Surface chemistry in relation to flotation selectivity: TOF-SIMS surface analysis of mineral phases from metallurgical tests in flotation circuits

Request for analysis:
Metallurgical testing on a poly metallic Cu/Pb/Zn ore indicated either copper or lead activation of sphalerite in a Cu/Pb flotation test.

Objective:
To establish and rank the factors controlling sphalerite flotation.

Methodology:
The surface composition of individual sulphide grains was examined by TOF-SIMS and comparative analyses of the surface chemistries on sphalerite grains from the feed, concentrate (fast floating particles) and tails (rejected particles) were performed.

Results of the study:
Both Cu and Pb were identified on the surface of the sphalerite grains examined. Figure 1 shows a Zn map (secondary ion image of Zn in the concentrate sample) along with an example of the positive ion spectra from the surface of sphalerite grains from the concentrate and tail samples in the mass region of Pb (Pb isotopes 206, 207 and 208 are shown). The spectra clearly illustrate peak positions and windows identified for peak (mass) intensity measurements.

Activators species on surface of sphalerite:
Plots of normalized counts for Pb and Cu on the surface of the sphalerite grains from the feed, concentrate and tails samples (Figure 2) reveal that:

  • The Pb content is not significantly different on the surface of the sphalerite grains in the concentrate relative to the feed.
  • The Pb content on the surface of the sphalerite grains in the tail is less than that in the feed and concentrate.
  • Cu is more abundant on the surface of the sphalerite grains in the concentrate relative to the feed.
  • The range of Cu content in the tail samples is dispersed over the entire range defined by the feed and concentrate.

Depressant species on surface of sphalerite:
Potential depressant species: Ca does not appear to be favoured on either the concentrate or tails sphalerites; Mg appears to be slightly more abundant on the sphalerites in the tail samples (Figure 3).

Statistical comparison of sphalerite surface composition between concentrate and tails:
The data in the scatter plots is emphasized in the T-test comparison analyses (Figure 4). T-test values for mass species that exhibit statistically significant differences at 95% confidence level will be presented in a green colour on the T-test graph, while species with t-values that are not as statistically significant will be presented in a grey colour.

  • The data show a strong statistically significant presence of Pb on the surface of the sphalerite from the concentrate relative to the tails.
  • Cu does occur on the surface of the sphalerite, however the strength of the presence is markedly less than that for Pb.

Relevant mechanisms based on surface analyses:

  • Analyses indicate that Cu and Pb are involved in the activation of the sphalerite grains.
  • The greater discrimination in the Pb signal between the concentrate and tail samples suggests that Pb may be dominant in the inadvertent activation of sphalerite. Moreover, the distribution of Pb on sphalerite surfaces in the concentrate is limited in range, relative to Cu, suggesting it may be a more consistent activator.
  • Depressant species (for example Ca and Mg) are not strongly discriminatory between concentrate and tail samples.  This indicates that depressant species are not likely controlling the flotation characteristics of the sphalerite.  The slight enrichment of Mg in the tail samples suggests that the sphalerite surfaces may contain a greater proportion of adsorbed gangue material, thus inhibiting activation by Cu or Pb.

Cu versus Pb activation:

  • Pb activation; given the similar proportion of Pb on sphalerites in the feed and concentrate suggests that adsorption likely occurred during grinding.
  • Cu activation; given the significant difference between the proportion in the feed and concentrate, adsorption likely occurred during conditioning and flotation.

Major findings:

  • Pb is the predominant activating agent.
  • Activation of sphalerite by Pb occurs during grinding.
  • Cu is mostly a secondary activation agent.
  • Activation by Cu likely occurs during conditioning and flotation.
  • No significant role of common depressants (Ca, Mg) observed.


Figure 1. Secondary ion image (map) for Zn in the concentrate. Area in the image is 300×300µm. Positive ion spectra from the surface of sphalerite in the concentrate and tails in the mass region for Pb (205.5 to 208.5 amu). The data in the spectra are normalized by total ion intensity.


Figure 2. Scatter plots showing the distribution for Pb and Cu versus Zn on sphalerite surfaces in the feed, concentrate and tail. The data are normalized by total ion intensity and area.


Figure 3. Scatter plots showing the distribution for Ca and Mg versus Zn on sphalerite surfaces in the feed, concentrate and tail. The data are normalized by total ion intensity


Figure 4. T-test statistical analyses for data from sphalerite grain surfaces from concentrate/tail flotation tests. All data in the tests were normalized by the total ion intensity and area. The surface components in bright green are considered to be statistically different between the concentrate and tail samples