Enhanced Flotation of Ultramafic Nickel Ores Using Carbon Dioxide as a Flotation Gas and Sodium Tripolyphosphate as a Serpentine Depressant

  • Author / Creator
    Ezeonyi, Nzubechukwu C
  • Challenges in the processing of minerals have been on the rise due to increasing low-grade ores which require to be finely ground to liberate valuable minerals. Low-grade ores like the ultramafic ores contain large amounts of gangue minerals which impacts recovery of the valuable pentlandite minerals. In ultramafic nickel ores, serpentine (MgO-bearing mineral) slime-coats and decreases the recovery of the nickel-bearing pentlandite. To improve the recovery of pentlandite and subsequently suppress serpentine in ultramafic nickel ores, CO2 gas (either as a depressant or a flotation gas) and sodium tripolyphosphate (STPP) as a reagent for serpentine depression are used in this study. Phosphate groups in STPP chelate magnesium ions and can facilitate serpentine depression in flotation systems. CO2 can also precipitate divalent cations like magnesium cations, and due to the high solubility of CO2 gas, it can form fine bubbles on hydrophobic valuable minerals to improve their recovery. The surface charge on the serpentine samples were completely reversed upon either the introduction of STPP at above 10 mg/L or by conditioning the suspension with CO2 gas during zeta potential measurements. The resulting negative charge of the serpentine minerals indicates that the heterogeneous agglomeration with pentlandite surface is weakened, which should allow for a more pentlandite floatability. Subsequently, an optimum concentration of 50 mg/L was obtained which was then used to perform XPS analysis and flotation tests. Flotation benefits were achieved as serpentine depression and enhanced pentlandite recovery was observed for both STPP and CO2 cases. STPP was more effective in depressing serpentine by 5%, while the highest pentlandite recovery of 88% was obtained when CO2 was used as a flotation gas, which is a 20% increase in recovery from the baseline case. The more effective STPP depressing ability was validated by XPS results and provides an opportunity to explore the combination of STPP and CO2 in future studies. Results from this study further re-emphasizes the need to explore the decarbonization strategy of using CO2 in flotation circuits and in mineral processing in general, while simultaneously improving recovery. This research also provides some information about the progress of CO2 in the mining industry and will serve as a guide for researchers to perform more experiments in the direction of CO2-assisted flotation.

  • Subjects / Keywords
  • Graduation date
    Spring 2024
  • Type of Item
  • Degree
    Master of Science
  • 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.