Understanding the effect of metastable sulphoxy compounds on the flotation of sulphide ores

Ngoni Pepukai Mhonde

Research output: ThesisDoctoral ThesisCollection of Articles


As restrictions on water usage become more prevalent, the practice of water recycling on mineral processing operations is considered best practice. Recycled water in flotation operations is thermodynamically unstable and carries various sulphoxy species that may have a positive or adverse effect on flotation separation. This study intricately focuses on two sulphoxy species, namely tetrathionate and dithionite ions, investigating the interaction of these species with sulphide mineral surfaces and reagents used in the beneficiation of sulphides ores. The effect of microbes present in solutions laden with these sulphoxy species from an electrochemical interactions viewpoint is also investigated. Fundamental studies (microflotation, electrochemistry, zeta potential, FTIR and XPS) and batch flotation were used to study the response of galena, chalcopyrite and pyrite to sulphoxy species and microbes in plant water. The flotation studies showed that metastable sulphoxy compounds reduced the flotation recovery of sulphide minerals. However, chalcopyrite depression only occurred at high sulphoxy species concentrations (ca. 2000ppm). The poor flotation performance of sulphide minerals was attributed to mineral oxidation and passivation by the sulphoxy species as confirmed by X-ray photoelectron spectroscopy studies. Electrochemical rest potential measurements showed that the interaction of thiol collectors and the sulphide mineral surface decreased in the presence of sulphoxy species. This was corroborated by Fourier Transform Infrared Technology measurements where the intensity of xanthate spectra peaks on minerals conditioned in sulphoxy species and xanthate solutions were low in comparison to xanthate peaks on minerals conditioned in the absence of sulphoxy compounds. The solution interaction of xanthate with tetrathionates and dithionites was also considered as a source of poor flotation performance. The degradation of xanthate by tetrathionate ions was not affected by the type of conditioning gas or pH. Xanthate degradation occurred in solution following first-order degradation kinetics with respect to xanthate concentration. The degradation of xanthate by dithionite ions was affected by the type of conditioning gas and it was faster at neutral pH. A mixed microbial community in plant water passivated sulphide mineral surfaces rendering the minerals hydrophilic. Rest potential measurements showed that the interaction between collectors and the minerals decreases in the event that microbes are attached to the mineral surface first before collector addition. The results from the thesis are pertinent to mineral processing professionals. It is evident that critical water quality considerations must be made when altering/controlling the water circuits in new or existing flotation plants. An understanding of the ore tolerance to water quality may aid in ensuring that flotation water recycle configurations do not negatively impact flotation performance.
Translated title of the contributionUnderstanding the effect of metastable sulphoxy compounds on the flotation of sulphide ores
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Dahl, Olli, Supervising Professor
  • Schreithofer, Nora, Thesis Advisor
  • Corin, Kirsten, Thesis Advisor, External person
  • Heiskanen, Kari, Thesis Advisor
Print ISBNs978-952-64-0546-9
Electronic ISBNs978-952-64-0547-6
Publication statusPublished - 2021
MoE publication typeG5 Doctoral dissertation (article)


  • froth flotation
  • oxidation
  • collector degradation
  • sulphoxy compounds
  • sulphide minerals


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