial phenomena in flotation. Atomic force microscopy (AFM) force mapping was applied to probe the nanoscale heterogeneity of surface hydrophobicity and surface interactions on sphalerite surface before/after conditioning treatment (i.e. copper activation and xanthate adsorption). It was shown that sphalerite surface was hydrophilic with homogeneous surface hydrophobicity, while conditioned sphalerite exhibited heterogeneous distribution of surface hydrophobicity due to non-uniform adsorption of xanthate. The significantly enhanced adhesion after conditioning treatment with chemical reagents originated from the additional hydrophobic attraction. Equipped with the electrochemical setup, the interfacial chemical reaction and evolution of surface characteristics (i.e. morphological changes and surface interactions) on galena surface were simultaneously measured using AFM at the nanoscale. The in-situ topographic imaging revealed homogeneous electrochemical oxidation across the mineral surface, leading to slight surface roughening at the applied potential of 0 V (0.206 V vs standard hydrogen electrode) and more pronounced surface roughening at higher potentials (e.g. 0.3 V and 0.45 V). The quantitative force results demonstrated that hydrophobic interaction was strengthened with increasing the applied potential from -0.7 V to 0.45 V, which agreed well with the enhanced hydrophobicity of galena surface. The electrochemical oxidation at 0 V was believed to be the formation of metal-deficient lead sulfide, while the oxidation at 0.45 V arose from the formation of elemental sulfur that was further confirmed by cryo-XPS. Furthermore, AFM bubble probe technique was employed to quantitatively measure the interaction forces between air bubbles and mineral surfaces (i.e. sphalerite before/after conditioning treatment and molybdenite before/after depressant adsorption). Surface forces were shown to play the critical role in bubble-mineral interaction and attachment, which agreed excellently with the theoretical calculations based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. Increasing the salt concentration led to weakened EDL repulsion, and thus facilitated the bubble-mineral attachment. For the hydrophilic sphalerite case, the bubble was more readily attached to the mineral surface after conditioning treatment, which was contributed from the strengthened hydrophobic attraction. For the hydrophobic molybdenite case, the adsorption of polymer depressant weakened hydrophobic attraction and induced steric repulsion, thereby stabilizing thin water film and inhibiting bubble-mineral attachment. This work provides novel methodologies to study the surface properties and interaction mechanisms of sulfide minerals in complex aqueous media at the nanoscale. The results in this work provide valuable and quantitative information on the fundamental understanding of surface heterogeneity, electrochemical properties and bubble-particle interaction mechanisms of sulfide minerals in complex aqueous media, which can be readily extended to many mineral systems and other related engineering processes.

• Subjects / Keywords

  • Mineral flotation
  • Surface interaction mechanisms
  • Bubble-mineral interactions
  • Atomic force microscopy
  • Electrochemical properties
  • Surface heterogeneity

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R38G8FW1Q

• 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.