Deactivation of Pb-contaminated sphalerite by polyphosphate

Rashchi, Fereshteh.; Rashchi, Fereshteh.

Thesis

Deactivation of Pb-contaminated sphalerite by polyphosphate

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Creator

Rashchi, Fereshteh.

Contributors

Finch, J. A. (Supervisor)

Abstract

English

Activation of sphalerite by lead ions in the presence of ethyl xanthate was investigated by microflotation, zeta potential measurements, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and extraction by ethylenediaminetetraacetate (EDTA). The source of lead, either from solution or contact with galena particles, proved immaterial. From EDTA extraction data flotation response was determined as a function of surface concentration of Pb ([Pb]surf, mg/cm2). A critical [Pb]surf ≃ 0.5 x 10-4 mg/cm2 causing activation was estimated. By combining with a Pb ion production model from the literature, the possibility of Pb activation for an ore of given Pb grade was explored. Ores with as little as 0.1% Pb are candidates for accidental activation. A mechanism of lead interaction is proposed: at weakly acidic to mildly alkaline conditions Pb2+ and PbOH+ adsorb on sphalerite and react with xanthate to form PbX2 and Pb(OH)X; at high pH, hydrophilic Pb(OH)2(s) precipitates depress flotation. Various candidate deactivators were compared using microflotation. The reagents were diethylenetriamine (DETA), sodium bicarbonate (NaHCO3), silica sol (SS), sodium phosphate (Na3PO4·12H 2O) and sodium polyphosphate (NaPO3)n. The latter had the strongest effect and was selected for detailed study. The mechanism of polyphosphate action was investigated by SEM and XPS. The results show that polyphosphate acted to remove Pb ("clean") from the sphalerite by forming soluble complexes. The polyphosphate (PP) to lead (Pb) ratio in the complexes was determined from conductometric titration of lead nitrate vs. polyphosphate. It was found that initially a precipitate formed with PP/Pb of 1/3. The precipitate dissolved in excess polyphosphate, resulting in a variety of complexes with PP/Pb of 1/2, 1/1, 3/2, 2/1, and 3/1. Knowing the amount of Pb to be removed and taking the lowest PP/Pb ratio, 1/2, the quantity of polyphosphate required to solubilize the Pb can be calculated.

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