The collectorless flotation of sphalerite
The flotation of sphalerite has been demonstrated without the use of collectors. The effect of redox potential, pH, and copper-activation have been investigated in tests using samples of pure mineral. It has been found that in general, collectorless flotation of sphalerite can be accomplished at potentials greater than -200 mV, SHE, and is more readily carried out in acidic solutions. It has also been shown that although copper-activation was necessary to achieve flotation recoveries above 35%, an excessive addition of cupric ions may result in a decrease in floatability.
Batch flotation experiments conducted using Elmwood Mine sphalerite ore have shown that in addition to copper-activation, the addition of sodium sulfide was required to obtain high grades and recoveries. If the ratio of the addition of these reagents is maintained such that the atomic ratio of cupric ions to sulfide ions is 0.31, good flotation is observed over a range of reagent dosages.
X-ray photoelectron spectroscopy (XPS) was conducted on pure mineral samples after microflotation testing. Based on the sulfur species identified on highly flotable samples, possible mechanisms for collectorless flotation of sphalerite have been suggested. These include: i) elemental sulfur formed under oxidizing conditions is responsible for collectorless flotation; ii) polysulfides or metal-deficient sulfides formed as a result of mineral oxidation are responsible for collectorless flotation; and iii) removal of HS- ions, which may render the surface hydrophilic, under oxidizing conditions. The third mechanism is based on the assumption that clean, unoxidized sphalerite surfaces are naturally hydrophobic. Evidence has been presented to suggest that the first mechanism may be responsible for collectorless flotation in acidic solutions, while the second mechanism may be of greater importance in nearly neutral or basic solutions where elemental sulfur is thermodynamically less stable.