Depression of Lead-activated Sphalerite by Sodium Hydrogen Phosphate for Red Dog Mine Operation

Abstract

The inadvertent activation of sphalerite by lead ions have been noticed and studied for decades. In this study, flotation behavior of sphalerite upon lead activation was studied. Sodium hydrogen phosphate was applied as a main depressant to test its effect on improving Pb-Zn selectivity. Surface characterizations, such as Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) were conducted to understand the basic mechanism happening on the sphalerite surface. Sphalerite showed a strongly enhanced floatability with xanthate after Pb activation. The addition of sodium hydrogen phosphate depressed the Pb-activated sphalerite flotation and did not put impacts on galena flotation. However, its performance was unsatisfactory during the mixed mineral flotation. XPS and ToF-SIMS analyses suggested that sodium hydrogen phosphate had limited ability to complex Pb ions, rather it worked mainly by oxidizing PbS to PbO. To compensate the limited depressing ability of sodium hydrogen phosphate in a mixed mineral system, zinc sulfate was introduced prior to sodium hydrogen phosphate addition. The combination usage of the two reagents showed good selectivity when both of their concentration was at 10-5 M, resulting in a Zn% recovery of 55.0% and a Pb% recovery of 90.2%.