Carboxymethyl Chitosan as a Selective Depressant in Differential Flotation of Galena and Chalcopyrite

• Author / Creator

  Xiang, Yahui

• Toxic inorganic depressants are routinely used in the differential flotation of polymetallic sulfide ores and it is desirable that they be replaced with environmentally benign chemicals. Chitosan, as a natural and non-toxic polymer, has been proven to be an efficient depressant for copper sulfide (e.g., chalcopyrite) while allowing lead sulfide (e.g., galena) to be floated by xanthate collectors. However, the poor solubility of chitosan limits its potential applications as the flotation could only be carried out at about pH 4 where chitosan is soluble. Three carboxymethyl derivatives of chitosan, named N-CMC, O-CMC and N-O-CMC, were synthesized by introducing carboxymethyl groups on the backbones of chitosan. The substitution on amino groups significantly improved the solubility of chitosan. The structures of CMC were studied and compared with chitosan via Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (NMR) spectrometry. Flotation tests were performed on single minerals and mineral mixtures (with weight ratio of 1:1) with the addition of appropriate amounts of potassium ethyl xanthate (KEX) and N-CMC. The solution pH was varied from neutral to alkaline. The flotation concentrates and tailings were collected and analysed for the contents of copper and lead. Single mineral flotation tests indicated that N-CMC could depress either chalcopyrite or galena depending on pH. The results were not affected by the sequence of KEX and N-CMC addition. Therefore, N-CMC is potentially useful in Cu-Pb sulfide separation following a bulk Cu-Pb flotation. The N-CMC was also found to have surface cleaning functions, and was able to remove contaminating copper ions from galena surfaces. The adsorption mechanisms of N-CMC on sulfide minerals were then delineated by several analysis techniques. Metal ions binding tests showed that N-CMC had a stronger interaction with Cu2+ than Pb2+. The distribution of N-CMC on mineral mixtures was mapped out by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results of ToF-SIMS analysis confirmed that N-CMC preferentially adsorbed on chalcopyrite at pH 7 but uniformly distributed on both minerals at pH 10. The high resolution N 1s X-ray photoelectron spectroscopic (XPS) spectra of N-CMC-treated chalcopyrite and galena showed that chemical bonds formed between the secondary amino groups of N-CMC and both mineral surfaces. At pH 7, the bond with Cu was stronger than with Pb, while at pH 10, one additional bond was formed between N-CMC and Pb. Zeta-potential measurements showed the presence of electrostatic interaction between N-CMC and both chalcopyrite and galena, but it was not the reason for N-CMC’s selective depression of chalcopyrite. Mineral surface cleaning tests explained the good flotation result in the absence of any chelating reagents, such as EDTA, since N-CMC also possesses the similar function of removing the Cu2+ adsorbed on the galena surface. Overall, the application of N-CMC in sulfide ore flotation is expected to be more robust than the original chitosan.

• Subjects / Keywords

  • Carboxymethyl chitosan
  • Sulfide minerals
  • Differential flotation
  • Depressant

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3N58CS7R

• 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.