Copper ion mobility in sphalerite activation

Migration of Cu from the surface into the bulk has been reported in the case of sphalerite. The phenomenon was examined here by X-ray photoelectron spectroscopy (XPS) and by determining the effect of time delay between Cu addition and xanthate (collector) addition on collector adsorption and flotation recovery. Delay time had no effect at pH 3 and 6 but at pH 9.2, collector adsorption decreased after a time delay of 20 min. However, sphalerite recovery was not affected in part due to a collectorless flotation response induced by oxidation promoted by Cu. XPS measurements showed the surface Cu concentration decreased with time but no corresponding increase in sub-surface concentration was detected. Addition of collector at zero delay time showed no decrease in the surface Cu concentration. These observations are attributed to a portion of the adsorbed Cu being in a colloidal Cu(OH)2 form. With delay time, some of the colloidal portion is lost to solution resulting in the decrease in surface Cu and collector uptake. The early addition of xanthate, by reacting with all forms of Cu present, prevents the loss. Copper mobility does not seem to be a factor in flotation practice.