Deactivation of Pb-contaminated sphalerite by polyphosphate

Various reagents were compared as deactivators in the sphalerite-lead system at near neutral conditions using microflotation: diethylenetriamine (DETA), sodium bicarbonate (NaHCO3), silica sol (SS), sodium phosphate (Na3PO4·12H2O) and sodium polyphosphate (PP). The latter showed the strongest effect and was selected for a detailed study. The mechanism of polyphosphate action was investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is concluded that polyphosphate acted to remove Pb (i.e., a “cleaning” mechanism) from sphalerite by forming a soluble complex. The presence of excess calcium ion did not markedly reduce the cleaning action. A model is used to estimate PP consumption as a function of ore Pb-grade and particle size.