The Roles of Non-polar Oil in Froth Flotation of Fine Particles

• Author / Creator

  Hao Li

• Oil-assisted flotation is one of the most promising techniques in fine mineral particle recovery in the beneficiation of low-grade finely-disseminated ores. However, literature reports show that when non-polar oil is used in conjunction with different types of collectors, the flotation response is often unpredictable and does not always lead to improved fine mineral recovery. In this research, a systematic study was carried out to examine the balance of the hydrophobicity enhancing effects and the antifoaming functions of neutral oil in froth flotation. Fine hematite (-20 µm) and quartz (-15 µm) were used as mineral samples; sodium oleate (NaOl), octyl hydroxamic acid (OHA), and oleoyl hydroxamic acid (OLHA) were used as typical anionic collectors; and kerosene was used as the non-polar oil. In micro-flotation of hematite single mineral using a custom-made glass tube where a froth layer did not exist, all three tested collectors were effective to float the hematite despite its fine size. The addition of emulsified kerosene showed a beneficial effect, particularly at high collector dosages, regardless of the type of collectors used. However, in batch flotation of either single hematite or hematite-quartz mixtures in a mechanically agitated stainless steel cell where a froth layer existed, kerosene behaved differently when used in conjunction with the three collectors. When NaOl or OLHA was used as a collector, kerosene emulsion improved the flotation performance as demonstrated by higher concentrate Fe2O3 grade and recovery. However, the addition of kerosene emulsion reduced concentrate weight yield, grade and recovery to a noticeable extent when OHA was used as a collector, especially at low OHA dosages. Contact angle, particle size measurements and image analysis showed that the improved flotation recovery of the fine hematite in the absence of a froth layer was due to both the enhanced surface hydrophobicity and increased (hydrophobic) floc size after adding kerosene to a collector-treated hematite suspension. The effects were most pronounced with the long chain collectors NaOl and OLHA, and much less in the case of the short chain collector OHA. Zeta potential distribution measurement coupled with an analysis of the interaction energies according to the extended-DLVO theory indicated that the hydrophobic interaction energies between hydrophobic hematite particles induced by NaOl or OLHA were stronger than by OHA. When kerosene was added, the hematite aggregates grew to a much larger size due to the stronger hydrophobic interaction between hematite particles and kerosene droplets when NaOl or OLHA was used, than when OHA was used. Efficient froth flotation in a batch flotation machine, however, depends on both the mineral surface hydrophobicity and the presence of a stable froth layer. The froth stability of NaOl and OHA solutions was analysed using Bikerman method in the absence or presence of kerosene emulsion. The results showed that, in the absence of kerosene, the foamability of NaOl was much better than OHA. In the presence of kerosene, the oil droplets may stabilize or destabilize the froth layer depending on the concentration of the collector. In the batch flotation process, froth stability was related to water recovery into the froth phase. Water recovery measurements showed that froth destabilization by the addition of kerosene occurred at low collector dosages, especially when short chain collectors such as OHA was used. At higher collector dosages, the froth was generally stable. It is likely that the water drainage and froth destabilization effect by kerosene was counter-balanced by the higher hematite surface hydrophobicity, bubble surface tension gradient and stable pseudo-emulsion film, which led to more stable froth layer.Therefore, a delicate balance exists when a neutral oil is used in froth flotation. The outcome depends on whether the beneficial effects of enhanced mineral surface hydrophobicity outweigh the detrimental effect of defrothing by the neutral oil. This study showed that when a short-chain collector such as OHA was used, the defrothing effects of neutral oil were predominant so that the combined use of neutral oil and OHA was counter-productive.

• Subjects / Keywords

  • Fine Particles
  • Octyl Hydroxamic Acid
  • Sodium Oleate
  • Non-polar Oil
  • Froth Flotation
  • Oleoyl Hydroxamic Acid

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-zpwn-q834

• 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.