Selective Depression of Hexagonal Pyrrhotite from Pentlandite Using Starch

  • Author / Creator
    da Costa Goncalves, Caroline
  • Pentlandite is very important to the mining industry since it is the main source of metallic nickel. However, its separation from hexagonal pyrrhotite is a challenge for processing engineers due to the similar floatabilities of these sulfide minerals. An inefficient separation of these minerals generates serious environmental issues caused by the emissions of sulfur oxide gases during the pyrometallurgy of final concentrates. Although successful, the current depressant used, diethylenetriamine (DETA), is also harmful to the environment when disposed. Due to stringent environmental policies being implemented, the mining industry is under the obligation of researching/developing alternative reagents which are non-toxic and biodegradable. Therefore, new flotation strategies must consider the use of reagents such as polysaccharides. Three non-toxic starch depressants for hexagonal pyrrhotite were used in this study. They include a paste starch with higher molecular weight distribution, a paste starch with lower molecular weight distribution, and a crosslinked starch formed using the paste starch with lower molecular weight distribution and copper ions. We hypothesize that the presence of crosslinking agents such as copper would provide a “driving” effect towards the main gangue mineral. The performance of depressants was investigated in single and binary mineral systems. For single minerals, comparing paste starches, the higher molecular weight paste starch was more detrimental to the recovery of pentlandite and hexagonal pyrrhotite than the lower molecular weight paste starch. In addition, the crosslinked starch further reduced the recoveries of both minerals. A better result for the binary mineral systems considering Ni recovery and Ni grade was achieved by using 9.66x10-6 M of PIBX (equivalent to 240 g/t) and 5 mg/L of starch depressants (equivalent to 660 g/t). Whereas the lower molecular weight paste starch almost did not affect Ni recovery (91.2%) comparing with the collector baseline (92.5%), the higher molecular weight paste starch and the crosslinked starch had a Fe recovery no greater than 31.0%. The choice of the best starch depressant showed to be complex since pentlandite and hexagonal pyrrhotite were able to chemically interact with the starch depressants as verified via XPS. The hydroxyl groups present on the α-D-glucose units of starch bound with the metal hydroxylate species. Moreover, the crosslinked starch also interacts with the mineral surfaces by electrostatic attraction due to the presence of weakly electronegative copper center. Kinetics and equilibrium adsorption tests allowed a more direct comparison of the effect of the starch depressants, regarding the mechanism of depression. It has been proven the importance of a balance of hydrophobic/hydrophilic species on both mineral surfaces. This was further as confirmed by contact angle measurements (Washburn method), QCM-D, and AFM tests. For the paste starches, it has been proposed that the mechanism of depression is related to the hydration levels of the adsorbed depressant layer. The amount of water molecules held by the polysaccharide structure is directly related the packing density (conformation). Furthermore, the latter is a function of the starch molecular weight, showing the importance of this parameter for mineral depression. For the crosslinked starch, however, the distribution of depressants across both mineral surfaces, given in terms of surface coverage, is the most relevant parameter dictating its depressing effect. The findings of this research will contribute with the advancement of topics related to the use of polysaccharides as depressants for sulfide minerals. The utilisation of non-toxic depressants can benefit the industry regarding the mitigation of safety and environmental problems.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • 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.